Cytokine production by a human microglial cell line:: Effects of β-amyloid and α-melanocyte-stimulating hormone

Senile plaques in the Alzheimer's disease (AD) are formed by aggregation of beta-amyloid (A beta) peptide. A beta peptide has been shown to activate microglia and stimulate their production of inflammatory factors, such as cytokines. In the AD brain, the continued presence of amyloid plaques may keep microglia persistently activated, leading to chronic inflammation in the CNS. It is well established that alpha-melanocyte-stimulating hormone (alpha-MSH) gives rise to anti-inflammatory and anti-pyretic effects. The biological activities of alpha-MSH are mediated by one or more of the melanocortin receptor (MCR) subtypes, Le., MCR1 - MCR5. The aim of the present study was to determine the effect of a-MSH alone and on A beta-activated microglial cells with regard to the secretion of inflammatory cytokines, such as interleukin-6 (IL-6), and to determine which receptor subtype mediates the effects of alpha-MSH. The human microglial cell line, CHME3, was incubated for 24 h with freshly dissolved A beta(1-40), interferon-gamma (IFN-gamma) and/or alpha-MSH. Freshly dissolved A beta(1-40) (5-60 mu M) resulted in a dose-dependent decrease in cell viability, along with a dose-dependent increase in IL-6 release. Neither IFN-gamma nor alpha-MSH affected the A beta-induced secretion of IL-6, but resulted in a dose-dependent increase in basal IL-6 release. Agouti, the endogenous antagonist of MCR1 and 4, further increased the alpha-MSH-induced secretion of IL-6. RT-PCR showed the expression of MCR1, MCR3, MCR4 and MCR5 mRNA. The combined data suggest that the effect of alpha-MSH in increasing IL-6 release from the human microglial cell line is mediated by MCR3 or MCR5.