Is Wnt3a an essential component in organoid culture?

Organoids are self-organized three-dimensional tissue cultures that are derived from mammalian pluripotent or adult stem cells. These in-vitro-grown cell clusters are given possibilities to replicate much of the complexity of an organ. There are potentially as many types of organoids as there are different tissues and organs. To date, researchers have been able to prepare brain, kidney, lung, intestine, stomach, liver and many more are developing.

In 2009, Dr. Sato described the successful derivation of epithelial organoid cultures from single Lgr5⁺ stem cells (Sato et al. 2009). To maintain the organoid culture, researchers must be able to maintain the stem cells niche without feeder. Stem cells proliferation first create cystic spheroids, which then form crypt-like buddings that further develop in “mini-guts” with distinct crypt-villus compartmentalization as seen in vivo. In organoid growth, proliferating cells also express stem cell markers such as Lgr5 (Shyer et al., 2015). This phenotype can be maintained in vitro by experimentally stabilizing b-catenin, the cytoplasmic effector of Wnt signaling (Clevers and Nusse, 2012), either by supplementing the medium with Wnt3a or by generating mutant organoids expressing non-degradable b-catenin (Drost et al., 2015; Sato et al., 2011b).

Wnt signaling plays an important role in early development, maintenance (Logan et al. 2004) and regeneration of stem cells (ten Berge 2011), and in cancer formation (Zimmerman 2012). Wnt3a has been revealed to be an essential niche component for maintaining the proliferation of Lgr5-positive stem cells in various organoids such as the small intestine, large intestine, stomach, pancreas and liver. Although Wnt3a has been conventionally used for the culture of gut organoids, it is a fat-soluble protein, so it forms aggregates in serum-free medium and cannot exert its activity sufficiently. Wnt secretion from cultured cells require the presence of bovine serum in the media (Willert, 2008). As a result, Wnt-containing culture media would always have to contain ~10% serum, precluding the use of such sample in biological assays that are sensitive to the factors contained in bovine serum.

In 2016, Mihara and Sato et al. found that high Wnt3a activity can be maintained by forming a complex with Wnt3a by Afamin, which is one of the components of serum. They found that Afamin and Wnt apparently make 1:1 complex in the culture media which is highly soluble in detergent-free buffers upon isolation. Afamin-Wnt complex is biologically active indicating that Afamin can deliver Wnt ligands to its receptors on cell surface (Mihara and Sato et al. 2016). In addition, by using Afamin and Wnt3a complex for organoid culture, long-term culture of organoid becomes possible. MBL International is proud to bring this medium into the market which will help our organoid researchers. This new medium will result in optimal success for your organoid experiments.