Gene expression and pathologic alterations in juvenile rainbow trout due to chronic dietary TCDD exposure

Abstract

The goal of this project was to use functional genomic methods to identify molecular biomarkers as indicators of the impact of TCDD exposure in rainbow trout. Specifically, we investigated the effects of chronic dietary TCDD exposure on whole juvenile rainbow trout global gene expression associated with histopathological analysis. Juvenile rainbow trout were fed Biodiet starter with TCDD added at 0, 0.1, 1, 10 and 100 ppb (ng TCDD / g food), and fish were sampled from each group at 7, 14, 28 and 42 days (d) after initiation of feeding. 100 ppb TCDD caused 100% mortality at 39 d. Fish fed with 100 ppb TCDD food had TCDD accumulation of 47.37 ppb (ng TCDD / g fish) in whole fish at 28 d. Histological analysis from TCDD-treated trout sampled from 28 d and 42 d revealed that obvious lesions were found in skin, oropharynx, liver, gas bladder, intestine, pancreas, nose and kidney. In addition, TCDD caused anemia in peripheral blood, decreases in abdominal fat, increases of remodeling of fin rays, edema in pericardium and retrobulbar hemorrhage in the 100 ppb TCDD-treated rainbow trout compared to the control group at 28 d. Dose- and time-dependent global gene expression analyses were performed using the cGRASP 16,000 (16K) cDNA microarray. TCDD-responsive whole body transcripts identified in the microarray experiments have putative functions involved in various biological processes including growth, cell proliferation, metabolic process, and immune system processes. Nine microarray-identified genes were selected for QPCR validation. CYP1A3 and CYP1A1 were common up-regulated genes and HBB1 was a common down-regulated gene among each group based on microarray data, and their QPCR validations are consistent with microarray data for the 10 and 100 ppb TCDD treatment groups after 28-d exposure (p< 0.05). In addition, in the 100 ppb group at 28d, expression of complement component C3-1 and trypsin-1 precursor have a more than 10-fold induction from the microarray experiments, and their QPCR validations are consistent and showed significant induction in the 100 ppb group at 28d (p< 0.05). Overall, lesion in nasal epithelium is a novel and significant result in this study, and TCDD-responsive rainbow trout transcripts identified in the present study may lead to the development of new molecular biomarkers for assessing the potential impacts of environmental TCDD on rainbow trout populations.

Histopathologic Alterations Associated with Global Gene Expression Due to Chronic Dietary TCDD Exposure in Juvenile Zebrafish

“…In zebrafish, embryonic exposure to TCDD reduces the number of neurons in the larval brain [50] and causes apoptosis in midbrain [51] . We reported the first evidence of TCDD-induced morphologic lesions in the olfactory organ of rainbow trout [38] , in this study we found similar results from TCDD-treated zebrafish that exhibited highly disorganized and poorly differentiated hyperplastic lamellae ( Figure 5 ). Evidence of TCDD-induced lesions in nasal epithelium of teleost is similar to results in rats which show hyperplastic and metaplastic changes within the nasal mucosa after chronic administration by gavage with TCDD [52] .…”

“…In adult fish, TCDD causes hepatic lipidosis and hypertrophy, glycogen depletion in liver, inhibition of fin regeneration and altered gonadogenesis [11], [36], [37]. In juvenile fish, the TCDD-induced lesions observed reflect similarity to exposed embryo/larvae and adults, including craniofacial malformations, degeneration in fin and gill, and altered pigmentation [25], [38].…”

“…We used much higher levels of TCDD in the laboratory since we wished to investigate the mechanisms of dietary TCDD toxicity in zebrafish, which are much more resistant to the toxic effects of TCDD than are salmonids using other means of exposure [26]–[28], [60]–[61]. In a recently published parallel study using rainbow trout [38], we found that dietary TCDD caused overt toxicity in juvenile rainbow trout at wide range (from 0.1 ppb to 100 ppb). Zebrafish in this study were more resistant to dietary TCDD exposure as indicated by lower observed mortality and fewer pathologic alterations in the lower dose groups.…”

The Aryl Hydrocarbon Receptor: A Key Bridging Molecule of External and Internal Chemical Signals

“…140 Microarray analysis found that genes involved in the immune system processes and immune response to stimuli were the most sensitive potential targets in juvenile rainbow trout fed with TCDD (10 and 100 ng TCDD/g food). 141 Immunologic toxicities such as decreased immune organ mass, lymphoid cell numbers and apoptotic thymocytes were also observed in chicken embryos with PCB-126 exposure. 142,143 Offspring from TCDD-exposed domestic chickens exhibited B cell suppression in their adulthood.…”

Immunotoxicity of Xenobiotics in Fish: A Role for the Aryl Hydrocarbon Receptor (AhR)?

“…The downregulation was observed for genes encoding for complement factors and for bacterioloytic proteins, such as lysozyme. Likewise, studies on the impact of TCDD on global gene expression in whole body extracts of zebrafish, Danio rerio, and rainbow trout revealed a general downregulation of immune gene transcripts [178,179]. Similarly, liver transcriptomes of fishes exposed to xenobiotic AhR agonists displayed prominent changes in immune pathways (e.g., [180,181]).…”