Neuroprotection by eIF2α-CHOP inhibition and XBP-1 activation in EAE/optic neuritiss

NFATc4 Knockout Promotes Neuroprotection and Retinal Ganglion Cell Regeneration After Optic Nerve Injury

Retinal ganglion cells (RGCs), neurons transmitting visual information via the optic nerve, fail to regenerate their axons after injury. The progressive loss of RGC function underlies the pathophysiology of glaucoma and other optic neuropathies, often leading to irreversible blindness. Therefore, there is an urgent need to identify the regulators of RGC survival and the regenerative program. In this study, we investigated the role of the family of transcription factors known as nuclear factor of activated T cells (NFAT), which are expressed in the retina; however, their role in RGC survival after injury is unknown. Using the optic nerve crush (ONC) model, widely employed to study optic neuropathies and central nervous system axon injury, we found that NFATc4 is specifically but transiently up-regulated in response to mechanical injury. In the injured retina, NFATc4 immunolocalized primarily to the ganglionic cell layer. Utilizing NFATc4-/- and NFATc3-/- mice, we demonstrated that NFATc4, but not NFATc3, knockout increased RGC survival, improved retina function, and delayed axonal degeneration. Microarray screening data, along with decreased immunostaining of cleaved caspase-3, revealed that NFATc4 knockout was protective against ONC-induced degeneration by suppressing pro-apoptotic signaling. Finally, we used lentiviral-mediated NFATc4 delivery to the retina of NFATc4-/- mice and reversed the pro-survival effect of NFATc4 knockout, conclusively linking the enhanced survival of injured RGCs to NFATc4-dependent mechanisms. In summary, this study is the first to demonstrate that NFATc4 knockout may confer transient RGC neuroprotection and decelerate axonal degeneration after injury, providing a potent therapeutic strategy for optic neuropathies.

Short chain fatty acids inhibit corneal inflammatory responses to TLR ligands via the ocular G-protein coupled receptor 43

PURPOSE

Short chain fatty acids (SCFAs) produced by gut microbiota are known to play primary roles in gut homeostasis by immunomodulation partially through G-protein coupled receptors (GPR) 43. Using mouse models of TLR ligand induced keratitis, we investigated whether SCFAs and GPR43 play any regulatory roles in the pathogenesis of inflammatory responses in the eye.

METHODS

Both human and mouse eyes were labeled with a specific antibody for GPR43 and imaged by a laser scanning confocal microscope. Corneal cups from naïve C57BL/6J (B6) and GPR43 knockout (KO) mice were stimulated with TLR ligands in the presence or absence of sodium butyrate overnight and then processed for RT-PCR assay for expression of GPR43 and cytokines. Keratitis was induced by Poly I:C in wild type (WT) B6, GPR43KO and chimeric mice and the disease severity was evaluated by the corneal fluorescein staining test, and infiltrating cell staining and calculating in corneal whole mount.

RESULTS

GPR43 is expressed in both human and mouse eyes and the expression is bidirectionally regulated by TLR ligands and butyrate. Butyrate significantly inhibited inflammation caused by several TLR ligands such as Poly I:C, Flagellin, and CpG-ODN (TLR-3, 5 and 9 agonists, respectively) in WT, but not GPR43KO, mice. Butyrate inhibition of TLR-induced keratitis is mediated by the GPR43 expressed in tissue but not hematopoietic, cells.

CONCLUSIONS

This is the first report to demonstrate of the protective effect of SCFAs on microbial keratitis, and the dynamic expression and anti-inflammatory function of GPR43 in the eye. SCFAs can modulate inflammation and immunity in the eye through GPR43.

Increased activity of IRE1 improves the clinical presentation of EAE

Activation of the endoplasmic reticulum (ER) stress sensor inositol-requiring enzyme-1α (IRE1α) contributes to neuronal development and is known to induce neuronal remodeling in vitro and in vivo. On the contrary, excessive IRE1 activity is often detrimental and may contribute to neurodegeneration. To determine the consequences of increased activation of IRE1α, we used a mouse model expressing a C148S variant of IRE1α with increased and sustained activation. Surprisingly, the mutation did not affect the differentiation of highly secretory antibody-producing cells but exhibited a beneficial effect in a mouse model of experimental autoimmune encephalomyelitis (EAE). Although mechanical allodynia was unaffected, significant improvement in motor function was found in IRE1C148S mice with EAE relative to wild type (WT) mice. Coincident with this improvement, there was reduced microgliosis in the spinal cord of IRE1C148S mice, with reduced expression of proinflammatory cytokine genes. This was accompanied by reduced axonal degeneration and enhanced 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) levels, suggesting improved myelin integrity. Interestingly, while the IRE1C148S mutation is expressed in all cells, the reduction in proinflammatory cytokines and in the microglial activation marker ionized calcium-binding adapter molecule (IBA1), along with preservation of phagocytic gene expression, all point to microglia as the cell type contributing to the clinical improvement in IRE1C148S animals. Our data suggest that sustained increase in IRE1α activity can be beneficial in vivo, and that this protection is cell type and context dependent. Considering the overwhelming but conflicting evidence for the role of ER stress in neurological diseases, a better understanding of the function of ER stress sensors in physiological contexts is clearly needed.

Non-Invasive Evaluation of Retinal Vascular Alterations in a Mouse Model of Optic Neuritis Using Laser Speckle Flowgraphy and Optical Coherence Tomography Angiography

Optic neuritis, a characteristic feature of multiple sclerosis (MS), involves the inflammation of the optic nerve and the degeneration of retinal ganglion cells (RGCs). Although previous studies suggest that retinal blood flow alterations occur during optic neuritis, the precise location, the degree of impairment, and the underlying mechanisms remain unclear. In this study, we utilized two emerging non-invasive imaging techniques, laser speckle flowgraphy (LSFG) and optical coherence tomography angiography (OCTA), to investigate retinal vascular changes in a mouse model of MS, known as experimental autoimmune encephalomyelitis (EAE). We associated these changes with leukostasis, RGC injury, and the overall progression of EAE. LSFG imaging revealed a progressive reduction in retinal blood flow velocity and increased vascular resistance near the optic nerve head in the EAE model, indicating impaired ocular blood flow. OCTA imaging demonstrated significant decreases in vessel density, number of junctions, and total vessel length in the intermediate and deep capillary plexus of the EAE mice. Furthermore, our analysis of leukostasis revealed a significant increase in adherent leukocytes in the retinal vasculature of the EAE mice, suggesting the occurrence of vascular inflammation in the early development of EAE pathology. The abovechanges preceded or were accompanied by the characteristic hallmarks of optic neuritis, such as RGC loss and reduced visual acuity. Overall, our study sheds light on the intricate relationship between retinal vascular alterations and the progression of optic neuritis as well as MS clinical score. It also highlights the potential for the development of image-based biomarkers for the diagnosis and monitoring of optic neuritis as well as MS, particularly in response to emerging treatments.

Acriflavine, a HIF-1 inhibitor, preserves vision in an experimental autoimmune encephalomyelitis model of optic neuritis

Introduction

Optic neuritis (ON) is often an early sign of multiple sclerosis (MS), and recent studies show a link between HIF-1 pathway activation and inflammation. This study aimed to determine if inhibition of the HIF-1 pathway using the HIF-1a antagonist acriflavine (ACF) can reduce clinical progression and rescue the ocular phenotype in an experimental autoimmune encephalomyelitis (EAE) ON model.

Methods

EAE-related ON was induced in 60 female C57BL/6J mice by immunization with MOG33-55, and 20 EAE mice received daily systemic injections of ACF at 5 mg/kg. Changes in the visual function and structure of ACF-treated EAE mice were compared to those of placebo-injected EAE mice and naïve control mice.

Results

ACF treatment improved motor-sensory impairment along with preserving visual acuity and optic nerve function. Analysis of retinal ganglion cell complex alsoshowed preserved thickness correlating with increased survival of retinal ganglion cells and their axons. Optic nerve cell infiltration and magnitude of demyelination were decreased in ACF-treated EAE mice. Subsequent in vitro studies revealed improvements not only attributed to the inhibition of HIF-1 butalso to previously unappreciated interaction with the eIF2a/ATF4 axis in the unfolded protein response pathway.

