Involvement of NT3 and P75(NTR) in photoreceptor degeneration following selective Müller cell ablation

Plasma levels of neurotrophin 4/5, NGF and pro-BDNF influence transition to mental disorders in a sample of individuals at ultra-high risk for psychosis

BACKGROUND

Neurotrophins (NTs) and their precursors (pro-NTs) are polypeptides with important roles in neuronal development, differentiation, growth, survival and plasticity, as well as apoptosis and neuronal death. Imbalance in NT levels were observed in schizophrenia spectrum disorders, but evidence in ultra-high risk for psychosis (UHR) samples is scarce.

METHODS

A naturalistic sample of 87 non-help-seeking UHR subjects and 55 healthy controls was drawn from the general population. Blood samples were collected and NT-3, NT-4/5, BDNF, pro-BDNF, NGF, pro-NGF were analyzed through enzyme linked immunosorbent assay (ELISA). Information on cannabis and tobacco use was also collected. Logistic regression models and path analysis were used to control for confounders (tobacco, age, cannabis use).

RESULTS

NT-4/5 was significantly decreased, and pro-BDNF was significantly increased in UHR individuals compared to controls. Cannabis use and higher NGF levels were significantly related to transition to psychiatric disorders among UHR subjects. Increased pro-BDNF and decreased NT-4/5 influenced transition by the mediation of perceptual abnormalities.

CONCLUSIONS

Our study shows for the first time that NTs are altered in UHR compared to healthy control individuals, and that they can be a predictor of transition to psychiatric illnesses in this population. Future studies should employ larger naturalistic samples to confirm the findings.

Overexpression of NT3P75-2 gene modified bone marrow mesenchymal stem cells supernatant promotes neurological function recovery in ICH rats

Intracerebral hemorrhage (ICH) is an acute cerebrovascular disease with high mortality and long-term disability rates. Stem cell transplantation and neurotrophic factor therapy have shown great potential in ICH. It has been established that mutated NT3 (NT3P75 - 2) can enhance the positive biological functions of NT3 by decreasing its affinity to the P75-2 receptor. The present study aimed to explore whether NT3P75-2 could further improve neurological recovery after ICH. First, we constructed three stable BMSC cell lines (GFP, GFP-NT3 overexpressed and GFP-NT3P75 - 2 overexpressed) by lentivirus infection. Next, rats were injected with fresh supernatants of these three cell lines on days 1 (24 h) and 3 (72 h) post-ICH induction. Behavioral evaluations were conducted to assess the neurological recovery of ICH rats. We further evaluated changes in microglia activation, neuron survival and proliferation of neural stem cells. Compared with the GFP group and the GFP-NT3 group, animals in the GFP-NT3P75 - 2 group exhibited better motor function improvements and milder neuroinflammation response. Meanwhile, overexpression of NT3P75 - 2 significantly decreased neuronal apoptosis and increased number of SOX2 - positive cells. Taken together, our study demonstrated that early administration of NT3P75 - 2 enriched BMMSC supernatants significantly enhanced neuro-functional recovery after ICH by regulating neuroinflammation response, neuronal survival and increasing neural stem cell number, providing a new therapeutic strategy and direction for early treatment of ICH.

Inhibition of vascular endothelial growth factor alleviates neovascular retinopathy with regulated neurotrophic/proinflammatory cytokines through the modulation of DBI-TSPO signaling

Diazepam binding inhibitor (DBI)-translocator protein (18kDa) (TSPO) signaling in the retina was reported to possess coordinated macroglia-microglia interactions. We investigated DBI-TSPO signaling and its correlation with vascular endothelial growth factor (VEGF), neurotrophic or inflammatory cytokines in neovascular retinopathy, and under hypoxic conditions. The vitreous expression of DBI, VEGF, nerve growth factor (NGF), and interleukin-1beta (IL-1β) were examined in proliferative diabetic retinopathy (PDR) patients with or without anti-VEGF therapy and nondiabetic controls. Retinal DBI-TSPO signaling and the effect of the anti-VEGF agent were evaluated in a mouse model of oxygen-induced retinopathy (OIR). Interactions between Müller cell-derived VEGF and DBI, as well as cocultured microglial cells under hypoxic conditions, were studied, using Western blot, real-time RT-PCR, enzyme-linked immunosorbent assay (ELISA), flow cytometry, and immunofluorescent labeling. Results showed that vitreous levels of DBI, VEGF, NGF, and IL-1β were significantly higher in PDR patients compared with controls, which further changed after anti-VEGF therapy. A statistical association was found between vitreous DBI and VEGF, NGF, IL-1β, and age. The application of the anti-VEGF agent in the OIR model induced retinal expression of DBI and NGF, and attenuated inflammation and microglial cell activation. Inhibition of Müller cell-derived VEGF could increase its DBI expression under hypoxic conditions, while the DBI-TSPO signaling pathway is essential for anti-VEGF agents exerting anti-inflammatory and neuroprotective effects, as well as limiting inflammatory magnitude, promoting its neurotrophin production and anti-inflammatory (M2) polarization in microglial cells. These findings suggest the beneficial effect of anti-VEGF therapy on inflammation and neurotrophy of retinal glial cells through modulation of the DBI-TSPO signaling pathway.

Interleukin-17A attenuates photoreceptor cell apoptosis in streptozotocin-induced diabetic mouse model

Diabetic retinopathy (DR) represents an important microvascular complication of diabetes, which is the top etiology of vision impairment worldwide. Although interleukin (IL)-17A is increasingly implicated in DR development, the underlying cellular mechanisms remain poorly defined. This work aims to evaluate IL-17A levels in the retina of streptozotocin (STZ)-induced diabetic mice and elucidate their potential roles. We found IL-17A was upregulated in diabetic retina after intraperitoneal injection of STZ and high-glucose (HG)-cultured primary Müller cells. IL-17A knockout (IL-17A^−/−) downregulated glial fibrillary acidic protein (GFAP) and inhibited the conversion of proneurotrophin-3 (proNT-3) to mature NT-3 in retinal specimens from diabetic mice as well as in Müller cells cultured under HG conditions. Induced apoptosis and upregulated Bax and cleaved caspase-3 were observed in retinal specimens from IL-17A^−/− diabetic mice and photoreceptor (661 W) cells after co-culture with IL-17A^−/− Müller cells. Moreover, RNA interference-induced gene silencing of tyrosine kinase C receptor (TrkC) in 661 W cells reversed the anti-apoptotic effect of IL-17A under HG conditions. Taken together, our findings suggest that IL-17A/NT-3/TrkC axis regulation suppresses apoptosis in photoreceptor cells, providing a new treatment strategy for DR.

The balance between cell survival and death in the placenta: Do neurotrophins have a role?

