Sigma 1 receptor regulates the oxidative stress response in primary retinal Müller glial cells via NRF2 signaling and system xc(-), the Na(+)-independent glutamate-cystine exchanger

Hypidone hydrochloride (YL-0919) ameliorates functional deficits after traumatic brain injury in mice by activating the sigma-1 receptor for antioxidation

JOURNAL/nrgr/04.03/01300535-202508000-00023/figure1/v/2024-09-30T120553Z/r/image-tiff Traumatic brain injury involves complex pathophysiological mechanisms, among which oxidative stress significantly contributes to the occurrence of secondary injury. In this study, we evaluated hypidone hydrochloride (YL-0919), a self-developed antidepressant with selective sigma-1 receptor agonist properties, and its associated mechanisms and targets in traumatic brain injury. Behavioral experiments to assess functional deficits were followed by assessment of neuronal damage through histological analyses and examination of blood-brain barrier permeability and brain edema. Next, we investigated the antioxidative effects of YL-0919 by assessing the levels of traditional markers of oxidative stress in vivo in mice and in vitro in HT22 cells. Finally, the targeted action of YL-0919 was verified by employing a sigma-1 receptor antagonist (BD-1047). Our findings demonstrated that YL-0919 markedly improved deficits in motor function and spatial cognition on day 3 post traumatic brain injury, while also decreasing neuronal mortality and reversing blood-brain barrier disruption and brain edema. Furthermore, YL-0919 effectively combated oxidative stress both in vivo and in vitro. The protective effects of YL-0919 were partially inhibited by BD-1047. These results indicated that YL-0919 relieved impairments in motor and spatial cognition by restraining oxidative stress, a neuroprotective effect that was partially reversed by the sigma-1 receptor antagonist BD-1047. YL-0919 may have potential as a new treatment for traumatic brain injury.

Central role of Sigma-1 receptor in ochratoxin A-induced ferroptosis

Ochratoxin A (OTA), a secondary fungal metabolite known for its nephrotoxic effects, is prevalent in various feeds and food items. Our recent study suggests that OTA-induced nephrotoxicity is linked to the Sigma-1 receptor (Sig-1R)-mediated mitochondrial pathway apoptosis in human proximal tubule epithelial-originated kidney-2 (HK-2) cells. However, the contribution of Sig-1R to OTA-induced nephrotoxicity involving other forms of regulated cell death, such as ferroptosis, remains unexplored. In this investigation, cell viability, malondialdehyde (MDA) levels, glutathione (GSH) levels, and protein expressions in HK-2 cells treated with OTA and/or Ferrostatin-1/blarcamesine hydrochloride/BD1063 dihydrochloride were assessed. The results indicate that a 24 h-treatment with 1 μM OTA significantly induces ferroptosis by inhibiting Sig-1R, subsequently promoting nuclear receptor coactivator 4 (NCOA4), long-chain fatty acid-CoA ligase 4 (ACSL4), arachidonate 5-lipoxygenase (ALOX5), autophagy protein 5 (ATG5), and ATG7, inhibiting ferritin heavy chain (FTH1), solute carrier family 7 member 11 (SLC7A11/xCT), glutathione peroxidase 4 (GPX4), peroxiredoxin 6 (PRDX6), and ferroptosis suppressor protein 1 (FSP1), reducing GSH levels, and increasing MDA levels (P < 0.05). In conclusion, OTA induces ferroptosis by inhibiting Sig-1R, subsequently promoting ferritinophagy, inhibiting GPX4/FSP1 antioxidant systems, reducing GSH levels, and ultimately increasing lipid peroxidation levels in vitro.

Functions of TRPs in retinal tissue in physiological and pathological conditions

The Transient Receptor Potential (TRP) constitutes a family of channels subdivided into seven subfamilies: Ankyrin (TRPA), Canonical (TRPC), Melastatin (TRPM), Mucolipin (TRPML), no-mechano-potential C (TRPN), Polycystic (TRPP), and Vanilloid (TRPV). Although they are structurally similar to one another, the peculiarities of each subfamily are key to the response to stimuli and the signaling pathway that each one triggers. TRPs are non-selective cation channels, most of which are permeable to Ca2+, which is a well-established second messenger that modulates several intracellular signaling pathways and is involved in physiological and pathological conditions in various cell types. TRPs depolarize excitable cells by increasing the influx of Ca2+, Na+, and other cations. Most TRP families are activated by temperature variations, membrane stretching, or chemical agents and, therefore, are defined as polymodal channels. All TPRs are expressed, at some level, in the central nervous system (CNS) and ocular-related structures, such as the retina and optic nerve (ON), except the TRPP in the ON. TRPC, TRPM, TRPV, and TRPML are found in the retinal pigmented cells, whereas only TRPA1 and TRPM are detected in the uvea. Accordingly, several studies have focused on the search to unravel the role of TRPs in physiological and pathological conditions related to the eyes. Thus, this review aims to shed light on endogenous and exogenous modulators, triggered cell signaling pathways, and localization and roles of each subfamily of TRP channels in physiological and pathological conditions in the retina, optic nerve, and retinal pigmented epithelium of vertebrates.

