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

Transcriptional Responses of Different Brain Cell Types to Oxygen Decline

Brain hypoxia is associated with a wide range of physiological and clinical conditions. Although oxygen is an essential constituent of maintaining brain functions, our understanding of how specific brain cell types globally respond and adapt to decreasing oxygen conditions is incomplete. In this study, we exposed mouse primary neurons, astrocytes, and microglia to normoxia and two hypoxic conditions and obtained genome-wide transcriptional profiles of the treated cells. Analysis of differentially expressed genes under conditions of reduced oxygen revealed a canonical hypoxic response shared among different brain cell types. In addition, we observed a higher sensitivity of neurons to oxygen decline, and dissected cell type-specific biological processes affected by hypoxia. Importantly, this study establishes novel gene modules associated with brain cells responding to oxygen deprivation and reveals a state of profound stress incurred by hypoxia.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

The Molecular Mechanisms Involved in Axonal Degeneration and Retrograde Retinal Ganglion Cell Death

Axonal degeneration is a pathologic change common to multiple retinopathies and optic neuropathies. Various pathologic factors, such as mechanical injury, inflammation, and ischemia, can damage retinal ganglion cell (RGC) somas and axons, eventually triggering axonal degeneration and RGC death. The molecular mechanisms of somal and axonal degeneration are distinct but also overlap, and axonal degeneration can result in retrograde somal degeneration. While the mitogen-activated protein kinase pathway acts as a central node in RGC axon degeneration, several newly discovered molecules, such as sterile alpha and Toll/interleukin-1 receptor motif-containing protein 1 and nicotinamide mononucleotide adenylyltransferase 2, also play a critical role in this pathological process following different types of injury. Therefore, we summarize the types of injury that cause RGC axon degeneration and retrograde RGC death and important underlying molecular mechanisms, providing a reference for the identification of targets for protecting axons and RGCs.

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.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

Retinal Ganglion Cell Death in Glaucoma: Advances and Caveats

Purpose: Retinal ganglion cell death occurs during the glaucoma pathological process, and it is significant because of the poor regeneration capacity of retinal ganglion cells. With a constantly increasing understanding of retinal cell death mechanisms, we now know that simply blocking a specific mechanism of cell death might not prevent retinal ganglion cell death. This review aimed to summarize the mechanisms of retinal cell death in glaucoma models and discuss the caveats in restoring visual function in these studies.Methods: A literature search was done on PubMed using key words including glaucoma, ocular hypertension, retinal ganglion cell, cell death, apoptosis, necroptosis, pyroptosis, ferroptosis, autophagic cell death, and parthanatos. The literature was reviewed to summarize the information about the lethal pathways of retinal ganglion cell in the glaucoma-like animal models.Results: Based on the purpose, 100 studies were selected and discussed in this review.Conclusions: The damage to ganglion cells in glaucoma-like animals can occur via multiple lethal pathways and the molecular mechanisms are still incompletely understood. Further investigations on the crosstalk between different cell death pathways and the common upstream regulators could augment the development of novel targeting agents for the curative treatment of glaucoma.

Chimonanthus salicifolius attenuated vascular remodeling by alleviating endoplasmic reticulum stress in spontaneously hypertensive rats

Chimonanthus salicifolius (CS), the leaves of Chimonanthus salicifolius S. Y. Hu., is an effective tea to prevent and treat hypertension in China. This study aimed to explore the effect and mechanism of CS in the protection against vascular remodeling in hypertension. Spontaneously hypertensive rats (SHRs) were orally administered with aqueous extracts of CS for 6 months. The blood pressure and morphological changes of the aorta were measured. Their mechanisms were studied by combining chemical identification, network pharmacology analysis and validation in vivo. Hypertensive rats showed an impaired vascular structure and dyslipidemia as illustrated by the increase of the vascular media thickness and collagen deposition in the aorta. CS treatment exhibited significant beneficial effects on blood pressure control and aortal morphology. A total of 21 compounds from CS were identified, which were linked to 106 corresponding targeted genes for vascular remodeling. The network pharmacology predicted that CS prevented vascular remodeling through the endoplasmic reticulum stress pathway. The in vivo experiments further showed that CS treatment upregulated Glucose-Regulated Protein 78 and downregulated CCAAT-enhancer-binding protein homologous protein at both mRNA and protein levels, paralleling reduced apoptotic cells in the arterial wall. Additionally, CS diminished the low-density lipoprotein cholesterol levels, total cholesterol contents and triglyceride/high-density lipoprotein cholesterol ratios in the sera of SHRs, which might also contribute to its protection of vessels. Collectively, CS protects against vascular modeling by suppressing endoplasmic reticulum stress-related apoptosis in hypertension, and it could be a potential agent for the prevention and treatment of vascular modeling.

