Change of the sex-dependent response to clofibrate in F344 rat liver during postnatal development

Tissue-specific transcriptional modulation of fatty acid-binding protein genes, fabp2, fabp3 and fabp6, by fatty acids and the peroxisome proliferator, clofibrate, in zebrafish (Danio rerio)

All fabp genes, except fabp2, fabp3 and fabp6, exist as duplicates in the zebrafish genome owing to a whole genome duplication event ~230-400 million years ago. Transcription of some duplicated fabp genes is modulated by fatty acids (FAs) and/or clofibrate, a peroxisome proliferator-activated receptor (PPAR) agonist. We had also shown previously that the steady-state level of acyl-CoA oxidase 1 (acox1) mRNA, a marker of PPARα activation, was elevated in liver, intestine, heart and muscle of fish fed clofibrate demonstrating that zebrafish, unlike some fishes, is responsive to this drug. acox1 transcripts were not induced in the brain of fish fed clofibrate, which suggests this drug may not cross the blood brain barrier. Here, we investigated the effect of dietary FAs and clofibrate on the transcription of single copy fabp genes, fabp2, fabp3 and fabp6, in five tissues of inbred zebrafish. The steady-state level of fabp2 transcripts increased in intestine, while fabp3 mRNA increased in liver of fish fed diets differing in FA content. In fish fed clofibrate, fabp3 mRNA in intestine, and fabp6 mRNA in intestine and heart, were elevated. Based on these findings, modulation of fabp2, fabp3 and fabp6 transcription by FAs and/or clofibrate in zebrafish implicates control of these genes by PPAR interaction with peroxisome proliferator response elements (PPRE) most likely in fabp promoters. Moreover, transcriptional induction of these fabp genes by dietary FAs and/or clofibrate is over-ridden by a tissue-specific mechanism(s), e.g., transcriptional activator or repressor proteins.

Tissue-specific differential induction of duplicated fatty acid-binding protein genes by the peroxisome proliferator, clofibrate, in zebrafish (Danio rerio)

Background

Force, Lynch and Conery proposed the duplication-degeneration-complementation (DDC) model in which partitioning of ancestral functions (subfunctionalization) and acquisition of novel functions (neofunctionalization) were the two primary mechanisms for the retention of duplicated genes. The DDC model was tested by analyzing the transcriptional induction of the duplicated fatty acid-binding protein (fabp) genes by clofibrate in zebrafish. Clofibrate is a specific ligand of the peroxisome proliferator-activated receptor (PPAR); it activates PPAR which then binds to a peroxisome proliferator response element (PPRE) to induce the transcriptional initiation of genes primarily involved in lipid homeostasis. Zebrafish was chosen as our model organism as it has many duplicated genes owing to a whole genome duplication (WGD) event that occurred ~230-400 million years ago in the teleost fish lineage. We assayed the steady-state levels of fabp mRNA and heterogeneous nuclear RNA (hnRNA) transcripts in liver, intestine, muscle, brain and heart for four sets of duplicated fabp genes, fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, fabp10a/fabp10b and fabp11a/fabp11b in zebrafish fed different concentrations of clofibrate.

Result

Electron microscopy showed an increase in the number of peroxisomes and mitochondria in liver and heart, respectively, in zebrafish fed clofibrate. Clofibrate also increased the steady-state level of acox1 mRNA and hnRNA transcripts in different tissues, a gene with a functional PPRE. These results demonstrate that zebrafish is responsive to clofibrate, unlike some other fishes. The levels of fabp mRNA and hnRNA transcripts for the four sets of duplicated fabp genes was determined by reverse transcription, quantitative polymerase chain reaction (RT-qPCR). The level of hnRNA coded by a gene is an indirect estimate of the rate of transcriptional initiation of that gene. Clofibrate increased the steady-state level of fabp mRNAs and hnRNAs for both the duplicated copies of fabp1a/fabp1b.1, and fabp7a/fabp7b, but in different tissues. Clofibrate also increased the steady-state level of fabp10a and fabp11a mRNAs and hnRNAs in liver, but not for fabp10b and fabp11b.

Conclusion

Some duplicated fabp genes have, most likely, retained PPREs, but induction by clofibrate is over-ridden by an, as yet, unknown tissue-specific mechanism(s). Regardless of the tissue-specific mechanism(s), transcriptional control of duplicated zebrafish fabp genes by clofibrate has markedly diverged since the WGD event.

