Mechanical strain and the aortic valve: influence on fibroblasts, extracellular matrix, and potential stenosis

Mechanical strain may affect aortic valve cusp, leading to an altered extracellular matrix ultrastructure and eventually aortic stenosis. The aim of this study was to evaluate the affect of these potential relationships on human tissue.

Extracellular matrix protein disposition was analyzed on human aortic valve cusp retrieved from 31 patients during routine aortic valve replacement surgery. Samples were immediately fixed in 2-hydroxyethyl methacrylate. Immunohistology and Western blot analysis were used to quantify decorin, tenascin-C, biglycan, alkaline-phosphatase, osteocalcin, and osteopontin content. Fibroblast function was analyzed on interstitial cells derived from aortic valve cups from patients undergoing aortic valve replacement. Cells were grown to confluency in modified Eagle's medium supplemented with 10% fetal calf serum under sterile conditions. Thereafter, mechanical strain was applied for 72 hours and 60 cycles per minute. Elongation of as much as 10% in comparison with no elongation (control group) was applied. All results were correlated to hemodynamic variables.

Decorin and biglycan were mostly located at the inflow aspects of the cusp, tenascin-C in the central layer, and osteopontin, osteocalcin, and alkaline phosphatase were concentrated near the cell populations surrounding calcified areas. The intensity of this protein expression was significantly related to the pressure gradient. Expression levels were twice to five times higher than normal in patients with a preoperative pressure gradient of more than 100 mm Hg. On fibroblasts subjected to mechanical strain, a similar significant increase in the expression for decorin, biglycan, alkaline-phosphatase, tenascin-C, osteocalcin, and osteopontin was found by immunohistology. Western blot analysis confirmed significantly enhanced expressions of two and eight times the normal levels.

A specific pattern of extracellular matrix protein expression was found in relation to mechanical strain on human aortic valve cusp tissue and in mechanically stimulated human valvular fibroblasts. This new insight into the process of aortic valve degeneration may be important for further therapeutic approaches to ameliorate the progression or even the initiation of potential aortic valve stenosis.