Gu Zhenglin, Jiang Qian, Fu Amy K Y, Ip Nancy Y, Yan Zhen
Department of Physiology and Biophysics, State University of New York at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, New York 14214, USA.
J Neurosci. 2005 May 18;25(20):4974-84. doi: 10.1523/JNEUROSCI.1086-05.2005.
Recent linkage studies have identified a significant association of the neuregulin gene with schizophrenia, but how neuregulin is involved in schizophrenia is primarily unknown. Aberrant NMDA receptor functions have been implicated in the pathophysiology of schizophrenia. Therefore, we hypothesize that neuregulin, which is present in glutamatergic synaptic vesicles, may affect NMDA receptor functions via actions on its ErbB receptors enriched in postsynaptic densities, hence participating in emotional regulation and cognitive processes that are impaired in schizophrenia. To test this, we examined the regulation of NMDA receptor currents by neuregulin signaling pathways in prefrontal cortex (PFC), a prominent area affected in schizophrenia. We found that bath perfusion of neuregulin significantly reduced whole-cell NMDA receptor currents in acutely isolated and cultured PFC pyramidal neurons and decreased NMDA receptor-mediated EPSCs in PFC slices. The effect of neuregulin was mainly blocked by application of the ErbB receptor tyrosine kinase inhibitor, phospholipase C (PLC) inhibitor, IP3 receptor (IP3R) antagonist, or Ca2+ chelators. The neuregulin regulation of NMDA receptor currents was also markedly attenuated in cultured neurons transfected with mutant forms of Ras or a dominant-negative form of MEK1 (mitogen-activated protein kinase kinase 1). Moreover, the neuregulin effect was prevented by agents that stabilize or disrupt actin polymerization but not by agents that interfere with microtubule assembly. Furthermore, neuregulin treatment increased the abundance of internalized NMDA receptors in cultured PFC neurons, which was also sensitive to agents affecting actin cytoskeleton. Together, our study suggests that both PLC/IP3R/Ca2+ and Ras/MEK/ERK (extracellular signal-regulated kinase) signaling pathways are involved in the neuregulin-induced reduction of NMDA receptor currents, which is likely through enhancing NR1 internalization via an actin-dependent mechanism.
近期的连锁研究已确定神经调节蛋白基因与精神分裂症之间存在显著关联，但神经调节蛋白如何参与精神分裂症的发病机制主要仍不清楚。异常的N-甲基-D-天冬氨酸（NMDA）受体功能被认为与精神分裂症的病理生理学有关。因此，我们推测，存在于谷氨酸能突触小泡中的神经调节蛋白，可能通过作用于富含突触后致密物的ErbB受体来影响NMDA受体功能，从而参与精神分裂症中受损的情绪调节和认知过程。为了验证这一推测，我们研究了神经调节蛋白信号通路对前额叶皮质（PFC）中NMDA受体电流的调节作用，前额叶皮质是精神分裂症中受影响的一个重要区域。我们发现，在急性分离和培养的PFC锥体神经元中，浴灌流神经调节蛋白可显著降低全细胞NMDA受体电流，并减少PFC脑片中NMDA受体介导的兴奋性突触后电流（EPSCs）。神经调节蛋白的作用主要被ErbB受体酪氨酸激酶抑制剂、磷脂酶C（PLC）抑制剂、肌醇三磷酸受体（IP3R）拮抗剂或Ca2+螯合剂所阻断。在用Ras突变体形式或MEK1（丝裂原活化蛋白激酶激酶1）的显性负性形式转染的培养神经元中，神经调节蛋白对NMDA受体电流的调节作用也明显减弱。此外，稳定或破坏肌动蛋白聚合的药物可阻止神经调节蛋白的作用，但干扰微管组装的药物则不能。此外，神经调节蛋白处理增加了培养的PFC神经元中内化NMDA受体的丰度，这对影响肌动蛋白细胞骨架的药物也敏感。总之，我们的研究表明，PLC/IP3R/Ca2+和Ras/MEK/细胞外信号调节激酶（ERK）信号通路均参与了神经调节蛋白诱导的NMDA受体电流减少，这可能是通过肌动蛋白依赖性机制增强NR1内化实现的。
