TIMP-4 is regulated by vascular injury in rats

The role of basement membrane-degrading matrix metalloproteinases (MMPs) in enabling Vascular smooth muscle cell migration after vascular injury has b een established in several animal models. In contrast, the role of their na tive inhibitors, the tissue inhibitors of matrix metalloproteinases (TIMPs) , has remained unproven despite frequent coregulation of MMPs and TIMPs in other disease states. We have investigated the time course of expression an d localization of TIMP-4 in rat carotid arteries 6 hours, 24 hours,3 days, 7 days, and 14 days after balloon injury by in situ hybridization, immunohi stochemistry, and Western blot analysis. TIMP-4 protein was present in the adventitia of injured carotid arteries from 24 hours after injury. At 7 and 14 days after injury, widespread immunostaining for TIMP-4 was observed th roughout the neointima, media, and adventitia of injured arteries. Western blot analysis confirmed the quantitative increase in TIMP-4 protein at 7 an d 14 days. In situ hybridization detected increased expression of TIMP-4 as early as 24 hours after injury and a marked induction in neointimal cells 7 days after injury. We then studied the effect of TIMP-4 protein on the mi gration of smooth muscle cells through a matrix-coated membrane in vitro an d demonstrated a 53% reduction in invasion of rat vascular smooth muscle ce lls. These data and the temporal relationship between the upregulation of T IMP-4, its accumulation, and the onset of collagen deposition suggest an im portant role for TIMP-4 in the proteolytic balance of the vasculature contr olling both smooth muscle migration and collagen accumulation in the injure d arterial wall.