Endoplasmic reticulum stress and the unfolded protein responses in retinal degeneration

New insights into the tenderization pattern of yak meat by ROS-ERS: Promotion of ERS-associated apoptosis through feedback regulation of PERK/IRE1/ATF6 and caspase-12 activity

This study aimed to investigate the molecular mechanisms of reactive oxygen species (ROS)-induced endoplasmic reticulum stress (ERS) in apoptosis and meat tenderization during postmortem aging. Yak longissimus dorsi muscle was incubated with N-acetylcysteine (NAC), 4-phenylbutyric acid (4-PBA) and NAC + 4-PBA, respectively, and stored at 4 °C for 0 h, 12 h, 24 h, 72 h, 120 h and 168 h. The results showed that NAC and 4-PBA treatments significantly reduced ROS content and endoplasmic reticulum stress levels. Meanwhile, the specific inhibitory effect of 4-PBA affected Ca2+ content, caspase-12 activity, endoplasmic reticulum apoptotic cascade reaction and meat tenderization by preventing myogenic fiber degradation. Additionally, the combined treatment of NAC + 4-PBA had a more significant effect than the other groups, confirming the necessity of targeted regulation of the ROS-ERS axis. Overall, our findings provide new insights into the critical role of ROS-mediated ERS in caspase-12-dependent apoptosis and yak meat tenderization during yak meat postmortem.

Retinal Pigment Epithelium Under Oxidative Stress: Chaperoning Autophagy and Beyond

The structural and functional integrity of the retinal pigment epithelium (RPE) plays a key role in the normal functioning of the visual system. RPE cells are characterized by an efficient system of photoreceptor outer segment phagocytosis, high metabolic activity, and risk of oxidative damage. RPE dysfunction is a common pathological feature in various retinal diseases. Dysregulation of RPE cell proteostasis and redox homeostasis is accompanied by increased reactive oxygen species generation during the impairment of phagocytosis, lysosomal and mitochondrial failure, and an accumulation of waste lipidic and protein aggregates. They are the inducers of RPE dysfunction and can trigger specific pathways of cell death. Autophagy serves as important mechanism in the endogenous defense system, controlling RPE homeostasis and survival under normal conditions and cellular responses under stress conditions through the degradation of intracellular components. Impairment of the autophagy process itself can result in cell death. In this review, we summarize the classical types of oxidative stress-induced autophagy in the RPE with an emphasis on autophagy mediated by molecular chaperones. Heat shock proteins, which represent hubs connecting the life supporting pathways of RPE cells, play a special role in these mechanisms. Regulation of oxidative stress-counteracting autophagy is an essential strategy for protecting the RPE against pathological damage when preventing retinal degenerative disease progression.

PRDX4 mitigates diabetic retinopathy by inhibiting reactive gliosis, apoptosis, ER stress, oxidative stress, and mitochondrial dysfunction in Müller cells

Diabetic retinopathy (DR) is a neurovascular complication of diabetes. As a crucial player in the retinal physiology, Müller cells are affected in DR, impairments of Müller cell function lead to retinal malfunctions. Therefore, searching for approaches to mitigate diabetes-induced injury in Müller cells is imperative for delaying DR. Peroxiredoxin 4 (PRDX4), an important endoplasmic reticulum (ER)-resident antioxidant, was explored in this study for its potential protective role against DR. Streptozotocin-induced mouse model of diabetes and high glucose (HG)-induced Müller cells were utilized to assess the impact of PRDX4. Compared with WT mice, PRDX4 knockout exacerbated retinal neurodegeneration, reactive gliosis, cell apoptosis, ER stress, oxidative stress, and mitochondrial dysfunction in diabetic retinas. Knockdown of PRDX4 aggravated HG-induced reactive gliosis, apoptosis, ER stress, oxidative stress, and mitochondrial dysfunction in Müller cells. Conversely, PRDX4 overexpression in Müller cells protected against HG-induced cell damage. Mechanistically, PRDX4 promoted the degradation of dipeptidyl peptidase-4, which is associated with DR in type 1 diabetics, thereby alleviating HG-stimulated Müller cell abnormalities. Our study indicated that PRDX4 is a crucial protective regulator in DR progression via destabilization of dipeptidyl peptidase-4 protein and suggested that enhancement of PRDX4 level may represent a promising approach for treating DR.

Endothelial Unfolded Protein Response-Mediated Cytoskeletal Effects

The endothelial semipermeable monolayers ensure tissue homeostasis, are subjected to a plethora of stimuli, and their function depends on cytoskeletal integrity and remodeling. The permeability of those membranes can fluctuate to maintain organ homeostasis. In cases of severe injury, inflammation or disease, barrier hyperpermeability can cause irreparable damage of endothelium-dependent issues, and eventually death. Elucidation of the signaling regulating cytoskeletal structure and barrier integrity promotes the development of targeted pharmacotherapies towards disorders related to the impaired endothelium (e.g., acute respiratory distress syndrome, sepsis). Recent reports investigate the role of unfolded protein response in barrier function. Herein we review the cytoskeletal components, the unfolded protein response function; and their interrelations on health and disorder. Moreover, we emphasize on unfolded protein response modulators, since they ameliorate illness related to endothelial leak.

Retinal light damage: From mechanisms to protective strategies

Visible light serves as a crucial medium for vision formation.;however, prolonged or excessive exposure to light is recognized as a significant etiological factor contributing to retinal degenerative diseases. The retina, with its unique structure and adaptability, relies on the homeostasis of cellular functions to maintain visual health. Under normal conditions, the retina can mount adaptive responses to various insults, including light-induced damage. Unfortunately, exposure to intense and excessive light triggers a cascade of pathological alterations in retinal photoreceptor cells, pigment epithelial cells, ganglion cells, and glial cells. These alterations encompass disruption of intracellular REDOX and Ca²⁺ homeostasis, pyroptosis, endoplasmic reticulum stress, autophagy, and the release of inflammatory cytokines, culminating in irreversible retinal damage. We first delineate the mechanisms of retinal light damage through 4 main avenues: mitochondria function, endoplasmic reticulum stress, cell autophagy, and inflammation. Subsequently, we discuss protective strategies against retinal light damage, aiming to guide research toward the prevention and treatment of light-induced retinal conditions.

PDZD8 Augments Endoplasmic Reticulum-Mitochondria Contact and Regulates Ca2+ Dynamics and Cypd Expression to Induce Pancreatic β-Cell Death during Diabetes

BACKGRUOUND

Diabetes mellitus (DM) is a chronic metabolic disease that poses serious threats to human physical and mental health worldwide. The PDZ domain-containing 8 (PDZD8) protein mediates mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) formation in mammals. We explored the role of PDZD8 in DM and investigated its potential mechanism of action.

METHODS

High-fat diet (HFD)- and streptozotocin-induced mouse DM and palmitic acid (PA)-induced insulin 1 (INS-1) cell models were constructed. PDZD8 expression was detected using immunohistochemistry, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting. MAM formation, interactions between voltage-dependent anion-selective channel 1 (VDAC1) and inositol 1,4,5-triphosphate receptor type 1 (IP3R1), pancreatic β-cell apoptosis and proliferation were detected using transmission electron microscopy (TEM), proximity ligation assay (PLA), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, immunofluorescence staining, and Western blotting. The mitochondrial membrane potential, cell apoptosis, cytotoxicity, and subcellular Ca2+ localization in INS-1 cells were detected using a JC-1 probe, flow cytometry, and an lactate dehydrogenase kit.

RESULTS

PDZD8 expression was up-regulated in the islets of HFD mice and PA-treated pancreatic β-cells. PDZD8 knockdown markedly shortened MAM perimeter, suppressed the expression of MAM-related proteins IP3R1, glucose-regulated protein 75 (GRP75), and VDAC1, inhibited the interaction between VDAC1 and IP3R1, alleviated mitochondrial dysfunction and ER stress, reduced the expression of ER stress-related proteins, and decreased apoptosis while increased proliferation of pancreatic β-cells. Additionally, PDZD8 knockdown alleviated Ca2+ flow into the mitochondria and decreased cyclophilin D (Cypd) expression. Cypd overexpression alleviated the promoting effect of PDZD8 knockdown on the apoptosis of β-cells.

CONCLUSION

PDZD8 knockdown inhibited pancreatic β-cell death in DM by alleviated ER-mitochondria contact and the flow of Ca2+ into the mitochondria.

