The yeast complex I equivalent NADH dehydrogenase rescues pink1 mutants.

Pink1is a mitochondrial kinase involved in Parkinson's disease, and loss of Pink1function affects mitochondrial morphology via a pathway involving Parkinand components of the mitochondrial remodeling machinery. Pink1loss also affects the enzymatic activity of isolated Complex I of the electron transport chain(ETC); however, the primary defect in pink1mutants is unclear. We tested the hypothesis that ETC deficiency is upstream of other pink1-associated phenotypes. We expressed Saccaromyces cerevisiae Ndi1p, an enzyme that bypasses ETC Complex I, or sea squirt Cionaintestinalis AOX, an enzyme that bypasses ETC Complex III and IV, in pink1mutant Drosophila and find that expression of Ndi1p, but not of AOX, rescues pink1-associated defects. Likewise, loss of function of subunits that encode for Complex I–associated proteins displays many of the pink1-associated phenotypes, and these defects are rescued by Ndi1p expression. Conversely, expression of Ndi1p fails to rescue any of the parkinmutant phenotypes. Additionally, unlike pink1mutants, fly parkinmutants do not show reduced enzymatic activity of Complex I, indicating that Ndi1p acts downstream or parallel to Pink1, but upstream or independent of Parkin. Furthermore, while increasing mitochondrial fissionor decreasing mitochondrial fusionrescues mitochondrial morphological defects in pink1mutants, these manipulations fail to significantly rescue the reduced enzymatic activity of Complex I, indicating that functional defects observed at the level of Complex I enzymatic activity in pink1mutant mitochondria do not arise from morphological defects. Our data indicate a central role for Complex I dysfunction in pink1-associated defects, and our genetic analyses with heterologous ETC enzymes suggest that Ndi1p-dependent NADH dehydrogenaseactivity largely acts downstream of, or in parallel to, Pink1but upstream of Parkinand mitochondrial remodeling.