Abstract
Vascular smooth muscle cells (VSMCs) are the predominant cell type in the blood vessel wall. Changes in VSMC actomyosin activity and morphology are prevalent in cardiovascular disease. The actin cytoskeleton actively defines cellular shape and the LInker of Nucleoskeleton and Cytoskeleton (LINC) complex, comprised of nesprin and the Sad1p, UNC-84 (SUN)-domain family members SUN1/2, has emerged as a key regulator of actin cytoskeletal organisation. Although SUN1 and SUN2 function is partially redundant, they possess specific functions and LINC complex composition is tailored for cell-type-specific functions. We investigated the importance of SUN1 and SUN2 in regulating actomyosin activity and cell morphology in VSMCs. We demonstrate that siRNA-mediated depletion of either SUN1 or SUN2 altered VSMC spreading and impaired actomyosin activity and RhoA activity. Importantly, these findings were recapitulated using aortic VSMCs isolated from wild-type and SUN2 knockout (SUN2 KO) mice. Inhibition of actomyosin activity, using the rho-associated, coiled-coil-containing protein kinase1/2 (ROCK1/2) inhibitor Y27632 or blebbistatin, reduced SUN2 mobility in the nuclear envelope and decreased the association between SUN2 and lamin A, confirming that SUN2 dynamics and interactions are influenced by actomyosin activity. We propose that the LINC complex exists in a mechanical feedback circuit with RhoA to regulate VSMC actomyosin activity and morphology.
Highlights
Vascular smooth muscle cells (VSMCs) line the blood vessel wall and their function is regulated by both soluble and insoluble mechanical cues, including blood flow-derived stretch and matrix stiffness [1,2,3]
Recent studies have shown that SUN1 and SUN2 possess independent functions, we set out to confirm that VSMCs possess SUN1 and SUN2. qPCR analysis and western blot (WB)
We we investigated the individual roles of SUN1 and SUN2 in VSMC function
Summary
Vascular smooth muscle cells (VSMCs) line the blood vessel wall and their function is regulated by both soluble and insoluble mechanical cues, including blood flow-derived stretch and matrix stiffness [1,2,3]. VSMCs normally exist in a quiescent, contractile phenotype and actomyosin activity drives VSMC contraction and regulates vascular tone and vessel compliance [4]. VSMCs are not terminally differentiated and changes in their mechanical environment promote VSMC dedifferentiation to a proliferative, synthetic phenotype [1,5]. Cell morphology is critical for normal tissue function and changes in VSMC morphology are observed during phenotypic modulation associated with development and disease [1]. Cell–matrix adhesions serve as signalling hubs that sense and initiate cellular response to changes in the mechanical environment [7]
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