Effects of electrically induced fatigue on the twitch and tetanus of paralyzed soleus muscle in humans

Shields, Richard K., Laura Frey Law, Brenda Reiling, KellySass, and Jason Wilwert. Effects of electrically induced fatigueon the twitch and tetanus of paralyzed soleus muscle in humans.J. Appl. Physiol. 82(5):1499-1507, 1997.We analyzed the twitch and summated torque(tetanus) during repetitive activation and recovery of the human soleusmuscle in individuals with spinal cord injury. Thirteen individualswith complete paralysis (9 chronic, 4 acute) had the tibial nerveactivated every 1,500 ms with a 20-Hz train (7 stimuli) for 300 ms anda single pulse at 1,100 ms. The stimulation protocol lasted 3 min andincluded 120 twitches and 120 tetani. Minimal changes were found forthe acute group. The chronic group showed a significant reduction inthe torque and a significant slowing of the contractile speeds of boththe twitch and tetanus. The decrease in the peak twitch torque was significantly greater than the decrease in the peak tetanus torque early during the fatigue protocol for the chronic group. The twitch time to peak and half relaxation time were prolonged during fatigue, which was associated with improved fusion of the tetanus torque. At theend of the fatigue protocol, the decrease in the peak twitch torque wasnot significantly different from the decrease in the peak tetanustorque. After 5 min of rest, the contractile speeds recovered causingthe tetanus to become unfused, but the tetanus torque became lessdepressed than the twitch torque. The differential responses for thetwitch and the tetanus suggest an interplay between optimal fusioncreated from contractile speed slowing and excitation contractioncoupling compromise. These issues make the optimal design of functionalelectrical stimulation systems a formidable task.

     

Terminal regions of mouse nebulin: sequence analysis and complementary localization with N-RAP

The regions of mouse nebulin extending from the ends of the super repeats to the C-terminus and N-terminus were cloned and sequenced. Comparison of the mouse sequence with the previously published human sequence shows that the terminal regions of nebulin are highly conserved. The four phosphorylation motifs and SH3 domain found at the C-terminus of mouse nebulin are identical to those found in human nebulin, with the exception of four conservative substitutions. The modules linking this C-terminal region to the super repeats have deletions relative to both fetal and adult human nebulins that correspond to integral numbers of modules, making the mouse C-terminal simple repeat region among the shortest observed to date. The N-terminal region and the C-terminal modules were expressed in Escherichia coli and used for antibody production. Immunofluorescent labeling of these regions of nebulin in isolated myofibrils demonstrates that they are located near the center of the sarcomere and near the Z-line, respectively. Immunogold labeling with antibodies raised against the N-terminal nebulin sequence localizes this region in the A-band near the tips of the thin filaments. Nebulin localization is complementary to that of N-RAP, another muscle-specific protein containing nebulin-like super repeats; nebulin is exclusively found in the sarcomeres, while N-RAP is confined to the terminal bundles of actin filaments at the myotendinous junction. Cell Motil. Cytoskeleton 3:211-222, 2000 Published 2000 Wiley-Liss, Inc.     

Measurements of gross and net ecosystem productivity and water vapour exchange of a Pinus ponderosa ecosystem,and an evaluation of two generalized models

Net ecosystem productivity (NEP), net primary productivity (NPP), and water vapour exchange of a mature Pinus ponderosa forest (44°30′ N, 121°37′ W) growing in a region subject to summer drought were investigated along with canopy assimilation and respiratory fluxes. This paper describes seasonal and annual variation in these factors, and the evaluation of two generalized models of carbon and water balance (PnET‐II and 3‐PG) with a combination of traditional measurements of NPP, respiration and water stress, and eddy covariance measurements of above‐and below‐canopy CO₂ and water vapour exchange. The objective was to evaluate the models using two years of traditional and eddy covariance measurements, and to use the models to help interpret the relative importance of processes controlling carbon and water vapour exchange in a water‐limited pine ecosystem throughout the year. PnET‐II is a monthly time‐step model that is driven by nitrogen availability through foliar N concentration, and 3‐PG is a monthly time‐step quantum‐efficiency model constrained by extreme temperatures, drought, and vapour pressure deficits. Both models require few parameters and have the potential to be applied at the watershed to regional scale. There was 2/3 less rainfall in 1997 than in 1996, providing a challenge to modelling the water balance, and consequently the carbon balance, when driving the models with the two years of climate data, sequentially. Soil fertility was not a key factor in modelling processes at this site because other environmental factors limited photosynthesis and restricted projected leaf area index to ～1.6. Seasonally, GEP and LE were overestimated in early summer and underestimated through the rest of the year. The model predictions of annual GEP, NEP and water vapour exchange were within 1–39% of flux measurements, with greater disparity in 1997 because soil water never fully recharged. The results suggest that generalized models can provide insights to constraints on productivity on an annual basis, using a minimum of site data.     

