Biomedical subjects

R Paschke

Publications and source records attributed to R Paschke.

At least 55 records · Page 3Linked to original sources

PubMed2003

Analysis of the relationship between PPAR-gamma 2 gene variants and severe insulin resistance in obese patients with impaired glucose tolerance.

Mutations in the peroxisome proliferator-activated receptor-gamma 2 (PPAR-gamma 2) gene may cause obesity and insulin resistance. Therefore we investigated whether known variants in the PPAR-gamma 2 gene are associated with obesity and extreme insulin resistance in obese patients with impaired glucose tolerance (IGT). The Pro115 Gln, Pro12Ala, Pro467Leu, Val290Met and a silent polymorphism C478 T were examined in 48 subjects with IGT and insulin resistance (IR), characterized by euglycemic hyperinsulinemic clamps, and in 52 healthy insulin sensitive (IS) controls. We found one proband in the IR group with the Pro115 Gln variant. This subject showed a lower whole body glucose uptake (18 micromol/kg per min) compared to the entire IR group (29 micromol/kg per min). The body weight of the proband (BMI 28.5 kg/m2) was within the average of the IR group (30.3 +/- 0.8 kg/m2). The Pro12Ala variant was not associated with differences in BMI, in the degree of insulin resistance between the IR and IS group. The Pro467Leu, Val290Met mutations and the silent polymorphism CAC478CAT were not detected in any group. In conclusion, the Pro115 Gln variant, but not the Pro12Ala mutation in the PPAR-gamma 2 gene, could be a rare cause of severe insulin resistance.

Adult↗

PubMed2003

Suppression of aquaporin adipose gene expression by isoproterenol, TNFalpha, and dexamethasone.

Aquaporin adipose (AQPap) is a putative glycerol channel in adipocytes. It has recently been shown to be upregulated in insulin resistance stimulated by thiazolidinediones and inhibited by insulin. To further clarify regulation of AQPap gene expression, 3T3-L1 adipocytes were chronically treated with various hormones known to influence insulin sensitivity and adipocyte metabolism, and AQPap mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction. Interestingly, treatment of 3T3-Ll adipocytes with 10 micro M isoproterenol, 10 ng/ml TNFalpha, and 100 nM dexamethasone for 16 h inhibited AQPap gene expression by 62 %, 60 %, and 39 %, respectively; angiotensin 2, growth hormone, and triiodothyronine did not have any effect. The inhibitory effects were dose-dependent with significant suppression detectable at concentrations as low as 1 nM isoproterenol, 1 ng/ml TNFalpha, and 10 nM dexamethasone. Furthermore, inhibition of AQPap gene expression could be almost completely reversed by pretreating 3T3-L1 adipocytes with the beta-adrenoceptor antagonist propranolol. Moreover, stimulation of Gs-proteins with cholera toxin and adenylyl cyclase with forskolin and dibutyryl-cAMP dramatically downregulated AQPap mRNA. Taken together, our results suggest that AQPap is an adipocyte-expressed glycerol channel selectively regulated and profoundly downregulated by hormones implicated in the pathogenesis of insulin resistance and dyslipidemia.

3T3-L1 Cells↗

PubMed2003

Therapy of hyperthyroidism.

Hyperthyroidism is a common disorder and affects approximately 2 % of women and 0.2 % of men. The review focuses on the therapy of overt hyperthyroidism with special emphasis on treatment strategies in Germany and Europe. Current treatment schedules for the different causes of hyperthyroidism are described and new therapeutic aspects are discussed. Special sections deal with the treatment of hyperthyroidism in pregnancy, neonates and children, and the treatment of thyrotoxic storm.

Antithyroid Agents↗

PubMed2003

Type 2 diabetes mellitus in children and adolescents: a review from a European perspective.

