The Phosphoarginine Energy-Buffering System of Trypanosoma brucei Involves Multiple Arginine Kinase Isoforms with Different Subcellular Locations

Phosphagen energy-buffering systems play an essential role in regulating the cellular energy homeostasis in periods of high-energy demand or energy supply fluctuations. Here we describe the phosphoarginine/arginine kinase system of the kinetoplastid parasite Trypanosoma brucei, consisting of three highly similar arginine kinase isoforms (TbAK1-3). Immunofluorescence microscopy using myc-tagged protein versions revealed that each isoform is located in a specific subcellular compartment: TbAK1 is exclusively found in the flagellum, TbAK2 in the glycosome, and TbAK3 in the cytosol of T. brucei. The flagellar location of TbAK1 is dependent on a 22 amino acid long N-terminal sequence, which is sufficient for targeting a GFP-fusion protein to the trypanosome flagellum. The glycosomal location of TbAK2 is in agreement with the presence of a conserved peroxisomal targeting signal, the C-terminal tripeptide ‘SNL’. TbAK3 lacks any apparent targeting sequences and is accordingly located in the cytosol of the parasite. Northern blot analysis indicated that each TbAK isoform is differentially expressed in bloodstream and procyclic forms of T. brucei, while the total cellular arginine kinase activity was 3-fold higher in bloodstream form trypanosomes. These results suggest a substantial change in the temporal and spatial energy requirements during parasite differentiation. Increased arginine kinase activity improved growth of procyclic form T. brucei during oxidative challenges with hydrogen peroxide. Elimination of the total cellular arginine kinase activity by RNA interference significantly decreased growth (>90%) of procyclic form T. brucei under standard culture conditions and was lethal for this life cycle stage in the presence of hydrogen peroxide. The putative physiological roles of the different TbAK isoforms in T. brucei are further discussed.     

A novel sensor concept for optimization of loosening diagnostics in total hip replacement

The main reason for the revision of total hip replacements is aseptic loosening, caused by stress shielding and wear particle induced osteolysis. In order to detect an implant loosening early, the osseointegration of endoprosthetic implants must be measured exactly. Currently applied diagnostic methods, such as standard radiographs and clinical symptomatology, often result in an imprecise diagnosis. A novel radiation-free method to improve the diagnostic investigation of implant loosening is presented. The osseointegration of an implant can be identified using mechanical magnetic sensors (oscillators), which impinge on small membranes inside an implant component, e.g., the femoral hip stem. The maximum velocity after impingement of the oscillator depends on the osseointegration of the implant. Excitation of the oscillator is realized by a coil outside the human body. Another external coil is used to detect the velocity of the oscillator. To demonstrate the principle of the novel loosening sensor, an overdimensioned test device was designed to measure simulated loosening phases in the first experimental tests with different material layers. The overdimensioned test device of the loosening sensor showed significant differences in the various phases of fixation. Analysis of the membrane without any material layer in the case of advanced loosening resulted in a 23% higher maximum velocity compared to an attached artificial bone layer. Based on these preliminary results, the sensor system shows potential for the detection of implant loosening. Moreover, the proposed system could be used in experimental applications to determine the quality of bioactive coatings and new implant materials.     

The in vitro resistance of IgG2 to proteolytic attack concurs with a comparative paucity of autoantibodies against peptide analogs of the IgG2 hinge

The mammalian antibody repertoire comprises immunoglobulin (Ig) molecules of multiple isotypes and subclasses with varying functional properties. Among the four subclasses of the human IgG isotype, we found that IgG2 exhibits a particular resistance to human and bacterial proteases that readily cleave the IgG1 hinge region in vitro. Autoantibodies (IgGs) that recognize points of proteolytic cleavage in the IgG1 hinge are widespread in the healthy human population, suggesting that IgG1 fragmentation and the generation of cryptic antigens for host immune surveillance commonly occur in vivo. We previously reported that autoantibodies to cleaved IgG1s can restore Fc-mediated effector functions that are lost following proteolytic cleavage of the hinge. In contrast, it was not possible to demonstrate an analogous cohort of autoantibodies to IgG2 hinge epitope analogs and there appeared to be no functional component in human serum with the ability to reconstitute Fc effector functions to a cell-bound IgG2 fragment. Thus, the results indicate that among the IgG subclasses, human IgG2 is uniquely resistant to a number of known pathological proteases and that autoimmune recognition to potential cleavage points in the IgG2 hinge appears to be absent in human circulation.Key words: antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, antibody-dependent cellular phagocytosis, autoantibodies     

A cluster randomised controlled trial of an occupational therapy intervention for residents with stroke living in UK care homes (OTCH): study protocol

