Heart disease is the leading cause of mortality in the United States in both men and women. Obesity is rapidly growing epidemic and a major risk factor for the development of cardiomyopathies and heart failure. The pathology of obesity-related cardiomyopathies is associated with abnormal cardiac accumulation of fat and lipotoxic metabolites. Preventing such lipotoxic effects is a potential avenue for therapeutic intervention in heart disease and heart failure. However, the molecular mechanisms of cardiac lipotoxicity remain elusive. In this proposal, we seek to address these gaps in knowledge by leveraging our established, robust Drosophila heart models of ceramide- and high-fat-diet (HFD)-induced lipotoxic cardiomyopathy (LCM), which exhibit LCM-like pathology observed in mammalian LCM, including compromised contractility and elevated accumulation of both triglyceride fat and sphingolipid ceramide with either diet. Drosophila is an extremely versatile genetic model system with highly conserved metabolic pathways and cardiac physiology, well suited to address fundamental mechanisms of LCM. Nevertheless, we will validate our findings in Drosophila in human cardiomyocytes that are derived from induced pluripotent stem cell (hiPSC-CMs) to gain further human relevant insights into the mechanisms of LCM (in collaboration with co-Investigator Dr. Alexandre Colas ? see letter). In ceramide-protein trap experiments we identified 3 enriched ontologies of putative ceramide interacting proteins (180 putative overlapping mouse-human CIPs): (1) sarcomeric regulatory proteins (40 CIPs), including the myosin chaperone Uncoordinated-45b (Unc45b), (2) metabolic regulatory proteins (33 CIPs), including fatty acid synthase FASN, and (3) apoptosis & DNA damage response (DDR) proteins (21 CIPs). Indeed, found that cardiac Unc45 overexpression or FASN RNAi knockdown in the fly heart prevents ceramide-induced LCM. LCM- inducing and subthreshold-sensitizing ceramide and high fat treatments will be used to interrogate the above CIPs in participating in LCM. This will be the first step in determining in detail the mechanisms how ceramide interacts with these 3 classes of proteins and how that disrupts or protects cardiac function and homeostasis. The goal is to construct and test a myofibrillar maintenance/lipogenesis/ apoptosis-centric regulatory network weighted with novel CIPs, which we will experimentally evaluate further in our LCM models.
Obesity has grown to global epidemic proportions. Over a billion adults are overweight, including a third that are clinically obese. The lipotoxic effects of obesity are a major contributor to cancer, diabetes and cardiovascular disease, but the complexity of mammalian genetics and metabolic controls involved in obesity-related cardiovascular dysfunctions pose significant obstacles to understanding the underlying mechanisms. This grant uses a simple genetic model and human cardiomyocytes derived from iPSCs in order to gain fundamental insights into the genetic mechanisms of cardiac lipotoxicity due to excess ceramide and lipid accumulation.
