Real-time RT-PCR for the detection of beta-adrenoceptor messenger RNAs in small human endomyocardial biopsies

Quantification of mRNAs from extremely small human samples remains a challenge. Requiring minimal amounts of tissue and no post-reaction manipulation, real-time reverse transcriptase-polymerase chain reaction (RT-PCR) is an attractive method to quantitatively assess the expression of rare mRNAs. We evaluated the applicability of the technique on RNA extracted from human endomyocardial biopsies and isolated cardiomyocytes, and compared the technique to the RT-competitive PCR approach. Primers and probes were designed to amplify the three subtypes of human beta -adrenoceptors (beta1-, beta2- and beta3 AR), as well as reference genes such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Hypoxanthine-guanine phosphoribosyltransferase (HPRT), and the oncogene ABL by real-time RT-PCR. Specific primers and a deleted competitor were synthetized to compare the quantitation of the beta 3 AR mRNA expression by RT-competitive PCR. We validated the technique on human cardiomyocytes either freshly isolated or selectively excised from fixed sections of human myocardium by Laser Capture Microdissection. The standard curves obtained for the cDNA's analysed showed mean slopes comprised between -3.3 and -3.7. Inter- and intra-assay variability of gene quantitation was reflected by mean values of the variance coefficients of Ct of 4.84+/-1.13% and 2.73+/-0.39% or 3.32+/-1.03% and 2.21+/-0.24% (corresponding to percent variances of copy numbers of 83.07+/-12.72% and 34.45+/-9.03% or 47.40+/-8.59% and 23.83+/-3.16%) for human beta3 AR and GAPDH genes, respectively. The expression of GAPDH, HPRT and ABL mRNA was characterized by a very low dispersion of individual values across cardiac pathologies, suggesting that these genes may be used as reference genes in quantitative PCR studies. Finally, we applied the technique to detect rare mRNAs, such as beta -AR mRNAs, from small human endomyocardial biopsies and even isolated cardiomyocytes. Real-time RT-PCR is appropriate to quantitate rare messenger RNAs, including in extremely small human tissue samples. This method appears very promising for futures studies of gene expression in several pathophysiological conditions, including heart failure.

Association of BMI with the beta3-adrenergic receptor gene polymorphism in Japanese: meta-analysis

OBJECTIVE

To assess the effect of the Trp64Arg polymorphism in the beta3-adrenergic receptor gene (ADRB3) on body mass index (BMI) in the Japanese population.

RESEARCH METHODS AND PROCEDURES

We selected studies that evaluated the association between BMI and ADRB3 polymorphism among Japanese, using MEDLINE and PubMed. After data collection, an extension of ANOVA was performed to assess the differences according to the genotype.

RESULTS

In a total of 35 subgroups including 2316 subjects with the Trp64Arg variant and 4266 subjects without this variant, the weighted mean difference in BMI was 0.26 kg/m(2) (95% confidence interval: 0.18 to 0.42; p < 0.01), indicating that variant carriers exhibited higher BMI than did normal homozygous subjects.

DISCUSSION

Although it is known that the allele frequency of the ADRB3 polymorphism differs among races, this study focuses on the Japanese population, which has a high allele frequency of ADRB3 polymorphism. We assumed that statistical errors would be prevented due to the sufficient number of subjects. In conclusion, the results support the hypothesis that ADRB3 gene polymorphism is associated with BMI.

The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice

Both human GH (hGH) and a lipolytic fragment (AOD9604) synthesized from its C-terminus are capable of inducing weight loss and increasing lipolytic sensitivity following long-term treatment in mice. One mechanism by which this may occur is through an interaction with the beta-adrenergic pathway, particularly with the beta(3)-adrenergic receptors (beta(3)-AR). Here we describe how hGH and AOD9604 can reduce body weight and body fat in obese mice following 14 d of chronic ip administration. These results correlate with increases in the level of expression of beta(3)-AR RNA, the major lipolytic receptor found in fat cells. Importantly, both hGH and AOD9604 are capable of increasing the repressed levels of beta(3)-AR RNA in obese mice to levels comparable with those in lean mice. The importance of beta(3)-AR was verified when long-term treatment with hGH and AOD9604 in beta(3)-AR knock-out mice failed to produce the change in body weight and increase in lipolysis that was observed in wild-type control mice. However, in an acute experiment, AOD9604 was capable of increasing energy expenditure and fat oxidation in the beta(3)-AR knock-out mice. In conclusion, this study demonstrates that the lipolytic actions of both hGH and AOD9604 are not mediated directly through the beta(3)-AR although both compounds increase beta(3)-AR expression, which may subsequently contribute to enhanced lipolytic sensitivity.

Augmentation of cardiac contractility mediated by the human beta(3)-adrenergic receptor overexpressed in the hearts of transgenic mice

BACKGROUND

Stimulation of beta(1)- and beta(2)-adrenergic receptors (ARs) in the heart results in positive inotropy. In contrast, it has been reported that the beta(3)AR is also expressed in the human heart and that its stimulation leads to negative inotropic effects.

METHODS AND RESULTS

To better understand the role of beta(3)ARs in cardiac function, we generated transgenic mice with cardiac-specific overexpression of 330 fmol/mg protein of the human beta(3)AR (TGbeta(3) mice). Hemodynamic characterization was performed by cardiac catheterization in closed-chest anesthetized mice, by pressure-volume-loop analysis, and by echocardiography in conscious mice. After propranolol blockade of endogenous beta(1)- and beta(2)ARs, isoproterenol resulted in an increase in contractility in the TGbeta(3) mice (30%), with no effect in wild-type mice. Similarly, stimulation with the selective human beta(3)AR agonist L-755,507 significantly increased contractility in the TGbeta(3) mice (160%), with no effect in wild-type mice, as determined by hemodynamic measurements and by end-systolic pressure-volume relations. The underlying mechanism of the positive inotropy incurred with L-755,507 in the TGbeta(3) mice was investigated in terms of beta(3)AR-G-protein coupling and adenylyl cyclase activation. Stimulation of cardiac membranes from TGbeta(3) mice with L-755,507 resulted in a pertussis toxin-insensitive 1.33-fold increase in [(35)S]GTPgammaS loading and a 1.6-fold increase in adenylyl cyclase activity.

CONCLUSIONS

Cardiac overexpression of human beta(3)ARs results in positive inotropy only on stimulation with a beta(3)AR agonist. Overexpressed beta(3)ARs couple to G(s) and activate adenylyl cyclase on agonist stimulation.

Association of a mutation in the beta3-adrenergic receptor gene with obesity and response to dietary intervention in Chinese children

This study aimed to determine whether the Trp64Arg mutation in the beta3-adrenergic receptor beta3-adr) gene is related to childhood obesity and the response to dietary intervention for obesity. The study included 311 healthy children aged 8-11 y selected at random from 4 primary schools in Beijing. Fasting insulin and lipids were measured and anthropometry was carried out for all samples. The mutation of the beta3-adr gene was determined by polymerase chain reaction-restriction fragment length polymorphism analysis. Forty-seven obese children were selected and divided into two groups. One group received dietary intervention (36 subjects); the other served as the control group (11 subjects). After 3 mo of dietary intervention, anthropometry was carried out again in 47 obese children. The frequency of the mutated allele was similar in 73 overweight and 238 normal-weight children (0.18 and 0.17, respectively). Adjusted for age and sex. there was no significant difference in body mass index (BMI) and the levels of fasting lipids and insulin between those with and without the mutation of the 311 children. However, after 3 mo of dietary intervention. increases in weight and BMI were significantly lower in obese children without the mutation than in the control group (2.41 +/- 0.56 vs 4.43 +/- 0.70. p < 0.05: 0.48 +/- 0.24 vs 1.55 +/- 0.35, p < 0.05. respectively), but the changes in weight and BMI in obese children with the mutation were similar to the results in the controls (4.32 +/- 0.69 vs 4.43 +/- 0.70; 1.47 +/- 0.32 vs 1.55 +/- 0.35).

CONCLUSION

The Trp64Arg mutation of the beta3-adr gene may predict the result of dietary intervention in obese children to some extent, but it was not a major factor affecting weight in Chinese children.

