Opposite modulation of astroglial proliferation by adenosine 5′-O-(2-thio)-diphosphate and 2-methylthioadenosine-5′-diphosphate: mechanisms involved

The contribution of P2Y12,13 receptors to astroglial proliferation was investigated by testing the effects of two agonists with high affinity for these receptors, adenosine 5′-O-(2-thio)-diphosphate (ADPβS) and 2-methylthioadenosine-5′-diphosphate (2-MeSADP), in the incorporation of [3H]-thymidine. The effect of ATP, an endogenous inducer of astroglial proliferation, was also investigated. ADPβS and ATP (0.01–1 mM) increased astroglial proliferation up to 282%, an effect inhibited by the P2Y1 receptor antagonist MRS 2179 (30 μM). The P2Y12 receptor antagonists MRS 2395 (10 μM) and AR-C 66096 (10 μM) also reduced ADPβS proliferative effect, whereas the effect of ATP was attenuated by the A2A and A2B receptor antagonists SCH 58261 (30 nM) and MRS 1706 (10 nM), respectively. Studies of the signalling pathway activated showed that ADPβS effect was attenuated by pertussis toxin and by inhibition of phopholipase C (PLC), protein kinase C (PKC) and extracellular signal-regulated kinase1/2 (ERK1/2). The effect of ATP was also attenuated by inhibition of protein kinase A (PKA). The agonist 2-MeSADP (0.001–10 μM) had no effect in astroglial proliferation, but at higher concentrations (0.1–1 mM) it inhibited up to 63%, by mechanisms independent of P2Y1,12,13 receptors activation. It was metabolised into 2-methylthioadenosine (2-MeSADO), the metabolite responsible for inhibition of astroglial proliferation. The effect of 2-MeSADO (0.1 mM) was attenuated by the A3 receptors antagonist MRS 1523 (10 μM) and by the inhibitor of nucleoside transporters uridine (0.3 mM). 2-MeSADO did not induce apoptosis but increased lactate dehydrogenase release, an indicator of necrotic cell death. Astroglial proliferation induced by ADPβS was mediated by P2Y1 and P2Y12 receptors, leading to activation of PLC-PKC-ERK1/2 signalling pathway. The ATP proliferative effect was also mediated by PKA, supporting the contribution of the A2 receptors. 2-MeSADP inhibition of astroglial proliferation depended on its conversion into 2-MeSADO, which activated A3 receptors, blocked [3H]-thymidine uptake by astrocytes and led to cell death.

▶ADPβS and 2-MeSADP mediate opposite effects in the proliferation of astrocytes. ▶ADPβS induces astroglial proliferation by activation of P2Y1 and P2Y12 receptors. ▶Proliferation of astrocytes is mediated through the PLC-PKC-ERK1/2 pathway. ▶2-MeSADP is metabolised into 2-MeSADO that inhibits astroglial proliferation. ▶2-MeSADO activates A3 receptors, blocks thymidine uptake and induces cell death.