Approximating complex musculoskeletal biomechanics using multidimensional autogenerating polynomials

Computational models of the musculoskeletal system are scientific tools used to study human movement, quantify the effects of injury and disease, plan surgical interventions, or control realistic high-dimensional articulated prosthetic limbs. If the models are sufficiently accurate, they may embed complex relationships within the sensorimotor system. These potential benefits are limited by the challenge of implementing fast and accurate musculoskeletal computations. A typical hand muscle spans over 3 degrees of freedom (DOF), wrapping over complex geometrical constraints that change its moment arms and lead to complex posture-dependent variation in torque generation. Here, we report a method to accurately and efficiently calculate musculotendon length and moment arms across all physiological postures of the forearm muscles that actuate the hand and wrist. Then, we use this model to test the hypothesis that the functional similarities of muscle actions are embedded in muscle structure. The posture dependent muscle geometry, moment arms and lengths of modeled muscles were captured using autogenerating polynomials that expanded their optimal selection of terms using information measurements. The iterative process approximated 33 musculotendon actuators, each spanning up to 6 DOFs in an 18 DOF model of the human arm and hand, defined over the full physiological range of motion. Using these polynomials, the entire forearm anatomy could be computed in <10 μs, which is far better than what is required for real-time performance, and with low errors in moment arms (below 5%) and lengths (below 0.4%). Moreover, we demonstrate that the number of elements in these autogenerating polynomials does not increase exponentially with increasing muscle complexity; complexity increases linearly instead. Dimensionality reduction using the polynomial terms alone resulted in clusters comprised of muscles with similar functions, indicating the high accuracy of approximating models. We propose that this novel method of describing musculoskeletal biomechanics might further improve the applications of detailed and scalable models to describe human movement.     

Structural basis for sequential cleavage of fibrinopeptides upon fibrin assembly

Nonsubstrate interaction of thrombin with fibrinogen promotes sequential cleavage of fibrinopeptides A and B (fpA and fpB, respectively) from the latter, resulting in its conversion into fibrin. The recently established crystal structure of human thrombin in complex with the central part of human fibrin clarified the mechanism of this interaction. Here, we reveal new details of the structure and present the results of molecular modeling of the fpA- and fpB-containing portions of the Aalpha and Bbeta chains, not identified in the complex, in both fibrinogen and protofibrils. The analysis of the results reveals that in fibrinogen the fpA-containing portions are in a more favorable position to bind in the active site cleft of bound thrombin. Surface plasmon resonance experiments establish that the fpB-containing portions interact with the fibrin-derived dimeric D-D fragment, suggesting that in protofibrils they bind to the newly formed DD regions bringing fpB into the vicinity of bound thrombin. These findings provide a coherent rationale for the preferential removal of fpA from fibrinogen at the first stage of fibrin assembly and the accelerated cleavage of fpB from protofibrils and/or fibrils at the second stage.     

GSM 900 MHz microwave radiation affects embryo development of Japanese quails

A wide range of non thermal biological effects of microwave radiation (MW) was revealed during the last decades. A number of reports showed evident hazardous effects of MW on embryo development in chicken. In this study, we aimed at elucidating the effects of MW emitted by a commercial model of GSM 900 MHz cell phone on embryo development in quails (Coturnix coturnix japonica) during both short and prolonged exposure. For that, fresh fertilized eggs were irradiated during the first 38 h or 14 days of incubation by a cell phone in "connecting" mode activated continuously through a computer system. Maximum intensity of incident radiation on the egg's surface was 0.2 μW/cm2.The irradiation led to a significant (p<0.001) increase in numbers of differentiated somites in 38-hour exposed embryos and to a significant (p<0.05) increase in total survival of embryos from exposed eggs after 14 days exposure. We hypothesized that observed facilitating effect was due to enhancement of metabolism in exposed embryos provoked via peroxidation mechanisms. Indeed, a level of thiobarbituric acid (TBA) reactive substances was significantly (p<0.05-0.001) higher in brains and livers of hatchlings from exposed embryos. Thus, observed effects of radiation from commercial GSM 900 MHz cell phone on developing quail embryos signify a possibility for non-thermal impact of MW on embryogenesis. We suggest that the facilitating effect of low doses of irradiation on embryo development can be explained by a hormesis effect induced by reactive oxygen species (ROS). Future studies need to be done to clarify this assumption.     

Tumour promoting and suppressing roles of the atypical MAP kinase signalling pathway ERK3/4-MK5

ABSTRACT: Perturbed action of signal transduction pathways, including the mitogen-activated protein (MAP) kinase pathways, is one of the hallmarks of many cancers. While the implication of the typical MAP kinase pathways ERK1/2-MEK1/2, p38MAPK and JNK is well established, recent findings illustrate that the atypical MAP kinase ERK3/4-MK5 may also be involved in tumorigenic processes. Remarkably, the ERK3/4-MK5 pathway seems to possess anti-oncogenic as well as pro-oncogenic properties in cell culture and aninal models. This review summarizes the mutations in the genes encoding ERK3, ERK4 and MK5 that have been detected in different cancers, reports aberrant expression levels of these proteins in human tumours, and discusses the mechanisms by which this pathway can induce senescence, stimulate angiogenesis and invasiveness.     