Effects of intestinal fatty acid-binding protein gene Ala54Thr polymorphism and beta3-adrenergic receptor gene Trp64Arg polymorphism on insulin resistance and fasting plasma glucose in young to older Japanese men

The present study was performed to investigate the effects of the intestinal fatty acid-binding protein (FABP2) gene Ala54Thr polymorphism and the beta(3)-adrenergic receptor (beta3AR) gene Trp64Arg polymorphism on body mass index (BMI), blood pressure, heart rate, glucose and lipid profiles, and serum leptin level in 196 young men aged 21 to 39 years, 186 older normoglycemic men (fasting plasma glucose [FPG] < 110 mg/dL) aged 40 to 65 years, and 122 older hyperglycemic men, including 77 type 2 diabetic patients. Genomic DNA was extracted from the peripheral blood, and these polymorphisms were assessed by the polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) method. In the older groups, the beta3AR Arg64-allele frequency tended to be lower and the FABP2 Thr/Thr54 genotype frequency tended to be higher in hyperglycemic patients, although these differences did not reach statistical significance. Also, there were no significant differences in the genotype or allele frequency of either variant between the 27 hyperlipidemic and 204 normolipidemic subjects. In the younger group, there were no significant differences in any of the parameters measured between the genotypes of beta3AR or FABP2. In the older normoglycemic subjects, heart rate was significantly lower (P =.037) in beta3AR Arg64-positive subjects, and FPG was significantly higher in subjects with the FABP2 Thr/Thr genotype than the other genotypes (99.8 +/- 5.6 v 96.5 +/- 5.6 mg/dL, P =.010). In the older hyperglycemic group, the beta3AR Arg64-positive group had significantly lower high-density lipoprotein (HDL) cholesterol and free fatty acid (FFA) levels (P =.024 and P =.043, respectively). There were no synergistic effects of these 2 variants on any measured parameter, but only the FABP2 Thr/Thr genotype was related to a higher FPG in the older normoglycemic men. In conclusion, no major difference was associated with the beta3AR Trp64Arg or FABP2 Ala54Thr polymorphism in terms of type 2 diabetes or hyperlipidemia in young to older Japanese men. However, a slight but significant increase in FPG was observed in older Japanese men with the FABP2 Thr/Thr genotype.

[Mutation of beta 3-adrenergic-receptor gene and the response to dietary intervention in obese children]

In order to study the relationship between mutation of beta 3-adrenergic-receptor gene and the response to dietary intervention in obese children, 47 obese children were randomly separated into two groups. One was dietary intervention group(36 subjects); the other was control group(11 subjects). The subjects were investigated by dietary survey and anthropometry before and after dietary intervention carried out for 3 months. The mutation of beta 3-adrenergic receptor gene resulting from the replacement of tryptophan by arginine at position 64(Trp64Arg) in encoding amino acid residues was detected by using a polymerase chain reaction-restriction fragment length polymorphisms. The results showed that dietary fat was higher (40.7% of energy from fat) in the obese children. After dietary intervention, the increase of weight(kg) and BMI(kg/m2) were significantly lower in the obese children without mutation than in control group(P < 0.05), but the changes of weight and BMI in the obese children with mutations were similar to those of control group. It was concluded that the Trp64Arg mutation of beta 3-adrenergic receptor gene might be one of the reasons why the effect of dietary intervention was poor in some obese children.

Beta(3)-adrenergic receptor gene variant is associated with upper body obesity only in obese Japanese-American men but not in women

We investigated gender differences in the relationships between the Trp64Arg variant of the beta(3)-adrenergic receptor (AR) gene in obesity and insulin resistance in nondiabetic subjects. In 476 nondiabetic Japanese-Americans (M/F=204/272), the Trp64Arg variant of the beta(3)-AR gene was examined. The presence or absence of the Trp64Arg mutation was examined in DNA separated from leukocytes in peripheral blood using the PCR-RFLP method. The frequency of abnormal allele of the beta(3)-AR gene was 0.18 for males and 0.17 for females, almost the same as the reported values in Japanese. There was no difference in the frequency of the beta(3)-AR gene variant between obese and non obese subjects for each gender. However, among obese males (body mass index > or =24.2 kg/m(2)), with the beta(3)-AR gene mutation, the waist-to-hip ratio, fasting insulin, 2-h insulin, total insulin, and HOMA, an index of insulin resistance, were all significantly higher than obese males without the mutation. In females, the index of obesity, insulin resistance, or lipid metabolism did not differ significantly between the subjects with or without the beta(3)-AR gene variant either in the obese and non-obese group. We suggest that the beta(3)-AR gene variant is not important as an obesity-inducing factor in Japanese. However, in males, when obesity becomes obvious, the beta(3)-AR gene variant is considered to influence the enhancement of insulin resistance, in association with visceral obesity.

Pancreatic beta-cells expressing the Arg64 variant of the beta(3)-adrenergic receptor exhibit abnormal insulin secretory activity

The Arg64 beta(3)-adrenergic receptor (beta(3)AR) variant is associated with an earlier age of onset of diabetes and lower levels of insulin secretion in humans. The aims of this study were to investigate whether beta(3)AR is expressed by islet cells, if receptor binding affects insulin secretion and, finally, if the beta(3)AR Arg64 variant induces abnormal insulin secretory activity. Human pancreas extracts were subjected to RT-PCR, Western blotting and immunostaining analyses. DNA sequencing and Western blotting demonstrated that the beta(3)AR gene is transcribed and translated in the human pancreas; immunostaining showed that it is expressed by the islets of Langerhans. Cultured rat beta-cells responded to human beta(3)AR agonists in a dose- and time-dependent manner. Transfection of cultured rat beta-cells with the wild-type human beta(3)AR produced an increased baseline and ligand-dependent insulin secretion compared with parental cells. On the other hand, cells transfected with the Arg64 variant of the beta(3)AR secreted less insulin, both spontaneously and after exposure to human beta(3)AR agonists. Furthermore, while transfection with the wild-type beta(3)AR preserved the glucose-dependent secretion of insulin, expression of the variant receptor rendered the host cells significantly less responsive to glucose. In summary, cells express the beta(3)AR, and its activation contributes to the regulation of insulin secretion. These findings may help explain the low levels of insulin secretion in response to an i.v. glucose tolerance test observed in humans carrying the Arg64 polymorphism.

Knockout models resulting in the development of obesity

Our understanding of body weight regulation has been greatly advanced by the characterization of previously existing mutations in mice that cause obesity. Subsequent analysis of a number of mouse knockout models has greatly expanded the number of genes known to influence adiposity by affecting metabolic rate, physical activity, and/or appetite.

Gender specific associations of the Trp64Arg mutation in the beta3-adrenergic receptor gene with obesity-related phenotypes in a Mediterranean population: interaction with a common lipoprotein lipase gene variation

OBJECTIVE

To investigate the association between the Trp64Arg beta3-adrenergic receptor (ADRB3) mutation and obesity-related phenotypes in a Mediterranean Spanish population considering the effect of other genetic and environmental factors. DESIGN AND SUBJECT: Cross-sectional study in 1063 (476 men and 587 women) randomly selected from this population (aged: 18-68 years).

MEASUREMENTS

Anthropometric (weight, height and waist-to-hip ratio), blood pressure, biochemical (lipids, fasting glucose, and uric acid), life-style variables, and the Trp64Arg, HindIII-Lipoprotein lipase (LPL) and apolipoprotein E polymorphism.

RESULTS

Frequency of the Arg64 allele was low (0.051; 95% CI: 0.042-0.060). We found gender-specific associations between the Trp64Arg mutation and obesity related phenotypes. In men, carriers of the Arg64 variant had higher body mass index (BMI) (27.63 +/- 3.81 vs. 26.34 +/- 3.57 kg m-2, P=0.049) and total cholesterol (5.85 +/- 1.45 vs. 5.28 +/- 1.06 mmol L-1; P=0.011) compared with wild-type individuals. Logistic regression analysis, revealed that the risk of overweight was two times higher in male carriers of the Arg64 allele. In women, the Arg64 variant was only associated with higher fasting glucose (P=0.031). These genotype effects persisted after adjustment for age, genetic and life-style variables. For the LPL polymorphism, the H-/H- genotype was associated with lower BMI and with lower risk of overweight (OR: 0.49; 95% CI: 0.30-0.81) in both men and women. However, after adjustment for covariates, these associations only remained statistically significant (P < 0.02) in women. Moreover, in women, a statistically significant interaction (P=0.026) between the LPL and the ADRB3 gene loci in determining BMI was found. Thus, the Arg64 allele was associated with a higher BMI only in H+/H+ women.

CONCLUSIONS

The Trp64Arg mutation was associated with BMI and lipids in men. In women, an additional gene-gene interaction with the LPL-HindIII polymorphism may explain the results.

[The role of beta3-adrenergic receptor Trp/Arg mutation in childhood obesity]

OBJECTIVE

To understand with greater clearness the role of beta3- adrenergic receptor Trp/Arg mutation in childhood obesity.

METHODS

One hundred and seventy-seven children, aged 6-12 years, were selected. The genotype was detected by restricted fragment length polymorphism, the children's dietaries were surveyed by a 3-day recalling and recording method. Their height, weight were measured, and the data on their living habits were collected from their parents.

