Introduction
The dynamic homeostasis of the female reproductive system is maintained by a highly regulated sequence of cellular events, whose dysregulation manifests as a spectrum of severe molecular pathologies (Ref. Reference Yao, Lopez-Tello and Sferruzzi-Perri1). While the genomic and proteomic landscapes of reproductive disorders have been extensively mapped (Refs Reference Zhang, Cao, Rajachandran, Grow, Evans and Chen2, Reference Winkler, Tolkachov, Lammers, Lacour, Daugelaite, Schneider, Koch, Panten, Grünschläger, Poth, Ávila, Schneider, Haas, Odom and Gonçalves3), these static profiles often fail to capture the real-time metabolic fluxes that dictate cell fate. Consequently, the lipidome – specifically the bioactive sphingolipid network – has emerged as a critical determinant of cellular survival and organ-level functional integrity (Refs Reference Hannun and Obeid4, Reference Gruevska, Leslie, Perpiñán, Maude, Collins, Johnson, Evangelista, Sabey, French, White, Moir, Robinson, Alrawashdeh, Thakkar, Forlano, Manousou, Goldin, Carling, Hoare, Thursz, Mann, Cebola, Posma, Safinia, Oakley and Hall5). Sphingolipids are no longer characterised merely as structural constituents of biological membranes; instead, they are recognised as pivotal lipid secondary messengers that orchestrate key signal transduction nodes, directly cross-linking with the PI3K/Akt/mTOR, MAPK/ERK and TGF-β/Smad cascades (Ref. Reference Fernandis and Wenk6).
Central to this lipid signalling network is the sphingolipid rheostat, a metabolic pivot governed by the interconversion of pro-apoptotic ceramide (Cer) and pro-survival sphingosine-1-phosphate (S1P). This rheostat operates as a decisive molecular switch in reproductive tissues: physiological S1P gradients drive primordial follicle activation, stabilise the vascular endothelium and support oocyte developmental competence (Ref. Reference Tabasi, Ghasemian and Tavana7). Conversely, a pathological shift towards ceramide accumulation facilitates mitochondrial outer membrane permeabilisation (MOMP) and cytochrome c release, driving the accelerated follicular atresia that underpins reproductive ageing and primary ovarian insufficiency (POI) (Ref. Reference Hernández-Coronado, Guzmán, Castillo-Juárez, Zamora-Gutiérrez and Rosales-Torres8).
Current literature remains fragmented, with mechanistic research often compartmentalised into either ovarian physiology or isolated gynaecological malignancies (Ref. Reference Hernández-Coronado, Guzmán, Castillo-Juárez, Zamora-Gutiérrez and Rosales-Torres8). While previous seminal reviews have discussed S1P dynamics in endometriosis or specific sphingolipid enzymes in folliculogenesis (Ref. Reference Yang, Zhao, Liu and Li9), a multi-dimensional integration that connects these metabolic shifts across the entire reproductive tract is severely lacking. To bridge this gap, this review transcends these singular perspectives by systematically evaluating the sphingolipid axis across the female reproductive continuum – spanning from the ovary to the uterine and peritoneal microenvironments. We examine how a singular metabolic node can yield divergent clinical phenotypes depending on its spatial context: ranging from the accelerated depletion of the ovarian reserve in POI and metabolic silencing in polycystic ovary syndrome (PCOS) to the hyper-proliferative, fibrotic and nociceptive microenvironments of endometriosis, adenomyosis and uterine fibroids.
Furthermore, the clinical significance of sphingolipid signalling extends beyond disease pathogenesis into precision medicine. The distinctive sphingolipid metabolic signatures in follicular fluid (FF) and serum offer high-resolution molecular candidates for non-invasive diagnostics and the prediction of assisted reproductive outcomes (Ref. Reference Turathum, Gao, Grataitong, Liu, Wang, Dai and Chian10). Moreover, the successful application of S1P receptor modulators in systemic inflammatory conditions has opened innovative avenues for drug repurposing, providing non-hormonal therapeutic alternatives that treat lesions without inducing a hypoestrogenic state or disrupting a patient’s desire for conception. By delineating the biochemical crosstalk between sphingolipid metabolites and disease-specific signalling hubs across a diverse spectrum of disorders, this review provides a strategic blueprint for next-generation, lipid-targeted therapeutics in women’s reproductive medicine.
Sources and selection criteria
This comprehensive review was conducted by performing a systematic and extensive literature search across the PubMed, Web of Science and Google Scholar databases for peer-reviewed articles published between 1996 and 2026. The search strategy employed an exhaustive combination of Boolean operators (AND/OR) and medical subject headings terms.
The core search strings integrated sphingolipid metabolic components (‘sphingolipids’, ‘sphingolipid rheostat’, ‘ceramide’, ‘sphingosine’, ‘sphingosine-1-phosphate’, and ‘sphingosine kinase’) with specific reproductive compartments and clinical entities. These entities included ovarian-centric conditions (‘oocyte quality’, ‘ovarian ageing’, ‘primary ovarian insufficiency’ and ‘polycystic ovary syndrome’), uterine and endometrial pathologies (‘endometriosis’, ‘adenomyosis’, ‘uterine fibroids’, ‘endometrial receptivity’, ‘pathological fibrosis’, ‘angiogenesis’ and ‘chronic pelvic pain’), as well as oncofertility paradigms (‘chemotherapy-induced gonadotoxicity’, ‘ovarian cancer’ and ‘fertility preservation’). Only articles published in English and focusing on high-resolution molecular mechanisms, translational animal models or human clinical trials were selected for inclusion in this review.
The sphingolipid metabolic network and molecular features
The sphingolipid rheostat: a decisive signalling hub
Sphingolipids are a diverse class of structural lipids defined by their 18-carbon amino alcohol sphingosine backbone (Ref. Reference Gault, Obeid, Hannun, Chalfant and Del Poeta11). Beyond serving as cell membrane scaffolds, they function as bioactive secondary messengers that orchestrate key physiological and pathological signal transduction nodes (Ref. Reference Bartke and Hannun12). Within this metabolic network, three primary metabolites – ceramide, sphingosine and S1P – form a fundamental regulatory axis termed the ‘sphingolipid rheostat’ (Ref. Reference Hannun and Obeid4).
The essence of this rheostat lies in the dynamic interconvertibility and functional antagonism of these species. Ceramide, the central metabolic hub and its immediate derivative sphingosine are potent inhibitors of cell growth and established mediators of programmed cell death and fibrosis (Ref. Reference Castro, Prieto and Silva13). In stark contrast, their phosphorylated product, S1P, acts as a pleiotropic signalling molecule that promotes cell survival, migration, proliferation and angiogenesis. This metabolic pivot allows reproductive cells to rapidly reprogram their fate in response to microenvironmental cues, such as hormonal surges or oxidative stress. Consequently, a chronic shift in this equilibrium towards either ceramide accumulation or unchecked S1P signalling represents a molecular hallmark of various female reproductive disorders (Figure 1).
Subcellular topography of the sphingolipid rheostat: organelle crosstalk and signalling dynamics.
The intracellular fate of reproductive cells is dictated by the dynamic balance between Cer and S1P across distinct subcellular compartments. (Left) The Cer-driven stress axis. Stress-induced de novo synthesis of Cer at the ER drives apoptosis. Pathological Cer accumulation initiates MOMP and the release of Cyt c, while concurrently activating PP2A to inhibit Bcl-2. (Right) The S1P-driven survival and epigenetic axis. The salvage pathway generates S1P via SphK1/2, establishing a bioenergetic network. Mitochondrial S1P interacts with PHB2 to enhance Complex IV respiration, while nuclear S1P inhibits HDAC1/2 to maintain an open chromatin state for the transcription of survival genes (c-fos, p21). Cytosolic S1P acts as an obligate cofactor for TRAF2 to trigger NF-
$ \kappa $
B-mediated inflammatory responses. (Top) Intracellular S1P is exported via Spns2 (‘inside-out signalling’) to engage specific S1PR1–3, driving downstream survival and fibrotic cascades. This localised rheostat is integrated with E2 and FSH through the non-genomic activation of SphK1.
Abbreviations: Cer, ceramide; S1P, sphingosine-1-phosphate; ER, endoplasmic reticulum; MOMP, mitochondrial outer membrane permeabilisation; Cyt c, cytochrome c; PP2A, protein phosphatase 2A; Bcl-2, B-cell lymphoma 2; SphK, sphingosine kinase; PHB2, prohibitin-2; HDAC, histone deacetylase; TRAF2, TNF receptor-associated factor 2; NF-
$ \kappa $
B, nuclear factor kappa B; Spns2, Spinster-2; S1PR, sphingosine-1-phosphate receptor; E2, oestrogen; FSH, follicle-stimulating hormone.
Figure 1. Long description
The diagram is divided into two main vertical zones.
Left Zone: Ceramide and Apoptosis Death Axis.
* At the top, the Endoplasmic Reticulum (E R) shows L-serine and Palmitoyl-C o A being converted by S P T and Cer S 1-6 into Ceramide.
* Below, Ceramide interacts with a mitochondrion, forming Ceramide Channels that lead to Catastrophic Cytochrome c release and Caspase-3 activation.
* To the far left, P P 2 A inhibits Bcl-2 to promote apoptosis.
Right Zone: S 1 P and Survival Axis.
* At the center, Ceramide is converted to S 1 P via Sph k 1 and Sph k 2.
