Molecular mechanisms of TBX5-related conduction disorders

Hintergrund Herz-Kreislauferkrankungen zählen zu den häufigsten Todesursachen. Mehr als 60% dieser Todesfälle sind auf den durch Arrhythmien ausgelösten plötzlichen Herztod zurückzuführen. Arrhythmien können sowohl durch chronische Herzerkrankungen als auch durch genetische Faktoren - besonders bei jüngeren Patienten - hervorgerufen werden. Einer dieser Faktoren ist der Transkriptionsfaktor T-box 5 (TBX5), der mit Arrhythmien assoziiert ist. Bisher hat sich die Forschung hauptsächlich auf die Rolle von TBX5 in der Entwicklungsbiologie und Erregungsleitung im Herzen konzentriert. Jedoch ist die Expression von TBX5 nicht nur im Kontext von genetischen Veränderungen, sondern auch in den kardialen Ventrikeln von Patienten oder Tiermodellen mit Herzinsuffizienz reduziert. Wegen dieser verminderten Expression im Arbeitsmyokard, stellten wir die Hypothese auf, dass TBX5 ebenfalls eine wichtige Rolle für die Homöostase des ventrikulären Arbeitsmyokards spielt. Methoden & Ergebnisse Um die Folgen des TBX5-Verlusts im Arbeitsmyokard zu untersuchen, generierten wir ein induzierbares TBX5-KO-Modell mit prädominanter ventrikulärer Spezifität (vTbx5KO). Dies hatte ein reduziertes Herzwachstum und eine diastolische Dysfunktion für die vTbx5KO zur Folge. Zudem zeigten die Mäuse eine verlangsamte Erregungsleistung, Arrhythmien wie atrioventrikulären Block und Kammertachykardien, die die Überlebenswahrscheinlichkeit der Mäuse auf 40% reduzierten, vermutlich durch das erhöhte Risiko eines plötzlichen Herztodes. Um den zugrundeliegenden molekularen Mechanismus zu untersuchen, führten wir eine integrierte Analyse der Chromatinbindung von TBX5 zusammen mit einer Transkriptomanalyse der fehlregulierten Transkripte durch. Diese Analyse zeigte 47 neue Zielgene von TBX5 in den adulten Ventrikeln. Die validierten Zielgene lassen sich drei Gruppen zuordnen: Gene, mit einer Funktion in der kardialen Elektrophysiologie (Gja1, Kcnj5, Kcng2, Cacna1g, Chrm2), Kardioprotektion (Fhl2, Gpr22, Fgf16) und Kontraktion (Fstl4, Cmya5, Emilin2, Pdlim4). Zur Evaluierung des therapeutischen Potentials einer Wiederherstellung der TBX5 Expression im Hinblick auf Arrhythmiereduzierung und Herztodprävention injizierten wir arrhythmische vTbx5KO-Mäuse mit TBX5-codierenden adeno-assozierten Viren. Tatsächlich konnte diese Transduktion die Expression von TBX5 und seiner Zielgene wiederherstellen und - noch wichtiger - die Erregungsweiterleitung normalisieren und das Arrhythmierisiko reduzieren. Schlussfolgerungen Diese Studie zeigt, dass TBX5 nicht nur in der Entwicklung und der Erregungsleitung eine essentielle Rolle spielt, sondern auch für die Homöostase des Arbeitsmyokards essentiell ist. Die Wiederherstellung der TBX5 Expression kann die Zielgenexpression und kardiale Elektrophysiologie normalisieren.Background Cardiovascular disease is a common cause of death. About 60 % of cardiovascular mortality is attributable to sudden cardiac death, mostly caused by arrhythmia. The origin of arrhythmia can be an underlying chronic cardiac disease, but genetic factors are involved as well, especially in younger patients. A genetic factor associated with arrhythmia is the transcription factor T-box 5 (TBX5). Most studies investigated TBX5 in the context of developmental processes or with respect to conduction properties of the heart. Interestingly, TBX5 expression is dysregulated not only due to genetic factors: Ventricular samples from patients or animal models with cardiomyopathy show lower TBX5 expression than controls. Because of this aberrant expression pattern in the working myocardium, we hypothesized, that TBX5 plays an important role for tissue homoeostasis of the ventricular working myocardium. Methods & Results To investigate the consequences of TBX5 loss in the working myocardium, we generated an inducible primarily ventricular TBX5 KO model (vTbx5KO). This led to reduced heart growth and diastolic dysfunction in the vTbx5KO. Moreover, the mice presented with impeded conduction marked by PR- and QRS-prolongation and arrhythmias characterized by atrioventricular block and ventricular tachycardia. The survival of the vTbx5KO mice was reduced to 40%, probably attributable to sudden cardiac death. For the determination of the underlying molecular mechanism, we performed integrative chromatin occupancy and transcriptome analysis. This analysis revealed 47 targets of TBX5 in the adult ventricle. More profound analysis on a subset of genes identified three clusters of novel targets implicated in cardiac electrophysiology (Gja1, Kcnj5, Kcng2, Cacna1g, Chrm2), cardioprotection (Fhl2, Gpr22, Fgf16) and contraction (Fstl4, Cmya5, Emilin2, Pdlim4). Furthermore, we aimed to evaluate the therapeutic potential of restoration of TBX5 expression to revert arrhythmia and prevent sudden cardiac death. For this purpose, adeno-associated virus (AAV) encoding TBX5 were injected in vTbx5KO mice, that already suffered from arrhythmia. Indeed, the AAV led to a restoration of TBX5 and its target genes and more importantly to a normalisation of conduction and reduced arrhythmic propensity. Conclusions This study showed that beyond its role in the developing and adult conduction system, TBX5 is required for tissue homoeostasis and electrical signal propagation of the working myocardium. Its restoration after TBX5 loss can normalise target gene expression and cardiac electrophysiology.2021-08-3

