Genome-wide association study and trans-ethnic meta-analysis identify novel susceptibility loci for type 2 diabetes mellitus

BACKGROUND

The genetic basis of type 2 diabetes (T2D) is under-investigated in the Middle East, despite the rapidly growing disease prevalence. We aimed to define the genetic determinants of T2D in Qatar.

METHODS

Using whole genome sequencing of 11,436 participants (2765 T2D cases and 8671 controls) from the population-based Qatar Biobank (QBB), we conducted a genome-wide association study (GWAS) of T2D with and without body mass index (BMI) adjustment.

RESULTS

We replicated 93 known T2D-associated loci in a BMI-unadjusted model, while 96 known loci were replicated in a BMI-adjusted model. The effect sizes and allele frequencies of replicated SNPs in the Qatari population generally concurred with those from European populations. We identified a locus specific to our cohort located between the APOBEC3H and CBX7 genes in the BMI-unadjusted model. Also, we performed a transethnic meta-analysis of our cohort with a previous GWAS on T2D in multi-ancestry individuals (180,834 T2D cases and 1,159,055 controls). One locus in DYNC2H1 gene reached genome-wide significance in the meta-analysis. Assessing polygenic risk scores derived from European- and multi-ancestries in the Qatari population showed higher predictive performance of the multi-ancestry panel compared to the European panel.

CONCLUSION

Our study provides new insights into the genetic architecture of T2D in a Middle Eastern population and identifies genes that may be explored further for their involvement in T2D pathogenesis.

Effectiveness of Messenger RNA Vaccines against SARS-CoV-2 Infection in Hemodialysis Patients: A Case-Control Study

Patients with end-stage kidney disease (ESKD) are at increased risk for SARS-CoV-2 infection and its complications compared with the general population. Several studies evaluated the effectiveness of COVID-19 vaccines in the dialysis population but showed mixed results. The aim of this study was to determine the effectiveness of COVID-19 mRNA vaccines against confirmed SARS-CoV-2 infection in hemodialysis (HD) patients in the State of Qatar. We included all adult ESKD patients on chronic HD who had at least one SARS-CoV-2 PCR test done after the introduction of the COVID-19 mRNA vaccines on 24 December 2020. Vaccinated patients who were only tested before receiving any dose of their COVID-19 vaccine or within 14 days after receiving the first vaccine dose were excluded from the study. We used a test-negative case−control design to determine the effectiveness of the COVID-19 vaccination. Sixty-eight patients had positive SARS-CoV-2 PCR tests (cases), while 714 patients had negative tests (controls). Ninety-one percent of patients received the COVID-19 mRNA vaccine. Compared with the controls, the cases were more likely to be older (62 ± 14 vs. 57 ± 15, p = 0.02), on dialysis for more than one year (84% vs. 72%, p = 0.03), unvaccinated (46% vs. 5%, p < 0.0001), and symptomatic (54% vs. 21%, p < 0.0001). The effectiveness of receiving two doses of COVID-19 mRNA vaccines against confirmed SARS-CoV-2 infection was 94.7% (95% CI: 89.9−97.2) in our HD population. The findings of this study support the importance of using the COVID-19 mRNA vaccine in chronic HD patients to prevent SARS-CoV-2 infection in such a high-risk population.

The Genetic Spectrum of Maturity-Onset Diabetes of the Young (MODY) in Qatar, a Population-Based Study

Maturity-onset diabetes of the young (MODY) is a rare monogenic form of diabetes mellitus. In this study, we estimated the prevalence and genetic spectrum of MODY in the Middle Eastern population of Qatar using whole-genome sequencing (WGS) of 14,364 subjects from the population-based Qatar biobank (QBB) cohort. We focused our investigations on 14 previously identified genes ascribed to the cause of MODY and two potentially novel MODY-causing genes, RFX6 and NKX6-1. Genetic variations within the 16 MODY-related genes were assessed for their pathogenicity to identify disease-causing mutations. Analysis of QBB phenotype data revealed 72 subjects (0.5%) with type 1 diabetes, 2915 subjects (20.3%) with type 2 diabetes and 11,377 (79.2%) without diabetes. We identified 22 mutations in 67 subjects that were previously reported in the Human Genetic Mutation Database (HGMD) as disease-causing (DM) or likely disease causing (DM?) for MODY. We also identified 28 potentially novel MODY-causing mutations, predicted to be among the top 1% most deleterious mutations in the human genome, which showed complete (100%) disease penetrance in 34 subjects. Overall, we estimated that MODY accounts for around 2.2-3.4% of diabetes patients in Qatar. This is the first population-based study to determine the genetic spectrum and estimate the prevalence of MODY in the Middle East. Further research to characterize the newly identified mutations is warranted.

iPSCs derived from insulin resistant offspring of type 2 diabetic patients show increased oxidative stress and lactate secretion

Background

The genetic factors associated with insulin resistance (IR) are not well understood. Clinical studies on first-degree relatives of type 2 diabetic (T2D) patients, which have the highest genetic predisposition to T2D, have given insights into the role of IR in T2D pathogenesis. Induced pluripotent stem cells (iPSCs) are excellent tools for disease modeling as they can retain the genetic imprint of the disease. Therefore, in this study, we aimed to investigate the genetic perturbations associated with insulin resistance (IR) in the offspring of T2D parents using patient-specific iPSCs.

Methods

We generated iPSCs from IR individuals (IR-iPSCs) that were offspring of T2D parents as well as from insulin-sensitive (IS-iPSCs) individuals. We then performed transcriptomics to identify key dysregulated gene networks in the IR-iPSCs in comparison to IS-iPSCs and functionally validated them.

Results

Transcriptomics on IR-iPSCs revealed dysregulated gene networks and biological processes indicating that they carry the genetic defects associated with IR that may lead to T2D. The IR-iPSCs had increased lactate secretion and a higher phosphorylation of AKT upon stimulation with insulin. IR-iPSCs have increased cellular oxidative stress indicated by a high production of reactive oxygen species and higher susceptibility to H2O2 -induced apoptosis.

Conclusions

IR-iPSCs generated from offspring of diabetic patients confirm that oxidative stress and increased lactate secretion, associated with IR, are inherited in this population, and may place them at a high risk of T2D. Overall, our IR-iPSC model can be employed for T2D modeling and drug screening studies that target genetic perturbations associated with IR in individuals with a high risk for T2D.

Differences in protein expression, at the basal state and at 2 h of insulin infusion, in muscle biopsies from healthy Arab men with high or low insulin sensitivity measured by hyperinsulinemic euglycemic clamp

BACKGROUND

Skeletal muscle is the main site for insulin-dependent glucose disposal. The hyperinsulinemic euglycemic clamp (HIEC) is the gold standard for the assessment of insulin sensitivity (IS). We have previously shown that insulin sensitivity, measured by HIEC, varied widely among a group of 60 young healthy men with normoglycemia. The aim of this study was to correlate the proteomic profile of skeletal muscles to insulin sensitivity.

METHODS

Muscle biopsies from 16 subjects having the highest (M ≥ 13; n = 8, HIS) and lowest (M ¾ 6, n = 8, LIS) IS were obtained at baseline and during insulin infusion after stabilization of the blood glucose level and glucose infusion rate at the end of the HIEC. The samples were processed using a quantitative proteomic analysis approach.

RESULTS

At baseline, 924 proteins were identified in the HIS and LIS groups. Among the 924 proteins detected in both groups, three were suppressed and three were increased significantly in the LIS subjects compared with the HIS subjects. Following insulin infusion, 835 proteins were detected in both groups. Among the 835 proteins, two showed differential responsiveness to insulin; ATP5F1 protein was decreased, and MYLK2 was higher in the LIS group compared with that in the HIS group. Our data suggest that alteration in mitochondrial proteins and an increased number of proteins involved in fast-twitch fiber correlate to insulin sensitivity in healthy young Arab men.

CONCLUSIONS

These results suggest a change in a small number of differentially expressed proteins. A possible reason for this small change could be our study cohorts representing a homogeneous and healthy population. Additionally, we show differences in protein levels from skeletal muscle in low and high insulin sensitivity groups. Therefore, these differences may represent early events for the development of insulin resistance, pre-diabetes, and type 2 diabetes.

MiRNA and associated inflammatory changes from baseline to hypoglycemia in type 2 diabetes

OBJECTIVE

Hypoglycemia in type 2 diabetes (T2D) increases morbidity and mortality but the underlying physiological response is still not fully understood, though physiological changes are still apparent 24 hours after the event. Small noncoding microRNA (miRNA) have multiple downstream biological effects that may respond rapidly to stress. We hypothesized that hypoglycemia would induce rapid miRNA changes; therefore, this pilot exploratory study was undertaken.

METHODS

A pilot prospective, parallel study in T2D (n=23) and controls (n=23). Insulin-induced hypoglycemia (2mmol/l: 36mg/dl) was induced and blood sampling performed at baseline and hypoglycemia. Initial profiling of miRNA was undertaken on pooled samples identified 96 miRNA that were differentially regulated, followed by validation on a custom designed 112 miRNA panel.

RESULTS

Nine miRNAs differed from baseline to hypoglycemia in control subjects; eight were upregulated: miR-1303, miR-let-7e-5p, miR-1267, miR-30a-5p, miR-571, miR-661, miR-770-5p, miR-892b and one was downregulated: miR-652-3p. None of the miRNAs differed from baseline in T2D subjects.

CONCLUSION

A rapid miRNA response reflecting protective pathways was seen in control subjects that appeared to be lost in T2D, suggesting that mitigating responses to hypoglycemia with blunting of the counter-regulatory response in T2D occurs even in patients with short duration of disease.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT03102801?term=NCT03102801&draw=2&rank=1, identifier NCT03102801.

Insulin sensitivity variations in apparently healthy Arab male subjects: correlation with insulin and C peptide

INTRODUCTION

Decreased insulin sensitivity occurs early in type 2 diabetes (T2D). T2D is highly prevalent in the Middle East and North Africa regions. This study assessed the variations in insulin sensitivity in normal apparently healthy subjects and the levels of adiponectin, adipsin and inflammatory markers.

RESEARCH DESIGN AND METHODS

A total of 60 participants (aged 18-45, body mass index <28) with a normal oral glucose tolerance test (OGTT) completed hyperinsulinemic-euglycemic clamp (40 mU/m²/min) and body composition test by dual-energy X-ray absorptiometry scan. Blood samples were assayed for glucose, insulin, C peptide, inflammatory markers, oxidative stress markers, adiponectin and adipsin.

