Activation of AMP-Activated Protein Kinase Inhibits Oxidized LDL-Triggered Endoplasmic Reticulum Stress In Vivo

Abstract

OBJECTIVEThe oxidation of LDLs is considered a key step in the development of atherosclerosis. How LDL oxidation contributes to atherosclerosis remains poorly defined. Here we report that oxidized and glycated LDL (HOG-LDL) causes aberrant endoplasmic reticulum (ER) stress and that the AMP-activated protein kinase (AMPK) suppressed HOG-LDL–triggered ER stress in vivo.RESEARCH DESIGN AND METHODSER stress markers, sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) activity and oxidation, and AMPK activity were monitored in cultured bovine aortic endothelial cells (BAECs) exposed to HOG-LDL or in isolated aortae from mice fed an atherogenic diet.RESULTSExposure of BAECs to clinically relevant concentrations of HOG-LDL induced prolonged ER stress and reduced SERCA activity but increased SERCA oxidation. Chronic administration of Tempol (a potent antioxidant) attenuated both SERCA oxidation and aberrant ER stress in mice fed a high-fat diet in vivo. Likewise, AMPK activation by pharmacological (5′-aminoimidazole-4-carboxymide-1-β-d-ribofuranoside, metformin, and statin) or genetic means (adenoviral overexpression of constitutively active AMPK mutants) significantly mitigated ER stress and SERCA oxidation and improved the endothelium-dependent relaxation in isolated mouse aortae. Finally, Tempol administration markedly attenuated impaired endothelium-dependent vasorelaxation, SERCA oxidation, ER stress, and atherosclerosis in ApoE−/− and ApoE−/−/AMPKα2−/− fed a high-fat diet.CONCLUSIONWe conclude that HOG-LDL, via enhanced SERCA oxidation, causes aberrant ER stress, endothelial dysfunction, and atherosclerosis in vivo, all of which are inhibited by AMPK activation.

Oleate prevents saturated-fatty-acid-induced ER stress, inflammation and insulin resistance in skeletal muscle cells through an AMPK-dependent mechanism

“…However, AMPK activation prevented the increase in ER stress markers in palmitate-exposed skeletal muscle cells. This is consistent with previous studies reporting that AMPK activation protects against hypoxic injury [18], atherosclerosis [19] and liver damage [21] by reducing ER stress. By using the AMPK inhibitor compound C and overproduction of a dominant negative AMPK construct we demonstrated that activation of this kinase was responsible for the reduction in ER stress attained by oleate in palmitate-exposed cells.…”

“…2b) Fig. 2c, d), confirming that Ca 2+ mobilisation is involved in ER stress in mouse skeletal muscle cells, as previously described [19]. However, co-incubation of cells with palmitate plus BAPTA-AM reduced neither sXbp1 nor Chop expression, indicating that under our conditions Ca 2+ mobilisation does not contribute to palmitate-induced ER stress.…”

“…Oleate prevents palmitate-induced ER stress through an AMPK-dependent mechanism It is worth noting that activation of AMPK, which is considered a pharmacological target for insulin resistance and type 2 diabetes mellitus [35], inhibits ER stress [18,19,21] whereas reduction of this kinase promotes ER stress [20]. To confirm a role for AMPK in the preventive effects of oleate on palmitateinduced ER stress in C2C12 myotubes, we used the AMPK activators AICAR and A-769662 and the AMPK inhibitor compound C. The increase in the expression of sXbp1, Atf3, Chop and Bip caused by palmitate was reduced in cells coincubated with palmitate plus either AICAR or A-769662 (Fig.…”

“…Of note, activation of AMPactivated protein kinase (AMPK) exhibits multiple protective effects, including inhibition of inflammation, oxidative stress and insulin resistance and reduces the risk for developing obesity and type 2 diabetes [17]. Recently it has been reported that AMPK activation protects against hypoxic injury [18], atherosclerosis [19,20] and lipid-induced hepatic disorders [21] by reducing ER stress.…”

Endoplasmic reticulum stress: a novel mechanism and therapeutic target for cardiovascular diseases

“…AMPK controls systemic energy balance and metabolism and has been found to improve endothelial function and reduce cardiovascular risk in diabetic patients [148] . Its activation suppresses ERS in endothelial cells [149] , which is associated with several diseases, including atherosclerosis and obesity. Peroxisome proliferator-activated receptor δ (PPARδ) is ubiquitously expressed, for example, in adipose and endothelial cells.…”