Biomedical subjects

Martin Hewison

Publications and source records attributed to Martin Hewison.

At least 37 records · Page 2Linked to original sources

PubMed2004

Response element binding proteins and intracellular vitamin D binding proteins: novel regulators of vitamin D trafficking, action and metabolism.

Using vitamin D-resistant New World primates as model of natural diversity for sterol/steroid action and metabolism, two families of novel intracellular vitamin D regulatory proteins have been discovered and their human homologs elucidated. The first family of proteins, heterogeneous nuclear ribonucleoproteins (hnRNPs), initially considered to function only as pre-mRNA-interacting proteins, have been demonstrated to be potent cis-acting, trans-dominant regulators of vitamin D hormone-driven gene transactivation. The second group of proteins bind 25-hydroxylated vitamin D metabolites. Their overexpression increases vitamin D receptor (VDR)-directed target gene expression. We found that these intracellular vitamin D binding proteins (IDBPs) are homologous to proteins in the heat shock protein-70 family. Our ongoing studies indicate directly or indirectly through a series of protein interactions that the IDBPs interact with hydroxylated vitamin D metabolites and facilitate their intracellular targeting.

Animals↗

PubMed2004

Expression of 25-hydroxyvitamin D3-1alpha-hydroxylase in pancreatic islets.

A number of studies have suggested that Vitamin D has a potential role in the development/treatment of diabetes. These effects may be mediated by circulating levels of 1alpha,25(OH)(2)D(3), but local production of 1alpha,25(OH)(2)D(3), catalysed by the enzyme 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-OHase), is also likely to be important. RT-PCR analyses demonstrated that both isolated rat islets and MIN6 cells (mouse insulin-secreting cell line, characteristic of beta cells) expressed 1alpha-OHase mRNA. The transcript in both cell types was similar to that seen in HKC-8 cells (a renal cell line, which expresses 1alpha-OHase). Western blot analysis and immunolocalisation identified 1alpha-OHase protein in MIN6 cells and human pancreatic tissue. In addition, suspensions of rat islets were able to convert [3H]-25-hydroxyvitamin D(3) to [3H]-1alpha,25(OH)(2)D(3), demonstrating 1alpha-OHase activity. Both cell systems expressed the Vitamin D receptor and 1alpha,25(OH)(2)D(3) (50nM) evoked a rapid rise in [Ca(2+)](i) in MIN6 cells. This data clearly demonstrates islets are able to produce 1alpha,25(OH)(2)D(3) and respond rapidly to treatment with 1alpha,25(OH)(2)D(3). Therefore, we would postulate that local production of 1alpha,25(OH)(2)D(3) maybe an important autocrine link between Vitamin D status and pancreatic function.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed2004

Vitamin D and placental-decidual function.

The active form of vitamin D (1,25-dihydroxyvitamin D(3), 1,25[OH](2)D(3)) has well-established effects on bone metabolism and mineral homeostasis. However, recently it has become clear that 1,25(OH)(2)D(3) has potent antiproliferative and immunomodulatory actions that are not immediately linked to its role as a skeletal regulator. Both the nuclear receptor for 1,25(OH)(2)D(3) (vitamin D receptor, VDR) and the vitamin D-activating enzyme 1alpha-hydroxylase are expressed in a wide variety of nonclassic tissues, highlighting the potential for local autocrine-paracrine responses rather than traditional endocrine effects. Prominent among the tissues that express 1alpha-hydroxylase is the placenta-decidua, and this has raised important questions concerning the potential role of locally generated 1,25(OH)(2)D(3) as a modulator of fetal-placental development and function. When bound to the VDR, 1,25(OH)(2)D(3) regulates key target genes associated with implantation, such as HOXA10, whereas the potent immunosuppressive effects of 1,25(OH)(2)D(3) suggest a role in implantation tolerance. These observations are further supported by data from our group showing increased expression of 1alpha-hydroxylase and VDR in first-trimester trophoblast and decidua from human pregnancies. Studies by other groups have reported abnormal expression of 1alpha-hydroxylase in preeclamptic pregnancies, revealing a potential role for 1,25(OH)(2)D(3) as a regulator of placentation. The effect of vitamin D on reproduction has been further endorsed by murine gene knockout models for 1alpha-hydroxylase and VDR, both of which are infertile. These observations and others are discussed in this article in which we postulate an active role for 1,25(OH)(2)D(3) in placenta-decidua. In particular, we describe how induction of the vitamin D-activating enzyme 1alpha-hydroxylase in early gestation might provide a mechanism by which environmental or dietary vitamin D can influence fetal-placental development.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed2004

Increased expression of 25-hydroxyvitamin D-1alpha-hydroxylase in dysgerminomas: a novel form of humoral hypercalcemia of malignancy.

