Molecular Mechanism of Protein Kinase Cbeta-Mediated Cholesterol Homeostasis

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DESCRIPTION (provided by applicant): Every year in the United States nearly 1 million deaths occur among the 7 million people affected with cardiovascular diseases. The dominant underlying factor for this disease includes elevated plasma low density lipoprotein (LDL)-cholesterol levels in association with hypertriglyceridemia, abdominal obesity, or insulin resistance. The plasma levels of LDL are strongly influenced by dietary cholesterol and body's ability to store and metabolize ingested cholesterol. Considering that adipose tissue accumulates one of the largest pools of exchangeable free cholesterol, there is no information available regarding the role and regulation of adipose LDL receptors and its relationship to whole body cholesterol homeostasis. Also, our knowledge of the signaling pathway controlling adipose endocrine and lipo-metabolic functions through sterol-response element binding protein-1c (SREBP-1c) is limited, as is the role of this kinase in diet-induced atherosclerosis. We previously showed, for the first time, involvement of specific isoforms of protein kinase C (PKC) in regulating hepatic LDL receptor expression. In order to extend these studies to whole animal, we have been studying consequences of PKCbeta deficiency on lipid homeostasis. Based on our most recent observations linking PKCbeta deficiency to reduced plasma LDL levels, increased adipose nuclear SREBP-1c resulting in LDL receptor induction, and changes in plasma adipokines levels, we propose that PKCbeta plays a critical role in cholesterol homeostasis by regulating adipose SREBP-1c processing, thus regulating genes of lipid homeostasis and atherosclerosis. In Specific Aim 1, role of PKCbeta in LDL homeostasis will be established by evaluating effects of PKCbeta deficiency on hepatic biosynthesis and clearance, as well as adipose uptake of plasma LDL. To understand the molecular basis, we will also determine PKCbeta-dependent changes in the adipose gene expression and whether overexpression of adipose PKCbeta rescues the phenotype or adipose-specific PKCbeta deficiency alone can account for this phenotype. Specific Aim beta will define the nuclear and cytoplasmic events at the molecular level by which PKCbeta deficiency promotes nuclear accumulation of SREBP-1c and induction of adipose LDL receptors, without affecting hepatic LDL receptor expression. Finally, Specific Aim 3 will investigate the role of PKCbeta in cholesterol-rich-diet-induced atherosclerosis in PKCbeta-/- x ApoE-/- mice under diabetic or nondiabetic conditions. We already have these mice and initial results are very encouraging and have the potential to provide the molecular basis of diabetes-induced atherosclerosis and an alternative to statin. The proposed studies will not only establish the role of PKCbeta in regulating whole body cholesterol homeostasis, but will also identify genes regulated by this kinase, to correlate regulatory mechanisms to animal physiology. Accomplishment of the above aims will unravel a central signaling component that may control dyslipidemia and atherosclerosis by regulating adipose tissue physiology; modulation of its activity may be the preferable mode for the treatment of lipid disorders and prevention of atherosclerosis in the beta1st century. PUBLIC HEALTH RELEVANCE: Cardiovascular disease remains the leading cause of death in industrialized nations despite major advances in its diagnosis, treatment, and prevention. The underlying aetiology is not clarified, but includes a strong genetic component as well as lifestyle factors such as physical inactivity, dietary habits and smoking. While there has been a trend over the last half century showing a general decline in the age-adjusted death rates of heart disease and stroke, the increasing epidemics of obesity, followed closely by insulin resistance and diabetes, will likely slow the decline and reverse this trend. It is both necessary and timely to define roles of protein kinase Cbeta isoform that simultaneously modify all risk factors. The greatest potential for arresting this epidemic is likely to come through a clearer understanding of its molecular pathogenesis to develop rational and mechanism based therapy.