SHOX2 overexpression favors differentiation of embryonic stem cells into cardiac pacemaker cells, improving biological pacing ability

iPSC-Derived Biological Pacemaker-From Bench to Bedside

Induced pluripotent stem cell (iPSC)-derived biological pacemakers have emerged as an alternative to traditional electronic pacemakers for managing cardiac arrhythmias. While effective, electronic pacemakers face challenges such as device failure, lead complications, and surgical risks, particularly in children. iPSC-derived pacemakers offer a promising solution by mimicking the sinoatrial node's natural pacemaking function, providing a more physiological approach to rhythm control. These cells can differentiate into cardiomyocytes capable of autonomous electrical activity, integrating into heart tissue. However, challenges such as achieving cellular maturity, long-term functionality, and immune response remain significant barriers to clinical translation. Future research should focus on refining gene-editing techniques, optimizing differentiation, and developing scalable production processes to enhance the safety and effectiveness of these biological pacemakers. With further advancements, iPSC-derived pacemakers could offer a patient-specific, durable alternative for cardiac rhythm management. This review discusses key advancements in differentiation protocols and preclinical studies, demonstrating their potential in treating dysrhythmias.

Odz4 upregulates SAN-specific genes to promote differentiation into cardiac pacemaker-like cells

Cardiac arrhythmias stemming from abnormal sinoatrial node (SAN) function can lead to sudden death. Developing a biological pacemaker device for treating sick sinus syndrome (SSS) could offer a potential cure. Understanding SAN differentiation is crucial, yet its regulatory mechanism remains unclear. We reanalyzed published RNA-seq data and identified Odz4 as a SAN-specific candidate. In situ hybridization revealed Odz4 expression in the cardiac crescent and throughout the cardiac conduction system (CCS). To assess the role of Odz4 in CCS differentiation, we utilized a Tet-Off inducible system for its intracellular domain (ICD). Embryonic bodies (EBs) exogenously expressing Odz4-ICD exhibited an increased propensity to develop into pacemaker-like cells with enhanced automaticity and upregulated expression of SAN-specific genes. CellChat and GO analyses unveiled SAN-specific enrichment of ligand-receptor sets, especially Ptn-Ncl, and extracellular matrix components in the group exogenously expressing Odz4-ICD. Our findings underscore the significance of Odz4 in SAN development and offer fresh insights into biological pacemaker establishment.

A new paradigm for generating high-quality cardiac pacemaker cells from mouse pluripotent stem cells

Cardiac biological pacing (BP) is one of the future directions for bradyarrhythmias intervention. Currently, cardiac pacemaker cells (PCs) used for cardiac BP are mainly derived from pluripotent stem cells (PSCs). However, the production of high-quality cardiac PCs from PSCs remains a challenge. Here, we developed a cardiac PC differentiation strategy by adopting dual PC markers and simulating the developmental route of PCs. First, two PC markers, Shox2 and Hcn4, were selected to establish Shox2:EGFP; Hcn4:mCherry mouse PSC reporter line. Then, by stepwise guiding naïve PSCs to cardiac PCs following naïve to formative pluripotency transition and manipulating signaling pathways during cardiac PCs differentiation, we designed the FSK method that increased the yield of SHOX2+; HCN4+ cells with typical PC characteristics, which was 12 and 42 folds higher than that of the embryoid body (EB) and the monolayer M10 methods respectively. In addition, the in vitro cardiac PCs differentiation trajectory was mapped by single-cell RNA sequencing (scRNA-seq), which resembled in vivo PCs development, and ZFP503 was verified as a key regulator of cardiac PCs differentiation. These PSC-derived cardiac PCs have the potential to drive advances in cardiac BP technology, help with the understanding of PCs (patho)physiology, and benefit drug discovery for PC-related diseases as well.

Differentiation of Sinoatrial-like Cardiomyocytes as a Biological Pacemaker Model

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are widely used for disease modeling and pharmacological screening. However, their application has mainly focused on inherited cardiopathies affecting ventricular cardiomyocytes, leading to extensive knowledge on generating ventricular-like hiPSC-CMs. Electronic pacemakers, despite their utility, have significant disadvantages, including lack of hormonal responsiveness, infection risk, limited battery life, and inability to adapt to changes in heart size. Therefore, developing an in vitro multiscale model of the human sinoatrial node (SAN) pacemaker using hiPSC-CM and SAN-like cardiomyocyte differentiation protocols is essential. This would enhance the understanding of SAN-related pathologies and support targeted therapies. Generating SAN-like cardiomyocytes offers the potential for biological pacemakers and specialized conduction tissues, promising significant benefits for patients with conduction system defects. This review focuses on arrythmias related to pacemaker dysfunction, examining protocols' advantages and drawbacks for generating SAN-like cardiomyocytes from hESCs/hiPSCs, and discussing therapeutic approaches involving their engraftment in animal models.

Gene and stem cell therapy for inherited cardiac arrhythmias

Inherited cardiac arrhythmias are a group of genetic diseases predisposing to sudden cardiac arrest, mainly resulting from variants in genes encoding cardiac ion channels or proteins involved in their regulation. Currently available therapeutic options (pharmacotherapy, ablative therapy and device-based therapy) can not preclude the occurrence of arrhythmia events and/or provide complete protection. With growing understanding of the genetic background and molecular mechanisms of inherited cardiac arrhythmias, advancing insight of stem cell technology, and development of vectors and delivery strategies, gene therapy and stem cell therapy may be promising approaches for treatment of inherited cardiac arrhythmias. Recent years have witnessed impressive progress in the basic science aspects and there is a clear and urgent need to be translated into the clinical management of arrhythmic events. In this review, we present a succinct overview of gene and cell therapy strategies, and summarize the current status of gene and cell therapy. Finally, we discuss future directions for implementation of gene and cell therapy in the therapy of inherited cardiac arrhythmias.

The cardiac conduction system: History, development, and disease

The heart is the first organ to form during embryonic development, establishing the circulatory infrastructure necessary to sustain life and enable downstream organogenesis. Critical to the heart's function is its ability to initiate and propagate electrical impulses that allow for the coordinated contraction and relaxation of its chambers, and thus, the movement of blood and nutrients. Several specialized structures within the heart, collectively known as the cardiac conduction system (CCS), are responsible for this phenomenon. In this review, we discuss the discovery and scientific history of the mammalian cardiac conduction system as well as the key genes and transcription factors implicated in the formation of its major structures. We also describe known human diseases related to CCS development and explore existing challenges in the clinical context.

Pluripotent stem cell-based cardiac regenerative therapy for heart failure

Cardiac regenerative therapy using human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) is expected to become an alternative to heart transplantation for severe heart failure. It is now possible to produce large numbers of human pluripotent stem cells (hPSCs) and eliminate non-cardiomyocytes, including residual undifferentiated hPSCs, which can cause teratoma formation after transplantation. There are two main strategies for transplanting hPSC-CMs: injection of hPSC-CMs into the myocardium from the epicardial side, and implantation of hPSC-CM patches or engineered heart tissues onto the epicardium. Transplantation of hPSC-CMs into the myocardium of large animals in a myocardial infarction model improved cardiac function. The engrafted hPSC-CMs matured, and microvessels derived from the host entered the graft abundantly. Furthermore, as less invasive methods using catheters, injection into the coronary artery and injection into the myocardium from the endocardium side have recently been investigated. Since transplantation of hPSC-CMs alone has a low engraftment rate, various methods such as transplantation with the extracellular matrix or non-cardiomyocytes and aggregation of hPSC-CMs have been developed. Post-transplant arrhythmias, imaging of engrafted hPSC-CMs, and immune rejection are the remaining major issues, and research is being conducted to address them. The clinical application of cardiac regenerative therapy using hPSC-CMs has just begun and is expected to spread widely if its safety and efficacy are proven in the near future.

