Laminar Shear Stress Enhances Cytosolic PINK1 Expression: Increased Mitophagic Sensitivity Toward Mitochondrial Dysfunction

Abstract

PURPOSEPhosphatase and tensin homolog (PTEN)‐induced putative kinase 1 (PINK1) is an essential molecule in mitophagy process and known to act as a cytoprotective protein in mammalian cells. Mutation or deficiency of PINK1 has been closely related to several disease conditions. The purpose of this study was to determine PINK1 expression levels and subcellular localization under exercise‐mimic laminar shear stress (LSS) condition in human aortic endothelial cells (HAECs) or in exercising mice, and its implication on endothelial homeostasis and cardiovascular disease (CVD) prevention.METHODS & RESULTSFirst, we measured full‐length PINK1 (FL‐PINK1) mRNA and protein expression levels in HAECs under unidirectional laminar shear stress (LSS) at 15 dyne/cm2 for 48h. LSS significantly elevated both FL‐PINK1 mRNA and protein expressions in HAECs compared to static control. Mitochondrial fractionation assays showed a decrease in FL‐PINK1 accumulation in the mitochondria with a compensatory increase in the cytosolic FL‐PINK1 level under LSS. Confocal microscopic analysis confirmed these subcellular localization patterns suggesting downregulation of mitophagy induction. Also, mitophagy flux was decreased under LSS, determined by a mtKeima probe. Mitochondrial morphometric analysis and mitochondrial membrane potential (JC‐1) showed mitochondrial elongation and increased mitochondrial membrane potential, respectively, suggesting that an elevation of cytosolic PINK1 is not related to an immediate induction of mitophagy. Based on this observation, we further hypothesized that the elevation of the cytosolic pool of FL‐PINK1 would increase the sensitivity to mitophagic signals in pathological conditions. Preconditioned HAECs with LSS showed lower mtDNA lesions under angiotensin II stimulation (100 nM, 6h). Moreover, LSS‐preconditioned ECs showed rapid Parkin recruitment and mitophagy induction in response to mitochondrial toxin (i.e. CCCP) treatment compared to the control. We measured PINK1 expression at ECs of the thoracic aorta in exercised mice, a physiological LSS‐enhanced model, which was significantly elevated compared to sedentary animals. In addition, exercise‐preconditioned mice were more protective to angiotensin II‐induced mtDNA lesion formation in the mouse abdominal aorta than sedentary mice, suggesting a potential protective mechanism of exercise in a PINK1‐dependent manner.CONCLUSIONLSS increases a cytosolic pool of FL‐PINK1, which may elevate the mitophagic sensitivity toward dysfunctional mitochondria or activate other cytoprotective mechanisms in endothelial cells. Our data suggest that exercise may support mitochondrial homeostasis in vascular endothelial cells by enhancing PINK1‐dependent cell protection mechanisms.