Humoral hypercalcemia of malignancy (HHM) is a common paraneoplastic disorder usually associated with increased synthesis of parathyroid hormone-related peptide (PTHrP). Unlike non-cancer forms of hypercalcemia, HHM does not routinely involve increased circulating levels of the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Dysgerminomas are a notable exception to this rule, previous reports having described hypercalcemia with elevated serum 1,25(OH)2D3. To investigate the etiology of this form of HHM we have characterized expression and activity of the enzyme that catalyzes synthesis of 1,25(OH)2D3, 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase), in a collection of 12 dysgerminomas. RT-PCR analyses indicated that mRNA for 1alpha-hydroxylase was increased 222-fold in dysgerminomas compared to non-tumor ovarian tissue. Parallel enzyme assays in tissue homogenates showed that dysgerminomas produced fivefold higher levels of 1,25(OH)2D3 compared to normal ovarian tissue. Immunolocalization studies indicated that 1alpha-hydroxylase was expressed by both tumor cells and by macrophages within the inflammatory cell infiltrate associated with dysgerminomas. The immunological nature of the increased 1,25(OH)2D3 production observed in dysgerminomas was further emphasized by correlation between expression of 1alpha-hydroxylase and the endotoxin recognition factors CD14 and toll-like receptor 4 (TLR4). These data suggest that inflammatory mechanisms associated with dysgerminomas are the underlying cause of the increased expression and activity of 1alpha-hydroxylase associated with these tumors. We further postulate that this autocrine/paracrine action of 1alpha-hydroxylase may lead to increased circulating levels of 1,25(OH)2D3 and a form of HHM which is distinct from that seen with PTHrP-secreting tumors.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed2004

Hormones and immune function: implications of aging.

Aging is associated with a decline in immunity described as immunosenescence. This is paralleled by a decline in the production of several hormones, as typically illustrated by the menopausal loss of ovarian oestrogen production. However, other hormonal changes that occur with aging and that potentially impact on immune function include the release of the pineal gland hormone melatonin and pituitary growth hormone, adrenal production of dehydroepiandrosterone and tissue-specific availability of active vitamin D. It remains to be established whether hormonal changes with aging actually contribute to immunosenescence and this area is at the interface of fact and fiction, clearly inviting systematic research efforts. As a step in this direction, the present review summarizes established facts on the physiology of secretion and function of hormones that, in most cases, decline with aging and that are likely to affect the immune system.

Aging↗

PubMed2004

11beta-hydroxysteroid dehydrogenase type 1: a tissue-specific regulator of glucocorticoid response.

11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) interconverts inactive cortisone and active cortisol. Although bidirectional, in vivo it is believed to function as a reductase generating active glucocorticoid at a prereceptor level, enhancing glucocorticoid receptor activation. In this review, we discuss both the genetic and enzymatic characterization of 11beta-HSD1, as well as describing its role in physiology and pathology in a tissue-specific manner. The molecular basis of cortisone reductase deficiency, the putative "11beta-HSD1 knockout state" in humans, has been defined and is caused by intronic mutations in HSD11B1 that decrease gene transcription together with mutations in hexose-6-phosphate dehydrogenase, an endoluminal enzyme that provides reduced nicotinamide-adenine dinucleotide phosphate as cofactor to 11beta-HSD1 to permit reductase activity. We speculate that hexose-6-phosphate dehydrogenase activity and therefore reduced nicotinamide-adenine dinucleotide phosphate supply may be crucial in determining the directionality of 11beta-HSD1 activity. Therapeutic inhibition of 11beta-HSD1 reductase activity in patients with obesity and the metabolic syndrome, as well as in glaucoma and osteoporosis, remains an exciting prospect.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗

PubMed2003

Late-onset apparent mineralocorticoid excess caused by novel compound heterozygous mutations in the HSD11B2 gene.

