Gastrodin protects retinal ganglion cells through inhibiting microglial-mediated neuroinflammation in an acute ocular hypertension model

AIM：To investigate the neuroprotective effect of gastrodin on retinal ganglion cells（RGCs）in an acute ocular hypertension（AOH）rat model and to identify its possible mechanism.METHODS：AOH rat model was performed in a randomly selected eye by anterior chamber perfusion and either received an intraperitoneal injection with various concentrations of gastrodin or normal saline.After 2wk,the rats were sacrificed.Fluoro Gold was used to label survival RGCs.Immunostaining with anti-Iba1 in the retinal flat mounts to calculate the microglia density in the ganglion cell layer（GCL）.Changes in microglial cytokines,tumour necrosis factor-alpha（TNF-α）and inducible NO synthase（i NOS）were examined with Western blot and reverse transcriptionquantitative polymerase chain reaction.Expression levels of total and phosphorylated p38 mitogen activated protein kinase（MAPK）were determined by Western blot.RESULTS：Results showed that AOH induced significant loss of RGCs and severe microglia activation in the GCL.Besides,AOH increased the phosphorylation of p38 MAPK and promoted the release of microglial cytokines in the retinas.Intraperitoneal injection with dose-dependent gastrodin significantly reduced the loss of RGCs and inhibited retinal microglia activation,accompanied with the decreased expression levels of microglial cytokines and p38 MAPK phosphorylation.CONCLUSION：Gastrodin exerts a neuroprotective effect on RGCs in an acute glaucoma animal model viainhibiting microglia activation and microglial-mediated neuroinflammation.The finding demonstrates the potential application of gastrodin in the neuroprotective therapy of acute glaucoma and other retinal neurodegenerative diseases characterized by microglia activation and RGCs death.

Characterization of intraocular pressure pattern and changes of retinal ganglion cells in DBA2J glaucoma mice

AIM： To characterize the pattern of intraocular pressure （lOP） change and the deficit of retinal ganglion cells （RGCs） in DBA2J, which is most well-characterized chronic glaucoma mouse model and wild type （WT） C57bl/6 mice, and to study the relationship between lOP change and RGCs deficit. METHODS： lOP was monitored with a rebound tonometer in C57bl/6 and DBA2J mice from 3 to 15-month-old. Retinal function was evaluated by dark -adapted electroretinogram （ERG） in DBA2J and WT mice of 15-month-old. A dye （Neurobiotin） was applied to optic nerve stump to retrograde label RGCs. TO-PRO-3 visualized all nuclei of cells in the RGC layer. RESULTS： The lOP in WT mice was 9.03-0.6 mm Hg on average and did not increase significantly as aging. The lOP in DBA2J mice, arranging from 7.2 to 28 mm Hg, was increasing significantly as aging, and it was normal at 3-month--old compared with WT mice, slightly increased from 7-month-old and increased in 50% animals at 11-month-old and in 38% animals at 15-month-old. The RGCs density in DBA2J mice started reducing by 7-month-old, continuously decreased until reached about 20% of RGC in WT retina by 15-month-old. RGC density was not linearly correlated with lOP in 15-month- old DBA2J mice. The amplitude of positive scotopic threshold response, and negative scotopic threshold response of ERG were significantly reduced in DBA2J mice of 15-month-old than that in age-paired WT mice. CONCLUSION： The present study found that DBA2J mice display pathological and functional deficits of the retina that was not linearly correlated with lOP.