RESULTS

The intake of total amount of food and energy of obese children were higher in children with Trp/Trp genotype, but there was no difference between the obese and non-obese children with Trp/Arg genotype. Among children with the Trp/Arg genotype, obese children were less active and did less exercise, they slept more, but there was no difference among children with Trp/Trp genotype.

CONCLUSION

The children with beta3-AR Trp/Arg mutation may become obese because of the low energy metabolism; less active and exercise may increase the risk of obesity.

Upregulation of functional beta(3)-adrenergic receptor in the failing canine myocardium

Altered expression and functional responses to cardiac beta(3)-adrenergic receptors (ARs) may contribute to progressive cardiac dysfunction in heart failure (CHF). We compared myocyte beta(3)-AR mRNA and protein levels and myocyte contractile, [Ca(2+)](i) transient, and Ca(2+) current (I(Ca,L)) responses to BRL-37344 (BRL, 10(-8) mol/L), a selective beta(3)-AR agonist, in 9 instrumented dogs before and after pacing-induced CHF. Myocytes were isolated from left ventricular myocardium biopsy tissues. Using reverse transcription-polymerase chain reaction, we detected beta(3)-AR mRNA from myocyte total RNA in each animal. Using a cloned canine beta(3)-AR cDNA probe and myocyte poly A(+) RNA, we detected a single band about 3.4 kb in normal and CHF myocytes. beta(3)-AR protein was detected by Western blot. beta(3)-AR mRNA and protein levels were significantly greater in CHF myocytes than in normal myocytes. Importantly, these changes were associated with enhanced beta(3)-AR-mediated negative modulation on myocyte contractile response and [Ca(2+)](i) regulation. Compared with normal myocytes, CHF myocytes had much greater decreases in the velocity of shortening and relengthening with BRL accompanied by larger reductions in the peak systolic [Ca(2+)](i) transient and I(Ca,L). These responses were not modified by pretreating myocytes with metoprolol (a beta(1)-AR antagonist) or nadolol (a beta(1)- and beta(2)-AR antagonist), but were nearly prevented by bupranolol or L-748,337 (beta(3)-AR antagonists). We conclude that in dogs with pacing-induced CHF, beta(3)-AR gene expression and protein levels are upregulated, and the functional response to beta(3)-AR stimulation is increased. This may contribute to progression of cardiac dysfunction in CHF.

Matrix-induced fragmentation of P3'-N5' phosphoramidate-containing DNA: high-throughput MALDI-TOF analysis of genomic sequence polymorphisms

Chemical and enzymatic approaches were used to produce polynucleotide fragments containing acid-labile internucleotide P3'-N5' phosphoramidate bonds, either in a surface-bound form or in solution. The primer extension reaction utilizing 5'-amino-5'-deoxynucleoside 5'-triphosphates generates polynucleotides that can be fragmented into short, easy-to-analyze pieces simply by being premixed with the acidic matrices typically used for MALDI-TOF mass spectrometry of nucleic acids. This leads to detection procedures that are simple, robust and easy to automate. Utilizing this approach, a polymorphic site in the human ADRB3 gene was interrogated. Primer extensions with phosphoramidate analogs of dNTPs allowed for unambiguous discrimination of all possible genotypes.

Genotype Arg/Arg, but not Trp/Arg, of the Trp64Arg polymorphism of the beta(3)-adrenergic receptor is associated with type 2 diabetes and obesity in a large Japanese sample

OBJECTIVE

Despite a large number of studies, no association of the Trp64Arg polymorphism of the beta(3)-adrenergic receptor gene with obesity and type 2 diabetes has yet to be clearly elucidated. We examined the associations in a large population-based sample.

RESEARCH DESIGN AND METHODS

A total of 1,685 subjects (935 women and 750 men, aged 58.7 +/- 12.4 years) from a cohort population (n = 3,706) of the Funagata Diabetes Study were divided into three groups according to genotypes: Trp/Trp (n = 1,155), Trp/Arg (n = 486), and Arg/Arg (n = 44). Glucose tolerance was diagnosed according to the 1985 World Health Organization criteria. Subjects who had a BMI > or =30 kg/m(2) were considered obese. Associations with the traits related to obesity, diabetes, hypertension, and dyslipidemia were also examined. The chi(2) test and analysis of variance were used for the association studies and to assess the differences in the traits' values, respectively.

RESULTS

More subjects with genotype Arg/Arg were obese and had diabetes (13.6% for each) than those with genotype Trp/Trp (3.29%, P < 0.001; and 4.16%, P = 0.007, respectively) or genotype Trp/Arg (2.06%, P < 0.001; and 5.97%, P = 0.051, respectively). No significant differences in the frequencies of occurrence of these conditions were observed between genotypes Trp/Arg and Trp/Trp. Traits related to obesity, such as percent body fat (28.82 +/- 7.95 vs. 25.93 +/- 7.21, P = 0.038) and BMI (25.07 +/- 3.84 vs. 23.63 +/- 3.18, P = 0.018), were higher in the genotype Arg/Arg than in the genotype Trp/Trp groups.

CONCLUSIONS

Genotype Arg/Arg, but not Trp/Arg, of the beta(3)-adrenergic receptor was associated with both obesity and type 2 diabetes in a large Japanese sample.

[Association of beta 3-adrenergic receptor gene with obesity in patients with type 2 diabetes mellitus]

OBJECTIVE

To investigate the association between the mutation of beta 3-adrenergoc receptor gene and obesity in patients with type 2 diabetes.

METHODS

Body mass, waist-hip ratio, blood pressure and blood lipids were measured in 154 type 2 diabetic patients. Polymerase chain reaction and the restriction fragment length polymorphism analysis were used to determine the wild, heterozygous and homozygous forms of beta 3-adrenergoc receptor gene.

RESULTS

The frequency of the Trp64Arg mutation was 42.5% and the frequency of Arg64 allele was 22.6%. The mutation frequency of the genetic types was significantly different between the obese and non-obese type 2 diabetes mellitus patients. The body mass, systolic blood pressure, diastolic blood pressure, HDL-cholesterol were significantly different, when those with Trp64Arg heterozygous were compared with those with Trp64 homozygous.

CONCLUSIONS

The genetic mutation of beta 3-adrenegoc receptor in patients with type 2 diabetes is probably related to obesity.

Desensitization of beta2-adrenoceptor function in non-pregnant rat myometrium is modulated by sex steroids

The effects of in vivo treatment with estrogen and progesterone on isoproterenol-induced uterine relaxation and beta(2)-adrenoceptor (beta(2)AR) mRNA production in non-pregnant rat myometrium were investigated. Whether homologous myometrial desensitization of beta(2)AR function was dependent on or modulated by the two steroids was also examined. Estrogen treatment alone or in combination with progesterone reduced maximal relaxation (E(max)) of isolated uterine strips subsequently challenged with isoproterenol whereas progesterone alone had no effect on this parameter. The reduction was accompanied by an enhanced beta(2)AR mRNA concentration. The concentration of isoproterenol giving half-maximal relaxing response (EC(50)) increased following estrogen treatment and this effect was curbed by progesterone. Isoproterenol had no effect on beta(2)AR transcription irrespective of the steroid regimes employed. E(max) of isolated uterine strips was reduced following prolonged in vivo treatment with isoproterenol but the effect was found only when estrogen alone was administered concomitantly. Finally, in vivo treatment with isoproterenol increased EC(50) of uterine strips subsequently stimulated with isoproterenol in vitro. This effect was independent of steroid treatment. We conclude that homologous desensitization of beta(2)AR function in non-pregnant rat myometrium in terms of sensitivity (EC(50)) is independent of sex steroids but in terms of maximal response (E(max)) occurs only in the presence of estrogen. We speculate whether progesterone withdrawal in connection with the well-known estrogen dominance at rat parturition may strengthen the desensitization induced by beta(2)AR activation and thus contribute to the transformation of the uterus from a quiescent to a highly contractile organ.

Synergistic effect of polymorphisms of uncoupling protein 1 and beta3-adrenergic receptor genes on autonomic nervous system activity

OBJECTIVE

To investigate the association of the promoter region -3826 A to G polymorphism of the uncoupling protein 1 (UCP1) gene with autonomic nervous system (ANS) activity and the interaction of the polymorphism with the Trp64Arg polymorphism of the beta3 adrenergic receptor (beta3AR).

SUBJECTS

Three-hundred and forty-nine young (mean age 20.4+/-2.1 y old), healthy Japanese males.

MEASUREMENTS

DNA was extracted from whole blood and genotyped by polymerase chain reaction restriction fragment length polymorphism. Plasma glucose, plasma insulin and body mass index (BMI) were measured. Frequency of family history of diabetes or obesity was determined by interview. Subjects randomly chosen from each genotype were examined for ANS activity during supine rest and standing by electrocardiogram power spectral analysis of heart rate variability.

