A data-driven transcriptional taxonomy of adipogenic chemicals to identify white and brite adipogens

Abstract

Background: Chemicals in disparate structural classes activate specific subsets of the transcriptional programs of peroxisome proliferator-activated receptor-y (PPARy) to generate adipocytes with distinct phenotypes. Objectives: Our objectives were to a) establish a novel classification method to predict PPARy ligands and modifying chemicals; and b) create a taxonomy to group chemicals on the basis of their effects on PPARy' s transcriptome and downstream metabolic functions. We tested the hypothesis that environmental adipogens highly ranked by the taxonomy, but segregated from therapeutic PPARy ligands, would induce white but not brite adipogenesis. Methods: 3T3-L1 cells were differentiated in the presence of 76 chemicals (negative controls, nuclear receptor ligands known to influence adipocyte biology, potential environmental PPARy ligands). Differentiation was assessed by measuring lipid accumulation. mRNA expression was determined by RNA-sequencing (RNA-Seq) and validated by reverse transcription-quantitative polymerase chain reaction. A novel classification model was developed using an amended random forest procedure. A subset of environmental contaminants identified as strong PPARy agonists were analyzed by their effects on lipid handling, mitochondrial biogenesis, and cellular respiration in 3T3-L1 cells and human preadipocytes. Results: We used lipid accumulation and RNA-Seq data to develop a classification system that a) identified PPARy agonists; and b) sorted chemicals into likely white or brite adipogens. Expression of Cidec was the most efficacious indicator of strong PPARy activation. 3T3-L1 cells treated with two known environmental PPARy ligands, tetrabromobisphenol A and triphenyl phosphate, which sorted distinctly from therapeutic ligands, had higher expression of white adipocyte genes but no difference in Pgcla and Ucpl expression, and higher fatty acid uptake but not mitochondrial biogenesis. Moreover, cells treated with two chemicals identified as highly ranked PPARy agonists, tonalide and quinoxyfen, induced white adipogenesis without the concomitant health-promoting characteristics of brite adipocytes in mouse and human preadipocytes. Discussion: A novel classification procedure accurately identified environmental chemicals as PPARy ligands distinct from known PPARy-activating therapeutics. Conclusion: The computational and experimental framework has general applicability to the classification of as-yet uncharacterized chemicals.