Mutations in the gene encoding 11beta-hydroxysteroid dehydrogenase type 2, 11beta-HSD2 (HSD11B2), explain the molecular basis for the syndrome of apparent mineralocorticoid excess (AME), characterized by severe hypertension and hypokalemic alkalosis. Cortisol is the offending mineralocorticoid in AME, as the result of a lack of 11beta-HSD2-mediated cortisol to cortisone inactivation. In this study, we describe mutations in the HSD11B2 gene in 3 additional AME kindreds in which probands presented in adult life, with milder phenotypes including the original seminal case reported by Stewart and Edwards. Genetic analysis of the HSD11B2 gene revealed that all probands were compound heterozygotes, for a total of 7 novel coding and noncoding mutations. Of the 7 mutations detected, 6 were investigated for their effects on gene expression and enzyme activity by the use of mutant cDNA and minigene constructs transfected into HEK 293 cells. Four missense mutations resulted in enzymes with varying degrees of activity, all <10% of wild type. A further 2 mutations generated incorrectly spliced mRNA and predicted severely truncated, inactive enzyme. The mothers of 2 probands heterozygous for missense mutations have presented with a phenotype indistinguishable from "essential" hypertension. These genetic and biochemical data emphasize the heterogeneous nature of AME and the effects that heterozygosity at the HSD11B2 locus can have on blood pressure in later life.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗

PubMed2003

Differential regulation of vitamin D receptor and its ligand in human monocyte-derived dendritic cells.

The functions of dendritic cells (DCs) are tightly regulated such that protective immune responses are elicited and unwanted immune responses are prevented. 1 alpha 25-dihydroxyvitamin D(3) (1 alpha 25(OH)(2)D(3)) has been identified as a major factor that inhibits the differentiation and maturation of DCs, an effect dependent upon its binding to the nuclear vitamin D receptor (VDR). Physiological control of 1 alpha 25(OH)(2)D(3) levels is critically dependent upon 25-hydroxyvitamin D(3)-1 alpha-hydroxylase (1 alpha OHase), a mitochondrial cytochrome P450 enzyme that catalyzes the conversion of inactive precursor 25-hydroxyvitamin D(3) (25(OH)D(3)) to the active metabolite 1 alpha 25(OH)(2)D(3). Using a human monocyte-derived DC (moDC) model, we have examined the relationship between DC VDR expression and the impact of exposure to its ligand, 1 alpha 25(OH)(2)D(3). We show for the first time that moDCs are able to synthesize 1 alpha 25(OH)(2)D(3) in vitro as a consequence of increased 1 alpha OHase expression. Following terminal differentiation induced by a diverse set of maturation stimuli, there is marked transcriptional up-regulation of 1 alpha OHase leading to increased 1 alpha OHase enzyme activity. Consistent with this finding is the observation that the development and function of moDCs is inhibited at physiological concentrations of the inactive metabolite 25(OH)D(3). In contrast to 1 alpha OHase, VDR expression is down-regulated as monocytes differentiate into immature DCs. Addition of 1 alpha 25(OH)(2)D(3) to moDC cultures at different time points indicates that its inhibitory effects are greater in monocyte precursors than in immature DCs. In conclusion, differential regulation of endogenous 1 alpha 25(OH)(2)D(3) ligand and its nuclear receptor appear to be important regulators of DC biology and represent potential targets for the manipulation of DC function.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed2003

Heterogeneous nuclear ribonucleoprotein (hnRNP) binding to hormone response elements: a cause of vitamin D resistance.

In previous studies, we have shown that steroid hormone resistance in New World primates occurs in the absence of abnormal expression of cognate nuclear receptors. Rather, these animals have elevated levels of heterogeneous nuclear ribonucleoproteins (hnRNPs) that act as hormone response element-binding proteins and attenuate target gene transactivation. Here we present evidence for a similar mechanism in humans via a patient with resistance to the active form of vitamin D [1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))] who presented with normal vitamin D receptor (VDR) expression. Initial cotransfection studies showed that the cells of the patient suppressed basal and hormone-induced transactivation by wild-type VDR. Electrophoretic mobility-shift assays and Western/Southwestern blot analyses indicated that this suppressive effect was due to overexpression of a nuclear protein that specifically interacts with a DNA response element known to bind retinoid X receptor-VDR heterodimers. Ab blocking in electrophoretic mobility-shift assays indicated that this dominant-negative acting protein was in the hnRNPA family of nucleic acid-binding proteins. Further studies have shown that several members of this family, most notably hnRNPA1, were able to suppress basal and 1,25(OH)(2)D(3)-induced luciferase activity. We therefore propose that this case of vitamin D resistance in a human subject is similar to that previously described for New World primates in which abnormal expression of a hormone response element-binding protein can cause target cell resistance to 1,25(OH)(2)D(3). That this protein is a member of the hnRNP family capable of interacting with double-stranded DNA highlights a potentially important new component of the complex machinery required for steroid hormone signal transduction.

