Gα _i1 and Gα _i3 regulate macrophage polarization by forming a complex containing CD14 and Gab1

Abstract

Heterotrimeric G proteins have been implicated in Toll-like receptor 4 (TLR4) signaling in macrophages and endothelial cells. However, whether guanine nucleotide-binding protein G(i) subunit alpha-1 and alpha-3 (Gαi1/3) are required for LPS responses remains unclear, and if so, the underlying mechanisms need to be studied. In this study, we demonstrated that, in response to LPS, Gαi1/3 form complexes containing the pattern recognition receptor (PRR) CD14 and growth factor receptor binding 2 (Grb2)-associated binding protein (Gab1), which are required for activation of PI3K-Akt signaling. Gαi1/3 deficiency decreased LPS-induced TLR4 endocytosis, which was associated with decreased phosphorylation of IFN regulatory factor 3 (IRF3). Gαi1/3 knockdown in bone marrow-derived macrophage cells (Gαi1/3 KD BMDMs) exhibited an M2-like phenotype with significantly suppressed production of TNF-α, IL-6, IL-12, and NO in response to LPS. The altered polarization coincided with decreased Akt activation. Further, Gαi1/3 deficiency caused LPS tolerance in mice. In vitro studies revealed that, in LPS-tolerant macrophages, Gαi1/3 were down-regulated partially by the proteasome pathway. Collectively, the present findings demonstrated that Gαi1/3 can interact with CD14/Gab1, which modulates macrophage polarization in vitro and in vivo.

Quaking Deficiency Amplifies Inflammation in Experimental Endotoxemia via the Aryl Hydrocarbon Receptor/Signal Transducer and Activator of Transcription 1–NF-κB Pathway

“…Given the reduced pro-inflammatory responses in LysMCre QKI fl/fl mice after transferring peritoneal macrophages that overexpress QKI5 in the LPS-induced mice model, alternatively activated macrophages (M2) were anticipated. Thus, we measured changes in the proportion of peritoneal M1 macrophages (F4/80 int CD11b int ) and M2 macrophages (F4/80 hi CD11b hi ) ( 35 ). Compared to macrophages in QKI fl/fl mice, an increase in M1 macrophages and a decrease in M2 macrophages were shown in LPS-treated LysMCre QKI fl/fl mice transferred with control cells.…”

The impact of RGS and other G-protein regulatory proteins on Gαi-mediated signaling in immunity

“…Thymocyte subsets are unperturbed, but splenic and Peyer’s patch B220 + cells are slightly reduced. The report alluded to above (53) showed that TLR4 signaling led to formation of a complex that contained Gα i3, CD14, and Gab1 (growth factor receptor binding 2 (Grb2)-associated binding protein 1), which promoted Akt activation. A deficiency in Gα i3 reduced LPS-induced TLR4 endocytosis and interfered with phosphorylation of interferon regulatory factor 3.…”

“…In contrast to the Gnai2 −/− mice few immune related phenotypes have been reported in the Gnai3 −/− mice although a recent report showed that Gα i3 functions along with Gα i1 in macrophage TLR4 signaling (53). Lymphocytes, neutrophils, and macrophages all express significant levels of Gα i3 yet, chemokine responses are intact in the above cells purified from Gnai3 −/− mice (10,52,54,55).…”

Thymopentin improves the survival of septic mice by promoting the production of 15‐deoxy‐prostaglandin J2 and activating the PPARγ signaling pathway

“…Macrophages were derived from bone marrow (BM) as done previously. 7 Briefly, male C57BL/6 mice (8 ~ 12 weeks old) were killed by cervical dislocation, and immersed in 75% of ethanol for 5 minutes. Then, the femur and the tibia were cut off, and the muscles and tissues around them were removed with sterile forceps and scissors.…”