* In the mitochondrion, S 1 P interacts with P H B 2 and Complex I V to produce A T P.
* In the nucleus, S 1 P inhibits H D A C 1/2, maintaining open chromatin for pro-survival genes like c-fos and p21.
* In the cytosol, S 1 P binds T R A F 2 to activate N F-kappa B.
Top Perimeter: Plasma Membrane and Signaling.
* S 1 P is exported via Spns 2 (Inside-Out Signaling) to bind extracellular receptors S 1 P R 1 and S 1 P R 2/3.
* S 1 P R 1 activates P I 3 K/Akt and M A P K/E R K pathways.
* S 1 P R 2/3 activates Rho/R O C K for cytoskeletal changes.
* On the far right, E 2 and F S H receptors trigger rapid non-genomic activation of Sph k 1.
Core metabolic pathways and enzymatic orchestration
The intracellular concentration of sphingolipid metabolites is governed by a highly compartmentalised and coordinated metabolic network that maintains a precise homeostatic balance between antagonistic bioactive species (Ref. Reference Hannun and Obeid4).
Ceramide generation and metabolism
Ceramide, the central structural and signalling hub of the sphingolipid network, is tightly regulated via three distinct biosynthetic pathways (Figure 1):
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• The de novo synthesis pathway: Occurring primarily in the endoplasmic reticulum, this pathway initiates with the rate-limiting condensation of L-serine and palmitoyl-CoA catalysed by serine palmitoyltransferase (SPT) (Ref. Reference Tabasi, Ghasemian and Tavana7). Subsequent sequential reactions mediated by 3-ketodihydrosphingosine reductase and ceramide synthases (CerS1–6) – which exhibit distinct fatty acid chain-length specificities – yield dihydroceramide, which is ultimately desaturated by dihydroceramide desaturase (DES1/2) to form ceramide (Ref. Reference Mostafa, Nader and Machaca14).
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• The sphingomyelin (SM) hydrolysis pathway: This rapid catabolic route involves the cleavage of membrane-bound SM by sphingomyelinases (SMases), notably the acid (aSMase/Smpd1) and neutral (nSMase/Smpd2/3) isoforms (Ref. Reference Tabasi, Ghasemian and Tavana7). This pathway allows for the instantaneous, localised generation of ceramide across diverse subcellular compartments – including the plasma membrane, lysosomes and mitochondria – frequently in response to external environmental stressors or inflammatory cytokines.
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• The salvage pathway: Complex glycosphingolipids undergo constitutive lysosomal degradation to regenerate ceramide, which is subsequently deacylated by ceramidases (CDases), particularly acid ceramidase (AC/Asah1), to yield sphingosine (Ref. Reference Birbes, El Bawab, Hannun and Obeid15). High basal AC activity is a critical prerequisite within the oocyte-granulosa microenvironment to prevent lipotoxic ceramide accumulation and subsequent germline apoptosis.
S1P generation and metabolism
The lifecycle of the pro-survival mediator S1P is orchestrated by a tightly balanced enzymatic rheostat governing its synthesis and catabolism:
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• Biosynthesis: Free sphingosine generated from the salvage pathway is phosphorylated to form S1P by two distinct isoforms of sphingosine kinase: SphK1 and SphK2 (Ref. Reference Gomez-Larrauri, Presa, Dominguez-Herrera, Ouro, Trueba and Gomez-Muñoz16). SphK1 is primarily cytosolic and translocates to the plasma membrane upon growth-factor activation to drive ‘inside-out’ signalling, whereas SphK2 predominantly localises to the nucleus, mitochondria or ER, where it exerts context-dependent epigenetic or metabolic effects.
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• Catabolism: Intracellular S1P levels are strictly capped to prevent unchecked proliferation via two distinct mechanisms: reversible dephosphorylation back to sphingosine by S1P phosphatases (SPP1/2 or SGPP1/2), or irreversible catabolic cleavage by endoplasmic reticulum-bound S1P lyase (SPL/Sgpl1) into hexadecenal and phosphoethanolamine (Ref. Reference Gault, Obeid, Hannun, Chalfant and Del Poeta11). Genetic loss or pathological downregulation of SPL results in aberrant intracellular S1P accumulation, disrupting the localised lipid gradients required for healthy germ cell maturation and follicular development.
S1P signalling dynamics: transporters and receptor heterogeneity
To execute its extracellular biological functions, intracellularly generated S1P must be exported across the plasma membrane, a process designated as ‘inside-out signalling’.
Vascular and Cellular Transporters: S1P export is strictly mediated by specialised transporters, predominantly Spinster-2 (Spns2) in endothelial/epithelial cells and MFSD2B in erythrocytes and platelets. These transporters establish the vital physiological S1P gradient between interstitial tissues (~0.1 μM in lymph) and systemic circulation (~1 μM in blood), which is indispensable for immune cell trafficking, localised cell migration and vascular barrier stability (Refs Reference Turathum, Gao, Grataitong, Liu, Wang, Dai and Chian10, Reference Zhang and Lu17).
G-Protein coupled Receptor (S1PR) Diversity: Extracellular S1P acts as a high-affinity ligand for five distinct G-protein coupled receptors (S1PR1–5). Within the female reproductive tract and its associated pathologies, S1PR1, S1PR2 and S1PR3 represent the dominant functional subtypes:
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• S1PR1: Couples exclusively with Gi proteins to activate downstream PI3K/Akt/mTOR and Ras/MAPK/ERK pathways. This cascade drives cell survival, directed migration, and the structural stabilisation of VE-cadherin at endothelial and epithelial junctions (Ref. Reference Kajimoto, Mohamed, Badawy, Matovelo, Hirase, Nakamura, Yoshida, Okada, Ijuin and Nakamura18).
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• S1PR2 and S1PR3: Exhibit multi-G-protein coupling capacity (Gi, Gq and G12/13) (Ref. Reference Takuwa, Okamoto, Yoshioka and Takuwa19). Crucially, they serve as the primary upstream activators of the Rho/Rho-kinase (ROCK) signalling network. This specific pathway governs fibroblast-to-myofibroblast transdifferentiation (FMT), tissue contractility and growth cone collapse/sensitisation in pelvic pain states.
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• S1PR4–5 and Endocrine Integration: While S1PR4 and S1PR5 are primarily restricted to hematopoietic and central nervous systems, their pathways cross-link heavily with the reproductive endocrine environment. Oestrogen (E2) and follicle-stimulating hormone rapidly stimulate SphK1 activation (Ref. Reference González-Aretia, Hernández-Coronado, Guzmán, Medina-Moctezuma, Gutiérrez and Rosales-Torres20). This lipid-hormone crosstalk triggers non-genomic oestrogenic effects, including acute intracellular calcium (Ca2+) surges and rapid ERK1/2 phosphorylation, which are mandatory for oocyte meiotic resumption and granulosa cell (GC) metabolic support.
Intracellular second messenger signalling and organelle crosstalk
Beyond their canonical roles in membrane architecture and receptor-mediated signalling, sphingolipid metabolites function as critical intracellular second messengers that modulate diverse organelle-specific physiological and pathological programmes (Ref. Reference Hannun and Obeid21).
Ceramide: a mediator of subcellular stress and apoptosis
Intracellular ceramide acts as a primary transducer of metabolic and environmental stress signals, localised predominantly within the mitochondria and endoplasmic reticulum (Figure 1).
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• Mitochondrial outer membrane permeabilisation: Upon accumulation in the outer mitochondrial membrane, ceramide self-assembles into large-diameter, stable ceramide channels. These channels facilitate MOMP, driving the accelerated efflux of pro-apoptotic intermembrane space proteins (cytochrome c and SMAC/DIABLO) into the cytosol, thereby triggering the caspase-3 executioner cascade (Refs Reference Colombini22, Reference Rego, Costa, Chaves, Matmati, Pereira, Sousa, Moradas-Ferreira, Hannun, Costa and Côrte-Real23).
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• Bcl-2 Family Interplay and PP2A Activation: Intracellular ceramide promotes structural apoptosis by facilitating the conformational change and mitochondrial recruitment of Bax (Ref. Reference Ganesan, Perera, Colombini, Datskovskiy, Chadha and Colombini24). Concurrently, it activates mitochondrial protein phosphatase 2A (PP2A) (Ref. Reference Supakul and Liangpunsakul25), which dephosphorylates and inactivates the anti-apoptotic rheostat Bcl-2, neutralising the follicle’s primary defense against atresia.
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• ER Stress and Lipotoxicity: In metabolic reproductive conditions, ceramide bridges nutrient excess with organelle dysfunction. Elevated palmitic acid (PA) flux drives de novo ceramide accumulation, which induces severe ER stress and robustly upregulates CHOP expression, driving GC apoptosis and arresting oocyte developmental competence (Refs Reference Huo, Liu, Lu, Li, Yang, Xu, Chen, Yin and Wang26, Reference Shibahara, Ishiguro, Inoue, Koumei, Kuwayama and Iwata27).
S1P: a regulator of bioenergetics and epigenetics
In functional antagonism to ceramide, intracellular S1P operates as a vital survival factor by modulating mitochondrial metabolism, nuclear transcription and cytosolic inflammatory pathways (Figure 1).
