Two factors contributing to the increased risk of coronary artery disease (CAD) in obesity/insulin resistance are death of macrophages (Mfs) in advanced atherosclerosis, which promotes plaque necrosis, and hepatic- derived dyslipidemia. Over the last decade, the Pi's lab has elucidated the mechanisms by which endoplasmic reticulum (ER) stress and Mf insulin resistance promote advanced lesional Mf death and plaque necrosis by complementary mechanisms. A recent key concept revealed by our mechanistic studies, and awaiting in vivo testing, is that prolonged ER stress triggers apoptosis through activation of the calcium- activated enzyme, calcium/calmodulin-dependent protein kinase ll-g (CaMKIIg). We also found that deletion or inhibition of hepatic CaMKIIg in obese mice protected against metabolic disturbances, including dyslipidemia. Thus, one enzyme may have critical effects on two complementary processes that promote CAD in insulin resistant subjects. Thus, the goals of this project are to test the hypotheses that Mf CaMKIIg deficiency will lessen advanced lesional Mf apoptosis and plaque necrosis in a murine model of Mf insulin resistance (Aim 1) and that hepatic CaMKIIg deficiency will improve atherogenic metabolic disturbances in insulin resistant obese mice (Aim 2).
In Aim 1, we will determine whether silencing of CaMKIIg in insulin resistant Mfs will suppress the high level of ER stress-induced apoptosis in these cells, followed by further exploration of the mechanisms of protection. We will also test the hypothesis that p-CaMKII, a measure of CaMKII activation, is higher in lesional Mfs in advanced vs. eariier stage human and murine atherosclerotic lesions. Most importantly, we will use a unique mouse model to test the hypothesis that the high level of advanced lesional Mf apoptosis and plaque necrosis in insulin resistant mice will be decreased by Mf- targeted CaMKII deficiency.
In Aim 2, we will characterize and explore the mechanisms whereby liver CaMKIIg deficiency in obesity improves the liver-derived metabolic disturbances, including dyslipidemia, and then use a unique model of liver-targeted CaMKIIg deficiency to test causation in vivo. We will complete the link with Aim 1 by testing the hypothesis that combined hepatic and Mf CaMKIIg deficiency will have a marked beneficial effect on all stages of atherosclerosis in insulin resistant mice. At the end of these studies, we hope to have comprehensive data to identify CaMKIIg as a prime, dual-action therapeutic target to prevent CAD in the setting of obesity and insulin resistance.
Obesity and insulin resistance (IR) are major drivers of CAD. The Mf studies are focused on plaque necrosis, a critical feature of dangerous human plaques and one which is increased in human IR. The liver studies focus on the most important systemic CAD risk factors for humans with IR. The project includes preliminary data and proposed studies using human plaque and liver specimens. The work should suggest new therapeutic strategies that target common pro-atherogenic pathways in the arterial wall and liver in IR subjects.
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