Abstract 204: Inhibition of Histone Deacetylase Activity Represses Matrix Metalloproteinase-9 Induction Through Regulation of Macrophage Polarization

Abstract

Post myocardial infarction (MI) the extracellular matrix (ECM) undergoes massive remodeling in order to prevent dilation of the infarct area and maintain cardiac output. Integral players in this remodeling are matrix metalloproteinases (MMP). Post-MI macrophages are a significant source of MMP production and have been shown to have temporal expression of the two phenotypes (M1 and M2). Differential expressions of macrophage phenotypes correlate with the different phases of ECM remodeling, ECM composition and MMP expression. Increased expression of MMP-9 is associated with deleterious effects to the ECM and left ventricular (LV) dilation following MI. MMPs major mechanism of expression regulation is transcription. Histone deacetylases (HDAC) are a class of enzymes that can greatly affect transcriptional regulation of genes during pathological conditions. Therefore, we hypothesize that HDAC inhibition controls the post-MI expression of MMP-9 by mediating macrophage polarization to improve LV function. The post-MI change in LV end-diastolic volume is significantly lower with treatment of the class I and IIb HDAC inhibitor trichostatin A (TSA) and ejection fraction is improved in mice. Immunohistochemical analysis and zymography revealed that MMP-9 expression at 7 days post-MI is attributable to infiltrating macrophages. Immunoblotting shows that TSA inhibits control levels and lipopolysacharide (LPS) stimulated upregulation of MMP-9 in cultured macrophages, while the class I specific inhibitor, PD106, only inhibits control. The HDAC 6 inhibitor, Tubastatin A (Tub A), partially inhibits LPS stimulated upregulation of MMP-9, but surprisingly appears to potentiate control levels of MMP-9. Immunofluorescence revealed that direct HDAC inhibition with PD106, Tub A, and TSA leads to M1 to M2 macrophage polarization and maintenance of anti-inflammatory, M2, phenotype even with LPS stimulation in culture. From these data we conclude that macrophage secretion of MMPs is an essential component in the promotion of adverse ECM remodeling post-MI. HDAC inhibition can attenuate this remodeling possibly through macrophage polarization, but HDAC inhibition mediated M2 polarization may not be sufficient to suppress MMP-9 expression.