Microglial-induced Müller cell gliosis is attenuated by progesterone in a mouse model of retinitis pigmentosa

Homer1a reduces inflammatory response after retinal ischemia/reperfusion injury

JOURNAL/nrgr/04.03/01300535-202407000-00042/figure1/v/2023-11-20T171125Z/r/image-tiff

Elevated intraocular pressure (IOP) is one of the causes of retinal ischemia/reperfusion injury, which results in NLRP3 inflammasome activation and leads to visual damage. Homer1a is reported to play a protective role in neuroinflammation in the cerebrum. However, the effects of Homer1a on NLRP3 inflammasomes in retinal ischemia/reperfusion injury caused by elevated IOP remain unknown. In our study, animal models were constructed using C57BL/6J and Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice with elevated IOP-induced retinal ischemia/reperfusion injury. For in vitro experiments, the oxygen-glucose deprivation/reperfusion injury model was constructed with Müller cells. We found that Homer1a overexpression ameliorated the decreases in retinal thickness and Müller cell viability after ischemia/reperfusion injury. Furthermore, Homer1a knockdown promoted NF-κB P65Ser536 activation via caspase-8, NF-κB P65 nuclear translocation, NLRP3 inflammasome formation, and the production and processing of interleukin-1β and interleukin-18. The opposite results were observed with Homer1a overexpression. Finally, the combined administration of Homer1a protein and JSH-23 significantly inhibited the reduction in retinal thickness in Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice and apoptosis in Müller cells after ischemia/reperfusion injury. Taken together, these studies demonstrate that Homer1a exerts protective effects on retinal tissue and Müller cells via the caspase-8/NF-κB P65/NLRP3 pathway after I/R injury.

Multimodal Imaging of Optic Nerve Head in Retinitis Pigmentosa

BACKGROUND

A pallor optic nerve head (ONH) is one of the three features of retinitis pigmentosa (RP). This study aimed to assess the ONH prospectively by color tone, presence of hyper-reflective tissue, blood flow, retinal nerve fiber layer (RNFL) thickness, ganglion cell complex (GCC) and investigate the change in these parameters with and without ONH pallor.

METHODS

The presence of ONH pallor was assessed by three independent examiners through careful examination using fundus photographs. The presence of a hyper-reflective structure on the ONH was carefully evaluated using a volume scan optical coherence tomography (OCT). RNFL thickness and ellipsoid zone (EZ) width around the macula were also evaluated by OCT. Laser speckle flowgraphy was used to measure the mean blur rate of the entire ONH area, which was subsequently divided into the vessel area (MV) and tissue area (MT).

RESULTS

Twenty-eight eyes of 28 patients with RP (55.4 ± 16.23 years of age) were included. The pale ONH was observed in 10 (35%) eyes. Hyper-reflective structures were observed in seven (25%) eyes. No significant correlation was found between the pale ONH and the presence of a hyper-reflective structure (Pearson's chi-squared test, p = .364). The average of the ONH area, MV, and MT was 8.65 ± 3.08 AU, 17.81 ± 7.54 AU, and 6.4 ± 2.66 AU, respectively, which significantly decreased in patients with pallor ONH (all p < .05). The global RNFL thickness was 73.54 ± 18.82 μm. The nasal and superior quadrants and global RNFL thickness in patients with a pale ONH were significantly thinner than in patients without a pale ONH (all p < .05). The global and superior and inferior GCC thickness in patients with a pale ONH were significantly thinner than in patients without a pale ONH(all p < .05).There was no difference in the EZ width between patients with and without a pale ONH (p = .107).

CONCLUSION

We conducted multiple assessments of the ONH in RP patients and investigated its clinical significance. Our findings suggest that ONH pallor may indicate a comprehensive change that emerges alongside the progression of retinal degeneration in RP.

TRIAL REGISTRATION

This trial was retrospectively registered in the UMIN Clinical Trial Registry (UMIN ID: 000048168).

NADPH and NAC synergistically inhibits chronic ocular hypertension-induced neurodegeneration and neuroinflammation through regulating p38/MAPK pathway and peroxidation

Glaucoma, the leading cause of irreversible blindness worldwide, is characterized by neurodegeneration and neuroinflammation with retinal NAD/NADP and GSH decline. Nicotinamide adenine dinucleotide (NAD)/NAD phosphate (NADP) and glutathione (GSH) are two redox reducers in neuronal and glial metabolism. However, therapeutic strategies targeting NAD/NADP or GSH do not exert ideal effects, and the underlying mechanisms are still poorly understood. We assessed morphological changes in retinal ganglion cells (RGCs), the affected neurons in glaucoma, and Müller cells, the major glial cells in the retina, as well as the levels of phosphorylated p38 (p-p38) and Caspase-3 in glaucoma patients. We constructed a modified chronic ocular hypertensive rat model and an oxygen-glucose deprivation (OGD) cell model. After applying NADPH and N-acetylcysteine (NAC), a precursor to cysteine, the rate-limiting substrate in GSH biosynthesis, to cells, apoptosis, axonal damage and peroxidation were reduced in the RGCs of the NAC group and p-p38 levels were decreased in the RGCs of the NADPH group, while in stimulated Müller cells cultured individually or cocultured with RGCs, gliosis and p38/MAPK, rather than JNK/MAPK, activation were inhibited. The results were more synergistic in the rat model, where either NADPH or NAC showed crossover effects on inhibiting peroxidation and p38/MAPK pathway activation. Moreover, the combination of NADPH and NAC ameliorated RGC electrophysiological function and prevented Müller cell gliosis to the greatest extent. These data illustrated conjoined mechanisms in glaucomatous RGC injury and Müller cell gliosis and suggested that NADPH and NAC collaborate as a neuroprotective and anti-inflammatory combination treatment for glaucoma and other underlying human neurodegenerative diseases.

Navigating the future of retinitis pigmentosa treatments: A comprehensive analysis of therapeutic approaches in rd10 mice

Retinitis pigmentosa (RP) is a degenerative disease, caused by genetic mutations that lead to a loss in photoreceptors. For research on RP, rd10 mice, which carry mutations in the phosphodiesterase (PDE) gene, exhibit degenerative patterns comparable to those of patients with RP, making them an ideal model for investigating potential treatments. Although numerous studies have reported the potential of biochemical drugs, gene correction, and stem cell transplantation in decelerating rd10 retinal degeneration, a comprehensive review of these studies has yet to be conducted. Therefore, here, a comparative analysis of rd10 mouse treatment research over the past decade was performed. Our findings suggest that biochemical drugs capable of inhibiting the inflammatory response may be promising therapeutics. Additionally, significant progress has been made in the field of gene therapy; nevertheless, challenges such as strict delivery requirements, bystander editing, and off-target effects still need to be resolved. Nevertheless, secretory function is the only unequivocal protective effect of stem cell transplantation. In summary, this review presents a comprehensive analysis and synthesis of the treatment approaches employing rd10 mice as experimental subjects, describing a clear pathway for future RP treatment research and identifies potential clinical interventions.

Taurine: A Source and Application for the Relief of Visual Fatigue

According to reports, supplementation with appropriate doses of taurine may help to reduce visual fatigue. Presently, some progress has been made in research related to taurine in eye health, but the lack of systematic summaries has led to the neglect of its application in the relief of visual fatigue. This paper, therefore, provides a systematic review of the sources of taurine, including the endogenous metabolic and exogenous dietary pathways, as well as a detailed review of the distribution and production of exogenous taurine. The physiological mechanisms underlying the production of visual fatigue are summarized and the research progress of taurine in relieving visual fatigue is reviewed, including the safety of consumption and the mechanism of action in relieving visual fatigue, in order to provide some reference basis and inspiration for the development and application of taurine in functional foods for relieving visual fatigue.