Changes in food consumption and exercise are fueling a worldwide increase in obesity in children and adolescents. As a consequence of this dramatic development, an increasing rate of type 2 diabetes mellitus has been recorded in children and adolescents in the USA and, more recently, in many countries around the world. Both genetic and environmental factors contribute to the pathogenesis of type 2 diabetes. Lower susceptibility in white Caucasians and higher susceptibility in Asians, Hispanics and blacks have been noted. There is a high hidden prevalence and a lack of exact data on the epidemiology of the disease in Europe: in Germany only 70 patients below the age of 15 years were identified in the systematic, nationwide DPV (Diabetessoftware für prospektive Verlaufsdokumentation) diabetes survey, but our calculations suggest that more than 5000 young people in Germany at present would meet the diagnostic criteria of type 2 diabetes. In Australasia, the prevalence of type 2 diabetes is reportedly high in some ethnic groups and again is linked very closely to the obesity epidemic. No uniform and evidence-based treatment strategy is available: many groups use metformin, exercise programmes and nutritional education as a comprehensive approach to treat type 2 diabetes in childhood and adolescence. The lack of clear epidemiological data and a strong need for accepted treatment strategies point to the key role of preventive programmes. Prevention of obesity will help to counteract the emerging worldwide epidemic of type 2 diabetes in youth. Preventive programmes should focus on exercise training and reducing sedentary behaviour such as television viewing, encouraging healthy nutrition and supporting general education programmes since shorter school education is clearly associated with higher rates of obesity and hence the susceptibility of an individual to acquire type 2 diabetes.

Adipose Tissue↗

PubMed2003

Biological activity of activating thyroid-stimulating hormone receptor mutants depends on the cellular context.

Activating TSH receptor (TSHR) mutations are a major cause of toxic thyroid adenoma and familial hyperthyroidism, and more than 37 such mutations have been described. Previously their functional activity had been assessed in terms of cAMP and inositol phosphate production and predominantly in transiently transfected COS-7 (monkey embryonic kidney cells), a model that does not reflect effects on thyrocyte proliferation and function. Here we have performed a systematic comparison of wild-type and seven gain-of-function TSHR mutants, introduced into rat FRTL-5 and human thyrocytes, using retroviral vectors. Our results show that 1) biological potency of TSHR mutants in thyroid cells does not correlate with their cAMP levels in transfected COS cells, highlighting the importance of cellular context and level of expression when assessing biological effects of oncogenic mutations; 2) dissociation between stimulation of function and growth occurs with thyrocyte differentiated functions more readily stimulated than growth; 3) TSHR mutants show a similar order of potency in FRTL-5 cells and human thyrocytes; 4) mutants inducing the highest stimulation of adenylyl cyclase may paradoxically fail to induce proliferation; and 5) biological effects of cAMP activating TSHR mutants are attenuated by complex counterregulatory mechanisms at least at the level of phosphodiesterases and cAMP regulatory element modulator isoforms.

Amino Acid Sequence↗

PubMed2003

Improvement of insulin sensitivity after adrenalectomy in patients with pheochromocytoma.

OBJECTIVE: Decreased insulin secretion is considered to be the main cause for pheochromocytoma-associated diabetes mellitus. Data from animal and evidence from clinical studies suggest that catecholamines can induce insulin resistance. However, there is no study investigating the effect of catecholamine excess on insulin resistance in patients with pheochromocytopma by the euglycemic hyperinsulinaemic clamp technique. RESEARCH DESIGN AND METHODS: We characterized the effect of high catecholamine plasma concentrations on glucose metabolism and insulin resistance. Euglycemic hyperinsulinemic clamps were performed in 10 patients with pheochromocytoma with and without diabetes mellitus before and 5 wk after adrenalectomy. RESULTS: In five patients with diabetes mellitus, glucose infusion rate required to maintain euglycemia during the clamp (mean +/- SEM) significantly improved from 27.5 +/- 6.5 micro mol/kg.min before surgery to 44.6 +/- 12.3 micro mol/kg.min 5 wk after adrenalectomy (P < 0.05). In five individuals without diabetes, total glucose disposal improved from 105 +/- 13.6 to 130 +/- 11.2 (P < 0.05). Improved insulin sensitivity after surgery was confirmed by a decrease of fasting hyperinsulinemia from 210 +/- 74 pmol/liter (diabetes mellitus) and 69 +/- 9 pmol/liter (no diabetes) before to 134 +/- 56 pmol/liter and 54 +/- 8 after surgery respectively (P < 0.01). In three patients, diabetes and hyperinsulinemia were reversed by the surgical removal of the pheochromocytoma. CONCLUSION: Our data provide evidence that endogenous catecholamine excess in patients with pheochromocytoma can induce or aggravate insulin resistance both in patients with type 2 diabetes and patients with normal glucose tolerance.