Discussion

This study suggests that ACF treatment is effective in an animal model of MS via its pleiotropic effects on the inhibition of HIF-1 and UPR signaling, and it may be a viable approach to promote rehabilitation in MS.

RGC-specific ATF4 and/or CHOP deletion rescues glaucomatous neurodegeneration and visual function

Endoplasmic reticulum (ER) stress has been linked with various acute and chronic neurodegenerative diseases. We previously found that optic nerve (ON) injury and diseases induce neuronal ER stress in retinal ganglion cells (RGCs). We further demonstrated that germline deletion of CHOP preserves the structure and function of both RGC somata and axons in mouse glaucoma models. Here we report that RGC-specific deletion of CHOP and/or its upstream regulator ATF4 synergistically promotes RGC and ON survival and preserves visual function in mouse ON crush and silicone oil-induced ocular hypertension (SOHU) glaucoma models. Consistently, topical application of the ATF4/CHOP chemical inhibitor ISRIB or RGC-specific CRISPR-mediated knockdown of the ATF4 downstream effector Gadd45a also delivers significant neuroprotection in the SOHU glaucoma model. These studies suggest that blocking the neuronal intrinsic ATF4/CHOP axis of ER stress is a promising neuroprotection strategy for neurodegeneration.

Characteristics of Autophagy-Related Genes, Diagnostic Models, and Their Correlation with Immune Infiltration in Keratoconus

Purpose

Keratoconus (KTCN) is one of the most common degenerative keratopathies, significantly affecting vision and even leading to blindness. This study identifies potential biomarkers of KTCN based on the characterization of autophagy-related genes (ARGs) and the construction of a diagnostic model; and explores their relevance to immune infiltrating cells in KTCN.

Methods

Gene Expression Omnibus (GEO) data were downloaded and ARGs were acquired from GeneCards and Molecular Signatures Database (MSigDB). Autophagy-related differential expression genes (ARDEGs) were discovered through the integration of differentially expressed genes (DEGs) with ARGs, while hub genes of KTCN were discovered by protein-protein interaction (PPI) network analysis. The probable biological roles of these hub ARDEGs were examined using functional enrichment analysis, and a KTCN diagnostic model was generated using the least absolute shrinkage and selection operator (LASSO) regression analysis. We also employed the CIBERSORTx and ssGSEA algorithms to identify potential regulatory pathways to compare the abundance of immune cell infiltrates and their association with hub genes. Finally, the hub gene expression levels were confirmed using validation datasets as well as blood samples from KTCN and healthy individuals.

Results

In this study, we identified 12 hub ARDEGs, of which 9 genes were substantially distinct between KTCN patients and normal groups. The LASSO risk score was used to generate the nomogram, and the calibration curve evaluated the model's effective diagnostic performance (C index of 0.961). Patients with KTCN had greater percentages of M2 Macrophages and Gamma delta T cells, according to CIBERSORTx and ssGSEA. The outcomes of the bioinformatics analysis were supported by the DDIT3 and BINP3 expression levels in KTCN patients and healthy controls, according to the qRT-PCR data.

Conclusion

Five biomarkers (CFTR, PLIN2, DDIT3, BAG3, and BNIP3) and diagnostic models offer fresh perspectives on identifying and managing KTCN.

Valproate reduces retinal ganglion cell apoptosis in rats after optic nerve crush

The retinal ganglion cells of the optic nerve have a limited capacity for self-repair after injury. Valproate is a histone deacetylase inhibitor and multitarget drug, which has been demonstrated to protect retinal neurons. In this study, we established rat models of optic nerve-crush injury and injected valproate into the vitreous cavity immediately after modeling. We evaluated changes in the ultrastructure morphology of the endoplasmic reticulum of retinal ganglion cells over time via transmission electron microscope. Immunohistochemistry and western blot assay revealed that valproate upregulated the expression of the endoplasmic reticulum stress marker glucose-regulated protein 78 and downregulated the expression of transcription factor C/EBP homologous protein, phosphorylated eukaryotic translation initiation factor 2α, and caspase-12 in the endoplasmic reticulum of retinal ganglion cells. These findings suggest that valproate reduces apoptosis of retinal ganglion cells in the rat after optic nerve-crush injury by attenuating phosphorylated eukaryotic translation initiation factor 2α-C/EBP homologous protein signaling and caspase-12 activation during endoplasmic reticulum stress. These findings represent a newly discovered mechanism that regulates how valproate protects neurons.

Differential effects of SARM1 inhibition in traumatic glaucoma and EAE optic neuropathies

Optic neuropathy is a group of optic nerve (ON) diseases with progressive degeneration of ON and retinal ganglion cells (RGCs). The lack of neuroprotective treatments is a central challenge for this leading cause of irreversible blindness. SARM1 (sterile α and TIR motif-containing protein 1) has intrinsic nicotinamide adenine dinucleotide (NAD⁺) hydrolase activity that causes axon degeneration by degrading axonal NAD⁺ significantly after activation by axon injury. SARM1 deletion is neuroprotective in many, but not all, neurodegenerative disease models. Here, we compare two therapy strategies for SARM1 inhibition, antisense oligonucleotide (ASO) and CRISPR, with germline SARM1 deletion in the neuroprotection of three optic neuropathy mouse models. This study reveals that, similar to germline SARM1 knockout in every cell, local retinal SARM1 ASO delivery and adeno-associated virus (AAV)-mediated RGC-specific CRISPR knockdown of SARM1 provide comparable neuroprotection to both RGC somata and axons in the silicone oil-induced ocular hypertension (SOHU) glaucoma model but only protect RGC axons, not somata, after traumatic ON injury. Surprisingly, neither of these two therapy strategies of SARM1 inhibition nor SARM1 germline knockout (KO) benefits RGC or ON survival in the experimental autoimmune encephalomyelitis (EAE)/optic neuritis model. Our studies therefore suggest that SARM1 inhibition by local ASO delivery or AAV-mediated CRISPR is a promising neuroprotective gene therapy strategy for traumatic and glaucomatous optic neuropathies but not for demyelinating optic neuritis.

Increased activity of IRE1 improves the clinical presentation of EAE

Activation of the ER stress sensor IRE1α contributes to neuronal development and is known to induce neuronal remodeling in vitro and in vivo. On the other hand, excessive IRE1 activity is often detrimental and may contribute to neurodegeneration. To determine the consequences of increased activation of IRE1α, we used a mouse model expressing a C148S variant of IRE1α with increased and sustained activation. Surprisingly, the mutation did not affect the differentiation of highly secretory antibody-producing cells, but exhibited a strong protective effect in a mouse model of experimental autoimmune encephalomyelitis (EAE). Significant improvement in motor function was found in IRE1C148S mice with EAE relative to WT mice. Coincident with this improvement, there was reduced microgliosis in the spinal cord of IRE1C148S mice, with reduced expression of pro-inflammatory cytokine genes. This was accompanied by reduced axonal degeneration and enhanced CNPase levels, suggestiing improved myelin integrity. Interestingly, while the IRE1C148S mutation is expressed in all cells, the reduction in proinflammatory cytokines and in the activation of microglial activation marker IBA1, along with preservation of phagocytic gene expression, all point to microglia as the cell type contributing to the clinical improvement in IRE1C148S animals. Our data suggest that sustained increase in IRE1α activity can be protective in vivo, and that this protection is cell type and context dependent. Considering the overwhelming but conflicting evidence for the role of the ER stress in neurological diseases, a better understanding of the function of ER stress sensors in physiological contexts is clearly needed.

