Molecular mechanisms of the toxicity of perfluorooctanoic acid (PFOA)

全氟辛酸（PFOA）是一种工业化学品，用于制造具有防油，防污和防水性能的许多产品。PFOA耐化学、热和生物降解，同时已成为土壤、水、空气和食品的全球污染物。全氟辛酸的毒理学数据令人担忧，因为该物质已被证明会损害啮齿动物的肝脏并损害胚胎发育。目前，PFOA对人类的潜在危害存在争议。我们自己的初步研究表明，在分子水平上，PFOA影响人类原代肝细胞中不同的信号传导和代谢途径。具体而言，PFOA在人肝细胞中引起（i）过氧化物酶体增殖物激活受体α（PPARalpha）的激活，（ii）肝细胞核因子4 α（HNF 4 α）的抑制，以及（iii）通过增强原癌基因c-Jun和c-Fos的表达调节AP-1转录因子的活性。在动物模型中也观察到PFOA介导的PPARalpha激活，而PFOA对转录因子HNF 4 alpha和AP-1的影响迄今尚未在这些动物模型中报道。因此，这些影响可能是本提案重点关注的人类特有影响。转录因子HNF 4 α在胚胎发生、肝脏发育以及脂质和能量代谢中具有中心功能。HNF 4 α活性降低可能促进糖尿病。该项目的重点是PFOA和HNF 4 α之间假定的直接相互作用的表征，以及PFOA对胰腺β细胞的假定损伤。在AP-1转录因子的情况下，c-Fos表达的增加与细胞增殖的增强相关。因此，将检查PFOA对细胞周期控制的影响。基于AP-1复合物的活性不仅通过AP-1组分（如c-Fos）的表达，而且通过这些组分的磷酸化来调节这一事实，将表征PFOA对磷酸化级联的影响，最后，旨在鉴定假定的膜受体，该膜受体被提议作为细胞外配体被PFOA刺激，从而触发磷酸化，综上所述，这些研究结果将有助于在分子水平上了解PFOA在人类肝细胞中的新作用模式。此外，它们将大大有助于PFOA的实际毒理学风险评估。

Perfluorooctanoic acid (PFOA) is an industrial chemical that is used for the fabrication of numerous products with oil-, dirt- and water-repellent properties. PFOA is resistant to chemical, thermal and biological degradation and has become a global contaminant of soil, water, air and food in the meantime. The toxicological data of PFOA give cause for concern as the substance was shown to damage the liver of rodents and to impair embryo development. Currently, the hazard potential of PFOA for humans is controversially discussed. Our own preliminary studies revealed that on the molecular level PFOA affects different signalling and metabolic pathways in human primary hepatocytes. Concretely, PFOA caused in human liver cells (i) an activation of peroxisome proliferator-activated receptor alpha (PPARalpha), (ii) an inhibition of hepatocyte nuclear factor 4 alpha (HNF4alpha), and (iii) a modulation of the activity of the AP-1 transcription factor via an enhanced expression of the proto-oncogenes c-Jun and c-Fos. PFOA-mediated activation of PPARalpha has also been observed in the animal models whereas effects of PFOA on the transcription factors HNF4alpha and AP-1 have not been reported so far for these animal models. Therefore, these effects might be human-specific effects which are in the focus of this proposal. The transcription factor HNF4alpha has central functions in embryogenesis, liver development and in lipid and energy metabolism. Reduced HNF4alpha activity may promote diabetes. This project focuses on the characterisation of the postulated direct interaction between PFOA and HNF4alpha as well as on a putative impairment of pancreatic beta-cells by PFOA. In the case of the AP-1 transcription factor an increased expression of c-Fos correlates with an enhanced cellular proliferation. Therefore, the impact of PFOA on cell cycle control will be examined. Based on the fact that the activity of the AP-1 complex is regulated not only via the expression of the AP-1 components such as c-Fos but also via the phosphorylation of these components, the impact of PFOA on this phosphorylation cascade will be characterised, finally aiming on the identification of the postulated membrane receptor that is proposed to be stimulated by PFOA as an extracellular ligand thereby triggering the phosphorylation cascade mentioned above.Taken together, the results of these studies will contribute to the understanding of novel modes of action of PFOA in human liver cells on the molecular level. Moreover, they will substantially contribute to the actual toxicological risk assessment of PFOA.