The dose- and time-dependent effects of perfluorooctanoic acid on rat liver

We reported the hepatic gene expression profiling in male Sprague-Dawley rats treated by different concentrations of perfluorooctanoic acid (PFOA) for 7, 14, and 28 days. We confirmed that PFOA induced liver tumor formation was mainly through the activation of peroxisome proliferator-activated receptor α (PPARα). We identified a panel of 7 genes (Cyp4a1, Nr1d1, Acot2, Vnn, Ehhadh, and Acot1) that might serve as the biomarkers for PPARα activation. We also meausred the apical endpoints of PPARα activation and found a good correlation with the expression level of these biomarker genes. Consitituitive androstane receptor mediated Cyp2b enzymatic activity and gene expression was also upregulated by PFOA in a dose-response manner. On the other hand, acyl hydrocarbon receptor (AhR) target gene Cyp1a2 were significantly downregulated at all time points studied. To our surprise, results of KEGG and Reactome pathway analyses suggested that PFOA did not drive the cell cycles and proliferations in the liver. While some of the DNA replication genes such as Pold2 and Mcm8 were upregulated by PFOA treatment, several key cyclin-dependent cell growth genes, including Ccnd1, Ccne2, Ccnb1, and Ccna2 were all significantly downregulated by PFOA in a dose-dependent manner, especailly at 28 days. Ingenuity Pathway Analysis also indicated that PFOA led to a suppression of liver cancer related pathways at later time points studied. These results suggest that while PFOA clearly induced PPARα activation, the increased cell growth (the second key event in the tumor mode of action), was transient and tightly regulated by feedback mechanisms. Whether such changes will eventually cause the formation of preneoplastic foci and liver tumors in rats remains unclear.本数据集报道了经不同浓度全氟辛酸（perfluorooctanoic acid, PFOA）处理的雄性斯普拉格-道利大鼠，在处理7、14及28天后的肝脏基因表达谱。我们证实，PFOA诱导肝脏肿瘤形成主要通过激活过氧化物酶体增殖物激活受体α（PPARα）。本研究筛选得到一组共7个基因（Cyp4a1、Nr1d1、Acot2、Vnn、Ehhadh及Acot1），可作为PPARα激活的潜在生物标志物。我们同时检测了PPARα激活的核心终点指标，发现其与上述生物标志物的表达水平具有良好相关性。组成型雄甾烷受体介导的Cyp2b酶活性及基因表达亦被PFOA以剂量依赖方式上调。另一方面，芳香烃受体（AhR）的靶基因Cyp1a2在所有检测时间点均显著下调。令人意外的是，KEGG与Reactome通路分析结果显示，PFOA并未驱动肝脏细胞周期进程与细胞增殖。尽管部分DNA复制相关基因（如Pold2、Mcm8）经PFOA处理后表达上调，但包括Ccnd1、Ccne2、Ccnb1及Ccna2在内的多个关键细胞周期依赖性生长基因均以剂量依赖方式显著下调，尤其在处理28天时最为显著。Ingenuity Pathway Analysis（英格enuity通路分析）亦表明，PFOA在后续检测时间点可抑制肝癌相关通路。上述结果提示，尽管PFOA可明确诱导PPARα激活，但其介导的细胞增殖（肿瘤作用模式中的第二个关键事件）具有一过性，且受反馈机制严格调控。此类变化最终是否会引发大鼠癌前病灶及肝脏肿瘤形成，目前仍不明确。