The Experts below are selected from a list of 720 Experts worldwide ranked by ideXlab platform
Jonathan R. Seckl - One of the best experts on this subject based on the ideXlab platform.
-
mast cells express 11β hydroxysteroid dehydrogenase type 1 a role in restraining mast cell degranulation
2013Co-Authors: Agnes E Coutinho, Jeremy K Brown, David G Brownstein, Mohini Gray, John Savill, Fu Yang, Jonathan R. Seckl, Karen E. ChapmanAbstract:Mast cells are key initiators of allergic, anaphylactic and inflammatory reactions, producing mediators that affect vascular permeability, angiogenesis and fibrosis. Glucocorticoid pharmacotherapy reduces mast cell number, maturation and activation but effects at physiological levels are unknown. Within cells, glucocorticoid concentration is modulated by the 11β-hydroxysteroid dehydrogenases (11β-HSDs). Here we show expression and activity of 11β-HSD1, but not 11β-HSD2, in mouse mast cells with 11β-HSD activity only in the keto-reductase direction, regenerating active glucocorticoids (cortisol, corticosterone) from inert substrates (cortisone, 11-Dehydrocorticosterone). Mast cells from 11β-HSD1-deficient mice show ultrastructural evidence of increased activation, including piecemeal degranulation and have a reduced threshold for IgG immune complex-induced mast cell degranulation. Consistent with reduced intracellular glucocorticoid action in mast cells, levels of carboxypeptidase A3 mRNA, a glucocorticoid-inducible mast cell-specific transcript, are lower in peritoneal cells from 11β-HSD1-deficient than control mice. These findings suggest that 11β-HSD1-generated glucocorticoids may tonically restrain mast cell degranulation, potentially influencing allergic, anaphylactic and inflammatory responses.
-
Mast cells express 11β-HSD1.
2013Co-Authors: Agnes E Coutinho, Jeremy K Brown, David G Brownstein, Mohini Gray, Fu Yang, Jonathan R. Seckl, John S. Savill, Karen E. ChapmanAbstract:(A) 11β-HSD1 reductase (conversion of 11-Dehydrocorticosterone to corticosterone; Solid lines/black squares) and dehydrogenase (conversion of corticosterone to 11-Dehydrocorticosterone; dashed lines/open squares) activities in BMD-MC (>98% pure, assessed by tryptase staining as previously described [24]) are expressed as % conversion of 200 nM substrate by 2×106 cells, over time (h). Values are mean ± SEM of 3 independent assays carried out on pooled BMD-MC. (B) BMD-MC express 11β-HSD1 mRNA (upper panel; 469 bp RT-PCR product with primers 868P and 869P) but not 11β-HSD2 mRNA (lower panel; 400 bp RT-PCR product). Lanes 5 and 6 show RT-PCR products from 2 independent Hsd11b1+/+ BMD-MC RNA samples. Positive controls (+) comprised liver mRNA (lane 4, upper panel) or kidney mRNA (lane 4, lower panel). Negative controls contained BMD-MC RNA but no reverse transcriptase (−, lane 3) or water (lane 2). Lane 1 contains a 100 bp ladder (Promega, Southampton, UK). (C) Hsd11b1−/− BMD-MC lack 11β-HSD1 activity. 11β-HSD1 reductase activity was measured in Hsd11b1+/+ (+/+) and Hsd11b1−/− (−/−) BMD-MC. Data are expressed as % conversion of 200 nM 11-Dehydrocorticosterone to corticosterone by 2×106 cells in a 10 h assay. Values are means of triplicate assays performed on pooled BMD-MC. ND, not detected. (D) Mast cells transcribe Hsd11b1 from the P1 promoter, whereas macrophages use the P2 promoter. Upper panel; RT-PCR products from 3 independent BMD-MC RNA samples showing the 627 bp RT-PCR product from P1 transcripts of 11β-HSD1 (lanes 4–6), but not P2 (predicted product of 647 bp, lanes 7–9) or P3 (predicted product of 542 bp, lanes 10–12). Kidney RNA confirmed transcription from P3 (not shown). Total 11β-HSD1 mRNA was detected using ex2 and 868P primers common to all transcripts (lanes 13–15, 587 bp product). Lower panel; RT-PCR products from BMD macrophage RNA showing the 647 bp RT-PCR P2 product (lane 3), but not the P1 (lane 2) or P3 products (lane 4). Total 11β-HSD1 mRNA (T) was detected using 868P and 869P primers, common to all transcripts (lanes 5, 6; 469 bp product). Lane 1 contains a 1 kb ladder (Invitrogen, Paisley, UK). Lanes marked (0) contain water only and lanes marked (−) show RT-PCR reactions from which the RT was omitted. (E) Flow cytometric staining revealed 11β-HSD1+CD117+ peritoneal cells. Freshly isolated peritoneal cells (∼5×105 cells per sample) from male C57BL/6 mice were stained with 11β-HSD1 and CD117+ antibodies. Total peritoneal cells were first gated according to side scatter (SSC) and forward scatter (FSC) (i), then cells with high granularity, where mast cells lie (see Figure S1), were assessed for 11β-HSD1 and CD117 staining (ii–vii). Controls included; (ii) high SSC cells alone, (iii) sheep IgG control for 11β-HSD1 antibody, (iv) 11β-HSD1 antibody only, (v) isotype control for CD117 and (vi) CD117 antibody only. Panel (vii) shows cells double stained with 11β-HSD1 and CD117 antibodies.