Activation of retinal glial cells contributes to the degeneration of ganglion cells in experimental glaucoma

Elevation of intraocular pressure (IOP) is a major risk factor for neurodegeneration in glaucoma. Glial cells, which play an important role in normal functioning of retinal neurons, are well involved into retinal ganglion cell (RGC) degeneration in experimental glaucoma animal models generated by elevated IOP. In response to elevated IOP, mGluR I is first activated and Kir4.1 channels are subsequently inhibited, which leads to the activation of Müller cells. Müller cell activation is followed by a complex process, including proliferation, release of inflammatory and growth factors (gliosis). Gliosis is further regulated by several factors. Activated Müller cells contribute to RGC degeneration through generating glutamate receptor-mediated excitotoxicity, releasing cytotoxic factors and inducing microglia activation. Elevated IOP activates microglia, and following morphological and functional changes, these cells, as resident immune cells in the retina, show adaptive immune responses, including an enhanced release of pro-inflammatory factors (tumor neurosis factor-α, interleukins, etc.). These ATP and Toll-like receptor-mediated responses are further regulated by heat shock proteins, CD200R, chemokine receptors, and metabotropic purinergic receptors, may aggravate RGC loss. In the optic nerve head, astrogliosis is initiated and regulated by a complex reaction process, including purines, transmitters, chemokines, growth factors and cytokines, which contributes to RGC axon injury through releasing pro-inflammatory factors and changing extracellular matrix in glaucoma. The effects of activated glial cells on RGCs are further modified by the interplay among different types of glial cells. This review is concluded by presenting an in-depth discussion of possible research directions in this field in the future.

Microglia: The breakthrough to treat neovascularization and repair blood-retinal barrier in retinopathy

Microglia are the primary resident retinal macrophages that monitor neuronal activity in real-time and facilitate angiogenesis during retinal development. In certain retinal diseases, the activated microglia promote retinal angiogenesis in hypoxia stress through neurovascular coupling and guide neovascularization to avascular areas (e.g., the outer nuclear layer and macula lutea). Furthermore, continuously activated microglia secrete inflammatory factors and expedite the loss of the blood-retinal barrier which causes irreversible damage to the secondary death of neurons. In this review, we support microglia can be a potential cellular therapeutic target in retinopathy. We briefly describe the relevance of microglia to the retinal vasculature and blood-retinal barrier. Then we discuss the signaling pathway related to how microglia move to their destinations and regulate vascular regeneration. We summarize the properties of microglia in different retinal disease models and propose that reducing the number of pro-inflammatory microglial death and conversing microglial phenotypes from pro-inflammatory to anti-inflammatory are feasible for treating retinal neovascularization and the damaged blood-retinal barrier (BRB). Finally, we suppose that the unique properties of microglia may aid in the vascularization of retinal organoids.

miR-181a/b downregulation: a mutation-independent therapeutic approach for inherited retinal diseases

Inherited retinal diseases (IRDs) are a group of diseases whose common landmark is progressive photoreceptor loss. The development of gene-specific therapies for IRDs is hampered by their wide genetic heterogeneity. Mitochondrial dysfunction is proving to constitute one of the key pathogenic events in IRDs; hence, approaches that enhance mitochondrial activities have a promising therapeutic potential for these conditions. We previously reported that miR-181a/b downregulation boosts mitochondrial turnover in models of primary retinal mitochondrial diseases. Here, we show that miR-181a/b silencing has a beneficial effect also in IRDs. In particular, the injection in the subretinal space of an adeno-associated viral vector (AAV) that harbors a miR-181a/b inhibitor (sponge) sequence (AAV2/8-GFP-Sponge-miR-181a/b) improves retinal morphology and visual function both in models of autosomal dominant (RHO-P347S) and of autosomal recessive (rd10) retinitis pigmentosa. Moreover, we demonstrate that miR-181a/b downregulation modulates the level of the mitochondrial fission-related protein Drp1 and rescues the mitochondrial fragmentation in RHO-P347S photoreceptors. Overall, these data support the potential use of miR-181a/b downregulation as an innovative mutation-independent therapeutic strategy for IRDs, which can be effective both to delay disease progression and to aid gene-specific therapeutic approaches.

Cellular and molecular alterations in neurons and glial cells in inherited retinal degeneration

Multiple gene mutations have been associated with inherited retinal dystrophies (IRDs). Despite the spectrum of phenotypes caused by the distinct mutations, IRDs display common physiopathology features. Cell death is accompanied by inflammation and oxidative stress. The vertebrate retina has several attributes that make this tissue vulnerable to oxidative and nitrosative imbalance. The high energy demands and active metabolism in retinal cells, as well as their continuous exposure to high oxygen levels and light-induced stress, reveal the importance of tightly regulated homeostatic processes to maintain retinal function, which are compromised in pathological conditions. In addition, the subsequent microglial activation and gliosis, which triggers the secretion of pro-inflammatory cytokines, chemokines, trophic factors, and other molecules, further worsen the degenerative process. As the disease evolves, retinal cells change their morphology and function. In disease stages where photoreceptors are lost, the remaining neurons of the retina to preserve their function seek out for new synaptic partners, which leads to a cascade of morphological alterations in retinal cells that results in a complete remodeling of the tissue. In this review, we describe important molecular and morphological changes in retinal cells that occur in response to oxidative stress and the inflammatory processes underlying IRDs.

Retinal Toxicity Induced by Chemical Agents

Vision is an important sense for humans, and visual impairment/blindness has a huge impact in daily life. The retina is a nervous tissue that is essential for visual processing since it possesses light sensors (photoreceptors) and performs a pre-processing of visual information. Thus, retinal cell dysfunction or degeneration affects visual ability and several general aspects of the day-to-day of a person's lives. The retina has a blood-retinal barrier, which protects the tissue from a wide range of molecules or microorganisms. However, several agents, coming from systemic pathways, reach the retina and influence its function and survival. Pesticides are still used worldwide for agriculture, contaminating food with substances that could reach the retina. Natural products have also been used for therapeutic purposes and are another group of substances that can get to the retina. Finally, a wide number of medicines administered for different diseases can also affect the retina. The present review aimed to gather recent information about the hazard of these products to the retina, which could be used to encourage the search for more healthy, suitable, or less risky agents.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.

Sex Hormones and Their Effects on Ocular Disorders and Pathophysiology: Current Aspects and Our Experience

Sex hormones are molecules produced by the gonads and to a small extent by the adrenal gland, which not only determine the primary and secondary sexual characteristics of an individual, differentiating man from woman, but also participate in the functioning of the various systems of the body. The evidence that many eye diseases differ in terms of prevalence between men and women has allowed us, in recent years, to carry out several studies that have investigated the association between sex hormones and the pathophysiology of eye tissues. Specific receptors for sex hormones have been found on the lacrimal and meibomian glands, conjunctiva, cornea, lens, retina, and choroid. This work summarizes the current knowledge on the role that sex hormones play in the pathogenesis of the most common ocular disorders and indicates our clinical experience in these situations. The aim is to stimulate an interdisciplinary approach between endocrinology, neurology, molecular biology, and ophthalmology to improve the management of these diseases and to lay the foundations for new therapeutic strategies.

