Investigating P2×7R‐mediated inflammatory signalling in Alzheimer’s disease

Abstract

AbstractBackgroundAlzheimer’s disease (AD) is pathologically characterised by the presence of amyloid plaques and neurofibrillary tangles accompanied by a marked neuroinflammation which contributes to the onset and progression of AD. Astrocytes and microglia recognize danger‐associated molecular patterns (Aß, ATP) through a myriad of sensors including the purinergic receptor P2×7 (P2×7R). These interactions lead to the release of inflammatory mediators that could participate in damaging inter‐cellular cascades. Inhibition of P2×7R in AD models ameliorates cognitive deficits and supports a neuroprotective effect of P2×7R blockade in vivo. However, the cell type‐specific inflammatory signals downstream of P2×7R in AD are not fully understood.MethodWe used biochemical and histological methods, including in situ RNA detection (RNAscope), to examine P2×7R expression and localization relative to disease hallmarks and local inflammatory features in temporal and prefrontal cortex at different Braak stages. A series of P2×7R antagonists were used to study P2×7R‐mediated responses to inflammatory stimuli in primary glial cells and to assess the effects of P2×7R blockage on tau and synapse health in brain slice cultures.ResultWe found elevated levels of P2×7R in AD relative to control brain together with an increased amyloid burden, synapse mislocalization of tau and loss of synaptic markers. P2×7R was detected in human astrocytes as well as other neural cell types and its increased abundance was accompanied by an upregulation of inflammatory cytokines including CCL2 and IL‐1ß. In cultured astrocytes, P2×7R activation contributes to the production of the inflammatory cytokines CCL2, IL‐6 and the synaptotoxic molecule lipocalin‐2, whereas microglial P2×7R activation induces IL‐1ß secretion through the NLRP3 inflammasome pathway. Treatment of organotypic brain slice cultures with specific P2×7R antagonists suggests that P2×7R inhibition modulates glial function in response to neurodegenerative disease relevant stimulation.ConclusionThese data show that P2×7R expression is elevated in AD prior to marked synapse loss and point towards distinct P2×7R‐mediated responses in astrocytes and microglia. Ongoing work aims to determine if pharmacological blockade of P2×7R‐inflammatory signals has benefits for tau‐associated neurodegeneration in AD.