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• Mitochondrial Bioenergetics: SphK2-generated S1P within the inner mitochondrial membrane binds specifically to prohibitin-2 (PHB2) (Ref. Reference Strub, Paillard, Liang, Gomez, Allegood, Hait, Maceyka, Price, Chen, Simpson, Kordula, Milstien, Lesnefsky and Spiegel28). This interaction is required for the optimal assembly and catalytic activity of cytochrome c oxidase (Complex IV), enhancing mitochondrial respiration and ATP synthesis, which is crucial for fueling oocyte meiotic progression.
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• Nuclear Epigenetic Programming: Within the nucleus, S1P binds to and inhibits histone deacetylases 1 and 2 (HDAC1/2) (Ref. Reference Sah, Anand, Dar, Jain, Kumari, Madan, Saini, Gupta, Joshi, Hada, Gupta, Pati and Singh29). This inhibition blocks the removal of acetyl groups from histone tails, maintaining an open chromatin state that permits the transcription of pro-survival genes such as p21 and c-fos. Additionally, nuclear S1P interacts with telomerase reverse transcriptase, enhancing its stability to support cellular longevity (Refs Reference Sah, Anand, Dar, Jain, Kumari, Madan, Saini, Gupta, Joshi, Hada, Gupta, Pati and Singh29, Reference Riccio30).
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• Cytosolic Pro-inflammatory Activation: SphK1-derived cytosolic S1P acts as an obligate cofactor for the E3 ubiquitin ligase TRAF2 (Ref. Reference Takuwa, Okamoto, Yoshioka and Takuwa31). This interaction promotes the polyubiquitination of RIP1, triggering NF-κB pathway activation (Ref. Reference Wang, Liu, Li, Guo, Xu, Zhou, Wang, Wu, Yan and Cui32) and the subsequent transcription of pro-inflammatory cytokines and chemokines (e.g. IL-6, CCL5) that drive the microenvironmental remodelling characteristic of endometriosis and gynaecological malignancies.
Sphingolipid and ovarian-centric disorders
Ovarian follicular fate – dormancy, growth or atresia – is tightly orchestrated by local signalling dynamics within the reproductive microenvironment. Disruption of the sphingolipid rheostat is closely associated with the pathogenesis of ovarian pathologies, typically characterised by an imbalance favouring pro-apoptotic ceramide accumulation over the protective S1P signalling axis (Ref. Reference Tabasi, Ghasemian and Tavana7).
Reproductive ageing and POI
Reproductive senescence entails a non-linear depletion of both the quantity and quality of the oocyte pool, culminating in the exhaustion of the ovarian reserve. Within this timeline, the sphingolipid network operates as both a distinctive molecular signature of cellular senescence and a direct mediator of follicular attrition (Ref. Reference Hernández-Coronado, Guzmán, Castillo-Juárez, Zamora-Gutiérrez and Rosales-Torres8). This age-related acceleration of germ cell death is fundamentally driven by a rheostat shift towards pro-apoptotic pathways, which lowers the threshold of oocyte vulnerability to microenvironmental stressors (Figure 2).
The spatial dichotomy of the sphingolipid rheostat in female reproductive pathologies.
The sphingolipid metabolic axis exerts divergent, tissue-specific effects across the female reproductive continuum, acting as a molecular pivot between apoptotic atresia and hyper-proliferative survival. (Left Panel: Ovarian Compartment) A pathological shift toward Cer drives follicular depletion and vascular dysfunction. In PCOS, PA-induced Cer synthesis triggers ER stress via CHOP, blocking Akt signalling and causing follicular arrest. In POI and chemotoxicity, Cer surges initiate MOMP and germline apoptosis, a process that can be therapeutically shielded by exogenous S1P. Additionally, localised S1P depletion in OHSS destabilises VE-cadherin, leading to acute paracellular leakage. (Right Panel: Uterine and Peritoneal Compartment) Conversely, hyper-activation of the S1P axis drives pathological expansion in endometriosis and uterine fibroids. Extracellular S1P engages S1PR2/3 to activate the Rho/ROCK and TGF-
$ \beta $
/Activin A pathways, inducing FMT and extensive ECM deposition. Concurrently, S1P promotes immune evasion by skewing macrophages towards an M2 phenotype and drives angiogenesis via the HIF-1α/S1PR1 axis. In the neuro-immune niche, NGF-stimulated S1P production sensitises nociceptive sensory neurons via TRPV4 channels, amplifying chronic pelvic pain. Bridging these two compartments, very long-chain ceramides from peritoneal endometriotic lesions exhibit retrograde toxicity, directly impairing adjacent oocyte competence.
Abbreviations: Cer, ceramide; S1P, sphingosine-1-phosphate; PCOS, polycystic ovary syndrome; PA, palmitic acid; ER, endoplasmic reticulum; CHOP, CCAAT/enhancer-binding protein homologous protein; Akt, protein kinase B; POI, primary ovarian insufficiency; MOMP, mitochondrial outer membrane permeabilisation; OHSS, ovarian hyperstimulation syndrome; VE-cadherin, vascular endothelial cadherin; S1PR, sphingosine-1-phosphate receptor; ROCK, Rho-associated protein kinase; TGF-
$ \beta $
, transforming growth factor-beta; FMT, fibroblast-to-myofibroblast transdifferentiation; ECM, extracellular matrix; M2, type 2 activated macrophage; HIF-1α, hypoxia-inducible factor 1-alpha; NGF, nerve growth factor; TRPV4, transient receptor potential vanilloid 4.
Figure 2. Long description
At the center is a balance scale labeled Sphingolipid Rheostat, with Ceramide (Death) on the left weighing down and S 1 P (Survival/Proliferation) on the right.
Left Panel (Ovarian Axis):
- Top left: P C O S and Lipotoxicity. Palmitic Acid (P A) leads to massive de novo Ceramide synthesis in granulosa cells, triggering E R Stress, C H O P activation, and blocking p-Akt, resulting in follicular arrest and G C apoptosis.
- Middle left: Ovarian Cortex diagram showing the transition from a primordial follicle pool to an arrested antral follicle and a very long depleted oocyte due to aging.
- Bottom left: P O I and Stress. Chemotherapy and R O S cause a Ceramide surge leading to M O M P and primordial follicle death. A ‘Shield’ pathway shows S 1 P R 1 3 and Bcl-2 inhibiting this process for fertility preservation.
- Bottom center: O H S S Vascular Leakage. Depleted S 1 P levels in follicular fluid lead to V E-cadherin dissociation on endothelial junctions and paracellular leakage in ovarian blood vessels.
Right Panel (Uterine/Peritoneal Axis):
- Center: A large, dense, hypervascularized ectopic endometriotic lesion.
- Top right: Pathological Fibrosis (F M T). Overactive SphK 1 and S 1 P R 2/3 signaling in stromal fibroblasts activate T G F-beta/Activin A and Rho/R O C K pathways, leading to alpha-S M A myofibroblast formation and E C M deposition (Collagen I/III, Fibronectin).
- Middle right: Neuro-Immune Pain Axis. T N F-alpha and I L-1 beta stimulate N G F, which activates nSMase and S 1 P. S 1 P engages S 1 P R 1/3 and T R P V 4 on nociceptive sensory nerves, causing pain and hyperalgesia.
- Bottom right: Angiogenic Inside-Out Signaling. Hypoxia stabilizes H I F-1 a, which upregulates SphK 1 to produce S 1 P, stabilizing chaotic neovessels feeding the lesion.
- Peritoneal Fluid: Shows immune evasion where macrophages are skewed to an M 2-phenotype by I L-6 and C O X-2.
- A bridging arrow shows very long-chain ceramides from the peritoneal fluid moving toward the ovarian cortex to impair oocytes.
Ceramide accumulation and subcellular mislocalisation
Oocyte apoptosis during ovarian ageing is an intercellular event reliant on biochemical crosstalk with surrounding somatic cumulus cells rather than an autonomous process. In senescent murine models, ceramide paradoxically accumulates within the cumulus cells while remaining low in basal-state oocytes (Ref. Reference Kujjo and Perez33). Upon stress activation, this somatic ceramide is translocated into the adjacent oocyte via gap junctions and intact lipid rafts. This influx generates an aberrant accumulation of ceramide that disrupts homeostatic balance in the aged oocyte; unlike young oocytes that safely sequester exogenous ceramide within mitochondria to maintain cytoplasmic homeostasis, aged oocytes fail to do so, causing pathological lipid accumulation in the cytoplasm and plasma membrane (Ref. Reference Kujjo, Acton, Perkins, Ellisman, D’Estaing, Casper, Jurisicova and Perez34). Concurrently, the upregulation of Bax mRNA and Bax protein in senescent oocytes cooperates with this mislocalised ceramide to induce spontaneous cytoplasmic fragmentation and initiate the apoptotic cascade, demonstrating how altered intercellular lipid trafficking drives age-related fertility decline (Ref. Reference Perez, Jurisicova, Matikainen, Moriyama, Kim, Takai, Pru, Kolesnick and Tilly35).
