Elsevier

Neuroscience Letters

Volume 547, 28 June 2013, Pages 21-25
Neuroscience Letters

Neurobehavioral deficits of epidermal growth factor-overexpressing transgenic mice: Impact on dopamine metabolism

https://doi.org/10.1016/j.neulet.2013.04.055Get rights and content

Highlights

  • We established the transgenic mice overexpressing EGF.

  • EGF-transgenic mice exhibited the behavioral deficits relevant to schizophrenia.

  • EGF-transgenic mice were hypersensitive to repeated cocaine administration.

  • Overexpression of EGF is associated with altered dopamine metabolism in a region-specific manner.

Abstract

Epidermal growth factor (EGF) and its family member neuregulin-1 are implicated in the etiology of schizophrenia. Our recent pharmacological studies indicate that EGF injections to neonatal and adult rats both induce neurobehavioral deficits relevant to schizophrenia. We, however, did not evaluate the genetic impact of EGF transgene on neurobehavioral traits. Here we analyzed transgenic mice carrying the transgene of mouse EGF cDNA. As compared to control littermates, heterozygous EGF transgenic mice had an increase in EGF mRNA levels and showed significant decreases in prepulse inhibition and context-dependent fear learning, but there were no changes in locomotor behaviors and sound startle responses. In addition, these transgenic mice exhibited higher behavioral sensitivity to the repeated cocaine injections. There were neurochemical alterations in metabolic enzymes of dopamine (i.e., tyrosine hydroxylase, dopa decarboxylase, catechol-O-methyl transferase) and monoamine contents in various brain regions of the EGF transgenic mice, but there were no apparent neuropathological signs in the brain. The present findings rule out the indirect influence of anti-EGF antibody production on the reported behavioral deficits of EGF-injected mice. These results support the argument that aberrant hyper-signals of EGF have significant impact on mouse behavioral traits and dopamine metabolism.

Introduction

We have been investigating etiologic and pathologic contributions of epidermal growth factor (EGF) and its family member neuregulin-1 in the etiology or neuropathology of schizophrenia [18]. Both cytokines activate ErbB receptors and influence dopaminergic, GABAergic, and glial development and/or neurotransmission [10]. The gene targeting of ErbB receptors and ligands result in the dysfunction of these cells [2], [19], [20], [25]. Our studies on EGF and ErbB1 started with our initial findings on an increase in ErbB1 levels in the forebrain regions of patients with schizophrenia [5]. Several genetic studies also indicate an association of this illness with the functional SNP promoting EGF transcription [6], [13]. Based on these observations, we attempted to establish animal models for this disease by administering EGF and other peptides in the EGF family to rodent pups or adults [5], [11], [16], [22], [23], [24]. The animals receiving EGF developed behavioral and cognitive deficits; most of which can be ameliorated by subchronic treatment with atypical antipsychotics [5]. In addition, these animal models exhibited hypersensitivity to psychostimulants [11], [17]. There are significant alterations in dopamine synthesis, metabolism and/or neurotransmission in these EGF-treated animals [3], [8], [9], [21], [22]. The phenotypic influences of EGF on GABAergic neurons or glial cell populations appear to be limited [1], [5].

One possible drawback in the previous studies is repeated injections or continuous administration of EGF might result in the production of the anti-EGF antibody that neutralizes endogenous EGF and down-regulates EGF signaling. This argument might be supported by clinical studies as schizophrenia patients often contain lower levels of EGF in their serum [5], [7]. To avoid the production of anti-EGF antibody, we established EGF-overexpressing mice by genetic manipulation. We explored various behavioral traits of these transgenic mice and examined their neurochemical alterations in dopaminergic markers.

