2,3,7,8-Tetrachlorodibenzo-p-dioxin abolishes circadian regulation of hepatic metabolic activity in mice

Abstract

Aryl hydrocarbon receptor (AhR) activation is reported to alter the hepatic expression of circadian clock regulators, however the impact on clock-controlled metabolism has not been thoroughly investigated. This study examines the effects of AhR activation on hepatic transcriptome and metabolome rhythmicity in male C57BL/6 mice orally gavaged with 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) every 4 days for 28 days. TCDD diminished the rhythmicity of several core clock regulators (e.g. Arntl , Clock , Nr1d1 , Per1 , Cry1 , Nfil3 ) in a dose-dependent manner, involving either a ≥ 3.3-fold suppression in amplitude or complete loss of oscillation. Accordingly, protein levels (ARNTL, REV-ERBα, NFIL3) and genomic binding (ARNTL) of select regulators were reduced and arrhythmic following treatment. As a result, the oscillating expression of 99.6% of 5,636 clock-controlled hepatic genes was abolished including genes associated with the metabolism of lipids, glucose/glycogen, and heme. For example, TCDD flattened expression of the rate-limiting enzymes in both gluconeogenesis ( Pck1 ) and glycogenesis ( Gys2 ), consistent with the depletion and loss of rhythmicity in hepatic glycogen levels. Examination of polar hepatic extracts by untargeted mass spectrometry revealed that virtually all oscillating metabolites lost rhythmicity following treatment. Collectively, these results suggest TCDD disrupted circadian regulation of hepatic metabolism, altering metabolic efficiency and energy storage.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) dysregulates hepatic one carbon metabolism during the progression of steatosis to steatohepatitis with fibrosis in mice

“…Using this dosing regimen, oral gavage of 30 µg/kg TCDD resulted in mouse hepatic tissue levels comparable to serum levels reported in Viktor Yushchenko following intentional poisoning, while 0.01 µg/kg TCDD increased hepatic levels compared to background levels in control mouse liver, and were comparable to the level of dioxin-like compounds in the serum of US, German, Spanish and United Kingdom populations 23,[55][56][57][58][59][60] . Similar doses and/or treatment regimens have been used in previous studies from this lab as well as other groups 33,44,[61][62][63] . Although there was an increase in serum ALT levels following oral gavage with 30 µg/kg TCDD every 4 days for 28 days for a total of 7 treatments, there was no evidence of overt toxicity, no body weight loss > 15%, no significant change in food consumption, and no histopathological evidence of necrosis or apoptosis 23,33,64 .…”

“…Similar doses and/or treatment regimens have been used in previous studies from this lab as well as other groups 33,44,[61][62][63] . Although there was an increase in serum ALT levels following oral gavage with 30 µg/kg TCDD every 4 days for 28 days for a total of 7 treatments, there was no evidence of overt toxicity, no body weight loss > 15%, no significant change in food consumption, and no histopathological evidence of necrosis or apoptosis 23,33,64 . Consequently, the dose-dependent effects of TCDD on OCM, the SAM/SAH ratio and the biosynthesis of polyamines and creatine cannot be attributed to overt toxicity.…”

Single-Nuclei RNA Sequencing Assessment of the Hepatic Effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin

“…The impact of diurnal rhythm in large studies places additional logistic constraints regarding sample collection within a specific time window. 21 Most importantly, it is difficult to predict how treatment and/or disease pathologies impact cell populations, structure and viability, digestion efficacy, and cell type selection for single-cell analysis without extensive a priori validation. Nuclei-based approaches address many of these challenges and produce results comparable to single-cell approaches.…”

Metabolism-Disrupting Chemicals and the Constitutive Androstane Receptor CAR

“…In addition, AhR activation may also lead to upregulation of CAR expression [ 249 ], perhaps as a secondary counteracting effect of the metabolic disruption. It is unclear if this is a direct transcriptional effect or due to AhR-mediated disruption of circadian regulation [ 250 ].…”