Perfluorooctanoic acid activates multiple nuclear receptor pathways and skews expression of genes regulating cholesterol homeostasis in liver of humanized PPARα mice fed an American diet

Abstract

Humans are exposed to per-and polyfluoroalkyl substances (PFAS) in their drinking water, food, air, dust in their homes, and by direct use of consumer products. Increased concentrations of serum total cholesterol and low density lipoprotein cholesterol are among the endpoints best supported by epidemiology. The objectives of this study were to generate a new model for examining PFAS-induced dyslipidemia and to conduct molecular studies to better define mechanism(s) of action. We tested the hypothesis that PFOA exposure at a human-relevant level dysregulates expression of genes controlling cholesterol homeostasis in livers of mice expressing human PPARα (hPPARα). Female and male hPPARα and PPARα null mice were fed a diet based on the "What we eat in America" analysis and exposed to perfluorooctanoic acid (PFOA) in drinking water (8 µM) for 6 weeks. This resulted in a serum PFOA concentration of 48 μg/ml. PFOA increased liver mass, which was associated with histologically-evident lipid accumulation. PFOA induced PPARα and constitutive androstane receptor target gene expression in liver.Expression of genes in four pathways regulating cholesterol homeostasis were also measured.PFOA decreased expression of Hmgcr in a PPARα-dependent manner. PFOA decreased expression of Ldlr and Cyp7a1 in a PPARα-independent manner. Apob expression was not changed. Gene expression in females appeared to be more sensitive to PFOA exposure than in males. This novel study design (hPPARα mice, American diet, long term exposure) generated new insight on the effects of PFOA on cholesterol regulation in the liver and the role of hPPARα.

Systemic PFOS and PFOA exposure and disturbed lipid homeostasis in humans: what do we know and what not?

“…This is seen by lower increase in transcripts and protein levels of PPARa target genes (Nakamura et al 2009;Nakagawa et al 2012). Still, in combination with these gene expression changes, PFOA-treated hPPARa mice showed increased lipid accumulation in liver (Nakagawa et al 2012;Schlezinger et al 2020). Actually, despite the reduced responsiveness of hPPARa to PFOA, hPPARa mice appeared to be substantially more susceptible to liver steatosis than the WT mice, as shown by larger increases in hepatic TG levels (Nakagawa et al 2012).…”

“…In parallel to the hypolipidemic effects in the blood, other lipid disturbances observed include enhanced intrahepatic accumulation of lipids, mainly TGs, in rodents for both PFOS (Bijland et al 2011;Wan et al 2012;Wang et al 2014), and PFOA (Nakagawa et al 2012;Tan et al 2013;Wang et al 2013;Das et al 2017;Hui et al 2017;Wu et al 2018;Schlezinger et al 2020) (see Table 2 for examples). The liver appears to be a major target organ for both compounds in rats and mice, as indicated by increased liver weight, hypertrophy of centrilobular hepatocytes, induction of peroxisomal and mitochondrial ß-oxidation, and in some cases necrosis.…”

“…In particular the transactivation of other nuclear receptors by PFOS/PFOA, such as PPARc, constitutive androstane receptor (CAR), pregnane X receptor (PXR), liver X receptor (LXR) and farsenoid X receptor (FXR), have been studied in rats and mice. It has been suggested that the nuclear receptors PPARc (Rosen, Lee, et al 2008), CAR (Rosen, Lee, et al 2008;Ren et al 2009;Abe et al 2017;Schlezinger et al 2020) and PXR (Ren et al 2009;Bjork et al 2011;Pouwer et al 2019), are also activated by PFOS/PFOA in the murine liver. These receptors are in general associated with cholesterol and TG homeostasis (Ory 2004;Yin et al 2011;, implying that they might also play a role in the effects induced by PFOS/PFOA.…”

Per‐ and Polyfluoroalkyl Substance Toxicity and Human Health Review: Current State of Knowledge and Strategies for Informing Future Research

“…Emerging animal toxicology and histology and human population data provide mechanistic clues that PFAS disrupt hepatic metabolism, leading to increased bile acid reuptake and lipid accumulation in liver (Salihovic et al 2020; Schlezinger et al 2020). A review of NAFLD and toxicant exposure concluded that PFAS are associated with early steatosis (“fatty liver”), the preclinical stage of NAFLD (Armstrong and Guo 2019).…”

“…Human PFAS lipid findings may be related to experimental findings of induced adipogenesis, impaired bile acid metabolism/synthesis, strongly decreased CYP7A1 enzyme activity, altered fatty acid transport, and intracellular lipid accumulation with steatosis, including in PPAR‐α‐null or PPAR‐α‐humanized animals (Guruge et al 2006; Lau et al 2007; Bijland et al 2011; Bjork et al 2011; Wang et al 2014; Filgo et al 2015; Das et al 2017; Salihovic et al 2019; Zhang et al 2019; Behr et al 2020a; Liu S et al 2020b; Schlezinger et al 2020). Independent of PFAS exposure, similar alterations in metabolic pathways have been related to disrupted fatty acid beta‐oxidation and increased free cholesterol in toxicology studies (Perla et al 2017).…”