Rubella virus E2 signal peptide is required for perinuclear localization of capsid protein and virus assembly

The rubella virus (RV) structural proteins capsid, E2, and E1 are synthesized as a polyprotein precursor. The signal peptide that initiates translocation of E2 into the lumen of the endoplasmic reticulum remains attached to the carboxy terminus of the capsid protein after cleavage by signal peptidase. Among togaviruses, this feature is unique to RV. The E2 signal peptide has previously been shown to function as a membrane anchor for the capsid protein. In the present study, we demonstrate that this domain is required for RV glycoprotein-dependent localization of the capsid protein to the juxtanuclear region and subsequent virus assembly at the Golgi complex.     

Lysosomal membrane permeabilization is involved in oxidative stress-induced apoptotic cell death in LAMP2-deficient iPSCs-derived cerebral cortical neurons

Patients with Danon disease may suffer from severe cardiomyopathy, skeletal muscle dysfunction as well as varying degrees of mental retardation, in which the primary deficiency of lysosomal membrane-associated protein-2 (LAMP2) is considerably associated. Owing to the scarcity of human neurons, the pathological role of LAMP2 deficiency in neural injury of humans remains largely elusive. However, the application of induced pluripotent stem cells (iPSCs) may shed light on overcoming such scarcity.In this study, we obtained iPSCs derived from a patient carrying a mutated LAMP2 gene that is associated with Danon disease. By differentiating such LAMP2-deficient iPSCs into cerebral cortical neurons and with the aid of various biochemical assays, we demonstrated that the LAMP2-deficient neurons are more susceptible to mild oxidative stress-induced injury.The data from MTT assay and apoptotic analysis demonstrated that there was no notable difference in cellular viability between the normal and LAMP2-deficient neurons under non-stressed condition. When exposed to mild oxidative stress (10 μM H₂O₂), the LAMP2-deficient neurons exhibited a significant increase in apoptosis. Surprisingly, we did not observe any aberrant accumulation of autophagic materials in the LAMP2-deficient neurons under such stress condition.Our results from cellular fractionation and inhibitor blockade experiments further revealed that oxidative stress-induced apoptosis in the LAMP2-deficient cortical neurons was caused by increased abundance of cytosolic cathepsin L. These results suggest the involvement of lysosomal membrane permeabilization in the LAMP2 deficiency associated neural injury.     

Trends in First-Line Antiretroviral Therapy in Asia: Results from the TREAT Asia HIV Observational Database

Background

Antiretroviral therapy (ART) has evolved rapidly since its beginnings. This analysis describes trends in first-line ART use in Asia and their impact on treatment outcomes.

Methods

Patients in the TREAT Asia HIV Observational Database receiving first-line ART for ≥6 months were included. Predictors of treatment failure and treatment modification were assessed.

Results

Data from 4662 eligible patients was analysed. Patients started ART in 2003–2006 (n = 1419), 2007–2010 (n = 2690) and 2011–2013 (n = 553). During the observation period, tenofovir, zidovudine and abacavir use largely replaced stavudine. Stavudine was prescribed to 5.8% of ART starters in 2012/13. Efavirenz use increased at the expense of nevirapine, although both continue to be used extensively (47.5% and 34.5% of patients in 2012/13, respectively). Protease inhibitor use dropped after 2004. The rate of treatment failure or modification declined over time (22.1 [95%CI 20.7–23.5] events per 100 patient/years in 2003–2006, 15.8 [14.9–16.8] in 2007–2010, and 11.6 [9.4–14.2] in 2011–2013). Adjustment for ART regimen had little impact on the temporal decline in treatment failure rates but substantially attenuated the temporal decline in rates of modification due to adverse event. In the final multivariate model, treatment modification due to adverse event was significantly predicted by earlier period of ART initiation (hazard ratio 0.52 [95%CI 0.33–0.81], p = 0.004 for 2011–2013 versus 2003–2006), older age (1.56 [1.19–2.04], p = 0.001 for ≥50 years versus <30years), female sex (1.29 [1.11–1.50], p = 0.001 versus male), positive hepatitis C status (1.33 [1.06–1.66], p = 0.013 versus negative), and ART regimen (11.36 [6.28–20.54], p<0.001 for stavudine-based regimens versus tenofovir-based).

Conclusions

The observed trends in first-line ART use in Asia reflect changes in drug availability, global treatment recommendations and prescriber preferences over the past decade. These changes have contributed to a declining rate of treatment modification due to adverse event, but not to reductions in treatment failure.     

The X-Ray Crystal Structure of Escherichia coli Succinic Semialdehyde Dehydrogenase; Structural Insights into NADP+/Enzyme Interactions

Background

In mammals succinic semialdehyde dehydrogenase (SSADH) plays an essential role in the metabolism of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) to succinic acid (SA). Deficiency of SSADH in humans results in elevated levels of GABA and γ-Hydroxybutyric acid (GHB), which leads to psychomotor retardation, muscular hypotonia, non-progressive ataxia and seizures. In Escherichia coli, two genetically distinct forms of SSADHs had been described that are essential for preventing accumulation of toxic levels of succinic semialdehyde (SSA) in cells.

