High plasma lipids are risk factors for various cardiovascular and metabolic disorders such as obesity, atherosclerosis and metabolic syndrome. Our long term goal is to find ways to lower plasma lipids by targeting lipoprotein assembly. Microsomal triglyceride transfer protein (MTP) is critical for lipoprotein assembly. We observed that miR-30c induces MTP mRNA degradation and reduces apoB secretion in hepatoma cells. Further, it lowers plasma lipids and hepatic lipoprotein production in mice. Hence, we hypothesize that miR- 30c targets MTP, reduces apoB secretion, lowers plasma lipids, and prevents atherosclerosis.
Aim 1 : We will evaluate the efficacy of miR-30c in reducing hyperlipidemia and atherosclerosis by manipulating its levels in the livers using overexpression and chemical antagonism approaches. First, effect of miR-30c, anti-miR-30c, and scramble miR (Scr) on hyperlipidemia will be assessed in male C57/Bl6 mice fed Western diet. Next, we will evaluate the efficacy of miR-30c in reducing plasma lipids in WHHL rabbits. Second, to test the hypothesis that miR-30c reduces atherosclerosis we will express miR-30c, anti-miR-30c and Scr in the livers of Western diet fed Apoe-/- and LDLr-/- mice. Mechanistic experiments will be performed to ascertain that miR-30c lowers hepatic lipoprotein production.
Aim 2 : We will evaluate how miR-30c reduces MTP expression, apoB secretion and hyperlipidemia using primary hepatocytes and mice. First, we will uncover mechanisms that lead to low plasma lipids. We hypothesize that decreases in plasma lipids occur due to reductions in apoB synthesis secondary to increased co-translational degradation. Second, experiments will be planned to document why miR-30c expression is not associated with steatosis despite lower MTP expression. We hypothesize that miR-30c reduces hepatic lipid biosynthesis and avoids steatosis. Third, we will identify mechanisms involved in the interactions between miR-30c and MTP mRNA. Our hypothesis is that interactions at the supplementary site are critical in the down regulation of MTP by miR-30c. We will (a) evaluate the importance of "supplementary sequences" in MTP/miR-30c interactions, (b) determine optimum base pairs required in the supplementary sequence of miR-30c to reduce MTP levels, and (c) assess the need of an asymmetric loop formation between seed and supplementary sites in inducing MTP mRNA degradation. At the end, we will have a novel understanding about the mode of action of miR-30c, and mechanisms involved in the lowering of hyperlipidemia and atherosclerosis. These studies might show that miR-30c regulates plasma apoB-containing lipoproteins by inducing posttranscriptional degradation of MTP mRNA and co-translational degradation of nascent apoB. Novel information about the molecular interactions between miR- 30c and MTP that lead to MTP mRNA destruction will be garnered. If proven, miR-30c might serve as a potentially new therapeutic agent to treat hyperlipidemia, atherosclerosis and other related metabolic disorders.
Reductions in plasma lipids are positively associated with lower incidence of atherosclerosis. Hence, novel approaches to reduce plasma lipids are needed. This application proposes to evaluate the mechanism of action of miR-30c in lowering plasma lipids and reducing atherosclerosis.