SIRT3 Blocks AGE-Driven Ovarian Aging by Boosting Mitophagy in Granulosa Cells
New research shows SIRT3 overexpression reverses AGE-induced senescence in human granulosa cells by restoring mitophagy and hormone output.
Summary
Advanced glycation end products (AGEs) — compounds that accumulate with normal aging — directly trigger senescence in human granulosa cells, the support cells surrounding eggs in the ovary. Researchers found AGEs impair mitochondrial function and suppress mitophagy, the cellular process that clears damaged mitochondria. The mitochondria-resident protein SIRT3 acts as a key protector: overexpressing it reduced senescence markers, restored mitochondrial membrane potential, lowered ROS, and boosted estradiol and progesterone production. Conversely, silencing SIRT3 or its downstream partner PINK1 worsened all these effects. The mitophagy activator urolithin A mimicked SIRT3's benefits, suggesting mitophagy enhancement is a viable therapeutic route to slow ovarian aging and preserve female fertility.
Detailed Summary
Female fertility declines significantly with age, driven largely by falling follicle numbers and deteriorating oocyte quality. Granulosa cells — which directly surround and nourish oocytes within ovarian follicles — are increasingly recognized as central to this decline. When granulosa cells undergo senescence, follicle growth stalls, leading to follicular atresia and reduced ovarian reserve. This study set out to determine whether advanced glycation end products (AGEs), which accumulate systemically and within the follicular fluid during normal aging, are a direct driver of granulosa cell senescence, and whether the mitochondrial deacetylase SIRT3 can counteract this process via mitophagy regulation.
The study used primary human granulosa cells (hGCs) isolated from 477 IVF patients aged ≤35 years, as well as the KGN granulosa cell line. Cells were treated with AGEs at concentrations ranging from 50 to 200 µg/ml, reflecting physiologically relevant follicular fluid accumulation. Senescence was assessed via SA-β-galactosidase staining, γ-H2AX immunocytochemistry (DNA damage foci), and cell cycle arrest markers. Mitochondrial health was evaluated by measuring mitochondrial membrane potential (MMP) via JC-1 dye, intracellular ROS via DCFH-DA, and ATP levels. Mitophagy was assessed by LC3 puncta formation and PINK1/Parkin pathway protein expression.
AGEs induced senescence in a clear dose-dependent manner. At 200 µg/ml, SA-β-gal-positive cells increased markedly compared to controls, accompanied by elevated γ-H2AX foci (DNA damage), reduced MMP, increased ROS, and significantly decreased ATP production. Critically, mitophagy was suppressed in AGEs-treated cells, as shown by reduced LC3-II levels and diminished PINK1/Parkin expression. When mitophagy was pharmacologically activated using urolithin A (20 µM), senescence markers were substantially reduced and mitochondrial function was restored. Conversely, blocking mitophagy with cyclosporine A (1 µM) exacerbated all AGEs-induced deficits, confirming mitophagy as a functional mediator of AGE-related granulosa cell senescence.
SIRT3 protein expression was lower in hGCs from older donors (≥38 years) compared to younger donors (≤35 years), establishing clinical relevance. Lentiviral knockdown of SIRT3 significantly worsened AGEs-induced senescence, ROS accumulation, MMP collapse, and ATP depletion. In contrast, SIRT3 overexpression attenuated all senescence markers, improved mitochondrial membrane potential, reduced ROS, and elevated ATP. Mechanistically, SIRT3 overexpression upregulated PINK1 and Parkin, key mitophagy pathway components, indicating SIRT3 drives mitophagy enhancement. Silencing PINK1 abolished the protective effects of SIRT3 overexpression, placing PINK1-mediated mitophagy downstream of SIRT3 in this pathway. Importantly, SIRT3 overexpression also significantly increased FSH-stimulated estradiol-17β and progesterone secretion by hGCs, demonstrating restoration of endocrine function.
These findings establish a mechanistic chain: aging-associated AGE accumulation → SIRT3 downregulation → impaired PINK1/Parkin mitophagy → dysfunctional mitochondria → granulosa cell senescence → reduced steroidogenesis → ovarian aging. The study positions both SIRT3 and mitophagy enhancement (achievable with agents like urolithin A) as actionable therapeutic targets. Limitations include the in vitro design, the use of a cell line alongside primary cells, and the absence of in vivo ovarian aging models. Whether systemic SIRT3 activation or urolithin A supplementation can meaningfully preserve ovarian reserve in aging women remains to be tested in clinical trials.
Key Findings
- AGEs at 200 µg/ml produced a dose-dependent increase in SA-β-gal-positive senescent granulosa cells and γ-H2AX DNA damage foci compared to untreated controls.
- AGEs treatment significantly reduced mitochondrial membrane potential (JC-1 red/green ratio decreased) and intracellular ATP, while markedly elevating ROS levels in hGCs.
- Mitophagy activator urolithin A (20 µM) reduced AGEs-induced senescence markers, restored MMP, and lowered ROS, while mitophagy inhibitor cyclosporine A (1 µM) worsened all deficits.
- SIRT3 protein expression was significantly lower in granulosa cells from older women (≥38 years) than in those from younger women (≤35 years), linking SIRT3 to ovarian aging.
- SIRT3 overexpression via lentiviral vector attenuated AGEs-induced senescence, restored mitochondrial function, and upregulated PINK1/Parkin mitophagy pathway proteins.
- PINK1 knockdown abolished the protective effects of SIRT3 overexpression, confirming PINK1-mediated mitophagy is required for SIRT3's anti-senescence action.
- SIRT3 overexpression significantly increased FSH-stimulated estradiol-17β and progesterone secretion in AGEs-treated hGCs, demonstrating restoration of ovarian steroidogenic function.
Methodology
Primary hGCs were isolated from 477 female IVF patients (≤35 years) via density gradient centrifugation of follicular aspirates; the KGN cell line served as a complementary model. AGEs (50–200 µg/ml) were applied for 24–48 h; mitophagy was pharmacologically modulated with urolithin A (20 µM) or cyclosporine A (1 µM). SIRT3 and PINK1 were knocked down using lentiviral shRNA delivery; SIRT3 was overexpressed via lentiviral vector. Readouts included SA-β-gal staining, γ-H2AX immunofluorescence, JC-1-based MMP measurement by confocal microscopy and flow cytometry, DCFH-DA ROS quantification, ATP luminescence assay, and ELISA for estradiol-17β and progesterone.
Study Limitations
The study is entirely in vitro, using isolated primary granulosa cells and a cell line, so it cannot capture the full complexity of the ovarian follicular microenvironment or systemic aging processes. No in vivo mouse ovarian aging model was employed to validate the cellular findings. The authors acknowledge the mechanistic pathway from SIRT3 to mitophagy to senescence needs further delineation, and no conflicts of interest were declared.
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