In silico analysis of the dynamic regulation of cardiac electrophysiology by K 11.1 ion-channel trafficking
Meier S, Grundland A, Dobrev D, Volders PGA and Heijman J
Cardiac electrophysiology is regulated by continuous trafficking and internalization of ion channels occurring over minutes to hours. K 11.1 (also known as hERG) underlies the rapidly activating delayed-rectifier K current (I ), which plays a major role in cardiac ventricular repolarization. Experimental characterization of the distinct temporal effects of genetic and acquired modulators on channel trafficking and gating is challenging. Computer models are instrumental in elucidating these effects, but no currently available model incorporates ion-channel trafficking. Here, we present a novel computational model that reproduces the experimentally observed production, forward trafficking, internalization, recycling and degradation of K 11.1 channels, as well as their modulation by temperature, pentamidine, dofetilide and extracellular K . The acute effects of these modulators on channel gating were also incorporated and integrated with the trafficking model in the O'Hara-Rudy human ventricular cardiomyocyte model. Supraphysiological dofetilide concentrations substantially increased K 11.1 membrane levels while also producing a significant channel block. However, clinically relevant concentrations did not affect trafficking. Similarly, severe hypokalaemia reduced K 11.1 membrane levels based on long-term culture data, but had limited effect based on short-term data. By contrast, clinically relevant elevations in temperature acutely increased I due to faster kinetics, while after 24 h, I was decreased due to reduced K 11.1 membrane levels. The opposite was true for lower temperatures. Taken together, our model reveals a complex temporal regulation of cardiac electrophysiology by temperature, hypokalaemia, and dofetilide through competing effects on channel gating and trafficking, and provides a framework for future studies assessing the role of impaired trafficking in cardiac arrhythmias. KEY POINTS: K 11.1 channels underlying the rapidly activating delayed-rectifier K current are important for ventricular repolarization and are continuously shuttled from the cytoplasm to the plasma membrane and back over minutes to hours. K 11.1 gating and trafficking are modulated by temperature, drugs and extracellular K concentration but experimental characterization of their combined effects is challenging. Computer models may facilitate these analyses, but no currently available model incorporates ion-channel trafficking. We introduce a new two-state ion-channel trafficking model able to reproduce a wide range of experimental data, along with the effects of modulators of K 11.1 channel functioning and trafficking. The model reveals complex dynamic regulation of ventricular repolarization by temperature, extracellular K concentration and dofetilide through opposing acute (millisecond) effects on K 11.1 gating and long-term (hours) modulation of K 11.1 trafficking. This in silico trafficking framework provides a tool to investigate the roles of acute and long-term processes on arrhythmia promotion and maintenance.
Genomic risk scores, biomolecules, and clinical conditions to predict atrial fibrillation: time to integrate what we can measure
Kääb S, Holm H and Kirchhof P
Characterisation of patients referred to a tertiary-level inherited cardiac condition clinic with suspected arrhythmogenic right ventricular cardiomyopathy (ARVC)
Aljehani A, Kew T, Baig S, Cox H, Sommerfeld LC, Ensam B, Kalla M, Steeds RP and Fabritz L
Arrhythmogenic right ventricular cardiomyopathy (ARVC) or arrhythmogenic cardiomyopathy is a rare inherited disease with incomplete penetrance and an environmental component. Although a rare disease, ARVC is a common cause of sudden cardiac death in young adults. Data on the different stages of ARVC remains scarce. The purpose of this study is to describe the initial presentation and cardiac phenotype of definite and non-definite ARVC for patients seen at a tertiary service.
Determinants and therapeutic potential of calcium handling abnormalities in atrial fibrillation: what can we learn from computer models?
Heijman J and Dobrev D
CACONET: a novel classification framework for microbial correlation networks
Xu Y, Nash K, Acharjee A and Gkoutos GV
Existing microbiome-based disease prediction relies on the ability of machine learning methods to differentiate disease from healthy subjects based on the observed taxa abundance across samples. Despite numerous microbes have been implicated as potential biomarkers, challenges remain due to not only the statistical nature of microbiome data but also the lack of understanding of microbial interactions which can be indicative of the disease.
Coagulation Factor Xa Induces Proinflammatory Responses in Cardiac Fibroblasts via Activation of Protease-Activated Receptor-1
D'Alessandro E, Scaf B, Munts C, van Hunnik A, Trevelyan CJ, Verheule S, Spronk HMH, Turner NA, Ten Cate H, Schotten U and van Nieuwenhoven FA
Coagulation factor (F) Xa induces proinflammatory responses through activation of protease-activated receptors (PARs). However, the effect of FXa on cardiac fibroblasts (CFs) and the contribution of PARs in FXa-induced cellular signalling in CF has not been fully characterised. To answer these questions, human and rat CFs were incubated with FXa (or TRAP-14, PAR-1 agonist). Gene expression of pro-fibrotic and proinflammatory markers was determined by qRT-PCR after 4 and 24 h. Gene silencing of (PAR-1) and (PAR-2) was achieved using siRNA. MCP-1 protein levels were measured by ELISA of FXa-conditioned media at 24 h. Cell proliferation was assessed after 24 h of incubation with FXa ± SCH79797 (PAR-1 antagonist). In rat CFs, FXa induced upregulation of (MCP-1; >30-fold at 4 h in atrial and ventricular CF) and (IL-6; ±7-fold at 4 h in ventricular CF). Increased MCP-1 protein levels were detected in FXa-conditioned media at 24 h. In human CF, FXa upregulated the gene expression of (>3-fold) and (>4-fold) at 4 h. Silencing of (PAR-1 gene), but not (PAR-2 gene), downregulated this effect. Selective activation of PAR-1 by TRAP-14 increased and gene expression; this was prevented by (PAR-1 gene) knockdown. Moreover, SCH79797 decreased FXa-induced proliferation after 24 h. In conclusion, our study shows that FXa induces overexpression of proinflammatory genes in human CFs via PAR-1, which was found to be the most abundant PARs isoform in this cell type.
Oxidative stress: a bystander or a causal contributor to atrial remodelling and fibrillation?
Dobrev D and Dudley SC
Remodeling of Ion Channel Trafficking and Cardiac Arrhythmias
Blandin CE, Gravez BJ, Hatem SN and Balse E
Both inherited and acquired cardiac arrhythmias are often associated with the abnormal functional expression of ion channels at the cellular level. The complex machinery that continuously traffics, anchors, organizes, and recycles ion channels at the plasma membrane of a cardiomyocyte appears to be a major source of channel dysfunction during cardiac arrhythmias. This has been well established with the discovery of mutations in the genes encoding several ion channels and ion channel partners during inherited cardiac arrhythmias. Fibrosis, altered myocyte contacts, and post-transcriptional protein changes are common factors that disorganize normal channel trafficking during acquired cardiac arrhythmias. Channel availability, described notably for hERG and K1.5 channels, could be another potent arrhythmogenic mechanism. From this molecular knowledge on cardiac arrhythmias will emerge novel antiarrhythmic strategies.
From translation to integration: how to approach the complexity of atrial fibrillation mechanisms
Schotten U