Muscle thixotropy: more than just cross-bridges?

AbstractAlthough Campbell and Lakie in a Comment to the Editor in this issue of Biophysical Journal suggested that exclusive cross-bridge action is behind muscle thixotropy, recent findings and our preliminary observations suggest that additional mechanisms could also be involved

Inotropic interventions do not change the resting state of myosin motors during cardiac diastole

When striated (skeletal and cardiac) muscle is in its relaxed state, myosin motors are packed in helical tracks on the surface of the thick filament, folded toward the center of the sarcomere, and unable to bind actin or hydrolyze ATP (OFF state). This raises the question of whatthe mechanism is that integrates the Ca2+-dependent thin filament activation, making myosin heads available for interaction with actin. Here we test the interdependency of the thin and thick filament regulatory mechanisms in intact trabeculae from the rat heart. We record the x-ray diffraction signals that mark the state of the thick filament during inotropic interventions (increase in sarcomere length from 1.95 to 2.25 µm and addition of 10-7 M isoprenaline), which potentiate the twitch force developed by an electrically paced trabecula by up to twofold. During diastole, none of the signals related to the OFF state of the thick filament are significantly affected by these interventions, except the intensity of both myosin-binding protein C- and troponin-related meridional reflections, which reduce by 20% in the presence of isoprenaline. These results indicate that recruitment of myosin motors from their OFF state occurs independently and downstream from thin filament activation. This is in agreement with the recently discovered mechanism based on thick filament mechanosensing in which the number of motors available for interaction with actin rapidly adapts to the stress on the thick filament and thus to the loading conditions of the contraction. The gain of this positive feedback may be modulated by both sarcomere length and the degree of phosphorylation of myosin-binding protein C

Parkinson's disease in Gaucher disease patients: What's changing in the counseling and management of patients and their relatives?

Background: How to address the counseling of lifetime risk of developing Parkinson's disease in patients with Gaucher disease and their family members carrying a single variant of the GBA1 gene is not yet clearly defined. In addition, there is no set way of managing Gaucher disease patients, taking into account the possibility that they may show features of Parkinson's disease. Methods: Starting from an overview on what has recently changed in our knowledge on this issue and grouping the experiences of healthcare providers of Gaucher disease patients, we outline a path of counseling and management of Parkinson's disease risk in Gaucher disease patients and their relatives. Conclusion: The approach proposed here will help healthcare providers to communicate Parkinson's disease risk to their patients and will reduce the possibility of patients receiving inaccurate information from inadequate sources. Furthermore, this resource will help to empower healthcare providers to identify early signs and/or symptoms of Parkinson's disease and decide when to refer these patients to the neurologist for appropriate specific therapy and follow-up

FSH treatment improves sperm DNA damage in men with idiopathic infertility carriers of the FSH receptor p.N680S homozygous N genotype: an interim analysis

Study question: To assess whether in men with idiopathic infertility, the sperm DNA fragmentation (sDF) improves depending on the FSH receptor (FSHR) genotype as assessed by the non-synonymous polymorphisms (SNP) rs6166 (wild type or p.N680S). Summary answer: FSH treatment improves sDF in a subgroup of idiopathic infertile men, although 40% of these men do not show any significant improve- ment. The response of sDF, a surrogate marker of sperm quality, together with the evaluation of FSHR SNP p.N680S might be useful to predict the response to FSH treatment. What is known already: FSH is fundamental for spermatogenesis and is em- pirically used to treat male idiopathic infertility. Several studies suggest that sDF could be a candidate predictor of response to FSH treatment, in terms of probability to conceive. Furthermore, it is widely accepted that the FSHR SNP p.N680S influences ovarian response in women and testicular volume in men. Study design, size, duration: Multicenter, longitudinal, prospective, open-la- bel, two-arms clinical trial. Subjects enrolled were idiopathic infertile men and received 150 IU of recombinant FSH (Gonal f®) every other day for 12 weeks and were then followed-up for further 12 weeks after FSH-withdrawal. Patients were evaluated at baseline and at the end of the two phases. Participants/materials, setting, methods: Eighty-eight men with idiopathic male infertility carrier of the homozygous FSHR p.N680S N or S genotype, FSH 15%, were enrolled. 66 patients completed the sDF analysis. sDF was centrally evaluated by TUNEL/PI assay coupled to flow cy- tometry, resolving two different sperm populations, namely: PIbrighter and PIdimmer. Main results and the role of chance: Thirty-seven men (56%) were carriers of the p.N680S homozygous-N and 29 (44%) of the homozygous-S genotype, respectively. Total sDF (PIbrighter + PIdimmer) was significantly lower at the end of the study in patients carriers of the p.N680S-N allele than patients carri- ers of p.N680S-S allele (p = 0.008). Only in patients carriers of the p.N680S-N allele, total sDF decreased significantly from baseline to the end of the study (p = 0.021) and this decrease was entirely sustained by the sperm population containing vital sperms (i.e., PIbrighter fraction) (p = 0.008). PIdimmer frac- tion, including only non-vital sperms, was significantly higher in patients car- riers of the p.N680S-S allele than in carriers of N allele (p = 0.018). Total sDF was inversely related to total sperm number (p = 0.020) and progressive sperm motility (p = 0.014). Limitations, reason for caution: The statistical power of the results obtained so far is 86.9%, with alpha-error 0.05. This is an interim-analysis. Wider implications of the findings: The study suggests that FSH treatment induces a significant improvement of total sDF in men carriers of the p.N680S homozygous N allele. This sDF decrease awaits confirmation, since the study will be completed by June 2015. Study funding/competing interest(s): Funding by commercial/corporate company(ies) – The study was supported by unrestricted grant by Merck Serono. Trial registration number: EudraCT number 2010-020240-35. Keywords: FSH treatment, male infertility, Sperm-DNA fragmentatio

