Department of Molecular Psychopharmacology, Mental Health Research Institute of Victoria, 155 Oak Street, Parkville, 3052, Victoria, Australia,
J Mol Neurosci. 2009 Sep;39(1-2):185-98. doi: 10.1007/s12031-009-9188-5. Epub 2009 Mar 10.
The atypical antipsychotic drug clozapine is effective in treatment-refractory schizophrenia. The intracellular signaling pathways that mediate clozapine action remain unknown. A potential candidate is the mitogen-activated protein kinase extracellular signal-regulated kinase (MAPK-ERK) cascade that links G-protein-coupled receptor and ErbB growth factor signaling systems, thereby regulating synaptic plasticity and connectivity, processes impaired in schizophrenia. Here, we examined how clozapine differentially modulated phosphorylation of the MAPK isoforms, ERK1/ERK2 in primary murine prefrontal cortical neurons compared to the typical antipsychotic drug haloperidol. While clozapine and haloperidol acutely decreased cortical pERK1 activation, only clozapine but not haloperidol stimulated pERK1 and pERK2 with continued drug exposure. This delayed ERK increase however, did not occur via the canonical dopamine D(2)-Gi/o-PKA or serotonin 5HT(2A)-Gq-phospholipase-C-linked signaling pathways. Rather, epidermal growth factor (EGF) receptor signaling mediated clozapine-induced ERK activation, given dose-dependent reduction of pERK1 and pERK2 stimulation with the EGF receptor inhibitor, AG1478. Immunocytochemical studies indicated that clozapine treatment increased EGF receptor (Tyr1068) phosphorylation. In vivo mouse treatment studies supported the in vitro findings with initial blockade, subsequent activation, and normalization of the cortical ERK response over 24 h. Furthermore, in vivo clozapine-induced ERK activation was significantly reduced by AG1478. This is the first report that clozapine action on prefrontal cortical neurons involves the EGF signaling system. Since EGF receptor signaling has not been previously linked to antipsychotic drug action, our findings may implicate the EGF system as a molecular substrate in treatment-resistant schizophrenia.
非典型抗精神病药物氯氮平对治疗抵抗性精神分裂症有效。介导氯氮平作用的细胞内信号通路仍不清楚。一个潜在的候选者是丝裂原激活的蛋白激酶细胞外信号调节激酶（MAPK-ERK）级联，它连接 G 蛋白偶联受体和 ErbB 生长因子信号系统，从而调节突触可塑性和连接，这些过程在精神分裂症中受损。在这里，我们研究了氯氮平如何与典型抗精神病药物氟哌啶醇相比，在原代小鼠前额皮质神经元中差异调节 MAPK 同工型 ERK1/ERK2 的磷酸化。虽然氯氮平和氟哌啶醇急性降低皮质 pERK1 的激活，但只有氯氮平而不是氟哌啶醇在继续药物暴露时刺激 pERK1 和 pERK2。然而，这种延迟的 ERK 增加并没有通过经典的多巴胺 D2-Gi/o-PKA 或 5-羟色胺 5HT2A-Gq-磷脂酶 C 连接的信号通路发生。相反，表皮生长因子（EGF）受体信号介导了氯氮平诱导的 ERK 激活，因为 EGF 受体抑制剂 AG1478 呈剂量依赖性降低 pERK1 和 pERK2 的刺激。免疫细胞化学研究表明，氯氮平处理增加了 EGF 受体（Tyr1068）的磷酸化。体内小鼠治疗研究支持体外研究结果，即初始阻断后，随后激活，并在 24 小时内使皮质 ERK 反应正常化。此外，体内氯氮平诱导的 ERK 激活被 AG1478 显著降低。这是第一个报道氯氮平对前额皮质神经元的作用涉及 EGF 信号系统的报告。由于 EGF 受体信号以前与抗精神病药物作用无关，我们的研究结果可能表明 EGF 系统作为治疗抵抗性精神分裂症的分子底物。