The Intertwined Roles of Oxidative Stress and Endoplasmic Reticulum Stress in Glaucoma

Glaucoma is the leading cause of irreversible blindness worldwide, and the burden of the disease continues to grow as the global population ages. Currently, the only treatment option is to lower intraocular pressure. A better understanding of glaucoma pathogenesis will help us to develop novel therapeutic options. Oxidative stress has been implicated in the pathogenesis of many diseases. Oxidative stress occurs when there is an imbalance in redox homeostasis, with reactive oxygen species producing processes overcoming anti-oxidant defensive processes. Oxidative stress works in a synergistic fashion with endoplasmic reticulum stress, to drive glaucomatous damage to trabecular meshwork, retinal ganglion cells and the optic nerve head. We discuss the oxidative stress and endoplasmic reticulum stress pathways and their connections including their key intermediary, calcium. We highlight therapeutic options aimed at disrupting these pathways and discuss their potential role in glaucoma treatment.

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.

Multifactorial Pathogenic Processes of Retinal Ganglion Cell Degeneration in Glaucoma towards Multi-Target Strategies for Broader Treatment Effects

Glaucoma is a chronic neurodegenerative disease characterized by apoptosis of retinal ganglion cell (RGC) somas, degeneration of axons, and loss of synapses at dendrites and axon terminals. Glaucomatous neurodegeneration encompasses multiple triggers, multiple cell types, and multiple molecular pathways through the etiological paths with biomechanical, vascular, metabolic, oxidative, and inflammatory components. As much as intrinsic responses of RGCs themselves, divergent responses and intricate interactions of the surrounding glia also play decisive roles for the cell fate. Seen from a broad perspective, multitarget treatment strategies have a compelling pathophysiological basis to more efficiently manipulate multiple pathogenic processes at multiple injury sites in such a multifactorial neurodegenerative disease. Despite distinct molecular programs for somatic and axonal degeneration, mitochondrial dysfunction and glia-driven neuroinflammation present interdependent processes with widespread impacts in the glaucomatous retina and optic nerve. Since dysfunctional mitochondria stimulate inflammatory responses and proinflammatory mediators impair mitochondria, mitochondrial restoration may be immunomodulatory, while anti-inflammatory treatments protect mitochondria. Manipulation of these converging routes may thus allow a unified treatment strategy to protect RGC axons, somas, and synapses. This review presents an overview of recent research advancements with emphasis on potential treatment targets to achieve the best treatment efficacy to preserve visual function in glaucoma.

Commonalities of optic nerve injury and glaucoma-induced neurodegeneration: Insights from transcriptome-wide studies

Glaucoma is a collection of diseases that lead to an irreversible vision loss due to damage of retinal ganglion cells (RGCs). Although the underlying events leading to RGC death are not fully understood, recent research efforts are beginning to define the genetic changes that play a critical role in the initiation and progression of glaucomatous injury and RGC death. Several genetic and experimental animal models have been developed to mimic glaucomatous neurodegeneration. These models differ in many respects but all result in the loss of RGCs. Assessing transcriptional changes across different models could provide a more complete perspective on the molecular drivers of RGC degeneration. For the past several decades, changes in the retinal transcriptome during neurodegeneration process were defined using microarray methods, RNA sequencing and now single cell RNA sequencing. It is understood that these methods have strengths and weaknesses due to technical differences and variations in the analytical tools used. In this review, we focus on the use of transcriptome-wide expression profiling of the changes occurring as RGCs are lost across different glaucoma models. Commonalities of optic nerve crush and glaucoma-induced neurodegeneration are identified and discussed.

Withaferin A and Ovarian Cancer Antagonistically Regulate Skeletal Muscle Mass

Cachexia is a complex wasting syndrome that overwhelmingly affects the majority of late-stage cancer patients. Additionally, there are currently no efficacious therapeutic agents to treat the muscle atrophy induced by the cancer. While several preclinical studies have investigated the molecular signals orchestrating cachexia, very little information exists pertaining to ovarian cancer and the associated cachexia. Work from our lab has recently demonstrated that the steroidal lactone Withaferin A (WFA) is capable of attenuating the atrophying effects of ovarian cancer in a preclinical mouse model. However, it remained to be determined whether WFA's effect was in response to its anti-tumorigenic properties, or if it was capable of targeting skeletal muscle directly. The purpose of this study was to uncover whether WFA was capable of regulating muscle mass under tumor-free and tumor-bearing conditions. Treatment with WFA led to an improvement in functional muscle strength and mass under tumor-bearing and naïve conditions. WFA and ovarian cancer were observed to act antagonistically upon critical skeletal muscle regulatory systems, notably myogenic progenitors and proteolytic degradation pathways. Our results demonstrated for the first time that, while WFA has anti-tumorigenic properties, it also exerts hypertrophying effects on skeletal muscle mass, suggesting that it could be an anti-cachectic agent in the settings of ovarian cancer.