-
Mast Cells Express 11b-hydroxysteroid Dehydrogenase Type 1: A Role in Restraining Mast Cell Degranulation
2013Co-Authors: Agnes E Coutinho, Jeremy K Brown, David G Brownstein, Mohini Gray, Fu Yang, Jonathan R. Seckl, John S. Savill, Karen E. ChapmanAbstract:Mast cells are key initiators of allergic, anaphylactic and inflammatory reactions, producing mediators that affect vascular permeability, angiogenesis and fibrosis. Glucocorticoid pharmacotherapy reduces mast cell number, maturation and activation but effects at physiological levels are unknown. Within cells, glucocorticoid concentration is modulated by the 11b-hydroxysteroid dehydrogenases (11b-HSDs). Here we show expression and activity of 11b-HSD1, but not 11b-HSD2, in mouse mast cells with 11b-HSD activity only in the keto-reductase direction, regenerating active glucocorticoids (cortisol, corticosterone) from inert substrates (cortisone, 11-Dehydrocorticosterone). Mast cells from 11b-HSD1-deficient mice show ultrastructural evidence of increased activation, including piecemeal degranulation and have a reduced threshold for IgG immune complex-induced mast cell degranulation. Consistent with reduced intracellular glucocorticoid action in mast cells, levels of carboxypeptidase A3 mRNA, a glucocorticoid-inducible mast cell-specific transcript, are lower in peritoneal cells from 11b-HSD1-deficient than control mice. These findings suggest that 11b-HSD1-generated glucocorticoids may tonicall
-
11β hydroxysteroid dehydrogenases in the brain
2003Co-Authors: Megan C Holmes, John J. Mullins, Joyce L W Yau, Yuri Kotelevtsev, Jonathan R. SecklAbstract:Glucocorticoids affect a wide range of processes in the brain, altering neurotransmission, electrophysiological activity, metabolism, cell division, and death. These actions are mediated by corticosteroid receptors (glucocorticoid and mineralocorticoid) that modify transcriptional activity of target genes. The amount of steroid available to activate these receptors is not only dependent on the circulating levels but also on pre-receptor metabolism of glucocorticoids occurring intracellularly. This metabolism is carried out by the enzymes 11beta-hydroxysteroid dehydrogenases (11beta-HSDs). There are two distinct isozymes, the products of distantly related genes. 11beta-HSD type 2 inactivates glucocorticoids to its inert 11-keto derivative, while 11alpha-HSD type 1 elevates intracellular glucocorticoid levels by regenerating active glucocorticoids from circulating 11-Dehydrocorticosterone or cortisone. This review highlights the important and very different roles the two enzymes play in the brain, outlining recent results obtained from studying mice with a targeted gene deletion in the 11beta-HSD1 or 11beta-HSD2 genes.
-
lack of tissue glucocorticoid reactivation in 11β hydroxysteroid dehydrogenase type 1 knockout mice ameliorates age related learning impairments
2001Co-Authors: Joyce L W Yau, John J. Mullins, Yuri Kotelevtsev, Christopher J. Kenyon, June Noble, Carina Hibberd, Jonathan R. SecklAbstract:11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1) intracellularly regenerates active corticosterone from circulating inert 11-Dehydrocorticosterone (11-DHC) in specific tissues. The hippocampus is a brain structure particularly vulnerable to glucocorticoid neurotoxicity with aging. In intact hippocampal cells in culture, 11β-HSD-1 acts as a functional 11β-reductase reactivating inert 11-DHC to corticosterone, thereby potentiating kainate neurotoxicity. We examined the functional significance of 11β-HSD-1 in the central nervous system by using knockout mice. Aged wild-type mice developed elevated plasma corticosterone levels that correlated with learning deficits in the watermaze. In contrast, despite elevated plasma corticosterone levels throughout life, this glucocorticoid-associated learning deficit was ameliorated in aged 11β-HSD-1 knockout mice, implicating lower intraneuronal corticosterone levels through lack of 11-DHC reactivation. Indeed, aged knockout mice showed significantly lower hippocampal tissue corticosterone levels than wild-type controls. These findings demonstrate that tissue corticosterone levels do not merely reflect plasma levels and appear to play a more important role in hippocampal functions than circulating blood levels. The data emphasize the crucial importance of local enzymes in determining intracellular glucocorticoid activity. Selective 11β-HSD-1 inhibitors may protect against hippocampal function decline with age.
