Incomplete Assembly of the Dystrophin-Associated Protein Complex in 2D and 3D-Cultured Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

In situ monolayer patch clamp of acutely stimulated human iPSC-derived cardiomyocytes promotes consistent electrophysiological responses to SK channel inhibition

Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) represent an in vitro model of cardiac function. Isolated iPSC-CMs, however, exhibit electrophysiological heterogeneity which hinders their utility in the study of certain cardiac currents. In the healthy adult heart, the current mediated by small conductance, calcium-activated potassium (SK) channels (ISK) is atrial-selective. Functional expression of ISK within atrial-like iPSC-CMs has not been explored thoroughly. The present study therefore aimed to investigate atrial-like iPSC-CMs as a model system for the study of ISK. iPSCs were differentiated using retinoic acid (RA) to produce iPSC-CMs which exhibited an atrial-like phenotype (RA-iPSC-CMs). Only 18% of isolated RA-iPSC-CMs responded to SK channel inhibition by UCL1684 and isolated iPSC-CMs exhibited substantial cell-to-cell electrophysiological heterogeneity. This variability was significantly reduced by patch clamp of RA-iPSC-CMs in situ as a monolayer (iPSC-ML). A novel method of electrical stimulation was developed to facilitate recording from iPSC-MLs via In situ Monolayer Patch clamp of Acutely Stimulated iPSC-CMs (IMPASC). Using IMPASC, > 95% of iPSC-MLs could be paced at a 1 Hz. In contrast to isolated RA-iPSC-CMs, 100% of RA-iPSC-MLs responded to UCL1684, with APD50 being prolonged by 16.0 ± 2.0 ms (p < 0.0001; n = 12). These data demonstrate that in conjunction with IMPASC, RA-iPSC-MLs represent an improved model for the study of ISK. IMPASC may be of wider value in the study of other ion channels that are inconsistently expressed in isolated iPSC-CMs and in pharmacological studies.

The new era of cardiovascular research: revolutionizing cardiovascular research with 3D models in a dish

Cardiovascular research has heavily relied on studies using patient samples and animal models. However, patient studies often miss the data from the crucial early stage of cardiovascular diseases, as obtaining primary tissues at this stage is impracticable. Transgenic animal models can offer some insights into disease mechanisms, although they usually do not fully recapitulate the phenotype of cardiovascular diseases and their progression. In recent years, a promising breakthrough has emerged in the form of in vitro three-dimensional (3D) cardiovascular models utilizing human pluripotent stem cells. These innovative models recreate the intricate 3D structure of the human heart and vessels within a controlled environment. This advancement is pivotal as it addresses the existing gaps in cardiovascular research, allowing scientists to study different stages of cardiovascular diseases and specific drug responses using human-origin models. In this review, we first outline various approaches employed to generate these models. We then comprehensively discuss their applications in studying cardiovascular diseases by providing insights into molecular and cellular changes associated with cardiovascular conditions. Moreover, we highlight the potential of these 3D models serving as a platform for drug testing to assess drug efficacy and safety. Despite their immense potential, challenges persist, particularly in maintaining the complex structure of 3D heart and vessel models and ensuring their function is comparable to real organs. However, overcoming these challenges could revolutionize cardiovascular research. It has the potential to offer comprehensive mechanistic insights into human-specific disease processes, ultimately expediting the development of personalized therapies.

