Precise Correction of Heterozygous SHOX2 Mutations in hiPSCs Derived from Patients with Atrial Fibrillation via Genome Editing and Sib Selection

Advances in human induced pluripotent stem cell (hiPSC)-based disease modelling in cardiogenetics

Human induced pluripotent stem cell (hiPSC)-based disease modelling has significantly advanced the field of cardiogenetics, providing a precise, patient-specific platform for studying genetic causes of heart diseases. Coupled with genome editing technologies such as CRISPR/Cas, hiPSC-based models not only allow the creation of isogenic lines to study mutation-specific cardiac phenotypes, but also enable the targeted modulation of gene expression to explore the effects of genetic and epigenetic deficits at the cellular and molecular level. hiPSC-based models of heart disease range from two-dimensional cultures of hiPSC-derived cardiovascular cell types, such as various cardiomyocyte subtypes, endothelial cells, pericytes, vascular smooth muscle cells, cardiac fibroblasts, immune cells, etc., to cardiac tissue cultures including organoids, microtissues, engineered heart tissues, and microphysiological systems. These models are further enhanced by multi-omics approaches, integrating genomic, transcriptomic, epigenomic, proteomic, and metabolomic data to provide a comprehensive view of disease mechanisms. In particular, advances in cardiovascular tissue engineering enable the development of more physiologically relevant systems that recapitulate native heart architecture and function, allowing for more accurate modelling of cardiac disease, drug screening, and toxicity testing, with the overall goal of personalised medical approaches, where therapies can be tailored to individual genetic profiles. Despite significant progress, challenges remain in the maturation of hiPSC-derived cardiomyocytes and the complexity of reproducing adult heart conditions. Here, we provide a concise update on the most advanced methods of hiPSC-based disease modelling in cardiogenetics, with a focus on genome editing and cardiac tissue engineering.

The Current State of Realistic Heart Models for Disease Modelling and Cardiotoxicity

One of the many unresolved obstacles in the field of cardiovascular research is an uncompromising in vitro cardiac model. While primary cell sources from animal models offer both advantages and disadvantages, efforts over the past half-century have aimed to reduce their use. Additionally, obtaining a sufficient quantity of human primary cardiomyocytes faces ethical and legal challenges. As the practically unlimited source of human cardiomyocytes from induced pluripotent stem cells (hiPSC-CM) is now mostly resolved, there are great efforts to improve their quality and applicability by overcoming their intrinsic limitations. The greatest bottleneck in the field is the in vitro ageing of hiPSC-CMs to reach a maturity status that closely resembles that of the adult heart, thereby allowing for more appropriate drug developmental procedures as there is a clear correlation between ageing and developing cardiovascular diseases. Here, we review the current state-of-the-art techniques in the most realistic heart models used in disease modelling and toxicity evaluations from hiPSC-CM maturation through heart-on-a-chip platforms and in silico models to the in vitro models of certain cardiovascular diseases.

Progress and Prospects of Gene Editing in Pluripotent Stem Cells

Applying programmable nucleases in gene editing has greatly shaped current research in basic biology and clinical translation. Gene editing in human pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), is highly relevant to clinical cell therapy and thus should be examined with particular caution. First, since all mutations in PSCs will be carried to all their progenies, off-target edits of editors will be amplified. Second, due to the hypersensitivity of PSCs to DNA damage, double-strand breaks (DSBs) made by gene editing could lead to low editing efficiency and the enrichment of cell populations with defective genomic safeguards. In this regard, DSB-independent gene editing tools, such as base editors and prime editors, are favored due to their nature to avoid these consequences. With more understanding of the microbial world, new systems, such as Cas-related nucleases, transposons, and recombinases, are also expanding the toolbox for gene editing. In this review, we discuss current applications of programmable nucleases in PSCs for gene editing, the efforts researchers have made to optimize these systems, as well as new tools that can be potentially employed for differentiation modeling and therapeutic applications.