Yuri Kotelevtsev - One of the best experts on this subject based on the ideXlab platform.
-
11β hydroxysteroid dehydrogenases in the brain
2003Co-Authors: Megan C Holmes, John J. Mullins, Joyce L W Yau, Yuri Kotelevtsev, Jonathan R. SecklAbstract:Glucocorticoids affect a wide range of processes in the brain, altering neurotransmission, electrophysiological activity, metabolism, cell division, and death. These actions are mediated by corticosteroid receptors (glucocorticoid and mineralocorticoid) that modify transcriptional activity of target genes. The amount of steroid available to activate these receptors is not only dependent on the circulating levels but also on pre-receptor metabolism of glucocorticoids occurring intracellularly. This metabolism is carried out by the enzymes 11beta-hydroxysteroid dehydrogenases (11beta-HSDs). There are two distinct isozymes, the products of distantly related genes. 11beta-HSD type 2 inactivates glucocorticoids to its inert 11-keto derivative, while 11alpha-HSD type 1 elevates intracellular glucocorticoid levels by regenerating active glucocorticoids from circulating 11-Dehydrocorticosterone or cortisone. This review highlights the important and very different roles the two enzymes play in the brain, outlining recent results obtained from studying mice with a targeted gene deletion in the 11beta-HSD1 or 11beta-HSD2 genes.
-
lack of tissue glucocorticoid reactivation in 11β hydroxysteroid dehydrogenase type 1 knockout mice ameliorates age related learning impairments
2001Co-Authors: Joyce L W Yau, John J. Mullins, Yuri Kotelevtsev, Christopher J. Kenyon, June Noble, Carina Hibberd, Jonathan R. SecklAbstract:11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1) intracellularly regenerates active corticosterone from circulating inert 11-Dehydrocorticosterone (11-DHC) in specific tissues. The hippocampus is a brain structure particularly vulnerable to glucocorticoid neurotoxicity with aging. In intact hippocampal cells in culture, 11β-HSD-1 acts as a functional 11β-reductase reactivating inert 11-DHC to corticosterone, thereby potentiating kainate neurotoxicity. We examined the functional significance of 11β-HSD-1 in the central nervous system by using knockout mice. Aged wild-type mice developed elevated plasma corticosterone levels that correlated with learning deficits in the watermaze. In contrast, despite elevated plasma corticosterone levels throughout life, this glucocorticoid-associated learning deficit was ameliorated in aged 11β-HSD-1 knockout mice, implicating lower intraneuronal corticosterone levels through lack of 11-DHC reactivation. Indeed, aged knockout mice showed significantly lower hippocampal tissue corticosterone levels than wild-type controls. These findings demonstrate that tissue corticosterone levels do not merely reflect plasma levels and appear to play a more important role in hippocampal functions than circulating blood levels. The data emphasize the crucial importance of local enzymes in determining intracellular glucocorticoid activity. Selective 11β-HSD-1 inhibitors may protect against hippocampal function decline with age.
