Cardiovascular disease is the major cause of morbidity and mortality in humans with obesity, insulin resistance and type 2 diabetes (T2DM). These conditions also independently increase the risk of heart failure, although mechanisms are incompletely understood. The focus of this proposal is to understand the role of autophagy in the pathophysiology of cardiac dysfunction in insulin resistant states. Autophagy is a dynamic process that is regulated by various upstream signaling pathways. Our preliminary studies indicate that myocardial autophagy is increased with fasting and reduced with re-feeding and this dynamic regulation is dependent upon an intact insulin signaling pathway. Indeed, disruption of insulin signaling in vivo or in vitro rapidly induces autophagy within cardiomyocytes. We have also observed that myocardial autophagy is increased in murine and pig models of insulin resistance and T2DM and in heart samples from humans with T2DM. In these models basal and insulin-mediated glucose uptake is reduced, despite normal or increased insulin signaling to Akt. Studies are proposed to determine the mechanisms by which insulin signaling regulates myocardial autophagy and mechanisms responsible for increased myocardial autophagy in insulin resistant states. Increased autophagy in the heart can be adaptive or maladaptive and the clinical significance in the context of obesity and T2DM are unknown. These mechanistic questions will be explored in three specific aims using cultured cells and by inducing T2DM in genetically modified mice with altered insulin or autophagic signaling or altered glucose uptake.
Aim 1 will determine the molecular mechanisms by which insulin signaling regulates myocardial autophagy.
Aim 2 will determine the mechanism for increased myocardial autophagy in the diet-induced obesity (DIO) model of type 2 diabetes (T2DM).
Aim 3 will determine the clinical and functional significance of altered myocardial autophagy in the progression of diabetic cardiomyopathy in the DIO model of type 2 diabetes (T2DM) by testing the hypothesis that increased autophagy in T2DM is an adaptive response and that reducing autophagic signaling will accelerate mitochondrial and cardiac dysfunction. Taken together, these studies will provide a comprehensive analysis of the regulation of myocardial autophagy by insulin signaling and determine the significance of and the mechanisms for increased myocardial autophagy in T2DM. They will also elucidate the consequence of modulating autophagy on mitochondrial and cardiac function in T2DM. The knowledge gained from these studies will shed novel insights into the important role that autophagy may play in the pathophysiology of cardiac dysfunction in diabetes and will have translational impact given that many therapeutic strategies in use for diabetes may profoundly impact autophagy in the heart.
The global increase in the prevalence of obesity, insulin resistance and type 2 diabetes is predicted to lead to an increase in cardiovascular morbidity, including heart failure. The mechanisms linking insulin resistance to heart failure are multifactorial. Although increased coronary ischemia, and ventricular hypertrophy play important roles, there is growing evidence for a role for intrinsic defects within cardiomyocytes that include altered mitochondrial function, altered calcium signaling and lipotoxicity. The current proposal will evaluate the significance if increased autophagy, which is a novel mechanism that may contribute to the pathophysiology of cardiac dysfunction in insulin resistant states. It is not known if this increase is autophagy represents an adaptation that maintains cardiac function or if it is deleterious. Because many diabetes therapies may alter myocardial autophagy, it is important to understand the impact of these therapies on cardiac autophagy. Recent evidence of adverse cardiovascular consequences of some diabetes therapeutics has prompted the FDA to require evidence for improved cardiovascular outcomes in addition to improved metabolic control as a pre-requisite for the approval of any new diabetes therapy. Moreover, the impact of tight glycemic control on cardiovascular outcomes in type 2 diabetes is mixed. Therefore, studies that will elucidate the molecular mechanisms linking diabetes-associated metabolic disturbances with cardiac dysfunction, and the way that these mechanisms could be altered by diabetes therapies are timely and important.
|Riehle, Christian; Wende, Adam R; Zhu, Yi et al. (2014) Insulin receptor substrates are essential for the bioenergetic and hypertrophic response of the heart to exercise training. Mol Cell Biol 34:3450-60|
|Riehle, Christian; Abel, E Dale (2014) Insulin regulation of myocardial autophagy. Circ J 78:2569-76|
|Symons, J David; Abel, E Dale (2013) Lipotoxicity contributes to endothelial dysfunction: a focus on the contribution from ceramide. Rev Endocr Metab Disord 14:59-68|
|Zhu, Yi; Soto, Jamie; Anderson, Brandon et al. (2013) Regulation of fatty acid metabolism by mTOR in adult murine hearts occurs independently of changes in PGC-1?. Am J Physiol Heart Circ Physiol 305:H41-51|
|Doenst, Torsten; Nguyen, Tien Dung; Abel, E Dale (2013) Cardiac metabolism in heart failure: implications beyond ATP production. Circ Res 113:709-24|