Hedgehog signalling controls sinoatrial node development and atrioventricular cushion formation

The molecular mechanisms of cardiac development and related diseases

Cardiac development is a complex and intricate process involving numerous molecular signals and pathways. Researchers have explored cardiac development through a long journey, starting with early studies observing morphological changes and progressing to the exploration of molecular mechanisms using various molecular biology methods. Currently, advancements in stem cell technology and sequencing technology, such as the generation of human pluripotent stem cells and cardiac organoids, multi-omics sequencing, and artificial intelligence (AI) technology, have enabled researchers to understand the molecular mechanisms of cardiac development better. Many molecular signals regulate cardiac development, including various growth and transcription factors and signaling pathways, such as WNT signaling, retinoic acid signaling, and Notch signaling pathways. In addition, cilia, the extracellular matrix, epigenetic modifications, and hypoxia conditions also play important roles in cardiac development. These factors play crucial roles at one or even multiple stages of cardiac development. Recent studies have also identified roles for autophagy, metabolic transition, and macrophages in cardiac development. Deficiencies or abnormal expression of these factors can lead to various types of cardiac development abnormalities. Nowadays, congenital heart disease (CHD) management requires lifelong care, primarily involving surgical and pharmacological treatments. Advances in surgical techniques and the development of clinical genetic testing have enabled earlier diagnosis and treatment of CHD. However, these technologies still have significant limitations. The development of new technologies, such as sequencing and AI technologies, will help us better understand the molecular mechanisms of cardiac development and promote earlier prevention and treatment of CHD in the future.

Exosomes derived from induced cardiopulmonary progenitor cells alleviate acute lung injury in mice

Cardiopulmonary progenitor cells (CPPs) constitute a minor subpopulation of cells that are commonly associated with heart and lung morphogenesis during embryonic development but completely subside after birth. This fact offers the possibility for the treatment of pulmonary heart disease (PHD), in which the lung and heart are both damaged. A reliable source of CPPs is urgently needed. In this study, we reprogrammed human cardiac fibroblasts (HCFs) into CPP-like cells (or induced CPPs, iCPPs) and evaluated the therapeutic potential of iCPP-derived exosomes for acute lung injury (ALI). iCPPs were created in passage 3 primary HCFs by overexpressing GLI1, WNT2, ISL1 and TBX5 (GWIT). Exosomes were isolated from the culture medium of passage 6-8 GWIT-iCPPs. A mouse ALI model was established by intratracheal instillation of LPS. Four hours after LPS instillation, ALI mice were treated with GWIT-iCPP-derived exosomes (5 × 109, 5 × 1010 particles/mL) via intratracheal instillation. We showed that GWIT-iCPPs could differentiate into cell lineages, such as cardiomyocyte-like cells, endothelial cells, smooth muscle cells and alveolar epithelial cells, in vitro. Transcription analysis revealed that GWIT-iCPPs have potential for heart and lung development. Intratracheal instillation of iCPP-derived exosomes dose-dependently alleviated LPS-induced ALI in mice by attenuating lung inflammation, promoting endothelial function and restoring capillary endothelial cells and the epithelial cells barrier. This study provides a potential new method for the prevention and treatment of cardiopulmonary injury, especially lung injury, and provides a new cell model for drug screening.

Development of the Cardiac Conduction System

The electrical impulses that coordinate the sequential, rhythmic contractions of the atria and ventricles are initiated and tightly regulated by the specialized tissues of the cardiac conduction system. In the mature heart, these impulses are generated by the pacemaker cardiomyocytes of the sinoatrial node, propagated through the atria to the atrioventricular node where they are delayed and then rapidly propagated to the atrioventricular bundle, right and left bundle branches, and finally, the peripheral ventricular conduction system. Each of these specialized components arise by complex patterning events during embryonic development. This chapter addresses the origins and transcriptional networks and signaling pathways that drive the development and maintain the function of the cardiac conduction system.

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.

Hedgehog signalling controls sinoatrial node development and atrioventricular cushion formation

Smoothened is a key receptor of the hedgehog pathway, but the roles of Smoothened in cardiac development remain incompletely understood. In this study, we found that the conditional knockout of Smoothened from the mesoderm impaired the development of the venous pole of the heart and resulted in hypoplasia of the atrium/inflow tract (IFT) and a low heart rate. The blockage of Smoothened led to reduced expression of genes critical for sinoatrial node (SAN) development in the IFT. In a cardiac cell culture model, we identified a Gli2–Tbx5–Hcn4 pathway that controls SAN development. In the mutant embryos, the endocardial-to-mesenchymal transition (EndMT) in the atrioventricular cushion failed, and Bmp signalling was downregulated. The addition of Bmp2 rescued the EndMT in mutant explant cultures. Furthermore, we analysed Gli2⁺ scRNAseq and Tbx5^−/− RNAseq data and explored the potential genes downstream of hedgehog signalling in posterior second heart field derivatives. In conclusion, our study reveals that Smoothened-mediated hedgehog signalling controls posterior cardiac progenitor commitment, which suggests that the mutation of Smoothened might be involved in the aetiology of congenital heart diseases related to the cardiac conduction system and heart valves.