The retinal toxicity of the pro-inflammatory and amyloidogenic S100A9 proteins

Abstract

Purpose : Age-related macular degeneration (AMD) is a complex multifactorial disease in which inflammation is considered a key factor, but the exact molecular mechanisms are unclear. The pro-inflammatory S100A9 proteins were amply found in drusen. These calcium-binding proteins have diverse signaling roles and can contribute to chronic inflammation, but their pathological and possibly physiological role in the retina is unknown. S100A9 were shown to be intrinsically amyloidogenic, possessing the capacity to self-assemble into amyloid structures in vitro and in vivo. Here, we hypothesized that the retinal effects exerted by S100A9 are related to their amyloid conformation.

Methods : ARPE-19 cells were treated with monomeric or fibrillary S100A9 (0.1 nM- 0.1 μM) for 12 h. Cell viability was determined by the XTT assay.
Wild type rats were treated with intravitreal injection (10μl) of monomeric or fibrillary S100A9 (0.1 μM) to right eye and vehicle in the left eye. Retinal function was assessed at baseline and through 28 days post injection. At each time point, electroretinography (ERG) measures were compared between eyes.

Results : Cell viability assays and ERG in rats delineated distinct retinal effects of S100A9. The number of living ARPE-19 cells was increased by exposure to 0.1- 1nM fibrillar S100A9 but was decreased by treatment with 0.01- 0.1 μM of the S100A9 fibrils. Monomeric S100A9 had no significant impact on the cellular counts.
Similarly, while retinal function remained normal in the eyes treated with monomeric S100A9, amplified ERG responses constituting increased amplitudes mostly of the b-wave were noted in the experimental eyes compared with their fellow (control) eyes through 14 days following injection of fibrillar S100A9 in rats. Thereafter, the retinal function became impaired, showing decreased ERG amplitudes in the treated eyes compared with controls.

Conclusions : Fibrillar S100A9 exerted pronounced effects on the retina, which included cell proliferation in vitro and increased amplitudes of the ERG responses in rats. In contrast, exposure to higher doses of S100A9 fibrils induced cell death in vitro and prolonged exposure to these assemblies resulted in decreased retinal function in vivo. This complex behavior supports the importance of the amyloid conformation of S100A9 to its retinal implications, and suggests a clue both to the pathological and possibly physiological role of S100A9 in the human retina.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.