Thioredoxin interacting protein is a novel mediator of retinal inflammation and neurotoxicity

Abstract

BACKGROUND AND PURPOSEUp-regulation of thioredoxin interacting protein (TXNIP), an endogenous inhibitor of thioredoxin (Trx), compromises cellular antioxidant and anti-apoptotic defences and stimulates pro-inflammatory cytokines expression, implying a role for TXNIP in apoptosis. Here we have examined the causal role of TXNIP expression in mediating retinal neurotoxicity and assessed the neuroprotective actions of verapamil, a calcium channel blocker and an inhibitor of TXNIP expression. EXPERIMENTAL APPROACHRetinal neurotoxicity was induced by intravitreal injection of NMDA in Sprague-Dawley rats, which received verapamil (10 mg·kg -1 , p.o.) or vehicle. Neurotoxicity was examined by terminal dUTP nick-end labelling assay and ganglion cell count. Expression of TXNIP, apoptosis signal-regulating kinase 1 (ASK-1), NF-kB, p38 MAPK, JNK, cleaved poly-ADP-ribose polymerase (PARP), caspase-3, nitrotyrosine and 4-hydroxy-nonenal were examined by Western and slot-blot analysis. Release of TNF-a and IL-1b was examined by ELISA. KEY RESULTSNMDA injection enhanced TXNIP expression, decreased Trx activity, causing increased oxidative stress, glial activation and release of TNF-a and IL-1b. Enhanced TXNIP expression disrupted Trx/ASK-1 inhibitory complex leading to release of ASK-1 and activation of the pro-apoptotic p38 MAPK/JNK pathway, as indicated by cleaved PARP and caspase-3 expression. Treatment with verapamil blocked these effects. CONCLUSION AND IMPLICATIONSElevated TXNIP expression contributed to retinal neurotoxicity by three different mechanisms, inducing release of inflammatory mediators such as TNF-a and IL-1b, altering antioxidant status and disrupting the Trx-ASK-1 inhibitory complex leading to activation of the p38 MAPK/JNK apoptotic pathway. Targeting TXNIP expression is a potential therapeutic target for retinal neurodegenerative disease. AbbreviationsASK-1, apoptosis signal-regulating kinase 1; GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; NFL, nerve fiber layer; NMLA, N-methyl-L-aspartate; ONL, inner plexiform layer into the outer nuclear layer; PARP, poly-ADP-ribose polymerase; RGC, retinal ganglion cell; ROD, relative optical density; Trx, thioredoxin; TUNEL, terminal dUTP nick-end labelling; TXNIP, thioredoxin interacting protein BJP British Journal of Pharmacology

Nod-like Receptor Protein 3 (NLRP3) Inflammasome Activation and Podocyte Injury via Thioredoxin-Interacting Protein (TXNIP) during Hyperhomocysteinemia

“…In other studies, inhibition of TXNIP expression by verapamil has also been reported (48), but this effect has been extended to other calcium channel blockers and inhibitors such as diltiazem and NiCl 2 , as well as with calcium chelator EGTA. This suggests that this inhibition of TXNIP function is perhaps not a direct effect of verapamil itself, but more likely due to a reduction in intracellular calcium concentrations (42).…”

Serum Levels of Thioredoxin Are Associated with Stroke Risk, Severity, and Lesion Volumes

“…It appears that TRX levels may be a useful marker of oxidative stress in a variety of disorders [17]. Previous studies also suggested serum TRX levels as indicator of inflammation [18] and immune dysregulation [19]. These findings indicated that TRX may be a useful marker of stroke.…”

Structural and functional changes in retinal vasculature induced by retinal ischemia-reperfusion in rats

“…In NMDA-induced neuronal injury or death, excessive Ca 2þ influx and subsequent activation of Ca 2þ -dependent responses, including formation of nitric oxide (NO) via neuronal NO synthase (NOS) (Morizane et al, 1997;Vorwerk et al, 1997), are thought to be important events. In addition, upregulation of inflammatory proteins and recruitment of leukocytes into the retina are involved (Nakazawa et al, 2007;Al-Gayyar et al, 2011). Furthermore, reductions in retinal blood flow may be an additional cause of progression of the ischemic retinal damage, because damage to the retinal microvasculature was observed in these experimental models of retinal neurodegeneration (Zheng et al, 2007;Chen et al, 2009).…”