Methodology/Principal Findings

Here we structurally characterise SSADH encoded by the E coli gabD gene by X-ray crystallographic studies and compare these data with the structure of human SSADH. In the E. coli SSADH structure, electron density for the complete NADP⁺ cofactor in the binding sites is clearly evident; these data in particular revealing how the nicotinamide ring of the cofactor is positioned in each active site.

Conclusions/Significance

Our structural data suggest that a deletion of three amino acids in E. coli SSADH permits this enzyme to use NADP⁺, whereas in contrast the human enzyme utilises NAD⁺. Furthermore, the structure of E. coli SSADH gives additional insight into human mutations that result in disease.     

Continuous-Flow Capillary Assay for Measuring Bacterial Chemotaxis

Bacterial chemotaxis may have a significant impact on the structure and function of bacterial communities. Quantification of chemotactic motion is necessary to identify chemoeffectors and to determine the bacterial transport parameters used in predictive models of chemotaxis. When the chemotactic bacteria consume the chemoeffector, the chemoeffector gradient to which the bacteria respond may be significantly perturbed by the consumption. Therefore, consumption of the chemoeffector can confound chemotaxis measurements if it is not accounted for. Current methods of quantifying chemotaxis use bacterial concentrations that are too high to preclude chemoeffector consumption or involve ill-defined conditions that make quantifying chemotaxis difficult. We developed a method of quantifying bacterial chemotaxis at low cell concentrations (~10⁵ CFU/ml), so metabolism of the chemoeffector is minimized. The method facilitates quantification of bacterial-transport parameters by providing well-defined boundary conditions and can be used with volatile and semivolatile chemoeffectors.     

Ecological processes in urban landscapes: mechanisms influencing the distribution and activity of insectivorous bats

Urbanisation affects indigenous fauna in many ways; some species persist and even increase in urban areas, whereas others are lost. The causative mechanisms determining changes in distributions and community structure remain elusive. We investigated three hypothesized mechanisms, which influence success or failure of the insectivorous bat assemblage across the urban landscape of Sydney, Australia; landscape heterogeneity (diversity of land uses), productivity (as indexed by landscape geology) and trait diversity. We present data on species richness and activity (bat passes per night) collected systematically using ultrasonic bat detectors from randomly selected landscapes (each 25 km²). Landscapes were categorized into classes including ‘urban’, ‘suburban’ and ‘vegetated’, where suburban sites were additionally stratified based on geology, as a proxy for productivity. Four landscape elements were sampled within each landscape, including remnant bushland (>2 ha), riparian areas, open space/parkland and residential/built space. We found that there was significantly greater bat activity and more species of bat in areas on fertile shale geologies (p<0.05), supporting the productivity, rather than the heterogeneity hypothesis. Within landscapes, there was no significant effect of the landscape element sampled, although bushland and riparian sites recorded greater bat activity than open space or backyard sites. Using general linear mixed models we found bat activity and species richness were sensitive to landscape geology and increasing housing density at a landscape scale. Using an RLQ analysis a significant relationship was found between these variables and species traits in structuring the community present (p<0.01). Specifically, open‐adapted bats were associated with areas of greater housing density, while clutter‐adapted bats were uncommon in urban areas and more associated with greater amounts of bushland in the landscape. Overall we found greater support for the productivity and traits hypotheses, rather than the heterogeneity hypothesis. The degree of urbanisation and amount of bushland remaining, in combination with landscape geology, influenced bat activity and mediated the trait response. Our findings reflect global trends of species diversity and abundance in urban landscapes, suggesting that processes affecting bat species distribution in urban ecosystems may be predictable at a landscape scale.     

Post-Operative Plasma Osteopontin Predicts Distant Metastasis in Human Colorectal Cancer

BackgroundThe overall prognosis of colorectal cancer (CRC) patients is unsatisfactory due to cancer metastasis after operation. This study aims to investigate the clinical significance of plasma osteopontin (OPN) levels as minimally invasive, predictive, and surrogate biomarkers for prognosis of CRC patients.MethodsThis randomized study design consists of pre-operative and post-operative plasma samples from a total of 79 patients. We determined plasma levels of OPN by ELISA and examined their correlation with the clinicopathological parameters of CRC patients. The effects of endogenous and exogenous OPN on CRC metastasis were investigated by examination of the effect on regulators of epithelial to messenchymal transition and migration assay.ResultsOur findings demonstrated for the first time the clinical correlation of plasma OPN with metastasis of CRC patients. High post-operative plasma OPN level (>153.02 ng/ml) associated with development of metastasis after curative resection (p<0.001). Moreover, post-operative plasma OPN level correlated with disease-free survival of CRC patients (p=0.009) and was an independent factor for predicting development of metastasis in CRC patients after curative resection (p=0.036). Our in vitro model showed that OPN ectopic expression induced DLD1 cell migration through Snail and Twist1 overexpression and E-cadherin repression, and secretory OPN level enhanced cell migration.ConclusionsThe results of the current study suggest that post-operative plasma OPN correlated with post-operative metastasis, suggesting that it is a potential non-invasive biomarker for the development of future metastasis in CRC patients. In addition, OPN was shown to be involved in the metastatic process and thus inhibition of OPN is a potential therapeutic approach to treat CRC patients.