Sodium channel slow inactivation interferes with open channel block

Mutations in the voltage-gated sodium channel Nav1.7 are linked to inherited pain syndromes such as erythromelalgia (IEM) and paroxysmal extreme pain disorder (PEPD). PEPD mutations impair Nav1.7 fast inactivation and increase persistent currents. PEPD mutations also increase resurgent currents, which involve the voltage-dependent release of an open channel blocker. In contrast, IEM mutations, whenever tested, leave resurgent currents unchanged. Accordingly, the IEM deletion mutation L955 (ΔL955) fails to produce resurgent currents despite enhanced persistent currents, which have hitherto been considered a prerequisite for resurgent currents. Additionally, ΔL955 exhibits a prominent enhancement of slow inactivation (SI). We introduced mutations into Nav1.7 and Nav1.6 that either enhance or impair SI in order to investigate their effects on resurgent currents. Our results show that enhanced SI is accompanied by impaired resurgent currents, which suggests that SI may interfere with open-channel block

Delineation of Diverse Macrophage Activation Programs in Response to Intracellular Parasites and Cytokines

Macrophages are a type of immune cell that engulf and digest microorganisms. Despite their role in protecting the host from infection, many pathogens have developed ways to hijack the macrophage and use the cell for their own survival and proliferation. This includes the parasites Trypanosoma cruzi and Leishmania mexicana. In order to gain further understanding of how these pathogens interact with the host macrophage, we compared macrophages that have been infected with these parasites to macrophages that have been stimulated in a number of different ways. Macrophages can be activated by a wide variety of stimuli, including common motifs found on pathogens (known as pathogen associated molecular patterns or PAMPs) and cytokines secreted by other immune cells. In this study, we have delineated the relationships between the macrophage activation programs elicited by a number of cytokines and PAMPs. Furthermore, we have placed the macrophage responses to T. cruzi and L. mexicana into the context of these activation programs, providing a better understanding of the interactions between these pathogens and macrophages

Global transcriptional response to mammalian temperature provides new insight into Francisella tularensis pathogenesis

<p>Abstract</p> <p>Background</p> <p>After infecting a mammalian host, the facultative intracellular bacterium, <it>Francisella tularensis</it>, encounters an elevated environmental temperature. We hypothesized that this temperature change may regulate genes essential for infection.</p> <p>Results</p> <p>Microarray analysis of <it>F. tularensis </it>LVS shifted from 26°C (environmental) to 37°C (mammalian) showed ~11% of this bacterium's genes were differentially-regulated. Importantly, 40% of the protein-coding genes that were induced at 37°C have been previously implicated in virulence or intracellular growth of <it>Francisella </it>in other studies, associating the bacterial response to this temperature shift with pathogenesis. Forty-four percent of the genes induced at 37°C encode proteins of unknown function, suggesting novel <it>Francisella </it>virulence traits are regulated by mammalian temperature. To explore this possibility, we generated two mutants of loci induced at 37°C [FTL_1581 and FTL_1664 (<it>deoB</it>)]. The FTL_1581 mutant was attenuated in a chicken embryo infection model, which was likely attributable to a defect in survival within macrophages. FTL_1581 encodes a novel hypothetical protein that we suggest naming <it>t</it>emperature-<it>i</it>nduced, <it>v</it>irulence-associated locus <it>A</it>, <it>tivA</it>. Interestingly, the <it>deoB </it>mutant showed diminished entry into mammalian cells compared to wild-type LVS, including primary human macrophages and dendritic cells, the macrophage-like RAW 264.7 line, and non-phagocytic HEK-293 cells. This is the first study identifying a <it>Francisella </it>gene that contributes to uptake into both phagocytic and non-phagocytic host cells.</p> <p>Conclusion</p> <p>Our results provide new insight into mechanisms of <it>Francisella </it>virulence regulation and pathogenesis. <it>F. tularensis </it>LVS undergoes considerable gene expression changes in response to mammalian body temperature. This temperature shift is important for the regulation of genes that are critical for the pathogenesis of <it>Francisella</it>. Importantly, the compilation of temperature-regulated genes also defines a rich collection of novel candidate virulence determinants, including <it>tivA </it>(FTL_1581). An analysis of <it>tivA </it>and <it>deoB </it>(FTL_1664) revealed that these genes contribute to intracellular survival and entry into mammalian cells, respectively.</p

Phagocytosis of Staphylococcus aureus by Macrophages Exerts Cytoprotective Effects Manifested by the Upregulation of Antiapoptotic Factors

It is becoming increasingly apparent that Staphylococcus aureus are able to survive engulfment by macrophages, and that the intracellular environment of these host cells, which is essential to innate host defenses against invading microorganisms, may in fact provide a refuge for staphylococcal survival and dissemination. Based on this, we postulated that S. aureus might induce cytoprotective mechanisms by changing gene expression profiles inside macrophages similar to obligate intracellular pathogens, such as Mycobacterium tuberculosis. To validate our hypothesis we first ascertained whether S. aureus infection could affect programmed cell death in human (hMDMs) and mouse (RAW 264.7) macrophages and, specifically, protect these cells against apoptosis. Our findings indicate that S. aureus-infected macrophages are more resistant to staurosporine-induced cell death than control cells, an effect partly mediated via the inhibition of cytochrome c release from mitochondria. Furthermore, transcriptome analysis of human monocyte-derived macrophages during S. aureus infection revealed a significant increase in the expression of antiapoptotic genes. This was confirmed by quantitative RT-PCR analysis of selected genes involved in mitochondria-dependent cell death, clearly showing overexpression of BCL2 and MCL1. Cumulatively, the results of our experiments argue that S. aureus is able to induce a cytoprotective effect in macrophages derived from different mammal species, which can prevent host cell elimination, and thus allow intracellular bacterial survival. Ultimately, it is our contention that this process may contribute to the systemic dissemination of S. aureus infection

Signaling probabilities in ambiguity: who reacts to vague news?

Ambiguity affects decisions of people who exhibit a distaste of and require a premium for dealing with it. Do ambiguity-neutral subjects completely disregard ambiguity and respond to any vague news? We couple decision-making in ambiguity with a preliminary information processing stage, where news is used to test prior beliefs and, possibly but not necessarily, update them. All decision-makers, including ambiguity-neutral, recognize and account for ambiguity at this stage; higher confidence makes ambiguity-neutral subjects less susceptible to vague news. In a two-color Ellsberg experiment with imprecise signals about the unknown probability of success they are less likely to respond to signals; the difference between them and non-neutral to ambiguity subjects vanishes for high precision signals. Less than 60% subjects choose the ambiguous urn, even for high communicated probabilities of success, suggesting many participants, especially ambiguity-neutral, discard vague news at the information processing stage. JEL: C90, D01, D81, as well as seminar participants at ETH-Zürich, University of Essex, University of Glasgow and University of Hamburg, and participants of iCare conference at HSE in Perm and JE on Ambiguity and Strategic Interactions at the University of Grenoble for helpful comments, suggestions and encouragement. All remaining errors are ours

Biomechanical evaluation of four femoral fixation configurations in a simulated anterior cruciate ligament replacement using a new generation of Ligament Advanced Reinforcement System (LARSTM AC)

Background: Recent improvements in manufacturing of biomaterials have made available a new generation of artificial ligaments with better biocompatibility and design that have led to a new interest in using them for ACL reconstructions.Purpose: To evaluate the biomechanical characteristics of four femoral fixations using a Ligament Advanced Reinforcement System (LARS™ AC; LARS, Arc sur Tille, France) for anterior cruciate ligament replacement.Method: Six femoral ACL fixations in four configurations using fresh calf femurs with an interference titanium screw inserted inside to outside, an interference titanium screw inserted outside to inside, an interference titanium screw inserted inside to outside with a staple and a new transversal cortical suspension device developed by LARS™ were compared in a static loading and failure test. Output values were ultimate strength, graft slippage, mode of failure, energy to failure and stiffness.Results: The transversal fixation performed with a significantly higher failure load than others (1804 N) (p < 0.001), whereas there were no significant differences between the three fixations with interference screws. There were no significant differences of stiffness between all fixations, and the transversal device had a significantly higher graft slippage (13.1 mm) than others (all p < 0.01).Conclusions: In this in vitro evaluation, the transversal fixation exhibited better biomechanical performance under static solicitations than others. The transversal device is expected to provide better clinical results than the well-established screw system fixations for femoral ACL fixation