Efficacy of exon-skipping therapy for DMD cardiomyopathy with mutations in actin binding domain 1

Exon-skipping therapy is a promising treatment strategy for Duchenne muscular dystrophy (DMD), which is caused by loss-of-function mutations in the DMD gene encoding dystrophin, leading to progressive cardiomyopathy. In-frame deletion of exons 3-9 (Δ3-9), manifesting a very mild clinical phenotype, is a potential targeted reading frame for exon-skipping by targeting actin-binding domain 1 (ABD1); however, the efficacy of this approach for DMD cardiomyopathy remains uncertain. In this study, we compared three isogenic human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) expressing Δ3-9, frameshifting Δ3-7, or intact DMD. RNA sequencing revealed a resemblance in the expression patterns of mechano-transduction-related genes between Δ3-9 and wild-type samples. Furthermore, we observed similar electrophysiological properties between Δ3-9 and wild-type hiPSC-CMs; Δ3-7 hiPSC-CMs showed electrophysiological alterations with accelerated CaMKII activation. Consistently, Δ3-9 hiPSC-CMs expressed substantial internally truncated dystrophin protein, resulting in maintaining F-actin binding and desmin retention. Antisense oligonucleotides targeting exon 8 efficiently induced skipping exons 8-9 to restore functional dystrophin and electrophysiological parameters in Δ3-7 hiPSC-CMs, bringing the cell characteristics closer to those of Δ3-9 hiPSC-CMs. Collectively, exon-skipping targeting ABD1 to convert the reading frame to Δ3-9 may become a promising therapy for DMD cardiomyopathy.

Optical Mapping of Cardiomyocytes in Monolayer Derived from Induced Pluripotent Stem Cells

Optical mapping is a powerful imaging technique widely adopted to measure membrane potential changes and intracellular Ca2+ variations in excitable tissues using voltage-sensitive dyes and Ca2+ indicators, respectively. This powerful tool has rapidly become indispensable in the field of cardiac electrophysiology for studying depolarization wave propagation, estimating the conduction velocity of electrical impulses, and measuring Ca2+ dynamics in cardiac cells and tissues. In addition, mapping these electrophysiological parameters is important for understanding cardiac arrhythmia mechanisms. In this review, we delve into the fundamentals of cardiac optical mapping technology and its applications when applied to hiPSC-derived cardiomyocytes and discuss related advantages and challenges. We also provide a detailed description of the processing and analysis of optical mapping data, which is a crucial step in the study of cardiac diseases and arrhythmia mechanisms for extracting and comparing relevant electrophysiological parameters.

Modeling Duchenne Muscular Dystrophy Cardiomyopathy with Patients' Induced Pluripotent Stem-Cell-Derived Cardiomyocytes

Duchenne muscular dystrophy (DMD) is an X-linked progressive muscle degenerative disease caused by mutations in the dystrophin gene, resulting in death by the end of the third decade of life at the latest. A key aspect of the DMD clinical phenotype is dilated cardiomyopathy, affecting virtually all patients by the end of the second decade of life. Furthermore, despite respiratory complications still being the leading cause of death, with advancements in medical care in recent years, cardiac involvement has become an increasing cause of mortality. Over the years, extensive research has been conducted using different DMD animal models, including the mdx mouse. While these models present certain important similarities to human DMD patients, they also have some differences which pose a challenge to researchers. The development of somatic cell reprograming technology has enabled generation of human induced pluripotent stem cells (hiPSCs) which can be differentiated into different cell types. This technology provides a potentially endless pool of human cells for research. Furthermore, hiPSCs can be generated from patients, thus providing patient-specific cells and enabling research tailored to different mutations. DMD cardiac involvement has been shown in animal models to include changes in gene expression of different proteins, abnormal cellular Ca²⁺ handling, and other aberrations. To gain a better understanding of the disease mechanisms, it is imperative to validate these findings in human cells. Furthermore, with the recent advancements in gene-editing technology, hiPSCs provide a valuable platform for research and development of new therapies including the possibility of regenerative medicine. In this article, we review the DMD cardiac-related research performed so far using human hiPSCs-derived cardiomyocytes (hiPSC-CMs) carrying DMD mutations.