Regulatory factors of Nrf2 in age-related macular degeneration pathogenesis

Age-related macular degeneration (AMD) is a complicated disease that causes irreversible visual impairment. Increasing evidences pointed retinal pigment epithelia (RPE) cells as the decisive cell involved in the progress of AMD, and the function of anti-oxidant capacity of PRE plays a fundamental physiological role. Nuclear factor erythroid 2 related factor 2 (Nrf2) is a significant transcription factor in the cellular anti-oxidant system as it regulates the expression of multiple anti-oxidative genes. Its functions of protecting RPE cells against oxidative stress (OS) and ensuing physiological changes, including inflammation, mitochondrial damage and autophagy dysregulation, have already been elucidated. Understanding the roles of upstream regulators of Nrf2 could provide further insight to the OS-mediated AMD pathogenesis. For the first time, this review summarized the reported upstream regulators of Nrf2 in AMD pathogenesis, including proteins and miRNAs, and their underlying molecular mechanisms, which may help to find potential targets via regulating the Nrf2 pathway in the future research and further discuss the existing Nrf2 regulators proved to be beneficial in preventing AMD.

SLC7A11 in hepatocellular carcinoma: potential mechanisms, regulation, and clinical significance

Exploring novel early detection biomarkers and developing more efficacious treatments remain pressing tasks in the current research landscape for hepatocellular carcinoma (HCC). Morphologically and molecularly separate from apoptosis, cell death, and autophagy, ferroptosis is a recently discovered, unique, controlled form of cell death. SLC7A11 (also known as xCT) represents a subunit of the cystine-glutamate antiporter (also known as system Xc(-)). A growing body of research suggests that induction of ferroptosis through SLC7A11 can effectively eliminate hepatocellular carcinoma (HCC) cells, particularly those exhibiting resistance to alternative forms of cell death. Thus, targeting ferroptosis via SLC7A11 may become a new direction for the design of therapeutic strategies for HCC. Although many research articles have investigated the possible roles of SLC7A11 in HCC, a study that summarizes the main findings, including the regulators and mechanisms of action of SLC7A11 in HCC is not available. Therefore, we present a comprehensive overview of the functions of ferroptosis, particularly SLC7A11, in the identification, development, and management of HCC in this review. In addition, we discuss how this knowledge can be translated into treatment by providing a systemic therapy in advanced HCC using sorafenib, the first-line drug targeting multiple kinases and SLC7A11. We further dissect the possible barriers as well as the corresponding solutions and provide insights on how to navigate effective treatment using this knowledge.

Emerging role of ferroptosis in diabetic retinopathy: a review

BACKGROUND

Diabetic retinopathy (DR) is a significant complication of diabetes and the primary cause of blindness among working age adults globally. The development of DR is accompanied by oxidative stress, characterised by an overproduction of reactive oxygen species (ROS) and a compromised antioxidant system. Clinical interventions aimed at mitigating oxidative stress through ROS scavenging or elimination are currently available. Nevertheless, these treatments merely provide limited management over the advanced stage of the illness. Ferroptosis is a distinctive form of cell death induced by oxidative stress, which is characterised by irondependent phospholipid peroxidation.

PURPOSE

This review aims to synthesise recent experimental evidence to examine the involvement of ferroptosis in the pathological processes of DR, as well as to explicate the regulatory pathways governing oxidative stress and ferroptosis in retina.

METHODS

We systematically reviewed literature available up to 2023.

RESULTS

This review included 12 studies investigating the involvement of ferroptosis in DR.

