Inhibition of endoplasmic reticulum stress by 4-phenylbutyrate alleviates retinal inflammation and the apoptosis of retinal ganglion cells after ocular alkali burn in mice

Endoplasmic Reticulum Stress Drives Neuroinflammation Through Lipocalin 2 Upregulation in Retinal Microglia After Optic Nerve Injury

Purpose

This study aims to explore how lipocalin 2 (LCN2) connects endoplasmic reticulum (ER) stress and inflammation in optic nerve injury (ONI) and identify potential therapeutic strategies.

Methods

An optic nerve crush (ONC) mouse model was used to investigate the role of ER stress and LCN2 in ONI. Immunofluorescence, quantitative PCR, and Western blot analyses were performed to assess ER stress markers, LCN2, inflammation-related genes, and retinal ganglion cell (RGC) survival, with or without treatment of 4PBA (an ER stress inhibitor) and TUN (an ER stress activator) in both the ONC model and BV2 cells. Lcn2 knockdown was achieved using small interfering RNA in BV2 cells and adeno-associated virus (AAV)-mediated gene silencing in vivo to explore underlying signaling pathways.

Results

ER stress markers (GRP78, ATF4, CHOP) and LCN2 expression were increased in ONC retinas, accompanied by microglial activation and RGC loss. Inhibition of ER stress using 4PBA effectively decreased LCN2 expression, attenuated microglial activation, and increased RGC survival post-ONC. Intravitreal injection of recombinant LCN2 induced a proinflammatory phenotype in microglia and exacerbated neurotoxicity. AAV-mediated Lcn2 silencing mitigated microglial activation, reduced neuroinflammation, and provided RGC neuroprotection, surpassing 4PBA treatment. In vitro studies further confirmed that Lcn2 knockdown significantly reduced the inflammatory response in BV2 cells by inhibiting NLRP3 inflammasome activation via the TLR4/NF-κB pathway.

Conclusions

This study elucidates the critical role of LCN2 in linking ER stress and inflammation in ONI, offering a promising therapeutic target. AAV-mediated Lcn2 silencing outperforms broad ER stress inhibition, providing a novel strategy for treating optic nerve injuries.

Oxidative stress mediates retinal damage after corneal alkali burn through the activation of the cGAS/STING pathway

Retinal damage accounts for irreversible vision loss following ocular alkali burn (OAB), but the underlying mechanisms remain largely unexplored. Herein, using an OAB mouse model, we examined the impact of oxidative stress (OS) in retinal damage and its molecular mechanism. Results revealed that OS in the retina was enhanced soon after alkali injury. Antioxidant therapy with N-acetylcysteine (NAC) preserved the retinal structure, suppressed cell apoptosis and decreased retinal inflammation, confirming the role of OS. Moreover, enhanced OS was linked to mitochondrial dysfunction, mtDNA leakage and initiation of the cytosolic DNA-sensing signaling. The activation of the major DNA sensors cyclic GMP-AMP Synthase (cGas) and cGAS-Stimulator of Interferon Genes (cGAS/STING) pathway was then identified. Notably, inhibiting cGAS/STING signaling with C-176 markedly reduced inflammation and cell apoptosis and ultimately protected the retina against OAB. Overall, our study reveals the vital function of OS in the occurrence of OAB-induced retinal damage and the involvement of cGAS/STING activation. Furthermore, our provides preclinical validation of the use of an antioxidant or a STING inhibitor as a potential therapeutic approach to protect the retina after OAB.

The prophylactic value of TNF-α inhibitors against retinal cell apoptosis and optic nerve axon loss after corneal surgery or trauma

BACKGROUND AND PURPOSE

Late secondary glaucoma is an often-severe complication after acute events like anterior segment surgery, trauma and infection. TNF-α is a major mediator that is rapidly upregulated, diffusing also to the retina and causes apoptosis of the ganglion cells and degeneration of their optic nerve axons (mediating steps to glaucomatous damage). Anti-TNF-α antibodies are in animals very effective in protecting the retinal cells and the optic nerve-and might therefore be useful prophylactically against secondary glaucoma in future such patients. Here we evaluate (1) toxicity and (2) efficacy of two TNF-α inhibitors (adalimumab and infliximab), in rabbits by subconjunctival administration.

