The Role Of LIPIN1in The Regulation Of Circadian Rhythms

The circadian system orchestrates the temporal organization of many aspects of physiology and behavior in synchrony with the24hour rotation of the Earth. Circadian rhythms are regulated by the negative feedback loop that consists of the positive regulatory elements and the negative regulatory elements. Besides the core transcription/translation regulator mechanism, circadian rhythms are regulated by many other factors. In particular, energy metabolism is one of the critical factors. The molecular mechanism of the energy metabolism regulating circadian rhythms is unclear. We found that molecular interactions between LIPIN1and BMAL1screened by the yeast double hybrid assay. LIPIN1protein is involved in lipogenesis and energy metabolism. In order to investigate the role of LIPIN1in the circadian rhythms and energy metabolism, and discuss the way of the energy metabolism influencing circadian rhythms, and then promote people to learn more about the relationship between energy metabolism and circadian rhythms.Aim:Illustrate the mechanisms about the relationship between energy metabolism and circadian rhythms in vitro and vivo.Method:We verified the interaction between LIPIN1and BMAL1, by coimmununoprecipitation assay; the interaction between LIPIN1and BMAL1/CLOCK was analyzed by the Glutathione S-transferase (GST) pull down assay. We utilized a luciferase reporter system to study the effect of LIPIN1on BMAL1/CLOCK trans-activity. We constructed mutant isoforms of the LIPIN1to identify the functional domain. We used the immunofluorescence assay to further characterize whether LIPIN1exerted its function in the cytoplasm or in the nucleus. To investigate whether this interaction occurred in vivo, we carried out co-IP experiments in mouse liver. We compared the circadian behavior of WT and LIPIN1-deficient mice by monitoring locomotion activity. We surveyed the temporal profiles of a number of clock genes in the liver from WT and LIPIN1-deficient mice by RT-PCR. We surveyed the clock genes in the liver from WT and LIPIN1-deficient mice by resetting feed-schedule.Results:There is interaction between LIPINland BMAL1/CLOCK, and the C-terminal domain of LIPINlb was sufficient for the interaction.In the mouse liver, the interaction between LIPEN1and BMAL1has the characteristics of circadian rhythms, which is the highest in the CT8-CT16.LIPIN1can inhibit transcriptional activities of CLOCK/BMAL1dose-dependently. The possible mechanism of action is to promote the transfer of BMAL1from the nucleus to the cytoplasm.The circadian rhythm expressed by some CLOCK/BMAL1target gene in the liver of the LIPIN1knockout mice does change. It shows that the expression quantity of CT9is higher than the wild-type mice, coinciding with the highest interaction of BMAL1and LIPIN1during that period.After day time feeding, the expression of clock genes in the mice liver can be gradually reversed, and yet the change in the LIPIN1knockout mice is slow.The LIPIN1expression in the nervous system of drosophila presents the characteristics of circadian rhythm. LIPINlRNAi in the nervous system of drosophila can cause the abnormalities of circadian behavior and clock gene expression.Conclusion:Our results have been shown that LIPIN1may be a molecular link between energy metabolism and the circadian clock in vivo and in vitro.