Crumbs proteins regulate layered retinal vascular development required for vision

Crumbs proteins are transmembrane proteins that regulate cellular apico-basal polarity. Animals carrying mutated crb1 present retinal vascular abnormalities; this mutation is associated with progressive retinal degeneration with intraretinal cystoid fluid collection in humans. This study aimed to evaluate a potential role of crumbs proteins in retinal vascular development and maintenance. We demonstrated that crumbs homologues (CRBs) were differentially expressed and changed dramatically during mouse retinal vascular development. Intravitreal injection of CRB1 and CRB2 siRNA induced delayed development of the deep capillary plexus and premature development of the intermediate capillary plexus, resulting in disrupted vascular integrity. However, microfluidic chip assay using human retinal endothelial cells revealed that CRBs do not directly affect in vitro retinal angiogenesis. CRBs control retinal angiogenesis by regulating neuroglial vascular endothelial growth factor-A (VEGFA) and matrix metalloproteinase-3 expression. These findings demonstrate a pivotal role of CRBs in providing critical neurotrophic support through normal layered vascular network development and maintenance. This implies that preserving CRBs and restoring layered retinal vascular networks could be novel targets for preventing vision-threatening retinal diseases.