In vivo P2X7 inhibition reduces amyloid plaques in Alzheimer's disease through GSK3ß and secretases.

ß-Amyloid (Aß) peptide production from amyloid precursor protein (APP) is essential in the formation of the ß-amyloid plaques characteristic of Alzheimer's disease. However, the extracellular signals that maintain the balance between nonpathogenic and pathologic forms of APP processing, mediated by α-secretase and ß-secretase respectively, remain poorly understood. In the present work, we describe regulation of the processing of APP via the adenosine triphosphate (ATP) receptor P2X7R. In 2 different cellular lines, the inhibition of either native or overexpressed P2X7R increased α-secretase activity through inhibition of glycogen synthase kinase 3 (GSK-3). In vivo inhibition of the P2X7R in J20 mice, transgenic for mutant human APP, induced a significant decrease in the number of hippocampal amyloid plaques. This reduction correlated with a decrease in glycogen synthase kinase 3 activity in J20 mice, increasing the proteolytic processing of APP through an increase in α-secretase activity. The in vivo findings presented here demonstrate for the first time the therapeutic potential of P2X7R antagonism in the treatment of familiar Alzheimer's disease (FAD).

Inhibition of the ATP-gated P2X7 receptor promotes axonal growth and branching in cultured hippocampal neurons.

During the establishment of neural circuits, the axons of neurons grow towards their target regions in response to both positive and negative stimuli. Because recent reports show that Ca2+ transients in growth cones negatively regulate axonal growth, we studied how ionotropic ATP receptors (P2X) might participate in this process. Our results show that exposing cultured hippocampal neurons to ATP induces Ca2+ transients in the distal domain of the axon and the concomitant inhibition of axonal growth. This effect is mediated by the P2X7 receptor, which is present in the growth cone of the axon. Pharmacological inhibition of P2X7 or its silencing by shRNA interference induces longer and more-branched axons, coupled with morphological changes to the growth cone. Our data suggest that these morphological changes are induced by a signalling cascade in which CaMKII and FAK activity activates PI3-kinase and modifies the activity of its downstream targets. Thus, in the absence or inactivation of P2X7 receptor, axons grow more rapidly and form more branches in cultured hippocampal neurons, indicative that ATP exerts a negative influence on axonal growth. These data suggest that P2X7 antagonists have therapeutic potential to promote axonal regeneration.