Modulation Of Fractalkine On The Expression Of Amyloid Precursor Protein And FPR2, TNF-α And IL-1β In Activated Microglia

Objective The present study was to investigate the expression of the genes encoding APP, FPR2, TNF-a and IL-1β in a murine microglia cell line N9 stimulated with bacterial endotoxin and beta-amyloid protein, respectively, and to study the effect of fractalkine, a new kind of chemokine, on the modulation of the cytokine/receptor expression in these experimental steps. This investigation is helpful to the exploration of the role of fractalkine in the mechanisms of neuro-degeneration in Alzheimer's disease.Methods Goups of log-phase N9 cells were cultured for 24h in the presence of LPS, beta-amyloid protein, fractalkine, LPS plus fractalkine, beta-amyloid protein plus fractalkine, respectively. Culture cells were harvested at different time points of incubation for the detection of cytokine/receptor mRNA expression by means of RT-PCR and culture supernatants were assayed for TNF-a production by ELISA.Results Incubation of N9 cells with LPS resulted in a successive increase of FPR2 expression but a low level expression of APP mRNA throughout 24h with a significant decline at 4h. The expression of inflammatory cytokines, IL-1β and TNF-a, had a peak time and significantly decreased at 24h. When Aβ was added to cultures instead, the expression of APP, IL-1β and TNF-a were also detected. When recombinant fractalkine was pre-incubated with N9 cells, the expression of APP and IL-lp mRNA and TNF-a (either detected by RT-PCR or ELISA) induced by Ap was significantly decreased while FPR2 mRNA expression was enhanced.Conclusion These findings suggest that beta-amyloid protein, similar to LPS, can stimulate the expression of TNF-a, IL-1β and Aβ precursor mRNA, which has been thought to be associated with the onset of Alzheimer's disease. Interestingly, it is indicated that exogenous FKN might be able to play an inhibitory role on the Ap and inflammatory cytokine production in CNS.