The Role of Immune Cells and Signaling Pathways in Diabetic Eye Disease: A Comprehensive Review

Diabetic eye disease (DED) encompasses a range of ocular complications arising from diabetes mellitus, including diabetic retinopathy, diabetic macular edema, diabetic keratopathy, diabetic cataract, and glaucoma. These conditions are leading causes of visual impairments and blindness, especially among working-age adults. Despite advancements in our understanding of DED, its underlying pathophysiological mechanisms remain incompletely understood. Chronic hyperglycemia, oxidative stress, inflammation, and neurodegeneration play central roles in the development and progression of DED, with immune-mediated processes increasingly recognized as key contributors. This review provides a comprehensive examination of the complex interactions between immune cells, inflammatory mediators, and signaling pathways implicated in the pathogenesis of DED. By delving in current research, this review aims to identify potential therapeutic targets, suggesting directions of research for future studies to address the immunopathological aspects of DED.

Molecular Mechanisms of Glaucoma Pathogenesis with Implications to Caveolin Adaptor Protein and Caveolin-Shp2 Axis

Glaucoma is a common retinal disorder characterized by progressive optic nerve damage, resulting in visual impairment and potential blindness. Elevated intraocular pressure (IOP) is a major risk factor, but some patients still experience disease progression despite IOP-lowering treatments. Genome-wide association studies have linked variations in the Caveolin1/2 (CAV-1/2) gene loci to glaucoma risk. Cav-1, a key protein in caveolae membrane invaginations, is involved in signaling pathways and its absence impairs retinal function. Recent research suggests that Cav-1 is implicated in modulating the BDNF/TrkB signaling pathway in retinal ganglion cells, which plays a critical role in retinal ganglion cell (RGC) health and protection against apoptosis. Understanding the interplay between these proteins could shed light on glaucoma pathogenesis and provide potential therapeutic targets.

Glial Cell Responses and Gene Expression Dynamics in Retinas of Treated and Untreated RPE65 Mutant Dogs

Purpose

The long-term evaluation of RPE65 gene augmentation initiated in middle-aged RPE65 mutant dogs previously uncovered notable inter-animal and intra-retinal variations in treatment efficacy. The study aims to gain deeper insights into the status of mutant retinas and assess the treatment impact.

Methods

Immunohistochemistry utilizing cell-specific markers and reverse transcription-quantitative PCR (RT-qPCR) analysis were conducted on archival retinal sections from normal and RPE65 mutant dogs.

Results

Untreated middle-aged mutant retinas exhibited marked downregulation in the majority of 20 examined genes associated with key retinal pathways. These changes were accompanied by a moderate increase in microglia numbers, altered expression patterns of glial-neuronal transmitter recycling proteins, and gliotic responses in Müller glia. Analysis of advanced-aged mutant dogs revealed mild outer nuclear layer loss in the treated eye compared to moderate loss in the corresponding retinal regions of the untreated control eye. However, persistent Müller glial stress response along with photoreceptor synapse loss were evident in both treated and untreated eyes. Photoreceptor synaptic remodeling, infrequent in treated regions, was observed in all untreated advanced-aged retinas, accompanied by a progressive increase in microglial cells indicative of ongoing inflammation. Interestingly, about half of the examined genes showed similar expression levels between treated and untreated advanced-aged mutant retinas, with some reaching normal levels.

Conclusions

Gene expression data suggest a shift from pro-degenerative mechanisms in middle-aged mutant retinas to more compensatory mechanisms in preserved retinal regions at advanced stages, despite ongoing degeneration. Such shift, potentially attributed to a number of surviving resilient cells, may influence disease patterns and treatment outcomes.

Misfolding and aggregation in neurodegenerative diseases: protein quality control machinery as potential therapeutic clearance pathways

The primary challenge in today's world of neuroscience is the search for new therapeutic possibilities for neurodegenerative disease. Central to these disorders lies among other factors, the aberrant folding, aggregation, and accumulation of proteins, resulting in the formation of toxic entities that contribute to neuronal degeneration. This review concentrates on the key proteins such as β-amyloid (Aβ), tau, and α-synuclein, elucidating the intricate molecular events underlying their misfolding and aggregation. We critically evaluate the molecular mechanisms governing the elimination of misfolded proteins, shedding light on potential therapeutic strategies. We specifically examine pathways such as the endoplasmic reticulum (ER) and unfolded protein response (UPR), chaperones, chaperone-mediated autophagy (CMA), and the intersecting signaling of Keap1-Nrf2-ARE, along with autophagy connected through p62. Above all, we emphasize the significance of these pathways as protein quality control mechanisms, encompassing interventions targeting protein aggregation, regulation of post-translational modifications, and enhancement of molecular chaperones and clearance. Additionally, we focus on current therapeutic possibilities and new, multi-target approaches. In conclusion, this review systematically consolidates insights into emerging therapeutic strategies predicated on protein aggregates clearance.

Systematic analysis of ocular features and responses of cultured spotted wolffish (Anarhichas minor)

A better understanding of unique anatomical and functional features of the visual systems of teleost fish could provide key knowledge on how these systems influence the health and survival of these animals in both wild and culture environments. We took a systematic approach to assess some of the visual systems of spotted wolffish (Anarhichas minor), a species of increasing importance in North Atlantic aquaculture initiatives. The lumpfish (Cyclopterus lumpus) was included in these studies in a comparative manner to provide reference. Histology, light and electron microscopy were used to study the spatial distribution and occurrence of cone photoreceptor cells and the nature of the retinal tissues, while immunohistochemistry was used to explore the expression patterns of two photoreceptor markers, XAP-1 and XAP-2, in both species. A marine bacterial infection paradigm in lumpfish was used to assess how host-pathogen responses might impact the expression of these photoreceptor markers in these animals. We define a basic photoreceptor mosaic and present an ultrastructural to macroscopic geographical configuration of the retinal pigment tissues in both animals. Photoreceptor markers XAP-1 and XAP-2 have novel distribution patterns in spotted wolffish and lumpfish retinas, and exogenous pathogenic influences can affect the normal expression pattern of XAP-1 in lumpfish. Live tank-side ophthalmoscopy and spectral domain optical coherence tomography (SD-OCT) revealed that normal cultured spotted wolffish display novel variations in the shape of the retinal tissue. These two complementary imaging findings suggest that spotted wolffish harbour unique ocular features not yet described in marine teleosts and that visual function might involve specific retinal tissue shape dynamics in these animals. Finally, extensive endogenous biofluorescence is present in the retinal tissues of both animals, which raises questions about how these animals might use retinal tissue in novel ways for visual perception and/or communication. This work advances fundamental knowledge on the visual systems of two economically important but now threatened North Atlantic teleosts and provides a basic foundation for further research on the visual systems of these animals in health versus disease settings. This work could also be useful for understanding and optimizing the health and welfare of lumpfish and spotted wolffish in aquaculture towards a one health or integrative perspective.

Comparative Proteomic Analysis of Type 2 Diabetic versus Non-Diabetic Vitreous Fluids

BACKGROUND

Diabetic retinopathy (DR) is a leading cause of vision loss, with complex mechanisms. The study aimed to comprehensively explore vitreous humor of diabetic and non-diabetic individuals, paving the way for identifying the potential molecular mechanisms underlying DR.

METHODS

Vitreous samples from type 2 diabetic and non-diabetic subjects, collected post-mortem, were analyzed using liquid chromatography-mass spectrometry. Pathway enrichment and gene ontology analyses were conducted to identify dysregulated pathways and characterize protein functions.

RESULTS

Pathway analysis revealed dysregulation in multiple metabolic and signaling pathways associated with diabetes, including glycerolipid metabolism, histidine metabolism, and Wnt signaling. Gene ontology analysis identified proteins involved in inflammation, immune response dysregulation, and calcium signaling. Notably, proteins such as Inositol 1,4,5-trisphosphate receptor type 2 (ITPR2), Calcium homeostasis endoplasmic reticulum protein (CHERP), and Coronin-1A (CORO1A) were markedly upregulated in diabetic vitreous, implicating aberrant calcium signaling, inflammatory responses, and cytoskeletal reorganization in DR.

CONCLUSIONS

Our study provides valuable insights into the intricate mechanisms underlying DR and highlights the significance of inflammation, immune dysregulation, and metabolic disturbances in disease progression. Identification of specific proteins as potential biomarkers underscores the multifactorial nature of DR. Future research in this area is vital for advancing therapeutic interventions and translating findings into clinical practice.

Network pharmacology and molecular-docking-based strategy to explore the potential mechanism of salidroside-inhibited oxidative stress in retinal ganglion cell

BACKGROUND

Salidroside (SAL), the main component of Rhodiola rosea extract, is a flavonoid with biological activities, such as antioxidative stress, anti-inflammatory, and hypolipidemic. In this study, the potential therapeutic targets and mechanisms of SAL against oxidative stress in retinal ganglion cells (RGCs) were investigated on the basis of in-vitro experiments, network pharmacology, and molecular docking techniques.