RESULTS

UCP1 or beta3AR polymorphism was not associated with BMI, plasma glucose, plasma insulin and frequency of family history of diabetes or obesity. The inhibitory effect of UCP1 polymorphism on ANS activity was observed only with occurrence of the variant of beta3AR. The very low frequency component associated with thermoregulation in the sympathetic nervous system of homozygotes of UCP1 (GG) at supine rest was significantly lower than normal (AA, 203.2+/-50.3 vs 462.2+/-83.6 ms(2); mean+/-s.e., P=0.021). A higher response to postural change to standing was also observed in both sympathetic and parasympathetic nervous activities of AA than of GG.

CONCLUSION

While UCP1 polymorphism alone does not affect ANS activity, it has a synergistic effect with beta3AR polymorphism in decreasing sympathetic nervous system activity.

The Trp64Arg polymorphism of the beta3-adrenergic receptor gene is not associated with training-induced changes in body composition: The HERITAGE Family Study

OBJECTIVE

To investigate the association between the Trp64Arg polymorphism of the beta3-adrenergic receptor gene and changes in body composition in response to endurance training.

RESEARCH METHODS AND PROCEDURES

Adult sedentary white and black subjects participating in the HERITAGE Family Study were measured before and after 20 weeks on endurance training for the body mass index, fat mass, percentage of body fat, fat-free mass, sum of eight skinfolds, and subcutaneous, visceral, and total abdominal fat areas. The association between the Trp64Arg polymorphism and the response phenotypes, computed as the difference between pre- and post-training values, was tested by analysis of covariance separately in men and women. The gene by race interaction term was also tested.

RESULTS

No race differences were observed for allelic and genotype frequencies. Training resulted in significant reduction of body fat in both men and women. No association of the Trp64Arg polymorphism was observed with training-induced changes for any of the body composition phenotypes in both men and women.

DISCUSSION

These results suggest that the Trp64Arg polymorphism of the beta3-adrenergic receptor gene is not related to changes in body composition in response to exercise training.

Association of polymorphisms in the beta-2 and beta-3 adrenoceptor genes with risk of colorectal cancer in Japanese

BACKGROUND

The adrenergic receptor system is involved in thermogenesis and in the activation of lipid mobilization in fat cells, and polymorphisms in the beta-2 and beta-3 adrenoceptor genes (BAR2 and BAR3) have been reported to be associated with obesity and insulin resistance. To examine links between polymorphisms in these genes and the risk of colorectal cancer in Japanese, we conducted the present hospital-based case-referent study.

METHODS

Mutations of the BAR2 gene at codon 27 (Gln27Glu) and of the BAR3 gene at codon 64 (Trp64Arg) were examined in 131 patients with colorectal cancer (cases) and in 239 cancer-free referents. We also collected information on environmental factors, using a questionnaire approach. Odds ratios (ORs) were estimated with an unconditional logistic model, after adjustment for potential confounding factors.

RESULTS

The proportional distribution of the mutations in BAR2 and BAR3 did not differ between cases and referents. Analysis of a subgroup with a higher body mass index showed that the Trp64Arg variant increased the OR (2.63; 95% confidence interval, 1.13-6.11) for colon cancer, but not for rectal cancer, compared with the Trp64 genotype. Altered ORs for colon and rectal cancers with the Gln27Glu variant were not observed in either the subgroup with the lower body mass index or the subgroup with the higher body mass index.

CONCLUSION

These findings suggest that the BAR3 polymorphism may alter the susceptibility to colon cancer risk in obese subjects. To confirm this finding, a further study with a larger number of subjects is now required.

Effect of oleoyl-estrone treatment on the expression of beta1- beta2- and beta3-adrenoreceptors in rat adipose tissues

Adult female rats received a constant i.v. infusion of oleoyl-estrone (3.5 pmol/kg day) in a lipidic suspension for 14 days. On days 0 (no treatment), 3, 6, 10 and 14, as well as on day 14 for controls (receiving only the lipid); the rats were killed and the expression of the beta1-, beta2- and beta3-adrenoceptor genes, in brown adipose tissue and in subcutaneous and periovaric white adipose tissue, were measured by RNA protection assay, and compared with that of cyclophyllin. The beta3-adrenoceptor was the most expressed in all adipose tissues, whereas beta2 was the less expressed in brown adipose tissue. Oleoyl-estrone significantly, but moderately, increased the expression of beta-adrenoceptors in the three adipose tissues: beta1 increased in subcutaneous, beta2 and beta3 in periovaric and beta3 in brown adipose tissue. Oleoyl-estrone also decreased beta3 expression in subcutaneous white adipose tissue. On day 10, adipocytes isolated from periovaric white adipose tissue of oleoyl-estrone-treated rats showed higher cAMP response to an isoproterenol challenge than the controls. The mechanism by which oleoyl-estrone elicits the wasting of fat reserves could be mediated by adrenergic pathways, at least in part.

Common variants in the beta2-(Gln27Glu) and beta3-(Trp64Arg)--adrenoceptor genes are associated with elevated serum NEFA concentrations and type II diabetes

AIMS/HYPOTHESIS

Higher NEFA concentrations predict Type II (non-insulin-dependent) diabetes mellitus but it is not known whether higher NEFA concentrations are genetically determined or reflect coexisting obesity. To address this question we studied whether common variants in two genes encoding for key regulators of lipolysis, the beta2- and beta3- adrenoceptors (B2AR and B3AR) are associated with NEFA concentrations and Type II diabetes.

METHODS

A total of 1054 Swedish subjects with varying degrees of glucose tolerance were genotyped for the Gln27Glu variant in the B2AR and for the Trp64Arg variant in the B3AR genes using PCR-RFLP.

RESULTS

The B2AR Gln27 allele was more frequent in 219 Type II diabetic patients than in 237 non-diabetic subjects (59.8 % vs 52.3 %; OR = 1.72, p = 0.02) while there was no significant difference in the frequency of the B3AR Arg64 allele. Subjects homozygous for the protective alleles (Glu27 and Trp64) had, however, a lower prevalence of diabetes than subjects with other genotype combinations (OR = 0.58, p = 0.03). Among sibling pairs discordant for the B2AR Gln27Glu polymorphism, siblings with an excess of the Gln27 allele had higher fasting insulin (n = 217; p = 0.02) and NEFA concentrations (107 sex-matched pairs; p = 0.01) than siblings with an excess of the Glu27 allele. Among sibling pairs discordant for the B3AR Trp64Arg variant, siblings with the Arg64 allele had higher 2 h glucose (n = 48; p = 0.01) and NEFA concentrations (16 pairs matched for sex; p < 0.04) than siblings with the Trp64Trp64 genotype.

CONCLUSIONS/INTERPRETATION

Common variants in the beta2- and beta3- adrenoceptor genes are associated with increased fasting insulin and NEFA concentrations and could increase susceptibility to Type II diabetes.

[Inhibition of uterine contractions: new in vitro pharmacological approaches on the pregnant human myometrium]

The aim of this study was to evaluate the in vitro effects of phosphodiesterase 4 inhibitors (PDE4I) and their combination with salbutamol (beta 2-adrenoceptor agonist) on spontaneous contractions and to investigate by in vitro and biochemical studies and analysis of mRNA expression the presence of beta 3-adrenoceptor in human near-term myometrium. Rolipram, RP 73401 and Ro 20-1724 (PDE4I) inhibited spontaneous myometrial contractions (Emax approximately 100 per cent; pD2 approximately 6.80 for the two first and 6.31 for Ro 20-1724). Rolipram 10(-8) M potentiated the response to salbutamol (Emax = 88 per cent vs. 40 per cent and pD2 = 6.93 and 6.36 with or without rolipram respectively). SR 59119A, a beta 3-adrenoceptor agonist, was more efficient than salbutamol in inhibiting the contractions (Emax 52 per cent and 27 per cent respectively, p < 0.05) but they both induced a significant increase of cAMP production. In both functional and biochemical studies, SR 59119A was only antagonized by the beta 3-adrenoceptor antagonist SR 59230A. The beta 3-AR mRNA was positively expressed in myometrium preparations in a reverse transcription polymerase chain assay. In conclusion, phosphodiesterase 4 inhibitors alone or combined with beta 2-adrenoceptor agonists and beta 3-adrenoceptor agonists might have potential interest as tocolytic agents.

