# The influence of TLR4 signaling on retinal ganglion cell survival and angiogenic response in a mouse model of oxygen-induced retinopathy

## TL;DR

This study shows that blocking TLR4 reduces harmful blood vessel growth and protects retinal cells in a mouse model of retinopathy of prematurity.

## Contribution

The study reveals TLR4 as a novel therapeutic target for retinopathy of prematurity by linking it to inflammation, angiogenesis, and neuronal survival.

## Key findings

- TLR4 knockout mice showed reduced VEGF and MCP1 upregulation in oxygen-induced retinopathy.
- TLR4 deficiency inhibited retinal neovascularization and protected retinal ganglion cells from death.
- Blocking TLR4 may offer a new treatment strategy for retinal diseases in premature infants.

## Abstract

Retinopathy of prematurity (ROP) is a critical concern in neonatal care and potentially leads to vision impairment. Despite advancements in anti-VEGF treatments, the mechanisms driving pathological vitreoretinal neovascularization remain unclear. I examined the role of Toll-like receptor 4 (TLR4) in modulating inflammatory cytokines, angiogenesis, and neuronal cell protection in a mouse model of oxygen-induced retinopathy (OIR).

C57BL/6J TLR4−/− mice were subjected to OIR by exposure to 75% oxygen from postnatal days 7 to 12 (P7 to P12) following approved protocols. I used immunohistochemistry to assess TLR4 expression at P19, real-time quantitative PCR for proinflammatory cytokines at P19, ex vivo fluorescent vascular imaging to evaluate retinal vascular changes at P19, and retinal neuronal cells death evaluated by whole-mounted retina stained with cresyl violet at P47. Statistical significance was determined using one-way ANOVA (p < 0.05).

Immunofluorescence demonstrated TLR4 expression in microglia in OIR retinas of wild-type mice but not in controls. Real-time PCR revealed significant upregulation of vascular endothelial growth factor (VEGF) and monocyte chemoattractant protein-1 (MCP1) in OIR retinas, which was mitigated in TLR4−/− mice. Retinal angiogenesis significantly increased in wild-type OIR mice, whereas TLR4 knockdown inhibited these changes. Additionally, OIR caused approximately 30% neuronal cell death in the retinal ganglion cell layer, which was largely prevented in the TLR4−/− mice.

These findings underscore TLR4's pivotal role in the regulation of inflammatory responses and angiogenesis in ROP. Targeting TLR4 may represent a novel therapeutic approach to preserve retinal integrity and improve visual outcomes in at-risk populations, particularly in premature infants.

•TLR4 modulates inflammation & angiogenesis in oxygen-induced retinopathy (OIR).•TLR4 knockout suppresses VEGF/MCP1 upregulation in OIR mouse retina.•Knockdown of TLR4 inhibits retinal neovascularization in the OIR model.•TLR4 deficiency protects retinal ganglion cells from death in OIR.•Targeting TLR4: a novel approach to treat retinal disease in premature infants.

TLR4 modulates inflammation & angiogenesis in oxygen-induced retinopathy (OIR).

TLR4 knockout suppresses VEGF/MCP1 upregulation in OIR mouse retina.

Knockdown of TLR4 inhibits retinal neovascularization in the OIR model.

TLR4 deficiency protects retinal ganglion cells from death in OIR.

Targeting TLR4: a novel approach to treat retinal disease in premature infants.