The −1562C/T MMP-9 promoter polymorphism does not predict MMP-9 expression levels or invasive capacity in saphenous vein smooth muscle cells cultured from different patients

Matrix metalloproteinase-9 (MMP-9) is an important regulator of vascular smooth muscle cell (SMC) invasion and proliferation. The T allele of the −1562C/T MMP-9 promoter polymorphism reportedly confers increased MMP-9 promoter activity, plasma MMP-9 levels and susceptibility to vascular pathologies. The aim of this study was to determine whether the MMP-9 −1562C/T polymorphism directly influences endogenous MMP-9 expression levels in saphenous vein (SV) SMC cultured from patients with different genotypes. Genotyping of 408 patients revealed −1562C/T genotype frequencies of 73.3% CC, 25.0% CT and 1.7% TT. Using a standardized, controlled protocol we investigated the effects of phorbol ester (TPA) and a physiological stimulus (PDGF + IL-1) on MMP-9 expression in cultured SV-SMC from 15 CC, 15 CT and 3 TT patients, and on PDGF + IL-1-induced SV-SMC invasion (Boyden chamber with Matrigel barrier). A strong correlation between MMP-9 mRNA levels (real-time RT-PCR) and MMP-9 protein secretion (gelatin zymography) was observed. However, no significant differences were observed in MMP-9 expression levels, or in SV-SMC invasion, between cells with different −1562C/T genotypes. Moreover, MMP-9 promoter activity of the C and T variants was similar. Our data challenge the functional nature of the −1562C/T polymorphism and its capacity to modulate MMP-9 expression levels and SV-SMC invasion, and hence susceptibility to vascular pathologies in vivo.