Effect of TCDD on mRNA expression of genes encoding bHLH/PAS proteins in rat hypothalamus.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) brings about a wide variety of toxic and biochemical effects via an AH receptor (AHR)-mediated signalling pathway. Wasting syndrome and acute lethality are TCDD-induced endpoints showing a striking sensitivity difference between two rat strains, TCDD-sensitive Long-Evans (Turku/AB) (L-E) and TCDD-resistant Han/Wistar (Kuopio) (H/W). These rat strains were used to study hypothalamic effects of TCDD on expression of genes encoding AHR-regulated bHLH/PAS proteins potentially involved in molecular pathogenesis of the wasting syndrome. In addition, two well-established target genes of TCDD, CYP1A1 and CYP1A2 were also examined. Quantitative RT-PCR was used to measure mRNA levels in hypothalamus, which is a major center of food intake and body weight regulation. At both 6 and 96 h after a single dose of 50 microg/kg TCDD, significant elevations were found in mRNA levels of AHR repressor (AHRR), CYP1A1 and CYP1A2, but not those of AHR, ARNT or ARNT2. Likewise, TCDD (100 microg/kg) did not alter the expression of SIM1, implicated in the suppressive impact of TCDD on food intake, nor that of PER2, involved in regulation of circadian rhythms. Differences between H/W and L-E rats appeared in constitutive levels of AHR and ARNT and in TCDD-induced levels of CYP1A2, AHRR, AHR and ARNT, which all were about two- to four-fold lower in H/W rats. Thus, although the changes found do not account for the wasting syndrome, expression of all principal genes of the AHR-signalling pathway in rat hypothalamus make it a candidate target for TCDD.
Korkalainen
Merja
M
National Public Health Institute, Department of Environmental Health, P.O. Box 95, FIN-70701 Kuopio, Finland. merja.korkalainen@ktl.fi
Lindén
Jere
J
Tuomisto
Jouko
J
Pohjanvirta
Raimo
R
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000235:genetics; D019388:Cytochrome P-450 CYP1A2 / Q000096:biosynthesis / Q000235:genetics; D004785:Environmental Pollutants / Q000633:toxicity*; D015870:Gene Expression / Q000187:drug effects; D018257:Helix-Loop-Helix Motifs; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D020318:Rats, Long-Evans; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D015534:Trans-Activators / Q000378:metabolism*; D000099162:Endothelial PAS Domain-Containing Protein 1
D051792:Basic Helix-Loop-Helix Proteins; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D004785:Environmental Pollutants; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D015534:Trans-Activators; D000099162:Endothelial PAS Domain-Containing Protein 1