Endothelial UNC5B regulates blood‑retinal barrier homeostasis

The blood‑retinal barrier (BRB), a critical component of the retinal neurovascular unit (NVU), is essential for maintaining retinal homeostasis. Dysfunction of the BRB contributes to vascular leakage, neuronal degeneration and gliosis, which are the core pathological hallmarks of diabetic retinopathy (DR) and retinal vein occlusion (RVO). Despite the importance of the BRB, the molecular mechanisms underlying the preservation of BRB integrity under pathological conditions remain unclear. The present study identified the endothelial receptor unc‑5 netrin receptor B (UNC5B) as a critical regulator of BRB and NVU homeostasis and a potential therapeutic target for neurovascular protection. Analysis of a public Gene Expression Omnibus single‑cell transcriptomic dataset, cell and animal models, and clinical samples revealed reduced UNC5B expression in the aqueous humor of patients and in the retinas of DR and RVO models. In vitro, endothelial knockdown of UNC5B increased apoptosis (assessed by PI/calcein‑AM staining), impaired barrier function (evaluated by BSA uptake and permeability of cell monolayer) and reduced pericyte recruitment, whereas UNC5B knockdown in pericytes had no detectable effects on pericyte proliferation, apoptosis or migration. In vivo, endothelial‑specific UNC5B deficiency markedly exacerbated retinal vascular leakage and structural damage in the DR model, as evidenced by Evans blue leakage, Periodic acid‑Schiff staining and immunofluorescence analyses. Furthermore, UNC5B knockdown abolished the protective effects of high‑dose netrin‑1 administration in DR mice. Endothelial UNC5B modulation, including knockdown and overexpression, affected not only the vascular integrity but also the neural components within the NVU, as evidenced by altered retinal ganglion cell degeneration and glial activation in the DR model, assessed using NeuN, β‑III tubulin and vimentin staining. In the RVO model, endothelial UNC5B deficiency aggravated retinal edema and thinning, as revealed by in vivo retinal imaging. Mechanistically, transcriptomic and protein analyses revealed that UNC5B downregulation was associated with increased extracellular matrix protein deposition and reduced Hippo pathway activity. Collectively, these findings established UNC5B as a key mediator of BRB and NVU stability, and highlighted its therapeutic potential in maintaining vascular integrity and protecting neural elements in retinal vascular diseases.