Mechano-sensing and cell migration: A 3D model approach

Cell migration is essential for tissue development in different physiological and pathological conditions. It is a complex process orchestrated by chemistry, biological factors, microstructure and surrounding mechanical properties. Focusing on the mechanical interactions, cells do not only exert forces on the matrix that surrounds them, but they also sense and react to mechanical cues in a process called mechano-sensing. Here, we hypothesize the involvement of mechano-sensing in the regulation of directional cell migration through a three-dimensional (3D) matrix. For this purpose, we develop a 3D numerical model of individual cell migration, which incorporates the mechano-sensing process of the cell as the main mechanism regulating its movement. Consistent with this hypothesis, we found that factors, such as substrate stiffness, boundary conditions and external forces, regulate specific and distinct cell movements

Cell Cytoskeleton Dynamics: Mechano-Sensing Properties

`The actin cytoskeleton network is the dominant structure of eukaryotic cells. It is highlydynamic and plays a central role in a wide range of mechanical and biological functions.Cytoskeleton is composed mainly of actin filaments (F-actin) resulting from the self-assemblyof monomeric actin (G-actin) and cross-linked by actin cross-linking proteins (ACPs) whosenature and concentration determine the morphological and rheological properties of thenetwork. These actin filaments are reversibly coupled to membrane proteins (critical to theresponse of cells to external stress) and in conjunction with motor proteins from the myosinfamily, are able to generate contractile force during cell migration. Knowledge of actincytoskeleton and its rheological properties is therefore indispensable for understanding theunderlying mechanics and various biological processes of cells. Here, we present a 3-DBrownian dynamics (BD) computational model in which actin monomers polymerize andbecome cross-linked by two types of ACPs, forming either parallel filament bundles ororthogonal networks. Also, the active and dynamic behaviour of motors is included. In thissimulation, actin monomers, filaments, ACPs, and motors experience thermal motion andinteract with each other with binding probabilities and defined potentials. Displacements aregoverned by the Langevin equation, and positions of all elements are updated using the Eulerintegration scheme.In this first part of the work, the mechano-sensing properties of active networks are investigatedby evaluating stress and strain rate in response to different substrate stiffness

Digital Deblurring of CMB Maps II: Asymmetric Point Spread Function

In this second paper in a series dedicated to developing efficient numerical techniques for the deblurring Cosmic Microwave Background (CMB) maps, we consider the case of asymmetric point spread functions (PSF). Although conceptually this problem is not different from the symmetric case, there are important differences from the computational point of view because it is no longer possible to use some of the efficient numerical techniques that work with symmetric PSFs. We present procedures that permit the use of efficient techniques even when this condition is not met. In particular, two methods are considered: a procedure based on a Kronecker approximation technique that can be implemented with the numerical methods used with symmetric PSFs but that has the limitation of requiring only mildly asymmetric PSFs. The second is a variant of the classic Tikhonov technique that works even with very asymmetric PSFs but that requires discarding the edges of the maps. We provide details for efficient implementations of the algorithms. Their performance is tested on simulated CMB maps.Comment: 9 pages, 13 Figure

Effect of Surface Patterning and Presence of Collagen I on the Phenotypic Changes of Embryonic Stem Cell Derived Cardiomyocytes

Embryonic stem cell derived cardiomyocytes have been widely investigated for stem cell therapy or in vitro model systems. This study examines how two specific biophysical stimuli, collagen I and cell alignment, affect the phenotypes of embryonic stem cell derived cardiomyocytes in vitro. Three phenotypic indicators are assessed: sarcomere organization, cell elongation, and percentage of binucleation. Murine embryonic stem cells were differentiated in a hanging drop assay and cardiomyocytes expressing GFP-α-actinin were isolated by fluorescent sorting. First, the effect of collagen I was investigated. Addition of soluble collagen I markedly reduced binucleation as a result of an increase in cytokinesis. Laden with a collagen gel layer, myocyte mobility and cell shape change were impeded. Second, the effect of cell alignment by microcontact printing and nanopattern topography was investigated. Both patterning techniques induced cell alignment and elongation. Microcontact printing of 20 μm line pattern accelerated binucleation and nanotopography with 700 nm ridges and 3.5 μm grooves negatively regulated binucleation. This study highlights the importance of biophysical cues in the morphological changes of differentiated cardiomyocytes and may have important implications on how these cells incorporate into the native myocardium.Singapore-MIT Alliance for Research and TechnologyNational Science Foundation (U.S.) ((Science and Technology Center (EBICS): Emergent Behaviors of Integrated Cellular Systems, Grant CBET-0939511)Charles Stark Draper Laboratory (Internal Research and Development Program

MicroRNA delivery through nanoparticles

MicroRNAs (miRNAs) are attracting a growing interest in the scientific community due to their central role in the etiology of major diseases. On the other hand, nanoparticle carriers offer unprecedented opportunities for cell specific controlled delivery of miRNAs for therapeutic purposes. This review critically discusses the use of nanoparticles for the delivery of miRNA-based therapeutics in the treatment of cancer and neurodegenerative disorders and for tissue regeneration. A fresh perspective is presented on the design and characterization of nanocarriers to accelerate translation from basic research to clinical application of miRNA-nanoparticles. Main challenges in the engineering of miRNA-loaded nanoparticles are discussed, and key application examples are highlighted to underline their therapeutic potential for effective and personalized medicine

Post-Collision Interaction with Wannier electrons

A theory of the Post-Collision Interaction (PCI) is developed for the case when an electron atom impact results in creation of two low-energy Wannier electrons and an ion excited into an autoionizing state. The following autoionization decay exposes the Wannier pair to the influence of PCI resulting in variation of the shape of the line in the autoionization spectrum. An explicit dependence of the autoionization profile on the wave function of the Wannier pair is found. PCI provides an opportunity to study this wave function for a wide area of distancesComment: 33 pages, Latex, IOP style, and 3 figures fig1.ps, fig2.ps, fig3.p

Knowledge of Objective 'Oughts': Monotonicity and the New Miners Puzzle

In the classic Miners case, an agent subjectively ought to do what they know is objectively wrong. This case shows that the subjective and objective ‘oughts’ are somewhat independent. But there remains a powerful intuition that the guidance of objective ‘oughts’ is more authoritative—so long as we know what they tell us. We argue that this intuition must be given up in light of a monotonicity principle, which undercuts the rationale for saying that objective ‘oughts’ are an authoritative guide for agents and advisors

Glucocorticoid hypersensitivity as a rare but potentially fatal side effect of paediatric asthma treatment: a case report

<p>Abstract</p> <p>Introduction</p> <p>Immediate-type hypersensitivity to glucocorticosteroids is rare but well known among allergists. Surprisingly, very few reports of glucocorticosteroid hypersensitivity in children exist although glucocorticosteroid treatment is particularly common in this age group.</p> <p>Case presentation</p> <p>We report the case of a 2-year-old boy who developed generalized urticaria, facial angio-oedema, nausea and severe dyspnoea after intravenous application of prednisolone-21-hydrogen succinate. Skin prick testing with prednisolone-21-hydrogen succinate elicited a positive result; no reactions were observed to prednisone, betamethasone or dexamethasone. While fluorescence enzyme immunoassay analysis revealed no specific IgE antibodies against prednisolone-21-hydrogen succinate, CD63-based basophil activation testing with the culprit drug prednisolone-21-hydrogen succinate was positive. In contrast, additional incubation of basophils with prednisone, betamethasone and dexamethasone did not elicit any significant response. Hence, we performed an oral provocation test with betamethasone and a titrated intravenous dexamethasone challenge. As both drugs were tolerated without any complications they were recommended for future treatment.</p> <p>Conclusion</p> <p>In a child with confirmed immediate-type hypersensitivity to glucocorticosteroids, it is still not possible to predict which glucocorticosteroid might be tolerated by solely relying on clinical history or results of skin and <it>in vitro </it>testing. Therefore, incremental glucocorticosteroid challenges under standardized clinical conditions remain necessary in order to facilitate a patient-tailored emergency treatment and to avoid severe reactions to glucocorticosteroids in these patients.</p

Temporal Effects of Cyclic Stretching on Distribution and Gene Expression of Integrin and Cytoskeleton by Ligament Fibroblasts In Vitro

Cyclic stretching is pivotal to maintenance of the ligaments. However, it is still not clear when ligament fibroblasts switch on expression of genes related to the mechanotransduction pathway in response to cyclic stretching. This in vitro study investigated, using ligament fibroblasts, the time-dependent changes in distribution and gene expression of β1 integrin, the cytoskeleton, and collagens after the application of 6% cyclic stretching at a frequency of 0.1 Hz for 3 hr on silicon membranes. We carried out confocal laser scanning microscopy to demonstrate changes in distribution of these components as well as quantitative real-time RT-PCR to quantify levels of these gene expression both during application of cyclic stretching and at 0, 2, 6, 12, and 18 hr after the termination of stretching. Control (unstretched) cells were used at each time point. Within 1 hr of the application of stretching, the fibroblasts and their actin stress fibers became aligned in a direction perpendicular to the major axis of stretch, whereas control (unstretched) cells were randomly distributed. In response to cyclic stretching, upregulation of actin at the mRNA level was first observed within 1 hr after the onset of stretching, while upregulation of β1 integrin and type I and type III collagens was observed between 2 and 12 hr after the termination of stretching. These results indicate that the fibroblasts quickly modify their morphology in response to cyclic stretching, and subsequently they upregulate the expression of genes related to the mechanotransduction pathway mainly during the resting period after the termination of stretching

The Early ANTP Gene Repertoire: Insights from the Placozoan Genome

The evolution of ANTP genes in the Metazoa has been the subject of conflicting hypotheses derived from full or partial gene sequences and genomic organization in higher animals. Whole genome sequences have recently filled in some crucial gaps for the basal metazoan phyla Cnidaria and Porifera. Here we analyze the complete genome of Trichoplax adhaerens, representing the basal metazoan phylum Placozoa, for its set of ANTP class genes. The Trichoplax genome encodes representatives of Hox/ParaHox-like, NKL, and extended Hox genes. This repertoire possibly mirrors the condition of a hypothetical cnidarian-bilaterian ancestor. The evolution of the cnidarian and bilaterian ANTP gene repertoires can be deduced by a limited number of cis-duplications of NKL and “extended Hox” genes and the presence of a single ancestral “ProtoHox” gene