Receptor interacting protein kinase mediates necrotic cone but not rod cell death in a mouse model of inherited degeneration

RIP1 inhibition protects retinal ganglion cells in glaucoma models of ocular injury

Receptor-interacting protein 1 (RIP1, RIPK1) is a critical mediator of multiple signaling pathways that promote inflammatory responses and cell death. The kinase activity of RIP1 contributes to the pathogenesis of a number of inflammatory and neurodegenerative diseases. However, the role of RIP1 in retinopathies remains unclear. This study demonstrates that RIP1 inhibition protects retinal ganglion cells (RGCs) in preclinical glaucoma models. Genetic inactivation of RIP1 improves RGC survival and preserves retinal function in the preclinical glaucoma models of optic nerve crush (ONC) and ischemia-reperfusion injury (IRI). In addition, the involvement of necroptosis in ONC and IRI glaucoma models was examined by utilizing RIP1 kinase-dead (RIP1-KD), RIP3 knockout (RIP3-KO), and MLKL knockout (MLKL-KO) mice. The number of RGCs, retinal thickness, and visual acuity were rescued in RIP1-kinase-dead (RIP1-KD) mice in both models, while wild-type (WT) mice experienced significant retinal thinning, RGC loss, and vision impairment. RIP3-KO and MLKL-KO mice showed moderate protective effects in the IRI model and limited in the ONC model. Furthermore, we confirmed that a glaucoma causative mutation in optineurin, OPTN-E50K, sensitizes cells to RIP1-mediated inflammatory cell death. RIP1 inhibition reduces RGC death and axonal degeneration following IRI in mice expressing OPTN-WT and OPTN-E50K variant mice. We demonstrate that RIP1 inactivation suppressed microglial infiltration in the RGC layer following glaucomatous damage. Finally, this study highlights that human glaucomatous retinas exhibit elevated levels of TNF and RIP3 mRNA and microglia infiltration, thus demonstrating the role of neuroinflammation in glaucoma pathogenesis. Altogether, these data indicate that RIP1 plays an important role in modulating neuroinflammation and that inhibiting RIP1 activity may provide a neuroprotective therapy for glaucoma.

Mechanisms of Rhodopsin-Related Inherited Retinal Degeneration and Pharmacological Treatment Strategies

Retinitis pigmentosa (RP) is a hereditary disease characterized by progressive vision loss ultimately leading to blindness. This condition is initiated by mutations in genes expressed in retinal cells, resulting in the degeneration of rod photoreceptors, which is subsequently followed by the loss of cone photoreceptors. Mutations in various genes expressed in the retina are associated with RP. Among them, mutations in the rhodopsin gene (RHO) are the most common cause of this condition. Due to the involvement of numerous genes and multiple mutations in a single gene, RP is a highly heterogeneous disease making the development of effective treatments particularly challenging. The progression of this disease involves complex cellular responses to restore cellular homeostasis, including the unfolded protein response (UPR) signaling, autophagy, and various cell death pathways. These mechanisms, however, often fail to prevent photoreceptor cell degradation and instead contribute to cell death under certain conditions. Current research focuses on the pharmacological modulation of the components of these pathways and the direct stabilization of mutated receptors as potential treatment strategies. Despite these efforts, the intricate interplay between these mechanisms and the diverse causative mutations involved has hindered the development of effective treatments. Advancing our understanding of the interactions between photoreceptor cell death mechanisms and the specific genetic mutations driving RP is critical to accelerate the discovery and development of therapeutic strategies for this currently incurable disease.

Mechanisms of retinal photoreceptor loss in spontaneously hypertensive rats

Retinal neurodegenerative diseases, including hypertensive retinopathy, involve progressive damage to retinal neurons, leading to visual impairment. In this study, we investigated the pathological mechanisms underlying retinal neurodegeneration in spontaneously hypertensive rats (SHR), using Wistar Kyoto (WKY) rats as normotensive controls. We observed that SHR exhibited significantly higher blood pressure and decreased retinal thickness, indicating retinal neurodegeneration. Molecular tests including quantitative real-time polymerase chain reaction, immunoblot, and immunofluorescent staining showed elevated levels of the pro-inflammatory cytokine tumor necrosis factor-α, apoptotic markers (Fas, FasL, caspase-8, active caspase-3, and cleaved poly (ADP-ribose) polymerase), and necroptotic markers (receptor-interacting protein kinase-1 and -3) in SHR retinas. Additionally, we found elevated transforming growth factor-β (TGF-β) levels in the retinal pigment epithelium (RPE) of SHR, with a decrease in lecithin retinol acyltransferase (LRAT), which regulates retinoid metabolism and photoreceptor health. In human RPE cells (ARPE-19), TGF-β administration suppressed mRNA and protein levels of LRAT; and vactosertib, a selective inhibitor of TGF-β receptor kinase type 1, reversed the effect of TGF-β. These findings suggest that hypertension-induced retinal neurodegeneration involves inflammation, apoptosis, necroptosis, and disrupted retinoid metabolism, providing potential therapeutic targets for hypertensive retinopathy.

Progression of retinitis pigmentosa on static perimetry, optical coherence tomography, and fundus autofluorescence

In retinitis pigmentosa (RP), photoreceptor degeneration leads to progressive visual field loss and visual impairment. Several therapeutic trials are ongoing aiming to establish effective treatments. Although functional evaluations are commonly used in clinical trials, residual ellipsoid zone (EZ) measurement on optical coherence tomography has been shown to be more sensitive to detect disease progression. Establishment of sensitive outcome measurement is essential to develop new therapeutic strategies. In the current study, we evaluated the progression rates of the disease in 76 eyes of 76 patients with RP, using the residual EZ length, ring-shaped macular hyperautofluorescent (AF), and visual field. Decrease rates measured by the residual EZ area and by the hyper-AF ring area were strongly positively correlated (P < 0.0001, r = 0.71). The reduction rates of the residual EZ length and hyper-AF ring radius were constant regardless of their baseline measurements. Faster annual reduction rates of the hyper-AF ring area or radius were significantly correlated with faster visual field progression (P = 0.03, r = 0.25 and P = 0.004, r = 0.33, respectively). These findings support the usage of morphological measurements such as EZ or hyper-AF ring measurements as outcome measurement for future clinical trials for RP.

Analysis of shared ceRNA networks and related-hub genes in rats with primary and secondary photoreceptor degeneration

Introduction

Photoreceptor degenerative diseases are characterized by the progressive death of photoreceptor cells, resulting in irreversible visual impairment. However, the role of competing endogenous RNA (ceRNA) in photoreceptor degeneration is unclear. We aimed to explore the shared ceRNA regulation network and potential molecular mechanisms between primary and secondary photoreceptor degenerations.

Methods

We established animal models for both types of photoreceptor degenerations and conducted retina RNA sequencing to identify shared differentially expressed long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and messenger RNAs (mRNAs). Using ceRNA regulatory principles, we constructed a shared ceRNA network and performed function enrichment and protein-protein interaction (PPI) analyses to identify hub genes and key pathways. Immune cell infiltration and drug-gene interaction analyses were conducted, and hub gene expression was validated by quantitative real-time polymerase chain reaction (qRT-PCR).

