Dynamic shear behavior of mandibular condylar cartilage is dependent on testing direction

Little information is available on the direction-dependency of shear behavior in mandibular condylar cartilage. Therefore, we tested the hypothesis that such a dependency of the dynamic shear properties is present in mandibular condylar cartilage. From each of 17 condyles, two cartilage-bone plugs were dissected and tested in a simple shear sandwich configuration under a compressive strain of 10%. Sinusoidal shear strain (frequency range: 0.01-10 Hz) was applied in the medio-lateral or antero-posterior direction with an amplitude of 1.0%, 2.0%, and 3.0%. The magnitudes of the dynamic shear moduli, as calculated from the resulting shear stress, were found to increase with applied frequency and the shear strain amplitude. The values |G*|, G' and G' for a medio-laterally applied shear were about 20-33% of those in the antero-posterior shear, although the loss tangent (elasticity/viscosity ratio) was almost the same. In conclusion, the present results clearly show the direction-dependent characteristic of the mandibular condylar cartilage in dynamic shear.     

The apparent permeability coefficient for proton flux through phosphatidylcholine vesicles is dependent on the direction of flux

A dioleoylphosphatidylcholine unilamellar vesicle model system was used to determine proton permeability. The fluorescence of the pH reporter group, pyranine, trapped within vesicles with a difference in pH across the bilayer, was digitized and analyzed with numerical integration. When H+ flux was initiated by the acidification of the external buffer (acid jump), the apparent H+ permeability was found to be a linear function of the reciprocal of the internal H+ concentration with the slope inversely proportional to the initial size of the H+ gradient. When flux was initiated by the alkalinization of the external buffer (base jump), the apparent permeability coefficient was constant for each external H+ concentration. However, the value of the apparent permeability was linearly dependent on the reciprocal of the external H+. The possibility that carbonates (carbon dioxide, carbonic acid, bicarbonate and carbonate) could be acting as proton carriers was tested by adding millimolar concentrations of bicarbonate to solutions greatly reduced in carbonates. The slopes of the graphs of apparent permeability coefficient vs. reciprocal H+ were linear functions of added bicarbonate concentration for both acid and base jump conditions. These observations were interpreted in terms of a model suggesting that carbonic acid or carbon dioxide together with bicarbonate was an efficient proton carrier across phospholipid bilayers.     

Kinetic stability of Cu/Zn superoxide dismutase is dependent on its metal ligands: implications for ALS

Over 100 mutants of the enzyme Cu/Zn superoxide dismutase (SOD) have been implicated in the neurodegenerative disease familial amyotrophic lateral sclerosis (FALS). Growing evidence suggests that the aggregation of SOD mutants may play a causative role in FALS and that aberrant copper chemistry, decreased thermodynamic stability, and decreased affinity for metals may contribute independently or synergistically to this process. Since the loss of the copper and zinc ions significantly decreases the thermodynamic stability of SOD, it is expected that this would also decrease its kinetic stability, thereby facilitating partial or global unfolding transitions that may lead to misfolding and aggregation. Here we used wild-type (WT) SOD and five FALS-related mutants (G37R, H46R, G85R, D90A, and L144F) to show that the metals contribute significantly to the kinetic stability of the protein, with demetalated (apo) SOD showing acid-induced unfolding rates about 60-fold greater than the metalated (holo) protein. However, the unfolding rates of SOD WT and mutants were similar to each other in both the holo and apo states, indicating that regardless of the effect of mutation on thermodynamic stability, the kinetic barrier toward SOD unfolding is dependent on the presence of metals. Thus, these results suggest that pathogenic SOD mutations that do not significantly alter the stability of the protein may still lead to SOD aggregation by compromising its ability to bind or retain its metals and thereby decrease its kinetic stability. Furthermore, the mutant-like decrease in the kinetic stability of apo WT SOD raises the possibility that the loss of metals in WT SOD may be involved in nonfamilial forms of ALS.     

Efficacy of RNA amplification is dependent on sequence characteristics: implications for gene expression profiling using a cDNA microarray

Minute tissue samples or single cells increasingly provide the starting material for gene expression profiling, which often requires RNA amplification. Although much effort has been put into optimizing amplification protocols, the relative abundance of RNA templates in the amplified product is frequently biased. We applied a T7 polymerase-based technique to amplify RNA from two tissues of a cichlid fish and compared expression levels of unamplified and amplified RNA on a cDNA microarray. Amplification bias was generally minor and comprised features that were lost (1.3%) or gained (2.5%) through amplification and features that were scored as regulated before but unregulated after amplification (4.2%) or vice versa (19.5%). We examined 10 sequence-specific properties and found that GC content, folding energy, hairpin length and number, and lengths of poly(A) and poly(T) stretches significantly affected RNA amplification. We conclude that, if RNA amplification is used in gene expression studies, preceding experiments controlling for amplification bias should be performed.     