-
phenotypic analysis of mice bearing targeted deletions of 11β hydroxysteroid dehydrogenases 1 and 2 genes
2001Co-Authors: Megan C Holmes, Yuri Kotelevtsev, John J. MullinsAbstract:Abstract The glucocorticoid metabolising enzymes, 11β-hydroxysteroid dehydrogenases (11β-HSD), play a critical role in determining the availability of glucocorticoids to activate their receptors and hence modulate target gene transcription. There are two isozymes, 11β-HSD-1 and -2, which act in opposing directions. 11β-HSD-2 acts as a dehydrogenase, converting active corticosterone (cortisol in humans) to its inactive 11-keto derivative (11-Dehydrocorticosterone in rodents and cortisone in humans), whereas 11β-HSD-1 acts as a reductase, regenerating active glucocorticoids in a tissue-specific manner. Owing to the lack of specific inhibitors of these enzymes, it has been difficult to confirm the roles and determine the importance of these enzymes in vivo. Hence, to address this, we produced transgenic mice with null-mutations in the genes encoding the 11β-HSD-1 or 11β-HSD-2 enzymes. 11β-HSD-2 −/− mice show signs of hypertension, hypotonic polyuria, hypokalemia and hypochloremia. These symptoms arise from illicit activation of mineralocorticoid receptors by glucocorticoids, in the absence of the protective action of 11β-HSD-2. The phenotype is directly comparable to the Syndrome of Apparent Mineralocorticoid Excess, seen in humans with mutations in the 11β-HSD-2 gene. Mice lacking 11β-HSD-1, however, show a more subtle phenotype with reduced activation of glucocorticoid-induced processes. They were unable to convert 11-Dehydrocorticosterone to corticosterone in vivo, confirming 11β-HSD-1 as the sole 11-reductase in the mouse. They have elevated circulating levels of plasma corticosterone levels and adrenal hyperplasia, but they also have attenuated glucocorticoid-induced activation of gluconeogenic enzymes in response to fasting, and lower glucose levels in response to obesity or stress. Overall, these transgenic models have proved very useful for elucidating the roles of 11β-HSDs in vivo and will be a unique resource for investigating the importance of each enzyme in the diverse actions of glucocorticoids.
-
intracellular regeneration of glucocorticoids by 11β hydroxysteroid dehydrogenase 11β hsd 1 plays a key role in regulation of the hypothalamic pituitary adrenal axis analysis of 11β hsd 1 deficient mice1
2001Co-Authors: Hayley J Harris, Jonathan R. Seckl, John J. Mullins, Yuri Kotelevtsev, Megan C HolmesAbstract:11β-Hydroxysteroid dehydrogenases (11β-HSDs) catalyze interconversion of active corticosterone and inert 11-Dehydrocorticosterone, thus regulating glucocorticoid access to intracellular receptors in vivo. 11β-HSD type 1 is a reductase, locally regenerating active glucocorticoids. To explore the role of this isozyme in the brain, we examined hypothalamic-pituitary-adrenal axis (HPA) regulation in mice homozygous for a targeted disruption of the 11β-HSD-1 gene. 11β-HSD-1-deficient mice showed elevated plasma corticosterone and ACTH levels at the diurnal nadir, with a prolonged corticosterone peak, suggesting abnormal HPA control and enhanced circadian HPA drive. Despite elevated corticosterone levels, several hippocampal and hypothalamic glucocorticoid-sensitive messenger RNAs were normally expressed in 11β-HSD-1-deficient mice, implying reduced effective glucocorticoid activity within neurons. 11β-HSD-1-deficient mice showed exaggerated ACTH and corticosterone responses to restraint stress, with a delayed ...
-
11β hydroxysteroid dehydrogenase type 1 knockout mice show attenuated glucocorticoid inducible responses and resist hyperglycemia on obesity or stress
1997Co-Authors: Yuri Kotelevtsev, Christopher R. W. Edwards, Megan C Holmes, Ann N Burchell, Pamela Houston, Dieter Schmoll, Pauline Jamieson, Ruth Best, Roger W Brown, J R SecklAbstract:Glucocorticoid hormones, acting via nuclear receptors, regulate many metabolic processes, including hepatic gluconeogenesis. It recently has been recognized that intracellular glucocorticoid concentrations are determined not only by plasma hormone levels, but also by intracellular 11β-hydroxysteroid dehydrogenases (11β-HSDs), which interconvert active corticosterone (cortisol in humans) and inert 11-Dehydrocorticosterone (cortisone in humans). 11β-HSD type 2, a dehydrogenase, thus excludes glucocorticoids from otherwise nonselective mineralocorticoid receptors in the kidney. Recent data suggest the type 1 isozyme (11β-HSD-1) may function as an 11β-reductase, regenerating active glucocorticoids from circulating inert 11-keto forms in specific tissues, notably the liver. To examine the importance of this enzyme isoform in vivo, mice were produced with targeted disruption of the 11β-HSD-1 gene. These mice were unable to convert inert 11-Dehydrocorticosterone to corticosterone in vivo. Despite compensatory adrenal hyperplasia and increased adrenal secretion of corticosterone, on starvation homozygous mutants had attenuated activation of the key hepatic gluconeogenic enzymes glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, presumably, because of relative intrahepatic glucocorticoid deficiency. The 11β-HSD-1 −/− mice were found to resist hyperglycamia provoked by obesity or stress. Attenuation of hepatic 11β-HSD-1 may provide a novel approach to the regulation of gluconeogenesis.
