The G2A Receptor Controls Polarization of Macrophage by Determining Their Localization Within the Inflamed Tissue

Abstract

Macrophages are highly versatile cells, which acquire, depending on their microenvironment, pro- (M1-like), or antiinflammatory (M2-like) phenotypes. Here, we studied the role of the G-protein coupled receptor G2A (GPR132), in chemotactic migration and polarization of macrophages, using the zymosan-model of acute inflammation. G2A-deficient mice showed a reduced zymosan-induced thermal hyperalgesia, which was reversed after macrophage depletion. Fittingly, the number of M1-like macrophages was reduced in the inflamed tissue in G2A-deficient mice. However, G2A activation was not sufficient to promote M1-polarization in bone marrow-derived macrophages. While the number of monocyte-derived macrophages in the inflamed paw was not altered, G2A-deficient mice had less macrophages in the direct vicinity of the origin of inflammation, an area marked by the presence of zymosan, neutrophil accumulation and proinflammatory cytokines. Fittingly neutrophil efferocytosis was decreased in G2A-deficient mice and several lipids, which are released by neutrophils and promote G2A-mediated chemotaxis, were increased in the inflamed tissue. Taken together, G2A is necessary to position macrophages in the proinflammatory microenvironment surrounding the center of inflammation. In absence of G2A the macrophages are localized in an antiinflammatory microenvironment and macrophage polarization is shifted toward M2-like macrophages.

The Lipid Receptor G2A (GPR132) Mediates Macrophage Migration in Nerve Injury-Induced Neuropathic Pain

“…Here, we demonstrated that G2A-deficient mice showed a strongly reduced infiltration of immune cells at the site of injury. Consistent with our findings, earlier studies also showed a reduced number of macrophages at the inflammatory site during peripheral inflammatory pain [ 22 ]. Interestingly, in dextran sulfate sodium (DSS)-induced colitis, a reduced number of T cells was observed in G2A-deficient mice, confirming our data of the sciatic nerve after nerve injury ( Figure 2 C) [ 65 ].…”

“…Since the number of macrophages was dramatically decreased in G2A-deficient mice in all three investigated tissues (sciatic nerve, DRGs and spinal cord), we hypothesized that G2A-deficiency affects the immunomodulatory and migratory properties of macrophages [ 22 ]. Therefore, we performed a global proteome analysis using a vanguard mass-spectrometry-based approach [ 33 ] using bone marrow-derived macrophages (BMDM) of wild-type and G2A.…”

“…Afterwards, the suspension was transferred to a 6-well plate. Cells were incubated over night at 37 °C and cultivated for seven days, as previously described [ 22 ].…”

“…Then cells were stimulated with 1 µM 9 HODE for 0, 5, 10 and 15 min, or 24 h. Afterwards, cells were harvested with a cell scraper in 50:50 Phosphosafe:cOmplete protease-inhibitor cocktail (100 µL/well). Then, the cells were sonicated twice (60%, 10 s) and total protein amount was determined by Bradford Protein Assay [ 16 , 22 , 32 ].…”

“…In the group of proton-sensing GPCRs, G2A shows the weakest response to acidic pH and seems to be a receptor for signaling lipids rather than for acidic conditions [ 20 , 21 ]. It has also been suggested before that G2A is responsible for the migration of leukocytes, but the underlying signaling pathways are still unclear [ 22 , 23 , 24 ].…”