Adrenal Gland Neoplasms↗

PubMed2003

Two somatic TSH receptor mutations in a patient with toxic metastasising follicular thyroid carcinoma and non-functional lung metastases.

In a 59-year-old patient, thyroid follicular cancer was diagnosed in two right-sided toxic thyroid nodules, which had presented clinically as unilateral thyroid autonomy. In addition, the patient had histologically proven lung metastases of thyroid cancer; however, these failed to exhibit iodine uptake and were resistant to radioiodine treatment. The functional activity of the thyroid nodules prompted us to screen for TSH receptor (TSHR) mutations, and the histological diagnosis of follicular carcinoma led us to search for the PAX8-PPARgamma1 rearrangement and mutations in the ras genes. Each thyroid nodule harboured a different TSHR mutation (large nodule, Asp633Tyr; small nodule, Phe631Ile). Presence of both mutations in one sample suggestive of local invasion of a thyroid carcinoma could not be demonstrated, although several specimens from different nodule locations were screened. Only the wild-type TSHR sequence was identified in the histologically normal left thyroid lobe, and no genetic alterations were found in the other investigated genes. No TSHR mutations were detected in the pulmonary metastases. This is the first case report of a patient with toxic follicular thyroid carcinoma harbouring two different TSHR mutations and presenting with non-functional lung metastases.

Adenocarcinoma, Follicular↗

PubMed2003

GH is a positive regulator of tumor necrosis factor alpha-induced adipose related protein in 3T3-L1 adipocytes.

Tumor necrosis factor (TNF) alpha-induced adipose-related protein (TIARP) has recently been cloned as a TNFalpha-stimulated protein expressed in adipocytes. Its expression is differentiation-dependent and potentially involved in mediating TNFalpha-induced insulin resistance. To further characterize regulation of TIARP gene expression, 3T3-L1 adipocytes were treated with key hormones modulating insulin sensitivity and influencing adipocyte metabolism, and TIARP gene expression was determined by quantitative real-time RT-PCR. Interestingly, TIARP mRNA expression was stimulated almost 9-fold after 500 ng/ml GH were added for 16 h whereas addition of 10 microM isoproterenol, 100 nM insulin and 100 nM dexamethasone for 16 h significantly decreased TIARP gene expression to between 35 and 50% of control levels. In contrast, angiotensin 2 (10 microM) and triiodothyronine (1 microM) did not have any effect. The stimulatory effect of GH was time- and dose-dependent with stimulation occurring as early as 1 h after effector addition and at concentrations as low as 5 ng/ml GH. Moreover, pharmacological inhibition of Janus kinase 2 and p42/44 mitogen-activated protein kinase reversed the stimulatory effect of GH, suggesting that both signaling molecules are involved in activation of TIARP gene expression by GH. Furthermore, an increase of TIARP mRNA could be completely reversed to control levels by withdrawal of GH for 24 h. Taken together, these results show that TIARP is not only responsive to TNFalpha but also to important other hormones influencing glucose homeostasis and adipocyte metabolism. Thus, this factor may play an integrative role in the pathogenesis of insulin resistance and its link to obesity.

3T3-L1 Cells↗

PubMed2002

Relation between glycaemic control, hyperinsulinaemia and plasma concentrations of soluble adhesion molecules in patients with impaired glucose tolerance or Type II diabetes.

