PROJECT SUMMARY/ABSTRACT Protein-energy undernutrition (PEU) is implicated in half of all global deaths under five years of age and remains one of the most pressing challenges in pediatrics today. PEU sets into motion a vicious cycle of liver function abnormalities that further erode health. For example, intestinal bile acids are markedly reduced in children with PEU, resulting in poor dietary fat absorption and impaired weight gain. In severe cases, vitamin K- independent coagulopathy can lead to catastrophic bleeding. Mechanisms by which PEU alters these two processes are unknown, although evidence implicates the nutrient-sensing nuclear receptors, farnesoid X receptor (FXR) and peroxisome proliferator-activated receptor (PPAR)α. FXR is activated in the fed state by bile acids, while PPARα is activated in the fasted state by products of lipolysis. These receptors regulate bile acid homeostasis and other liver functions, competing for binding to many of the same promoter regions with opposite transcriptional effects. Children with mutations in the gene encoding FXR also have vitamin K-independent coagulopathy with transcriptional repression of multiple coagulation factors including fibrinogen, implicating FXR signaling in the coagulopathy of PEU. To investigate the role of nuclear receptors in these two liver functions, we examined mouse models of early-life PEU, each of which exhibits globally decreased bile acids and coagulopathy. Gene expression patterns in our young adult mice demonstrate Pparα activation, Fxr signal loss, and transcriptional repression of genes that promote bile acid synthesis and coagulation. Based on these findings, our hypothesis is that Pparα activation by products of lipolysis generated in PEU transcriptionally represses key genes in bile acid synthesis leading to decreased intestinal bile acids and impaired weight gain. Furthermore, we hypothesize that activated Pparα displaces Fxr from shared DNA promoter regions, mediating coagulopathy by decreasing transcription of Fxr-dependent genes. This hypothesis will be tested with two specific aims. In Aim 1, PEU and healthy wild type mice treated with Pparα agonist or antagonist, along with PEU and healthy Pparα-/- mice, will be used to determine how Pparα drives changes in the expression of genes that regulate bile acid pool size by qPCR, bile acid concentrations by LC-MS/MS, and growth impairment over time. In Aim 2, wild type mice treated with Pparα and Fxr agonists and antagonists will be used to determine whether competitive DNA binding between the two nuclear receptors results in coagulopathy through transcriptional repression of Fxr-dependent coagulation factors; these studies will employ ChIP-seq, RNA-seq, and plasma coagulation measurements. Our expected outcomes are characterization of a novel molecular link, mediated by nuclear hormone receptors, between the regulation of bile acid homeostasis and coagulation, both of which are pathologically altered in PEU. Thes...