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Regulation of glucocorticoid metabolism: a novel function for thyroid hormones?
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Edité par CCSD ; Oxford University Press -
International audience. Glucocorticoid hormone metabolism and action are regulated by the 11-beta hydroxysteroid dehydrogenase (11bHSD) isozymes: the 11bHSD2, mostly expressed in the distal nephron, converts cortisol [F] into cortisone [E] in humans or corticosterone [B] into 11-dehydrocorticosterone [A] in rodents (11-dehydro derivatives being inactive compounds), and the 11bHSD1, ubiquitously expressed but abundant in the liver, catalyzes the opposite reaction. Under pathophysiological conditions of severe hypothyroidism, altered glucocorticoid metabolism has been observed, with decreased [F] to [E] conversion 1,2. However, direct functional relationship between these two hormonal pathways has never been demonstrated to date. Using bioinformatics analyses, we identified five thyroid hormone response elements in the promoter region of the murine hsd11b2 gene. Therefore, we aimed at investigating whether thyroid hormones (T3) directly regulate expression and/or activity of the 11bHSD2 enzyme. We used three complementary models: human and mouse translational studies and molecular analyses in HEK293T cells and in fully differentiated KC3AC1 cortical collecting duct cells. Children and adults in hypo-or hyperthyroidism status were first compared either to age-and sex-matched euthyroid controls, or to themselves after reaching a euthyroid status. The urinary [E]/[F] ratio measured by LC-MS/MS method, was used as an index of renal 11bHSD2 activity. Interestingly, a 60% decrease in the [E]/[F] ratio was observed in hypothyroid patients, corroborating our hypothesis (p<0.05). Next, a mouse model of hyperthyroidism, generated by administrating T3 in drinking water, led to a significant 10% increase in renal 11bHSD2 mRNA and protein levels compared to wild type mice (n=10, p<0.05). Furthermore, we demonstrated in HEK293T cells that T3 transactivates the mouse hsd11b2 promoter cloned upstream the luciferase reporter gene via the Thyroid Receptor a1(TRa1). Finally, we showed that T3 exposure induces a 50% increase in 11bHSD2 mRNA levels in KC3AC1 cells, in a dose-dependent and time-dependent manner (as early as 6 h) (p<0.01). This induction was abrogated by Actinomycin D or DRB, two inhibitors of transcription, underlining a transcriptional regulatory mechanism. In addition, 11bHSD2 enzymatic activity, quantified by the [F] to [E] conversion ratio measured by LC-MS/MS in cell supernatants, increased significantly by 20% (p<0.05) after 24 h exposure to 100 nM T3. ChIP experiments further demonstrated a T3-dependent specific recruitment of the TRa1 onto the hsd11b2 promoter region. Altogether, our findings constitute the first demonstration that thyroid hormones directly regulate expression and activity of the renal 11bHSD2 enzyme, thereby controlling glucocorticoid metabolism and action. References: (1) Boonen et al, NEJM, 2013; (2) Warner et al, J Endocrinol, 2010.
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