Cypermethrin and/or sulfamethoxazole exposure effect on apoptosis and endoplasmic reticulum of grass carp cardiomyocyte

With the soar use range of pesticides and antibiotics in agricultural production, the pollution of surrounding runoff has become more severe; thus, the health and safety of non-target species such as fish are at risk. Excessive amounts of cypermethrin (CMN, 0.651 mg/l) and sulfamethoxazole (SMZ, 0.3 mg/l) are known to trigger oxidative stress and endoplasmic reticulum stress, resulting in toxic effects on cells. The damage degree of poisons on grass carp and the effect of the corresponding axis pathway PERK/eif2α/CHOP are still unknown. Therefore, our study set up two single poison groups (CMN/SMZ) and a combined poison group (CMN&SMZ) to detect this pathway and related indicators. After detection, the content of MDA both in CMN and SMZ group myocardium tissue was increased, while the SOD, CAT activity and GSH levels were decreased. Apoptosis-related genes (Bax, PUMA, P53 and Caspase-3/9), inflammation-related genes (TNF-α, iNOS and IL-1β/6/8), ER stress pathway PERK/eif2α/CHOP and related genes (ATF6, IRE1a and GRP78) were all increased; in contrast, the anti-apoptotic gene Bcl-2 was down-regulated. From the overall trend observation, the apoptosis proportion of cardiomyocytes in the combined poison group was higher than that of the single poison. In summary, this study shows that CMZ and SMZ can induce oxidative stress and subsequent ER stress in grass carp cardiomyocytes by regulating the PERK/eif2α/CHOP signaling axle, thereby inducing apoptosis, and followed by inflammatory responses. The combined effect of the CMZ and SMZ mixture was severer than that of a single poison (CMZ or SMZ), so it can be inferred that the damage degree of grass carp myocardium tissue would be aggravated with the appearance of CMZ or/and SMZ. The experimental results of this study have suggestions and warnings for the toxicological research of CMZ and SMZ and the management of industrial and ecological balance.

Gene Therapy, A Potential Therapeutic Tool for Neurological and Neuropsychiatric Disorders: Applications, Challenges and Future Perspective

Neurological and neuropsychiatric disorders are the main risks for the health care system, exhibiting a huge socioeconomic load. The available range of pharmacotherapeutics mostly provides palliative consequences and fails to treat such conditions. The molecular etiology of various neurological and neuropsychiatric disorders is mostly associated with a change in genetic background, which can be inherited/triggered by other environmental factors. To address such conditions, gene therapy is considered a potential approach claiming a permanent cure of the disease primarily by deletion, silencing, or edition of faulty genes and by insertion of healthier genes. In gene therapy, vectors (viral/nonvial) play an important role in delivering the desired gene to a specific region of the brain. Targeted gene therapy has unraveled opportunities for the treatment of many neurological and neuropsychiatric disorders. For improved gene delivery, the current techniques mainly focus on designing a precise viral vector, plasmid transfection, nanotechnology, microRNA, and in vivo clustered regulatory interspaced short palindromic repeats (CRISPR)-based therapy. These latest techniques have great benefits in treating predominant neurological and neurodevelopmental disorders, including Parkinson's disease, Alzheimer's disease, and autism spectrum disorder, as well as rarer diseases. Nevertheless, all these delivery methods have their limitations, including immunogenic reactions, off-target effects, and a deficiency of effective biomarkers to appreciate the effectiveness of therapy. In this review, we present a summary of the current methods in targeted gene delivery, followed by the limitations and future direction of gene therapy for the cure of neurological and neuropsychiatric disorders.

Evaluation of Retinal Ganglion Cell via Visual Evoked Potential

Visual Evoked Potential (VEP) is an electrical signal recorded from the visual cortex in response to light stimulation. It can be used as an in vivo method to objectively access the functional integrity of the retinogeniculocortical pathway. Here we describe the methods to perform flash VEP (FVEP) recording in rodents and goat and pattern VEP (PVEP) recording in rhesus macaque.

Maprotiline restores ER homeostasis and rescues neurodegeneration via Histamine Receptor H1 inhibition in retinal ganglion cells

When the protein or calcium homeostasis of the endoplasmic reticulum (ER) is adversely altered, cells experience ER stress that leads to various diseases including neurodegeneration. Genetic deletion of an ER stress downstream effector, CHOP, significantly protects neuron somata and axons. Here we report that three tricyclic compounds identified through a small-scale high throughput screening using a CHOP promoter-driven luciferase cell-based assay, effectively inhibit ER stress by antagonizing their common target, histamine receptor H1 (HRH1). We further demonstrated that systemic administration of one of these compounds, maprotiline, or CRISPR-mediated retinal ganglion cell (RGC)-specific HRH1 inhibition, delivers considerable neuroprotection of both RGC somata and axons and preservation of visual function in two mouse optic neuropathy models. Finally, we determine that maprotiline restores ER homeostasis by inhibiting HRH1-mediated Ca²⁺ release from ER. In this work we establish maprotiline as a candidate neuroprotectant and HRH1 as a potential therapeutic target for glaucoma.

Single-cell transcriptome analysis of regenerating RGCs reveals potent glaucoma neural repair genes

Axon regeneration holds great promise for neural repair of CNS axonopathies, including glaucoma. Pten deletion in retinal ganglion cells (RGCs) promotes potent optic nerve regeneration, but only a small population of Pten-null RGCs are actually regenerating RGCs (regRGCs); most surviving RGCs (surRGCs) remain non-regenerative. Here, we developed a strategy to specifically label and purify regRGCs and surRGCs, respectively, from the same Pten-deletion mice after optic nerve crush, in which they differ only in their regeneration capability. Smart-Seq2 single-cell transcriptome analysis revealed novel regeneration-associated genes that significantly promote axon regeneration. The most potent of these, Anxa2, acts synergistically with its ligand tPA in Pten-deletion-induced axon regeneration. Anxa2, its downstream effector ILK, and Mpp1 dramatically protect RGC somata and axons and preserve visual function in a clinically relevant model of glaucoma, demonstrating the exciting potential of this innovative strategy to identify novel effective neural repair candidates.

Inhibition of endoplasmic reticulum stress by 4-phenylbutyrate alleviates retinal inflammation and the apoptosis of retinal ganglion cells after ocular alkali burn in mice

OBJECTIVE

Retinal ganglion cell (RGC) apoptosis is one of the most severe complications that causes permanent visual impairment following ocular alkali burn (OAB). Currently, very few treatment options exist for this condition. This study was conducted to determine the effect of 4-phenylbutyric acid (4-PBA) on endoplasmic reticulum (ER) stress after OAB using a well-established OAB mouse model.

METHODS

Ocular alkali burn was induced in C57BL/6 mouse corneas using 1 M NaOH. 4-PBA (10 mg/kg; 250 μL per injection) or saline (250 μL per injection) was injected intraperitoneally once per day for 3 days before the establishment of the OAB model. The apoptosis of retinal ganglion cells (RGCs) was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and the histological damage was examined by hematoxylin and eosin and immunofluorescence assay on retinal flat mounts. The key inflammatory response and the expression of ER stress-related markers in the retinal tissues were assessed by real-time PCR, western blotting and histologic analyses.

RESULTS

4-PBA significantly alleviated the apoptosis of RGCs and prevented the structural damage of the retina, as determined by the evaluation of RGC density and retinal thickness. Inhibition of ER stress by 4-PBA decreased the expression of vital proinflammatory cytokines, tumor necrosis factor alpha, and interleukin-1 beta; and suppressed the activation of retinal microglial cells and nuclear factor-kappa B (NF-κB). 4-PBA reduced the expression of the ER stress molecules, glucose-regulated protein 78, activated transcription factor 6, inositol-requiring enzyme-1 (IRE1), X-box-binding protein 1 splicing, and CCAAT/enhancer-binding protein homologous protein, in the retinal tissues and RGCs of OAB mice.

CONCLUSIONS

The present study demonstrated that the inhibition of ER stress by 4-PBA alleviates the inflammatory response via the IRE1/NF-κB signaling pathway and protects the retina and RGCs from injury in an OAB mouse model. Such findings further suggest that 4-PBA might have potential therapeutic implications for OAB treatment.

