Ole Hartvig Mortensen

Structural and Evolutionary Relationships among Protein Tyrosine Phosphatase Domains

With the current access to the whole genomes of various organisms and the completion of the first draft of the human genome, there is a strong need for a structure-function classification of protein families as an initial step in moving from DNA databases to a comprehensive understanding of human biology. As a result of the explosion in nucleic acid sequence information and the concurrent development of methods for high-throughput functional characterization of gene products, the genomic revolution also promises to provide a new paradigm for drug discovery, enabling the identification of molecular drug targets in a significant number of human diseases. This molecular view of diseases has contributed to the importance of combining primary sequence data with three-dimensional structure and has increased the awareness of computational homology modeling and its potential to elucidate protein function. In particular, when important proteins or novel therapeutic targets are identified—like the family of protein tyrosine phosphatases (PTPs) (reviewed in reference 53)—a structure-function classification of such protein families becomes an invaluable framework for further advances in biomedical science. Here, we present a comparative analysis of the structural relationships among vertebrate PTP domains and provide a comprehensive resource for sequence analysis of phosphotyrosine-specific PTPs.

A genomic perspective on protein tyrosine phosphatases: gene structure, pseudogenes, and genetic disease linkage

The protein tyrosine phosphatases (PTPs) are now recognized as critical regulators of signal transduction under normal and pathophysiological conditions. In this analysis we have explored the sequence of the human genome to define the composition of the PTP family. Using public and proprietary sequence databases, we discovered one novel human PTP gene and defined chromosomal loci and exon structure of the additional 37 genes encoding known PTP transcripts. Direct orthologs were present in the mouse genome for all 38 human PTP genes. In addition, we identified 12 PTP pseudogenes unique to humans that have probably contaminated previous bioinformatics analysis of this gene family. PCR amplification and transcript sequencing indicate that some PTP pseudogenes are expressed, but their function (if any) is unknown. Furthermore, we analyzed the enhanced diversity generated by alternative splicing and provide predicted amino acid sequences for four human PTPs that are currently defined by fragments only. Finally, we correlated each PTP locus with genetic disease markers and identified 4 PTPs that map to known susceptibility loci for type 2 diabetes and 19 PTPs that map to regions frequently deleted in human cancers. We have made our analysis available at http://ptp.cshl.edu or http://science.novonordisk.com/ptp and we hope this resource will facilitate the functional characterization of these key enzymes.—Andersen, J. N., Jansen, P. G., Echwald, S. M., Mortensen, O. H., Fukada, T., Del Vecchio, R., Tonks, N. K., M⊘ller, N. P. H. A genomic perspective on protein tyrosine phosphatases: gene structure, pseudogenes, and genetic disease linkage. FASEB J. 18, 8–30 (2004)

Brain-derived neurotrophic factor is produced by skeletal muscle cells in response to contraction and enhances fat oxidation via activation of AMP-activated protein kinase

It has been brought to our attention following an investigation into the work of Bente Klarlund Pedersen by the Danish Committees for Scientific Dishonesty, that the erratum published in 2012 was insufficient to correct this article. Although the data published in the Diabetologia paper were previously unpublished, the data from the biological material collected from the additional eight healthy men presented in Fig. 1b and c originated from a previous study that was not referenced [1]. In addition, while these eight healthy subjects performed the same type of exercise at the same intensity, the duration was different. The following description of the methodology and Fig. 1 legend correct these oversights. The authors would like to reiterate that these methodological oversights in no way affect either the data presented in the paper or the conclusions reached. The authors also apologise to both the journal and its readership for these oversights.

A 2-wk reduction of ambulatory activity attenuates peripheral insulin sensitivity

US adults take between approximately 2,000 and approximately 12,000 steps per day, a wide range of ambulatory activity that at the low range could increase risk for developing chronic metabolic diseases. Dramatic reductions in physical activity induce insulin resistance; however, it is uncertain if and how low ambulatory activity would influence peripheral insulin sensitivity. We aimed to explore if healthy, nonexercising subjects who went from a normal to a low level of ambulatory activity for 2 wk would display metabolic alterations including reduced peripheral insulin sensitivity. To do this, ten healthy young men decreased their daily activity level from a mean of 10,501+/-808 to 1,344+/-33 steps/day for 2 wk. Hyperinsulinemic-euglycemic clamps with stable isotopes and muscle biopsies, maximal oxygen consumption (VO2 max) tests, and blood samples were performed pre- and postintervention. A reduced number of daily steps induced a significant reduction of 17% in the glucose infusion rate (GIR) during the clamp. This reduction was due to a decline in peripheral insulin sensitivity with no effect on hepatic endogenous glucose production. The insulin-stimulated ratio of pAktthr308/total Akt decreased after step reduction, with a post hoc analysis revealing the most pronounced effect after 4 h of insulin infusion. In addition, the 2-wk period induced a 7% decline in VO2 max (ml/min; cardiovascular fitness). Lean mass of legs, but not arms and trunk, decreased concurrently. Taken together, one possible biological cause for the public health problem of Type 2 diabetes has been identified. Reduced ambulatory activity for 2 wk in healthy, nonexercising young men significantly reduced peripheral insulin sensitivity, cardiovascular fitness, and lean leg mass.

