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Transcriptional profilling of liver from C57BL/6 wildtype and PPARα-knockout mice treated with PFOA and GenX after 20 weeks of high-fat diet

ABSTRACT: Perfluoroalkyl substances (PFAS) are man-made chemicals with suspected endocrine-disrupting properties. Exposure to perfluorooctanoic acid (PFOA) has been linked to disturbed metabolism via the liver, although the exact mechanism is not clear. Moreover, information on the metabolic effects of the new PFAS alternative GenX is limited. We tested whether low-dose exposure to PFOA and GenX induces metabolic disturbances, including NAFLD, dyslipidemia, and glucose tolerance in mice and studied the involvement of PPARα. To this end, male C57BL/6J wildtype and PPARα−/− mice were given 0.05 or 0.3 mg/kg bw/day PFOA, or 0.3 mg/kg bw/day GenX next to a high-fat diet for 20 weeks. RNA sequencing was performed on liver, next to thorough assesment of metabolic parameters. RNA sequencing revealed that whereas the effects of GenX are entirely dependent on PPARα, effects of PFOA are mostly dependent on PPARα. In the absence of PPARα, the involvement of PXR/CAR becomes more prominent. Exposure to high-dose PFOA in mice decreased body weights and increased liver weights in wildtype and PPARα−/− mice. High-dose but not low-dose PFOA reduced plasma triglycerides and cholesterol, which for triglycerides, showed PPARα dependency. PFOA and GenX increased hepatic triglycerides in a PPARα-dependent manner. Overall, we show that long-term and low-dose exposure to PFOA and GenX disrupts lipid metabolism in mice. Whereas the effects of PFOA are mediated by multiple nuclear receptors, effects of GenX are entirely mediated by PPARα. Our data underscore the potential of PFAS to disrupt metabolism by altering signaling pathways in the liver.

ORGANISM(S): Mus musculus

PROVIDER: GSE212294 | GEO | 2022/09/02

REPOSITORIES: GEO

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Project description:Background: Previous epidemiological studies have repeatedly found per- and polyfluoroalkyl substances (PFAS) exposure associated with higher circulating cholesterol, one of the greatest risk factors for development of coronary artery disease. The main route of cholesterol catabolism is through its conversion to bile acids, which circulate between the liver and ileum via enterohepatic circulation. Patients with coronary artery disease have decreased bile acid excretion, indicating that PFAS-induced changes of enterohepatic circulation may play a critical role in cardiovascular risk. Objectives: Using a mouse model with high LDL-VLDL cholesterol and aortic lesion development similar to humans, the current study investigates mechanisms linking exposure to a PFAS mixture with increased cholesterol. Methods: Male and female Ldlr-/- mice were fed an atherogenic diet (Clinton/Cybulsky low fat, 0.15% cholesterol) and exposed to a mixture of 5 PFAS representing legacy, replacement, and emerging subtypes (i.e., PFOA, PFOS, PFNA, PFHxS, GenX), each at a concentration of 2 mg/L, for 7 weeks. Blood was collected longitudinally for cholesterol measurements and mass spectrometry was used to measure circulating and fecal bile acids. Transcriptomic analysis of ileal samples was performed via RNA-sequencing. Results: After 7 weeks of PFAS exposure, average circulating PFAS levels were measured at 21.6, 20.1, 31.2, 23.5, and 1.5 µg/mL in PFAS-exposed females and 12.9, 9.7, 23, 14.3, and 1.7 µg/mL in PFAS-exposed males for PFOA, PFOS, PFHxS, PFNA, and GenX, respectively. PFAS exposure led to elevated circulating cholesterol levels after 7 weeks compared to vehicle mice, with females increasing 18% and males increasing 24%. Total circulating bile acid levels were elevated in PFAS-exposed mice by 230% in males and 290% in females compared to vehicle. PFAS decreased fecal bile acid levels by 62% in females and 59% in males. In the ileum, expression levels of the bile acid reuptake transporter ASBT were increased due to PFAS exposure. Discussion: Mice exposed to a PFAS mixture display increased circulating cholesterol and bile acids perhaps due to changes in enterohepatic circulation. This study implicates PFAS-mediated effects at the site of the ileum as a possible critical mediator of increased cardiovascular risk due to PFAS.

Project description:Per- and polyfluoroalkyl substances (PFAS) are some of the most prominent organic contaminants in human blood that have the potential to disrupt biological processes and pathways in the liver. Although the toxicological implications from human exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are well established, data on other, lesser-understood PFAS are limited. A challenge for regulatory authorities is to determine acceptable levels of human exposure to large, diverse classes of environmental contaminants. New approach methodologies (NAMs) that apply bioinformatics tools to interpret biological data are being increasingly considered to inform risk assessment when traditional toxicology methodologies are not amenable. The aim of the current investigation was to identify the biological responses relevant to PFAS mode of action as the concentration (benchmark dose) that these effects take place in order to utililze this information to inform/facilitate read-across for risk assessment of data-poor PFAS. A TempO-Seq platform (BioSpyder) measured gene expression changes in human liver microtissues (i.e., spheroids) after 1-day and 10-day exposures to increasing concentrations of PFAS. A bioinformatics framework was applied to 23 PFAS sub-classed into carboxylates (PFCAs), sulfonates (PFSAs), or PFAS precursors that were analyzed for the total altered transcripts, the concentration where effects take place, and identifying target genes of interest. Both PFCAs and PFSAs exhibited a trend toward increased transcriptional changes with carbon chain-length. Specifically, longer-chain compounds (7 to 10 carbons) were more likely to surpass liver-toxic transcriptomic thresholds established from previous studies than shorter chain PFAS. Longer-chain PFAS were also more potent, inducing transcriptional effects at lower concentrations. However, PFOS was the most potent PFAS and of all precursors, only PFOSA (a PFOS precursor) induced a response. The combined high-throughput transcriptomic and bioinformatics analyses revealed the capability of NAMs to assess the effects of PFAS in liver microtissues; such data improves our understanding of PFAS-related effects in humans and facilitates the use of read-across in human health risk assessment for other data-poor chemicals.

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Transcriptional profilling of liver from C57BL/6 wildtype and PPARα-knockout mice treated with PFOA and GenX after 20 weeks of high-fat diet

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