Drosophila odorant receptors are both ligand-gated and cyclic-nucleotide-activated cation channels

From worm to man, many odorant signals are perceived by the binding of volatile ligands to odorant receptors that belong to the G-protein-coupled receptor (GPCR) family. They couple to heterotrimeric G-proteins, most of which induce cAMP production. This second messenger then activates cyclic-nucleotide-gated ion channels to depolarize the olfactory receptor neuron, thus providing a signal for further neuronal processing. Recent findings, however, have challenged this concept of odorant signal transduction in insects, because their odorant receptors, which lack any sequence similarity to other GPCRs, are composed of conventional odorant receptors (for example, Or22a), dimerized with a ubiquitously expressed chaperone protein, such as Or83b in Drosophila. Or83b has a structure akin to GPCRs, but has an inverted orientation in the plasma membrane. However, G proteins are expressed in insect olfactory receptor neurons, and olfactory perception is modified by mutations affecting the cAMP transduction pathway. Here we show that application of odorants to mammalian cells co-expressing Or22a and Or83b results in non-selective cation currents activated by means of an ionotropic and a metabotropic pathway, and a subsequent increase in the intracellular Ca(2+) concentration. Expression of Or83b alone leads to functional ion channels not directly responding to odorants, but being directly activated by intracellular cAMP or cGMP. Insect odorant receptors thus form ligand-gated channels as well as complexes of odorant-sensing units and cyclic-nucleotide-activated non-selective cation channels. Thereby, they provide rapid and transient as well as sensitive and prolonged odorant signalling.

Cardioprotection and cardiac regeneration by mesenchymal stem cells

Mesenchymal stem cells (MSC) are promising candidates in the emerging field of regenerative medicine. MSC have been applied in numerous experimental and preclinical studies evaluating their therapeutical potential in various models of diseases. For cardiac applications, especially myocardial ischemia, MSC have been shown to provide an interesting therapeutical potential. However, to date the mechanisms of their beneficial effects on the cardiac tissue are only faintly elucidated. On the one hand we do not completely understand the biology of the MSC, on the other hand their interactions with the complex in vivo situation e. g. after myocardial infarction and the following remodeling processes are difficult to study. Initially, with respect to their in vitro differentiation capacity, it has been assumed that transplanted MSC may, promoted by the local microenvironment, differentiate in vivo into cells of cardiomyogenic phenotype or even cardiomyocytes, integrate themselves into the myocardium and help to regenerate the damaged tissue. The finding that after transplantation only a minor percentage of the MSC showed long term survival and persistent lack of evidence for in vivo differentiation make the original mechanistic concept of in vivo cardiomyogenic differentiation questionable. More recent studies suggest that the transplanted MSC may interact with the local tissue releasing paracrine factors and may hereby support the regenerative process. In this article, referring to experimental and preclinical studies, characteristics, sources, differentiation and paracrine activity of MSC contributing to cardioprotection and cardiac regeneration will be discussed.

An improved time-of-flight method for cluster deposition and ion-scattering experiments

A molecular beam apparatus has been developed for deposition and scattering experiments of size-selected clusters. The new setup combines a bimetallic laser ablation cluster source with a collinear time-of-flight mass spectrometer. Mass selection is achieved with a pulsed electrostatic mirror. A significantly improved transmission in combination with a reduction of the kinetic energy distribution of the mass selected clusters has been obtained. Without further modification of the apparatus, surface-induced dissociation of mass selected tin clusters has been investigated, demonstrating the possibility to combine cluster beam deposition and scattering experiments.

Aptamer-based isolation and subsequent imaging of mesenchymal stem cells in ischemic myocard by magnetic resonance imaging

PURPOSE

Mesenchymal stem cells (MSC) seem to be a promising cell source for cellular cardiomyoplasty. We recently developed a new aptamer-based specific selection of MSC to provide "ready to transplant" cells directly after isolation. We evaluated MRI tracking of newly isolated and freshly transplanted MSC in the heart using one short ex vivo selection step combining specific aptamer-based isolation and labeling of the cells.

