Effects of matrix rigidity on endothelial cell fate

Atherosclerosis, which involves arterial hardening, is a common cause of cardiovascular diseases. Alterations in the microenvironment of the arterial walls in diseased vessels may lead to significant changes in endothelial function. The extracellular matrix (ECM) is a vital component of the cellular microenvironment and has been shown to play an important role in endothelial cell (EC) function. The aim of the current study is to investigate the role played by matrix rigidity in the modulation of EC function and the underlying molecular signaling mechanisms. Using a synthetic substrate with a range of stiffness that may mimic the various states of cellular microenvironment, my results show that stiff matrices increased EC proliferation, while softer matrices decreased proliferation without the accompaniment of apoptosis. In addition to changes in proliferation, EC spreading area increased with the increase in rigidity of the matrix. Although ECs on stiffer matrices had larger cell areas than ECs on softer matrices, comparisons of the ellipticity ratio indicates there are no differences in cell shape. To examine the regulatory events between matrix rigidity and EC proliferation, an RGD blocking peptide was used to block integrin interactions between the ECM and ECs. The RGD peptide significantly decreased proliferation of cells on the hard matrix, indicating the role of integrins in mediating the hard matrix-induced EC proliferation. Src and Akt phosphorylations were significantly lower on stiff matrix than on the soft one. The RGD peptide increased the phosphorylation levels of Akt and Src of ECs on the hard matrix to levels comparable to those on the soft matrix. Increasing the Akt and Src activities in ECs by transfecting with a constitutively active Akt construct or a wild-type Src cDNA caused the reversion of EC proliferation on the stiff matrix. These results indicate that ECs interact with their matrix through the integrin-Src/Akt pathway to regulate their proliferation. These findings on the effects of matrix rigidity on EC proliferation and their regulation by the integrin-Src/Akt pathway provide new insights for the understanding of EC-matrix interaction in health and disease