A Data-Driven Transcriptional Taxonomy of Adipogenic Chemicals to Identify Emerging Metabolic Health Threats

Abstract

BackgroundChemicals in disparate structural classes activate specific subsets of PPAR{gamma}s transcriptional programs to generate adipocytes with distinct phenotypes. ObjectivesOur objectives were to 1) establish a novel classification method to predict PPAR{gamma} ligands and modifying chemicals, and 2) create a taxonomy to group chemicals based on their effects on PPAR{gamma}s transcriptome and downstream metabolic functions. We tested the hypothesis that environmental adipogens highly ranked by the taxonomy, but segregated from therapeutic PPAR{gamma} ligands, would induce white but not brite adipogenesis. Methods3T3-L1 cells were differentiated in the presence of 76 chemicals (negative controls, nuclear receptor ligands known to influence adipocyte biology, potential environmental PPAR{gamma} ligands). Differentiation was assessed by measuring lipid accumulation. mRNA expression was determined by RNA-Seq and validated by RT-qPCR. A novel classification model was developed using an amended random forest procedure. A subset of environmental contaminants identified as strong PPAR{gamma} agonists were analyzed by their effects on lipid handling, mitochondrial biogenesis and cellular respiration in 3T3-L1 cells and human preadipocytes. ResultsWe used lipid accumulation and RNA sequencing data to develop a classification system that 1) identified PPAR{gamma} agonists, and 2) sorted chemicals into likely white or brite adipogens. Expression of Cidec was the most efficacious indicator of strong PPAR{gamma} activation. Two known environmental PPAR{gamma} ligands, tetrabromobisphenol A and triphenyl phosphate, which sorted distinctly from therapeutic ligands, induced white adipocyte genes but failed to induce Pgc1a and Ucp1, and induced fatty acid uptake but not mitochondrial biogenesis in 3T3-L1 cells. Moreover, two chemicals identified as highly ranked PPAR{gamma} agonists, tonalide and quinoxyfen, induced white adipogenesis without the concomitant health-promoting characteristics of brite adipocytes in mouse and human preadipocytes. DiscussionA novel classification procedure accurately identified environmental chemicals as PPAR{gamma} ligands distinct from known PPAR{gamma}-activating therapeutics. The computational and experimental framework has general applicability to the classification of as-yet uncharacterized chemicals.