Results

We identified 37 shared differentially expressed lncRNAs, 34 miRNAs, and 247 mRNAs and constructed a ceRNA network consisting of 3 lncRNAs, 5 miRNAs, and 109 mRNAs. Furthermore, we examined 109 common differentially expressed genes (DEGs) through functional annotation, PPI analysis, and regulatory network analysis. We discovered that these diseases shared the complement and coagulation cascades pathway. Eight hub genes were identified and enriched in the immune system process. Immune infiltration analysis revealed increased T cells and decreased B cells in both photoreceptor degenerations. The expression of hub genes was closely associated with the quantities of immune cell types. Additionally, we identified 7 immune therapeutical drugs that target the hub genes.

Discussion

Our findings provide new insights and directions for understanding the common mechanisms underlying the development of photoreceptor degeneration. The hub genes and related ceRNA networks we identified may offer new perspectives for elucidating the mechanisms and hold promise for the development of innovative treatment strategies.

Excessive Thyroid Hormone Signaling Induces Photoreceptor Degeneration in Mice

Rod and cone photoreceptors degenerate in inherited and age-related retinal degenerative diseases, ultimately leading to loss of vision. Thyroid hormone (TH) signaling regulates cell proliferation, differentiation, and metabolism. Recent studies have shown a link between TH signaling and retinal degeneration. This work investigates the effects of excessive TH signaling on photoreceptor function and survival in mice. C57BL/6, Thra1 -/-, Thrb2 -/-, Thrb -/-, and the cone dominant Nrl -/- mice received triiodothyronine (T3) treatment (5-20 μg/ml in drinking water) for 30 d, followed by evaluations of retinal function, photoreceptor survival/death, and retinal stress/damage. Treatment with T3 reduced light responses of rods and cones by 50-60%, compared with untreated controls. Outer nuclear layer thickness and cone density were reduced by ∼18% and 75%, respectively, after T3 treatment. Retinal sections prepared from T3-treated mice showed significantly increased numbers of TUNEL-positive, p-γH2AX-positive, and 8-OHdG-positive cells, and activation of Müller glial cells. Gene expression analysis revealed upregulation of the genes involved in oxidative stress, necroptosis, and inflammation after T3 treatment. Deletion of Thra1 prevented T3-induced degeneration of rods but not cones, whereas deletion of Thrb2 preserved both rods and cones. Treatment with an antioxidant partially preserved photoreceptors and reduced retinal stress responses. This study demonstrates that excessive TH signaling induces oxidative stress/damage and necroptosis, induces photoreceptor degeneration, and impairs retinal function. The findings provide insights into the role of TH signaling in retinal degeneration and support the view of targeting TH signaling for photoreceptor protection.

Choi E, Gao F, Lewandowski D, Halabi M, L. Sander C, Wu A, Wang JM, Singh R, Gao S, Lessieur EM, Dong Z, Palczewska G, Mullins RF, Peachey NS, Kiser PD, Tabaka M, Kern TS, Palczewski K. Stress resilience-enhancing drugs preserve tissue structure and function in degenerating retina via phosphodiesterase inhibition

Chronic, progressive retinal diseases, such as age-related macular degeneration (AMD), diabetic retinopathy, and retinitis pigmentosa, arise from genetic and environmental perturbations of cellular and tissue homeostasis. These disruptions accumulate with repeated exposures to stress over time, leading to progressive visual impairment and, in many cases, legal blindness. Despite decades of research, therapeutic options for the millions of patients suffering from these disorders remain severely limited, especially for treating earlier stages of pathogenesis when the opportunity to preserve the retinal structure and visual function is greatest. To address this urgent, unmet medical need, we employed a systems pharmacology platform for therapeutic development. Through integrative single-cell transcriptomics, proteomics, and phosphoproteomics, we identified universal molecular mechanisms across distinct models of age-related and inherited retinal degenerations, characterized by impaired physiological resilience to stress. Here, we report that selective, targeted pharmacological inhibition of cyclic nucleotide phosphodiesterases (PDEs), which serve as critical regulatory nodes that modulate intracellular second messenger signaling pathways, stabilized the transcriptome, proteome, and phosphoproteome through downstream activation of protective mechanisms coupled with synergistic inhibition of degenerative processes. This therapeutic intervention enhanced resilience to acute and chronic forms of stress in the degenerating retina, thus preserving tissue structure and function across various models of age-related and inherited retinal disease. Taken together, these findings exemplify a systems pharmacology approach to drug discovery and development, revealing a new class of therapeutics with potential clinical utility in the treatment or prevention of the most common causes of blindness.

Cones and cone pathways remain functional in advanced retinal degeneration

Most defects causing retinal degeneration in retinitis pigmentosa (RP) are rod-specific mutations, but the subsequent degeneration of cones, which produces loss of daylight vision and high-acuity perception, is the most debilitating feature of the disease. To understand better why cones degenerate and how cone vision might be restored, we have made the first single-cell recordings of light responses from degenerating cones and retinal interneurons after most rods have died and cones have lost their outer-segment disk membranes and synaptic pedicles. We show that degenerating cones have functional cyclic-nucleotide-gated channels and can continue to give light responses, apparently produced by opsin localized either to small areas of organized membrane near the ciliary axoneme or distributed throughout the inner segment. Light responses of second-order horizontal and bipolar cells are less sensitive but otherwise resemble those of normal retina. Furthermore, retinal output as reflected in responses of ganglion cells is less sensitive but maintains spatiotemporal receptive fields at cone-mediated light levels. Together, these findings show that cones and their retinal pathways can remain functional even as degeneration is progressing, an encouraging result for future research aimed at enhancing the light sensitivity of residual cones to restore vision in patients with genetically inherited retinal degeneration.

RIPK necrotic cell death pathway in both donor photoreceptor and host immune cells synergize to affect photoreceptor graft survival

Photoreceptor transplant has been put forward as a repair strategy to tackle degenerated retinas. Nonetheless, cell death and immune rejection seriously limit the success of this strategy, with only a small fraction of transplanted cells surviving. Improving the survival of transplanted cells is of critical importance. Recent evidence has identified receptor-interacting protein kinase 3 (RIPK3) as a molecular trigger controlling necroptotic cell death and inflammation. However, its role in photoreceptor transplantation and regenerative medicine has not been studied. We hypothesized that modulation of RIPK3 to address both cell death and immunity could have advantageous effects on photoreceptor survival. In a model of inherited retinal degeneration, deletion of RIPK3 in donor photoreceptor precursors significantly increases the survival of transplanted cells. Simultaneous RIPK3 deletion in donor photoreceptors and recipients maximizes graft survival. Lastly, to discern the role of RIPK3 in the host immune response, bone marrow transplant experiments demonstrated that peripheral immune cell RIPK3 deficiency is protective for both donor and host photoreceptor survival. Interestingly, this finding is independent of photoreceptor transplantation, as the peripheral protective effect is also observed in an additional retinal detachment photoreceptor degeneration model. Altogether, these results indicate that immunomodulatory and neuroprotective strategies targeting the RIPK3 pathway can aid regenerative therapies of photoreceptor transplantation.