The phenotype of inflammatory macrophages is stimulus dependent: implications for the nature of the inflammatory response

Many diseases are characterized by inflammatory reactions involving both the innate and adaptive arms of the immune system. Thioglycolate medium (TM) injection into the peritoneal cavity has long been used as a stimulus for eliciting inflammatory macrophages for study and for determining the importance of a particular mediator in inflammation. However, the response to this irritant may not be relevant to many inflammatory diseases. Therefore, we have developed an Ag-specific peritonitis model using methylated BSA (mBSA) as the stimulus. Priming mice intradermally with mBSA in adjuvant and boosting 14 days later, followed by an i.p. challenge with mBSA after an additional 7 days, led to an inflammatory reaction equivalent in magnitude to that induced with TM as judged by the number of exudate cells. The inflammatory macrophages elicited by the mBSA protocol differed, being smaller and less vacuolated than TM-elicited macrophages. Also, macrophages from 4-day mBSA-induced exudates expressed more MHC class II than TM-induced exudates, were able to stimulate allogeneic T lymphocytes, and upon in vitro stimulation with LPS secreted greater levels of IL-6 and IL-1beta. Macrophages from 4-day TM-induced exudates, on the other hand, expressed Ly6C and ER-MP58, immature myeloid markers. The inflammatory response elicited using the Ag mBSA may be more relevant for studying the inflammatory responses in many diseases, such as those of autoimmune origin and those involving an acquired immune response.     

Variability and its implications for host-parasite interactions

Variability in host-parasite interactions has considerable impact on the ecology and evolution of parasites and on the epidemiology of disease. The nature of the impact depends largely on the level of ecological organization where variability occurs: variability of parasites within their individual hosts, variability of host individuals within populations, or variability of hosts and parasites among populations. In this review, Paul Schmid-Hempel and Jacob Koella give some examples of variability at each of these levels, with particular emphasis on microparasites (defined broadly as viruses, bacteria and protozoa), consider the maintenance of the variability, and describe the implications of variability for the epidemiology of disease and the ecology of host parasite associations. In particular, they describe how variability at each level of ecological organization can affect the perception of AIDS and the evolution of virulence.     

Force variability is mostly not motor noise: Theoretical implications for motor control

Variability in muscle force is a hallmark of healthy and pathological human behavior. Predominant theories of sensorimotor control assume ‘motor noise’ leads to force variability and its ‘signal dependence’ (variability in muscle force whose amplitude increases with intensity of neural drive). Here, we demonstrate that the two proposed mechanisms for motor noise (i.e. the stochastic nature of motor unit discharge and unfused tetanic contraction) cannot account for the majority of force variability nor for its signal dependence. We do so by considering three previously underappreciated but physiologically important features of a population of motor units: 1) fusion of motor unit twitches, 2) coupling among motoneuron discharge rate, cross-bridge dynamics, and muscle mechanics, and 3) a series-elastic element to account for the aponeurosis and tendon. These results argue strongly against the idea that force variability and the resulting kinematic variability are generated primarily by ‘motor noise.’ Rather, they underscore the importance of variability arising from properties of control strategies embodied through distributed sensorimotor systems. As such, our study provides a critical path toward developing theories and models of sensorimotor control that provide a physiologically valid and clinically useful understanding of healthy and pathologic force variability.     

Learning new gait patterns is enhanced by specificity of training rather than progression of task difficulty

The use of motor learning strategies may enhance rehabilitation outcomes of individuals with neurological injuries (e.g., stroke or cerebral palsy). A common strategy to facilitate learning of challenging tasks is to use sequential progression – i.e., initially reduce task difficulty and slowly increase task difficulty until the desired difficulty level is reached. However, the evidence related to the use of such sequential progressions to improve learning is mixed for functional skill learning tasks, especially considering situations where practice duration is limited. Here, we studied the benefits of sequential progression using a functional motor learning task that has been previously used in gait rehabilitation. Three groups of participants (N = 43) learned a novel motor task during treadmill walking using different learning strategies. Participants in the specific group (n = 21) practiced only the criterion task (i.e., matching a target template that was scaled-up by 30%) throughout the training. Participants in the sequential group (n = 11) gradually progressed to the criterion task (from 3% to 30% in increments of 3%), whereas participants in the random group (n = 11) started at 3% and progressed in random increments (involving both increases and decreases in task difficulty) to the criterion task. At the end of training, kinematic tracking performance on the criterion task was evaluated in all participants both with and without visual feedback. Results indicated that the tracking error was significantly lower in the specific group, and no differences were observed between the sequential and the random progression groups. The findings indicate that the amount of practice in the criterion task is more critical than the difficulty and variations of task practice when learning new gait patterns during treadmill walking.     

