GPR37 regulates macrophage phagocytosis and resolution of inflammatory pain
Sangsu Bang, … , Zhen-Zhong Xu, Ru-Rong Ji
Sangsu Bang, … , Zhen-Zhong Xu, Ru-Rong Ji
Published July 16, 2018
Citation Information: J Clin Invest. 2018;128(8):3568-3582. https://doi.org/10.1172/JCI99888.
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Research Article Inflammation Neuroscience Article has an altmetric score of 11

GPR37 regulates macrophage phagocytosis and resolution of inflammatory pain

Abstract

The mechanisms of pain induction by inflammation have been extensively studied. However, the mechanisms of pain resolution are not fully understood. Here, we report that GPR37, expressed by macrophages (MΦs) but not microglia, contributes to the resolution of inflammatory pain. Neuroprotectin D1 (NPD1) and prosaptide TX14 increase intracellular Ca2+ (iCa2+) levels in GPR37-transfected HEK293 cells. NPD1 and TX14 also bind to GPR37 and cause GPR37-dependent iCa2+ increases in peritoneal MΦs. Activation of GPR37 by NPD1 and TX14 triggers MΦ phagocytosis of zymosan particles via calcium signaling. Hind paw injection of pH-sensitive zymosan particles not only induces inflammatory pain and infiltration of neutrophils and MΦs, but also causes GPR37 upregulation in MΦs, phagocytosis of zymosan particles and neutrophils by MΦs in inflamed paws, and resolution of inflammatory pain in WT mice. Mice lacking Gpr37 display deficits in MΦ phagocytic activity and delayed resolution of inflammatory pain. Gpr37-deficient MΦs also show dysregulations of proinflammatory and antiinflammatory cytokines. MΦ depletion delays the resolution of inflammatory pain. Adoptive transfer of WT but not Gpr37-deficient MΦs promotes the resolution of inflammatory pain. Our findings reveal a previously unrecognized role of GPR37 in regulating MΦ phagocytosis and inflammatory pain resolution.

Authors

Sangsu Bang, Ya-Kai Xie, Zhi-Jun Zhang, Zilong Wang, Zhen-Zhong Xu, Ru-Rong Ji

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Figure 4

GPR37 is necessary for MΦ phagocytosis in inflamed hind paw skin.

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GPR37 is necessary for MΦ phagocytosis in inflamed hind paw skin. (A) Sc...
(A) Schematic illustration of MΦ phagocytosis of pH-sensitive and dye-conjugated zymosan (pH-R-zymosan) particles. Note that only phagocytized zymosan particles show red fluorescence. (B) Experimental diagram showing the timeline of i.pl. injection of pH-R-zymosan, FACS analysis, immunostaining, and edema tests. (C) Edema in a hind paw following zymosan (20 μg/20 μl) injection, as measured by paw volume. *P < 0.05 versus baseline (BL); 1-way ANOVA. n = 5 mice/group. (D) IHC showing the time courses of zymosan-induced changes in neutrophils (Gr-1+), MΦs (CD68+), GPR37, and phagocytized zymosan in inflamed hind paw skins. *P < 0.05 versus baseline in naive animals; 1-way ANOVA. n = 4 mice/group. (E) Images of phagocytized zymosan particles in skins of naive mice and inflamed mice 4 hours, 1 day, and 5 days after zymosan injection. Scale bar: 50 μm. (F) Quadruple staining of CD68 (green), DAPI (blue), GRP37 (purple), and zymosan particles (red) in inflamed skin 5 days after zymosan injection. Note that phagocytized zymosan particles are present inside GPR37+ MΦs. Scale bars: 20 μm and 5 μm (enlarged images). (G) Phagocytized zymosan levels (revealed by staining intensity) in naive and inflamed paws of WT and Gpr37−/− mice. *P < 0.05; 2-way ANOVA. n = 4 mice/group. (H) Quantification of CD68 IR in hind paw skin. n = 4 mice/group. (I) Flow cytometry showing the percentage of GPR37-expressing MΦs in WT and Gpr37–/– mice at different time points of zymosan injection. *P < 0.05; Student’s t test. n = 4–5 mice/group. Data represent the mean ± SEM.