Abstract P154: Focal Adhesion Kinase Plays a Critical Role in Upregulating Fibrogenesis in Load-Induced Cardiac Hypertrophy
Myocardial fibrosis is maladaptive, accelerating the evolution of diseased hearts to failure. The pathogenesis of myocardial fibrosis is critically dependent on complex processes of activation (i.e. enhanced proliferation, production and secretion of soluble factors, collagen and matrix metalloproteinases) and terminal differentiation of cardiac fibroblasts into myofibroblasts, resultant from the mobilization of numerous signaling molecules by physical and humoral stimuli. Noting that Focal Adhesion Kinase (FAK) is activated in areas of ongoing myocardial fibrosis, we sought to examine whether it is a critical mediator of fibrogenesis in load-induced hypertrophic hearts. Isolated fibroblasts from hypertrophic hearts of mice subjected to transverse aortic constriction (TAC; 1 to 8 weeks) were highly activated as recognized by markers that indicate enhanced proliferation (nuclear Ki67), production of collagen and matrix metalloproteinase-2 (MMP-2) and differentiation into myofibroblasts (expression of α-smooth muscle actin - α-SMA). In these cells, FAK was upregulated, as also were its dowstream pathways Src/ERK1/2 and PI3K/AKT/mTOR. Depletion of FAK (∼80%) after treatment with small interfering RNA (siRNA-FAK) markedly attenuated cardiac hypertrophy and fibrosis, and significantly reduced the number of activated fibroblasts harvested from overloaded hearts. Restoration of FAK function by overexpressing a full-length FAK construct in these cells, selectively enhanced the activity of the downstream PI3K/AKT/mTOR and rescued the activated phenotype of fibroblasts. Transfection with an inactive FAK mutant (Tyr397 substituted by phenylalanine) did not rescue the activated phenotype of fibroblasts harvested from overloaded hearts depleted of FAK. However, cells harvested from overloaded hearts depleted of FAK and treated with the mTOR activating aminoacid leucine showed typical phenotype of activated fibroblasts. These findings uncover a role for FAK in regulating the signaling cascade PI3K/AKT/mTOR in cardiac fibroblasts, which seems to be critical for the pathogenesis of myocardial fibrosis in hypertrophic hearts. Targeting this pathway may provide a novel strategy for treating hypertrophic heart diseases.
- © 2011 by American Heart Association, Inc.