Neurotrophins (NT) are a closely related family of growth factors, which regulate the nervous system's development, maintenance, and function. Although NTs have been well studied in neuronal cells, they are also expressed in the placenta. Despite their suggested role in regulating fetoplacental development, their precise functional significance in the placenta remains elusive. NT activate two different classes of receptors. These include the Trk, tropomyosin-related kinase family of high-affinity tropomyosin-related kinase receptors, which induces cell survival, and the p75NTR, p75 neurotrophin receptor, a member of the tumor necrosis factor(TNF) receptor superfamily, which induces apoptosis in neuronal cells. Mature NT molecule results from proteolysis of a biologically active precursor form called pro-neurotrophins (pro-NT) by the intracellular proprotein convertase or furin. Pro-NTs have a regulatory role in determining cell survival and apoptosis. Here, we review the literature on the expression and functions of NTs and their receptors in the placenta and discuss their possible role in placental tissue development and apoptosis. The possible implications of imbalance in pro-NT and mature-NT levels for fetoplacental development are also discussed.Abbreviations AGE/ALEs: Advanced glycation/lipoxidation end products; Bax: Bcl 2 Associated X; Bcl-2: B-cell lymphoma 2; BDNF: Brain-derived neurotrophic factor; FAS/FASL: Fas cell surface death receptor/ ligand; IUGR: Intrauterine growth restriction; JNK: c-Jun amino-terminal kinase; MAP: mitogen-activated protein k; mRNA: Messenger ribonucleic acid; NGF: Nerve growth factor; NT: Neurotrophins; NRAGE: Neurotrophin receptor-interacting MAGE homolog; NRIF: Neurotrophin receptor interacting factor; PE: Preeclampsia; PI3k: Phosphoinositide 3- kinase; PLC: Phospholipase C; p75NTR: p75 neurotrophin receptor; Pro-NT: Pro-neurotrophins; PTB: Preterm birth; p53: Tumor protein p53; TNF: Tumor necrosis factor; TRAF: TNFR-associated factors; Trk: Tropomyosin-related kinase; siRNA: small interfering ribonucleic acid.

TGFβ-Neurotrophin Interactions in Heart, Retina, and Brain

Ischemic insults to the heart and brain, i.e., myocardial and cerebral infarction, respectively, are amongst the leading causes of death worldwide. While there are therapeutic options to allow reperfusion of ischemic myocardial and brain tissue by reopening obstructed vessels, mitigating primary tissue damage, post-infarction inflammation and tissue remodeling can lead to secondary tissue damage. Similarly, ischemia in retinal tissue is the driving force in the progression of neovascular eye diseases such as diabetic retinopathy (DR) and age-related macular degeneration (AMD), which eventually lead to functional blindness, if left untreated. Intriguingly, the easily observable retinal blood vessels can be used as a window to the heart and brain to allow judgement of microvascular damages in diseases such as diabetes or hypertension. The complex neuronal and endocrine interactions between heart, retina and brain have also been appreciated in myocardial infarction, ischemic stroke, and retinal diseases. To describe the intimate relationship between the individual tissues, we use the terms heart-brain and brain-retina axis in this review and focus on the role of transforming growth factor β (TGFβ) and neurotrophins in regulation of these axes under physiologic and pathologic conditions. Moreover, we particularly discuss their roles in inflammation and repair following ischemic/neovascular insults. As there is evidence that TGFβ signaling has the potential to regulate expression of neurotrophins, it is tempting to speculate, and is discussed here, that cross-talk between TGFβ and neurotrophin signaling protects cells from harmful and/or damaging events in the heart, retina, and brain.

Effect of selectively knocking down key metabolic genes in Müller glia on photoreceptor health

The importance of Müller glia for retinal homeostasis suggests that they may have vulnerabilities that lead to retinal disease. Here, we studied the effect of selectively knocking down key metabolic genes in Müller glia on photoreceptor health. Immunostaining indicated that murine Müller glia expressed insulin receptor (IR), hexokinase 2 (HK2) and phosphoglycerate dehydrogenase (PHGDH) but very little pyruvate dehydrogenase E1 alpha 1 (PDH-E1α) and lactate dehydrogenase A (LDH-A). We crossed Müller glial cell-CreER (MC-CreER) mice with transgenic mice carrying a floxed IR, HK2, PDH-E1α, LDH-A, or PHGDH gene to study the effect of selectively knocking down key metabolic genes in Müller glia cells on retinal health. Selectively knocking down IR, HK2, or PHGDH led to photoreceptor degeneration and reduced electroretinographic responses. Supplementing exogenous l-serine prevented photoreceptor degeneration and improved retinal function in MC-PHGDH knockdown mice. We unexpectedly found that the levels of retinal serine and glycine were not reduced but, on the contrary, highly increased in MC-PHGDH knockdown mice. Moreover, dietary serine supplementation, while rescuing the retinal phenotypes caused by genetic deletion of PHGDH in Müller glial cells, restored retinal serine and glycine homeostasis probably through regulation of serine transport. No retinal abnormalities were observed in MC-CreER mice crossed with PDH-E1α- or LDH-A-floxed mice despite Cre expression. Our findings suggest that Müller glia do not complete glycolysis but use glucose to produce serine to support photoreceptors. Supplementation with exogenous serine is effective in preventing photoreceptor degeneration caused by PHGDH deficiency in Müller glia.

Selective knockdown of hexokinase 2 in rods leads to age-related photoreceptor degeneration and retinal metabolic remodeling

Photoreceptors, the primary site of phototransduction in the retina, require energy and metabolites to constantly renew their outer segments. They preferentially consume most glucose through aerobic glycolysis despite possessing abundant mitochondria and enzymes for oxidative phosphorylation (OXPHOS). Exactly how photoreceptors balance aerobic glycolysis and mitochondrial OXPHOS to regulate their survival is still unclear. We crossed rhodopsin-Cre mice with hexokinase 2 (HK2)-floxed mice to study the effect of knocking down HK2, the first rate-limiting enzyme in glycolysis, on retinal health and metabolic remodeling. Immunohistochemistry and Western blots were performed to study changes in photoreceptor-specific proteins and key enzymes in glycolysis and the tricarboxylic acid (TCA) cycle. Changes in retinal structure and function were studied by optical coherence tomography and electroretinography. Mass spectrometry was performed to profile changes in ¹³C-glucose-derived metabolites in glycolysis and the TCA cycle. We found that knocking down HK2 in rods led to age-related photoreceptor degeneration, evidenced by reduced expression of photoreceptor-specific proteins, age-related reductions of the outer nuclear layer, photoreceptor inner and outer segments and impaired electroretinographic responses. Loss of HK2 in rods led to upregulation of HK1, phosphorylation of pyruvate kinase muscle isozyme 2, mitochondrial stress proteins and enzymes in the TCA cycle. Mass spectrometry found that the deletion of HK2 in rods resulted in accumulation of ¹³C-glucose along with decreased pyruvate and increased metabolites in the TCA cycle. Our data suggest that HK2-mediated aerobic glycolysis is indispensable for the maintenance of photoreceptor structure and function and that long-term inhibition of glycolysis leads to photoreceptor degeneration.

