Markus Eszlinger

Adiponectin gene expression is inhibited by β‐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 β‐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 (GS)‐proteins with cholera toxin and adenylyl cyclase with forskolin. Thus, our results suggest that adiponectin gene expression is severely suppressed by β‐adrenergic agents via activation of a GS‐protein–PKA‐dependent pathway. The data support a possible role of adiponectin in catecholamine‐induced insulin resistance.

Current State and Future Perspective of Molecular Diagnosis of Fine-Needle Aspiration Biopsy of Thyroid Nodules

CONTEXT Fine-needle aspiration biopsy (FNAB) is the most sensitive and specific tool for the differential diagnosis of thyroid malignancy. Some limitations of FNAB can be overcome by the molecular analysis of FNAB. This review analyzes the current state and problems of the molecular analysis of FNAB as well as possible goals for increasing the diagnostic rate, especially in the indeterminate/follicular lesion cytological group. EVIDENCE ACQUISITION Twenty publications were evaluated for the diagnostic material and assay systems used, the type, and the number of mutations screened. Sensitivity, specificity, and false-negative and false-positive rates were calculated for all publications. EVIDENCE SYNTHESIS Testing for a panel of somatic mutations is most promising to reduce the number of indeterminate FNAB. A mean sensitivity of 63.7% was achieved for indeterminate lesions. However, there is a broad sensitivity range for the investigation of mutations in the indeterminate lesions. Therefore, additional molecular markers should be defined by mRNA and microRNA expression studies and evaluated in FNAB samples of thyroid carcinomas without known somatic mutations, and especially for the many benign nodules in the indeterminate/follicular lesion fine-needle aspiration cytology category. This approach should improve the differential diagnosis of indeterminate/follicular lesion FNAB samples. CONCLUSION Testing for a panel of somatic mutations has led to an improvement of sensitivity/specificity for indeterminate/follicular proliferation FNAB samples. Further methodological improvements, standardizations, and further molecular markers should soon lead to a broader application of molecular FNAB cytology for the differential diagnosis of thyroid nodules and to a substantial reduction of diagnostic surgeries.

Molecular fine-needle aspiration biopsy diagnosis of thyroid nodules by tumor specific mutations and gene expression patterns.

Fine-needle aspiration biopsy (FNAB) is currently the most sensitive and specific tool for the presurgical differential diagnosis of thyroid malignancy, but has also substantial limitations. While approximately 75% of FNAB reveal benign lesions and 5% already cytologically prove malignancy, up to 20% of FNAB show follicular proliferation for which follicular adenoma, follicular carcinoma, and follicular variant of papillary carcinoma can only be distinguished histologically, thus requiring thyroid surgery. However, new biomarkers that might improve the accuracy of FNAB come along with the discovery of more and more details of the molecular etiology of thyroid tumors. So far molecular testing for somatic mutations is most promising (e.g., BRAF), since the proposed biomarkers from mRNA- and miRNA-expression studies need further evaluation, especially in FNAB samples. Nevertheless, the application of molecular markers will significantly improve thyroid tumor diagnosis and thus it will help to prevent unnecessary surgeries and it will also help to guide mutation-specific targeted therapies.

Isoproterenol inhibits resistin gene expression through a GS-protein-coupled pathway in 3T3-L1 adipocytes

Resistin was recently identified as a hormone secreted by adipocytes which leads to insulin resistance in vivo and in vitro and might therefore be an important link between obesity and diabetes. To clarify the regulation of resistin gene expression, 3T3‐L1 adipocytes were treated with various agents known to modulate insulin sensitivity, and resistin mRNA was measured by quantitative real‐time reverse transcription‐polymerase chain reaction. Interestingly, isoproterenol treatment reduced the level of resistin mRNA to 20% of non‐treated control cells. This effect was dose‐dependent with significant inhibition occurring at concentrations as low as 10 nM isoproterenol. Moreover, pretreatment of adipocytes with the β‐adrenergic antagonist propranolol almost completely reversed the inhibitory effect of isoproterenol, whereas addition of the α‐adrenergic antagonist phentolamine did not have any effect. Furthermore, the effect of isoproterenol could be mimicked by activation of GS‐proteins and adenylyl cyclase. Thus, both cholera toxin and forskolin decreased resistin mRNA expression in a dose‐dependent fashion by up to 90% of control levels. Taken together, these results suggest that resistin gene expression is regulated by a protein kinase A‐dependent pathway in 3T3‐L1 adipocytes.

