Regulation And Mechanism Of Bone Mesenchymal Stem Cells To Aβ-Activated Microglia

Objective: microglia(MI) are the primary immune cells of the brain, they display aprogression of functional changes in response to the changes in their microenvironment.CD200-CD200R interaction has been showned to be critical for maintaining microglia in aquiescent state. In the aging brain, expression of transmembrane glycoprotein CD200byneuronal cell surface is decreased, leading to the CD200-CD200R signaling dysfunctional.Aβ-induced inflammatory process is characterized by an significant increase incytokines,chemokines, activated microglia sustain a local inflammatory response andincrease neuronal death during chronic Aβ accumulation. Bone Mesenchymal StemCells(BMSCs) are bone marrow derived stem cells with the capacity of self-renewal anddifferentiate into several tissues in vitro. Bone Mesenchymal Stem Cell transplantation inAlzheimer’s disease improve cognitive function. The mechanisms that BMSCs regulatemicroglia involve soluble factors and cell-cell contact. BMSCs also express CD200thatinteract with their corresponding ligand, CD200R, on microglia. So, we considerCD200-CD200R interaction may be a mechanism that BMSCs treating Alzheimer’sdisease.We primary cultured, isolated, purified the microglia and BMSCs, observed expressionof CD200, CD200R on cell surface. And we observe the fact that if the addition ofanti-CD200antibodies can reverse the suppression effect of BMSCs for microgliaactivation and cytokines secretion, in order to investigate the possible new mechanism ofBMSCs for the regulation of Aβ-induced microglia activation in vitro.Methods: BMSCs were isolated and purified from the bone marrow of human byadhering to the culture plastic, microglia were isolated from the brain. We observed the biological characteristics and morphology of BMSCs and microglia by phase contrastmicroscopy. Immunofluorescence was employed to investigate the CD200expression onhuman bone mesenchymal stem cells and CD200R expression on microglia. Aβ was addedpreviously to activate microglia, BMSCs were co-cultured with MI in the presence or inthe absence of Aβ for48hours. The groups wereMI,BMSCs,MI+Aβ,MI+BMSCs,MI+Aβ+BMSCs,MI+Aβ+BMSCs+anti-CD200antibody.Then CD200R was confirmed expressed by Immunofluorescence and cytokines such asTNF-α,IL-6,NO was measured by means of ELISA. All results were expressed asmean±SD. The statistical comparison were performed using one-way ANOVA bySPSS16.0software. A p value less than0.05was considered significantly different.Results: Cultured MI expressed CD200R, BMSCs expressed CD200. The morphologyof activated microglia was amoeboid appearance, secreting large amount of TNF-α, IL-6,NO when compared to the resting state (P <0.05), confirming the role of Aβ activation ofmicroglia in vitro, TNF-α, IL-6, NO in the supernatant from BMSCs co-cultured withactivated MI group was significantly decreased(p <0.05), after the addition of anti-CD200antibody group microglial morphology and inflammatory factor levels has been changed.The production of TNF-α,IL-6,NO was lower than the Aβ activated MI group but higherthan BMSCs co-cultured activated MI group, the difference was statistically significant (p<0.05).Conclusion: Aβ-induced microglia activation can be partially suppressed byCD200-CD200R interaction with BMSCs in vitro.