METHODS

RGC oxidative stress models were constructed, and cell activity, reactive oxygen species (ROS), and apoptosis levels were examined for differences. The genes corresponding to rhodopsin, RGCs, and oxidative stress were screened from GeneCards, TCMSP database, and an analysis platform. The intersection of the three was taken, and a Venn diagram was drawn. Protein interactions, GO functional enrichment, and KEGG pathway enrichment data were analyzed by STRING database, Cytohubba plugin, and Metascape database. The key factors in the screening pathway were validated using qRT-PCR. Finally, molecular docking prediction was performed using MOE 2019 software, molecular dynamic simulations was performed using Gromacs 2018 software.

RESULTS

In the RGC oxidative stress model in vitro, the cell activity was enhanced, ROS was reduced, and apoptosis was decreased after SAL treatment. A total of 16 potential targets of oxidative stress in SAL RGCs were obtained, and the top 10 core targets were screened by network topology analysis. GO analysis showed that SAL retinal oxidative stress treatment mainly involved cellular response to stress, transcriptional regulatory complexes, and DNA-binding transcription factor binding. KEGG analysis showed that most genes were mainly enriched in multiple cancer pathways and signaling pathways in diabetic complications, nonalcoholic fatty liver, and lipid and atherosclerosis. Validation by PCR, molecular docking and molecular dynamic simulations revealed that SAL may attenuate oxidative stress and reduce apoptosis in RGCs by regulating SIRT1, NRF2, and NOS3.

CONCLUSION

This study initially revealed the antioxidant therapeutic effects and molecular mechanisms of SAL on RGCs, providing a theoretical basis for subsequent studies.

Endoplasmic reticulum stress and quality control in relation to cisplatin resistance in tumor cells

The endoplasmic reticulum (ER) is a crucial organelle that orchestrates key cellular functions like protein folding and lipid biosynthesis. However, it is highly sensitive to disturbances that lead to ER stress. In response, the unfolded protein response (UPR) activates to restore ER homeostasis, primarily through three sensors: IRE1, ATF6, and PERK. ERAD and autophagy are crucial in mitigating ER stress, yet their dysregulation can lead to the accumulation of misfolded proteins. Cisplatin, a commonly used chemotherapy drug, induces ER stress in tumor cells, activating complex signaling pathways. Resistance to cisplatin stems from reduced drug accumulation, activation of DNA repair, and anti-apoptotic mechanisms. Notably, cisplatin-induced ER stress can dualistically affect tumor cells, promoting either survival or apoptosis, depending on the context. ERAD is crucial for degrading misfolded proteins, whereas autophagy can protect cells from apoptosis or enhance ER stress-induced apoptosis. The complex interaction between ER stress, cisplatin resistance, ERAD, and autophagy opens new avenues for cancer treatment. Understanding these processes could lead to innovative strategies that overcome chemoresistance, potentially improving outcomes of cisplatin-based cancer treatments. This comprehensive review provides a multifaceted perspective on the complex mechanisms of ER stress, cisplatin resistance, and their implications in cancer therapy.

Regulatory Non-coding RNAs Involved in Oxidative Stress and Neuroinflammation: An Intriguing Crosstalk in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the accumulation of α-synuclein and the degeneration of dopaminergic neurons in the substantia nigra. Although the molecular bases for PD development are not fully recognized, extensive evidence has suggested that the development of PD is strongly associated with neuroinflammation. It is noteworthy that while neuroinflammation might not be a primary factor in all patients with PD, it seems to be a driving force for disease progression, and therefore, exploring the role of pathways involved in neuroinflammation is of great importance. Besides, the importance of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and competing endogenous RNAs (ceRNAs), has been widely studied with a focus on the pathogenesis of PD. However, there is no comprehensive review regarding the role of neuroinflammation- related ncRNAs as prospective biomarkers and therapeutic targets involved in the pathogenesis of PD, even though the number of studies connecting ncRNAs to neuroinflammatory pathways and oxidative stress has markedly increased in the last few years. Hence, the present narrative review intended to describe the crosstalk between regulatory ncRNAs and neuroinflammatory targets with respect to PD to find and propose novel combining biomarkers or therapeutic targets in clinical settings.

Essential Role of XBP1 in Maintaining Photoreceptor Synaptic Integrity in Early Diabetic Retinopathy

Purpose

Diabetic retinopathy (DR) is a leading cause of blindness in working-age adults characterized by retinal dysfunction and neurovascular degeneration. We previously reported that deletion of X-box binding protein 1 (XBP1) leads to accelerated retinal neurodegeneration in diabetes; however, the mechanisms remain elusive. The goal of this study is to determine the role of XBP1 in the regulation of photoreceptor synaptic integrity in early DR.

Methods

Diabetes was induced by streptozotocin in retina-specific XBP1 conditional knockout (cKO) or wild-type (WT) mice to generate diabetic cKO (cKO/DM) or WT/DM mice for comparison with nondiabetic cKO (cKO/NDM) and WT/NDM mice. Retinal morphology, structure, and function were assessed by immunohistochemistry, optical coherence tomography, and electroretinogram (ERG) after 3 months of diabetes. The synapses between photoreceptors and bipolar cells were examined by confocal microscopy, and synaptic integrity was quantified using the QUANTOS algorithm.

Results

We found a thinning of the outer nuclear layer and a decline in the b-wave amplitude in dark- and light-adapted ERG in cKO/DM mice compared to all other groups. In line with these changes, cKO mice showed increased loss of synaptic integrity compared to WT mice, regardless of diabetes status. In searching for candidate molecules responsible for the loss of photoreceptor synaptic integrity in diabetic and XBP1-deficient retinas, we found decreased mRNA and protein levels of DLG4/PSD-95 in cKO/DM retina compared to WT/DM.

Conclusions

These findings suggest that XBP1 is a crucial regulator in maintaining synaptic integrity and retinal function, possibly through regulation of synaptic scaffold proteins.

Tempol improves optic nerve histopathology and ultrastructures in cisplatin-induced optic neuropathy in rats by targeting oxidative stress-Endoplasmic reticulum stress-Autophagy signaling pathways

Introduction

Optic neuropathy is an affection of the optic neurons, which ends with blindness and occurs either primarily due to direct affection of the optic nerve or secondarily as a complication of chronic diseases and/or adverse effects of their therapy. The search for novel therapeutic tools is crucial in addressing the limited therapeutic approaches for optic neuropathy. Therefore, the present study was developed to investigate the possible ameliorative effect of tempol against cisplatin-induced optic neuropathy and its underlying mechanism.

Methods

Forty-eight adult male albino Wistar rats were divided into four equal groups-control, tempol (TEM), cisplatin (CIS), and tempol and cisplatin combined (TEM+CIS). Optic nerve oxidative stress (MDA, SOD, and GPx), gene expression of endoplasmic reticulum stress (ATF-6, XBP-1, BIP, CHOP, and JNK), autophagy 6 (LC3, Beclin-1, and p62) markers, nerve growth factor-1, immunohistochemical expression of (LC3 and p62), histopathological, and electron microscopic examination were performed.

Results

Histopathological and ultrastructure examination validated that cisplatin caused optic neuropathy by inducing oxidative stress, upregulating ER stress markers, and downregulating autophagy markers, and NGF-1 expression. TEM + CIS showed improvement in optic nerve structure and ultrastructure along with oxidative stress, ER stress mRNA, autophagy (immunohistochemical proteins and mRNA) markers, and nerve growth factor mRNA expression.

Conclusions

Based on previous findings, tempol represents a valid aid in cisplatin-induced optic neuropathy by implicating new molecular drug targets (ER stress and autophagy) for optic neuropathy therapy.

PERK Inhibition Suppresses Neovascularization and Protects Neurons During Ischemia-Induced Retinopathy

Purpose

Retinal ischemia is a common cause of a variety of eye diseases, such as retinopathy of prematurity, diabetic retinopathy, and vein occlusion. Protein kinase RNA-activated-like endoplasmic reticulum (ER) kinase (PERK), one of the main ER stress sensor proteins, has been involved in many diseases. In this study, we investigated the role of PERK in ischemia-induced retinopathy using a mouse model of oxygen-induced retinopathy (OIR).

Methods

OIR was induced by subjecting neonatal pups to 70% oxygen at postnatal day 7 (P7) followed by returning to room air at P12. GSK2606414, a selective PERK inhibitor, was orally administrated to pups right after they were returned to room air once daily until 1 day before sample collection. Western blot, immunostaining, and quantitative PCR were used to assess PERK phosphorylation, retinal changes, and signaling pathways in relation to PERK inhibition.

