Abstract
Heart failure is characterized by an imbalance of matrix synthesis/turnover, finally resulting in fibrosis. Cardiac myocytes and fibroblasts play a pivotal role in the remodeling process. Cardiac remodeling involves the expression of TGF-beta1 and matrix metalloproteinases (MMPs) in cardiac fibroblasts (CFBs). Furin, a subtilisin/kexin-like proprotein convertase (PC), activates TGF-beta1 and membrane-bound MT1-MMP, which facilitates pro-gelatinase A (MMP-2) activation. Even though several reports identified TGF-beta1 as a pro-fibrotic cytokine in the heart, it increases MMP-activity and cell migration/invasion in several cell types. The present study was done to investigate the contribution of TGF-beta1 and furin to CFBs MMP-activity and motility. Stimulation of CFBs from adult Sprague-Dawley rats with TGF-beta1 (20 ng/ml) induced furin, but had no effect on the closely related PC5. Inhibition of furin inhibited angiotensin II-induced TGF-beta1 activation, indicating that TGF-beta1 amplifies its activating convertase in CFBs. Pretreatment of CFBs with TGF-beta1 (20 ng/ml, 24 h) increased their migration by about two-fold (p<0.05), which was accompanied by an enhanced expression and activity of MT1-MMP and MMP-2. Brefeldin A (BFA), a Golgi-disturbing agent, inhibited MT1-MMP activation, indicating that it occurs in the trans-Golgi network (TGN), where furin is concentrated and colocalized with MT1-MMP. Inhibition of furin significantly inhibited TGF-beta1-induced MT1-MMP/MMP-2 activation. Furthermore, inhibition of furin attenuated TGF-beta1-enhanced migration on gelatin-coated membranes (p<0.05). This was comparable to the effects of the MMP-inhibitor GM6001, pointing out that MMPs are major mediators of TGF-beta1-enhanced CFB motility. We demonstrate that TGF-beta1 induces MMP-activity in CFBs, thereby facilitating CFBs motility. Furthermore, TGF-beta1 amplifies its activating convertase furin, which is also required for MT1-MMP/MMP-2 activation in CFBs. Thus, furin is central for TGF-beta1 and MT1-MMP activation and might be a novel target in cardiac remodeling.
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