Cell transplantation to replace retinal ganglion cells faces challenges-the Switchboard Dilemma

The mammalian retina displays incomplete intrinsic regenerative capacities;therefore,retina degeneration is a major cause of irreversible blindness such as glaucoma,agerelated macular degeneration and diabetic retinopathy.These diseases lead to the loss of retinal cells and serious vision loss in the late stage.Stem cell transplantation is a great promising novel treatment for these incurable retinal degenerative diseases and represents an exciting area of regenerative neurotherapy.Several suitable stem cell sources for transplantation including human embryonic stem cells,induced pluripotent stem cells and adult stem cells have been identified as promising target populations.However,the retina is an elegant neuronal complex composed of various types of cells with different functions.The replacement of these different types of cells by transplantation should be addressed separately.So far,retinal pigment epithelium transplantation has achieved the most advanced stage of clinical trials,while transplantation of retinal neurons such as retinal ganglion cells and photoreceptors has been mostly studied in pre-clinical animal models.In this review,we opine on the key problems that need to be addressed before stem cells transplantation,especially for replacing injured retinal ganglion cells,may be used practically for treatment.A key problem we have called the Switchboard Dilemma is a major block to have functional retinal ganglion cell replacement.We use the public switchboard telephone network as an example to illustrate different difficulties for replacing damaged components in the retina that allow for visual signaling.Retinal ganglion cell transplantation is confronted by significant hurdles,because retinal ganglion cells receive signals from different interneurons,integrate and send signals to the correct targets of the visual system,which functions similar to the switchboard in a telephone network-therefore the Switchboard Dilemma.

Melanopsin expression is an indicator of the well-being of melanopsin-expressing retinal ganglion cells but not of their viability

Light is an electromagnetic stimulus that in mammals is sensed by specialized neurons in the retina.The physiological response to light encompasses two fundamental and different functional outputs：image-forming and non-image forming.

Effects of Qingguang’an Granules on mitochondrial autophagy of retinal ganglion cells in rats with chronic ocular hypertension

Objective To investigate the effect and underlying mechanism of Qingguang’an Granules(青光安颗粒剂,QGAG)on mitochondrial autophagy(mitophagy)of retinal ganglion cells(RGCs)in rats with chronic ocular hypertension(COH).Methods Sixty Sprague Dawley(SD)rats,half males and half females,were randomly assigned to three groups:the control,model,and QGAG(2.5 g/kg)groups,with 20 rats in each group.Rats’model of COH was established by cauterizing episcleral veins in the model group and QGAG group.Three weeks after successful modeling,rats in the QGAG group were intra-gastrically administered with QGAG,while rats in the control group and the model group received an equal dose of normal saline.After three months of intragastric administration,intraocular pressure(IOP)of all rats was measured.The mitophagy was monitored by the immunofluorescence method,the mitochondrial membrane potential was measured using the JC-1 method,and the morphological changes of mitophagy in RGCs were observed by transmission electron microscopy.Meanwhile,rat RGCs were labeled using the fluorescent gold method,and RGCs density in each group was calculated.Moreover,RGCs apoptosis was observed by TdT-mediated dUTP Nick-End Labeling(TUNEL)assay.Finally,the expression levels of Parkin,optineurin,microtubule-associated protein 1 light chain 3-Ⅱ/microtubule-associated protein 1 light chain 3-Ⅰ(LC3-Ⅱ/LC3-Ⅰ),recombinant lysosomal associated membrane protein 1(LAMP1),and B-cell lymphoma-2(Bcl-2)in RGCs were determined by Western blot assay.The corresponding mRNAs were detected through quantitative real-time polymerase chain reaction(qRT-PCR).Results The QGAG reduced IOP in COH rats,and inhibited mitophagy and apoptosis of RGCs(P<0.05).Besides,the QGAG significantly increased the expression levels of Parkin and Bcl-2(P<0.05),and inhibited the expression levels of optineurin,LAMP1,and LC3-Ⅱ/LC3-Ⅰ(P<0.05)in RGCs of COH rats.Conclusion The QGAG can inhibit mitophagy in RGCs of COH rats and show a protective effect against optic nerve damage caused by glaucoma,which may be mediated through the mitophagy ubiquitination via the Parkin/PINK1-related pathway.