Psychedelics for acquired brain injury: a review of molecular mechanisms and therapeutic potential

Acquired brain injury (ABI), such as traumatic brain injury and stroke, is a leading cause of disability worldwide, resulting in debilitating acute and chronic symptoms, as well as an increased risk of developing neurological and neurodegenerative disorders. These symptoms can stem from various neurophysiological insults, including neuroinflammation, oxidative stress, imbalances in neurotransmission, and impaired neuroplasticity. Despite advancements in medical technology and treatment interventions, managing ABI remains a significant challenge. Emerging evidence suggests that psychedelics may rapidly improve neurobehavioral outcomes in patients with various disorders that share physiological similarities with ABI. However, research specifically focussed on psychedelics for ABI is limited. This narrative literature review explores the neurochemical properties of psychedelics as a therapeutic intervention for ABI, with a focus on serotonin receptors, sigma-1 receptors, and neurotrophic signalling associated with neuroprotection, neuroplasticity, and neuroinflammation. The promotion of neuronal growth, cell survival, and anti-inflammatory properties exhibited by psychedelics strongly supports their potential benefit in managing ABI. Further research and translational efforts are required to elucidate their therapeutic mechanisms of action and to evaluate their effectiveness in treating the acute and chronic phases of ABI.

Endoplasmic Reticulum Protein TXNDC5 Interacts with PRDX6 and HSPA9 to Regulate Glutathione Metabolism and Lipid Peroxidation in the Hepatic AML12 Cell Line

Non-alcoholic fatty liver disease or steatosis is an accumulation of fat in the liver. Increased amounts of non-esterified fatty acids, calcium deficiency, or insulin resistance may disturb endoplasmic reticulum (ER) homeostasis, which leads to the abnormal accumulation of misfolded proteins, activating the unfolded protein response. The ER is the primary location site for chaperones like thioredoxin domain-containing 5 (TXNDC5). Glutathione participates in cellular oxidative stress, and its interaction with TXNDC5 in the ER may decrease the disulfide bonds of this protein. In addition, glutathione is utilized by glutathione peroxidases to inactivate oxidized lipids. To characterize proteins interacting with TXNDC5, immunoprecipitation and liquid chromatography-mass spectrometry were used. Lipid peroxidation, reduced glutathione, inducible phospholipase A2 (iPLA2) and hepatic transcriptome were assessed in the AML12 and TXNDC5-deficient AML12 cell lines. The results showed that HSPA9 and PRDX6 interact with TXNDC5 in AML12 cells. In addition, TXNDC5 deficiency reduced the protein levels of PRDX6 and HSPA9 in AML12. Moreover, lipid peroxidation, glutathione and iPLA2 activities were significantly decreased in TXNDC5-deficient cells, and to find the cause of the PRDX6 protein reduction, proteasome suppression revealed no considerable effect on it. Finally, hepatic transcripts connected to PRDX6 and HSPA9 indicated an increase in the Dnaja3, Mfn2 and Prdx5 and a decrease in Npm1, Oplah, Gstp3, Gstm6, Gstt1, Serpina1a, Serpina1b, Serpina3m, Hsp90aa1 and Rps14 mRNA levels in AML12 KO cells. In conclusion, the lipid peroxidation system and glutathione mechanism in AML12 cells may be disrupted by the absence of TXNDC5, a novel protein-protein interacting partner of PRDX6 and HSPA9.

Sigma Receptors: Novel Regulators of Iron/Heme Homeostasis and Ferroptosis

Sigma receptors are non-opiate/non-phencyclidine receptors that bind progesterone and/or heme and also several unrelated xenobiotics/chemicals. They reside in the plasma membrane and in the membranes of the endoplasmic reticulum, mitochondria, and nucleus. Until recently, the biology/pharmacology of these proteins focused primarily on their role in neuronal functions in the brain/retina. However, there have been recent developments in the field with the discovery of unexpected roles for these proteins in iron/heme homeostasis. Sigma receptor 1 (S1R) regulates the oxidative stress-related transcription factor NRF2 and protects against ferroptosis, an iron-induced cell death process. Sigma receptor 2 (S2R), which is structurally unrelated to S1R, complexes with progesterone receptor membrane components PGRMC1 and PGRMC2. S2R, PGRMC1, and PGRMC2, either independently or as protein-protein complexes, elicit a multitude of effects with a profound influence on iron/heme homeostasis. This includes the regulation of the secretion of the iron-regulatory hormone hepcidin, the modulation of the activity of mitochondrial ferrochelatase, which catalyzes iron incorporation into protoporphyrin IX to form heme, chaperoning heme to specific hemoproteins thereby influencing their biological activity and stability, and protection against ferroptosis. Consequently, S1R, S2R, PGRMC1, and PGRMC2 potentiate disease progression in hemochromatosis and cancer. These new discoveries usher this intriguing group of non-traditional progesterone receptors into an unchartered territory in biology and medicine.

The Neuroprotective Effect of Activation of Sigma-1 Receptor on Neural Injury by Optic Nerve Crush

Purpose

This study aimed to explore the neuroprotective effects of sigma-1 receptor (S1R) on optic nerve crush (ONC) mice by upregulating its expression through intravitreal injection of adeno-associated virus (AAV).

