| Summary: | 碩士 === 國立陽明大學 === 神經科學研究所 === 101 === ABSTRACT
ATP is an extracellular signaling molecule that regulates multiple physiological functions during CNS development. Recent studies implicated that purinergic signaling is involved in neural development, including proliferation. Previous studies also demonstrated the P2X7 purinergic receptor emerged at the stage of neurogenesis. However, the exact role of P2X7 receptors during neural development has not been thoroughly examined. The aim of this study is to investigate the effect of P2X7 receptors on proliferation of neural progenitor cells (NPCs) and elucidate the underlying molecular mechanisms involved. In this study, we found that NPCs expressed functional P2X7 purinergic receptors. Treatment of NPCs with P2X7 receptors selective agonist BzATP decreased cell number, cell viability, and the number of bromouridine (BrdU)-incorporated cells, but did not affect cell survival in trypan blue exclusion test. The effect was inhibited by the action of a P2X7 receptor selective antagonist A 438079 and by using P2X7 shRNA to knockdown the receptor expression. Using flow cytometry, BzATP treatment arrested cell cycle at the S phase. Thus, activation P2X7 receptor decreased proliferation and altered cell cycle progression of NPCs. To further examine the molecular mechanism involved, we also found that BzATP stimulated ERK1/2 activation in a time-dependent manner. By using EGTA to chelate extracellular Ca2+, or by using GF 109203X to inhibit PKC or PD98059 to inhibit MEK, significantly attenuated the BzATP-induced ERK1/2 activation. In contrast the ERK1/2 activation was not affected by using CaMKII inhibitor KN 93, or by using PI3K inhibitor LY294002. In addition, BzATP induced cytosol-to-membrane translocation of PKC α, γ, ε isozymes. Moreover, either PD98059 or GF 109203X blocked the BzATP-decreased proliferation of these cells. The physiological ligand of P2X7 receptors, ATP also inhibited proliferation of NPCs and that was suppressed by P2X7 receptors antagonist but not by P2X1-6 receptor antagonist, TNP-ATP. ATP also induced transient ERK1/2 activation. Together, these results indicated that activation of P2X7 receptors inhibits proliferation by arresting cell cycle progression and that is via Ca2+-PKC-ERK1/2 signal pathway in NPCs.
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