Abstract 223: Histone Deacetylase Inhibition Mediated Macrophage Polarization Suppresses Matrix Metalloproteinase-9 Upregulation Post Myocardial Infarction

Background: Following a myocardial infarction (MI) the extracellular matrix (ECM) undergoes massive remodeling to prevent rupture and maintain cardiac output. Large increases in matrix metalloproteinase-9 (MMP-9) are associated with adverse ECM remodeling. We found that treatment with an HDAC inhibitor repressed post-MI upregulation of MMP-9. Significant sources of MMP-9 in the post-MI LV are M1 macrophages. Both phenotypes (M1 and M2) can contribute to MMP expression, but this is dependant on the phase of ECM remodeling. We hypothesize that HDAC inhibition regulates the post-MI expression of MMP-9 by mediating the M1 to M2 macrophage polarization. Methods: CD1 and MMP-9 β-gal reporter mice were induced with MI by LAD ligation then administered HDAC inhibitors: trichostatin A (TSA; class I and IIb), PD106 (class I), or Tubastatin A (HDAC 6) until termination at 5 or 7 days post-MI. Heart function evaluated by echocardiogram and cells or tissue by immunohistochemistry and immunoblotting. Results: The post-MI change in LV end-diastolic volume (49±9%) is significantly lower and ejection fraction (-44±8%) is improved with treatment of TSA vs. control (69±12%; -59±6%) respectively [n=28]. Immunohistochemical analysis revealed that infiltrating macrophages express MMP-9 at 5 and 7 days post-MI. HDAC inhibition decreases this expression and did so without reducing presence of macrophages within infarct. Immunoblotting shows that expression of all class I HDACs are increased following MI; however, in cultured macrophages only HDAC2 and HDAC3 are increased. TSA and PD106, inhibit control levels and lipopolysacharide (LPS) stimulated upregulation of MMP-9 in cultured RAW264.7 and bone marrow derived macrophages. Immunofluorescence revealed that treatment with PD106, Tub A, and TSA leads to M1 to M2 morphology specific polarization and maintenance of anti-inflammatory, M2, phenotype even with LPS stimulation in culture. However, only PD106 and TSA reduced MMP-9 expression in cultured macrophages. Conclusions: Macrophage mediated secretion of MMP-9 contributes to adverse ECM remodeling and loss of LV function post-MI. Class I HDAC inhibition promotes both M2 macrophage polarization and attenuates adverse remodeling by reducing MMP-9 expression.