Aggregated low density lipoproteins decrease metalloproteinase-9 expression and activity in human coronary smooth muscle cells

Plaque stability largely depends on vascular smooth muscle cell (VSMC) function. VSMC secrete metalloproteinases (MMPs), matrix degrading endopeptidases, that regulate VSMC migration and function. Among them, gelatinase B or MMP-9 seems to have a protective effect by promoting a stable plaque phenotype. In macrophage foam cells oxidized LDL (oxLDL) uptake regulates MMP-9 expression. However, it is unknown whether VSMC-lipid loading by aggregated LDL (agLDL) internalization produces any effect on MMP-9 production by human resident vascular cells. In the present study, we analyzed the effect of lipid-internalization in MMP-9 and MMP-2 expression and activity and its consequences in VSMC migration. Our results show that agLDL-internalization down-regulates MMP-9 activity in a time-dependent manner up to 42% at 48 h and in a dose-dependent manner up to 87% at 300 μg/mL. nLDL induced similar but not sustained decrease on MMP-9 activity. However, neither agLDL nor nLDL exerted any significant effect on MMP-2 and TIMP-1. VSMC regrowth after a scratch injury was significantly reduced by exposure to agLDL. We conclude that agLDL-lipid loading reduces MMP-9 activity and this effect is associated to inhibition of VSMC migration. Thus, agLDL internalization may have consequences on vascular remodeling after injury, and the stability of lipid-rich atherosclerotic plaques.