Section snippets

Animals

All transgenic mice were housed in a plastic cage (200 mm x 300 mm x 140 mm) and given free access to food and water. Each cage contained 2–4 mice and was kept in a temperature-controlled colony room (22 ± 1.0 °C) under a 12-h light–dark cycle (8:00 on–20:00 off). We used both male and female mice following studies (total n = 80). All of the animal experiments described here were approved by the Animal Use and Care Committee of Niigata University and performed in accordance with the Guiding Principles for

Effects of EGF transgene on mouse behavioral traits

We assessed sound startle responses and prepulse inhibition of the EGF transgenic mice at the stage of young adults. The EGF transgenic mice and their wild-type littermates exhibited indistinguishable strengths of startle responses to various levels of tone stimuli (Fig. 1A). This contrasts with the fact that mice challenged with EGF as neonates have higher startle responses [23]. The transgenic mice showed significantly lower levels of prepulse inhibition at all prepulse levels [F(1,18) = 9.05, p

Discussion

To investigate the neurobehavioral consequences of continuous EGF hyper-signaling, we obtained the transgenic mouse line carrying mouse EGF cDNA driven by the ubiquitous transcription promoter of CMV. These transgenic mice are known to exhibit hair follicle deficits and thin fur with the EGF hyper-signaling [15]. In agreement, there were marked increases in EGF mRNA levels in various tissues of the transgenic mice. As indicated by the neurotrophic action of EGF on dopamine neurons [8], [9], the

Conflict of interest

The authors have declared that no conflict of interest exists.

Acknowledgments

This work was supported by MEXT KAKENHI (No. 24116010) and JSPS KAKENHI (No. 22300107). The funders and the company had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

References (25)

  • T. Futamura et al.

    Neonatal perturbation of neurotrophic signaling results in abnormal sensorimotor gating and social interaction in adults: implication for epidermal growth factor in cognitive development

    Mol. Psychiatry

    (2003)
  • T. Futamura et al.

    Abnormal expression of epidermal growth factor and its receptor in the forebrain and serum of schizophrenic patients

    Mol. Psychiatry

    (2002)
  • Cited by (14)

    • Schizophrenia-relevant behaviours of female mice overexpressing neuregulin 1 type III

      2018, Behavioural Brain Research
      Citation Excerpt :

      Female Nrg1 III tg mice exhibited WT-like locomotor activity. Unaltered locomotor activity is consistent with several other genetic mouse models for Nrg1 [52–54], including the type III Nrg1 knockout mouse [23,55]. However, a hyperlocomotive phenotype has been observed in Nrg1 TM HET mice [34,56] as well as Nrg1 type I overexpressing mice [57,58].

    • Epidermal growth factor, from gene organization to bedside

      2014, Seminars in Cell and Developmental Biology
      Citation Excerpt :

      In line with the transgenic mice with human EGF overexpression, transgenic mice with mouse EGF overexpression also showed stunted growth, which was much more severe in homozygous than heterozygous progenies. In addition, those transgenic mice exhibited: (1) hair follicle deficits and thin fur that could be rescued by inhibiting the EGFR signaling by crossing with waved-2 mice, which harbor a point mutation in EGFR that greatly diminishes its tyrosine kinase activity [50]; (2) hypersensitivity to psychostimulants, such as cocaine, which may due to the neurotrophic action of EGF on dopamine neurons; (3) behavioral deficits relevant to schizophrenia [43]. In humans, EGF A61G polymorphism in the 5′ untranslated region (UTR), a single nucleotide substitution (G to A) at position 61 of the EGF gene that results in increased EGF expression (G/G > G/A > A/A) has been associated with lower birth weight and fetal growth restriction in individuals from Western Europe [51,52].

    • Dopaminergic function in relation to genes associated with risk for schizophrenia: Translational mutant mouse models

      2014, Progress in Brain Research
      Citation Excerpt :

      These EGF transgenics also showed a decrease in striatal TH and an increase in striatal COMT protein levels, as well as an increase in DOPA decarboxylase protein levels in the accumbens and PFC. HPLC analysis of brain monoamine levels in these mutants also demonstrated increased DA and DOPAC content in the accumbens, with such DA alterations being generally dependent on the region examined. Behaviorally, these EGF mutants also exhibited an increase in sensitized behavioral responsivity to repeated cocaine administration (Eda et al., 2013). A different approach to clarifying NRG1 expression in relation to DA-linked behaviors comes from studies of rats selectively bred for reduced PPI (Rhein et al., 2013; Swerdlow et al., 2012); rats with lower levels of PPI displayed higher levels of brain NRG1 expression (Swerdlow et al., 2012) and lower levels of NRG1 methylation in the PFC and accumbens (Rhein et al., 2013).

    View all citing articles on Scopus
    View full text