Megan C Holmes - One of the best experts on this subject based on the ideXlab platform.
-
the role of 11β hydroxysteroid dehydrogenases in the brain
2006Co-Authors: Megan C HolmesAbstract:Abstract Glucocorticoids have a plethora of effects within the body to maintain homeostasis. In the brain they modify learning, memory and fear behaviours as well as regulating their own secretion by a negative feedback action. 11β-Hydroxysteroid dehydrogenases (11β-HSDs) are glucocorticoid metabolising enzymes that modify actions of glucocorticoids in a tissue specific manner. 11β-HSD1 regenerates active glucocorticoids from their inactive 11-keto derivatives, hence boosting tissue levels of corticosterone and cortisol. Removal of this enzyme (11β-HSD1−/− mice) results in apparent lower intra-hippocampal corticosterone levels and reduces glucocorticoid-associated cognitive decline during ageing. This low corticosterone tissue environment is maintained even though there is a hyperactive hypothalamic-pituitary-adrenal axis and elevated basal and stress-induced plasma corticosterone levels. Conversely, the major central effects of 11β-HSD2 are seen in development, as expression of 11β-HSD2 is high in fetal and certain parts of the neonate brain, but is confined to a few discrete regions of the adult brain. 11β-HSD2 acts as a dehydrogenase, inactivating corticosterone or cortisol through conversion to 11-Dehydrocorticosterone and cortisone. Loss of 11β-HSD2 from the fetus and fetally derived tissues results in altered development of the cerebellum in the neonatal period and a life-long phenotype of anxiety, consistent with early life glucocorticoid programming.
-
11β hydroxysteroid dehydrogenases in the brain
2003Co-Authors: Megan C Holmes, John J. Mullins, Joyce L W Yau, Yuri Kotelevtsev, Jonathan R. SecklAbstract:Glucocorticoids affect a wide range of processes in the brain, altering neurotransmission, electrophysiological activity, metabolism, cell division, and death. These actions are mediated by corticosteroid receptors (glucocorticoid and mineralocorticoid) that modify transcriptional activity of target genes. The amount of steroid available to activate these receptors is not only dependent on the circulating levels but also on pre-receptor metabolism of glucocorticoids occurring intracellularly. This metabolism is carried out by the enzymes 11beta-hydroxysteroid dehydrogenases (11beta-HSDs). There are two distinct isozymes, the products of distantly related genes. 11beta-HSD type 2 inactivates glucocorticoids to its inert 11-keto derivative, while 11alpha-HSD type 1 elevates intracellular glucocorticoid levels by regenerating active glucocorticoids from circulating 11-Dehydrocorticosterone or cortisone. This review highlights the important and very different roles the two enzymes play in the brain, outlining recent results obtained from studying mice with a targeted gene deletion in the 11beta-HSD1 or 11beta-HSD2 genes.
-
phenotypic analysis of mice bearing targeted deletions of 11β hydroxysteroid dehydrogenases 1 and 2 genes
2001Co-Authors: Megan C Holmes, Yuri Kotelevtsev, John J. MullinsAbstract:Abstract The glucocorticoid metabolising enzymes, 11β-hydroxysteroid dehydrogenases (11β-HSD), play a critical role in determining the availability of glucocorticoids to activate their receptors and hence modulate target gene transcription. There are two isozymes, 11β-HSD-1 and -2, which act in opposing directions. 11β-HSD-2 acts as a dehydrogenase, converting active corticosterone (cortisol in humans) to its inactive 11-keto derivative (11-Dehydrocorticosterone in rodents and cortisone in humans), whereas 11β-HSD-1 acts as a reductase, regenerating active glucocorticoids in a tissue-specific manner. Owing to the lack of specific inhibitors of these enzymes, it has been difficult to confirm the roles and determine the importance of these enzymes in vivo. Hence, to address this, we produced transgenic mice with null-mutations in the genes encoding the 11β-HSD-1 or 11β-HSD-2 enzymes. 11β-HSD-2 −/− mice show signs of hypertension, hypotonic polyuria, hypokalemia and hypochloremia. These symptoms arise from illicit activation of mineralocorticoid receptors by glucocorticoids, in the absence of the protective action of 11β-HSD-2. The phenotype is directly comparable to the Syndrome of Apparent Mineralocorticoid Excess, seen in humans with mutations in the 11β-HSD-2 gene. Mice lacking 11β-HSD-1, however, show a more subtle phenotype with reduced activation of glucocorticoid-induced processes. They were unable to convert 11-Dehydrocorticosterone to corticosterone in vivo, confirming 11β-HSD-1 as the sole 11-reductase in the mouse. They have elevated circulating levels of plasma corticosterone levels and adrenal hyperplasia, but they also have attenuated glucocorticoid-induced activation of gluconeogenic enzymes in response to fasting, and lower glucose levels in response to obesity or stress. Overall, these transgenic models have proved very useful for elucidating the roles of 11β-HSDs in vivo and will be a unique resource for investigating the importance of each enzyme in the diverse actions of glucocorticoids.
