Function and therapeutic potential of glutaredoxin (Grx) system in the lens

Abstract

Purpose : To evaluate the function and therapeutic potential of glutaredoxin (Grx) system, both glutaredoxin 1 (Grx1) and glutaredoxin 2 (Grx2), using Grx1/Grx2 double knockout (DKO) mice and the Grx activators as research models.

Methods : Two-month old Grx1/Grx2 DKO and age-matched wild-type (WT) mice were exposed to 20.6 kJ/m² UV radiation for 15 mins to induce cataracts. Mice were euthanized at 4 days post-exposure. The degree of the cataract and lens morphology were evaluated under a dissecting microscope. To further define the crosstalk between the Grx system and nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant pathway, Nrf2 and its downstream target proteins were examined by using Western blot analysis. Addtionally, we have developed a series of Grx modulators, molecules L1-L4, which are a family of pyridol-containing N-heterocyclic amines. The therapeutic potential of these Grx activators was evaluated using ex-vivo lens organ culture system.

Results : We found that UV radiation caused more severe anterior subcapsular cataract in Grx1/Grx2 DKO than that of WT mice. The opacity of the lenses in DKO mice, appeared to extend deeper into the cortical and even nuclear regions. Lenses of Grx1/Grx2 DKO mice contained significant lower levels of glutathione (GSH) and higher levels of glutathionylated proteins (PSSG), a marker for protein thiol oxidation. Deletion of Grx1 and Grx2 also decreased the expression of antioxidant enzyme transcription factor regulator, Nrf2, and its downstream antioxidant genes, including catalase, superoxide dismutase (SOD), and thioredoxin (Trx). Our ex vivo study showed that L1-L4 dose-dependently protected the lens from H₂O₂-induced opacification.

Conclusions : Grx1 and Grx2 gene deletion impairs Nrf2-dependent antioxidant response, causing elevation of oxidative stress that may increase the lens susceptibility to UV-induced damage. Grx activators can improve the redox homeostasis in the lens and prevent H₂O₂-induced cataract formation.

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