Expression of the human beta(3)-adrenergic receptor gene in SK-N-MC cells is under the control of a distal enhancer

Mechanisms of transcriptional regulation of the human beta(3)-adrenergic receptor were studied using SK-N-MC cells, a human neuroblastoma cell line that expresses beta(3)- and beta(1)-adrenergic receptors endogenously. Deletions spanning different portions of a 7-kb 5'-flanking region of the human beta(3)-adrenergic receptor gene were linked to a luciferase reporter and transfected in SK-N-MC, CV-1, and HeLa cells. Maximal luciferase activity was observed when a 200-bp region located between -6.5 and -6.3 kb from the translation start site was present. This region functioned only in SK-N-MC cells. Electrophoretic mobility shift assays of nuclear extracts from SK-N-MC, CV-1, and HeLa cells using double stranded oligonucleotides spanning different portions of the 200-bp region as probes and transient transfection studies revealed the existence of three cis-acting regulatory elements: A) -6.468 kb-AGGTGGACT--6.458 kb, B) -6.448 kb-GCCTCTCTGGGGAGCAGCTTCTCC-6.428 kb, and C) -6.405 kb-20 repeats of CCTT-6.385 kb. These elements act together to achieve full transcriptional activity. Mutational analysis, antibody supershift, and electrophoretic mobility shift assay competition experiments indicated that element A binds the transcription factor Sp1, element B binds protein(s) present only in nuclear extracts from SK-N-MC cells and brown adipose tissue, and element C binds protein(s) present in both SK-N-MC and HeLa cells. In addition, element C exhibits characteristics of an S1 nuclease-hypersensitive site. These data indicate that cell-specific positive cis-regulatory elements located 6.5 kb upstream from the translation start site may play an important role in transcriptional regulation of the human beta(3)-adrenergic receptor. These data also suggest that brown adipose tissue-specific transcription factor(s) may be involved in the tissue-specific expression of the beta(3)-adrenergic receptor gene.

Candidate gene analysis in premature pubarche and adolescent hyperandrogenism

OBJECTIVE

To identify genetic markers associated with premature pubarche in children and hyperandrogenism in adolescent girls.

DESIGN

Association study.

SETTING

Academic research environment.

PATIENT(S)

Forty children with premature pubarche (PP), 29 adolescent girls with hyperandrogenism (HA), and 15 healthy control women.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Genetic variations at five loci selected because of known associations with hyperandrogenism, insulin resistance, hyperinsulinemia, or obesity.

RESULT(S)

Heterozygosity for CYP21 mutations was identified in 14 of 40 (35%) PP, 8 of 29 (28%) HA, and 1 of 30 (3%) controls. Heterozygosity for HSD3B2 variants was identified in 3 of 40 (7.5%) PP, 5 of 29 (17%) HA, and 0/15 controls. Among the PP, 11 of 80 (14%), 5 of 80 (6%), and 7 of 80 (9%) alleles showed the IRS-1, GRL, and ADRB3 variants, respectively. Among the HA, 5 of 58 (8.6%), 3 of 58 (5%), and 6 of 58 (10%) alleles showed the IRS-1, GRL, and ADRB3 variants, respectively. Among the control participants, variant allele frequency was 1 of 30 (3.3%) for IRS-1, 2 of 30 (6.6%) for GRL, and 2 of 30 (6.6%) for ADRB3.

CONCLUSION(S)

Our findings suggest that the development of PP and HA can be associated with the occurrence of multiple sequence variants at five susceptibility loci, especially steroidogenic enzyme genes. This approach offers a novel paradigm to investigate and identify the genetic factors relevant to polycystic ovary syndrome.

Interactions between variants in the beta3-adrenergic receptor and peroxisome proliferator-activated receptor-gamma2 genes and obesity

OBJECTIVE

Previous studies have reported modest associations between measures of obesity and the Trp64-Arg variant of the beta3-adrenergic receptor (ADRbeta3) and the Pro12Ala variant of the peronisome proliferator-activated receptor (PPAR)-gamma2. We hypothesized that these single gene variants may mark mutations that act through convergent pathways to produce synergistic effects on obesity.

RESEARCH DESIGN AND METHODS

The sample included 453 subjects from 10 large Mexican-American families participating in the population-based San Antonio Family Heart Study. The effects of each gene variant singly and jointly were estimated as fixed effects using the measured genotype approach framework. Analyses were conditioned on the pedigree structures to account for the correlations among family members. Statistical significance was evaluated by the likelihood ratio test with adjustment for age, sex and diabetes status.

RESULTS

The allele frequencies for the ADRbeta3 Trp64Arg and PPARgamma2 Pro12Ala variants were 18 and 12%, respectively. The ADRbeta3 variant was not significantly associated with any of the obesity-related traits, but subjects with the PPAR-gamma2 variant (n = 98) had significantly higher levels of lasting insulin (P = 0.03), leptin (P = 0.009), and waist circumference (P = 0.03) than those without. Subjects with the gene variants (n = 32) had significantly higher BMI, insulin, and leprtin levels than those with only the PPARgamma2 variant (n = 66) (P for interaction: 0.04, 0.02, and 0.01 for BMI, fasting insulin, and leptin, respectively).

CONCLUSIONS

Our results suggest that epistatic models with genes that have modest individual effects may be useful in understanding the genetic underpinnings of typical obesity in humans.

Relationship of the Trp64Arg polymorphism of the beta3-adrenoceptor gene to central adiposity and high blood pressure: interaction with age. Cross-sectional and longitudinal findings of the Olivetti Prospective Heart Study

METHODS

The association of the Trp64Arg polymorphism of the beta3-adrenoceptor (beta3-AR) gene with high blood pressure, central adiposity and other features of the metabolic syndrome was investigated in a large unselected sample of a white male working population in Southern Italy (n = 979).

RESULTS

In the whole population, subjects heterozygous for the Trp64Arg mutation (11.2%) were not different from the homozygous Trp64Trp for any of the variables investigated. However, upon stratification for age, among men in the upper tertile of age (> 53 years), the Trp64Arg genotype was associated with higher waist: hip ratio (0.992 +/- 0.021 versus 0.982 +/- 0.037, P< 0.05), serum uric acid (6.34 +/- 1.50 versus 5.75 +/- 1.30 micromol/l, P < 0.05) and systolic blood pressure (144.3 +/- 19.4 versus 136.9 +/- 18.9 mmHg, P< 0.05) compared with the wild-type homozygotes. Accordingly, in the same age group, the carriers of Trp64Arg genotype were more often in the upper tertile of abdominal adiposity (69.7 versus 43.7%, P< 0.02) and serum uric acid (56.3 versus 34.8%, P < 0.02) and were more often hypertensive (68.6 versus 57.6%, P< 0.058) than the Trp64Trp homozygotes. No such differences were observed in younger age groups. No association was found with fasting serum insulin and the homeostasis model assessment (HOMA) index of insulin resistance. Furthermore, in a subgroup of 457 men for whom retrospective 20-year follow-up data were available, the variant genotype was associated with a higher probability of developing overweight (44.7 versus 27.0%, P < 0.05) and a trend to higher blood pressure (52.6 versus 38.4%, P = 0.09) over 20 years.

CONCLUSION

We conclude that the Trp64Arg variant of the beta3-AR receptor predicts a greater tendency to develop abdominal adiposity and high blood pressure with advancing age.

Beta 3-adrenergic receptor gene polymorphism and type 2 diabetes in a Caucasian population

AIM

The beta 3-adrenergic receptor (beta 3-AR) is suspected to play a key role in the regulation of energy balance by increasing lipolysis and thermogenesis. A mutation in the beta 3-AR gene (Trp64Arg) has been associated with the capacity of weight gain and with early onset of noninsulin dependent diabetes mellitus (type 2 diabetes). In this study we investigated the prevalence of the two beta 3-AR alleles in a Caucasian population and studied the association between the beta 3-AR genotype and metabolic disorders (obesity and type 2 diabetes).

METHODS

Genomic DNA extracted from peripheral blood leucocytes of 200 Caucasian subjects (137 subjects with and 63 subjects without type 2 diabetes). The MvaI polymorphism of beta 3-AR, which detects the Trp64Arg mutation, was determined by polymerase chain reaction (PCR). We studied the correlation between the Trp64Arg mutation and the body mass index (b.m.i. kg/m2).

RESULTS

There was no significant difference between the patients with type 2 diabetes and control subjects in the frequency of the Arg64 allele (5.5% and 4.8%, respectively). Within the group of type 2 diabetes patients were 14 subjects with the Trp64Arg mutation (b.m.i., mean +/- s.d.: 31 +/- 8.5 kg/m2) and 123 without the mutation (b.m.i. 29 +/- 4.8). There was no association between the beta 3-AR gene polymorphism and sex, obesity, blood pressure, glycohaemoglobin concentration, proteinuria.

CONCLUSION

Our results suggest that the Trp64Arg mutation is not a major determinant of metabolic disorders (type 2 diabetes, obesity) and chronic complications of type 2 diabetes in a Dutch population.

