Role Of SM22α In Angiotensin-Ⅱ Induced Vasular Smooth Muscle Cell Contraction

Objective: Angiotensin-Ⅱ(Ang-Ⅱ), a vasoactive peptide, induces vascular smooth muscle cell (VSMC) contraction. SM22α, an actin binding protein, is highly expressed in differentiated VSMCs. It is unclear whether SM22αplays a role in Ang-Ⅱ-induced contraction. In the present study, redifferentiation of VSMCs was induced by all-trans retinoic acid (ATRA), and the roles of SM22αin Ang-Ⅱ-induced contraction of VSMCs were assessed using specific siRNA to knockdown expression of endogenous SM22α.Methods and results:1 Induction of VSMC redifferentiation by ATRA Western blot analysis showed that the expression of contractile marker SM22αand SM-α-actin significantly increased after ATRA treatment for 40 hours, compared with control group cultured in DMEM contained 10% FBS.2 Contractility of VSMCs in response to Ang-ⅡstimulationCell contractility was determined by observing planar cell areas changes, and was expressed as the contraction index,ΔA/A0. After Ang-Ⅱstimulation following ATRA treatment for 40 hours, the contraction index of VSMCs significantly increased, compared with control group(0.28±0.019 vs. 0.06±0.01)(P<0.05).3 Roles of SM22αin Ang-Ⅱinduced contractionKnockdown of endogenous SM22αexpression resulted in the inhibition of VSMC contraction induced by Ang-Ⅱ. The contraction index in siSM22α-transfected VSMCs was lower than that of the siControl group(0.11±0.015 vs. 0.29±0.021)(P<0.05).4 ERK activation in Ang-Ⅱ-induced contraction in a SM22α- dependent mannerWestern blot analysis showed that Ang-Ⅱinduced ERK phosphorylation with VSMC contraction. The contraction index was significantly decreased when activation of ERK was inhibited by PD98059, a inhibitor of the upstream kinase of ERK (0.13±0.012), compared with the untreated group (0.26±0.023). Knockdown of the endogenous expression of SM22αby siRNA significantly inhibited ERK phosphorylation induced by Ang-Ⅱ.5 Role of SM22αin formation of actin stress fibresImmunofluorescent staining showed that abundant actin stress fibres co-localized with SM22αin ATRA-treated cells without SM22αknockdown. However, there was scant actin stress fibre formation after SM22αknockdown. The results suggest that SM22αis involved in ATRA-induced actin stress fibre formation.Conclusion:1 ATRA induces redifferentiation and restoration of contractility in VSMCs.2 SM22αregulates VSMC contraction induced by Ang-Ⅱ.3 SM22αmediates activation of ERK pathway and formation of actin stress fibres in VSMCs induced by Ang-Ⅱ.