Effects of receptor clustering on ligand dissociation: Theory and simulations

Receptor-ligand binding is a critical first step in signal transduction and the duration of the interaction can impact signal generation. In mammalian cells, clustering of receptors may be facilitated by heterogeneous zones of lipids, known as lipid rafts. In vitro experiments show that disruption of rafts significantly alters the dissociation of fibroblast growth factor-2 (FGF-2) from heparan sulfate proteoglycans, co-receptors for FGF-2. In this paper, we develop a continuum stochastic formalism in order to (i) study how rebinding affects the dissociation of ligands from a planar substrate, and (ii) address the question of how receptor clustering influences ligand rebinding. We find that clusters reduce the effective dissociation rate dramatically when the clusters are dense and the overall surface density of receptors is low. The effect is much less pronounced in the case of high receptor density and shows non-monotonic behavior with time. These predictions are verified via lattice Monte Carlo simulations. Comparison with experimental results suggests that the theory does not capture the complete biological system. We speculate that additional co-operative mechanisms might be present in order to increase ligand retention, and present one possible ``internal diffusion'' model.Comment: Expanded text and added figures, revised version to appear in Biophys.

Predicting Outcome in dogs with Primary Immune-Mediated Hemolytic Anemia: Results of a Multicenter Case Registry

BACKGROUND: Outcome prediction in dogs with immune‐mediated hemolytic anemia (IMHA) is challenging and few prognostic indicators have been consistently identified. OBJECTIVES: An online case registry was initiated to: prospectively survey canine IMHA presentation and management in the British Isles; evaluate 2 previously reported illness severity scores, Canine Hemolytic Anemia Score (CHAOS) and Tokyo and to identify independent prognostic markers. ANIMALS: Data from 276 dogs with primary IMHA across 10 referral centers were collected between 2008 and 2012. METHODS: Outcome prediction by previously reported illness‐severity scores was tested using univariate logistic regression. Independent predictors of death in hospital or by 30‐days after admission were identified using multivariable logistic regression. RESULTS: Purebreds represented 89.1% dogs (n = 246). Immunosuppressive medications were administered to 88.4% dogs (n = 244), 76.1% (n = 210) received antithrombotics and 74.3% (n = 205) received packed red blood cells. Seventy‐four per cent of dogs (n = 205) were discharged from hospital and 67.7% (n = 187) were alive 30‐days after admission. Two dogs were lost to follow‐up at 30‐days. In univariate analyses CHAOS was associated with death in hospital and death within 30‐days. Tokyo score was not associated with either outcome measure. A model containing SIRS‐classification, ASA classification, ALT, bilirubin, urea and creatinine predicting outcome at discharge was accurate in 82% of cases. ASA classification, bilirubin, urea and creatinine were independently associated with death in hospital or by 30‐days. CONCLUSIONS AND CLINICAL IMPORTANCE: Markers of kidney function, bilirubin concentration and ASA classification are independently associated with outcome in dogs with IMHA. Validation of this score in an unrelated population is now warranted

Continuous subcutaneous insulin infusion versus multiple daily injection regimens in children and young people at diagnosis of type 1 diabetes: pragmatic randomised controlled trial and economic evaluation

