Soft Substrate Induces Endothelial Cell Inflammation and Disrupts Endothelium Integrity

Abstract

Atherosclerosis (AS) is the main cause of death and disability all over the world. A lot of efforts have been devoted to treat AS, among which tissue engineering blood vessel materials, including artificial blood vessels, stents and vascular patches, have brought hope to ameliorate the symptoms in AS patients. However, there remains a large percentage of implantation failure due to the incompatibility of the material with the body. AS is a multi-factor related disease, and chronic inflammation is a major event that involves with its pathogenesis and development. Since previous studies suggested that the stiffness of the blood vessel might affect the inflammatory conditions, in this paper, we investigate the mechanism of how substrate stiffness could affect the inflammation response of the endothelial cells (ECs). Polyacrylamide (PA) based hydrogels at different concentrations were used as the culture substrate for ECs. The mRNA expression level of VCAM-1 and ICAM-1 was determined by qRT-PCR. EC chemotactic effect was evaluated by the number of THP-1 adhered to EC monolayer. The protein levels of IκBα and NF-κB were determined by western blotting analysis. The expression and localization of the major adherens junctions (AJs) proteins, VE-cadherin and β-catenin, were evaluated by western blotting and immunofluorescence staining. Our results showed that ECs cultured on soft substrate (1 kPa) demonstrated more chemotactic effect and the amount of the monocytes adhered to them was higher than that on harder substrate (20 kPa, p < 0.05). Moreover, NF-κB signaling pathway in ECs on 1 kPa substrate was more activated compared to those on 20 kPa substrate, with the IκBα protein expression level in the cytoplasm decreasing and NF-κB translocating more into the nuclear. In addition, the AJs of the endothelial monolayer changed with the substrate stiffness. Compared with ECs on normal substrate (20 kPa), the protein expression level of β-catenin decreased (p < 0.05), and immunofluorescence staining of VE-cadherin and β-catenin showed the AJs between the ECs on soft substrate (1 kPa) were punctuated. Taken together, our results suggested the stiffness of the substrate was important in regulating inflammation of the ECs and the integrity of the cell-cell junction. Therefore, the stiffness of the tissue engineering blood vessel material should be considered as an important criterium to avoid EC inflammation.