Eine dreidimensionale Bewegungsanalyse des Angriffsschlages im Faustball

Due to its relevancy to point scoring, the spike is considered as one of the most important skills in fistball. Biomechanical analyses of this sport are very rare. In the present study, we performed a three-dimensional kinematic analysis of the fistball spike, which helps to specify performance parameters on a descriptive level. Recorded by four synchronized cameras (120 Hz) and linked to the motion capture software Simi Motion® 5.0, three female fistball players of the second German league (24–26 years, 1.63–1.69 m) performed several spikes under standardized conditions. Results show that the segment velocities of the arm reached their maximum successively from proximal to distal, following the principle of temporal coordination of single impulses. The wrist shows maximum speed when the fist hits the ball. The elbow joint angle performs a rapid transition from a strong flexion to a (almost) full extension; however, the extension is completed after the moment of ball impact. In contrast, the shoulder joint angle increases almost linearly until the fistball contact and decreases afterward. The findings can be used to optimize the training of the spike

A Three-Dimensional Movement Analysis of the Spike in Fistball

Due to its relevancy to point scoring, the spike is considered as one of the most important skills in fistball. Biomechanical analyses of this sport are very rare. In the present study, we performed a three-dimensional kinematic analysis of the fistball spike, which helps to specify performance parameters on a descriptive level. Recorded by four synchronized cameras (120 Hz) and linked to the motion capture software Simi Motion® 5.0, three female fistball players of the second German league (24–26 years, 1.63–1.69 m) performed several spikes under standardized conditions. Results show that the segment velocities of the arm reached their maximum successively from proximal to distal, following the principle of temporal coordination of single impulses. The wrist shows maximum speed when the fist hits the ball. The elbow joint angle performs a rapid transition from a strong flexion to a (almost) full extension; however, the extension is completed after the moment of ball impact. In contrast, the shoulder joint angle increases almost linearly until the fistball contact and decreases afterward. The findings can be used to optimize the training of the spike

Atrial fibrillation and heart failure-associated remodeling of two-pore-domain potassium (K2P) channels in murine disease models: focus on TASK-1

Understanding molecular mechanisms involved in atrial tissue remodeling and arrhythmogenesis in atrial fibrillation (AF) is essential for developing specific therapeutic approaches. Two-pore-domain potassium (K2P) channels modulate cellular excitability, and TASK-1 (K2P3.1) currents were recently shown to alter atrial action potential duration in AF and heart failure (HF). Finding animal models of AF that closely resemble pathophysiological alterations in human is a challenging task. This study aimed to analyze murine cardiac expression patterns of K2P channels and to assess modulation of K2P channel expression in murine models of AF and HF. Expression of cardiac K2P channels was quantified by real-time qPCR and immunoblot in mouse models of AF [cAMP-response element modulator (CREM)-IbΔC-X transgenic animals] or HF (cardiac dysfunction induced by transverse aortic constriction, TAC). Cloned murine, human, and porcine TASK-1 channels were heterologously expressed in Xenopus laevis oocytes. Two-electrode voltage clamp experiments were used for functional characterization. In murine models, among members of the K2P channel family, TASK-1 expression displayed highest levels in both atrial and ventricular tissue samples. Furthermore, K2P2.1, K2P5.1, and K2P6.1 showed significant expression levels. In CREM-transgenic mice, atrial expression of TASK-1 was significantly reduced in comparison with wild-type animals. In a murine model of TAC-induced pressure overload, ventricular TASK-1 expression remained unchanged, while atrial TASK-1 levels were significantly downregulated. When heterologously expressed in Xenopus oocytes, currents of murine, porcine, and human TASK-1 displayed similar characteristics. TASK-1 channels display robust cardiac expression in mice. Murine, porcine, and human TASK-1 channels share functional similarities. Dysregulation of atrial TASK-1 expression in murine AF and HF models suggests a mechanistic contribution to arrhythmogenesis

A context-specific cardiac β-catenin and GATA4 interaction influences TCF7L2 occupancy and remodels chromatin driving disease progression in the adult heart

Chromatin remodelling precedes transcriptional and structural changes in heart failure. A body of work suggests roles for the developmental Wnt signalling pathway in cardiac remodelling. Hitherto, there is no evidence supporting a direct role of Wnt nuclear components in regulating chromatin landscapes in this process. We show that transcriptionally active, nuclear, phosphorylated(p)Ser675-β-catenin and TCF7L2 are upregulated in diseased murine and human cardiac ventricles. We report that inducible cardiomyocytes (CM)-specific pSer675-β-catenin accumulation mimics the disease situation by triggering TCF7L2 expression. This enhances active chromatin, characterized by increased H3K27ac and TCF7L2 occupancies to cardiac developmental and remodelling genes in vivo. Accordingly, transcriptomic analysis of β-catenin stabilized hearts shows a strong recapitulation of cardiac developmental processes like cell cycling and cytoskeletal remodelling. Mechanistically, TCF7L2 co-occupies distal genomic regions with cardiac transcription factors NKX2–5 and GATA4 in stabilized-β-catenin hearts. Validation assays revealed a previously unrecognized function of GATA4 as a cardiac repressor of the TCF7L2/β-catenin complex in vivo, thereby defining a transcriptional switch controlling disease progression. Conversely, preventing β-catenin activation post-pressure-overload results in a downregulation of these novel TCF7L2-targets and rescues cardiac function. Thus, we present a novel role for TCF7L2/β-catenin in CMs-specific chromatin modulation, which could be exploited for manipulating the ubiquitous Wnt pathway.Open-Access-Publikatinsfonds 201