Biomechanical environments affect the function of cells. In this study we analysed the effects of five mechanical stimuli on the gene expression of human umbilical vein endothelial cells (HUVECs) in mRNA level using real-time PCR. The following loading regimes were applied on HUVECs for 48 h: intermittent (0-5 dyn/cm(2) , 1 Hz) and uniform (5 dyn/cm(2) ) shear stresses concomitant by 10% intermittent equiaxial stretch (1 Hz), uniform shear stress alone (5 dyn/cm(2) ), and intermittent uniaxial and equiaxial stretches (10%, 1 Hz). A new bioreactor was made to apply uniform/cyclic shear and tensile loadings. Three endothelial suggestive specific genes (vascular endothelial growth factor receptor-2 (VEGFR-2, also known as FLK-1), von Willebrand Factor (vWF) and vascular endothelial-cadherin (VE-cadherin)), and two smooth muscle genes (α-smooth muscle actin (α-SMA) and smooth muscle myosin heavy chain (SMMHC)) were chosen for assessment of alteration in gene expression of endothelial cells and transdifferentiation toward smooth cells following load applications. Shear stress alone enhanced the endothelial gene expression significantly, while stretching alone was identified as a transdifferentiating factor. Cyclic equiaxial stretch contributed less to elevation of smooth muscle genes compared to uniaxial stretch. Cyclic shear stress in comparison to uniform shear stress concurrent with cyclic stretch was more influential on promotion of endothelial genes expression. Influence of different mechanical stimuli on gene expression may open a wider horizon to regulate functions of cell for tissue engineering purposes.

It has been well established that biomechanical environment can influence functionality of biological cells. There are evidences that show mechanical cyclic stretch can promote smooth muscle cell (SMC) markers in endothelial cells (ECs). The objective of this study was to determine whether mechanical stimuli in the forms of uniaxial and equiaxial cyclic stretches (UNCS and EQCS) can affect endothelial and smooth muscle gene expressions in mRNA level of human umbilical vein endothelial cells (HUVECs). For this purpose, 10% uniaxial UNCS and EQCS (60 cycles/min for 24 h) were applied on HUVECs, and using real-time PCR expressions of three EC specific markers, vascular endothelial growth factor receptor-2 (VEGFR-2, also known as FLK-1), von Willebrand Factor (vWF) and vascular endothelial-cadherin (VE-cadherin) and two SMC specific genes, α-smooth muscle actin (α-SMA) and smooth muscle myosin heavy chain (SMMHC) were quantified. Moreover, alterations in cell height were analyzed by atomic force microscopy (AFM). Results showed that cyclic UNCS for 24 h downregulated the expression of all EC markers and upregulated the expression of all SMC markers while low effects on HUVECs height were observed. Cyclic EQCS in the same conditions resulted in minor effect on SMC gene expression in HUVECs, while led to strong reduction in vWF with no significant change in other two endothelial genes. Cyclic EQCS considerably elevated cell height. Results proposed that ECs can transdifferentiate to SMC phenotype under specific microenvironmental conditions.