SIRT1 promotes proliferation and prevents senescence through targeting LKB1 in primary porcine aortic endothelial cells.
BACKGROUND
Endothelial senescence causes endothelial dysfunction, promotes atherogenesis and contributes to age-related vascular disorders. SIRT1 is a conserved NAD(+)-dependent deacetylase possessing beneficial effects against aging-related diseases, despite that the detailed functional mechanisms are largely uncharacterized.


OBJECTIVE
The present study is designed to evaluate the protective effects of SIRT1 on endothelial senescence and to elucidate the underlying mechanisms.


RESULTS
An in vitro senescence model was established by prolonged culture of primary endothelial cells isolated from porcine aorta. The freshly isolated "young" cells gradually underwent senescence during 1 month of repetitive passages. Both mRNA and protein expressions of SIRT1 were progressively decreased. In contrast, the protein levels of LKB1, a serine/threonine kinase and tumor suppressor, and the phosphorylation of its downstream target AMPK(Thr172) were dramatically increased in senescent cells. Overexpression of LKB1 promoted cellular senescence and retarded endothelial proliferation, which could be blocked by increasing SIRT1 levels. Knocking down of SIRT1 induced senescence and elevated the protein levels of LKB1 and phosphorylated AMPK(Thr172). Regardless of the nutritional status, hyperactivation of AMPK was able to induce endothelial senescence. SIRT1 antagonized LKB1-dependent AMPK activation through promoting the deacetylation, ubiquitination and proteasome-mediated degradation of LKB1. The survival signaling of Akt was also found to be modulated by SIRT1 and LKB1, and could cross-regulate AMPK activity.


CONCLUSIONS
SIRT1 and LKB1/AMPK are the 2 key sensor systems for regulating endothelial cell survival, proliferation and senescence. The protective activities of SIRT1 may be achieved at least in part by fine tuning the acetylation/deacetylation status and stabilities of LKB1 protein.
Zu
Yi
Y
Department of Pharmacology, University of Hong Kong, Hong Kong, China.
Liu
Ling
L
Lee
Mary Y K
MY
Xu
Cheng
C
Liang
Yan
Y
Man
Ricky Y
RY
Vanhoutte
Paul M
PM
Wang
Yu
Y
D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000107:Acetylation; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000187:drug effects; D015536:Down-Regulation; D042783:Endothelial Cells / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D004789:Enzyme Activation; D005260:Female; D005838:Genotype; D006801:Humans; D007274:Injections, Intraperitoneal; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D010269:Paraquat / Q000008:administration & dosage; D010641:Phenotype; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D056564:Sirtuin 1 / Q000235:genetics / Q000378:metabolism*; D013552:Swine; D013912:Threonine; D013997:Time Factors; D014162:Transfection; D054875:Ubiquitination; D015854:Up-Regulation
D012333:RNA, Messenger; D013912:Threonine; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C491654:Stk11 protein, mouse; D055372:AMP-Activated Protein Kinases; D046988:Proteasome Endopeptidase Complex; C447939:SIRT1 protein, human; D056564:Sirtuin 1; D010269:Paraquat