B-Lymphocytes↗

PubMed2003

The aldo-keto reductase AKR1C3 is a novel suppressor of cell differentiation that provides a plausible target for the non-cyclooxygenase-dependent antineoplastic actions of nonsteroidal anti-inflammatory drugs.

We and others have demonstrated expression of the aldo-keto reductase AKR1C3 in myeloid leukemia cell lines and that inhibitors of the enzyme, including nonsteroidal anti-inflammatory drugs (NSAIDs), promote HL-60 differentiation in response to all-trans retinoic acid (ATRA) and 1alpha,25-dihydroxyvitamin D3 (D3). Here, we demonstrate that overexpression of AKR1C3 reciprocally desensitizes HL-60 cells to ATRA and D3, thus confirming the enzyme as a novel regulator of cell differentiation. AKR1C3 possesses marked 11-ketoreductase activity converting prostaglandin (PG) D2 to PGF2alpha. Supplementing HL-60 cultures with PGD2 mimicked treatment with AKR1C3-inhibitors by enhancing the differentiation of the cells in response to ATRA. However, PGD2 is chemically unstable, being converted first to PGJ2 and then stepwise to 15-deoxy-Delta(12,14)-prostaglandin J2(15Delta-PGJ2), a natural ligand for the peroxisome proliferator-activated receptor-gamma (PPARgamma). Consistent with this, PGD2 was rapidly converted to PGJ2 under normal tissue culture conditions but not in the presence of recombinant AKR1C3 when PGF2alpha was predominantly formed. In addition, PGJ2 but not PGF2alpha recapitulated the potentiation of HL-60 differentiation by PGD2 and AKR1C3 inhibitors. Furthermore, the capacity of all of these treatments to potentiate HL-60 cell differentiation was significantly reduced in the presence of the PPARgamma-antagonist GW 9662. We conclude that AKRIC3 protects HL-60 cells against ATRA and D3-induced cell differentiation by limiting the production of natural PPARgamma ligands via the diversion of PGD2 toward PGF2alpha and away from PGJ2. In addition, these observations identify AKR1C3 as plausible target for the non-cyclooxygenase-dependent antineoplastic actions of NSAIDs.

3-Hydroxysteroid Dehydrogenases↗

PubMed2003

Mutations in the genes encoding 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase interact to cause cortisone reductase deficiency.

In cortisone reductase deficiency (CRD), activation of cortisone to cortisol does not occur, resulting in adrenocorticotropin-mediated androgen excess and a phenotype resembling polycystic ovary syndrome (PCOS; refs. 1,2). This suggests a defect in the gene HSD11B1 encoding 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), a primary regulator of tissue-specific glucocorticoid bioavailability. We identified intronic mutations in HSD11B1 that resulted in reduced gene transcription in three individuals with CRD. In vivo, 11beta-HSD1 catalyzes the reduction of cortisone to cortisol whereas purified enzyme acts as a dehydrogenase converting cortisol to cortisone. Oxo-reductase activity can be regained using a NADPH-regeneration system and the cytosolic enzyme glucose-6-phosphate dehydrogenase. But the catalytic domain of 11beta-HSD1 faces into the lumen of the endoplasmic reticulum (ER; ref. 6). We hypothesized that endolumenal hexose-6-phosphate dehydrogenase (H6PDH) regenerates NADPH in the ER, thereby influencing directionality of 11beta-HSD1 activity. Mutations in exon 5 of H6PD in individuals with CRD attenuated or abolished H6PDH activity. These individuals have mutations in both HSD11B1 and H6PD in a triallelic digenic model of inheritance, resulting in low 11beta-HSD1 expression and ER NADPH generation with loss of 11beta-HSD1 oxo-reductase activity. CRD defines a new ER-specific redox potential and establishes H6PDH as a potential factor in the pathogenesis of PCOS.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗

PubMed2003

Serum- and glucocorticoid-regulated kinase isoform-1 and epithelial sodium channel subunits in human ocular ciliary epithelium.

