HPK1 Associates with SKAP-HOM to Negatively Regulate Rap1-Mediated B-Lymphocyte Adhesion

BACKGROUND: Hematopoietic progenitor kinase 1 (HPK1) is a Ste20-related serine/threonine kinase activated by a range of environmental stimuli including genotoxic stress, growth factors, inflammatory cytokines and antigen receptor triggering. Being inducibly recruited to membrane-proximal signalling scaffolds to regulate NFAT, AP-1 and NFkappaB-mediated gene transcription in T-cells, the function of HPK1 in B-cells to date remains rather ill-defined. METHODOLOGY/PRINCIPAL FINDINGS: By using two loss of function models, we show that HPK1 displays a novel function in regulating B-cell integrin activity. Wehi 231 lymphoma cells lacking HPK1 after shRNA mediated knockdown exhibit increased basic activation levels of Ras-related protein 1 (Rap1), accompanied by a severe lymphocyte function-associated antigen-1 (LFA-1) dependent homotypic aggregation and increased adhesion to intercellular adhesion molecule 1 (ICAM-1). The observed phenotype of enhanced integrin activity is caused downstream of Src, by a signalling module independent of PI3K and PLC, involving HPK1, SKAP55 homologue (SKAP-HOM) and Rap1-GTP-interacting adaptor molecule (RIAM). This alters actin dynamics and renders focal adhesion kinase (FAK) constitutively phosphorylated. Bone marrow and splenic B-cell development of HPK1(-/-) mice are largely unaffected, except age-related tendencies for increased splenic cellularity and BCR downregulation. In addition, naïve splenic knockout B-cells appear hyperresponsive to a range of stimuli applied ex vivo as recently demonstrated by others for T-cells. CONCLUSIONS/SIGNIFICANCE: We therefore conclude that HPK1 exhibits a dual function in B-cells by negatively regulating integrin activity and controlling cellular activation, which makes it an interesting candidate to study in pathological settings like autoimmunity and cancer

Effects of autologous bone marrow stem cell transplantation on beta-adrenoceptor density and electrical activation pattern in a rabbit model of non-ischemic heart failure

BACKGROUND: Since only little is known on stem cell therapy in non-ischemic heart failure we wanted to know whether a long-term improvement of cardiac function in non-ischemic heart failure can be achieved by stem cell transplantation. METHODS: White male New Zealand rabbits were treated with doxorubicine (3 mg/kg/week; 6 weeks) to induce dilative non-ischemic cardiomyopathy. Thereafter, we obtained autologous bone marrow stem cells (BMSC) and injected 1.5–2.0 Mio cells in 1 ml medium by infiltrating the myocardium via a left anterolateral thoracotomy in comparison to sham-operated rabbits. 4 weeks later intracardiac contractility was determined in-vivo using a Millar catheter. Thereafter, the heart was excised and processed for radioligand binding assays to detect β(1)- and β(2)-adrenoceptor density. In addition, catecholamine plasma levels were determined via HPLC. In a subgroup we investigated cardiac electrophysiology by use of 256 channel mapping. RESULTS: In doxorubicine-treated animals β-adrenoceptor density was significantly down-regulated in left ventricle and septum, but not in right ventricle, thereby indicating a typical left ventricular heart failure. Sham-operated rabbits exhibited the same down-regulation. In contrast, BMSC transplantation led to significantly less β-adrenoceptor down-regulation in septum and left ventricle. Cardiac contractility was significantly decreased in heart failure and sham-operated rabbits, but was significantly higher in BMSC-transplanted hearts. Norepinephrine and epinephrine plasma levels were enhanced in heart failure and sham-operated animals, while these were not different from normal in BMSC-transplanted animals. Electrophysiological mapping revealed unaltered electrophysiology and did not show signs of arrhythmogeneity. CONCLUSION: BMSC transplantation improves sympathoadrenal dysregualtion in non-ischemic heart failure

Strategic Reasoning About Bundling in Swarming Systems

Abstract — The objects of study of this paper are swarming systems, a special kind of peer-to-peer systems where users interested in the same content at the same time cooperate with each other. In particular, we consider the problem of how to combine files into bundles in such systems. First, we analyze the case of a monopoly where a single publisher decides how to aggregate its files so as to satisfy user demands while mitigating its serving costs. We establish conditions for the existence and uniqueness of an equilibrium and how the publisher’s bundling strategy affects its profit. Then, we consider the competitive case where bundling decisions of one publisher affect the outcome of other publishers. Using normal form games we analyze the impact of different system parameters on the Nash equilibrium. I

Modeling Unavailability in Peer-to-Peer Systems

In this paper we model peer-to-peer systems where content may become unavailable. First, using Markov Chains we capture the impact of parameters such as the server upload rate and the popularity of the files on the performance of the system. Then, we show the applicability of our model to the problem of optimal bundling. Bundling files together, rather than disseminating them separately, is a possible solution to improve availability in BitTorrent

The role of redox signalling in cardiovascular regeneration

© Springer Nature Singapore Pte Ltd. 2019. Cardiovascular disease (CVD) is a major public health problem, particularly in the industrialised world, with diverse causes. Central to these underlying aetiologies is a progressive loss of functional cardiomyocytes, maladaptive remodelling, and resultant cardiac dysfunction. The ageing heart is characterised by perturbations in numerous signalling pathways, impairing its ability to repair and replace injured cardiomyocytes. This is caused at least in part by dysregulation of redox signalling- both in regard to production of reactive oxygen species (ROS), and disruption of cellular protective mechanisms. Cardiac regeneration is one area of particular therapeutic promise, which seeks to ameliorate cardiac function by either (1) direct application of stem cells, (2) modification of molecular signalling pathways to restore the endogenous reparative capacity of the heart, or (3) a combination of these two approaches. Unravelling these molecular and cellular signalling pathways is paramount to unlocking the potential of cardiac regenerative therapies, and theoretically revolutionising the medical management of patients with heart failure. In this chapter, we will review the role of oxidative stress in cardiovascular disease, and the pathophysiological molecular signalling pathways that are involved in the transition from young to ageing heart. We will then provide an overview of the molecular therapies that are used to target these pathways to enhance heart regeneration, future directions involving cellular and novel ‘bio-printing’ based approaches, in addition to current promising clinical trials

Heart repair by reprogramming non-myocytes with cardiac transcription factors

The adult mammalian heart possesses little regenerative potential following injury. Fibrosis due to activation of cardiac fibroblasts impedes cardiac regeneration and contributes to loss of contractile function, pathological remodeling and susceptibility to arrhythmias. Cardiac fibroblasts account for a majority of cells in the heart and represent a potential cellular source for restoration of cardiac function following injury through phenotypic reprogramming to a myocardial cell fate. Here we show that four transcription factors, GATA4, Hand2, MEF2C and Tbx5 can cooperatively reprogram adult mouse tail-tip and cardiac fibroblasts into beating cardiac-like myocytes in vitro. Forced expression of these factors in dividing non-cardiomyocytes in mice reprograms these cells into functional cardiac-like myocytes, improves cardiac function and reduces adverse ventricular remodeling following myocardial infarction. Our results suggest a strategy for cardiac repair through reprogramming fibroblasts resident in the heart with cardiogenic transcription factors or other molecules