Chronic corticosterone disrupts the circadian rhythm of CRH expression and mA RNA methylation in the chicken hypothalamus.

BACKGROUND

Corticotropin-releasing hormone (CRH), the major secretagogue of the hypothalamic-pituitary-adrenal (HPA) axis, is intricately intertwined with the clock genes to regulate the circadian rhythm of various body functions. N6-methyladenosine (mA) RNA methylation is involved in the regulation of circadian rhythm, yet it remains unknown whether CRH expression and mA modification oscillate with the clock genes in chicken hypothalamus and how the circadian rhythms change under chronic stress.

RESULTS

Chronic exposure to corticosterone (CORT) eliminated the diurnal patterns of plasma CORT and melatonin levels in the chicken. The circadian rhythms of clock genes in hippocampus, hypothalamus and pituitary are all disturbed to different extent in CORT-treated chickens. The most striking changes occur in hypothalamus in which the diurnal fluctuation of CRH mRNA is flattened, together with mRNA of other feeding-related neuropeptides. Interestingly, hypothalamic mA level oscillates in an opposite pattern to CRH mRNA, with lowest mA level after midnight (ZT18) corresponding to the peak of CRH mRNA before dawn (ZT22). CORT diminished the circadian rhythm of mA methylation with significantly increased level at night. Further site-specific mA analysis on 3'UTR of CRH mRNA indicates that higher mA on 3'UTR of CRH mRNA coincides with lower CRH mRNA at night (ZT18 and ZT22).

CONCLUSIONS

Our results indicate that chronic stress disrupts the circadian rhythms of CRH expression in hypothalamus, leading to dysfunction of HPA axis in the chicken. RNA mA modification is involved in the regulation of circadian rhythms in chicken hypothalamus under both basal and chronic stress conditions.