AIMS/HYPOTHESIS: Increased plasma concentrations of circulating adhesion molecules in patients with Type II (non-insulin-dependent) diabetes mellitus could be associated with the increased cardiovascular risk in these patients. However, it is controversial whether increased adhesion molecule plasma concentrations are primarily related to hyperglycaemia or to hyperinsulinaemia. METHODS: We evaluated the plasma concentrations of soluble E-selectin, intracellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) at baseline and during euglycaemic hyperinsulinaemic clamp in three different groups without additional cardiovascular risk factors: group A (control group), 28 healthy volunteers with normal glucose tolerance; group B, 24 subjects with fasting hyperinsulinaemia, normal fasting glucose but impaired glucose tolerance; group C, 32 patients with Type II diabetes, fasting hyperinsulinaemia and chronic hyperglycaemia. RESULTS: Plasma soluble E-selectin, ICAM-1, and VCAM-1 concentrations were higher ( p < 0.05) in patients with Type II diabetes (group C) compared with the other groups. The adhesion molecule concentrations correlate with the fasting plasma glucose ( r = 0.59, p < 0.001), the 2-h OGTT plasma glucose ( r = 0.70, p < 0.01), and the HbA(1 c) value ( r = 0.61, p < 0.05). The E-selectin but not the ICAM-1 and VCAM-1 plasma concentrations correlated with the fasting insulin concentrations ( r = 0.62, p < 0.05) or the whole body glucose uptake ( r = 0.59, p < 0.05) in the clamp. The hyperinsulinaemia during the euglycaemic hyperinsulinaemic clamp had no significant effect on the plasma concentrations of E-selectin, ICAM-1, and VCAM-1 in all three groups. CONCLUSION/INTERPRETATION: Our results suggest that increased E-selectin concentrations are related to hyperglycaemia, hyperinsulinaemia and insulin resistance, whereas increased ICAM-1 and VCAM-1 plasma concentrations in patients with Type II diabetes are rather related to hyperglycaemia than to hyperinsulinaemia or insulin resistance.

Adult↗

PubMed2002

Adrenocorticotrope deficiency with clinical evidence for late onset in combined pituitary hormone deficiency caused by a homozygous 301-302delAG mutation of the PROP1 gene.

Combined pituitary hormone deficiency (CPHD) can be caused by mutation of the pituitary transcription factors POU1F1 or PROP1. More recently mutations in the HESX1, the LHX3 and LHX4 transcription factor genes have also been described as a cause in patients with CPHD. In most patients the disorder is characterized by an impaired production of GH, TSH, PRL and gonadotropins. In some cases of CPHD adrenocorticotropin deficiency is also present. We report the progressive CPHD and its molecular etiology in a woman with CPHD presenting with first symptoms of ACTH/cortisol deficiency at the age of 48 years. The 49 year old patient's initial symptoms were growth retardation at the age of 2 years and symptoms of hypothyroidism at the age of 5 years. The patient never entered puberty spontaneously. No familial history of delayed puberty, growth retardation or other symptoms of CPHD were present. At the age of 48 years the patient presented with the first symptoms of hypocortisolism such as recurring hypoglycaemias and hyponatriaemia with coma. Cortisol, ACTH, TSH, fT3, fT4 and GH as well as LH, FSH and PRL were measured in basal conditions. GH, cortisol and ACTH were also measured in response to an Insulin Tolerance Test. Molecular analysis was performed by PCR amplification and sequencing of exon 1-3 of the PROP1 gene. The patient had insufficiencies of TSH, LH, FSH and GH. PRL was normal. Serum cortisol was low and basal ACTH was normal. However, there were no responses of cortisol, ACTH and GH to hypoglycaemia. Magnetic resonance imaging showed a hypoplastic anterior pituitary lobe. Direct sequencing revealed a homozygous 2 base-pair deletion 301-302delAG in exon 2 of the PROP1 gene. This case suggests that in patients with CPHD ACTH producing cells may be involved at a rather late age.

Adrenocorticotropic Hormone↗

PubMed2002

Induction of TSH-receptor antibodies in patients with toxic multinodular goitre by radioiodine treatment.

Previous studies have indicated pre-existing subclinical Graves' disease (GD) in many patients with the scintigraphic diagnosis of disseminated thyroid autonomy (DISA) or toxic multinodular goitre (TMG) type A. After radioiodine (RAI) treatment, an increase or the induction of TSH-receptor antibodies (TRAbs) in patients with GD or TMG has been repeatedly reported. In the present study, we investigated whether RAI could induce TRAbs in patients with TMG in whom pre-existing GD was excluded with highly sensitive TBII and TSAB assays. Therefore, TRAbs, anti-thyroperoxidase antibodies (anti-TPO-Abs) and anti-thyroglobulin antibodies (anti-TG-Abs) were determined in 43 consecutive patients at the nuclear medicine outpatient clinic with the scintigraphic diagnosis of toxic adenoma (TA; n = 20) or TMG type A (n = 11) or type B (n = 12) before and after RAI treatment. After RAI therapy, we detected TRAbs in 36 % (4 of 11) of patients with TMG type A only, whereas TRAbs were not detectable in patients with TMG type B or in patients with TA. Furthermore, 3 of the 4 patients with detectable TRAbs after RAI showed positive anti-TPO-Abs before RAI therapy. These findings provide further evidence for pre-existing GD in patients with TMG type A or DISA as previously suggested. Therefore, patients with TMG type A and high anti-TPO-Abs seem to be at increased risk of developing TRAbs or side-effects such as relapse of hyperthyroidism or thyroid associated ophthalmopathy. These patients therefore require more frequent evaluation after RAI treatment.

