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)?. FXR is activated in the fed state by bile acids, while PPAR? 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 Ppar? activation, Fxr signal loss, and transcriptional repression of genes that promote bile acid synthesis and coagulation. Based on these findings, our hypothesis is that Ppar? 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 Ppar? 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 Ppar? agonist or antagonist, along with PEU and healthy Ppar?-/- mice, will be used to determine how Ppar? 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 Ppar? 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. These studies will provide the foundation for developing new pharmacologic and diet-based therapeutic strategies that could ultimately be generalizable to children with weight loss due to a variety of medical and socioeconomic causes. Geoffrey A. Preidis, M.D., Ph.D. is currently a fellow in Pediatric Gastroenterology, Hepatology, and Nutrition at Baylor College of Medicine. He has a strong publication record in metagenomics, global health, and nutrition research with children and animal models of PEU. His long-term goal is to become an independent NIH-funded physician-scientist investigating co-morbidities that result from nutrient deprivation early in life.
These research aims support the PI?s career development by building upon his background in pediatric gastroenterology and graduate work in metagenomics, with new training in nuclear receptor biology and advanced applications of high- throughput sequencing and bioinformatic analysis. Additional key elements of the training plan include: 1) A mentorship and advisory team of internationally recognized, independently funded investigators with expertise in all aspects of the development plan, including David Moore, Ph.D. (nuclear receptor biology), Aleksandar Milosavljevic, Ph.D. (genome-wide bioinformatics), and Robert Shulman, M.D. (clinical translational research and pediatric gastroenterologist academic career development); 2) Advanced coursework in nuclear receptor biology and bioinformatics from the Baylor College of Medicine Graduate School of Biomedical Sciences, Cold Spring Harbor Laboratory, FASEB Science Research Conferences, and Keystone Symposia; and 3) Scholarly activities designed to foster independence. The PI?s training environment is a premiere academic research institution closely allied with the world?s largest medical center, the nation?s largest children?s hospital, and the NIH-funded Texas Medical Center Digestive Disease Center. This environment will provide a collaborative, supportive, and productive atmosphere to facilitate completion of all research aims and development goals in the proposed timeline. In summary, this training plan will place the PI on a direct route to a successful career as an independent investigator while identifying novel pathways by which liver function impairments in PEU develop and may ultimately be prevented and treated.
Protein-energy undernutrition is the most pressing health problem facing children today, contributing to half of all global child deaths, affecting more than 1% of children in the United States, and producing co-morbid liver function abnormalities that make it difficult for an undernourished child to re-gain weight. The goal of this proposal and our long term goals are to understand how early-life undernutrition impacts two aspects of liver function, regulation of bile acid levels and coagulation. Results from these studies will uncover novel mechanisms by which these two fundamental processes are regulated, and will facilitate the development of new therapies that will reduce mortality, hospitalizations, and medical costs, improving the quality of life for children with profound weight loss due to multiple medical and socioeconomic causes.