NMNAT2 is downregulated in glaucomatous RGCs, and RGC-specific gene therapy rescues neurodegeneration and visual function

The lack of neuroprotective treatments for retinal ganglion cells (RGCs) and optic nerve (ON) is a central challenge for glaucoma management. Emerging evidence suggests that redox factor NAD+ decline is a hallmark of aging and neurodegenerative diseases. Supplementation with NAD+ precursors and overexpression of NMNAT1, the key enzyme in the NAD+ biosynthetic process, have significant neuroprotective effects. We first profile the translatomes of RGCs in naive mice and mice with silicone oil-induced ocular hypertension (SOHU)/glaucoma by RiboTag mRNA sequencing. Intriguingly, only NMNAT2, but not NMNAT1 or NMNAT3, is significantly decreased in SOHU glaucomatous RGCs, which we confirm by in situ hybridization. We next demonstrate that AAV2 intravitreal injection-mediated overexpression of long half-life NMNAT2 mutant driven by RGC-specific mouse γ-synuclein (mSncg) promoter restores decreased NAD+ levels in glaucomatous RGCs and ONs. Moreover, this RGC-specific gene therapy strategy delivers significant neuroprotection of both RGC soma and axon and preservation of visual function in the traumatic ON crush model and the SOHU glaucoma model. Collectively, our studies suggest that the weakening of NMNAT2 expression in glaucomatous RGCs contributes to a deleterious NAD+ decline, and that modulating RGC-intrinsic NMNAT2 levels by AAV2-mSncg vector is a promising gene therapy for glaucomatous neurodegeneration.

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.

Endoplasmic Reticulum Stress-Associated Neuronal Death and Innate Immune Response in Neurological Diseases

Neuronal death and inflammatory response are two common pathological hallmarks of acute central nervous system injury and chronic degenerative disorders, both of which are closely related to cognitive and motor dysfunction associated with various neurological diseases. Neurological diseases are highly heterogeneous; however, they share a common pathogenesis, that is, the aberrant accumulation of misfolded/unfolded proteins within the endoplasmic reticulum (ER). Fortunately, the cell has intrinsic quality control mechanisms to maintain the proteostasis network, such as chaperone-mediated folding and ER-associated degradation. However, when these control mechanisms fail, misfolded/unfolded proteins accumulate in the ER lumen and contribute to ER stress. ER stress has been implicated in nearly all neurological diseases. ER stress initiates the unfolded protein response to restore proteostasis, and if the damage is irreversible, it elicits intracellular cascades of death and inflammation. With the growing appreciation of a functional association between ER stress and neurological diseases and with the improved understanding of the multiple underlying molecular mechanisms, pharmacological and genetic targeting of ER stress are beginning to emerge as therapeutic approaches for neurological diseases.

GSK2606414 attenuates PERK/p-eIF2α/ATF4/CHOP axis and augments mitochondrial function to mitigate high glucose induced neurotoxicity in N2A cells

Neuronal dysfunction and subsequent apoptosis under high glucose conditions during diabetes contribute majorly to the manifestation of diabetic peripheral neuropathy (DPN). PERK (protein kinase RNA (PKR)-like ER kinase) one among the three canonical arms of unfolded protein response (UPR), is believed to play a crucial role in determining the cell fate during endoplasmic reticulum stress (ERS/ER stress) conditions. We evaluated the role of PERK inhibitor GSK2606414 in high glucose (30 ​mM) treated neuroblastoma (N2A) cells. High glucose resulted in disruption of ER proteostasis by activation of UPR which is evident through increased (p ​< ​0.001) expression of GRP78, p-PERK, p-eIF2α, ATF-4 and CHOP when compared to normal cells. It is accompanied with enhanced GRP78 localization in Endoplasmic Reticulum (ER) lumen evident from ER labeling Immunofluorescence (IF) staining. PERK activation resulted in altered mitochondrial function evident by increased mitochondrial superoxide production and compromised mitochondrial homeostasis with decrease in Mfn-2 levels. Additionally, ER stress induced neuronal apoptosis was attenuated by GSK2606414 treatment via inhibiting the PERK-eIF2α-ATF4-CHOP axis that not only curtailed the levels of apoptotic proteins like Bax and caspase 3 but also elevated the levels of anti-apoptotic Bcl-2. Collectively, our findings revealed the neuroprotective potential of GSK2606414 against high glucose induced neurotoxicity in N2A cells.

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Unregulated ER stress drives neuronal (N2A) apoptosis following high glucose (HG) exposure (30 ​mM).

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Mitochondrial dysfunction aggravated by ER stress under hyperglycemic conditions.

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PERK/p-eIF2α/ATF4/CHOP axis underlies the apoptosis of N2A cells upon HG exposure.

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GSK2606414 attenuates PERK/p-eIF2α/ATF4/CHOP axis to mitigate HG induced neurotoxicity in N2A cells.

Citrus Naringenin Increases Neuron Survival in Optic Nerve Crush Injury Model by Inhibiting JNK-JUN Pathway

Traumatic nerve injury activates cell stress pathways, resulting in neuronal death and loss of vital neural functions. To date, there are no available neuroprotectants for the treatment of traumatic neural injuries. Here, we studied three important flavanones of citrus components, in vitro and in vivo, to reveal their roles in inhibiting the JNK (c-Jun N-terminal kinase)-JUN pathway and their neuroprotective effects in the optic nerve crush injury model, a kind of traumatic nerve injury in the central nervous system. Results showed that both neural injury in vivo and cell stress in vitro activated the JNK-JUN pathway and increased JUN phosphorylation. We also demonstrated that naringenin treatment completely inhibited stress-induced JUN phosphorylation in cultured cells, whereas nobiletin and hesperidin only partially inhibited JUN phosphorylation. Neuroprotection studies in optic nerve crush injury mouse models revealed that naringenin treatment increased the survival of retinal ganglion cells after traumatic optic nerve injury, while the other two components had no neuroprotective effect. The neuroprotection effect of naringenin was due to the inhibition of JUN phosphorylation in crush-injured retinal ganglion cells. Therefore, the citrus component naringenin provides neuroprotection through the inhibition of the JNK-JUN pathway by inhibiting JUN phosphorylation, indicating the potential application of citrus chemical components in the clinical therapy of traumatic optic nerve injuries.

Neuronal NMNAT2 Overexpression Does Not Achieve Significant Neuroprotection in Experimental Autoimmune Encephalomyelitis/Optic Neuritis

Optic neuritis, inflammation, and demyelination of the optic nerve (ON), is one of the most common clinical manifestations of multiple sclerosis; affected patients suffer persistent visual symptoms due to ON degeneration and secondary retinal ganglion cell (RGC) death. The mouse experimental autoimmune encephalomyelitis (EAE) model replicates optic neuritis and significant RGC soma and axon loss. Nicotinamide mononucleotide adenylyltransferases (NMNATs) are NAD⁺-synthetic enzymes that have been shown to be essential for axon integrity, activation of which significantly delays axonal Wallerian degeneration. NMNAT2, which is enriched in axons, has been proposed as a promising therapeutic target for axon injury-induced neurodegeneration. We therefore investigated whether activation of NMNAT2 can be used as a gene therapy strategy for neuroprotection in EAE/optic neuritis. To avoid the confounding effects in inflammatory cells, which play important roles in EAE initiation and progression, we used an RGC-specific promoter to drive the expression of the long half-life NMNAT2 mutant in mouse RGCs in vivo. However, optical coherence tomography in vivo retina imaging did not reveal significant protection of the ganglion cell complex, and visual function assays, pattern electroretinography, and optokinetic response also showed no improvement in mice with NMNAT2 overexpression. Postmortem histological analysis of retina wholemounts and semithin sections of ON confirmed the in vivo results: NMNAT2 activation in RGCs does not provide significant neuroprotection of RGCs in EAE/optic neuritis. Our studies suggest that a different degenerative mechanism than Wallerian degeneration is involved in autoimmune inflammatory axonopathy and that NMNAT2 may not be a major contributor to this mechanism.