MATERIALS AND METHODS

Bone marrow (BM) was collected from healthy pigs. The animals were euthanized and the heart was placed in a perfusion model. During cold ischemia, immunomagnetic isolation of MSC from the BM by MSC-specific aptamers labeled with Dynabeads was performed within 2 h. For histological identification the cells were additionally stained with PKH26. Approx. 3 x 10(6) of the freshly aptamer-isolated cells were injected into the ramus interventricularis anterior (RIVA) and 5 x 10(5) cells were injected directly into myocardial tissue after damaging the respective area by freezing (cryo-scar). 3 x 10(6) of the aptamer-isolated cells were kept for further characterization (FACS and differentiation assays). 20 h after cell transplantation, MRI of the heart using a clinical 3.0 Tesla whole body scanner (Magnetom Trio, Siemens, Germany) was performed followed by histological examinations.

RESULTS

The average yield of sorted cells from 120 ml BM was 7 x 10(6) cells. The cells were cultured and showed MSC-like properties. MRI showed reproducible artifacts within the RIVA-perfusion area and the cryo-scar with surprisingly excellent quality. The histological examination of the biopsies showed PKH26-positive cells within the areas which were positive in the MRI in contrast to the control biopsies.

CONCLUSION

Immunomagnetic separation of MSC by specific aptamers linked to magnetic particles is feasible, effective and combines a specific separation and labeling technique to a "one stop shop" strategy.

„Tissue engineering“ und Stammzellforschung in der Urologie für den rekonstruktiven bzw. regenerativen Therapieansatz

With the involvement of clinical reconstructive urology in the field of tissue engineering, outstanding results have been achieved in basic research as well as in some clinics. Stem cell research has even opened up possibilities for regenerative aspects. In close cooperation with various disciplines, the Department of Urology at the University of Tübingen investigates different clinical aspects with regard to reconstructive and regenerative urology. The regeneration of the external urethral sphincter requires functionally integrated muscle cells. In addition stricture reconstruction with multilayer urothelium should become less invasive and the re-stricture rate reduced. After the application of differentiating stem cells was proven, the clinical setting needed to be set for legal issues. In addition to the specification of culture media and verification in the animal model, the possibility to harvest omnipotent stem cells out of human testis and to differentiate those into the three germ layers was demonstrated. With the reduced invasiveness of harvesting the urothelium cells by a bladder wash using specific culture fluids, the cell culture was significantly improved enabling successful creation of urothelium by stratification. In addition urothelial cells in a matrix are further improved for endoscopic application. The close cooperation of different disciplines shortens the time to develop therapeutic approaches with a close clinical relationship in reconstructive and regenerative urology.

Donor myocardial HIF-1alpha is an independent predictor of cardiac allograft dysfunction: a 7-year prospective, exploratory study

Knowledge on interplay between the cardiac molecular response to transplantation-induced stress and primary graft dysfunction (PGD) is limited. A cDNA array identified HIF-1, EGR-1, NAB-2, VEGF-A and uPA as mediators of cardiac tissue response to transplantation-induced stress. mRNA expression of these molecules was measured in left ventricular biopsies from 200 donors before and after aortic cross-clamping and at 10-, 30- and 60-min reperfusion by real-time RT-PCR. HIF-1alpha expression at two time points was significantly associated with PGD, as shown by univariate analysis, receiver operating characteristic curve and multivariate logistic regression. At a cut-off level of 200 arbitrary units, HIF-1alpha after aortic cross-clamping in donors (78% sensitivity, 83% specificity) and at 10-min reperfusion (85% sensitivity, 83% specificity) identified PGD. HIF-1alpha demonstrates the potential to be a predictive marker for PGD; however, as multiple factors were tested at different time points, prospective evaluation is clearly necessary to confirm this observation.

Präklinische transtracheale Notfallventilation

INTRODUCTION

Prehospital transtracheal ventilation via a needle cricothyroidotomy may be lifesaving in cannot-intubate-cannot-ventilate situations. A self-made device consisting of a three-way stopcock placed between a transtracheal airway catheter and an oxygen supply was constructed and the effectiveness of the device was compared with a hand-triggered emergency jet generator in animal experiments.

MATERIALS AND METHODS

An emergency transtracheal airway catheter was inserted into the trachea of 10 anesthetized pigs (18-35 kgbw) and a situation of partial expiratory airway obstruction was established. All pigs were ventilated in a randomized order via the transtracheal airway catheter with the hand-triggered emergency jet injector and the self-made device for 15 min each.

RESULTS

With both devices satisfactory oxygenation and ventilation was achieved in all animals.

CONCLUSIONS

The efficacy of the self-made device during the experiment was comparable with the efficacy of the hand-triggered emergency jet injector.

