Mainly expressed in liver, kidney and small intestine, the enzyme proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low-density lipoprotein-cholesterol receptor (LDLr), and causes degradation of LDLs. Although not proven, it has been suggested that these agents may reduce cardiovascular events. Recent work from our group shows that besides the liver, kidney and small intestine, cardiomyocytes also express PCSK9. The secretion of PCSK9 increases during ischemia by >10 fold. PCSK9 expression is maximal in the region adjacent to the infarcted area (border zone). Cardiomyocytes in the border zone also exhibit intense inflammation and autophagy. Other recent work in our laboratory suggests that PCSK9 secretion may regulate inflammation and autophagy. Based on these new findings, we wish to critically examine the role of myocardial PCSK9 in ischemia, an issue not previously studied. The 2 major aims of the grant proposal are:
Aim 1 : To examine the role of PCSK9 in the determination of infarct size and cardiac function. Approach: These studies will be done in a mouse model of permanent left coronary artery (LCA)] ligation. Studies will be performed in wild-type C57BL/6 and PCSK-/- mice. PCSK9 expression, inflammation (with emphasis on infiltration of tissue injurious CCR2+Ly6Chigh monocytes and neutrophils) and autophagy along with infarct size and cardiac function (echocardiography) will be measured at different time points. Molecular biology studies, histology and immunohistochemistry will be performed in different regions of the heart. To determine the role of inflammation in PCSK9 release and its effects, parallel studies will be performed in TNF?-/- mice and IL-1?-/- mice. Lastly, to confirm the role of PCSK9 in ischemic injury, studies will be performed in mice with selective PCSK9 deletion in the heart. Impact: These in vivo studies will clarify the role of PCSK9 in determination of infarct size and cardiac function/remodeling. Further, these studies will reveal the role of inflammation in the induction of PCSK9 secretion during chronic ischemia.
Aim 2 : To examine mechanisms underlying PCSK9?s effects on the heart during ischemia. Approach: To study the complex interaction between PCSK9, inflammation and autophagy during ischemia, primary mouse cardiomyocytes will be exposed to varying periods of hypoxia (in vitro studies). We will study the impact of hypoxia-induced PCSK9 release on leukocyte migration, mitochondrial ROS generation and mitochondrial DNA damage and autophagy signals. Impact of PCSK9 (along with inflammatory signals) on the generation of collagen (in fibroblasts) will also be studied. Impact: These studies will reveal the mechanisms by which PCSK9 influences inflammation and autophagy, and subsequently cardiac remodeling during chronic myocardial ischemia. Innovation and Significance: PCSK9 inhibition by lowering LDL-C may significantly influences atherogenesis and cardiovascular events. We believe that the proposed studies will test a novel hypothesis that it is the local release of PCSK9 that regulates pro-inflammatory and autophagy signals and collagen generation (cardiac remodeling). Its inhibition may modulate myocardial infarct size and subsequent cardiac modeling. The results of these innovative studies may impact the lives of millions of patients (and elderly veterans) who suffer from chronic myocardial ischemia and may be treated with PCSK9 inhibitors.
The enzyme proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the LDL receptor, and causes its degradation. Recent work shows that cardiomyocytes during ischemia express large amounts of PCSK9. The proposed studies are designed to examine the role of cardiomyocyte-derived PCSK9 in the determination of infarct size and cardiac function in a mouse model of permanent ischemia. Studies will be performed in a variety of transgenic mice with deletion of inflammation and PCSK9 genes. Other studies will be performed in primary cardiomyocytes to study the impact of hypoxia-induced PCSK9 release on leukocyte migration, mitochondrial ROS generation and DNA damage and autophagy signals. Impact of PCSK9 on the generation of collagen (in fibroblasts) will also be studied. Impact: These studies will reveal the mechanisms by which PCSK9 influences inflammation and autophagy, and subsequently cardiac remodeling during chronic myocardial ischemia. The results of these innovative studies may impact the lives of millions of patients who suffer from chronic myocardial ischemia and may be treated with PCSK9 inhibitors.
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