Targeting Necroptosis: A Novel Therapeutic Option for Retinal Degenerative Diseases

The discovery of the necroptosis, a form of regulated necrosis that is mediated by receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed-lineage kinase domain-like pseudokinase (MLKL), represents a major breakthrough that has dramatically altered the conception of necrosis - traditionally thought of as uncontrolled cell death - in various human diseases. Retinal cell death is a leading cause of blindness and has been identified in most retinal diseases, e.g., age-related macular degeneration, glaucoma, retinal detachment, retinitis pigmentosa, etc. Increasing evidence demonstrates that retinal degenerative diseases also share a common mechanism in necroptosis. Exacerbated necroptotic cell death hinders the treatment for retinal degenerative diseases. In this review, we highlight recent advances in identifying retinal necroptosis, summarize the underlying mechanisms of necroptosis in retinal degenerative diseases, and discuss potential anti-necroptosis strategies, such as selective inhibitors and chemical agents, for treating retinal degenerative diseases.

The Potential Role of Regulated Cell Death in Dry Eye Diseases and Ocular Surface Dysfunction

The research on new treatments for dry eye diseases (DED) has exponentially grown over the past decades. The increased prevalence of dry eye conditions, particularly in the younger population, has received much attention. Therefore, it is of utmost importance to identify novel therapeutical targets. Regulated cell death (RCD) is an essential process to control the biological homeostasis of tissues and organisms. The identification of different mechanisms of RCD stimulated the research on their involvement in different human pathologies. Whereas apoptosis has been widely studied in DED and included in the DED vicious cycle, the role of RCD still needs to be completely elucidated. In this review, we will explore the potential roles of different types of RCD in DED and ocular surface dysfunction. Starting from the evidence of oxidative stress and inflammation in dry eye pathology, we will analyse the potential therapeutic applications of the following principal RCD mechanisms: ferroptosis, necroptosis, and pyroptosis.

Novel compound heterozygous variants in the USH2A gene associated with autosomal recessive retinitis pigmentosa without hearing loss

Background: Retinitis pigmentosa (RP) is a group of progressive inherited retinal dystrophies characterized by the primary degeneration of rod photoreceptors and the subsequent loss of cone photoreceptors because of cell death. It is caused by different mechanisms, including inflammation, apoptosis, necroptosis, pyroptosis, and autophagy. Variants in the usherin gene (USH2A) have been reported in autosomal recessive RP with or without hearing loss. In the present study, we aimed to identify causative variants in a Han-Chinese pedigree with autosomal recessive RP. Methods: A six-member, three-generation Han-Chinese family with autosomal recessive RP was recruited. A full clinical examination, whole exome sequencing, and Sanger sequencing, as well as co-segregation analysis were performed. Results: Three heterozygous variants in the USH2A gene, c.3304C>T (p.Q1102*), c.4745T>C (p.L1582P), and c.14740G>A (p.E4914K), were identified in the proband, which were inherited from parents and transmitted to the daughters. Bioinformatics analysis supported the pathogenicity of the c.3304C>T (p.Q1102*) and c.4745T>C (p.L1582P) variants. Conclusions: Novel compound heterozygous variants in the USH2A gene, c.3304C>T (p.Q1102*) and c.4745T>C (p.L1582P), were identified as the genetic causes of autosomal recessive RP. The findings may enhance the current knowledge of the pathogenesis of USH2A-associated phenotypes, expand the spectrum of the USH2A gene variants, and contribute to improved genetic counseling, prenatal diagnosis, and disease management.

UVA induces retinal photoreceptor cell death via receptor interacting protein 3 kinase mediated necroptosis

Ultraviolet light A (UVA) is the only UV light that reaches the retina and can cause indirect damage to DNA via absorption of photons by non-DNA chromophores. Previous studies demonstrate that UVA generates reactive oxygen species (ROS) and leads to programmed cell death. Programmed cell death (PCD) has been implicated in numerous ophthalmologic diseases. Here, we investigated receptor interacting protein 1 and 3 (RIPK1 and RIPK3) kinases, key signaling molecules of PCD, in UVA-induced photoreceptor injury using in vitro and ex vivo models. UVA irradiation activated RIPK3 but not RIPK1 and mediated necroptosis through MLKL that lie downstream of RIPK3 and induced apoptosis through increased oxidative stress. Moreover, RIPK3 but not RIPK1 inhibition suppresses UVA-induced cell death along with the downregulation of MLKL and attenuates the levels of oxidative stress and DNA fragmentation. In conclusion, these results identify RIPK3, not RIPK1, as a critical regulator of UVA-induced necroptosis cell death in photoreceptors and highlight RIPK3 potential as a neuroprotective target.

Dysregulation of B7 family and its association with tumor microenvironment in uveal melanoma

Background

Uveal melanoma (UVM) is the most common primary intraocular malignancy in adults with a poor prognosis. B7 family is an important modulator of the immune response. However, its dysregulation and underlying molecular mechanism in UVM still remains unclear.

Methods

Data were derived from TCGA and GEO databases. The prognosis was analyzed by Kaplan-Meier curve. The ESTIMATE algorithm, CIBERSORT algorithm, and TIMER database were used to demonstrate the correlation between B7 family and tumor immune microenvironment in UVM. Single-cell RNA sequencing was used to detect the expression levels of the B7 family in different cell types of UVM. UVM was classified into different types by consistent clustering. Enrichment analysis revealed downstream signaling pathways of the B7 family. The interaction between different cell types was visualized by cell chat.

Results

The expression level of B7 family in UVM was significantly dysregulated and negatively correlated with methylation level. The expression of B7 family was associated with prognosis and immune infiltration, and B7 family plays an important role in the tumor microenvironment (TME). B7 family members were highly expressed in monocytes/macrophages of UVM compared with other cell types. Immune response and visual perception were the main functions affected by B7 family. The result of cell chat showed that the interaction between photoreceptor cells and immune-related cells was mainly generated by HLA-C-CD8A. CABP4, KCNJ10 and RORB had the strongest correlation with HLA-C-CD8A, and their high expression was significantly correlated with poor prognosis. CABP4 and RORB were specifically expressed in photoreceptor cells.

Conclusions

Dysregulation of the B7 family in UVM is associated with poor prognosis and affects the tumor immune microenvironment. CABP4 and RORB can serve as potential therapeutic targets for UVM, which can be regulated by the B7 family to affect the visual perception and immune response function of the eye, thus influencing the prognosis of UVM.

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.

Drinking hydrogen water improves photoreceptor structure and function in retinal degeneration 6 mice

Retinitis pigmentosa (RP) is a genetically heterogeneous group of inherited retinal disorders involving the progressive dysfunction of photoreceptors and the retinal pigment epithelium, for which there is currently no treatment. The rd6 mouse is a natural model of autosomal recessive retinal degeneration. Given the known contributions of oxidative stress caused by reactive oxygen species (ROS) and selective inhibition of potent ROS peroxynitrite and OH·by H₂ gas we have previously demonstrated, we hypothesized that ingestion of H₂ water may delay the progression of photoreceptor death in rd6 mice. H₂ mice showed significantly higher retinal thickness as compared to controls on optical coherence tomography. Histopathological and morphometric analyses revealed higher thickness of the outer nuclear layer for H₂ mice than controls, as well as higher counts of opsin red/green-positive cells. RNA sequencing (RNA-seq) analysis of differentially expressed genes in the H₂ group versus control group revealed 1996 genes with significantly different expressions. Gene and pathway ontology analysis showed substantial upregulation of genes responsible for phototransduction in H₂ mice. Our results show that drinking water high in H₂ (1.2-1.6 ppm) had neuroprotective effects and inhibited photoreceptor death in mice, and suggest the potential of H₂ for the treatment of RP.

