Effect of glial cell line-derived neurotrophic factor on the expression of microglial integrin alpha5 and beta1

• Main Authors: Yu-Ping Chang, 張毓萍
• Other Authors: Shun-Fen Tzeng
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/66498820949503566122

碩士 === 國立成功大學 === 生物學系碩博士班 === 91 === Glial cell line-derived neurotrophic factor (GDNF) is characterized as a survival factor for dopaminergic neurons and spinal motor neurons. It utilizes a special receptor complex consisting of the tyrosine kinase receptor c-Ret and one of the GDNF family receptor (GFR) ? glycosylphosphatidylinositol (GPI)-linked receptors. The GDNF receptor complex is generally expressed in neurons and glia. However, the effect of GDNF on glia is still unclear. Microglia, one of glial cell types, serve as macrophages of the central nervous system (CNS) and are believed to play the critical role in neuropathogenesis. After CNS injury, they are activated and migrate toward the injuried site. Previously, we found that GDNF increased the growth of rat primary microglia and microglial NO production, indicating the regulatory effect of GDNF on microglial activation. In this study, we attempted to understand the role of GDNF on the expression of microglial integrins, which basically comprise of α and β subunits and regulate a variety of cell behavior including proliferation, migration and adhesion. It was found that GDNF upregulated integrin α5 and β1 subunits in a dose-dependent manner on rat primary microglia and BV2 cells, a mouse microglial cell line. The upregulation of integrin α5 and β1 was observed on BV2 cells treated with 10 ng/ml GDNF in a time-dependent manner. Moreover, RT-PCR analyse revealed that integrin α5 mRNA expression in BV2 cells was increased 2 hr following GDNF treatment. In contrast, integrin β1 mRNA was only slightly increased from 0.5 hr to 2 hr after GDNF treatment. According to western blotting assays, we found that U0126 (a MEK inhibitor) and LY294002 (a PI3 kinase inhibitor) completely suppressed the upregulation of integrin α5 and β1 by GDNF, implying that GDNF enhanced integrin α5 and β1 expression through Erk1/2 or PI3 kinase activation. Furthermore, the morphological examination of GDNF-treated BV2 cells and primary microglia showed greater attachment when compared with control. Adhesion Index reconfirmed the result of GDNF enhancing the adhesion capacity of BV2 cells. Finally, the effects of GDNF on regulating microglial integrin α5 were examined in the injuried spinal cord by immunohistochemistry. The ED1, an intracellular marker for activated microglia, and integrin ?? positive cells were observed in GDNF-treated spinal cord, suggesting that GDNF might induce integrin α5 expression in activated microglia of the injured spinal cord. Based on these observations, we demonstrated that GDNF may upregulate the expression of microglial integrin α5 through transcriptional control and integrin β1 through modulating translational level. The upregulation of integrin α5 and β1 may be due to the stimulation of Erk1/2 and PI3 kinase by GDNF, thereby improving adhesive ability of BV2 cells. After SCI, activated microglia is beneficial for neuronal regeneration via scavenging cell debris and releasing neurotrophins. Therefore, our results suggest that GDNF-enhanced proliferation and adhesive ability of microglia in the SCI may improve spinal cord repair.