The PI3K inhibitor LY294002 blocks drug export from resistant colon carcinoma cells overexpressing MRP1

Multidrug resistance may be achieved by the activation of membrane transporters, detoxification, alterations in DNA repair or failure in apoptotic pathways. Recent data have suggested an involvement of mitogenic signalling pathways mediated by Ras and phosphoinositol-3-kinase (PI3K/Akt) in controlling multidrug resistance. Since these pathways are important targets for therapeutic interference, we sought to investigate whether blocking effectors kinases by specific inhibitors would result in a sensitization toward cytotoxic drugs. We found that cotreatment of drug-resistant HT29RDB colon cancer cells with the topoisomerase inhibitor doxorubicin and the PI3K-inhibitor LY294002 resulted in massive apoptosis, while cotreatment with the Mek inhibitors PD98059 or U0126 had no effect. This suggested that the PI3K-pathways controls cell survival and drug resistance in these cells. Besides blocking Akt phosphorylation, the PI3K-inibitor increased the intracellular doxorubicin concentration threefold. LY294002 inhibits drug export in a competitive manner as revealed by measuring drug efflux in the presence and the absence of inhibitor. The efficacy of drug efflux inhibition by LY294002 was similar to that achieved by the MRP1 inhibitors MK571 and genistein. We conclude that the PI3K inhibitor LY294002 may have therapeutic potential when combined with doxorubicin in the treatment of MRP1-mediated drug resistance.

Oncogenic HRAS suppresses clusterin expression through promoter hypermethylation

Silencing of gene expression by methylation of CpG islands in regulatory elements is frequently observed in cancer. However, an influence of the most common oncogenic signalling pathways onto DNA methylation has not yet been investigated thoroughly. To address this issue, we identified genes suppressed in HRAS-transformed rat fibroblasts but upregulated after treatment with the demethylating agent 5-Aza-2-deoxycytidine and with the MEK1,2 inhibitor U0126. Analysis of gene expression by microarray and Northern blot analysis revealed the MEK/ERK target genes clusterin, matrix metalloproteinase 2 (Mmp2), peptidylpropyl isomerase C-associated protein, syndecan 4, Timp2 and Thbs1 to be repressed in the HRAS-transformed FE-8 cells in a MEK/ERK- and methylation-dependent manner. Hypermethylation of putative regulatory elements in HRAS-transformed cells as compared to immortalized fibroblasts was detected within a CpG island 14.5 kb upstream of clusterin, within the clusterin promoter and within a CpG island of the Mmp2 promoter by bisulphite sequencing. Furthermore, hypermethylation of the clusterin promoter was observed 10 days after induction of HRAS in immortalized rat fibroblasts and a clear correlation between reduced clusterin expression and hypermethlyation could also be observed in distinct rat tissues. These results suggest that silencing of individual genes by DNA methylation is controlled by oncogenic signalling pathways, yet the mechanisms responsible for initial target gene suppression are variable.

Experimental verification of fidelity decay: from perturbative to fermi golden rule regime

The scattering matrix was measured for a flat microwave cavity with classically chaotic dynamics. The system can be perturbed by small changes of the geometry. We define the "scattering fidelity" in terms of parametric correlation functions of scattering matrix elements. In chaotic systems and for weak coupling, the scattering fidelity approaches the fidelity of the closed system. Without free parameters, the experimental results agree with random matrix theory in a wide range of perturbation strengths, reaching from the perturbative to the Fermi golden rule regime.

Endocytosis mechanism of P2Y2 nucleotide receptor tagged with green fluorescent protein: clathrin and actin cytoskeleton dependence

Extracellular nucleotides exert a large number of physiological effects through activation of P2Y receptors. We expressed rat P2Y2 (rP2Y2) receptor, tagged with green fluorescent protein (GFP) in HEK-293 cells and visualized receptor translocation in live cells by confocal microscopy. Functional receptor expression was confirmed by determining [Ca2+]i responses. Agonist stimulation caused a time-dependent translocation of the receptor from the plasma membrane to the cytoplasm. Rearrangement of the actin cytoskeleton was observed during agonist-mediated rP2Y2-GFP receptor internalization. Colocalization of the internalized receptor with early endosomes, clathrin and lysosomes was detected by confocal microscopy. The inhibition of receptor endocytosis by either high-density medium or chlorpromazine in the presence of UTP indicates that the receptor was internalized by the clathrin-mediated pathway. The caveolin-mediated pathway was not involved. Targeting of the receptor from endosomes to lysosomes seems to involve the proteasome pathway, because proteasomal inhibition increased receptor recycling back to the plasma membrane.