Imbalance of the nerve growth factor and its precursor as a potential biomarker for diabetic retinopathy.

Our previous studies have demonstrated that diabetes-induced oxidative stress alters homeostasis of retinal nerve growth factor (NGF) resulting in accumulation of its precursor, proNGF, at the expense of NGF which plays a critical role in preserving neuronal and retinal function. This imbalance coincided with retinal damage in experimental diabetes. Here we test the hypothesis that alteration of proNGF and NGF levels observed in retina and vitreous will be mirrored in serum of diabetic patients. Blood and vitreous samples were collected from patients (diabetic and nondiabetic) undergoing vitrectomy at Georgia Regents University under approved IRB. Levels of proNGF, NGF, and p75(NTR) shedding were detected using Western blot analysis. MMP-7 activity was also assayed. Diabetes-induced proNGF expression and impaired NGF expression were observed in vitreous and serum. Vitreous and sera from diabetic patients (n = 11) showed significant 40.8-fold and 3.6-fold increases, respectively, compared to nondiabetics (n = 9). In contrast, vitreous and sera from diabetic patients showed significant 44% and 64% reductions in NGF levels, respectively, compared to nondiabetics. ProNGF to NGF ratios showed significant correlation between vitreous and serum. Further characterization of diabetes-induced imbalance in the proNGF to NGF ratio will facilitate its utility as an early biomarker for diabetic complications.

Deletion of thioredoxin-interacting protein preserves retinal neuronal function by preventing inflammation and vascular injury.

BACKGROUND AND PURPOSE: Retinal neurodegeneration is an early and critical event in several diseases associated with blindness. Clinically, therapies that target neurodegeneration fail. We aimed to elucidate the multiple roles by which thioredoxin-interacting protein (TXNIP) contributes to initial and sustained retinal neurodegeneration. EXPERIMENTAL APPROACH: Neurotoxicity was induced by intravitreal injection of NMDA into wild-type (WT) and TXNIP-knockout (TKO) mice. The expression of apoptotic and inflammatory markers was assessed by immunohistochemistry, elisa and Western blot. Microvascular degeneration was assessed by periodic acid-Schiff and haematoxylin staining and retinal function by electroretinogram. KEY RESULTS: NMDA induced early (1 day) and significant retinal PARP activation, a threefold increase in TUNEL-positive nuclei and 40% neuronal loss in ganglion cell layer (GCL); and vascular permeability in WT but not TKO mice. NMDA induced glial activation, expression of TNF-α and IL-1ß that co-localized with Müller cells in WT but not TKO mice. In parallel, NMDA triggered the expression of NOD-like receptor protein (NLRP3), activation of caspase-1, and release of IL-1ß and TNF-α in primary WT but not TKO Müller cultures. After 14 days, NMDA induced 1.9-fold microvascular degeneration, 60% neuronal loss in GCL and increased TUNEL-labelled cells in the GCL and inner nuclear layer in WT but not TKO mice. Electroretinogram analysis showed more significant reductions in b-wave amplitudes in WT than in TKO mice. CONCLUSION AND IMPLICATIONS: Targeting TXNIP expression prevented early retinal ganglion cell death, glial activation, retinal inflammation and secondary neuro/microvascular degeneration and preserved retinal function. TXNIP is a promising new therapeutic target for retinal neurodegenerative diseases.