Neuroprotective Effect of Melatonin on Retinal Ganglion Cells in Rats

To investigate the neuroprotective effect of melatonin （MT） on retinal ganglion cells （RGCs） in rats with ischemia reperfusion injury （RIR）, 24 healthy SD rats were randomly divided into two groups： group A and group B. RIR model was induced in the left eyes by increasing the pressure of the anterior chamber. Group A was treated with 10 % alcohol- normal saline （1 mL/ kg/d, ip）, while group B was treated with 0.5 % MT （1 mL/kg/d, ip）. On the basis of the time interval between the left eyes RIR and the sacrifice, rats in both group A and group B were further divided into 3 subgroups： groups A1 and B1 （days 7）, groups A2 and B2 （days 14）, groups A3 and B3 （days 30）, with 4 rats in each subgroup. 7 day before the sacrifice, 3 % fluorogold was bilaterally injected into superior colliculi and geniculate body. The eyes were enucleated after being sacrificed, and mounting of the retina from both eyes was performed on a slide and observed under a fluorescence microscope. Four photos were taken from each of the four quadrants of the retina. The labeled-RGCs were counted by using a computerized image analyzer. The rate of the labeled- RGCs was used for statistical analysis. Our results showed that, in group A, the rate of the la- beled-RGCs was （77.16±6.35） %, （65.53±7.01） %, （53.85±4.38） % on day 7, 14 and 30. In group B, the rate of the labeled-RGCs was （81.33±9.27） %, （79.80±8.36） %, （80. 34±11. 05） % on day 7, 14 and 30. In group B, which was treated with MT after RIR, the rate of labeled- RGCs was significantly higher than that of group A on day 14 and day 30 （P〈0.05）. It is concluded that, in the RIR rats, MT therapy could increase the survival rate of the RGCs and could rescue and restore the injured RGCs.

Primary retinal ganglion cells for neuron replacement therapy

Optic nerve damage as a result of trauma, ischemia, glaucoma or other forms of optic neuropathy disease, leads to disconnection between the eye and brain and death of retinal ganglion cells(RGCs), causing permanent loss of vision. Therapeutic options for treating optic neuropathy are limited and represent a significant unmet medical need. Development of a regenerative strategy for replacement of lost RGCs lies at the core of the future cell-based therapy for these conditions. Successful long-term restoration of visual function depends on the type of cells for transplantation. Primary RGCs of neonatal mice are now reported to have the potential for serving such a purpose.

Retinal ganglion cells regenerate long-distance axons through neural activity stimulation and find their way back to the brain

Human central nerve system(CNS)is an extremely complex and delicate structure.While regeneration is possible in some reptiles and fish CNS,the regeneration capacity seems completely lost in adult mammals.Therefore,the classic concept is that once neurons in mammal

AB004:Resuscitation of axon regenerative potential in mature retinal ganglion cells

Axon regeneration capacity declines in mature retinal ganglion cells(RGCs).While a number of transcription factors and signaling molecules have been implicated to the loss of regenerative potential of RGC axon,their upstream regulators are unclear.We investigated the association between developmental decline of RGC regenerative potential and age-related changes in microRNA(miRNA)expression and showed that loss of axon regenerative potential can be partially restored by upregulating miR-19a in RGCs in vitro and in vivo.Regulating miRNA expression represents a new potential therapeutic approach to resuscitate age-related loss of axon growth ability.