RESULTS

The subjects showed wide variations in the whole-body glucose disposal rate (M value) from 2 to 20 mg/kg/min and were divided into three groups: most responsive (M>12 mg/kg/min, n=17), least responsive (M≤6 mg/kg/min, n=14) and intermediate responsive (M=6.1-12 mg/kg/min, n=29). Insulin and C peptide responses to OGTT were highest among the least insulin sensitive group. Triglycerides, cholesterol, alanine transaminase (ALT) and albumin levels were higher in the least responsive group compared with the other groups. Among the inflammatory markers, C reactive protein (CRP) was highest in the least sensitivity group compared with the other groups; however, there were no differences in the level of soluble receptor for advanced glycation end products and Tumor Necrosis Factor Receptor Superfamily 1B (TNFRS1B). Plasma levels of insulin sensitivity markers, adiponectin and adipsin, and oxidative stress markers, oxidized low-density lipoprotein, total antioxidant capacity and glutathione peroxidase 1, were similar between the groups.

CONCLUSIONS

A wide range in insulin sensitivity and significant differences in triglycerides, cholesterol, ALT and CRP concentrations were observed despite the fact that the study subjects were homogenous in terms of age, gender and ethnic background, and all had normal screening comprehensive chemistry and normal glucose response to OGTT. The striking differences in insulin sensitivity reflect differences in genetic predisposition and/or environmental exposure. The low insulin sensitivity status associated with increased insulin level may represent an early stage of metabolic abnormality.

Regulation of circulating CTRP-2/CTRP-9 and GDF-8/GDF-15 by intralipids and insulin in healthy control and polycystic ovary syndrome women following chronic exercise training

Background

Polycystic ovary syndrome (PCOS) is associated with obesity, diabetes, and insulin resistance. The circulating C1Q/TNF-related proteins (CTRP-2, CTRP-9) and growth differentiation factors (GDF-8, GDF-15) contribute to glucose and lipid homeostasis. The effects of intralipids and insulin infusion on CTRP-2, CTRP-9, GDF-8 and GDF-15 in PCOS and control subjects before and after chronic exercise training were examined.

Methods

Ten PCOS and nine healthy subjects were studied at baseline status and after moderate-intensity chronic exercise training (1 h exercise, 3 times per week, 8 weeks). All participants were infused with 1.5 mL/min of saline or intralipids (20%) for 5 h, and during the last 2 h of saline or intralipids infusion hyperinsulinemic-euglycemic clamp (HIEC) was performed. CTRP-2, CTRP-9, GDF-8 and GDF-15 levels were measured at 0, 3 and 5 h.

Results

Intralipids dramatically increased CTRP-2 levels in PCOS (P = 0.02) and control (P = 0.004) subjects, which was not affected by insulin infusion or by exercise. Intralipids alone had no effects on CTRP-9, GDF-8, or GDF-15. Insulin increased the levels of GDF-15 in control subjects (P = 0.05) during the saline study and in PCOS subjects (P = 0.04) during the intralipid infusion. Insulin suppressed CTRP9 levels during the intralipid study in both PCOS (P = 0.04) and control (P = 0.01) subjects. Exercise significantly reduced fasting GDF-8 levels in PCOS (P = 0.03) and control (P = 0.04) subjects; however, intralipids infusion after chronic exercise training increased GDF-8 levels in both PCOS (P = 0.003) and control (P = 0.05) subjects and insulin infusion during intralipid infusion reduced the rise of GDF-8 levels.

Conclusion

This study showed that exogenous lipids modulate CTRP-2, which might have a physiological role in lipid metabolism. Since chronic exercise training reduced fasting GDF-8 levels; GDF-8 might have a role in humoral adaptation to exercise. GDF-15 and CTRP-9 levels are responsive to insulin, and thus they may play a role in insulin responses.

Metformin is comparable to insulin for pharmacotherapy in gestational diabetes mellitus: A network meta-analysis evaluating 6046 women

CONTEXT

The comparative efficacy of gestational diabetes (GDM) treatments lack conclusive evidence for choice of first-line treatment.

OBJECTIVES

The aim of this study was to compare the efficacy of metformin and glibenclamide to insulin using a core outcome set (COS) to unify outcomes across trials investigating the treatment of gestational diabetes mellitus.

STUDY DESIGN

A network meta-analysis (NMA) was conducted.

DATA-SOURCE

PubMed, Embase, and Cochrane Controlled Register of Trials were searched from inception to January 2020.

STUDY SELECTION

RCTs that enrolled pregnant women who were diagnosed with GDM and that compared the efficacy of different pharmacological interventions for the treatment of GDM were included.

META-ANALYSIS

A generalized pairwise modelling framework was employed.

RESULTS

A total of 38 RCTs with 6046 participants were included in the network meta-analysis. Compared to insulin, the estimated effect of metformin indicated improvements for weight gain (WMD -2·39 kg; 95% CI -3·31 to -1·46), maternal hypoglycemia (OR 0.34; 95% CI 0.12 to 0·97) and LGA (OR 0.61; 95% CI 0.38 to 0·98). There were also improvements in estimated effects for neonatal hypoglycemia (OR 0.48; 95% CI 0.19 to 1·25), pregnancy induced hypertension (OR 0.63; 95% CI 0.37 to 1·06), and preeclampsia (OR 0.74; 95% CI 0.538 to 1·04), though with limited evidence against our model hypothesis of equivalence with insulin for these outcomes.

CONCLUSION

Metformin is, at least, comparable to insulin for the treatment of GDM. Glibenclamide appears less favorable, in comparison to insulin, than metformin.

apoA2 correlates to gestational age with decreased apolipoproteins A2, C1, C3 and E in gestational diabetes

INTRODUCTION

Pregnant women with gestational diabetes mellitus (GDM) are at risk of adverse outcomes, including gestational hypertension, pre-eclampsia, and preterm delivery. This study was undertaken to determine if apolipoprotein (apo) levels differed between pregnant women with and without GDM and if they were associated with adverse pregnancy outcome.

RESEARCH DESIGN AND METHODS

Pregnant women (46 women with GDM and 26 women without diabetes (ND)) in their second trimester were enrolled in the study. Plasma apos were measured and correlated to demographic, biochemical, and pregnancy outcome data.

RESULTS

apoA2, apoC1, apoC3 and apoE were lower in women with GDM compared with control women (p=0.0019, p=0.0031, p=0.0002 and p=0.015, respectively). apoA1, apoB, apoD, apoH, and apoJ levels did not differ between control women and women with GDM. Pearson bivariate analysis revealed significant correlations between gestational age at delivery and apoA2 for women with GDM and control women, and between apoA2 and apoC3 concentrations and C reactive protein (CRP) as a measure of inflammation for the whole group.

CONCLUSIONS

Apoproteins apoA2, apoC1, apoC3 and apoE are decreased in women with GDM and may have a role in inflammation, as apoA2 and C3 correlated with CRP. The fact that apoA2 correlated with gestational age at delivery in both control women and women with GDM raises the hypothesis that apoA2 may be used as a biomarker of premature delivery, and this warrants further investigation.

Metabolomic Profiling of Pregnancies With Polycystic Ovary Syndrome Identifies a Unique Metabolic Signature and Potential Predictive Biomarkers of Low Birth Weight

BACKGROUND

Polycystic ovary syndrome (PCOS) is a complex syndrome with clinical features of an endocrine/metabolic disorder. Various metabolites show significant association with PCOS; however, studies comparing the metabolic profile of pregnant women with and without PCOS are lacking. In this study, metabolomics analysis of blood samples collected from PCOS women and age and BMI matched controls in the second trimester of pregnancy was performed to identify metabolic differences between the two groups and determine their association with pregnancy outcome.

METHODS

Sixteen PCOS and fifty-two healthy women in their second trimester underwent targeted metabolomics of plasma samples using tandem mass spectrometry with the Biocrates MxP^® Quant 500 Kit. Linear regression models were used to identify the metabolic alterations associated with PCOS, followed by enrichment and Receiver Operating Characteristic (ROC) analyses to determine the best indicators of pregnancy outcomes.

RESULTS

PCOS women had lower birth weight babies compared to healthy controls. As a group, systolic blood pressure (SBP) at both second trimester and at delivery negatively correlated with birth weight. Regression models indicated significant increases in the triglycerides C20:4_C34:3 and C18:2_C38:6 in the PCOS group [false discovery rate (FDR) <0.05]. Enrichment analysis revealed significant elevations in triglycerides containing arachidonic acid, linoleic acid and palmitic acid in the PCOS group. A number of indicators of baby birth weight were identified including SBP at delivery, hexosylceramide (d18:2/24:0), ceramide (d18.0/24.1) and serine, with an AUC for all predictors combined for low birth weight (≤2500grams) of 0.88 (95%CI: 0.75-1.005, p<0.001).

CONCLUSIONS

PCOS pregnancies resulted in babies with a lower birth weight, marked by a unique metabolic signature that was enriched with specific triglycerides and unsaturated fatty acids. The functional significance of these associations needs further investigation.

Clinical and metabolic characteristics of the Diabetes Intervention Accentuating Diet and Enhancing Metabolism (DIADEM-I) randomised clinical trial cohort

OBJECTIVES

Diabetes Intervention Accentuating Diet and Enhancing Metabolism-I (DIADEM-I) is the first randomised controlled trial (RCT) in the Middle East and North Africa (MENA) region testing the effectiveness of an intensive lifestyle intervention (ILI) for weight loss and diabetes remission. We report on the recruitment process and baseline characteristics of the DIADEM-I cohort based on origin (Middle East vs North Africa), and waist circumference.

DESIGN

DIADEM-I is an open-label randomised, controlled, parallel group RCT recruiting young individuals (18-50 years) with early type 2 diabetes (≤3 years since diagnosis) originating from MENA. Individuals from primary care were randomised to usual medical care or ILI (total dietary replacement phase using meal replacement products, followed by staged food reintroduction and physical activity support). The primary outcome is weight loss at 12 months. Other outcomes are glycaemic control and diabetes remission.

SETTING

Primary care, Qatar.

PARTICIPANTS

147 (73% men) randomised within DIADEM-I who were included in the final trial data analysis.

OUTCOME MEASURES

Recruitment metrics, and baseline clinical and metabolic characteristics.

RESULTS

Of 1498 people prescreened, 267 (18%) were invited for screening and 209 (78%) consented. 173 (83%) were eligible. 15 (7%) withdrew before randomisation and the remaining 158 were randomised. Mean age was 42.1 (SD 5.6) years and mean body mass index was: 36.3 (5.5) kg/m² (women) and 34.4 (5.4) kg/m² (men). Mean diabetes duration was 1.8 (1.0) years and mean glycosylated haemoglobin (HbA1c) was 7.0% (1.30) (52.5 mmol/mol (SD 14.3)). Participants originated from 13 countries. Those from North Africa reported greater physical activity and had lower family history of diabetes. 90% of subjects were taking diabetes medications and 31% antihypertensives. Those with greater waist circumference had significantly higher insulin resistance and lower quality of life.

