This editorial refers to ‘Mapping the developing human cardiac endothelium at single-cell resolution identifies MECOM as a regulator of arteriovenous gene expression’ by I.R. McCracken et al., https://doi.org/10.1093/cvr/cvac023.
The coronary vasculature and the blood vessels supplying the heart are formed during embryonic and post-natal development. While the development of the coronary vasculature in mice has been well-studied, a better understanding of human coronary artery development is essential for efforts to promote arterial regeneration in injured adult hearts. In this study, McCracken et al.1 performed single-cell RNA sequencing (scRNAseq) of over 10 000 coronary endothelial cells (ECs) from developing human hearts (Figure 1). Although prior studies2–3 have performed scRNAseq on human hearts, the enrichment of such a large number of ECs is critical for deeper interrogations that answer questions about cell origins and predict cell fate trajectories.
Figure 1.
Summary of the study conducted by McCracken et al.1 on endothelial cells from developing human hearts.
McCracken et al. conducted scRNAseq on human hearts at gestational weeks 13 and 14. The equivalent stage of mouse development, between e15 and e18, is notable for significant vascular growth and remodelling. Their data comprise a variety of EC types including capillary, artery, vein, lymphatic, and endocardial. They uncovered both micro- and macro-vascular arterial populations, as well as two populations of capillary cells marked by expression of either INMT or KIT, consistent with a previous study.4
Importantly, the authors employed gene regulatory network analysis using SCENIC5 to uncover transcription factors (TFs) regulating human coronary development. MECOM is one of the arterial regulators identified through this analysis, in addition to previously known TFs including HEY1 and SOX17. The authors validated MECOM expression in the arteries of human fetal hearts using in situ hybridization. Mecom expression was also found in arterial ECs of mouse hearts, supporting its importance in arterial development. The authors further validated its role in achieving and/or maintaining an arterial phenotype with an siRNA-mediated knockdown of MECOM in arterial EC differentiated from human embryonic stem cells (hESC-ECs).6 After MECOM knockdown, hESC-ECs took on a more venous transcriptional profile while retaining expression of arterial markers, indicating that MECOM is involved in the suppression of venous gene expression.
McCracken et al. also used this new dataset to investigate the origins of vascular ECs in the human heart. In mice, coronary ECs are derived from one of two developmental sources: the sinus venosus, the major inflow tract of the developing heart, and the endocardium, the inner lining of the heart chambers. These progenitor sources have been discovered and validated through Cre-based lineage tracing,7–9 and scRNAseq has been used to uncover the mechanisms underlying the transitions from progenitor cell type to mature coronary endothelium. However, the source of human coronary endothelium remained elusive. Although in silico lineage tracing in humans using sequencing data has been reported,10 the simplest approach to identifying sources of human coronary endothelium with current technology would be to find evidence of a transition from a progenitor cell type to vascular ECs in scRNAseq data. Yet, such a transition has not been uncovered in prior published datasets. This could either be due to the timing of the transition not being captured in the developmental stages that were sequenced or due to the transitioning cell populations being rare, as we have seen in the mouse endocardial-to-vascular EC transition,11 requiring a large number of ECs to be sequenced for them to be isolated.
McCracken et al.’s analysis suggest that a population of venous endothelium represents a bridge of transitioning cells between endocardium and capillary ECs. The transition is supported by trajectory analysis with RNA velocity12 as well as Slingshot.13 These cells are marked by expression of ACKR1, a known venous marker. Interestingly, these cells are enriched in BMP2, which has recently been shown to mark the endocardial-to- vascular EC transition in mouse, a finding that was validated with genetic lineage tracing.11 Thus, the authors present evidence that, similar to mice, the endocardium is a progenitor for human coronary ECs, although further studies to validate and localize the expression of BMP2 and ACKR1 in human fetal hearts will help to support this conclusion. Additionally, the authors compared their data with an available scRNAseq dataset from developing mouse hearts, which also supported equivalent cellular subsets being present in mice and humans.
The new study from McCracken et al. sheds additional light on human coronary vessel development and provides a high-quality resource for further investigations of vascular formation and remodeling in human hearts. Future experiments in human hearts to localize marker genes of transitioning cell populations, especially if done across multiple stages of development, will validate the conclusions of this study and add to our understanding of human coronary angiogenesis.
Contributor Information
Ragini Phansalkar, School of Medicine, Stanford University, Stanford, CA 94305, USA.
Kristy Red-Horse, Department of Biology, Stanford University, Stanford, CA 94305, USA; Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
Funding
Kristy Red-Horse is supported by R01 2R01HL128503-06 from the NHLBI.