Methods

The animals were divided into four groups. Mice that underwent ONC were administered an intravitreal injection with blank vector (ONC group), with AAV targeting downregulation of S1R (S1R-sh group), or with AAV targeting overexpression of S1R (S1R-AAV group). Mice in the control group underwent intravitreal injection with blank vector. The thickness of each layer of the retina was measured through optical coherence tomography, and the apoptotic rate of retinal neurons was determined using the TUNEL assay. The expression levels of brain-derived neurotrophic factor (BDNF) and S1R were quantified through western blot. Electroretinogram (ERG) was performed to evaluate the visual function.

Results

The thickness of the total retina (P = 0.001), ganglion cell layer (P = 0.017), and inner nuclear layer (P = 0.002) in S1R-AAV group was significantly thicker than that of the ONC group. The number of retinal apoptotic cells in the S1R-AAV group was 23% lower than that in the ONC group (P = 0.002). ERG results showed that, compared to the ONC group, the amplitudes of the a- and b-waves were higher in the S1R-AAV group (a-wave, P < 0.001; b-wave, P = 0.007). Western blot showed that the expression of BDNF in the S1R-AAV group was higher than that in the ONC group (P < 0.001).

Conclusions

Activation of S1R in the retina through intravitreal injection of AAV can effectively maintain the retina structure, promote neuronal cell survival, and protect visual function.

Evaluation of the role of Sigma 1 receptor and Cullin3 in retinal photoreceptor cells

Sigma 1 receptor (Sig1R), a pluripotent modulator of cell survival, is neuroprotective in models of retinal degeneration when activated by the high-affinity, high-specificity ligand (+)-pentazocine ((+)-PTZ). The molecular mechanisms of Sig1R-mediated retinal neuroprotection are under investigation. We previously reported that the antioxidant regulatory transcription factor Nrf2 may be involved in Sig1R-mediated retinal photoreceptor cell (PRC) rescue. Cullin 3 (Cul3) is a component of the Nrf2-Keap1 antioxidant pathway and facilitates Nrf2 ubiquitination. Our earlier transcriptome analysis revealed decreased Cul3 in retinas lacking Sig1R. Here, we asked whether Sig1R activation can modulate Cul3 expression in 661 W cone PRCs. Proximity ligation and co-immunoprecipitation (co-IP) showed that Cul3 resides closely to and co-IPs with Sig1R. Activation of Sig1R using (+)-PTZ significantly increased Cul3 at the gene/protein level; silencing Sig1R decreased Cul3 gene/protein levels. Experiments in which Cul3 was silenced in cells exposed to tBHP resulted in increased oxidative stress, which was not attenuated with Sig1R activation by (+)-PTZ, whereas cells transfected with scrambled siRNA (and incubated with tBHP) responded to (+)-PTZ treatment by decreasing levels of oxidative stress. Assessment of mitochondrial respiration and glycolysis revealed significantly improved maximal respiration, spare capacity and glycolytic capacity in oxidatively-stressed cells transfected with scrambled siRNA and treated with (+)-PTZ, but not in (+)-PTZ treated, oxidatively-stressed cells in which Cul3 had been silenced. The data provide the first evidence that Sig1R co-localizes/interacts with Cul3, a key player in the Nrf2-Keap1 antioxidant pathway. The data suggest that the preservation of mitochondrial respiration/glycolytic function and reduction of oxidative stress observed upon activation of Sig1R occur in part in a Cul3-dependent manner.

Targeting Sigma Receptors for the Treatment of Neurodegenerative and Neurodevelopmental Disorders

The sigma-1 receptor is a 223 amino acid-long protein with a recently identified structure. The sigma-2 receptor is a genetically unrelated protein with a similarly shaped binding pocket and acts to influence cellular activities similar to the sigma-1 receptor. Both proteins are highly expressed in neuronal tissues. As such, they have become targets for treating neurological diseases, including Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), multiple sclerosis (MS), Rett syndrome (RS), developmental and epileptic encephalopathies (DEE), and motor neuron disease/amyotrophic lateral sclerosis (MND/ALS). In recent years, there have been many pre-clinical and clinical studies of sigma receptor (1 and 2) ligands for treating neurological disease. Drugs such as blarcamesine, dextromethorphan and pridopidine, which have sigma-1 receptor activity as part of their pharmacological profile, are effective in treating multiple aspects of several neurological diseases. Furthermore, several sigma-2 receptor ligands are under investigation, including CT1812, rivastigmine and SAS0132. This review aims to provide a current and up-to-date analysis of the current clinical and pre-clinical data of drugs with sigma receptor activities for treating neurological disease.

