Ablating The Rab-GTPase Activating Protein TBC1D1 Predisposes Rats To High Fat Diet-Induced Cardiomyopathy

Abstract

While the pathogenesis of diabetic cardiomyopathy is poorly understood, impaired insulin signalling within the heart is thought to contribute to the development of this pathology. TBC1D1, a Rab-GTPase activating protein, is involved in glucose homeostasis and substrate metabolism within skeletal muscle, however, the function of TBC1D1 within the heart is relatively unknown. PURPOSE: To examine the role of TBC1D1 in overall cardiac morphology and substrate utilization using a rat knock-out (KO) model. METHODS: 7 weeks of high-fat feeding was provided as a metabolic perturbation to further elucidate the interaction between TBC1D1 and diet-induced cardiac contractile function. Experiments were conducted at 12 weeks of age, with the exception of cardiomyocyte isolation, which was conducted at 7 weeks of age. Animals were anaesthetized with 2.5% isoflurane before assessments of cardiac function, or surgical removal of the left ventricle. The left ventricle was immediately utilized for bioenergetics assessments, fixed for histology or immediately frozen in liquid nitrogen for Western blotting. RESULTS: In chow-fed animals, TBC1D1 ablation increased plasma membrane GLUT4 content and glucose uptake, as well as plasma membrane FABPpm content and palmitate oxidation, consistent with activating cellular trafficking through the ablation of TBC1D1. While echocardiograms suggested indices of cardiac function were unaltered in chow fed KO animals, when challenged with a 7 week high-fat diet, TBC1D1 KO rats displayed a 4-fold increase in fibrosis in association with attenuated stroke volume, cardiac output and end diastolic volume, suggesting a predisposition to diet-induced cardiomyopathy. Mitochondrial respiratory capacity and substrate sensitivity to pyruvate and ADP were not altered by diet or TBC1D1 ablation, nor were rates of mitochondrial hydrogen peroxide emission, or markers of oxidative stress. CONCLUSIONS: Altogether, ablation of TBC1D1 improves indices of cardiovascular function in rats fed a standard diet, but increases fibrosis and compromises indices of cardiac function in rats consuming a high-fat diet. Therefore, TBC1D1 may exert cardioprotective effects in the development of diabetic cardiomyopathy. This research is supported by NSERC funding.