Oligodendrocyte-specific deletion of Xbp1 exacerbates the endoplasmic reticulum stress response and restricts locomotor recovery after thoracic spinal cord injury

The endoplasmic reticulum stress response (ERSR) is activated in various neurodegenerative diseases and/or after CNS traumatic injuries. The ERSR is comprised of three major arms, PERK, IRE-1, and activating transcription factor-6, with the latter two contributing to the unfolded protein response (UPR). PERK activity overlaps with the integrated stress response (ISR) kinases, PKR, HRI, and GCN2 which all signal through, eukaryotic initiation factor 2α, ATF4, and CHOP. All initially attempt to restore endoplasmic reticulum (ER) homeostasis, but if ER stress is unresolved, ATF4/CHOP-mediated cell death is initiated. Here, we investigate the contribution of the inositol-requiring protein-1α-X-box binding protein-1 (XBP1)-mediated UPR signaling pathway to the pathogenesis of spinal cord injury (SCI). We demonstrate that deletion of Xbp1 caused an exacerbated ATF4/CHOP signaling in cultured mouse oligodendrocyte (OL) progenitor cells and enhanced their sensitivity to ER stress. Similar effects were also observed with the Xbp1 pathway inhibitor toyocamycin. Furthermore, OL lineage-specific loss of Xbp1 resulted in enhanced ISR in mice that underwent moderate contusive SCI at the T9 level. Consistently, post-injury recovery of hindlimb locomotion and white matter sparing were reduced in OL Xbp1-deficient mice, which correlated with chronically decreased relative density of OPCs and OLs at the injury epicenter at 6 weeks post-SCI. We conclude that the IRE1-XBP1-mediated UPR signaling pathway contributes to restoration of ER homeostasis in OLs and is necessary for enhanced white matter sparing and functional recovery post-SCI.

Effects of Retinal Transcription Regulation After GB20 Needling Treatment in Retina With Optic Neuritis

Optic neuritis (ON) is one of the most frequent symptoms of multiple sclerosis (MS) that results in progressive loss of axons and neurons. In clinical trials of Traditional Chinese Medicine, needling at the GB20 acupoint has been widely used for the treatment of ocular diseases, including ON. However, the molecular mechanisms of needling at this site are still unclear. In this study, we generated an experimental autoimmune encephalomyelitis (EAE) mouse model and investigated the effects of needling treatment at the GB20 acupoint on retina with EAE-associated ON. RNA sequencing of the retinal transcriptome revealed that, of the 234 differentially expressed genes induced by ON, 100 genes were upregulated, and 134 genes were downregulated by ON, while needling at the GB20 acupoint specifically reversed the expression of 21 genes compared with control treatment at GV16 acupoint. Among the reversed genes, Nr4a3, Sncg, Uchl1, and Tppp3 were involved in axon development and regeneration and were downregulated by ON, indicating the beneficial effect of needling at GB20. Further gene ontology (GO) enrichment analysis revealed that needling at GB20 affected the molecular process of Circadian rhythm in mouse retina with ON. Our study first reported that needling treatment after ON at the GB20 acupoint regulated gene expression of the retina and reversed the expression of downregulated axon development-related genes. This study also demonstrated that GV16 was a perfect control treatment site for GB20 in animal research. Our study provided a scientific basis for needling treatments at GB20 for ocular diseases.

Dual Specific Phosphatase 14 Deletion Rescues Retinal Ganglion Cells and Optic Nerve Axons after Experimental Anterior Ischemic Optic Neuropathy

PURPOSE

Understanding molecular changes is essential for designing effective treatments for nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in adults older than 50 years. We investigated changes in the mitogen-activated protein kinase (MAPK) pathway after experimental AION and focused on dual specificity phosphatase 14 (Dusp14), an atypical MAPK phosphatase that is downstream of Krüppel-like transcription factor (KLF) 9-mediated inhibition of retinal ganglion cell (RGC) survival and axonal regeneration.

MATERIALS AND METHODS

We induced severe AION in a photochemical thrombosis model in adult C57BL/6 wild-type and Dusp14 knockout mice. For comparison, some studies were performed using an optic nerve crush model. We assessed changes in MAPK pathway molecules using Western blot and immunohistochemistry, measured retinal thickness using optical coherence tomography (OCT), and quantified RGCs and axons using histologic methods.

RESULTS

Three days after severe AION, there was no change in the retinal protein levels of MAPK ERK1/2, phosphorylated-ERK1/2 (pERK1/2), downstream effector Elk-1 and phosphatase Dusp14 on Western blot. Western blot analysis of purified RGCs after a more severe model using optic nerve crush also showed no change in Dusp14 protein expression. Because of the known importance of the Dusp14 and MAPK pathway in RGCs, we examined changes after AION in Dusp14 knockout mice. Three days after AION, Dusp14 knockout mice had significantly increased pERK1/2⁺, Brn3A⁺ RGCs on immunohistochemistry. Three weeks after AION, Dusp14 knockout mice had significantly greater preservation of retinal thickness, increased number of Brn3A⁺ RGCs on whole mount preparation, and increased number of optic nerve axons compared with wild-type mice.

CONCLUSIONS

Genetic deletion of Dusp14, a MAPK phosphatase important in KFL9-mediated inhibition of RGC survival, led to increased activation of MAPK ERK1/2 and greater RGC and axonal survival after experimental AION. Inhibiting Dusp14 or activating the MAPK pathway should be examined further as a potential therapeutic approach to treatment of AION.

Abbreviations: AION: anterior ischemic optic neuropathy; Dusp14: dual specific phosphatase 14; ERK1/2: extracellular signal-regulated kinases 1/2; Elk-1: ETS Like-1 protein; GCC: ganglion cell complex; GCL: ganglion cell layer; inner nuclear layer; KO: knockout; MAPK: mitogen-activated phosphokinase; OCT: optical coherence tomography; RGC: retinal ganglion cell; RNFL: retinal nerve fiber layer.

Gene therapy for neurodegenerative disorders: advances, insights and prospects

Gene therapy is rapidly emerging as a powerful therapeutic strategy for a wide range of neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Some early clinical trials have failed to achieve satisfactory therapeutic effects. Efforts to enhance effectiveness are now concentrating on three major fields: identification of new vectors, novel therapeutic targets, and reliable of delivery routes for transgenes. These approaches are being assessed closely in preclinical and clinical trials, which may ultimately provide powerful treatments for patients. Here, we discuss advances and challenges of gene therapy for neurodegenerative disorders, highlighting promising technologies, targets, and future prospects.

In vivo evaluation of retinal ganglion cells and optic nerve's integrity in large animals by multi-modality analysis

Large animal models of optic nerve injury are essential for translating novel findings into effective therapies due to their similarity to humans in many respects. However, most current tests evaluating the integrity of retinal ganglion cells (RGCs) and optic nerve (ON) are based on rodent animal models. We aimed to evaluate and optimize the in vivo methods to assess RGCs and ON's function and structure in large animals in terms of reproducibility, simplicity and sensitivity. Both goats and rhesus macaques were employed in this study. By using goats, we found anesthesia with isoflurane or xylazine resulted in different effects on reproducibility of flash visual evoked potential (FVEP) and pattern electroretinogram (PERG). FVEP with the large-Ganzfeld stimulator was significantly more stable than that with mini-Ganzfeld stimulator. PERG with simultaneous binocular stimulation, with superior simplicity over separate monocular stimulation, was appliable in goats due to undetectable interocular crosstalk of PERG signals. After ON crush in goats, some FVEP components, PERG, OCT and PLR demonstrated significant changes, in line with the histological study. By using rhesus macaque, we found the implicit time of PVEP, FVEP and PERG were significantly more reproducible than amplitudes, and OCT and PLR demonstrated small intersession variation. In summary, we established an optimized system to evaluate integrity of RGCs and ON in large animals in vivo, facilitating usage of large animal models of optic nerve diseases.

Longitudinal Morphological and Functional Assessment of RGC Neurodegeneration After Optic Nerve Crush in Mouse

The mouse optic nerve crush (ONC) model has been widely used to study optic neuropathies and central nervous system (CNS) axon injury and repair. Previous histological studies of retinal ganglion cell (RGC) somata in retina and axons in ON demonstrate significant neurodegeneration after ONC, but longitudinal morphological and functional assessment of RGCs in living animals is lacking. It is essential to establish these assays to provide more clinically relevant information for early detection and monitoring the progression of CNS neurodegeneration. Here, we present in vivo data gathered by scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), and pattern electroretinogram (PERG) at different time points after ONC in mouse eyes and corresponding histological quantification of the RGC somata and axons. Not surprisingly, direct visualization of RGCs by SLO fundus imaging correlated best with histological quantification of RGC somata and axons. Unexpectedly, OCT did not detect obvious retinal thinning until late time points (14 and 28-days post ONC) and instead detected significant retinal swelling at early time points (1–5 days post-ONC), indicating a characteristic initial retinal response to ON injury. PERG also demonstrated an early RGC functional deficit in response to ONC, before significant RGC death, suggesting that it is highly sensitive to ONC. However, the limited progression of PERG deficits diminished its usefulness as a reliable indicator of RGC degeneration.