脂肪间充质干细胞外泌体对体外培养压力损伤的大鼠RGCs的保护作用

目的:通过体外建立大鼠视网膜神经节细胞(RGCs)压力损伤模型,研究脂肪间充质干细胞(ADSCs)外泌体对损伤的RGCs的保护作用。方法:培养ADSCs收集上清提取并鉴定外泌体,将体外培养大鼠RGCs分为正常培养的RGCs对照组、不同压力(40、80、120 mmHg)培养的RGCs模型组、不同压力培养的RGCs加入外泌体治疗组,通过CCK-8法检测各组RGCs细胞增殖活力,qPCR法检测各组RGCs中BDNF、Caspase-3的mRNA表达水平,Western Blot检测各组RGCs中BDNF、Caspase-3的蛋白表达水平。结果:CCK-8法检测发现,在对照组中,与24 h的细胞增殖活力相比,48 h时细胞增殖活力上升(P<0.05)。在48 h时,与加压40、80、120 mmHg模型组相比,加入外泌体后细胞活力均上升(均P<0.05)。qPCR法检测发现,与对照组比较,40 mmHg组中BDNF mRNA表达下降,但无差异(P>0.05),80、120 mmHg组中BDNF mRNA表达下降(均P<0.05)。加压40、80 mmHg组加入外泌体后RGCs的BDNF mRNA表达均上升(均P<0.05),加压120 mmHg组加入外泌体后RGCs的BDNF mRNA表达上升,但无差异(P>0.05)。与对照组比较,加压40 mmHg组中Caspase-3的mRNA表达上升,但无差异(P>0.05),加压80、120 mmHg组中Caspase-3 mRNA表达均上升(均P<0.05)。加压40、80 mmHg组加入外泌体治疗后RGCs的Caspase-3 mRNA表达下降(P<0.05),加压120 mmHg组加入外泌体治疗后RGCs Caspase-3的mRNA表达下降,但无差异(P>0.05)。Western Blot检测发现,与对照组比较,加压40 mmHg组中BDNF蛋白表达下降,但无差异(P>0.05),加压80、120 mmHg组中BDNF蛋白表达下降(均P<0.001)。与模型组相比,加入外泌体治疗后BDNF蛋白表达均上升(均P<0.05)。与对照组比,加压后各模型组中Caspase-3蛋白表达均上升(均P<0.05);与模型组相比,加入外泌体治疗后各组Caspase-3蛋白表达均下降(均P<0.05)。结论:ADSCs来源的外泌体能够增加体外培养不同压力损伤的大鼠RGCs的细胞增殖活力,提高BDNF的mRNA及蛋白表达水平,降低Caspase-3的mRNA及蛋白表达水平,说明ADSCs来源的外泌体对体外培养压力损伤的大鼠RGCs具有保护作用。

Overexpressing NeuroD1 reprograms Müller cells into various types of retinal neurons

The onset of retinal degenerative disease is often associated with neuronal loss. Therefore, how to regenerate new neurons to restore vision is an important issue. NeuroD1 is a neural transcription factor with the ability to reprogram brain astrocytes into neurons in vivo. Here, we demonstrate that in adult mice, NeuroD1 can reprogram Müller cells, the principal glial cell type in the retina, to become retinal neurons. Most strikingly, ectopic expression of NeuroD1 using two different viral vectors converted Müller cells into different cell types. Specifically, AAV7 m8 GFAP681::GFP-ND1 converted Müller cells into inner retinal neurons, including amacrine cells and ganglion cells. In contrast, AAV9 GFAP104::ND1-GFP converted Müller cells into outer retinal neurons such as photoreceptors and horizontal cells, with higher conversion efficiency. Furthermore, we demonstrate that Müller cell conversion induced by AAV9 GFAP104::ND1-GFP displayed clear dose-and time-dependence. These results indicate that Müller cells in adult mice are highly plastic and can be reprogrammed into various subtypes of retinal neurons.

Single-cell RNA sequencing analysis of the retina under acute high intraocular pressure

High intraocular pressure causes retinal ganglion cell injury in primary and secondary glaucoma diseases,yet the molecular landscape characteristics of retinal cells under high intraocular pressure remain unknown.Rat models of acute hypertension ocular pressure were established by injection of cross-linked hyaluronic acid hydrogel(Healaflow■).Single-cell RNA sequencing was then used to describe the cellular composition and molecular profile of the retina following high intraocular pressure.Our results identified a total of 12 cell types,namely retinal pigment epithelial cells,rod-photoreceptor cells,bipolar cells,Müller cells,microglia,cone-photoreceptor cells,retinal ganglion cells,endothelial cells,retinal progenitor cells,oligodendrocytes,pericytes,and fibroblasts.The single-cell RNA sequencing analysis of the retina under acute high intraocular pressure revealed obvious changes in the proportions of various retinal cells,with ganglion cells decreased by 23%.Hematoxylin and eosin staining and TUNEL staining confirmed the damage to retinal ganglion cells under high intraocular pressure.We extracted data from retinal ganglion cells and analyzed the retinal ganglion cell cluster with the most distinct expression.We found upregulation of the B3gat2 gene,which is associated with neuronal migration and adhesion,and downregulation of the Tsc22d gene,which participates in inhibition of inflammation.This study is the first to reveal molecular changes and intercellular interactions in the retina under high intraocular pressure.These data contribute to understanding of the molecular mechanism of retinal injury induced by high intraocular pressure and will benefit the development of novel therapies.

