Inflammatory cytokines and oxidized low density lipoproteins increase endothelial cell expression of membrane type 1-matrix metalloproteinase

We investigated whether inflammatory cytokines or oxidized low density lipoproteins (Ox-LDL) present in human atheroma modulate extracellular matrix degradation by inducing membrane type 1-matrix metalloproteinase (MT1-MMP) expression. Cultured human endothelial cells (EC) constitutively expressed MT1-MMP mRNA and protein with enzymatic activity. Tumor necrosis factor-α (TNF-α), interleukin-1α, or interleukin-1β caused a time-dependent increase in the steady-state MT1-MMP mRNA levels within 4 h of exposure, peaking about 4-fold by 6 h, and remaining elevated for 12 h. Increased MT1- MMP mRNA correlated with a 2.5-fold increase in MT1-MMP protein in EC membranes. Ox-LDL also increased MT1-MMP mRNA levels that varied with the duration of exposure and degree of LDL oxidation. The increase in MT1-MMP mRNA occurred within 6 h of exposure to Ox-LDL and peaked over 3-fold by 6 h. Ox-LDL, but not native LDL, increased MT1-MMP protein by 2-fold in EC membranes. A combination of TNF-α and Ox-LDL was additive in increasing MT1- MMP expression. Nuclear run-on assays showed that TNF-α or Ox-LDL augmented steady-state mRNA levels by increased transcription of the MT1-MMP gene. These findings indicate that activation of EC by inflammatory cytokines and/or Ox-LDL increase MT1-MMP expression. Since MT1-MMP promotes matrix degradation by activating pro-MMP-2, these results suggest a novel mechanism whereby cytokines or Ox-LDL may influence extracellular matrix remodeling.