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Activation of AMP-activated protein kinase inhibits oxidized LDL-triggered endoplasmic reticulum stress in vivo.

Dong Y, Zhang M, Wang S, Liang B, Zhao Z, Liu C, Wu M, Choi HC, Lyons TJ, Zou MH - Diabetes (2010)

Bottom Line: Exposure of BAECs to clinically relevant concentrations of HOG-LDL induced prolonged ER stress and reduced SERCA activity but increased SERCA oxidation.Likewise, AMPK activation by pharmacological (5'-aminoimidazole-4-carboxymide-1-beta-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.We 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.

View Article: PubMed Central - PubMed

Affiliation: ection of Endocrinology and Diabetes, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.

ABSTRACT

Objective: The 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 methods: ER stress markers, sarcoplasmic/endoplasmic reticulum Ca(2+) 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.

Results: Exposure 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-beta-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(-/-)/AMPKalpha2(-/-) fed a high-fat diet.

Conclusion: We 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.

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Inhibition of SERCA oxidation by antioxidant Tempol reduced ER stress and atherosclerosis in vivo. A and B: Supplement of antioxidant Tempol significantly reduced ER stress. ApoE−/− and ApoE−/−/AMPKα2−/− mice exhibited ER stress when fed with HFD compared with ApoE−/− mice fed with normal diet (ND) or HFD, as described in the “Research Design and Methods” section. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/− plus HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. C: Tempol supplementation protects aortic SERCA activity in vivo. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/−/HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. D: Tempol supplement ablates HFD-induced reduction of acetylcholine-induced endothelium-dependent vasorelaxation in isolated mouse aortae from ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD. *P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; #P < 0.05 ApoE−/−/AMPKα2−/− vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. E: Tempol administration reduces ox-LDL, ER stress, and aortic lesion progression in ApoE−/− mice detected by immunostaining; n ≥ 4 in each group. F: Tempol administration inhibits aortic lesions in aortic roots and aortic arches (en face staining); n ≥ 5 in each group. # and ‡ indicate P < 0.05 Tempol treatment vs. control in each group; †P < 0.05 ApoE−/−/AMPKα2−/− vs. ApoE−/− in each group. (A high-quality digital representation of this figure is available in the online issue.)
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Figure 7: Inhibition of SERCA oxidation by antioxidant Tempol reduced ER stress and atherosclerosis in vivo. A and B: Supplement of antioxidant Tempol significantly reduced ER stress. ApoE−/− and ApoE−/−/AMPKα2−/− mice exhibited ER stress when fed with HFD compared with ApoE−/− mice fed with normal diet (ND) or HFD, as described in the “Research Design and Methods” section. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/− plus HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. C: Tempol supplementation protects aortic SERCA activity in vivo. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/−/HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. D: Tempol supplement ablates HFD-induced reduction of acetylcholine-induced endothelium-dependent vasorelaxation in isolated mouse aortae from ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD. *P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; #P < 0.05 ApoE−/−/AMPKα2−/− vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. E: Tempol administration reduces ox-LDL, ER stress, and aortic lesion progression in ApoE−/− mice detected by immunostaining; n ≥ 4 in each group. F: Tempol administration inhibits aortic lesions in aortic roots and aortic arches (en face staining); n ≥ 5 in each group. # and ‡ indicate P < 0.05 Tempol treatment vs. control in each group; †P < 0.05 ApoE−/−/AMPKα2−/− vs. ApoE−/− in each group. (A high-quality digital representation of this figure is available in the online issue.)

Mentions: It was important to determine whether AMPK is essential in maintaining SERCA activity and inhibiting ER stress in vivo. Compared with ApoE−/− mice fed normal diet, ApoE−/− mice fed high-fat diet (HFD) had a reduced SERCA activity and exhibited greater degree of ER stress in the aorta (Fig. 7A–C). In addition, AMPKα2 depletion caused further reduction of SERCA activity with higher degree of ER stress in the aorta than ApoE counterparts (Fig. 7A–C).


Activation of AMP-activated protein kinase inhibits oxidized LDL-triggered endoplasmic reticulum stress in vivo.