ObjectiveTo compare the efficacy, safety, and cost utility of continuous subcutaneous insulin infusion (CSII) with multiple daily injection (MDI) regimens during the first year following diagnosis of type 1 diabetes in children and young people.DesignPragmatic, multicentre, open label, parallel group, randomised controlled trial and economic evaluation.Setting15 paediatric National Health Service (NHS) diabetes services in England and Wales. The study opened to recruitment in May 2011 and closed in January 2017.ParticipantsPatients aged between 7 months and 15 years, with a new diagnosis of type 1 diabetes were eligible to participate. Patients who had a sibling with the disease, and those who took drug treatments or had additional diagnoses that could have affected glycaemic control were ineligible.InterventionsParticipants were randomised, stratified by age and treating centre, to start treatment with CSII or MDI within 14 days of diagnosis. Starting doses of aspart (CSII and MDI) and glargine or detemir (MDI) were calculated according to weight and age, and titrated according to blood glucose measurements and according to local clinical practice.Main outcome measuresPrimary outcome was glycaemic control (as measured by glycated haemoglobin; HbA1c) at 12 months. Secondary outcomes were percentage of patients in each treatment arm with HbA1c within the national target range, incidence of severe hypoglycaemia and diabetic ketoacidosis, change in height and body mass index (as measured by standard deviation scores), insulin requirements (units/kg/day), partial remission rate (insulin dose adjusted HbA1c Results294 participants were randomised and 293 included in intention to treat analyses (CSI, n=144; MDI, n=149). At 12 months, mean HbA1c was comparable with clinically unimportant differences between CSII and MDI participants (60.9 mmol/mol v 58.5 mmol/mol, mean difference 2.4 mmol/mol (95% confidence interval -0.4 to 5.3), P=0.09). Achievement of HbA1c lower than 58 mmol/mol was low among the two groups (66/143 (46%) CSII participants v 78/142 (55%) MDI participants; relative risk 0.84 (95% confidence interval 0.67 to 1.06)). Incidence of severe hypoglycaemia and diabetic ketoacidosis were low in both groups. Fifty four non-serious and 14 serious adverse events were reported during CSII treatment, and 17 non-serious and eight serious adverse events during MDI treatment. Parents (but not children) reported superior PedsQL scores for those patients treated with CSII compared to those treated with MDI. CSII was more expensive than MDI by £1863 (€2179; $2474; 95% confidence interval £1620 to £2137) per patient, with no additional QALY gains (difference -0.006 (95% confidence interval -0.031 to 0.018)).ConclusionDuring the first year following type 1 diabetes diagnosis, no clinical benefit of CSII over MDI was identified in children and young people in the UK setting, and treatment with either regimen was suboptimal in achieving HbA1c thresholds. CSII was not cost effective.Trial registrationCurrent Controlled Trials ISRCTN29255275; European Clinical Trials Database 2010-023792-25

Confidence of UK Ophthalmology Registrars in Managing Posterior Capsular Rupture: Results from a National Trainee Survey

Introduction: To establish the level of confidence amongst UK ophthalmology specialist registrars (residents) in managing posterior capsule rupture (PCR) during cataract surgery. / Methods: An online nine-item questionnaire was distributed to all registrars, recruited nationwide via regional representatives. Data collected included stage of training, number of completed cataract operations, cumulative PCR rate, number of PCRs independently managed, understanding of vitrectomy settings and fluidic parameters and access to simulation. Respondents self-evaluated their confidence in managing PCR with vitreous loss. / Results: Complete responses were obtained from 248 registrars (35% response rate). Mean number of phacoemulsification procedures performed was 386. For senior registrars (OST 6–7), 35 out of 70 (50%) felt confident to manage PCR independently and 55 out of 70 (78.6%) were either quite confident or very confident at deciding when to implant an intraocular lens during PCR management. Lower confidence levels were noted for junior trainees (OST 1–2). Over 65% of survey respondents had access to relevant simulation. / Conclusions: Our results represent the largest UK survey analysing the confidence of PCR management amongst registrars. Confidence improves with duration of training and increased exposure to management of PCR. However, 50% of senior registrars still lacked confidence to independently manage PCR and vitreous loss. A specific competency-based framework, potentially using a simulator or simulating a PCR event, incorporated into the curriculum may be desirable

Conducting Economic Evaluations Alongside Randomised Trials: Current Methodological Issues and Novel Approaches

Trial-based economic evaluations are an important aspect of health technology assessment. The availability of patient-level data coupled with unbiased estimates of clinical outcomes means that randomised controlled trials are effective vehicles for the generation of economic data. However there are methodological challenges to trial-based evaluations, which include the collection of reliable data on resource use and cost, choice of health outcome measure, calculating minimally important differences, dealing with missing data, extrapolating outcomes and costs over time and the analysis of multinational trials. This review focuses on the state of the art of selective elements concerning the design, conduct, analysis and reporting of trial-based economic evaluations. The limitations of existing approaches are detailed and novel methods introduced. The review is internationally relevant but with a focus towards practice in the UK

Impact of the British Lung Foundation Active Steps service on patient reported outcomes: (i) concurrent cohort study, (ii) process evaluation, (iii) economic evaluation. Presentations at European Respiratory Society International Congress 2021

Background: Active Steps is a remote behaviour change service supporting inactive adults with a lung condition to become physically active. Aim: To determine the efficacy of Active Steps in improving physical activity and quality life

Molecular Networks in FGF Signaling: Flotillin-1 and Cbl-Associated Protein Compete for the Binding to Fibroblast Growth Factor Receptor Substrate 2