Preclinical and clinical studies of photobiomodulation therapy for macular oedema

AIMS/HYPOTHESIS

Diabetic macular oedema (DME) is the leading cause of visual impairment in people with diabetes. Intravitreal injections of vascular endothelial growth factor inhibitors or corticosteroids prevent loss of vision by reducing DME, but the injections must be given frequently and usually for years. Here we report laboratory and clinical studies on the safety and efficacy of 670 nm photobiomodulation (PBM) for treatment of centre-involving DME.

METHODS

The therapeutic effect of PBM delivered via a light-emitting diode (LED) device was tested in transgenic mice in which induced Müller cell disruption led to photoreceptor degeneration and retinal vascular leakage. We also developed a purpose-built 670 nm retinal laser for PBM to treat DME in humans. The effect of laser-delivered PBM on improving mitochondrial function and protecting against oxidative stress was studied in cultured rat Müller cells and its safety was studied in pigmented and non-pigmented rat eyes. We then used the retinal laser to perform PBM in an open-label, dose-escalation Phase IIa clinical trial involving 21 patients with centre-involving DME. Patients received 12 sessions of PBM over 5 weeks for 90 s per treatment at a setting of 25, 100 or 200 mW/cm² for the three sequential cohorts of 6-8 patients each. Patients were recruited from the Sydney Eye Hospital, over the age of 18 and had centre-involving DME with central macular thickness (CMT) of >300 μm with visual acuity of 75-35 Log minimum angle of resolution (logMAR) letters (Snellen visual acuity equivalent of 20/30-20/200). The objective of this trial was to assess the safety and efficacy of laser-delivered PBM at 2 and 6 months. The primary efficacy outcome was change in CMT at 2 and 6 months.

RESULTS

LED-delivered PBM enhanced photoreceptor mitochondrial membrane potential, protected Müller cells and photoreceptors from damage and reduced retinal vascular leakage resulting from induced Müller cell disruption in transgenic mice. PBM delivered via the retinal laser enhanced mitochondrial function and protected against oxidative stress in cultured Müller cells. Laser-delivered PBM did not damage the retina in pigmented rat eyes at 100 mW/cm². The completed clinical trial found a significant reduction in CMT at 2 months by 59 ± 46 μm (p = 0.03 at 200 mW/cm²) and significant reduction at all three settings at 6 months (25 mW/cm²: 53 ± 24 μm, p = 0.04; 100 mW/cm²: 129 ± 51 μm, p < 0.01; 200 mW/cm²: 114 ± 60 μm, p < 0.01). Laser-delivered PBM was well tolerated in humans at settings up to 200 mW/cm² with no significant side effects.

CONCLUSIONS/INTERPRETATION

PBM results in anatomical improvement of DME over 6 months and may represent a safe and non-invasive treatment. Further testing is warranted in randomised clinical trials.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02181400 Graphical abstract.

Targeting the Notch and TGF-β signaling pathways to prevent retinal fibrosis in vitro and in vivo

Rationale: The Notch and transforming growth factor-β (TGFβ) signaling pathways are two intracellular mechanisms that control fibrosis in general but whether they play a major role in retinal fibrosis is less clear. Here we study how these two signaling pathways regulate Müller cell-dominated retinal fibrosis in vitro and in vivo.

Methods: Human MIO-M1 Müller cells were treated with Notch ligands and TGFβ1, either alone or in combination. Western blots were performed to study changes in γ-secretase proteases, Notch downstream effectors, endogenous TGFβ1, phosphorylated Smad3 (p-Smad3) and extracellular matrix (ECM) proteins. We also studied the effects of RO4929097, a selective γ-secretase inhibitor, on expression of ECM proteins after ligand stimulation. Müller cell viability was studied by AlamarBlue and cytotoxicity by lactate cytotoxicity assays. Finally, we studied changes in Notch and TGFβ signaling and tested the effect of intravitreal injections of the Notch pathway inhibitor RO4929097 on retinal fibrosis resulted from Sodium iodate (NaIO₃)-induced retinal injury in mice. We also studied the safety of intravitreal injections of RO4929097 in normal mice.

Results: Treatment of Müller cells with Notch ligands upregulated γ-secretase proteases and Notch downstream effectors, with increased expression of endogenous TGFβ1, TGFβ receptors and p-Smad3. TGFβ1 upregulated the expression of proteins associated with both signaling pathways in a similar manner. Notch ligands and TGFβ1 had additive effects on overexpression of ECM proteins in Müller cells which were inhibited by RO4929097. Notch and TGFβ ligands stimulated Müller cell proliferation which was inhibited by RO4929097 without damaging the cells. NaIO₃-induced retinal injury activated both Notch and TGFβ signaling pathways in vivo. Intravitreal injection of RO4929097 prevented Müller cell gliosis and inhibited overexpression of ECM proteins in this murine model. We found no safety concerns for up to 17 days after an intravitreal injection of RO4929097.

Conclusions: Inhibiting Notch signaling might be an effective way to prevent retinal fibrosis. This study is of clinical significance in developing a treatment for preventing fibrosis in proliferative vitreoretinopathy, proliferative diabetic retinopathy and wet age-related macular degeneration.

Plasma BDNF and TrkB mRNA in PBMCs Are Correlated With Anti-depressive Effects of 12-Weeks Supervised Exercise During Protracted Methamphetamine Abstinence

Purpose: The aim of this study was to evaluate the potential neurotrophic factors and expression of neurotrophin receptors in peripheral blood mononuclear cells linked with the antidepressant action of exercise intervention during protracted methamphetamine (METH) abstinence.

Materials and Methods: A total of 72 male METH addicts, including 47 individuals with depression and 25 individuals without depression, were recruited in this study. Individuals with depression were divided into the depression control group and the depression exercised group. Consequently, 12 weeks of supervised exercise intervention was applied. Depression and anxiety were analyzed; plasma brain-derived neurotrophic factor (BDNF), neuronal growth factor (NGF), neurotrophin-3 (NT-3), NT-4, and proBDNF levels were tested using enzyme-linked immunosorbent assay; the mRNA expressions of TrkA, TrkB-FL, TrkB-T1, TrkCB, and P75NTR in peripheral blood mononuclear cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR).

Results: NT-4 plasma levels were correlated with depression (r = −0.330, p = 0.005), which remained significant after Bonferroni correction. In addition, the BDNF and NT-3 levels in the plasma were significantly correlated with depression (r = −0.268, p = 0.023; r = −0.259, p = 0.028), but did not reach significance after Bonferroni correction. The BDNF, NT-3, and NT-4 plasma levels were significantly different between the depressive control group and the depressive exercise group using pre-exercise values as the covariate. The fold changes in TrkB-FL and TrkB-T1 mRNA in peripheral blood mononuclear cells between the post-exercise and pre-exercise demonstrated a remarkable decrease (fold change = −11.056 and −39.055).

Conclusions: Exercise intervention can alleviate depression and anxiety during protracted METH abstinence. Decrease in BDNF and the expression of TrkB in peripheral blood mononuclear cells occur following the exercise intervention.