Necroptosis and Neuroinflammation in Retinal Degeneration

Necroptosis mediates the chronic inflammatory phenotype in neurodegeneration. Receptor-interacting protein kinase (RIPK) plays a pivotal role in the induction of necroptosis in various cell types, including microglia, and it is implicated in diverse neurodegenerative diseases in the central nervous system and the retina. Targeting RIPK has been proven beneficial for alleviating both neuroinflammation and degeneration in basic/preclinical studies. In this review, we discuss the role of necroptosis in retinal degeneration, including (1) the molecular pathways involving RIPK, (2) RIPK-dependent microglial activation and necroptosis, and (3) the interactions between necroptosis and retinal neuroinflammation/degeneration. This review will contribute to a renewed focus on neuroinflammation induced by necroptosis and to the development of anti-RIPK drugs against retinal degeneration.

Stage-Dependent Changes of Visual Function and Electrical Response of the Retina in the rd10 Mouse Model

One of the critical prerequisites for the successful development of retinal prostheses is understanding the physiological features of retinal ganglion cells (RGCs) in the different stages of retinal degeneration (RD). This study used our custom-made rd10 mice, C57BL/6-Pde6bem1(R560C)Dkl/Korl mutated on the Pde6b gene in C57BL/6J mouse with the CRISPR/Cas9-based gene-editing method. We selected the postnatal day (P) 45, P70, P140, and P238 as representative ages for RD stages. The optomotor response measured the visual acuity across degeneration stages. At P45, the rd10 mice exhibited lower visual acuity than wild-type (WT) mice. At P140 and older, no optomotor response was observed. We classified RGC responses to the flashed light into ON, OFF, and ON/OFF RGCs via in vitro multichannel recording. With degeneration, the number of RGCs responding to the light stimulation decreased in all three types of RGCs. The OFF response disappeared faster than the ON response with older postnatal ages. We elicited RGC spikes with electrical stimulation and analyzed the network-mediated RGC response in the rd10 mice. Across all postnatal ages, the spikes of rd10 RGCs were less elicited by pulse amplitude modulation than in WT RGCs. The ratio of RGCs showing multiple peaks of spike burst increased in older ages. The electrically evoked RGC spikes by the pulse amplitude modulation differ across postnatal ages. Therefore, degeneration stage-dependent stimulation strategies should be considered for developing retinal prosthesis and successful vision restoration.

Neuroprotection for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. Early to intermediate AMD is characterized by the accumulation of lipid- and protein-rich drusen. Late stages of the disease are characterized by the development of choroidal neovascularization, termed "exudative" or "neovascular AMD," or retinal pigment epithelium (RPE) cell and photoreceptor death, termed "geographic atrophy" (GA) in advanced nonexudative AMD. Although we have effective treatments for exudative AMD in the form of anti-VEGF agents, they have no role for patients with GA. Neuroprotection strategies have emerged as a possible way to slow photoreceptor degeneration and vision loss in patients with GA. These approaches include reduction of oxidative stress, modulation of the visual cycle, reduction of toxic molecules, inhibition of pathologic protein activity, prevention of cellular apoptosis or programmed necrosis (necroptosis), inhibition of inflammation, direct activation of neurotrophic factors, delivery of umbilical tissue-derived cells, and RPE replacement. Despite active investigation in this area and significant promise based on preclinical studies, many clinical studies have not yielded successful results. We discuss selected past and current neuroprotection trials for AMD, highlight the lessons learned from these past studies, and discuss our perspective regarding remaining questions that must be answered before neuroprotection can be successfully applied in the field of AMD research.

Protective effect of C-phycocyanin and apo-phycocyanin subunit on programmed necrosis of GC-1 spg cells induced by H2 O2

C-phycocyanin (C-PC) is an effective antioxidant and has an important value in medical research. Oxidative stress is considered to be one of the main underlying mechanisms of cell death, and reducing oxidative stress is one of the strategies to enhance germ cell viability. Herein, we investigated the protective effect and the mechanism of C-PC and apo-phycocyanin subunit on oxidative stress damage induced by H₂ O₂ in GC-1 spg cells. C-PC genes were cloned into the pGEX-4T-1 vectorand transformed into Escherichia coli BL21 to achieve the efficient expression of C-PC subunit. GC-1 spg cells were treated with 600 μM H₂ O₂ for 24 h to establish the oxidative stress damage model. Cell viability was detected by CCK-8. The degree of oxidative stress was detected by testing Superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities and glutathione (GSH) and Malondialdehyde (MDA) levels. Reactive oxygen species (ROS) was evaluated utilizingby 2', 7'-dichlorofluorescent-diacetate (DCFH-DA). Mitochondrial membrane potential was determined by JC-1. Cell necrosis rate was detected by Annexin V-FITC/PI. Expression of protein was detected by western blot. We found that C-PC and GST-CPC β significantly inhibited H₂ O₂ -induced oxidative damage of GC-1 spg cells, improved the ability of antioxidation, reduced ROS overproduction, and mitochondrial membrane potential loss, and inhibited the RIP-1/RIP-3/ p-MLKL signaling pathway to reduce the necrosis rate. The results demonstrated that C-PC played a protective role against H₂ O₂ -induced cell damage, especially its β subunit. This study provides a theoretical basis for C-PC as a potential protective agent of reproductive system.

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.

Retinitis Pigmentosa: Progress in Molecular Pathology and Biotherapeutical Strategies

Retinitis pigmentosa (RP) is genetically heterogeneous retinopathy caused by photoreceptor cell death and retinal pigment epithelial atrophy that eventually results in blindness in bilateral eyes. Various photoreceptor cell death types and pathological phenotypic changes that have been disclosed in RP demand in-depth research of its pathogenic mechanism that may account for inter-patient heterogeneous responses to mainstream drug treatment. As the primary method for studying the genetic characteristics of RP, molecular biology has been widely used in disease diagnosis and clinical trials. Current technology iterations, such as gene therapy, stem cell therapy, and optogenetics, are advancing towards precise diagnosis and clinical applications. Specifically, technologies, such as effective delivery vectors, CRISPR/Cas9 technology, and iPSC-based cell transplantation, hasten the pace of personalized precision medicine in RP. The combination of conventional therapy and state-of-the-art medication is promising in revolutionizing RP treatment strategies. This article provides an overview of the latest research on the pathogenesis, diagnosis, and treatment of retinitis pigmentosa, aiming for a convenient reference of what has been achieved so far.

Retinoic acid signaling mediates peripheral cone photoreceptor survival in a mouse model of retina degeneration

Retinitis Pigmentosa (RP) is a progressive, debilitating visual disorder caused by mutations in a diverse set of genes. In both humans with RP and mouse models of RP, rod photoreceptor dysfunction leads to loss of night vision, and is followed by secondary cone photoreceptor dysfunction and degeneration, leading to loss of daylight color vision. A strategy to prevent secondary cone death could provide a general RP therapy to preserve daylight color vision regardless of the underlying mutation. In mouse models of RP, cones in the peripheral retina survive long-term, despite complete rod loss. The mechanism for such peripheral cone survival had not been explored. Here, we found that active retinoic acid (RA) signaling in peripheral Muller glia is necessary for the abnormally long survival of these peripheral cones. RA depletion by conditional knockout of RA synthesis enzymes, or overexpression of an RA degradation enzyme, abrogated the extended survival of peripheral cones. Conversely, constitutive activation of RA signaling in the central retina promoted long-term cone survival. These results indicate that RA signaling mediates the prolonged peripheral cone survival in the rd1 mouse model of retinal degeneration, and provide a basis for a generic strategy for cone survival in the many diseases that lead to loss of cone-mediated vision.