Fibroblast growth factor receptor substrate 2 (FRS2α) is a signaling adaptor protein that regulates downstream signaling of many receptor tyrosine kinases. During signal transduction, FRS2 can be both tyrosine and threonine phosphorylated and forms signaling complexes with other adaptor proteins and tyrosine phosphatases. We have here identified flotillin-1 and the cbl-associated protein/ponsin (CAP) as novel interaction partners of FRS2. Flotillin-1 binds to the phosphotyrosine binding domain (PTB) of FRS2 and competes for the binding with the fibroblast growth factor receptor. Flotillin-1 knockdown results in increased Tyr phosphorylation of FRS2, in line with the inhibition of ERK activity in the absence of flotillin-1. CAP directly interacts with FRS2 by means of its sorbin homology (SoHo) domain, which has previously been shown to interact with flotillin-1. In addition, the third SH3 domain in CAP binds to FRS2. Due to the overlapping binding domains, CAP and flotillin-1 appear to compete for the binding to FRS2. Thus, our results reveal a novel signaling network containing FRS2, CAP and flotillin-1, whose successive interactions are most likely required to regulate receptor tyrosine kinase signaling, especially the mitogen activated protein kinase pathway

Developmental Transcriptional Networks Are Required to Maintain Neuronal Subtype Identity in the Mature Nervous System

During neurogenesis, transcription factors combinatorially specify neuronal fates and then differentiate subtype identities by inducing subtype-specific gene expression profiles. But how is neuronal subtype identity maintained in mature neurons? Modeling this question in two Drosophila neuronal subtypes (Tv1 and Tv4), we test whether the subtype transcription factor networks that direct differentiation during development are required persistently for long-term maintenance of subtype identity. By conditional transcription factor knockdown in adult Tv neurons after normal development, we find that most transcription factors within the Tv1/Tv4 subtype transcription networks are indeed required to maintain Tv1/Tv4 subtype-specific gene expression in adults. Thus, gene expression profiles are not simply “locked-in,” but must be actively maintained by persistent developmental transcription factor networks. We also examined the cross-regulatory relationships between all transcription factors that persisted in adult Tv1/Tv4 neurons. We show that certain critical cross-regulatory relationships that had existed between these transcription factors during development were no longer present in the mature adult neuron. This points to key differences between developmental and maintenance transcriptional regulatory networks in individual neurons. Together, our results provide novel insight showing that the maintenance of subtype identity is an active process underpinned by persistently active, combinatorially-acting, developmental transcription factors. These findings have implications for understanding the maintenance of all long-lived cell types and the functional degeneration of neurons in the aging brain

Amaze: a randomized controlled trial of adjunct surgery for atrial fibrillation

OBJECTIVES: Atrial fibrillation (AF) reduces survival and quality of life (QoL). It can be treated at the time of major cardiac surgery using ablation procedures ranging from simple pulmonary vein isolation to a full maze procedure. The aim of this study is to evaluate the impact of adjunct AF surgery as currently performed on sinus rhythm (SR) restoration, survival, QoL and costeffectiveness. METHODS: In a multicentre, Phase III, pragmatic, double-blinded, parallel-armed randomized controlled trial, 352 cardiac surgery patients with >3 months of documented AF were randomized to surgery with or without adjunct maze or similar AF ablation between 2009 and 2014. Primary outcomes were SR restoration at 1 year and quality-adjusted life years at 2 years. Secondary outcomes included SR at 2 years, overall and stroke-free survival, medication, QoL, cost-effectiveness and safety. RESULTS: More ablation patients were in SR at 1 year [odds ratio (OR) 2.06, 95% confidence interval (CI) 1.20–3.54; P = 0.009]. At 2 years, the OR increased to 3.24 (95% CI 1.76–5.96). Quality-adjusted life years were similar at 2 years (ablation - control -0.025, P = 0.6319). Significantly fewer ablation patients were anticoagulated from 6 months postoperatively. Stroke rates were 5.7% (ablation) and 9.1% (control) (P = 0.3083). There was no significant difference in stroke-free survival [hazard ratio (HR) = 0.99, 95% CI 0.64–1.53; P = 0.949] nor in serious adverse events, operative or overall survival, cardioversion, pacemaker implantation, New York Heart Association, EQ-5D-3L and SF-36. The mean additional ablation cost per patient was £3533 (95% CI £1321–£5746). Cost-effectiveness was not demonstrated at 2 years. CONCLUSIONS: Adjunct AF surgery is safe and increases SR restoration and costs but not survival or QoL up to 2 years. A continued follow-up will provide information on these outcomes in the longer term