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The differentiation of valvular interstitial cells (VICs) to a myofibroblastic or osteoblast-like phenotype is commonly found in calcific valvular stenosis, although the molecular-level mechanisms of this process remain poorly understood. Due to the role of the Rho pathway in various vascular diseases and in the expression of a myofibroblast phenotype, the present study was inspired by the hypothesis that Rho activation is involved in regulating cellular processes related to valve calcification. It was found that increased RhoA and Rho kinase (ROCK) activity was associated with increased nodule formation in VIC cultures in vitro, and intentional induction of RhoA activity led to a further increase in nodules and expression of α-smooth muscle actin. VICs treated with ROCK inhibitors were also examined for nodule formation, proliferation, apoptosis, and expression of myofibroblastic or osteoblastic markers. ROCK inhibition dramatically reduced myofibroblast-regulated nodule formation in VIC cultures, as evidenced by a decrease in nodule number, total nodule area, α-smooth muscle actin-positive stress fibers, apoptosis, and gene expression of myofibroblast-related phenotypic markers. Meanwhile, ROCK inhibition was less effective at reducing nodule formation associated with osteogenic activity. In fact, ROCK inhibition increased the expression of alkaline phosphatase and effected only a modest decrease in nodule number when applied to VIC cultures with higher osteogenic activity. Thus, the Rho pathway possesses a complex role in regulating the VIC phenotype and nodule formation, and it is hoped that further elucidation of these molecular-level events will lead to an improved understanding of valvular disease and identification of potential treatments. [ABSTRACT FROM AUTHOR]

Gu X, Masters KS. Role of the MAPKIERK pathway in valvular interstitial cell calcification. Am J Physiol Heart Circ Physiol 296:H1748-Hl757, 2009. First published April 10, 2009; doi:l0.1 152/ajpheart.00099.2009.-Much remains to be discovered about the etiology of heart valve disease and the molecular level mechanisms that drive it. The MAPK/ERK pathway influences calcification in many cell types and has been linked to the expression of a contractile phenotype in valvular interstitial cells (VICs). However, a direct correlation between MAPK/ERK pathway activity and VIC calcification has not been previously described. Thus the role of the MAPK pathway in the calcification of VIC cultures was investigated by measuring ERK activation in both calcifying and noncalcifying VIC enviroments and then, conversely, analyzing the effects of ERK pathway inhibition on VIC calcification and phenotype. Prolonged elevation of Phosphorylated ERK-1/2 was found in calcifying VIC cultures, whereas directly blocking phosphorylation of ERK1/2 resulted in a dramatic decrease in nodule number, nodule size, and total calcified area. Application of the ERK pathway inhibitor was also associated with a dramatic decrease in apoptosis, which may have contributed to the decreased nodule formation obtained via ERK inhibition. Real-time PCR analysis revealed that calcified samples exhibited significantly elevated expression of several myofibroblastic and osteoblastic markers, while ERK inhibition substantially reduced the expression of these markers, often to levels comparable to the noncalcifying control. These data suggest that the MAPK pathway plays an impbrtant role in regulating the phenotype and calcification of VICs, wherein sustained pathway activation is associated with increased VIC calcification. These findings may be used to further elucidate the mechanisms of valvular disease and identify potential treatment targets. [ABSTRACT FROM AUTHOR]