Mitochondrial dysfunction and the MOMP pathway
Mitochondrial decay is a defining feature of age-related oocyte quality decline (Ref. Reference Zhang, Zhang and Xiang36), with ceramide serving as its principal executioner. Elevated outer mitochondrial membrane ceramide self-assembles into stable, macro-diameter ‘ceramide channels’, facilitating MOMP (Ref. Reference Fisher-Wellman, Hagen, Neufer, Kassai and Cabot37). This permeabilisation triggers the accelerated efflux of cytochrome c and SMAC/DIABLO into the cytosol, activating the caspase-3 proteolytic cascade and irreversible cellular fragmentation (Refs Reference Fisher-Wellman, Hagen, Neufer, Kassai and Cabot37, Reference Ueda38). Beyond disrupting membrane integrity, Cer actively suppresses metabolic survival pathways by activating protein phosphatase 2A (PP2A), which dephosphorylates and neutralises anti-apoptotic Bcl-2, thus lowering the oocyte’s apoptotic threshold (Ref. Reference Kobeissy, Hage-Sleiman, Dakdouk, Kozhaya and Dbaibo39). Recent single-cell RNA-sequencing confirms that excess ceramide severely impairs developmental competence primarily via this organelle dysfunction (Ref. Reference Takashima, Fujimaru and Obata40). Mechanistically, ceramide accumulation suppresses the intrafollicular AMPK/SIRT3 signalling axis, inducing mitochondrial protein hyperacetylation and metabolic collapse, a pathological state directly reproducible via exogenous ceramide administration in culture media (Ref. Reference Itami, Shirasuna, Kuwayama and Iwata41).
The role of ceramide transfer protein (CERT) and metabolism enzymes
Mitochondrial disintegration in senescent oocytes is structurally tied to the downregulation of CERT, which mediates non-vesicular ceramide transport from the endoplasmic reticulum to the Golgi or mitochondria (Ref. Reference Kumagai and Hanada42). Loss of CERT causes pathological lipid accumulation and organelle stress; notably, murine CERT mutations induce embryonic lethality via structural mitochondrial degeneration rather than canonical apoptosis, proving its necessity for early developmental organelle integrity (Ref. Reference Wang, Rao, Kosakowska-Cholody, Masood, Southon, Zhang, Berthet, Nagashim, Veenstra, Tessarollo, Acharya and Acharya43). This metabolic imbalance is compounded by the age-related loss of AC activity, which prevents the deacylation of ceramide into sphingosine for subsequent conversion into the pro-survival mediator S1P. Deficient AC activity shifts the metabolic profile towards elevated Bax/PARP expression and reduced Anti-Müllerian hormone levels, which is indicative of ovarian reserve depletion (Refs Reference Eliyahu, Shtraizent, Shalgi and Schuchman44, Reference Jain, Beutel, Ebell, Korneev and Holthuis45). This enzymatic imbalance coincides with a cytotoxic microenvironment associated with the clinical manifestation of POI. Conversely, restoring AC expression or administering exogenous S1P neutralises ceramide toxicity, stabilises mitochondrial potential and rescues the developmental competence of aged oocytes, establishing these metabolic enzymes as viable therapeutic targets for expanding reproductive longevity.
PCOS and metabolic lipotoxicity
PCOS – or polyendocrine-metabolic ovarian syndrome (PMOS) – is a prevalent systemic endocrine-metabolic disorder affecting up to 15% of reproductive-aged women globally (Refs Reference Dapas and Dunaif46, Reference Teede, Khomami, Morman, Laven, Joham, Costello, Patil, Rees, Berry, Cree, Zhao, Norman, Dokras and Piltonen47). Marked by disordered gonadotropin secretion, hyperandrogenism and chronic anovulation, PCOS is fundamentally underpinned by insulin resistance and obesity. A major component contributing to the accompanying reproductive failure is lipotoxicity, wherein ectopic lipid deposition within the ovarian compartment induces oxidative stress, worsens local insulin resistance and creates a pro-inflammatory follicular microenvironment that compromises oocyte developmental competence (Ref. Reference Brennan, Kroener, Chazenbalk and Dumesic48) (Figure 2).
Dysregulation of sphingolipid metabolism
FF lipidomic profiling reveals profound sphingolipid remodelling in PCOS, though specific signatures vary across clinical phenotypes. Several cohorts exhibit a metabolic ‘silencing’ or downregulation of multiple FF sphingolipids – including ceramide, glucosylceramide and SM – which correlates with impaired oocyte development in assisted reproductive technology (ART) cycles (Refs Reference Liu, Yin, Chen, Li, Yin, Ding, Yang and Feng49, Reference Cordeiro, Cataldi, do Vale Teixeira da Costa, de Lima, Stevanato, Zylbersztejn, Ferreira, Eberlin, Cedenho and Turco50). Conversely, other subgroups display elevated systemic and local S1P, Cer and SM levels, pointing to potential regulatory links between circulating insulin or androgens, and altered bioactive lipid production (Ref. Reference Li, Chu, Ma, Sun, Tao, Huang, Liao, Yue, Zheng, Wang, Xue, Zhu, Kang, Yin and Liu51).
Advanced bioinformatic modelling (WGCNA and machine learning) of GC RNA-Seq datasets links this dysregulated sphingolipid metabolism directly to cellular senescence within the PCOS ovary (Ref. Reference Shi, Lin, Di, He and Shen52). These lipid aberrations, particularly within ceramide subclasses and lysophosphatidylglycerol (LPG), serve as sensitive markers of oocyte quality, with LPG concentrations significantly depleted in obese, insulin-resistant subgroups (Ref. Reference Ding, Jiang, Zhu, Zhu, He, Lu, Wang, Qi, Feng, Huang, Yin, Li and Sun53). This disrupted landscape can be modulated therapeutically: metformin alters these aberrant sphingolipid profiles, while brown adipose tissue transplantation mitigates PCOS phenotypes by restoring lipid metabolites that regulate the PI3K/Akt and MAPK survival pathways (Refs Reference Yao, Wang, Zhang, Wang, Liu, Di, Song and Xu54, Reference Pradas, Rovira-Llopis, Naudí, Bañuls, Rocha, Hernandez-Mijares, Pamplona, Victor and Jové55).
YAP signalling and follicular arrest
The hallmark follicular arrest of PCOS is tightly coupled to Hippo signalling pathway aberrations, where activation of the effector yes-associated protein (YAP) is driven by distorted follicular sphingolipid flux (Ref. Reference Shi, Zhao, Shi, Cao, Yang, Li, Zhang, Liang, Li, Chen, Shen, Zhao, You, Gao, Zhu, Zhao, Yan, Qin, Li, Yan, Wang, Zhao, Geng, Ma, Zhao, He, Zhang, Zou, Yang, Liu, Li, Li, Wan, Qin, Shi, Yang, Jiang, Xu, Qi, Sun, Zhang, Hao, Ju, Zhao, Ren, Li, Zhang, Zhang, Zhang, Wu, Zhang, He and Chen56). Physiologically, S1P disrupts Hippo signalling to stimulate GC proliferation and healthy follicular growth; thus, diminished S1P bioavailability or altered S1PR expression profiles promote the antral follicle arrest characteristic of PCOS. Pharmacologically, transcriptomic data suggest that low-dose aspirin may restore GC health and rescue follicular growth by normalising these senescence-associated sphingolipid pathways (Ref. Reference Shi, Lin, Di, He and Shen52).
Lipotoxicity, ER stress and granulosa cell viability
In obesity-complicated PCOS, ectopic accumulation of saturated free fatty acids, particularly PA, drives de novo ceramide synthesis within the ovary (Ref. Reference Shibahara, Ishiguro, Inoue, Koumei, Kuwayama and Iwata27). This ceramide surge triggers GC lipotoxicity, inducing severe endoplasmic reticulum stress marked by the robust upregulation of CHOP mRNA expression (Ref. Reference Shibahara, Ishiguro, Inoue, Koumei, Kuwayama and Iwata27). This lipotoxic environment compromises the insulin signalling cascade – evidenced by a suppressed phospho-Akt/Akt ratio – thereby decreasing cell viability and driving GC apoptosis. This ceramide-mediated ER stress-apoptosis axis provides a key pathological correlate linking systemic metabolic dysfunction to localised oocyte maturation failure in PCOS/PMOS patients.
Ovarian and gynaecological cancers
Receptor dynamics in tumour expansion
The physiological versatility of the sphingolipid rheostat shifts towards oncogenesis in gynaecological malignancies, particularly ovarian cancer, where the balance between ceramide-mediated apoptosis and S1P-driven survival is altered (Figure 2). Malignant tissues reprogramme their metabolic machinery to upregulate SphK1 and SphK2, driving a marked depletion of pro-apoptotic ceramide and a concomitant surge in intracellular and extracellular S1P levels (Ref. Reference Knapp, Chomicz, Świderska, Chabowski and Jach57). Clinically, S1P concentrations are significantly elevated in both the plasma and ascites of patients with epithelial ovarian cancer (Ref. Reference Sutphen, Xu, Wilbanks, Fiorica, Grendys, LaPolla, Arango, Hoffman, Martino, Wakeley, Griffin, Blanco, Cantor, Xiao and Krischer58), correlating strongly with advanced tumour stage, lymph node metastasis and poor overall survival (Ref. Reference Li, Zhi, Lin, Sun, Sun, Abudousalamu, Xue, Zheng, Li, Yao and Chen59). Following surgical cytoreduction, these systemic S1P levels decline significantly, establishing this lipid mediator as both a critical oncogenic driver and a sensitive biomarker for disease recurrence (Ref. Reference Sutphen, Xu, Wilbanks, Fiorica, Grendys, LaPolla, Arango, Hoffman, Martino, Wakeley, Griffin, Blanco, Cantor, Xiao and Krischer58). Mechanistically, this oncogenic lipid shift accelerates tumour progression through multiple receptor-dependent pathways governing cell proliferation, migration and the epithelial-to-mesenchymal transition (EMT). Extracellular S1P, secreted into the tumour microenvironment, engages in ‘inside-out signalling’ primarily through S1PR1 and S1PR3, which are markedly overexpressed in malignant ovarian cells (Ref. Reference Tao, Zhu, Shi, Wang, Hua, Hu, Zhou, Zhou, Sun, Wang, Wang, Zhang, Guo, Wang, Che, Xu, Zhang, Heger, Tao, Zheng, Xu, Ao, Liu, Liu, Cheng and Pan60). This receptor engagement couples with Gi and G12/13 proteins to potently stimulate downstream PI3K/Akt/mTOR and MAPK/ERK signalling cascades (Ref. Reference Takuwa, Okamoto, Yoshioka and Takuwa19), modulating cell cycle checkpoints and conferring a robust anti-apoptotic phenotype upon cancer cells.