Topical Ocular Administration of Progesterone Decreases Photoreceptor Cell Death in Retinal Degeneration Slow (rds) Mice

Retinitis pigmentosa (RP) is an inherited eye disorder which triggers a cascade of retinal disorders leading to photoreceptor cell death and for which there is currently no effective treatment. The purpose of this research was to study whether ocular administration of a solution of progesterone (PG) in β-cyclodextrins (CD) could delay photoreceptor cell death and counteract the gliosis process in an animal model of RP (rds mice). The possible effect of PG reaching the contralateral eye through the circulatory system was also evaluated. Finally, this research discusses and evaluates the diffusion of the drug from possible topical formulations for ocular administration of PG. A group of rds mice received one drop of a solution of PG in CD every 12 h for 10 days to the left eye, while the right eye was left untreated. Another group of rds mice (control) received the drug vehicle (PBS) on the left eye and, again, the right eye was left untreated. Once the treatment was finished on postnatal day 21, the animals were euthanized and histological immunofluorescence studies (TUNEL, GFAP, and DAPI staining) were carried out. Our results showed that the administration of a solution of PG in CD (CD-PG) as drops significantly decreased cell death and inflammation in the retina of the PG-treated eyes of rds mice. No effect was seen in the contralateral eye from PG that may have entered systemic circulation. In conclusion, CD-PG applied topically as drops to the eye decreases photoreceptor cell death in the early stages of RP, delaying vision loss and decreasing gliosis.

Microglia-derived TNF-α mediates Müller cell activation by activating the TNFR1-NF-κB pathway

Microglia and its interaction with Müller cells are responsible to retinal surveillance during retinal neurodegeneration, however, the role and mechanism of microglia-derived tumor necrosis factor (TNF)-α in the activation of retinal Müller cells have not been fully elucidated. In the present study, primary microglia and Müller cells were isolated from newborn Sprague-Dawley (SD) rats with purities of 88.2 ± 6.2% and 92.2 ± 2.2%, respectively. By performing immunofluorescence and Western blot analysis, we found that TNF receptor (TNFR)-1 and TNFR2 were expressed in Müller cells. After co-cultured with microglia-conditioned medium (MCM), the elevated mRNA levels of glial fibrillary acidic protein (GFAP), proinflammatory factors (TNF-α, IL-1β, CXCL-1, CSF-1, NOS2, COX2) and decreased CNTF mRNA levels were found in Müller cells. However, pretreatment with R-7050 (a TNF-α receptor inhibitor) or anti-TNFR1 significantly abrogated the changes. Simultaneously, pretreatment with anti-TNFR2 slightly inhibited the expression of GFAP in MCM-incubated Müller cells. Meanwhile, anti-TNFR1 treatment reversed the increased expression of CSF-1 and IL-1β induced by TNF-α. Compared to the control groups, the phosphorylation of NF-κB P65, MAPK P38 and ERK1/2 in TNF-α-treated Müller cells was significantly increased. Nevertheless, pretreatment with anti-TNFR1 inhibited the phosphorylation of NF-κB P65 and MAPK p38, especially NF-κB P65. Additionally, pretreatment with Bay117082 (an NF-κB inhibitor) also significantly inhibited NF-κB P65 phosphorylation and GFAP expression. Moreover, anti-TNFR1 and Bay117082 treatment reduced NF-κB P65 phosphorylation of Müller cells induced by MCM. These results suggested that microglia-derived TNF-α served as a vital role in regulating Müller cells activation during retinal neurodegeneration.

Early manifestations and differential gene expression associated with photoreceptor degeneration in Prom1-deficient retina

Retinitis pigmentosa (RP) and macular dystrophy (MD) are characterized by gradual photoreceptor death in the retina and are often associated with genetic mutations, including those in the prominin-1 (Prom1) gene. Prom1-knockout (KO) mice recapitulate key features of these diseases including light-dependent retinal degeneration and constriction of retinal blood vessels. The mechanisms underlying such degeneration have remained unclear, however. We here analysed early events associated with retinal degeneration in Prom1-KO mice. We found that photoreceptor cell death and glial cell activation occur between 2 and 3 weeks after birth. Whereas gene expression was not affected at 2 weeks, the expression of several genes was altered at 3 weeks in the Prom1-KO retina, with the expression of that for endothelin-2 (Edn2) being markedly upregulated. Expression of Edn2 was also induced by light stimulation in Prom1-KO mice reared in the dark. Treatment with endothelin receptor antagonists attenuated photoreceptor cell death, gliosis and retinal vessel stenosis in Prom1-KO mice. Our findings thus reveal early manifestations of retinal degeneration in a model of RP/MD and suggest potential therapeutic agents for these diseases. This article has an associated First Person interview with the first author of the paper.

Short-term high-fat feeding exacerbates degeneration in retinitis pigmentosa by promoting retinal oxidative stress and inflammation

A high-fat diet (HFD) can induce hyperglycemia and metabolic syndromes that, in turn, can trigger visual impairment. To evaluate the acute effects of HFD feeding on retinal degeneration, we assessed retinal function and morphology, inflammatory state, oxidative stress, and gut microbiome in dystrophic retinal degeneration 10 (rd10) mice, a model of retinitis pigmentosa, fed an HFD for 2 to 3 wk. Short-term HFD feeding impaired retinal responsiveness and visual acuity and enhanced photoreceptor degeneration, microglial cell activation, and Müller cell gliosis. HFD consumption also triggered the expression of inflammatory and oxidative markers in rd10 retinas. Finally, an HFD caused gut microbiome dysbiosis, increasing the abundance of potentially proinflammatory bacteria. Thus, HFD feeding drives the pathological processes of retinal degeneration by promoting oxidative stress and activating inflammatory-related pathways. Our findings suggest that consumption of an HFD could accelerate the progression of the disease in patients with retinal degenerative disorders.

The TGFβ/Notch axis facilitates Müller cell-to-epithelial transition to ultimately form a chronic glial scar

Background

Contrasting with zebrafish, retinal regeneration from Müller cells (MCs) is largely limited in mammals, where they undergo reactive gliosis that consist of a hypertrophic response and ultimately results in vision loss. Transforming growth factor β (TGFβ) is essential for wound healing, including both scar formation and regeneration. However, targeting TGFβ may affect other physiological mechanisms, owing its pleiotropic nature. The regulation of various cellular activities by TGFβ relies on its interaction with other pathways including Notch. Here, we explore the interplay of TGFβ with Notch and how this regulates MC response to injury in zebrafish and mice. Furthermore, we aimed to characterize potential similarities between murine and human MCs during chronic reactive gliosis.

Methods

Focal damage to photoreceptors was induced with a 532 nm diode laser in TgBAC (gfap:gfap-GFP) zebrafish (ZF) and B6-Tg (Rlbp1-GFP) mice. Transcriptomics, immunofluorescence, and flow cytometry were employed for a comparative analysis of MC response to laser-induced injury between ZF and mouse. The laser-induced injury was paired with pharmacological treatments to inhibit either Notch (DAPT) or TGFβ (Pirfenidone) or TGFβ/Notch interplay (SIS3). To determine if the murine laser-induced injury model translates to the human system, we compared the ensuing MC response to human donors with early retinal degeneration.

Results

Investigations into injury-induced changes in murine MCs revealed TGFβ/Notch interplay during reactive gliosis. We found that TGFβ1/2 and Notch1/2 interact via Smad3 to reprogram murine MCs towards an epithelial lineage and ultimately to form a glial scar. Similar to what we observed in mice, we confirmed the epithelial phenotype of human Müller cells during gliotic response.

Conclusion

The study indicates a pivotal role for TGFβ/Notch interplay in tuning MC stemness during injury response and provides novel insights into the remodeling mechanism during retinal degenerative diseases.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-021-00482-z.

