Shared and cell type-specific mitochondrial defects and metabolic adaptations in primary cells from PINK1-deficient mice

Background: Mutations in PTEN-induced kinase 1 (PINK1) cause early-onset recessive parkinsonism. PINK1 and Parkin regulate mitochondrial quality control. However, PINK1 ablation in Drosophila and cultured mammalian cell lines affected mitochondrial function/dynamics in opposite ways, confounding the elucidation of the role of PINK1 in these processes. Objective: We recently generated PINK1-deficient (PINK1^-/-) mice and reasoned that primary cells from these mice provide a more physiological substrate to study the role of PINK1 in mammals and to investigate metabolic adaptations and neuron-specific vulnerability in PINK1 deficiency. Methods and Results: Using real-time measurement of oxygen consumption and extracellular acidification, we show that basal mitochondrial respiration is increased, while maximum respiration and spare respiratory capacity are decreased in PINK1^-/- mouse embryonic fibroblasts (MEF), as is the membrane potential. In addition, a Warburg-like effect in PINK1^-/- MEF promotes survival that is abrogated by inhibition of glycolysis. Expression of uncoupling protein-2 is decreased in PINK1^-/- MEF and the striatum of PINK1^-/- mice, possibly increasing the sensitivity to oxidative stress. Mitochondria accumulate in large foci in PINK1^-/- MEF, indicative of abnormal mitochondrial dynamics and/or transport. Like in PINK1^-/-Drosophila, enlarged/swollen mitochondria accumulate in three different cell types from PINK1^-/- mice (MEF, primary cortical neurons and embryonic stem cells). However, mitochondrial enlargement is greatest and most prominent in primary cortical neurons that also develop cristae fragmentation and disintegration. Conclusion: Our results reveal mechanisms of PINK1-related parkinsonism, show that the function of PINK1 is conserved between Drosophila and mammals when studied in primary cells, and demonstrate that the same PINK1 mutation can affect mitochondrial morphology/degeneration in a cell type-specific manner, suggesting that tissue-/cell-specific metabolic capacity and adaptations determine phenotypes and cellular vulnerability in PINK1^-/- mice and cells.