Neurite outgrowth mediated by the heat shock protein Hsp90α: a novel target for the antipsychotic drug aripiprazole

T Ishima,K Hashimoto,M Iyo

doi:10.1038/tp.2012.97

Abstract

Aripiprazole is an atypical antipsychotic drug approved for the treatment of psychiatric disorders such as schizophrenia, bipolar disorder, major depressive disorder and autism. The drug shows partial agonistic activity at dopamine D2 receptors and 5-hydroxytryptamine (5-HT) 5-HT1A receptors, and antagonistic activity at 5-HT2A receptors. However, the precise mechanistic pathways remain unclear. In this study, we examined the effects of aripiprazole on neurite outgrowth. Aripiprazole significantly potentiated nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells, in a concentration-dependent manner. The 5-HT1A receptor antagonist WAY-100635, but not the dopamine D2 receptor antagonist sulpiride, blocked the effects of aripiprazole, although, only partially. Specific inhibitors of inositol 1,4,5-triphosphate (IP3) receptors and BAPTA-AM, a chelator of intracellular Ca2+, blocked the effects of aripiprazole. Moreover, specific inhibitors of several common signaling pathways phospholipase C-γ (PLC-γ), phosphatidylinositol-3 kinase (PI3K), mammalian target of rapamycin, p38 MAPK, c-Jun N-terminal kinase, Akt, Ras, Raf, ERK, MAPK) also blocked the effects of aripiprazole. Using proteomic analysis, we found that aripiprazole significantly increased levels of the heat shock protein Hsp90α in cultured cells. The effects of aripiprazole on NGF-induced neurite outgrowth were significantly attenuated by treatment with Hsp90α RNA interference, but not by the negative control of Hsp90α. These findings suggest that both 5-HT1A receptor activation and Ca2+ signaling via IP3 receptors, as well as their downstream cellular signaling pathways play a role in the promotion of aripiprazole-induced neurite outgrowth. Furthermore, aripiprazole-induced increases in Hsp90α protein expression may form part of the therapeutic mechanism for this drug.

Highlights

This study found that aripiprazole potentiated nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells, mediating this at the molecular level, at least in part, via an increase in Hsp90a protein
We found that aripiprazole potentiated NGF-induced neurite outgrowth in PC12 cells, and that this potentiation could be partially blocked by the selective 5-HT1A receptor antagonist WAY-100635, but not the dopamine D2 receptor antagonist sulpiride
The selective 5-HT1A receptor agonist 8OH-DPAT potentiated NGFinduced neurite outgrowth in PC12 cells, to a lesser degree than aripiprazole. This result is in agreement with findings from human neuroblastoma SK-N-SH cells, which showed that 8OH-DPAT increased neurite outgrowth that could be blocked by the selective 5-HT1A receptor antagonist WAY-100169.48 it is likely that activation of 5-HT1A receptors plays a role in the mechanisms that lead to aripiprazole-driven enhancement of NGF-induced neurite outgrowth

Summary

Introduction

Aripiprazole is an atypical antipsychotic drug, approved for the treatment of schizophrenia, acute manic or mixed episodes associated with bipolar I disorder, as an adjunct treatment for major depressive disorder, and for irritability in children with autism.[1,2,3,4,5,6,7,8,9] Aripiprazole shows high affinity at dopamine D2, and D3 receptors, 5-hydroxytryptamine (5-HT) 5-HT1A, and 5-HT2A receptors, and moderate affinity at dopamine D4 receptors, 5-HT2C receptors, a1 adrenergic receptors and histamine H1 receptors.[10,11] While it is known that aripiprazole is a partial agonist at dopamine D2 and 5-HT1A receptors and an antagonist at 5-HT2A receptors, the precise mechanisms underlying its clinical efficacy in psychiatric disorders are unknown.[12,13,14]Accumulating evidence suggests that at the cellular level, neuronal plasticity, such as neurite outgrowth and neuroprotection, underlie the therapeutic effect of atypical antipsychotic drugs.[15,16,17,18] PC12 cells, a cell line derived from a pheochromocytoma of the rat adrenal medulla, are widely used as a model system for nerve growth factor (NGF)-induced neurite outgrowth.[19,20,21,22,23,24,25] It is reported that atypical antipsychotic drugs such as olanzapine, quetiapine and clozapine could enhance neurite outgrowth in PC12 cells.[15]. A number of signaling molecules, including phospholipase C-g (PLC-g), phosphatidylinositol-3 kinase (PI3K), the mammalian target of rapamycin (mTOR), p38 MAPK, c-Jun N-terminal kinase (JNK), Akt and the Ras/Raf/ERK/MAPK pathways plays a role in the NGFinduced neurite outgrowth in PC12 cells.[19,20,21,22,23,24,25] To date, there are no reports on precisely how aripiprazole induces neurite outgrowth, it is reported that this drug protects rat cortical neurons against glutamate toxicity.[26]

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