Results

PERK phosphorylation was prominently increased in OIR retinas, which was inhibited by GSK2606414. Concomitantly, PERK inhibition significantly reduced retinal neovascularization (NV) and retinal ganglion cell (RGC) loss, restored astrocyte network, and promoted revascularization. Furthermore, PERK inhibition downregulated the recruitment/proliferation of mononuclear phagocytes but did not affect OIR-upregulated canonical angiogenic pathways.

Conclusions

Our results demonstrate that PERK is involved in ischemia-induced retinopathy and its inhibition using GSK2606414 could offer an effective therapeutic intervention aimed at alleviating retinal NV while preventing neuron loss during retinal ischemia.

Endogenous and Exogenous Antioxidants as Agents Preventing the Negative Effects of Contrast Media (Contrast-Induced Nephropathy)

The use of conventional contrast media for diagnostic purposes (in particular, Gd-containing and iodinated agents) causes a large number of complications, the most common of which is contrast-induced nephropathy. It has been shown that after exposure to contrast agents, oxidative stress often occurs in patients, especially in people suffering from various diseases. Antioxidants in the human body can diminish the pathological consequences of the use of contrast media by suppressing oxidative stress. This review considers the research studies on the role of antioxidants in preventing the negative consequences of the use of contrast agents in diagnostics (mainly contrast-induced nephropathy) and the clinical trials of different antioxidant drugs against contrast-induced nephropathy. Composite antioxidant/contrast systems as theranostic agents are also considered.

Endogenous and Exogenous Regulation of Redox Homeostasis in Retinal Pigment Epithelium Cells: An Updated Antioxidant Perspective

The retinal pigment epithelium (RPE) performs a range of necessary functions within the neural layers of the retina and helps ensure vision. The regulation of pro-oxidative and antioxidant processes is the basis for maintaining RPE homeostasis and preventing retinal degenerative processes. Long-term stable changes in the redox balance under the influence of endogenous or exogenous factors can lead to oxidative stress (OS) and the development of a number of retinal pathologies associated with RPE dysfunction, and can eventually lead to vision loss. Reparative autophagy, ubiquitin-proteasome utilization, the repair of damaged proteins, and the maintenance of their conformational structure are important interrelated mechanisms of the endogenous defense system that protects against oxidative damage. Antioxidant protection of RPE cells is realized as a result of the activity of specific transcription factors, a large group of enzymes, chaperone proteins, etc., which form many signaling pathways in the RPE and the retina. Here, we discuss the role of the key components of the antioxidant defense system (ADS) in the cellular response of the RPE against OS. Understanding the role and interactions of OS mediators and the components of the ADS contributes to the formation of ideas about the subtle mechanisms in the regulation of RPE cellular functions and prospects for experimental approaches to restore RPE functions.

Signal Peptide Variants in Inherited Retinal Diseases: A Multi-Institutional Case Series

Signal peptide (SP) mutations are an infrequent cause of inherited retinal diseases (IRDs). We report the genes currently associated with an IRD that possess an SP sequence and assess the prevalence of these variants in a multi-institutional retrospective review of clinical genetic testing records. The online databases, RetNet and UniProt, were used to determine which IRD genes possess a SP. A multicenter retrospective review was performed to retrieve cases of patients with a confirmed diagnosis of an IRD and a concurrent SP variant. In silico evaluations were performed with MutPred, MutationTaster, and the signal peptide prediction tool, SignalP 6.0. SignalP 6.0 was further used to determine the locations of the three SP regions in each gene: the N-terminal region, hydrophobic core, and C-terminal region. Fifty-six (56) genes currently associated with an IRD possess a SP sequence. Based on the records review, a total of 505 variants were present in the 56 SP-possessing genes. Six (1.18%) of these variants were within the SP sequence and likely associated with the patients' disease based on in silico predictions and clinical correlation. These six SP variants were in the CRB1 (early-onset retinal dystrophy), NDP (familial exudative vitreoretinopathy) (FEVR), FZD4 (FEVR), EYS (retinitis pigmentosa), and RS1 (X-linked juvenile retinoschisis) genes. It is important to be aware of SP mutations as an exceedingly rare cause of IRDs. Future studies will help refine our understanding of their role in each disease process and assess 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.

Key biomarkers and latent pathways of dysferlinopathy: Bioinformatics analysis and in vivo validation

Background

Dysferlinopathy refers to a group of muscle diseases with progressive muscle weakness and atrophy caused by pathogenic mutations of the DYSF gene. The pathogenesis remains unknown, and currently no specific treatment is available to alter the disease progression. This research aims to investigate important biomarkers and their latent biological pathways participating in dysferlinopathy and reveal the association with immune cell infiltration.

Methods

GSE3307 and GSE109178 were obtained from the Gene Expression Omnibus (GEO) database. Based on weighted gene co-expression network analysis (WGCNA) and differential expression analysis, coupled with least absolute shrinkage and selection operator (LASSO), the key genes for dysferlinopathy were identified. Functional enrichment analysis Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were applied to disclose the hidden biological pathways. Following that, the key genes were approved for diagnostic accuracy of dysferlinopathy based on another dataset GSE109178, and quantitative real-time polymerase chain reaction (qRT-PCR) were executed to confirm their expression. Furthermore, the 28 immune cell abundance patterns in dysferlinopathy were determined with single-sample GSEA (ssGSEA).

Results

1,579 differentially expressed genes (DEGs) were screened out. Based on WGCNA, three co-expression modules were obtained, with the MEskyblue module most strongly correlated with dysferlinopathy. 44 intersecting genes were recognized from the DEGs and the MEskyblue module. The six key genes MVP, GRN, ERP29, RNF128, NFYB and KPNA3 were discovered through LASSO analysis and experimentally verified later. In a receiver operating characteristic analysis (ROC) curve, the six hub genes were shown to be highly valuable for diagnostic purposes. Furthermore, functional enrichment analysis highlighted that these genes were enriched mainly along the ubiquitin-proteasome pathway (UPP). Ultimately, ssGSEA showed a significant immune-cell infiltrative microenvironment in dysferlinopathy patients, especially T cell, macrophage, and activated dendritic cell (DC).

Conclusion

Six key genes are identified in dysferlinopathy with a bioinformatic approach used for the first time. The key genes are believed to be involved in protein degradation pathways and the activation of muscular inflammation. And several immune cells, such as T cell, macrophage and DC, are considered to be implicated in the progression of dysferlinopathy.

Proteomic Analysis of Retinal Mitochondria-Associated ER Membranes Identified Novel Proteins of Retinal Degeneration in Long-Term Diabetes

The mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) is the physical contact site between the ER and the mitochondria and plays a vital role in the regulation of calcium signaling, bioenergetics, and inflammation. Disturbances in these processes and dysregulation of the ER and mitochondrial homeostasis contribute to the pathogenesis of diabetic retinopathy (DR). However, few studies have examined the impact of diabetes on the retinal MAM and its implication in DR pathogenesis. In the present study, we investigated the proteomic changes in retinal MAM from Long Evans rats with streptozotocin-induced long-term Type 1 diabetes. Furthermore, we performed in-depth bioinformatic analysis to identify key MAM proteins and pathways that are potentially implicated in retinal inflammation, angiogenesis, and neurodegeneration. A total of 2664 unique proteins were quantified using IonStar proteomics-pipeline in rat retinal MAM, among which 179 proteins showed significant changes in diabetes. Functional annotation revealed that the 179 proteins are involved in important biological processes such as cell survival, inflammatory response, and cellular maintenance, as well as multiple disease-relevant signaling pathways, e.g., integrin signaling, leukocyte extravasation, PPAR, PTEN, and RhoGDI signaling. Our study provides comprehensive information on MAM protein changes in diabetic retinas, which is helpful for understanding the mechanisms of metabolic dysfunction and retinal cell injury in DR.

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.

Retinal Glutamate Neurotransmission: From Physiology to Pathophysiological Mechanisms of Retinal Ganglion Cell Degeneration

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

Tools and Biomarkers for the Study of Retinal Ganglion Cell Degeneration

The retina is part of the central nervous system, its analysis may provide an idea of the health and functionality, not only of the retina, but also of the entire central nervous system, as has been shown in Alzheimer’s or Parkinson’s diseases. Within the retina, the ganglion cells (RGC) are the neurons in charge of processing and sending light information to higher brain centers. Diverse insults and pathological states cause degeneration of RGC, leading to irreversible blindness or impaired vision. RGCs are the measurable endpoints in current research into experimental therapies and diagnosis in multiple ocular pathologies, like glaucoma. RGC subtype classifications are based on morphological, functional, genetical, and immunohistochemical aspects. Although great efforts are being made, there is still no classification accepted by consensus. Moreover, it has been observed that each RGC subtype has a different susceptibility to injury. Characterizing these subtypes together with cell death pathway identification will help to understand the degenerative process in the different injury and pathological models, and therefore prevent it. Here we review the known RGC subtypes, as well as the diagnostic techniques, probes, and biomarkers for programmed and unprogrammed cell death in RGC.