Expression of interleukin-15 in human skeletal muscle – effect of exercise and muscle fibre type composition

The cytokine interleukin‐15 (IL‐15) has been demonstrated to have anabolic effects in cell culture systems. We tested the hypothesis that IL‐15 is predominantly expressed by type 2 skeletal muscle fibres, and that resistance exercise regulates IL‐15 expression in muscle. Triceps brachii, vastus lateralis quadriceps and soleus muscle biopsies were obtained from normally physically active, healthy, young male volunteers (n= 14), because these muscles are characterized by having different fibre‐type compositions. In addition, healthy, normally physically active male subjects (n= 8) not involved in any kind of resistance exercise underwent a heavy resistance exercise protocol that stimulated the vastus lateralis muscle and biopsies were obtained from this muscle pre‐exercise as well as 6, 24 and 48 h post‐exercise. IL‐15 mRNA levels were twofold higher in the triceps (type 2 fibre dominance) compared with the soleus muscle (type 1 fibre dominance), but Western blotting and immunohistochemistry revealed that muscle IL‐15 protein content did not differ between triceps brachii, quadriceps and soleus muscles. Following resistance exercise, IL‐15 mRNA levels were up‐regulated twofold at 24 h of recovery without any changes in muscle IL‐15 protein content or plasma IL‐15 at any of the investigated time points. In conclusion, IL‐15 mRNA level is enhanced in skeletal muscles dominated by type 2 fibres and resistance exercise induces increased muscular IL‐15 mRNA levels. IL‐15 mRNA levels in skeletal muscle were not paralleled by similar changes in muscular IL‐15 protein expression suggesting that muscle IL‐15 may exist in a translationally inactive pool.

Antioxidant Supplementation Does Not Alter Endurance Training Adaptation

BACKGROUND There is a considerable commercial market, especially within the sports community, claiming the need for antioxidant supplementation. One argument for antioxidant supplementation in sports is that physical exercise is associated with increased reactive oxygen and nitrogen species (RONS) production, which may cause cell damage. However, RONS production may also activate redox-sensitive signaling pathways and transcription factors, which subsequently, may promote training adaptation. PURPOSE Our aim was to investigate the effects of combined vitamin C and E supplementation to healthy individuals on different measures of exercise performance after endurance training. METHODS Using a double-blinded placebo-controlled design, moderately trained young men received either oral supplementation with vitamins C and E (n = 11) or placebo (n = 10) before and during 12 wk of supervised, strenuous bicycle exercise training of a frequency of 5 d x wk(-1). Muscle biopsies were obtained before and after training. RESULTS After the training period, maximal oxygen consumption, maximal power output, and workload at lactate threshold increased markedly (P < 0.01) in both groups. Also, glycogen concentration, citrate synthase, and beta-hydroxyacyl-CoA dehydrogenase activity in the muscle were significantly higher in response to training (P < 0.01) in both groups. However, there were no differences between the two groups concerning any of the physiological and metabolic variables measured. CONCLUSIONS Our results suggest that administration of vitamins C and E to individuals with no previous vitamin deficiencies has no effect on physical adaptations to strenuous endurance training.

Association between Interleukin-15 and Obesity: Interleukin-15 as a Potential Regulator of Fat Mass

OBJECTIVE IL-15 decreases lipid deposition in preadipocytes and decreases the mass of white adipose tissue in rats, indicating that IL-15 may take part in regulating this tissue. IL-15 is expressed in human skeletal muscle and skeletal muscle may be a source of plasma IL-15 and in this way regulate adipose tissue mass. DESIGN The relation between skeletal muscle IL-15 mRNA expression, plasma IL-15, and adipose tissue mass was studied in 199 humans divided into four groups on the basis of obesity and type 2 diabetes. Furthermore, using a DNA electrotransfer model, we assessed the effect of IL-15 overexpression in skeletal muscle of mice. RESULTS In humans, multiple regression analysis showed a negative association between plasma IL-15 and total fat mass (P<0.05), trunk fat mass (P<0.01), and percent fat mass (P<0.05), independent of type 2 diabetes. Negative associations were also found between muscle IL-15 mRNA and obesity parameters. IL-15 overexpression in skeletal muscle of mice reduced trunk fat mass but not sc fat mass. CONCLUSIONS Our results indicate that IL-15 may be a regulator of trunk fat mass.

Associations between insulin resistance and TNF-α in plasma, skeletal muscle and adipose tissue in humans with and without type 2 diabetes

AbstractAims/hypothesisClear evidence exists that TNF-α inhibits insulin signalling and thereby glucose uptake in myocytes and adipocytes. However, conflicting results exist with regard to the role of TNF-α in type 2 diabetes.MethodsWe obtained blood and biopsy samples from skeletal muscle and subcutaneous adipose tissue in patients with type 2 diabetes (n = 96) and healthy controls matched for age, sex and BMI (n = 103).ResultsPatients with type 2 diabetes had higher plasma levels of fasting insulin (p < 0.0001) and glucose (p < 0.0001) compared with controls, but there was no difference between groups with regard to fat mass. Plasma levels of TNF-α (p = 0.0009) and soluble TNF receptor 2 (sTNFR2; p = 0.002) were elevated in diabetic patients. Insulin sensitivity was correlated with quartiles of plasma TNF-α after adjustment for age, sex, obesity, WHR, neutrophils, IL-6 and maximum O2 uptake

Calprotectin — A Novel Marker of Obesity

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