Insulin controls hepatic bile acid metabolism by the spatial repatterning of gene expression
Insulin regulation of hepatic gene expression is critical for controlling metabolism and preventing diabetes, atherosclerosis and NAFLD; yet, how insulin regulates gene expression in the spatial context of the liver lobule is largely unexplored.  Here, we find that insulin regulates bile acid metabolism by segregating CYP8B1, the enzyme that catalyzes the 12a-hydroxylation of bile acids, from the other enzymes required for bile acid synthesis.  When insulin signaling is disrupted, Cyp8b1 and the other bile acid synthesis genes become co-localized within the same zone, and 12a-hydroxylated bile acids, which drive atherosclerosis and NAFLD, are increased. Novel zone-specific genetic manipulations of Cyp8b1 that mimic the effects of insulin result in a more benign bile salt profile. Mechanistically, the zonal effects of insulin are not due to gradients of insulin concentration or signaling, but through insulin crosstalk with positional Wnt signals: Wnt and insulin act together to determine the complement of transcription factors active in the pericentral hepatocytes and thereby regulate Cyp8b1 zonation.  Taken together, these data show that by repatterning gene expression in the liver lobule, insulin can transcriptionally regulate the outputs of a metabolic pathway.  The spatial dimension of transcriptional regulation represents a novel lens with which to view the control of metabolism that may ultimately lead us to more precise therapies. Overall design: Single nuclei sequencing of liver tissue from mus musculus following a 16-24 hour fast and compared to a fed control.