Clozapine-Induced ERK1 and ERK2 Signaling in Prefrontal Cortex Is Mediated by the EGF Receptor

Abstract

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.

The involvement of GABAA receptor in the molecular mechanisms of combined selective serotonin reuptake inhibitor-antipsychotic treatment

“…These findings support previous reports which implicated MAPK pathway in pharmacological actions of antipsychotic and antidepressant drugs (Fumagalli et al 2005 ;Kim et al 2008 ;Pereira et al 2009). Studies of the effects of SSRIs and antipsychotic medications on ERK, describe a complex and unclear picture.…”

“…There is no evidence of synthesis of DA or 5-HT in primary cortical cultures, thus, Hal-Flu or Clz are unlikely to mediate GABA A phosphorylation increase through DA antagonism or 5-HT reuptake inhibition and this mechanism is unlikely to be explained by the classic receptor/transporter action of the drugs. Several in-vitro studies suggested that antipsychotic and antidepressant compounds may act via mechanisms that include effects on cell-signalling regulators, such as ERK, PKC, and GSK-3b (Li et al 2007 ;Pakaski et al 2005 ;Pereira et al 2009) and our findings support such potential mechanisms.…”

“…Chronic fluoxetine administration decreased ERK2 phosphorylation levels in PFC of naive rats (Fumagalli et al 2005), but increased ERK2 phosphorylation levels in rats exposed to chronic forced swim stress (Qi et al 2008). Reports on acutely administered Hal showed down-regulation of ERK2 phosphorylation in murine primary cortical neurons (Pereira et al 2009) and in rat PFC (Fumagalli et al 2006), while Kim et al (2008) described a biphasic effect of Hal in rat PFC. One explanation for such inconsistencies is that ERK2 phosphorylation is a dynamic process, and that dosages and timing of examination in relation to drug administration can substantially affect results.…”

A Model of Neuregulin Control of NMDA Receptors on Synaptic Spines

“…For example, Model 2 indicates that the excess release of neuregulin onto the ErbB4 receptor excessively removes activated Src and so decreases phosphorylation of NMDA receptor subunits, thus decreasing their efficiency. A key approach to preventing this is to use inhibitors of the ErbB4 receptor kinases, such as blockers of the type AG1478 (Yaish et al 1988;Pereira et al 2009). It has been established that antagonists such as AG1478 do block the decrease in activated Src kinase by neuregulin in cell preparations and slices (Pitcher et al 2011).…”

Chronic treatment with serotonin reuptake inhibitor antidepressant (SSRI) combined with an antipsychotic regulates GABA-A receptor in rat prefrontal cortex

“…The MAPK pathway has been implicated in the pharmacological actions of antipsychotic and antidepressant drugs (Fumagalli et al 2005;Kim et al 2008;Pereira et al 2009). Several reports linked decrease in ERK2 phosphorylation in the rodent brain to GABA receptor activation (Kalluri and Ticku 2002;Zheng et al 2007Zheng et al , 2009, so the change in ERK2 phosphorylation induced by HALO-FLU may occur down-stream to the effect on GABA-A receptors.…”