Retinal degeneration in mice lacking the cyclic nucleotide-gated channel subunit CNGA1

Cyclic nucleotide-gated (CNG) channels are important mediators in the transduction pathways of rod and cone photoreceptors. Native CNG channels are heterotetramers composed of homologous A and B subunits. Biallelic mutations in CNGA1 or CNGB1 genes result in autosomal recessive retinitis pigmentosa (RP). To investigate the pathogenic mechanism of CNG channel-associated retinal degeneration, we developed a mouse model of CNGA1 knock-out using CRISPR/Cas9 technology. We observed progressive retinal thinning and a concomitant functional deficit in vivo as typical phenotypes for RP. Immunofluorescence and TUNEL staining showed progressive degeneration in rods and cones. Moreover, microglial activation and oxidative stress damage occurred in parallel. RNA-sequencing analysis of the retinae suggested down-regulated synaptic transmission and phototransduction as early as 9 days postnatal, possibly inducing later photoreceptor degeneration. In addition, the down-regulated PI3K-AKT-mTOR pathway indicated upregulation of autophagic process, and chaperone-mediated autophagy was further shown to coincide with the time course of photoreceptor death. Taken together, our studies add to a growing body of research exploring the mechanisms of photoreceptor death during RP progression and provide a novel CNGA1 knockout mouse model for potential development of therapies.

Development, characterization, and ex vivo evaluation of an insert for the ocular administration of progesterone

Progesterone (PG) affords neuroprotection in degenerative diseases associated to oxidative stress, such as cataracts, age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa. The aim of this project was to develop ocular inserts for delivery of PG to the eye. Different inserts with PG in its composition were formulated and the insert with the best characteristics (59% polyvinyl alcohol, 39% polyvinylpyrrolidone K30 and 2% propylene glycol) was selected for ex vivo studies. Physical characteristics and drug release patterns of the insert were analysed. In vitro diffusion studies revealed a controlled diffusion of progesterone. Ex vivo experiments demonstrated similar trans-corneal and trans-scleral PG diffusion (corneal apparent permeability coefficient 6.46 ± 0.38 × 10^-7 cm/s and scleral apparent permeability coefficient 5.87 ± 1.18 × 10^-7 cm/s; mean ± SD; n = 5). However, the amount of PG accumulated in scleras was statistically higher than in corneas (30.07 ± 9.09 μg/cm² and 15.56 ± 4.36 μg/cm² respectively). The PG-loaded inserts (55.6 μg/cm²) were thin, translucent, showed no irritancy (HET-CAM test) and were elastic and robust, all suitable properties for its potential use in the treatment of several ocular diseases.

Serum progesterone and retinopathy in male patients with type 2 diabetes: A cross-sectional study

AIMS/INTRODUCTION

The aim of this study was to investigate the relationship between serum progesterone (P) and retinopathy in male patients with type 2 diabetes mellitus, and to investigate whether P is associated with its progression.

MATERIALS AND METHODS

A total of 1,376 male participants with type 2 diabetes mellitus were recruited from Affiliated Hospital of Medical College Qingdao University (Qingdao, China). Through logistic regression analysis after adjusting the potential confounding variation, the odds ratio (OR) and the corresponding 95% confidence interval related to the quartiles of progesterone were obtained.

RESULTS

According to the quartiles of P levels, the prevalence rate of diabetic retinopathy (DR) in the last quartile is obviously greater to other quartiles (52.5-34.9%, 31.9%, 37.5%, P < 0.001). Compared with those in the first quartile, the prevalence of DR for the last quartile had an OR of 1.85 in the non-proliferative diabetic retinopathy group, while the OR was 8.35 in the proliferative diabetic retinopathy group (P < 0.001, unadjusted model). When adjusted for age, body mass index, duration of type 2 diabetes mellitus, glycated hemoglobin, blood pressure and other variables, the ORs for DR in the fourth quartile were 2.13 (95% confidence interval 1.49-3.06) in the non-proliferative diabetic retinopathy group and 8.44 (95% confidence interval 2.69-26.43) in the proliferative diabetic retinopathy group (P < 0.001). The positive association between P and DR risk was independent in adjusted logistic regression.

CONCLUSIONS

High levels of serum progesterone are significantly associated with DR in male hospitalized patients. This could mean that a higher P level in men is a potential clinical factor to identify DR, and the causality remains to be further explored.

The Interaction Between Microglia and Macroglia in Glaucoma

Glaucoma, a neurodegenerative disease that leads to irreversible vision loss, is characterized by progressive loss of retinal ganglion cells (RGCs) and optic axons. To date, elevated intraocular pressure (IOP) has been recognized as the main phenotypic factor associated with glaucoma. However, some patients with normal IOP also have glaucomatous visual impairment and RGC loss. Unfortunately, the underlying mechanisms behind such cases remain unclear. Recent studies have suggested that retinal glia play significant roles in the initiation and progression of glaucoma. Multiple types of glial cells are activated in glaucoma. Microglia, for example, act as critical mediators that orchestrate the progression of neuroinflammation through pro-inflammatory cytokines. In contrast, macroglia (astrocytes and Müller cells) participate in retinal inflammatory responses as modulators and contribute to neuroprotection through the secretion of neurotrophic factors. Notably, research results have indicated that intricate interactions between microglia and macroglia might provide potential therapeutic targets for the prevention and treatment of glaucoma. In this review, we examine the specific roles of microglia and macroglia in open-angle glaucoma, including glaucoma in animal models, and analyze the interaction between these two cell types. In addition, we discuss potential treatment options based on the relationship between glial cells and neurons.

Rod Photoreceptor Neuroprotection in Dark-Reared Pde6brd10 Mice

Purpose

The purpose of this study was to test the hypothesis that anti-oxidant and / or anti-inflammation drugs that suppress rod death in cyclic light-reared Pde6brd10 mice are also effective in dark-reared Pde6brd10 mice.

Methods

In untreated dark-reared Pde6brd10 mice at post-natal (P) days 23 to 24, we measured the outer nuclear layer (ONL) thickness (histology) and dark-light thickness difference in external limiting membrane-retinal pigment epithelium (ELM-RPE) (optical coherence tomography [OCT]), retina layer oxidative stress (QUEnch-assiSTed [QUEST] magnetic resonance imaging [MRI]); and microglia/macrophage-driven inflammation (immunohistology). In dark-reared P50 Pde6brd10 mice, ONL thickness was measured (OCT) in groups given normal chow or chow admixed with methylene blue (MB) + Norgestrel (anti-oxidant, anti-inflammatory), or MB or Norgestrel separately.

Results

P24 Pde6brd10 mice showed no significant dark-light ELM-RPE response in superior and inferior retina consistent with high cGMP levels. Norgestrel did not significantly suppress the oxidative stress of Pde6brd10 mice that is only found in superior central outer retina of males at P23. Overt rod degeneration with microglia/macrophage activation was observed but only in the far peripheral superior retina in male and female P23 Pde6brd10 mice. Significant rod protection was measured in female P50 Pde6brd10 mice given 5 mg/kg/day MB + Norgestrel diet; no significant benefit was seen with MB chow or Norgestrel chow alone, nor in similarly treated male mice.

Conclusions

In early rod degeneration in dark-reared Pde6brd10 mice, little evidence is found in central retina for spatial associations among biomarkers of the PDE6B mutation, oxidative stress, and rod death; neuroprotection at P50 was limited to a combination of anti-oxidant/anti-inflammation treatment in a sex-specific manner.

Retinal Inflammation, Cell Death and Inherited Retinal Dystrophies

Inherited retinal dystrophies (IRDs) are a group of retinal disorders that cause progressive and severe loss of vision because of retinal cell death, mainly photoreceptor cells. IRDs include retinitis pigmentosa (RP), the most common IRD. IRDs present a genetic and clinical heterogeneity that makes it difficult to achieve proper treatment. The progression of IRDs is influenced, among other factors, by the activation of the immune cells (microglia, macrophages, etc.) and the release of inflammatory molecules such as chemokines and cytokines. Upregulation of tumor necrosis factor alpha (TNFα), a pro-inflammatory cytokine, is found in IRDs. This cytokine may influence photoreceptor cell death. Different cell death mechanisms are proposed, including apoptosis, necroptosis, pyroptosis, autophagy, excessive activation of calpains, or parthanatos for photoreceptor cell death. Some of these cell death mechanisms are linked to TNFα upregulation and inflammation. Therapeutic approaches that reduce retinal inflammation have emerged as useful therapies for slowing down the progression of IRDs. We focused this review on the relationship between retinal inflammation and the different cell death mechanisms involved in RP. We also reviewed the main anti-inflammatory therapies for the treatment of IRDs.