Programmed Cell Death and Autophagy in an in vitro Model of Spontaneous Neuroretinal Degeneration

Retinal neurodegenerative diseases are the leading causes of visual impairment and irreversible blindness worldwide. Although the retinal response to injury remains closely similar between different retinal neurodegenerative diseases, available therapeutic alternatives are only palliative, too expensive, or very specific, such as gene therapy. In that sense, the development of broad-spectrum neuroprotective therapies seems to be an excellent option. In this regard, it is essential to identify molecular targets involved in retinal degeneration, such as cell death mechanisms. Apoptosis has been considered as the primary cell death mechanism during retinal degeneration; however, recent studies have demonstrated that the only use of anti-apoptotic drugs is not enough to confer good neuroprotection in terms of cell viability and preservation. For that reason, the interrelationship that exists between apoptosis and other cell death mechanisms needs to be characterized deeply to design future therapeutic options that simultaneously block the main cell death pathways. In that sense, the study aimed to characterize the programmed cell death (in terms of apoptosis and necroptosis) and autophagy response and modulation in retinal neurodegenerative diseases, using an in vitro model of spontaneous retinal neurodegeneration. For that purpose, we measured the mRNA relative expression through qPCR of a selected pool of genes involved in apoptosis (BAX, BCL2, CASP3, CASP8, and CASP9), necroptosis (MLKL, RIPK1, and RIPK3), and autophagy (ATG7, BCLIN1, LC3B, mTOR, and SQSTM1); besides, the immunoexpression of their encoding proteins (Casp3, MLKL, RIPK1, LC3B, and p62) were analyzed using immunohistochemistry. Our results showed an increase of pro-apoptotic and pro-necroptotic related genes and proteins during in vitro retinal neurodegeneration. Besides, we describe for the first time the modulation between programmed cell death mechanisms and autophagy in an in vitro retinal neurodegeneration model. This study reinforces the idea that cell death mechanisms are closely interconnected and provides new information about molecular signaling and autophagy along the retinal degeneration process.

Primary and Secondary Cone Cell Death Mechanisms in Inherited Retinal Diseases and Potential Treatment Options

Inherited retinal diseases (IRDs) are a leading cause of blindness. To date, 260 disease-causing genes have been identified, but there is currently a lack of available and effective treatment options. Cone photoreceptors are responsible for daylight vision but are highly susceptible to disease progression, the loss of cone-mediated vision having the highest impact on the quality of life of IRD patients. Cone degeneration can occur either directly via mutations in cone-specific genes (primary cone death), or indirectly via the primary degeneration of rods followed by subsequent degeneration of cones (secondary cone death). How cones degenerate as a result of pathological mutations remains unclear, hindering the development of effective therapies for IRDs. This review aims to highlight similarities and differences between primary and secondary cone cell death in inherited retinal diseases in order to better define cone death mechanisms and further identify potential treatment options.

The Role of Inflammation in Retinal Neurodegeneration and Degenerative Diseases

Retinal neurodegeneration is predominantly reported as the apoptosis or impaired function of the photoreceptors. Retinal degeneration is a major causative factor of irreversible vision loss leading to blindness. In recent years, retinal degenerative diseases have been investigated and many genes and genetic defects have been elucidated by many of the causative factors. An enormous amount of research has been performed to determine the pathogenesis of retinal degenerative conditions and to formulate the treatment modalities that are the critical requirements in this current scenario. Encouraging results have been obtained using gene therapy. We provide a narrative review of the various studies performed to date on the role of inflammation in human retinal degenerative diseases such as age-related macular degeneration, inherited retinal dystrophies, retinitis pigmentosa, Stargardt macular dystrophy, and Leber congenital amaurosis. In addition, we have highlighted the pivotal role of various inflammatory mechanisms in the progress of retinal degeneration. This review also offers an assessment of various therapeutic approaches, including gene-therapies and stem-cell-based therapies, for degenerative retinal diseases.

Nuclear NAD+-biosynthetic enzyme NMNAT1 facilitates development and early survival of retinal neurons

Despite mounting evidence that the mammalian retina is exceptionally reliant on proper NAD+ homeostasis for health and function, the specific roles of subcellular NAD+ pools in retinal development, maintenance, and disease remain obscure. Here, we show that deletion of the nuclear-localized NAD+ synthase nicotinamide mononucleotide adenylyltransferase-1 (NMNAT1) in the developing murine retina causes early and severe degeneration of photoreceptors and select inner retinal neurons via multiple distinct cell death pathways. This severe phenotype is associated with disruptions to retinal central carbon metabolism, purine nucleotide synthesis, and amino acid pathways. Furthermore, transcriptomic and immunostaining approaches reveal dysregulation of a collection of photoreceptor and synapse-specific genes in NMNAT1 knockout retinas prior to detectable morphological or metabolic alterations. Collectively, our study reveals previously unrecognized complexity in NMNAT1-associated retinal degeneration and suggests a yet-undescribed role for NMNAT1 in gene regulation during photoreceptor terminal differentiation.

The role of necroptosis in disease and treatment

Necroptosis, a distinctive type of programmed cell death different from apoptosis or necrosis, triggered by a series of death receptors such as tumor necrosis factor receptor 1 (TNFR1), TNFR2, and Fas. In case that apoptosis process is blocked, necroptosis pathway is initiated with the activation of three key downstream mediators which are receptor-interacting serine/threonine protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL). The whole process eventually leads to destruction of the cell membrane integrity, swelling of organelles, and severe inflammation. Over the past decade, necroptosis has been found widely involved in life process of human beings and animals. In this review, we attempt to explore the therapeutic prospects of necroptosis regulators by describing its molecular mechanism and the role it played in pathological condition and tissue homeostasis, and to summarize the research and clinical applications of corresponding regulators including small molecule inhibitors, chemicals, Chinese herbal extracts, and biological agents in the treatment of various diseases.

Receptor interacting protein 3 kinase, not 1 kinase, through MLKL-mediated necroptosis is involved in UVA-induced corneal endothelium cell death

Ultraviolet (UV) is one of the most energetic radiations in the solar spectrum that can result in various tissue injury disorders. Previous studies demonstrated that UVA, which represents 95% of incident photovoltaic radiation, induces corneal endothelial cells (CECs) death. Programmed cell death (PCD) has been implicated in numerous ophthalmologic diseases. Here, we investigated receptor-interacting protein 3 kinase (RIPK3), a key signaling molecule of PCD, in UVA-induced injury using a short-term corneal endothelium (CE) culture model. UVA irradiation activated RIPK3 and mediated necroptosis both in mouse CE and primary human CECs (pHCECs). UVA irradiation was associated with upregulation of key necroptotic molecules (DAI, TRIF, and MLKL) that lie downstream of RIPK3. Moreover, RIPK3 inhibition or silencing in primary corneal endothelial cells suppresses UVA-induced cell death, along with downregulation of MLKL in pHCECs. In addition, genetic inhibition or knockout of RIPK3 in mice (RIPK3^K51A and RIPK3^-/- mice) similarly attenuates cell death and the levels of necroptosis in ex vivo UVA irradiation experiments. In conclusion, these results identify RIPK3, not RIPK1, as a critical regulator of UVA-induced cell death in CE and indicate its potential as a future protective target.

