Ligand-Dependent Downregulation of Guanylyl Cyclase/Natriuretic Peptide Receptor-A: Role of miR-128 and miR-195.

Cardiac hormones act on the regulation of blood pressure (BP) and cardiovascular homeostasis. These hormones include atrial and brain natriuretic peptides (ANP, BNP) and activate natriuretic peptide receptor-A (NPRA), which enhance natriuresis, diuresis, and vasorelaxation. In this study, we established the ANP-dependent homologous downregulation of NPRA using human embryonic kidney-293 (HEK-293) cells expressing recombinant receptor and MA-10 cells harboring native endogenous NPRA. The prolonged pretreatment of cells with ANP caused a time- and dose-dependent decrease in 125I-ANP binding, Guanylyl cyclase (GC) activity of receptor, and intracellular accumulation of cGMP leading to downregulation of NPRA. Treatment with ANP (100 nM) for 12 h led to an 80% decrease in 125I-ANP binding to its receptor, and BNP decreased it by 62%. Neither 100 nM c-ANF (truncated ANF) nor C-type natriuretic peptide (CNP) had any effect. ANP (100 nM) treatment also decreased GC activity by 68% and intracellular accumulation cGMP levels by 45%, while the NPRA antagonist A71915 (1 µM) almost completely blocked ANP-dependent downregulation of NPRA. Treatment with the protein kinase G (PKG) stimulator 8-(4-chlorophenylthio)-cGMP (CPT-cGMP) (1 µM) caused a significant increase in 125I-ANP binding, whereas the PKG inhibitor KT 5823 (1 µM) potentiated the effect of ANP on the downregulation of NPRA. The transfection of miR-128 significantly reduced NPRA protein levels by threefold compared to control cells. These results suggest that ligand-dependent mechanisms play important roles in the downregulation of NPRA in target cells.

Novel nucleotide insertions in two unrelated Indian patients with 5α reductase 2 deficiency leading to premature termination of SRD5A2 enzyme.

T is converted to a more potent androgen, DHT by the action of microsomal membrane enzyme 5α reductase 2. Defects in 5α reductase 2 isozyme results in incomplete virilisation of external male genitalia. Mutations in SRD5A2 gene leads to diminished enzyme activity, thus hampering DHT synthesis from T. We describe two unrelated patients from India with 5αRD2 due to novel insertion of nucleotides in the exon 1 of SRD5A2 gene that lead to premature termination of protein. Master S (case 1; III.8) was 3 years old at initial evaluation, had perineoscrotal hypospadias, microphallus and both testes were palpable in the inguinal region. Master P (case 2; III.9) was born as normal full term baby. He had primary complaint of microphallus, penoscrotal hypospadias and gonads in the inguinal region. Diagnosis of 5αRD2 was made, as T/DHT ratio in the two cases was 41 and 131.2 respectively. Sequence analysis of SRD5A2 gene showed an insertion of nucleotides TA in exon 1 (c.188_189). This resulted in premature termination of the protein due to stop codon at amino acid position 7. The protein formed is drastically truncated and inadequate protein synthesized explains the phenotypic characteristics of our patients.

Morning plasma cortisol is low among obese women with polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is the most common cause for androgen excess in women. It is associated with wide variety of metabolic disorders. The present study assessed morning plasma cortisol in women with PCOS. One hundred and ninety seven cases and 55 controls were enrolled for this study. The mean age of patients and controls were 23 ± 5.6 years and 25 ± 4.3 years. One hundred twelve (56%) women with PCOS had BMI >25. Serum cortisol levels were significantly higher in lean PCOS women compared to controls (13.4 ± 5.1 versus 11.3 ± 4.5, p < 0.01) and over-weight PCOS women group (13.4 ± 5.1 versus 9.3 ± 3.2, p < 0.01). There was a trend for less acne and hirsutism with increase in BMI. Morning plasma cortisol was lower among obese women with PCOS. Morning plasma cortisol correlated negatively with BMI in PCOS women with normal glucose tolerance.

