Inhibition of Constitutive Retinal Prostaglandin D₂ by a Topical NSAID Amplifies Neurodegeneration in Response to Ocular Hypertension

Abstract

Purpose : Prostaglandin D₂ (PGD₂) is the most abundant PG in the healthy brain and is also a clinical target for inhibition in allergic diseases. We investigate the role of PGD₂ in the healthy retina/optic nerve and its regulation during ocular hypertension (OHT).

Methods : Single-cell RNAseq, bulk RNAseq, in situ hybridization, LC-MS/MS-based lipidomics, qPCR, and immunohistochemistry (IHC) were used to study the cell-specific expression and functions of the PGD₂ pathway (PGD₂, biosynthetic enzymes HPGDS and LPGDS, and receptors DP1 and DP2) in healthy retinas (mice and non-human primate). To inhibit PGD₂ formation, a topical NSAID (0.07% Bromfenac) was administered to the eyes of healthy and OHT mice, with OCT used to assess the neurodegeneration.

Results : PGD₂ is produced constitutively at very high levels in the retina and optic nerve of healthy mice and the optic nerve of non-human primates, with levels 200-fold higher than any other PG, eicosanoid, or lipoxygenase-derived product. Single-cell RNAseq data identified high expression of LPGDS in RPE, Muller glia, and astrocytes, while HPGDS is expressed in microglia. DP1 and DP2 expression was established in the ganglion cell layer of mice retina by IHC and in situ hybridization, suggesting a significant role for PGD₂ receptors in the retina. Remarkably, severe OHT (at 2 weeks) and mild OHT (at 8 weeks) led to decreased expression of the PGD₂ pathway in mice retina assessed by qPCR. After 8 weeks, mild OHT showed a 50% decrease in PGD₂ levels. Topical bromfenac significantly reduced the constitutive PGD₂ level by 60-75% in the retina and optic nerve without affecting IOP. Importantly, in OHT-induced RGC degeneration, 2 weeks of topical bromfenac treatment significantly amplified ganglion cell loss by 42% (p<0.01, n=10) compared to untreated OHT mice, as measured by OCT. Bulk RNA sequencing revealed amplified activation of astrocyte and microglia reactivity markers in the NSAID-treated OHT group.

Conclusions : This study introduces the novel concept that the PGD₂ pathway is a highly active constitutive pathway in the retina and optic nerve, implying an essential homeostatic function. Importantly, the deletion of retinal PDG₂ by a primary topical ophthalmic NSAID amplified OHT-induced neurodegeneration, which may have important clinical implications.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.