Sustained (+)-pentazocine treatment in an in vivo model of retinal degeneration conferred significant neuroprotection, reduced evidence of oxidative stress, and preserved retinal architecture, suggesting that sigmaR1 ligands are promising therapeutic agents for intervention in neurodegenerative diseases of the retina.

Aims/hypothesis Diabetic retinopathy is characterised by early blood–retina barrier (BRB) breakdown and neurodegeneration. Diabetes causes imbalance of nerve growth factor (NGF), leading to accumulation of the NGF precursor (proNGF), as well as the NGF receptor, p75 neurotrophin receptor (p75NTR), suggesting a possible pathological role of the proNGF–p75NTR axis in the diabetic retina. To date, the role of this axis in diabetes-induced retinal inflammation and BRB breakdown has not been explored. We hypothesised that modulating p75NTR would prevent diabetes- and proNGF-induced retinal inflammation and BRB breakdown. Methods Diabetes was induced by streptozotocin in wild-type and p75NTR knockout (p75KO) mice. After 5 weeks, the expression of inflammatory mediators, ganglion cell loss and BRB breakdown were determined. Cleavage-resistant proNGF was overexpressed in rodent retinas with and without p75NTR short hairpin RNA or with pharmacological inhibitors. In vitro, the effects of proNGF were investigated in retinal Müller glial cell line (rMC-1) and primary Müller cells. Results Deletion of p75NTR blunted the diabetes-induced decrease in retinal NGF expression and increases in proNGF, nuclear factor κB (NFκB), p-NFκB and TNF-α. Deletion of p75NTR also abrogated diabetes-induced glial fibrillary acidic protein expression, ganglion cell loss and vascular permeability. Inhibited expression or cleavage of p75NTR blunted proNGF-induced retinal inflammation and vascular permeability. In vitro, proNGF induced p75NTR-dependent production of inflammatory mediators in primary wild-type Müller and rMC-1 cultures, but not in p75KO Müller cells. Conclusions/interpretation The proNGF–p75NTR axis contributes to retinal inflammation and vascular dysfunction in the rodent diabetic retina. These findings underscore the importance of p75NTR as a novel regulator of inflammation and potential therapeutic target in diabetic retinopathy.

Purpose-The cystine-glutamate transporter, system x c -, mediates the Na + -independent exchange of cystine into cells coupled to the efflux of intracellular glutamate. Within cells, cystine is reduced to cysteine, a component of glutathione, thus system x c -plays a critical role in glutathione homeostasis. Studies in brain had initially suggested that system x c -was present primarily in astrocytes and not neurons, but more recent work suggests that certain brain neurons have an active system x c -. In the retina, system x c -has been demonstrated in retinal Müller and RPE cells. Recent immunohistochemical work from our lab suggested that the two protein components of system x c -, xCT and 4F2hc, are present in ganglion cells of the intact retina. The purpose of this investigation was to determine whether system x c -was present in primary ganglion cells isolated from neonatal mouse retinas and, if so, to study its regulation by oxidative stress in a retinal ganglion cell line, RGC-5.Methods-The presence of xCT and 4F2hc in RGC-5 cells was established by RT-PCR, immunoblotting and immunohistochemistry and in primary mouse retinal ganglion cells by immunoblotting and immunohistochemistry; the function of the transporter in RGC-5 cells was established by measuring radiolabeled glutamate uptake in the absence of Na + . To assess regulation of system x c -by oxidative stress in ganglion cells, RGC-5 cells were incubated in the presence or absence of nitric oxide (NO) donors (3-nitroso-N-acetylpenicillamine (SNAP), Snitrosoglutathione (SNOG), or 3-morpholinosydnonimine hydrochloride (SIN-1) and reactive oxygen species (ROS) donors menadione sodium bisulfite, hydrogen peroxide and xanthine sodium salt/xanthine oxidase and system x c -was analyzed using functional assays, RT-PCR and immunoblotting.Results-RGC-5 cells and primary ganglion cells isolated from mouse retina express xCT and 4F2hc as demonstrated by RT-PCR, immunoblotting and immunohistochemistry. RGC-5 cells take up glutamate in the absence of Na + and this uptake was blocked by known inhibitors of system x c -, glutamate, cysteine, and cystine as well as quisqualic acid. Treatment of RGC-5 cells with NO donors and donors of ROS led to an increase in the functional activity of system x c -. Kinetic analysis of SNAP-treated RGC-5 cells compared to control cells showed that the increase was associated with an increase in the maximal velocity of the transporter with no significant change in the substrate affinity. Molecular analyses showed that the upregulation is associated with an increase in the expression of xCT with no detectable change in the expression of 4F2hc. Conclusions-RGC-5 cells and ganglion cells isolated from neonatal mice express the cystine/ glutamate transporter x c -(the light chain xCT and the heavy chain 4F2hc) as is evident from functional and molecular studies. Oxidative stress upregulates this transport system in RGC-5 cells and the process is associated with an increase in xCT mRNA and protein but no change in 4F2hc mRNA or...