Effect of a Large Dose of Di (2-ethylhexyl) phthalate (DEHP) on Hepatic Peroxisome in Cynomolgus Monkeys (Macaca Fascicularis)

To elucidate the effect of a large dose of di (2-ethylhexyl) phthalate (DEHP), a plasticizer and peroxisome proliferator-activated receptor-α (PPARα) agonist, on hepatic peroxisomes, we orally administered 1,000 mg/kg/day, once daily, to 3 male and 4 female cynomolgus monkeys for 28 days consecutively. Light-microscopic and electron microscopic examinations of the liver were carried out in conjunction with measurement of the hepatic fatty acid β-oxidation system (FAOS), carnitine acetyltransferase (CAT) and carnitine palmitoyltransferase (CPT) activities, which are peroxisomal and/or mitochondrial enzyme activities. Electron microscopically, enlargement of the mitochondria was observed with lamellar orientation of the cristae along the major axis. Although the number of peroxisomes showed a tendency to increase when compared with those in a biopsied specimen before treatment, no abnormality in morphology was observed. A slight increase in CPT activity was noted at termination. No changes were noted in hepatic FAOS or CAT activity. In conclusion, although repeated oral treatment of cynomolgus monkeys with a large dose of DEHP induced a subtle increase in the numbers of peroxisomes with slight enlargements of the mitochondria, this low-sensitivity response to peroxisome proliferators in cynomolgus monkeys was considered to be closer to the response in humans than that in rodents.

Differential induction of peroxisomal beta-oxidation enzymes by clofibric acid and aspirin in piglet tissues

Peroxisomal beta-oxidation (POX) of fatty acids is important in lipid catabolism and thermogenesis. To investigate the effects of peroxisome proliferators on peroxisomal and mitochondrial beta-oxidation in piglet tissues, newborn pigs (1-2 days old) were allowed ad libitum access to milk replacer supplemented with 0.5% clofibric acid (CA) or 1% aspirin for 14 days. CA increased ratios of liver weight to body weight (P < 0.07), kidney weight to body weight (P < 0.05), and heart weight to body weight (P < 0.001). Aspirin decreased daily food intake and final body weight but increased the ratio of heart weight to body weight (P < 0.01). In liver, activities of POX, fatty acyl-CoA oxidase (FAO), total carnitine palmitoyltransferase (CPT), and catalase were 2.7-, 2.2-, 1.5-fold, and 33% greater, respectively, for pigs given CA than for control pigs. In heart, these variables were 2.2-, 4.1-, 1.9-, and 1.8-fold greater, respectively, for pigs given CA than for control pigs. CA did not change these variables in either kidney or muscle, except that CPT activity was increased approximately 110% (P < 0.01) in kidney. Aspirin increased only hepatic FAO and CPT activities. Northern blot analysis revealed that CA increased the abundance of catalase mRNA in heart by approximately 2.2-fold. We conclude that 1) POX and CPT in newborn pigs can be induced by peroxisomal proliferators with tissue specificity and 2) the relatively smaller induction of POX in piglets (compared with that in young or adult rodents) may be related to either age or species differences.

Hepatic drug metabolizing enzymes induced by clofibrate in rasH2 mice

Hepatic drug metabolizing enzyme activities were determined, after treatment with clofibrate, in transgenic mice carrying human c-Ha-ras (rasH2 mice). Changes in the drug metabolizing enzyme activities in these mice by gene integration were also evaluated. Male and female rasH2 mice (Tg) and the litter mates not carrying the gene (non-Tg) received orally 500 mg/kg of clofibrate or the vehicle for 12 consecutive days. Liver homogenate and microsomes were prepared and the contents and activities of cytochrome P450 (CYP), cytochrome b5 content and enzyme activities related to peroxisome proliferation were determined. Relative liver weights, CYP4A and activities of catalase and carnitine palmitoyl transferase increased to the same extent in Tg and non-Tg mice treated with clofibrate. In Tg and non-Tg groups that received vehicle, contents and activities of CYP and cytchrome b5 contents were comparable. It was concluded that gene integration did not alter drug metabolizing enzymes and responses to clofibrate.