A multi-gene approach to differentiate papillary thyroid carcinoma from benign lesions: gene selection using support vector machines with bootstrapping

Selection of novel molecular markers is an important goal of cancer genomics studies. The aim of our analysis was to apply the multivariate bioinformatical tools to rank the genes – potential markers of papillary thyroid cancer (PTC) according to their diagnostic usefulness. We also assessed the accuracy of benign/malignant classification, based on gene expression profiling, for PTC. We analyzed a 180-array dataset (90 HG-U95A and 90 HG-U133A oligonucleotide arrays), which included a collection of 57 PTCs, 61 benign thyroid tumors, and 62 apparently normal tissues. Gene selection was carried out by the support vector machines method with bootstrapping, which allowed us 1) ranking the genes that were most important for classification quality and appeared most frequently in the classifiers (bootstrap-based feature ranking, BBFR); 2) ranking the samples, and thus detecting cases that were most difficult to classify (bootstrap-based outlier detection). The accuracy of PTC diagnosis was 98.5% for a 20-gene classifier, its 95% confidence interval (CI) was 95.9–100%, with the lower limit of CI exceeding 95% already for five genes. Only 5 of 180 samples (2.8%) were misclassified in more than 10% of bootstrap iterations. We specified 43 genes which are most suitable as molecular markers of PTC, among them some well-known PTC markers (MET, fibronectin 1, dipeptidylpeptidase 4, or adenosine A1 receptor) and potential new ones (UDP-galactose-4-epimerase, cadherin 16, gap junction protein 3, sushi, nidogen, and EGF-like domains 1, inhibitor of DNA binding 3, RUNX1, leiomodin 1, F-box protein 9, and tripartite motif-containing 58). The highest ranking gene, metallophosphoesterase domain-containing protein 2, achieved 96.7% of the maximum BBFR score.

Association of FTO variants with BMI and fat mass in the self-contained population of Sorbs in Germany

The association between common variants in the FTO gene with weight, adiposity and body mass index (BMI) has now been widely replicated. Although the causal variant has yet to be identified, it most likely maps within a 47 kb region of intron 1 of FTO. We performed a genome-wide association study in the Sorbian population and evaluated the relationships between FTO variants and BMI and fat mass in this isolate of Slavonic origin resident in Germany. In a sample of 948 Sorbs, we could replicate the earlier reported associations of intron 1 SNPs with BMI (eg, P-value=0.003, β=0.02 for rs8050136). However, using genome-wide association data, we also detected a second independent signal mapping to a region in intron 2/3 about 40–60 kb away from the originally reported SNPs (eg, for rs17818902 association with BMI P-value=0.0006, β=−0.03 and with fat mass P-value=0.0018, β=−0.079). Both signals remain independently associated in the conditioned analyses. In conclusion, we extend the evidence that FTO variants are associated with BMI by putatively identifying a second susceptibility allele independent of that described earlier. Although further statistical analysis of these findings is hampered by the finite size of the Sorbian isolate, these findings should encourage other groups to seek alternative susceptibility variants within FTO (and other established susceptibility loci) using the opportunities afforded by analyses in populations with divergent mutational and/or demographic histories.

Gene expression analysis reveals evidence for inactivation of the TGF-β signaling cascade in autonomously functioning thyroid nodules

Molecular eventsthat lead to the development of autonomously functioning thyroid nodules (AFTNs) are somatic mutations of the thyrotropin receptor (TSHR) in approximately 60% of the nodules and less frequently, somatic mutations in the Gsα protein. However, AFTNs without known mutations indicate that other causes remain to be identified. Moreover, the impact of constitutively activating TSHR mutations on the signal transduction network of the thyroid epithelial cell is unknown. We therefore investigated gene expression in 15 AFTNs and their surrounding tissue using Affymetrix GeneChips. Most prominently, data analysis revealed a changed pattern of gene expression in the TGF-β signaling cascade and 25 differentially regulated genes in AFTNs, including thyroid peroxidase, type I iodothyronine deiodinase and sialyltransferase (SIAT) 1. Strikingly coexpression of SIAT 1 and TSHR in COS-7 cells increased TSH binding and cell surface expression of the TSHR. Moreover, differences in gene expression patterns for AFTNs with and without TSHR mutations indicate specific alterations of signal transduction in AFTNs without TSHR mutations. These results suggest that AFTNs with TSHR mutations harbor further mechanisms of forward stimulation. Furthermore, they give important leads to elucidate the molecular etiology of AFTNs without TSHR mutations.

Detection of PAX8/PPARG and RET/PTC rearrangements is feasible in routine air-dried fine needle aspiration smears.