Cellular stress signaling and the unfolded protein response in retinal degeneration: mechanisms and therapeutic implications

Background

The retina, as part of the central nervous system (CNS) with limited capacity for self-reparation and regeneration in mammals, is under cumulative environmental stress due to high-energy demands and rapid protein turnover. These stressors disrupt the cellular protein and metabolic homeostasis, which, if not alleviated, can lead to dysfunction and cell death of retinal neurons. One primary cellular stress response is the highly conserved unfolded protein response (UPR). The UPR acts through three main signaling pathways in an attempt to restore the protein homeostasis in the endoplasmic reticulum (ER) by various means, including but not limited to, reducing protein translation, increasing protein-folding capacity, and promoting misfolded protein degradation. Moreover, recent work has identified a novel function of the UPR in regulation of cellular metabolism and mitochondrial function, disturbance of which contributes to neuronal degeneration and dysfunction. The role of the UPR in retinal neurons during aging and under disease conditions in age-related macular degeneration (AMD), retinitis pigmentosa (RP), glaucoma, and diabetic retinopathy (DR) has been explored over the past two decades. Each of the disease conditions and their corresponding animal models provide distinct challenges and unique opportunities to gain a better understanding of the role of the UPR in the maintenance of retinal health and function.

Method

We performed an extensive literature search on PubMed and Google Scholar using the following keywords: unfolded protein response, metabolism, ER stress, retinal degeneration, aging, age-related macular degeneration, retinitis pigmentosa, glaucoma, diabetic retinopathy.

Results and conclusion

We summarize recent advances in understanding cellular stress response, in particular the UPR, in retinal diseases, highlighting the potential roles of UPR pathways in regulation of cellular metabolism and mitochondrial function in retinal neurons. Further, we provide perspective on the promise and challenges for targeting the UPR pathways as a new therapeutic approach in age- and disease-related retinal degeneration.

Ligand-based rational design, synthesis and evaluation of novel potential chemical chaperones for opsin

Inherited blinding diseases retinitis pigmentosa (RP) and a subset of Leber's congenital amaurosis (LCA) are caused by the misfolding and mistrafficking of rhodopsin molecules, which aggregate and accumulate in the endoplasmic reticulum (ER), leading to photoreceptor cell death. One potential therapeutic strategy to prevent the loss of photoreceptors in these conditions is to identify opsin-binding compounds that act as chemical chaperones for opsin, aiding its proper folding and trafficking to the outer cell membrane. Aiming to identify novel compounds with such effect, a rational ligand-based approach was applied to the structure of the visual pigment chromophore, 11-cis-retinal, and its locked analogue 11-cis-6mr-retinal. Following molecular docking studies on the main chromophore binding site of rhodopsin, 49 novel compounds were synthesized according to optimized one-to seven-step synthetic routes. These agents were evaluated for their ability to compete for the chromophore binding site of opsin, and their capacity to increase the trafficking of the P23H opsin mutant from the ER to the cell membrane. Different new molecules displayed an effect in at least one assay, acting either as chemical chaperones or as stabilizers of the 9-cis-retinal-rhodopsin complex. These compounds could provide the basis to develop novel therapeutics for RP and LCA.

Role of Oxidative Stress in Ocular Diseases Associated with Retinal Ganglion Cells Degeneration

Ocular diseases associated with retinal ganglion cell (RGC) degeneration is the most common neurodegenerative disorder that causes irreversible blindness worldwide. It is characterized by visual field defects and progressive optic nerve atrophy. The underlying pathophysiology and mechanisms of RGC degeneration in several ocular diseases remain largely unknown. RGCs are a population of central nervous system neurons, with their soma located in the retina and long axons that extend through the optic nerve to form distal terminals and connections in the brain. Because of this unique cytoarchitecture and highly compartmentalized energy demand, RGCs are highly mitochondrial-dependent for adenosine triphosphate (ATP) production. Recently, oxidative stress and mitochondrial dysfunction have been found to be the principal mechanisms in RGC degeneration as well as in other neurodegenerative disorders. Here, we review the role of oxidative stress in several ocular diseases associated with RGC degenerations, including glaucoma, hereditary optic atrophy, inflammatory optic neuritis, ischemic optic neuropathy, traumatic optic neuropathy, and drug toxicity. We also review experimental approaches using cell and animal models for research on the underlying mechanisms of RGC degeneration. Lastly, we discuss the application of antioxidants as a potential future therapy for the ocular diseases associated with RGC degenerations.

Multiomic analysis on human cell model of wolfram syndrome reveals changes in mitochondrial morphology and function

BACKGROUND

Wolfram syndrome (WFS) is a rare autosomal recessive syndrome in which diabetes mellitus and neurodegenerative disorders occur as a result of Wolframin deficiency and increased ER stress. In addition, WFS1 deficiency leads to calcium homeostasis disturbances and can change mitochondrial dynamics. The aim of this study was to evaluate protein levels and changes in gene transcription on human WFS cell model under experimental ER stress.

METHODS

We performed transcriptomic and proteomic analysis on WFS human cell model-skin fibroblasts reprogrammed into induced pluripotent stem (iPS) cells and then into neural stem cells (NSC) with subsequent ER stress induction using tunicamycin (TM). Results were cross-referenced with publicly available RNA sequencing data in hippocampi and hypothalami of mice with WFS1 deficiency.

RESULTS

Proteomic analysis identified specific signal pathways that differ in NSC WFS cells from healthy ones. Next, detailed analysis of the proteins involved in the mitochondrial function showed the down-regulation of subunits of the respiratory chain complexes in NSC WFS cells, as well as the up-regulation of proteins involved in Krebs cycle and glycolysis when compared to the control cells. Based on pathway enrichment analysis we concluded that in samples from mice hippocampi the mitochondrial protein import machinery and OXPHOS were significantly down-regulated.

CONCLUSIONS

Our results show the functional and morphological secondary mitochondrial damage in patients with WFS. Video Abstract.

The emerging role of noncoding RNAs in neuroinflammation: Implications in pathogenesis and therapeutic approaches

Noncoding RNAs (ncRNAs) are important regulators of gene expression in different cell processes. Due to their ability in monitoring neural development genes, these transcripts confer neurons with the potential to exert broad control over the expression of genes for performing neurobiological functions. Although the change of ncRNA expression in different neurodegenerative diseases has been reviewed elsewhere, only recent evidence drove our attention to unravel the involvement of these molecules in neuroinflammation within these devastating disorders. Remarkably, the interactions between ncRNAs and inflammatory pathways are not fully recognized. Therefore, this review has focused on the interplay between diverse inflammatory pathways and the related ncRNAs, including microRNAs, long noncoding RNAs, and competing endogenous RNAs in Alzheimer's disease, Parkinson's diseases, amyotrophic lateral sclerosis, epilepsy, multiple sclerosis, Huntington's disease, and prion diseases. Providing novel insights in the field of combining biomarkers is a critical step for using them as diagnostic tools and therapeutic targets in clinical settings.

Mitochondrial Dysfunction and Endoplasmic Reticulum Stress in Age Related Macular Degeneration, Role in Pathophysiology, and Possible New Therapeutic Strategies

Age related macular degeneration (AMD) is the main cause of legal blindness in developed countries. It is a multifactorial disease in which a combination of genetic and environmental factors contributes to increased risk of developing this vision-incapacitating condition. Oxidative stress plays a central role in the pathophysiology of AMD and recent publications have highlighted the importance of mitochondrial dysfunction and endoplasmic reticulum stress in this disease. Although treatment with vascular endothelium growth factor inhibitors have decreased the risk of blindness in patients with the exudative form of AMD, the search for new therapeutic options continues to prevent the loss of photoreceptors and retinal pigment epithelium cells, characteristic of late stage AMD. In this review, we explain how mitochondrial dysfunction and endoplasmic reticulum stress participate in AMD pathogenesis. We also discuss a role of several antioxidants (bile acids, resveratrol, melatonin, humanin, and coenzyme Q10) in amelioration of AMD pathology.