Mouse γ-Synuclein Promoter-Mediated Gene Expression and Editing in Mammalian Retinal Ganglion Cells

Optic neuropathies are a group of optic nerve (ON) diseases caused by various insults including glaucoma, inflammation, ischemia, trauma, and genetic deficits, which are characterized by retinal ganglion cell (RGC) death and ON degeneration. An increasing number of genes involved in RGC intrinsic signaling have been found to be promising neural repair targets that can potentially be modulated directly by gene therapy, if we can achieve RGC specific gene targeting. To address this challenge, we first used adeno-associated virus (AAV)-mediated gene transfer to perform a low-throughput in vivo screening in both male and female mouse eyes and identified the mouse γ-synuclein (mSncg) promoter, which specifically and potently sustained transgene expression in mouse RGCs and also works in human RGCs. We further demonstrated that gene therapy that combines AAV-mSncg promoter with clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing can knock down pro-degenerative genes in RGCs and provide effective neuroprotection in optic neuropathies.SIGNIFICANCE STATEMENT Here, we present an RGC-specific promoter, mouse γ-synuclein (mSncg) promoter, and perform extensive characterization and proof-of-concept studies of mSncg promoter-mediated gene expression and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing in RGCs in vivo To our knowledge, this is the first report demonstrating in vivo neuroprotection of injured RGCs and optic nerve (ON) by AAV-mediated CRISPR/Cas9 inhibition of genes that are critical for neurodegeneration. It represents a powerful tool to achieve RGC-specific gene modulation, and also opens up a promising gene therapy strategy for optic neuropathies, the most common form of eye diseases that cause irreversible blindness.

Inhibition of protein disulfide isomerase has neuroprotective effects in a mouse model of experimental autoimmune encephalomyelitis

Endoplasmic reticulum (ER) stress is strictly linked to neuroinflammation and involves in the development of neurodegenerative disorders. Protein disulfide isomerase (PDI) is an enzyme that catalyzes formation and isomerization of disulfide bonds and also acts as a chaperone that survives the cells against cell death by removal of misfolded proteins. Our previous work revealed that PDI is explicitly upregulated in response to myelin oligodendrocyte glycoprotein (MOG)-induced ER stress in the brain of experimental autoimmune encephalomyelitis (EAE) mice. The significance of overexpression of PDI in the apoptosis of neural cells prompted us to study the effect of CCF642, efficient inhibitor of PDI, in the recovery of EAE clinical symptoms. Using this in vivo model, we characterized the ability of CCF642 to decrease the expression of ER stress markers and neuroinflammation in the hippocampus of EAE mice. Our observations suggested that CCF642 administration attenuates EAE clinical symptomsand the expression of ER stress-related proteins. Further, it suppressed the inflammatory infiltration of CD4 + T cells and the activation of hippocampus-resident microglia and Th17 cells. We reported here that the inhibition of PDI protected EAE mice against neuronal apoptosis induced by prolonged ER stress and resulted in neuroprotection.

Assessing the anterior visual pathway in optic neuritis: recent experimental and clinical aspects

PURPOSE OF REVIEW

Multiple sclerosis (MS) and related autoimmune disorders of the central nervous system such as neuromyelitis optica spectrum disorders (NMOSD) are characterized by chronic disability resulting from autoimmune neuroinflammation, with demyelination, astrocyte damage, impaired axonal transmission and neuroaxonal loss. Novel therapeutics stopping or reversing the progression of disability are still urgently warranted. This review addresses research on optic neuritis in preclinical experimental models and their translation to clinical trials.

RECENT FINDINGS

Optic neuritis can be used as paradigm for an MS relapse which can serve to evaluate the efficacy of novel therapeutics in clinical trials with a reasonable duration and cohort size. The advantage is the linear structure of the visual pathway allowing the assessment of visual function and retinal structure as highly sensitive outcome parameters. Experimental autoimmune encephalomyelitis is an inducible, inflammatory and demyelinating central nervous system disease extensively used as animal model of MS. Optic neuritis is part of the clinicopathological manifestations in a number of experimental autoimmune encephalomyelitis models. These have gained increasing interest for studies evaluating neuroprotective and/or remyelinating substances as longitudinal, visual and retinal readouts have become available.

SUMMARY

Translation of preclinical experiments, evaluating neuroprotective or remyelinating therapeutics to clinical studies is challenging. In-vivo readouts like optical coherence tomography, offers the possibility to transfer experimental study designs to clinical optic neuritis trials.

Systemic hypoxia led to little retinal neuronal loss and dramatic optic nerve glial response

Vision loss is a devastating consequence of systemic hypoxia, but the cellular mechanisms are unclear. We investigated the impact of acute hypoxia in the retina and optic nerve. We induced systemic hypoxia (10% O₂) in 6-8w mice for 48 h and performed in vivo imaging using optical coherence tomography (OCT) at baseline and after 48 h to analyze structural changes in the retina and optic nerve. We analyzed glial cellular and molecular changes by histology and immunofluorescence and the impact of pretreatment with 4-phenylbutyric acid (4-PBA) in oligodendroglia survival. After 48 h hypoxia, we found no change in ganglion cell complex thickness and no loss of retinal ganglion cells. Despite this, there was significantly increased expression of CCAAT-enhancer-binding protein homologous protein (CHOP), a marker of endoplasmic reticulum stress, in the retina and optic nerve. In addition, hypoxia induced obvious increase of GFAP expression in the anterior optic nerve, where it co-localized with CHOP, and significant loss of Olig2⁺ oligodendrocytes. Pretreatment with 4-PBA, which has been shown to reduce endoplasmic reticulum stress, rescued total Olig2⁺ oligodendrocytes and increased the pool of mature (CC-1⁺) but not of immature (PDGFRa+) oligodendrocytes. Consistent with a selective vulnerability of the retina and optic nerve in hypoxia, the most striking changes in the 48 h murine model of hypoxia were in glial cells in the optic nerve, including increased CHOP expression in the astrocytes and loss of oligodendrocytes. Our data support a model where glial dysfunction is among the earliest events in systemic hypoxia - suggesting that glia may be a novel target in treatment of hypoxia.

Acupuncture Treatment Reverses Retinal Gene Expression Induced by Optic Nerve Injury via RNA Sequencing Analysis

Glaucoma and traumatic optic nerve crush (ONC) injury result in progressive loss of retinal ganglion cells (RGCs) and defects in visual function. In clinical trials of Traditional Chinese Medicine, acupuncture has been widely used for the treatment of ocular diseases. However, the molecular mechanisms of acupuncture treatment are still unclear. In this study, we used technique of RNA sequencing (RNA-seq) to study the effects of acupuncture treatment on retinal transcriptome after axotomy injury. RNA-seq results revealed that 436 genes including 31 transcription factors (TFs) were changed after injury, among them were many well-known neural degeneration related TFs such as Jun, Ddit3, Atf3, and Atf4. Interestingly, acupuncture treatment at acupoint GB20 (Fengchi) significantly reversed a series of differential expressed genes (DEGs) induced by optic nerve injury. While treatments at BL1 (Jingming) or GB20 sham control acupoint-GV16 (Fengfu), led to limited DEG reversal. In contrast, treatments at these two sites further enhanced the trend of DEG expression induced by axotomy injury. At last, retina immunostaining results revealed that only GB20 acupoint treatment increased RGC survival, in consistent with RNA-seq results. Therefore, our study first reported that acupuncture treatment regulated retinal transcriptome and reversed the gene expression induced by axotomy injury, and GB20 acupoint treatment increased RGC survival, which will provide novel therapeutic targets for treatment of ocular diseases.

