Abstract
Purpose :
Norrin/Frizzled4 signaling plays an important role in the development of retinal blood vessels, blood-retina barrier (BRB) function, and ultimately retinal function. We recently reported that the antibody-based Norrin mimetic F4L5.13, a novel agonist for Frizzled4 and LRP5, promotes angiogenesis and BRB function in the Tspan12 KO model of impaired Norrin/Frizzled4 signaling. Here, we sought to define the pharmacodynamic effects of the agonist in the presence or absence of vascular malformations, determine if the agonist restores visual function, monitor gene expression responses in multiple retinal cell populations, and determine the duration of its barrier promoting effects after intraperitoneal or intravitreal administration.
Methods :
ERG, fluorescein angiography, single cell RNA-sequencing, immuno-staining of vascular endothelial cells, and staining with pimonidazole/hypoxyprobe were performed after F4L5.13 administration to Tspan12 systemic KO mice. In addition, Tspan12 endothelial-cell-specific KO mice (ECKO) were generated by activation of Cdh5-CreERT2 at P28, resulting in a BRB disease model without vascular malformations. Effects of F4L5.13 on BRB function in Tspan12 ECKO mice were monitored longitudinally using fluorescein angiography.
Results :
Administration of F4L5.13 from P6-28 fully restored the ERG b-wave in Tspan12 KO mice, restored angiogenesis and BRB function, alleviated hypoxia, and largely restored gene expression profiles in the neuroretina of Tspan12 KO mice. Administration after P28 did not restore the ERG b-wave, revert vascular malformations, or establish normoxia, but it resulted in substantial restoration of BRB function. In adult Tspan12 ECKO mice without vascular malformations, F4L5.13 restored BRB function efficiently, and a single intravitreal injection suppressed BRB phenotypes for 2-4 weeks.
Conclusions :
Vascular malformations in Tspan12 KO mice, once developed, cannot be resolved by F4L5.13, yet, the agonist partially promotes BRB function even in the malformed vasculature. When F4L5.13 is administered before vascular malformations have formed, it induces the development of a normal vasculature, restores the ERG, and normalizes gene expression profiles. In the Tspan12 ECKO model of BRB dysfunction without vascular malformations, F4L5.13 demonstrates excellent efficacy in promoting BRB function, even after a single intravitreal injection.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.