Role of Fc.GAMMA. receptors in immune regulation and diseases

FcγRIIb Exacerbates LPS-Induced Neuroinflammation by Binding with the Bridging Protein DAP12 and Promoting the Activation of PI3K/AKT Signaling Pathway in Microglia

Introduction

This paper focuses on the expression and role of FcγRIIb in neuroinflammation, exploring the molecular mechanisms by which FcγRIIb interacts with the bridging protein DAP12 to regulate the PI3K-AKT signaling pathway that promote neuroinflammation and aggravate neuronal injury.

Methods

LPS-induced neuroinflammation models in vivo and in vitro were constructed to explore the role and mechanism of FcγRIIb in CNS inflammation. Subsequently, FcγRIIb was knocked down or overexpressed to observe the activation of BV2 cell and the effect on PI3K-AKT pathway. Then the PI3K-AKT pathway was blocked to observe its effect on cell activation and FcγRIIb expression. We analyzed the interaction between FcγRIIb and DAP12 by Immunoprecipitation technique. Then FcγRIIb was overexpressed while knocking down DAP12 to observe its effect on PI3K-AKT pathway. Finally, BV2 cell culture supernatant was co-cultured with neuronal cell HT22 to observe its effect on neuronal apoptosis and cell activity.

Results

In vivo and in vitro, we found that FcγRIIb expression was significantly increased and activated the PI3K-AKT pathway. Contrary to the results of overexpression of FcγRIIb, knockdown of FcγRIIb resulted in a significant low level of relevant inflammatory factors and suppressed the PI3K-AKT pathway. Furthermore, LPS stimulation induced an interaction between FcγRIIb and DAP12. Knockdown of DAP12 suppressed inflammation and activation of the PI3K-AKT pathway in BV2 cells, and meantime overexpression of FcγRIIb suppressed the level of FcγRIIb-induced AKT phosphorylation. Additionally, knockdown of FcγRIIb inhibited microglia activation, which induced neuronal apoptosis.

Discussion

Altogether, our experiments indicate that FcγRIIb interacts with DAP12 to promote microglia activation by activating the PI3K-AKT pathway while leading to neuronal apoptosis and exacerbating brain tissue injury, which may provide a new target for the treatment of inflammatory diseases in the central nervous system.

Altered balance of inhibitory and active Fc gamma receptors in murine autoimmune glomerulonephritis

Mag is an MRL-derived glomerulonephritis susceptibility locus that includes the Fcgr2b and Fcgr3 genes encoding the inhibitory Fc gamma receptor IIB (FcgammaRIIB) and active FcgammaRIII, respectively. We measured changes in gene balance in three B6.MRLc1 congenic mouse strains containing the 82-86, 92-100 and 100 cM regions of the MRL chromosome 1. We found that only the strain that has 92-100 (which includes Fcgr loci) developed glomerulonephritis. These congenic mice had splenomegaly, elevated blood urea nitrogen, anti-dsDNA antibodies and higher urinary albumin excretion compared to the parental strain C57BL/6(B6). Prior to the development of glomerulonephritis, large CD3- (T cell) and B220- (B cell) positive areas were identified in the spleens of B6.MRLc1(92-100) mice. Both Fc receptors were found in mesangial and dendritic cells; important sites of immune-complex clearance and antigen presentation. The FcgammaRIII-positive areas were more prominent in the congenic strain. Fcgr2b mRNA was lower in the B6.MRLc1(92-100) kidney and spleen than in those organs of the B6 mice while Fcgr3 expression and the Fcgr3 to Fcgr2b mRNA ratio was higher in the congenic strain kidneys, spleen and thymus than in those of the B6 prior to and at an early stage of glomerulonephritis. We conclude that the imbalance of inhibitory and active Fc gamma receptors influences the pathogenesis of glomerulonephritis.