Recent advances in pluripotent stem cell-derived cardiac organoids and heart-on-chip applications for studying anti-cancer drug-induced cardiotoxicity

Cardiovascular disease (CVD) caused by anti-cancer drug-induced cardiotoxicity is now the second leading cause of mortality among cancer survivors. It is necessary to establish efficient in vitro models for early predicting the potential cardiotoxicity of anti-cancer drugs, as well as for screening drugs that would alleviate cardiotoxicity during and post treatment. Human induced pluripotent stem cells (hiPSCs) have opened up new avenues in cardio-oncology. With the breakthrough of tissue engineering technology, a variety of hiPSC-derived cardiac microtissues or organoids have been recently reported, which have shown enormous potential in studying cardiotoxicity. Moreover, using hiPSC-derived heart-on-chip for studying cardiotoxicity has provided novel insights into the underlying mechanisms. Herein, we summarize different types of anti-cancer drug-induced cardiotoxicities and present an extensive overview on the applications of hiPSC-derived cardiac microtissues, cardiac organoids, and heart-on-chips in cardiotoxicity. Finally, we highlight clinical and translational challenges around hiPSC-derived cardiac microtissues/organoids/heart-on chips and their applications in anti-cancer drug-induced cardiotoxicity. • Anti-cancer drug-induced cardiotoxicities represent pressing challenges for cancer treatments, and cardiovascular disease is the second leading cause of mortality among cancer survivors. • Newly reported in vitro models such as hiPSC-derived cardiac microtissues/organoids/chips show enormous potential for studying cardio-oncology. • Emerging evidence supports that hiPSC-derived cardiac organoids and heart-on-chip are promising in vitro platforms for predicting and minimizing anti-cancer drug-induced cardiotoxicity.

The method of sinus node-like pacemaker cells from human induced pluripotent stem cells by BMP and Wnt signaling

The embryonic development of sinus nodes (SAN) is co-regulated by multiple signaling pathways. Among these, the bone morphogenetic protein (BMP) and Wnt signaling pathways are involved in the development of SAN. In this study, the effects of BMP and Wnt signaling on the differentiation of SAN-like pacemaker cells (SANLPCs) were investigated. Human induced pluripotent stem cells (hiPSCs) were divided into four groups: control, BMP4, CHIR-3, and BMP4 + CHIR (CHIR: a Wnt signaling activator). The samples were tested at day (D) 15 of differentiation. The final protocol for the activation of BMP signaling at D0-D3 and reactivation of Wnt signaling at D5-D7 in the differentiation of hiPSCs were determined. The results showed that the mRNA levels of pacemaker markers (TBX18, SHOX2, TBX3, HCN4, and HCN1) were higher in the BMP4 + CHIR group than in the control group, and working myocardial genes were downregulated. The immunofluorescence assay revealed that the expression of SHOX2 and HCN4 increased in the BMP4 + CHIR group compared to that in the other groups. In addition, the results of patch clamps revealed that a funny current of higher density and typical SAN action potentials were recorded, except in the control group, in which the L-type calcium current was higher in the BMP4 + CHIR group than in the other groups. Finally, the proportion of SANLPCs (cTnT+ NKX2.5-) was further enhanced by the combination of BMP4 and CHIR treatment. In summary, the combination of BMP and Wnt signaling promotes the differentiation of SANLPCs from hiPSCs.

Tbx5 overexpression in embryoid bodies increases TAK1 expression but does not enhance the differentiation of sinoatrial node cardiomyocytes

Genetic studies place Tbx5 at the apex of the sinoatrial node (SAN) transcriptional program. To understand its role in SAN differentiation, clonal embryonic stem (ES) cell lines were made that conditionally overexpress Tbx5, Tbx3, Tbx18, Shox2, Islet-1, and MAP3k7/TAK1. Cardiac cells differentiated using embryoid bodies (EBs). EBs overexpressing Tbx5, Islet1, and TAK1 beat faster than cardiac cells differentiated from control ES cell lines, suggesting possible roles in SAN differentiation. Tbx5 overexpressing EBs showed increased expression of TAK1, but cardiomyocytes did not differentiate as SAN cells. EBs showed no change in the expression of the SAN transcription factors Shox2 and Islet1 and decreased expression of the SAN channel protein HCN4. EBs constitutively overexpressing TAK1 direct cardiac differentiation to the SAN fate but have reduced phosphorylation of its targets, p38 and Jnk. This opens the possibility that blocking the phosphorylation of TAK1 targets may have the same impact as forced overexpression. To test this, we treated EBs with 5z-7-Oxozeanol (OXO), an inhibitor of TAK1 phosphorylation. Like TAK1 overexpressing cardiac cells, cardiomyocytes differentiated in the presence of OXO beat faster and showed increased expression of SAN genes (Shox2, HCN4, and Islet1). This suggests that activation of the SAN transcriptional network can be accomplished by blocking the phosphorylation of TAK1.

Local tissue mechanics control cardiac pacemaker cell embryonic patterning

Cardiac pacemaker cells (CPCs) initiate the electric impulses that drive the rhythmic beating of the heart. CPCs reside in a heterogeneous, ECM-rich microenvironment termed the sinoatrial node (SAN). Surprisingly, little is known regarding the biochemical composition or mechanical properties of the SAN, and how the unique structural characteristics present in this region of the heart influence CPC function remains poorly understood. Here, we have identified that SAN development involves the construction of a "soft" macromolecular ECM that specifically encapsulates CPCs. In addition, we demonstrate that subjecting embryonic CPCs to substrate stiffnesses higher than those measured in vivo results in loss of coherent electrical oscillation and dysregulation of the HCN4 and NCX1 ion channels required for CPC automaticity. Collectively, these data indicate that local mechanics play a critical role in maintaining the embryonic CPC function while also quantitatively defining the range of material properties that are optimal for embryonic CPC maturation.

Nr2f1a maintains atrial nkx2.5 expression to repress pacemaker identity within venous atrial cardiomyocytes of zebrafish

Maintenance of cardiomyocyte identity is vital for normal heart development and function. However, our understanding of cardiomyocyte plasticity remains incomplete. Here, we show that sustained expression of the zebrafish transcription factor Nr2f1a prevents the progressive acquisition of ventricular cardiomyocyte (VC) and pacemaker cardiomyocyte (PC) identities within distinct regions of the atrium. Transcriptomic analysis of flow-sorted atrial cardiomyocytes (ACs) from nr2f1a mutant zebrafish embryos showed increased VC marker gene expression and altered expression of core PC regulatory genes, including decreased expression of nkx2.5, a critical repressor of PC differentiation. At the arterial (outflow) pole of the atrium in nr2f1a mutants, cardiomyocytes resolve to VC identity within the expanded atrioventricular canal. However, at the venous (inflow) pole of the atrium, there is a progressive wave of AC transdifferentiation into PCs across the atrium toward the arterial pole. Restoring Nkx2.5 is sufficient to repress PC marker identity in nr2f1a mutant atria and analysis of chromatin accessibility identified an Nr2f1a-dependent nkx2.5 enhancer expressed in the atrial myocardium directly adjacent to PCs. CRISPR/Cas9-mediated deletion of the putative nkx2.5 enhancer leads to a loss of Nkx2.5-expressing ACs and expansion of a PC reporter, supporting that Nr2f1a limits PC differentiation within venous ACs via maintaining nkx2.5 expression. The Nr2f-dependent maintenance of AC identity within discrete atrial compartments may provide insights into the molecular etiology of concurrent structural congenital heart defects and associated arrhythmias.

Conversion of Unmodified Stem Cells to Pacemaker Cells by Overexpression of Key Developmental Genes

Arrhythmias of the heart are currently treated by implanting electronic pacemakers and defibrillators. Unmodified adipose tissue-derived stem cells (ASCs) have the potential to differentiate into all three germ layers but have not yet been tested for the generation of pacemaker and Purkinje cells. We investigated if-based on overexpression of dominant conduction cell-specific genes in ASCs-biological pacemaker cells could be induced. Here we show that by overexpression of certain genes that are active during the natural development of the conduction system, the differentiation of ASCs to pacemaker and Purkinje-like cells is feasible. Our study revealed that the most effective procedure consisted of short-term upregulation of gene combinations SHOX2-TBX5-HCN2, and to a lesser extent SHOX2-TBX3-HCN2. Single-gene expression protocols were ineffective. Future clinical implantation of such pacemaker and Purkinje cells, derived from unmodified ASCs of the same patient, could open up new horizons for the treatment of arrythmias.