PURPOSE: In peripheral sodium-transporting tissues, the serum- and glucocorticoid-regulated kinase (SGK) isoform-1 is an early corticosteroid target gene in the activation of epithelial sodium channels (ENaCs). Sodium transport across the human ocular nonpigmented and pigmented ciliary epithelial bilayer (NPE-PE) is essential for aqueous humor production, but the expression of SGK1 and ENaC subunits remain to be defined. METHODS: SGK1 and ENaC subunits were evaluated by in situ hybridization and RT-PCR analysis on human NPE-PE sections and an NPE cell line (ODM-2). Northern blot analyses were conducted on ODM-2 cells incubated with dexamethasone (DEX) or aldosterone (ALDO) and RU38486 (a glucocorticoid receptor [GR] antagonist) or RU26752 (a mineralocorticoid receptor [MR] antagonist) or both inhibitors. The affinity of the GRs and MRs for DEX and ALDO was assessed by radioligand-binding assays. RESULTS: Expression of SGK1 and ENaC subunits was confirmed in NPE-PE tissues and ODM-2 cells. Dose-dependent induction of SGK1 mRNA in the ODM-2 cells was demonstrated after incubation with DEX or ALDO. While response to DEX was not inhibited by RU38486 or RU26752, there was a moderate reduction in induction by ALDO in the presence of RU26752 that was completely abolished in the presence of both inhibitors. Specific binding of (3)[H]DEX and (3)[H]ALDO was established, revealing greater expression of GRs than MRs. CONCLUSIONS: The expression of ENaCs within the NPE-PE and corticosteroid regulation of SGK1 through the GR and MR, indicate that this mechanism may be a feature of sodium transport in the human ocular ciliary epithelium.

Aldosterone↗

PubMed2003

11beta-hydroxysteroid dehydrogenase type 1 activity predicts the effects of glucocorticoids on bone.

Individual susceptibility to glucocorticoid-induced osteoporosis is difficult to predict clinically. We recently characterized expression of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in human osteoblasts. This enzyme generates active cortisol (or prednisolone) from inactive cortisone (or prednisone) and regulates glucocorticoid action in vitro. We, thus, hypothesized that osteoblastic 11beta-HSD1 mediates susceptibility to glucocorticoid-induced osteoporosis. Twenty healthy males ingested 5 mg prednisolone twice daily for 7 d, and relationships between changes in bone turnover markers and urinary measures of corticosteroid metabolism were examined. The bone formation markers osteocalcin and N-terminal propeptide of type I collagen decreased in all subjects (P < 0.001), but resorption markers were unchanged. The extent of fall in formation markers correlated with baseline 11beta-HSD1 activity with high activity predicting the greatest fall [for osteocalcin d 4 and 7, r = -0.58 and -0.56 (P < 0.01); for N-terminal propeptide of type I collagen d 4, r = -0.51 (P < 0.05)]. There was no correlation with measures of glucocorticoid inactivation or total corticosteroid metabolite production. Urinary measures of 11beta-HSD1 activity predict the response of bone formation markers to glucocorticoids, and this appears to reflect increased generation of active glucocorticoids within osteoblasts. Measures of 11beta-HSD1 activity may predict individual susceptibility to glucocorticoid-induced osteoporosis, and these data should facilitate the development of bone-sparing glucocorticoids.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗

PubMed2003

Vitamin D-mediated hypercalcemia in lymphoma: evidence for hormone production by tumor-adjacent macrophages.

Nearly one-half of all hypercalcemic patients with lymphoma present with inappropriately elevated circulating concentrations of the active vitamin D metabolite 1,25-dihydroxyvitamin D (1,25(OH)2D3). However, the cellular source of the vitamin D hormone in lymphomas remains unclear. To address this, we report the case of a 75-year-old man with hypercalcemia associated with raised circulating concentrations of 1,25(OH)2D3 and suppressed parathyroid hormone (PTH) levels. Positron emission tomographic (PET) and computed tomographic (CT) imaging revealed the presence of a large lymphoma that was confined to the spleen; subsequent pathological analysis showed that this was an intermediate grade B-cell lymphoma. After surgical removal of the spleen, serum calcium and 1,25(OH)2D3 levels became normalized within 24 h. Immunolocalization of the vitamin D-activating enzyme 25-hydroxyvitamin D3-1alpha-hydroxylase (la-hydroxylase) in sections of resected spleen showed that staining was negative in the lymphoma cells but positive in neighboring macrophages. This case study indicates that the hypercalcemia associated with lymphomas may be due, in some instances, to excessive extrarenal production of 1,25(OH)2D3. Furthermore, by using immunohistochemistry to assess the distribution of la-hydroxylase, we have been able to show for the first time that tissue macrophages, rather than actual tumor cells, are the most likely ectopic source of this enzyme. Based on this case study, we propose that the abnormal synthesis of 1,25(OH)2D3 associated with some lymphomas is because of paracrine regulation of tumor-associated macrophages.

