Wnt5a Does Not Support Hematopoiesis in Stroma-Free, Serum-Free Cultures

Previously we reported that Wnt5a is highly expressed in the murine urogenital ridge-derived UG26-1B6 cells but not embryonic liver-derived EL08-1D2 cells. Mouse long-term repopulating hematopoietic stem cells (LTR-HSC) were maintained in non-contact UG26-1B6 cultures but not EL08-1D2 non-contact cultures, unless Wnt5a was also added to the cultures, suggesting a role for Wnt5a in the in vitro maintenance of LTR-HSC. Here, we investigated if the effect of Wnt5a on adult LTR-HSC activity is HSC-autonomous. To test the effect of Wnt5a on maintenance of LTR-HSC, we performed limiting dilution competitive transplantation assays of murine Lin-Sca1(+) c-kit(+) (LSK) cells cultured for 5 days with TPO and SCF with and without Wnt5a. The effect of Wnt5a on the generation of colony forming units (CFU) and the homing ability of LSK progeny was also tested. No effects were found of Wnt5a on total cell expansion, the number of CFU, or homing ability of day 5 LSK progeny. Furthermore, addition of Wnt5a did not improve, but may have impeded maintenance of LTR-HSC. In conclusion, our data indicate that Wnt5a does not enhance the maintenance and expansion of adult murine LTR-HSCs or committed progenitors cultured in vitro in serum-and stroma-free conditions.