Novel mutation of SRD5A2 gene in a patient with 5α-reductase 2 deficiency from India.

Master N had genital malformation at birth and had bilateral gonads in the labial fold. He was reared as a boy and corrective surgery was done at the age of 4 years and was reassessed at the age of 14 years. His testosterone/dihydrotestosterone (DHT) was 11.8 (reference range <=10). Molecular analysis of SRD5A2 gene indicated the presence of a novel heterozygous missense mutation of p.A52T in exon 1, which was also detected in mother. The father, sister and maternal grandfather were found to have normal SRD5A2 gene sequence. We also detected an intronic (1-2) homozygous T>C transition in patient, whereas both parents were found to have the same transition in heterozygous form. Although 5α-steroid reductase 2 deficiency is an autosomal-recessive disorder, in this case, it appears that there may be a dominant inheritance because only one identified mutation was present which was passed from mother to son.

Molecular genetic analysis of CYP21A2 gene in patients with congenital adrenal hyperplasia.

CONTEXT: Congenital adrenal hyperplasia (CAH) is one of the inborn errors of metabolic disorder inherited in an autosomal recessive manner caused by the defects in the steroid 21 hydroxylase CYP21A2 gene. We analyzed the genotype of 62 patients with classic CAH. AIMS: To find out the underlying mutations of CYP21A2 gene. SETTINGS AND DESIGN: Cohort of CAH patients. MATERIALS AND METHODS: Sixty-two patients with CAH were recruited from the endocrine clinic at AIIMS. Electrochemiluminiscence method was used for estimating the levels of cortisol. Radioimmunoassay kit-based method was used for estimating the 17 OHP levels. Polymerase chain reaction amplification was done using specific primers to amply the CYP21A2 gene. STATISTICAL ANALYSIS USED: Statistical analysis was done by using Epi Info Version 3.5.1.2008. RESULTS: Out of 62 patients, 50 were simple virilizers (SV) and 12 were salt wasters (SW). Fifty-six were females and six were males. Five 46, XX children were reared as males. Age at presentation varied from 8 months to 38 years. Molecular genetic analysis revealed that the highest number of patients harboured (In 2) IVS2-13 A/C > G (48%), followed by p.P30L (46%), p.Q318X (35%), (D 8 bp) deletion 8 bp (26%), p.I172N (26%), and p. R356W (20%) mutations. CONCLUSION: This is among the few studies to analyze the mutational spectrum of CYP21A2 gene in a large CAH cohort from India. Molecular diagnosis of CYP21A2 gene should be considered as part of the CAH evaluation to assess the risk of the patients/parents/siblings and to offer genetic counseling.

Insulin sensitivity and ß-cell function in normoglycemic offspring of individuals with type 2 diabetes mellitus: Impact of line of inheritance.

AIMS: The aim was to study the effect of family history of type 2 diabetes mellitus (T2DM) on insulin sensitivity and ß-cell function in normoglycemic offspring. MATERIAL AND METHODS: Offspring of T2DM patients (cases) and individuals without family history of T2DM (controls) were the subjects for this cross-sectional study. All participants underwent 75 g OGTT and samples were collected for plasma insulin, C-peptide, and proinsulin at 0, 30, 60, and 120 minutes. RESULTS: A total of 271 cases (age 22 ± 10 years; 53% males) and 259 controls (28 ± 10 years, 66% males) were enrolled for the study. BMI, plasma insulin, C-peptide, proinsulin, HOMA-IR, and insulinogenic index (0-120) were significantly higher and whole-body insulin sensitivity (WBISI) and disposition index (0-120) [DI 120] were lower in cases compared to controls. After adjusting for BMI, proinsulin at 120 minutes, area under the curve (AUC) of proinsulin (during OGTT) and AUC proinsulin/AUC C-peptide were significantly higher in cases. Cases were subdivided into four groups according to inheritance pattern; paternal DM (PDM), maternal DM (MDM), grandparental DM (GPDM), and both parents DM (BPDM). The magnitude of differences varied with relationship (greater when both parents and grandparents were affected). Mean HOMA-IR was higher by 127% and 50% and DI 120 was lower by 33% and 18% (adjusted for age and gender) in the BPDM and GPDM groups respectively compared to controls. CONCLUSIONS: We observed higher BMI, plasma insulin, C-peptide, and proinsulin and lower insulin sensitivity and ß-cell compensation in normoglycemic offspring of T2DM subjects compared to controls. Differences were greater when both parents and grandparents had T2DM.