Adenoma↗

PubMed2002

Prediction of remission or relapse for Graves' hyperthyroidism by the combined determination of stimulating, blocking and binding TSH-receptor antibodies after the withdrawal of antithyroid drug treatment.

The most likely reasons for the low predictive value of TSH-receptor antibodies (TRAbs) determinations in previous investigations are the biological heterogeneity of TRAbs and changes of the different stimulating (TSAb) or blocking (TSBAb) antibody bioactivities of TRAbs during the course of Graves' disease (GD), which have not been taken into account in most previous studies. Furthermore, in a recent study it has been demonstrated that the decline of TRAb values detected with highly sensitive hTBII or TSAB assays is not useful in evaluating remission or relapse of GD at the end of antithyroid drug treatment (ATDT). In order to make a thorough investigation of the predictive values of all different TRAb qualities for the recurrence for GD after the withdrawal, we investigated hTBII, TSAbs and TSBAbs in 54 consecutive patients with GD at the end of ATDT and 12 - 13.5 months after stopping ATDT. Using the TRAb values at the time of reinvestigation in a model, recurrence for GD was better predicted compared to the determination at the time of withdrawal of ATDT. Furthermore, using this model, the combined determination of hTBII, TSAbs, and TSBAbs revealed the highest level of significance for the prediction of remission or relapse of GD (OR = 15; p < 0.0001) compared to the detection of hTBII, TSAbs and TSBAbs alone. Therefore, significant changes of TSAbs after the end of ATDT and the biological heterogeneity of TRAb define the conditions for predicting remission or relapse of GD after ATDT by TRAb determinations. Consequently, our results suggest that the prediction of the individual course of GD can only be improved by combined determinations of all TRAb qualities (hTBII, TSAbs and TSBAbs) after the end of ATDT.

Adult↗

PubMed2002

Lack of association between peroxisome proliferator-activated receptor-gamma-2 gene variants and the occurrence of coronary heart disease in patients with diabetes mellitus.

OBJECTIVE: Recent evidence indicates that peroxisome proliferator-activated receptor-gamma (PPARgamma) is expressed at high levels in foam cells of atherosclerotic lesions, that PPARgamma agonists may directly modulate vessel wall function and that mutations in the PPARgamma-2 gene are associated with a reduced risk of coronary artery disease. METHODS: We investigated whether known variants in the PPARgamma-2 gene are associated with the occurrence of coronary heart disease (CHD) in 365 patients with type 2 diabetes, prospectively characterised for the presence or absence of CHD. The Pro115Gln, Pro12Ala, Pro467Leu, Val290Met mutations and two polymorphisms C478T and C161T of the PPARgamma-2 gene were examined using PCR, denaturing gradient gel electrophoresis and direct sequencing. RESULTS: The distribution of the Pro12Ala, Ala12Ala, C161T and T161T variants was not significantly different between patients with and without CHD, independent of the gender. The Pro12Ala (P=0.011) and the Ala12Ala (P=0.006) variant were associated with a higher body mass index (BMI) compared with the Pro12Pro genotype. A multiple logistic regression analysis introducing the typical risk factors for CHD (age, sex, hypertension, smoking, BMI >26 kg/m2, elevated low density lipoprotein cholesterol and haemoglobin A1c >7%) identified age >60, male gender, hypertension and a higher BMI, but not the PPARgamma-2 variants, as significant risk factors for CHD in our study groups. CONCLUSION: The PPARgamma-2 genotype was not associated with an increased or reduced risk of the occurrence of CHD and can therefore not be regarded as an independent risk factor for CHD in patients with diabetes mellitus.

Adult↗

PubMed2002

Isoproterenol is a positive regulator of the suppressor of cytokine signaling-3 gene expression in 3T3-L1 adipocytes.

