Narrative engineering of the liver

Abstract

Liver organoids are primary or pluripotent stem cell-derived three-dimensional structures that recapitulate regenerative or ontogenetic processes in vitro towards biomedical applications including disease modelling and diagnostics, drug safety and efficacy prediction, and therapeutic use. The cellular composition and structural organization of liver organoids may vary depending on the goal at hand, and the key challenge in general is to direct their development in a rational and controlled fashion for gaining targeted maturity, reproducibility, and scalability. Such endeavor begins with a detailed understanding of the biological processes in space and time behind hepatogenesis, followed by precise translation of these narrative processes through a bioengineering approach. Here, we discuss advancements in liver organoid technology through the lens of 'narrative engineering' in an attempt to synergize evolving understanding around molecular and cellular landscape governing hepatogenesis with engineering-inspired approaches for organoidgenesis.

Keywords: developmental biology; liver organoid; narrative engineering; pluripotent stem cell.

Figure 1

Narrative engineering approach for liver begins with defining the spatial default and subsequently using both biological and synthetic controls of the environment to fine-tune liver development in vitro. Biological environmental control include: soluble factors/paracrine signals deduced from developmental biology (FGF, BMP, RA) and computationally predicted signal pathways; liver-specific cell types such as liver sinusoidal endothelial cells (LSECs), stellate cells (SCs), Kupffer cells (KCs), hepatic nervous system (HNS); liver-specific ECM including glycosaminoglycans, collagen, laminin, and fibronectin [34] as well as decellularized whole liver scaffolds [38]; niche-generated specification signals (STM, cardiac mesoderm (CM), pancreato-biliary boundary [40], anterior-posterior gut boundary [41,42]). Synthetic environmental control include gene circuits [44,45], stiffness control via mechano-modulatory 3D culture [46], 3D perfusable chip [50], bioprinting cells into hexagonal shape [47] or organoids onto needle array for scalable liver tissue [48]. The engineered liver may have different complexities and scalabilities that is goal dependent (e.g. disease modelling vs. transplant).

Figure 2

Early liver development and scRNA-seq of the developing liver at different time points. (A) In the mouse embryo, hepatoblasts are specified from foregut progenitors by BMP and FGF signals that derive from STM and the heart, respectively, around E8.25. Hepatic diverticulum begins to emerge by E8.5. Then, by E9.5, hepatoblasts become pseudostratified and delamination occurs partly via downregulation of E-cadherin and release of MMPs that are derived from endothelial cells and hepatoblasts. Hepatoblasts continue to expand and endothelial cells begin to form liver sinusoids by E 10.5 [17,18]. (B) By performing scRNA-seq of the developing liver at different time points, a dynamic transcriptome is generated, which allow for trajectory analysis, cell-cell interaction analysis, and more. These computational analyses have led to discovery of novel cell types and signaling pathways in silico, some of which have been experimentally validated [,–9].