Sinus node dysfunction: current understanding and future directions

The sinoatrial node (SAN) is the primary pacemaker of the heart. Normal SAN function is crucial in maintaining proper cardiac rhythm and contraction. Sinus node dysfunction (SND) is due to abnormalities within the SAN, which can affect the heartbeat frequency, regularity, and the propagation of electrical pulses through the cardiac conduction system. As a result, SND often increases the risk of cardiac arrhythmias. SND is most commonly seen as a disease of the elderly given the role of degenerative fibrosis as well as other age-dependent changes in its pathogenesis. Despite the prevalence of SND, current treatment is limited to pacemaker implantation, which is associated with substantial medical costs and complications. Emerging evidence has identified various genetic abnormalities that can cause SND, shedding light on the molecular underpinnings of SND. Identification of these molecular mechanisms and pathways implicated in the pathogenesis of SND is hoped to identify novel therapeutic targets for the development of more effective therapies for this disease. In this review article, we examine the anatomy of the SAN and the pathophysiology and epidemiology of SND. We then discuss in detail the most common genetic mutations correlated with SND and provide our perspectives on future research and therapeutic opportunities in this field.

Human-Induced Pluripotent Stem Cell-Based Differentiation of Cardiomyocyte Subtypes for Drug Discovery and Cell Therapy

Drug attrition rates have increased over the past few years, accompanied with growing costs for the pharmaceutical industry and consumers. Lack of in vitro models connecting the results of toxicity screening assays with clinical outcomes accounts for this high attrition rate. The emergence of cardiomyocytes derived from human pluripotent stem cells provides an amenable source of cells for disease modeling, drug discovery, and cardiotoxicity screening. Functionally similar to to embryonic stem cells, but with fewer ethical concerns, induced pluripotent stem cells (iPSCs) can recapitulate patient-specific genetic backgrounds, which would be a huge revolution for personalized medicine. The generated iPSC-derived cardiomyocytes (iPSC-CMs) represent different subtypes including ventricular-, atrial-, and nodal-like cardiomyocytes. Purifying these subtypes for chamber-specific drug screening presents opportunities and challenges. In this chapter, we discuss the strategies for the purification of iPSC-CMs, the use of iPSC-CMs for drug discovery and cardiotoxicity test, and the current limitations of iPSC-CMs that should be overcome for wider and more precise cardiovascular applications.

Disruption of the Gut Microbiota Confers Cisplatin Resistance in Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is the leading cause of gynecologic cancer death. Despite initial responses to intervention, up to 80% of patient tumors recur and require additional treatment. Retrospective clinical analysis of patients with ovarian cancer indicates antibiotic use during chemotherapy treatment is associated with poor overall survival. Here, we assessed whether antibiotic (ABX) treatment would impact growth of EOC and sensitivity to cisplatin. Immunocompetent or immunocompromised mice were given untreated control or ABX-containing (metronidazole, ampicillin, vancomycin, and neomycin) water prior to intraperitoneal injection with EOC cells, and cisplatin therapy was administered biweekly until endpoint. Tumor-bearing ABX-treated mice exhibited accelerated tumor growth and resistance to cisplatin therapy compared with control treatment. ABX treatment led to reduced apoptosis, increased DNA damage repair, and enhanced angiogenesis in cisplatin-treated tumors, and tumors from ABX-treated mice contained a higher frequency of cisplatin-augmented cancer stem cells than control mice. Stool analysis indicated nonresistant gut microbial species were disrupted by ABX treatment. Cecal transplants of microbiota derived from control-treated mice was sufficient to ameliorate chemoresistance and prolong survival of ABX-treated mice, indicative of a gut-derived tumor suppressor. Metabolomics analyses identified circulating gut-derived metabolites that were altered by ABX treatment and restored by recolonization, providing candidate metabolites that mediate the cross-talk between the gut microbiome and ovarian cancer. Collectively, these findings indicate that an intact microbiome functions as a tumor suppressor in EOC, and perturbation of the gut microbiota with ABX treatment promotes tumor growth and suppresses cisplatin sensitivity.

SIGNIFICANCE

Restoration of the gut microbiome, which is disrupted following antibiotic treatment, may help overcome platinum resistance in patients with epithelial ovarian cancer. See related commentary by Hawkins and Nephew, p. 4511.

Regulation of cardiac ion channels by transcription factors: Looking for new opportunities of druggable targets for the treatment of arrhythmias

Cardiac electrical activity is governed by different ion channels that generate action potentials. Acquired or inherited abnormalities in the expression and/or function of ion channels usually result in electrophysiological changes that can cause cardiac arrhythmias. Transcription factors (TFs) control gene transcription by binding to specific DNA sequences adjacent to target genes. Linkage analysis, candidate-gene screening within families, and genome-wide association studies have linked rare and common genetic variants in the genes encoding TFs with genetically-determined cardiac arrhythmias. Besides its critical role in cardiac development, recent data demonstrated that they control cardiac electrical activity through the direct regulation of the expression and function of cardiac ion channels in adult hearts. This narrative review summarizes some studies showing functional data on regulation of the main human atrial and ventricular Na⁺, Ca²⁺, and K⁺ channels by cardiac TFs such as Pitx2c, Tbx20, Tbx5, Zfhx3, among others. The results have improved our understanding of the mechanisms regulating cardiac electrical activity and may open new avenues for therapeutic interventions in cardiac acquired or inherited arrhythmias through the identification of TFs as potential drug targets. Even though TFs have for a long time been considered as 'undruggable' targets, advances in structural biology have led to the identification of unique pockets in TFs amenable to be targeted with small-molecule drugs or peptides that are emerging as novel therapeutic drugs.

RA signaling pathway combined with Wnt signaling pathway regulates human-induced pluripotent stem cells (hiPSCs) differentiation to sinus node-like cells

BACKGROUND

The source of SAN is debated among researchers. Many studies have shown that RA and Wnt signaling are involved in heart development. In this study, we investigated the role of retinoic acid (RA) and Wnt signaling in the induction of sinus node-like cells.

METHODS

The experimental samples were divided into four groups: control group (CHIR = 0), CHIR = 3, RA + CHIR = 0 andRA + CHIR = 3. After 20 days of differentiation, Western blot, RT-qPCR, immunofluorescence and flow cytometry were performed to identify sinus node-like cells. Finally, whole-cell patch clamp technique was used to record pacing funny current and action potential (AP) in four groups.

RESULTS

The best intervention method used in our experiment was RA = 0.25 µmol/L D5-D9 + CHIR = 3 µmol/L D5-D7. Results showed that CHIR can increase the expression of ISL-1 and TBX3, while RA mainly elevated Shox2. Immunofluorescence assay and flow cytometry further illustrated that combining RA with CHIR can induce sinus node-like cells (CTNT+Shox2+Nkx2.5-). Moreover, CHIR might reduce the frequency of cell beats, but in conjunction with RA could partly compensate for this side effect. Whole cell patch clamps were able to record funny current and the typical sinus node AP in the experimental group, which did not appear in the control group.

CONCLUSIONS

Combining RA with Wnt signaling within a specific period can induce sinus node-like cells.