The beta3-adrenergic receptor Trp64Arg mutation is not associated with coronary artery disease

There is some evidence that the Trp64Arg polymorphism of the beta3-adrenergic receptor (beta3-AR) is associated with atherogenic risk factors that include weight gain, insulin resistance, and diabetes. The objective of this cross-sectional study was to investigate the relationship between the Trp64Arg polymorphism and coronary artery disease (CAD). A total of 1,000 consecutive patients with angiographically confirmed CAD and 1,000 controls, carefully matched for age and sex, were genotyped for the Trp64Arg polymorphism by polymerase chain restriction and subsequent restriction fragment length polymorphism analysis. Among cases with CAD, 83.3% were wild-type Trp/Trp, 15.8% were heterozygotes, and 0.9% were homozygous Arg/Arg compared with 82.3%, 17.3%, and 0.4%, respectively, among controls (P = .27). The odds ratios for the presence of Trp/Arg and Arg/Arg in cases and controls were 0.90 (95% confidence interval [CI] 0.7 to 1.2; P = .40) and 2.2 (95% CI 0.7 to 7.2; P = .17), respectively. There was no effect modification by gender and atherogenic risk factors, including diabetes, hypercholesterolemia, hypertension, and smoking. Furthermore, there was no evidence of an association with premature disease onset (< 40 years) or extent of disease. In conclusion, the results of this study in a large sample of clinically well-characterized patients indicate that neither the Trp/Arg nor the Arg/Arg genotype represents a major risk factor for angiographically confirmed coronary artery disease.

CCAAT/enhancer-binding protein alpha is required for transcription of the beta 3-adrenergic receptor gene during adipogenesis

The beta(3)-adrenergic receptor (beta(3)AR) is expressed predominantly in adipocytes, and it plays a major role in regulating lipolysis and adaptive thermogenesis. Its expression in a variety of adipocyte cell models is preceded by the appearance of CCAAT/enhancer-binding protein alpha (C/EBP alpha), which has been shown to regulate a number of other adipocyte-specific genes. Importantly, it has been demonstrated that several adipocyte cell lines that fail to express C/EBP alpha exhibit reduced insulin sensitivity, despite an apparent adipogenic phenotype. Here we show that transcription and function of the beta(3)AR correlates with C/EBP alpha expression in these adipocyte models. A 5.13-kilobase pair fragment of the mouse beta(3)AR promoter was isolated and sequenced. This fragment conferred a 50-fold increase in luciferase reporter gene expression in adipocytes. Two putative C/EBP binding sites exist at -3306 to -3298 and at -1462 to -1454, but only the more distal site is functional. Oligonucleotides corresponding to both the wild-type and mutated -3306 element were inserted upstream of a thymidine kinase luciferase construct. When cotransfected in fibroblasts with a C/EBP alpha expression vector, reporter gene expression increased 3-fold only in the wild-type constructs. The same mutation, when placed into the intact 5.13-kilobase pair promoter, reduced promoter activity in adipocytes from 50-fold to <10-fold. Electrophoretic mobility shift analysis demonstrated that the site at -3306 generated a specific protein-oligonucleotide complex that was supershifted by C/EBP alpha antibody, while a probe corresponding to a putative site at -1462 did not. These results define C/EBP alpha as a key transcriptional regulator of the mouse beta(3)AR gene during adipogenesis.

beta(1)-Adrenoceptors compensate for beta(3)-adrenoceptors in ileum from beta(3)-adrenoceptor knock-out mice

1. This study examines beta(1)-, beta(2)- and beta(3)-adrenoceptor (AR)-mediated responses, mRNA levels and radioligand binding in ileum from beta(3)-AR knock-out (-/-) (KO) and wild type (+/+) (FVB) mice. 2. In KO and FVB mice, SR59230A (100 nM) (beta(3)-AR antagonist) antagonized responses to (-)-isoprenaline in both KO and FVB mice. (-)-Isoprenaline mediated relaxation of ileum was antagonized weakly by ICI118551 (100 nM) (beta(2)-AR antagonist). Responses to (-)-isoprenaline were more strongly antagonized by CGP20712A (100 nM) (beta(1)-AR antagonist), propranolol (1 microM) (beta(1)-/beta(2)-AR antagonist), carvedilol (100 nM) (non-specific beta-AR antagonist), and CGP12177A (100 nM) (beta(1)-/beta(2)-AR antagonist) in ileum from KO than in FVB mice. 3. Responses to CL316243 (beta(3)-AR agonist) in ileum from FVB mice were antagonized by SR59230A (100 nM) but not by propranolol (1 microM) or carvedilol (100 nM). CL316243 was ineffective in relaxing ileum from KO mice. 4. CGP12177A had no agonist actions in ileum from either KO or FVB mice. 5. beta(1)-AR mRNA levels were increased 3 fold in ileum from KO compared to FVB mice. This was associated with an increased maximum number of beta(1)-/beta(2)-AR binding sites (B(max)). beta(2)-AR mRNA levels were unaffected while no beta(3)-AR mRNA was detected in KO mice. 6. In mouse ileum, beta(3)-ARs and to a lesser extent beta(1)-ARs are the predominant adrenoceptor subtypes mediating relaxation in ileum from FVB mice. In KO mice beta(1)-ARs functionally compensate for the lack of beta(3)-ARs, and this is associated with increased beta(1)-AR mRNA and levels of binding.

Genetic and environmental nature of the insulin resistance syndrome in Indo-Mauritian subjects with premature coronary heart disease: contribution of beta3-adrenoreceptor gene polymorphism and beta blockers on triglyceride and HDL concentrations

AIMS/HYPOTHESIS

Insulin resistance syndrome is an important risk factor for developing premature coronary heart disease. It is a complex syndrome which could arise from the interaction of several genes modulated by environmental factors. The Trp64Arg polymorphism in the beta3-adrenoreceptor gene has been found to be associated with insulin resistance, obesity or with earlier onset of Type II (non-insulin-dependent) diabetes mellitus in different populations. We aimed to study whether features of the insulin resistance syndrome are associated with this polymorphism in Indo-Mauritian patients with premature coronary heart disease.

METHODS

We carried out a case control study using PCR-RFLP techniques, of consecutive Indo-Mauritian patients (n = 338) with premature coronary heart disease (onset below age of 60 years) and unrelated control subjects (n = 148) of the same ethnicity.

RESULTS

In Indo-Mauritian patients with premature coronary heart disease who were not treated by beta blockers, triglyceride concentrations were lower (median: 1.44 vs 1.93 mmol/l, p < 0.008) and HDL cholesterol concentrations higher (mean: 0.98 vs 0.85 mmol/l, p < 0.015) in those carrying the wild type of the beta3-adrenoreceptor gene than in those carrying the Trp64Arg variant. The latter genotype specific effect on HDL was inverse in patients treated with beta blockers.

CONCLUSION/INTERPRETATION

The beta3-adrenoreceptor gene variant seems to modulate the effects of beta blockers on triglyceride and HDL cholesterol concentrations in this group of Indo-Mauritian population. Dyslipidaemia, a key component of the metabolic syndrome has a heterogeneous nature in Indo-Mauritian subjects. This potent risk factor for early-onset coronary heart disease is influenced by the interaction between genetic and environmental effects.

The beta 3-adrenergic receptor gene and obesity in a population sample of African Americans

OBJECTIVE

To examine the role of the Trp64Arg polymorphism in the beta 3-adrenergic receptor gene and the beta 3-adrenergic receptor gene locus in obesity-related traits in African Americans.

SUBJECTS

A total of 687 individuals representing 193 African American families who were residents of metropolitan Chicago.

MEASUREMENTS

Genotyping of the Trp64Arg polymorphism in the beta 3-adrenergic receptor gene and three microsatellite markers flanking the beta 3-adrenergic receptor gene (ADRB3) locus and measuring various obesity-related traits, including body mass index (BMI), fat-free mass, fat mass, percentage fat mass, waist circumference and serum lipid levels.

RESULTS

The prevalence of obesity (defined as body mass index > or = 30 kg/m(2)) in the population was 27.3% and 51.2% in men and women, respectively. The frequency of the Arg64 allele was 10.0%. Multivariate regression analyses confirmed the existence of a significant contribution of familial variance to each of the five obesity-related traits noted above. Likelihood ratio statistics computed in a multivariate regression analysis failed to demonstrate a significant association between the Arg64 allele and any of the five obesity-related traits. Single and multipoint analyses using extended Haseman--Elston regression analyses failed to demonstrate suggestive evidence of linkage of three microsatellite markers that flank the beta 3-adrenergic receptor gene to BMI, percentage body fat, waist circumference or serum leptin levels.

