Validation of a Genomics-Based Hypothetical Adverse Outcome Pathway: 2,4-Dinitrotoluene Perturbs PPAR Signaling Thus Impairing Energy Metabolism and Exercise Endurance

2,4-dinitrotoluene (2,4-DNT) is a nitroaromatic used in industrial dyes and explosives manufacturing processes that is found as a contaminant in the environment. Previous studies have implicated antagonism of PPAR signaling as a principal process affected by 2,4-DNT. Here, we test the hypothesis that 2,4-DNT-induced perturbations in PPAR signaling and resultant downstream deficits in energy metabolism, especially from lipids, cause organism-level impacts on exercise endurance. PPAR nuclear activation bioassays demonstrated inhibition of PPAR signaling by 2,4-DNT whereas PPAR signaling increased. PPAR (-/-) and wild-type (WT) female mice were exposed for 14 days to vehicle or 2,4-DNT (134 mg/kg/day) and performed a forced swim to exhaustion 1 day after the last dose. 2,4-DNT significantly decreased body weights and swim times in WTs, but effects were significantly mitigated in PPAR (-/-) mice. 2,4-DNT decreased transcript expression for genes downstream in the PPAR signaling pathway, principally genes involved in fatty acid transport. Results indicate that PPAR signaling increased resulting in enhanced cycling of lipid and carbohydrate substrates into glycolytic/gluconeogenic pathways favoring energy production versus storage in 2,4-DNT-exposed WT and PPAR (-/-) mice. PPAR (-/-) mice appear to have compensated for the loss of PPAR by shifting energy metabolism to PPAR-independent pathways resulting in lower sensitivity to 2,4DNT when compared with WT mice. Our results validate 2,4-DNTinduced perturbation of PPAR signaling as the molecular initiating event for impaired energy metabolism, weight loss, and decreased exercise performance.