Activation of blood coagulation in cancer: implications for tumour progression

Several studies have suggested a role for blood coagulation proteins in tumour progression. Herein, we discuss (1) the activation of the blood clotting cascade in the tumour microenvironment and its impact on primary tumour growth; (2) the intravascular activation of blood coagulation and its impact on tumour metastasis and cancer-associated thrombosis; and (3) antitumour therapies that target blood-coagulation-associated proteins. Expression levels of the clotting initiator protein TF (tissue factor) have been correlated with tumour cell aggressiveness. Simultaneous TF expression and PS (phosphatidylserine) exposure by tumour cells promote the extravascular activation of blood coagulation. The generation of blood coagulation enzymes in the tumour microenvironment may trigger the activation of PARs (protease-activated receptors). In particular, PAR1 and PAR2 have been associated with many aspects of tumour biology. The procoagulant activity of circulating tumour cells favours metastasis, whereas the release of TF-bearing MVs (microvesicles) into the circulation has been correlated with cancer-associated thrombosis. Given the role of coagulation proteins in tumour progression, it has been proposed that they could be targets for the development of new antitumour therapies.     

DMRT3 is associated with gait type in Mangalarga Marchador horses,but does not control gait ability

The Mangalarga Marchador (MM) is a Brazilian horse breed known for a uniquely smooth gait. A recent publication described a mutation in the DMRT3 gene that the authors claim controls the ability to perform lateral patterned gaits (Andersson et al. 2012). We tested 81 MM samples for the DMRT3 mutation using extracted DNA from hair bulbs using a novel RFLP. Horses were phenotypically categorized by their gait type (batida or picada), as recorded by the Brazilian Mangalarga Marchador Breeders Association (ABCCMM). Statistical analysis using the plink toolset (Purcell, 2007) revealed significant association between gait type and the DMRT3 mutation (P = 2.3e‐22). Deviation from Hardy–Weinberg equilibrium suggests that selective pressure for gait type is altering allele frequencies in this breed (P = 1.00e‐5). These results indicate that this polymorphism may be useful for genotype‐assisted selection for gait type within this breed. As both batida and picada MM horses can perform lateral gaits, the DMRT3 mutation is not the only locus responsible for the lateral gait pattern.     

The effects of muscle vibration on gait control: a review

Abstract

Background: The purpose of the review is to summarize the literature surrounding the use of muscle vibration as it relates to modifying human gait.

Methods: After a brief introduction concerning historical uses and early research identifying the effect of vibration on muscle activation, we reviewed 32 articles that used muscle vibration during walking. The review is structured to address the literature within four broad categories: the effect of vibration to ‘trigger’ gait-like lower limb motions, the effect of vibration on gait control of healthy individuals and individuals with clinical conditions in which gait disorders are a prominent feature, and the effect of vibration training protocols on gait.

Results: The acute effects of vibration during gait involving healthy participants is varied. Some authors reported differences in segmental kinematic and spatiotemporal measures while other authors reported no differences in these outcome measures. The literature involving participants with clinical conditions revealed that vibration consistently had a significant impact on gait, suggesting vibration may be an effective rehabilitation tool. All of the studies that used vibration therapy over time reported significant improvement in gait performance.

Conclusions: This review highlights the difficulties in drawing definitive conclusions as to the impact of vibration on gait control, partly because of differences in walking protocols, site of vibration application, and outcome measures used across different investigative teams. It is suggested that the development of common investigative methodologies and outcome measures would accelerate the identification of techniques that may provide optimal rehabilitation protocols for individuals experiencing disordered gait control.     

