Hormonally and chemically defined expansion conditions for organoids of biliary tree Stem Cells

Wholly defined <i>ex vivo</i> expansion conditions for biliary tree stem cell (BTSC) organoids were established, consisting of a defined proliferative medium (DPM) used in combination with soft hyaluronan hydrogels. The DPM consisted of commercially available Kubota's Medium (KM), to which a set of small molecules, particular paracrine signals, and heparan sulfate (HS) were added. The small molecules used were DNA methyltransferase inhibitor (RG108), TGF- β Type I receptor inhibitor (A83-01), adenylate cyclase activator (Forskolin), and L-type Ca²⁺ channel agonist (Bay K8644). A key paracrine signal proved to be R-spondin 1 (RSPO1), a secreted protein that activates Wnts. Soluble hyaluronans, 0.05 % sodium hyaluronate, were used with DPM to expand monolayer cultures. Expansion of organoids was achieved by using DPM in combination with embedding organoids in Matrigel that was replaced with a defined thiol-hyaluronan triggered with PEGDA to form a hydrogel with a rheology [<i>G*</i>] of less than 100 Pa. The combination is called the BTSC-Expansion-Glycogel-System (BEX-gel system) for expanding BTSCs as a monolayer or as organoids. The BTSC organoids were expanded more than 3000-fold <i>ex vivo</i> in the BEX-gel system within 70 days while maintaining phenotypic traits indicative of stem/progenitors. Stem-cell-patch grafting of expanded BTSC organoids was performed on the livers of Fah^-/- mice with tyrosinemia and resulted in the rescue of the mice and restoration of their normal liver functions. The BEX-gel system for BTSC organoid expansion provides a strategy to generate sufficient numbers of organoids for the therapeutic treatments of liver diseases.