Sigma-1 Receptor Signaling: In Search of New Therapeutic Alternatives for Cardiovascular and Renal Diseases

Cardiovascular and renal diseases are among the leading causes of death worldwide, and regardless of current efforts, there is a demanding need for therapeutic alternatives to reduce their progression to advanced stages. The stress caused by diseases leads to the activation of protective mechanisms in the cell, including chaperone proteins. The Sigma-1 receptor (Sig-1R) is a ligand-operated chaperone protein that modulates signal transduction during cellular stress processes. Sig-1R interacts with various ligands and proteins to elicit distinct cellular responses, thus, making it a potential target for pharmacological modulation. Furthermore, Sig-1R ligands activate signaling pathways that promote cardioprotection, ameliorate ischemic injury, and drive myofibroblast activation and fibrosis. The role of Sig-1R in diseases has also made it a point of interest in developing clinical trials for pain, neurodegeneration, ischemic stroke, depression in patients with heart failure, and COVID-19. Sig-1R ligands in preclinical models have significantly beneficial effects associated with improved cardiac function, ventricular remodeling, hypertrophy reduction, and, in the kidney, reduced ischemic damage. These basic discoveries could inform clinical trials for heart failure (HF), myocardial hypertrophy, acute kidney injury (AKI), and chronic kidney disease (CKD). Here, we review Sig-1R signaling pathways and the evidence of Sig-1R modulation in preclinical cardiac and renal injury models to support the potential therapeutic use of Sig-1R agonists and antagonists in these diseases.

Ferroptosis and its interaction with tumor immune microenvironment in liver cancer

Exploring effective systemic treatments for liver cancer is still a great challenge worldwide. As a novel form of regulated cell death, ferroptosis has been paid more and more attention in the cancer research field. In recent years, targeting ferroptosis has become an encouraging strategy for liver cancer treatment. Cancer cells can be directly killed by inducing ferroptosis; in contrast, ferroptosis can also ameliorate the tumor immunosuppressive microenvironment and sensitize cancers to immunotherapy. Here, we summarize fully current progress in the iron homeostasis in the liver, the internal association between imbalanced iron homeostasis and ferroptosis in liver carcinogenesis and development, as well as ferroptosis-related regulators in liver cancer. Furthermore, we discuss thoroughly the interaction between ferroptosis and tumor immune microenvironment. Finally, we provide certainly a future insight on the potential value of ferroptosis in the immunotherapy of liver cancer.

The impact of oxidative stress-induced mitochondrial dysfunction on diabetic microvascular complications

Diabetes mellitus (DM) is a metabolic disease characterized by chronic hyperglycaemia, with absolute insulin deficiency or insulin resistance as the main cause, and causes damage to various target organs including the heart, kidney and neurovascular. In terms of the pathological and physiological mechanisms of DM, oxidative stress is one of the main mechanisms leading to DM and is an important link between DM and its complications. Oxidative stress is a pathological phenomenon resulting from an imbalance between the production of free radicals and the scavenging of antioxidant systems. The main site of reactive oxygen species (ROS) production is the mitochondria, which are also the main organelles damaged. In a chronic high glucose environment, impaired electron transport chain within the mitochondria leads to the production of ROS, prompts increased proton leakage and altered mitochondrial membrane potential (MMP), which in turn releases cytochrome c (cyt-c), leading to apoptosis. This subsequently leads to a vicious cycle of impaired clearance by the body's antioxidant system, impaired transcription and protein synthesis of mitochondrial DNA (mtDNA), which is responsible for encoding mitochondrial proteins, and impaired DNA repair systems, contributing to mitochondrial dysfunction. This paper reviews the dysfunction of mitochondria in the environment of high glucose induced oxidative stress in the DM model, and looks forward to providing a new treatment plan for oxidative stress based on mitochondrial dysfunction.

Sigma-1 receptor agonist, (+)-pentazocine, is neuroprotective in a Brown Norway rat microbead model of glaucoma

PURPOSE

Glaucoma is a worldwide leading cause of irreversible blindness. Standard treatments lower intraocular pressure (IOP). Novel treatments to prevent optic nerve (ON) degeneration are needed. Here, we investigate the hypothesis that sigma-1 receptor (S1R) agonist (+)-pentazocine (PTZ) is neuroprotective in a Brown Norway (BN) rat, microbead model of glaucoma.