Müller cells derived neurotrophin-3 inhibits hypoxia-induced photoreceptor apoptosis via the TrkC/ERK pathway

Neurotrophin-3 (NT-3), a neurotrophic factor that mainly binds to the tyrosine kinase C (trkC) receptor, has been shown to play a crucial role in proliferation, differentiation, and survival. However, the role of NT-3 in the hypoxia-induced retinopathy has not been investigated extensively. Here, we created a model of hypoxia (1% O₂) in vitro and found that hypoxia promoted the apoptosis of mouse cone photoreceptor-derived 661W cells, increased the expression of TrkC and cleaved caspase-3. In contrast, the hypoxia-mediated 661W cell apoptosis was markedly alleviated by co-culturing with primary mouse Müller cells. Further mechanism studies revealed that hypoxia increased the synthesis and secretion of NT-3 by Müller cells, and exogenous NT-3 stimulation increased the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 by binding to TrkC in 661W cells. Besides, both siRNA knockdown of TrkC expression and incubation with an ERK-specific inhibitor PD98059 triggered apoptosis in hypoxic 661W cells. Altogether, these data suggest that NT-3 originating from Müller cells protects photoreceptors from hypoxia-induced apoptosis through a TrkC/ERK-dependent pathway. Our findings may facilitate future studies on the therapeutic implications of NT-3 in the treatment of hypoxia-relevant retinal diseases.

Microglia in Retinal Degeneration

The retina is a complex tissue with multiple cell layers that are highly ordered. Its sophisticated structure makes it especially sensitive to external or internal perturbations that exceed the homeostatic range. This necessitates the continuous surveillance of the retina for the detection of noxious stimuli. This task is mainly performed by microglia cells, the resident tissue macrophages which confer neuroprotection against transient pathophysiological insults. However, under sustained pathological stimuli, microglial inflammatory responses become dysregulated, often worsening disease pathology. In this review, we provide an overview of recent studies that depict microglial responses in diverse retinal pathologies that have degeneration and chronic immune reactions as key pathophysiological components. We also discuss innovative immunomodulatory therapy strategies that dampen the detrimental immunological responses to improve disease outcome.

Anti-apoptotic effect of interleukin-17 in a mouse model of oxygen-induced retinopathy

Retinopathy of prematurity (ROP) is an important cause of visual loss in children born prematurely. Although the involvement of inflammation in the development of ROP is gaining increasing attention, the role of IL-17A in ROP progress remains unclear. The aim of this study was to assess the levels of IL-17A production in the mice model of oxygen-induced retinopathy (OIR) and elucidate its potential roles. Wild-type (WT) and IL-17A knockout (IL-17A^-/-) mice were exposed to 75% O₂ from postnatal day 7 (P7) to P12. Age-matched controls were maintained in room air. Primary Müller cells isolated from WT or IL-17A^-/- mice retina were co-cultured with 661W cells and exposed to hypoxic conditions. Western blotting and immunofluorescent staining were used to assess the expression of target protein. Apoptosis in OIR retinal sections and 661W cells was detected by TUNEL staining. Results turned out that IL-17A expression was increased and reached a peak at P22 in OIR retina and at 8 h in hypoxic-cultured Müller cells. IL-17A knockout decreased the expression of glial fibrillary acidic protein (GFAP) and mature neurotrophin-3 (NT-3) in retina of OIR mice as well as hypoxic-cultured Müller cells. The NT-3 release induced by IL-17 was prevented by an ERK-specific inhibitor. In addition, more apoptosis cells and higher levels of Bax and cleaved caspase-3 was detected in the retina tissues of IL-17A^-/- OIR and the 661W cells co-cultured with IL-17A^-/- Müller cells. Taken together, our findings suggest that Müller cell was the potential source of IL-17A under the hypoxic conditions. Modulation of the IL-17A/ERK/NT-3 pathway exerts anti-apoptotic effect on photoreceptor cell and may be a novel therapeutic strategy for ROP.

A Combination Therapy Targeting Endoglin and VEGF-A Prevents Subretinal Fibro-Neovascularization Caused by Induced Müller Cell Disruption

Purpose

Subretinal fibroneovascularization is one of the most common causes of vision loss in neovascular AMD (nAMD). Anti-VEGF therapy effectively inhibits vascular leak and neovascularization but has little effect on fibrosis. This study aimed to identify a combination therapy to concurrently inhibit subretinal neovascularization and prevent fibrosis.

Methods

We generated transgenic mice in which induced disruption of Müller cells leads to subretinal neovascularization, which is reliably accompanied by subretinal fibrosis. We conducted Western blots and immunohistochemistry to study changes in transforming growth factor-β (TGFβ) signaling including endoglin, a coreceptor essential for TGFβ signaling, and then tested the effects of monthly intravitreal injection of anti-VEGF-A and anti-endoglin, either alone or in combination, on the development of subretinal fibroneovascularization in our transgenic mice.

Results

Müller cell disruption increased expression of TGFβ1, TGFβ type 1 receptor, and phosphorylated-Smad3. Endoglin was strongly expressed in subretinal fibroneovascular tissue. Fluorescein angiography and measurements of retinal vascular permeability indicated that intravitreal anti-VEGF-A in combination with anti-endoglin treatment more efficiently inhibited vascular leak compared with either monotherapy. Immunostaining of retinal wholemounts with antibodies against glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 indicated that the combination therapy also effectively prevented subretinal fibrosis and inhibited microglial activation. Luminex cytokine assays indicated that intravitreal anti-VEGF-A and anti-endoglin treatment, either alone or in combination, reduced the production of IL33 and macrophage inflammatory protein-3α.

Conclusions

Our findings offer a potentially novel combination approach to concurrently managing subretinal neovascularization and fibrosis in nAMD.

Resident Microglia Activate before Peripheral Monocyte Infiltration and p75NTR Blockade Reduces Microglial Activation and Early Brain Injury after Subarachnoid Hemorrhage

Early brain injury (EBI) after aneurysmal subarachnoid hemorrhage (SAH) contributes to high morbidity and mortality. Although it is well recognized that acute neuroinflammation reaction is one of the most important triggers of EBI, pharmacotherapy proved to be clinically effective against the initiating of neuroinflammation after SAH is lacking. The resident microglia and infiltrated peripheral monocyte are two main types of immune cells in central nervous system (CNS) and control the inflammation process in brain after SAH. But the time course and relative contributions of these two immune cell activations after SAH are unknown. The p75 neurotrophin receptor (p75NTR), member of TNF receptor superfamily, expresses on infiltrated peripheral monocytes and suppresses their proinflammatory action after brain insults. But the p75NTR expression on resident microglia in vivo is rarely explored and their function keeps elusive. Therefore, we designed this study to investigate the time course of resident microglia activation and peripheral monocyte infiltration, as well as the microglial expression of p75NTR by using CX3C-chemokine receptor 1 (Cx3cr1) and chemokine receptor 2 (Ccr2) double transgenic mice (Cx3cr1GFP/+Ccr2RFP/+) after SAH. The results showed activated microglia was observed in cortex as early as 24 h and further increased at 48 and 72 h post SAH, while the infiltrated monocyte was not found until 72h. In addition, activated microglia expressed p75NTR acutely and p75NTR specific antagonist TAT-Pep5 significantly reduced microglia activation, neuroinflammation and EBI from 24 to 72 h. Together, these data suggest that the early neuroinflammation reaction might be initiated and intensified mainly by resident microglia rather than infiltrated monocyte at least in the first 48 h after SAH and p75NTR blockading by TAT-Pep5P might alleviate EBI through mediating microglial activation.