BACKGROUND The diagnostic limitations of fine needle aspiration (FNA), like the indeterminate category, can be partially overcome by molecular analysis. As PAX8/PPARG and RET/PTC rearrangements have been detected in follicular thyroid carcinomas (FTCs) and papillary thyroid carcinomas (PTCs), their detection in FNA smears could improve the FNA diagnosis. To date, these rearrangements have never been analyzed in routine air-dried FNA smears, but only in frozen tissue, formalin-fixed paraffin-embedded (FFPE) tissue, and in fresh FNA material. Fixed routine air-dried FNA samples have hitherto been judged as generally not suitable for testing these rearrangements in a clinical setting. Therefore, the objective of the present study was to investigate the feasibility of extracting RNA from routine air-dried FNA smears for the detection of these rearrangements with real-time polymerase chain reaction (RT-PCR). METHODS A new method for RNA extraction from routine air-dried FNA smears was established, which allowed analysis for the presence of four variants of PAX8/PPARG and RET/PTC 1 and RET/PTC 3, which were analyzed in 106 routine FNA smears and the corresponding surgically obtained FFPE tissues using real-time quantitative PCR (RT-qPCR). To assess RNA quality, an intron-spanning PAX8 cDNA was amplified. RESULTS Acceptable RNA quality was obtained from 95% of the FNA samples and 92% of the FFPE samples. PAX8/PPARG was detected in 4 of 96 FFPEs and in 6 of 96 FNAs. PAX8/PPARG was present in 4 of 10 FTCs and in 3 of 42 follicular adenomas (FAs). Similarly, RET/PTC was found in 3 of 96 FFPEs and in 4 of 96 FNAs. Two of 21 PTC samples and 3 of 42 FA samples carried this rearrangement. CONCLUSION These data are the first to show the feasibility of extracting RNA from routine air-dried FNA smears for the detection of PAX8/PPARG and RET/PTC rearrangements with RT-qPCR. These promising methodological advances, if confirmed in larger series of FNA and FFPE samples, may lead to the introduction of molecular analysis of routine air-dried FNA smears in everyday practice.

Differential miRNA expression defines migration and reduced apoptosis in follicular thyroid carcinomas.

The objective of the study was to identify microRNAs (miRs) characteristic for follicular thyroid carcinoma (FTC) and to define their role in tumorigenesis. A miR-microarray study was conducted to identify miRs differentially expressed between FTCs and their surrounding tissues. Selection was further reinforced by a literature review. Four miRs were selected and confirmed by RT-qPCR: miR-146b, -183, -221 were up-regulated, whereas miR-199b down-regulated in FTCs. The influence of these miRs on cell proliferation, cell cycle, apoptosis and migration was studied in HTori and FTC-133 cells. Functional characterization suggests an impact of miR-183 and miR-146b in FTC development. Overexpression of both miRs significantly induces migration. Moreover, overexpression of miR-183 significantly represses apoptosis. MiR-199b and -221 do not have significant effects on proliferation, cell cycle, apoptosis or migration in HTori and FTC-133 cells. Our data suggest that miR-146b and miR-183 may influence FTC development through the induction of migration and apoptosis inhibition.

Perspectives for Improved and More Accurate Classification of Thyroid Epithelial Tumors

CONTEXT Histologic examination of thyroid nodules is the current standard to distinguish benign from malignant thyroid epithelial tumors and to classify histologic subtypes. This review analyzes the problems in histological differential diagnosis as well as contradictions between histology and molecular data and describes possibilities to combine histology with molecular data in an effort to more accurately classify thyroid epithelial tumors. EVIDENCE ACQUISITION Published literature, addressing the current recommendations for thyroid tumor classification, as well as literature on the application of histology and molecular studies on the etiology of thyroid tumors is analyzed. EVIDENCE SYNTHESIS The current histologic criteria to classify thyroid tumors, especially follicular-patterned tumors, are hampered by considerable interobserver variability. The detection of somatic mutations via genotyping and the definition of potentially informative gene expression signatures by microarray analyses, which can distinguish cancer subtypes as well as low- and high-risk cohorts, have recently demonstrated significant diagnostic potential. Moreover, in a routine diagnostic setting, micro-RNA profiling appears most promising due to their relative stability and the high accuracy of their expression profiles. CONCLUSIONS It is very likely that molecular definitions of thyroid tumors mentioned in the current World Health Organization classification will be further developed, leading to future progress in defining thyroid tumor types by an integrated histologic and molecular approach. These integrated classifications need to be evaluated for their specific impact on thyroid tumor diagnosis and prognosis.