Nitroalkenes confer acute cardioprotection via adenine nucleotide translocase 1

Electrophilic nitrated lipids (nitroalkenes) are emerging as an important class of protective cardiovascular signaling molecules. Although species such as nitro-linoleate (LNO(2)) and nitro-oleate can confer acute protection against cardiac ischemic injury, their mechanism of action is unclear. Mild uncoupling of mitochondria is known to be cardioprotective, and adenine nucleotide translocase 1 (ANT1) is a key mediator of mitochondrial uncoupling. ANT1 also contains redox-sensitive cysteines that may be targets for modification by nitroalkenes. Therefore, in this study we tested the hypothesis that nitroalkenes directly modify ANT1 and that nitroalkene-mediated cardioprotection requires ANT1. Using biotin-tagged LNO(2) infused into intact perfused hearts, we obtained mass spectrometric (MALDI-TOF-TOF) evidence for direct modification (nitroalkylation) of ANT1 on cysteine 57. Furthermore, in a cell model of ischemia-reperfusion injury, siRNA knockdown of ANT1 inhibited the cardioprotective effect of LNO(2). Although the molecular mechanism linking ANT1-Cys(57) nitroalkylation and uncoupling is not yet known, these data suggest that ANT1-mediated uncoupling may be a mechanism for nitroalkene-induced cardioprotection.     

Modulation of Cell Surface Protein Free Thiols: A Potential Novel Mechanism of Action of the Sesquiterpene Lactone Parthenolide

Background

There has been much interest in targeting intracellular redox pathways as a therapeutic approach for cancer. Given recent data to suggest that the redox status of extracellular protein thiol groups (i.e. exofacial thiols) effects cell behavior, we hypothesized that redox active anti-cancer agents would modulate exofacial protein thiols.

Methodology/Principal Findings

To test this hypothesis, we used the sesquiterpene lactone parthenolide, a known anti-cancer agent. Using flow cytometry, and western blotting to label free thiols with Alexa Fluor 633 C₅ maleimide dye and N-(biotinoyl)-N-(iodoacetyl) ethylendiamine (BIAM), respectively, we show that parthenolide decreases the level of free exofacial thiols on Granta mantle lymphoma cells. In addition, we used immuno-precipitation techniques to identify the central redox regulator thioredoxin, as one of the surface protein thiol targets modified by parthenolide. To examine the functional role of parthenolide induced surface protein thiol modification, we pretreated Granta cells with cell impermeable glutathione (GSH), prior to exposure to parthenolide, and showed that GSH pretreatment; (a) inhibited the interaction of parthenolide with exofacial thiols; (b) inhibited parthenolide mediated activation of JNK and inhibition of NFκB, two well established mechanisms of parthenolide activity and; (c) blocked the cytotoxic activity of parthenolide. That GSH had no effect on the parthenolide induced generation of intracellular reactive oxygen species supports the fact that GSH had no effect on intracellular redox. Together these data support the likelihood that GSH inhibits the effect of parthenolide on JNK, NFκB and cell death through its direct inhibition of parthenolide''s modulation of exofacial thiols.

Conclusions/Significance

Based on these data, we postulate that one component of parthenolide''s anti-lymphoma activity derives from its ability to modify the redox state of critical exofacial thiols. Further, we propose that cancer cell exofacial thiols may be important and novel targets for therapy.     

PKA-induced F-actin rearrangement requires phosphorylation of Hsp27 by the MAPKAP kinase MK5

Mitogen-activated protein kinase (MAPK) pathways can play a role in F-actin dynamics. In particular, the p38 MAPK/MAPK-activated protein kinase 2 (MK2)/heat shock protein 27 (Hsp27) pathway is involved in F-actin alternations. Previously, we showed that MK5 is implicated in F-actin rearrangement induced by the cAMP/cAMP-dependent protein kinase pathway in PC12 cells, while others found Hsp27 to be a good in vitro MK5 substrate. Here we demonstrate that MK5 can specifically interact with Hsp27 in vivo and can induce phosphorylation at serine residues 78 and 82 in cells. siRNA-mediated depletion of Hsp27 protein levels, as well as overexpression of the non-phosphorylatable Hsp27-3A mutant prevented forskolin-induced F-actin reorganization. While ectopic expression of a constitutive active MK5 mutant was sufficient to induce F-actin rearrangement in PC12 cells, co-expression of Hsp27-3A could ablate this process. Our results imply that MK5 is involved in Hsp27-controlled F-actin dynamics in response to activation of the cAMP-dependent protein kinase pathway. These findings render the MK5/Hsp27 connection into a putative therapeutic target for conditions with aberrant Hsp27 phosphorylation such as metastasis, cardiovascular diseases, muscle atrophy, autoimmune skin disease and neuropathology.     

Synthesis and biological study of 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines as potent and selective serotonin 5-HT6 receptor antagonists

A number of 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines were prepared and their 5-HT₆ receptor binding affinity and ability to inhibit the functional cellular responses to serotonin were evaluated. 3-[(3-Chlorophenyl)sulfonyl]-N-(tetrahydrofuran-2-ylmethyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidin-5-amine 2{5,26} appeared to be the most active in a functional assay (IC₅₀ = 29.0 nM) and 3-(phenylsulfonyl)-N-(2-thienylmethyl) thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidin-5-amine 2{1,28} demonstrated the greatest affinity in a 5-HT₆ receptor radioligand binding assay (K_i = 1.7 nM). A screening of 5-HT_2A and 5-HT_2B receptor affinity revealed that 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines are highly selective 5-HT₆ receptor ligands.