Abstract
Low oocyte quality is a possible causal factor of obesity-induced infertility. High palmitic acid (PA) concentration in follicular fluid is a crucial feature noted in obese women. This study examined how high PA concentration reduced mitochondrial quality in oocytes and investigated a possible countermeasure against mitochondrial dysfunction. Cumulus cell-oocyte complexes were obtained from the ovaries of gilts, and incubated in medium containing PA (0.5 mM) or vehicle (BSA) for 44 h. Culturing oocytes at high PA concentration induced mitochondrial dysfunction determined by high reactive oxygen species and low ATP content in oocytes. Furthermore, high PA levels increased mitochondrial acetylation levels determined by a high degree of co-localization of TOMM20 and acetylated-lysine. In addition, high PA levels reduced the expression of Sirtuin 3 (SIRT3) and phosphorylated AMP-activated protein kinase (AMPK), while the AMPK activator, AICAR, restored mitochondrial function as well as oocyte ability and reduced the acetylation of mitochondrial protein. Supplementation of culture medium with dorsomorphin dihydrochloride (an AMPK inhibitor) reduced mitochondrial function and increased mitochondrial protein acetylation. Treatment of oocytes with LB100 (an inhibitor of AMPK dephosphorylation) reduced mitochondrial acetylation levels and restored mitochondrial function. Furthermore, high PA levels increased ceramide accumulation in oocytes, and addition of ceramide to the culture medium also induced mitochondrial dysfunction and increased mitochondrial acetylation. This detrimental effect of ceramide was diminished by AICAR treatment of oocytes. Our results indicated that PA induces ceramide accumulation and downregulates the AMPK/SIRT3 pathway causing mitochondrial protein hyperacetylation and dysfunction in oocytes.