Differential regulation of resolution in inflammation induced by amyloid-β42 and lipopolysaccharides in human microglia

Abstract

Resolution of inflammation terminates the inflammatory response in physiological conditions and promotes restoration and healing of the tissue; however, failure in resolution results in chronic inflammation that may lead to disease. Chronic inflammation mediated by microglia is a feature of Alzheimer's disease (AD) and can be a pathogenic factor in which both treatment targets and diagnostic markers may be found. In addition, there is evidence that the resolution pathway is altered in AD. It is therefore relevant to investigate whether amyloid-β (Aβ) peptide, the major component of senile plaque in AD brain, may have a negative influence on components of the resolution cascade. In this pursuit, we exposed microglia to Aβ42, and with bacterial lipopolysaccharides (LPS) for comparison with a general infectious stimulus. Differential effects were observed: LPS upregulated components of the resolution pathway including the LXA4 receptor/formyl peptide receptor 2 (ALX/FPR2) and phosphorylated 5-lipoxygenase (p-5-LOX), as well as cholinergic alpha 7 nicotinic receptor (α7nAChR) and peroxisome proliferator-activated receptor (PPAR)-δ whereas Aβ42 had an opposite or insignificant effect. Our results indicate that LPS-induced changes in the microglia were conducive for resolution of inflammation, whereas these responses were absent or suppressed in microglia treated with Aβ42. Further studies may prove if Aβ42-induced dysfunction of resolution in microglia contributes to the impaired resolution in the AD brain, and if stimulation of microglial resolution constitutes a treatment strategy for AD.

Keywords: ALX/FPR2; Alzheimer's disease; amyloid; lipopolysaccharide; microglia; specialized pro-resolving mediators; α7nAChR.