SS-31 Peptide Reverses Age-Related Oocyte Decline by Restoring Mitochondrial Function

Advanced maternal age is one of the most significant and growing challenges in reproductive medicine. As women increasingly delay childbearing, oocyte quality deteriorates sharply after the mid-30s, driven by mitochondrial dysfunction, oxidative stress accumulation, spindle abnormalities, and chromosomal aneuploidy. Assisted reproductive technologies offer partial compensation but cannot fully overcome age-driven deficits in meiotic competence and early embryonic development. This study investigated whether SS-31 (Elamipretide, D-Arg-2′6′-dimethylTyr-Lys-Phe-NH2), a small mitochondria-targeting tetrapeptide known for its cardiolipin-binding and antioxidant properties, could rescue these defects when added to in vitro maturation (IVM) culture medium.

The experimental model compared oocytes collected from young (6–8-week-old) and aged (52–56-week-old) KM female mice following PMSG stimulation. Cumulus-oocyte complexes were matured in M16 medium with or without 10 μM SS-31 for 12–16 hours. Oocyte maturation rates, spindle morphology, chromosome structure, aneuploidy rates, reactive oxygen species (ROS) levels, DNA damage (γ-H2A.X staining), mitochondrial membrane potential (ΔΨm by JC-1), mitochondrial distribution, mitophagy activity, sperm binding, and embryo development to blastocyst were all assessed. Single-cell transcriptomics (SMART-seq protocol) and untargeted single-cell metabolomics (UPLC-MS/MS) were performed to map the molecular mechanisms.

SS-31 treatment produced marked improvements across all functional endpoints. Aged oocytes showed severely disrupted spindle morphology and elevated aneuploidy, both of which were significantly restored by SS-31. ROS fluorescence intensity and γ-H2A.X-positive foci (a DNA double-strand break marker) were substantially reduced in the SS-31-treated aged group compared to untreated aged controls. Critically, mitochondrial distribution shifted from the peripherally clustered, dysfunctional pattern typical of aged oocytes back toward the homogeneous cytoplasmic distribution seen in young oocytes. JC-1 aggregate-to-monomer fluorescence ratios confirmed recovery of ΔΨm. Mitophagy activity, assessed with a Mitophagy Detection Kit alongside LysoTracker and MitoTracker co-staining, was also significantly enhanced by SS-31.

Single-cell transcriptome analysis (3 oocytes per sample, 3 replicates per group) revealed that SS-31 upregulated key mitophagy and mitochondrial biogenesis genes — Pink1, Rps27a, Tomm7, and Map1lc3b — in aged oocytes. SS-31 also promoted maternal mRNA degradation pathways (consistent with proper oocyte-to-embryo transition) while suppressing chromatin organization, histone modification, and chromatin remodeling gene sets. Real-time PCR validated these transcriptomic findings. On the metabolome side, single-cell UPLC-MS/MS identified spermidine and glutathione (GSH) as the most significantly elevated metabolites following SS-31 treatment — both are established anti-aging molecules with roles in autophagy induction and ROS neutralization respectively.

Fertilization competence and developmental potential were likewise improved. Sperm binding to the zona pellucida was enhanced in SS-31-treated aged oocytes, and subsequent embryo culture showed higher rates of 2-cell, morula, and blastocyst formation compared to untreated aged controls. The study is preclinical and limited to a mouse model, and translation to clinical IVM protocols will require further validation in human oocytes. Nonetheless, the mechanistic convergence across functional assays, transcriptomics, and metabolomics makes a compelling case that SS-31 supplementation in IVM media could be a practical, low-cost strategy to extend reproductive healthspan.