Suppression of cGMP-Dependent Photoreceptor Cytotoxicity With Mycophenolate Is Neuroprotective in Murine Models of Retinitis Pigmentosa

Purpose

To determine the effect of mycophenolate mofetil (MMF) on retinal degeneration on two mouse models of retinitis pigmentosa.

Methods

Intraperitoneal injections of MMF were administered daily in rd10 and c57 mice starting at postoperative day 12 (P12) and rd1 mice starting at P8. The effect of MMF was assessed with optical coherence tomography, immunohistochemistry, electroretinography, and OptoMotry. Whole retinal cyclic guanosine monophosphate (cGMP) and mycophenolic acid levels were quantified with mass spectrometry. Photoreceptor cGMP cytotoxicity was evaluated with cell counts of cGMP immunostaining.

Results

MMF treatment significantly delays the onset of retinal degeneration and cGMP-dependent photoreceptor cytotoxicity in rd10 and rd1 mice, albeit a more modest effect in the latter. In rd10 mice, treatment with MMF showed robust preservation of the photoreceptors up to P22 with associated suppression of cGMP immunostaining and microglial activation; The neuroprotective effect diminished after P22, but outer retinal thickness was still significantly thicker by P35 and OptoMotry response was significantly better up to P60. Whereas cGMP immunostaining of the photoreceptors were present in rd10 and rd1 mice, hyperphysiological whole retinal cGMP levels were observed only in rd1 mice.

Conclusions

Early treatment with MMF confers potent neuroprotection in two animal models of RP by suppressing the cGMP-dependent common pathway for photoreceptor cell death. The neuroprotective effect of MMF on cGMP-dependent cytotoxicity occurs independently of the presence of hyperphysiological whole retinal cGMP levels. Thus our data suggest that MMF may be an important new class of neuroprotective agent that could be useful in the treatment of patients with RP.

17β-Oestradiol Attenuates the Photoreceptor Apoptosis in Mice with Retinitis Pigmentosa by Regulating N-myc Downstream Regulated Gene 2 Expression

Retinitis pigmentosa (RP) is a heterogeneous group of retinal degenerative diseases in which the final pathological feature is photoreceptor cell apoptosis. Currently, the pathogenesis of RP remains poorly understood and therapeutics are ineffective. 17β-Oestradiol (βE2) is universally acknowledged as a neuroprotective factor in neurodegenerative diseases and has manifested neuroprotective effects in a light-induced retinal degeneration model. Recently, we identified N-myc downstream regulated gene 2 (NDRG2) suppression as a molecular marker of mouse retinal photoreceptor-specific cell death. βE2 has also been reported to regulate NDRG2 in salivary acinar cells. Therefore, in this study, we investigated whether βE2 plays a protective role in RP and regulates NDRG2 in photoreceptor cells. To this end, we generated RP models and observed that βE2 not only reduced the apoptosis of photoreceptor cells, but also restored the level of NDRG2 expression in RP models. Then, we showed that siNDRG2 inhibits the anti-apoptotic effect of βE2 on photoreceptor cells in a cellular RP model. Subsequently, we used a classic oestrogen receptor (ER) antagonist to attenuate the effects of βE2, suggesting that βE2 exerted its effects on RP models via the classic ERs. In addition, we performed a bioinformatics analysis, and the results indicated that the reported oestrogen response element (ERE) sequence is present in the promoter region of the mouse NDRG2 gene. Overall, our results suggest that βE2 attenuated the apoptosis of photoreceptor cells in RP models by maintaining NDRG2 expression via a classic ER-mediated mechanism.

Sectoral activation of glia in an inducible mouse model of autosomal dominant retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of blinding disorders caused by diverse mutations, including in rhodopsin (RHO). Effective therapies have yet to be discovered. The I307N Rho mouse is a light-inducible model of autosomal dominant RP. Our purpose was to describe the glial response in this mouse model to educate future experimentation. I307N Rho mice were exposed to 20,000 lx of light for thirty minutes to induce retinal degeneration. Immunofluorescence staining of cross-sections and flat-mounts was performed to visualize the response of microglia and Müller glia. Histology was correlated with spectral-domain optical coherence tomography imaging (SD-OCT). Microglia dendrites extended between photoreceptors within two hours of induction, withdrew their dendrites between twelve hours and one day, appeared ameboid by three days, and assumed a ramified morphology by one month. Glial activation was more robust in the inferior retina and modulated across the boundary of light damage. SD-OCT hyper-reflectivity overlapped with activated microglia. Finally, microglia transiently adhered to the RPE before which RPE cells appeared dysmorphic. Our data demonstrate the spatial and temporal pattern of glial activation in the I307N Rho mouse, and correlate these patterns with SD-OCT images, assisting in interpretation of SD-OCT images in preclinical models and in human RP.

Novel Insights into Beta 2 Adrenergic Receptor Function in the rd10 Model of Retinitis Pigmentosa

Background: In retinitis pigmentosa (RP), inherited rod death is followed by cone loss and blindness. Why cones die is still a matter of consideration. Here, we investigate the pathogenic role of the sympathetic transmission in the rd10 mouse model of RP. Methods: Retinal levels of beta adrenergic receptor (BAR) 2 and norepinephrine (NE) were measured. After administration of the BAR1/2 blocker propranolol or the hypoxia-inducible factor (HIF)-1 activator dimethyloxalylglycine (DMOG), retinal levels of HIF-1α, BAR2 or proteins involved in BAR2 desensitization were also measured. In DMOG treated mice, expression and localization of BAR2, inflammatory markers and cone arrestin were determined. Finally, rd10 mice were subjected to electroretinogram (ERG) analysis to assess rod and cone function. Results: In the rd10 retina, BAR2 overexpression and NE accumulation were found, with BAR2 immunoreactivity localized to Müller cells. BAR2 overexpression was likely due to desensitization defects. Upregulated levels of BAR2 were drastically reduced by propranolol that also restored desensitization defects. Due to the low level of HIF-1 consequent to the hyperoxic environment in the rd10 retina, we hypothesized a link between HIF-1 and BAR2. HIF-1α stabilization with DMOG resulted in i. increased HIF-1α accumulation, ii. decreased BAR2 levels, iii. restored desensitization processes, iv. reduced expression of inflammatory markers and v. increased cone survival without improved retinal function. Conclusions: Our results support a pathogenic role of the sympathetic system in RP that might help to understand why rd10 mice show a positive response to BAR blockers.

Selective Histone Deacetylase 6 Inhibitors Restore Cone Photoreceptor Vision or Outer Segment Morphology in Zebrafish and Mouse Models of Retinal Blindness

Blindness arising from retinal or macular degeneration results in significant social, health and economic burden. While approved treatments exist for neovascular (‘wet’) age-related macular degeneration, new therapeutic targets/interventions are needed for the more prevalent atrophic (‘dry’) form of age-related macular degeneration. Similarly, in inherited retinal diseases, most patients have no access to an effective treatment. Although macular and retinal degenerations are genetically and clinically distinct, common pathological hallmarks can include photoreceptor degeneration, retinal pigment epithelium atrophy, oxidative stress, hypoxia and defective autophagy. Here, we evaluated the potential of selective histone deacetylase 6 inhibitors to preserve retinal morphology or restore vision in zebrafish atp6v0e1^–/– and mouse rd10 models. Histone deacetylase 6 inhibitor, tubastatin A-treated atp6v0e1^–/– zebrafish show marked improvement in photoreceptor outer segment area (44.7%, p = 0.027) and significant improvement in vision (8-fold, p ≤ 0.0001). Tubastatin A-treated rd10/rd10 retinal explants show a significantly (p = 0.016) increased number of outer-segment labeled cone photoreceptors. In vitro, ATP6V0E1 regulated HIF-1α activity, but significant regulation of HIF-1α by histone deacetylase 6 inhibition in the retina was not detected. Proteomic profiling identified ubiquitin-proteasome, phototransduction, metabolism and phagosome as pathways, whose altered expression correlated with histone deacetylase 6 inhibitor mediated restoration of vision.