METHODS

For drug toxicity, animals with normal, unburned corneas were injected with adalimumab (0.4, 4, or 40 mg), or infliximab (1, 10, or 100 mg). For drug efficacy, other animals were subjected to alkali burn before such injection, or steroids (for control). The rabbits were evaluated clinically with slit lamp and photography, electroretinography, optical coherence tomography, and intraocular pressure manometry. A sub-set of eyes were stained ex vivo after 3 days for retinal cell apoptosis (TUNEL). In other experiments the optic nerves were evaluated by paraphenylenediamine staining after 50 or 90 days. Loss of retinal cells and optic nerve degeneration were quantified.

RESULTS

Subconjunctival administration of 0.4 mg or 4.0 mg adalimumab were well tolerated, whereas 40.0 mg was toxic to the retina. 1, 10, or 100 mg infliximab were also well tolerated. Analysis of the optic nerve axons after 50 days confirmed the safety of 4.0 mg adalimumab and of 100 mg infliximab. For efficacy, 4.0 mg adalimumab subconjunctivally in 0.08 mL provided practically full protection against retinal cell apoptosis 3 days following alkali burn, and infliximab 100 mg only slightly less. At 90 days following burn injury, control optic nerves showed about 50% axon loss as compared to 8% in the adalimumab treatment group.

CONCLUSIONS

Subconjunctival injection of 4.0 mg adalimumab in rabbits shows no eye toxicity and provides excellent neuroprotection, both short (3 days) and long-term (90 days). Our total. accumulated data from several of our studies, combined with the present paper, suggest that corneal injuries, including surgery, might benefit from routine administration of anti-TNF-α biologics to reduce inflammation and future secondary glaucoma.

Effect of Tauroursodeoxycholic Acid on Inflammation after Ocular Alkali Burn

Inflammation is the main cause of corneal and retinal damage in an ocular alkali burn (OAB). The aim of this study was to investigate the effect of tauroursodeoxycholic acid (TUDCA) on ocular inflammation in a mouse model of an OAB. An OAB was induced in C57BL/6j mouse corneas by using 1 M NaOH. TUDCA (400 mg/kg) or PBS was injected intraperitoneally (IP) once a day for 3 days prior to establishing the OAB model. A single injection of Infliximab (6.25 mg/kg) was administered IP immediately after the OAB. The TUDCA suppressed the infiltration of the CD45-positive cells and decreased the mRNA and protein levels of the upregulated TNF-α and IL-1β in the cornea and retina of the OAB. Furthermore, the TUDCA treatment inhibited the retinal glial activation after an OAB. The TUDCA treatment not only ameliorated CNV and promoted corneal re-epithelization but also attenuated the RGC apoptosis and preserved the retinal structure after the OAB. Finally, the TUDCA reduced the expression of the endoplasmic reticulum (ER) stress molecules, IRE1, GRP78 and CHOP, in the retinal tissues of the OAB mice. The present study demonstrated that the TUDCA inhibits ocular inflammation and protects the cornea and retina from injury in an OAB mouse model. These results provide a potential therapeutic intervention for the treatment of an OAB.

Th17 Activation and Th17/Treg Imbalance in Prolonged Anterior Intraocular Inflammation after Ocular Alkali Burn

Ocular alkali burn (OAB) is a sight-threatening disease with refractory ocular inflammation causing various blinding complications. Th17 lymphocytes account for the pathogeneses of the autoimmune disease and chronic inflammation, but their role in prolonged anterior intraocular inflammation after OAB is still unknown. A rat OAB model was established for this purpose. Anterior intraocular inflammation was observed in both the acute and late phases of OAB, and histological examination confirmed the presence of inflammatory cell infiltration and fibrin exudation in the anterior segment. Luminex xMAP technology and qPCR were used to evaluate the intraocular levels of cytokines. The levels of IL-1β, IL-6, and TNF-α were significantly elevated during the acute phase. The expression of IL-17A gradually increased from day 7 onwards and remained at a relatively high level. Immunofluorescence was performed to identify Th17 cells. CD4 and IL-17A double positive cells were detected in the anterior chamber from days 7 to 28. Flow cytometry showed that the frequency of Th17 cells increased in both lymph nodes and spleen, while the frequency of Treg cells remained unchanged, resulting in an elevated Th17/Treg ratio. The present study suggests that Th17 activation and Th17/Treg imbalance account for prolonged anterior intraocular inflammation after OAB.