Iron Overload Drives Premature Ovarian Aging in Endometriosis-Linked Infertility
Single-cell and spatial transcriptomics reveal how excess iron triggers cellular senescence and metabolic dysfunction in ovarian follicles, explaining poor oocyte quality in endometriosis.
Summary
Researchers used single-cell RNA sequencing of follicular fluid from ovarian endometriosis (OE) patients, spatial transcriptomics (Stereo-seq) in iron-overloaded mouse ovaries, and reanalysis of aging human ovarian datasets to map how iron overload disrupts follicular function. They found that elevated iron in the pre-ovulatory microenvironment induces cellular senescence, metabolic reprogramming, and abnormal immune polarization—particularly in granulosa and cumulus cells—that collectively impair oocyte quality. These iron-driven senescence signatures were conserved across OE patients, iron-overloaded mice, and naturally aging human ovaries, suggesting iron dysregulation is a shared mechanism bridging endometriosis-associated and age-related ovarian decline, and a viable therapeutic target.
Detailed Summary
Ovarian endometriosis (OE) affects up to 44% of endometriosis cases and is a leading cause of infertility, yet why oocyte quality is so severely compromised in affected women has remained poorly understood. This study provides the most detailed molecular map to date of how iron overload—a hallmark of OE-affected ovaries—reshapes the follicular microenvironment at single-cell resolution.
The team began with a retrospective cohort of 4,087 IVF/ICSI patients, using propensity score matching to compare 308 OE patients against tubal-factor and male-factor infertility controls. OE patients had significantly fewer antral follicles, fewer mature oocytes, and fewer high-quality embryos, with notably higher rates of congenital and neonatal defects, despite similar live birth rates. Integrating public Smart-seq2 MII oocyte data with their own bulk RNA-seq of follicular fluid granulosa cells confirmed elevated DNA damage, impaired repair pathways, and dysregulated iron metabolism signatures in OE follicles.
The centerpiece of the study is a first-of-its-kind single-cell atlas of pre-ovulatory follicular fluid from OEI patients, revealing dynamic iron metabolism changes across multiple cell types—granulosa cells, cumulus cells, macrophages, and others. Iron accumulation was linked to upregulation of senescence markers (p21, p16), SASP (senescence-associated secretory phenotype) components, and oxidative stress pathways. Cumulus cells showed iron-sensitive differentiation trajectory disruptions, and macrophages displayed skewed M1/M2 polarization states tied to iron handling, suggesting a pro-inflammatory, senescence-promoting microenvironment.
To validate spatial and temporal dynamics in vivo, the team applied Stereo-seq spatial transcriptomics to iron-overloaded mouse ovaries, confirming localized senescence signatures in follicular compartments mirroring the human data. Critically, reanalysis of public single-cell datasets from aging human ovaries identified nearly identical iron dysregulation and senescence patterns, linking OE-associated pathology to physiological ovarian aging at the molecular level.
These findings position iron overload as a convergent driver of both pathological (endometriosis) and physiological (aging) ovarian decline, opening avenues for iron chelation or antioxidant strategies to preserve oocyte quality in OE patients. Limitations include the cross-sectional nature of follicular fluid sampling, the inability to fully recapitulate in vivo temporal follicular dynamics, and the need for prospective clinical trials to test iron-targeting interventions.
Key Findings
- OE patients had significantly fewer mature oocytes and high-quality embryos than matched tubal or male-factor infertility controls.
- Single-cell atlas of OEI follicular fluid revealed iron overload-induced senescence (p21/p16 upregulation) and SASP across granulosa and cumulus cells.
- Iron excess skewed macrophage polarization toward M1-like pro-inflammatory states, disrupting the follicular immune microenvironment.
- Stereo-seq spatial transcriptomics in iron-overloaded mouse ovaries confirmed localized senescence signatures in follicular compartments.
- Aging human ovaries showed conserved iron dysregulation and senescence patterns, linking OE pathology to physiological ovarian aging.
Methodology
The study combined retrospective IVF/ICSI cohort analysis (n=4,087, propensity-matched), Smart-seq2 single-cell and bulk RNA-seq of follicular fluid, a novel scRNA-seq atlas of pre-ovulatory follicular fluid from OEI patients, Stereo-seq spatial transcriptomics in iron-overloaded mouse ovaries, and reanalysis of public human ovarian aging scRNA-seq datasets. Propensity score matching controlled for age and BMI confounders.
Study Limitations
Follicular fluid sampling is cross-sectional and cannot capture full temporal dynamics of in vivo follicular development. Mouse iron-overload models may not perfectly replicate the complex endometriosis disease milieu. Clinical translation requires prospective trials testing iron-targeted interventions on oocyte and embryo outcomes.
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