The expression signature of in vitro senescence resembles mouse but not human aging

BACKGROUND: The biological mechanisms that underlie aging have not yet been fully identified. Senescence, a phenomenon occurring in vitro, limits the number of cell divisions in mammalian cell cultures and has been suggested to contribute to aging. RESULTS: We investigated whether the changes in gene expression that occur during mammalian aging and induction of cellular senescence are similar. We compared changes of gene expression in seven microarray datasets from aging human, mouse and rat, as well as four microarray datasets from senescent cells of man and mouse. The datasets were publicly available or obtained from other laboratories. Correlation measures were used to establish similarities of the expression profiles and gene ontology analyses to identify functional groups of genes that are co-regulated. Robust similarities were established between aging in different species and tissues, indicating that there is an aging transcriptome. Although some cross-species comparisons displayed high correlation, intra-species similarities were more reliable. Similarly, a senescence transcriptome was demonstrated that is conserved across cell types. A similarity between the expression signatures of cellular senescence and aging could be established in mouse, but not in human. CONCLUSION: Our study is the first to use microarray data from several studies and laboratories for dissection of a complex biological phenotype. We demonstrate the presence of a mammalian aging transcriptome, and discuss why similarity between cellular senescence and aging is apparent in aging mice only

What can one learn from two-state single molecule trajectories?

A time trajectory of an observable that fluctuates between two values (say, on and off), stemming from some unknown multi-substate kinetic scheme, is the output of many single molecule experiments. Here we show that when all successive waiting times along the trajectory are uncorrelated the on and the off waiting time probability density functions (PDFs) contain all the information. By relating the lack of correlation in the trajectory to the topology of kinetic schemes, we can immediately specify those kinetic schemes that are equally consistent with experiment, which means that it is impossible to differentiate between them by any sophisticated analyses of the trajectory. Correlated trajectories, however, contain additional information about the underlying kinetic scheme, and we consider the strategy that one should use to extract it. An example is given on correlations in the activity of individual lipase molecules.Comment: Biophys. J., in press (2005

Endosomal signalling via exosome surface TGF beta-1

Extracellular vesicles such as exosomes convey biological messages between cells, either by surface-to-surface interaction or by shuttling of bioactive molecules to a recipient cell's cytoplasm. Here we show that exosomes released by mast cells harbour both active and latent transforming growth factor beta-1 (TGF beta-1) on their surfaces. The latent form of TGF beta-1 is associated with the exosomes via heparinase-II and pH-sensitive elements. These vesicles traffic to the endocytic compartment of recipient human mesenchymal stem cells (MSCs) within 60 min of exposure. Further, the exosomes-associated TGF beta-1 is retained within the endosomal compartments at the time of signalling, which results in prolonged cellular signalling compared to free-TGF beta-1. These exosomes induce a migratory phenotype in primary MSCs involving SMAD-dependent pathways. Our results show that mast cell-derived exosomes are decorated with latent TGF beta-1 and are retained in recipient MSC endosomes, influencing recipient cell migratory phenotype. We conclude that exosomes can convey signalling within endosomes by delivering bioactive surface ligands to this intracellular compartment.11Ysciescopu

A simple method for assigning genomic grade to individual breast tumours

<p>Abstract</p> <p>Background</p> <p>The prognostic value of grading in breast cancer can be increased with microarray technology, but proposed strategies are disadvantaged by the use of specific training data or parallel microscopic grading. Here, we investigate the performance of a method that uses no information outside the breast profile of interest.</p> <p>Results</p> <p>In 251 profiled tumours we optimised a method that achieves grading by comparing rank means for genes predictive of high and low grade biology; a simpler method that allows for truly independent estimation of accuracy. Validation was carried out in 594 patients derived from several independent data sets. We found that accuracy was good: for low grade (G1) tumors 83- 94%, for high grade (G3) tumors 74- 100%. In keeping with aim of improved grading, two groups of intermediate grade (G2) cancers with significantly different outcome could be discriminated.</p> <p>Conclusion</p> <p>This validates the concept of microarray-based grading in breast cancer, and provides a more practical method to achieve it. A simple R script for grading is available in an additional file. Clinical implementation could achieve better estimation of recurrence risk for 40 to 50% of breast cancer patients.</p

Complex osteoclastogenic inductive effects of nicotine over hydroxyapatite

Cigarette smoke is associated to pathological weakening of bone tissue, being considered an important playmaker in conditions such as osteoporosis and periodontal bone loss. In addition, it is also associated with an increased risk of failure in bone regeneration strategies. The present work aimed to characterize the effects of nicotine on human osteoclastogenesis over a hydroxyapatite substrate. Osteoclast precursors were maintained in the absence or presence of the osteoclastogenesis enhancers M-CSF and RANKL, and were further treated with nicotine levels representative of the concentrations observed in the plasma and saliva of smokers. It was observed that nicotine at low concentrations elicit an increase in osteoclast differentiation, but only in the presence of M-CSF and RANKL it was also able to significantly increase the resorbing ability of osteoclasts. A slight downregulation of NFkB pathway and an increase in the production of TNF-α and, particularly PGE2, were involved in the observed effects of nicotine. At high concentrations, nicotine revealed cytotoxic effects, causing a decrease in cell density. In conclusion, nicotine at levels found in the plasma of the smokers, has the ability to act directly on osteoclast precursors, inducing its osteoclastogenic differentiation. The stimulatory behavior appears to be dependent on the stage of osteoclastic differentiation of the precursor cells, which means, in the absence of M-CSF and RANKL, it only favors the initial stages of osteoclast differentiation, while in the presence of the growth factors, a significant increase in their resorbing ability is also achieved.info:eu-repo/semantics/publishedVersio