Identification of early-onset photoreceptor degeneration in transgenic mouse models of Alzheimer's disease

Light sensitivity of the vertebrate retina relies on the integrity of photoreceptors, including rods and cones. Research in patients with Alzheimer's disease (AD) and in AD transgenic mice reports that accumulated amyloid-β (Aβ) plaques in the retina are toxic to retinal neurons. Moreover, Aβ plaques are deposited around the rods and cones, yet photoreceptor anomalies remain unclear in AD. Here, we identify the progressive degeneration of rods and cones characterized by impaired expression of phototransduction proteins, morphological alterations, functional deficits, and even cell loss. Furthermore, we demonstrate that cell senescence and necroptosis were involved in rod degeneration. Importantly, using in vivo scotopic electroretinogram, we detected rod degeneration in early-stage AD transgenic mice before Aβ plaques were observed in the brain. Moreover, we demonstrate that rod degeneration was among the earliest AD retinal manifestations compared with other types of retinal neurons. Overall, our study is the first to identify and detect in vivo, early-onset photoreceptor degeneration in AD.

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Progressive rod degeneration has been identified in AD transgenic mice

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Cell senescence and necroptosis were involved in rod degeneration

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Rod degeneration can be detected by in vivo scotopic electroretinogram

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Rod degeneration has earlier onset than amyloid-β plaques in the brain

Local photoreceptor cell death differences in the murine model of retinal detachment

To investigate local cell death differences in the attached and detached retina at different regions in a murine experimental retinal detachment model. Subretinal injection of sodium hyaluronate was performed in eight-week-old C57BL/6J mice. Retinal regions of interest were defined in relation to their distance from the peak of the retinal detachment, as follows: (1) attached central; (2) attached paracentral; (3) detached apex; and (4) detached base. At day 0, the outer nuclear layer cell count for the attached central, attached paracentral, detached apex, and detached base was 1247.60 ± 64.62, 1157.80 ± 163.33, 1264.00 ± 150.7, and 1013.80 ± 67.16 cells, respectively. There were significant differences between the detached base vs. attached central, and between detached base vs. detached apex at day 0. The detached apex region displayed a significant and progressive cell count reduction from day 0 to 14. In contrast, the detached base region did not show progressive retinal degeneration in this model. Moreover, only the detached apex region had a significant and progressive cell death rate compared to baseline. Immediate confounding changes with dramatic differences in cell death rates are present across regions of the detached retina. We speculate that mechanical and regional differences in the bullous detached retina can modify the rate of cell death in this model.

Technological advancements to study cellular signaling pathways in inherited retinal degenerative diseases

Inherited retinal degenerative diseases (IRDs) are rare neurodegenerative disorders with mutations in hundreds of genes leading to vision loss, primarily owing to photoreceptor cell death. This genetic diversity is impeding development of effective treatment options. Gene-based therapies have resulted in the first FDA-approved drug (Luxturna) for RPE65-specific IRD. Although currently explored in clinical trials, genomic medicines are mutation-dependent, hence suitable only for patients harboring a specific mutation. Better understanding of the pathways leading to photoreceptor degeneration may help to determine common targets and develop mutation-independent therapies for larger groups of patients with IRDs. In this review, we discuss the key pathways involved in photoreceptor cell death studied by transcriptomics, proteomics, and metabolomics techniques to identify potential therapeutic targets in IRDs.

Large-scale phenotypic drug screen identifies neuroprotectants in zebrafish and mouse models of retinitis pigmentosa

Retinitis pigmentosa (RP) and associated inherited retinal diseases (IRDs) are caused by rod photoreceptor degeneration, necessitating therapeutics promoting rod photoreceptor survival. To address this, we tested compounds for neuroprotective effects in multiple zebrafish and mouse RP models, reasoning drugs effective across species and/or independent of disease mutation may translate better clinically. We first performed a large-scale phenotypic drug screen for compounds promoting rod cell survival in a larval zebrafish model of inducible RP. We tested 2934 compounds, mostly human-approved drugs, across six concentrations, resulting in 113 compounds being identified as hits. Secondary tests of 42 high-priority hits confirmed eleven lead candidates. Leads were then evaluated in a series of mouse RP models in an effort to identify compounds effective across species and RP models, that is, potential pan-disease therapeutics. Nine of 11 leads exhibited neuroprotective effects in mouse primary photoreceptor cultures, and three promoted photoreceptor survival in mouse rd1 retinal explants. Both shared and complementary mechanisms of action were implicated across leads. Shared target tests implicated parp1-dependent cell death in our zebrafish RP model. Complementation tests revealed enhanced and additive/synergistic neuroprotective effects of paired drug combinations in mouse photoreceptor cultures and zebrafish, respectively. These results highlight the value of cross-species/multi-model phenotypic drug discovery and suggest combinatorial drug therapies may provide enhanced therapeutic benefits for RP patients.

Regulation of crystal induced inflammation: current understandings and clinical implications

Introduction: Accumulation of abnormal crystals in the body, derived from endogenous or exogenous materials can drive a wide spectrum of inflammatory disease states. It is well established that intra-articular deposition of monosodium urate (MSU) and calcium pyrophoshate (CPP) crystals contributes to joint destruction through pro-inflammatory processes.Areas covered: This review will focus on current understanding and recent novelty about the mechanisms and the clinical implications of the inflammation induced by MSU and CPP crystals.Expert opinion: Advances in molecular biology reveal that at the base of the inflammatory cascade, stimulated by MSU or CPP crystals, there are many complex cellular mechanisms mainly involving the NLRP3 inflammasome, the hallmark of autoinflammatory syndromes. The extensive studies carried out through in vitro and in vivo models along with a better clinical definition of the disease has led to an optimized use of existing drugs and the introduction of novel therapeutic strategies. In particular, the identification of IL-1 as the most important target in gout and pseudogout has made it possible to expand the pharmacological indications of anti-IL-1 biological drugs, opening new therapeutic perspectives for patients.

AAV-Txnip prolongs cone survival and vision in mouse models of retinitis pigmentosa

Retinitis pigmentosa (RP) is an inherited retinal disease affecting >20 million people worldwide. Loss of daylight vision typically occurs due to the dysfunction/loss of cone photoreceptors, the cell type that initiates our color and high-acuity vision. Currently, there is no effective treatment for RP, other than gene therapy for a limited number of specific disease genes. To develop a disease gene-agnostic therapy, we screened 20 genes for their ability to prolong cone photoreceptor survival in vivo. Here, we report an adeno-associated virus vector expressing Txnip, which prolongs the survival of cone photoreceptors and improves visual acuity in RP mouse models. A Txnip allele, C247S, which blocks the association of Txnip with thioredoxin, provides an even greater benefit. Additionally, the rescue effect of Txnip depends on lactate dehydrogenase b (Ldhb) and correlates with the presence of healthier mitochondria, suggesting that Txnip saves RP cones by enhancing their lactate catabolism.

Apoptosis in health and diseases of the eye and brain

Apoptosis is a form of programmed cell death (PCD) and enables the immunologically silent disposal of senescent or unwanted cells, causing minimal damage to the surrounding environment. Apoptosis can occur via intrinsic or extrinsic pathways that initiate a series of intracellular and extracellular signaling events. This ultimately leads to the clearance of the cell by phagocytes. This normal physiological mechanism may be accelerated in several diseases including those involving the eyes and brain, leading to loss of structure and function. This review presents the role of PCD in the health of the eyes and brain, and the evidence presented for its aberrant role in disease.

