Abstract 262: Knockout of Type VI Collagen Preserves Mitochondrial Structure and Function Following Myocardial Infarction

Abstract

Cardiac remodeling is a dynamic process that is accelerated after myocardial infarction (MI), and the traditional focus of key extracellular matrix proteins that mediate remodeling has been on the fibrillar types I and III collagen. We have previously reported that knockout mice of the lesser-known, non-fibrillar collagen VI (Col6-/-) are protected from MI injury as evidenced by significantly reduced infarct size, fibrosis and apoptosis leading to preserved long-term cardiac function. Determining the mechanisms underlying this cardioprotection is the goal of this study. Interestingly, the Col6-/- mice are a model for Bethlam Myopathy, a rare skeletal muscular dystrophy that is characterized by mitochondrial dysfunction leading to premature apoptosis of skeletal myocytes. We hypothesized that alterations in mitochondrial structure and function in the myocardium of Col6-/- mice may play key mechanistic roles responses to ischemic injury. Mitochondrial morphology was visualized by transmission electron microscopy to compare pre- and post-MI changes. Mitochondria from uninjured Col6-/- LV tissue had similar morphology as WT, and at 3 days post-MI the mitochondrial morphology was similarly compromised in both WT and Col6-/- mice. However, at 14 days post-MI the Col6-/- mitochondria were less swollen (43 ± 5.1% decrease in overall volume) and displayed improved orientation/organization over WT (continuous strands). We measured basal O2 consumption and 24 hours post-MI in mitochondria isolated from the infarcted zones of both genotypes. The respiratory control index (RCI) of the Col6-/- mitochondria was lower in the basal, uninjured hearts (7.2 ± 0.9 in WT vs. 4.9 ± 0.6 in Col6-/-). However, the RCI of mitochondria in the infarcted region of Col6-/- hearts at 24 hours post-MI declined less than WT (post-MI values of 2.7 ± 0.5 in WT vs. 2.8 ± 0.7 in Col6-/-) . These data indicate that Col6-/- mice have preserved mitochondrial morphology and a smaller decline in respiration following MI, which may represent a novel homeostatic mechanism underlying protection from ischemic injury in the Col6-/- heart.