Beyond tumour-intrinsic survival, the SphK/S1P axis is a regulator of tumour angiogenesis and neuro-angiogenic niches within the gynaecological tumour microenvironment (Ref. Reference Dai, Wang, Song, Wang and di61). S1P acts as a potent angiogenic factor that complements and frequently compensates for vascular endothelial growth factor (VEGF) signalling (Ref. Reference Hernández-Coronado, Guzmán, Rodríguez, Mondragón, Romano, Gutiérrez and Rosales-Torres62). By binding to endothelial S1PR1, tumour-derived S1P promotes endothelial cell migration, capillary sprouting and neovessel stabilisation via pericyte recruitment (Ref. Reference Visentin, Vekich, Sibbald, Cavalli, Moreno, Matteo, Garland, Lu, Yu, Hall, Kundra, Mills and Sabbadini63).
Chemoresistance paradigms
Mechanistically, this S1P signalling network underlies the molecular basis of chemoresistance to standard platinum- and taxane-based therapies (Ref. Reference Pyne, Tonelli, Lim, Long, Edwards and Pyne64). While chemotherapeutic agents like cisplatin typically induce cellular stress to trigger a spike in de novo ceramide synthesis and initiate MOMP (Ref. Reference Sawada, Nakashima, Banno, Yamakawa, Takenaka, Shinoda, Nishimura, Sakai and Nozawa65), the overproduction of S1P effectively neutralises this ceramide accumulation, shifting the rheostat away from death and towards survival. This evasion of mitochondrial apoptosis presents a profound dilemma in oncofertility: while exogenous S1P administration holds immense therapeutic promise as an adjuvant to safeguard the primordial follicle pool against chemotherapy-induced gonadotoxicity, its systemic use carries the potential risk of protecting residual micrometastases or accelerating the recurrence of sphingolipid-dependent malignancies.
Iatrogenic and environmental ovarian damage
The longevity and functional capacity of the ovarian reserve are constantly threatened by external perturbations, from gonadotoxic medical interventions to adverse environmental factors. The molecular node at the intersection of these disparate insults is the sphingolipid rheostat, which acts as a master sensor of follicle health versus atresia. Under homeostatic conditions, a high ratio of S1P to ceramide ensures cellular proliferation and survival within the follicular niche; however, exposure to iatrogenic or environmental stressors disrupts this equilibrium, tilting the molecular balance towards ceramide accumulation (Refs Reference Hernández-Coronado, Guzmán, Espinosa-Cervantes, Romano, Verde-Calvo and Rosales-Torres66, Reference Van Brocklyn and Williams67). This metabolic shift initiates an intracellular cascade that couples lipid signalling with oxidative stress, ultimately accelerating germ cell elimination and driving premature ovarian insufficiency.
Chemotherapy-induced follicular atresia
The clinical management of malignancies in reproductive-aged women frequently involves cytotoxic agents, such as cyclophosphamide and doxorubicin, which deplete the primordial follicle pool by inducing massive apoptosis in both oocytes and surrounding GCs (Ref. Reference Touraine, Chabbert-Buffet, Plu-Bureau, Duranteau, Sinclair and Tucker68). Mechanistically, these chemotherapeutic insults trigger a marked increase in cellular ceramide levels, mirroring core stress-induced cell death pathways across experimental models. This ceramide accumulation serves as an upstream signalling molecule that destabilises organelle integrity and commits the follicle to programmed atresia.
To counteract this gonadotoxic depletion, modulating the SphK-dependent seesaw represents a recognised approach in oncofertility. Exogenous S1P administration or intracellular SphK upregulation acts as a protective agent, safeguarding ovarian grafts and preserving the primordial pool. S1P mediates this cytoprotective effect by engaging its specific cell-surface G-protein coupled receptors, predominantly S1PR1 and S1PR3 (Ref. Reference Ogretmen69). Upon binding, S1P activates the downstream PI3K/Akt survival pathway, which upregulates the anti-apoptotic protein Bcl-2 and significantly reduces the recruitment of cleaved caspase-3-positive executioner cells within the ovarian cortex (Ref. Reference Giaccari, Antonouli, Anifandis, Cecconi and di Nisio70). This receptor-mediated stabilisation effectively blocks chemotherapy-induced apoptosis, offering a viable strategy to preserve female fertility during oncological treatments.
Heat Stress (HS) and oxidative balance
Beyond iatrogenic interventions, environmental HS represents a profound physical disruptor of oocyte maturation, acting primarily through the subversion of the intrafollicular lipid profile. In porcine and bovine models, HS induces a marked upregulation of ceramide generation specifically within the GC layer of antral follicles, leaving the surrounding theca cells unaffected (Refs Reference Hernández-Coronado, Guzmán, Castillo-Juárez, Zamora-Gutiérrez and Rosales-Torres8, Reference Lee, Kang, Jeong, Kim, Park, Song, Sim and Kim71). This localised collapse of the S1P-to-ceramide ratio serves as a critical pathological switch; the resulting ceramide accumulation triggers excessive production of reactive oxygen species, severe oxidative stress and extensive mitochondrial fragmentation within the maturing oocyte (Ref. Reference Lee, Kang, Jeong, Kim, Park, Song, Sim and Kim71).
The control of the ceramide/S1P balance by SphK is highly sensitive to the cellular redox state, where oxidative stress can paralyse the survival arm of the rheostat and lock the cell into a pro-apoptotic cycle (Ref. Reference Van Brocklyn and Williams67). Paradoxically, while physiological levels of S1P modulate normal redox signalling – such as engaging Gi-coupled S1PR1 receptors to promote controlled superoxide and nitric oxide generation required for germ cells to achieve functional competency – a pathological shift due to environmental insults completely overwhelms this homeostatic window. When tilted towards ceramide, the rheostat functions as a primary determinant of oxidative stress-mediated cellular injury, analogous to ischemic and toxic tissue degradation pathways (Ref. Reference Ueda72). Pharmacological supplementation with S1P breaks this vicious cycle by restoring the structural and metabolic equilibrium within the follicle. By counteracting ceramide-mediated lipotoxicity, S1P stabilises the mitochondrial membrane potential, mitigates oxidative damage and restores the meiotic and developmental potential of immature oocytes subjected to thermal stress (Refs Reference Hernández-Coronado, Guzmán, Castillo-Juárez, Zamora-Gutiérrez and Rosales-Torres8, Reference Lee, Kang, Jeong, Kim, Park, Song, Sim and Kim71).
Ovarian hyperstimulation syndrome (OHSS)
Endothelial junction dissolution and localised S1P depletion
OHSS is a severe iatrogenic complication of controlled ovarian stimulation during ART, characterised by cystic ovarian enlargement and a significant systemic increase in capillary permeability (Ref. 73). The central pathophysiological hallmark of OHSS is an acute fluid shift from the intravascular compartment into third spaces (peritoneal and pleural cavities), driving ascites, pleural effusion and hemoconcentration. At the molecular level, this vascular hyperpermeability is tied to the disruption of endothelial barrier integrity, where the sphingolipid network acts as a key regulator of endothelial junctions (Ref. Reference Ata and Humaidan74). Physiologically, vascular S1P regulates endothelial stability by engaging cell-surface S1PR1 receptors to promote the assembly and localised retention of VE-cadherin at cell–cell appositions, thereby reinforcing the cortical actin cytoskeleton and sealing the paracellular barrier against unwanted fluid exudation.
In patients with severe OHSS, this protective endothelial shield coincides with a significant localised reduction of S1P concentrations within the FF microenvironment. This S1P deficiency deprives endothelial cells of an essential stabilising signal, leaving the ovarian and peritoneal vasculature highly vulnerable to hyperpermeability factors that run unchecked during hyperstimulation, most notably VEGF. The consequent loss of S1P-mediated S1PR1 signalling leads to the destabilisation and internalisation of VE-cadherin complexes, facilitating endothelial barrier dissolution, cellular fenestration and paracellular leakage (Ref. Reference Scotti, Di Pietro, Pascuali, Irusta, de Zúñiga, Gomez Peña, Pomilio, Saravia, Tesone, Abramovich and Parborell75) (Figure 2).
