Heart Cell Blueprint: Insights on Structure and Disease Repair

In a recent study unveiled in the esteemed journal Nature, a substantial consortium of researchers hailing from the United States (U.S.) employed single-cell ribonucleic acid (RNA) sequencing, coupled with high-resolution fluorescence in situ hybridization, to delineate the cellular identities orchestrating the intricate morphological architecture of the heart.

Background

Every intricate component of the human heart plays specific roles contributing to its efficient function, and any disruption to these functions can result in congenital anomalies like congenital heart disease in children and cardiac afflictions such as valvulopathies and cardiomyopathies in adults. However, despite the heart’s pivotal role in the human physiology, understanding the organization and functionality of its structures, and their interplay, remains largely elusive.

About the Study

In this present investigation, scholars employed a single-cell RNA sequencing (scRNAseq) methodology in conjunction with multiplexed error-robust fluorescence in situ hybridization (MER-FISH). This approach facilitated the integration of single-cell transcriptomes with spatial biology, enabling the visualization, examination, and quantification of RNA transcripts from myriad genes within a single cell.

Commencing with the identification of cell lineages contributing to heart development, the researchers elucidated how various cardiac cell types assemble into complex structures and coordinate to regulate human heart function. Conducted across multiple replicates, scRNAseq analysis encompassed human hearts at various developmental stages, from nine to 16 weeks post-conception.

The amassed single cells, numbering over 140 million, were transcriptionally categorized into five cell compartments: cardiomyocytes, endothelial, mesenchymal, neuronal, and blood. Subsequent analysis of gene markers within these compartments led to the identification of 12 cell classes, with further clustering revealing 39 populations and 75 subpopulations of cells.

MER-FISH was then employed to spatially map heart cells and investigate the cellular mechanisms governing heart remodeling and morphogenesis, including ventricular wall development. MER-FISH imaging was instrumental in exploring the organization of cells identified via scRNAseq, particularly during developmental milestones like myocardial wall compaction.

The study aimed to decode the assembly of specific cardiovascular cells into cellular neighborhoods forming multicellular structures vital for heart function. Additionally, the researchers delved into the organizational and cellular intricacies of specific heart regions, such as the ventricles, by scrutinizing and mapping cells within these regions using MER-FISH. In vivo experiments utilizing mouse models and in vitro experiments utilizing human pluripotent stem cells were also conducted to probe cell interactions.

Results

The findings unveiled distinct cardiac cell types residing in specific subpopulations forming unique communities, with functional specialization dictated by anatomical location and cellular milieu. Cardiomyocyte lineages emerged as the predominant cell compartment identified via MER-FISH. Moreover, non-cardiomyocyte cell compartments also underwent segregation into populations and subpopulations, contributing to specific cardiac structures and regions.

Subpopulations of cardiomyocytes within ventricular regions exhibited the ability to construct intricate laminal structures within the ventricular wall and form cellular communities with other cardiac cell subpopulations. Furthermore, investigations into cell interactions through in vivo and in vitro experiments revealed that spatial organization of cardiac cell subpopulations during ventricular wall morphogenesis occurred via diverse signaling pathways.

The study also identified cardiac regions composed of spatially organized combinations of cell populations termed cellular communities. These communities varied in the number and types of cell populations, with distinct cellular signaling pathways delineating their structure and function. Within these communities, neighboring cardiac cells within a 150-micrometer radius were defined, each harboring unique cellular signaling pathways.

Conclusions In essence, the study elucidated that cardiomyocytes constituted the predominant cell type within the developing heart, with all cell types exhibiting distinct structural and regional distributions. Specific cell populations coalesced into cellular communities of varied compositions, with intercellular signaling pathways shaping their structure and function. This study significantly advances understanding of human heart structure development, offering potential avenues for treating structural heart diseases.

For more information: Spatially organized cellular communities form the developing human heart, Nature,  https://doi.org/10.1038/s41586-024-07171-z