Period 2 Gene Deletion Abolishes β‐Endorphin Neuronal Response to Ethanol

Abstract

Background Ethanol exposure during early life has been shown to permanently alter the circadian expression of clock regulatory genes and the β-endorphin precursor proopiomelanocortin (POMC) gene in the hypothalamus. Ethanol also alters the stress- and immune-regulatory functions of β-endorphin neurons in laboratory rodents. Our aim was to determine whether the circadian clock regulatory Per2 gene modulates the action of ethanol on β-endorphin neurons in mice. Methods Per2 mutant (mPer2Brdml) and wild type (C57BL/6J) mice were used to determine the effect of Per2 mutation on ethanol-regulated β-endorphin neuronal activity during neonatal period using an in vitro mediobasal hypothalamic (MBH) cell culture model and an in vivo milk formula feeding animal model. The β-endorphin neuronal activity following acute and chronic ethanol treatments, was evaluated by measuring the peptide released from cultured cells or peptide levels in the MBH tissues, using enzyme-linked immunosorbent assay (ELISA). Results Per2 mutant mice showed a higher basal level of β-endorphin release from cultured MBH cells and a moderate increase in the peptide content in the MBH in comparison to control mice. However, unlike wild type mice, Per2 mutant mice showed no stimulatory or inhibitory β-endorphin secretory responses to acute and chronic ethanol challenges in vitro. Furthermore, Per2 mutant mice, but not wild type mice, failed to show the stimulatory and inhibitory responses of MBH β-endorphin levels to acute and chronic ethanol challenges in vivo. Conclusions These results suggest for the first time that the Per2 gene may be critically involved in regulating β-endorphin neuronal function. Furthermore, the data revealed an involvement of the Per2 gene in regulating β-endorphin neuronal responses to ethanol.

Involvement of Activated Brain Stress Responsive Systems in Excessive and “Relapse” Alcohol Drinking in Rodent Models: Implications for Therapeutics

“…Both male and female mice display escalated alcohol intake after 3 weeks of chronic IA exposure, mainly occurring at the first 4-hour dark cycle (25-30% in total daily intake), without much change in the other two-time periods [Zhou et al, 2017a, b]. Of interest, hypothalamic POMC deficient mice displayed lower alcohol intake than wild-type mice during the first 4-hour dark cycle in both sexes [Zhou et al, 2017b], suggesting a potential contribution of hypothalamic POMC to the genetically determined tendency of hypothalamic POMC deficient mice towards reduced alcohol consumption, with potential clock genes' influence, as found in other studies with alcohol [Spanagel et al, 2005;Agapito et al, 2010;Partonen, 2015].…”

Association of PER2 Genotype and Stressful Life Events with Alcohol Drinking in Young Adults

“…Since there is distinct temporal variation and pronounced expression differences of Per2 across the life span (Figure 2) indicating temporal and regional-specific regulatory mechanisms, these results do not rule out a role of SNP rs56013859 or perhaps rare or intermediate variants in linkage disequilibrium with this SNP in transcriptional regulation. Recently, Agapito et al [36] demonstrated a PER2 mutation in mice to be associated with the regulation of β-endorphin release to acute and chronic ethanol challenges, providing another clue to the mechanism of different effectiveness of alcohol drinking as a means to cope with life events.…”

Circadian rhythms and addiction: Mechanistic insights and future directions.

“…In the mediobasal hypothalamus, the overall expression levels and rhythm amplitudes of Per1 and Per2 were significantly reduced in animals exposed to alcohol during early development (Agapito, Barreira, Logan, & Sarkar, 2012; Chen, Kuhn, Advis, & Sarkar, 2006). The lack of Per2 reduced the stimulatory response of ethanol on hypothalamic genes and neuropeptides involved in metabolism and stress regulation (Agapito et al, 2010). Developmental alcohol exposure may alter Per2 expression and subsequent downstream pathways by a number of molecular mechanisms, such as accelerating degradation by CK1ε and epigenetic modifications.…”