Toward improved understanding of cardiac development and congenital heart disease: The advent of cardiac organoids

Induced Pluripotent Stem Cell-Based Modeling of Single-Ventricle Congenital Heart Diseases

PURPOSE OF REVIEW

Congenital heart disease includes a wide variety of structural cardiac defects, the most severe of which are single ventricle defects (SVD). These patients suffer from significant morbidity and mortality; however, our understanding of the developmental etiology of these conditions is limited. Model organisms offer a window into normal and abnormal cardiogenesis yet often fail to recapitulate complex congenital heart defects seen in patients. The use of induced pluripotent stem cells (iPSCs) derived from patients with single-ventricle defects opens the door to studying SVD in patient-derived cardiomyocytes (iPSC-CMs) in a variety of different contexts, including organoids and chamber-specific cardiomyocytes. As the genetic and cellular causes of SVD are not well defined, patient-derived iPSC-CMs hold promise for uncovering mechanisms of disease development and serve as a platform for testing therapies. The purpose of this review is to highlight recent advances in iPSC-based models of SVD.

RECENT FINDINGS

Recent advances in patient-derived iPSC-CM differentiation, as well as the development of both chamber-specific and non-myocyte cardiac cell types, make it possible to model the complex genetic and molecular architecture involved in SVD development. Moreover, iPSC models have become increasingly complex with the generation of 3D organoids and engineered cardiac tissues which open the door to new mechanistic insight into SVD development. Finally, iPSC-CMs have been used in proof-of-concept studies that the molecular underpinnings of SVD may be targetable for future therapies. While each platform has its advantages and disadvantages, the use of patient-derived iPSC-CMs offers a window into patient-specific cardiogenesis and SVD development. Advancement in stem-cell based modeling of SVD promises to revolutionize our understanding of the developmental etiology of SVD and provides a tool for developing and testing new therapies.

Endocardial Regulation of Cardiac Development

The endocardium is a specialized form of endothelium that lines the inner side of the heart chambers and plays a crucial role in cardiac development. While comparatively less studied than other cardiac cell types, much progress has been made in understanding the regulation of and by the endocardium over the past two decades. In this review, we will summarize what is currently known regarding endocardial origin and development, the relationship between endocardium and other cardiac cell types, and the various lineages that endocardial cells derive from and contribute to. These processes are driven by key molecular mechanisms such as Notch and BMP signaling. These pathways in particular have been well studied, but other signaling pathways and mechanical cues also play important roles. Finally, we will touch on the contribution of stem cell modeling in combination with single cell sequencing and its potential translational impact for congenital heart defects such as bicuspid aortic valves and hypoplastic left heart syndrome. The detailed understanding of cellular and molecular processes in the endocardium will be vital to further develop representative stem cell-derived models for disease modeling and regenerative medicine in the future.