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

Abstract

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.

Adenylate cyclase 5 coordinates the action of ADP, P2Y1, P2Y13 and ATP-gated P2X7 receptors on axonal elongation

“…Taken together with our previous findings, our results indicate that activation of P2Y1 potentiates the PI3K-Akt-GSK3 pathway to promote axon elongation, whereas ATP exerts an opposing effect, downregulating the signaling through this pathway and inhibiting axon growth. ADP activation of P2Y1 increases Akt and GSK3 phosphorylation while promoting axon elongation, an effect previously demonstrated following P2X7 inhibition (Diaz-Hernandez et al, 2008). This enhanced elongation can be impaired by inhibiting PI3K, whereas the attenuation of axon growth by P2Y1 inhibition can be counteracted by inhibiting GSK3, and such inhibition has been previously shown to induce axonal elongation (Garrido et al, 2007).…”

“…However, their role in the development of neuronal morphology and axon growth remains largely unknown. We previously demonstrated that ATP, acting at the purinergic P2X7 receptor, negatively modulates axon growth, generating an increase in calcium at the distal axon (Diaz-Hernandez et al, 2008), whereas inhibition or suppression of this receptor promotes axon elongation. The present study demonstrates that ADP enhances axon growth in cultured hippocampal neurons through the activation of the metabotropic P2Y1 receptor.…”

“…In the light of previous results demonstrating how ATP modulates axon elongation through the ionotropic P2X7 receptor (Diaz-Hernandez et al, 2008), we analyzed whether ADP, acting through the metabotropic P2Y1 and P2Y13 receptors, can regulate axonal elongation. Both these receptors are expressed in the hippocampus and hippocampal neurons (supplementary material Fig.…”

“…Enhanced axon growth following P2X7 inhibition appears to be mediated through the phosphoinositide 3-kinase (PI3K)-Akt-GSK3 pathway (Diaz-Hernandez et al, 2008) and, moreover, P2Y13 activity can regulate GSK3 phosphorylation (Ortega et al, 2008). Thus, we examined whether the effects of ADP in axon elongation were mediated by the PI3K pathway.…”

ATP induces the death of developing avian retinal neurons in culture via activation of P2X7 and glutamate receptors

“…Both P2X3 and P2X7 receptors were shown to inhibit axonal growth and branching of developing motor axons [19], cultured hippocampal neurons [21], and neuroblastoma cells [22]. Moreover, activation of P2X7 receptors was shown to promote the survival of cerebellar granule cells [23,24], but the death of cultured striatum-derived neural progenitors [25], a conflicting observation that now can be explained by the recent detection and characterization of P2X7 receptor splice variants with distinct functional properties [26,27].…”