Overexpression of Tissue Inhibitor of Matrix Metalloproteinase-1 Inhibits Vascular Smooth Muscle Cell Functions In Vitro and In Vivo

Arterial smooth muscle cells (SMCs) are in a quiescent growth state under normal physiological conditions, but they can be stimulated to proliferate and migrate from one tissue compartment to another if the vessel is injured. This response might require a selective and focal increase in tissue degradation, which might be mediated through the increased production of matrix metalloproteinases (MMPs). Blockade of MMP activity might therefore inhibit the SMC response to injury. To test this hypothesis, we developed clones of rat SMCs that overexpress baboon tissue inhibitor of matrix metalloproteinase-I (TIMP-1), using retrovirally mediated gene transfer, and characterized the functional capacity of these cells in vitro and in vivo. SMCs transduced with the TIMP-1 vector (LTSN) grew more slowly and also migrated through a gel matrix in a Boyden chamber assay more slowly than the vector alone (LXSN) cells. The conditioned medium from LTSN cells completely inhibited the platelet-derived growth factor-BB-induced migration of normal SMCs across a matrix-coated filter, while the LXSN cell conditioned medium had no effect. The inhibitor activity in the LTSN conditioned medium could be neutralized with an antibody to TIMP-1. In vivo, local overexpression of TIMP-1 using LTSN cells implanted onto balloon-injured rat carotid artery inhibited intimal hyperplasia. Neutralizing antibodies against TIMP-1 suppressed the effect of LTSN cell seeding on intimal thickening. These data support the conclusion that the process of SMC activation leading to a thickened intima is dependent on MMP activity and that TIMP-1 could be utilized to inhibit this process.