Improved Generation of Human Induced Pluripotent Stem Cell-Derived Cardiac Pacemaker Cells Using Novel Differentiation Protocols

Current protocols for the differentiation of human-induced pluripotent stem cells (hiPSC) into cardiomyocytes only generate a small amount of cardiac pacemaker cells. In previous work, we reported the generation of high amounts of cardiac pacemaker cells by co-culturing hiPSC with mouse visceral endoderm-like (END2) cells. However, potential medical applications of cardiac pacemaker cells generated according to this protocol, comprise an incalculable xenogeneic risk. We thus aimed to establish novel protocols maintaining the differentiation efficiency of the END2 cell-based protocol, yet eliminating the use of END2 cells. Three protocols were based on the activation and inhibition of the Wingless/Integrated (Wnt) signaling pathway, supplemented either with retinoic acid and the Wnt activator CHIR99021 (protocol B) or with the NODAL inhibitor SB431542 (protocol C) or with a combination of all three components (protocol D). An additional fourth protocol (protocol E) was used, which was originally developed by the manufacturer STEMCELL Technologies for the differentiation of hiPSC or hESC into atrial cardiomyocytes. All protocols (B, C, D, E) were compared to the END2 cell-based protocol A, serving as reference, in terms of their ability to differentiate hiPSC into cardiac pacemaker cells. Our analysis revealed that protocol E induced upregulation of 12 out of 15 cardiac pacemaker-specific genes. For comparison, reference protocol A upregulated 11, while protocols B, C and D upregulated 9, 10 and 8 cardiac pacemaker-specific genes, respectively. Cells differentiated according to protocol E displayed intense fluorescence signals of cardiac pacemaker-specific markers and showed excellent rate responsiveness to adrenergic and cholinergic stimulation. In conclusion, we characterized four novel and END2 cell-independent protocols for the differentiation of hiPSC into cardiac pacemaker cells, of which protocol E was the most efficient.

Cellular and Engineered Organoids for Cardiovascular Models

An ensemble of in vitro cardiac tissue models has been developed over the past several decades to aid our understanding of complex cardiovascular disorders using a reductionist approach. These approaches often rely on recapitulating single or multiple clinically relevant end points in a dish indicative of the cardiac pathophysiology. The possibility to generate disease-relevant and patient-specific human induced pluripotent stem cells has further leveraged the utility of the cardiac models as screening tools at a large scale. To elucidate biological mechanisms in the cardiac models, it is critical to integrate physiological cues in form of biochemical, biophysical, and electromechanical stimuli to achieve desired tissue-like maturity for a robust phenotyping. Here, we review the latest advances in the directed stem cell differentiation approaches to derive a wide gamut of cardiovascular cell types, to allow customization in cardiac model systems, and to study diseased states in multiple cell types. We also highlight the recent progress in the development of several cardiovascular models, such as cardiac organoids, microtissues, engineered heart tissues, and microphysiological systems. We further expand our discussion on defining the context of use for the selection of currently available cardiac tissue models. Last, we discuss the limitations and challenges with the current state-of-the-art cardiac models and highlight future directions.

Chemically defined and small molecules-based generation of sinoatrial node-like cells

Background

Existing methods for in vitro differentiation of human pluripotent stem cells (hPSCs) into sinoatrial node-like cells (SANLCs) require complex and undefined medium constituents. This might hinder the elucidation of the molecular mechanisms involved in cardiac subtype specification and prevent translational application. In our study, we aimed to establish a chemically defined differentiation methods to generate SANLCs effectively and stably.

Methods

We induced human embryonic stem cells (hESCs)/induced PSCs (hiPSCs) to pan-cardiomyocytes by temporal modulation of the WNT/β-catenin (WNT) signaling pathway with GSK3 inhibitor and WNT inhibitor. During cardiac mesoderm stage of the differentiation process, signaling of WNT, retinoid acid (RA), and fibroblast growth factor (FGF) was manipulated by three specific molecules. Moreover, metabolic selection was designed to improve the enrichment of SANLCs. Finally, RT-PCR, immunofluorescence, flow cytometry, and whole cell patch clamp were used to identify the SANLCs.

Results

WNT, RA, and FGF signaling promote the differentiation of hPSCs into SANLCs in a concentration- and time window-sensitive manner, respectively. Synergetic modulation of WNT, FGF, and RA signaling pathways enhance the pacemaker phenotype and improve the differentiation efficiency of SANLCs (up to 45%). Moreover, the purification based on lactate metabolism and glucose starvation further reached approximately 50% of SANLCs. Finally, the electrophysiological data demonstrate that cells differentiated with the proposed protocol produce a considerable number of SANLCs that display typical electrophysiological characteristics of pacemaker cells in vitro.

Conclusion

We provide an optimized and chemically defined protocol to generate SANLCs by combined modulation of WNT, RA, and FGF signaling pathways and metabolic selection by lactate enrichment and glucose starvation. This chemically defined method for generating SANLCs might provide a platform for disease modeling, drug discovery, predictive toxicology, and biological pacemaker construction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02834-y.

A dual SHOX2:GFP; MYH6:mCherry knockin hESC reporter line for derivation of human SAN-like cells

The sinoatrial node (SAN) is the primary pacemaker of the heart. The human SAN is poorly understood due to limited primary tissue access and limitations in robust in vitro derivation methods. We developed a dual SHOX2:GFP; MYH6:mCherry knockin human embryonic stem cell (hESC) reporter line, which allows the identification and purification of SAN-like cells. Using this line, we performed several rounds of chemical screens and developed an efficient strategy to generate and purify hESC-derived SAN-like cells (hESC-SAN). The derived hESC-SAN cells display molecular and electrophysiological characteristics of bona fide nodal cells, which allowed exploration of their transcriptional profile at single-cell level. In sum, our dual reporter system facilitated an effective strategy for deriving human SAN-like cells, which can potentially be used for future disease modeling and drug discovery.

Effect of Shenfu Injection on Differentiation of Bone Marrow Mesenchymal Stem Cells into Pacemaker-Like Cells and Improvement of Pacing Function of Sinoatrial Node

Sick sinus syndrome (SSS), a complex type of cardiac arrhythmia, is a major health threat to humans. Shenfu injection (SFI), a formula of traditional Chinese medicine (TCM), is effective in improving bradyarrhythmia. However, the underlying mechanism of SFI’s therapeutic effect is subject to few systematic investigations. The purpose of the present research is to examine whether SFI can boost the differentiation effectiveness of bone marrow mesenchymal stem cells (BMSCs) into pacemaker-like cells and whether the transplantation of these cells can improve the pacing function of the sinoatrial node (SAN) in a rabbit model of SSS. BMSCs from New Zealand rabbits were extracted, followed by incubation in vitro. The flow cytometry was utilized to identify the expression of CD29, CD44, CD90, and CD105 surface markers. The isolated BMSCs were treated with SFI, and the whole-cell patch-clamp method was performed to detect hyperpolarization-the activated cyclic nucleotide-gated potassium channel 4 (HCN4) channel current activation curve. The SSS rabbit model was established using the formaldehyde wet dressing method, and BMSCs treated with SFI were transplanted into the SAN of the SSS rabbit model. We detected changes in the body-surface electrocardiogram and recorded dynamic heart rate measurements. Furthermore, transplanted SFI-treated BMSCs were subjected to HE staining, TUNEL staining, qPCR, western blotting, immunofluorescence, immunohistochemistry, and enzyme-linked immunosorbent assay to study their characteristics. Our results indicate that the transplantation of SFI-treated BMSCs into the SAN of SSS rabbits improved the pacing function of the SAN. In vitro data showed that SFI induced the proliferation of BMSCs, promoted their differentiation capacity into pacemaker-like cells, and increased the HCN4 expression in BMSCs. In vivo, the transplantation of SFI treated-BMSCs preserved the function of SAN in SSS rabbits, improved the expression of the HCN4 gene and gap junction proteins (Cx43 and Cx45), and significantly upregulated the expression of cAMP in the SAN, compared to the SSS model group. In summary, the present research demonstrated that SFI might enhance the differentiation capacity of BMSCs into pacemaker-like cells, hence offering a novel approach for the development of biological pacemakers. Additionally, we confirmed the effectiveness and safety of pacemaker-like cells differentiated from BMSCs in improving the pacing function of the SAN.

