The Regulation of Hepatic Metabolic Zonation by the Diabetes Gene TCF7L2

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ABSTRACT The mammalian liver consists of functional units called lobules, which are spatially separated into zones relative to the portal triad and central vein. Each zone contains hepatocytes with distinct functions that differentially impact metabolic processes. This spatial division of labor in liver has been appreciated for decades, but the molecular and physiological determinants of metabolic zonation are poorly understood. Moreover, whether dis- ordered hepatic metabolic architecture plays a pathophysiological role in prevalent liver diseases remains un- clear. As part of our long-term effort to dissect the functional role of leading type 2 diabetes (T2D) candidate genes, we have identified the protein encoded by the transcription factor 7-like 2 (TCF7L2) gene as a key regu- lator of hepatic metabolic zonation. Leveraging a unique mouse model of TCF7L2 inactivation in liver and an integrative combination of cellular, genomic and in vivo physiological approaches, we will examine the regulation of metabolic zonation by TCF7L2, and will determine the significance of the zonated pathways regulated by TCF7L2 to the development of hepatic fibrosis in nonalcoholic steatohepatitis (NASH). In published studies, we unveiled a striking role for TCF7L2 in the transcriptional regulation of a diverse set of metabolic genes in hepato- cytes, including those involved in zonated pathways of glucose, lipid, and amino acid metabolism. In preliminary studies we discovered that the expression of the Tcf7l2 gene is ubiquitous across the liver lobule, but TCF7L2 transcriptional activity is highly restricted to a population of hepatocytes surrounding the central vein in adult mouse liver. These data, and additional preliminary studies, prompted us to develop a unique mouse model that expresses transcriptionally inactive TCF7L2 exclusively in the liver (Hep-TCF7L2ΔDBD). Using this model, in this proposal we will test the central hypothesis that TCF7L2 is an important regulator of hepatic metabolic zonation, and that TCF7L2-mediated disruption of pericentral amino acid metabolism predisposes Hep-TCF7L2ΔDBD mice to dietary induced fibrosis and NASH. In specific aim 1, we will dissect the spatiotemporal transcriptional function of TCF7L2 in liver using cutting-edge single-nuclei Assay for Transposase-Accessible Chromatin sequencing (snATAC-Seq) with snRNA-Seq in distinct hepatocyte populations across the mouse liver lobule. In Specific Aim 2, we will determine the role of TCF7L2 in the maintenance of hepatic metabolic zonation and will test the impact of TCF7L2 inactivation on the lobular distribution of pericentral and periportal hepatocyte populations in Hep- TCF7L2ΔDBD mice. Finally, in Specific Aim 3 we will link hepatic fibrosis disrupted zonal amino acid metabolism in Hep-TCF7L2ΔDBD mice using integrative in vivo physiological approaches. These experiments will dissect the molecular and physiological mechanisms by which TCF7L2 influences hepatic metabolic zonation, and will de- scribe the consequences of disordered hepatic organization on the development of metabolic diseases.