P2Y receptors on astrocytes and microglia mediate opposite effects in astroglial proliferation

Abstract

Nucleotides released upon brain injury signal to astrocytes and microglia playing an important role in astrogliosis, but the participation of microglia in the purinergic modulation of astrogliosis is still unclear. Highly enriched astroglial cultures and co-cultures of astrocytes and microglia were used to investigate the influence of microglia in the modulation of astroglial proliferation mediated by nucleotides. In highly enriched astroglial cultures, adenosine-5'-triphosphate (ATP), adenosine 5'-O-(3-thio)-triphosphate (ATPγS), adenosine 5'-O-(3-thio)-diphosphate (ADPβS; 0.01-1 mM), and adenosine-5'-diphosphate (ADP; 0.1-1 mM) increased proliferation up to 382%, an effect abolished in co-cultures containing 8% of microglia. The loss of ATP proliferative effect in co-cultures is supported by its fast metabolism and reduced ADP accumulation, an agonist of P2Y 1,12 receptors that mediate astroglial proliferation. No differences in ADPβS and ATPγS metabolism or P2Y 1,12 receptors expression were found in co-cultures that could explain the loss of their proliferative effect. However, conditioned medium from microglia cultures or co-cultures treated with ADPβS, when tested in highly enriched astroglial cultures, also prevented ADPβS proliferative effect. None of the uracil nucleotides tested had any effect in proliferation of highly enriched astroglial cultures, but uridine-5′-triphosphate (UTP; 0.1-1 mM) inhibited proliferation up to 66% in co-cultures, an effect that was dependent on uridine-5'-diphosphate (UDP) accumulation, coincident with a co-localization of P2Y 6 receptors in microglia and due to cell apoptosis. The results indicate that microglia control astroglial proliferation by preventing the proliferative response to adenine nucleotides and favouring an inhibitory effect of UTP/UDP. Several microglial P2Y receptors may be involved by inducing the release of messengers that restrain astrogliosis, a beneficial effect for neuronal repair mechanisms following brain injury.

Microglia P2Y6 receptors mediate nitric oxide release and astrocyte apoptosis

“…In contrast, in highly enriched astroglial cultures, either treated or not with LPS, uracil nucleotides had no effect in cell proliferation [22], suggesting a fundamental role of microglial cells to the P2Y 6 receptor-mediated inhibitory effect. In LPS cultures, UTP also inhibited cell proliferation and this effect was extensive to UDP and to the selective agonist of the P2Y 6 receptors PSB 0474 [29], but not to the selective agonist of P2Y 14 receptors UDP-glucose [30].…”

“…Nevertheless, it seems that in co-cultures of astrocytes and microglia, LPS potentiates astrocyte apoptosis mediated by uracil nucleotides, since it increases from 6% in co-cultures without LPS treatment [22] to 15% in LPS cultures. LPS facilitates P2Y 6 receptor-mediated NO release by microglia, but other cytokines such as IL-1β or TNF-α [44] may come into play contributing to astroglial cell death.…”

Purinergic neurone-glia signalling in cognitive-related pathologies

“…P2Y 12 receptors regulate the migration of microglia to the site of ATP release and P2Y 6 receptor activation by UDP results in a drastic increase in the motility of microglia, leading to engulfment and phagocytosis of targeted molecules . These microglial effects are deeply involved in the regulation of astrogliosis, in that microglia prevent the proliferative effects of adenine nucleotides and favour an inhibitory effect of uracil nucleotides (Quintas et al, 2011). Hence UTP appears to support astrogliosis by direct stimulation of astrocytic P2Y2 receptors, but at the same time UDP attenuates it by activating microglial P2Y6 receptors.…”

Purinergic modulation of norepinephrine release and uptake in rat brain cortex: contribution of glial cells

“…Confluent 2-wk-old cultures were used in the experiments to evaluate the uptake of [ 3 H]NE. These cultures were characterized by immunocytochemistry and contained ϳ90% astrocytes (Quintas et al 2011). …”