Generation of JAG1 gene c.1615C > T heterozygous mutation human embryonic stem cell line (SDQLCHe001-A) using cytosine base editor

Pathogenic variants in Jagged-1 (JAG1), which encodes the ligand of the Notch receptor, had been demonstrated to cause Alagille syndrome. However, there is no evidence to support any genotype-phenotype correlations. Here, we generated a gene-edited human embryonic stem cell (hESC) line (H9) carrying the c.1615C > T mutation in JAG1 that was identified in a patient with Alagille syndrome (ALGS). This modified cell line was accomplished by using cytosine base editor (CBE), and may serve as a valuable model for JAG1 mutaion related disease, and facilitate to gain more insight into the biological function of JAG1.

Novel Candidate Regulators and Developmental Trajectory of Pituitary Thyrotropes

The pituitary gland regulates growth, metabolism, reproduction, the stress response, uterine contractions, lactation, and water retention. It secretes hormones in response to hypothalamic input, end organ feedback, and diurnal cues. The mechanisms by which pituitary stem cells are recruited to proliferate, maintain quiescence, or differentiate into specific cell types, especially thyrotropes, are not well understood. We used single-cell RNA sequencing in juvenile P7 mouse pituitary cells to identify novel factors in pituitary cell populations, with a focus on thyrotropes and rare subtypes. We first observed cells coexpressing markers of both thyrotropes and gonadotropes, such as Pou1f1 and Nr5a1. This was validated in vivo by both immunohistochemistry and lineage tracing of thyrotropes derived from Nr5a1-Cre; mTmG mice and demonstrates that Nr5a1-progenitors give rise to a proportion of thyrotropes during development. Our data set also identifies novel factors expressed in pars distalis and pars tuberalis thyrotropes, including the Shox2b isoform in all thyrotropes and Sox14 specifically in Pou1f1-negative pars tuberalis thyrotropes. We have therefore used single-cell transcriptomics to determine a novel developmental trajectory for thyrotropes and potential novel regulators of thyrotrope populations.

Generation of two homozygous SHOX2 knock-out human induced pluripotent stem cell lines using CRISPR/Cas9

SHOX2 is a homeobox transcription factor associated with atrial fibrillation (AF) and sinus node dysfunction. Here, we generated two homozygous SHOX2 knock-out hiPSC lines from a healthy control line and a corrected AF patient line (disease-specific SHOX2 mutation corrected to WT) using CRISPR/Cas9. These cell lines maintained pluripotency, an ability to differentiate into all three germlayers and a normal karyotype, presenting a valuable tool to investigate the impact of a full SHOX2 knock-out with respect to arrhythmogenic diseases on a cellular level.

An mRNA assay system demonstrates proteasomal-specific degradation contributes to cardiomyopathic phospholamban null mutation

Background

The human L39X phospholamban (PLN) cardiomyopathic mutant has previously been reported as a null mutation but the detailed molecular pathways that lead to the complete lack of detectable protein remain to be clarified. Previous studies have shown the implication between an impaired cellular degradation homeostasis and cardiomyopathy development. Therefore, uncovering the underlying mechanism responsible for the lack of PLN protein has important implications in understanding the patient pathology, chronic human calcium dysregulation and aid the development of potential therapeutics.

Methods

A panel of mutant and wild-type reporter tagged PLN modified mRNA (modRNA) constructs were transfected in human embryonic stem cell-derived cardiomyocytes. Lysosomal and proteasomal chemical inhibitors were used together with cell imaging and protein analysis tools in order to dissect degradation pathways associated with expressed PLN constructs. Transcriptional profiling of the cardiomyocytes transfected by wild-type or L39X mutant PLN modRNA was analysed with bulk RNA sequencing.

Results

Our modRNA assay system revealed that transfected L39X mRNA was stable and actively translated in vitro but with only trace amount of protein detectable. Proteasomal inhibition of cardiomyocytes transfected with L39X mutant PLN modRNA showed a fourfold increase in protein expression levels. Additionally, RNA sequencing analysis of protein degradational pathways showed a significant distinct transcriptomic signature between wild-type and L39X mutant PLN modRNA transfected cardiomyocytes.

Conclusion

Our results demonstrate that the cardiomyopathic PLN null mutant L39X is rapidly, actively and specifically degraded by proteasomal pathways. Herein, and to the best of our knowledge, we report for the first time the usage of modified mRNAs to screen for and illuminate alternative molecular pathways found in genes associated with inherited cardiomyopathies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00362-8.