Inhibition of the ISG15 prevents inflammation-dependent ovarian aging

Inflammation is a hallmark of aging and negatively affects ovarian function and female fertility. ISGylation is a post-translational modification regulating many life activities, including inflammation, immunomodulation, and embryo implantation. However, the exact role of ISGylation in ovarian aging remains unclear. In this study, age-dependent increase in Isg15 expression was observed in murine ovaries during reproductive aging. Wild-type female mice displayed progressively reduced ovarian reserve, disrupted endocrine function, and ultimately impaired fertility with age, but Isg15 knockdown partly mitigated this phenomenon. Transcriptome sequencing of ovaries from Isg15-/- and WT mice at 12 months of age revealed that Isg15 deletion ameliorated the genes and pathways associated with inflammation process and ovarian function. Meanwhile, Isg15 knockout in mice inhibited ovarian oxidative stress, and then, protected ovarian mitochondrial structure and function. Mechanistically, ISG15 resulted in degradation of proteasome 26S subunit non-ATPase 14 (PSMD14), a negative regulator of inflammasome activation. Furthermore, the degradation of ISGylated PSMD14 suppressed the K63-linked ubiquitination of Pro-IL-1β, and eventually facilitated inflammatory cytokine IL-1β maturation and inflammation activation. These results suggest that Isg15 accelerates the senescence of ovarian granulosa cells by promoting inflammation and thereby reduces reproductive lifespan during aging. The present study demonstrates that a novel regulatory axis of ISG15-PSMD14-IL-1β activates inflammation, and therefore Isg15 deficiency mitigates the age-related decline in female fertility via reducing ovarian inflammation. Overall, our findings provide a new mechanistic insight into the decline of female fertility during ovarian aging, and offer a potential therapeutic strategy for ameliorating age-related female infertility.