P2Y₂ Receptor Up-Regulation Induced by Guanosine or UTP in Rat Brain Cultured Astrocytes

Abstract

Among P2 metabotropic ATP receptors, P2Y2 subtype seems to be peculiar as its upregulation triggers important biological events in different cells types. In non-stimulated cells including astrocytes, P2Y2 receptors are usually expressed at levels lower than P2Y1 sites, however the promoter region of the P2Y2 receptors has not yet been studied and little is known about the mechanisms underlying the regulation of the expression of this ATP receptor. We showed that not only UTP and ATP are the most potent and naturally occurring agonist for P2Y2 sites, but also guanosine induced an up-regulation of astrocyte P2Y2 receptor mRNA evaluated by Northern blot analysis. We also focused our attention on this nucleoside since in our previous studies it was reported to be released by cultured astrocytes and to exert different neuroprotective effects. UTP and guanosine-evoked P2Y2 receptor up-regulation in rat brain cultured astrocytes was linked to an increased P2Y2-mediated intracellular calcium response, thus suggesting an increased P2Y2 activity. Actinomycin D, a RNA polymerase inhibitor, abrogated both UTP and guanosine-mediated P2Y2 up-regulation, thus indicating that de novo transcription was required. The effect of UTP and guanosine was also evaluated in astrocytes pretreated with different inhibitors of signal transduction pathways including ERK, PKC and PKA reported to be involved in the regulation of other cell surface receptor mRNAs. The results show that ERK1-2/MAPK pathway play a key role in the P2Y2 receptor up-regulation mediated by either UTP or guanosine. Moreover, our data suggest that PKA is also involved in guanosine-induced transcriptional activation of P2Y2 mRNA and that increased intracellular calcium levels and PKC activation may also mediate P2Y2 receptor up-regulation triggered by UTP. The extracellular release of ATP under physiological and pathological conditions has been widely studied. On the contrary, little is known about the release of pyrimidines and in particular of UTP. Here we show that astrocytes are able to release UTP, either at rest or during and following hypoxia/hypoglycemia obtained by submitting the cells to glucose-oxygen deprivation (OGD). Interestingly, also P2Y2 receptor mRNA increased by about two-fold the control values when the cultures were submitted to OGD. It has been recently reported that P2Y2 receptors can play a protective role in astrocytes, thus either guanosine administration or increased extracellular concentrations of guanosine and UTP reached locally following CNS injury may increase P2Y2-mediated biological events aimed at promoting a protective astrocyte response.

Purinoceptors on Neuroglia

“…Similar remodelling of P2Y receptor profile and Ca 2+ wave propagation was also observed after treatment of astroglial cultures with the cytokine IL-1β [200]. Interestingly, in the inflammatory conditions (for example, in astroglial cultures chronically treated with IL-1β), activation of P2Y 2 receptors decreases gap junction communications [201].…”

Expression and Secretion of CXCL8 (IL-8), Release of Tryptase and Transcription of Histidine Decarboxylase mRNA by Anti-IgE-Activated Human Umbilical Cord Blood-Derived Cultured Mast Cells

“…Inflammatory cells such as activated PMN identified in bronchoalveolar lavage in allergic patients are associated with increased levels of IL-8 and proinflammatory mediators [16,27,30,45,47,48] . The persistence of inflammatory cells at the site of inflammation, particularly mast cells, which respond poorly to corticosteroids, could be in part responsible for the epithelial damage and permeability.…”

Purinergic Signalling in the CNS

“…Another study has shown that cultured astrocytes are able to release UTP either at rest or following hypoxia and that P2Y 2 receptor mRNA increased by 2-fold during glucoseoxygen deprivation [93]. P2Y 2 and P2Y 4 receptors are strongly expressed in glial endfeet apposed to blood vessel walls [94,95].…”