-
intracellular regeneration of glucocorticoids by 11β hydroxysteroid dehydrogenase 11β hsd 1 plays a key role in regulation of the hypothalamic pituitary adrenal axis analysis of 11β hsd 1 deficient mice1
2001Co-Authors: Hayley J Harris, Jonathan R. Seckl, John J. Mullins, Yuri Kotelevtsev, Megan C HolmesAbstract:11β-Hydroxysteroid dehydrogenases (11β-HSDs) catalyze interconversion of active corticosterone and inert 11-Dehydrocorticosterone, thus regulating glucocorticoid access to intracellular receptors in vivo. 11β-HSD type 1 is a reductase, locally regenerating active glucocorticoids. To explore the role of this isozyme in the brain, we examined hypothalamic-pituitary-adrenal axis (HPA) regulation in mice homozygous for a targeted disruption of the 11β-HSD-1 gene. 11β-HSD-1-deficient mice showed elevated plasma corticosterone and ACTH levels at the diurnal nadir, with a prolonged corticosterone peak, suggesting abnormal HPA control and enhanced circadian HPA drive. Despite elevated corticosterone levels, several hippocampal and hypothalamic glucocorticoid-sensitive messenger RNAs were normally expressed in 11β-HSD-1-deficient mice, implying reduced effective glucocorticoid activity within neurons. 11β-HSD-1-deficient mice showed exaggerated ACTH and corticosterone responses to restraint stress, with a delayed ...
-
11β hydroxysteroid dehydrogenase type 1 knockout mice show attenuated glucocorticoid inducible responses and resist hyperglycemia on obesity or stress
1997Co-Authors: Yuri Kotelevtsev, Christopher R. W. Edwards, Megan C Holmes, Ann N Burchell, Pamela Houston, Dieter Schmoll, Pauline Jamieson, Ruth Best, Roger W Brown, J R SecklAbstract:Glucocorticoid hormones, acting via nuclear receptors, regulate many metabolic processes, including hepatic gluconeogenesis. It recently has been recognized that intracellular glucocorticoid concentrations are determined not only by plasma hormone levels, but also by intracellular 11β-hydroxysteroid dehydrogenases (11β-HSDs), which interconvert active corticosterone (cortisol in humans) and inert 11-Dehydrocorticosterone (cortisone in humans). 11β-HSD type 2, a dehydrogenase, thus excludes glucocorticoids from otherwise nonselective mineralocorticoid receptors in the kidney. Recent data suggest the type 1 isozyme (11β-HSD-1) may function as an 11β-reductase, regenerating active glucocorticoids from circulating inert 11-keto forms in specific tissues, notably the liver. To examine the importance of this enzyme isoform in vivo, mice were produced with targeted disruption of the 11β-HSD-1 gene. These mice were unable to convert inert 11-Dehydrocorticosterone to corticosterone in vivo. Despite compensatory adrenal hyperplasia and increased adrenal secretion of corticosterone, on starvation homozygous mutants had attenuated activation of the key hepatic gluconeogenic enzymes glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, presumably, because of relative intrahepatic glucocorticoid deficiency. The 11β-HSD-1 −/− mice were found to resist hyperglycamia provoked by obesity or stress. Attenuation of hepatic 11β-HSD-1 may provide a novel approach to the regulation of gluconeogenesis.
John J. Mullins - One of the best experts on this subject based on the ideXlab platform.
-
Genetic manipulation of 11β-hydroxysteroid dehydrogenases in mice
2005Co-Authors: Janice M. Paterson, John J. MullinsAbstract:11β-Hydroxysteroid dehydrogenases (HSDs) interconvert active 11-hydroxy glucocorticoids (cortisol, corticosterone) and their inert 11-keto derivatives (cortisone, 11-Dehydrocorticosterone). 11β-HSD...