Atheroprotective immunization with malondialdehyde-modified LDL is hapten specific and dependent on advanced MDA adducts: implications for development of an atheroprotective vaccine

Immunization with homologous malondialdehyde (MDA)-modified LDL (MDA-LDL) leads to atheroprotection in experimental models supporting the concept that a vaccine to oxidation-specific epitopes (OSEs) of oxidized LDL could limit atherogenesis. However, modification of human LDL with OSE to use as an immunogen would be impractical for generalized use. Furthermore, when MDA is used to modify LDL, a wide variety of related MDA adducts are formed, both simple and more complex. To define the relevant epitopes that would reproduce the atheroprotective effects of immunization with MDA-LDL, we sought to determine the responsible immunodominant and atheroprotective adducts. We now demonstrate that fluorescent adducts of MDA involving the condensation of two or more MDA molecules with lysine to form malondialdehyde-acetaldehyde (MAA)-type adducts generate immunodominant epitopes that lead to atheroprotective responses. We further demonstrate that a T helper (Th) 2-biased hapten-specific humoral and cellular response is sufficient, and thus, MAA-modified homologous albumin is an equally effective immunogen. We further show that such Th2-biased humoral responses per se are not atheroprotective if they do not target relevant antigens. These data demonstrate the feasibility of development of a small-molecule immunogen that could stimulate MAA-specific immune responses, which could be used to develop a vaccine approach to retard or prevent atherogenesis.     

Ligand-dependent tau filament formation: implications for Alzheimer's disease progression.

The mechanism through which arachidonic acid induces the polymerization of tau protein into filaments under reducing conditions was characterized through a combination of fluorescence spectroscopy and electron microscopy. Results show that polymerization follows a ligand-mediated mechanism, where binding of arachidonic acid is an obligate step preceding tau-tau interaction. Homopolymerization begins with rapid (on the order of seconds) nucleation, followed by a slower elongation phase (on the order of hours). Although essentially all synthetic filaments have straight morphology at early time points, they interact with thioflavin-S and monoclonal antibody Alz50 much like authentic paired helical filaments, suggesting that the conformation of tau protein is similar in the two filament forms. Over a period of days, synthetic straight filaments gradually adopt paired helical morphology. These results define a novel pathway of tau filament formation under reducing conditions, where oxidation may contribute to final paired helical morphology, but is not a necessary prerequisite for efficient nucleation or elongation of tau filaments.     

Mutation is modulated: implications for evolution

Evolution occurs through genome variation followed by selection. Because DNA sequence context affects the activity of enzymes that copy, move and repair DNA, there are intrinsic variations in the probability of genetic variation along a genome. These intrinsic variations can be affected by selective pressure. Codon changes that do not alter the encoded amino acids may still have effects on the local rate of sequence change. Large gene families could encode a successful genetic framework by which to evolve new, functional members. The speed of adaptation to environmental challenges may be improved when the distinct mechanisms of genetic change come under regulatory control. Natural selection operates on mechanisms that generate and modulate diversity as it does on all biological functions.     

Influence of gait speed on the control of mediolateral dynamic stability during gait initiation

This study investigated the influence of gait speed on the control of mediolateral dynamic stability during gait initiation. Thirteen healthy young adults initiated gait at three self-selected speeds: Slow, Normal and Fast. The results indicated that the duration of anticipatory postural adjustments (APA) decreased from Slow to Fast, i.e. the time allocated to propel the centre of mass (COM) towards the stance-leg side was shortened. Likely as an attempt at compensation, the peak of the anticipatory centre of pressure (COP) shift increased. However, COP compensation was not fully efficient since the results indicated that the mediolateral COM shift towards the stance-leg side at swing foot-off decreased with gait speed. Consequently, the COM shift towards the swing-leg side at swing heel-contact increased from Slow to Fast, indicating that the mediolateral COM fall during step execution increased as gait speed rose. However, this increased COM fall was compensated by greater step width so that the margin of stability (the distance between the base-of-support boundary and the mediolateral component of the “extrapolated centre of mass”) at heel-contact remained unchanged across the speed conditions. Furthermore, a positive correlation between the mediolateral extrapolated COM position at heel-contact and step width was found, indicating that the greater the mediolateral COM fall, the greater the step width. Globally, these results suggest that mediolateral APA and step width are modulated with gait speed so as to maintain equivalent mediolateral dynamical stability at the time of swing heel-contact.     

Chemotaxis: Movement,direction, control

This review focuses on basic principles of motility in different cell types, formation of the specific cell structures that enable directed migration, and how external signals are transduced into cells and coupled to the motile machinery. Feedback mechanisms and their potential role in maintenance of internal chemotactic gradients and persistence of directed migration are highlighted.