DDIT3 (CHOP) contributes to retinal ganglion cell somal loss but not axonal degeneration in DBA/2J mice

Glaucoma is an age-related neurodegenerative disease characterized by the progressive loss of retinal ganglion cells (RGCs). Chronic ocular hypertension, an important risk factor for glaucoma, leads to RGC axonal injury at the optic nerve head. This insult triggers molecularly distinct cascades governing RGC somal apoptosis and axonal degeneration. The molecular mechanisms activated by ocular hypertensive insult that drive both RGC somal apoptosis and axonal degeneration are incompletely understood. The cellular response to endoplasmic reticulum stress and induction of pro-apoptotic DNA damage inducible transcript 3 (DDIT3, also known as CHOP) have been implicated as drivers of neurodegeneration in many disease models, including glaucoma. RGCs express DDIT3 after glaucoma-relevant insults, and importantly, DDIT3 has been shown to contribute to both RGC somal apoptosis and axonal degeneration after acute induction of ocular hypertension. However, the role of DDIT3 in RGC somal and axonal degeneration has not been critically tested in a model of age-related chronic ocular hypertension. Here, we investigated the role of DDIT3 in glaucomatous RGC death using an age-related, naturally occurring ocular hypertensive mouse model of glaucoma, DBA/2J mice (D2). To accomplish this, a null allele of Ddit3 was backcrossed onto the D2 background. Homozygous Ddit3 deletion did not alter gross retinal or optic nerve head morphology, nor did it change the ocular hypertensive profile of D2 mice. In D2 mice, Ddit3 deletion conferred mild protection to RGC somas, but did not significantly prevent RGC axonal degeneration. Together, these data suggest that DDIT3 plays a minor role in perpetuating RGC somal apoptosis caused by chronic ocular hypertension-induced axonal injury, but does not significantly contribute to distal axonal degeneration.

Increased ER Stress After Experimental Ischemic Optic Neuropathy and Improved RGC and Oligodendrocyte Survival After Treatment With Chemical Chaperon

Purpose

Increased endoplasmic reticulum (ER) stress is one of the earliest subcellular changes in neuro-ophthalmic diseases. In this study, we investigated the expression of key molecules in the ER stress pathways following nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in adults over 50, and assessed the impact of chemical chaperon 4-phenylbutyric acid (4-PBA) in vivo.

Methods

We induced AION using photochemical thrombosis in adult mice and performed histologic analyses of key molecules in the ER stress pathway in the retina and optic nerve. We also assessed the effects of daily intraperitoneal injections of 4-PBA after AION.

Results

In the retina at baseline, there was low proapoptotic transcriptional regulator C/EBP homologous protein (CHOP) and high prosurvival chaperon glucose-regulated protein 78 (GRP78) expression in retinal ganglion cells (RGCs). One day after AION, there was significantly increased CHOP and reduced GRP78 expressions in the ganglion cell layer. In the optic nerve at baseline, there was little CHOP and high GRP78 expression. One day after AION, there was significantly increased CHOP and no change in GRP78 expression. Treatment immediately after AION using daily intraperitoneal injection of chemical chaperone 4-PBA for 19 days significantly rescued Brn3A⁺ RGCs and Olig2⁺ optic nerve oligodendrocytes.

Conclusions

We showed for the first time that acute AION resulted in increased ER stress and differential expression of ER stress markers CHOP and GRP78 in the retina and optic nerve. Rescue of RGCs and oligodendrocytes with 4-PBA provides support for ER stress reduction as possible treatment for AION.

Ac-SDKP ameliorates the progression of experimental autoimmune encephalomyelitis via inhibition of ER stress and oxidative stress in the hippocampus of C57BL/6 mice

Despite the attention given to the treatment of multiple sclerosis (MS), still no certain cure is available. The main purpose of MS drugs is acting against neuroinflammation which underlies the pathology of MS. Neuroinflammation is associated with endoplasmic reticulum (ER) stress that mediates neural apoptosis. In the present study, we hypothesized that the tetrapeptide N-acetyl-ser-asp-lys-pro (Ac-SDKP) with the previously described anti-fibrotic effects might have anti-inflammatory, anti-oxidative and anti-ER stress roles in the hippocampus. We used myelin oligodendrocyte glycoprotein (MOG) to induce experimental autoimmune encephalomyelitis (EAE), a widely-accepted animal model of MS, in C57BL/6 mice. The protein levels of ER stress-related molecules including caspase-12, C/EBP homologous protein (CHOP), and protein disulfide isomerase (PDI) in the hippocampus were examined by immunoblotting. Hence, reactive oxygen species (ROS) production, lipid peroxidation and antioxidant capacity of the hippocampus were studied. Moreover, hippocampal morphology changes, leukocytes infiltration, and the levels of IL-6 and IL-1β pro-inflammatory cytokines were evaluated. Our results displayed that Ac-SDKP down regulates caspase-12 and CHOP expression in the hippocampus-resident oligodendrocytes of EAE mice. Further, treatment with Ac-SDKP decreased oxidative stress markers and caspase-3 activation in the hippocampus of EAE mice. According to our findings, Ac-SDKP showed beneficial effects against ER stress and oxidative stress in addition to inflammation in the hippocampus of EAE mice. The present study provides the basis for further research on the therapeutic applications of Ac-SDKP to reduce ER stress and oxidative stress-induced apoptosis in neurodegenerative disorders.

Modulating Expression of Thioredoxin Interacting Protein (TXNIP) Prevents Secondary Damage and Preserves Visual Function in a Mouse Model of Ischemia/Reperfusion

Retinal neurodegeneration, an early characteristic of several blinding diseases, triggers glial activation, resulting in inflammation, secondary damage and visual impairment. Treatments that aim only at neuroprotection have failed clinically. Here, we examine the impact of modulating thioredoxin interacting protein (TXNIP) to the inflammatory secondary damage and visual impairment in a model of ischemia/reperfusion (IR). Wild type (WT) and TXNIP knockout (TKO) mice underwent IR injury by increasing intraocular pressure for 40 min, followed by reperfusion. An additional group of WT mice received intravitreal TXNIP-antisense oligomers (ASO, 100 µg/2 µL) 2 days post IR injury. Activation of Müller glial cells, apoptosis and expression of inflammasome markers and visual function were assessed. IR injury triggered early TXNIP mRNA expression that persisted for 14 days and was localized within activated Müller cells in WT-IR, compared to sham controls. Exposure of Müller cells to hypoxia-reoxygenation injury triggered endoplasmic reticulum (ER) stress markers and inflammasome activation in WT cells, but not from TKO cells. Secondary damage was evident by the significant increase in the number of occluded acellular capillaries and visual impairment in IR-WT mice but not in IR-TKO. Intervention with TXNIP-ASO prevented ischemia-induced glial activation and neuro-vascular degeneration, and improved visual function compared to untreated WT. Targeting TXNIP expression may offer an effective approach in the prevention of secondary damage associated with retinal neurodegenerative diseases.

AAV2-mediated GRP78 Transfer Alleviates Retinal Neuronal Injury by Downregulating ER Stress and Tau Oligomer Formation

Purpose

Retinal ganglion cell (RGC) death following axonal injury occurring in traumatic optic neuropathy (TON) causes irreversible vision loss. GRP78 is a molecular chaperone that enhances protein folding and controls activation of endoplasmic reticulum (ER) stress pathways. This study determined whether adeno-associated virus (AAV)-mediated gene transfer of GRP78 protected RGCs from death in a mouse model of TON induced by optic nerve crush (ONC).

Methods

ONC was induced by a transient crush of optic nerve behind the eye globe. AAV was used to deliver genes into retina. Molecules in the ER stress branches, tau oligomers, and RGC injury were determined by immunohistochemistry or Western blot.

