Developmental alteration of the chromatin state at promoter/replication origin region of the aldolase B locus precedes transcriptional activation in the liver

Bisphenol a induces steatosis in HepaRG cells using a model of perinatal exposure

Human exposure to bisphenol A (BPA) could favor obesity and related metabolic disorders such as hepatic steatosis. Investigations in rodents have shown that these deleterious effects are observed not only when BPA is administered during the adult life but also with different protocols of perinatal exposure. Whether perinatal BPA exposure could pose a risk in human is currently unknown, and thus appropriate in vitro models could be important to tackle this major issue. Accordingly, we determined whether long-term BPA treatment could induce steatosis in human HepaRG cells by using a protocol mimicking perinatal exposure. To this end, the kinetics of expression of seven proteins differentially expressed during liver development was determined during a 4-week period of cell culture required for proliferation and differentiation. By analogy with data reported in rodents and humans, our results indicated that the period of cell culture around day 15 and day 18 after seeding could be considered as the "natal" period. Consequently, HepaRG cells were treated for 3 weeks with BPA (from 0.2 to 2000 nM), with a treatment starting during the proliferating period. BPA was able to induce steatosis with a nonmonotonic dose response profile, with significant effects on neutral lipids and triglycerides observed for the 2 nM concentration. However, the expression of many enzymes involved in lipid and carbohydrate homeostasis was unchanged in exposed HepaRG cells. The expression of other potential BPA targets and enzymes involved in BPA biotransformation was also determined, giving answers as well as new questions regarding the mechanisms of action of BPA. Hence, HepaRG cells provide a valuable model that can prove useful for the toxicological assessment of endocrine disruptors on hepatic metabolisms, in particular in the developing liver. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1024-1036, 2017.

A novel murine P-450 gene, Cyp4a14, is part of a cluster of Cyp4a and Cyp4b, but not of CYP4F, genes in mouse and humans

Genomic clones for Cyp4a12 and a novel member of the murine Cyp4a gene family were isolated. The novel gene, designated Cyp4a14, has a GC rich sequence immediately 5' of the transcription start site, and is similar to the rat CYP4A2 and CYP4A3 genes. The Cyp4a14 gene spans approximately 13 kb, and contains 12 exons; sequence similarity to the rat CYP4A2 gene sequence falls off 300 bp upstream from the start site. In view of the known sex-specific expression of the rat CYP4A2 gene, the expression and inducibility of Cyp4a14 was examined. The gene was highly inducible in the liver when mice were treated with the peroxisome proliferator, methylclofenapate; induction levels were low in control animals and no sex differences in expression were observed. By contrast, the Cyp4a12 RNA was highly expressed in liver and kidney of control male mice but was expressed at very low levels in liver and kidney of female mice. Testosterone treatment increased the level of this RNA in female liver slightly, and to a greater extent in the kidney of female mice. In agreement with studies on the cognate RNA, expression of Cyp4a12 protein was male-specific in the liver of control mice and extremely high inducibility of Cyp4a10 protein, with no sex differences, was also demonstrated. In view of the overlapping patterns of inducibility of the three Cyp4a genes, we investigated whether the three genes were co-localized in the genome. Two overlapping yeast artificial chromosome (YAC) clones were isolated, and the three Cyp4a genes were shown to be present on a single YAC of 220 kb. The Cyp4a genes are adjacent to the Cyp4b1 gene, with Cyp4a12 most distant from Cyp4b1. The clustering of these two gene subfamilies in the mouse was replicated in the human, where the CYPA411 and CYP4B1 genes were present in a single YAC clone of 440 kb. However, the human CYP4F2 gene was mapped to chromosome 19. Phylogenetic analysis of the CYP4 gene families demonstrated that CYP4A and CYP4B are more closely related than CYP4F.