CONCLUSION

Given the contribution of familial variance to obesity-related traits in this population, neither the null finding for the Arg64 allele nor the lack of evidence of linkage of the ADRB3 locus to obesity-related traits could be attributed to lack of transmissibility of the traits suggesting that neither the Arg64 variant of the beta 3-adrenergic receptor gene nor another genetic variant in or near the ADRB3 locus contribute significantly to familial aggregation of obesity-related traits in African Americans. International Journal of Obesity (2001) 25, 54-60

Possible association of beta2- and beta3-adrenergic receptor gene polymorphisms with susceptibility to breast cancer

BACKGROUND

The involvement of beta2-adrenergic receptor (ADRB2) and beta3-adrenergic receptor (ADRB3) in both adipocyte lipolysis and thermogenic activity suggests that polymorphisms in the encoding genes might be linked with interindividual variation in obesity, an important risk factor for postmenopausal breast cancer. In order to examine the hypothesis that genetic variations in ADRB2 and ADRB3 represent interindividual susceptibility factors for obesity and breast cancer, we conducted a hospital-based, case-control study in the Aichi Cancer Center, Japan.

METHODS

A self-administered questionnaire was given to 200 breast cancer patients and 182 control individuals, and pertinent information on lifestyle, family history and reproduction was collected. ADRB2 and ADRB3 genotypes were determined by polymerase chain reaction (PCR) restriction fragment length polymorphism assessment.

RESULTS

Twenty-five (12.4%) breast cancer patients and 32 (17.6%) control individuals were found to bear a glutamic acid (Glu) allele for the ADRB2 gene (odds ratio [OR] 0.67, 95% confidence interval [CI] 0.38-1.18), and 60 (30.0%) breast cancer patients and 61 (33.5%) control individuals were found to bear an Arg allele for the ADRB3 gene (OR 0.85, 95% CI 0.55-1.31). A significantly lower risk was observed in those who carried the Glu ADRB2 allele and who reported first childbirth when they were younger than 25 years (OR 0.35; 95% CI 0.13-0.99).

CONCLUSION

A potential association may exist between risk of breast cancer and polymorphisms in the ADRB2 and ADRB3 genes; further studies in larger samples and/or in different ethnic groups are warranted to investigate this potential association.

[Genomic approach to obesity: understanding a complex syndrome]

Obesity is a multifactoral condition. Environmental risk factors related to sedentary lifestyle and unlimited access to food apply constant pressure in subjects with a genetic make-up predisposing to gaining weight. Recent genetic studies have demonstrated a continuum among the different forms of human obesity: certain cases, mainly very severe forms beginning in childhood, are monogenic conditions transmitted by recessive inheritance, the environment simply playing a permissive role. Other more frequent mutations, such as mutation of the melanocortin receptor 4 gene, have variable expression, but inactivity is sufficient to lead to early eating disorders. The common forms of obesity are however polygenic. The extreme pressure of the modern environment over-runs the capacity of homeostatic adaptation in individuals genetically predisposed to obesity, leading to an energy imbalance favoring energy storage in the form of fat; Certain candidate genes such as decoupling proteins, adrenergic beta-3 receptor, or regions regulating the leptin gene play a minor role in the development or aggravation of obesity. Recently, "whole genome" screening in families of obese subjects has localized major obesity genes on chromosomes 2, 5, 10, 11 and 20. Their identification using techniques of positional cloning and functional genomics will help better understand the molecules determining obesity and define targets for future therapy.

Expression of human alpha 2-adrenergic receptors in adipose tissue of beta 3-adrenergic receptor-deficient mice promotes diet-induced obesity

Catecholamines play an important role in controlling white adipose tissue function and development. beta- and alpha 2-adrenergic receptors (ARs) couple positively and negatively, respectively, to adenylyl cyclase and are co-expressed in human adipocytes. Previous studies have demonstrated increased adipocyte alpha 2/beta-AR balance in obesity, and it has been proposed that increased alpha 2-ARs in adipose tissue with or without decreased beta-ARs may contribute mechanistically to the development of increased fat mass. To critically test this hypothesis, adipocyte alpha 2/beta-AR balance was genetically manipulated in mice. Human alpha 2A-ARs were transgenically expressed in the adipose tissue of mice that were either homozygous (-/-) or heterozygous (+/-) for a disrupted beta 3-AR allele. Mice expressing alpha 2-ARs in fat, in the absence of beta 3-ARs (beta 3-AR -/- background), developed high fat diet-induced obesity. Strikingly, this effect was due entirely to adipocyte hyperplasia and required the presence of alpha2-ARs, the absence of beta 3-ARs, and a high fat diet. Of note, obese alpha 2-transgenic beta 3 -/- mice failed to develop insulin resistance, which may reflect the fact that expanded fat mass was due to adipocyte hyperplasia and not adipocyte hypertrophy. In summary, we have demonstrated that increased alpha 2/beta-AR balance in adipocytes promotes obesity by stimulating adipocyte hyperplasia. This study also demonstrates one way in which two genes (alpha 2 and beta 3-AR) and diet interact to influence fat mass.

Insulin response to glucose is lower in individuals homozygous for the Arg 64 variant of the beta-3-adrenergic receptor

Type 2 diabetes mellitus (type 2 DM) is a polygenic disorder with a variable phenotype that includes both insulin resistance and insulin secretory dysfunction. The Arg 64 beta-3-adrenergic receptor variant allele is associated with an earlier age of onset of type 2 DM. The purpose of this study was to examine the in vivo pathophysiology of this variant allele to determine its contribution to the components of glucose metabolism. We used the frequently sampled iv glucose tolerance tests, minimal model analysis, and analysis of covariance to examine age- and fat-mass-adjusted differences among genotypes. The results demonstrate that individuals homozygous for the Arg 64 allele secrete significantly less insulin in response to a glucose infusion (562+/-116 vs. 962+/-94 pmol/microL), have the highest fasting glucose levels (100.4+/-1.9 vs. 92.48+/-1.60 mg/dL), and have lower glucose effectiveness (0.014+/-0.003 vs. 0.019+/-0.002 min(-1)), compared with those homozygous for the Trp 64 allele. This first report of decreased acute insulin release and lower glucose effectiveness in the Arg 64 genotype may help explain the earlier onset of type 2 DM observed in several populations of individuals with the Arg64 beta-3-adrenergic receptor variant allele.

Effects of cafeteria diet feeding on beta3-adrenoceptor expression and lipolytic activity in white adipose tissue of male and female rats

OBJECTIVE

To investigate the effects of short term (15 days) cafeteria diet feeding on the expression of beta3-AR in vivo and its association with lipolytic stimulation induced by beta3-AR agonist CGP12177A in isolated white adipocytes.

ANIMALS

Six female and 6 male Wistar rats (at 4 weeks of age) were fed on a cafeteria diet plus standard diet for 15 days. The remaining 12 age- and sex-matched rats always received standard diet only.

MEASUREMENTS

White gonadal adipose tissue was isolated and used for the determination of beta3-AR and leptin expression, and for in vitro studies of lipolytic activity.

RESULTS

Control male rats had higher levels of both beta3-AR and leptin mRNA in white adipose tissue than their female counterparts. Both male and female rats up-regulated the levels of both beta3-AR and leptin mRNA in response to 15 day cafeteria diet feeding. Noradrenaline- and isoprenaline-induced lipolysis were significantly increased in fat cells from control females compared to their male counterparts. CGP12177A stimulation resulted in significantly higher glycerol release in fat cells from cafeteria diet-fed female rats, whereas there were no differences due to dietary treatment in male rats. The maximal lipolytic response of forskolin (stimulating adenylyl cyclase) and dibutyryl cyclic AMP (cyclic AMP analogous) was not affected by sex or cafeteria diet feeding.

CONCLUSION

Cafeteria diet feeding brings about higher excess body weight and impaired adipose tissue lipolytic activity in female rats compared to male rats. Thus, the higher levels of beta3-AR mRNA induced by cafeteria feeding are not indicative per se of an increase of the lipolytic response of the adipocytes. The changes seen in other adrenoceptor subtypes (beta1 and beta2) may be more determinant of the overall lipolytic response of adipocytes.

Lack of responses to a beta3-adrenergic agonist in lipoatrophic A-ZIP/F-1 mice

Stimulation of beta3-adrenergic receptors increases metabolic rate via lipolysis in white adipose tissue (WAT) and thermogenesis in brown adipose tissue (BAT). Other acute effects include decreased gastrointestinal motility and food intake and increased insulin secretion. Chronic treatment with a beta3 agonist ameliorates diabetes and obesity in rodents. We studied the effects of beta3 stimulation in A-ZIP/F-1 mice, which have virtually no WAT, a reduced amount of BAT, severe insulin resistance, and diabetes. In contrast with wild-type mice, treatment of A-ZIP/F-1 mice with CL316243, a beta3-adrenergic agonist, did not increase O2 consumption. A single dose of CL316243 produced a 2-fold increase in serum free fatty acids, a 53-fold increase in insulin, and a 2.4-fold decrease in glucose levels in wild-type mice but no change in A-ZIP/F-1 animals. The A-ZIP/F-1 mice also did not show reduced gastrointestinal motility or 24-h food intake during beta3 stimulation. Chronic administration of CL316243 to the A-ZIP/F-1 mice did not improve their thermogenesis, hyperglycemia, or hyperinsulinemia. Thus, all of the beta3 effects studied were absent in the lipoatrophic A-ZIP/F-1 mice, including the effects on nonadipose tissues. From these results, we suggest that all of the effects of beta3 agonists are initiated at the adipocyte with the nonadipose effects being secondary events presumably mediated by signals from adipose tissue.