Dental pulp stem cells, a paracrine-mediated therapy for the retina

Author contributions： Mead B was responsible for study conception and design, collection and^or assembly of data, data analysis and interpretation and manuscript writing. Logan A participated in study conception and design, data analysis and interpretation and manuscript writing. Berry M was responsible for manuscript writing. Scheven BA was in charge of study conception and design, data analysis and interpretation and manuscript writing. Leadbeater W participated in study conception and design, data analysis and interpretation and manuscript writing. All authors approved the final version of this paper.

The role of miRNA in retinal ganglion cell health and disease

miRNA are short non-coding RNA responsible for the knockdown of proteins through their targeting and silencing of complimentary m RNA sequences.The mi RNA landscape of a cell thus affects the levels of its proteins and has significant consequences to its health.Deviations in this mi RNA landscape have been implicated in a variety of neurodegenerative diseases and have also garnered interest as targets for treatment.Retinal ganglion cells are the sole projection neuron of the retina with their axons making up the optic nerve.They are a focus of study not only for their importance in vision and the myriad of blinding diseases characterized by their dysfunction and loss,but also as a model of other central nervous system diseases such as spinal cord injury and traumatic brain injury.This review summarizes current knowledge on the role of mi RNA in retinal ganglion cell function,highlighting how perturbations can result in disease,and how modulating their abundance may provide a novel avenue of therapeutic research.

Mesenchymal stem cell therapy for retinal ganglion cell neuroprotection and axon regeneration

Retinal ganglion cells （RGCs） are responsible for propagat- ing signals derived from visual stimuli in the eye to the brain, along their axons within the optic nerve to the superior colliculus, lateral geniculate nucleus and visu- al cortex of the brain. Damage to the optic nerve either through trauma, such as head injury, or degenerative dis- ease, such as glaucoma causes irreversible loss of function through degeneration of non-regenerating RGC axons and death of irreplaceable RGCs, ultimately leading to blindness （Berry et al., 2008）. The degeneration of RGCs and their axons is due to the loss of the necessary source of retrogradely transported neurotrophic factors （NTFs） being hindered by axonal injury. NTFs are survival factors for neurons and play a pivotal part in axon regeneration. Stem cells particularly mesenchymal stem cells （MSCs） have been shown to possess a natural intrinsic capacity for paracrine support, releasing multiple signalling mol- ecules including NTFs. By transplanting MSCs into the vitreous, they are positioned adjacent to the injured reti- na to provide paracrine-mediated therapy for the retinal neuronal cells （Johnson et al., 2010a; Mead et al., 2013）. Additionally, MSCs may be pre-differentiated into sup- portive glial-like cells, such as Schwann cells, which could further increase their potential for paracrine support of injured neurons （Martens et al., 2013）. Thus, MSCs have received considerable attention as a new cellular therapy for both traumatic and degenerative eye disease, acting as an alternative source of NTFs, protecting injured RGCs and promoting regeneration of their axons （Figure 1）.

