Mitochondrial unfolding protein CLPX is required for oocyte competence during ovarian aging

Ovarian aging has reproductive and overall health implications with increased infertility, miscarriage rates, and adverse outcomes associated with menopause. Mitochondrial dysfunction is one of the main mechanisms of female reproductive aging. Mitochondrial protein homeostasis maintains mitochondrial function and globally dysregulated unfolded mitochondrial protein response accelerates reproductive aging. However, the role of oocyte mitochondrial proteostasis in determining oocyte quality is unknown. ClpX (Caseinolytic Protease X) is a mitochondrial protein unfoldase that maintains mitochondrial protein homeostasis. In this study, we uncovered that Clpx deficiency, either through genetic ablation or natural decline with aging in mice, leads to the disrupted mitochondrial proteostasis in oocytes. Oocyte-specific knockout of Clpx impaired oocyte quality and developmental competence, thereby leading to female subfertility. Transcriptomic and micro-proteomic analyses of Clpx null oocytes revealed dysregulated mitochondrial function, protein processing and meiosis. Notably, Clpx deficiency promoted PGD2 synthesis and DP1/PKA/cAMP and DP2/AKT/mTOR signaling pathways by upregulating Ptgds. The PGD2 synthesis inhibitor AT-56 restored the developmental competence of Clpx knockout and aged oocytes. Our findings indicate the pivotal role of oocyte mitochondrial proteostasis in the regulation of oocyte quality with aging and pave the way for future investigations assessing the potential therapeutic value of these pathways to improve infertility treatment outcomes.