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.

Rod photoreceptor clearance due to misfolded rhodopsin is linked to a DAMP-immune checkpoint switch

Chronic endoplasmic reticulum stress resulting from misfolding of the visual pigment rhodopsin (RHO) can lead to loss of rod photoreceptors, which initiates retinitis pigmentosa, characterized initially by diminished nighttime and peripheral vision. Cone photoreceptors depend on rods for glucose transport, which the neurons use for assembly of visual pigment-rich structures; as such, loss of rods also leads to a secondary loss of cone function, diminishing high-resolution color vision utilized for tasks including reading, driving, and facial recognition. If dysfunctional rods could be maintained to continue to serve this secondary cone preservation function, it might benefit patients with retinitis pigmentosa, but the mechanisms by which rods are removed are not fully established. Using pigs expressing mutant RHO, we find that induction of a danger-associated molecular pattern (DAMP) "eat me" signal on the surface of mutant rods is correlated with targeting the live cells for (PrCR) by retinal myeloid cells. Glucocorticoid therapy leads to replacement of this DAMP with a "don't eat me" immune checkpoint on the rod surface and inhibition of PrCR. Surviving rods then continue to promote glucose transport to cones, maintaining their viability.

Exogenous sodium hydrosulfide protects against high glucose‑induced injury and inflammation in human umbilical vein endothelial cells by inhibiting necroptosis via the p38 MAPK signaling pathway

In recent years hydrogen sulfide (H2S) has demonstrated vasculoprotective effects against cell death, which suggests its promising therapeutic potential for numerous types of disease. Additionally, a protective effect of exogenous H2S in HG‑induced injuries in HUVECs was demonstrated, suggesting a potential protective effect for diabetic vascular complications. The present study aimed to investigate the mechanism accounting for the cytoprotective role of exogenous H2S against high glucose [HG (40 mM glucose)]‑induced injury and inflammation in human umbilical vein endothelial cells (HUVECs). HUVECs were exposed to HG for 24 h to establish an in vitro model of HG‑induced cytotoxicity. The cells were pretreated with sodium hydrosulfide (NaHS), a donor of H2S, or inhibitors of necroptosis and p38 MAPK prior to the exposure to HG. Cell viability, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), IL‑1β, IL‑6, IL‑8, TNF‑α, phosphorylated‑(p)38 and receptor‑interacting protein 3 (RIP3) expression levels were detected using the indicated methods, including Cell Counting Kit 8, fluorescence detection, western blotting, immunofluorescence assay and ELISAs. The results demonstrated that necroptosis and the p38 MAPK signaling pathway mediated HG‑induced injury and inflammation. Notably, NaHS was discovered to significantly ameliorate p38 MAPK/necroptosis‑mediated injury and inflammation in response to HG, as evidenced by an increase in cell viability, a decrease in ROS generation and loss of MMP, as well as the reduction in the secretion of proinflammatory cytokines. In addition, the upregulated expression of RIP3 induced by HG was repressed by treatment with SB203580, while the HG‑induced upregulation of p‑p38 expression levels were significantly downregulated following the treatment of Nec‑1 and RIP3‑siRNA. In conclusion, the findings of the present study indicated that NaHS may protect HUVECs against HG‑induced injury and inflammation by inhibiting necroptosis via the p38 MAPK signaling pathway, which may represent a promising drug for the therapy of diabetic vascular complications.

ThicknessTool: automated ImageJ retinal layer thickness and profile in digital images

To develop an automated retina layer thickness measurement tool for the ImageJ platform, to quantitate nuclear layers following the retina contour. We developed the ThicknessTool (TT), an automated thickness measurement plugin for the ImageJ platform. To calibrate TT, we created a calibration dataset of mock binary skeletonized mask images with increasing thickness masks and different rotations. Following, we created a training dataset and performed an agreement analysis of thickness measurements between TT and two masked manual observers. Finally, we tested the performance of TT measurements in a validation dataset of retinal detachment images. In the calibration dataset, there were no differences in layer thickness between measured and known thickness masks, with an overall coefficient of variation of 0.00%. Training dataset measurements of immunofluorescence retina nuclear layers disclosed no significant differences between TT and any observer’s average outer nuclear layer (ONL) (p = 0.998), inner nuclear layer (INL) (p = 0.807), and ONL/INL ratio (p = 0.944) measurements. Agreement analysis showed that bias between TT vs. observers’ mean was lower than between any observers’ mean against each other in the ONL (0.77 ± 0.34 µm vs 3.25 ± 0.33 µm) and INL (1.59 ± 0.28 µm vs 2.82 ± 0.36 µm). Validation dataset showed that TT can detect significant and true ONL thinning (p = 0.006), more sensitive than manual measurement capabilities (p = 0.069). ThicknessTool can measure retina nuclear layers thickness in a fast, accurate, and precise manner with multi-platform capabilities. In addition, the TT can be customized to user preferences and is freely available to download.

Mechanisms of Photoreceptor Death in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is the most common cause of inherited blindness and is characterised by the progressive loss of retinal photoreceptors. However, RP is a highly heterogeneous disease and, while much progress has been made in developing gene replacement and gene editing treatments for RP, it is also necessary to develop treatments that are applicable to all causative mutations. Further understanding of the mechanisms leading to photoreceptor death is essential for the development of these treatments. Recent work has therefore focused on the role of apoptotic and non-apoptotic cell death pathways in RP and the various mechanisms that trigger these pathways in degenerating photoreceptors. In particular, several recent studies have begun to elucidate the role of microglia and innate immune response in the progression of RP. Here, we discuss some of the recent progress in understanding mechanisms of rod and cone photoreceptor death in RP and summarise recent clinical trials targeting these pathways.

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.

The necroptosis pathway and its role in age-related neurodegenerative diseases: will it open up new therapeutic avenues in the next decade?

INTRODUCTION

Necroptosis is a programmed form of necrotic cell death. Growing evidence demonstrates that necroptosis contributes to cell demise in different pathological conditions including age-dependent neurodegenerative diseases (NDs). These findings open new avenues for understanding the mechanisms of neuronal loss in NDs, which might eventually translate into novel therapeutic interventions.

AREAS COVERED

We reviewed key aspects of necroptosis, in health and disease, focusing on evidence demonstrating its involvement in the pathogenesis of age-related NDs. We then highlight the activation of this pathway in the mechanism of axonal degeneration. We searched on PubMed the literature regarding necroptosis published between 2008 and 2020 and reviewed all publications were necroptosis was studied in the context of age-related NDs.

EXPERT OPINION

Axonal loss and neuronal death are the ultimate consequences of NDs that translate into disease phenotypes. Targeting degenerative mechanisms of the neuron appears as a strategy that might cover a wide range of diseases. Thus, the participation of necroptosis as a common mediator of neuronal demise emerges as a promising target for therapeutic intervention. Considering evidence demonstrating that necroptosis mediates axonal degeneration, we propose and discuss the potential of targeting necroptosis-mediated axonal destruction as a strategy to tackle NDs before neuronal loss occurs.

SARM1 deficiency promotes rod and cone photoreceptor cell survival in a model of retinal degeneration

This study reports that activation of SARM1 causes destruction of NAD pools in photoreceptor cells of the retina and identifies a role for SARM1-dependent photoreceptor cell death in retinal degeneration.

