Effect And Mechanism Of SIRT1 On Cyclic Strain Induced Phenotypic Differentiation Vascular Smooth Muscle Cells

As one of the most important cells in vascular wall, vascular smooth muscle cells (VSMCs) could switch their phenotype from contractile state to synthetic state in response to pathiological stimuli, which consists the essential event in vascular remodeling. Hemodynamics play vital role of in vascular remodeling as well as modulate the differentiation, migration, proliferation, and apoptosis of vascular cells. VSMCs are permanently exposed to the cyclic tensile strain for pulsatile blood flow in vivo. The sduty on the effect and mechanism of cyclic strain on VSMCs phenotypic differentiation will contribute a lot to illustrate the mechanobiological mechanism in vascular remodeling.The cultured rat VSMCs were subjected to 10%-1.25Hz-cyclic strain using FX-4000T Flexercell system for 24 hours. VSMCs without strain were used as a static control. The expression of histone deaceytlase SIRT1 in VSMCs was examined by RT-PCR and Western blotting. The expressions of contractile phenotypic markers,α-actin,calponin and SM22α, in VSMCs were determined by Western blotting. The activator and inhibitor of SIRT1 were used, as well as the methods of overexpression and RNA interference were applied to activate or block the expression and activity of possible message molecules including SIRT1 and protein kinase B/Akt in order to investage the regulatory role and mechanism of SIRT1 in the VSMC phenotypic differentiation induced by physiological cyclic strain.The results are as follows: (1) After loading 10%-1.25Hz-cyclic strain, the expressions of contractile phenotypic markers,α-actin, calponin and SM22α, were enhanced in VSMCs. (2) Cyclic strain induced an increase of the SIRT1 expression at both mRNA transcription and protein level in VSMCs. (3) Resveratrol, an activator of SIRT1, treatment or SIRT1 overexpression with mammalian expression plasmid transfection increased the expressions of contractile phenotypic markers in VSMCs. On the contrary, nicotinamide, an inhibitor of SIRT1, treatment or siRNA mediated decreased the expression of SIRT1, and inhibited the VSMC differentiation. (4) Overexpression of FOXO4 inhibited the expressions of contractile phenotypic markers in VSMCs. Meanwhile, the FOXO3aA3 overexpression in VSMCs played diffferent role in VSMC phenotypic modulation in contrast to FOXO4.Our data indicate that physiological cyclic strain could promote the phenotypic differentiation of VSMCs, and it is mediated at least partly by the activation of SIRT1 pathway, and is closely related with the interaction of SIRT1 and transcription modulator FOXOs. It suggests that physiological cyclic strain protects the phenotype of VSMCs switching from contractile state to synthesis state, which exerts a protective role in maintaining the vascular structure and function at a homeostaic state.