Long-term culture of patient-derived cardiac organoids recapitulated Duchenne muscular dystrophy cardiomyopathy and disease progression

Duchenne Muscular Dystrophy (DMD) is an X-linked neuromuscular disease which to date is incurable. The major cause of death is dilated cardiomyopathy however, its pathogenesis is unclear as existing cellular and animal models do not fully recapitulate the human disease phenotypes. In this study, we generated cardiac organoids from patient-derived induced pluripotent stem cells (DMD-COs) and isogenic-corrected controls (DMD-Iso-COs) and studied if DMD-related cardiomyopathy and disease progression occur in the organoids upon long-term culture (up to 93 days). Histological analysis showed that DMD-COs lack initial proliferative capacity, displayed a progressive loss of sarcoglycan localization and high stress in endoplasmic reticulum. Additionally, cardiomyocyte deterioration, fibrosis and aberrant adipogenesis were observed in DMD-COs over time. RNA sequencing analysis confirmed a distinct transcriptomic profile in DMD-COs which was associated with functional enrichment in hypertrophy/dilated cardiomyopathy, arrhythmia, adipogenesis and fibrosis pathways. Moreover, five miRNAs were identified to be crucial in this dysregulated gene network. In conclusion, we generated patient-derived cardiac organoid model that displayed DMD-related cardiomyopathy and disease progression phenotypes in long-term culture. We envision the feasibility to develop a more complex, realistic and reliable in vitro 3D human cardiac-mimics to study DMD-related cardiomyopathies.

Full-length dystrophin deficiency leads to contractile and calcium transient defects in human engineered heart tissues

Cardiomyopathy is currently the leading cause of death for patients with Duchenne muscular dystrophy (DMD), a severe neuromuscular disorder affecting young boys. Animal models have provided insight into the mechanisms by which dystrophin protein deficiency causes cardiomyopathy, but there remains a need to develop human models of DMD to validate pathogenic mechanisms and identify therapeutic targets. Here, we have developed human engineered heart tissues (EHTs) from CRISPR-edited, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) expressing a truncated dystrophin protein lacking part of the actin-binding domain. The 3D EHT platform enables direct measurement of contractile force, simultaneous monitoring of Ca2+ transients, and assessment of myofibril structure. Dystrophin-mutant EHTs produced less contractile force as well as delayed kinetics of force generation and relaxation, as compared to isogenic controls. Contractile dysfunction was accompanied by reduced sarcomere length, increased resting cytosolic Ca2+ levels, delayed Ca2+ release and reuptake, and increased beat rate irregularity. Transcriptomic analysis revealed clear differences between dystrophin-deficient and control EHTs, including downregulation of genes related to Ca2+ homeostasis and extracellular matrix organization, and upregulation of genes related to regulation of membrane potential, cardiac muscle development, and heart contraction. These findings indicate that the EHT platform provides the cues necessary to expose the clinically-relevant, functional phenotype of force production as well as mechanistic insights into the role of Ca2+ handling and transcriptomic dysregulation in dystrophic cardiac function, ultimately providing a powerful platform for further studies in disease modeling and drug discovery.

Mesoangioblasts at 20: From the embryonic aorta to the patient bed

In 2002 we published an article describing a population of vessel-associated progenitors that we termed mesoangioblasts (MABs). During the past decade evidence had accumulated that during muscle development and regeneration things may be more complex than a simple sequence of binary choices (e.g., dorsal vs. ventral somite). LacZ expressing fibroblasts could fuse with unlabelled myoblasts but not among themselves or with other cell types. Bone marrow derived, circulating progenitors were able to participate in muscle regeneration, though in very small percentage. Searching for the embryonic origin of these progenitors, we identified them as originating at least in part from the embryonic aorta and, at later stages, from the microvasculature of skeletal muscle. While continuing to investigate origin and fate of MABs, the fact that they could be expanded in vitro (also from human muscle) and cross the vessel wall, suggested a protocol for the cell therapy of muscular dystrophies. We tested this protocol in mice and dogs before proceeding to the first clinical trial on Duchenne Muscular Dystrophy patients that showed safety but minimal efficacy. In the last years, we have worked to overcome the problem of low engraftment and tried to understand their role as auxiliary myogenic progenitors during development and regeneration.