CONCLUSION

Recruitment of participants originating from the MENA region into the RCT was successful, and study participation was readily accepted. While DIADEM-I participants originated from 13 countries, there were few baseline differences amongst participants from Middle East versus North Africa, supporting generalisability of RCT results.

TRIAL REGISTRATION NUMBER

ISRCTN20754766; NCT03225339.

Artificial Intelligence (AI) based machine learning models predict glucose variability and hypoglycaemia risk in patients with type 2 diabetes on a multiple drug regimen who fast during ramadan (The PROFAST - IT Ramadan study)

OBJECTIVE

To develop a machine-based algorithm from clinical and demographic data, physical activity and glucose variability to predict hyperglycaemic and hypoglycaemic excursions in patients with type 2 diabetes on multiple glucose lowering therapies who fast during Ramadan.

PATIENTS AND METHODS

Thirteen patients (10 males and three females) with type 2 diabetes on 3 or more anti-diabetic medications were studied with a Fitbit-2 pedometer device and Freestyle Libre (Abbott Diagnostics) 2 weeks before and 2 weeks during Ramadan. Several machine learning techniques were trained to predict blood glucose levels in a regression framework utilising physical activity and contemporaneous blood glucose levels, comparing Ramadan to non-Ramadan days.

RESULTS

The median age of participants was 51 years (IQR 49-52); median BMI was 33.2 kg/m² (IQR 33.0-35.9) and median HbA1c was 7.3% (IQR 6.7-7.8). The optimal model using physical activity achieved an R² of 0.548 and a mean absolute error (MAE) of 30.30. The addition of electronic health record (ehr) information increased R² to 0.636 and reduced MAE to 26.89 and the time of the day feature further increased R² to 0.768 and reduced MAE to 20.55. Combining all the features together resulted in an optimal XGBoost model with an R² of 0.836 and MAE of 17.47. This model accurately estimated normal glucose levels in 2584/2715 (95.2%) readings and hyperglycaemic events in 852/1031 (82.6%) readings, but fewer hypoglycaemic events (48/172 (27.9%)). The optimal XGBoost model prioritized age, gender, BMI and HbA1c followed by glucose levels and physical activity. Interestingly, the blood glucose level prediction by our model was influenced by use of SGLT2i.

CONCLUSION

XGBoost, a machine learning AI algorithm achieves high predictive performance for normal and hyperglycaemic excursions, but has limited predictive value for hypoglycaemia in patients on multiple therapies who fast during Ramadan.

The metabolic footprint of compromised insulin sensitivity under fasting and hyperinsulinemic-euglycemic clamp conditions in an Arab population

Metabolic pathways that are corrupted at early stages of insulin resistance (IR) remain elusive. This study investigates changes in body metabolism in clinically healthy and otherwise asymptomatic subjects that may become apparent already under compromised insulin sensitivity (IS) and prior to IR. 47 clinically healthy Arab male subjects with a broad range of IS, determined by hyperinsulinemic-euglycemic clamp (HIEC), were investigated. Untargeted metabolomics and complex lipidomics were conducted on serum samples collected under fasting and HIEC conditions. Linear models were used to identify associations between metabolites concentrations and IS levels. Among 1896 identified metabolites, 551 showed significant differences between fasting and HIEC, reflecting the metabolic switch in energy utilization. At fasting, 336 metabolites, predominantly di- and tri-acylglycerols, showed significant differences between subjects with low and high levels of IS. Changes in amino acid, carbohydrate and fatty acid metabolism in response to insulin were impaired in subjects with low IS. Association of altered mannose and amino acids with IS was also replicated in an independent cohort of T2D patients. We identified metabolic phenotypes that characterize clinically healthy Arab subjects with low levels of IS at their fasting state. Our study is providing further insights into the metabolic pathways that precede IR.

Metabolic profiling of pre-gestational and gestational diabetes mellitus identifies novel predictors of pre-term delivery

Background

Pregnant women with gestational diabetes mellitus (GDM) or type 2 diabetes mellitus (T2DM) are at increased risks of pre-term labor, hypertension and preeclampsia. In this study, metabolic profiling of blood samples collected from GDM, T2DM and control pregnant women was undertaken to identify potential diagnostic biomarkers in GDM/T2DM and compared to pregnancy outcome.

Methods

Sixty-seven pregnant women (21 controls, 32 GDM, 14 T2DM) in their second trimester underwent targeted metabolomics of plasma samples using tandem mass spectrometry with the Biocrates MxP^® Quant 500 Kit. Linear regression models were used to identify the metabolic signature of GDM and T2DM, followed by generalized linear model (GLMNET) and Receiver Operating Characteristic (ROC) analysis to determine best predictors of GDM, T2DM and pre-term labor.

Results

The gestational age at delivery was 2 weeks earlier in T2DM compared to GDM and controls and correlated negatively with maternal HbA1C and systolic blood pressure and positively with serum albumin. Linear regression models revealed elevated glutamate and branched chain amino acids in GDM + T2DM group compared to controls. Regression models also revealed association of lower levels of triacylglycerols and diacylglycerols containing oleic and linoleic fatty acids with pre-term delivery. A generalized linear model ROC analyses revealed that that glutamate is the best predictors of GDM compared to controls (area under curve; AUC = 0.81). The model also revealed that phosphatidylcholine diacyl C40:2, arachidonic acid, glycochenodeoxycholic acid, and phosphatidylcholine acyl-alkyl C34:3 are the best predictors of GDM + T2DM compared to controls (AUC = 0.90). The model also revealed that the triacylglycerols C17:2/36:4 and C18:1/34:1 are the best predictors of pre-term delivery (≤ 37 weeks) (AUC = 0.84).

Conclusions

This study highlights the metabolite alterations in women in their second trimester with diabetes mellitus and identifies predictive indicators of pre-term delivery. Future studies to confirm these associations in other cohorts and investigate their functional relevance and potential utilization for targeted therapies are warranted.

Effect of intensive lifestyle intervention on bodyweight and glycaemia in early type 2 diabetes (DIADEM-I): an open-label, parallel-group, randomised controlled trial

BACKGROUND

Type 2 diabetes is affecting people at an increasingly younger age, particularly in the Middle East and in north Africa. We aimed to assess whether an intensive lifestyle intervention would lead to significant weight loss and improved glycaemia in young individuals with early diabetes.

METHODS

This open-label, parallel-group, randomised controlled trial (DIADEM-I), done in primary care and community settings in Qatar, compared the effects of an intensive lifestyle intervention with usual medical care on weight loss and glycaemic outcomes in individuals with type 2 diabetes, aged 18-50 years, with a short diabetes duration (≤3 years), had a BMI of 27·0 kg/m² or more, and who were from the Middle East and north Africa region. Participants were randomly allocated (1:1) either to the intensive lifestyle intervention group or the usual medical care control group by a computer-generated sequence and an online randomisation service. The intensive lifestyle intervention comprised a total diet replacement phase, in which participants were given formula low-energy diet meal replacement products followed by gradual food reintroduction combined with physical activity support, and a weight-loss maintenance phase, involving structured lifestyle support. Participants in the control group received usual diabetes care, which was based on clinical guidelines. The primary outcome was weight loss at 12 months after receiving the assigned intervention. Our analysis was based on the intention-to-treat principle. Key secondary outcomes included diabetes control and remission. The trial was registered with the ISRCTN registry, ISRCTN20754766, and ClinicalTrials.gov, NCT03225339.

FINDINGS

Between July 16, 2017, and Sept 30, 2018, we enrolled and randomly assigned 158 participants (n=79 in each group) to the study. 147 participants (70 in the intervention group and 77 in the control group) were included in the final intention-to-treat analysis population. Between baseline and 12 months, the mean bodyweight of participants in the intervention group reduced by 11·98 kg (95% CI 9·72 to 14·23) compared with 3·98 kg (2·78 to 5·18) in the control group (adjusted mean difference -6·08 kg [95% CI -8·37 to -3·79], p<0·0001). In the intervention group, 21% of participants achieved more than 15% weight loss between baseline and 12 months compared with 1% of participants in the control group (p<0·0001). Diabetes remission occurred in 61% of participants in the intervention group compared with 12% of those in the control group (odds ratio [OR] 12·03 [95% CI 5·17 to 28·03], p<0·0001). 33% of participants in the intervention group had normoglycaemia compared with 4% of participants in the control group (OR 12·07 [3·43 to 42·45], p<0·0001). Five serious adverse events were reported in four participants in the control group; four admissions to hospital because of unanticipated events (supraventricular tachycardia, abdominal pain, pneumonia, and epididymo-orchitis), and one admission to hospital for an anticipanted event (hyperglycaemia).

INTERPRETATION

Our findings show that the intensive lifestyle intervention led to significant weight loss at 12 months, and was associated with diabetes remission in over 60% of participants and normoglycaemia in over 30% of participants. The provision of this lifestyle intervention could allow a large proportion of young individuals with early diabetes to achieve improvements in key cardiometabolic outcomes, with potential long-term benefits for health and wellbeing.

FUNDING

Qatar National Research Fund.

Prediabetes and older age increase the risk of post-transplantation diabetes mellitus: Qatar experience

Post-transplantation diabetes mellitus (PTDM) is a major complication in kidney transplant recipients leading to reduced allograft and patient survival. Given the high prevalence of diabetes in Qatar, which is twice the global average, we were interested in determining the incidence of PTDM, identifying risk factors, and comparing clinical outcomes in kidney transplant recipients with and without diabetes. We retrospectively followed up 191 adult kidney allograft recipients transplanted between January 1, 2012, and December 31, 2016, for a median of 41 months. A total of 76 patients (40%) had pre-existing diabetes. A total of 39 patients developed PTDM during follow-up; they represent 34% of patients who did not have diabetes prior to transplantation. Two thirds of PTDM occurred within 3-6 months post-transplantation. Prediabetes before transplant [OR = 6.07 (1.24-29.74), P = .026] older recipient's age at the time of transplantation [OR = 1.10 (1.00-1.20), P = .039] and average fasting blood sugar during 3-6 months post-transplant [OR = 1.06 (1.01-1.11), P = .010] were independently associated with PTDM. Patient and kidney allograft survival rates exceeded 97% in all groups. The incidence of PTDM in kidney transplant recipients living in Qatar is high. Older age and prediabetes are independent risk factors for developing PTDM.

Association of low serum magnesium with diabetes and hypertension: Findings from Qatar Biobank study

AIM

We aimed to examine the association between serum magnesium and diabetes and hypertension among Qatari adults.