Comprehensive transcriptome-wide analysis of spliceopathy correction of myotonic dystrophy using CRISPR-Cas9 in iPSCs-derived cardiomyocytes

CTG repeat expansion (CTG_exp) is associated with aberrant alternate splicing that contributes to cardiac dysfunction in myotonic dystrophy type 1 (DM1). Excision of this CTG_exp repeat using CRISPR-Cas resulted in the disappearance of punctate ribonuclear foci in cardiomyocyte-like cells derived from DM1-induced pluripotent stem cells (iPSCs). This was associated with correction of the underlying spliceopathy as determined by RNA sequencing and alternate splicing analysis. Certain genes were of particular interest due to their role in cardiac development, maturation, and function (TPM4, CYP2J2, DMD, MBNL3, CACNA1H, ROCK2, ACTB) or their association with splicing (SMN2, GCFC2, MBNL3). Moreover, while comparing isogenic CRISPR-Cas9-corrected versus non-corrected DM1 cardiomyocytes, a prominent difference in the splicing pattern for a number of candidate genes was apparent pertaining to genes that are associated with cardiac function (TNNT, TNNT2, TTN, TPM1, SYNE1, CACNA1A, MTMR1, NEBL, TPM1), cellular signaling (NCOR2, CLIP1, LRRFIP2, CLASP1, CAMK2G), and other DM1-related genes (i.e., NUMA1, MBNL2, LDB3) in addition to the disease-causing DMPK gene itself. Subsequent validation using a selected gene subset, including MBNL1, MBNL2, INSR, ADD3, and CRTC2, further confirmed correction of the spliceopathy following CTG_exp repeat excision. To our knowledge, the present study provides the first comprehensive unbiased transcriptome-wide analysis of the differential splicing landscape in DM1 patient-derived cardiac cells after excision of the CTG_exp repeat using CRISPR-Cas9, showing reversal of the abnormal cardiac spliceopathy in DM1.

Tbx18 promoted the conversion of human-induced pluripotent stem cell-derived cardiomyocytes into sinoatrial node-like pacemaker cells

Sinoatrial node (SAN) pacemaker cells originate from T-box transcription factor 18 (Tbx18)-expressing progenitor cells. The present study aimed to investigate whether overexpression of human transcription factor Tbx18 could reprogram human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) into SAN-like pacemaker cells (SANLPCs) in vitro. In the study, hiPSCs were first differentiated into hiPSC-CMs through regulating the Wnt/β-catenin pathway, then purified hiPSC-CMs were transfected by Tbx18 adenovirus (Tbx18-CMs group) or green fluorescent protein (GFP) adenovirus (GFP-CMs group). The beating frequency of the Tbx18-CMs group was significantly higher than that of the hiPSC-CMs group and GFP-CMs group. Compared with the other two groups, the expression levels of hyperpolarization-activated cyclic nucleotide-gated potassium channel isoform 4, connexin-45 in the Tbx18-CMs group were markedly upregulated, while the expressions of transcription factor NKX2.5, CX43 were significantly downregulated. Whole-cell patch-clamp results illustrated that action potential and "funny" current (I_f ) similar to SAN pacemaker cells could be recorded in the Tbx18-CMs group. In conclusion, this present study demonstrated that overexpression of Tbx18 promoted the conversion of hiPSC-CMs into SANLPCs.

Implementing Biological Pacemakers: Design Criteria for Successful

Each heartbeat that pumps blood throughout the body is initiated by an electrical impulse generated in the sinoatrial node (SAN). However, a number of disease conditions can hamper the ability of the SAN's pacemaker cells to generate consistent action potentials and maintain an orderly conduction path, leading to arrhythmias. For symptomatic patients, current treatments rely on implantation of an electronic pacing device. However, complications inherent to the indwelling hardware give pause to categorical use of device therapy for a subset of populations, including pediatric patients or those with temporary pacing needs. Cellular-based biological pacemakers, derived in vitro or in situ, could function as a therapeutic alternative to current electronic pacemakers. Understanding how biological pacemakers measure up to the SAN would facilitate defining and demonstrating its advantages over current treatments. In this review, we discuss recent approaches to creating biological pacemakers and delineate design criteria to guide future progress based on insights from basic biology of the SAN. We emphasize the need for long-term efficacy in vivo via maintenance of relevant proteins, source-sink balance, a niche reflective of the native SAN microenvironment, and chronotropic competence. With a focus on such criteria, combined with delivery methods tailored for disease indications, clinical implementation will be attainable.

SHOX2 cooperates with STAT3 to promote breast cancer metastasis through the transcriptional activation of WASF3

BACKGROUND

Metastasis is most often the root cause of cancer-related death. Human short stature homeobox 2 (SHOX2), a homeodomain transcription factor, is a novel inducer of epithelial-to-mesenchymal transition in breast cancer cells, though its exact role and underlying mechanisms in metastasis are not well understood.

METHODS

TCGA analysis was performed to identify the clinical relevance of SHOX2 in breast cancer. Gene depletion was achieved by short hairpin RNA and small interfering RNA. Molecular regulations and alterations were assessed by Western blotting, immunoprecipitation, immunohistochemistry, qRT-PCR, chromatin immunoprecipitation coupled with qPCR (ChIP-qPCR), and ChIP/re-ChIP. The impact of SHOX2 signaling on tumor growth and metastasis was evaluated in orthotopic breast tumor mice.

RESULTS

The expression level of SHOX2 is strongly associated with poor distant metastasis-free survival in breast cancer patients and inactivation of SHOX2 suppresses breast tumor growth and metastasis in mice. In breast cancer cells, SHOX2 directly activates Wiskott-Aldridge syndrome protein family member 3 (WASF3), a metastasis-promoting gene, at the transcriptional level, leading to a significant increase in metastatic potential. Mechanistically, SHOX2 activates signal transducer and activator of transcription 3 (STAT3) and recruits it to the WASF3 promoter, where STAT3 cooperates with SHOX2 to form a functional immunocomplex to promote WASF3 transcriptional activity in breast cancer cells. WASF3 knockdown abrogates SHOX2-induced metastasis, but not SHOX2-dependent tumorigenesis.

CONCLUSIONS

These findings provide a critical link between the SHOX2-STAT3-WASF3 signaling axis and metastasis and suggest that the targeting of this signaling node may represent a valuable alternative strategy for combating breast cancer metastasis.

Bioengineering the Cardiac Conduction System: Advances in Cellular, Gene, and Tissue Engineering for Heart Rhythm Regeneration

Heart rhythm disturbances caused by different etiologies may affect pediatric and adult patients with life-threatening consequences. When pharmacological therapy is ineffective in treating the disturbances, the implantation of electronic devices to control and/or restore normal heart pacing is a unique clinical management option. Although these artificial devices are life-saving, they display many limitations; not least, they do not have any capability to adapt to somatic growth or respond to neuroautonomic physiological changes. A biological pacemaker could offer a new clinical solution for restoring heart rhythms in the conditions of disorder in the cardiac conduction system. Several experimental approaches, such as cell-based, gene-based approaches, and the combination of both, for the generation of biological pacemakers are currently established and widely studied. Pacemaker bioengineering is also emerging as a technology to regenerate nodal tissues. This review analyzes and summarizes the strategies applied so far for the development of biological pacemakers, and discusses current translational challenges toward the first-in-human clinical application.