Gene therapy and the regeneration of retinal ganglion cell axons

Because the adult mammalian central nervous system （CNS） has only limited intrinsic capacity to regenerate connections after injury, due to factors both intrinsic and extrinsic to the mature neuron （Shen et al., 1999; Berry et al., 2008; Lingor et al., 2008; Sun and He, 2010; Moore et al., 2011 ）, therapies are required to support the survival of injured neu-rons and to promote the long-distance regrowth of axons back to their original target structures. The retina and optic nerve （ON） are part of the CNS and this system is much used in experiments designed to test new ways of promoting regeneration after injury （Harvey et al., 2006; Benowitz and Yin, 2008; Berry et al., 2008; Fischer and Leibinger, 2012）. Testing of therapies designed to improve retinal ganglion cell （RGC） viability also has direct clinical relevance because there is loss of these centrally projecting neurons in many ophthalmic diseases.

Retinal ganglion cell complex changes using spectral domain optical coherence tomography in diabetic patients without retinopathy

AIM：To assess the ganglion cell complex（GCC）thickness in diabetic eyes without retinopathy. METHODS：Two groups included 45 diabetic eyes without retinopathy and 21 non diabetic eyes. All subjects underwent full medical and ophthalmological history,full ophthalmological examination,measuring GCC thickness and central foveal thickness（CFT）using the RTVue~？ spectral domainoptical coherence tomography（SD-OCT）,and HbA1C level.RESULTS：GCC focal loss volume（FLV%）was significantly more in diabetic eyes（22.2% below normal）than normal eyes（P=0.024）. No statistically significant difference was found between the diabetic group and the control group regarding GCC global loss volume（GLV%）（P=0.160）. CFT was positively correlated to the average,superior and inferior GCC（P=0.001,0.000 and 0.001 respectively）and negatively correlated to GLV% and FLV%（P=0.002 and0.031 respectively）in diabetic eyes. C/D ratio in diabetic eyes was negatively correlated to average,superior and inferior GCC（P=0.015,0.007 and 0.017 respectively）. The FLV% was negatively correlated to the refraction and level of Hb A1c（P=0.019 and 0.013 respectively）and positively correlated to the best corrected visual acuity（BCVA）in log MAR in diabetic group（P=0.004）.CONCLUSION：Significant GCC thinning in diabetes predates retinal vasculopathy,which is mainly focal rather than diffuse. It has no preference to either the superior or inferior halves of the macula. Increase of myopic error is significantly accompanied with increased focal GCC loss. GCC loss is accompanied with increased C/D ratio in diabetic eyes.

NLRP3 inflammasome in retinal ganglion cell loss in optic neuropathy

In neurodegenerative diseases,neuroinflammatory responses are often activated in resident immune cells in the central nervous system（CNS）（Schroder and Tschopp,2010）.Optic neuropathy refers to dysfunction and degeneration of retinal ganglion cells（RGCs）and their axons,which is often induced by optic nerve injury or glaucomatous insult.Studies,

Physiological significance of Rag1 in retinal ganglion cell death

Although the transcription factor, nudear factor-κB （NF-κB） is known to regulate cell death and survival, its precise role in cell death within the central nervous system （CNS） remains unknown. We previously reported that mice with a homozygous deficiency for NF-κBp50 spon- taneously developed optic neuropathy. We examined the expression and activation of pro-apoptotic factor（s） that mediate optic neuropathy in p50-/- mice. Recombination activating gene 1 （Ragl） is known to regulate the recombination of immunoglobulin V（D）J.

The intricacies of neurotrophic factor therapy for retinal ganglion cell rescue in glaucoma: a case for gene therapy

Regeneration of damaged retinal ganglion cells（RGC） and their axons is an important aspect of reversing vision loss in glaucoma patients. While current therapies can effectively lower intraocular pressure, they do not provide extrinsic support to RGCs to actively aid in their protection and regeneration. The unmet need could be addressed by neurotrophic factor gene therapy, where plasmid DNA, encoding neurotrophic factors, is delivered to retinal cells to maintain sufficient levels of neurotrophins in the retina. In this review, we aim to describe the intricacies in the design of the therapy including： the choice of neurotrophic factor, the site and route of administration and target cell populations for gene delivery. Furthermore, we also discuss the challenges currently being faced in RGC-related therapy development with special considerations to the existence of multiple RGC subtypes and the lack of efficient and representative in vitro models for rapid and reliable screening in the drug development process.