Differential roles of extracellular signal-regulated kinase 1/2 and p38MAPK in mechanical load-induced procollagen alpha1(I) gene expression in cardiac fibroblasts.

OBJECTIVE AND METHODS We have previously demonstrated that mechanical loading of cardiac fibroblasts leads to increased synthesis and gene expression of the extracellular matrix protein collagen. We hypothesised that the upregulation of procollagen gene expression in cardiac fibroblasts, in response to cyclic mechanical load, is mediated by one or more members of the MAP kinase family. To test this hypothesis, the effect of mechanical load on the activation of extracellular signal-regulated kinase (ERK) 1/2, p46/54JNK, and p38MAPK was examined in rat cardiac fibroblasts. RESULTS Peak phosphorylation of ERK 1/2, p38MAPK kinases, and p46/54JNK was observed following 10-20 min of continuous cyclic mechanical load. Mechanical load significantly increased procollagen alpha1(I) mRNA levels up to twofold above static controls after 24 h. This increase was completely abolished by the MEK 1/2 inhibitor U0126, with no effect on basal levels. In contrast, SB203580, a specific inhibitor of p38MAPK, enhanced both basal and stretch-stimulated levels of procollagen mRNA. Consistent with this finding, selective activation of the p38MAPK signalling pathway by expression of MKK6(Glu), a constitutive activator of p38MAPK, significantly reduced procollagen alpha1(I) promoter activity. SB203580-dependent increase in procollagen alpha1(I) was accompanied by ERK 1/2 activation, and inhibition of this pathway completely prevented SB203580-induced procollagen alpha1(I) expression. CONCLUSIONS These results suggest that mechanical load-induced procollagen alpha1(I) gene expression requires ERK 1/2 activation and that the p38MAPK pathway negatively regulates gene expression in cardiac fibroblasts. These pathways are likely to be key in events leading to matrix deposition during heart growth and remodelling induced by mechanical load.