Therapeutic restoration of capillary barrier integrity
Demonstrating the therapeutic potential of targeting this lipid node, preclinical interventions show that restoring S1P bioavailability effectively rescues the vascular phenotype. Specifically, in vivo intrabursal administration of S1P into the ovarian microenvironment significantly increases vascular integrity in rat models of OHSS (Ref. Reference Di Pietro, Pascuali, Scotti, Irusta, Bas, May, Tesone, Abramovich and Parborell76). This localised delivery of exogenous S1P counteracts systemic and local capillary leakage, significantly reducing peritoneal fluid (PF) accumulation, normalising ovarian weight and reversing hyperstimulation-related vascular disorders (Ref. Reference Di Pietro, Pascuali, Scotti, Irusta, Bas, May, Tesone, Abramovich and Parborell76). Collectively, these insights underscore that local S1P depletion is a critical permissive step in OHSS-associated vascular breakdown; its pharmacological reactivation offers a powerful, non-hormonal strategy to preserve vascular integrity and mitigate the clinical severity of ovarian hyperstimulation.
Sphingolipid and uterine and endometrial disorders
Endometriosis
While ovarian dysregulation of the sphingolipid rheostat typically promotes atresia, its manifestation within uterine and peritoneal microenvironments drives survival, pathological fibrosis and immune remodelling. Endometriosis is an oestrogen-dependent inflammatory disease characterised by ectopic endometrial-like stroma and glands (Ref. Reference Smolarz, Szyłło and Romanowicz77). Metabolomic analyses reveal systemic dysregulation in patients, marked by elevated circulating fatty acyl groups and ceramides (Ref. Reference Lin, Zeleznik, Vitonis, Laliberte, Shafrir, Avila-Pacheco, Clish, Terry, Missmer and Sasamoto78). Paradoxically, within both eutopic and ectopic endometrium, upregulated SMases decrease SM levels to inhibit apoptosis (Ref. Reference Lee, Tan, Venkatratnam, Tan, Cui, Loh, Griffith, Tannenbaum and Chan79). This survival phenotype is supported by accumulated local SM and phosphatidylcholine subspecies associated with altered lipid signalling during ectopic implantation (Ref. Reference Vouk, Hevir, Ribić-Pucelj, Haarpaintner, Scherb, Osredkar, Möller, Prehn, Lanišnik Rižner and Adamski80).
The hyper-activated S1P signalling axis serves as a prominent hallmark of these invasive features, mediating neuropeptide S-induced cell migration and lesion expansion (Ref. Reference Prisinzano, Bernacchioni, Seidita, Rossi, Raeispour, Cencetti, Vannuccini, Fambrini, Petraglia, Bruni and Donati81). Notably, ectopic lesions exert a retro-axial pathogenic effect on the ovary, driving altered autophagy in GCs and elevating very long-chain ceramides within the PF (Ref. Reference Turathum, Gao, Grataitong, Liu, Wang, Dai and Chian10). These peritoneal ceramides act as lipotoxic agents that disrupt neighbouring oocyte meiotic maturation, highlighting a strong correlation between pelvic lipid dysregulation and subfertility. This retrograde metabolic crosstalk underlines how localised pelvic lesions project lipotoxic damage back onto the ovarian niche, compromising the oocyte microenvironment (Figure 2).
Peritoneal evasion and immune remodelling
Concurrently, PF accumulation of S1P drives local immune evasion and microenvironmental remodelling. This peritoneal S1P surge functions as a chemokine that recruits monocytes and macrophages while preventing their apoptosis via constitutive PI3K/Akt and ERK1/2 activation (Ref. Reference Weigert, Johann, von Knethen, Schmidt, Geisslinger and Brüne82). Crucially, S1P skews these cells towards an immunosuppressive M2 macrophage phenotype (Ref. Reference Ono, Kawakita, Yoshino, Sato, Kano, Ohba, Okuno, Ito, Koga, Honda, Furue, Hiraoka, Wada, Iwasa, Yokomizo, Aoki, Maeda, Unno, Osuga and Hirata83). These M2 macrophages establish an inflammatory loop: S1P stimulates their expression of IL-6 and cyclooxygenase-2 (COX-2), promoting chronic pelvic inflammation and lesion growth (Ref. Reference Yoshino, Yamada-Nomoto, Kano, Ono, Kobayashi, Ito, Yoneda, Nakashima, Shima, Onda, Osuga, Aoki and Saito84).
Pathological fibrosis and fibroblast-to-myofibroblast transdifferentiation
Pathological fibrosis is an irreversible feature of endometriotic progression that causes severe pelvic scarring and chronic pain. The SphK1/S1P/S1PRs axis is closely involved in this fibrotic engine by synergising with canonical TGF-β1/Smad signalling (Ref. Reference An, Li, Yuan, Li, Zhang and Wang85). Locally elevated S1P potently stimulates FMT, prompting stromal fibroblasts to express α-smooth muscle actin (α-SMA) and secrete excessive extracellular matrix (ECM) proteins like collagen and fibronectin (Ref. Reference Zhang, Duan, Olson, Fazleabas and Guo86). This FMT process is primarily orchestrated by S1PR2 and S1PR3 coupling with G12/13 proteins to activate downstream Rho/ROCK signalling (Ref. Reference Quarta, Camprubí-Robles, Schweigreiter, Matusica, Haberberger, Proia, Bandtlow, Ferrer-Montiel and Kress87). Rho/ROCK activation increases myofibroblast contractility and tissue stiffness, maintaining the lesion in a fibrotic state.
Angiogenic ‘Inside-Out’ signalling
To sustain its hyper-proliferative phenotype, the ectopic lesion establishes a persistent blood supply via angiogenic ‘inside-out signalling’. Unlike physiological angiogenesis, endometriotic vascularisation is chaotic, excessive and resistant to pruning. While VEGF initiates premature microvessel sprouting, S1PR1 is indispensable for structural stabilisation (Ref. Reference Gavard and Gutkind88). Lesion-exported S1P binds endothelial S1PR1, consolidating VE-cadherin at cell–cell junctions to form a functional vascular barrier. Within the expanding lesion, local hypoxia stabilises HIF-1α, which directly upregulates SphK1 (Ref. Reference Semenza89). This hypoxia-induced enzymatic activation creates a feed-forward loop that ensures a continuous supply of S1P to the peritoneal microenvironment, stabilising the vascular network and supporting sustained ectopic growth.
Adenomyosis and uterine fibroids
Both adenomyosis and uterine fibroids are benign, oestrogen-responsive gynaecological disorders characterised by severe dysregulation of the S1P axis, which promotes aberrant smooth muscle cell proliferation, ECM deposition and pathological tissue rigidity (Figure 2).
Uterine adenomyosis
Uterine adenomyosis, characterised by the invasion of endometrial glands and stroma into the myometrium, exhibits a heavily distorted sphingolipid profile (Ref. Reference Vannuzzi, Bernacchioni, Muccilli, Castiglione, Nozzoli, Vannuccini, Capezzuoli, Ceccaroni, Bruni, Donati and Petraglia90). Ectopic lesions selectively upregulate the S1P3 receptor subtype compared to healthy endometrium (Ref. Reference Vannuzzi, Bernacchioni, Muccilli, Castiglione, Nozzoli, Vannuccini, Capezzuoli, Ceccaroni, Bruni, Donati and Petraglia90). This dysregulation links directly to TGF-β1 signalling, where S1P3 acts as a non-hormonal transducer that amplifies TGF-β-induced fibrotic cascades (Ref. Reference Bernacchioni, Capezzuoli, Vannuzzi, Malentacchi, Castiglione, Cencetti, Ceccaroni, Donati, Bruni and Petraglia91). Hyper-activation of the S1P/S1P3 axis correlates with the robust transcriptional activation of ACTA2 (encoding α-smooth muscle actin), driving the fibrotic transdifferentiation of endometrial stromal cells.
This fibrotic remodelling exhibits distinct stage-dependent and postmenopausal dynamics. While adenomyosis typically regresses symptomatically after menopause due to oestrogen withdrawal, α-SMA expression and tissue fibrosis can paradoxically increase in persistent postmenopausal lesions (Ref. Reference Vannuccini, Gabbrielli, Castiglione, Nardi, Rossi, Orlandi, Wu, Bertoli, Miele, Donati and Petraglia92). This progression is closely associated with defective S1P catabolism – marked by the downregulation of S1P lyase or S1P phosphatases – and altered downstream signalling, which locks the senescent myometrial microenvironment into a chronic fibrotic state (Ref. Reference Vannuccini, Gabbrielli, Castiglione, Nardi, Rossi, Orlandi, Wu, Bertoli, Miele, Donati and Petraglia92).
In tandem with structural stiffening, defects in the opposing arm of the sphingolipid rheostat enable adenomyotic cells to survive within the myometrium. Eutopic and ectopic stromal cells exhibit a severely damaged ceramide apoptotic pathway. When exposed to cellular stress or pro-apoptotic cues, these pathologically altered cells fail to accumulate ceramide or initiate mitochondrial channel formation, demonstrating a robust resistance to canonical apoptosis that facilitates deep myometrial infiltration (Ref. Reference Chrobak, Sieradzka, Sozański, Chełmońska-Soyta, Gabryś and Jerzak93). Given these temporal fluctuations across disease progression, implementing a stage-dependent therapeutic strategy using S1P3-selective antagonists offers a promising, non-hormonal approach for long-term adenomyosis management.
