Renal oncocytoma (RO) is a benign renal neoplasm characterized by dense accumulation of dysfunctional mitochondria possibly resulting from increased mitochondrial biogenesis and decreased mitophagy; however, the mechanisms controlling these mitochondrial changes are unclear. ROs harbor recurrent inactivating mutations in mitochondrial genes encoding the Electron Transport Chain (ETC) Complex I, and we hypothesize that Complex I loss in ROs directly impairs mitophagy. Our analysis of ROs and normal kidney (NK) tissues shows that a significant portion (8 out of 17) of ROs have mtDNA Complex I loss-of-function mutations with high variant allele frequency (>50%). ROs indeed exhibit reduced Complex I expression and activity. Analysis of the various steps of mitophagy pathway demonstrates that AMPK activation in ROs leads to induction of mitochondrial biogenesis, autophagy, and formation of autophagosomes. However, the subsequent steps involving lysosome biogenesis and function are defective, resulting in an overall inhibition of mitophagy. Inhibiting Complex I in a normal kidney cell line recapitulated the observed lysosomal and mitophagy defects. Our data suggest Complex I loss in RO results in defective mitophagy due to lysosomal loss and dysfunction.
Keywords: autophagy/mitophagy; complex I; lysosome; metabolism; mitochondrial dysfunction; renal oncocytoma.