Aged↗

PubMed2002

The ontogeny of 25-hydroxyvitamin D(3) 1alpha-hydroxylase expression in human placenta and decidua.

In addition to its classical calciotropic effects, the active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) is a potent anti-proliferative/immunomodulatory secosteroid. The enzyme that catalyzes the synthesis of 1,25(OH)(2)D(3), 1alpha-hydroxylase (1alpha-OHase), is expressed in many human tissues, highlighting its possible role as an autocrine/paracrine activator of vitamin D. Immunohistochemical and RNA analyses were used to characterize the ontogeny of 1alpha-OHase expression in human placenta and decidua. Protein for 1alpha-OHase was detectable in trophoblast and decidua; the latter being stronger in decidualized stromal cells than macrophages, with no staining of lymphocytes. Quantitative reverse transcriptase-polymerase chain reaction was used to assess changes in mRNA expression for 1alpha-OHase at different gestations: first (mean, 9.1 +/- 1.5 weeks); second (mean, 14 +/- 1.8 weeks), and third trimester (mean, 39.3 +/- 2.5 weeks). 1alpha-OHase expression in decidua was approximately 1000-fold higher in first (95% confidence limits, 611 to 1376) and second (95% confidence limits, 633 to 1623) trimester biopsies when compared with the third trimester (95% confidence limits, 0.36 to 2.81) (both P < 0.001). In placenta, 1alpha-OHase expression was 80-fold higher in the first (range, 42 to 137) and second (range, 30 to 199) trimester when compared with third trimester biopsies (0.6 to 1.6) (both P < 0.001). Similar results were obtained by semiquantitative IHC. Parallel analysis of the receptor for 1,25(OH)(2)D(3) (vitamin D receptor) indicated that, as with 1alpha-OHase, highest levels of expression occurred in first trimester decidua. However, changes in vitamin D receptor mRNA expression across gestation were less pronounced than 1alpha-OHase. These spatiotemporal data emphasize the potential importance of 1alpha-OHase during early fetoplacental life and, in particular, suggest an autocrine/paracrine immunomodulatory function for the enzyme.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed2002

11Beta-hydroxysteroid dehydrogenase type 1 in differentiating omental human preadipocytes: from de-activation to generation of cortisol.

In humans, glucocorticoids are important regulators of adipose tissue distribution and function but circulating cortisol concentrations are normal in most patients with obesity. However, intracellular glucocorticoid levels can be modified by a microsomal enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) expressed mainly in the liver and adipose tissue. Locally generated cortisol within human adipose tissue can induce preadipocyte differentiation, but the relationship between 11beta-HSD1 expression and adipogenesis is unknown. Our present study has shown that in intact, undifferentiated omental (OM) but not subcutaneous (SC) preadipocytes, 11beta-HSD1 acts primarily as a dehydrogenase inactivating cortisol to cortisone. When preadipocytes become "committed" to adipocyte differentiation, oxo-reductase activity predominates generating cortisol. Since glucocorticoids are not only essential for OM preadipocyte differentiation but also inhibit cell proliferation, we postulate that 11beta-HSD1 dehydrogenase activity in "uncommitted" OM preadipocytes may provide an autocrine mechanism to protect preadipocytes from differentiation, in turn facilitating their proliferation. Once early differentiation is initiated, a "switch" to 11beta-HSD1 oxo-reductase activity generates cortisol, thus promoting adipogenesis. The differences in set-point of 11beta-HSD1 activity between OM and SC human adipose tissue may be an important factor in the pathogenesis of visceral obesity.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗

PubMed2002

Prereceptor regulation of glucocorticoid action by 11beta-hydroxysteroid dehydrogenase: a novel determinant of cell proliferation.

