Regulated differentiation of stem cells into an artificial 3D liver as a transplantable source

Abstract

End-stage liver disease is one of the leading causes of death around the world. Since insufficient sources of transplantable liver and possible immune rejection severely hinder the wide application of conventional liver transplantation therapy, artificial three-dimensional (3D) liver culture and assembly from stem cells have become a new hope for patients with end-stage liver diseases, such as cirrhosis and liver cancer. However, the induced differentiation of single-layer or 3D-structured hepatocytes from stem cells cannot physiologically support essential liver functions due to the lack of formation of blood vessels, immune regulation, storage of vitamins, and other vital hepatic activities. Thus, there is emerging evidence showing that 3D organogenesis of artificial vascularized liver tissue from combined hepatic cell types derived from differentiated stem cells is practical for the treatment of end-stage liver diseases. The optimization of novel biomaterials, such as decellularized matrices and natural macromolecules, also strongly supports the organogenesis of 3D tissue with the desired complex structure. This review summarizes new research updates on novel differentiation protocols of stem cell-derived major hepatic cell types and the application of new supportive biomaterials. Future biological and clinical challenges of this concept are also discussed.

Keywords: Decellularized matrix; Differentiation; Natural macromolecules; Stem cells; Synthetic polymers.

Figure 1.

Key functional markers of liver cell types differentiated from stem cells (e.g., embryonic stem cells, mesenchymal stem cells, and inducible pluripotent stem cells). Major liver cell types, including hepatocytes, Kupffer cells, hepatic stellate cells, liver sinusoidal endothelial cells, and cholangiocytes can be reprogrammed from various stem cells using defined medium and chemical compounds during in vitro culture. Key functional markers can be used to validate the successful reprogramming of each cell type. ALB, albumin; HNF4α, hepatocyte nuclear factor 4 α; CK, cytokeratin; AFP, α-fetoprotein; AAT, α-1 antitrypsin; CYP, cytochrome P family enzymes; PECAM, platelet endothelial cell adhesion molecule-1; eNOS, endothelial nitric oxide synthase; ESCs, embryonic stem cells; MSCs, mesenchymal stem cells; iPSCs, inducible pluripotent stem cells; ALCAM, activated leukocyte cell adhesion molecule; CRBP, cellular retinol-binding protein; COL1α1, collagen type 1 α 1; GFAP, glial fibrillary acidic protein; RELN, reelin; PCDH7, protocadherin-7; aFGF, acidic fibroblast growth factor.

Figure 2.

Human 3D liver bud assembly from human umbilical cord blood stem cells (hUCBSCs). (A) Schematic representation of our strategy to assemble human 3D liver buds from naive MSC and MSC-derived hepatocytes, HSC-like cells, and LSEC-like cells. (B) The time-lapse representative images of the self-assembly process. This data and description have been published by Li et al. [60] MSC, mesenchymal stem cell; HSC, hepatic stellate cell; LSEC, liver sinusoidal endothelial cell.

Figure 3.

Assembly of transplantable 3D liver tissue. Natural macromolecules and synthetic polymers can be used to construct a decellularized matrix scaffold. Differentiated liver cells (hepatocytes, Kupffer cells, hepatic stellate cells, liver sinusoidal endothelial cells, and cholangiocytes) are then mixed and transplanted into the matrix scaffold to allow organogenesis for possible transplantation. PLA, polylactic acid; PLGA, poly(lactide-co-glycolide); PEG, poly(ethyleneglycol).