Up-regulation of Fas Ligand Expression by Sirtuin 1 in both Flow-restricted Vessels and Serum-stimulated Vascular Smooth Muscle Cells

Objective To study the role of sirtuin 1 (SIRT1) in Fas ligand (FasL) expression regulation during vascular lesion formation and to elucidate the potential mechanisms.Methods SIRT1 and FasL protein levels were detected by Western blotting in either mouse arteries extract or the whole rat aortic vascular smooth muscle cell (VSMC) lysate.Smooth muscle cell (SMC)-specific human SIRT1 transgenic (Tg) C57BL/6 mice and their littermate wild-type (WT) controls underwent complete carotid artery ligation (ligation groups) or the ligation-excluded operation (sham groups).The carotid arteries were collected 1 day after operation.Reverse transcription-polymerase chain reaction was performed to detect the mRNA levels of SIRT1 and FasL.Luciferase reporter assays were performed to detect the effect of WT-SIRT1,a dominant-negative form of SIRT1 (SIRT1H363Y),and GATA-6 on the promoter activity of FasL.Flow cytometry assay was applied to measure the hypodiploid DNA content of VSMC so as to monitor cellular apoptosis.Results SIRT1 was expressed in both rat aortic VSMCs and mouse arteries.Forced SIRT1 expression increased FasL expression both in injured mouse carotid arteries 1 day after ligation (P<0.001) and VSMCs treated with serum (P<0.05 at the transcriptional level,P<0.001 at the protein level).No notable apoptosis was observed.Furthermore,transcription factor GATA-6 increased the promoter activity of FasL (P<0.001).The induction of FasL promoter activity by GATA-6 was enhanced by WT-SIRT1 (P<0.001),while SIRT1H363Y significantly relieved the enhancing effect of WT-SIRT1 on GATA-6 (P<0.001).Conclusions Overexpression of SIRT1 up-regulates FasL expression in both flow-restricted mouse carotid arteries and serum-stimulated VSMCs.The transcription factor GATA-6 participates in the transcriptional regulation of FasL expression by SIRT1.

SIRT6 is an epigenetic repressor of thoracic aortic aneurysms via inhibiting inflammation and senescence

Thoracic aortic aneurysms(TAAs)develop asymptomatically and are characterized by dilatation of the aorta.This is considered a life-threating vascular disease due to the risk of aortic rupture and without effective treatments.The current understanding of the pathogenesis of TAA is still limited,especially for sporadic TAAs without known genetic mutation.Sirtuin 6(SIRT6)expression was significantly decreased in the tunica media of sporadic human TAA tissues.Genetic knockout of Sirt6 in mouse vascular smooth muscle cells accelerated TAA formation and rupture,reduced survival,and increased vascular inflammation and senescence after angiotensin II infusion.Transcriptome analysis identified interleukin(IL)-1βas a pivotal target of SIRT6,and increased IL-1βlevels correlated with vascular inflammation and senescence in human and mouse TAA samples.Chromatin immunoprecipitation revealed that SIRT6 bound to the Il1b promoter to repress expression partly by reducing the H3K9 and H3K56 acetylation.Genetic knockout of Il1b or pharmacological inhibition of IL-1βsignaling with the receptor antagonist anakinra rescued Sirt6 deficiency mediated aggravation of vascular inflammation,senescence,TAA formation and survival in mice.The findings reveal that SIRT6 protects against TAA by epigenetically inhibiting vascular inflammation and senescence,providing insight into potential epigenetic strategies for TAA treatment.

Human paraoxonase gene cluster overexpression alleviates angiotensin II-induced cardiac hypertrophy in mice

Cardiac hypertrophy is the strongest predictor of the development of heart failure, and anti-hypertrophic treatment holds the key to improving the clinical syndrome and increasing the survival rates for heart failure. The paraoxonase(PON) gene cluster(PC) protects against atherosclerosis and coronary artery diseases. However, the role of PC in the heart is largely unknown. To evaluate the roles of PC in cardiac hypertrophy, transgenic mice carrying the intact human PON1, PON2, and PON3 genes and their flanking sequences were studied. We demonstrated that the PC transgene(PC-Tg) protected mice from cardiac hypertrophy induced by Ang II; these mice had reduced heart weight/body weight ratios, decreased left ventricular wall thicknesses and increased fractional shortening compared with wild-type(WT) control. The same protective tendency was also observed with an Apoe^(-/-)background. Mechanically, PC-Tg normalized the disequilibrium of matrix metalloproteinases(MMPs)/tissue inhibitors of MMPs(TIMPs) in hypertrophic hearts, which might contribute to the protective role of PC-Tg in cardiac fibrosis and, thus, protect against cardiac remodeling. Taken together, our results identify a novel anti-hypertrophic role for the PON gene cluster, suggesting a possible strategy for the treatment of cardiac hypertrophy through elevating the levels of the PON gene family.