SOCS (suppressor of cytokine signaling)-3 has recently been shown to be an insulin- and tumor necrosis factor (TNF)-alpha-induced negative regulator of insulin signaling. To further clarify a potential involvement of SOCS-3 in the development of insulin resistance, we measured differentiation-dependent SOCS-3 mRNA expression in 3T3-L1 adipocytes and studied its regulation by various hormones known to impair insulin signaling using quantitative real-time RT-PCR. There was a differentiation-dependent downregulation of SOCS-3 mRNA by 50% over the 9 day adipocyte differentiation course. Interestingly, besides insulin and TNF-alpha, chronic treatment of differentiated 3T3-L1 cells with 10 microM isoproterenol for 16 h stimulated SOCS-3 gene expression by about 3.5-fold. Furthermore, isoproterenol stimulated SOCS-3 mRNA expression in a dose-dependent manner with significant activation detectable at concentrations as low as 10 nM isoproterenol. Moreover, a strong 27- and 47-fold activation of SOCS-3 mRNA expression could be seen after 1 h of isoproterenol and GH treatment respectively. The stimulatory effect of isoproterenol could be almost completely reversed by pretreatment of 3T3-L1 cells with the beta-adrenergic antagonist propranolol. Finally, isoproterenol's action could be mimicked by stimulation of G(S)-proteins with cholera toxin and of adenylyl cyclase with forskolin and dibutyryl cAMP. Taken together, our results demonstrate a differentiation-dependent downregulation of SOCS-3 in adipocytes and suggest that SOCS-3 gene expression is stimulated by beta-adrenergic agents via activation of a G(S)-protein-adenylyl cyclase-dependent pathway. As SOCS-3 is a novel inhibitor of insulin signaling, the data support a possible role of this protein as a selectively regulated mediator of catecholamine-induced insulin resistance.

3T3 Cells↗

PubMed2002

Reduced expression of Th1-associated chemokine receptors on peripheral blood lymphocytes at diagnosis of type 1 diabetes.

We investigated the expression of Th1- and Th2-associated chemokine receptors on peripheral blood lymphocytes at diagnosis and in the first phase of type 1 diabetes. Peripheral blood mononuclear cells (PBMCs) of 25 patients with newly diagnosed type 1 diabetes, 10 patients with longstanding type 1 diabetes, and 35 healthy control subjects were examined for expression of the chemokine receptors CXCR4 (naive T-cells), CCR5 and CXCR3 (Th1 associated), and CCR3 and CCR4 (Th2 associated) on CD3+ lymphocytes. Furthermore, we analyzed chemokine serum levels (monocyte chemoattractant protein [MCP]-1, macrophage inflammatory protein [MIP]-1alpha, MIP-1beta, and RANTES [regulated on activation, normal T-cell expressed and secreted]) and phytohemagglutinin (PHA)-stimulated cytokine secretion of Th1- (gamma-interferon [IFN-gamma] and tumor necrosis factor-alpha [TNF-alpha]) and Th2 (interleukin [IL]-4 and -10)-associated cytokines by PBMC. The patients with newly diagnosed type 1 diabetes were followed for these parameters at 6-12 months after diagnosis. The PBMCs of patients with newly diagnosed but not with longstanding type 1 diabetes showed reduced expression of the Th1-associated chemokine receptors CCR5 (P < 0.001 vs. control subjects) and CXCR3 (P < 0.002 vs. control subjects). This reduction correlated with reduced IFN-gamma and TNF-alpha production of PBMCs after PHA stimulation and reversed 6-12 months after diagnosis to normal levels. CCR4 cells were reduced in both newly diagnosed and longstanding type 1 diabetic patients, which correlated to reduced PHA-stimulated IL-4 production. MIP-1alpha and MIP-1beta levels were considerably elevated in a subgroup of patients with newly diagnosed diabetes. We assume that Th1-associated peripheral T-cells are reduced in a narrow time window at the time of diagnosis of diabetes, possibly due to extravasation in the inflamed pancreas. Thus, chemokine receptor expression of peripheral blood lymphocytes may be a useful surrogate marker for the immune activity of type 1 diabetes (e.g., in intervention trials).

Adolescent↗

PubMed2001

Tumor necrosis factor alpha is a negative regulator of resistin gene expression and secretion in 3T3-L1 adipocytes.