Downregulated lncRNA RCPCD promotes differentiation of embryonic stem cells into cardiac pacemaker-like cells by suppressing HCN4 promoter methylation

Long non-coding RNA (lncRNA) is receiving increasing attention in embryonic stem cells (ESCs) research. However, the roles of lncRNA in the differentiation of ESCs into pacemaker-like cells are still unclear. Therefore, the present study aims to explore the roles and mechanisms of lncRNA in the differentiation of ESCs into pacemaker-like cells. ESCs were cultured and induced differentiation to pacemaker-like cells. RNA sequencing was used to identify the differential expression lncRNAs during the differentiation of ESCs into pacemaker-like cells. Cell morphology observation, flow cytometry, quantitative real-time polymerase chain reaction, western blot, and immunofluorescence were used to detect the differentiation of ESCs into pacemaker-like cells. LncRNA and genes overexpression or knockdown through transfected adenovirus in the differentiation process. The fluorescence in situ hybridization (FISH) detected the lncRNA location in the differentiated ESCs. Luciferase reporter gene assay, methylation-specific PCR, chromatin immunoprecipitation assay, and RNA immunoprecipitation assay were performed to reveal the mechanism of lncRNA-regulating HCN4 expression. Rescue experiments were used to confirm that lncRNA regulates the differentiation of ESCs into pacemaker-like cells through HCN4. We cultured the ESCs and induced the differentiation of ESCs into pacemaker-like cells successfully. The expression of lncRNA RCPCD was significantly decreased in the differentiation of ESCs into pacemaker-like cells. Overexpression of RCPCD inhibited the differentiation of ESCs into pacemaker-like cells. RCPCD inhibited the expression of HCN4 by increasing HCN4 methylation at the promoter region through DNMT1, DNMT2, and DNMT3. RCPCD inhibited the differentiation of ESCs into pacemaker-like cells by inhibiting the expression of HCN4. Our results confirm the roles and mechanism of lncRNA RCPCD in the differentiation of ESCs into pacemaker-like cells, which could pave the path for the development of a cell-based biological pacemaker.

A dual cardiomyocyte reporter model derived from human pluripotent stem cells

Cardiovascular diseases (CVD) remain the leading cause of death in the USA. Cardiomyocytes (CMs) derived from human pluripotent stem cells (hPSCs) provide a valuable cell source for regenerative therapy, disease modeling, and drug screening. Here, we established a hPSC line integrated with a mCherry fluorescent protein driven by the alpha myosin heavy chain (aMHC) promoter, which could be used to purify CMs based on the aMHC promoter activity in these cells. Combined with a fluorescent voltage indicator, ASAP2f, we achieved a dual reporter CM platform, which enables purification and characterization of CM subtypes and holds great potential for disease modeling and drug discovery of CVD.

TBX3 induces biased differentiation of human induced pluripotent stem cells into cardiac pacemaker-like cells

BACKGROUND

TBX3 plays a critical role in the formation of the sinoatrial node (SAN) during embryonic heart development. However, the contribution of TBX3 in driving the differentiation of human induced pluripotent stem cells (hiPSC)into pacemaker cells remains to be explored.

RESULTS

Using the pan-cardiomyocyte differentiation protocol of human induced pluripotent stem cells (hiPSC)，TBX3 gene was introduced into the differentiating hiPSC on day 5 post-differentiation, and the differentiation of pacemaker-like cardiomyocytes was evaluated on day 21. The results showed that TBX3 significantly induced biased differentiation of hiPSC into pacemaker-like cells as judged by significantly increased expression of SAN-specific marker gene, SHOX2, and slightly decreased expression of SAN-detrimental transcription factor, NKX2-5.

CONCLUSION

Our results suggest that TBX3 plays an important role in driving the differentiation of hiPSC into pacemaker-like cells, and manipulation of TBX3 expression during pan-cardiomyocyte differentiation may lead to the development of therapeutic pacemaker cells.

Bioengineering Clinically Relevant Cardiomyocytes and Cardiac Tissues from Pluripotent Stem Cells

The regenerative capacity of cardiomyocytes is insufficient to functionally recover damaged tissue, and as such, ischaemic heart disease forms the largest proportion of cardiovascular associated deaths. Human-induced pluripotent stem cells (hiPSCs) have enormous potential for developing patient specific cardiomyocytes for modelling heart disease, patient-based cardiac toxicity testing and potentially replacement therapy. However, traditional protocols for hiPSC-derived cardiomyocytes yield mixed populations of atrial, ventricular and nodal-like cells with immature cardiac properties. New insights gleaned from embryonic heart development have progressed the precise production of subtype-specific hiPSC-derived cardiomyocytes; however, their physiological immaturity severely limits their utility as model systems and their use for drug screening and cell therapy. The long-entrenched challenges in this field are being addressed by innovative bioengingeering technologies that incorporate biophysical, biochemical and more recently biomimetic electrical cues, with the latter having the potential to be used to both direct hiPSC differentiation and augment maturation and the function of derived cardiomyocytes and cardiac tissues by mimicking endogenous electric fields.

Reciprocal interaction between IK1 and If in biological pacemakers: A simulation study

Pacemaking dysfunction (PD) may result in heart rhythm disorders, syncope or even death. Current treatment of PD using implanted electronic pacemakers has some limitations, such as finite battery life and the risk of repeated surgery. As such, the biological pacemaker has been proposed as a potential alternative to the electronic pacemaker for PD treatment. Experimentally and computationally, it has been shown that bio-engineered pacemaker cells can be generated from non-rhythmic ventricular myocytes (VMs) by knocking out genes related to the inward rectifier potassium channel current (IK1) or by overexpressing hyperpolarization-activated cyclic nucleotide gated channel genes responsible for the "funny" current (If). However, it is unclear if a bio-engineered pacemaker based on the modification of IK1- and If-related channels simultaneously would enhance the ability and stability of bio-engineered pacemaking action potentials. In this study, the possible mechanism(s) responsible for VMs to generate spontaneous pacemaking activity by regulating IK1 and If density were investigated by a computational approach. Our results showed that there was a reciprocal interaction between IK1 and If in ventricular pacemaker model. The effect of IK1 depression on generating ventricular pacemaker was mono-phasic while that of If augmentation was bi-phasic. A moderate increase of If promoted pacemaking activity but excessive increase of If resulted in a slowdown in the pacemaking rate and even an unstable pacemaking state. The dedicated interplay between IK1 and If in generating stable pacemaking and dysrhythmias was evaluated. Finally, a theoretical analysis in the IK1/If parameter space for generating pacemaking action potentials in different states was provided. In conclusion, to the best of our knowledge, this study provides a wide theoretical insight into understandings for generating stable and robust pacemaker cells from non-pacemaking VMs by the interplay of IK1 and If, which may be helpful in designing engineered biological pacemakers for application purposes.

SETD4 in the Proliferation, Migration, Angiogenesis, Myogenic Differentiation and Genomic Methylation of Bone Marrow Mesenchymal Stem Cells

Epigenetic modification is a crucial mechanism affecting the biological function of stem cells. SETD4 is a histone methyltransferase, and its biological role in bone marrow mesenchymal stem cells (BMSCs) is currently unknown. In this study, we employed CRISPR/Cas9 technology edited mouse model and found that SETD4 knockout significantly promoted the proliferation of BMSCs, impaired BMSCs migration and differentiation potentials of lineages of cardiacmyocyte and smooth muscle cell, and even the angiogenesis via paracrine of VEGF. Through Reduced Representation Bisulfite Sequencing (RRBS) method, we verified that the overall genomic methylation of BMSCs in the SETD4 knockout group only was decreased by 0.47 % compared with wild type. However, the changed genomic methylation covers a total of 96,331 differential methylated CpG sites and 8,692 differential methylation regions (DMRs), with part of them settled in promoter regions. Bioinformatic analysis revealed that differential CpG islands and DMRs in promoter impacted 270 GO functions and 34 KEGG signaling pathways, with some closely related to stem cell biology. Mechanismly, SETD4 knockout inhibited sets of monomethylases and dimethylases for histone lysine, along with significant changes in some factors including Nkx2.5, Gata4, Gli2, Grem2, E2f7, Map7, Nr2f2 and Shox2 that associated with stem cell biology. These results are the first to reveal that even though SETD4 changes the genome's overall methylation to a limited extent in BMSCs, it still affects the numerous cellular functions and signaling pathways, implying SETD4-altered genomic methylation serves a crucial molecular role in BMSCs' biological functions.

