Gαi2 Signaling Regulates Inflammasome Priming and Cytokine Production by Biasing Macrophage Phenotype Determination

Macrophages exist as innate immune subsets that exhibit phenotypic heterogeneity and functional plasticity. Their phenotypes are dictated by inputs from the tissue microenvironment. G-protein-coupled receptors are essential in transducing signals from the microenvironment, and heterotrimeric G alpha signaling links these receptors to downstream effectors. Several G alpha(i)-coupled G-protein-coupled receptors have been implicated in macrophage polarization. In this study, we use genetically modified mice to investigate the role of G alpha(i2) on inflammasome activity and macrophage polarization. We report that G alpha(i2) in murine bone marrow-derived macrophages (BMDMs) regulates IL1 beta release after activation of the NLRP3, AIM2, and NLRC4 inflammasomes. We show this regulation stems from the biased polarity of G alpha(i2) deficient (Gnai2(-/-)) and RGS-insensitive G alpha(i2) (Gnai2(G184S/G184S)) BMDMs. We determined that although Gnai2(G184S/G184S) BMDMs (excess G alpha(i2) signaling) have a tendency toward classically activated proinflammatory (M1) phenotype, Gnai2(-/-) BMDMs (G alpha(i2) deficient) are biased toward alternatively activated anti-inflammatory (M2) phenotype. Finally, we find that G alpha(i2)-deficient macrophages have increased Akt activation and IFN-beta production but defects in ERK1/2 and STAT3 activation after LPS stimulation. G alpha(i2)-deficient macrophages also exhibit increased STAT6 activation after IL-4 stimulation. In summary, our data indicates that excess G alpha(i2) signaling promotes an M1 macrophage phenotype, whereas G alpha(i2) signaling deficiency promotes an M2 phenotype. Understanding G alpha(i2)-mediated effects on macrophage polarization may bring to light insights regarding disease pathogenesis and the reprogramming of macrophages for the development of novel therapeutics.