Effects Of FcγRIIB Overexpression On Oligomeric Aβ-exposed Microglia

Background:Microglia is best known as immune cel s of CNS and plays a crucial role in removing excessive Aβ. The well balanced physiological functions of Aβ account for neurotransmitter and neurotrophy of synapse by virtue of surveillance and scavenger of microglia. Aβ has been proved to be the pathogenic factor of Alzheimer’s disease. During the progression of AD, microglia is disease modified under the burden of Aβ Plaque. From the initial effective activation to the later paralysis, Mass of Aβ has successfully transformed microglia to the immunosuppressed state. The devastating capacity to spark inflam matory response and inability to phagocytize Aβ has created a vicious cycle between microglia dysfunction and Aβ impairment. FcγRIIB is the only inhibitory receptor bearing the specific motif of tyrosine-based inhibition motif(ITIM) within its cytoplasmic region and can recruit SHP-1 or- 2 upon contradicting other activating FcγRs functions of endocytosis and cytokine release. FcγRIIB may induce apoptosis of B cells independent of ITIM motif. It’s reported FcγRIIB is significantly upregulated in the hippocampus of AD brains and neuronal cels exposed to synthetic Aβ, thus mediating Aβ neurotoxicity and neurodegeneration; over expression of FcγRIIB in the macrophage is sufficient to decrease glial phagocytosis and chemotaxis. As FcγRIIB is rich expressed in the microglia, largely is unknown about the link between the microglia dysfuction and FcγRIIB. Here, we construct h- FcγRIIB to infect microglia under the low dosage of Aβ to simulate the same mechanism but different phenotype of microglia.Objective: To determine whether FcγRIIB mediating neuronal toxicity reflected in the same way of microglia.Methods: Using different species of Aβ in a time and dosage scale to decide the optimal condition by western blotting and CCK8; confirming the result by immunostaining of FcγRIIB in BV-2 and primary microglia; over expression of FcγRIIB, cell extracts were subjected to western blotting by applying apotosis markers of caspase 3, caspase 12, PARP and Aβ downstream effector molecules of JNK or ERK; over expression of FcγRIIB, DNA strand break was measured by Tunel and microglia activation was measured by the intensity of colocalization of CD68 and GFP(h-FcγRIIB).Result: FcγRIIB was upregulated by oligomeric Aβ at the time peak of 12 h after incubation; FcγRIIB expression was increased in the BV-2 and primary microglia by FcγRIIB immunofluorence; apoptosis markers associated with p-JNK/JNK selectively augmented by over expression of FcγRIIB under low dosage of Aβ; over expression of FcγRIIB activated microglia.Conclusion: FcγRIIB mediated Aβ incuced microglia activation and the caspase 12/caspase 3 associated apoptosis, the mechanisms involved JNK upregulation and ER stress.