Stem Cell Injections Reverse Ovarian Aging at the Single-Cell Level in Mice
HucMSCs injected into aged mouse ovaries reprogrammed stromal metabolism, restored oocyte gene expression, and partially recovered fertility.
Summary
Researchers injected human umbilical cord mesenchymal stem cells (HucMSCs) directly into the ovaries of aged mice and tracked the effects using single-cell RNA sequencing. Four weeks later, treated mice showed more antral follicles, higher estradiol and AMH levels, and partially restored fertility. Critically, 75% of aging-dysregulated genes in oocytes reverted to youthful expression patterns, especially genes governing mitochondrial respiratory chain assembly. In ovarian stromal cells, HucMSCs redirected cell fate away from fibrosis and toward steroidogenesis and follicle support. Granulosa cells upregulated glycolysis, while stromal cells boosted pregnenolone synthesis — a key steroid precursor. Transplanting HucMSC-primed stromal cells alone replicated these restorative effects, identifying stromal metabolic reprogramming as a central therapeutic mechanism.
Detailed Summary
Ovarian aging is a primary driver of female infertility, characterized by declining follicle reserves, hormonal imbalance, and deteriorating oocyte quality. As delayed childbearing becomes more common, the need for effective rejuvenation strategies is acute. Human umbilical cord-derived mesenchymal stem cells (HucMSCs) have shown promise in restoring ovarian function after chemotherapy and in patients with premature ovarian insufficiency, but the precise cellular and molecular mechanisms — especially across different ovarian cell types — remained poorly understood until this study.
The research team administered in situ ovarian injections of 1×10⁶ HucMSCs (25 µl per ovary) into 8–10-month-old aged C57BL/6 female mice, with a saline-injected aged group as control and 6–8-week-old young mice as a reference. After four weeks, ovaries were harvested for histology, hormone assays, low-input RNA-seq on oocytes, and single-cell RNA sequencing (scRNA-seq) on somatic cells. GFP-labeled HucMSCs were tracked to confirm localization predominantly within the ovarian stroma rather than in follicular structures.
Functionally, HucMSC-treated aged mice showed significantly increased antral follicle counts and elevated serum AMH and estradiol levels compared to controls. Fertility testing confirmed partial restoration of litter sizes. At the transcriptomic level, oocyte RNA-seq revealed that 75% of aging-dysregulated genes reverted toward youthful expression patterns following HucMSC treatment. The most prominently restored gene categories were those encoding mitochondrial respiratory chain complex assembly factors, consistent with improved ATP production capacity — a known limiting factor in oocyte meiotic competence and embryo viability.
scRNA-seq of somatic ovarian cells provided the most mechanistically detailed findings. In granulosa cells, HucMSC treatment upregulated transcription activity and glycolytic gene expression, supporting the energy demands of follicular development. In stromal cells — where HucMSCs predominantly engrafted — cell fate was redirected away from pro-fibrotic pathways and toward steroidogenic and folliculogenic programs. Specifically, HucMSCs promoted pregnenolone synthesis in stromal cells, elevating this foundational steroid precursor that feeds downstream hormone production including progesterone and estradiol. Masson staining confirmed reduced collagen deposition (fibrosis) in treated ovaries.
To isolate the stromal contribution, the team harvested stromal cells that had been co-cultured with HucMSCs in vitro (HucMSC-primed stromal cells) and transplanted them alone into aged mouse ovaries. This intervention replicated the key restorative effects observed with direct HucMSC injection — increased follicle numbers, improved hormone profiles, and reduced fibrosis — demonstrating that reprogrammed stromal cells are themselves sufficient to rejuvenate the ovarian microenvironment. This finding positions ovarian stromal cells as both a target and a vehicle for anti-aging intervention. The study is the first to map HucMSC-induced changes at single-cell resolution across oocyte, granulosa, and stromal compartments simultaneously, revealing a coordinated metabolic reprogramming axis spanning all three cell types.
Key Findings
- 75% of aging-dysregulated oocyte genes reverted to youthful expression patterns after HucMSC treatment, predominantly mitochondrial respiratory chain complex assembly genes
- HucMSC-treated aged mice showed significantly increased antral follicle counts and elevated serum AMH and estradiol levels vs. saline controls after 4 weeks
- Single-cell RNA sequencing identified stromal cell fate redirection away from fibrosis and toward steroidogenesis and folliculogenesis in response to HucMSCs
- HucMSCs promoted pregnenolone synthesis in ovarian stromal cells, boosting the foundational steroid precursor for downstream hormone production
- Granulosa cells in HucMSC-treated ovaries upregulated both transcriptional activity and glycolytic gene expression, supporting follicle energy demands
- Transplantation of HucMSC-primed stromal cells alone into aged ovaries replicated the restorative effects of direct HucMSC injection, confirming stromal reprogramming as a primary mechanism
- GFP-labeled HucMSCs localized predominantly in ovarian stroma rather than follicular structures, explaining the stromal-first mechanism of action
Methodology
Aged (8–10-month) and young (6–8-week) female C57BL/6 mice received in situ bilateral ovarian injections of either 1×10⁶ HucMSCs or saline (25 µl per ovary); mice were harvested after 4 weeks. Oocyte transcriptomics used low-input RNA-seq; somatic cell heterogeneity was mapped by scRNA-seq. GFP-labeled HucMSCs tracked cell localization; HucMSC-primed stromal cell transplantation was used to isolate stromal contributions. Hormone levels (AMH by ELISA; estradiol and progesterone by immunoassay) and follicle counts from serial 3-µm H&E sections were primary outcome measures; Masson staining quantified fibrosis.
Study Limitations
The study was conducted entirely in an aged mouse model, and direct translation to human ovarian aging — which involves decades-long depletion rather than months — requires cautious interpretation. Sample sizes for functional assays were not determined by formal power calculations but by field convention, potentially limiting statistical confidence. The authors did not report specific p-values or effect sizes for many of the scRNA-seq-derived pathway findings, and long-term durability of the restorative effects beyond four weeks was not assessed.
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