Deletion of p75NTR prevents vaso-obliteration and retinal neovascularization via activation of Trk- A receptor in ischemic retinopathy model

Ischemic retinopathy is characterized by ischemia followed by retinal neovascularization (RNV) resulting in visual impairment. Given the role of neuron-secreted growth factors in regulating angiogenesis, we examined how genetic deletion of the neurotrophin receptor; p75NTR can overcome retinal ischemia using oxygen-induced retinopathy (OIR) mouse model. Wildtype (WT) or p75NTR-/- mice pups were subjected to hyperoxia (70% O2, p7-p12) then returned to normal air (relative hypoxia, p12-p17). Vascular alterations were assessed at p12 and p17 time-points. Deletion of p75NTR prevented hyperoxia-associated central vascular cell death (p12) and hypoxia-associated RNV and enhanced central vascular repair (p17). Decreased expression of apoptotic markers; preserved Akt survival signal decreased proNGF were also observed at p12. During hypoxia, deletion of p75NTR maintained VEGF and VEGFR2 activation and restored NGF/proNGF and BDNF/proBDNF levels. Deletion of p75NTR coincided with significant increases in expression and activation of NGF survival receptor, TrkA at basal and hyperoxic condition. Pharmacological inhibition of TrkA using compound K-252a (0.5 μg 1 μl-1/eye) resulted in 2-fold increase in pathological RNV and 1.34-fold increase in central vascular cell death in p75NTR-/- pups. In conclusion, deletion of p75NTR protected against retinal ischemia and prevented RNV, in part, through restoring neurotrophic support and activating TrkA receptor.

A Novel and Multivalent Role of Pax6 in Cerebellar Development

Pax6 is a prominent gene in brain development. The deletion of Pax6 results in devastated development of eye, olfactory bulb, and cortex. However, it has been reported that the Pax6-null Sey cerebellum only has minor defects involving granule cells despite Pax6 being expressed throughout cerebellar development. The present work has uncovered a requirement of Pax6 in the development of all rhombic lip (RL) lineages. A significant downregulation of Tbr1 and Tbr2 expression is found in the Sey cerebellum, these are cell-specific markers of cerebellar nuclear (CN) neurons and unipolar brush cells (UBCs), respectively. The examination of Tbr1 and Lmx1a immunolabeling and Nissl staining confirmed the loss of CN neurons from the Sey cerebellum. CN neuron progenitors are produced in the mutant but there is an enhanced death of these neurons as shown by increased presence of caspase-3-positive cells. These data indicate that Pax6 regulates the survival of CN neuron progenitors. Furthermore, the analysis of experimental mouse chimeras suggests a cell-extrinsic role of Pax6 in CN neuron survival. For UBCs, using Tbr2 immunolabeling, these cells are significantly reduced in the Sey cerebellum. The loss of UBCs in the mutant is due partly to cell death in the RL and also to the reduced production of progenitors from the RL. These results demonstrate a critical role for Pax6 in regulating the generation and survival of UBCs. This and previous work from our laboratory demonstrate a seminal role of Pax6 in the development of all cerebellar glutamatergic neurons.

SIGNIFICANCE STATEMENT

Pax6 is a key molecule in development. Pax6 is best known as the master control gene in eye development with mutations causing aniridia in humans. Pax6 also plays important developmental roles in the cortex and olfactory bulb. During cerebellar development, Pax6 is robustly expressed in the germinal zone of all glutamatergic neurons [cerebellar nuclear (CN) neurons, granule cells, and unipolar brush cells (UBCs)]. Past work has not found abnormalities in the CN and UBC populations. Our study reveals that the Pax6-null mutation dramatically affects these cells and identifies Pax6 as a key regulator of cell survival in CN neurons and of cell production in UBCs. The present study shows how Pax6 is key to the development of glutamatergic cells in the cerebellum.

Expression and signaling of NGF in the healthy and injured retina

This review summarizes the present knowledge concerning the retinal localization of the nerve growth factor (NGF), its precursor proNGF, and the receptors TrkA and p75NTR in the developing and mature rodent retina. We further discuss the changes in the expression of NGF and the receptors in experimental models of retinal disorders and diseases like inherited retinitis pigmentosa, retinal detachment, glaucoma, and diabetic retinopathy. Since proNGF is now recognized as a bioactive signaling molecule which induces cell death through p75NTR activation, the role of proNGF in the induction of retinal cell loss under neurodegenerative conditions is also highlighted. In addition, we present the evidences for a potential therapeutic intervention with NGF for the treatment of retinal neurodegenerative diseases. Different strategies have been developed and experimentally tested in mice and rats in order to reduce cell loss and Müller cell gliosis, e.g., increasing the availability of endogenous NGF, administration of exogenous NGF, activation of TrkA, and inhibition of p75NTR. Here, we discuss the several lines of evidence supporting a protective effect of NGF on retinal cell loss, with specific emphasis on photoreceptor and retinal ganglion cell degeneration. A better understanding of the mechanisms underlying the effects of NGF and proNGF in the modulation of neurodegeneration and gliosis in the retina will help to develop efficient therapeutic strategies for various retinal diseases.

Effects of Ranibizumab and Aflibercept on Human Müller Cells and Photoreceptors under Stress Conditions

Anti-vascular endothelial growth factor (VEGF) therapy has revolutionized the treatment of retinal vascular diseases. However, constitutive VEGF also acts as a trophic factor on retinal nonvascular cells. We have studied the effects of aflibercept and ranibizumab on human Müller cells and photoreceptors exposed to starvation media containing various concentrations of glucose, with or without CoCl2-induced hypoxia. Cell survival was assessed by calcein-AM cell viability assays. Expression of heat shock proteins (Hsp) and redox proteins thioredoxin 1 and 2 (TRX1, TRX2) was studied by Western blots. The production of neurotrophic factors in Müller cells and interphotoreceptor retinoid-binding protein (IRBP) in photoreceptors was measured by enzymelinked immunosorbent assays. Aflibercept and ranibizumab did not affect the viability of both types of cells. Neither aflibercept nor ranibizumab affected the production of neurotrophic factors or expression of Hsp60 and Hsp90 in Müller cells. However, aflibercept but not ranibizumab affected the expression of Hsp60, Hsp9, TRX1 and TRX2 in photoreceptors. Aflibercept and ranibizumab both inhibited the production of IRBP in photoreceptors, aflibercept more so than ranibizumab. Our data indicates that the potential influence of aflibercept and ranibizumab on photoreceptors should be specifically monitored in clinical studies.

