Abstract

Mitochondrial function in atherosclerosis and vascular smooth muscle cells

Johannes Reinhold

Atherosclerosis is the leading cause of death in the Western world. Although mitochondrial DNA (mtDNA) damage has been implicated in atherosclerosis, it is unclear whether the damage is sufficient to impair mitochondrial respiration, and mitochondrial dysfunction has not been demonstrated. Treatment of vascular smooth muscle cells (VSMCs) with an atherogenic lipid, oxidised low-density lipoprotein (OxLDL), dose dependently decreased basal and maximal respiration and fat-feeding of apolipoprotein E deficient (ApoE-/-) mice reduced mitochondrial DNA copy number relative to nuclear DNA in aortas. Mitochondrial respiration of ApoE-/- mouse aortas, assessed through a 24-well Seahorse extracellular flux analyser, was not affected prior to the development of atherosclerotic plaques. Developed human carotid atherosclerotic plaques were dissected into defined regions including healthy media, shoulder region, fibrous cap and core and their respiration was investigated. The respiratory reserve capacity (RRC) of the shoulder region was similar to the media. However, the cap RRC was significantly reduced compared to healthy media. In contrast, the extracellular acidification rates (ECAR) of the media, shoulder, cap and core regions were similar. In addition, mtDNA copy number was significantly reduced in tissues derived from human plaques compared to healthy arteries and expression of complexes I and II of the electron transfer chain (ETC) were significantly reduced in plaque VSMCs. OxLDL induced mitophagy in human VSMCs and plaque VSMCs demonstrated increased levels of mitophagy without compensatory upregulation of proteins involved in mitochondrial biogenesis. Understanding the role of mitochondrial metabolism and signalling is important for our understanding of disease progression and may lead to future therapeutic targets.