CB1R-Mediated Activation of Caspase-3 Causes Epigenetic and Neurobehavioral Abnormalities in Postnatal Ethanol-Exposed Mice.

Shivakumar Subbanna,Delphine Psychoyos,Vikram Joshi,Nagaraja N Nagre,Nagavedi S Umapathy,Abdullah Kutlar,Madhu Shivakumar,Balapal S Basavarajappa

doi:10.3389/fnmol.2018.00045

Abstract

Alcohol exposure can affect brain development, leading to long-lasting behavioral problems, including cognitive impairment, which together is defined as fetal alcohol spectrum disorder (FASD). However, the fundamental mechanisms through which this occurs are largely unknown. In this study, we report that the exposure of postnatal day 7 (P7) mice to ethanol activates caspase-3 via cannabinoid receptor type-1 (CB1R) in neonatal mice and causes a reduction in methylated DNA binding protein (MeCP2) levels. The developmental expression of MeCP2 in mice is closely correlated with synaptogenesis and neuronal maturation. It was shown that ethanol treatment of P7 mice enhanced Mecp2 mRNA levels but reduced protein levels. The genetic deletion of CB1R prevented, and administration of a CB1R antagonist before ethanol treatment of P7 mice inhibited caspase-3 activation. Additionally, it reversed the loss of MeCP2 protein, cAMP response element binding protein (CREB) activation, and activity-regulated cytoskeleton-associated protein (Arc) expression. The inhibition of caspase-3 activity prior to ethanol administration prevented ethanol-induced loss of MeCP2, CREB activation, epigenetic regulation of Arc expression, long-term potentiation (LTP), spatial memory deficits and activity-dependent impairment of several signaling molecules, including MeCP2, in adult mice. Collectively, these results reveal that the ethanol-induced CB1R-mediated activation of caspase-3 degrades the MeCP2 protein in the P7 mouse brain and causes long-lasting neurobehavioral deficits in adult mice. This CB1R-mediated instability of MeCP2 during active synaptic maturation may disrupt synaptic circuit maturation and lead to neurobehavioral abnormalities, as observed in this animal model of FASD.

Highlights

Ethanol abuse during pregnancy is considered to be one of the most common causes of non-genetic mental impairments in the Western world (Mattson et al, 2011)
Because degenerating neurons in ethanol-exposed postnatal day 7 (P7) mice undergo nuclear changes that lead to caspase-3-mediated loss of DNA methyltransferases (DNMT1 and DNMT3A), and reduced DNA methylation (Nagre et al, 2015), we examined DNA methylation status and MeCP2 levels in ethanol-treated P7 mice
Consistent with our previous observation (Nagre et al, 2015), we found that P7 ethanol treatment significantly reduced DNA methylation (HP, F(1,36) = 92, p < 0.01; NC, F(1,36) = 80, p < 0.01; one-way analysis of variance (ANOVA); Figure 1A)

Summary

Introduction

Ethanol abuse during pregnancy is considered to be one of the most common causes of non-genetic mental impairments in the Western world (Mattson et al, 2011). It can cause a range of developmental, cognitive, and behavioral problems, which together is known as fetal alcohol spectrum disorder (FASD). The brain is especially susceptible to ethanol exposure between postnatal days 4 and 10 (P4–10), which is comparable to the third trimester of human pregnancy (Bayer et al, 1993). A single day of binge-like ethanol treatment at P7 elicits widespread caspase-3 activation (CC3, a marker of neurodegeneration) in numerous regions of the brain, such as the HP and NC (Ikonomidou et al, 2000; Saito et al, 2010; Wilson et al, 2011; Sadrian et al, 2012; Subbanna et al, 2013b); it causes persistent deficits in the olfactory and hippocampal pathway (Wilson et al, 2011; Sadrian et al, 2012) and impairs cognitive function in adults (Abel et al, 1983; Bonthius and West, 1991; Bellinger et al, 1999, 2002; Berman and Hannigan, 2000; Alati et al, 2006; Brown et al, 2007; Brady et al, 2013; Subbanna et al, 2013a, 2015a; Subbanna and Basavarajappa, 2014; Basavarajappa, 2015)

Methods

Results

Conclusion