Ablation of SM22α decreases contractility and actin contents of mouse vascular smooth muscle

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Abstract
The actin‐binding protein SM22α marks contractile differentiation in smooth muscle, but its function is unknown. We tested its role in arterial contractility and stretch‐sensitive vascular protein synthesis. Active stress in depolarised mesenteric resistance arteries and portal veins was reduced by 40% in SM22α−/− mice. Passive and active arterial circumference–force relationships were shifted leftwards, whereas α1‐adrenergic responses were increased. Actin contents were 10–25% lower in vessels from SM22α−/− mice, but protein composition was otherwise similar. Synthesis of SM22α, calponin and α‐actin, but not β‐actin, was sensitive to stretch. Ablation of SM22α did not affect stretch sensitivity of any of these proteins. Thus, SM22α plays a role in contractility, possibly by affecting actin filament organisation.