Intravitreal administration of adalimumab delays retinal degeneration in rd10 mice

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by the progressive and irreversible loss of vision. We previously found that intraperitoneal administration of Adalimumab, a monoclonal anti-TNFα antibody, slowed down retinal degeneration in the murine model of RP, the rd10 mice. The aims of this study were to improve its neuroprotective effect and to deepen understanding of the molecular mechanisms involved in this effect. We analyzed (i) the in vitro effect of Adalimumab on the TNFα-mediated cell death in retinal cells; (ii) the effect of a single intravitreal injection of Adalimumab on retinal degeneration in rd10 mice at postnatal day (P) 23. In vitro studies showed that TNFα induced caspase and poly ADP ribose polymerase (PARP) activation, downregulation of (kinase receptor-interacting protein 1) RIPK1 and upregulation of RIPK3 in retinal cells. Adalimumab reduced cell death probably through the inhibition of caspase 3 activation. In vivo studies suggested that PARP and NLRP3 inflammasome are mainly activated and to a lesser extent caspase-dependent mechanisms in rd10 retinas at P23. Necroptosis seems to be inhibited by the downregulation of RIPK1. Adalimumab prevented from retinal degeneration without affecting caspase -dependent mechanisms but decreasing PARP activation, microglia activation as well as NLRP3 inflammasome.

Retinitis Pigmentosa and Retinal Degenerations: Deciphering Pathways and Targets for Drug Discovery and Development

Inherited retinal diseases (IRDs) are a group of retinopathies generally caused by genetic mutations. Retinitis pigmentosa (RP) represents one of the most studied IRDs. RP leads to intense vision loss or blindness resulting from the degeneration of photoreceptor cells. To date, RP is mainly treated with palliative supplementation of vitamin A and retinoids, gene therapies, or surgical interventions. Therefore, a pharmacologically based therapy is an urgent need requiring a medicinal chemistry approach, to validate molecular targets able to deal with retinal degeneration. This Review aims at outlining the recent research efforts in identifying new drug targets for RP, especially focusing on the neuroprotective role of the Wnt/β-catenin/GSK3β pathway and apoptosis modulators (in particular PARP-1) but also on growth factors such as VEGF and BDNF. Furthermore, the role of spatiotemporally expressed G protein-coupled receptors (GPR124) in the retina and the emerging function of histone deacetylase inhibitors in promoting retinal neuroprotection will be discussed.

Coordinated Intervention of Microglial and Müller Cells in Light-Induced Retinal Degeneration

Purpose

To analyze the role of microglial and Müller cells in the formation of rings of photoreceptor degeneration caused by phototoxicity.

Methods

Two-month-old Sprague-Dawley rats were exposed to light and processed 1, 2, or 3 months later. Retinas were dissected as whole-mounts, immunodetected for microglial cells, Müller cells, and S- and L/M-cones and analyzed using fluorescence, thunder imaging, and confocal microscopy. Cone populations were automatically counted and isodensity maps constructed to document cone topography.

Results

Phototoxicity causes a significant progressive loss of S- and L/M-cones of up to 68% and 44%, respectively, at 3 months after light exposure (ALE). One month ALE, we observed rings of cone degeneration in the photosensitive area of the superior retina. Two and 3 months ALE, these rings had extended to the central and inferior retina. Within the rings of cone degeneration, there were degenerating cones, often activated microglial cells, and numerous radially oriented processes of Müller cells that showed increased expression of intermediate filaments. Between 1 and 3 months ALE, the rings coalesced, and at the same time the microglial cells resumed a mosaic-like distribution, and there was a decrease of Müller cell gliosis at the areas devoid of cones.

Conclusions

Light-induced photoreceptor degeneration proceeds with rings of cone degeneration, as observed in inherited retinal degenerations in which cone death is secondary to rod degeneration. The spatiotemporal relationship of cone death microglial cell activation and Müller cell gliosis within the rings of cone degeneration suggests that, although both glial cells are involved in the formation of the rings, they may have coordinated actions and, while microglial cells may be more involved in photoreceptor phagocytosis, Müller cells may be more involved in cone and microglial cell migration, retinal remodeling and glial seal formation.

A New Cerkl Mouse Model Generated by CRISPR-Cas9 Shows Progressive Retinal Degeneration and Altered Morphological and Electrophysiological Phenotype

Purpose

Close to 100 genes cause retinitis pigmentosa, a Mendelian rare disease that affects 1 out of 4000 people worldwide. Mutations in the ceramide kinase-like gene (CERKL) are a prevalent cause of autosomal recessive cause retinitis pigmentosa and cone-rod dystrophy, but the functional role of this gene in the retina has yet to be fully determined. We aimed to generate a mouse model that resembles the phenotypic traits of patients carrying CERKL mutations to undertake functional studies and assay therapeutic approaches.

Methods

The Cerkl locus has been deleted (around 97 kb of genomic DNA) by gene editing using the CRISPR-Cas9 D10A nickase. Because the deletion of the Cerkl locus is lethal in mice in homozygosis, a double heterozygote mouse model with less than 10% residual Cerkl expression has been generated. The phenotypic alterations of the retina of this new model have been characterized at the morphological and electrophysiological levels.

Results

This CerklKD/KO model shows retinal degeneration, with a decreased number of cones and progressive photoreceptor loss, poorly stacked photoreceptor outer segment membranes, defective retinal pigment epithelium phagocytosis, and altered electrophysiological recordings in aged retinas.

Conclusions

To our knowledge, this is the first Cerkl mouse model to mimic many of the phenotypic traits, including the slow but progressive retinal degeneration, shown by human patients carrying CERKL mutations. This useful model will provide unprecedented insights into the retinal molecular pathways altered in these patients and will contribute to the design of effective treatments.

Diverse Signaling by TGFβ Isoforms in Response to Focal Injury is Associated with Either Retinal Regeneration or Reactive Gliosis

Müller cells may have stem cell-like capability as they regenerate photoreceptor loss upon injury in some vertebrates, but not in mammals. Indeed, mammalian Müller cells undergo major cellular and molecular changes summarized as reactive gliosis. Transforming growth factor beta (TGFβ) isoforms are multifunctional cytokines that play a central role, both in wound healing and in tissue repair. Here, we studied the role of TGFβ isoforms and their signaling pathways in response to injury induction during tissue regeneration in zebrafish and scar formation in mouse. Our transcriptome analysis showed a different activation of canonical and non-canonical signaling pathways and how they shaped the injury response. In particular, TGFβ3 promotes retinal regeneration via Smad-dependent canonical pathway upon regulation of junb gene family and mycb in zebrafish Müller cells. However, in mice, TGFβ1 and TGFβ2 evoke the p38MAPK signaling pathway. The activation of this non-canonical pathway leads to retinal gliosis. Thus, the regenerative versus reparative effect of the TGFβ pathway observed may rely on the activation of different signaling cascades. This provides one explanation of the different injury response in zebrafish and mouse retina.