Endothelin 1-induced retinal ganglion cell death is largely mediated by JUN activation

Glaucoma is a neurodegenerative disease characterized by loss of retinal ganglion cells (RGCs), the output neurons of the retina. Multiple lines of evidence show the endothelin (EDN, also known as ET) system is important in glaucomatous neurodegeneration. To date, the molecular mechanisms within RGCs driving EDN-induced RGC death have not been clarified. The pro-apoptotic transcription factor JUN (the canonical target of JNK signaling) and the endoplasmic reticulum stress effector and transcription factor DNA damage inducible transcript 3 (DDIT3, also known as CHOP) have been shown to act downstream of EDN receptors. Previous studies demonstrated that JUN and DDIT3 were important regulators of RGC death after glaucoma-relevant injures. Here, we characterized EDN insult in vivo and investigated the role of JUN and DDIT3 in EDN-induced RGC death. To accomplish this, EDN1 ligand was intravitreally injected into the eyes of wildtype, Six3-cre⁺Jun^fl/fl (Jun^-/-), Ddit3 null (Ddit3^-/-), and Ddit3^-/-Jun^-/- mice. Intravitreal EDN1 was sufficient to drive RGC death in vivo. EDN1 insult caused JUN activation in RGCs, and deletion of Jun from the neural retina attenuated RGC death after EDN insult. However, deletion of Ddit3 did not confer significant protection to RGCs after EDN1 insult. These results indicate that EDN caused RGC death via a JUN-dependent mechanism. In addition, EDN signaling is known to elicit potent vasoconstriction. JUN signaling was shown to drive neuronal death after ischemic insult. Therefore, the effects of intravitreal EDN1 on retinal vessel diameter and hypoxia were explored. Intravitreal EDN1 caused transient retinal vasoconstriction and regions of RGC and Müller glia hypoxia. Thus, it remains a possibility that EDN elicits a hypoxic insult to RGCs, causing apoptosis via JNK-JUN signaling. The importance of EDN-induced vasoconstriction and hypoxia in causing RGC death after EDN insult and in models of glaucoma requires further investigation.

Cytotoxic Screening and Transcriptomics Reveal Insights into the Molecular Mechanisms of Trihexyl Phosphate-Triggered Hepatotoxicity

Mounting evidence shows that organophosphate flame retardants (OPFRs), especially aryl- and halogenated-OPFRs, exert various adverse health effects on living organisms. This study evaluated the hepatotoxic effect of trihexyl phosphate (THP) as a long-chain alkyl-OPFR on human hepatocyte cells (LO2) and mouse hepatocyte cells (AML12) by performing screening of cytotoxicity in vitro. In combination with transcriptomic analysis, toxicological mechanisms in vitro were further investigated. Results showed that THP triggered hepatotoxicity in vitro by altering four signaling pathways: endoplasmic reticulum (ER) stress, apoptosis, cell cycle, and the glycolysis signaling pathway. Exposure of LO2 and AML12 liver cells to THP (25 μg/mL) significantly induced ER stress-mediated apoptosis and cell cycle arrest. Meanwhile, downregulation of glycolysis caused the blockage of energy metabolism. Furthermore, the high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF-MS/MS) revealed that much of THP was absorbed into the cells and displayed stability in the two liver cell lines. In vivo assays using a mouse model demonstrated that exposure to THP at 400 mg/kg induced the ballooning degeneration of hepatocytes in liver tissue, whereas exposure to THP at 800 mg/kg caused acute liver injury with high alanine aminotransferase levels. This study provides novel insights into the impact of THP on hepatotoxicity in vitro and in vivo and uncovers the underlying toxicological mechanisms, which may serve as a guide for further ecological risk assessment and reasonable application of alkyl-OPFRs.

A broad perspective on the molecular regulation of retinal ganglion cell degeneration in glaucoma

Glaucoma is a complex neurodegenerative disease involving RGC axons, somas, and synapses at dendrites and axon terminals. Recent research advancements in the field have revealed a bigger picture of glaucomatous neurodegeneration that encompasses multiple stressors, multiple injury sites, multiple cell types, and multiple signaling pathways for asynchronous degeneration of RGCs during a chronic disease period. Optic nerve head is commonly viewed as the critical site of injury in glaucoma, where early injurious insults initiate distal and proximal signaling for axonal and somatic degeneration. Despite compartmentalized processes for degeneration of RGC axons and somas, there are intricate interactions between the two compartments and mechanistic overlaps between the molecular pathways that mediate degeneration in axonal and somatic compartments. This review summarizes the recent progress in the molecular understanding of RGC degeneration in glaucoma and highlights various etiological paths with biomechanical, metabolic, oxidative, and inflammatory components. Through this growing body of knowledge, the glaucoma community moves closer toward causative treatment of this blinding disease.

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

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

Ambroxol Improves Neuronal Survival and Reduces White Matter Damage through Suppressing Endoplasmic Reticulum Stress in Microglia after Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) has been becoming a serious public health problem. Pneumonia, occurring in 43% of all ICH patients, is a common complication heavily influencing outcome and accounting for more than 1/3 of the overall mortality in patients with ICH. Ambroxol may be an effective additional treatment for ICH patients with pneumonia. But its effect and potential mechanism on functional recovery post-ICH still remain elusive. In the present study, the results indicated that 35 mg/kg and 70 mg/kg ambroxol facilitated neuronal survival and reduced white matter fiber bundle damage due to mitigating microglial activation and reducing proinflammatory cytokine accumulation in mice with ICH. The possible mechanism might be due to suppressing endoplasmic reticulum stress involving the IRE1α/TRAF2 signaling pathway, which paves a new path for the treatment of ICH and opens a new window for the use of ambroxol in clinical practice.