ABSTRACT: BACKGROUND: The occupational therapy (OT) in care homes study (OTCH) aims to investigate the effect of a targeted course of individual OT (with task training, provision of adaptive equipment, minor environmental adaptations and staff education) for stroke survivors living in care homes, compared to usual care. METHODS/DESIGN: A cluster randomised controlled trial of United Kingdom (UK) care homes (n?=?90) with residents (n?=?900) who have suffered a stroke or transient ischaemic attack (TIA), and who are not receiving end-of-life care. Homes will be stratified by centre and by type of care provided and randomised (50:50) using computer generated blocked randomisation within strata to receive either the OT intervention (3 months intervention from an occupational therapist) or control (usual care). Staff training on facilitating independence and mobility and the use of adaptive equipment, will be delivered to every home, with control homes receiving this after the 12 month follow-up.Allocation will be concealed from the independent assessors, but the treating therapists, and residents will not be masked to the intervention. Measurements are taken at baseline prior to randomisation and at 3, 6 and 12 months post randomisation. The primary outcome measure is independence in self-care activities of daily living (Barthel Activities of Daily Living Index). Secondary outcome measures are mobility (Rivermead Mobility Index), mood (Geriatric Depression Scale), preference based quality of life measured from EQ-5D and costs associated with each intervention group. Quality adjusted life years (QALYs) will be derived based on the EQ-5D scores. Cost effectiveness analysis will be estimated and measured by incremental cost effectiveness ratio. Adverse events will be recorded. DISCUSSION: This study will be the largest cluster randomised controlled trial of OT in care homes to date and will clarify the currently inconclusive literature on the efficacy of OT for stroke and TIA survivors residing in care homes. TRIAL REGISTRATION: ISRCTN00757750.     

Hydrogen-bonded structure of the complex N-linked fetuin glycopeptide

The conformation of the N-linked complex glycopeptide of fetuin was examined with hydrogen-exchange techniques. The glycopeptide molecule contains eight acetamido hydrogens stemming from five N-acetylglucosamine residues and three N-acetylneuraminic acid residues and also one from the remaining sugar-peptide linkage. The hydrogen-exchange rates of these secondary amides were compared with small molecule model compounds having identical primary structures at their exchangeable hydrogen sites. Differences between the model rates and glycopeptide rates therefore cannot be accounted for by primary structure effects but reflect conformational features of the glycopeptide. Two glycopeptide hydrogens exhibit significantly hindered exchange; the rest exchange at the model rates. Removal of the three N-acetylneuraminic acid residues from terminal positions on the three branches of the glycopeptide removes the slowed hydrogens. The remaining ones continue to exchange at the model rate. These results indicate that two of the eight sugar acetamido hydrogens are involved in intramolecular hydrogen bonds. A likely structure includes two hydrogen bonds between the three N-acetylneuraminic acid residues. These two hydrogens, slowed to a moderate degree, reflect a preferred conformation stabilized by about 1 kcal/mol in free energy. The solution conformation of the glycopeptide suggested by these results is one that is partially ordered and can be easily modulated, owing to the relatively small amount of energy stabilizing the preferred conformation.     

Poly(ADP-ribose) polymerase-1 protects from oxidative stress induced endothelial dysfunction

Background

Generation of reactive oxygen species (ROS) is a key feature of vascular disease. Activation of the nuclear enzyme poly (adenosine diphosphate [ADP]-ribose) polymerase-1 (PARP-1) is a downstream effector of oxidative stress.

Methods

PARP-1(−/−) and PARP-1(+/+) mice were injected with paraquat (PQ; 10 mg/kg i.p.) to induce intracellular oxidative stress. Aortic rings were suspended in organ chambers for isometric tension recording to analyze vascular function.

Results

PQ treatment markedly impaired endothelium-dependent relaxations to acetylcholine in PARP-1(−/−), but not PARP-1(+/+) mice (p < 0.0001). Maximal relaxation was 45% in PQ treated PARP-1(−/−) mice compared to 79% in PARP-1(+/+) mice. In contrast, endothelium-independent relaxations to sodium nitroprusside (SNP) were not altered. After PQ treatment, l-NAME enhanced contractions to norepinephrine by 2.0-fold in PARP-1(−/−) mice, and those to acetylcholine by 3.3-fold, respectively, as compared to PARP-1(+/+) mice. PEG-superoxide dismutase (SOD) and PEG-catalase prevented the effect of PQ on endothelium-dependent relaxations to acetylcholine in PARP-1(−/−) mice (p < 0.001 vs. PQ treated PARP-1(+/+) mice. Indomethacin restored endothelium-dependent relaxations to acetylcholine in PQ treated PARP-1(−/−) mice (p < 0.05 vs. PQ treated PARP-1(+/+).

Conclusion

PARP-1 protects from acute intracellular oxidative stress induced endothelial dysfunction by inhibiting ROS induced production of vasoconstrictor prostanoids.     

Microarray-based, high-throughput gene expression profiling of microRNAs

MicroRNAs (miRNAs) are small regulatory RNAs that serve fundamental biological roles across eukaryotic species. We describe a new method for high-throughput miRNA detection. The technique is termed the RNA-primed, array-based Klenow enzyme (RAKE) assay, because it involves on-slide application of the Klenow fragment of DNA polymerase I to extend unmodified miRNAs hybridized to immobilized DNA probes. We used RAKE to study human cell lines and brain tumors. We show that the RAKE assay is sensitive and specific for miRNAs and is ideally suited for rapid expression profiling of all known miRNAs. RAKE offers unique advantages for specificity over northern blots or other microarray-based expression profiling platforms. Furthermore, we demonstrate that miRNAs can be isolated and profiled from formalin-fixed paraffin-embedded tissue, which opens up new opportunities for analyses of small RNAs from archival human tissue. The RAKE assay is theoretically versatile and may be used for other applications, such as viral gene profiling.