METHODS

In the cross-sectional study, we used data from 9693 Qatari participants aged 20 years and above attending the Qatar Biobank (QBB) Study. Blood samples were analyzed in a central lab. Habitual food consumption was assessed by a food frequency questionnaire. Reduced rank regression was used to construct magnesium related dietary pattern (MRDP) using serum magnesium as a response variable. Diabetes was defined by blood glucose, HbA1c or known diabetes. Prediabetes was defined as HbA1c between 5.7% and 6.4%. Subclinical magnesium deficiency was defined as serum magnesium <0.85 mmol/L.

RESULTS

The prevalence of diabetes, prediabetes and subclinical magnesium deficiency was 18.9%, 11.5% and 59.5%, respectively. Across the quartiles of serum magnesium from high to low, the prevalence ratios (PR 95%CI) for diabetes were 1.00, 1.35, 1.88, and 2.70 (95%CI 2.38-3.05), respectively (p for trend <0.001). The presence of hypertension significantly increased the probability of diabetes along a wide range of low serum magnesium. A low intake of MRDP was also positively associated with diabetes and high HbA1c.

CONCLUSION

Subclinical magnesium deficiency is common in Qatar and associates with diabetes, prediabetes and hypertension in Qatari adults.

DNAJB3 attenuates metabolic stress and promotes glucose uptake by eliciting Glut4 translocation

Failure of the heat shock response is a key event that leads to insulin resistance and type 2 diabetes. We recently showed that DNAJB3 co-chaperone is downregulated in obese and diabetic patients and that physical exercise restores its normal expression with a significant improvement of the clinical outcomes. In 3T3-L1 adipocytes, DNAJB3 has a role in improving the sensitivity to insulin and glucose uptake. In co-immunoprecipitation assays, DNAJB3 interacts with both JNK1 and IKKβ kinases. However, the functional impact of such interaction on their activities has not been investigated. Here, we assessed the effect of DNAJB3 on the respective activity of JNK1 and IKKβ in cell-based assays. Using JNK1- and IKKβ-dependent luciferase reporters, we show a marked decrease in luciferase activity by DNAJB3 in response to PMA and TNF-α that was consistent with a decrease in the translocation of p65/NF-κB to the nucleus in response to LPS. Furthermore, TNF-α-mediated IL-6 promoter activation and endogenous mRNA expression are significantly abrogated by DNAJB3 both in 3T3-L1 and C2C12 cells. The ability of DNAJB3 to mitigate ER stress and oxidative stress was also investigated and our data show a significant improvement of both forms of stress. Finally, we examined the effect of overexpressing and knocking down the expression of DNAJB3 on glucose uptake in C2C12 as well as the molecular determinants. Accordingly, we provide evidence for a role of DNAJB3 in promoting both basal and insulin-stimulated glucose uptake. Our finding reveals also a novel role of DNAJB3 in eliciting Glut4 translocation to the plasma membrane. These results suggest a physiological role of DNAJB3 in mitigating metabolic stress and improving glucose homeostasis and could therefore represent a novel therapeutic target for type 2 diabetes.

Diabetes Intervention Accentuating Diet and Enhancing Metabolism (DIADEM-I): a randomised controlled trial to examine the impact of an intensive lifestyle intervention consisting of a low-energy diet and physical activity on body weight and metabolism in early type 2 diabetes mellitus: study protocol for a randomized controlled trial

Background

Type 2 diabetes mellitus (T2DM) and obesity are syndemic and will have a significant impact on affected individuals and healthcare services worldwide. Evidence shows that T2DM remission can be achieved with significant weight loss in those who are younger with early diabetes and requiring fewer medications for glycaemic control. DIADEM-I aims to examine the impact of an intensive lifestyle intervention (ILI) using a low-energy diet (LED) meal replacement approach combined with physical activity in younger individuals with early T2DM.

Methods

The planned study is an ongoing, non-blinded, pragmatic, randomised controlled, parallel-group trial examining the impact of an LED-based ILI on body weight and diabetes remission in younger (18–50 years) T2DM individuals with early diabetes (≤ 3-year duration). The ILI will be compared to usual medical care (UMC). The primary outcome will be weight loss at 12 months. Other key outcomes of interest include diabetes remission, glycaemic control, diabetes complications, cardiovascular health, physical activity, mental health, and quality of life. It is planned for the study to include 138 subjects for assessment of the primary outcome. Safety will be assessed throughout.

Discussion

If DIADEM-I demonstrates a clinically significant effect for younger individuals with early T2DM, it will inform clinical guidelines and services of the future for management of T2DM.

Trial registration

ISRCTN: ISRCTN20754766 (date assigned: 7 June 2017); ClinicalTrials.gov, ID: NCT03225339 Registered on 26 June 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2660-1) contains supplementary material, which is available to authorized users.

Measurement of 1,5-anhydroglucitol in blood and saliva: from non-targeted metabolomics to biochemical assay

Background

Diabetes testing using saliva, rather than blood and urine, could facilitate diabetes screening in public spaces. We previously identified 1,5-anhydro-d-glucitol (1,5-AG) in saliva as a diabetes biomarker. The Glycomark™ assay kit is FDA approved for 1,5-AG measurement in blood. Here we evaluated its applicability for 1,5-AG quantification in saliva.

Methods

Using pooled saliva samples, we validated Glycomark™ assay use with a RX Daytona⁺ clinical chemistry analyser. We then used this set-up to analyse 82 paired blood and saliva samples from a diabetes case–control study, for which broad mass spectrometry-based characterization of the blood and saliva metabolome was also available. Osmolality was measured to account for potential variability in saliva samples.

Results

The technical variability of the read-outs for the pooled saliva samples (CV = 2.05 %) was comparable to that obtained with manufacturer-provided blood surrogate quality controls (CV = 1.38–1.8 %). We found a high correlation between Glycomark assay and mass spectrometry measurements of serum 1,5-AG (r² = 0.902), showing reproducibility of the non-targeted metabolomics results. The significant correlation between the osmolality measurements performed at two independent platforms with the time interval of 2 years (r² = 0.887), also indicates the sample integrity. The assay read-out for saliva was not correlated with the mass spectrometry-based 1,5-AG saliva measurements. Comparison with the full saliva metabolome revealed a high correlation of the saliva assay read-outs with galactose.

Conclusions

Glycomark™ assay read-outs for saliva were stable and replicable. However, the signal was dominated by galactose, which is biochemically similar to 1,5-AG and absent in blood. Adapting the 1,5-AG kit for saliva analysis will require enzymatic depletion of galactose. This should be feasible, since the assay already includes a similar step for glucose depletion from blood samples.

Nuclear export mediated regulation of microRNAs: potential target for drug intervention

MicroRNAs (miRNAs) are short non-coding RNAs that have been recognized to regulate the expression of uncountable number of genes. Their aberrant expression has been found to be linked to the pathology of many diseases including cancer. There is a drive to develop miRNA targeted therapeutics for different diseases especially cancer. Nevertheless, reining in these short non-coding RNAs is not as straightforward as originally thought. This is in view of the recent discoveries that miRNAs are under epigenetic regulations at multiple levels. Exportin 5 protein (XPO5) nuclear export mediated regulation of miRNAs is one such important epigenetic mechanism. XPO5 is responsible for exporting precursor miRNAs through the nuclear membrane to the cytoplasm, and is thus a critical step in miRNA biogenesis. A number of studies have shown that variations in components of the miRNA biogenesis pathways, particularly the aberrant expression of XPO5, increase the risk of developing cancer. In addition to XPO5, the Exportin 1 protein (XPO1) or chromosome region maintenance 1 (CRM1) can also carry miRNA export function. These findings are supported by pathway analyses that reveal certain miRNAs as direct interaction partners of CRM1. An in depth understanding of miRNA export mediated regulatory mechanisms is important for the successful design of clinically viable therapeutics. In this review, we describe the current knowledge on the mechanisms of miRNA nuclear transport mediated regulation and propose strategies to selectively block this important mechanism in cancer.

N-glycosylation of CRF receptor type 1 is important for its ligand-specific interaction

The corticotropin-releasing factor (CRF) receptor type 1 (CRFR1) contains five potential N-glycosylation sites: N38, N45, N78, N90, and N98. Cells expressing CRFR1 were treated with tunicamycin to block receptor glycosylation. The nonglycosylated receptor did not bind the radioligand and had a decreased cAMP stimulation potency in response to CRF. To determine which of the polysaccharide chain(s) is/are involved in ligand interaction, the polysaccharide chains were deleted using site-directed mutagenesis of the glycosylation consensus, N-X-S/T. Two sets of mutations were performed for each glycosylation site: N to Q and S/T to A, respectively. The single mutants Q38, Q45, Q78, Q90, Q98, A40, A47, A80, A92, and A100 and the double mutants A40/A47 and A80/A100 were well expressed, bound CRF, sauvagine (SVG), and urotensin-I (UTS-I) with a normal affinity, and increased cAMP accumulation with a high efficiency. In contrast, the combined mutations A80/A92/A100, A40/A80/A92/A100, and A40/A47/A80/A92/A100 had low levels of expression, did not bind the radioligand, and had a decreased cAMP stimulation. These data indicate the requirement for three or more polysaccharide chains for normal CRFR1 function.

Parathyroid hormone receptor internalization is independent of protein kinase A and phospholipase C activation

Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) binding to their common receptor stimulates second messenger accumulation, receptor phosphorylation, and internalization. LLC-PK(1) cells expressing a green fluorescent protein-tagged PTH/PTHrP receptor show time- and dose-dependent receptor internalization. The internalized receptors colocalize with clathrin-coated pits. Internalization is stimulated by PTH analogs that bind to and activate the PTH/PTHrP receptor. Cell lines expressing a mutant protein kinase A regulatory subunit that is resistant to cAMP and/or a mutant receptor (DSEL mutant) that does not activate phospholipase C internalize their receptors normally. In addition, internalization of the wild-type receptor and the DSEL mutant is stimulated by the PTH analog [Gly(1),Arg(19)]hPTH-(1-28), which does not stimulate phospholipase C. Forskolin, IBMX, and the active phorbol ester, phorbol-12-myristate-13-acetate, did not promote receptor internalization or increase PTH-induced internalization. These data indicate that ligand-induced internalization of the PTH/PTHrP receptor requires both ligand binding and receptor activation but does not involve stimulation of adenylate cyclase/protein kinase A or phospholipase C/protein kinase C.

