Serum albumin maintains Wnt3a water solubility and activity

Wnt proteins regulate adult tissue homeostasis and repair by driving stem cell self-renewal and differentiation. High-performance Wnt preparations have enormous therapeutic potential, especially alongside various stem cell technologies. Currently, a major limitation of most Wnt preparations is that they inevitably require fetal bovine serum (FBS) or detergents to maintain Wnt solubility and activity. Recently, afamin (AFM) was identified as a serum factor that solubilizes Wnt3a in conditioned media (CM), obviating the requirement for animal sera. Here, we show that serum albumin (SA) helps maintain the activity and stability of AFM-solubilized Wnt3a in CM, likely through a stabilizing effect. We further demonstrate, using test-tube assays, that SA alone efficiently solubilizes purified Wnt3a (pWnt3a) independently of AFM. This approach enables the conversion of conventional detergent-solubilized pWnt3a (CHAPS-pWnt3a) into SA-pWnt3a through dialysis-mediated detergent removal. Together, these findings define a simple and robust SA-based strategy for preserving Wnt3a activity, addressing a long-standing challenge in both experimental and therapeutic settings.