Project description:Tert-Butylhydroquinone (tBHQ), a preservative used to prevent oxidative deterioration of oil, fat, and meat products, has been linked to both chemoprotective and adverse effects. This study investigates the impact of chronic dietary tBHQ on survival, growth parameters, organ development, and gene expression in zebrafish (Danio rerio). As tBHQ activates the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2a), a zebrafish line with a mutation in the DNA-binding domain was used to identify Nrf2a-dependent vs. independent effects. Homozygous Nrf2a wildtype (wt) and mutant (m) larvae were fed a diet containing 5% tBHQ or a control diet. Survival and growth parameters were assessed at 15 days and at 5 months, and samples collected for RNA sequencing at 5 months. Chronic dietary exposure to tBHQ throughout the larval and juvenile periods negatively impacted growth and survival. RNA-seq analysis found differentially expressed genes related to growth and development and upregulation of several immune pathways. The findings herein demonstrate that chronic dietary tBHQ exposure may impair growth and survival in both Nrf2a dependent and independent manners.
Project description:Polychlorinated biphenyls (PCBs) are persistent and ubiquitously distributed environmental pollutants. Based on their chemical structure, PCBs are classified into non-ortho substituted and ortho-substituted congeners. Non-ortho-substituted PCBs are structurally similar to dioxin or TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) and their mode of action and toxic effects are well established. In contrast, much less is known about the effects of ortho-substituted PCBs. Studies conducted so far have focused on tissue-specific effects but there is limited knowledge about the effects on the whole organism, particularly the sensitive developmental stages in vertebrates. Hence, in this study we investigated the effects of exposure to an environmentally relevant ortho-substituted PCB (2,2’,4,4’,5,5’-hexachlorobiphenyl; PCB153) on zebrafish embryos. We exposed zebrafish embryos to either DMSO (0.1%; solvent control) or three different concentrations of PCB153 (0.1, 1 and 10 μM) from 4 hours post-fertilization (hpf) to 120 hpf. At the end of the exposure, larvae were sampled for determining transcriptional changes (RNA sequencing) and the remaining embryos were maintained in contaminant-free environment. At 7 and 14 days post-fertilization (dpf), zebrafish larvae were assessed for locomotory behavior. We did not observe any overt phenotypes during the exposure period, but observed a spinal phenotype in the 10μM PCB153 treated group starting at 7 dpf. This phenotype was observed in a dose-dependent manner and majority of the embryos with this phenotype died by 14 dpf. RNA sequencing of 5 dpf larvae exposed to PCB153 also revealed dose-dependent changes in gene expression patterns. A total of 633, 2227, and 3378 differentially expressed genes were observed in 0.1, 1 and 10 μM PCB153 treated embryos, respectively. Among these, 301 genes were common to all treatment groups, and KEGG pathway analysis revealed enrichment of genes related to circadian rhythm, FOXO signaling and insulin resistance pathways. We are currently investigating the functions of genes that are uniquely altered by different PCB153 concentrations. Overall, these results suggest that developmental exposure to PCB153, a PCB congener highly prevalent in the environment, targets multiple physiological processes including photoperiod regulation and metabolism. [Funded by NIH P01ES021923 and NSF OCE-1314642].
Project description:Juvenile zebrafish were fed Biodiet starter (4% body weight per day) for 42 d with TCDD added at 0 ppb, 0.1 ppb, 1 ppb, 10 ppb or 100 ppb. Fish were collected, sexed, weighed and length measured at 0, 7, 14, 28 or 42 d for TCDD assessment, histopathologic and microarray analysis. Microarray experiments were conducted in TCDD-treated (at 0, 0.1, 1, 10 and 100 ppb) for male and female sexed zebrafish at 28 d. NimbleGen Gene Expression 12X135K zebrafish microarrays and One-Color DNA labeling Kit (NimbleGen, WI) were used for genome-wide expression analysis of TCDD-treated zebrafish. TCDD accumulated in a dose- and time-dependent manner and 100 ppb TCDD caused TCDD accumulation in female (15.49 ppb) and male (18.04 ppb) fish at 28 d post exposure. TCDD caused multiple lesions in liver, kidney, intestine and ovary of zebrafish and functional dysregulation such as depletion of glycogen in liver, retrobulbar edema, degeneration of neurosensory epithelium, underdevelopment of intestine, and diminution in the fraction of ovarian follicles containing vitellogenic oocytes. Microarray gene expression analysis comparing control to post TCDD diet revealed dysregulated genes located in pathways associated with cardiac necrosis/cell death, cardiac fibrosis, renal necrosis/cell death and liver necrosis/cell death. These baseline toxicological effects provide evidence for the potential biomarkers, mechanisms and pathology of TCDD induced dysregulation.