Isozymes of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) act at a prereceptor level to regulate the tissue-specific availability of active glucocorticoids. To examine the effect of this on cell proliferation and differentiation, we have developed transfectant variants of a rat osteosarcoma cell line that express cDNA for 11beta-HSD1 (ROS 17/2.8beta1) or 11beta-HSD2 (ROS 17/2.8beta2). ROS 17/2.8beta1 showed net conversion of cortisone to cortisol whereas ROS 17/2.8beta2 showed only inactivation of cortisol to cortisone. There was no significant difference in glucocorticoid receptor (GR) expression between the different clones. However, in proliferation and differentiation studies, ROS 17/2.8beta2 cells were completely resistant to cortisol. In contrast, ROS 17/2.8beta1 were sensitive to both cortisone and cortisol. Expression of 11beta-HSD1 decreased cell proliferation whereas 11beta-HSD2 increased proliferation. These responses appear to be due to metabolism of endogenous serum glucocorticoids; proliferation of ROS 17/2.8beta1 decreased further with exogenous cortisone or cortisol whereas ROS 17/2.8beta2 were resistant to both compounds. The pro-proliferative effects of 11beta-HSD2 were abrogated by 18beta-glycyrrhetinic acid, an 11beta-HSD inhibitor, and in cells transfected with cDNA encoding inactive 11beta-HSD2. Data indicate that differential regulation of 11beta-HSD1 and 2 (rather than GR expression) is a key determinant of cell proliferation. Dysregulated expression of 11beta-HSD2 may be a novel feature of tumorigenesis.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗

PubMed2002

A switch in dehydrogenase to reductase activity of 11 beta-hydroxysteroid dehydrogenase type 1 upon differentiation of human omental adipose stromal cells.

As exemplified in patients with Cushing's syndrome, glucocorticoids play an important role in regulating adipose tissue distribution and function, but circulating cortisol concentrations are normal in most patients with obesity. However, human omental adipose stromal cells (ASCs) can generate glucocorticoid locally through the expression of the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) type 1 (11 beta-HSD1), which, in intact cells, has been considered to be an oxoreductase, converting inactive cortisone (E) to cortisol (F). Locally produced F can induce ASC differentiation, but the relationship between 11 beta-HSD1 expression and adipocyte differentiation is unknown. Primary cultures of paired omental (om) and sc ASC and adipocytes were prepared from 17 patients undergoing elective abdominal surgery and cultured for up to 14 d. Expression and activity of 11 beta-HSD isozymes were analyzed together with early (lipoprotein lipase) and terminal (glycerol 3 phosphate dehydrogenase) markers of adipocyte differentiation. On d 1 of culture, 11 beta-HSD1 activity in intact om ASCs exceeded oxoreductase activity in every patient (78.9 +/- 24.9 vs. 15.8 +/- 3.7 [mean +/- SE] pmol/mg per hour, P < 0.001), and in sc ASCs, relative activities were similar (40.6 +/- 12.2 vs. 36.9 +/- 8.8). Conversely, in freshly isolated om adipocytes, reductase activity exceeded dehydrogenase activity (23.6 +/- 1.5 vs. 6.2 +/- 0.8 pmol/mg per hour, P < 0.01). Following 14 d of culture in serum-free conditions with addition of 10 nM insulin (Ctr) or insulin with 100 nM F (+F), lipoprotein lipase/18S RNA levels increased in both the Ctr- and +F-treated ASCs, but glycerol 3 phosphate dehydrogenase increased only in the +F cultures. In both cases, however, 11 beta-HSD1 oxoreductase activity exceeded dehydrogenase activity (Ctr: 53.3 +/- 9.0 vs. 32.4 +/- 10.5, P < 0.05; +F: 65.6 +/- 15.6 vs. 37.1 +/- 11.5 pmol/mg per hour, P < 0.05), despite no significant changes in 11 beta-HSD1 mRNA levels. In sc ASCs, dehydrogenase activity was similar to reductase activity in both Ctr- and +F-treated cells. Type 2 11 beta-HSD expression was undetectable in each case. These data show that in intact, undifferentiated om ASCs, 11 beta-HSD1 acts primarily as a dehydrogenase, but in mature adipocytes oxoreductase activity predominates. Because glucocorticoids inhibit cell proliferation, we postulate that 11 beta-HSD1 activity in uncommitted ASCs may facilitate proliferation rather than differentiation. Once early differentiation is initiated, a "switch" to 11 beta-HSD1 oxoreductase activity generates F, thus promoting adipogenesis. Site-specific regulation of the set-point of 11 beta-HSD1 activity may be an important mechanism underpinning visceral obesity.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