An oxidation resistant radioligand for corticotropin-releasing factor receptors

The methionine residues in Tyr-corticotropin-releasing factor (CRF) and Tyr-sauvagine radioligands are subject to oxidation, which renders them biologically inactive. Therefore [Tyr(0,) Gln(1,) Leu(17)]sauvagine (YQLS), in which the methionine was replaced with leucine was synthesized and labeled with (125)Iodine using chloramine-T. Mass spectroscopy revealed that chloramine-T-treatment did not oxidize YQLS. (125)I-YQLS bound with high affinity to cells expressing the murine CRF receptor 1 (CRFR1), CRF receptor 2 (CRFR2), and the mouse brain regions known to express both CRF receptors. (125)I-YQLS chemically cross-linked to CRFR1. In conclusion, (125)I-YQLS is oxidation-resistant, high affinity radioligand that can be chemically cross-linked to the CRF receptors.

Juxtamembrane region of the amino terminus of the corticotropin releasing factor receptor type 1 is important for ligand interaction

The functional properties of the amino terminus (NT) of the corticotropin releasing factor (CRF) receptor type 1 (R1) were studied by use of murine (m) CRFR1 and rat (r) parathyroid hormone (PTH)/parathyroid hormone-related peptide receptor (PTH1R) chimeras. The chimeric receptor CXP, in which the NT of mCRFR1 was annealed to the TMs of PTH1R, and the reciprocal hybrid, PXC, bound radiolabeled analogues of sauvagine and PTH(3--34), respectively. Neither hybrid bound radiolabeled CRF or PTH(1--34). CRF and PTH(1--34) weakly stimulated intracellular cAMP accumulation in COS-7 cells transfected with PXC and CXP, respectively. Thus the NT is required for ligand binding and the TMs are required for agonist-stimulated cAMP accumulation. Replacing individual intercysteine segments of PXC with their mCRFR1 counterparts did not rescue CRF or sauvagine radioligand binding or stimulation of cAMP accumulation. Replacement of residues 1--31 of mCRFR1 with their PTH1R counterparts resulted in a chimeric receptor, PEC, which had normal CRFR1 functional properties. In addition, a series of chimeras (F1PEC--F6PEC) were generated by replacement of the NT intercysteine residues of PEC with their PTH1R counterparts. Only F1PEC, F2PEC, and F3PEC showed detectable CRF and sauvagine radioligand binding. All of the PEC chimeras except F5PEC increased cAMP accumulation. These data indicate that the Cys(68)(-)Glu(109) domain is important for binding and that the Cys(87)(-)Cys(102) region plays an important role in CRFR1 activation.

Characterization of three corticotropin-releasing factor receptors in catfish: a novel third receptor is predominantly expressed in pituitary and urophysis

The present study reports the isolation of three complementary DNA (cDNA) clones encoding distinct subtypes of CRF receptors from the diploid catfish (cf) species, Ameiurus nebulosus. The first clone encodes a 446-amino acid protein (cfCRF-R1) that is highly homologous to mouse (m) CRF-R1 (93% identical). The cfCRF-R1 messenger RNA is highly expressed in the brain, and its distribution pattern correlates well with that of mammalian CRF-R1, except for weak expression in the pituitary. When transiently expressed in COS-7 cells, cfCRF-R1 bound CRF, urotensin I, and sauvagine with similar affinities. The second full-length cDNA, which was cloned from catfish heart, encodes a 406-amino acid protein that showed homology to murine CRF-R2 (88%) and when expressed in COS-7 cells preferentially bound sauvagine. The highest level of cfCRF-R2 expression was observed in the heart. The third full-length cDNA clone, which encodes a 428-amino acid protein, is structurally closer to cfCRF-R1 (85%) than to cfCRF-R2 (80%). This novel CRF receptor (cfCRF-R3) bound CRF with a 5-fold higher affinity than urotensin I and sauvagine and was expressed in the pituitary gland, urophysis, and brain. The presence of three different CRF receptors, each with distinct tissue distribution and ligand binding properties, suggests a complex CRF/urotensin I system.

The transcription factors SP1 and MAZ regulate expression of the parathyroid hormone/parathyroid hormone-related peptide receptor gene

The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor regulates extracellular calcium concentrations and is therefore important for mineral homeostasis. ROS 17/2.8 cells, a rat osteoblast-like osteosarcoma cell line, express the PTH/PTHrP receptor and provide a good model for examining the transcriptional regulation of its gene. The rat PTH/PTHrP receptor gene has two promoters, U1 and U3, which were shown to be important for its expression. Using extracts from ROS 17/2.8 cells, we have demonstrated two regions (termed FP1 and FP2) of nuclear protein/DNA interaction within promoter sequences previously shown to be important for the activity of the U3 promoter. Nuclear extracts from rat 2 fibroblasts, which do not express the PTH/PTHrP receptor, produced one site of protein/DNA interaction which was found at a position on the promoter identical to the position of FP1 produced by a ROS 17/2.8 nuclear extract. Mutation of these two sites of protein/DNA interaction resulted in reduced U3 promoter activity. Furthermore, we have demonstrated that the transcription factors SP1 and MAZ regulate U3 promoter expression and have shown their functional significance using mutational analysis. These data demonstrate that SP1 and MAZ bind to the PTH/PTHrP receptor promoter and that they are involved in cell-specific expression of its gene product.

Role of asparagine-linked oligosaccharides in the function of the rat PTH/PTHrP receptor

The receptor for parathyroid hormone (PTH) and PTH-related peptide (PTHrP) is a G-protein-coupled receptor with four potential sites for N-linked glycosylation. The contribution of the oligosaccharide moieties to cell surface expression, ligand binding, and signal transduction was investigated. Site-directed mutagenesis of the rat PTH/PTHrP receptor cDNA was performed at single or combination of the four potential glycosylation sites to determine the effect of the putative carbohydrate chains on the activities of the receptor. The results revealed that all four potential N-glycosylation sites in the PTH/PTHrP receptor are glycosylated. Receptors missing a single or multiple glycosylation consensus but with at least one intact glycosylation site expressed sufficiently and functioned normally. In contrast, the nonglycosylated receptor, in which all four glycosylation sites were mutated, is deficient in these functions. These data indicate important roles for N-linked glycosylation in PTH/PTHrP receptor functions.

Identification of a retinoic acid-inducible element in the murine PTH/PTHrP (parathyroid hormone/parathyroid hormone-related peptide) receptor gene

We have shown previously that the PTH/PTHrP (PTH-related peptide) receptor mRNA becomes expressed very early in murine embryogenesis, i.e. during the formation of extraembryonic endoderm. Retinoic Acid (RA) is a potent inducer of extraembryonic endoderm formation and PTH/PTHrP-receptor expression in embryonal carcinoma (EC) and embryonal stem (ES) cells. Using the P19 EC cell line, we have characterized promoter elements of the murine PTH/PTHrP-receptor gene that are involved in this RA-induced expression. The data show that RA-induced expression of the PTH/ PTHrP-receptor gene is mediated by the downstream P2 promoter. Analysis of promoter reporter constructs in transiently transfected P19 cells treated with RA identified an enhancer region between nucleotides -2714 and -2702 upstream of the P2 transcription start site that is involved in the RA effect. This region matches a consensus hormone response element consisting of a direct repeat with an interspacing of 1 bp (R-DR1). The R-DR1 efficiently binds retinoic acid receptor-alpha (RARalpha)-retinoid X receptor-alpha (RXRalpha) and chicken ovalbumin upstream promoter (COUP)-transcription factor I (TFI)-RXRalpha heterodimers and RXRalpha and COUP-TFI homodimers in a bandshift assay using extracts of transiently transfected COS-7 cells. RA differentiation of P19 EC cells strongly increases protein binding to the R-DR1 in a band-shift assay. This is caused by increased expression of RXR (alpha, beta, or gamma) and by the induction of expression of RARbeta and COUP TFI/TFII, which bind to the R-DR1 as shown by supershifting antibodies. The presence of RXR (alpha, beta, or gamma) in the complexes binding to the R-DR1 suggests that RXR homodimers are involved in RA-induced expression of the PTH/PTHrP-receptor gene. The importance of the R-DR1 for RA-induced expression of PTH/ PTHrP-receptor was shown by an inactivating mutation of the R-DR1, which severely impairs RA-induced expression of PTH/PTHrP-receptor promoter reporter constructs. Since this mutation does not completely abolish RA-induced expression of PTH/PTHrP-receptor promoter reporter constructs, sequences other than the R-DR1 might also be involved in the RA effect. Finally, we show that the RA-responsive promoter region is also able to induce expression of a reporter gene in extraembryonic endoderm of 7.5 day-old transgenic mouse embryos.

Characterization of an element within the rat parathyroid hormone/parathyroid hormone-related peptide receptor gene promoter that enhances expression in osteoblastic osteosarcoma 17/2.8 cells

Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) mediate their actions via a common G-protein-coupled receptor. High levels of PTH/PTHrP receptor expression have been detected in many tissues including bone and kidney. This study has demonstrated specific PTH/PTHrP receptor expression from the U3 promoter in the osteoblastic osteosarcoma ROS 17/2.8 cell line, which expresses the endogenous PTH/PTHrP receptor, compared to rat 2 fibroblasts which do not express the endogenous PTH/PTHrP receptor gene. Transient transfection studies revealed cell-specific expression of a construct containing 4391 bp of DNA upstream of exon U3 of the PTH/PTHrP receptor gene fused to a luciferase reporter gene. Deletion mapping of the 5' region of U3 revealed that a construct containing 206 bp upstream of U3 confers cell-specific expression. These data suggest that cell-specific expression in ROS 17/2.8 involves cell-specific elements within the PTH/PTHrP receptor promoter.

Epitope tag mapping of the extracellular and cytoplasmic domains of the rat parathyroid hormone (PTH)/PTH-related peptide receptor

The PTH/PTH-related peptide (PTHrP) receptor is predicted to span the plasma membrane seven times with an amino-terminal extracellular extension and a cytoplasmic carboxyl-terminal tail. To assess this prediction, we inserted 10- or 9-amino acid epitope tags from c-myc or hemophilus influenza hemaglutinin (HA), which are recognized by the monoclonal antibodies 9E10 and 12Ca5, respectively, in different extracellular and cytoplasmic regions of the receptor and examined the immunoreactivity of the epitopes in intact and permeabilized cells. The data show that the epitopes were well tolerated when introduced into the E2 region of the extracellular amino-terminus (E2-myc and E2-HA), in the first extracellular loop (EL1), in the second and third cytoplasmic loops (CL2c and CL3), or in the carboxyl-terminal tail (T-myc). Receptors tagged at these locations were well expressed, bound PTH with high affinity, and increased cAMP accumulation with a good efficiency. Receptors tagged in the second and third extracellular loops (EL2c and EL3c) or the first cytoplasmic loop (CL1c) bound the PTH radioligand with a low affinity, stimulated cAMP accumulation with a low efficiency, and had low expression levels. The receptors tagged on presumed extracellular regions, E2-myc, E2-HA, EL1, EL2c, and EL3c, were readily detected on the surface of intact cells with the monoclonal antibody against the epitope tag. In contrast, receptors tagged with the c-myc epitope in the cytoplasmic loops (CL1c, CL2c, and CL3) or in the carboxyl-terminal tail (T-myc) did not show any 9E10 binding in intact cells. These receptors, however, were well expressed on the cell surface, as detected by the binding of the monoclonal antibody, 12Ca5, to the HA tag that was introduced into the E2 region of these constructs. The c-myc epitopes, however, became accessible after permeabilization of the cell membrane. In conclusion, these data provide experimental evidence for the sidedness of the extracellular and cytoplasmic domains of the PTH/PTHrP receptor.

