Ammerschlaeger Manuel, Beigel Jürgen, Klein Kai-Uwe, Mueller Stefan O
Molecular Toxicology, Institute of Toxicology, Merck KGaA, 64271 Darmstadt, Germany.
Toxicol Sci. 2004 Apr;78(2):229-40. doi: 10.1093/toxsci/kfh071. Epub 2004 Feb 19.
Peroxisome proliferation is a well-defined pleiotropic effect that is mediated by the ligand inducible transcription factor peroxisome proliferator-activated receptor (PPAR) alpha. Because marked peroxisome proliferation occurs in rodents but not in humans, we aimed to elucidate the molecular and cellular determinants of this species-specificity in hepatocytes. Analysis of peroxisomal marker enzyme activities confirmed that peroxisome proliferators induced acyl-CoA oxidase (ACOX) and to a lesser extent catalase in rat hepatocytes, but not in human hepatoma HepG2 cells. Transient transfection assays revealed that ciprofibrate and Wy 14,643 induced rat but not human PPARalpha-mediated reporter gene activity in rat FAO and primary hepatocytes on rat but not on human PPARalpha response elements (PPREs). In contrast, in human HepG2 and primary human hepatocytes, peroxisome proliferators did not induce either human or rat PPARalpha activity regardless of rat or human PPRE sequences. In addition, no induction of ACOX gene expression was observed in human hepatocytes independent of the expression level of human PPARalpha. Remarkably, no distinct peroxisome proliferation related responses were observed in human hepatocytes when rat PPARalpha was transfected, although human hepatocytes were responsive to PPARalpha-mediated induction of carnitine palmitoyl transferase-1A and 3-hydroxy-3-methylglutaryl-CoA synthase. These results confirmed that PPARalpha and PPREs are important determinants for the species-specificity of peroxisome proliferation. Nevertheless, our results showed that human hepatocytes limit the extent of peroxisome proliferation regardless of PPARalpha expression.
过氧化物酶体增殖是一种由配体诱导转录因子过氧化物酶体增殖物激活受体（PPAR）α介导的明确的多效性效应。由于在啮齿动物中会发生明显的过氧化物酶体增殖，而在人类中则不会，因此我们旨在阐明肝细胞中这种物种特异性的分子和细胞决定因素。对过氧化物酶体标记酶活性的分析证实，过氧化物酶体增殖剂可诱导大鼠肝细胞中的酰基辅酶A氧化酶（ACOX），并在较小程度上诱导过氧化氢酶，但在人肝癌HepG2细胞中则不会。瞬时转染试验表明，环丙贝特和Wy 14,643在大鼠FAO和原代大鼠肝细胞中可诱导大鼠而非人类PPARα介导的报告基因活性，作用于大鼠而非人类的PPARα反应元件（PPRE）。相反，在人HepG2细胞和原代人肝细胞中，无论PPRE序列是大鼠的还是人类的，过氧化物酶体增殖剂都不会诱导人类或大鼠的PPARα活性。此外，在人肝细胞中未观察到ACOX基因表达的诱导，与人类PPARα的表达水平无关。值得注意的是，当转染大鼠PPARα时，在人肝细胞中未观察到明显的与过氧化物酶体增殖相关的反应，尽管人肝细胞对PPARα介导的肉碱棕榈酰转移酶-1A和3-羟基-3-甲基戊二酰辅酶A合酶的诱导有反应。这些结果证实，PPARα和PPRE是过氧化物酶体增殖物种特异性的重要决定因素。然而，我们的结果表明，无论PPARα表达如何，人肝细胞都会限制过氧化物酶体增殖的程度。
