Matrix metalloproteinase 2 activation of transforming growth factor-beta 1 (TGF-beta 1) and TGF-beta 1-type II receptor signaling within the aged arterial wall

Objective - To study matrix metalloproteinase 2 (MMP-2) effects on transforming growth factor-beta 1 (TGF-beta 1) activation status and downstream signaling during arterial aging. Methods and Results - Western blotting and immunostaining showed that latent and activated TGF-beta 1 are markedly increased within the aorta of aged Fisher 344 cross-bred Brown Norway (30 months of age) rats compared with adult (8 months of age) rats. Aortic TGF-beta 1-type II receptor (T beta RII), its downstream molecules p-similar to mad-mother against decapentaplegic (SMAD)2/3 and SMAD4, fibronectin, and collagen also increased with age. Moreover, TGF-beta 1 staining is colocalized with that of activated MMP-2 within the aged arterial wall and vascular smooth muscle cell (VSMC) in vitro, and this physical association was confirmed by coimmunoprecipitation. Incubation of young aortic rings ex vivo or VSMCs in vitro with activated MMP-2 enhanced active TGF-beta 1, collagen, and fibronectin expression to the level of untreated old counterparts, and this effect was abolished via inhibitors of MMP-2. Interestingly, in old untreated rings or VSMCs, the increased TGF-beta 1, fibronectin, and collagen were also substantially reduced by inhibition of MMP-2. Conclusions - Active TGF-beta 1, its receptor, and receptor-mediated signaling increase within the aortic wall with aging. TGF-beta 1 activation is dependent, in part at least, by a concomitant age-associated increase in MMP-2 activity. Thus, MMP-2 - activated TGF-beta 1, and subsequently T beta RII signaling, is a novel molecular mechanism for arterial aging.