Purinergic stimulation of astroblast proliferation: Guanosine and its nucleotides stimulate cell division in chick astroblasts

Abstract

A highly active fraction that was mitogenic for astroblasts but which contained no amino acids was identified during the purification of peptides from chick embryo brains. This material was purified by ultracentrifugation, ultrafiltration through Diaflo PM-30 and YM-2 membranes and retention on Diaflo YC-05, followed by ion exchange chromatography and reversed phase high performance liquid chromatography (HPLC) on a C18 Deltapak column. On thin layer chromatography and HPLC the material co-chromatographed with authentic commercially-obtained GMP. Its ultraviolet absorption spectrum was also identical with that of GMP. 1H and 31P nuclear magnetic resonance spectra of the isolated material were identical with those of GMP. The close match between the fast atom bombardment (FAB) mass spectra of the unknown material and authentic GMP indicated that the unknown material was GMP of molecular weight 363 Da. Authentic, commercial GMP stimulated the growth of cultured chick astroblasts in the same dose-dependent manner as the material from chick embryo brains; maximal stimulation was at 50 microM. Guanosine, GDP, and GTP also stimulated cell proliferation. The nucleotides were equally as effective as guanosine. 5'-Guanylyl imidodiphosphate, guanosine 5'-O-(2-thiodiphosphate), and guanosine 5'-N-(3-thiotriphosphate), guanine nucleotides which are relatively resistant to enzymatic hydrolysis, were also mitogenic, indicating that the nucleotides do not need to be degraded to nucleosides to be active and that they probably act extracellularly. Guanine nucleosides and nucleotides promoted astroblast growth when other growth factors were removed from the culture medium. The mitogenic effects of guanosine and its nucleotides were inhibited in a dose-dependent fashion by micromolar concentrations of theophylline, a characteristic of phenomena mediated by purinergic receptors. Guanosine and its nucleotides are released in micromolar concentrations by hypoxic or dying cells. Under these circumstances these compounds may stimulate division of adjacent cells in vivo.

Guanosine Inhibits CD40 Receptor Expression and Function Induced by Cytokines and β Amyloid in Mouse Microglia Cells

“…Guanosine exhibits antiinflammatory and immunosuppressive properties (35,36) and exerts a number of neurotrophic and neuroprotective effects, including astrocyte proliferation (37,38), promotion of neurite outgrowth (39), increased synthesis, and release of neuro/pleiotrophins such as nerve growth factor, TGF-␤ and basic fibroblast growth factor, from several cell types (40,41), and enhanced glutamate uptake by astrocytes (42). Recently, we demonstrated that guanosine protects astrocytes against apoptotic death caused by staurosporine (43) and SH-SY5Y human neuroblastoma cells against apoptosis induced by A␤ peptides (44).…”

Guanosine and its role in neuropathologies

“…Of note, the neurotrophic effects of the nucleotide GTP (including its proliferative and neuritogenic activities, which are mediated by the release of trophic factors) are similar to those of guanosine [37,[43][44][45]. However, these effects are not dependent on the conversion of GTP into guanosine by ectonucleotidases and seem to involve the activation of distinct (and in some cases even complementary) pathways by these two GBPs [41,46].…”

“…It was demonstrated that, although guanosine is not considered an effective ligand for P1 receptors [41,81], antagonists of these receptors are able to, at least partially, inhibit the proliferative [41,45] and antiinflammatory [82,83] activities elicited by this nucleoside. This evidence suggests that extracellular guanosine may contribute to cell signaling, through an indirect mechanism involving the adenosinergic system [84,85].…”

Electrophysiological effects of guanosine and MK-801 in a quinolinic acid-induced seizure model

“…Guanosine occurs naturally in the brain and has been reported to present a myriad of biological effects when administered extracellularly, including trophic effects on neural cells (Ciccarelli et al, 2001;Rathbone et al, 1999), stimulation of astrocyte proliferation (Ciccarelli et al, 2000;Kim et al, 1991), and modulation of glutamatergic activity (reviewed in Schmidt et al, 2007). Although these effects might be related to its uptake into the intracellular compartment, a consensus has emerged that some of guanosine actions involve its binding to a specific membrane protein (Traversa et al, 2002(Traversa et al, , 2003, postulated by some to be a G protein-coupled receptor (Ciccarelli et al, 2001;Traversa et al, 2002Traversa et al, , 2003.…”