GHRH receptor antagonist MIA-602 suppresses the GHRH-R/JAK2/STAT3 inflammatory cascade in acute ocular inflammation

Ocular inflammation, particularly acute anterior uveitis, is a significant cause of visual impairment and stems from immune system dysregulation. While the receptor for growth-hormone-releasing hormone (GHRH-R) is known to influence various inflammatory processes, its specific role in the pathological cascades of eye inflammation has been unclear. Lipopolysaccharide (LPS), a component of bacterial cell walls, is commonly used to induce experimental uveitis. This model allows researchers to investigate how inflammatory signaling pathways are activated. The study explores the hypothesis that GHRH-R is a key mediator in this process, potentially offering a new target for therapeutic intervention beyond existing treatments.

The study used multiple models to investigate the GHRH-R pathway. First, human ciliary epithelial cells were stimulated with lipopolysaccharide (LPS) to observe cellular responses, including NF-κB activation. Bioinformatics and coimmunoprecipitation assays were used to identify direct protein interactions with GHRH-R. A rat model of endotoxin-induced uveitis was established using LPS treatment to study in vivo effects on the ciliary body and iris. Finally, both explants of iris and ciliary body and the live rat model were treated with the GHRH-R antagonist MIA-602 or the JAK inhibitor Ruxolitinib to assess the therapeutic effect on inflammatory markers and cellular infiltration.

Stimulation with LPS led to the phosphorylation of the NF-κB subunit p65 in human ciliary epithelial cells, which in turn caused transcriptional up-regulation of GHRH-R. Bioinformatics and co-immunoprecipitation revealed a direct interaction between GHRH-R and JAK2. In the rat uveitis model, LPS treatment elevated JAK2 levels (but not JAK1, JAK3, or TYK2) in the ciliary body and iris. This JAK2 elevation augmented the phosphorylation of STAT3 and increased the production of proinflammatory factors, including IL-6, IL-17A, COX2, and iNOS. The study demonstrated that targeting this pathway had significant anti-inflammatory effects.

In explants of iris and ciliary body, the GHRH-R antagonist MIA-602 successfully suppressed phosphorylation of STAT3 and attenuated the expression of these downstream proinflammatory factors after LPS treatment. A similar suppression of STAT3 phosphorylation was observed in human ciliary epithelial cells. The JAK inhibitor Ruxolitinib also alleviated ocular inflammation in vivo, reducing inflammatory cells and protein leakage in the aqueous humor.