Results

Among tested AAV serotypes, AAV2 was the most efficient for delivering genes to RGCs. Intravitreal delivery of AAV2-GRP78 markedly attenuated ER stress and RGC death 3 days after ONC, and significantly improved RGC survival and function 7 days after ONC. Protein aggregation is increased during ER stress and aggregated proteins such as tau oligomers are key players in neurodegenerative diseases. AAV2-GRP78 alleviated ONC-induced increases in tau phosphorylation and oligomerization. Furthermore, tau oligomers directly induced RGC death, and blocking tau oligomers with tau oligomer monoclonal antibody (TOMA) attenuated ONC-induced RGC loss.

Conclusion

These data indicate that the beneficial effect of AAV2-GRP78 is partially mediated by the reduction of misfolded tau, and provide compelling evidence that gene therapy with AAV2-GRP78 or immunotherapy with TOMA offers novel therapeutic approaches to alleviate RGC loss in TON.

The UPR-PERK pathway is not a promising therapeutic target for mutant SOD1-induced ALS

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease, characterized by motor neuron death in the brain and spinal cord. Mutations in the Cu/Zn superoxide dismutase (SOD1) gene account for ~20% of all familial ALS forms, corresponding to 1%-2% of all ALS cases. One of the suggested mechanisms by which mutant SOD1 (mtSOD1) exerts its toxic effects involves intracellular accumulation of abnormal mtSOD1 aggregates, which trigger endoplasmic reticulum (ER) stress and activate its adaptive signal transduction pathways, including the unfolded protein response (UPR). PERK, an eIF2α kinase, is central to the UPR and is the most rapidly activated pathway in response to ER stress. Previous reports using mtSOD1 transgenic mice indicated that genetic or pharmacological enhancement of the UPR-PERK pathway may be effective in treating ALS. We investigated the response to PERK haploinsufficiency, and the response to deficiency of its downstream effectors GADD34 and CHOP, in five distinct lines of mtSOD1 mice. We demonstrate that, in contrast to a previously published study, PERK haploinsufficiency has no effect on disease in all mtSOD1 lines examined. We also show that deficiency of GADD34, which enhances the UPR by prolonging the phosphorylation of eIF2α, does not ameliorate disease in these mtSOD1 mouse lines. Finally, we demonstrate that genetic ablation of CHOP transcription factor, which is known to be pro-apoptotic, does not ameliorate disease in mtSOD1 mice. Cumulatively, our studies reveal that neither genetic inhibition of the UPR via ablation of PERK, nor genetic UPR enhancement via ablation of GADD34, is beneficial for mtSOD1-induced motor neuron disease. Therefore, the PERK pathway is not a likely target for therapeutic intervention in mtSOD1-induced ALS.

Connexin32 plays a crucial role in ROS-mediated endoplasmic reticulum stress apoptosis signaling pathway in ischemia reperfusion-induced acute kidney injury

BACKGROUND

Ischemia-reperfusion (I/R)-induced acute kidney injury (AKI) not only prolongs the length of hospital stay, but also seriously affects the patient's survival rate. Although our previous investigation has verified that reactive oxygen species (ROS) transferred through gap junction composed of connexin32 (Cx32) contributed to AKI, its underlying mechanisms were not fully understood and viable preventive or therapeutic regimens were still lacking. Among various mechanisms involved in organs I/R-induced injuries, endoplasmic reticulum stress (ERS)-related apoptosis is currently considered to be an important participant. Thus, in present study, we focused on the underlying mechanisms of I/R-induced AKI, and postulated that Cx32 mediated ROS/ERS/apoptosis signal pathway activation played an important part in I/R-induced AKI.

METHODS

We established renal I/R models with Cx32+/+ and Cx32-/- mice, which underwent double kidneys clamping and recanalization. ROS scavenger (N-acetylcysteine, NAC) and ERS inhibitors (4-phenyl butyric acid, 4-PBA, and tauroursodeoxycholic acid, TUDCA) were used to decrease the content of ROS and attenuate ERS activation, respectively.

RESULTS

Renal damage was progressively exacerbated in a time-dependent manner at the reperfusion stage, that was consistent with the alternation of ERS activation, including glucose regulated protein 78 (BiP/GRP78), X box-binding protein1, and C/EBP homologous protein expression. TUDCA or 4-PBA application attenuated I/R-induced ERS activation and protected against renal tubular epithelial cells apoptosis and renal damage. Cx32 deficiency decreased ROS generation and distribution between the neighboring cells, which attenuated I/R-induced ERS activation, and improved cell apoptosis and renal damage.

CONCLUSION

Cx32 mediated ROS/ERS/apoptosis signal pathway activation played an important part in I/R-induced AKI. Cx32 deficiency, ROS elimination, and ERS inhibition all could protect against I/R-induced AKI.

Hepatic steatosis associated with decreased β-oxidation and mitochondrial function contributes to cell damage in obese mice after thermal injury

Severely burned patients who are morbidly obese have poor clinical outcomes with aggravated metabolic consequences, a higher incidence of multiple organ dysfunction/failure, and significantly increased morbidity and mortality. The underlying mechanisms of these adverse outcomes are essentially unknown. Since the liver is one of the central metabolic organs, we hypothesized that thermal injury in obese patients leads to substantially increased lipolysis, hepatic fat infiltration, resulting in profound hepatic cellular and organellar alterations, consequently causing liver damage and severely augmented metabolic dysfunction. We tested this hypothesis using an obese mouse model subjected to a 20% total body surface area burn injury. C57BL/6 mice were randomly divided into low-fat diet (LFD) and high-fat diet (HFD) sham and burn groups (n = 6 per group) and fed for 16 weeks. 7 days after the thermal injury portal and cardiac blood were taken separately and liver tissue was collected for western blotting and immunohistochemical analysis. Gross examination of the liver showed apparent lipid infiltration in HFD fed and burned mice. We confirmed that augmented ER stress and inhibition of Akt-mTOR signaling dysregulated calcium homeostasis, contributed to the decrease of ER–mitochondria contact, and reduced mitochondrial β-oxidation in HFD fed and burned mice, leading to profound hepatic fat infiltration and substantial liver damage, hence increased morbidity and mortality. We conclude that obesity contributes to hepatic fat infiltration by suppressing β-oxidation, inducing cell damage and subsequent organ dysfunction after injury.

Gene Therapy Strategies to Restore ER Proteostasis in Disease

Proteostasis alterations are proposed as a transversal hallmark of several pathological conditions, including metabolic disorders, mechanical injury, cardiac malfunction, neurodegeneration, and cancer. Strategies to improve proteostasis aim to reduce the accumulation of specific disease-related misfolded proteins or bolster the endogenous mechanisms to fold and degrade abnormal proteins. Endoplasmic reticulum (ER) stress is a common pathological signature of a variety of diseases, which engages the unfolded protein response (UPR) as a cellular reaction to mitigate ER stress. Pharmacological modulation of the UPR is challenging considering the physiological importance of the pathway in various organs. However, local targeting of ER stress responses in the affected tissue using gene therapy is emerging as a possible solution to overcome side effects. The delivery of ER chaperones or active UPR components using adeno-associated virus (AAV) has demonstrated outstanding beneficial effects in several disease models (e.g., neurodegenerative conditions, eye disorders, and metabolic diseases). Here, we discuss current efforts to design and optimize gene therapy strategies to improve ER proteostasis in different disease contexts.

Neurodegeneration: Keeping ATF4 on a Tight Leash

Activation of the endoplasmic reticulum (ER) stress and ER stress response, also known as the unfolded protein response (UPR), is common to various degenerative disorders. Therefore, signaling components of the UPR are currently emerging as potential targets for intervention and treatment of human diseases. One UPR signaling member, activating transcription factor 4 (ATF4), has been found up-regulated in many pathological conditions, pointing to therapeutic potential in targeting its expression. In cells, ATF4 governs multiple signaling pathways, including autophagy, oxidative stress, inflammation, and translation, suggesting a multifaceted role of ATF4 in the progression of various pathologies. However, ATF4 has been shown to trigger both pro-survival and pro-death pathways, and this, perhaps, can explain the contradictory opinions in current literature regarding targeting ATF4 for clinical application. In this review, we summarized recent published studies from our labs and others that focus on the therapeutic potential of the strategy controlling ATF4 expression in different retinal and neurodegenerative disorders.