Morning cortisol is lower in obese individuals with normal glucose tolerance.

BACKGROUND: There is no consensus on the role of cortisol in the pathogenesis of obesity and metabolic syndrome (MS). This cross-sectional study aimed to analyze the relationship of morning plasma cortisol and adrenocorticotropic hormone (ACTH) levels with body mass index (BMI) and glucose tolerance. SUBJECTS AND METHODS: The sample frame was the "Offspring of individuals with diabetes study" database. A total of 358 offspring of individuals with type 2 diabetes mellitus (T2DM) and 287 individuals without a known family history of T2DM were recruited for the study. Subjects who were ≥10 years of age were selected from the database for analysis. Subjects with T2DM were excluded. All participants underwent a 75 g oral glucose tolerance test (OGTT), and blood samples were collected at 0, 30, 60, and 120 minutes for glucose, insulin and C-peptide. Plasma cortisol, ACTH, and lipid profile were estimated from the fasting sample. RESULTS: Four hundred and ninety-five participants (305 males [62%] and 190 females [38%]) were included in the analysis. ACTH and cortisol levels were higher in normal-weight subjects than in overweight/obese subjects. Both ACTH and cortisol increased as fasting plasma glucose increased. Cortisol levels were significantly lower in offspring of T2DM subjects with MS than in offspring of T2DM subjects without MS. When adjusted for BMI, the significance was marginal. In males, cortisol levels were negatively correlated with early insulin secretion during OGTT (insulinogenic index [0-30]) and positively with waist circumference and serum high-density lipoprotein cholesterol. In females, fasting glucose and systolic blood pressure were significantly and positively correlated. CONCLUSION: Body weight was correlated negatively with morning plasma cortisol and ACTH, whereas fasting glucose was correlated positively.

Demographic, breast-feeding, and nutritional trends among children with type 1 diabetes mellitus.

BACKGROUND: The pathogenesis of type 1 diabetes mellitus (T1DM) requires a genetic predisposition to particular environmental triggers that may activate mechanisms leading to progressive loss of pancreatic beta cells. AIMS: We tried to compare the impact of some demographic and environmental factors and breast-feeding on children (aged < 18 years) with recent onset diabetes mellitus (≤1 year) with that on age, sex, and socioeconomic status-matched controls. MATERIAL AND METHODS: A total of 43 consecutive patients (male, 24, mean age ± SD = 12.58 ± 9.6 years) and equal number of controls without diabetes mellitus or dysglycemia were included in this hospital-based case-control study. RESULTS AND CONCLUSIONS: A distinct peak in the incidence noted in the early adolescence with segregation in the winter months. Our patients did not differ significantly from the controls with regard to birth order, mode of delivery, parental age, parental education, dietary practices, breast-feeding, and migration in the family. Growth characteristics and nutritional status were also similar. A population study with more power will be better equipped to answer such queries.

Low HDL-cholesterol among normal weight, normoglycemic offspring of individuals with type 2 diabetes mellitus.

