Tuning Wnt-signaling to enhance cardiomyogenesis in human embryonic and induced pluripotent stem cells

HOPX-associated molecular programs control cardiomyocyte cell states underpinning cardiac structure and function

Genomic regulation of cardiomyocyte differentiation is central to heart development and function. This study uses genetic loss-of-function human-induced pluripotent stem cell-derived cardiomyocytes to evaluate the genomic regulatory basis of the non-DNA-binding homeodomain protein HOPX. We show that HOPX interacts with and controls cardiac genes and enhancer networks associated with diverse aspects of heart development. Using perturbation studies in vitro, we define how upstream cell growth and proliferation control HOPX transcription to regulate cardiac gene programs. We then use cell, organoid, and zebrafish regeneration models to demonstrate that HOPX-regulated gene programs control cardiomyocyte function in development and disease. Collectively, this study mechanistically links cell signaling pathways as upstream regulators of HOPX transcription to control gene programs underpinning cardiomyocyte identity and function.

Recapitulating human tissue damage, repair, and fibrosis with human pluripotent stem cell-derived organoids

As new applications for human pluripotent stem cell-derived organoids in drug screenings and tissue replacement therapies emerge, there is a need to examine the mechanisms of tissue injury and repair recently reported for various organoid models. In most cases, organoids contain the main cell types and tissues present in human organs, spatially arranged in a manner that largely resembles the architecture of the organ. Depending on the differentiation protocol used, variations may exist in cell type ratios relative to the organ of reference, and certain tissues, including some parenchymal components and the endothelium, might be poorly represented, or lacking altogether. Despite those caveats, recent studies have shown that organoid tissue injury recapitulates major events and histopathological features of damaged human tissues. In particular, major mechanisms of parenchyma cell damage and interstitial fibrosis can be reproduced with remarkable faithfulness. Although further validation remains to be done in order to establish the relevance of using organoid for either mechanistic studies or drug assays, this technology is becoming a promising tool for the study of human tissue homeostasis, injury, and repair.

Epigenetic Contribution of High-Mobility Group A Proteins to Stem Cell Properties

High-mobility group A (HMGA) proteins have been examined to understand their participation as structural epigenetic chromatin factors that confer stem-like properties to embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and cancer stem cells (CSCs). The function of HMGA was evaluated in conjunction with that of other epigenetic factors such as histones and microRNAs (miRs), taking into consideration the posttranscriptional modifications (PTMs) of histones (acetylation and methylation) and DNA methylation. HMGA proteins were coordinated or associated with histone and DNA modification and the expression of the factors related to pluripotency. CSCs showed remarkable differences compared with ESCs and iPSCs.

Human-Induced Pluripotent Stem Cell-Based Modeling of Cardiac Storage Disorders

PURPOSE OF REVIEW

The aim of this study is to review the published human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) models of cardiac storage disorders and to evaluate the limitations and future applications of this technology.

RECENT FINDINGS

Several cardiac storage disorders (CSDs) have been modeled using patient-specific hiPSC-CMs, including Anderson-Fabry disease, Danon disease, and Pompe disease. These models have shown that patient-specific hiPSC-CMs faithfully recapitulate key phenotypic features of CSDs and respond predictably to pharmacologic manipulation. hiPSC-CMs generated from patients with CSDs are representative models of the patient disease state and can be used as an in vitro system for the study of human cardiomyocytes. While these models suffer from several limitations, they are likely to play an important role in future mechanistic studies of cardiac storage disorders and the development of targeted therapeutics for these diseases.

Development of a human cardiac organoid injury model reveals innate regenerative potential

The adult human heart possesses a limited regenerative potential following an ischemic event, and undergoes a number of pathological changes in response to injury. Although cardiac regeneration has been documented in zebrafish and neonatal mouse hearts, it is currently unknown whether the immature human heart is capable of undergoing complete regeneration. Combined progress in pluripotent stem cell differentiation and tissue engineering has facilitated the development of human cardiac organoids (hCOs), which resemble fetal heart tissue and can be used to address this important knowledge gap. This study aimed to characterize the regenerative capacity of immature human heart tissue in response to injury. Following cryoinjury with a dry ice probe, hCOs exhibited an endogenous regenerative response with full functional recovery 2 weeks after acute injury. Cardiac functional recovery occurred in the absence of pathological fibrosis or cardiomyocyte hypertrophy. Consistent with regenerative organisms and neonatal human hearts, there was a high basal level of cardiomyocyte proliferation, which may be responsible for the regenerative capacity of the hCOs. This study suggests that immature human heart tissue has an intrinsic capacity to regenerate.

Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes as a Model for Heart Development and Congenital Heart Disease

Congenital heart disease (CHD) remains a significant health problem, with a growing population of survivors with chronic disease. Despite intense efforts to understand the genetic basis of CHD in humans, the etiology of most CHD is unknown. Furthermore, new models of CHD are required to better understand the development of CHD and to explore novel therapies for this patient population. In this review, we highlight the role that human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes can serve to enhance our understanding of the development, pathophysiology and potential therapeutic targets for CHD. We highlight the use of hiPSC-derived cardiomyocytes to model gene regulatory interactions, cell-cell interactions and tissue interactions contributing to CHD. We further emphasize the importance of using hiPSC-derived cardiomyocytes as personalized research models. The use of hiPSCs presents an unprecedented opportunity to generate disease-specific cellular models, investigate the underlying molecular mechanisms of disease and uncover new therapeutic targets for CHD.

Current status of drug screening and disease modelling in human pluripotent stem cells

The emphasis in human pluripotent stem cell (hPSC) technologies has shifted from cell therapy to in vitro disease modelling and drug screening. This review examines why this shift has occurred, and how current technological limitations might be overcome to fully realise the potential of hPSCs. Details are provided for all disease-specific human induced pluripotent stem cell lines spanning a dozen dysfunctional organ systems. Phenotype and pharmacology have been examined in only 17 of 63 lines, primarily those that model neurological and cardiac conditions. Drug screening is most advanced in hPSC-cardiomyocytes. Responses for almost 60 agents include examples of how careful tests in hPSC-cardiomyocytes have improved on existing in vitro assays, and how these cells have been integrated into high throughput imaging and electrophysiology industrial platforms. Such successes will provide an incentive to overcome bottlenecks in hPSC technology such as improving cell maturity and industrial scalability whilst reducing cost.

Wnt signaling strength regulates normal hematopoiesis and its deregulation is involved in leukemia development

A strict balance between self-renewal and differentiation of hematopoietic stem cells (HSCs) is required in order to maintain homeostasis, as well as to efficiently respond to injury and infections. Numbers and fate decisions made by progenitors derived from HSC must also be carefully regulated to sustain large-scale production of blood cells. The complex Wnt family of molecules generally is thought to be important to these processes, delivering critical signals to HSC and progenitors as they reside in specialized niches. Wnt proteins have also been extensively studied in connection with malignancies and are causatively involved in the development of several types of leukemias. However, studies with experimental animal models have produced contradictory findings regarding the importance of Wnt signals for normal hematopoiesis and lymphopoiesis. Here, we will argue that dose dependency of signaling via particular Wnt pathways accounts for much, if not all of this controversy. We conclude that there seems little doubt that Wnt proteins are required to sustain normal hematopoiesis, but are likely to be presented in carefully controlled gradients in a tissue-specific manner.