Therapeutic blood-brain barrier modulation and stroke treatment by a bioengineered FZD4-selective WNT surrogate in mice

Derangements of the blood-brain barrier (BBB) or blood-retinal barrier (BRB) occur in disorders ranging from stroke, cancer, diabetic retinopathy, and Alzheimer’s disease. The Norrin/FZD 4 /TSPAN12 pathway activates WNT/β-catenin signaling, which is essential for BBB and BRB function. However, systemic pharmacologic FZD 4 stimulation is hindered by obligate palmitoylation and insolubility of native WNTs and suboptimal properties of the FZD 4 -selective ligand Norrin. Here, we develop L6-F4-2, a non-lipidated, FZD 4 -specific surrogate which significantly improves subpicomolar affinity versus native Norrin. In Norrin knockout ( Ndp KO ) mice, L6-F4-2 not only potently reverses neonatal retinal angiogenesis deficits, but also restores BRB and BBB function. In adult C57Bl/6J mice, post-stroke systemic delivery of L6-F4-2 strongly reduces BBB permeability, infarction, and edema, while improving neurologic score and capillary pericyte coverage. Our findings reveal systemic efficacy of a bioengineered FZD 4 -selective WNT surrogate during ischemic BBB dysfunction, with potential applicability to adult CNS disorders characterized by an aberrant blood-brain barrier. The WNT/b-catenin pathway is essential for bloodbrain barrier (BBB) and blood-retina barrier (BRB) function. A bioengineered FZD4-selective WNT surrogate demonstrated systemic efficacy during BRB and ischemic stroke BBB dysfunction in mice.