ErbB2 and bone sialoprotein as markers for metastatic osteosarcoma cells

Osteosarcoma is the most common malignant bone neoplasia occurring in young patients in the first two decades of life, and represents 20% of all primitive malignant bone tumours. At present, treatment of metastatic osteosarcoma is unsatisfactory. High-dose chemotherapy followed by CD34+ leukapheresis rescue may improve these poor results. Neoplastic cells contaminating the apheresis may, however, contribute to relapse. To identify markers suitable for detecting osteosarcoma cells in aphereses we analysed the expression of bone-specific genes (Bone Sialoprotein (BSP) and Osteocalcin) and oncogenes (Met and ErbB2) in 22 patients with metastatic osteosarcoma and six healthy stem cell donors. The expression of these genes in aphereses of patients affected by metastatic osteosarcoma was assessed by RT–PCR and Southern blot analysis. Met and Osteocalcin proved to be not useful markers since they are positive in aphereses of both patients with metastatic osteosarcoma and healthy stem cell donors. On the contrary, BSP was expressed at significant levels in 85% of patients. Moreover, 18% of patients showed a strong and significantly positive (seven to 16 times higher than healthy stem cell donors) ErbB2 expression. In all positive cases, neoplastic tissue also expressed ErbB2. Our data show that ErbB2 can be a useful marker for tumour contamination in aphereses of patients affected by ErbB2-expressing osteosarcomas and that analysis of Bone Sialoprotein expression can be an alternative useful marker

Interactions between Connected Half-Sarcomeres Produce Emergent Mechanical Behavior in a Mathematical Model of Muscle

Most reductionist theories of muscle attribute a fiber's mechanical properties to the scaled behavior of a single half-sarcomere. Mathematical models of this type can explain many of the known mechanical properties of muscle but have to incorporate a passive mechanical component that becomes ∼300% stiffer in activating conditions to reproduce the force response elicited by stretching a fast mammalian muscle fiber. The available experimental data suggests that titin filaments, which are the mostly likely source of the passive component, become at most ∼30% stiffer in saturating Ca2+ solutions. The work described in this manuscript used computer modeling to test an alternative systems theory that attributes the stretch response of a mammalian fiber to the composite behavior of a collection of half-sarcomeres. The principal finding was that the stretch response of a chemically permeabilized rabbit psoas fiber could be reproduced with a framework consisting of 300 half-sarcomeres arranged in 6 parallel myofibrils without requiring titin filaments to stiffen in activating solutions. Ablation of inter-myofibrillar links in the computer simulations lowered isometric force values and lowered energy absorption during a stretch. This computed behavior mimics effects previously observed in experiments using muscles from desmin-deficient mice in which the connections between Z-disks in adjacent myofibrils are presumably compromised. The current simulations suggest that muscle fibers exhibit emergent properties that reflect interactions between half-sarcomeres and are not properties of a single half-sarcomere in isolation. It is therefore likely that full quantitative understanding of a fiber's mechanical properties requires detailed analysis of a complete fiber system and cannot be achieved by focusing solely on the properties of a single half-sarcomere

Tracker Operation and Performance at the Magnet Test and Cosmic Challenge

During summer 2006 a fraction of the CMS silicon strip tracker was operated in a comprehensive slice test called the Magnet Test and Cosmic Challenge (MTCC). At the MTCC, cosmic rays detected in the muon chambers were used to trigger the readout of all CMS sub-detectors in the general data acquisition system and in the presence of the 4 T magnetic field produced by the CMS superconducting solenoid. This document describes the operation of the Tracker hardware and software prior, during and after data taking. The performance of the detector as resulting from the MTCC data analysis is also presented