Regulation of proteolytic enzymes and inhibitors in two smooth muscle cell phenotypes

Rat arterial smooth muscle cells (SMC) are diverse in nature. In addition to SMC cultures which grow to the typical 'hill and valley' morphology at confluence, there are other SMC which show spindle shape, or thin and long fusiform swirling pattern, or which have a cobblestone appearance at confluence. The growth of these cell types is variably dependent on serum growth factors, and they display different cytoskeletal proteins. We wish to study the secretion of proteolytic enzymes and enzyme inhibitors from these SMC which may be important for their biological activities.

Two phenotypes, an 'epithelioid-like' SMC and a 'swirling' SMC, were isolated and cloned from rat carotid arteries. The proteolytic enzymes and inhibitors produced after stimulation with exogenous mediators were investigated with enzyme assays, zymography and immunoblotting.

Epithelioid SMC, but not swirling SMC, secreted MMP-2 in response to uPA and tPA. Epithelioid SMC produced small amounts of uPA and tPA in control cultures, but these proteinase secretions were enhanced by bFGF and PDGF. On the other hand, control swirling SMC secreted large amounts of uPA and tPA, which were reduced by the growth factors. In both cell types, the secretion of PAI-1 was stimulated by bFGF and PDGF, as well as by uPA and tPA. Furthermore, in both cell types, the secretion of TIMP-2 was enhanced by tPA and PDGF, but not by uPA or bFGF.

When challenged with mediators, two rat SMC phenotypes behaved differently in terms of proteinase secretions, but they were similar in terms of proteinase inhibitor secretions.