Dysferlin links excitation-contraction coupling to structure and maintenance of the cardiac transverse-axial tubule system.

AIMS: The multi-C2 domain protein dysferlin localizes to the T-Tubule system of skeletal and heart muscles. In skeletal muscle, dysferlin is known to play a role in membrane repair and in T-tubule biogenesis and maintenance. Dysferlin deficiency manifests as muscular dystrophy of proximal and distal muscles. Cardiomyopathies have been also reported, and some dysferlinopathy mouse models develop cardiac dysfunction under stress. Generally, the role and functional relevance of dysferlin in the heart is not clear. The aim of this study was to analyse the effect of dysferlin deficiency on the transverse-axial tubule system (TATS) structure and on Ca2+ homeostasis in the heart. METHODS AND RESULTS: We studied dysferlin localization in rat and mouse cardiomyocytes by immunofluorescence microscopy. In dysferlin-deficient ventricular mouse cardiomyocytes, we analysed the TATS by live staining and assessed Ca2+ handling by patch-clamp experiments and measurement of Ca2+ transients and Ca2+ sparks. We found increasing co-localization of dysferlin with the L-type Ca2+-channel during TATS development and show that dysferlin deficiency leads to pathological loss of transversal and increase in longitudinal elements (axialization). We detected reduced L-type Ca2+-current (ICa,L) in cardiomyocytes from dysferlin-deficient mice and increased frequency of spontaneous sarcoplasmic reticulum Ca2+ release events resulting in pro-arrhythmic contractions. Moreover, cardiomyocytes from dysferlin-deficient mice showed an impaired response to ß-adrenergic receptor stimulation. CONCLUSIONS: Dysferlin is required for TATS biogenesis and maintenance in the heart by controlling the ratio of transversal and axial membrane elements. Absence of dysferlin leads to defects in Ca2+ homeostasis which may contribute to contractile heart dysfunction in dysferlinopathy patients.

Dysferlin mediates membrane tubulation and links T-tubule biogenesis to muscular dystrophy.

The multi-C2 domain protein dysferlin localizes to the plasma membrane and the T-tubule system in skeletal muscle; however, its physiological mode of action is unknown. Mutations in the DYSF gene lead to autosomal recessive limb-girdle muscular dystrophy type 2B and Miyoshi myopathy. Here, we show that dysferlin has membrane tubulating capacity and that it shapes the T-tubule system. Dysferlin tubulates liposomes, generates a T-tubule-like membrane system in non-muscle cells, and links the recruitment of phosphatidylinositol 4,5-bisphosphate to the biogenesis of the T-tubule system. Pathogenic mutant forms interfere with all of these functions, indicating that muscular wasting and dystrophy are caused by the dysferlin mutants' inability to form a functional T-tubule membrane system.

Multiple Localization by Functional Translational Readthrough.

In a compartmentalized cell, correct protein localization is crucial for function of virtually all cellular processes. From the cytoplasm as a starting point, proteins are imported into organelles by specific targeting signals. Many proteins, however, act in more than one cellular compartment. In this chapter, we discuss mechanisms by which proteins can be targeted to multiple organelles with a focus on a novel gene regulatory mechanism, functional translational readthrough, that permits multiple targeting of proteins to the peroxisome and other organelles. In mammals, lactate and malate dehydrogenase are the best-characterized enzymes whose targeting is controlled by functional translational readthrough.

Integrated care for older multimorbid heart failure patients: protocol for the ESCAPE randomized trial and cohort study.

ESCAPE: Evaluation of a patient-centred biopsychosocial blended collaborative care pathway for the treatment of multimorbid elderly patients. THERAPEUTIC AREA: Healthcare interventions for the management of older patients with multiple morbidities. AIMS: Multi-morbidity treatment is an increasing challenge for healthcare systems in ageing societies. This comprehensive cohort study with embedded randomized controlled trial tests an integrated biopsychosocial care model for multimorbid elderly patients. HYPOTHESIS: A holistic, patient-centred pro-active 9-month intervention based on the blended collaborative care (BCC) approach and enhanced by information and communication technologies can improve health-related quality of life (HRQoL) and disease outcomes as compared with usual care at 9 months. METHODS: Across six European countries, ESCAPE is recruiting patients with heart failure, mental distress/disorder plus ≥2 medical co-morbidities into an observational cohort study. Within the cohort study, 300 patients will be included in a randomized controlled assessor-blinded two-arm parallel group interventional clinical trial (RCT). In the intervention, trained care managers (CMs) regularly support patients and informal carers in managing their multiple health problems. Supervised by a clinical specialist team, CMs remotely support patients in implementing the treatment plan-customized to the patients' individual needs and preferences-into their daily lives and liaise with patients' healthcare providers. An eHealth platform with an integrated patient registry guides the intervention and helps to empower patients and informal carers. HRQoL measured with the EQ-5D-5L as primary endpoint, and secondary outcomes, that is, medical and patient-reported outcomes, healthcare costs, cost-effectiveness, and informal carer burden, will be assessed at 9 and ≥18 months. CONCLUSIONS: If proven effective, the ESCAPE BCC intervention can be implemented in routine care for older patients with multiple morbidities across the participating countries and beyond.