P2X receptor overexpression induced by soluble oligomers of amyloid beta peptide potentiates synaptic failure and neuronal dyshomeostasis in cellular models of Alzheimer's disease

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Abstract

The most common cause of dementia is Alzheimer's disease. The etiology of the disease is unknown, although considerable evidence suggests a critical role for the soluble oligomers of amyloid beta peptide (Aβ). Because Aβ increases the expression of purinergic receptors (P2XRs) in vitro and in vivo, we studied the functional correlation between long-term exposure to Aβ and the ability of P2XRs to modulate network synaptic tone. We used electrophysiological recordings and Ca2+ microfluorimetry to assess the effects of chronic exposure (24 h) to Aβ oligomers (0.5 μM) together with known inhibitors of P2XRs, such as PPADS and apyrase on synaptic function. Changes in the expression of P2XR were quantified using RT-qPCR. We observed changes in the expression of P2X1R, P2X7R and an increase in P2X2R; and also in protein levels in PC12 cells (143%) and hippocampal neurons (120%) with Aβ. In parallel, the reduction on the frequency and amplitude of mEPSCs (72% and 35%, respectively) were prevented by P2XR inhibition using a low PPADS concentration. Additionally, the current amplitude and intracellular Ca2+ signals evoked by extracellular ATP were increased (70% and 75%, respectively), suggesting an over activation of purinergic neurotransmission in cells pre-treated with Aβ. Taken together, our findings suggest that Aβ disrupts the main components of synaptic transmission at both pre- and post-synaptic sites, and induces changes in the expression of key P2XRs, especially P2X2R; changing the neuromodulator function of the purinergic tone that could involve the P2X2R as a key factor for cytotoxic mechanisms. These results identify novel targets for the treatment of dementia and other diseases characterized by increased purinergic transmission.

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