Perrin C. White

Disease expression and molecular genotype in congenital adrenal hyperplasia due to 21-hydroxylase deficiency.

Genotyping for 10 mutations in the CYP21 gene was performed in 88 families with congenital adrenal hyperplasia due to 21-hydroxylase deficiency. Southern blot analysis was used to detect CYP21 deletions or large gene conversions, and allele-specific hybridizations were performed with DNA amplified by the polymerase chain reaction to detect smaller mutations. Mutations were detected on 95% of chromosomes examined. The most common mutations were an A----G change in the second intron affecting pre-mRNA splicing (26%), large deletions (21%), Ile-172----Asn (16%), and Val-281----Leu (11%). Patients were classified into three mutation groups based on degree of predicted enzymatic compromise. Mutation groups were correlated with clinical diagnosis and specific measures of in vivo 21-hydroxylase activity, such as 17-hydroxyprogesterone, aldosterone, and sodium balance. Mutation group A (no enzymatic activity) consisted principally of salt-wasting (severely affected) patients, group B (2% activity) of simple virilizing patients, and group C (10-20% activity) of nonclassic (mildly affected) patients, but each group contained patients with phenotypes either more or less severe than predicted. These data suggest that most but not all of the phenotypic variability in 21-hydroxylase deficiency results from allelic variation in CYP21. Accurate prenatal diagnosis should be possible in most cases using the described strategy.

Mutations in the genes encoding 11β-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 11β-hydroxysteroid dehydrogenase type 1 (11β-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, 11β-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 11β-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 11β-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 11β-HSD1 expression and ER NADPH generation with loss of 11β-HSD1 oxo-reductase activity. CRD defines a new ER-specific redox potential and establishes H6PDH as a potential factor in the pathogenesis of PCOS.

Associations Between Human Aldosterone Synthase (CYP11B2) Gene Polymorphisms and Left Ventricular Size, Mass, and Function

BACKGROUND Aldosterone has direct and indirect effects on the heart, and genetic variations in aldosterone synthesis could therefore influence cardiac structure and function. Such variations might be associated with polymorphisms in the gene encoding aldosterone synthase (CYP11B2), the enzyme catalyzing the last steps of aldosterone biosynthesis. METHODS AND RESULTS A Finnish population sample of 84 persons (44 women) aged 36 to 37 years was studied by M-mode and Doppler echocardiography to assess left ventricular size, mass, and function. Subjects were genotyped through the use of the polymerase chain reaction for two diallelic polymorphisms in CYP11B2: one in the transcriptional regulatory region (promoter) and the other in the second intron. In multiple regression analyses, the CYP11B2 promoter genotype predicted statistically significant variations in left ventricular end-diastolic diameter (beta=.40, P<.0001), end-systolic diameter (beta=.33, P=.0009), and mass (beta=.17, P=.023). These effects were independent of potentially confounding factors, including sex, body size, blood pressure, physical activity, smoking, and ethanol consumption. Genotype groups also differed in a measure of left ventricular diastolic function, the heart rate-adjusted atrial filling fraction (P=.018). Increased dietary salt, which is known to predict increased left ventricular mass, had this effect only in association with certain CYP11B2 genotypes (P<.001). CONCLUSIONS Genetic variations in or near the aldosterone synthase (CYP11B2) gene strongly affect left ventricular size and mass in young adults free of clinical heart disease. These polymorphisms may also influence the response of the left ventricle to increases in dietary salt.

Hexose-6-phosphate dehydrogenase knock-out mice lack 11β- hydroxysteroid dehydrogenase type 1-mediated glucocorticoid generation

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.