METHODS

BN rats (9-11 weeks, male and female) were treated by intraperitoneal injection, 3 times per week with (+)-PTZ (2 mg/kg) or vehicle (VEH) alone. Treatment started 1 week prior to intraocular injection of polystyrene microbeads to elevate IOP. IOP was measured 2-3 times per week. Five weeks post microbead injection, rats were euthanized. ONs were removed, then fixed and processed for 63x oil, light microscope imaging of toluidine blue stained ON cross sections. To facilitate comparison of ON morphology from VEH and (+)-PTZ treated rats with similar ocular hypertensive insults, rats were assigned to low (IOP ≤15.8 mmHg), moderate (15.8 < IOP <28.0 mmHg), and high (IOP ≥28.0 mmHg) groups based on average IOP in the microbead injected eye. Axon numbers, axon density, axonal and glial areas, axon loss, and axon size distributions of naïve, bead, and contralateral ONs were assessed using QuPath program for automated image analysis.

RESULTS

(+)-PTZ treatment of BN rats protected ONs from damage caused by moderate IOP elevation. Treatment with (+)-PTZ significantly reduced axon loss and glial areas, and increased axon density and axonal areas compared to ONs from VEH treated rats with moderate IOP. (+)-PTZ-mediated neuroprotection was independent of IOP lowering effects. At average IOP ≥28.0 mmHg, (+)-PTZ treatment did not provide measurable neuroprotection. ONs from contralateral eyes exhibited subtle, complex changes in response to conditions in the bead eyes.

CONCLUSIONS

S1R agonist (+)-PTZ shows promise as a neuroprotective treatment for glaucoma. Future studies to understand the complex molecular mechanisms by which (+)-PTZ provides this neuroprotection are needed.

Sigma-1 receptor agonist PRE-084 confers protection against TAR DNA-binding protein-43 toxicity through NRF2 signalling

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting upper and lower motor neurons. As a consequence, ALS patients display a locomotor disorder related to muscle weakness and progressive paralysis. Pathological mechanisms that participate in ALS involve deficient unfolded protein response, mitochondrial dysfunction and oxidative stress, among others. Finding a therapeutic target to break the vicious circle is particularly challenging. Sigma-1 receptor (S1R) is an endoplasmic reticulum (ER) chaperone that may be one of those targets. We here address and decipher the efficiency of S1R activation on a key ALS gene, TDP43, in zebrafish vertebrate model. While expression of mutant TDP43 (TDP43^G348C) led to locomotor defects, treatment with the reference S1R agonist PRE-084 rescued motor performances in a zebrafish model. Treatment with the agonist ameliorated maximal mitochondrial respiration in the TDP43 context. We observed that TDP43^G348C exacerbated ER stress induced by tunicamycin, resulting in increased levels of ER stress chaperone BiP and pro-apoptotic factor CHOP. Importantly, PRE-084 treatment in the same condition further heightened BiP levels but also EIF2α/ATF4 and NRF2 signalling cascades, both known to promote antioxidant protection during ER stress. Moreover, we showed that increasing NRF2 levels directly or by sulforaphane treatment rescued locomotor defects of TDP43^G348C zebrafish. For the first time, we here provide the proof of concept that PRE-084 prevents mutant TDP43 toxicity by boosting ER stress response and antioxidant cascade through NRF2 signalling.

Generation and characterization of a Müller-glial-cell-specific Il6ra knockout mouse to delineate the effects of IL-6 trans-signaling in the retina

Interleukin-6 (IL-6) is implicated in various retinal and vascular complications associated with diabetic retinopathy (DR). This cytokine functions through two main modalities: classical signaling, in cells expressing the membrane-bound receptor (IL-6Rα); and trans-signaling, possible in most cells through a soluble form of the receptor (sIL-6R). These pathways are considered to be anti-inflammatory and pro-inflammatory, respectively. Our recent studies in retinal endothelial cells and diabetic mice have shown that inhibiting only IL-6 trans-signaling is sufficient to prevent increased vascular leakage, oxidative stress, and inflammation characteristic of DR. Isolating the specific effects of each signaling pathway, however, remains difficult in cells expressing IL-6Rα that are thus capable of both classical and trans-signaling. Müller glial cells (MGCs), the most abundant retinal macroglial cells, span the entire retinal thickness with vital roles in maintaining retinal homeostasis and regulating the blood-retinal barrier through secreted factors. The specific effects of IL-6 trans-signaling in MGCs remain poorly understood given their responsiveness to both IL-6 signaling modalities. In this study, we addressed these concerns by generating an MGC-specific knockout mouse using Cre-loxP deletion of the Il6ra cytokine-binding region. We assessed transcriptional and translational Il6ra expression to confirm the knockout and characterized the effects of knockout on visual functioning in these mice.

