Abstract 18687: PARP9 and PARP14 are Novel Regulators of Macrophage Activation

Background: Pro-inflammatory “M1” macrophages may promote atherogenesis, while “M2” macrophages may favor an anti-inflammatory milieu. Our global proteomics of M1 and M2 cells identified ADP-ribosylation enzymes PARP9 and PARP14 as novel regulators of macrophage activation. The present study has examined the underlying mechanisms and explored in vivo evidence for their role in vascular disease. Methods and Results: IFN gamma (M1) stimulation induced and IL-4 (M2) decreased PARP9 and PARP14 in mouse and human macrophages. siRNA silencing of PARP14 enhanced expression of M1 genes (e.g. TNFα, iNOS) and activation (phosphorylation) of pro-inflammatory STAT1 while suppressing M2 markers (e.g., Arginase 1) and anti-inflammatory STAT6. Conversely, PARP9 silencing suppressed M1 polarization and STAT1 activation. These results suggest that PARP14 inhibits and PARP9 promotes a pro-inflammatory macrophage phenotype. Co-immunoprecipitation indicated that PARP14 and PARP9 physically interact. ADP-ribosylation assays revealed that PARP9 impairs PARP14-induced ribosylation (Figure A). Targeted proteomics via high-resolution mass spectrometry demonstrated that PARP14 ADP-ribosylates at least two sites in STAT1α, which PARP9 suppressed. Mechanically injured arteries of Parp14-/- mice had accelerated lesion formation and macrophage accumulation. Peritoneal and plaque macrophages of PARP14-/- mice showed increased STAT1 phosphorylation, decreased STAT6 phosphorylation, enhanced M1 gene expression, and reduced M2 responses (Figure B, laser capture microdissection). More macrophages[[Unable to Display Character: ]]were immunoreactive for PARP9 in human “unstable” plaques than in “stable” plaques (64.6±16.2% vs. 30.8±12.3%, p Conclusions: PARP14 and PARP9 reciprocally regulate the mechanisms of macrophage activation, offering the potential for new therapies for cardiovascular diseases and other conditions, in which macrophage activity impacts outcomes.