References
- 1. McCracken IR, Dobie R, Bennett M, Passi R, Beqqali A, Henderson NC, Mountford JC, Riley PR, Ponting CP, Smart N, Brittan M, Baker AH. Mapping the developing human cardiac endothelium at single cell resolution identifies MECOM as a regulator of arteriovenous gene expression. Cardiovasc Res 2022;118:2960–2972. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2. Suryawanshi H, Clancy R, Morozov P, Halushka MK, Buyon JP, Tuschl T. Cell atlas of the foetal human heart and implications for autoimmune-mediated congenital heart block. Cardiovasc Res 2020;116:1446–1457. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3. Cui Y, Zheng Y, Liu X, Yan L, Fan X, Yong J, Hu Y, Dong J, Li Q, Wu X, Gao S, Li J, Wen L, Qiao J, Tang F. Single-cell transcriptome analysis maps the developmental track of the human heart. Cell Rep 2019;26:1934–1950.e5. [DOI] [PubMed] [Google Scholar]
- 4. Phansalkar R, Krieger J, Zhao M, Kolluru SS, Jones RC, Quake SR, Weissman I, Bernstein D, Winn VD, D’Amato G, Red-Horse K. Coronary blood vessels from distinct origins converge to equivalent states during mouse and human development. eLife 2021;10:e70246. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5. Aibar S, González-Blas CB, Moerman T, Huynh-Thu VA, Imrichova H, Hulselmans G, Rambow F, Marine J-C, Geurts P, Aerts J, van den Oord J, Atak ZK, Wouters J, Aerts S. SCENIC: Single-cell regulatory network inference and clustering. Nat Methods 2017; 14:1083–1086. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6. McCracken IR, Taylor RS, Kok FO, de la Cuesta F, Dobie R, Henderson BEP, Mountford JC, Caudrillier A, Henderson NC, Ponting CP, Baker AH. Transcriptional dynamics of pluripotent stem cell-derived endothelial cell differentiation revealed by single-cell RNA sequencing. Eur Heart J 2020; 41:1024–1036. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7. Red-Horse K, Ueno H, Weissman IL, Krasnow MA. Coronary arteries form by developmental reprogramming of venous cells. Nature 2010;464:549–553. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8. Chen HI, Sharma B, Akerberg BN, Numi HJ, Kivelä R, Saharinen P, Aghajanian H, McKay AS, Bogard PE, Chang AH, Jacobs AH, Epstein JA, Stankunas K, Alitalo K, Red-Horse K. The sinus venosus contributes to coronary vasculature through VEGFC-stimulated angiogenesis. Development 2014;141:4500–4512. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9. Tian X, Hu T, Zhang H, He L, Huang X, Liu Q, Yu W, He L, Yang Z, Yan Y, Yang X, Zhong TP, Pu WT, Zhou B. De novo formation of a distinct coronary vascular population in neonatal heart. Science 2014;345:90–94. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10. Ludwig LS, Lareau CA, Ulirsch JC, Christian E, Muus C, Li LH, Pelka K, Ge W, Oren Y, Brack A, Law T, Rodman C, Chen JH, Boland GM, Hacohen N, Rozenblatt-Rosen O, Aryee MJ, Buenrostro JD, Regev A, Sankaran VG. Lineage tracing in humans enabled by mitochondrial mutations and single-cell genomics. Cell 2019;176:1325–1339.e22. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11. D’Amato G, Phansalkar R, Naftaly JA, Coronado PER, Cowley DO, Quinn KE, Sharma B, Caron KM, Vigilante A, Red-Horse K. Endocardium-to-coronary artery differentiation during heart development and regeneration involves sequential roles of Bmp2 and Cxcl12/Cxcr4.bioRxiv [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12. La Manno G, Soldatov R, Zeisel A, Braun E, Hochgerner H, Petukhov V, Lidschreiber K, Kastriti ME, Lönnerberg P, Furlan A, Fan J, Borm LE, Liu Z, van Bruggen D, Guo J, He X, Barker R, Sundström E, Castelo-Branco G, Cramer P, Adameyko I, Linnarsson S, Kharchenko PV. RNA velocity of single cells. Nature 2018;560:494–498. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13. Street K, Risso D, Fletcher RB, Das D, Ngai J, Yosef N, Purdom E, Dudoit S. Slingshot: cell lineage and pseudotime inference for single-cell transcriptomics. BMC Genomics 2018;19:477. [DOI] [PMC free article] [PubMed] [Google Scholar]