Proline improves the developmental competence of in vitro matured porcine oocytes by enhancing mitochondrial function

The in vitro maturation of oocytes is essential to embryo engineering. Mitochondrial function is essential for both oocyte maturation and the acquisition of developmental potential. In this study, we focused on proline, a natural antioxidant with permeability-protective properties; we hypothesized that proline could enhance porcine oocytes maturation in vitro by improving mitochondrial function. To test this hypothesis, we explored the effects of proline on mitochondrial function and the developmental competence of porcine oocytes. Treatment with 0.4 mM proline significantly increased the maturation rate, development rate, and the ratio of normal spindle morphology in porcine oocytes. The results indicated that proline supplementation enhanced both the quantity and function of mitochondria; specifically, the content of mitochondria and their mtDNA increased, with a more uniform distribution observed. Additionally, the mRNA expression of genes associated with mitochondrial division, fusion, and function showed marked increased following the addition of 0.4 mM proline. The mitochondrial membrane potential and ATP levels were significantly elevated, and the activities of mitochondrial respiratory chain complexes I and IV were also markedly enhanced after proline treatment. Moreover, proline supplementation not only reduced reactive oxygen species levels but also improved glutathione levels. These results suggested that proline enhances oocyte maturation quality by improving mitochondrial content and function during IVM in porcine.