Central leptin regulates the UCP1 and ob genes in brown and white adipose tissue via different beta-adrenoceptor subtypes

The three known subtypes of beta-adrenoreceptors (beta(1)-AR, beta(2)-AR, and beta(3)-AR) are differentially expressed in brown and white adipose tissue and mediate peripheral responses to central modulation of sympathetic outflow by leptin. To assess the relative roles of the beta-AR subtypes in mediating leptin's effects on adipocyte gene expression, mice with a targeted disruption of the beta(3)-adrenoreceptor gene (beta(3)-AR KO) were treated with vehicle or the beta(1)/beta(2)-AR selective antagonist, propranolol (20 microgram/g body weight/day) prior to intracerebroventricular (ICV) injections of leptin (0.1 microgram/g body weight/day). Leptin produced a 3-fold increase in UCP1 mRNA in brown adipose tissue of wild type (FVB/NJ) and beta(3)-AR KO mice. The response was unaltered by propranolol in wild type mice, but was completely blocked by this antagonist in beta(3)-AR KO mice. In contrast, ICV leptin had no effect on leptin mRNA in either epididymal or retroperitoneal white adipose tissue (WAT) from beta(3)-AR KOs. Moreover, propranolol did not block the ability of exogenous leptin to reduce leptin mRNA in either WAT depot site of wild type mice. These results demonstrate that the beta(3)-AR is required for leptin-mediated regulation of ob mRNA expression in WAT, but is interchangeable with the beta(1)/beta(2)-ARs in mediating leptin's effect on UCP1 mRNA expression in brown adipose tissue.

Frequency of and interaction between polymorphisms in the beta3-adrenergic receptor and in uncoupling proteins 1 and 2 and obesity in Germans

OBJECTIVE

To determine the role of polymorphisms in the genes for beta3-adrenergic receptor (beta3-AR) and in uncoupling proteins 1 and 2 (UCP-1, UCP-2) in obesity.

DESIGN

Association study with three polymorphisms and obesity.

SUBJECTS

Two hundred and thirty-six morbidly obese patients who underwent gastric banding surgery, 381 patients from the medical clinic and 198 healthy blood donors.

MEASUREMENTS

The frequencies of the W64R in beta3-AR, the 3826A-->G in UCP-1 and the 45bp insertion in the 3 untranslated region of exon 8 in UCP-2 polymorphisms were determined.

RESULTS

There were no significant differences in the frequencies of the beta3-AR and UCP-1 polymorphisms between obese (body mass index, BMI > 30 kg/m2) and lean subjects. Lean, but not obese, carriers of the R allele of beta3-AR had a significantly higher BMI. The mean age of obese subjects (excluding diabetics) who were carriers of the G allele of the UCP-1 polymorphism, 36y, was significantly younger than wild-type, 40y (P= 0.007). This effect was not seen in lean subjects. The effect of the G allele on the mean age of obese subjects was more apparent in subjects who were also carriers of the R allele of the beta3-AR polymorphism. The frequency of the ins allele of UCP-2 was significantly higher in obese subjects, 0.31, than in lean, 0.24 (P= 0.002) and carriers of the ins allele had a significantly higher BMI, 38 vs 35 (P= 0.005). There was no association between any of the polymorphisms and type II diabetes.

CONCLUSION

In a German population, there was no association between the W64R in beta3-AR or the 3826A-->G in UCP-1 polymorphisms and obesity. However, they act synergistically to accelerate the development of obesity. The 45bp insertion in the 3 untranslated region of exon 8 in UCP-2 polymorphism is associated with obesity.

Binding properties of beta-blockers at recombinant beta1-, beta2-, and beta3-adrenoceptors

The human heart contains at least four distinct beta-adrenoceptor subtypes, three of which have been cloned. However, the binding properties of beta-blockers to the different beta-adrenoceptor subpopulations are not yet thoroughly characterized. Human beta1-, beta2- and beta3-adrenoceptors were expressed in COS-7 cells and [125I]iodocyanopindolol saturation binding, and competition experiments with commonly used beta-blockers were performed in the respective membrane preparations. Atenolol and metoprolol were about fivefold selective for beta1- versus beta2- and beta3-adrenoceptors. Bisoprolol was approximately 15-fold selective for beta1- versus beta2- and approximately 31-fold selective for beta1- versus beta3-adrenoceptors. Carvedilol was nonselective for any beta-adrenoceptor subtype. We conclude that the beta1-selectivities of atenolol, metoprolol, and bisoprolol are lower in COS cell membranes compared with previous investigations performed in native membranes. All beta-blockers investigated bind to beta3-adrenoceptors. Differential binding properties to beta3-adrenoceptors might imply different responses as to body weight, cardiac contractility, heart rate, and growth regulation. This might imply differential indications for the drugs investigated.

Functional, biochemical and molecular biological evidence for a possible beta(3)-adrenoceptor in human near-term myometrium

The possible existence of a beta(3)-adrenoceptor (beta(3)-AR) in human near-term myometrium was investigated by in vitro functional and biochemical studies and analysis of mRNA expression. SR 59119A and SR 59104A and CGP 12177 (two selective agonists and a partial agonist, respectively, of the beta(3)-AR), salbutamol and terbutaline (beta(2)-AR agonists) each produced a concentration-dependent relaxation of the myometrial spontaneous contractions. There were no differences in pD(2) values for the relaxing potencies of terbutaline, salbutamol, CGP 12177 and SR 59119A. The rank order for their relaxing efficacies was SR 59119A>SR 59104A>terbutaline approximately salbutamol approximately CGP 12177 (E(max)=52+/-7%, 42+/-12% and approximately 30% respectively). Propranolol, a beta(1)- and beta(2)-AR antagonist, and ICI 118551, a beta(2)-AR antagonist (both at 0.1 microM), did not affect the SR 59119A-induced relaxation whereas SR 59230A, a selective beta(3)-AR antagonist (1 microM), significantly reduced the maximal relaxing effect of SR 59119A. SR 59119A and salbutamol induced a significant increase in cyclic AMP levels that was antagonized by SR 59230A but not by propranolol for SR 59119A, and by propranolol but not by SR 59230A for salbutamol. The beta(3)-AR mRNA was positively expressed in myometrium preparations in a reverse transcription polymerase chain assay. The results presented provide the first evidence for the existence of the beta(3)-AR subtype in human near-term myometrium and suggest that the effects of SR 59119A might be mediated through an increase in cyclic AMP level.

Study of the Trp64Arg polymorphism of the beta3-adrenergic receptor in Greek women with gestational diabetes

OBJECTIVE

This study assessed whether the Trp(64)Arg polymorphism of the beta3-adrenergic receptor (beta3-AR), which has been associated with obesity, insulin resistance, weight gain, and earlier onset of type 2 diabetes, is more frequent in women who develop gestational diabetes mellitus (GDM) or whether it is associated with weight gain during pregnancy

RESEARCH DESIGN AND METHODS

A total of 311 Greek pregnant women (180 with GDM and 131 without GDM [control]) who underwent a 100-g oral glucose tolerance test (OGTT) in the third trimester of pregnancy were genotyped for the beta3-AR Arg(64) polymorphism. Insulin levels were also determined during the OGTT.

RESULTS

The frequency of Trp(64)Arg heterozygotes in this population was approximately 7% and was similar in the GDM and control groups (6.7 vs. 6.9%) as well as in the obese (BMI > or =27 kg/m2) and the nonobese (6.3 vs. 6.8%) subgroups. In the GDM group, BMI, fasting insulin resistance index, and diastolic blood pressure were significantly higher in Trp(64)Arg carriers; these differences were no longer observed when obesity was considered. In the 4 subgroups (control Trp(64)Trp and Trp(64)Arg and GDM Trp(64)Trp and Trp(64)Arg), a highly significant trend was evident of an increase in the percentage of subjects with shorter height.

CONCLUSIONS

The frequency of the Arg(64) allele in Greek pregnant women is relatively rare compared with other ethnic groups and is probably not related to the development of GDM or obesity The observed tendency for shorter body height in Arg(64) carriers merits further evaluation in larger population samples.