Systemic treatment with Cucurbitacin I protects in light-induced retinal degeneration (LIRD) mice

Abstract

Purpose : Tauroursodeoxycholic acid (TUDCA) is neuroprotective in retinal degeneration models. Cucurbitacin I has a chemical structure similar to TUDCA and has been shown to be protective in models of CNS neurodegeneration. Therefore, we sought to test whether systemic treatment with Cucurbitacin I is protective in a light induced retinal degeneration (LIRD) model.

Methods : Adult male (n=15) and female (n=14) BALB/cAnNCrl mice received two injections of either vehicle (10% DMSO+PBS, n=13) or Cucurbitacin I treatment (1.3 mg/kg; 10 μl/gram of mouse weight, n=16). After the first injection, mice were dark-adapted overnight and injected again 30-60 min prior to LIRD. Mice were either exposed to 2500 lux, to induce LIRD, or dim light (50 lux) for 4 hours. One week after light exposure, retinal function was assessed by electroretinograms (ERG) and eyes were collected for histology. Outer Nuclei Layer (ONL) counts were assessed in retinal sections stained with hematoxylin and eosin. Retinal sections were stained for GFAP and IBA1 to assess retinal glial inflammatory response. Two-way ANOVA was conducted to analyze data (mean±SD).

Results : Exposure to toxic light diminished scotopic ERG at 1 cd s/m² a- and b-wave amplitudes, compared to dim light exposure (-118μV±43.2 vs -256μV±57.9 and 370μV±130 vs 558μV±158, respectively; p<0.04). ONL nuclei counts were diminished to 70% in comparison to dim light exposed mice (p<0.003). Systemic treatment with Cucurbitacin I prevented the losses in ERG a- and b-wave amplitudes (-228μV±33.2 vs -256μV±57.9 and 526μV±91 vs 558μV±158, respectively; p>0.28) and ONL nuclei count (p>0.5), with outcomes statistically indistinguishable from dim light exposed groups. Retinal sections from vehicle-treated mice undergoing LIRD showed increased labeling of both GFAP (p<0.03) and IBA1 (p<0.03) compared to dim groups or mice undergoing LIRD but treated with Cucurbitacin I.

Conclusions : Systemic treatment with Cucurbitacin I protects against retinal degeneration. Injections of Cucurbitacin I protected both retinal function and structure of adult BALB/cAnNCrl mice model of LIRD. The suppression of inflammatory responses likely occurred in microglia and Müller glial cells. As CNS neuroprotection by Cucurbitacin I treatment is mediated by inhibiting JAK2-STAT3 signaling and preventing microglial overactivation, we plan future studies to examine these potential mechanistic pathways in retina.

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