An Inducible and Vascular Smooth Muscle Cell-Specific Pink1 Knockout Induces Mitochondrial Energetic Dysfunction during Atherogenesis.

DNA damage and mitochondrial dysfunction are defining characteristics of aged vascular smooth muscle cells (VSMCs) found in atherosclerosis. Pink1 kinase regulates mitochondrial homeostasis and recycles dysfunctional organelles critical for maintaining energetic homeostasis. Here, we generated a new vascular-specific Pink1 knockout and assessed its effect on VSMC-dependent atherogenesis in vivo and VSMC energetic metabolism in vitro. A smooth muscle cell-specific and MHC-Cre-inducible flox'd Pink1f/f kinase knockout was made on a ROSA26+/0 and ApoE-/- C57Blk6/J background. Mice were high fat fed for 10 weeks and vasculature assessed for physiological and pathogical changes. Mitochondrial respiratory activity was then assessed in wild-type and knockout animals vessels and isolated cells for their reliance on oxidative and glycolytic metabolism. During atherogenesis, we find that Pink1 knockout affects development of plaque quality rather than plaque quantity by decreasing VSMC and extracellular matrix components, collagen and elastin. Pink1 protein is important in the wild-type VSMC response to metabolic stress and induced a compensatory increase in hexokinase II, which catalyses the first irreversible step in glycolysis. Pink1 appears to play an important role in VSMC energetics during atherogenesis but may also provide insight into the understanding of mitochondrial energetics in other diseases where the regulation of energetic switching between oxidative and glycolytic metabolism is found to be important.

Impaired mitochondrial respiration in human carotid plaque atherosclerosis: A potential role for Pink1 in vascular smooth muscle cell energetics.

BACKGROUND AND AIMS: DNA damage and mitochondrial dysfunction are thought to play an essential role in ageing and the energetic decline of vascular smooth muscle cells (VSMCs) essential for maintaining plaque integrity. We aimed to better understand VSMCs and identify potentially useful compensatory pathways that could extend their lifespan. Moreover, we wanted to assess if defects in mitochondrial respiration exist in human atherosclerotic plaques and to identify the appropriate markers that may reflect a switch in VSMC energy metabolism. METHODS: Human plaque tissue and cells were assessed for composition and evidence of DNA damage, repair capacity and mitochondrial dysfunction. Fresh plaque tissue was evaluated using high resolution oxygen respirometry to assess oxidative metabolism. Recruitment and processing of the mitochondrial regulator of autophagy Pink1 kinase was investigated in combination with transcriptional and protein markers associated with a potential switch to a more glycolytic metabolism. RESULTS: Human VSMC have increased nuclear (nDNA) and mitochondrial (mtDNA) damage and reduced repair capacity. A subset of VSMCs within plaque cap had decreased oxidative phosphorylation and expression of Pink1 kinase. Plaque cells demonstrated increased glycolytic activity in response to loss of mitochondrial function. A potential compensatory glycolytic program may act as energetic switch via AMP kinase (AMPK) and hexokinase 2 (Hex2). CONCLUSIONS: We have identified a subset of plaque VSMCs required for plaque stability that have increased mitochondrial dysfunction and decreased oxidative phosphorylation. Pink1 kinase may initiate a cellular response to promote a compensatory glycolytic program associated with upregulation of AMPK and Hex2.