Background— Oxidized LDL (ox-LDL) accumulation in the atherosclerotic region may enhance plaque instability. Both accumulation of ox-LDL and expression of its lectin-like receptor, LOX-1, have been shown in atherosclerotic regions. This study was designed to examine the role of LOX-1 in the modulation of metalloproteinases (MMP-1 and MMP-3) in human coronary artery endothelial cells (HCAECs).

Methods and Results— HCAECs were incubated with ox-LDL (10 to 80 μg/mL) for 1 to 24 hours. Ox-LDL increased the expression of MMP-1 (collagenase) and MMP-3 (stromelysin-1) in a concentration- and time-dependent manner. Ox-LDL also increased collagenase activity. Ox-LDL did not significantly affect the expression of tissue inhibitors of metalloproteinases. Native LDL had no effect on the expression of MMPs. The effects of ox-LDL were mediated by its endothelial receptor, LOX-1, because pretreatment of HCAECs with a blocking antibody to LOX-1 (JTX92, 10 μg/mL) prevented the expression of MMPs in response to ox-LDL (P<0.01). In parallel experiments, ox-LDL caused the activation of protein kinase C (PKC), which was inhibited by LOX-1 antibody. The PKC-β isoform played a critical role in the expression of MMPs, because the PKC-β inhibitor hispidin reduced ox-LDL-induced activation of PKC and the expression of MMPs. Other PKC subunits (α, γ, and ε) did not affect the expression of MMPs.

Conclusions— These findings indicate that ox-LDL, via LOX-1 activation, modulates the expression and activity of MMPs in HCAECs. In this process, activation of the PKC-β subunit plays an important signaling role.