Keep an eye on adenosine: Its role in retinal inflammation

Adenosine is an endogenous purine nucleoside ubiquitously distributed throughout the body that interacts with G protein-coupled receptors, classified in four subtypes: A₁R, A_2AR, A_2BR and A₃R. Among the plethora of functions of adenosine, it has been increasingly recognized as a key mediator of the immune response. Neuroinflammation is a feature of chronic neurodegenerative diseases and contributes to the pathophysiology of several retinal degenerative diseases. Animal models of retinal diseases are helping to elucidate the regulatory roles of adenosine receptors in the development and progression of those diseases. Mounting evidence demonstrates that the adenosinergic system is altered in the retina during pathological conditions, compromising retinal physiology. This review focuses on the roles played by adenosine and the elements of the adenosinergic system (receptors, enzymes, transporters) in the neuroinflammatory processes occurring in the retina. An improved understanding of the molecular and cellular mechanisms of the signalling pathways mediated by adenosine underlying the onset and progression of retinal diseases will pave the way towards the identification of new therapeutic approaches.

Norgestrel, a Progesterone Analogue, Promotes Significant Long-Term Neuroprotection of Cone Photoreceptors in a Mouse Model of Retinal Disease

Purpose

Retinitis pigmentosa (RP) refers to a group of inherited blinding retinal diseases, whereby the death of mutated rod photoreceptors is followed closely by the death of cone photoreceptors. Cone cell death can be hugely debilitating as color/daytime vision becomes impaired. Thus, treatments that are effective against cone cell death are urgently needed. Our research has been working toward development of a neuroprotective treatment for RP. We have previously demonstrated significant neuroprotective properties of norgestrel, a progesterone analogue, in the mouse retina. The current study further investigates the potential of norgestrel as a treatment for RP, with a focus on long-term preservation of cone photoreceptors.

Methods

Using the well-established rd10 mouse model of RP, we administered a norgestrel-supplemented diet at postnatal day (P)30, following widespread loss of rod photoreceptors and at the outset of cone degeneration. We subsequently assessed cone cell morphology and retinal function at P50, P60, and P80, using immunohistochemistry, electroretinograph recordings, and optomotor testing.

Results

While cone cell degeneration was widespread in the untreated rd10 retina, we observed profound preservation of cone photoreceptor morphology in the norgestrel-treated mice for at least 50 days, out to P80. This was demonstrated by up to 28-fold more cone arrestin-positive photoreceptors. This protection transpired to functional preservation at all ages.

Conclusions

This work presents norgestrel as an incredibly promising long-term neuroprotective compound for the treatment of RP. Crucially, norgestrel could be used in the mid-late stages of the disease to protect remaining cone cells and help preserve color/daytime vision.

Glucocorticoid and progesterone mechanisms in photoreceptor survival

Death of retinal photoreceptors is the basis of prevalent blinding diseases. Since steroids might have a therapeutic role in retinal degenerations, we compared the protective effects of dexamethasone and progesterone on photoreceptor death induced by mifepristone and light exposure. Therefore, we studied the effective protection doses for each steroid in the two models. In addition, we analyzed changes in the levels of pro- and antiapoptotic molecules, glucocorticoid receptors α and β (GRα and GRβ), and rhodopsin under conditions of successful protection and photoreceptor survival. Mifepristone and light exposure selectively damaged photoreceptors. In light exposed retinas, photoreceptors mainly disappeared in the dorsotemporal region, while mifepristone produced a uniform damage. Dexamethasone and progesterone, at the same dose of 4 mg/kg/day for 2 days, preserved over 88% photoreceptor nuclei in both models. Assessment of cell death regulators showed that, in control retinas, both steroids activated BCL-X_L, a prosurvival molecule, and decreased BID, a proapoptotic regulator. After steroid treatment of damaged retinas, BCL-X_L, BCL2 and BAX showed characteristic patterns depending on the use of dexamethasone or progesterone on mifepristone or light exposed retinas. By contrast, BID decreased with any injury-steroid combination. Changes in GRα or GRβ levels did not correlate with survival but were consistent with a mechanism of ligand induced downregulation of receptor expression. GRβ might be upregulated by progesterone. Both dexamethasone and progesterone increased retinal rhodopsin stores, suggesting a link between photoreceptor protection and transduction pathways. Results show that dexamethasone and progesterone induced comparable but not identical protection responses in each model.

Systemic knockout of Tspo in mice does not affect retinal morphology, function and susceptibility to degeneration

Translocator protein (18 kDa) (TSPO) is a mitochondrial protein expressed by reactive microglia and astrocytes at the site of neuronal injury. Although TSPO function has not been fully determined, synthetic TSPO ligands have beneficial effects on different pathologies of the central nervous system, including the retina. Here, we studied the pattern of Tspo expression in the aging human retina and in two mouse models of retinal degeneration. Using a newly generated Tspo-KO mouse, we investigated the impact of the lack of TSPO on retinal morphology, function and susceptibility to degeneration. We show that TSPO was expressed in both human and mouse retina and retinal pigment epithelium (RPE). Tspo was induced in the mouse retina upon degeneration, but constitutively expressed in the RPE. Similarly, TSPO expression levels in healthy human retina and RPE were not differentially regulated during aging. Tspo-KO mice had normal retinal morphology and function up to 48 weeks of age. Photoreceptor loss caused either by exposure to excessive light levels or by a mutation in the phosphodiesterase 6b gene was not affected by the absence of Tspo. The reactivity states of retinal mononuclear phagocytes following light-damage were comparable in Tspo-KO and control mice. Our data suggest that lack of endogenous TSPO does not directly influence the magnitude of photoreceptor degeneration or microglia activation in these two models of retinal degeneration. We therefore hypothesize that the interaction of TSPO with its ligands may be required to modulate disease progression.

The urokinase-type plasminogen activator system as drug target in retinitis pigmentosa: New pre-clinical evidence in the rd10 mouse model

Retinitis pigmentosa (RP) is characterized by progressive loss of vision due to photoreceptor degeneration leading to secondary inflammation. The urokinase-type plasminogen activator (uPA) system contributes to retinal inflammation, but its role in RP is unknown. In the rd10 mouse model of RP, we addressed this question with the use of the peptide UPARANT designed to interact with the uPA system. UPARANT was systemically administered from post-natal day (PD) 10 to PD30 when its efficacy in RP rescue was investigated using electroretinographic recordings, Western blot and immunocytochemistry. Temporal profile of protein expression in the uPA system was also investigated. UPARANT reduced both Müller cell gliosis and up-regulated levels of inflammatory markers and exerted major anti-apoptotic effects without influencing the autophagy cascade. Rescue from retinal cell degeneration was accompanied by improved retinal function. No scotopic phototransduction was rescued in the UPARANT-treated animals as determined by the kinetic analysis of rod-mediated a-waves and confirmed by rod photoreceptor markers. In contrast, the cone photopic b-wave was recovered and its rescue was confirmed in the whole mounts using cone arrestin antibody. Investigation of the uPA system regulation over RP progression revealed extremely low levels of uPA and its receptor uPAR both of which were recovered by HIF-1α stabilization indicating that HIF-1 regulates the expression of the uPA/uPAR gene in the retina. Ameliorative effects of UPARANT were likely to occur through an inhibitory action on up-regulated activity of the αvβ3 integrin/Rac1 pathway that was suggested as a novel target for the development of therapeutic approaches against RP.

Histopathologic Assessment of Optic Nerves and Retina From a Patient With Chronically Implanted Argus II Retinal Prosthesis System

Purpose

To characterize histologic changes in the optic nerve and the retina of an end-stage retinitis pigmentosa (RP) patient after long-term implantation with the Argus II retinal prosthesis system.

Methods

Serial cross sections from the patient's both eyes were collected postmortem 6 years after implantation. Optic nerve from both eyes were morphometrically analyzed and compared. Retina underneath and outside the array was analyzed and compared with corresponding regions in the fellow eye.