Patient derived stem cells for discovery and validation of novel pathogenic variants in inherited retinal disease

Our understanding of inherited retinal disease has benefited immensely from molecular genetic analysis over the past several decades. New technologies that allow for increasingly detailed examination of a patient's DNA have expanded the catalog of genes and specific variants that cause retinal disease. In turn, the identification of pathogenic variants has allowed the development of gene therapies and low-cost, clinically focused genetic testing. Despite this progress, a relatively large fraction (at least 20%) of patients with clinical features suggestive of an inherited retinal disease still do not have a molecular diagnosis today. Variants that are not obviously disruptive to the codon sequence of exons can be difficult to distinguish from the background of benign human genetic variations. Some of these variants exert their pathogenic effect not by altering the primary amino acid sequence, but by modulating gene expression, isoform splicing, or other transcript-level mechanisms. While not discoverable by DNA sequencing methods alone, these variants are excellent targets for studies of the retinal transcriptome. In this review, we present an overview of the current state of pathogenic variant discovery in retinal disease and identify some of the remaining barriers. We also explore the utility of new technologies, specifically patient-derived induced pluripotent stem cell (iPSC)-based modeling, in further expanding the catalog of disease-causing variants using transcriptome-focused methods. Finally, we outline bioinformatic analysis techniques that will allow this new method of variant discovery in retinal disease. As the knowledge gleaned from previous technologies is informing targets for therapies today, we believe that integrating new technologies, such as iPSC-based modeling, into the molecular diagnosis pipeline will enable a new wave of variant discovery and expanded treatment of inherited retinal disease.

Gypenosides Alleviate Cone Cell Death in a Zebrafish Model of Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a group of visual disorders caused by mutations in over 70 genes. RP is characterized by initial degeneration of rod cells and late cone cell death, regardless of genetic abnormality. Rod cells are the main consumers of oxygen in the retina, and after the death of rod cells, the cone cells have to endure high levels of oxygen, which in turn leads to oxidative damage and cone degeneration. Gypenosides (Gyp) are major dammarane-type saponins of Gynostemma pentaphyllum that are known to reduce oxidative stress and inflammation. In this project we assessed the protective effect of Gyp against cone cell death in the rpgrip1 mutant zebrafish, which recapitulate the classical pathological features found in RP patients. Rpgrip1 mutant zebrafish were treated with Gyp (50 µg/g body weight) from two-months post fertilization (mpf) until 6 mpf. Gyp treatment resulted in a significant decrease in cone cell death compared to that of untreated mutant zebrafish. A markedly low level of reactive oxygen species and increased expression of antioxidant genes were detected in Gyp-incubated mutant zebrafish eyes compared to that of untreated mutant zebrafish. Similarly, the activities of catalase and superoxide dismutase and the level of glutathione were significantly increased in Gyp-treated mutant zebrafish eyes compared to that of untreated mutant zebrafish. Gyp treatment also decreased endoplasmic reticulum stress in rpgrip1 mutant eyes. Expression of proinflammatory cytokines was also significantly decreased in Gyp-treated mutant zebrafish eyes compared to that of untreated mutant zebrafish. Network pharmacology analysis demonstrated that the promotion of cone cell survival by Gyp is possibly mediated by multiple hub genes and associated signalling pathways. These data suggest treatment with Gyp will benefit RP patients.

Resveratrol and endoplasmic reticulum stress: A review of the potential protective mechanisms of the polyphenol

The endoplasmic reticulum (ER) is an organelle that performs a set of essential functions in cellular biology. These include synthesis of lipids, homeostasis of calcium, and controlling the folding of proteins. Inflammation and oxidative stress are two important reasons behind the accumulation of misfolded or unfolded proteins in the ER. In such circumstances, a series of measures are undertaken in the cell which are collectively called unfolded protein response (UPR). The aim of UPR is to reduce the burden of protein aggregates and promote survival. However, extended and unrestricted ER stress (ERS) can induce further inflammation and apoptosis. ERS and the UPR are involved in different diseases such as neurodegenerative and cardiovascular diseases. Resveratrol (RSV), a natural polyphenol, has well-documented evidence supporting its numerous biological properties including antioxidant, antiinflammatory, antiobesity, antidiabetic, and antiischemic activities. The compound is also known for its potential beneficial effects on cognitive function and liver, kidney, and lung health. In this review, the role of ERS in several pathological conditions and the potential protective effects of RSV are discussed. However, the scarcity of clinical data means that more research needs to be conducted to gain a lucid understanding of RSV's effects on endoplasmic reticulum stress (ERS) in humans.

Traumatic Optic Neuropathy Is Associated with Visual Impairment, Neurodegeneration, and Endoplasmic Reticulum Stress in Adolescent Mice

Traumatic brain injury (TBI) results in a number of impairments, often including visual symptoms. In some cases, visual impairments after head trauma are mediated by traumatic injury to the optic nerve, termed traumatic optic neuropathy (TON), which has few effective options for treatment. Using a murine closed-head weight-drop model of head trauma, we previously reported in adult mice that there is relatively selective injury to the optic tract and thalamic/brainstem projections of the visual system. In the current study, we performed blunt head trauma on adolescent C57BL/6 mice and investigated visual impairment in the primary visual system, now including the retina and using behavioral and histologic methods at new time points. After injury, mice displayed evidence of decreased optomotor responses illustrated by decreased optokinetic nystagmus. There did not appear to be a significant change in circadian locomotor behavior patterns, although there was an overall decrease in locomotor behavior in mice with head injury. There was evidence of axonal degeneration of optic nerve fibers with associated retinal ganglion cell death. There was also evidence of astrogliosis and microgliosis in major central targets of optic nerve projections. Further, there was elevated expression of endoplasmic reticulum (ER) stress markers in retinas of injured mice. Visual impairment, histologic markers of gliosis and neurodegeneration, and elevated ER stress marker expression persisted for at least 30 days after injury. The current results extend our previous findings in adult mice into adolescent mice, provide direct evidence of retinal ganglion cell injury after head trauma and suggest that axonal degeneration is associated with elevated ER stress in this model of TON.

Transcriptomic Changes Associated with Loss of Cell Viability Induced by Oxysterol Treatment of a Retinal Photoreceptor-Derived Cell Line: An In Vitro Model of Smith-Lemli-Opitz Syndrome

Smith–Lemli–Opitz Syndrome (SLOS) results from mutations in the gene encoding the enzyme DHCR7, which catalyzes conversion of 7-dehydrocholesterol (7DHC) to cholesterol (CHOL). Rats treated with a DHCR7 inhibitor serve as a SLOS animal model, and exhibit progressive photoreceptor-specific cell death, with accumulation of 7DHC and oxidized sterols. To understand the basis of this cell type specificity, we performed transcriptomic analyses on a photoreceptor-derived cell line (661W), treating cells with two 7DHC-derived oxysterols, which accumulate in tissues and bodily fluids of SLOS patients and in the rat SLOS model, as well as with CHOL (negative control), and evaluated differentially expressed genes (DEGs) for each treatment. Gene enrichment analysis and compilation of DEG sets indicated that endoplasmic reticulum stress, oxidative stress, DNA damage and repair, and autophagy were all highly up-regulated pathways in oxysterol-treated cells. Detailed analysis indicated that the two oxysterols exert their effects via different molecular mechanisms. Changes in expression of key genes in highlighted pathways (Hmox1, Ddit3, Trib3, and Herpud1) were validated by immunofluorescence confocal microscopy. The results extend our understanding of the pathobiology of retinal degeneration and SLOS, identifying potential new druggable targets for therapeutic intervention into these and other related orphan diseases.

Different Doses of β-Cryptoxanthin May Secure the Retina from Photooxidative Injury Resulted from Common LED Sources

Retinal damage associated with loss of photoreceptors is a hallmark of eye diseases such as age-related macular degeneration (AMD) and diabetic retinopathy. Potent nutritional antioxidants were previously shown to abate the degenerative process in AMD. β-Cryptoxanthin (BCX) is an essential dietary carotenoid with antioxidant, anti-inflammatory, and provitamin A activity. It is a potential candidate for developing intervention strategies to delay the development/progression of AMD. In the current study, the effect of a novel, highly purified BCX oral formulation on the rat retinal damage model was evaluated. Rats were fed with BCX for four weeks at the doses of 2 and 4 mg/kg body weight in the form of highly bioavailable oil suspension, followed by retinal damage by exposing to the bright light-emitting diode (LED) light (750 lux) for 48 hrs. Animals were sacrificed after 48 hours, and eyes and blood samples were collected and analyzed. BCX supplementations (2 and 4 mg/kg) showed improvements in the visual condition as demonstrated by histopathology of the retina and measured parameters such as total retinal thickness and outer nuclear layer thickness. BCX supplementation helped reduce the burden of oxidative stress as seen by decreased serum and retinal tissue levels of malondialdehyde (MDA) and restored the antioxidant enzyme activities in BCX groups. Further, BCX supplementation modulated inflammatory markers (IL-1β, IL-6, and NF-κB), apoptotic proteins (Bax, Bcl-2, caspase 3), growth proteins and factors (GAP43, VEGF), glial and neuronal proteins (GFAP, NCAM), and heme oxygenase-1 (HO-1), along with the mitochondrial stress markers (ATF4, ATF6, Grp78, Grp94) in the rat retinal tissue. This study indicates that oral supplementation of BCX exerts a protective effect on light-induced retinal damage in the rats via reducing oxidative stress and inflammation, also protected against mitochondrial DNA damage and cellular death.