OBJECTIVE: Offspring of type 2 diabetics have an increased risk of dyslipidemia, glucose intolerance and obesity. The aim of this study was to assess the lipid levels in the offspring of diabetics with normal glucose tolerance and normal body weight. DESIGN: Normal weight offspring of patients with type 2 diabetes mellitus (DM) who had normal glucose tolerance, and healthy gender matched controls of comparable age without a family history of diabetes mellitus, were the subjects of this study. Lipid profiles were determined in cases and controls. RESULTS: The study included 114 subjects (64 males and 50 females) in each group, aged (mean ± SD) 24.0 ± 7.9 in cases and 24.1 ± 8.0 years in controls. The body mass index (BMI) was 20.8 ± 3.0 and 20.2 ± 3.1 kg/m2 in cases and controls, respectively. Serum total cholesterol, triglycerides, plasma glucose, fasting insulin, C-peptide and proinsulin levels were comparable in cases and controls. Serum high density lipoprotein (HDL) cholesterol was lower (p <0.001), whilst the serum triglyceride/HDL ratio, low density lipoprotein (LDL) cholesterol and area under the curve for insulin and proinsulin during an oral glucose tolerance test were higher in cases compared to controls. HDL cholesterol showed no significant correlation with plasma glucose, insulin or proinsulin. CONCLUSION: Plasma HDL cholesterol is low among normal weight, normoglycemic offspring of subjects with type 2 diabetes mellitus. The implications of this finding are not apparent.

Comparison of gliclazide with insulin as initial treatment modality in newly diagnosed type 2 diabetes.

AIM: This study was designed to compare effectiveness and remission rate between gliclazide and insulin as initial treatment in newly diagnosed, drug-naive patients with type 2 diabetes. METHODS: Newly diagnosed, drug-naive subjects with type 2 diabetes having mean fasting blood glucose >200 mg/dL were enrolled into either of two groups (gliclazide or insulin). The former received gliclazide modified-release 60 mg daily, while the insulin group received 16 units of premixed insulin as two divided doses along with medical nutrition therapy. Premeal blood glucose was monitored, and the dose was adjusted accordingly. Glycosylated hemoglobin (HbA1c), lipid profile, and postmeal C-peptide were estimated at baseline and 6 months. Remission was defined as euglycemia off drug for a minimum duration of 1 month. RESULTS: Baseline and 6-month blood glucose, HbA1c, and lipid profile were comparable between groups. Blood glucose levels normalized in 2-6 weeks in both groups. At 6 months, one of 30 (3.33%) in the gliclazide group and 24 of 30 (80%) in the insulin group were in remission. Ten of 16 (62.5%) in the insulin group and one of 20 (.5%) in the gliclazide group continued to maintain euglycemia off all pharmacological treatment at 12 months. At 6 months, C-peptide increased in the insulin group (3.21+/-1.61 ng/mL at baseline vs. 5.82+/-2.23 ng/mL at 6 months), while it remained unchanged in the gliclazide group (3.4+/-1.87 ng/mL at baseline vs. 3.82+/-1.78 ng/mL at 6 months) (P=0.0003). CONCLUSIONS: Comparable glycemic control could be achieved with both insulin and oral hypoglycemic agent in newly diagnosed type 2 diabetes subjects. Insulin treatment exceeded gliclazide in the remission (drug-free) rate.

Molecular diagnosis of 5alpha-reductase-2 gene mutation in two Indian families with male pseudohermaphroditism.

AIM: To identify the genotype of two Indians with male pseudohermaphroditism. METHODS: Standard radioimmunoassay procedure was used for estimating hormonal levels. Conventional cytogenetic analysis was carried out for diagnosing the genetic sex in these subjects with genital ambiguity. Molecular analysis was carried out by standard polymerase chain reaction procedure using different sets of primers and reaction conditions specific for the 5alpha-reductase type 2 gene (SRD5A2) gene. Direct sequencing was carried out using the ABI Prism dye terminator sequencing kit and the ABI 310 sequencing apparatus. RESULTS: We found an SRD5A2 gene mutation in exon 5, where arginine is substituted with glutamine (R246Q), in two males with pseudohermaphroditism and ambiguous genitalia from unrelated families. This is the first time this mutation has been reported in individuals from India. CONCLUSION: Identification of the R246Q mutation of the SRD5A2 gene from two unrelated Indian families possibly extends the founder gene effect.

