Noncanonical Wnt signaling is an evolutionarily conserved pathway that regulates cellular filament organization and directional migration. This pathway has been implicated in multiple biological processes, including embryonic tissue morphogenesis1,2,3, lymphatic and vascular angiogenesis4,5,6,7, and cancer growth and metastasis8,9,10. At the cellular level, noncanonical Wnt signaling is carried out through coordinated paracrine interactions between signal-sending and signal-receiving cells. These interactions frequently occur between cells of different lineages or types and involve a diverse molecular network that includes up to 19 ligands and multiple receptors, co-receptors, and downstream signal transduction effectors11. Further complicating this signaling process, previous studies have shown that ligand-receptor combinations can vary in a context- and tissue-dependent manner12,13, and that the same source ligands that drive noncanonical Wnt signaling in signal-receiving cells can be produced by multiple signal-sending cell types14,15. Given the cellular and molecular complexity associated with noncanonical Wnt signaling, the ability to study individual and clinically relevant mechanisms in vivo has been limited.
Attempts have been made to study noncanonical Wnt signaling using cell culture techniques in vitro. For example, wound-healing assays performed in cellular monolayers have been used to functionally assess cellular directional migration4,16,17,18,19. Immunostaining techniques have been used to perform spatial analyses of surface protein expression to evaluate noncanonical Wnt-induced changes in cellular morphology7,10, architecture, and asymmetric polarization18,19,20. Although these approaches have provided important tools for characterizing Wnt-related phenotypes in signal-receiving cells, the lack of signal-sending components in these protocols limits their ability to accurately model paracrine signaling mechanisms observed in vivo. As a result, there remains a critical need to develop in vitro systems that allow robust and reproducible evaluation of paracrine signaling interactions between signal-sending and receiving cells of the noncanonical Wnt pathway, particularly those of different cell types.
To this end, the primary objective of this study was to establish a protocol to model paracrine noncanonical Wnt signaling interactions in vitro. We developed a non-contact coculture system that recapitulates signal-sending and signal-receiving components of these interactions and allows the use of standard molecular, genetic, or pharmacologic approaches to independently study specific ligand-receptor mechanisms in the noncanonical Wnt pathway. Mechanisms of NCC-mediated Wnt signaling were examined in myoblasts using established murine cell lines. As proof of principle, this model was used to corroborate findings of prior in vivo studies in mice that implicate the Wnt5a-ROR2 axis as a relevant noncanonical Wnt signaling pathway between NCCs21 and SHF cardiomyoblast progenitors3,22,23.