Investigating P2X7R-mediated inflammatory signalling in Alzheimer's disease.

Abstract

Neuroinflammation is thought to contribute to the onset and/or progression of Alzheimer´s disease (AD). Astrocytes and microglia sense danger-associated molecules (e.g. Aβ species, ATP) through membrane receptors including the purinergic receptor P2X7 (P2X7R). These interactions activate pro-inflammatory pathways and lead to the release of cytokines that participate in damaging inter-cellular cascades. Inhibition of P2X7R in AD models ameliorates cognitive deficits, pointing towards a neuroprotective effect of P2X7R blockade in vivo potentially associated with the modulation of inflammatory responses. However, the action of P2X7R and downstream signals on tau-mediated neurodegeneration in AD remains elusive. We used biochemical and immunohistochemical methods in combination with in-situ hybridization technology (RNAscope) in post-mortem AD and control (Braak 0-VI) BA9 prefrontal cortex to examine early changes in P2X7R expression, determine the spatial pattern of P2X7R activation relative to Aβ and pathological tau accumulation, and evaluate the association between P2X7R and local inflammatory responses. Primary glial and organotypic slice cultures are being used to model glial responses to physiological Aβ species and assess downstream effects on neurons, including alterations in tau and synapse health. We found elevated levels of P2X7R from Braak stage II relative to controls accompanied by an increased amyloid burden, synaptic mislocalization of tau and an altered astrocyte reactivity. P2X7R was markedly expressed in astrocytes surrounding AD hallmarks and also in disease-associated microglia neighbouring Aβ plaques. Investigation of inflammatory mediators linked with P2X7R-positive glia revealed higher activation of the NLRP3 inflammasome and NFkB pathways with disease progression. Preliminary data from in vitro and ex vivo models show inflammatory changes and tau redistribution to the synapses following stimulation with oligomeric Aß. These data suggest that P2X7R expression and activation are altered in the early stages of AD, prior to marked synapse loss. Ongoing studies aim to determine if the blockade of P2X7R-mediated inflammatory signals has benefits for tau-associated neurodegeneration in AD models.