Mutations in the splicing regulator Prp31 lead to retinal degeneration in Drosophila

Retinitis pigmentosa (RP) is a clinically heterogeneous disease affecting 1.6 million people worldwide. The second-largest group of genes causing autosomal dominant RP in human encodes regulators of the splicing machinery. Yet, how defects in splicing factor genes are linked to the aetiology of the disease remains largely elusive. To explore possible mechanisms underlying retinal degeneration caused by mutations in regulators of the splicing machinery, we induced mutations in Drosophila Prp31, the orthologue of human PRPF31, mutations in which are associated with RP11. Flies heterozygous mutant for Prp31 are viable and develop normal eyes and retina. However, photoreceptors degenerate under light stress, thus resembling the human disease phenotype. Degeneration is associated with increased accumulation of the visual pigment rhodopsin 1 and increased mRNA levels of twinfilin, a gene associated with rhodopsin trafficking. Reducing rhodopsin levels by raising animals in a carotenoid-free medium not only attenuates rhodopsin accumulation, but also retinal degeneration. Given a similar importance of proper rhodopsin trafficking for photoreceptor homeostasis in human, results obtained in flies presented here will also contribute to further unravel molecular mechanisms underlying the human disease.

This paper has an associated First Person interview with the co-first authors of the article.

Summary: Retinitis pigmentosa (RP) is a human disease resulting in blindness, which affects 1 in 4.000 people worldwide. So far >90 genes have been identified that are causally related to RP. Mutations in the splicing factor PRPF31 are linked to RP11. We induced mutations in the Drosophila orthologue Prp31 and show that flies heterozygous for Prp31 undergo light-dependent retinal degeneration. Degeneration is associated with increased accumulation of the light-sensitive molecule, rhodopsin 1. In fact, reducing rhodopsin levels by dietary intervention modifies the extent of retinal degeneration. This model will further contribute to better understand the aetiology of the human disease.

In Vivo Anti-Inflammation Potential of Aster koraiensis Extract for Dry Eye Syndrome by the Protection of Ocular Surface

Dry eye syndrome (DES) is a corneal disease often characterized by an irritating, itching feeling in the eyes and light sensitivity. Inflammation and endoplasmic reticulum (ER) stress may play a crucial role in the pathogenesis of DES, although the underlying mechanism remains elusive. Aster koraiensis has been used traditionally as an edible herb in Korea. It has been reported to have wound-healing and inhibitory effects against insulin resistance and inflammation. Here, we examined the inhibitory effects of inflammation and ER stress by A. koraiensis extract (AKE) in animal model and human retinal pigmented epithelial (ARPE-19) cells. Oral administration of AKE mitigated DE symptoms, including reduced corneal epithelial thickness, increased the gap between lacrimal gland tissues in experimental animals and decreased tear production. It also inhibited inflammatory responses in the corneal epithelium and lacrimal gland. Consequently, the activation of NF-κB was attenuated by the suppression of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Moreover, AKE treatment ameliorated TNF-α-inducible ocular inflammation and thapsigargin (Tg)-inducible ER stress in animal model and human retinal pigmented epithelial (ARPE-19) cells. These results prove that AKE prevents detrimental functional and histological remodeling on the ocular surface and in the lacrimal gland through inhibition of inflammation and ER stress, suggesting its potential as functional food material for improvement of DES.

Computational Studies towards the Identification of Novel Rhodopsin-Binding Compounds as Chemical Chaperones for Misfolded Opsins

Accumulation of misfolded and mistrafficked rhodopsin on the endoplasmic reticulum of photoreceptor cells has a pivotal role in the pathogenesis of retinitis pigmentosa and a subset of Leber’s congenital amaurosis. One potential strategy to reduce rhodopsin misfolding and aggregation in these conditions is to use opsin-binding compounds as chemical chaperones for opsin. Such molecules have previously shown the ability to aid rhodopsin folding and proper trafficking to the outer cell membranes of photoreceptors. As means to identify novel chemical chaperones for rhodopsin, a structure-based virtual screening of commercially available drug-like compounds (300,000) was performed on the main binding site of the visual pigment chromophore, the 11-cis-retinal. The best 24 virtual hits were examined for their ability to compete for the chromophore-binding site of opsin. Among these, four small molecules demonstrated the ability to reduce the rate constant for the formation of the 9-cis-retinal-rhodopsin complex, while five molecules surprisingly enhanced the formation of this complex. Compound 7, 13, 20 and 23 showed a weak but detectable increase in the trafficking of the P23H mutant, widely used as a model for both retinitis pigmentosa and Leber’s congenital amaurosis, from the ER to the cell membrane. The compounds did not show any relevant cytotoxicity in two different human cell lines, with the only exception of 13. Based on the structures of these active compounds, a series of in silico studies gave important insights on the potential structural features required for a molecule to act either as chemical chaperone or as stabiliser of the 11-cis-retinal-rhodopsin complex. Thus, this study revealed a series of small molecules that represent a solid foundation for the future development of novel therapeutics against these severe inherited blinding diseases.

Gypenosides attenuate retinal degeneration in a zebrafish retinitis pigmentosa model

Retinitis pigmentosa (RP) is a collection of heterogenous genetic retinal disorders resulting in cumulative retinal deterioration involving progressive loss of photoreceptors and eventually in total blindness. Oxidative stress plays a central role in this photoreceptor loss. Gypenosides (Gyp) are the main functional component isolated from the climbing vine Gynostemma pentaphyllum and have been shown to defend cells against the effects of oxidative stress and inflammation, providing protection in experimentally-induced optic neuritis. The zebrafish model has been used to investigate a range of human diseases. Previously we reported early retinal degeneration in a mutant zebrafish line carrying a point-nonsense mutation in the retinitis pigmentosa GTPase regulator interacting protein 1 (rpgrip1) gene that is mutated in RP patients. The current study investigated the potential protective effects of Gyp against photoreceptor degeneration in the Rpgrip1 deleted zebrafish. Rpgrip1 mutant zebrafish were treated with 5 μg/ml of Gyp in E3 medium from 6 h post fertilization (hpf) till 1 month post fertilization (mpf). Rpgrip1 mutant zebrafish treated with 5 μg/ml of Gyp showed a significant decrease by 68.41% (p = 0.0002) in photoreceptor cell death compared to that of untreated mutant zebrafish. Expression of antioxidant genes catalase, sod1, sod2, gpx1, gclm, nqo-1 and nrf-2 was significantly decreased in rpgrip1 mutant zebrafish eyes by 61.51%, 77.40%, 60.11%, 81.17%, 72.07%, 78.95% and 85.42% (all p < 0.0001), respectively, when compared to that of wildtype zebrafish; superoxide dismutase and catalase activities, and glutathione levels in rpgrip1 mutant zebrafish eyes were significantly decreased by 87.21%, 21.55% and 96.51% (all p < 0.0001), respectively. There were marked increases in the production of reactive oxygen species (ROS) and malondialdehyde (MDA) by 2738.73% and 510.69% (all p < 0.0001), respectively, in rpgrip1 mutant zebrafish eyes; expression of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α was also significantly increased by 150.11%, 267.79% and 190.72% (all p < 0.0001), respectively, in rpgrip1 mutant zebrafish eyes, compared to that of wildtype zebrafish. Treatment with Gyp significantly counteracted these effects. This study indicates that Gyp has a potential role in the treatment of RP.