Emerging Technologies in Cardiac Pacing From Leadless Pacers to Stem Cells

Modern pacemakers can sense and pace multiple chambers of the heart. These pacemakers have different modes and features to optimize atrioventricular synchrony and promote intrinsic conduction. Despite recent advancements, current pacemakers have several drawbacks that limit their feasibility. In this review article, we discuss several of these limitations and detail several emerging technologies in cardiac pacing aimed to solve some of these limitations. We present several technological advancements in cardiac pacing, including the use of leadless pacemakers, physiologic pacing, battery improvements, and bioartificial pacemakers. More research still needs to be done in testing the safety and efficacy of these new developments.

Enhancing Matured Stem-Cardiac Cell Generation and Transplantation: A Novel Strategy for Heart Failure Therapy

Heart failure (HF) remains one of the major causes of morbidity and mortality worldwide. Recent studies have shown that stem cells (SCs) including bone marrow mesenchymal stem (BMSC), embryonic bodies (EB), embryonic stem (ESC), human induced pluripotent stem (hiPSC)-derived cardiac cells generation, and transplantation treated myocardial infarction (MI) in vivo and in human. However, the immature phenotypes compromise their clinical application requiring immediate intervention to improve stem-derived cardiac cell (S-CCs) maturation. Recently, an unbiased multi-omic analysis involving genomics, transcriptomics, epigenomics, proteomics, and metabolomics identified specific strategies for the generation of matured S-CCs that may enhance patients' recovery processes upon transplantation. However, these strategies still remain undisclosed. Here, we summarize the recently discovered strategies for the matured S-CC generation. In addition, cardiac patch formation and transplantation that accelerated HF recuperation in clinical trials are discussed. A better understanding of this work may lead to efficient generation of matured S-CCs for regenerative medicine. Graphical abstract.

Fluorescent PSC-Derived Cardiomyocyte Reporter Lines: Generation Approaches and Their Applications in Cardiovascular Medicine

Recent advances have made pluripotent stem cell (PSC)-derived cardiomyocytes an attractive option to model both normal and diseased cardiac function at the single-cell level. However, in vitro differentiation yields heterogeneous populations of cardiomyocytes and other cell types, potentially confounding phenotypic analyses. Fluorescent PSC-derived cardiomyocyte reporter systems allow specific cell lineages to be labelled, facilitating cell isolation for downstream applications including drug testing, disease modelling and cardiac regeneration. In this review, the different genetic strategies used to generate such reporter lines are presented with an emphasis on their relative technical advantages and disadvantages. Next, we explore how the fluorescent reporter lines have provided insights into cardiac development and cardiomyocyte physiology. Finally, we discuss how exciting new approaches using PSC-derived cardiomyocyte reporter lines are contributing to progress in cardiac cell therapy with respect to both graft adaptation and clinical safety.

NODAL inhibition promotes differentiation of pacemaker-like cardiomyocytes from human induced pluripotent stem cells

Directed cardiomyogenesis from human induced pluripotent stem cells (hiPSCs) has been greatly improved in the last decade but directed differentiation to pacemaking cardiomyocytes (CMs) remains incompletely understood. In this study, we demonstrated that inhibition of NODAL signaling by a specific NODAL inhibitor (SB431542) in the cardiac mesoderm differentiation stage downregulated PITX2c, a transcription factor that is known to inhibit the formation of the sinoatrial node in the left atrium during cardiac development. The resulting hiPSC-CMs were smaller in cell size, expressed higher pro-pacemaking transcription factors, TBX3 and TBX18, and exhibited pacemaking-like electrophysiological characteristics compared to control hiPSC-CMs differentiated from established Wnt-based protocol. The pacemaker-like subtype increased up to 2.4-fold in hiPSC-CMs differentiated with the addition of SB431542 relative to the control. Hence, Nodal inhibition in the cardiac mesoderm stage promoted pacemaker-like CM differentiation from hiPSCs. Improving the yield of human pacemaker-like CMs is a critical first step in the development of functional human cell-based biopacemakers.

Human Pluripotent Stem Cell-Derived Cardiovascular Cells: From Developmental Biology to Therapeutic Applications

Advances in our understanding of cardiovascular development have provided a roadmap for the directed differentiation of human pluripotent stem cells (hPSCs) to the major cell types found in the heart. In this Perspective, we review the state of the field in generating and maturing cardiovascular cells from hPSCs based on our fundamental understanding of heart development. We then highlight their applications for studying human heart development, modeling disease-performing drug screening, and cell replacement therapy. With the advancements highlighted here, the promise that hPSCs will deliver new treatments for degenerative and debilitating diseases may soon be fulfilled.

Cardiopharyngeal Progenitor Specification: Multiple Roads to the Heart and Head Muscles

During embryonic development, the heart arises from various sources of undifferentiated mesodermal progenitors, with an additional contribution from ectodermal neural crest cells. Mesodermal cardiac progenitors are plastic and multipotent, but are nevertheless specified to a precise heart region and cell type very early during development. Recent findings have defined both this lineage plasticity and early commitment of cardiac progenitors, using a combination of single-cell and population analyses. In this review, we discuss several aspects of cardiac progenitor specification. We discuss their markers, fate potential in vitro and in vivo, early segregation and commitment, and also intrinsic and extrinsic cues regulating lineage restriction from multipotency to a specific cell type of the heart. Finally, we also discuss the subdivisions of the cardiopharyngeal field, and the shared origins of the heart with other mesodermal derivatives, including head and neck muscles.

Biological pacemaker: from biological experiments to computational simulation

Pacemaking dysfunction has become a significant disease that may contribute to heart rhythm disorders, syncope, and even death. Up to now, the best way to treat it is to implant electronic pacemakers. However, these have many disadvantages such as limited battery life, infection, and fixed pacing rate. There is an urgent need for a biological pacemaker (bio-pacemaker). This is expected to replace electronic devices because of its low risk of complications and the ability to respond to emotion. Here we survey the contemporary development of the bio-pacemaker by both experimental and computational approaches. The former mainly includes gene therapy and cell therapy, whilst the latter involves the use of multi-scale computer models of the heart, ranging from the single cell to the tissue slice. Up to now, a bio-pacemaker has been successfully applied in big mammals, but it still has a long way from clinical uses for the treatment of human heart diseases. It is hoped that the use of the computational model of a bio-pacemaker may accelerate this process. Finally, we propose potential research directions for generating a bio-pacemaker based on cardiac computational modeling.

Subtype-specific cardiomyocytes for precision medicine: Where are we now?

Patient-derived pluripotent stem cells (PSCs) have greatly transformed the current understanding of human heart development and cardiovascular disease. Cardiomyocytes derived from personalized PSCs are powerful tools for modeling heart disease and performing patient-based cardiac toxicity testing. However, these PSC-derived cardiomyocytes (PSC-CMs) are a mixed population of atrial-, ventricular-, and pacemaker-like cells in the dish, hindering the future of precision cardiovascular medicine. Recent insights gleaned from the developing heart have paved new avenues to refine subtype-specific cardiomyocytes from patients with known pathogenic genetic variants and clinical phenotypes. Here, we discuss the recent progress on generating subtype-specific (atrial, ventricular, and nodal) cardiomyocytes from the perspective of embryonic heart development and how human pluripotent stem cells will expand our current knowledge on molecular mechanisms of cardiovascular disease and the future of precision medicine.

Signaling pathways and clinical application of RASSF1A and SHOX2 in lung cancer

BACKGROUND

An increasing number of studies have focused on the early diagnostic value of the methylation of RASSF1A and SHOX2 in lung cancer. However, the intricate cellular events related to RASSF1A and SHOX2 in lung cancer are still a mystery. For researchers and clinicians aiming to more profoundly understand the diagnostic value of methylated RASSF1A and SHOX2 in lung cancer, this review will provide deeper insights into the molecular events of RASSF1A and SHOX2 in lung cancer.

METHODOLOGY

We searched for relevant publications in the PubMed and Google Scholar databases using the keywords "RASSF1A", "SHOX2" and "lung cancer" etc. First, we reviewed the RASSF1A and SHOX2 genes, from their family structures to the functions of their basic structural domains. Then we mainly focused on the roles of RASSF1A and SHOX2 in lung cancer, especially on their molecular events in recent decades. Finally, we compared the value of measuring RASSF1A and SHOX2 gene methylation with that of the common methods for the diagnosis of lung cancer patients.