Results

Although the optic nerve of the implant eye demonstrated significantly more overall atrophy than the fellow eye (P < 0.01), the temporal quadrant that retinotopically corresponded to the location of the array did not show additional damage. The total neuron count of the macular area was not significantly different between the two eyes, but the tack locations and their adjacent areas showed significantly fewer neurons than other perimacular areas. There was an increased expression of glial fibrillary acidic protein (GFAP) throughout the retina in the implant eye versus the fellow eye, but there was no significant difference in the cellular retinaldehyde-binding protein (CRALBP) expression. Except for the revision tack site, no significant increase of inflammatory reaction was detected in the implant eye.

Conclusion

Long-term implantation and electrical stimulation with an Argus II retinal prosthesis system did not result in significant tissue damage that could be detected by a morphometric analysis.

Translational Relevance

This study supports the long-term safety of the Argus II device and encourages further development of bioelectronics devices at the retina-machine interface.

Progesterone anti-inflammatory properties in hereditary retinal degeneration

The interactions between steroid gonadal hormones and the retina (a part of the visual system and the central nervous system (CNS)) have received limited attention and beneficial effects of these hormones in retinal diseases is controversial. Retinitis pigmentosa (RP) is the most common cause of retinal hereditary blindness and to date no treatment is available. However, results regarding the effects of progesterone on the progression of RP are promising. With the idea of demonstrating if the progesterone retinal protection in RP is related to its possible anti-inflammatory properties, we have administered orally progesterone to rd10 mice, an animal model of RP. We observed that progesterone decreased photoreceptors cell death, reactive gliosis and the increase in microglial cells caused by RP. We also examined the expression of neuronal and inducible nitric oxide synthase (nNOS and iNOS), the enzyme responsible for NO production. The results demonstrated a decrease in nNOS expression only in control mice treated with progesterone. Inflammation has been related with an increase in lipid peroxidation. Noticeably progesterone administration was able to diminish retinal malondialdehyde (MDA, a lipid peroxidation product) concentrations in rd10 mice. Altogether, we can conclude that progesterone could be a good therapeutic option not only in RP but also for other retinal diseases that have been associated with inflammation and lipid peroxidation.

Progesterone, Lipoic Acid, and Sulforaphane as Promising Antioxidants for Retinal Diseases: A Review

Oxidative stress has been documented to be a key factor in the cause and progression of different retinal diseases. Oxidative cellular unbalance triggers a sequence of reactions which prompt cell degeneration and retinal dysfunction, both hallmarks of several retinal pathologies. There is no effective treatment, yet, for many retinal diseases. Antioxidant treatment have been pointed out to be an encouraging palliative treatment; the beneficial effects documented involve slowing the progression of the disease, a reduction of cell degeneration, and improvement of retinal functions. There is a vast information corpus on antioxidant candidates. In this review, we expose three of the main antioxidant treatments, selected for their promising results that has been reported to date. Recently, the sulforaphane, an isothiocyanate molecule, has been unveiled as a neuroprotective candidate, by its antioxidant properties. Progesterone, a neurosteroid has been proposed to be a solid and effective neuroprotective agent. Finally, the lipoic acid, an organosulfur compound, is a well-recognized antioxidant. All of them, have been tested and studied on different retinal disease models. In this review, we summarized the published results of these works, to offer a general view of the current antioxidant treatment advances, including the main effects and mechanisms described.

The agonistic TSPO ligand XBD173 attenuates the glial response thereby protecting inner retinal neurons in a murine model of retinal ischemia

BACKGROUND

Ligand-driven modulation of the mitochondrial translocator protein 18 kDa (TSPO) was recently described to dampen the neuroinflammatory response of microglia in a retinal light damage model resulting in protective effects on photoreceptors. We characterized the effects of the TSPO ligand XBD173 in the postischemic retina focusing on changes in the response pattern of the major glial cell types of the retina-microglia and Müller cells.

METHODS

Retinal ischemia was induced by increasing the intraocular pressure for 60 min followed by reperfusion of the tissue in mice. On retinal cell types enriched via immunomagnetic separation expression analysis of TSPO, its ligand diazepam-binding inhibitor (DBI) and markers of glial activation were performed at transcript and protein level using RNA sequencing, qRT-PCR, lipid chromatography-mass spectrometry, and immunofluorescent labeling. Data on cell morphology and numbers were assessed in retinal slice and flatmount preparations. The retinal functional integrity was determined by electroretinogram recordings.

RESULTS

We demonstrate that TSPO is expressed by Müller cells, microglia, vascular cells, retinal pigment epithelium (RPE) of the healthy and postischemic retina, but only at low levels in retinal neurons. While an alleviated neurodegeneration upon XBD173 treatment was found in postischemic retinae as compared to vehicle controls, this neuroprotective effect of XBD173 is mediated putatively by its action on retinal glia. After transient ischemia, TSPO as a marker of activation was upregulated to similar levels in microglia as compared to their counterparts in healthy retinae irrespective of the treatment regimen. However, less microglia were found in XBD173-treated postischemic retinae at 3 days post-surgery (dps) which displayed a more ramified morphology than in retinae of vehicle-treated mice indicating a dampened microglia activation. Müller cells, the major retinal macroglia, show upregulation of the typical gliosis marker GFAP. Importantly, glutamine synthetase was more stably expressed in Müller glia of XBD173-treated postischemic retinae and homeostatic functions such as cellular volume regulation typically diminished in gliotic Müller cells remained functional.

CONCLUSIONS

In sum, our data imply that beneficial effects of XBD173 treatment on the postischemic survival of inner retinal neurons were primarily mediated by stabilizing neurosupportive functions of glial cells.

Immunological Considerations for Retinal Stem Cell Therapy

There is an increasing effort toward generating replacement cells for neuronal application due to the nonregenerative nature of these tissues. While much progress has been made toward developing methodologies to generate these cells, there have been limited improvements in functional restoration. Some of these are linked to the degenerative and often nonreceptive microenvironment that the new cells need to integrate into. In this chapter, we will focus on the status and role of the immune microenvironment of the retina during homeostasis and disease states. We will review changes in both innate and adaptive immunity as well as the role of immune rejection in stem cell replacement therapies. The chapter will end with a discussion of immune-modulatory strategies that have helped to ameliorate these effects and could potentially improve functional outcome for cell replacement therapies for the eye.

Neuroprotective strategies for retinal disease

Diseases that affect the eye, including photoreceptor degeneration, diabetic retinopathy, and glaucoma, affect 11.8 million people in the US, resulting in vision loss and blindness. Loss of sight affects patient quality of life and puts an economic burden both on individuals and the greater healthcare system. Despite the urgent need for treatments, few effective options currently exist in the clinic. Here, we review research on promising neuroprotective strategies that promote neuronal survival with the potential to protect against vision loss and retinal cell death. Due to the large number of neuroprotective strategies, we restricted our review to approaches that we had direct experience with in the laboratory. We focus on drugs that target survival pathways, including bile acids like UDCA and TUDCA, steroid hormones like progesterone, therapies that target retinal dopamine, and neurotrophic factors. In addition, we review rehabilitative methods that increase endogenous repair mechanisms, including exercise and electrical stimulation therapies. For each approach, we provide background on the neuroprotective strategy, including history of use in other diseases; describe potential mechanisms of action; review the body of research performed in the retina thus far, both in animals and in humans; and discuss considerations when translating each treatment to the clinic and to the retina, including which therapies show the most promise for each retinal disease. Despite the high incidence of retinal diseases and the complexity of mechanisms involved, several promising neuroprotective treatments provide hope to prevent blindness. We discuss attractive candidates here with the goal of furthering retinal research in critical areas to rapidly translate neuroprotective strategies into the clinic.