Homma Kohei, Kitamura Yoshiichiro, Ogawa Hiroto, Oka Kotaro
Center for Life Science and Technology, School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio University, Yokohama, Kanagawa, Japan.
J Neurosci Res. 2006 Aug 1;84(2):316-25. doi: 10.1002/jnr.20894.
As a neurotransmitter and neuromodulator, serotonin (5-HT) influences neuronal outgrowth in the nervous systems of several species. In PC12 cells, 5-HT is known to have neuritogenic effects, although the signal transduction pathway responsible for these effects is not understood. In this study, we hypothesized that a 5-HT-induced increase in intracellular Ca(2+) concentration (Ca(2+)) could be involved in mediating the effects of 5-HT. Application of 5-HT to PC12 cells enhanced nerve growth factor (NGF)-induced neurite outgrowth in a dose-dependent manner, and the sensitivity of this neuritogenic effect was increased in differentiated PC12 cells. In accordance, an increase in Ca(2+) was observed following application of 5-HT in differentiated PC12 cells. This increase was amplified by further NGF treatment. 5-HT-induced increases in Ca(2+) were inhibited by MDL 72222, a selective 5-HT(3) receptor antagonist, and nifedipine, an L-type calcium channel blocker, but not by ketanserin, a 5-HT(2) receptor antagonist, or thapsigargin, a specific inhibitor of endoplasmic reticulum Ca(2+)-ATPase. These pharmacological tests indicated that 5-HT-induced increases in Ca(2+) are mediated by activation of voltage-gated calcium channels via 5-HT(3) receptors and that 5-HT-induced increases in Ca(2+) are likely to be independent of activation of 5-HT(2) receptors in PC12 cells. Furthermore, the neuritogenic effect of 5-HT was suppressed by MDL 72222, nifedipine, calmodulin (CaM) inhibitor, and calcineurin inhibitors. Taken together, our results indicate that 5-HT-induced increases in Ca(2+), which are mediated via 5-HT(3) receptors and L-type calcium channels in PC12 cells, and subsequent activation of CaM and calcineurin enhance NGF-induced neurite outgrowth.
作为一种神经递质和神经调质，血清素（5-羟色胺，5-HT）影响多种物种神经系统中的神经元生长。在PC12细胞中，已知5-HT具有促神经突生长的作用，尽管负责这些作用的信号转导途径尚不清楚。在本研究中，我们假设5-HT诱导的细胞内Ca(2+)浓度（[Ca(2+)]i）升高可能参与介导5-HT的作用。将5-HT应用于PC12细胞以剂量依赖的方式增强了神经生长因子（NGF）诱导的神经突生长，并且这种促神经突生长作用的敏感性在分化的PC12细胞中增加。相应地，在分化的PC12细胞中应用5-HT后观察到[Ca(2+)]i升高。进一步的NGF处理放大了这种升高。5-HT诱导的[Ca(2+)]i升高被选择性5-HT(3)受体拮抗剂MDL 72222和L型钙通道阻滞剂硝苯地平抑制，但不被5-HT(2)受体拮抗剂酮色林或内质网Ca(2+)-ATP酶的特异性抑制剂毒胡萝卜素抑制。这些药理学试验表明，5-HT诱导的[Ca(2+)]i升高是通过5-HT(3)受体激活电压门控钙通道介导的，并且5-HT诱导的[Ca(2+)]i升高可能与PC12细胞中5-HT(2)受体的激活无关。此外，5-HT的促神经突生长作用被MDL 72222、硝苯地平、钙调蛋白（CaM）抑制剂和钙调神经磷酸酶抑制剂抑制。综上所述，我们的结果表明，5-HT诱导的[Ca(2+)]i升高（在PC12细胞中通过5-HT(3)受体和L型钙通道介导）以及随后CaM和钙调神经磷酸酶的激活增强了NGF诱导的神经突生长。