RESULTS

The RASSF1A and SHOX2 genes were confirmed to be regulators or effectors of multiple cancer signaling pathways, driving tumorigenesis and lung cancer progression. The detection of RASSF1A and SHOX2 gene methylation has higher sensitivity and specificity than other commonly used methods for diagnosing lung cancer, especially in the early stage.

CONCLUSIONS

The RASSF1A and SHOX2 genes are critical for the processes of tumorigenesis, development, metastasis, drug resistance, and recurrence in lung cancer. The combined detection of RASSF1A and SHOX2 gene methylation was identified as an excellent method for the screening and surveillance of lung cancer that exhibits high sensitivity and specificity.

A Brief History of Pacemaking

Cardiac pacemaking is a most fundamental cardiac function, thoroughly investigated for decades with a multiscale approach at organ, tissue, cell and molecular levels, to clarify the basic mechanisms underlying generation and control of cardiac rhythm. Understanding the processes involved in pacemaker activity is of paramount importance for a basic physiological knowledge, but also as a way to reveal details of pathological dysfunctions useful in the perspective of a therapeutic approach. Among the mechanisms involved in pacemaking, the "funny" (I_f) current has properties most specifically fitting the requirements for generation and control of repetitive activity, and has consequently received the most attention in studies of the pacemaker function. Present knowledge of the basic mechanisms of pacemaking and the properties of funny channels has led to important developments of clinical relevance. These include: (1) the successful development of heart rate-reducing agents, such as ivabradine, able to control cardiac rhythm and useful in the treatment of diseases such as coronary artery disease, heart failure and tachyarrhythmias; (2) the understanding of the genetic basis of disorders of cardiac rhythm caused by HCN channelopathies; (3) the design of strategies to implement biological pacemakers based on transfer of HCN channels or of stem cell-derived pacemaker cells expressing I_f, with the ultimate goal to replace electronic devices. In this review, I will give a brief historical account of the discovery of the funny current and the development of the concept of I_f-based pacemaking, in the context of a wider, more complex model of cardiac rhythmic function.

HCN2 and TBX3 Reprogram Human-Induced Pluripotent Stem Cells-Derived Cardiomyocytes into Pacemaker-Like Cells

TBX3 reprograms cardiac myocytes into cells that possess sinoatrial node phenotype, but no specific funny current (If) was detected. We explore whether overexpression of TBX3 alone or combined with HCN2 can reprogram human-induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) into pacemaker-like cells. HiPSC-CMs were transfected with TBX3 and/or HCN2 in this study. Expression analysis showed that overexpression of TBX3 induces a reduced reduction expression profile of working cardiomyocytes into that of pacemaker cells. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and electrophysiological analyses showed a reduced expression of connexins subunits (CX40, CX43), the sodium current (SCN5A, INa), the inward rectified potassium channels (Kir2.1, IK1), and an increased expression of connexins subunits (CX30.2, CX45). No If was detected. The reduction of IK1 resulted in a more depolarized maximum diastolic potential together with an expression of If (generated by HCN2), which they work in synergy to generate spontaneous diastolic depolarization that was the most typical characteristic of pacemaker cells. In conclusion, overexpression of TBX3 and HCN2 could reprogram hiPSC-CMs into pacemaker-like cells. The ability to enable diastolic depolarization formation provides a new strategy for the construction of a biological pacemaker.

Canonical Wnt signaling promotes pacemaker cell specification of cardiac mesodermal cells derived from mouse and human embryonic stem cells

Cardiac differentiation of embryonic stem cells (ESCs) can give rise to de novo chamber cardiomyocytes and nodal pacemaker cells. Compared with our understanding of direct differentiation toward atrial and ventricular myocytes, the mechanisms for nodal pacemaker cell commitment are not well understood. Taking a cue from the prominence of canonical Wnt signaling during cardiac pacemaker tissue development in chick embryos, we asked if modulations of Wnt signaling influence cardiac progenitors to bifurcate to either chamber cardiomyocytes or pacemaker cells. Omitting an exogenous Wnt inhibitor, which is routinely added to maximize cardiac myocyte yield during differentiation of mouse and human ESCs, led to increased yield of spontaneously beating cardiomyocytes with action potential properties similar to those of native sinoatrial node pacemaker cells. The pacemaker phenotype was accompanied by enhanced expression of genes and gene products that mark nodal pacemaker cells such as Hcn4, Tbx18, Tbx3, and Shox2. Addition of exogenous Wnt3a ligand, which activates canonical Wnt/β-catenin signaling, increased the yield of pacemaker-like myocytes while reducing cTNT-positive pan-cardiac differentiation. Conversely, addition of inhibitors of Wnt/β-catenin signaling led to increased chamber myocyte lineage development at the expense of pacemaker cell specification. The positive impact of canonical Wnt signaling on nodal pacemaker cell differentiation was evidenced in direct differentiation of two human ESC lines and human induced pluripotent stem cells. Our data identify the Wnt/β-catenin pathway as a critical determinant of cardiac myocyte subtype commitment during ESC differentiation: endogenous Wnt signaling favors the pacemaker lineage, whereas its suppression promotes the chamber cardiomyocyte lineage.

Genetically Modified Porcine Mesenchymal Stem Cells by Lentiviral Tbx18 Create a Biological Pacemaker

Background

Tbx18 is a vital transcription factor involved in embryonic sinoatrial node (SAN) formation process but is gradually vanished after birth. Myocardial injection of lentiviral Tbx18 converts cardiomyocytes into pacemaker-like cells morphologically and functionally. In this in vitro and in vivo study, genetical modification of porcine bone mesenchymal stem cells (BMSCs) by recapturing the Tbx18 expression creates a biological pacemaker which was examined.

Methods

The isolated porcine BMSCs were transfected with lentiviral Tbx18, and the induced pacemaker-like cells were analyzed using real-time polymerase chain reaction and western blotting to investigate the efficiency of transformation. Then, the induced pacemaker-like cells were implanted into the right ventricle of the SAN dysfunction porcine model after the differentiation process. Biological pacemaker activity and ectopic pacing region were tested by an electrocardiograph (ECG) monitor.

Results

The isolated porcine BMSCs expressed specific surface markers of stem cells; meanwhile, the expression of myocardial markers was upregulated significantly after lentiviral Tbx18 transfection. The porcine SAN dysfunction model was constructed by electrocoagulation using a surgical electrotome. The results showed that the mean heart beat (HR) of BMSCs-Tbx18 was significantly higher than that of BMSCs-GFP. An ectopic pacing region was affirmed into the right ventricle by ECG after implantation of BMSCs-Tbx18.

Conclusion

It was verified that Lenti-Tbx18 is capable of transducing porcine BMSCs into pacemaker-like cells. Genetically modified porcine BMSCs by lentiviral Tbx18 could create a biological pacemaker. However, further researches in large-scale animals are required to rule out unexpected complications prior to application in clinical practice.

Dynamic Cellular Integration Drives Functional Assembly of the Heart's Pacemaker Complex

Impulses generated by a multicellular, bioelectric signaling center termed the sinoatrial node (SAN) stimulate the rhythmic contraction of the heart. The SAN consists of a network of electrochemically oscillating pacemaker cells encased in a heterogeneous connective tissue microenvironment. Although the cellular composition of the SAN has been a point of interest for more than a century, the biological processes that drive the tissue-level assembly of the cells within the SAN are unknown. Here, we demonstrate that the SAN’s structural features result from a developmental process during which mesenchymal cells derived from a multipotent progenitor structure, the proepicardium, integrate with and surround pacemaker myocardium. This process actively remodels the forming SAN and is necessary for sustained electrogenic signal generation and propagation. Collectively, these findings provide experimental evidence for how the microenvironmental architecture of the SAN is patterned and demonstrate that proper cellular arrangement is critical for cardiac pacemaker biorhythmicity.