Retinal degeneration is the leading cause of incurable blindness worldwide and is characterised by progressive loss of light-sensing photoreceptors in the neural retina. SARM1 is known for its role in axonal degeneration, but a role for SARM1 in photoreceptor cell degeneration has not been reported. SARM1 is known to mediate neuronal cell degeneration through depletion of essential metabolite NAD and induction of energy crisis. Here, we demonstrate that SARM1 is expressed in photoreceptors, and using retinal tissue explant, we confirm that activation of SARM1 causes destruction of NAD pools in the photoreceptor layer. Through generation of rho^−/−sarm1^−/− double knockout mice, we demonstrate that genetic deletion of SARM1 promotes both rod and cone photoreceptor cell survival in the rhodopsin knockout (rho^−/−) mouse model of photoreceptor degeneration. Finally, we demonstrate that SARM1 deficiency preserves cone visual function in the surviving photoreceptors when assayed by electroretinography. Overall, our data indicate that endogenous SARM1 has the capacity to consume NAD in photoreceptor cells and identifies a previously unappreciated role for SARM1-dependent cell death in photoreceptor cell degeneration.

Endoplasmic reticulum stress: New insights into the pathogenesis and treatment of retinal degenerative diseases

Physiological equilibrium in the retina depends on coordinated work between rod and cone photoreceptors and can be compromised by the expression of mutant proteins leading to inherited retinal degeneration (IRD). IRD is a diverse group of retinal dystrophies with multifaceted molecular mechanisms that are not fully understood. In this review, we focus on the contribution of chronically activated unfolded protein response (UPR) to inherited retinal pathogenesis, placing special emphasis on studies employing genetically modified animal models. As constitutively active UPR in degenerating retinas may activate pro-apoptotic programs associated with oxidative stress, pro-inflammatory signaling, dysfunctional autophagy, free cytosolic Ca²⁺ overload, and altered protein synthesis rate in the retina, we focus on the regulatory mechanisms of translational attenuation and approaches to overcoming translational attenuation in degenerating retinas. We also discuss current research on the role of the UPR mediator PERK and its downstream targets in degenerating retinas and highlight the therapeutic benefits of reprogramming PERK signaling in preclinical animal models of IRD. Finally, we describe pharmacological approaches targeting UPR in ocular diseases and consider their potential applications to IRD.

Improvement of reduced electroretinographic responses in thymoma-associated retinopathy: a case report and literature review

PURPOSE

To report a patient with thymoma-associated retinopathy presenting as having a good visual prognosis.

METHODS

Case report and literature review.

CASE REPORT

A 42-year-old female patient was referred to our hospital for complaints of sudden visual-field defects bilaterally. Decimal corrected visual acuity (VA) was 1.5 and 1.2 in the right (RE) and left eyes (LE), respectively. Fundus autofluorescence revealed hyper-autofluorescence from the posterior pole to mid-peripheral retina in both eyes. Full-field electroretinography (ERG) amplitudes were reduced to 20-50% and 30-50% of our controls for the scotopic and photopic conditions, respectively. A systemic examination revealed the presence of thymoma, and the patient underwent thymectomy and immunosuppression therapies. Immunohistochemical analysis using the patient's serum showed immunolabeling on the photoreceptor inner segment and outer plexiform layer in the monkey retina. Two years later, VA remained at 1.5 and 1.2 in RE and LE. ERG amplitudes improved to 30-60% of the controls for the scotopic conditions. However, photopic ERG showed no remarkable change.

CONCLUSIONS

To our knowledge, improvement of reduced rod-mediated ERG responses has not been described in seven previously reported patients with thymoma-associated retinopathy. The good visual prognosis of our patient may be associated with well-timed intervention.

Necroptosis, ADAM proteases and intestinal (dys)function

Recently, an unexpected connection between necroptosis and members of the a disintegrin and metalloproteinase (ADAM) protease family has been reported. Necroptosis represents an important cell death routine which helps to protect from viral, bacterial, fungal and parasitic infections, maintains adult T cell homeostasis and contributes to the elimination of potentially defective organisms before parturition. Equally important for organismal homeostasis, ADAM proteases control cellular processes such as development and differentiation, immune responses or tissue regeneration. Notably, necroptosis as well as ADAM proteases have been implicated in the control of inflammatory responses in the intestine. In this review, we therefore provide an overview of the physiology and pathophysiology of necroptosis, ADAM proteases and intestinal (dys)function, discuss the contribution of necroptosis and ADAMs to intestinal (dys)function, and review the current knowledge on the role of ADAMs in necroptotic signaling.

Multitasking Kinase RIPK1 Regulates Cell Death and Inflammation

Receptor-interacting serine threonine kinase 1 (RIPK1) is a widely expressed kinase that is essential for limiting inflammation in both mice and humans. Mice lacking RIPK1 die at birth from multiorgan inflammation and aberrant cell death, whereas humans lacking RIPK1 are immunodeficient and develop very early-onset inflammatory bowel disease. In contrast to complete loss of RIPK1, inhibiting the kinase activity of RIPK1 genetically or pharmacologically prevents cell death and inflammation in several mouse disease models. Indeed, small molecule inhibitors of RIPK1 are in phase I clinical trials for amyotrophic lateral sclerosis, and phase II clinical trials for psoriasis, rheumatoid arthritis, and ulcerative colitis. This review focuses on which signaling pathways use RIPK1, how activation of RIPK1 is regulated, and when activation of RIPK1 appears to be an important driver of inflammation.

Optimal control with MANF treatment of photoreceptor degeneration

People afflicted with diseases such as retinitis pigmentosa and age-related macular degeneration experience a decline in vision due to photoreceptor degeneration, which is currently unstoppable and irreversible. Currently there is no cure for diseases linked to photoreceptor degeneration. Recent experimental work showed that mesencephalic astrocyte-derived neurotrophic factor (MANF) can reduce neuron death and, in particular, photoreceptor death by reducing the number of cells that undergo apoptosis. In this work, we build on an existing system of ordinary differential equations that represent photoreceptor interactions and incorporate MANF treatment for three experimental mouse models having undergone varying degrees of photoreceptor degeneration. Using MANF treatment levels as controls, we investigate optimal control results in the three mouse models. In addition, our numerical solutions match the experimentally observed surviving percentage of photoreceptors and our uncertainty and sensitivity analysis identifies significant parameters in the math model both with and without MANF treatment.

Involvement of regulated necrosis in blinding diseases: Focus on necroptosis and ferroptosis

Besides apoptosis, necrosis can also occur in a highly regulated and genetically controlled manner, defined as regulated necrosis, which is characterized by a loss of cell membrane integrity and release of cytoplasmic content. Depending on the involvement of its signal pathway, regulated necrosis can be further classified as necroptosis, ferroptosis, pyroptosis and parthanatos. Numerous studies have demonstrated that regulated necrosis is involved in the pathogenesis of many diseases covering almost all organs including the brain, heart, liver, kidney, intestine, blood vessel, eye and skin, particularly myocardial infarction and stroke. Most recently, growing evidence suggests that multiple types of regulated necrosis contribute to the degeneration of retinal ganglion cells, retinal pigment epithelial cells or photoreceptor cells, which are the main pathologic features for glaucoma, age-related macular degeneration or retinitis pigmentosa, respectively. This review focuses on the involvement of necroptosis and ferroptosis in these blinding diseases.