Haplotype analysis of CYP11B2

Polymorphisms affecting the synthesis of aldosterone or its regulation may have effects on blood pressure. For example, an autosomal dominant form of human hypertension, glucocorticoid suppressible hyperaldosteronism, is caused by recombination between the genes for aldosterone synthase (CYP11B2) and steroid 11 beta-hydroxylase (CYP11B1), creating a chimeric gene in which the CYP11B1 promoter and CYP11B2-specific coding sequences are juxtaposed. Thus, aldosterone synthesis is improperly regulated. We have begun an analysis of the human CYP11B2 and CYP11B1 genes to see if frequent polymorphisms exist and if they are correlated with differences in blood pressure. We have found frequent polymorphisms in CYP11B2. One in the promoter influences binding of the transcriptional regulatory protein, SF-1. Another is a gene conversion in intron 2 so that most of the intron has a sequence corresponding to CYP11B1. These polymorphisms are in linkage disequilibrium, defining 3 haplotypes. Blacks and whites differ significantly (p < 0.001) in the frequency with which these haplotypes occur. Further studies are required to determine if the observed differences between blacks and whites in blood pressure and in aldosterone levels can be explained in part by these allelic differences in CYP11B2 or by other polymorphisms in linkage disequilibrium on these haplotypes.

11 beta-hydroxysteroid dehydrogenase.

Publisher Summary This chapter reviews the historical perspective into the conceptual evolution of 11β-hydroxysteroid dehydrogenase (HSD) from its pedestrian origin as an enzyme that catalyzes reversible inactivation of corticosteroids to its currently more prestigious role as mediator of steroid-receptor interactions. An enzyme responsible for catalyzing the oxidation of cortisol to cortisone is found in rat liver and named “l lβ-hydroxy dehydrogenase.” The transformations catalyzed by this enzyme are illustrated in the chapter. The catalysis of 11-oxidation and 11-oxoreduction is not uniformly distributed among tissues. In liver, 11-oxoreduction is the dominant activity; in most other tissues, it is 11β-hydroxy oxidation. The recognition of clinical disorders whose symptomatology could be rationalized as being because of defects in 11-HSD expression. It helps in the development of the tools—antibodies, complementary DNA (cDNA)—that facilitate exploration of the enzyme at the molecular level. 11-HSD protects cells against the toxic effects of excess corticosteroid. The enzyme also serves a conservationist function, as the oxidized form of the steroid can be reduced by 11-oxoreductase to its active reduced form thus contributing to the circulating cortisol, and providing a buffer against the changes in blood level caused by paroxysmal secretion of the adrenal.

Minireview: steroidogenic factor 1: its roles in differentiation, development, and disease.

The orphan nuclear receptor steroidogenic factor 1 (SF-1, also called Ad4BP, encoded by the NR5A1 gene) is an essential regulator of endocrine development and function. Initially identified as a tissue-specific transcriptional regulator of cytochrome P450 steroid hydroxylases, studies of both global and tissue-specific knockout mice have demonstrated that SF-1 is required for the development of the adrenal glands, gonads, and ventromedial hypothalamus and for the proper functioning of pituitary gonadotropes. Many genes are transcriptionally regulated by SF-1, and many proteins, in turn, interact with SF-1 and modulate its activity. Whereas mice with heterozygous mutations that disrupt SF-1 function have only subtle abnormalities, humans with heterozygous SF-1 mutations can present with XY sex reversal (i.e. testicular failure), ovarian failure, and occasionally adrenal insufficiency; dysregulation of SF-1 has been linked to diseases such as endometriosis and adrenocortical carcinoma. The current state of knowledge of this important transcription factor will be reviewed with a particular emphasis on the pioneering work on SF-1 by the late Keith Parker.

The Very Large G-Protein-Coupled Receptor VLGR1: A Component of the Ankle Link Complex Required for the Normal Development of Auditory Hair Bundles

Sensory hair bundles in the inner ear are composed of stereocilia that can be interconnected by a variety of different link types, including tip links, horizontal top connectors, shaft connectors, and ankle links. The ankle link antigen is an epitope specifically associated with ankle links and the calycal processes of photoreceptors in chicks. Mass spectrometry and immunoblotting were used to identify this antigen as the avian ortholog of the very large G-protein-coupled receptor VLGR1, the product of the Usher syndrome USH2C (Mass1) locus. Like ankle links, Vlgr1 is expressed transiently around the base of developing hair bundles in mice. Ankle links fail to form in the cochleae of mice carrying a targeted mutation in Vlgr1 (Vlgr1/del7TM), and the bundles become disorganized just after birth. FM1-43 [N-(3-triethylammonium)propyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide] dye loading and whole-cell recordings indicate mechanotransduction is impaired in cochlear, but not vestibular, hair cells of early postnatal Vlgr1/del7TM mutant mice. Auditory brainstem recordings and distortion product measurements indicate that these mice are severely deaf by the third week of life. Hair cells from the basal half of the cochlea are lost in 2-month-old Vlgr1/del7TM mice, and retinal function is mildly abnormal in aged mutants. Our results indicate that Vlgr1 is required for formation of the ankle link complex and the normal development of cochlear hair bundles.

