Moisan, Marie-Pierre

2018-01-31T11:23:20Z

2018-01-31T11:23:20Z

1993

Adrenal corticosteroid hormones play diverse and important roles in development and homeostasis. Their complex effects are predominantly mediated by intracellular receptors, which are of two types; mineralocorticoid (MR, type I) and glucocorticoid (GR, type II). MR bind aldosterone and physiological glucocorticoids (Cortisol, corticosterone) with equivalent high affinity in vitro, whereas GR show a low affinity for aldosterone but bind physiological glucocorticoids and the synthetic glucocorticoid dexamethasone with high affinity. In vivo, kidney MR selectively bind aldosterone despite a hundred-fold molar excess of circulating glucocorticoids. This selectivity is due to the high activity of the enzyme 11ß-hydroxysteroid dehydrogenase (11ß-OHSD) which catalyses the reversible conversion of physiological glucocorticoids to inactive products, but does not metabolise aldosterone, thus preventing glucocorticoid access to renal MR. This thesis describes firstly the presence and subregional distribution of 11ß-OHSD in rat brain using Northern analysis, in situ hybridisation, and an 11ß-OHSD activity assay. The enzyme was not only found in aldosterone selective regions, such as periventricular areas of the hypothalamus, but also in hippocampus where corticosterone is the physiological ligand for MR, and, more surprisingly, in cerebellum which contains very low levels of MR. Therefore it was postulated that 11ß-OHSD might modulate glucocorticoid access to both types of corticosteroid receptor in brain. Furthermore, brain but not renal, 11ß-OHSD was up-regulated by chronic glucocorticoid but not aldosterone administration, suggesting a role for the enzyme in controlling long-term neuronal glucocorticoid exposure. The importance of 11ß-OHSD in brain was further substantiated by the finding of high 11ß-OHSD mRNA levels and activity in rat brain subregions in the early postnatal period, with regionally specific developmental patterns of activity. The enzyme may play an important role in the developing brain by protecting tissues from (or exposing them to) elevated corticosterone levels. To understand the molecular mechanisms underlying tissuespecific and ontogenic regulation of 11ß-OHSD a rat genomic clone was isolated and partially sequenced. Differential promoter usage of the gene was demonstrated in kidney; three transcription start sites were detected within one kilobase of 5' flanking region of the gene, using primer extension and ribonuclease protection analyses. Corresponding transcripts were detected on Northern blots of kidney, but not liver RNA, using specific oligonucleotide probes. Sequence analysis revealed a number of putative transcription factor binding sites. These findings might explain, at least in part, tissue-specific differences in the regulation of 11ß-OHSD mRNA and activity.

http://hdl.handle.net/1842/26785

The University of Edinburgh

Annexe Thesis Digitisation Project 2017 Block 15

Regulation of 11 beta-hydroxysteroid dehydrogenase in rat brain and cloning of the gene promoter region

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy