Since the adult mammalian heart has limited regenerative capacity, cardiac trauma, disease, and aging cause permanent loss of contractile tissue. This has fueled the development of stem cell-based ...strategies to provide the damaged heart with new cardiomyocytes. Bone marrow-derived mesenchymal stem cells (BM-MSCs) are capable of self-renewal and differentiation into cardiomyocytes, albeit inefficiently. MicroRNAs (miRNAs, miRs) are non-coding RNAs that have the potential to control stem cell fate decisions and are employed in cardiac regeneration and repair. In this study, we tested the hypothesis that overexpression of miR-499a induces cardiomyogenic differentiation in BM-MSCs. Human BM-MSCs (hBM-MSCs) were transduced with lentiviral vectors encoding miR-499a-3p or miR-499a-5p and analyzed by immunostaining and western blotting methods 14 days post-transduction. MiR-499a-5p-transduced cells adopted a polygonal/rod-shaped (myocyte-like) phenotype and showed an increase in the expression of the cardiomyocyte markers α-actinin and cTnI, as cardiogenic differentiation markers. These results indicate that miR-499a-5p overexpression promotes the cardiomyogenic differentiation of hBM-MSCs and may thereby increase their therapeutic efficiency in cardiac regeneration.
Current treatments of ventricular arrhythmias rely on modulation of cardiac electrical function through drugs, ablation or electroshocks, which are all non-biological and rather unspecific, ...irreversible or traumatizing interventions. Optogenetics, however, is a novel, biological technique allowing electrical modulation in a specific, reversible and trauma-free manner using light-gated ion channels. The aim of our study was to investigate optogenetic termination of ventricular arrhythmias in the whole heart.
Systemic delivery of cardiotropic adeno-associated virus vectors, encoding the light-gated depolarizing ion channel red-activatable channelrhodopsin (ReaChR), resulted in global cardiomyocyte-restricted transgene expression in adult Wistar rat hearts allowing ReaChR-mediated depolarization and pacing. Next, ventricular tachyarrhythmias (VTs) were induced in the optogenetically modified hearts by burst pacing in a Langendorff setup, followed by programmed, local epicardial illumination. A single 470-nm light pulse (1000 ms, 2.97 mW/mm2) terminated 97% of monomorphic and 57% of polymorphic VTs vs. 0% without illumination, as assessed by electrocardiogram recordings. Optical mapping showed significant prolongation of voltage signals just before arrhythmia termination. Pharmacological action potential duration (APD) shortening almost fully inhibited light-induced arrhythmia termination indicating an important role for APD in this process.
Brief local epicardial illumination of the optogenetically modified adult rat heart allows contact- and shock-free termination of ventricular arrhythmias in an effective and repetitive manner after optogenetic modification. These findings could lay the basis for the development of fundamentally new and biological options for cardiac arrhythmia management.
Chiral effects appear in a wide variety of natural phenomena and are of fundamental importance in science, from particle physics to metamaterials. The standard technique of chiral ...discrimination—photoabsorption circular dichroism—relies on the magnetic properties of a chiral medium and yields an extremely weak chiral response. Here, we propose and demonstrate an orders of magnitude more sensitive type of circular dichroism in neutral molecules: photoexcitation circular dichroism. This technique does not rely on weak magnetic effects, but takes advantage of the coherent helical motion of bound electrons excited by ultrashort circularly polarized light. It results in an ultrafast chiral response and the efficient excitation of a macroscopic chiral density in an initially isotropic ensemble of randomly oriented chiral molecules. We probe this excitation using linearly polarized laser pulses, without the aid of further chiral interactions. Our time-resolved study of vibronic chiral dynamics opens a way to the efficient initiation, control and monitoring of chiral chemical change in neutral molecules at the level of electrons.
Mesenchymal stem cells (MSCs) of mammals have been isolated from many tissues and are characterized by their aptitude to differentiate into bone, cartilage, and fat. Differentiation into cells of ...other lineages like skeletal muscle, tendon/ligament, nervous tissue, and epithelium has been attained with MSCs derived from some tissues. Whether such abilities are shared by MSCs of all tissues is unknown. We therefore compared for three human donors the myogenic properties of MSCs from adipose tissue (AT), bone marrow (BM), and synovial membrane (SM). Our data show that human MSCs derived from the three tissues differ in phenotype, proliferation capacity, and differentiation potential. The division rate of AT-derived MSCs (AT-MSCs) was distinctly higher than that of MSCs from the other two tissue sources. In addition, clear donor-specific differences in the long-term maintenance of MSC proliferation ability were observed. Although similar in their in vitro fusogenic capacity with murine myoblasts, MSCs of the three sources contributed to a different extent to skeletal muscle regeneration in vivo. Transplanting human AT-, BM-, or SM-MSCs previously transduced with a lentiviral vector encoding β-galactosidase into cardiotoxin-damaged tibialis anterior muscles (TAMs) of immunodeficient mice revealed that at 30 days after treatment the frequency of hybrid myofibers was highest in the TAMs treated with AT-MSCs. Our finding of human-specific β-spectrin and dystrophin in hybrid myofibers containing human nuclei argues for myogenic programming of MSCs in regenerating murine skeletal muscle. For the further development of MSC-based treatments of myopathies, AT-MSCs appear to be the best choice in view of their efficient contribution to myoregeneration, their high ex vivo expansion potential, and because their harvesting is less demanding than that of BM- or SM-MSCs.
