Abstract 15262: Matrix Metalloproteinase-9 Stimulated Osteopontin Proteolysis Enhances the Extracellular Matrix Response Post Myocardial Infarction
Osteopontin (OPN) is a glycoprotein markedly and consistently upregulated post-injury as a result of macrophage infiltration. OPN functions as a cytokine when secreted as soluble form and as a matricellular protein when immobilized to the extracellular matrix (ECM). OPN associates with the development of heart failure, but the mechanisms remain unclear. Matrix metalloproteinase (MMP)-9 has several cytokine and growth factor substrates, but whether OPN is an MMP-9 substrate in the post-myocardial infarction (MI) left ventricle (LV) has not been determined. We tested the hypothesis that MMP-9 could generate an OPN fragment in vivo post-MI and that this fragment would stimulate LV remodeling.
We studied OPN levels in the infarct of wild type (WT) and MMP-9 null mice at days 0 (d0, control), 1, 3, 5, and 7 post-MI. OPN protein levels increased post-MI and peaked at d5 in both WT and Null groups (WT 7-fold increase, Null 6-fold increase; p<0.05 compared to d0). At d5 post-MI, a 35 kDa OPN fragment was increased 5-fold in the WT compared to d0 values (p<0.05), but not in the Null group, indicating that this OPN fragment was MMP-9 dependent. By ECM gene array analysis, the MMP-9 null LV also showed an attenuated fibrotic response at d5 post-MI. OPN gene levels increased post-MI (>400-fold), but this increase was not affected by MMP-9 deletion, indicating that OPN regulation by MMP-9 was post-translational. At d5 post-MI, several OPN-associated proteins and receptors were overexpressed compared to d0 in the WT. In particular, gene levels of Col1a1, Itga5, Mmp2, Sparc, Thbs1, and Tnc were all elevated at least 2-fold (all p<0.05). This effect was attenuated in the Null mice (Figure 1. p<0.05 for all compared to WT d5), suggesting that OPN proteolysis stimulated the fibrotic response. In conclusion, our data suggest OPN proteolysis plays an important role in regulating post-MI LV remodeling by promoting ECM synthesis. This effect is MMP-9 dependent and modulates the overall fibrotic response.
- © 2013 by American Heart Association, Inc.