Extracellular cysteines of the corticotropin-releasing factor receptor are critical for ligand interaction

The corticotropin-releasing factor receptor (CRF-R) contains six conserved cysteines in its amino-terminal domain (C30, C44, C54, C68, C87, and C102) and one cysteine in its first and second extracellular loops (C188 and C258, respectively). Additionally, several other cysteines are located in the transmembrane domains (C128, C211, C233, and C364) and first intracellular loop (C150). Reduction of disulfide bonds with DTT decreased CRF binding to detergent-solubilized membranes, suggesting an important role for disulfide bonds in ligand recognition. Therefore, site-directed mutagenesis was used to introduce single and paired Cys (C) to Ser (S) or Ala (A) mutations. A silent nine amino acid tag from c myc was introduced in the amino terminus of the mouse CRF-R. With the exception of C258S and C188S/C258S mutations, all C to S or to A receptor mutants had good surface expression that was at least 52.5% of control. C30S, C54S, and C30S/C54S mutations had good CRF binding and CRF-stimulated cAMP accumulation. No CRF binding was detected for the C44S, C68S, C87S, C102S, C188S, C258S, C30S/C44S, C30S/C68S, C54S/C68S, C87S/C102S, and C188S/C258S mutants, while CRF-stimulated cAMP accumulation occurred with high EC50 values. In particular, receptors carrying double mutations, C44S/C102S and C68S/C87S, had an improved signaling property as compared to receptors carrying the respective single cysteine mutations. These data, together with the effects of DTT on CRF binding, indicate that disulfide bridges are important for receptor functions. Functional data from single and paired cysteine mutations suggest potential pairings between C44 and C102, C68 and C87, and C188 and C258 that are critical for ligand-receptor interactions.

Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by PTH in primary fetal rat osteoblasts

We studied the effects of parathyroid hormone (PTH) on PTH parathyroid hormone related peptide (PTHrP) receptor mRNA level, PTHrP binding and PTH-stimulated cyclic adenosine monophosphate (cAMP) accumulation in osteoblasts, derived from fetal rat calvariae (ROB). Cells isolated during 10-70 minutes of collagenase treatment were seeded at a density of 25,000 cells/cm2 and cultured for 4 days. These cells show a fast increase in cAMP production after stimulation for 5 minutes with 20 nM bovine parathyroid hormone(1-34) (bPTH(1-34)). When ROB are incubated with bPTH(1-34) (0.04-40nM) for 24 h, a dose-dependent decrease of the PTH/PTHrP receptor mRNA level, PTHrP binding, and PTH-stimulated cAMP accumulation can be observed. Pretreatment of ROB with a high concentration of bPTH(1-34) (40 nM) leads within 15 minutes to a decrease in PTH-stimulated cAMP accumulation. However, it takes > or = 3 h before a significant decrease in PTH/PTHrP receptor mRNA level can be observed. Also a significant decrease in PTHrP binding is observed after only 4 h of incubation with bPTH(1-34). Compared with bPTH(1-34), pretreatment of ROB with bPTH(3-34) (40 and 100 nM) for 24 h causes smaller decreases in PTH-stimulated cAMP accumulation, PTHrP binding, and in the PTH/PTHrP receptor mRNA level. We investigated the possible involvement of the protein kinase A signaling pathway in the regulation of the PTH/PTHrP receptor mRNA expression. Both forskolin and (Bu)2cAMP decreased PTHrP binding and PTH/PTHrP mRNA levels. These observations suggest that chronic activation of the PKA signaling pathway may down-regulate PTH/PTHrP receptor expression and thus hormone responsiveness in "normal" osteoblasts. In short, we found that the decrease of the PTH-stimulated cAMP accumulation after long-term pretreatment with bPTH(1-34) is correlated with both PTH/PTHrP receptor mRNA level and PTHrP binding. These data also suggest that the initial desensitization (< 30 minutes) of PTH-stimulated cAMP responsiveness by pretreatment with a high concentration of bPTH(1-34) (40 nM) is not dependent on the number of available PTH/PTHrP receptors. The protein kinase A signaling pathway is involved in the regulation of the PTH/PTHrP receptor, but, regarding the effect of bPTH(3-34), other signaling systems are also involved.

PTH/PTHrP receptor in early development and Indian hedgehog-regulated bone growth

The PTH/PTHrP receptor binds to two ligands with distinct functions: the calcium-regulating hormone, parathyroid hormone (PTH), and the paracrine factor, PTH-related protein (PTHrP). Each ligand, in turn, is likely to activate more than one receptor. The functions of the PTH/PTHrP receptor were investigated by deletion of the murine gene by homologous recombination. Most PTH/PTHrP receptor (-/-) mutant mice died in mid-gestation, a phenotype not observed in PTHrP (-/-) mice, perhaps because of the effects of maternal PTHrP. Mice that survived exhibited accelerated differentiation of chondrocytes in bone, and their bones, grown in explant culture, were resistant to the effects of PTHrP and Sonic hedgehog. These results suggest that the PTH/PTHrP receptor mediates the effects of Indian Hedgehog and PTHrP on chondrocyte differentiation.

Downregulation of the PTH/PTHrP receptor by vitamin D3 in the osteoblast-like ROS 17/2.8 cells

Effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the expression of the parathyroid hormone (PTH)/PTH-related peptide (rP) receptor protein and mRNA in ROS 17/2.8 cells were studied. Treatment of ROS 17/2.8 cells with 1,25(OH)2D3 caused time- and dose-dependent suppression of PTH/PTHrP receptor number and immunoreactivity. The effects required more than 24 h incubation with 1,25(OH)2D3 and were maximal by 72 h. The cells did not recover their PTH/PTHrP receptors even after 4 days of treatment with control medium. Treatment with low concentrations of 1,25(OH)2D3 (0.1 M) dramatically decreased the PTH/PTHrP receptor mRNA levels, which were maximal after 24 h of incubation. The half-life of the PTH/PTHrP receptor transcript, 6-8 h, was similar in control and 1,25(OH)2D3-treated cells, suggesting that 1,25(OH)2D3 acts in controlling transcription of the PTH/PTHrP receptor gene but does not change the degradation rate of the PTH/PTHrP receptor transcripts. These data indicate that 1,25(OH)2D3 has a potent inhibitory effect on the expression of the PTH/PTHrP receptor protein and mRNA in ROS 17/2.8 cells.

Molecular cloning of a type A chicken corticotropin-releasing factor receptor with high affinity for urotensin I

The hypothalamic-pituitary-adrenal axis is an essential physiological system in many species. CRF, the major neuropeptide regulating ACTH secretion, is highly conserved in its primary sequence. Evolutionary conservation of the CRF sequence suggests that the CRF receptor (CRF-R) complementary DNA and examined its properties. The avian CRF-R complementary DNA encodes a 420-amino acid protein that is 87-88% identical to those of human, rat, and mouse. Most sequence divergence occurs in the putative signal peptide and the extracellular amino-terminus of the receptor. Five additional amino acids are inserted in the amino-terminus of the cCRF-R. When expressed in COS-7 cells, the cCRF-R binds the CRF and urotensin I radioligands with high affinities. Urotensin I competes for binding to the chicken CRF-R, expressed in COS-7 cells, with an apparent affinity 20 times higher than that of CRF. Both urotensin I and sauvagine were more effective in stimulating cAMP accumulation in COS-7 cells transfected with the cCRF-R than CRF. The effects of CRF and urotensin I on inositol phosphate accumulation were also tested. Urotensin I was an effective as CRF in stimulating inositol phosphate accumulation in COS-7 cells transfected with the cCRF-R. These data suggest that the sequence of the CRF-R is highly conserved from avian to mammalian species and that, despite its high sequence homology to the type A mammalian CRF-R, the ligand binding properties of cCRF-R are similar to those of the type B CRF-R i.e. a higher affinity for urotensin I than for CRF.

Parathyroid hormone (PTH)/PTH-related peptide receptor density modulates activation of phospholipase C and phosphate transport by PTH in LLC-PK1 cells

We showed previously that a single species of cloned PTH/PTH-related peptide (PTHrP) receptors, when stably expressed in LLC-PK1 kidney cells, couples to multiple second messenger signals and biological responses. To address the linkages of individual messenger signals to specific biological responses in these cells, we examined the relations among PTH/PTHrP receptor expression, PTH-activated phospholipase C (PLC) and adenylyl cyclase, and PTH-regulated phosphate transport in LLC-PK1 cells that stably express cloned rat PTH/PTHrP receptors. Among 18 such subclones, PTH stimulation of intracellular cAMP accumulation was nearly equivalent, despite differences in receptor density ranging from 20,000-400,000 sites/cell. In contrast, activation of PLC by PTH was directly and continuously dependent upon receptor density. PTH-stimulated phosphate uptake also was strongly dependent upon receptor expression, correlated well with PLC activity, was mimicked by active phorbol esters but not by cAMP analogs or forskolin, and was strikingly inhibited by the protein kinase C inhibitor, staurosporine. The peptide analog [Arg2]human PTH-(1-34), which significantly stimulated cAMP accumulation but failed to activate PLC, also did not increase phosphate uptake. We conclude that in LLC-PK1 cells, PTH-modulated PLC activation, unlike adenylyl cyclase activation, is strongly dependent upon PTH/PTHrP receptor density. This feature is reflected in the analogous relation between receptor density and PTH regulation of phosphate uptake, which appears to be mediated via a PKC-dependent pathway in these transfected cells. The results suggest that regulation of PTH/PTHrP receptor expression on target cells may provide a mechanism for altering the character as well as the magnitude of the signaling response to the hormone.

Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by transforming growth factor-beta in primary fetal rat osteoblasts

We studied the effects of transforming growth factor-beta 2 (TGF beta 2) on the level of PTH/PTH-related peptide-(PTHrP) receptor messenger RNA (mRNA), PTHrP binding, and PTH-stimulated cAMP accumulation in cultured osteoblasts derived from fetal rat calvariae (ROB). When ROB were pretreated with TGF beta 2 at concentrations ranging from 1-100 pM for 24 h, dose-dependent decreases in the level of PTH/PTHrP receptor mRNA, PTHrP binding, and PTH-stimulated cAMP accumulation were observed. For the PTH/PTHrP receptor mRNA level and PTH-stimulated cAMP accumulation, the half-maximal effective concentration was approximately 4 pM. For the inhibition of PTHrP binding, the half-maximal effective concentration was much higher. A 50% decrease in both PTH/PTHrP receptor mRNA level and PTH-stimulated cAMP accumulation was obtained when ROB were treated with 100 pM TGF beta 2 for 4 h. A comparable decrease in PTHrP binding was only observed after 24 h of incubation with 100 pM TGF beta 2. Actinomycin D induced a rapid decrease in the PTH/PTHrP receptor mRNA level (70% after 4 h), indicating a half-life for the receptor mRNA of 2-3 h. Under the same conditions, PTHrP binding and PTH-stimulated cAMP accumulation did not change. When ROB were treated with cycloheximide for the same period, only a small decrease in PTHrP binding (20%) was observed, suggesting that PTH/PTHrP receptors do not have a rapid turnover. Cycloheximide also reduced PTH-stimulated cAMP production; after coincubation of cycloheximide with TGF beta 2, this inhibition was smaller than that in ROB cultures treated with TGF beta 2 exclusively. From these observations we conclude that TGF beta 2 induces a decrease in steady state levels of PTH/PTHrP receptor mRNA that results in decreased PTHrP receptor binding. The PTH-stimulated cAMP accumulation is at least to some extent independent of the PTH/PTHrP receptor availability. Furthermore, there is a high turnover of PTH/PTHrP receptor mRNA, whereas turnover of the receptor protein is much slower. Finally, protein synthesis is required for TGF beta 2-induced desensitization of cAMP responsiveness to PTH.

The alternatively spliced type II corticotropin-releasing factor receptor, stably expressed in LLCPK-1 cells, is not well coupled to the G protein(s)

Two alternatively spliced corticotropin-releasing factor receptor (CRF-R) cDNAs, type I and type II, were recently isolated from a human cDNA library. The two cDNAs are identical except that the type II cDNA encodes an additional 29 amino acid inserted in the first putative cytoplasmic loop. Since the first cytoplasmic loop is highly conserved in all the members of the hCRF receptor family we have examined whether the presence of the 29 amino acid cassette in CRF-RII influences G protein coupling in LLCPK-1 cells stably expressing the type I and type II hCRF receptors. Whether measured in intact cells or in membrane preparations, LLCPK-1 cells stably expressing CRF-RII have a 4-5 fold lower binding affinity. Maximal CRF-stimulated cAMP accumulation in LLCPK-1 cells stably expressing CRF-RI was 10-15-fold higher than that in LLCPK-1 cells expressing CRF-RII. The EC50 for CRF-stimulated cAMP accumulation in hCRF-RI-expressing cells was in the range of 0.5 +/- 0.2 nM. In contrast, the EC50 for CRF-stimulated cAMP accumulation in hCRF-RII expressing cells was 7.7 +/- 0.2 nM. hCRF increased phosphoinositide turnover in LLCPK-1 cells stably expressing CRF-RI but not in those expressing CRF-RII; this effect required hCRF concentrations of 100 nM and higher. In membrane preparations, GTP-gamma-S inhibited hCRF binding to CRF-RI and shifted the binding Kd from 4.5 nM to 16.7 nM. Conversely, GTP-gamma-S did not influence hCRF binding to CRF-RII in broken cell membranes. Additionally, CRF-stimulated adenylate cyclase activity in cell membranes expressing CRF-RI was potentiated by GTP, whereas CRF-stimulated adenylate cyclase activity in cell membranes expressing CRF-RII was insensitive to GTP. These data indicate that CRF-RII is not well coupled to the G protein. Since the only difference between the CRF-RII and CRF-RI is the insert in the first putative cytoplasmic loop, these data indicate that the first cytoplasmic loop plays a crucial role in hCRF receptor coupling to the G protein.

Further evidence for a novel receptor for amino-terminal parathyroid hormone-related protein on keratinocytes and squamous carcinoma cell lines

PTH and PTH-related peptides (PTHrPs) interact with a common PTH/PTHrP receptor (type I), which is expressed in many tissues, including bone and kidney. Amino-terminal PTH and PTHrPs also recognize receptors in several nonclassical PTH target tissues, and in some of these, the signaling mechanisms differ qualitatively from those of the classical type I receptor. In normal keratinocytes and squamous carcinoma cell lines, PTH and PTHrP stimulate a rise in intracellular calcium, but not cAMP, suggesting the existence of an alternate, type II PTH/PTHrP receptor. SqCC/Y1 squamous carcinoma cells stably expressing the type I receptor displayed sensitive intracellular cAMP responses to PTHrP and PTH, indicating that these cells express functional GS proteins and that the type I receptor is capable of signaling through adenylyl cyclase in this cell line. Therefore, the endogenous type II receptor in SqCC/Y1 cells differs from the cloned type I receptor. We next examined whether messenger RNA (mRNA) from keratinocytes and squamous cell lines could hybridize to a human type I PTH/PTHrP receptor complementary DNA [1.9 kilobases (kb)]. No type I receptor mRNA (2.3 kb) was detected in polyadenylated RNA from any of the squamous cell lines. However, squamous cell lines did express several mRNA transcripts that hybridized with the type I receptor probe, yet were smaller (1 and 1.5 kb) or larger (3.5-5 kb) than the cloned receptor mRNA. The predominant mRNA in two squamous carcinoma cell lines and normal keratinocytes was a 1-kb transcript. Northern analysis with five different region-specific probes that span the entire coding region of the human type I receptor was used to map homologous regions within each of the transcripts. Several of the transcripts identified in squamous lines are also present in polyadenylated RNA from SaOS-2 human bone cells, but a unique 1-kb transcript hybridizing to probe 2 (nucleotides 490-870) was observed only in squamous cells. The smaller 1- and 1.5-kb transcripts did not hybridize to probes corresponding to the extreme 5'- and 3'-coding regions of the type I receptor complementary DNA. Ribonuclease protection analysis employing riboprobes that correspond to the five region-specific DNA probes revealed strong RNA signals of the expected size in SaOS-2 cells, but no hybridization with squamous cell RNA. Several smaller, but minor, bands that were unique to squamous cells were observed with riboprobe 2 only, suggesting partial homology of this region with the type I receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Parathyroidectomy does not prevent the renal PTH/PTHrP receptor down-regulation in uremic rats

In a recent study we demonstrated that the PTH/PTHrP receptor (PTH-R) mRNA was markedly down-regulated in the remnant kidney of uremic rats with severe secondary hyperparathyroidism. Among the factors potentially implicated in this down-regulation, to date only PTH has been demonstrated to modulate PTH-R expression. Here, we examined the effect of thyroparathyroidectomy (TPTX) on the renal expression of PTH-R in rats with normal renal function or with chronic renal failure (CRF) induced by 5/6 nephrectomy. Four groups of rats were studied: control, TPTX, CRF, and CRF + TPTX. Moderate-degree renal failure was documented by mean (+/- SD) creatinine clearances (microliter/min/100 g body wt) of 259 +/- 40 and 212 +/- 45 in CRF and CRF + TPTX rats, compared with 646 +/- 123 and 511 +/- 156 in control and TPTX rats, respectively. Plasma phosphorus, calcitriol, and ionized calcium were significantly lower in CRF and CRF + TPTX than in control animals. Plasma ionized calcium and calcitriol were also lower in TPTX than in control rats. Plasma PTH levels (pg/ml) were increased in CRF rats (41.8 +/- 29.4), and markedly decreased in TPTX (10.1 +/- 7.8) and CRF + TPTX (8.0 +/- 3.8) rats compared with control rats (21.7 +/- 7.5). Northern blot analysis showed that the level of the steady-state PTH-R mRNA in the kidney of CRF and CRF + TPTX rats was markedly decreased compared with that of control rats, the ratios of PTH-R mRNA/beta-actin mRNA being 0.28 +/- 0.04 and 0.27 +/- 0.03 versus 0.54 +/- 0.05, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Signaling properties of mouse and human corticotropin-releasing factor (CRF) receptors: decreased coupling efficiency of human type II CRF receptor

CRF is the primary neuroregulator of the function of the hypothalamic-pituitary-adrenal axis. We have recently cloned a mouse CRF receptor (mCRF-R) complementary DNA (cDNA) from an AtT-20 cell cDNA library by polymerase chain reaction. To compare the functions of mCRF-R to those of the human type I and type II CRF receptors (hCRF-RI and hCRF-RII), cDNAs were cloned into the expression vector pcDNA1 and transfected into COS-7 cells. CRF binding and CRF-stimulated cAMP accumulation as well as phosphoinositide hydrolysis were measured. Scatchard analysis of the binding of 125I-labeled [Tyr0]r/hCRF ([125I]CRF) to COS-7 cells expressing mCRF-R and hCRF-RI cDNAs revealed the same apparent Kd (9 nM). In contrast, the apparent binding Kd for hCRF-RII was 20 nM CRF. Maximal stimulatory concentrations (1 microM) of rat/human CRF-(1-41) (r/hCRF) increased cAMP accumulation in COS-7 cells transfected with mCRF-R, hCRF-RI, and hCRF-RII cDNA plasmid (10 micrograms each) from basal values of 8-19 pmol/10(5) cells.15 min to 84 +/- 10, 87 +/- 16, and 45 +/- 16 pmol/10(5) cells.15 min, respectively. The EC50 values of r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing mCRF-R and hCRF-RI cDNAs were similar at 0.4 +/- 0.2 and 0.7 +/- 0.2 nM, respectively. Conversely, the EC50 of r/hCRF-stimulated cAMP accumulation in hCRF-RII-transfected COS-7 cells was 47.5 +/- 18.9 nM. As the level of expression of hCRF-RII was lower than that of hCRF-RI, we compared r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing low and high levels of hCRF-RI. The EC50 for r/hCRF-stimulated cAMP accumulation in COS-7 cells transfected with hCRF-RI did not change when receptor expression was varied by a factor of 1- to 8.4-fold. In contrast, the EC50 for r/hCRF-stimulated cAMP accumulation mediated by hCRF-RII was at least 100-fold higher than that mediated by the hCRF-RI in COS-7 cells, which suggests poor coupling between hCRF-RII and adenylate cyclase. Inositol phosphate (IP) levels were also determined in mCRF-R, hCRF-RI, and hCRF-RII cDNA-transfected COS-7 cells stimulated with increasing concentrations of r/hCRF. r/hCRF-stimulated IPs accumulation was dose dependent in COS-7 cells expressing mCRF-R and hCRF-RI using 100 and 1000 nM r/hCRF. Concentrations of 10 (or less) nM r/hCRF had no effect on IP generation. hCRF-RII did not mediate stimulation of IP even at 1000 nM r/hCRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Truncation of the carboxyl-terminal region of the rat parathyroid hormone (PTH)/PTH-related peptide receptor enhances PTH stimulation of adenylyl cyclase but not phospholipase C

