Striatal but not frontal cortical up-regulation of the epidermal growth factor receptor in rats exposed to immune activation in utero and cannabinoid treatment in adolescence

doi:10.1016/j.psychres.2016.04.026

Psychiatry Research

Volume 240, 30 June 2016, Pages 260-264

https://doi.org/10.1016/j.psychres.2016.04.026 Get rights and content

Highlights

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Effect of maternal immune activation and cannabis treatment on EGFR-system in rat striatum and cortex.
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EGFR protein but not ErbB4 was increased in the dorsal striatum and nucleus accumbens of two-hit rats.
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No change in mRNA expression of ErbB4 and PI3K p110δ.
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EGFR system dysregulation may be a plausible animal model of schizophrenia.

Abstract

In utero maternal immune activation (MIA) and cannabinoid exposure during adolescence constitute environmental risk factors for schizophrenia. We investigated these risk factors alone and in combination (“two-hit”) on epidermal growth factor receptor (EGFR) and neuregulin-1 receptor (ErbB4) levels in the rat brain. EGFR but not ErbB4 receptor protein levels were significantly increased in the nucleus accumbens and striatum of “two-hit” rats only, with no changes seen at the mRNA level. These findings support region specific EGF-system dysregulation as a plausible mechanism in this animal model of schizophrenia pathogenesis.

Introduction

Numerous studies have implicated EGF-system dysfunction in schizophrenia with regards to its ligands such as EGF (Futamura et al., 2002) neuregulin-1 (Stefansson et al., 2002, Williams et al., 2003) and betacellulin (Schwarz et al., 2012); their cognate receptors EGFR (Futamura et al., 2002) and ErbB4 (Hahn et al., 2006, Pitcher et al., 2011, Stefansson et al., 2002); and associated signalling molecules such as PI3K p110δ isoform (Law et al., 2012). A number of aetiological risk factors for schizophrenia have also been identified including MIA (as result of maternal infection during pregnancy) and peri-adolescent cannabis use. However, it is not known how these factors may interact to mediate their increased risk for the disorder. We postulated that these two environmental risk factors may perturb the EGF-system to exert their effects. To test this we used a “two-hit” animal model in which rats were exposed to the viral mimetic, polyriboinosinic: polyribocytidylic acid (polyIC) in utero and the synthetic cannabinoid CB1 receptor (CB1R) agonist (HU210) in adolescence. Although selective CBIR agonist such as HU210 does not reflect the range of cannabinoids present in marijuana, it is an active component of some available synthetic cannabinoid preparations. Additionally it allows more focussed examination of the role of CB1R in influencing the EGF-system in the adult brain. We then measured a number of EGF-system components including EGFR, ErbB4 and PI3K p110δ in adult brains of these animals to investigate if these environmental factors perturb EGF-system signalling as seen in schizophrenia. The cortex was examined given its link with cognitive, negative and deficit syndrome symptoms in schizophrenia and connection with ErbB signalling through innervation by mesocortical dopamine tracts and glutamatergic and gamma-amino-butyric acid (GABA)-ergic neurons (Stefansson et al., 2002), whilst changes in ErbB signalling have been shown in the striatum (Pereira et al., 2014) and CB1Rs identified in both regions (Eggan et al., 2008, McLeod et al., 2008).

Section snippets

Animals

Pregnant Wistar rat dams were sourced from the Animal Resource Centre (Perth, Australia). They were kept at a constant temperature of 22±2 °C on a 12–12 h light-dark cycle with lights on at 9am. All animal handling and procedures were carried out in accordance with guidelines established by the Animal Care and Ethics Committee at the Australian Nuclear Science and Technology Organisation (Ethics #244).

The experimental design and treatment protocol has been described previously (Dalton et al., 2012

Results

One-way ANOVA for EGFR protein levels showed there was an overall effect of treatment in the NAcc (F_3,12=5.18, P=0.016) and in the dorsal striatum (F_3,12=8.54, P=0.003) with no changes seen in the mPFC (F_3,14=0.58, P=0.64) or oPFC (F_3,15=0.37, P=0.77) (Table 1). Rats exposed to both MIA and adolescent cannabis had significantly increased levels of EGFR protein in the NAcc compared to controls and polyI:C treated animals (P=0.03 and P=0.04 respectively, post-hoc Tukey's test, Fig. 2). “Two-hit”

Discussion

This pilot study found an increase in EGFR protein levels in the NAcc and striatum of rats exposed to two environmental risk factors implicated in schizophrenia, namely, MIA in utero and CB1R agonist treatment in adolescence. It demonstrates an interaction of two biologically and temporally distinct environmental schizophrenia risk factors, MIA and cannabis use, on EGFR in the striatum of rats. These two factors acted in concert to increase EGFR protein levels only in the dorsal striatum and

Contributors

Rejhan Idrizi performed the qPCR procedures and analysis and also wrote the manuscript. Peter Malcolm was responsible for tissue preparation and performing the Western procedures. Katerina Zavitsanou designed the experiments, provided the rat brains, intellectual input and was involved in the manuscript editing. Cynthia Shannon Weickert helped with interpretation of results and manuscript writing. Suresh Sundram conceived of the study, provided intellectual input and was involved in writing the

Acknowledgements

The authors declare that no conflict of interest arises from this work. This study was supported by One-in-Five Association Incorporated, the Victorian State Government Operational Infrastructure Support program, in part by Australia’s National Health & Medical Research Council and Parkinson’s Victoria and by an Australian Nuclear Science and Technology Organisation Senior Research Fellowship to Katerina Zavitsanou. Cynthia Shannon Weickert (CSW) is supported by Schizophrenia Research Institute

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EGFR levels were unaltered in adult offspring after MIA but increased in the striatum after the second hit. Similar to the current study, there were no changes in ErbB4 or PI3K-110δ protein levels in the dorsal striatum, NAc or PFC (Idrizi et al., 2016). The difference between the ‘two-hit’ model and the model described here suggests there is an earlier stage of brain development when the foetal brain is more vulnerable to neurochemical/neurotrophic changes that result in postnatal behavioural abnormalities.
Environmental risk factors that operate at foetal or neonatal levels increase the vulnerability to schizophrenia, plausibly via stress-immune activation that perturbs the epidermal growth factor (EGF) system, a system critical for neurodevelopment. We investigated potential associations between environmental insults and immune and EGF system changes through a maternal immune activation (MIA) model, using the precocial spiny mice (Acomys cahirinus). After mid-gestation MIA prepubescent offspring showed elevated NF-κB1 protein in nucleus accumbens, decreased EGFR in caudate putamen and a trend for increased PI3K-110δ in ventral hippocampus. Thus, prenatal stress may cause a heightened NF-κB1-mediated immune attenuation of EGF system signalling.
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¹: Current address: Department of Psychiatry, Monash University, Clayton Victoria, Australia.

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Short communicationStriatal but not frontal cortical up-regulation of the epidermal growth factor receptor in rats exposed to immune activation in utero and cannabinoid treatment in adolescence