Effect And Its Mechnism Of Cyclic Mechanical Strain On Phenotype Modulation Of Vascular Smooth Muscle Cells

Phenotype transformation of vascular smooth muscle cells (VSMCs) is known to be modulated by cyclic mechanical strain. It is known to all that at least three kinds of information are included within a cyclic stretch, i.e., magnitude, frequency and exposure time, in vitro. However, it remains unclear how different frequencies of mechanical strains affect the VSMCs. The clinical studies have shown that heart rate variability is a significant risk factor in atherosclerosis. Thus, the present study was designed to investigate whether different frequencies of mechanical strains affected VSMCs phenotype.VSMCs were subjected to mechanical strains of 10 % elongation at 0 Hz, 0.5 Hz, 1 H and 2 Hz for 24 hours using a Flexercell strain unit. VSMCs phenotype was assayed by cell morphology, measurement of two-dimensional area of cells, western blotting for protein and RT-PCR for mRNA expression of differentiation markers of VSMCs. Possible protein kinases involved were evaluated by western blotting with their specific inhibitors or by targeted siRNA'knock-down'. The cyclic mechanical strains at certain frequencies could induce VSMCs to be contractile morphology and to align nearly perpendicular to the strain direction. Mechanical strains also regulated the protein and mRNA expression of several differentiation markers, as well as the activation of extracellular signal-regulated kinases (ERKs), p38 MAP kinase and protein kinase B (Akt) in a frequency-dependent manner. Furthermore, the inhibition of p38 pathway could block the strain-frequency induced the phenotype modulation of VSMCs, neither ERKs nor Akt. Frequency of mechanical strain, not conditioned medium, regulated the phenotype of VSMCs in a frequency-dependent manner. Rho-GDI alpha was suppressed by the mechanical strain at 1Hz. Inhibition of Rho-GDI alpha, by targeted siRNA'knock-down', enhanced the activation of p38 and the expression of h1-calponin, which suggested that maybe through inhibiting the expression of Rho-GDI alpha, the mechanical strain induced VSMCs differentiation.Our data indicate that the frequency of cyclic strain can result in the differentiated phenotype of VSMCs, and it is mediated at least partly by the activation of p38 pathway and down-regulation of Rho-GDI alpha. These results suggest apart from the amplitude, the frequency of strain may play an important role in VSMCs phenotype alterations in the sense of vascular diseases. In vivo there may be the most suitable frequency for cardiovascular system, which could protect the contractile phenotype VSMCs against transforming to synthetic phenotype unnormally, make the stable structure and function of vascular well. Furthermore, choosing the certain frequency of strain is very important for the creation of an engineered vascular construct.