Circadian disorder such as light exposure at night are risk factors for NAFLD Prolactin (PRL), a pituitary derived hormone, is recently shown to improve fatty liver. Noteworthy, PRL is secreted in an oscillating pattern. We aimed to explore the role of PRL rhythm in hepatic lipid metabolism. Serum PRL levels in 8:00, 16:00, and 24:00 of subjects without or with NAFLD were evaluated. A cosine model was fitted to the curve of dynamic PRL levels. Luciferase report assay, ChIP and EMSA were used to examine the mechanism of PRL rhythm. Hight fat diet (HFD) C57BL/6 mice were categorized into HFD, HFD+jet-lag group for 16 weeks and serum PRL levels at ZT0, ZT4, ZT8, ZT12, ZT16, ZT20 were determined. Then mice in HFD+jet-lag group were randomly assigned to HFD+ jet lag and HFD+jet-lag+PRL for 14 days. Hepatic lipid content, clock genes and lipid metabolic genes in liver were detected. PRL in 8:00, 16:00 and 24:00 were all significantly lower in NAFLD group than in controls. Cosine curve analysis showed that NAFLD patients had reduced amplitude and delayed phase shift of PRL levels. After adjusted for confounders, light exposure at night is a risk factor for NAFLD, yet this association was dampened after adjusted for PRL rhythm. Luciferase report assay in 293T cell and EMSA assay in human pituitary tissue showed that Prl can be transactivated by core clock gene Rorα via RORα response element RORE. In mice, dynamic PRL attained highest levels at ZT12 in HFD mice but remained low in HFD+jet-lag mice. ChIP analysis showed that binding of Rorα and Prl promoter in HFD mouse pituitary at ZT12 was inhibited under HFD+jet-lag. Furthermore, hepatic lipid content was significantly higher in HFD+jet-lag group than that in HFD, and can be mitigated after 14 days PRL intervention at ZT12. We also found that PRL injection reversed changes of clock and lipid metabolic gene rhythm caused by jet-lag. PRL can serve as an endocrine sensor that transmits rhythmic signals from central nervous system to liver and thus regulating hepatic lipid metabolism.
B. Yan: None. P. Zhang: None. D. Zhu: None.
National Natural Science Foundation of China (81900787, 81770819)