Frizzled-4:Low-density lipoprotein receptor-related protein 6 receptor complex (FZD4:LRP6)

The Frizzled-4:Low-density lipoprotein receptor-related protein 6 (FZD4:LRP6) receptor complex is a critical mediator of the canonical Wnt/β-catenin signaling pathway, specifically activated by the ligand Norrin (NDP) or certain Wnt proteins (UniProt Consortium, 2023). FZD4 is a seven-transmembrane protein classified within the Frizzled family of G protein-coupled receptors, while LRP6 serves as an essential single-pass transmembrane co-receptor (Xu et al., 2004). Upon ligand binding, these two proteins dimerize, initiating a signaling cascade that prevents the degradation of cytoplasmic β-catenin, allowing it to enter the nucleus and drive the expression of genes involved in vascular development and tissue regeneration (Junge et al., 2009). This complex plays a pivotal role in the formation and maintenance of the blood-retinal barrier and retinal angiogenesis. Mutations in the components of this complex or its ligands are primary causes of vitreoretinal diseases such as Familial Exudative Vitreoretinopathy (FEVR). Consequently, the FZD4:LRP6 complex is a major therapeutic target for regenerative medicine, with investigational drugs like bispecific antibodies being developed to mimic Norrin activity and restore vascular integrity in the eye (Surrozen, 2024). Targeting this complex requires careful modulation to avoid systemic Wnt-related toxicities or potential tumorigenesis.

Other names

Frizzled-4:LRP6 complexFZD4:LRP6 signaling complexNorrin receptor complexWnt receptor complex

Ligand-induced dimerization of FZD4 and LRP6 triggers the canonical Wnt signaling pathway by inhibiting the β-catenin destruction complex, leading to β-catenin stabilization, nuclear translocation, and activation of target genes involved in vascular development and tissue repair (Xu et al., 2004; Junge et al., 2009).