The rapid progress that plasma wakefield accelerators are experiencing is now posing the question as to whether they could be included in the design of the next generation of high-energy ...electron-positron colliders. However, the typical structure of the accelerating wakefields presents challenging complications for positron acceleration. Despite seminal proof-of-principle experiments and theoretical proposals, experimental research in plasma-based acceleration of positrons is currently limited by the scarcity of positron beams suitable to seed a plasma accelerator. Here, we report on the first experimental demonstration of a laser-driven source of ultra-relativistic positrons with sufficient spectral and spatial quality to be injected in a plasma accelerator. Our results indicate, in agreement with numerical simulations, selection and transport of positron beamlets containing
positrons in a 5% bandwidth around 600 MeV, with femtosecond-scale duration and micron-scale normalised emittance. Particle-in-cell simulations show that positron beams of this kind can be guided and accelerated in a laser-driven plasma accelerator, with favourable scalings to further increase overall charge and energy using PW-scale lasers. The results presented here demonstrate the possibility of performing experimental studies of positron acceleration in a laser-driven wakefield accelerator.
Because of suboptimal therapeutic strategies, restoration of sinus rhythm in symptomatic atrial fibrillation (AF) often requires in-hospital delivery of high-voltage shocks, thereby precluding ...ambulatory AF termination. Continuous, rapid restoration of sinus rhythm is desired given the recurring and progressive nature of AF. Here, we present an automated hybrid bioelectronic system for shock-free termination of AF that enables the heart to act as an electric current generator for autogenous restoration of sinus rhythm. We show that local, right atrial delivery of adenoassociated virus vectors encoding a light-gated depolarizing ion channel results in efficient and spatially confined transgene expression. Activation of an implanted intrathoracic light-emitting diode device allows for termination of AF by illuminating part of the atria. Combining this newly obtained antiarrhythmic effector function of the heart with the arrhythmia detector function of a machine-based cardiac rhythm monitor in the closed chest of adult rats allowed automated and rapid arrhythmia detection and termination in a safe, effective, repetitive, yet shock-free manner. These findings hold translational potential for the development of shock-free antiarrhythmic device therapy for ambulatory treatment of AF.
Propagation of non-linear waves is key to the functioning of diverse biological systems. Such waves can organize into spirals, rotating around a core, whose properties determine the overall wave ...dynamics. Theoretically, manipulation of a spiral wave core should lead to full spatiotemporal control over its dynamics. However, this theory lacks supportive evidence (even at a conceptual level), making it thus a long-standing hypothesis. Here, we propose a new phenomenological concept that involves artificially dragging spiral waves by their cores, to prove the aforementioned hypothesis in silico, with subsequent in vitro validation in optogenetically modified monolayers of rat atrial cardiomyocytes. We thereby connect previously established, but unrelated concepts of spiral wave attraction, anchoring and unpinning to demonstrate that core manipulation, through controlled displacement of heterogeneities in excitable media, allows forced movement of spiral waves along pre-defined trajectories. Consequently, we impose real-time spatiotemporal control over spiral wave dynamics in a biological system.
A thorough understanding of the developmental signals that direct pluripotent stem cells (PSCs) toward a cardiac fate is essential for translational applications in disease modeling and therapy. We ...screened a panel of 44 cytokines/signaling molecules for their ability to enhance Nkx2.5+ cardiac progenitor cell (CPC) formation during in vitro embryonic stem cell (ESC) differentiation. Treatment of murine ESCs with insulin or insulin‐like growth factors (IGF1/2) during early differentiation increased mesodermal cell proliferation and, consequently, CPC formation. Furthermore, we show that downstream mediators of IGF signaling (e.g., phospho‐Akt and mTOR) are required for this effect. These data support a novel role for IGF family ligands to expand the developing mesoderm and promote cardiac differentiation. Insulin or IGF treatment could provide an effective strategy to increase the PSC‐based generation of CPCs and cardiomyocytes for applications in regenerative medicine. Stem Cells 2014;32:1493–1502
Affinity maturation is an evolutionary process by which the affinity of antibodies (Abs) against specific antigens (Ags) increases through rounds of B-cell proliferation, somatic hypermutation, and ...positive selection in germinal centres (GC). The positive selection of B cells depends on affinity, but the underlying mechanisms of affinity discrimination and affinity-based selection are not well understood. It has been suggested that selection in GC depends on both rapid binding of B-cell receptors (BcRs) to Ags which is kinetically favourable and tight binding of BcRs to Ags, which is thermodynamically favourable; however, it has not been shown whether a selection bias for kinetic properties is present in the GC. To investigate the GC selection bias towards rapid and tight binding, we developed an agent-based model of GC and compared the evolution of founder B cells with initially identical low affinities but with different association/dissociation rates for Ag presented by follicular dendritic cells in three Ag collection mechanisms. We compared an Ag collection mechanism based on association/dissociation rates of B-cell interaction with presented Ag, which includes a probabilistic rupture of bonds between the B-cell and Ag (Scenario-1) with a reference scenario based on an affinity-based Ag collection mechanism (Scenario-0). Simulations showed that the mechanism of Ag collection affects the GC dynamics and the GC outputs concerning fast/slow (un)binding of B cells to FDC-presented Ags. In particular, clones with lower dissociation rates outcompete clones with higher association rates in Scenario-1, while remaining B cells from clones with higher association rates reach higher affinities. Accordingly, plasma cell and memory B cell populations were biased towards B-cell clones with lower dissociation rates. Without such probabilistic ruptures during the Ag extraction process (Scenario-2), the selective advantage for clones with very low dissociation rates diminished, and the affinity maturation level of all clones decreased to the reference level.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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