Abstract 17616: AMP-activated Protein Kinase is Critical for Regulating Cholesterol Homeostasis in Macrophages
Atherosclerosis is an inflammatory condition in which modified lipids, immune cells and fibrous debris accumulate in the intimal space of coronary and larger arteries. We have shown that genetic deletion of the AMPK β1 subunit (AMPK β1-/-) dramatically reduces (>95%) AMPK activity in macrophages causing lipid accumulation and inflammation (Galic et al, J Clin Invest 121:4903-15, 2011) and that the active ingredient in aspirin, salicylate, is a direct activator of AMPK β1 containing complexes (Hawley et al Science 336:918-22, 2012). We subsequently sought to determine the importance of macrophage AMPK in the regulation of cholesterol homeostasis in vitro, and the progression of atherosclerosis in vivo using this model of macrophage AMPK deletion. Bone marrow derived macrophages (BMDM) from AMPK β1-/- mice have a higher lipogenic capacity, where 3H-acetate incorporation into fatty acids and sterol fractions were significantly increased compared to wild-type (WT) control cells. Cholesterol efflux was diminished by ~40% in AMPK β1-/- cells, where cholesterol uptake was unaffected, suggesting a necessity for AMPK signaling in maintaining macrophage cholesterol balance. Importantly, the isoform specific activation of AMPK β1-/- via A-769662 or salicylate decreased synthesis of both fatty acid and sterol fractions, decreased cholesterol uptake and increased cholesterol efflux in a AMPK β1-dependent manner. To examine whether these changes in macrophage cholesterol homeostasis might have an impact atherogenesis, we transplanted WT or AMPK β1-/- bone marrow into low-density lipoprotein receptor knockout mice (LDLr-/- WT+/+ or LDLr-/- β1-/-). After recovery, mice were fed a Western diet for 8 and 16 weeks. LDLr-/- β1-/- mice were hyperglycemic and glucose intolerant compared to LDLr-/- WT+/+ controls. However, the progression of atherosclerosis, as evinced by the aortic root lesion size, necrotic core and lipid accumulation along the length of the descending aorta was not different between genotypes. Studies in ApoE and LDLr -/- mice are currently examining whether pharmacological activation of AMPK β1 complexes may attenuate atherosclerosis by favourably regulating cholesterol homeostasis and inflammation.
- © 2013 by American Heart Association, Inc.