Alteration in ovarian gene expression in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin: reduction of cyclooxygenase-2 in the blockage of ovulation.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a reproductive toxicant and endocrine disrupter that is known to block ovulation. This study was designed to investigate alterations in relevant ovarian genes that may be involved in the blockage of ovulation by TCDD in immature intact rats primed with equine chorionic gonadotropin (eCG). In this ovulation model, rats were given either 32 microg/kg TCDD or corn oil by gavage on 25 days of age. The next day, eCG (5 IU) was injected subcutaneously (s.c.) to stimulate follicular development. Ovulation occurs 72 h after administration of eCG in controls of this model. TCDD blocked ovulation at the expected time and also reduced both ovarian and body weights. At 72 h after eCG (the morning after expected ovulation), TCDD did not alter significantly serum concentrations of progesterone (P4) and androstenedione (A4). However, estradiol (E2) was significantly higher at 72 h after eCG in TCDD-treated rats when compared with controls. Western blots revealed that ovarian CYP1A1 was induced by TCDD. In addition, the aryl hydrocarbon receptor (AhR) and AhR nuclear translocator (ARNT) were down- and up-regulated by TCDD, respectively, indicating that AhR-mediated signal transduction was altered in the ovary. Ovarian estrogen receptor (ER)alpha, ER beta and progesterone receptor (PR) were not altered significantly by TCDD, but ovarian glucocorticoid receptor (GR) was increased at 24h after TCDD and decreased at 72 h after eCG when compared with controls. TCDD induced the early appearance of ovarian plasminogen activator inhibitor type-1 (PAI-1), plasminogen activator inhibitor type-2 (PAI-2), urokinase plasminogen activator (uPA), and tissue plasminogen activator (tPA) at 24h after dosing when compared with controls. On the morning after ovulation (72 h after eCG), no significant differences between control and TCDD-treated rats were observed except that TCDD had still increased tPA and decreased PAI-2 when compared with controls. Interestingly, ovarian COX-2 was induced on the morning after ovulation (72 h after eCG) in controls, but was greatly inhibited in TCDD-treated rats at that time. On the other hand, COX-1 was constitutively expressed throughout the ovulatory period and remained unaffected by TCDD. Immunolocalization of COX-2 in the ovary revealed that TCDD inhibited COX-2 expression in the granulosa cell layer when assessed in the morning of expected ovulation. In conclusion, AhR signaling is activated in the ovary by TCDD and inhibition of COX-2 appeared to be a critical step in the TCDD blockage of ovulation because blockage or reduction of COX-2 expression is well known to be associated with failure of ovulation.
Mizuyachi
Kaori
K
Center of Reproductive Sciences and Department of Molecular & Integrative Physiology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160-7417, USA.
Son
Deok-Soo
DS
Rozman
Karl K
KK
Terranova
Paul F
PF
D000284:Administration, Oral; D000818:Animals; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis; D004785:Environmental Pollutants / Q000008:administration & dosage / Q000633:toxicity*; D004958:Estradiol / Q000097:blood; D005260:Female; D018507:Gene Expression Regulation, Developmental; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics*; D008565:Membrane Proteins; D010053:Ovary / Q000187:drug effects* / Q000201:enzymology; D010060:Ovulation / Q000187:drug effects* / Q000378:metabolism; D010960:Plasminogen Activators / Q000378:metabolism; D015849:Plasminogen Inactivators / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000008:administration & dosage / Q000633:toxicity*; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D012269:Ribosomal Proteins / Q000096:biosynthesis / Q000235:genetics; D012741:Sexual Maturation; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism
D006063:Chorionic Gonadotropin; D004785:Environmental Pollutants; D007527:Isoenzymes; D008565:Membrane Proteins; D015849:Plasminogen Inactivators; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D012269:Ribosomal Proteins; D014157:Transcription Factors; C050482:Rpl19 protein, rat; D004958:Estradiol; D019363:Cytochrome P-450 CYP1A1; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496513:Ptgs1 protein, rat; D010960:Plasminogen Activators