Uterine fibroids
Uterine fibroids (leiomyomas) are benign clonal tumours characterised by massive myometrial smooth muscle cell expansion and disproportionate ECM accumulation. Molecular profiling confirms extensive dysregulation of the SphK/S1P/S1PR axis in leiomyoma tissues compared to adjacent healthy myometrium. Quantitatively, mRNA and protein levels of SphK1, SphK2 and receptors S1P2, S1P3 and S1P5 are significantly elevated within fibroid nodules (Refs Reference Rossi, Seidita, Prisinzano, Raeispour, Romeo, Sorbi, Fambrini, Ciarmela, Petraglia, Bernacchioni and Donati94, Reference Bernacchioni, Ciarmela, Vannuzzi, Greco, Vannuccini, Malentacchi, Pellegrino, Capezzuoli, Sorbi, Cencetti, Bruni, Donati and Petraglia95). This localised enzymatic hyper-activation shifts the lipid microenvironment, allowing S1P to act as a potent, constitutive proliferative and fibrotic cue that drives leiomyoma growth and tissue stiffening.
A central mechanism of this fibrotic phenotype is the synergistic crosstalk between S1P and Activin A, a member of the TGF-β superfamily. Activin A expression is markedly upregulated in uterine fibroids, establishing a pro-fibrotic microenvironmental niche (Ref. Reference Bernacchioni, Ciarmela, Vannuzzi, Greco, Vannuccini, Malentacchi, Pellegrino, Capezzuoli, Sorbi, Cencetti, Bruni, Donati and Petraglia95). Secreted S1P serves as an essential downstream mediator and amplifier of Activin A-induced cascades, engaging overexpressed S1PRs to activate downstream Smad and non-Smad pathways. This receptor-mediated activation functionalises a feed-forward loop with Activin A, significantly enhancing the transcription and deposition of key ECM structural proteins, including collagen type I, collagen type III and fibronectin (Refs Reference Bernacchioni, Ciarmela, Vannuzzi, Greco, Vannuccini, Malentacchi, Pellegrino, Capezzuoli, Sorbi, Cencetti, Bruni, Donati and Petraglia95, Reference Islam, Akhtar and Segars96).
Furthermore, the S1P-Activin A axis contributes directly to the structural rigidity of leiomyomas by promoting cellular hypertrophy and mechanosensitive adaptation. Hyper-activation of S1P2 and S1P3 receptors triggers downstream G-protein-coupled Rho/ROCK signalling, leading to stress fibre formation, increased cellular tension and the subsequent activation of mechanosensitive gene transcription (Ref. Reference Rossi, Seidita, Prisinzano, Raeispour, Romeo, Sorbi, Fambrini, Ciarmela, Petraglia, Bernacchioni and Donati94). This lipid-dependent structural stabilisation provides a basis for understanding how fibroids maintain matrix remodelling independent of canonical steroid hormone pathways. Targeting the SphK/S1P/S1PRs-Activin A axis represents a highly promising, non-hormonal therapeutic strategy that treats fibroids without compromising the systemic endocrine baseline (Refs Reference Bernacchioni, Ciarmela, Vannuzzi, Greco, Vannuccini, Malentacchi, Pellegrino, Capezzuoli, Sorbi, Cencetti, Bruni, Donati and Petraglia95, Reference Islam, Akhtar and Segars96).
Endometrial receptivity and implantation
Bioactive sphingolipids and their phospholipid derivatives serve as indispensable homeostatic regulators required for the successful establishment of early pregnancy, orchestrating synchronised maternal–embryonic crosstalk during the peri-implantation window (Refs Reference Fakhr, Brindley and Hemmings97, Reference Ye, Zeng, Cai, Qiao and Zeng98). Dynamic lipidomic profiling reveals that localised lipid metabolism undergoes precise spatio-temporal reprogramming to dictate uterine receptivity, blastocyst attachment and subsequent decidualisation (Ref. Reference Ye, Zeng, Cai, Qiao and Zeng98). A foundational element of this uterine preparation is the tightly regulated fluctuation of sphingolipids within the endometrial stroma. In murine models, embryo implantation triggers a synchronous surge in local ceramide levels, strictly coupled with the transcriptional upregulation of the acid SMase gene (Smpd1) at active implantation sites (Ref. Reference Kaneko-Tarui, Zhang, Austin, Henkes, Johnson, Hansen and Pru99). This coordinated enzymatic activation ensures rapid, localised ceramide generation from SM hydrolysis, providing the membrane fluidity and signalling platforms necessary for initial embryo apposition. Conversely, genetic or pathological impairments in new SM synthesis disrupt this specialised lipid landscape, causing profound decidualisation defects, compromised placental bed formation and early pregnancy loss (Ref. Reference Ding, Qi, Gu, Zuo, Liu and Yang100).
Central to this early gestational cascade is S1P, which functions as a master coordinator of early pregnancy dynamics. Translating evidence from animal models and human clinical cohorts associates S1P signalling with the molecular execution of endometrial receptivity, optimal interembryonic spacing along the uterine horns and the initiation of uterine stromal decidualisation (Ref. Reference Yang, Zhao, Liu and Li9). Beyond organising the maternal compartment, S1P plays a vital paracrine role in guiding trophoblast behaviour and driving placental vascularisation. Secreted S1P acts through specific receptor networks to regulate the directional migration and proliferation of the invading chorionic villus trophoblast layer, anchoring the developing placenta to the maternal uterine wall while simultaneously promoting localised angiogenesis (Ref. Reference Fakhr, Brindley and Hemmings97). Given this absolute dependency on precise S1P gradients, either a localised deficiency in S1P synthesis or its pathological overproduction can disrupt uterine receptivity required for embryonic acceptance, presenting a cryptic, non-hormonal factor associated with recurrent implantation failure.
The pathological consequences of disrupting this sphingolipid-dependent pathway are clearly illustrated in chronic endometritis. Chronic inflammatory stress triggers severe endoplasmic reticulum stress within the endometrial epithelium, driving the aberrant activation of the transcription factor CCAAT/enhancer-binding protein delta (CEBPD) (Ref. Reference Wang, Chen, You, Yu, Chen, Lian, Diao, Li and Yin101). Once activated, CEBPD protein transcriptionally upregulates the S1P phosphatase 2 (SGPP2) gene, leading to S1P degradation. This pathological overexpression of SGPP2 causes an acute local exhaustion of S1P signalling, dismantling the essential receptor-mediated pathways required for physiological vascular remodelling and endothelial barrier stabilisation during the secretory phase. This inflammation–ER stress–SGPP2 axis induces a failure of endometrial receptivity and structural decidualisation, providing a direct mechanistic link bridging localised chronic inflammation to endometritis-related reproductive failure (Ref. Reference Wang, Chen, You, Yu, Chen, Lian, Diao, Li and Yin101).
Chronic pain and neuro-immune crosstalk
Chronic pelvic pain is the most debilitating symptom in patients with gynaecological disorders like endometriosis and provoked vestibulodynia, severely compromising quality of life and sexual function. Emerging translational evidence establishes the sphingolipid axis as a key mediator of pain amplification bridging localised inflammation and pathological neuro-immune crosstalk (Ref. Reference Labus, Mayer, Tillisch, Aagaard, Stains, Broniowska, van Remortel, Tun and Rapkin102). Within the pelvic microenvironment, ectopic lesion-derived inflammatory cytokines, such as TNF-α and IL-1β, stimulate the robust release of nerve growth factor (NGF) (Ref. Reference Stanisz and Stanisz103). Mechanistically, localised ceramide accumulation induces thermal hyperalgesia by stimulating a reciprocal increase in tissue TNF-α and obligating the recruitment of the downstream S1P-to-S1PR1 signalling pathway (Figure 2).
Once generated within this neuro-immune niche, S1P engages S1PR1 and S1PR3 receptors on primary afferent sensory neurons to profoundly lower their mechanical and thermal excitation thresholds, driving clinical allodynia and hyperalgesia. This axis amplifies persistent pain by cross-linking with nociceptive transient receptor potential (TRP) channels, notably functionalising the S1P/S1PRs–TRPV4 axis to gate pro-nociceptive ion fluxes and perpetuate chronic mechanical hypersensitivity (Ref. Reference Zhang, Zhou, Wang, Ren, Wang, Liu, Feng, Li, Qi, Yang, Zhu, Wang, Ma, Tang and Yu104). Furthermore, this lipid-driven nociceptive signature is systemic and phenotype-dependent. Circulating ceramides and SMs are significantly elevated in obese cohorts, correlating with pain severity and linking metabolic obesity to chronic musculoskeletal and pelvic pain syndromes (Ref. Reference Gonzalez, Simcox, Raff, Wade, von Bank, Weisman and Hainsworth105). Disruption of these sphingolipid pathways directly associates with vulvar pain, levator ani muscle tenderness and altered functional connectivity within pain-processing brain regions, while early-life pain experiences can cause a long-term reduction in long-chain sphingolipids that correlates with later compulsive pain behaviours (Ref. Reference Labus, Mayer, Tillisch, Aagaard, Stains, Broniowska, van Remortel, Tun and Rapkin102).
In tandem with functional peripheral sensitisation, the sphingolipid rheostat governs the structural remodelling of the pelvic nervous system via pathological innervation dynamics. Within deep infiltrating endometriotic lesions, S1P exerts a complex, receptor-dependent dual effect on neurogenesis and nerve sprouting. Activation of neuronal S1PR1 potently promotes axonal elongation and the directional sprouting of unmyelinated sensory nerve fibres towards inflammatory foci. Conversely, when S1P engages S1PR3 on the same growth cones, it couples with G12/13 proteins to trigger downstream RhoA/ROCK pathway activation, mediating growth cone collapse and localised neurite retraction (Ref. Reference Quarta, Camprubí-Robles, Schweigreiter, Matusica, Haberberger, Proia, Bandtlow, Ferrer-Montiel and Kress87). The localised imbalance between S1PR1-mediated elongation and S1PR3-mediated growth cone steering leads to highly disorganised, hyper-dense and hypersensitive sensory nerve networks within the subperitoneal space. This aberrant neurovascular niche remains locked in a state of persistent activation, rendering the S1P axis a promising, non-hormonal therapeutic target to disrupt the feed-forward cycle of neuro-immune inflammation and chronic pelvic pain.