Dong Y, Zhang M, Wang S, Liang B, Zhao Z, Liu C, Wu M, Choi HC, Lyons TJ, Zou MH - Diabetes (2010)

Inhibition of SERCA oxidation by antioxidant Tempol reduced ER stress and atherosclerosis in vivo. A and B: Supplement of antioxidant Tempol significantly reduced ER stress. ApoE−/− and ApoE−/−/AMPKα2−/− mice exhibited ER stress when fed with HFD compared with ApoE−/− mice fed with normal diet (ND) or HFD, as described in the “Research Design and Methods” section. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/− plus HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. C: Tempol supplementation protects aortic SERCA activity in vivo. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/−/HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. D: Tempol supplement ablates HFD-induced reduction of acetylcholine-induced endothelium-dependent vasorelaxation in isolated mouse aortae from ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD. *P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; #P < 0.05 ApoE−/−/AMPKα2−/− vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. E: Tempol administration reduces ox-LDL, ER stress, and aortic lesion progression in ApoE−/− mice detected by immunostaining; n ≥ 4 in each group. F: Tempol administration inhibits aortic lesions in aortic roots and aortic arches (en face staining); n ≥ 5 in each group. # and ‡ indicate P < 0.05 Tempol treatment vs. control in each group; †P < 0.05 ApoE−/−/AMPKα2−/− vs. ApoE−/− in each group. (A high-quality digital representation of this figure is available in the online issue.)
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Figure 7: Inhibition of SERCA oxidation by antioxidant Tempol reduced ER stress and atherosclerosis in vivo. A and B: Supplement of antioxidant Tempol significantly reduced ER stress. ApoE−/− and ApoE−/−/AMPKα2−/− mice exhibited ER stress when fed with HFD compared with ApoE−/− mice fed with normal diet (ND) or HFD, as described in the “Research Design and Methods” section. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/− plus HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. C: Tempol supplementation protects aortic SERCA activity in vivo. n = 5. *P < 0.05 ApoE−/− with HFD vs. ApoE−/− with ND; #P < 0.05 ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD; †P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; ‡P < 0.05 ApoE−/−/AMPKα2−/−/HFD vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. D: Tempol supplement ablates HFD-induced reduction of acetylcholine-induced endothelium-dependent vasorelaxation in isolated mouse aortae from ApoE−/−/AMPKα2−/− with HFD vs. ApoE−/− with HFD. *P < 0.05 ApoE−/− with HFD vs. Tempol-treated ApoE−/− with HFD; #P < 0.05 ApoE−/−/AMPKα2−/− vs. Tempol-treated ApoE−/−/AMPKα2−/− with HFD. E: Tempol administration reduces ox-LDL, ER stress, and aortic lesion progression in ApoE−/− mice detected by immunostaining; n ≥ 4 in each group. F: Tempol administration inhibits aortic lesions in aortic roots and aortic arches (en face staining); n ≥ 5 in each group. # and ‡ indicate P < 0.05 Tempol treatment vs. control in each group; †P < 0.05 ApoE−/−/AMPKα2−/− vs. ApoE−/− in each group. (A high-quality digital representation of this figure is available in the online issue.)
Mentions: It was important to determine whether AMPK is essential in maintaining SERCA activity and inhibiting ER stress in vivo. Compared with ApoE−/− mice fed normal diet, ApoE−/− mice fed high-fat diet (HFD) had a reduced SERCA activity and exhibited greater degree of ER stress in the aorta (Fig. 7A–C). In addition, AMPKα2 depletion caused further reduction of SERCA activity with higher degree of ER stress in the aorta than ApoE counterparts (Fig. 7A–C).

Bottom Line: Exposure of BAECs to clinically relevant concentrations of HOG-LDL induced prolonged ER stress and reduced SERCA activity but increased SERCA oxidation.Likewise, AMPK activation by pharmacological (5'-aminoimidazole-4-carboxymide-1-beta-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.We 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.

View Article: PubMed Central - PubMed

Affiliation: ection of Endocrinology and Diabetes, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.

ABSTRACT

Objective: The 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 methods: ER stress markers, sarcoplasmic/endoplasmic reticulum Ca(2+) 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.

Results: Exposure 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-beta-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(-/-)/AMPKalpha2(-/-) fed a high-fat diet.

Conclusion: We 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.

Show MeSH
Related in: MedlinePlus