Sigma-1 receptor: A potential target for the development of antidepressants

Though a great many of studies on the development of antidepressants for the therapy of major depression disorder (MDD) and the development of antidepressants have been carried out, there still lacks an efficient approach in clinical practice. The involvement of Sigma-1 receptor in the pathological process of MDD has been verified. In this review, recent research focusing on the role of Sigma-1 receptor in the etiology of MDD were summarized. Preclinical studies and clinical trials have found that stress induce the variation of Sigma-1 receptor in the blood, brain and heart. Dysfunction and absence of Sigma-1 receptor result in depressive-like behaviors in rodent animals. Agonists of Sigma-1 receptor show not only antidepressant-like activities but also therapeutical effects in complications of depression. The mechanisms underlying antidepressant-like effects of Sigma-1 receptor may include suppressing neuroinflammation, regulating neurotransmitters, ameliorating brain-derived neurotrophic factor and N-Methyl-D-Aspartate receptor, and alleviating the endoplasmic reticulum stress and mitochondria damage during stress. Therefore, Sigma-1 receptor represents a potential target for antidepressants development.

Widespread cell stress and mitochondrial dysfunction occur in patients with early Alzheimer's disease

Cell stress and impaired oxidative phosphorylation are central to mechanisms of synaptic loss and neurodegeneration in the cellular pathology of Alzheimer's disease (AD). In this study, we quantified the in vivo expression of the endoplasmic reticulum stress marker, sigma 1 receptor (S1R), using [¹¹C]SA4503 positron emission tomography (PET), the mitochondrial complex I (MC1) with [¹⁸F]BCPP-EF, and the presynaptic vesicular protein SV2A with [¹¹C]UCB-J in 12 patients with early AD and in 16 cognitively normal controls. We integrated these molecular measures with assessments of regional brain volumes and cerebral blood flow (CBF) measured with magnetic resonance imaging arterial spin labeling. Eight patients with AD were followed longitudinally to estimate the rate of change of the physiological and structural pathology markers with disease progression. The patients showed widespread increases in S1R (≤ 27%) and regional reduction in MC1 (≥ -28%) and SV2A (≥ -25%) radioligand binding, brain volume (≥ -23%), and CBF (≥ -26%). [¹⁸F]BCPP-EF PET MC1 binding (≥ -12%) and brain volumes (≥ -5%) showed progressive reductions over 12 to 18 months, suggesting that they both could be used as pharmacodynamic indicators in early-stage therapeutics trials. Associations of reduced MC1 and SV2A and increased S1R radioligand binding with reduced cognitive performance in AD, although exploratory, suggested a loss of metabolic functional reserve with disease. Our study thus provides in vivo evidence for widespread, clinically relevant cellular stress and bioenergetic abnormalities in early AD.

Perspectives and mechanisms for targeting ferroptosis in the treatment of hepatocellular carcinoma

Ferroptosis is a novel process of regulated cell death discovered in recent years, mainly caused by intracellular lipid peroxidation. It is morphologically manifested as shrinking of mitochondria, swelling of cytoplasm and organelles, rupture of plasma membrane, and formation of double-membrane vesicles. Work done in the past 5 years indicates that induction of ferroptosis is a promising strategy in the treatment of hepatocellular carcinoma (HCC). System xc^-/GSH/GPX4, iron metabolism, p53 and lipid peroxidation pathways are the main focus areas in ferroptosis research. In this paper, we analyze the ferroptosis-inducing drugs and experimental agents that have been used in the last 5 years in the treatment of HCC. We summarize four different key molecular mechanisms that induce ferroptosis, i.e., system xc^-/GSH/GPX4, iron metabolism, p53 and lipid peroxidation. Finally, we outline the prognostic analysis associated with ferroptosis in HCC. The findings summarized suggest that ferroptosis induction can serve as a promising new therapeutic approach for HCC and can provide a basis for clinical diagnosis and prevention of this disease.

Sigma-1 Receptor in Retina: Neuroprotective Effects and Potential Mechanisms

Retinal degenerative diseases are the major factors leading to severe visual impairment and even irreversible blindness worldwide. The therapeutic approach for retinal degenerative diseases is one extremely urgent and hot spot in science research. The sigma-1 receptor is a novel, multifunctional ligand-mediated molecular chaperone residing in endoplasmic reticulum (ER) membranes and the ER-associated mitochondrial membrane (ER-MAM); it is widely distributed in numerous organs and tissues of various species, providing protective effects on a variety of degenerative diseases. Over three decades, considerable research has manifested the neuroprotective function of sigma-1 receptor in the retina and has attempted to explore the molecular mechanism of action. In the present review, we will discuss neuroprotective effects of the sigma-1 receptor in retinal degenerative diseases, mainly in aspects of the following: the localization in different types of retinal neurons, the interactions of sigma-1 receptors with other molecules, the correlated signaling pathways, the influence of sigma-1 receptors to cellular functions, and the potential therapeutic effects on retinal degenerative diseases.

