Androgens alter mitophagy in the refed metabolic state

Abstract

We previously showed that depletion of androgens via castration increased markers of autophagy activation (i.e. increased LC3 II/I ratio and reduced p62 protein content) in the tibialis anterior (TA) following nutrient consumption. Importantly, this androgen‐mediated effect occurred despite no differences in measures of known putative autophagy regulatory factors. Because of this, it is likely that the sustained elevation in autophagy‐activation was specific to a cellular organelle(s) rather than global autophagy. As others have shown that castration reduced skeletal muscle oxidative capacity, we sought to determine whether autophagic clearance of mitochondria, termed mitophagy, could be contributing to the sustained increase in autophagic markers. To answer this, mice were randomized to sham or castration surgery. After 8 weeks of recovery, all mice were fasted overnight. The next morning, mice remained fasted or were refed for 30 min, and sacrificed 4.5 hr following completion of the refeeding. In the TA muscle, castration reduced mitochondrial protein content as the mitochondria specific proteins cytochrome c oxidase subunit IV (COX IV) and voltage‐dependent anion channel (VDAC) were decreased. An inverse relationship was observed between the protein content of either COX IV or VDAC with p62, suggesting enhanced mitophagy. Castration also reduced the protein expression of the mitophagy regulatory protein, BCL2/adenovirus E1B 19 kDa protein‐interacting protein 3 (BNIP3), despite no change in BNIP3 mRNA suggesting enhanced turnover of the protein during mitophagy. Indeed, direct relationships were observed between the protein content of BNIP3 and either p62, COX IV, or VDAC supporting a role of BNIP3 in castration‐induced mitophagy. Additional analysis also supports a role of Pink1 and Parkin as castration enhanced the mRNA levels of each without a corresponding change in the protein expression, consistent with enhanced turnover of these proteins during mitophagy. Lastly, fasting conditions that enhance global autophagy prevented the castration‐induced reduction in mitochondrial proteins and enhancement of mitophagy markers. In all, these data support a model in which androgens prevent BNIP3/Pink1/Parkin‐mediated mitophagy in skeletal muscle during the refed, but not the fasted, metabolic state.Support or Funding InformationNIH Grant F32 AA‐023422 to JLS