Understanding and Engineering the Pulmonary Vasculature.

Blood vessels play essential roles in regulating embryonic organogenesis and adult tissue homeostasis. The inner lining of blood vessels is covered by vascular endothelial cells, which exhibit tissue-specific phenotypes in term of their molecular signature, morphology, and function. The pulmonary microvascular endothelium is continuous and non-fenestrae to ensure stringent barrier function while allowing efficient gas exchange across the alveoli-capillary interface. During respiratory injury repair, pulmonary microvascular endothelial cells secrete unique angiocrine factors and actively participate in the molecular and cellular events mediating alveolar regeneration. Advances in stem cell and organoid engineering are offering new ways to produce vascularized lung tissue models to investigate vascular-parenchymal interactions during lung organogenesis and pathogenesis. Further, technology developments in 3D biomaterial fabrication are enabling construction of vascularized tissues and microdevices with organotypic features at high resolution to recapitulate the air-blood interface. In parallel, whole-lung decellularization produces biomaterial scaffolds with naturally occurring, acellular vascular bed with preserved tissue architecture and complexity. Emerging efforts in combining cells with synthetic or natural biomaterials open vast opportunities for engineering the organotypic pulmonary vasculature to address current limitations in regenerating and repairing damaged lungs and pave the way towards next-generation therapies for pulmonary vascular diseases.

Alliance of Heart and Endoderm: Multilineage Organoids to Model Co-development.

Studies in animal models tracing organogenesis of the mesoderm-derived heart have emphasized the importance of signals coming from adjacent endodermal tissues in coordinating proper cardiac morphogenesis. Although in vitro models such as cardiac organoids have shown great potential to recapitulate the physiology of the human heart, they are unable to capture the complex crosstalk that takes place between the co-developing heart and endodermal organs, partly due to their distinct germ layer origins. In an effort to address this long-sought challenge, recent reports of multilineage organoids comprising both cardiac and endodermal derivatives have energized the efforts to understand how inter-organ, cross-lineage communications influence their respective morphogenesis. These co-differentiation systems have produced intriguing findings of shared signaling requirements for inducing cardiac specification together with primitive foregut, pulmonary, or intestinal lineages. Overall, these multilineage cardiac organoids offer an unprecedented window into human development that can reveal how the endoderm and heart cooperate to direct morphogenesis, patterning, and maturation. Further, through spatiotemporal reorganization, the co-emerged multilineage cells self-assemble into distinct compartments as seen in the cardiac-foregut, cardiac-intestine, and cardiopulmonary organoids and undergo cell migration and tissue reorganization to establish tissue boundaries. Looking into the future, these cardiac incorporated, multilineage organoids will inspire future strategies for improved cell sourcing for regenerative interventions and provide more effective models for disease investigation and drug testing. In this review, we will introduce the developmental context of coordinated heart and endoderm morphogenesis, discuss strategies for in vitro co-induction of cardiac and endodermal derivatives, and finally comment on the challenges and exciting new research directions enabled by this breakthrough.

Co-differentiation and Co-maturation of Human Cardio-pulmonary Progenitors and Micro-Tissues from Human Induced Pluripotent Stem Cells.

Currently, there are several in vitro protocols that focus on directing human induced pluripotent stem cell (hiPSC) differentiation into either the cardiac or pulmonary lineage. However, these systemsprotocols are unable to recapitulate the critical exchange of signals and cells between the heart and lungs during early development. To address this gap, here we describe a protocol to co-differentiate cardiac and pulmonary progenitors within a single hiPSC culture by temporal specific modulation of Wnt and Nodal signaling. Subsequently, human cardio-pulmonary micro-tissues (µTs) can be generated by culturing the co-induced cardiac and pulmonary progenitors in 3D suspension culture. Anticipated results include expedited alveolarization in the presence of cardiac cells, and segregation of the cardiac and pulmonary µTs in the absence of exogenous Wnt signaling. This protocol can be used to model cardiac and pulmonary co-development, with potential applications in drug testing, and as a platform for expediting the maturation of pulmonary cells for lung tissue engineering.

Reconstructing the pulmonary niche with stem cells: a lung story.

The global burden of pulmonary disease highlights an overwhelming need in improving our understanding of lung development, disease, and treatment. It also calls for further advances in our ability to engineer the pulmonary system at cellular and tissue levels. The discovery of human pluripotent stem cells (hPSCs) offsets the relative inaccessibility of human lungs for studying developmental programs and disease mechanisms, all the while offering a potential source of cells and tissue for regenerative interventions. This review offers a perspective on where the lung stem cell field stands in terms of accomplishing these ambitious goals. We will trace the known stages and pathways involved in in vivo lung development and how they inspire the directed differentiation of stem and progenitor cells in vitro. We will also recap the efforts made to date to recapitulate the lung stem cell niche in vitro via engineered cell-cell and cell-extracellular matrix (ECM) interactions.