Purpose To determine the effects of endogenous elevation of homocysteine on the retina using the cystathionine β-synthase (cbs) mutant mouse. Methods Retinal homocysteine in cbs mutant mice was measured by high-performance liquid chromatography (HPLC). Retinal cryosections from cbs−/− mice and cbs+/− mice were examined for histologic changes by light and electron microscopy. Morphometric analysis was performed on retinas of cbs+/− mice maintained on a high-methionine diet (cbs+/− HM). Changes in retinal gene expression were screened by microarray. Results HPLC analysis revealed an approximate twofold elevation in retinal homocysteine in cbs+/− mice and an approximate sevenfold elevation in cbs−/− mice. Distinct alterations in the ganglion, inner plexiform, inner nuclear, and epithelial layers were observed in retinas of cbs−/− and 1-year-old cbs+/− mice. Retinas of cbs+/− HM mice demonstrated an approximate 20% decrease in cells of the ganglion cell layer (GCL), which occurred as early as 5-weeks after onset of the HM diet. Microarray analysis revealed alterations in expression of several genes, including increased expression of Aven, Egr1, and Bat3 in retinas of cbs+/− HM mice. Conclusions This study provides the first analysis of morphologic and molecular effects of endogenous elevations of retinal homocysteine in an in vivo model. Increased retinal homocysteine alters inner and outer retinal layers in cbs homozygous mice and older cbs heterozygous mice, and it primarily affects the cells of the GCL in younger heterozygous mice. Elevated retinal homocysteine alters expression of genes involved in endoplasmic reticular stress, N-methyl-D-aspartate (NMDA) receptor activation, cell cycle, and apoptosis.

SummaryHepcidin is a hormone central to the regulation of iron homeostasis in the body. It is believed to be produced exclusively by the liver. Ferroportin, an iron exporter, is the receptor for hepcidin. This transporter/receptor is expressed in Müller cells, photoreceptor cells, and retinal pigment epithelium (RPE) within the retina. Since the retina is protected by the retinal-blood barriers, we asked whether ferroportin in the retina is regulated by hepcidin in the circulation or whether the retina produces hepcidin for regulation of its own iron homeostasis. Here we show that hepcidin is expressed robustly in Müller cells, photoreceptor cells, and RPE, closely resembling the expression pattern of ferroportin. We also show that bacterial lipopolysaccharide (LPS) is a regulator of hepcidin expression in Müller cells and RPE, both in vitro and in vivo, and that the regulation occurs at the transcriptional level. The action of LPS on hepcidin expression is mediated by the Toll-like receptor-4. The upregulation of hepcidin by LPS occurs independent of Hfe (Human leukocyte antigen-like protein involved in Fe homeostasis). The increase in hepcidin levels in retinal cells in response to LPS treatment is associated with a decrease in ferroportin levels. The LPS-induced upregulation of hepcidin and consequent downregulation of ferroportin is associated with increased oxidative stress and apoptosis within the retina in vivo. We conclude that retinal iron homeostasis may be regulated in an autonomous manner by hepcidin generated within the retina and that chronic bacterial infection/inflammation of the retina may disrupt iron homeostasis and retinal function.

BACKGROUND AND PURPOSERetinal 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 APPROACHNeurotoxicity 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 RESULTSNMDA 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-1β 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-1β 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 IMPLICATIONSTargeting 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.

Accumulation of the nerve growth factor precursor (proNGF) and its receptor p75NTR have been associated with several neurodegenerative diseases in both brain and retina. However, whether proNGF contributes to microvascular degeneration remain unexplored. This study seeks to investigate the mechanism by which proNGF/p75NTR induce endothelial cell (EC) death and development of acellular capillaries, a surrogate marker of retinal ischemia. Stable overexpression of the cleavage-resistant proNGF and molecular silencing of p75NTR were utilized in human retinal EC and rat retinas in vivo. Stable overexpression of proNGF decreased NGF levels and induced retinal vascular cell death evident by 1.9-fold increase in acellular capillaries and activation of JNK and cleaved-PARP that were mitigated by p75NTRshRNA. In vitro, overexpression of proNGF did not alter TNF-α level, reduced NGF, however induced EC apoptosis evident by activation of JNK and p38 MAPK, cleaved-PARP. Silencing p75NTR using siRNA restored expression of NGF and TrkA activation and prevented EC apoptosis. Treatment of EC with human-mutant proNGF induced apoptosis that coincided with marked protein interaction and nuclear translocation of p75NTR and the neurotrophin receptor interacting factor. These effects were abolished by a selective p75NTR antagonist. Therefore, targeting p75NTR represents a potential therapeutic strategy for diseases associated with aberrant expression of proNGF.

MCs express sigmaR1 and demonstrate robust sigmaR1 binding activity, which is inhibited by sigmaR1 ligands and is stimulated during oxidative stress. The potential of Müller cells to bind sigmaR1 ligands may prove beneficial in retinal degenerative diseases such as diabetic retinopathy.