During the previous period of funding we used a transgenic approach to address the role of tumor necrosis factor (TNF) in cardiac remodeling. These studies showed that targeted overexpression of secretable TNF provokes a dilated cardiac phenotype through increased activation of matrix metalloproteinases (MMPs). One of the unexpected observations from these studies was that TNF-induced activation of matrix metalloproteinases and fibrillar collagen degradation was transient, and was followed by decreased MMP activation and progressive myocardial fibrosis. These studies further showed that there was increased expression of transforming growth factor-beta (TGF-beta) in the hearts of the mice that overexpressed secretable TNF (referred to as MHCsTNF mice), raising the intriguing possibility that TGF-beta might act as a """"""""molecular switch"""""""" that allows matrix degradation to proceed unchecked when not activated, and that favors matrix accumulation when activated. A second preliminary observation was that the cardiac fibroblasts isolated from the hearts of the MHCsTNF mice manifest a """"""""profibrotic phenotype"""""""" that was maintained during serial passaging in culture. Based upon two observations, as well as our long-term goal of understanding how inflammation leads to cardiac remodeling, we have focused this competitive renewal on delineating the basic mechanisms that contribute to the myocardial fibrosis that develops in our line of MHCsTNF mice. The overall hypothesis to be tested in this competing renewal is that TGF-beta mediated Smad dependent signaling pathways are responsible for both the activated fibroblast phenotype and the myocardial fibrosis that we have observed in the MHCsTNF mice. This hypothesis wilt be tested by examining the mechanisms that are responsible for the profibrotic fibroblast phenotype in the MHCsTNF cardiac fibroblasts (Specific Aim 1), as well as the role of TGF-beta mediated signaling (Specific Aim 2) as a mechanism for the profibrotic fibroblast phenotype and myocardial fibrosis in the MHCsTNF mice. Finally, we will determine whether the effects of TGF-beta are mediated through Smad3 (Specific Aim 3) and whether increased Smad7 expression will attenuate myocardial fibrosis (Specific Aim 4). Taken together, these studies will provide definitive new information with respect to the role of TGF-beta mediated Smad dependent signaling and myocardial fibrosis in an experimental model of sustained inflammation.
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