Identification of functional networks associated with cell death in the retina of OXYS rats during the development of retinopathy

Age-related macular degeneration (AMD) is a major cause of blindness in developed countries, and the molecular pathogenesis of early events in AMD is poorly understood. Senescence-accelerated OXYS rats develop AMD-like retinopathy. The aim of this study was to explore the differences in retinal gene expression between OXYS and Wistar (control) rats at age 20 d and to identify the pathways of retinal cell death involved in the OXYS retinopathy initiation and progression. Retinal mRNA profiles of 20-day-old OXYS and Wistar rats were generated at the sequencing read depth 40 mln, in triplicate, using Illumina GAIIx. A terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) assay was performed to measure the apoptosis level. GeneMANIA was used to construct interaction networks for differentially expressed (DE) apoptosis-related genes at ages 20 d and 3 and 18 months. Functional analysis was suggestive of a developmental process, signal transduction, and cell differentiation as the most enriched biological processes among 245 DE genes at age 20 d An increased level of apoptosis was observed in OXYS rats at age 20 d but not at advanced stages. We identified functional clusters in the constructed interaction networks and possible hub genes (Rasa1, cFLAR, Birc3, Cdk1, Hspa1b, Erbb3, and Ntf3). We also demonstrated the significance of the extrinsic apoptotic pathway at preclinical, early, and advanced stages of retinopathy development. Besides the cell death signaling pathways, immune system-related processes and lipid-metabolic processes showed overrepresentation in the clusters of all networks. These characteristics of the expression profile of the genes functionally associated with apoptosis may contribute to the pathogenesis of AMD-like retinopathy in senescence-accelerated OXYS rats.

Biomarkers for Diabetic Retinopathy - Could Endothelin 2 Be Part of the Answer?

Purpose

The endothelins are a family of three highly conserved and homologous vasoactive peptides that are expressed across all organ systems. Endothelin (Edn) dysregulation has been implicated in a number of pathophysiologies, including diabetes and diabetes-related complications. Here we examined Edn2 and endothelin receptor B (Endrb) expression in retinae of diabetic mouse models and measured serum Edn2 to assess its biomarker potential.

Materials and Methods

Edn2 and Ednrb mRNA and Edn2 protein expression were assessed in young (8wk) and mature (24wk) C57Bl/6 (wild type; wt), Kimba (model of retinal neovascularisation, RNV), Akita (Type 1 diabetes; T1D) and Akimba mice (T1D plus RNV) by qRT-PCR and immunohistochemistry. Edn2 protein concentration in serum was measured using ELISA.

Results

Fold-changes in Edn2 and Ednrb mRNA were seen only in young Kimba (Edn2: 5.3; Ednrb: 6.0) and young Akimba (Edn2: 7.9, Ednrb: 8.8) and in mature Kimba (Edn2:9.2, Ednrb:11.2) and mature Akimba (Edn2:14.0, Ednrb:17.5) mice. Co-localisation of Edn2 with Müller-cell-specific glutamine synthetase demonstrated Müller cells and photoreceptors as the major cell types for Edn2 expression in all animal models. Edn2 serum concentrations in young Kimba, Akita and Akimba mice were not elevated compared to wt. However, in mature mice, Edn2 serum concentration was increased in Akimba (6.9pg/mg total serum protein) compared to wt, Kimba and Akita mice (3.9, 4.6, and 3.8pg/mg total serum protein, respectively; p<0.05).

Conclusions

These results demonstrated that long-term hyperglycaemia in conjunction with VEGF-driven RNV increased Edn2 serum concentration suggesting Edn2 might be a candidate biomarker for vascular changes in diabetic retinopathy.

Differential expression of microRNAs in retinal vasculopathy caused by selective Müller cell disruption

Vascular changes and photoreceptor degeneration are features of age-related macular degeneration, diabetic retinopathy and macular telangiectasis. We have profiled the differential expression of microRNAs and analysed their target genes in transgenic mice in which induced Müller cell disruption results in photoreceptor degeneration, vascular leak and deep retinal neovascularisation. We identified 9 miRNAs which were differentially expressed during the development of retinal neovascularization and chose miR-200b and its target genes for further study. Using qRT-PCR and western blot analysis, we found that downregulation of miR-200b was negatively correlated with its target genes, including zinc finger E-box binding homeobox (ZEB) 1 and 2 and vascular endothelial growth factor receptor 1. Double immunofluorescence labelling revealed that the newly formed vessels in the outer retina were positive for ZEB2. Furthermore, intravitreal injections of a miR-200b-mimic and anti-miR-200b confirmed the negative correlation of miR-200b and its target gene expression. We also found that the miR-200b-mimic inhibited vascular leak in the established mild vascular lesions, whereas anti-miR-200b promoted it. Taken together, these data suggest that miR-200b may play a role in the development of intraretinal neovascularisation.

A novel antagonist of p75NTR reduces peripheral expansion and CNS trafficking of pro-inflammatory monocytes and spares function after traumatic brain injury

Background

Traumatic brain injury (TBI) results in long-term neurological deficits, which may be mediated in part by pro-inflammatory responses in both the injured brain and the circulation. Inflammation may be involved in the subsequent development of neurodegenerative diseases and post-injury seizures. The p75 neurotrophin receptor (p75NTR) has multiple biological functions, affecting cell survival, apoptotic cell death, axonal growth, and degeneration in pathological conditions. We recently found that EVT901, a novel piperazine derivative that inhibits p75NTR oligomerization, is neuroprotective, reduces microglial activation, and improves outcomes in two models of TBI in rats. Since TBI elicits both CNS and peripheral inflammation, we used a mouse model of TBI to examine whether EVT901 would affect peripheral immune responses and trafficking to the injured brain.

Methods

Cortical contusion injury (CCI)-TBI of the sensory/motor cortex was induced in C57Bl/6 wild-type mice and CCR2^+/RFP heterozygote transgenic mice, followed by treatment with EVT901, a selective antagonist of p75NTR, or vehicle by i.p. injection at 4 h after injury and then daily for 7 days. Brain and blood were collected at 1 and 6 weeks after injury. Flow cytometry and histological analysis were used to determine peripheral immune responses and trafficking of peripheral immune cells into the lesion site at 1 and 6 weeks after TBI. A battery of behavioral tests administered over 6 weeks was used to evaluate neurological outcome, and stereological estimation of brain tissue volume at 6 weeks was used to assess tissue damage. Finally, multivariate principal components analysis (PCA) was used to evaluate the relationships between inflammatory events, EVT901 treatment, and neurological outcomes.

Results

EVT901 is neuroprotective in mouse CCI-TBI and dramatically reduced the early trafficking of CCR2+ and pro-inflammatory monocytes into the lesion site. EVT901 reduced the number of CD45^highCD11b+ and CD45^highF4/80+ cells in the injured brain at 6 weeks. TBI produced a significant increase in peripheral pro-inflammatory monocytes (Ly6C^int-high pro-inflammatory monocytes), and this peripheral effect was also blocked by EVT901 treatment. Further, we found that blocking p75NTR with EVT901 reduces the expansion of pro-inflammatory monocytes, and their response to LPS in vitro, supporting the idea that there is a peripheral EVT901 effect that blunts inflammation. Further, 1 week of EVT901 blocks the expansion of pro-inflammatory monocytes in the circulation after TBI, reduces the number of multiple subsets of pro-inflammatory monocytes that enter the injury site at 1 and 6 weeks post-injury, and is neuroprotective, as it was in the rat.

