Wnt5b regulates mesenchymal cell aggregation and chondrocyte differentiation through the planar cell polarity pathway.

Although genetic evidence has demonstrated a role for Wnt5b during cartilage and limb development, little is known about the mechanisms underlying Wnt5b-regulated chondrocyte differentiation. We observed that Wnt5b inhibited chondrocyte hypertrophy and expression of type X collagen. In addition, Wnt5b regulated the overall size of chondrogenic cultures, suggesting that Wnt5b regulates other processes involved in cartilage development. We therefore investigated the signaling pathways by which Wnt5b influences differentiation. Wnt5b activated known calcium-dependent signaling pathways and JNK, a component of the planar cell polarity pathway. Since the planar cell polarity pathway regulates process such as cell migration and cell aggregation that are involved in limb development, we assayed for effects of Wnt5b on these processes. We observed a marked increase chondroprogenitor cell migration with Wnt5b expression. This effect was blocked by inhibition of JNK, but not by inhibition of other Wnt5b-responsive factors. Expression of Wnt5b also disrupted the cellular aggregation associated with mesenchymal condensation. Decreased aggregation was associated with reduced cadherin expression as well as increased cadherin receptor turnover. This increase in cadherin receptor turnover was associated with an increase in Src-dependent beta-catenin phosphorylation downstream of Wnt5b. Our data demonstrate that not only does Wnt5b inhibit chondrocyte hypertrophy, but document a novel role for Wnt5b in modulating cellular migration through the JNK-dependent and cell adhesion through an activation of Src and subsequent cadherin receptor turnover.