Regulation of thyroid receptors mRNA and protein expression by hyperthyroidism in corpus luteum of rats in late pregnancy

NAVAS,PAOLA; JAHN GA; HAPON MB

Florencia

Congreso; 15th World Congress of Gynecological Endocrinology - Firenze, 7-10 March 2012; 2012

the international society of gynecological endocrinology

Introduction: Thyroid hormones (THs) play critical roles in differentiation, growth and metabolism. THs are needed in an adequate concentration to support CL formation and pregnancy. We have found that experimental hypothyroidism in pregnant rats produces a delay in luteolysis and parturition. Conversely, hyperthyroidism (hyperT) advances the decrease in circulating progesterone and parturition by approximately 12 hours. The classic genomic action of THs are mediated by nuclear receptors (TR) acting as hormone inducible transcription factors. The TRα1, TRα2 and TRβ1 isoforms are widely expressed whereas TRβ2 is mostly restricted to the hypothalamus-pituitary axis. TRα1, α2 and β1 mRNA and protein are present in ovarian surface epithelial cells in human, while human oocyte, granulose and cumulus cells also express TRβ2 in addition to the other isoforms. Although at present the presence of TRs in corpus luteum has not been confirmed, we have found that experimental hypothyroidism/hyperT delay or advance luteolysis and parturition in rats. Thus, thyroid hormones affect luteal function. In order to establish the existence of luteal TRs, we determined which isoforms of thyroid receptor are expressed in rat corpus luteum by real time PCR and Western-Blot and if these proteins are regulated by experimental hyperthyroidism. Materials and methods: For this purpose, groups of Co (control) and hyperT (induced by daily injection of 0.25 mg/kg of T4) Wistar rats (n= 6-8) were sacrificed at day 19 (G19), 20 (G20) and 21 (G21) of gestation. Total CL RNA and proteins were prepared using TRIzol. Luteal TR mRNA was measured by real time RT-PCR and expressed relative to the expression of the housekeeping gene rat ribosomal protein S16 cDNA. Proteins, isolated from the phenol-ethanol supernatant obtained from RNA isolation, were analyzed for TRα1 and TRβ1 abundance by Western blot and expressed as the ratio of signal intensity for the protein relative to that of b-tubulin. Results and conclusions: Corpus luteum of pregnancy expresses TRα1, TRα2 and TRβ1 mRNA. There were no changes in TRα1 and TRα2 expression between days and groups studied. TRβ1 expression was similar in the three days in controls and was increased in hyperT rats on G19 and G21. TRα1 and TRβ1 protein decreased significantly in hyperT rats on G20. This decline in TRα1 and TRβ1 protein can be due to degradation at the time of functional luteolysis that occurs in this day in hyperT rats. These results show that both isoforms of TRs are present at luteal level, that they are sensitive to regulation by thyroid hormones and that there may be a dissociation between TH regulation in the expression at mRNA and protein levels.