Background: In cardiomyocytes and cardiac fibroblasts, stretch induces a growth response.
Methods: To investigate which signal transduction pathways are involved in the stretch-induced growth response of cardiomyocytes and cardiac fibroblasts, we used a model of mechanical stress in which cells are submitted to biaxial cyclic stretch.
Results: In stretched cardiomyocytes major bands of tyrosine-phosphorylated (P-Tyr) proteins of 58, 49, and 27 kDa were detected and minor bands of 65 and 40 kDa. Furthermore, major bands of serine/threonine phosphorylated (P-Ser/Thr) proteins of 46, 42, and 21 kDa were detected. Phosphorylation of the 40 kDa P-Tyr protein increased significantly upon stretch. In cardiac fibroblasts major bands of P-Tyr proteins of 63, 53, and 23 kDa were detected and minor bands of 72 and 39 kDa. In addition, major bands of P-Ser/Thr proteins of 51, 47, and 23 kDa were detected and minor bands of 54 and 33 kDa. Phosphorylation of the 54 and 33 kDa P-Ser/Thr proteins increased significantly upon stretch. Phosphorylated JNK 1 and JNK 2 activities were not detected in fibroblasts. In cardiomyocytes levels of phosphorylated JNK 1 and 2 were very low, but tend to increase upon stretch. Phosphorylated p38 MAPK could not be identified in both cell types. The intensity of phosphorylation of paxillin increased upon stretch in both cell types, although the increases were only significantly different in stretched fibroblasts. Finally, stretch increased PLC activity in cardiomyocytes as well as in fibroblasts.
Conclusion: Our findings are in favour of mechanotransduction of the stretch signal via integrins and focal adhesion components such as FAK, Src kinase, PLC and paxillin. The activation of the last two focal adhesion components by stretch of cardiomyocytes and fibroblasts is demonstrated in this article.
Keywords: cardiac fibroblasts; cardiomyocytes; paxillin; phosphorylation; signal transduction.