Glutaredoxin regulates nuclear factor κ-B and intercellular adhesion molecule in Muller cells -: Model of diabetic retinopathy

Reversible S-glutathionylation of proteins is a focal point of redox signaling and cellular defense against oxidative stress. This post-translational modification alters protein function, and its reversal ( deglutathionylation) is catalyzed specifically and efficiently by glutaredoxin ( GRx, thioltransferase), a thioldisulfide oxidoreductase. We hypothesized that changes in glutaredoxin might be important in the development of diabetic retinopathy, a condition characterized by oxidative stress. Indeed, GRx protein and activity were increased in retinal homogenates from streptozotocin-diabetic rats. Also, incubation of rat retinal Muller cells ( rMC-1) in normal glucose ( 5 mM) or diabetic-like glucose ( 25 mM) medium led to selective up-regulation of GRx in contrast to thioredoxin, the other thioldisulfide oxidoreductase system. Under analogous conditions, NF-kappa B ( p50-p65) translocated to the nucleus, and expression of ICAM-1 ( intercellular adhesion molecule-1), a transcriptional product of NF-kappa B, increased. Proinflammatory ICAM-1 is increased in diabetic retinae, and it is implicated in pathogenesis of retinopathy. To evaluate the role of GRx in mediating these changes, intracellular GRx content and activity in rMC-1cells were increased independently under normal glucose via infection with an adenoviral GRx1 construct ( Ad-GRx). rMC-1 cells exhibited adenovirus concentration-dependent increases in GRx and corresponding increases in NF-kappa B nuclear translocation, NF-kappa B luciferase reporter activity, and ICAM-1 expression. Blocking the increase in GRx1 via small interfering RNA in rMC-1 cells in high glucose prevented the increased ICAM-1 expression. These data suggest that redox regulation by glutaredoxin in retinal glial cells is perturbed by hyperglycemia, leading to NF-kappa B activation and a pro-inflammatory response. Thus, GRx may represent a novel therapeutic target to inhibit diabetic retinopathy.