Impaired liver function in Xenopus tropicalis exposed to benzo[a]pyrene: transcriptomic and metabolic evidence

Abstract

BackgroundDespite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropogenic stresses, the role pollutants play in the decline of amphibian populations remains unclear. Amongst the most common aquatic contaminants, polycyclic aromatic hydrocarbons (PAHs) have been shown to induce several adverse effects on amphibian species in the larval stages. Conversely, adults exposed to high concentrations of the ubiquitous PAH, benzo[a]pyrene (BaP), tolerate the compound thanks to their highly efficient hepatic detoxification mechanisms. Due to this apparent lack of toxic effect on adults, no studies have examined in depth the potential toxicological impact of PAH on the physiology of adult amphibian livers. This study sheds light on the hepatic responses of Xenopus tropicalis when exposed to high environmentally relevant concentrations of BaP, by combining a high throughput transcriptomic approach (mRNA deep sequencing) and a characterization of cellular and physiological modifications to the amphibian liver.ResultsTranscriptomic changes observed in BaP-exposed Xenopus were further characterized using a time-dependent enrichment analysis, which revealed the pollutant-dependent gene regulation of important biochemical pathways, such as cholesterol biosynthesis, insulin signaling, adipocytokines signaling, glycolysis/gluconeogenesis and MAPK signaling. These results were substantiated at the physiological level with the detection of a pronounced metabolic disorder resulting in a possible insulin resistance-like syndrome phenotype. Hepatotoxicity induced by lipid and cholesterol metabolism impairments was clearly identified in BaP-exposed individuals.ConclusionsOur data suggested that BaP may disrupt overall liver physiology, and carbohydrate and cholesterol metabolism in particular, even after short-term exposure. These results are further discussed in terms of how this deregulation of liver physiology can lead to general metabolic impairment in amphibians chronically exposed to contaminants, thereby illustrating the role xenobiotics might play in the global decline in amphibian populations.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-666) contains supplementary material, which is available to authorized users.

Concomitant exposure to benzo[a]pyrene and triclosan at environmentally relevant concentrations induces metabolic syndrome with multigenerational consequences in Silurana (Xenopus) tropicalis

“…The frozen sections of liver were stained with Hematoxylin and Erythrosin (HE) and Gomori's trichrome to study tissue organization, with Oil Red O (ORO) to assess total lipid hepatic content and with Periodic Acid Schiff (PAS) staining to assess glycogen content. All staining and procedures have been previously described in Regnault et al (2014). PAS scoring was performed by two people independently.…”

“…The PAS staining score (0-4) was assigned according to the percentage of glycogen in the cells, with a score of 0 corresponding to no glycogen, and a score of 4 corresponding to a cell full of glycogen. For ORO, lipid quantifications were performed as previously described (Regnault et al, 2014). In short, an image segmentation was processed using R, G and B layer similarity, with the default sharpness and compactness parameters.…”

“…Insulin production was quantified by immunohistochemistry on frozen pancreas sections as previously described (Regnault et al, 2014).…”

“…Read mapping and gene expression quantification and differential analysis were performed using Trimmomatic (v0.32.1) (Bolger et al, 2014), Bowtie-0.12.7 / TopHat 2 (v0.6) software (Trapnell et al, 2009), Cufflinks (v0.0.7), Cuffmerge (v0.0.6) and Cuffdiff (v0.0.7) (Trapnell et al, 2012) tools implemented in a Galaxy pipeline( http://galaxyproject.org).Differentially expressed genes were subjected to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and General Ontology terms (GO-term) enrichment analysis, using the online functional annotation tool DAVID (Database for Annotation, Visualisation and Integrated Discovery, http://david.abcc.ncifcrf.gov) (Huang et al, 2009) as previously described (Regnault et al, 2014).…”

“…However, despite experimental evidence from mammals and epidemiological correlations in humans suggesting that ED could induce metabolic diseases (Alonso-Magdalena et al, 2010;Jiang et al, 2014;Chevalier and Fénichel, 2015a;Chevalier and Fénichel, 2015b;Susiarjo et al, 2015;Fénichel, 2016, Medic-Stojanoska, 2019), their potential involvement in metabolic disorders associated with amphibian population decline has been largely neglected. The first evidence that ED could alter frog metabolism was shown in S. tropicalis after acute exposure to the suspected ED triclosan A C C E P T E D M A N U S C R I P T 4 (TCS) (Regnault et al, 2016) and the well-known benzo[a]pyrene (BaP) (Regnault et al, 2014(Regnault et al, , 2016. More recently, two independent controlled exposures of S. tropicalis throughout their life cycle to these two ED at environmentally relevant concentrations induced a metabolic syndrome featuring a pre-diabetes state.…”