PROJECT SUMMARY Millions of Americans are exposed daily to per- and polyfluoroalkyl substances (PFAS) due to the current and historical use of these chemicals in consumer and industrial products. PFAS exposure in humans is associated with liver disease and serum hyperlipidemia (increased serum cholesterol, in particular). However, understanding the mechanism(s) linking PFAS exposure to dyslipidemia is hindered by 1) the ability of PFAS to activate peroxisome proliferator activated receptor α (PPARα), a receptor activated by fibrate drugs that reduces serum triacylglycerides, 2) apparently disparate effects of PFAS on serum lipids in human and rodents (in which PFAS can decrease serum lipids), 3) lack of understanding if/how PFAS congeners exert distinct effects on lipid homeostasis, and 4) species differences in nuclear receptors that regulate PFAS-induced effects. Our overarching objective is to determine the mechanisms by which PFAS disrupt systemic lipid homeostasis. Our research focuses on nuclear receptors that are activated by PFAS and are directly involved in lipid regulation: PPARα, constitutive androstane receptor (CAR), and pregnane X receptor (PXR). PPARα activation decreases hepatic and serum lipids while CAR and PXR activation can have the opposite effect. There are two major chemical classes of PFAS: perfluoroalkyl carboxylic acids (PFCA) and perfluoroalkyl sulfonic acids (PFSA). We used a human-relevant model in vitro to show that PFCA and PFSA activate human PPARα (huPPARα) with differing efficacies. Using mice expressing huPPARα and fed an American diet, we showed that: 1) perfluorooctanoic acid (PFOA) activates hepatic huPPARα in vivo at body burdens found in humans, 2) CAR and PXR also are strongly activated, 3) PFOA increases liver lipids and serum cholesterol, and 4) PFOA’s effects are sex-dependent. Given the strength of the PFAS-induced CAR/PXR signal, the potential for CAR/PXR to differentiate the effects of PFCAs and PFSAs, and that CAR/PXR also are activated in a species-specific manner, we propose that the most human relevant in vivo model should be multi-humanized. Thus, our Specific Aims are as follows. In Aim 1, we will refine our novel mouse model to investigate human relevant mechanisms of PFAS action by incorporating human CAR (huCAR) and PXR (huPXR) into the huPPARα mouse and update our novel “What we eat in America” diet. In Aim 2, we will test the contribution of huPPARα to PFAS-induced toxicological effects in vivo in the context of huCAR and huPXR by comparing effects in huPPARα+:huCAR+:huPXR+ and PPARαNull(mouse/human):huCAR+:huPXR+ mice exposed to human-relevant PFAS levels. We will test the hypotheses that a) activation of PPARα by PFAS limits their capacity to stimulate hepatic steatosis and serum hyperlipidemia by counteracting effects of CAR/PXR activation and b) PFAS structure will determine the balance of huPPARα:huCAR/huPXR activation resulting in differences in toxicological effects. Results will fill critical gaps by generating an in vivo, human-relevant model to investigate PFAS-induced, clinically-relevant disease and providing novel insights into the mechanisms of action of PFAS in liver and intestine.

PROJECT NARRATIVE Americans are exposed daily to per- and polyfluoroalkyl substances (PFAS) in their drinking water, food and air. PFAS cause adverse birth outcomes, suppress vaccine responses, and induce metabolic disease in people, although how this happens is unknown. We propose to determine how PFAS cause adverse health effects, focusing on metabolic disease in humans, by developing tools that focus on essential molecular regulators of lipids, the nuclear receptors PPARα, CAR and PXR.