Clinical translation and future perspectives
The multi-layered involvement of the sphingolipid rheostat in both physiological reproduction and gynaecological pathologies presents significant clinical opportunities. Shifting the paradigm from systemic hormonal suppression – which routinely induces hypoestrogenic side effects and halts ovulation – to targeted lipid interventions offers a non-hormonal frontier for precision diagnosis and therapeutic management.
Sphingolipid metabolites as fluid-based diagnostic biomarkers
The state-dependent fluctuations of ceramide and S1P within plasma and FF mirror the real-time pathophysiological status of the reproductive microenvironment, serving as sensitive candidates for non-invasive biomarker discovery. In ART, lipidomic fingerprinting provides critical predictive insights into ovarian reserve and individual cycle outcomes. In women with diminished ovarian reserve or reproductive ageing, quantitative assessments of serum and FF ceramide levels serve as independent indicators of oocyte quality and in vitro fertilisation success (Ref. Reference Timur, Aldemir, İnan, Kaplanoğlu and Dilbaz106). Furthermore, FF profiling from patients with unexplained infertility reveals a distinct phenotype marked by enriched triacylglycerols and severe depletion of functional phospholipids and sphingolipids (Ref. Reference Batushansky, Zacharia, Shehadeh, Bruck-Haimson, Saidemberg, Kogan, Thomas Mannully, Herzberg, Ben-Meir and Moussaieff107). This discriminative signature links local sphingolipid deficits to a suboptimal follicular niche, offering an innovative diagnostic layer to identify metabolic etiologies of reproductive failure prior to controlled ovarian stimulation.
Beyond predicting ART outcomes, specific sphingolipid subclasses furnish disease-specific signatures that enable early detection and risk stratification. In PCOS, a coordinated downregulation of multiple FF sphingolipid species and phosphatidylcholines correlates with gonadotropin hyper-responsiveness and impaired oocyte maturation (Ref. Reference Cordeiro, Cataldi, do Vale Teixeira da Costa, de Lima, Stevanato, Zylbersztejn, Ferreira, Eberlin, Cedenho and Turco50). Conversely, advanced epithelial ovarian cancer features a profound accumulation of circulating and tissue-level long-chain ceramides, SMs and glycolipids, which drop precipitously following surgical cytoreduction, serving as sensitive diagnostic and staging biomarkers (Ref. Reference Knapp, Bodnar, Błachnio-Zabielska, Świderska and Chabowski108).
In benign proliferative disorders, targeted metabolomics demonstrates that pelvic endometriosis is characterised by elevated systemic and local SM and phosphatidylcholine levels (Ref. Reference Vouk, Hevir, Ribić-Pucelj, Haarpaintner, Scherb, Osredkar, Möller, Prehn, Lanišnik Rižner and Adamski80). Crucially, high-resolution liquid chromatography discriminates between generalised peritoneal endometriosis and localised ovarian endometriomas based on unique mass-to-charge ratio (m/z) signatures of their respective lipid pools, providing an advanced tool for differential diagnosis. Finally, in acute vascular emergencies like OHSS, a precipitous collapse of pre-ovulatory FF S1P levels acts as an early biomonitoring index predicting endothelial junction breakdown and severe vascular hyperpermeability (Ref. Reference Di Pietro, Pascuali, Scotti, Irusta, Bas, May, Tesone, Abramovich and Parborell76). Together, these multi-disease lipid signatures pave the way for incorporating targeted sphingolipid panels into standard gynaecological triage and personalised reproductive medicine.
Therapeutic frontiers: modulating the sphingolipid network for fertility preservation
The transition of the sphingolipid rheostat from a diagnostic tool to a therapeutic target represents a major frontier in non-hormonal gynaecological pharmacology. Because the balance between ceramide-mediated apoptosis and S1P- or ceramide-1-phosphate (C1P)-mediated survival dictates cell fate, interventions designed to selectively tilt this rheostat offer unprecedented strategies for restoring ovarian health. This approach is vital in oncofertility, where safeguarding the primordial follicle pool against gonadotoxic insults remains a primary clinical challenge.
In this context, C1P – synthesised via ceramide kinase – functions as a potent cytoprotective agent within the ovarian niche. Preclinical evidence in murine models of POI demonstrates that exogenous C1P administration exerts robust protective properties against cyclophosphamide-induced ovarian damage (Ref. Reference Pascuali, Scotti, Di Pietro, Oubiña, Bas, May, Muñoz, Cuasnicú, Cohen, Tesone, Abramovich and Parborell109). Mechanistically, C1P neutralises the excessive de novo ceramide accumulation triggered by alkylating chemotherapeutic agents, thereby suppressing GC apoptosis, preserving ovarian cortical integrity, and maintaining baseline follicle pool viability. Targeting specific bioactive derivatives like C1P provides a promising, receptor-specific framework to counteract iatrogenic ovarian insufficiency and extend female reproductive longevity.
Current limitations and future directions
Despite the substantial diagnostic and therapeutic potential of the sphingolipid metabolic network, several critical bottlenecks and clinical hurdles must be resolved before these lipid-targeted interventions can transition into standard gynaecological practice.
The primary pharmacological challenge stems from the inherent conflict between receptor ubiquity and systemic toxicity. Because sphingosine-1-phosphate receptors (S1PR1–5) are ubiquitously expressed across the cardiovascular and immune systems, broad-spectrum lipid modulators carry a high risk of inducing severe off-target effects, such as bradycardia and profound immunosuppression. To bypass these systemic liabilities, future drug discovery pipelines must prioritise the design of next-generation, highly selective sub-receptor antagonists – such as JTE013 for S1P2 or TY-52156 for S1P3. These subtype-specific small molecules hold the key to precisely dismantling localised pelvic fibrotic and nociceptive pathways without disrupting systemic homeostatic functions.
A secondary clinical dilemma involves establishing the long-term oncological safety of these survival-promoting lipids within oncofertility. Because S1P is inherently anti-apoptotic and angiogenic, its application as a pharmacological shield to safeguard the primordial follicle pool against gonadotoxic chemotherapy introduces a severe risk of inadvertently protecting residual micrometastases or accelerating tumour recurrence.
Furthermore, a major methodological challenge in reproductive lipidomics lies in delineating whether the altered sphingolipid profiles observed in clinical cohorts represent primary upstream drivers of pathology or secondary downstream manifestations of systemic metabolic dysfunction. The majority of current human dataset matrices rely on cross-sectional clinical associations, which capture correlative biomarker signatures rather than direct causal networks. While these fluid-based profiles provide valuable predictive indicators for clinical triage, establishing absolute pathogenic causality requires validation through functional loss- or gain-of-function transgenic animal models. Disentangling these associative metabolic reflections from authentic molecular etiologies remains a prerequisite for the accurate identification of therapeutic targets.
Finally, navigating the context-dependent, pleiotropic nature of sphingolipid flux demands a transition towards high-resolution mechanistic mapping within the reproductive tract. S1P signalling is highly dynamic, capable of driving either pro-inflammatory M1 or immunosuppressive M2 macrophage polarisation depending on localised cytokine cues. Consequently, relying on bulk tissue lysates no longer suffices. The future of this field depends on integrating single-cell multi-omics – including transcriptomics and proteomics – with high-resolution spatial metabolomics and mass spectrometry imaging. Unlocking this spatial and cellular granularity is an absolute prerequisite to accurately map localised lipid fluxes across distinct cellular subpopulations, transforming our understanding of the sphingolipid network into a predictable, finely controlled therapeutic landscape for female reproductive health.
Conclusion
The sphingolipid rheostat acts as a fundamental molecular switch in the female reproductive system, balancing the balance between cell survival and apoptosis. Disruptions in this lipid network lie at the pathogenic core of a wide spectrum of disorders, from ovarian ageing and PCOS to the fibrotic and inflammatory landscapes of endometriosis and uterine fibroids. By decoding these intricate metabolic pathways, the field is poised to unlock novel, targeted therapeutic strategies that not only alleviate debilitating symptoms but also preserve and restore reproductive longevity.
Acknowledgements
The authors declare that no additional acknowledgements are applicable to this work.
Author contribution
All authors met the criteria for authorship. M.R.L. wrote the manuscript and collected the references; M.R.L and L.W modified the manuscript; J.L. and L.W. acquired the funding; M.R.L and L.W. designed the manuscript and supervised the study. All authors critically revised the manuscript and approved the final version for publication.
Funding statement
This work is supported by the National Natural Science Foundation of China (No. 82501968) and the National Key Research and Development Program of China (No. 2025YFC3508002–01).
Competing interests
The authors declare that they have no competing interests.
Ethical standard
Not applicable.
Disclosure of use of AI tools
This manuscript utilised Grammarly (https://www.grammarly.com/) to enhance the language quality and readability. No other AI-generated content was utilised in the preparation of this manuscript. The authors take full responsibility for the integrity and originality of the work.
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