AMP-activated protein kinase (AMPK) is an evolutionally conserved cellular energy sensor that regulates metabolic pathways in lipid, cholesterol and glucose metabolism. We have reported that macrophage AMPK protects against lipid-induced inflammation and insulin resistance in vitro. In addition, activating AMPK by 5- aminoimidazole-4-carboxamide-1-2-4-ribofuranoside (AICAR) in ApoE-/- mice alleviates atherosclerosis burden. However, the pleiotropic functions of AMPK make it difficult to determine specifically the role of macrophage AMPK in the pathogenesis of inflammation-associated metabolic disorders, including atherosclerosis and insulin resistance. In this proposal, transgenic mice with macrophage-specific over- expression of dominant negative or constitutively active 11AMPK (DN11 and CA11, respectively), and macrophage-specific 11MAPK knockout (MAKO) mice will be used to study the role of macrophage AMPK in these metabolic disorders. We find that macrophages from CA11 mice have significantly lower lipid- and cholesterol-induced ER stress, inflammation and apoptosis, which is associated with up-regulation of genes involved in fatty acid oxidation and cholesterol efflux. We hypothesize that macrophage AMPK regulates macrophage lipid and cholesterol homeostasis by promoting fatty oxidation and cholesterol efflux, thereby preventing lipid- and cholesterol-induced ER stress, inflammation and apoptosis. This may contribute to macrophage AMPK's protective effects against atherosclerosis and insulin resistance.
Specific aim 1 will determine mechanisms by which macrophage AMPK prevents lipid- and cholesterol-induced ER stress, inflammation and apoptosis using macrophages from CA11, DN11 and MAKO mice. We will determine: 1) whether AMPK regulates macrophage lipid and cholesterol homeostasis by promoting cholesterol efflux and fatty acid oxidation, and 2) whether these pathways are necessary in mediating AMPK's suppression of lipid- and cholesterol-induced ER stress, inflammation and apoptosis.
Specific aim 2 will determine the protective effects of macrophage AMPK against atherosclerosis using CA11, DN11 and MAKO mice crossed with low density lipoprotein receptor knockout mice. We will determine: 1) plasma lipoprotein phenotype, 2) in vivo reverse cholesterol transport from macrophages, 3) atherosclerosis extent, 4) macrophage number, lipid content, ER stress, inflammation and apoptosis in atherosclerotic lesions, and 5) kinetics of macrophage accumulation, ER stress, inflammation and apoptosis development in early and late atherosclerotic lesions in these mice fed an atherogenic diet.
Specific aim 3 will determine the protective effects of macrophage AMPK against insulin resistance using CA11, DN11 and MAKO mice. The insulin sensitivity and adipose tissue macrophage infiltration, ER stress and inflammation will be determined in these mice on a high fat diet. Completing these studies will greatly improve our knowledge on the role of macrophage AMPK in the protection against inflammation-associated metabolic disorders, including atherosclerosis and insulin resistance.
The goal of this project is to understand AMPK as a key signaling molecule linking cellular nutrient metabolism to inflammatory responses and to identify mechanisms mediating the protective effects of macrophage AMPK against both atherosclerosis and insulin resistance through suppression of lipid-mediated macrophage endoplasmic reticulum stress, inflammation and apoptosis.
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