Cytosolic glutaredoxin 1 is upregulated in AMD and controls retinal pigment epithelial cells proliferation via β-catenin

Thioredoxin (Trx) family proteins are key players in redox signaling. Here, we have analyzed glutaredoxin (Grx) 1 and Grx2 in age-related macular degeneration (AMD) and in retinal pigment epithelial (ARPE-19) cells. We hypothesized that these redoxins regulate cellular functions and signaling circuits such as cell proliferation, Wnt signaling and VEGF release that have been correlated to the pathophysiology of AMD. ARPE-19 cells were transfected with specific siRNAs to silence the expression of Grx1 and Grx2 and were analyzed for proliferation/viability, migration capacity, β-catenin activation, and VEGF release. An active site-mutated C-X-X-S Grx1 was utilized to trap interacting proteins present in ARPE-19 cell extracts. In both, AMD retinas and in ARPE-19 cells incubated under hypoxia/reoxygenation conditions, Grx1 showed an increased nuclear localization. Grx1-silenced ARPE-19 cells showed a significantly reduced proliferation and migration rate. Our trapping approach showed that Grx1 interacts with β-catenin in a dithiol-disulfide exchange reaction. Knock-down of Grx1 led to a reduction in both total and active β-catenin levels. These findings add redox control to the regulatory mechanisms of β-catenin signaling in the retinal pigment epithelium and open the door to novel therapeutic approaches in AMD that is currently treated with VEGF-inhibitors.