Sigma-1 receptor agonist ameliorates trabecular meshwork fibrosis by modulating extracellular matrix remodeling and increasing nitric oxide production

Abstract

Purpose : Maintenance of normal tissue homeostasis in the trabecular meshwork (TM) is crucial for undisturbed aqueous humor drainage and consequently unaltered intraocular pressure (IOP). Fibrotic-like changes such as accumulation of extracellular matrix (ECM) components, result in altered stiffness and impaired outflow leading to increased IOP, which is the main risk factor of glaucoma. Thus, anti-fibrotic drugs could be novel therapeutics for glaucoma. Nitric oxide (NO) has been recognized as an important regulator of TM outflow and maintain IOP. Recently, we reported that fluvoxamine (FLU), a potent sigma-1 receptor (S1R) agonist, decreases the levels of key elements of fibrosis in the kidney and in lung. Therefore, here we investigated the antifibrotic effectiveness of FLU in mouse and human TM cells.

Methods : Fibrosis was induced with platelet-derived growth factor (PDGF, 20 ng/mL, 24h) in human and mouse primary TM cells (wild type: WT; and S1R knockout: KO). All cells were treated with 10 µM FLU for 24h. Then localization of S1R, cell -toxicity, -proliferation and -migration, and levels of F-actin, αSMA, fibronectin, and cathepsin K were determined with immunofluorescence or brightfield microscopy. NO production was measured with a fluorescent reader.

Results : S1R is localized in the endoplasmic reticulum and TM cells' cytoplasm. FLU treatment is non-toxic and reduces the PDGF-induced cell proliferation (p=0.04), migration (p<0.001), and fibrotic protein levels (fibronectin p=0.02; αSMA p=0.014). Furthermore, in human TM cells, FLU increases NO production (p=0.01) and the level of the protease, cathepsin K (p=0.002), thus moderating the cytoskeletal rearrangements. The protective role of S1R in fibrosis is confirmed by the more prominent increase of αSMA (p=0.04) and F-actin (p=0.003) bundle and clumps in the KO cells.

Conclusions : S1R is protective in fibrosis and the agonist FLU treatment reduces fibrosis-related processes in TM cells by increasing NO production and facilitating ECM degradation. We propose in vivo investigations as a next step, since we believe that FLU could be a novel and efficient treatment in glaucoma.
Grants: OTKA- K135398, LP2021-3/2021, TKP2021-EGA-24

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.