-
11β hydroxysteroid dehydrogenases in the brain
2003Co-Authors: Megan C Holmes, John J. Mullins, Joyce L W Yau, Yuri Kotelevtsev, Jonathan R. SecklAbstract:Glucocorticoids affect a wide range of processes in the brain, altering neurotransmission, electrophysiological activity, metabolism, cell division, and death. These actions are mediated by corticosteroid receptors (glucocorticoid and mineralocorticoid) that modify transcriptional activity of target genes. The amount of steroid available to activate these receptors is not only dependent on the circulating levels but also on pre-receptor metabolism of glucocorticoids occurring intracellularly. This metabolism is carried out by the enzymes 11beta-hydroxysteroid dehydrogenases (11beta-HSDs). There are two distinct isozymes, the products of distantly related genes. 11beta-HSD type 2 inactivates glucocorticoids to its inert 11-keto derivative, while 11alpha-HSD type 1 elevates intracellular glucocorticoid levels by regenerating active glucocorticoids from circulating 11-Dehydrocorticosterone or cortisone. This review highlights the important and very different roles the two enzymes play in the brain, outlining recent results obtained from studying mice with a targeted gene deletion in the 11beta-HSD1 or 11beta-HSD2 genes.
-
lack of tissue glucocorticoid reactivation in 11β hydroxysteroid dehydrogenase type 1 knockout mice ameliorates age related learning impairments
2001Co-Authors: Joyce L W Yau, John J. Mullins, Yuri Kotelevtsev, Christopher J. Kenyon, June Noble, Carina Hibberd, Jonathan R. SecklAbstract:11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1) intracellularly regenerates active corticosterone from circulating inert 11-Dehydrocorticosterone (11-DHC) in specific tissues. The hippocampus is a brain structure particularly vulnerable to glucocorticoid neurotoxicity with aging. In intact hippocampal cells in culture, 11β-HSD-1 acts as a functional 11β-reductase reactivating inert 11-DHC to corticosterone, thereby potentiating kainate neurotoxicity. We examined the functional significance of 11β-HSD-1 in the central nervous system by using knockout mice. Aged wild-type mice developed elevated plasma corticosterone levels that correlated with learning deficits in the watermaze. In contrast, despite elevated plasma corticosterone levels throughout life, this glucocorticoid-associated learning deficit was ameliorated in aged 11β-HSD-1 knockout mice, implicating lower intraneuronal corticosterone levels through lack of 11-DHC reactivation. Indeed, aged knockout mice showed significantly lower hippocampal tissue corticosterone levels than wild-type controls. These findings demonstrate that tissue corticosterone levels do not merely reflect plasma levels and appear to play a more important role in hippocampal functions than circulating blood levels. The data emphasize the crucial importance of local enzymes in determining intracellular glucocorticoid activity. Selective 11β-HSD-1 inhibitors may protect against hippocampal function decline with age.
-
phenotypic analysis of mice bearing targeted deletions of 11β hydroxysteroid dehydrogenases 1 and 2 genes
2001Co-Authors: Megan C Holmes, Yuri Kotelevtsev, John J. MullinsAbstract:Abstract The glucocorticoid metabolising enzymes, 11β-hydroxysteroid dehydrogenases (11β-HSD), play a critical role in determining the availability of glucocorticoids to activate their receptors and hence modulate target gene transcription. There are two isozymes, 11β-HSD-1 and -2, which act in opposing directions. 11β-HSD-2 acts as a dehydrogenase, converting active corticosterone (cortisol in humans) to its inactive 11-keto derivative (11-Dehydrocorticosterone in rodents and cortisone in humans), whereas 11β-HSD-1 acts as a reductase, regenerating active glucocorticoids in a tissue-specific manner. Owing to the lack of specific inhibitors of these enzymes, it has been difficult to confirm the roles and determine the importance of these enzymes in vivo. Hence, to address this, we produced transgenic mice with null-mutations in the genes encoding the 11β-HSD-1 or 11β-HSD-2 enzymes. 11β-HSD-2 −/− mice show signs of hypertension, hypotonic polyuria, hypokalemia and hypochloremia. These symptoms arise from illicit activation of mineralocorticoid receptors by glucocorticoids, in the absence of the protective action of 11β-HSD-2. The phenotype is directly comparable to the Syndrome of Apparent Mineralocorticoid Excess, seen in humans with mutations in the 11β-HSD-2 gene. Mice lacking 11β-HSD-1, however, show a more subtle phenotype with reduced activation of glucocorticoid-induced processes. They were unable to convert 11-Dehydrocorticosterone to corticosterone in vivo, confirming 11β-HSD-1 as the sole 11-reductase in the mouse. They have elevated circulating levels of plasma corticosterone levels and adrenal hyperplasia, but they also have attenuated glucocorticoid-induced activation of gluconeogenic enzymes in response to fasting, and lower glucose levels in response to obesity or stress. Overall, these transgenic models have proved very useful for elucidating the roles of 11β-HSDs in vivo and will be a unique resource for investigating the importance of each enzyme in the diverse actions of glucocorticoids.