Resistin has recently been implicated as an adipocytokine leading to insulin resistance and, therefore, potentially linking obesity and diabetes. To further characterize the regulation of this fat-secreted protein by insulin sensitivity-modulating hormones, 3T3-L1 adipocytes were treated with tumor necrosis factor (TNF) alpha, angiotensin (AT) 2, as well as growth hormone (GH), and resistin gene expression and protein secretion were determined by quantitative real-time reverse transcription-polymerase chain reaction and Western blotting. Interestingly, both, resistin mRNA expression and protein secretion, were inhibited by 70-90% after TNFalpha-treatment whereas AT2 and GH did not have any effect. The inhibitory effect of TNFalpha was time- and dose-dependent with significant inhibition occurring as early as 4 h after effector addition and at concentrations as low as 1 ng/ml TNFalpha. Pharmacological inhibition of protein kinase A (PKA), p44/42, and p38 mitogen-activated protein (MAP) kinase did not reverse the inhibitory effect of TNFalpha suggesting that neither of these signaling molecules is involved in suppression of resistin gene expression by TNFalpha. Furthermore, suppression of resistin mRNA levels could be completely reversed to control levels by withdrawal of TNFalpha for 24 h. Taken together, these results suggest that TNFalpha is a pivotal negative regulator of resistin gene expression. This may have important implications for the pathogenesis of insulin resistance and its link to obesity.

3T3 Cells↗

PubMed2001

Adiponectin gene expression is inhibited by beta-adrenergic stimulation via protein kinase A in 3T3-L1 adipocytes.

Recently, it has been shown that the fat-derived factor adiponectin is downregulated in insulin resistance and obesity and that replenishment of this adipocytokine reverses insulin resistance in mice. Growing evidence, on the other hand, suggests that raised levels of catecholamines due to increased activity of the sympathetic nervous system are an integral part in the development of insulin resistance. To clarify whether catecholamines might exert their insulin resistance-inducing effects at least partly via downregulation of adiponectin gene expression, 3T3-L1 adipocytes were treated with isoproterenol, and adiponectin mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction. In fact, isoproterenol treatment reduced the level of adiponectin mRNA by about 75% in a dose-dependent fashion with significant inhibition detectable at concentrations as low as 10 nM isoproterenol. Furthermore, the inhibitory effect of isoproterenol was almost completely reversed by pretreatment of 3T3-L1 cells with the beta-adrenergic antagonist propranolol and the protein kinase A (PKA) inhibitor H-89. Moreover, the effects of isoproterenol could be mimicked by stimulation of stimulatory guanine nucleotide-binding (G(S))-proteins with cholera toxin and adenylyl cyclase with forskolin. Thus, our results suggest that adiponectin gene expression is severely suppressed by beta-adrenergic agents via activation of a G(S)-protein-PKA-dependent pathway. The data support a possible role of adiponectin in catecholamine-induced insulin resistance.

3T3 Cells↗

PubMed2001

Thyrotropin receptor mutations as a tool to understand thyrotropin receptor action.

A large number of mutations have been identified in the thyrotropin (TSH) receptor (TSHR) gene causing human diseases. Toxic thyroid nodules are frequently associated with somatic constitutively activating TSHR mutations. Autosomal dominant non-autoimmune hyperthyroidism is caused by activating TSHR germline mutations. Inactivating germline mutations cause TSH unresponsiveness. Discovery of the different TSHR mutations in various regions of the receptor molecule has led to the identification of important domains for intramolecular TSHR signal transduction. However, despite the functional characterization of the naturally occurring mutations the precise molecular mechanisms of receptor activation including the processes of hormone binding, intramolecular signaling between the different TSHR domains and of G protein coupling are not completely understood. This review discusses the importance of the various receptor domains for TSHR activation identified on the basis of the naturally occurring gain or loss of function mutations and in vitro investigations performed with site-directed mutagenesis, synthetic peptides, or antibodies. Several in vitro studies have provided new insights into structure-function relationships by site-directed mutagenesis in combination with molecular modeling. These in vitro investigations have often been guided by naturally occurring mutations and have provided new insights into intramolecular changes during receptor activation. This has led to progress in understanding the mechanism of TSHR activation.

Animals↗