Involvement of the NF-kappa B/matrix metalloproteinase pathway in cardiac fibrosis of mice lacking guanylyl cyclase/natriuretic peptide receptor A.

Mice carrying a targeted disruption of the Npr1 gene (coding for guanylyl cyclase/natriuretic peptide receptor A (NPRA)) exhibit increased blood pressure, cardiac hypertrophy, and congestive heart failure, similar to untreated human hypertensive patients. The objective of this study was to determine whether permanent ablation of NPRA signaling in mice alters the expression of matrix metalloproteinase (MMP)-2 and MMP-9 and pro-inflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha), leading to myocardial collagen remodeling. Here, we report that expression levels of the MMP-2 and MMP-9 genes were increased by 3-5-fold and that the expression of the TNF-alpha gene was enhanced by 8-fold in Npr1 homozygous null mutant (Npr1-/-) mouse hearts compared with wild-type (Npr1+/+) control mouse hearts. Myocardial fibrosis, total collagen, and the collagen type I/III ratio (p < 0.01) were dramatically increased in adult Npr1-/- mice compared with age-matched wild-type counterparts. Hypertrophic marker genes, including the beta-myosin heavy chain and transforming growth factor-beta1, were significantly up-regulated (3-5-fold) in both young and adult Npr1-/- mouse hearts. NF-kappa B binding activity in ventricular tissues was enhanced by 4-fold with increased translocation of the p65 subunit from the cytoplasmic to nuclear fraction in Npr1-/- mice. Our results show that reduced NPRA signaling activates MMP, transforming growth factor-beta1, and TNF-alpha expression in Npr1-/- mouse hearts. The findings of this study demonstrate that disruption of NPRA/cGMP signaling promotes hypertrophic growth and extracellular matrix remodeling, leading to the development of cardiac hypertrophy, myocardial fibrosis, and congestive heart failure.

Internalization and trafficking of guanylyl (guanylate) cyclase/natriuretic peptide receptor A is regulated by an acidic tyrosine-based cytoplasmic motif GDAY.

We have identified a GDAY motif in the C-terminal domain of guanylyl cyclase (guanylate cyclase)/NPRA (natriuretic peptide receptor A) sequence, which serves a dual role as an internalization signal and a recycling signal. To delineate the role of the GDAY motif in receptor internalization and sequestration, we mutated Gly920, Asp921 and Tyr923 to alanine residues (GDAY/AAAA) in the NPRA cDNA sequence. The cDNAs encoding wild-type and mutant receptors were transfected in HEK-293 cells (human embryonic kidney 293 cells). The internalization studies of ligand-receptor complexes revealed that endocytosis of 125I-ANP by HEK-293 cells expressing G920A, Y923A or GDAY/AAAA mutant receptor was decreased by almost 50% (P<0.001) when compared with cells expressing the wild-type receptor. However, the effect of D921A mutation on receptor internalization was minimal. Ligand-mediated down-regulation of G920A, Y923A and GDAY/AAAA mutant receptors was decreased by 35-40% when compared with wild-type NPRA. Subsequently, the recycling of internalized D921A and GDAY/AAAA mutant receptors from the intracellular pool was decreased by more than 40+/-4% when compared with wild-type NPRA. Recycling of G920A and Y923A mutant receptors was also decreased, but to a significantly lesser extent compared with the D921A or GDAY/AAAA mutant receptors. We conclude that the Gly920 and Tyr923 residues within the GDAY consensus motif are necessary for internalization, and that residue Asp921 is important for recycling of NPRA. The current results provide new evidence for a dual role of the GDAY sequence motif in ligand-mediated internalization, recycling and down-regulation of a single-transmembrane receptor protein NPRA.