Purinergic signaling in the cerebellum: Bergmann glial cells express functional ionotropic P2X₇ receptors

Abstract

Astrocytes constitute active networks of intercommunicating cells that support the metabolism and the development of neurons and affect synaptic functions via multiple pathways. ATP is one of the major neurotransmitters mediating signaling between neurons and astrocytes. Potentially acting through both purinergic metabotropic P2Y receptors (P2YRs) and ionotropic P2X receptors (P2XRs), up until now ATP has only been shown to activate P2YRs in Bergmann cells, the radial glia of the cerebellar cortex that envelopes Purkinje cell afferent synapses. In this study, using multiple experimental approaches in acute cerebellar slices we demonstrate the existence of functional P2XRs on Bergmann cells. In particular, we show here that Bergmann cells express uniquely P2X7R subtypes: (i) immunohistochemical analysis revealed the presence of P2X7Rs on Bergmann cell processes, (ii) in whole cell recordings P2XR pharmacological agonists induced depolarizing currents that were blocked by specific antagonists of P2X7Rs, and could not be elicited in slices from P2X₇R-deficient mice and finally, (iii) calcium imaging experiments revealed two distinct calcium signals triggered by application of exogenous ATP: a transient signal deriving from release of calcium from intracellular stores, and a persistent one following activation of P2X7Rs. Our data thus reveal a new pathway by which extracellular ATP may affect glial cell function, thus broadening our knowledge on purinergic signaling in the cerebellum.

The contribution of astrocytes to the regulation of cerebral blood flow

“…Evidence from the retina suggests that neuron-glia signaling may be mediated by neuronally released ATP acting on glial P2Y receptors rather than via activation of mGluRs by glutamate (Newman, 2005; Metea and Newman, 2006). Indeed, it has been shown that astrocyte [Ca 2+ ] i signals can be evoked by ATP in the cerebral cortex (Sun et al, 2013) and in cerebellar slices (Piet and Jahr, 2007; Habbas et al, 2011). Alternative hypotheses of astrocyte control of vessel diameter also include the efflux of K + through Ca 2+ -activated K + channels in astrocyte endfeet (Filosa et al, 2006), although the functional, in vivo , significance of this pathway remains to be demonstrated.…”

“…Activation of P2Y receptors (which are highly expressed in astrocyte endfeet: Simard et al, 2003), activates phospholipase C (PLC) and the downstream calcium-dependent signaling pathways discussed above (Figure 2). ATP can also act on glial P2X 7 receptors, resulting in an increase in astrocyte [Ca 2+ ] i (Carrasquero et al, 2009; Habbas et al, 2011) and triggering the formation and release of vasoactive substances (Figure 2). In addition to neuronally released ATP, calcium-dependent ATP exocytosis by glial cells may occur (Pangrsic et al, 2007; Blum et al, 2008).…”

Glial cells in (patho)physiology

“…2010). Cortical astrocytes and cerebellar Bergmann glial cells also express P2X 7 purinoceptors (Habbas et al. 2011; Oliveira et al.…”

Neuroprotective potential of astroglia

“…For example, it has been shown that in mature mice, mGluR5, which is usually expected to mediate astrocytic Ca 2+ responses to glutamate, is downregulated, suggesting that this coupling mechanism might be more relevant for the very young brain (Sun et al, ). Other evidence suggests that neuron–glia signaling may be mediated by neuronally released ATP acting on glial P2Y receptors rather than via activation of mGluRs by glutamate (Calcinaghi et al, ; Habbas et al, ; Nizar et al, ; Sun et al, ). Group I mGluRs and the ATP receptor P2Y1 are both G protein–coupled receptors associated with Gαq signaling that induces Ca 2+ release from internal stores by generating IP3.…”