The functional role of the rat parathyroid hormone(PTH)/PTH-related peptide (PTHrP) receptor's carboxyl-terminal region was characterized by comparing the binding and signaling properties of receptors that have 78 and 111 amino acid deletions (R513 and R480, respectively), with those of the 591-amino acid wild-type (WT) receptor. R480 and R513 have 4- and 1.5-fold lower apparent Kd values for rat PTH-(1-34) (rPTH), compared with the WT receptor (WT, 1.81 +/- 0.19 nM; R513, 1.24 +/- 0.12 nM; R480, 0.48 +/- 0.05 nM, mean +/- S.E.). PTH (100 nM)-stimulated cAMP accumulation and polyphosphoinositide hydrolysis both correlated positively with receptor expression. However, whereas PTH-stimulated polyphosphoinositide hydrolysis was indistinguishable among WT and either truncated mutant at comparable levels of expressed receptors, maximal PTH-stimulated cAMP accumulation was 4-6- and 2-3-fold higher in cells expressing R480 and R513, respectively. Furthermore, pretreatment of COS-7 cells with 100 ng/ml of pertussis toxin (PTX) enhanced PTH-stimulated cAMP accumulation in cells expressing the WT receptor, but failed to do so in cells expressing either R480 or R513. Thus, sequences in the PTH/PTHrP receptor's carboxyl-terminal tail lower the affinity of the WT receptor for agonist; directly interact with, or indirectly facilitate the interaction of the receptor with a PTX-sensitive G protein that inhibits adenylyl cyclase; and decrease the efficacy with which the receptor interacts with Gs.

Down-regulation of parathyroid (PTH)/PTH-related peptide receptor immunoreactivity and PTH binding in opossum kidney cells by PTH and dexamethasone

Recent data have shown that PTH down-regulation of its receptor on opossum kidney (OK) cells is not associated with any change in the steady state level of the PTH/PTH-related peptide (PTHrP) receptor messenger RNA. For analysis of down-regulation of the PTH/PTHrP receptor in OK cells, the present work uses a specific receptor anti-serum, SR-2, that is useful for detection and quantification of PTH/PTHrP receptor immunoreactivity on intact cells bearing the opossum PTH/PTHrP receptor. SR-2 specifically binds to COS-7 cells transiently expressing the opossum PTH/PTHrP receptor complementary DNA (OK-O), to LLCPK1 cells stably expressing the recombinant opossum PTH/PTHrP receptor (AOK cells), and to OK cells expressing endogenous PTH/PTHrP receptors, but not to mock-transfected COS-7 cells or untransfected LLCPK1 cells. SR-2 binding was also linearly correlated with PTH binding in COS-7 cells transfected with different amounts of OK-O plasmid DNA. Treatment with PTH (100 nM) for 4 and 6 h did not significantly down-regulate the PTH/PTHrP receptor immunoreactivity, although PTH binding was decreased to 51% and 49% of control, respectively, and PTH-stimulated cAMP accumulation was decreased to 27% and 28% of control, respectively. Treatment with PTH (100 nM) for 24 and 48 h significantly decreased PTH binding to 51% and 60% of control and decreased PTH/PTHrP receptor immunoreactivity to 68% and 58% of control, respectively. Incubation of OK cells with 0.1 nM to 1 microM PTH for 4 h did not down-regulate the PTH/PTHrP receptor immunoreactivity, although PTH binding was decreased dramatically. Scatchard blot analysis revealed that the binding affinity was decreased by 7-fold in OK cells treated with PTH for 4 h without change in receptor number. Conversely, treatment of OK cells with PTH for 24 h resulted in a parallel decrease in both receptor number and receptor immunoreactivity without any change in receptor binding affinity. Treatment of OK cells with dexamethasone (0.1 nM to 1 microM) had no effect on PTH binding or PTH/PTHrP receptor immunoreactivity. Incubation of OK cells with both dexamethasone (1 microM) and PTH (0.1 nM to 1 microM), however, caused a significantly greater down-regulation of both PTH binding and PTH/PTHrP receptor immunoreactivity than in cells treated with PTH alone. These data indicate that during the first 4 h of exposure of OK cells to PTH, PTH/PTHrP receptors remain on the cell surface but have lowered affinity to bind the ligand and that dexamethasone potentiates the effect of PTH on PTH/PTHrP receptor down-regulation in OK cells.

Chromosomal localization of the parathyroid hormone/parathyroid hormone-related protein receptor gene to human chromosome 3p21.1-p24.2

The human PTH/PTH-related peptide (PTH/PTHrP) receptor could be involved in hereditary disorders of PTH or PTHrP action. Knowledge of the gene's chromosomal location would allow studies linking it to specific disease traits. Therefore, we mapped the human PTH/PTHrP receptor gene by polymerase chain reaction of human/rodent somatic cell hybrid panels using oligonucleotide primers designed to amplify a portion of the gene from genomic DNA. The PTH/PTHrP gene was unambiguously assigned to the short arm of human chromosome 3, in the region designated 3p21.1-p24.2. Analysis of a second chromosome 3-specific mapping panel suggests that the gene is located near the 3p21.2-p21.3 boundary. The availability of highly polymorphic markers located in this region will permit exploration of the PTH/PTHrP receptor locus in genetic linkage searches for the causes of bone, calcium, and other potential disorders.

Role of the extracellular regions of the parathyroid hormone (PTH)/PTH-related peptide receptor in hormone binding

The PTH/PTH-related peptide receptor is a member of a newly discovered family of G-protein-coupled receptors. Strikingly conserved features among these receptors include the positioning of eight extracellular cysteines and several other residues that are located predominantly within the membrane-embedded region. Deletion mutants or receptors with point mutations of the highly conserved cysteine residues were transiently expressed in COS-7 cells to evaluate PTH binding and PTH-stimulated cAMP production. Deletion of residues 61-105, which are encoded by exon E2 in the PTH/PTH-related peptide receptor gene, did not affect receptor function. An epitope derived from Haemophilus influenza hemagglutinin was, therefore, introduced into this portion of most receptors to allow the independent assessment of cell surface expression. PTH binding capacity was not reduced by the deletion of residues 258-278 in the first extracellular loop. Receptors with deletion of either residues 31-47 in the amino-terminal extension or residues 431-440 in the third extracellular loop failed to bind PTH, although expression of the receptor on the cell surface was only marginally reduced. Most other receptor mutants, including those in which each of the six cysteines in the amino-terminus was replaced by serines, failed to be processed and/or expressed appropriately, whereas the substitution of cysteine-281 or -351 had a less severe effect. The combined replacement of both cysteines concomitantly increased PTH binding and cell surface expression, suggesting the formation of a disulfide bond between these two residues. Our data indicate that residues near the amino-terminus and within the third extracellular loop are necessary for ligand binding, whereas more than 25% of the receptor's extracellular region appears not to be involved.

Determinants of [Arg2]PTH-(1-34) binding and signaling in the transmembrane region of the parathyroid hormone receptor

Previously, we reported that [Arg2]PTH-(1-34) bound to the rat osteosarcoma cell line, ROS 17/2.8, with 2-fold higher apparent affinity than it did to the opossum kidney cell line, OK, yet the analog was only a weak partial agonist for cAMP stimulation with ROS 17/2.8 cells, whereas it was a full cAMP agonist with OK cells. These results suggested that the rat and opossum PTH receptors differ in a region recognized by the hormone's amino-terminus. In this report we show that the cloned PTH receptors derived from ROS 17/2.8 and OK cells, expressed in COS-7 cells, also displayed altered responses to [Arg2]PTH-(1-34). Thus, [Arg2]PTH-(1-34) bound to the cloned rat PTH receptor with 7-fold higher affinity than it did to the cloned opossum PTH receptor, and in cAMP stimulation assays, it was a much weaker agonist with the rat receptor than it was with the opossum receptor. Studies with rat/opossum PTH receptor chimeras suggested that the membrane-spanning region of the receptor contributed to the different binding and signaling responses to [Arg2]PTH-(1-34). Point mutation analysis identified three sites in or near the extracellular ends of transmembrane domains V and VI, which specifically affected [Arg2]PTH-(1-34) binding and signaling.

Parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor and its messenger ribonucleic acid in rat aortic vascular smooth muscle cells and UMR osteoblast-like cells: cell-specific regulation by angiotensin-II and PTHrP

PTH-related protein (PTHrP) is produced in vascular smooth muscle, where it is believed to act as a local vasorelaxant by activating either the classical PTH or a unique PTHrP receptor. We used a newly cloned complementary DNA encoding the rat PTH/PTHrP receptor to study the expression of its messenger RNA (mRNA) in primary aortic vascular smooth muscle cells (VSMC) and in UMR-106 osteoblast-like cells under basal conditions and in response to treatment with agonists. Both cell types expressed a 2.4-kilobase PTH/PTHrP receptor mRNA transcript and exhibited hormone-induced desensitization of PTHrP-(1-34)NH2-stimulated cAMP. In VSMC, angiotensin-II, which induces PTHrP expression, also rapidly (30 min) desensitized the cAMP response and down-regulated (75-90%) receptor mRNA within 1 h. Treatment of cells with phorbol 12-myristate 13-acetate (0.1 microM) mimicked these effects, whereas neither PTHrP-(1-34)NH2, forskolin, nor (Bu)2cAMP altered receptor mRNA expression. By contrast, in UMR-106 cells, PTHrP-(1-34)NH2 induced time- and dose-dependent decreases in receptor mRNA that were preceded by pronounced desensitization (cAMP and ligand binding) of cell surface receptors. These effects were mimicked by (Bu)2cAMP and forskolin, but not by phorbol 12-myristate 13-acetate, suggesting that both receptor mRNA down-regulation and receptor desensitization in UMR cells were mediated through a protein kinase-A pathway. We suggest that VSMC and UMR cells express a common receptor, which is subject to cell-specific regulation. Such diversity in the PTH/PTHrP receptor regulatory mechanisms provides a means for restricting the length and duration of the cellular response to hormone in a cell/tissue-specific manner.