Background: Angiotensin II (Ang II) signalling, including matrix metalloproteinase type II (MMP2) activation, has been linked to an age-associated increase in migration capacity of vascular smooth muscle cells (VSMS) and to other proinflammatory features of arterial aging. Calpain-1 activation is required fo MMP2 expression in fibroblasts and is induced in cardiomyocytes by Ang II. The consequencies of engagement of calpain-1 with its substrates, however, in governing the age-associated proinflammatory status within the arterial wall, remains unknown. Methodology/Principal Findings: The present findings demonstrate that transcription, translation, and activity of calpain-1 are significantly up-regulated in rat aortae or early-passage aortic VSMC from old (39-mo) rats compared to young (8-mo). Dual immunolabeling of the arterial wall indicates that colocalization of calpain-1 and Ang II increases within the aged arterial wall. To further explore the relationship of calpain-1 to Ang II, we chronically infused Ang II into young rats, and treated cultured aortic rings or VSMC with Ang II. We also constructed adenoviruses harboring calpain-1 (CANP1) or its endogenous inhibitor calpastatin (CAST) and infected these into VSMC. Ang II induces calpain-1 expression in the aortic walls in vivo and ex vivo and VSMC in vitro. The Ang II mediated, age-associated increased MMP2 activity and migration in VSMC are both blocked by calpain inhibitor 1 or CAST. Over expression of calpain-1 in young VSMC results in cleavage of intact vimentin, and an increased migratory capacity mimicking that of old VSMC, which is blocked by the MMP inhibitor, GM6001. Concluson/Significance: Calpain-1 activation is a pivotal molecular event in the age-associated arterial Ang II/MMP2 signalling cascade that is linked to cytoskeleton protein retructuring, and VSMC migration. Therefore, targeting calpain-1 has the potential to delay or reverse the arterial remodeling that underlies age-associated diseases i.e. atherosclerosis.
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