Generation of homogeneous populations of subtype-specific cardiomyocytes (CMs) derived from human induced pluripotent stem cells (iPSCs) and their comprehensive phenotyping is crucial for a better understanding of the subtype-related disease mechanisms and as tools for the development of chamber-specific drugs. The goals of this study were to apply a simple and efficient method for differentiation of iPSCs into defined functional CM subtypes in feeder-free conditions and to obtain a comprehensive understanding of the molecular, cell biological, and functional properties of atrial and ventricular iPSC-CMs on both the single-cell and engineered heart muscle (EHM) level. By a stage-specific activation of retinoic acid signaling in monolayer-based and well-defined culture, we showed that cardiac progenitors can be directed towards a highly homogeneous population of atrial CMs. By combining the transcriptome and proteome profiling of the iPSC-CM subtypes with functional characterizations via optical action potential and calcium imaging, and with contractile analyses in EHM, we demonstrated that atrial and ventricular iPSC-CMs and -EHM highly correspond to the atrial and ventricular heart muscle, respectively. This study provides a comprehensive understanding of the molecular and functional identities characteristic of atrial and ventricular iPSC-CMs and -EHM and supports their suitability in disease modeling and chamber-specific drug screening.

Cardiomyocytes can be implanted to remuscularize the failing heart^1–7. Challenges include sufficient cardiomyocyte retention for a sustainable therapeutic impact without intolerable side effects, such as arrhythmia and tumour growth. We investigated the hypothesis that epicardial engineered heart muscle (EHM) allografts from induced pluripotent stem cell-derived cardiomyocytes and stromal cells structurally and functionally remuscularize the chronically failing heart without limiting side effects in rhesus macaques. After confirmation of in vitro and in vivo (nude rat model) equivalence of the newly developed rhesus macaque EHM model with a previously established Good Manufacturing Practice-compatible human EHM formulation⁸, long-term retention (up to 6 months) and dose-dependent enhancement of the target heart wall by EHM grafts constructed from 40 to 200 million cardiomyocytes/stromal cells were demonstrated in macaques with and without myocardial infarction-induced heart failure. In the heart failure model, evidence for EHM allograft-enhanced target heart wall contractility and ejection fraction, which are measures for local and global heart support, was obtained. Histopathological and gadolinium-based perfusion magnetic resonance imaging analyses confirmed cell retention and functional vascularization. Arrhythmia and tumour growth were not observed. The obtained feasibility, safety and efficacy data provided the pivotal underpinnings for the approval of a first-in-human clinical trial on tissue-engineered heart repair. Our clinical data confirmed remuscularization by EHM implantation in a patient with advanced heart failure.

Stable expression of truncated titin proteins and titin haploinsufficiency characterizeTTNcardiomyopathy and represent targets for therapy.

Dystrophin maintains the integrity of striated muscles by linking the actin cytoskeleton with the cell membrane. Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene ( DMD ) that result in progressive, debilitating muscle weakness, cardiomyopathy, and a shortened lifespan. Mutations of dystrophin that disrupt the amino-terminal actin-binding domain 1 (ABD-1), encoded by exons 2–8, represent the second-most common cause of DMD. In the present study, we compared three different strategies for CRISPR/Cas9 genome editing to correct mutations in the ABD-1 region of the DMD gene by deleting exons 3–9, 6–9, or 7–11 in human induced pluripotent stem cells (iPSCs) and by assessing the function of iPSC-derived cardiomyocytes. All three exon deletion strategies enabled the expression of truncated dystrophin protein and restoration of cardiomyocyte contractility and calcium transients to varying degrees. We show that deletion of exons 3–9 by genomic editing provides an especially effective means of correcting disease-causing ABD-1 mutations. These findings represent an important step toward eventual correction of common DMD mutations and provide a means of rapidly assessing the expression and function of internally truncated forms of dystrophin-lacking portions of ABD-1.

Background: Human pluripotent stem cell‐derived muscle models show great potential for translational research. Here, we describe developmentally inspired methods for the derivation of skeletal muscle cells and their utility in skeletal muscle tissue engineering with the aim to model skeletal muscle regeneration and dystrophy in vitro.Methods: Key steps include the directed differentiation of human pluripotent stem cells to embryonic muscle progenitors followed by primary and secondary foetal myogenesis into three‐dimensional muscle. To simulate Duchenne muscular dystrophy (DMD), a patient‐specific induced pluripotent stem cell line was compared to a CRISPR/Cas9‐edited isogenic control line.Results: The established skeletal muscle differentiation protocol robustly and faithfully recapitulates critical steps of embryonic myogenesis in two‐dimensional and three‐dimensional cultures, resulting in functional human skeletal muscle organoids (SMOs) and engineered skeletal muscles (ESMs) with a regeneration‐competent satellite‐like cell pool. Tissue‐engineered muscle exhibits organotypic maturation and function (up to 5.7 ± 0.5 mN tetanic twitch tension at 100 Hz in ESM). Contractile performance could be further enhanced by timed thyroid hormone treatment, increasing the speed of contraction (time to peak contraction) as well as relaxation (time to 50% relaxation) of single twitches from 107 ± 2 to 75 ± 4 ms (P < 0.05) and from 146 ± 6 to 100 ± 6 ms (P < 0.05), respectively. Satellite‐like cells could be documented as largely quiescent PAX7⁺ cells (75 ± 6% Ki67⁻) located adjacent to muscle fibres confined under a laminin‐containing basal membrane. Activation of the engineered satellite‐like cell niche was documented in a cardiotoxin injury model with marked recovery of contractility to 57 ± 8% of the pre‐injury force 21 days post‐injury (P < 0.05 compared to Day 2 post‐injury), which was completely blocked by preceding irradiation. Absence of dystrophin in DMD ESM caused a marked reduction of contractile force (−35 ± 7%, P < 0.05) and impaired expression of fast myosin isoforms resulting in prolonged contraction (175 ± 14 ms, P < 0.05 vs. gene‐edited control) and relaxation (238 ± 22 ms, P < 0.05 vs. gene‐edited control) times. Restoration of dystrophin levels by gene editing rescued the DMD phenotype in ESM.Conclusions: We introduce human muscle models with canonical properties of bona fide skeletal muscle in vivo to study muscle development, maturation, disease and repair.

Pharmacological inhibition of AQP1 prevents H ₂ O ₂ transport and hypertrophy of cardiac myocytes.