-
intracellular regeneration of glucocorticoids by 11β hydroxysteroid dehydrogenase 11β hsd 1 plays a key role in regulation of the hypothalamic pituitary adrenal axis analysis of 11β hsd 1 deficient mice1
2001Co-Authors: Hayley J Harris, Jonathan R. Seckl, John J. Mullins, Yuri Kotelevtsev, Megan C HolmesAbstract:11β-Hydroxysteroid dehydrogenases (11β-HSDs) catalyze interconversion of active corticosterone and inert 11-Dehydrocorticosterone, thus regulating glucocorticoid access to intracellular receptors in vivo. 11β-HSD type 1 is a reductase, locally regenerating active glucocorticoids. To explore the role of this isozyme in the brain, we examined hypothalamic-pituitary-adrenal axis (HPA) regulation in mice homozygous for a targeted disruption of the 11β-HSD-1 gene. 11β-HSD-1-deficient mice showed elevated plasma corticosterone and ACTH levels at the diurnal nadir, with a prolonged corticosterone peak, suggesting abnormal HPA control and enhanced circadian HPA drive. Despite elevated corticosterone levels, several hippocampal and hypothalamic glucocorticoid-sensitive messenger RNAs were normally expressed in 11β-HSD-1-deficient mice, implying reduced effective glucocorticoid activity within neurons. 11β-HSD-1-deficient mice showed exaggerated ACTH and corticosterone responses to restraint stress, with a delayed ...
Gareth G Lavery - One of the best experts on this subject based on the ideXlab platform.
-
hexose 6 phosphate dehydrogenase h6pd and corticosteroid metabolism
2007Co-Authors: Perrin C White, Daniela Rogoff, Randy D Mcmillan, Gareth G LaveryAbstract:Cortisone or (in rodents) 11-Dehydrocorticosterone are reduced to cortisol or corticosterone, respectively, by the oxo-reductase activity of 11β-hydroxysteroid dehydrogenase type 1 (11-HSD1). This requires NADPH, generated by hexose-6-phosphate dehydrogenase (H6PD), a component of the pentose phosphate pathway. H6PD is located along with 11-HSD1 in the lumen of the endoplasmic reticulum (ER). Increasing or decreasing expression levels of H6PD in cultured cells has corresponding effects on the reductase activity of 11-HSD1. Mice carrying a targeted mutation in H6PD have drastically decreased 11-HSD1 oxo-reductase activity, but their 11-dehydrogenase activity is increased. They have many phenotypic features in common with mice carrying a mutation of 11-HSD1 itself. Polymorphisms in both H6PD and 11-HSD1 were originally identified in patients with apparent cortisone reductase deficiency (who have signs of hyperandrogenism and decreased urinary excretion of cortisol versus cortisone metabolites). However, these polymorphisms do not have detectable biochemical or physiologic effects when prospectively ascertained.
-
hexose 6 phosphate dehydrogenase knock out mice lack 11β hydroxysteroid dehydrogenase type 1 mediated glucocorticoid generation
2006Co-Authors: Gareth G Lavery, Elizabeth A Walker, Nicole Draper, Pancharatnam Jeyasuria, Josep Marcos, Cedric H L Shackleton, Keith L Parker, Perrin C WhiteAbstract:The local generation of active glucocorticoid by NADPH-dependent, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) oxoreductase activity, has emerged as an important factor in regulating hepatic glucose output and visceral adiposity. We have proposed that this NADPH is generated within the endoplasmic reticulum by the enzyme hexose-6-phosphate dehydrogenase. To address this hypothesis, we generated mice with a targeted inactivation of the H6PD gene. These mice were unable to convert 11-Dehydrocorticosterone (11-DHC) to corticosterone but demonstrated increased corticosterone to 11-DHC conversion consistent with lack of 11β-HSD1 oxoreductase and a concomitant increase in dehydrogenase activity. This increased corticosterone clearance in the knock-out mice resulted in a reduction in circulating corticosterone levels. Our studies define the critical requirement of hexose-6-phosphate dehydrogenase for 11β-HSD1 oxoreductase activity and add a new dimension to the investigation of 11β-HSD1 as a therapeutic target in patients with the metabolic syndrome.