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

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.

Distinct functions of endogenous cannabinoid system in alcohol abuse disorders

“…The inhibition of CDK5 activity by roscovitine (seliciclib) in P7 mice also rescues neurodegeneration in neonatal mice and augments pERK1/2, pCREB, and Arc signalling deficits and the loss of Rac1 gene expression, synaptic plasticity, and behavioural defects in adult mice exposed to alcohol at P7. These data indicate that the CB 1 receptor‐mediated (Subbanna et al, ; Subbanna et al, ) up‐regulation of CDK5/p25 activity followed by the inhibition of pERK, pCREB, and the epigenetic suppression of Arc (Subbanna et al, ) and Rac1 expression is responsible for the long‐lasting neurobehavioural defects observed in adult mice exposed to alcohol at P7.…”

CB1R regulates CDK5 signaling and epigenetically controls Rac1 expression contributing to neurobehavioral abnormalities in mice postnatally exposed to ethanol

“…Therefore, we next evaluated the role of caspase 3 activation in p35 protein degradation using a broadspectrum caspase inhibitor (Q-VD-OPh). We have previously shown that preadministration of an optimum dose (1 mg/kg) of Q-VD-OPh before ethanol treatment in P7 mice effectively prevented the formation of CC3 without altering BELs [11,34]. Thus, in the present study, a 1 mg/kg dose of Q-VD-OPh was used.…”

“…Postnatal ethanol exposure reduced Rac1 expression to adulthood via epigenetic mechanisms; postnatal ethanol-induced deficits in activity-regulated cytoskeleton-associated protein (Arc), pCREB, and Rac1 levels in adult mice were rescued by pretreatment with RV We have previously demonstrated that P7 ethanol treatment causes persistent impairment of pCREB followed by Arc expression in adult animals [11,37]. To understand whether RV treatment at P7 rescues these signaling deficits in the adulthood, we analyzed Arc and pCREB protein levels in HP tissues of adult mice treated with RV at P7.…”

“…The brain is the most susceptible organ affected by prenatal alcohol exposure, which results in reduced academic performance; an increased frequency of learning disabilities; impaired executive functions; poor hand/eye coordination; tremors; gait and balance difficulties; and impairments in attention, reaction time, motor skills, memory, and social and adaptive functions [1,[5][6][7]. Our laboratory and others have previously demonstrated that exposure of mice to ethanol at postnatal day 7 (P7), which is corresponding to the third trimester of human pregnancy, affects synaptogenesis, induces neuronal cell death, and results in longlasting neurobehavioral dysfunctions [8][9][10][11][12][13].…”

“…Error bars, SEM (n = 12 pups/group) cognitive function [30,31]. Because ethanol exposure of P7 mice results in cognitive defects [8,[11][12][13]32], it is important to understand CDK5 and Rho GTPase signaling during this period. Hence, we explored the functions of CDK5 and Rac1 in P7 ethanolinduced neurodegeneration and their impact on long-lasting learning and memory abnormalities.…”