GM-CSF increases LPS-induced production of proinflammatory mediators via upregulation of TLR4 and CD14 in murine microglia

Background: microglia are resident macrophage-like cells in the central nervous system (cns) and cause innate immune responses via the lps receptors,toll-like receptor (tlr) 4 and cd14,in a variety of neuroinflammatory disorders including bacterial infection,alzheimer's disease,and amyotrophic lateral sclerosis. granulocyte macrophage-colony stimulating factor (gm-csf) activates microglia and induces inflammatory responses via binding to gm-csf receptor complex composed of two different subunit gm-csf receptor α (gm-csfrα) and common β chain (βc). gm-csf has been shown to be associated with neuroinflammatory responses in multiple sclerosis and alzheimer's disease. however,the mechanisms how gm-csf promotes neuroinflammation still remain unclear.methods: microglia were stimulated with 20 ng/ml gm-csf and the levels of tlr4 and cd14 expression were evaluated by rt-pcr and flowcytometry. lps binding was analyzed by flowcytometry. gm-csf receptor complex was analyzed by immunocytechemistry. the levels of il-1β,il-6 and tnf-α in culture supernatant of gm-csf-stimulated microglia and nf-κb nuclear translocation were determined by elisa. production of nitric oxide (no) was measured by the griess method. the levels of p-erk1/2,erk1/2,p-p38 and p38 were assessed by western blotting. statistically significant differences between experimental groups were determined by one-way anova followed by tukey test for multiple comparisons.results: gm-csf receptor complex was expressed in microglia. gm-csf enhanced tlr4 and cd14 expressions in microglia and subsequent lps-binding to the cell surface. in addition,gm-csf priming increased lps-induced nf-κb nuclear translocation and production of il-1β,il-6,tnf-α and no by microglia. gm-csf upregulated the levels of p-erk1/2 and p-p38,suggesting that induction of tlr4 and cd14 expression by gm-csf was mediated through erk1/2 and p38,respectively.conclusions: these results suggest that gm-csf upregulates tlr4 and cd14 expression in microglia through erk1/2 and p38,respectively,and thus promotes the lps receptor-mediated inflammation in the cns. © 2012 parajuli et al.; licensee biomed central ltd.