Chronic Amyloid beta Oligomer Infusion Evokes Sustained Inflammation and Microglial Changes in the Rat Hippocampus via NLRP3

Fekete, Csaba and Vastagh, Csaba and Dénes, Ádám and Hrabovszky, Erik and Nyíri, Gábor and Kalló, Imre and Liposits, Zsolt and Sárvári, Miklós (2019) Chronic Amyloid beta Oligomer Infusion Evokes Sustained Inflammation and Microglial Changes in the Rat Hippocampus via NLRP3. NEUROSCIENCE, 405. pp. 35-46. ISSN 0306-4522

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Abstract

Microglia are instrumental for recognition and elimination of amyloid beta1-42 oligomers (AbetaOs), but the long-term consequences of AbetaO-induced inflammatory changes in the brain are unclear. Here, we explored microglial responses and transciptome-level inflammatory signatures in the rat hippocampus after chronic AbetaO challenge. Middle-aged Long Evans rats received intracerebroventricular infusion of AbetaO or vehicle for 4weeks, followed by treatment with artificial CSF or MCC950 for the subsequent 4weeks. AbetaO infusion evoked a sustained inflammatory response including activation of NF-kappaB, triggered microglia activation and increased the expression of pattern recognition and phagocytic receptors. Abeta1-42 plaques were not detectable likely due to microglial elimination of infused oligomers. In addition, we found upregulation of neuronal inhibitory ligands and their cognate microglial receptors, while downregulation of Esr1 and Scn1a, encoding estrogen receptor alpha and voltage-gated sodium-channel Na(v)1.1, respectively, was observed. These changes were associated with impaired hippocampus-dependent spatial memory and resembled early neurological changes seen in Alzheimer's disease. To investigate the role of inflammatory actions in memory deterioration, we performed MCC950 infusion, which specifically blocks the NLRP3 inflammasome. MCC950 attenuated AbetaO-evoked microglia reactivity, restored expression of neuronal inhibitory ligands, reversed downregulation of ERalpha, and abolished memory impairments. Furthermore, MCC950 abrogated AbetaO-invoked reduction of serum IL-10. These findings provide evidence that in response to AbetaO infusion microglia change their phenotype, but the resulting inflammatory changes are sustained for at least one month after the end of AbetaO challenge. Lasting NLRP3-driven inflammatory alterations and altered hippocampal gene expression contribute to spatial memory decline.

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