Conclusions

Together, these findings suggest that p75NTR signaling participates in the production of the peripheral pro-inflammatory response to CNS injury and implicates p75NTR as a part of the pro-inflammatory cascade. Thus, the neuroprotective effects of p75NTR antagonists might be due to a combination of central and peripheral effects, and p75NTR may play a role in the production of peripheral inflammation in addition to its many other biological roles. Thus, p75NTR may be a therapeutic target in human TBI.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0544-4) contains supplementary material, which is available to authorized users.

Protective Effects of Human iPS-Derived Retinal Pigmented Epithelial Cells in Comparison with Human Mesenchymal Stromal Cells and Human Neural Stem Cells on the Degenerating Retina in rd1 mice

Retinitis pigmentosa (RP) is a group of visual impairments characterized by progressive rod photoreceptor cell loss due to a genetic background. Pigment epithelium-derived factor (PEDF) predominantly secreted by the retinal pigmented epithelium (RPE) has been reported to protect photoreceptors in retinal degeneration models, including rd1. In addition, clinical trials are currently underway outside Japan using human mesenchymal stromal cells and human neural stem cells to protect photoreceptors in RP and dry age-related macular degeneration, respectively. Thus, this study aimed to investigate the rescue effects of induced pluripotent stem (iPS)-RPE cells in comparison with those types of cells used in clinical trials on photoreceptor degeneration in rd1 mice. Cells were injected into the subretinal space of immune-suppressed 2-week-old rd1 mice. The results demonstrated that human iPS-RPE cells significantly attenuated photoreceptor degeneration on postoperative days (PODs) 14 and 21 and survived longer up to at least 12 weeks after operation than the other two types of graft cells with less immune responses and apoptosis. The mean PEDF concentration in the intraocular fluid in RPE-transplanted eyes was more than 1 µg/ml at PODs 14 and 21, and this may have contributed to the protective effect of RPE transplantation. Our findings suggest that iPS-RPE cells serve as a competent source to delay photoreceptor degeneration through stable survival in degenerating ocular environment and by releasing neuroprotective factors such as PEDF.

Imbalance of the Nerve Growth Factor and Its Precursor: Implication in Diabetic Retinopathy

Diabetic retinopathy is the leading cause of blindness in working age in US and worldwide. Neurotrophins including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) are known to be essential for growth, differentiation and survival of neurons in the developing and mature retina. Nevertheless, a growing body of evidence supports an emerging role of neurotrophins in retinal diseases and in particular, diabetic retinopathy. Neurotrophins are initially synthesized in a pro-form and undergo proteolytic cleavage to produce the mature form that activates two distinctive receptors, the tyrosine kinase tropomycin receptor (Trk) and, to lesser extent, the common low affinity p75 neurotrophin receptor (p75^NTR). Despite tight glycemic and metabolic control, many diabetic patients continue to experience progressive retinal damage. Understanding the molecular events involved in diabetic retinopathy is extremely important to identify novel therapeutic strategies to halt the disease progression. Diabetes induces imbalance in neurotrophins by increasing its proform, which is associated with upregulation of the p75^NTR receptor in the retina. A growing body of evidence supports a link between the imbalance of pro-neurotrophins and early retinal inflammation, neuro-and microvascular degeneration. Therefore, examining changes in the levels of neurotrophins and its receptors might provide a therapeutically beneficial target to combat disease progression in diabetic patients. This commentary aims to highlight the impact of diabetes-impaired balance of neurotrophins and in particular, the NGF and its receptors; TrkA and p75^NTR in the pathology of DR.

Probing Metabolism in the Intact Retina Using Stable Isotope Tracers

Vertebrate retinas have several characteristics that make them particularly interesting from a metabolic perspective. The retinas have a highly laminated structure, high energy demands, and they share several metabolic features with tumors, such as a strong Warburg effect and abundant pyruvate kinase M2 isoform expression. The energy demands of retinas are both qualitatively and quantitatively different in light and darkness and metabolic dysfunction could cause retinal degeneration. Stable isotope-based metabolic analysis with mass spectrometry is a powerful tool to trace the dynamic metabolic reactions and reveal novel metabolic pathways within cells and between cells in retina. Here, we describe methods to quantify retinal metabolism in intact retinas and discuss applications of these methods to the understanding of neuron-glia interaction, light and dark adaptation, and retinal degenerative diseases.

Dysregulation of inter-photoreceptor retinoid-binding protein (IRBP) after induced Müller cell disruption

Reduced expression of a ~150 kDa protein was unexpectedly observed while investigating Norrin protein in a transgenic murine model in which Müller cells can be selectively and inducibly disrupted. Isolation of this unknown protein via ion exchange and hydrophobic interaction chromatography followed by Tandem mass spectrometry identified it as Inter-photoreceptor retinoid-binding protein (IRBP). Significantly reduced IRBP mRNA expression was observed at the early and late stages after Müller cell disruption. IRBP protein expression was also consistently reduced to 5.7% of the control level as early as 1 week after Müller cell disruption. This down-regulation of IRBP was accompanied by focal hyperfluorescent dots and cytotoxic N-retinylidene-N-retinylethanolamine (A2E) accumulation. In vitro treatment of cone photoreceptor cell lines with conditioned medium collected from stressed Müller cells suggested that Müller cells regulated photoreceptors expression of IRBP via secreted factor(s). In vivo studies suggested that one of these secreted factors was tumour necrosis factor alpha (TNFα). These findings suggest that dysregulation of IRBP expression caused by Müller cell dysfunction may be an important early event in photoreceptor degeneration in some retinal diseases. This study reports down-regulation of inter-photoreceptor retinoid-binding protein (IRBP) in photoreceptors and retinoid cycle derangement after Müller cell disruption in a transgenic mouse model. The findings indicate that Müller cells communicate with photoreceptors in response to stress by secreting soluble protein factor(s). We propose that down-regulation of IRBP may represent an early and novel pathogenic mechanism in degenerative retinal diseases.