Tauroursodeoxycholic Acid Protects Retinal Pigment Epithelial Cells from Oxidative Injury and Endoplasmic Reticulum Stress In Vitro

Retinal degeneration is characterized by the dysfunction of retinal cells. Oxidative and endoplasmic reticulum (ER) stress play an important role in the pathogenesis and progression of retinal degeneration. Tauroursodeoxycholic acid (TUDCA) has been demonstrated to have protective effects in in vitro and in vivo retinal degeneration models. To fully understand the molecular mechanisms of TUDCA’s protection, we first treated human retinal pigment epithelial (RPE) cells, ARPE-19, with H₂O₂ or H₂O₂ plus TUDCA for 24 h. RPE cells co-exposed to TUDCA had higher cell viability and lower cell death rate compared to cells exposed to H₂O₂ alone. TUDCA significantly increased antioxidant capacity in H₂O₂-treated RPE cells by decreasing the generation of reactive oxygen species (ROS) and Malondialdehyde (MDA), upregulating the expression of antioxidant genes, and increasing the generation of glutathione (GSH). TUDCA also inhibited inflammation in H₂O₂-challenged RPE cells by decreasing the expression of proinflammatory cytokines. Furthermore, TUDCA suppressed thapsigargin-induced ER stress in RPE cells, as demonstrated by decreased the expression of CCAAT-enhancer-binding protein homologous protein (CHOP) and apoptosis. Our present study suggests that TUDCA can protect RPE cells against oxidative damage, inflammation, and ER stress and may benefit patients with retinal degeneration.

Characterization of Retinal Microvascular Complications and the Effects of Endoplasmic Reticulum Stress in Mouse Models of Diabetic Atherosclerosis

Purpose

Recent evidence suggests that there is a correlation between the micro- and macrovascular complications of diabetes mellitus. The aim of this study is to investigate the molecular mechanisms by which diabetes promotes the development of microvascular disease (diabetic retinopathy [DR]) through characterization of the effects of hyperglycemia in the retina of mouse models of diabetic atherosclerosis.

Methods

Hyperglycemia was induced in apolipoprotein E-deficient (ApoE-/-) mice, a model of accelerated atherosclerosis, either through streptozotocin (STZ) injection or introduction of the Ins2Akita mutation (ApoE-/-Ins2+/Akita). Another subset of ApoE-/- mice was supplemented with glucosamine (GlcN). To attenuate atherosclerosis, subsets of mice from each experimental group were treated with the chemical chaperone, 4-phenylbutyric acid (4PBA). Eyes from 15-week-old mice were either trypsin digested and stained with periodic acid-Schiff (PAS) or frozen for cryostat sectioning and immunostained for endoplasmic reticulum (ER) stress markers, including C/EBP homologous protein (CHOP) and 78-kDa glucose-regulated protein (GRP78). PAS-stained retinal flatmounts were analyzed for microvessel density, acellular capillaries, and pericyte ghosts.

Results

Features of DR, including pericyte ghosts and reduced microvessel density, were observed in hyperglycemic and GlcN-supplemented mice. Treatment with 4PBA reduced ER stress in the retinal periphery and attenuated DR in the experimental groups.

Conclusions

Mouse models of diabetic atherosclerosis show characteristic pathologies of DR that correlate with atherosclerosis. The increased magnitude of these changes and responses to 4PBA in the peripheral retina suggest that future studies should be aimed at assessing regional differences in mechanisms of ER stress-related pathways in these mouse models.

Caveolin-1 Ablation Imparts Partial Protection Against Inner Retinal Injury in Experimental Glaucoma and Reduces Apoptotic Activation

Retinal ganglion cell degeneration is a characteristic feature of glaucoma, and accordingly, protection of these cells constitutes a major therapeutic objective in the disease. Here, we demonstrate the key influence of caveolin (Cav) in regulating the inner retinal homeostasis in two models of experimentally elevated intraocular pressure (IOP). Two groups of Cav-1^-/- and wild-type mice were used in the study. Animals were subjected to experimentally induced chronic and acutely elevated IOP and any changes in their retinal function were assessed by positive scotopic threshold response recordings. TUNEL and cleaved caspase-3 assays were performed to evaluate apoptotic changes in the retina while Brn3a immunostaining was used as a marker to assess and quantify ganglion cell layer (GCL) changes. H&E staining was carried out on retinal sections to evaluate histological differences in retinal laminar structure. Cav-1 ablation partially protected the inner retinal function in both chronic and acute models of elevated IOP. The protective effects of Cav-1 loss were also evident histologically by reduced loss of GCL density in both models. The phenotypic protection in Cav-1^-/- glaucoma mice paralleled with increased TrkB phosphorylation and reduced endoplasmic reticulum stress markers and apoptotic activation in the inner retinas. This study corroborated previous findings of enhanced Shp2 phosphorylation in a chronic glaucoma model and established a novel role of Cav-1 in mediating activation of this phosphatase in the inner retina in vivo. Collectively, these findings highlight the critical involvement of Cav-1 regulatory mechanisms in ganglion cells in response to increased IOP, implicating Cav-1 as a potential therapeutic target in glaucoma.

Molecular characterization and expression pattern of inositol-requiring enzyme 1 (IRE1) in blunt snout bream (Megalobrama amblycephala): its role of IRE1 involved in inflammatory response induced by lipopolysaccharide

This study aimed to characterize the full-length cDNA of IRE1 from fish Megalobrama amblycephala and investigate its role in the pro-inflammatory response. A full-length cDNA coding IRE1 was cloned from blunt snout bream by RT-PCR and RACE approaches. The cDNA obtained covered 3665 bp with an open reading frame of 3096 bp encoding 1031 amino acids. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (74-92%) among various species, retaining one signal peptide, one luminal domain, one serine/threonine kinase domain, one RNase domain, one activation loop, two N-linked glycosylation sites, and several phosphorylation sites. The highest IRE1 expression was observed in the trunk kidney followed by the brain and spleen, whereas relatively low expression levels were detected in the liver, intestine, adipose, skin, and heart. After lipopolysaccharide (LPS) challenge, the expressions of glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1 (IRE1), spliced X-box binding protein 1 (XBP1s), C/EBP homologous protein (CHOP), nuclear factor kappa B (NF-κB), tumor necrosis factor alpha (TNFα), and interleukin-6 (IL-6) all increased remarkably in the spleen and brain at different sampling time points, while LPS also upregulated all the genes tested in the intestine except C/EBP homologous protein. Overall, the results indicated that the IRE1 gene of Megalobrama amblycephala shared a high similarity compared with other vertebrates including several bony fish species. Its expression in three tissues was induced remarkably by the LPS challenge, which indicated that IRE1 played a vital role in LPS-induced inflammation on fish.

The Relevance of Oxidative Stress in the Pathogenesis and Therapy of Retinal Dystrophies

Retinal cell survival requires an equilibrium between oxygen, reactive oxygen species, and antioxidant molecules that counteract oxidative stress damage. Oxidative stress alters cell homeostasis and elicits a protective cell response, which is most relevant in photoreceptors and retinal ganglion cells, neurons with a high metabolic rate that are continuously subject to light/oxidative stress insults. We analyze how the alteration of cellular endogenous pathways for protection against oxidative stress leads to retinal dysfunction in prevalent (age-related macular degeneration, glaucoma) as well as in rare genetic visual disorders (Retinitis pigmentosa, Leber hereditary optic neuropathy). We also highlight some of the key molecular actors and discuss potential therapies using antioxidants agents, modulators of gene expression and inducers of cytoprotective signaling pathways to treat damaging oxidative stress effects and ameliorate severe phenotypic symptoms in multifactorial and rare retinal dystrophies.

Overexpression of cortistatin alleviates oxygen/glucose-deprivation-induced ER stress and prompts neural stem cell proliferation via SSTR2

Cerebral infarction (CI), a blood circulatory disorder, causes a high mortality and disability rate worldwide. Intriguingly, a newly discovered neuropeptide, Cortistatin (CST), has been indicated to inhibit the cortical activity. In our research, we aimed to explore the functional relevance of CST in neural stem cells (NSCs) in CI rats. The expression of CST was determined in NSCs induced by oxygen-glucose deprivation (OGD). NSCs isolated from the embryonic rat brain were treated with OGD to establish an in vitro CI model while dithiothreitol (DTT) was introduced to induce endoplasmic reticulum stress (ERS), which were evaluated by assessment of GRP94, caspase-12 and CHOP expression. Then CST expression was restored by transfection of oe-CST, followed by assessment of NSC proliferation ability and cytotoxicity. Finally, the expression of CST and its receptor Somatostatin receptor subtype 2 (SSTR2) was quantified for mechanism exploration. CST was downregulated in CI, which was further confirmed in NSCs under OGD treatment. Overexpressed CST was found to promote cell activity and attenuate OGD-induced cytotoxicity of NSCs. Meanwhile, it was observed that the injured proliferation ability of NSCs was restored by CST overexpression. Besides, lower expression of GRP94, caspase-12 and CHOP was indicative of suppressed occurrence of ERS by CST. Mechanically, CST inhibited ERS through SSTR2. CST could facilitate the proliferation of NSCs in CI induced by OGD, ultimately highlighting a novel therapeutic target for CI treatment.