Determining the role of REV-ERBs in the SCN and liver circadian hierarchy

点击翻译按钮获取中文摘要

PROJECT SUMMARY/ABSTRACT The maintenance and synchrony of circadian rhythms throughout the body is essential for metabolic health and homeostasis. In mammals, the hypothalamic suprachiasmatic nucleus (SCN) acts as the master circadian regulator, but organs such as the liver possess cell-autonomous clocks that regulate circadian gene expression in a tissue-specific manner. The REV-ERBα and β nuclear receptors are important components of the mammalian molecular clock that synchronize metabolic and circadian rhythms. Published data from the Lazar lab using a REV-ERBα/β hepatocyte double knock-out (HepDKO) mouse suggests that there are distinct sets of genes in the liver with varying degrees of cell-autonomy. Indeed, hundreds of normally oscillating genes lose rhythmicity under HepDKO conditions, but a nearly equal number of circadian oscillating genes retained rhythmicity in HepDKO livers. This implies that these genes have non-cell-autonomous rhythms dictated by signals from the SCN. There are several proposed SCN-derived outputs that can dictate hepatic rhythmicity, but innervation via the common hepatic branch (CHB) of the vagus nerve an understudied option. The vagus nerve is an established mode of communication between the brain and periphery that can integrate circadian rhythms of fed/fasting state. However, the role of the CHB in relaying circadian signals between the SCN and liver has yet to be examined. Therefore, I hypothesize that REV-ERB-mediated signals from the SCN clock are necessary for regulation of genes retained in HepDKO livers and that the CHB acts as an integral communicator of these regulatory signals. Specific Aim 1 will characterize hepatic physiology and rhythmicity in a mouse model lacking REV-ERBs in the SCN and liver by knocking out REV-ERBs in the SCN of HepDKO animals and performing circadian and metabolic phenotyping experiments. I will also collect tissues from these animals every 3 hours for 24 hours to compare molecular and gene regulatory phenotypes resulting from REV-ERBs DKO using next generation sequencing (NGS)-based -omics techniques. Specific Aim 2 will determine the role of the CHB in relaying REV-ERB-mediated circadian signals by severing the CHB through vagotomy (CHBx) in HepDKO mice. I will perform circadian and metabolic phenotyping experiments and collect tissues every 3 hours for 24 hours to compare molecular and gene regulatory phenotypes resulting from CHBx using NGS-based -omics. I predict that the rhythm of gene expression and regulation as well as behavioral and metabolic rhythmicity in HepDKO mice will be significantly disrupted without SCN REV-ERBs and in response to CHBx. The experiments outlined herein not only provide significant advances in the understanding of circadian and metabolic rhythm synchronization but provide substantial training opportunities for me by utilizing the Lazar lab's unique REV-ERB DKO mouse models and their expertise in state-of-the-art NGS tools to probe the role of REV-ERB-meditated rhythmicity.