Mitophagy pathways in cellular cross-talk in the myocardium

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Myocardial infarction (MI) with resultant ischemic cardiomyopathy and heart failure rank among the leading causes of morbidity and mortality among Veterans in the United States. In ischemic cardiomyopathy, sustained and unregulated inflammatory signaling is recognized as a driver of heart failure pathogenesis. Therefore, understanding the crosstalk between immune cells and cardiac myocytes has the potential to inform therapeutic strategies. Immune cells in the myocardium affect cardiac myocyte structure and function via cell autonomous and non-autonomous mechanisms. Cardiac macrophages are increasingly recognized as the dominant immune cell type driving pro-inflammatory signaling under stress. On the other hand, studies also point to critical homeostatic roles for resident cardiac macrophages in maintenance of cardiac structure and function. Indeed, in the post-MI period, infiltrated peripheral monocytes differentiate into macrophages and are postulated to play a dual role in concert with the resident cardiac macrophages, characterized by pro- inflammatory signaling and phagocytic removal of dead cells in the early phase and a shift towards anti- inflammatory signaling to promote reparative phase. In published VA MERIT-supported studies, we have uncovered evidence for impaired lysosome function in macrophages as a driver of pro-inflammatory signaling. Our studies further demonstrated the efficacy of stimulating the macrophage lysosome biogenesis program by activation of TFEB, a master regulator of autophagy-lysosome pathway, in engendering a phenotypic switch in macrophages and promoting post-MI healing. In parallel studies, we have uncovered an essential role for TRAF2 in cardiac myocytes in executing physiologic mitophagy, a selective lysosomal degradative pathway that removes damaged mitochondria to prevent mitochondrial DNA leak and suppress sterile inflammation in the myocardium. In this proposal, we will examine the role of TRAF2 and mitophagy in macrophages in shaping myocardial homeostasis; to understand how targeting mitophagy affects cellular crosstalk in the myocardium in homeostasis and under stress. Our preliminary data suggest the hypothesis that TRAF2 plays an essential role in macrophages by facilitating macrophage mitophagy and generation of 25- hydroxycholesterol to restrain inflammasome activation, to maintain myocardial homeostasis. Indeed, our preliminary studies demonstrate that inducible macrophage TRAF2 ablation using genetic approaches induces cardiac myocyte hypertrophy, left ventricular hypertrophy and systolic dysfunction, and increased inflammatory cell infiltration in the myocardium. We have acquired reagents and developed collaborations to test the hypothesis. In specific aim, we will evaluate the consequences of loss of TRAF2 in macrophages on inflammatory signaling. In specific aim 2, we will evaluate the consequences of loss of TRAF2 in macrophages on cardiac myocyte mitophagy, and perform mechanistic studies to understand the role of cardiac myocyte mitophagy in the observed phenotype. In aim 3, we will define the role of 25-hydroxycholesterol generation in macrophage-myocyte crosstalk in the myocardium. Successful completion of these studies will define subcellular mechanisms of macrophage-myocyte crosstalk in the myocardium. Harnessing macrophage mitophagy and oxysterol signaling has the potential to mitigate inflammation and treat ischemic cardiomyopathy that contributes to 2/3rds of all heart failure case burden.