MITOPHAGY-REGULATING GENE PARKIN IS REQUIRED FOR FEMALE FERTILITY

Mitophagy is the selective autophagy of mitochondria. It allows removal of aged and damaged mitochondria through specialized sequestration and engulfment. In mammals, mitophagy requires the E3 ubiquitin ligase Parkin, which mediates ubiquitination of multiple mitochondrial substrates, designating them for degradation by the proteasome. Impaired mitophagy has been implicated in a number of disorders and loss of Parkin activity plays a role in the development of Parkinson’s disease. However, the role of mitophagy in general and Parkin in particular has not yet been determined in the context of reproduction. In this study, we aimed to investigate the role of Parkin in female reproductive competence and senescence using a mouse model. Mice withglobal deletion of Parkin were obtained from the Jackson Laboratory (Bar Harbor, ME, USA; stock # 006582). In all experiments, adult (8-weeks-old) Parkin-/- female mice were compared to wild-type (WT). To assess fertility, female mice from each group (n=4) were mated with adult WT males of proven fertility for 12 weeks. The ability to generate oocytes (germinal vesicle [GV] and metaphase II [MII]) was assessed after injection with PMSG (10IU) or PMSG and hCG (10IU). Unfertilized MII oocytes were collected after 14 hours of hCG injection. Follicle development was assessed in ovaries from Parkin-/- and WT mice after fixation, paraffin embedding, and sectioning, followed by hematoxylin and eosin (H&E) staining. Student’s t-test was applied for statistical analyses. Parkin-/- female mice had decreased fertility compared to WT (13.5±1.64 pups per female vs 22.0±1.67, p<0.05). 2-month-old female Parkin-/- had a similar number of primordial, primary, secondary, early antral and antral follicles compared to WT. The number of GV (30±1.52 vs 52.6±6.96 (p<0.05)) and MII stage oocytes (7.6±0.66 vs 22.3±0.88 (p<0.001)) were significantly decreased in KO mice compared to WT). Our findings demonstrate that lack of mitophagy-regulating gene Parkin causes female subfertility associated with decreased number and maturation of oocytes.