CA-Repeat Polymorphism in Intron 1 of HSD11B2: Effects on Gene Expression and Salt Sensitivity

Mutations in the HSD11B2 gene encoding the kidney (11-HSD2) isozyme of 11beta-hydroxysteroid dehydrogenase cause apparent mineralocorticoid excess, a form of familial hypertension. Because the hypertension associated with AME is of the salt-sensitive type, it seemed possible that decreases in 11-HSD2 activity might be associated with salt sensitivity. To examine this, Italians with mild hypertension underwent a protocol consisting of a rapid intravenous saline infusion and subsequent furosemide diuresis. To determine whether there were genetic associations between HSD11B2 and salt sensitivity, 198 Italians were genotyped for a CA repeat polymorphism (11 alleles) in the first intron. Increased differences in mean arterial pressure between the sodium loaded and depleted states were correlated with shorter CA repeat length (R=0.214, P=0. 0025). The effect behaved as a recessive trait. This suggested that decreased HSD11B2 expression was associated with shorter CA repeat length. Furthermore, activity of renal 11-HSD2 as measured by an increase in the ratio of urinary-free cortisol/urinary-free cortisone was lower in 33 salt-sensitive subjects (urinary-free cortisol/urinary-free cortisone 0.89+/-0.04 [mean+/-SE]) compared with 34 salt-resistant subjects (0.71+/-0.04, P<0.001). However, when minigenes containing either 14 or 23 CA repeats were transfected into rabbit or human kidney cortical collecting duct cells, the construct with 14 repeats was instead expressed at levels 50% higher than those of the construct with 23 repeats, as determined by reverse transcription-polymerase chain reaction. We conclude that polymorphisms in HSD11B2 and decreased 11-HSD2 activity are associated with sensitivity to sodium loading, but a functional explanation for these associations remains to be elucidated.

Gene Expression in Peripheral Blood Mononuclear Cells from Children with Diabetes

OBJECTIVE We hypothesized that type 1 diabetes (T1D) is accompanied by changes in gene expression in peripheral blood mononuclear cells due to dysregulation of adaptive and innate immunity, counterregulatory responses to immune dysregulation, insulin deficiency, and hyperglycemia. RESEARCH DESIGN AND METHODS Microarray analysis was performed on peripheral blood mononuclear cells from 43 patients with newly diagnosed T1D, 12 patients with newly diagnosed type 2 diabetes (T2D), and 24 healthy controls. One- and 4-month follow-up samples were obtained from 20 of the T1D patients. RESULTS Microarray analysis identified 282 genes differing in expression between newly diagnosed T1D patients and controls at a false discovery rate of 0.05. Changes in expression of IL1B, early growth response gene 3, and prostaglandin-endoperoxide synthase 2 resolved within 4 months of insulin therapy and were also observed in T2D, suggesting that they resulted from hyperglycemia. With use of a knowledge base, 81 of 282 genes could be placed within a network of interrelated genes with predicted functions including apoptosis and cell proliferation. IL1B and the MYC oncogene were the most highly connected genes in the network. IL1B was highly overexpressed in both T1D and T2D, whereas MYC was dysregulated only in T1D. CONCLUSION T1D and T2D likely share a final common pathway for beta-cell dysfunction that includes secretion of IL-1beta and prostaglandins by immune effector cells, exacerbating existing beta-cell dysfunction, and causing further hyperglycemia. The results identify several targets for disease-modifying therapy of diabetes and potential biomarkers for monitoring treatment efficacy.