Profiling of microRNAs involved in retinal degeneration caused by selective Müller cell ablation

Dysfunction of Müller cells has been implicated in the pathogenesis of several retinal diseases. In order to understand the potential contribution of Müller cells to retinal disease better, we have developed a transgenic model in which foci of Müller cell ablation can be selectively induced. MicroRNAs (miRNAs), small non-coding RNAs that are involved in post-transcriptional modulation, have critical functions in various biological processes. The aim of this study was to profile differential expression of miRNAs and to examine changes in their target genes 2 weeks after Müller cell ablation. We identified 20 miRNAs using the miScript HC PCR array. Data analysis using two target gene prediction databases (TargetScan and mirTarBase) revealed 78 overlapping target genes. DAVID and KEGG pathway analysis suggested that the target genes were generally involved in cell apoptosis, p53, neurotrophin, calcium, chemokine and Jak-STAT signalling pathways. Changes in seven target genes including Cyclin D2, Caspase 9, insulin-like growth factor 1, IL-1 receptor-associated kinase (IRAK), calmodulin (CALM) and Janus kinase 2 (Jak2), were validated with qRT-PCR and western blots. The cellular localisation of cleaved-caspase 9, Cyclin D2, Jak2 and CALM was examined by immunofluorescence studies. We found that the transcription of some miRNAs was positively, rather than negatively, correlated with their target genes. After confirming that overexpressed miR-133a-3p was localised to the outer nuclear layer in the damaged retina, we validated the correlation between miR-133a-3p and one of its predicted target genes, cyclin D2, with a luciferase assay in 661 photoreceptor cells. Results revealed by miRNA profiling, target gene analysis and validation were generally consistent with our previous findings that selective Müller cell ablation causes photoreceptor degeneration and neuroinflammation. Our data on alterations of miRNAs and their target gene expression after Müller cell ablation provide further insights into the potential role of Müller cell dysfunction in retinal disease.

Systemic administration of erythropoietin inhibits retinopathy in RCS rats

Objective

Royal College of Surgeons (RCS) rats develop vasculopathy as photoreceptors degenerate. The aim of this study was to examine the effect of erythropoietin (EPO) on retinopathy in RCS rats.

Methods

Fluorescein angiography was used to monitor retinal vascular changes over time. Changes in retinal glia and vasculature were studied by immunostaining. To study the effects of EPO on retinal pathology, EPO (5000 IU/kg) was injected intraperitoneally in 14 week old normal and RCS rats twice a week for 4 weeks. Changes in the retinal vasculature, glia and microglia, photoreceptor apoptosis, differential expression of p75 neurotrophin receptor (p75^NTR), pro-neurotrophin 3 (pro-NT3), tumour necrosis factor-α (TNFα), pigment epithelium derived factor (PEDF) and vascular endothelial growth factor-A (VEGF-A), the production of CD34⁺ cells and mobilization of CD34⁺/VEGF-R2⁺ cells as well as recruitment of CD34⁺ cells into the retina were examined after EPO treatment.

Results

RCS rats developed progressive capillary dropout and subretinal neovascularization which were accompanied by retinal gliosis. Systemic administration of EPO stabilized the retinal vasculature and inhibited the development of focal vascular lesions. Further studies showed that EPO modulated retinal gliosis, attenuated photoreceptor apoptosis and p75^NTR and pro-NT3 upregulation, promoted the infiltration of ramified microglia and stimulated VEGF-A expression but had little effect on TNFα and PEDF expression. EPO stimulated the production of red and white blood cells and CD34⁺ cells along with effective mobilization of CD34⁺/VEGF-R2⁺ cells. Immunofluorescence study demonstrated that EPO enhanced the recruitment of CD34⁺ cells into the retina.

Conclusions

Our results suggest that EPO has therapeutic potentials in treatment of neuronal and vascular pathology in retinal disease. The protective effects of EPO on photoreceptors and the retinal vasculature may involve multiple mechanisms including regulation of retinal glia and microglia, inhibition of p75^NTR-pro-NT3 signaling together with stimulation of production and mobilization of bone marrow derived cells.

Differential effects of P2Y1 deletion on glial activation and survival of photoreceptors and amacrine cells in the ischemic mouse retina

Gliosis of retinal Müller glial cells may have both beneficial and detrimental effects on neurons. To investigate the role of purinergic signaling in ischemia-induced reactive gliosis, transient retinal ischemia was evoked by elevation of the intraocular pressure in wild-type (Wt) mice and in mice deficient in the glia-specific nucleotide receptor P2Y₁ (P2Y₁ receptor-deficient (P2Y1R-KO)). While control retinae of P2Y1R-KO mice displayed reduced cell numbers in the ganglion cell and inner nuclear layers, ischemia induced apoptotic death of cells in all retinal layers in both, Wt and P2Y1R-KO mice, but the damage especially on photoreceptors was more pronounced in retinae of P2Y1R-KO mice. In contrast, gene expression profiling and histological data suggest an increased survival of amacrine cells in the postischemic retina of P2Y1R-KO mice. Interestingly, measuring the ischemia-induced downregulation of inwardly rectifying potassium channel (Kir)-mediated K⁺ currents as an indicator, reactive Müller cell gliosis was found to be weaker in P2Y1R-KO (current amplitude decreased by 18%) than in Wt mice (decrease by 68%). The inner retina harbors those neurons generating action potentials, which strongly rely on an intact ion homeostasis. This may explain why especially these cells appear to benefit from the preserved Kir4.1 expression in Müller cells, which should allow them to keep up their function in the context of spatial buffering of potassium. Especially under ischemic conditions, maintenance of this Müller cell function may dampen cytotoxic neuronal hyperexcitation and subsequent neuronal cell loss. In sum, we found that purinergic signaling modulates the gliotic activation pattern of Müller glia and lack of P2Y₁ has janus-faced effects. In the end, the differential effects of a disrupted P2Y₁ signaling onto neuronal survival in the ischemic retina call the putative therapeutical use of P2Y₁-antagonists into question.

Effect of glucocorticoids on neuronal and vascular pathology in a transgenic model of selective Müller cell ablation

Retinal diseases such as macular telangiectasis type 2 (MacTel), age-related macular degeneration (AMD) and diabetic retinopathy (DR) affect both neurons and blood vessels. Treatments addressing both at the same time might have advantages over more specific approaches, such as vascular endothelial growth factor (VEGF) inhibitors, which are used to treat vascular leak but are suspected to have a neurotoxic effect. Here, we studied the effects of an intravitreal injection of triamcinolone acetonide (TA) in a transgenic model in which patchy Müller cell ablation leads to photoreceptor degeneration, vascular leak, and intraretinal neovascularization. TA was injected 4 days before Müller cell ablation. Changes in photoreceptors, microglia and Müller cells, retinal vasculature, differential expression of p75 neurotrophin receptor (p75(NTR) ), tumor necrosis factor-α (TNFα), the precursor and mature forms of neurotrophin 3 (pro-NT3 and mature NT3) and activation of the p53 and p38 stress-activated protein kinase (p38/SAPK) signaling pathways were examined. We found that TA prevented photoreceptor degeneration and inhibited activation of microglial and Müller cells. TA attenuated Müller cell loss and inhibited overexpression of p75(NTR) , TNFα, pro-NT, and the activation of p53 and p38/SAPK signaling pathways. TA not only prevented the development of retinal vascular lesions but also inhibited fluorescein leakage from established vascular lesions. TA inhibited overexpression of VEGF in transgenic mice but without affecting its basal level expression in the normal retina. Our data suggest that glucocorticoid treatment may be beneficial for treatment of retinal diseases such as MacTel, AMD, and DR that affect both neurons and the vasculature.