Neuroinflammation in Alzheimer’s disease and obesity

Sammanfattning: Alzheimer’s disease (AD) and obesity are both major problems in the western world. Although they may appear to have little in common at first glance, they are both characterized by chronic inflammation. Exactly how inflammation affects these disorders is far from clear. Microglia, the resident immune cells of the brain, can take on different phenotypes in response to inflammatory stimuli. They can become classically or alternatively activated, where they secrete pro- or anti-inflammatory cytokines respectively. The inflammatory response is to a large part regulated by transcription factors, such as C/EBPδ, which regulate gene expression. The aim of this thesis was to investigate 1) effects of the Alzheimer’s related peptide amyloid-β (Aβ) on C/EBPδ in astrocytes and microglia during inflammatory conditions, 2) how microglia is affected by elevated levels of free fatty acids (FFAs) occurring in obesity and 3) possible cellular sources of the neuroprotective peptide GLP-1 in the brain. In paper I we found that IL-1β-induced C/EBPδ appears to be blocked by Aβ fibrils but not Aβ oligomers in mixed glial cells. In paper II we found that the decreased levels of C/EBPδ were limited to astrocytes under inflammatory conditions and that there was no blocking of IL-1β-induced C/EBPδ in microglia. In paper III we found that the FFA palmitate induces an alternative activation in microglia with no effect on the expression of C/EBPδ or the pro-inflammatory cytokines TNF-α, IL-1β and IL-6. However, pre-exposure to palmitate potentiated microglia phagocytosis and changed the mRNA expression profile of some pro-inflammatory cytokines in response to inflammatory stimuli. In paper IV we found microglia to be a novel source of secreted GLP-1. Further, we found that the GLP-1 secretion could be decreased by inflammatory stimuli. In summary, the inflammatory response of C/EBPδ in AD appears to be disturbed. In addition, palmitate affects the response to inflammatory stimuli in microglia.