Intraluminal Pressure Is Essential for the Maintenance of Smooth Muscle Caldesmon and Filamin Content in Aortic Organ Culture

Abstract

Abstract-Different forms of mechanical stimulation are among the physiological factors constantly acting on the vessel wall. We previously demonstrated that subjecting vascular smooth muscle cells (VSMCs) in culture to cyclic stretch increased the expression of high-molecular-weight caldesmon, a marker protein of a differentiated, contractile, VSMC phenotype. In the present work the effects of mechanical factors, in the form of circumferential stress and shear stress, on the characteristics of SM contractile phenotype were studied in an organ culture of rabbit aorta. Application of an intralumininal pressure of 80 mm Hg to aortic segments cultured in Dulbecco's modified Eagle's medium containing 20% fetal calf serum for 3 days prevented the decrease in high-molecular-weight caldesmon content (70Ϯ4% of initial level in nonpressurized vessel, 116Ϯ17% at 80 mm Hg) and filamin content (80Ϯ5% in nonpressurized vessel, 100Ϯ2% at 80 mm Hg). SM myosin and low-molecular-weight caldesmon contents showed no dependence on vessel pressurization. Neither endothelial denudation nor alteration of intraluminal flow rates affected marker protein content in 3-day vessel culture, thus excluding the possibility of any shear or endothelial effects. Maintenance of high high-molecular-weight caldesmon and filamin levels in the organ cultures of pressurized and stretched vessels demonstrates the positive role of mechanical factors in the control of the VSMC differentiated phenotype. (Arterioscler Thromb Vasc Biol. 1998;18:922-927.)Key Words: stretch Ⅲ aorta Ⅲ marker protein Ⅲ caldesmon Ⅲ filamin T he arterial wall is continuously subjected to the action of mechanical forces in the form of tensile stress and shear stress. In addition, the pulsatile nature of blood pressure imposes cyclic stretch on the wall. In vivo studies and clinical observations suggest that decreased values of tensile and shear stress in surgically injured vessels are correlated with activation of cell proliferation and extracellular matrix production, which may result in vessel occlusion.1 In contrast, reestablishment of baseline tensile stress and shear stress levels is correlated with inhibition of cell proliferation and restoration of vessel wall morphology and cellular ultrastructure characteristic of the differentiated VSMC phenotype. 1,2These features and morphology indicate that VSMCs undergo phenotypic changes in regions of altered hemodynamic patterns. Experiments on isolated vessels suggest that appropriate mechanical stimulation is essential for the maintenance of VSMC contractile function and sensitivity to vasoconstrictors, 3 as well as morphology of the vessel wall. 4,5 However, the role of mechanical stimulation in the maintenance of SM marker protein content is still unclear.Changes in the expression of VSMC marker proteins are usually coordinated during VSMC transition to the synthetic phenotype in primary culture or at the loci of vascular injury.6,7 However, under certain conditions, expression of some marker proteins may be regulated independent...

Mechanical Stretch-Induced Apoptosis in Smooth Muscle Cells Is Mediated by β 1 -Integrin Signaling Pathways

“…33 Cultured SMCs increase SMC-specific markers when they are subjected to cyclic mechanical stretch. 34 In cardiomyocytes, overstretching induces signaling pathways that induce growth inhibition and apoptosis.…”

Regulation and characteristics of vascular smooth muscle cell phenotypic diversity

“…In another study, mechanical strain applied to SMCs grown on laminin caused a greater increase in h-caldesmon when com- pared with SMCs grown on collagen type I or IV. 58 The signal transduction pathways that are activated by stretch and shear stress 59 have also been shown to increase expression of SM-MHC. 60 Similar to the various effects reported on SMC marker gene expression, conflicting data exist on the growth response of SMCs to mechanical strain in culture.…”

The early- and late stages in phenotypic modulation of vascular smooth muscle cells: Differential roles for lysophosphatidic acid

“…While endothelial cells are primarily subjected to the shear stress resulting from blood flow, VSMC are primarily subjected to the stretch resulting from blood pressure. When VSMC are dissociated, they become deprived of the mechanical stimuli, which have been proved by numerous studies [12][13][14][15][16][17][18][19][20][21] to play a role in PM. Second, if inhibition of ERK and the p38 MAPK pathways is a prerequisite for maintaining the differentiated phenotype [40][41][42][43], how can one explain the findings that stretch not only increased ERK and p38 MAPK activity [44][45][46], but also at the same time was sufficient for maintaining the differentiated phenotype [16,17]?…”

“…Mechanical factors, soluble biochemical factors, and extracellular matrix components have been proved to induce PM. Studies with cultured cells [12][13][14][15][16][17] and with intact cultured vessels [18][19][20][21] have shown that mechanical stimulation is able to maintain VSMC in the differentiated phenotype, typified by a high level of SMC-specific marker genes or a low proliferation rate. Soluble biochemical factors, including platelet-derived growth factor (PDGF) [22][23][24][25], transforming growth factor (TGF)-β [26,27], and retinoic acid [28][29][30][31] have been shown to affect PM.…”