The Critical Role of Ferroptosis in Hepatocellular Carcinoma

Liver cancer is the sixth most frequently diagnosed cancer and the third dominant cause of cancer death worldwide. Ferroptosis is characterized as an iron-dependent form of regulated cell death, with accumulation of lipid peroxides to lethal amounts. Evidences have showed that ferroptosis is closely associated with HCC, but the mechanisms are still poorly understood. In this review, we mainly summarize the roles of several typical molecules as well as radiotherapy in regulating the ferroptosis process in HCC. Chances are that this review may help address specific issues in the treatment of HCC.

Chronic Sigma 1 receptor activation alleviates right ventricular dysfunction secondary to pulmonary arterial hypertension

Sigma 1 receptor (S1R) has shown a preferable protective effect on left ventricular function, but whether it protects right ventricular (RV) function is still elusive.This study aimed to determine the effects of S1R on RV dysfunction secondary to pulmonary arterial hypertension.Sixty wild-type male Sprague–Dawley rats were randomly divided into the control group, the fluvoxamine group, the pulmonary arterial hypertension group and the pulmonary arterial hypertension combined with fluvoxamine group. Monocrotaline (60 mg/kg) was administered to induce pulmonary arterial hypertension, and fluvoxamine was given for 21 consecutive days to activate S1R after one week of monocrotaline administration. Echocardiographic, serologic, and histologic parameters, qRT-PCR, and western blotting were conducted after 4 weeks of monocrotaline administration.The expression of S1R was decreased in the right ventricle in pulmonary arterial hypertension. TAPSE, and the FAC of the right ventricle were significantly decreased, and RV EDP and the plasma concentration of N-terminal pro-B-type natriuretic peptide was increased in the pulmonary arterial hypertension group, but fluvoxamine partly restored those abnormalities (all P < 0.05). Moreover, pulmonary arteriole remodeling, and fibrosis and hypertrophy in the RV were shown in the pulmonary arterial hypertension group; interestingly, fluvoxamine recovered RV structural remodeling (all P < 0.05) but neither alleviated pulmonary arteriole remodeling nor reduced pulmonary artery pressure. Furthermore, S1R activation protects RV function by upgrading the NRF 2/HO 1-mediated antioxidant stress pathway. In conclusion, chronic S1R activation ameliorates structural remodeling and RV dysfunction secondary to pulmonary arterial hypertension without altering pulmonary artery pressure.

Knocking Out Sigma-1 Receptors Reveals Diverse Health Problems

Sigma-1 receptor (Sig-1R) is a protein present in several organs such as brain, lung, and heart. In a cell, Sig-1R is mainly located across the membranes of the endoplasmic reticulum and more specifically at the mitochondria-associated membranes. Despite numerous studies showing that Sig-1R could be targeted to rescue several cellular mechanisms in different pathological conditions, less is known about its fundamental relevance. In this review, we report results from various studies and focus on the importance of Sig-1R in physiological conditions by comparing Sig-1R KO mice to wild-type mice in order to investigate the fundamental functions of Sig-1R. We note that the Sig-1R deletion induces cognitive, psychiatric, and motor dysfunctions, but also alters metabolism of heart. Finally, taken together, observations from different experiments demonstrate that those dysfunctions are correlated to poor regulation of ER and mitochondria metabolism altered by stress, which could occur with aging.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood-retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

Ferroptosis in Cancer Immunotherapy—Implications for Hepatocellular Carcinoma

Ferroptosis is a recently recognized iron-dependent form of non-apoptotic regulated cell death (RCD) characterized by lipid peroxide accumulation to lethal levels. Cancer cells, which show an increased iron dependency to enable rapid growth, seem vulnerable to ferroptosis. There is also increasing evidence that ferroptosis might be immunogenic and therefore could synergize with immunotherapies. Hepatocellular carcinoma (HCC) is the most common primary liver tumor with a low survival rate due to frequent recurrence and limited efficacy of conventional chemotherapies, illustrating the urgent need for novel drug approaches or combinatorial strategies. Immunotherapy is a new treatment approach for advanced HCC patients. In this setting, ferroptosis inducers may have substantial clinical potential. However, there are still many questions to answer before the mystery of ferroptosis is fully unveiled. This review discusses the existing studies and our current understanding regarding the molecular mechanisms of ferroptosis with the goal of enhancing response to immunotherapy of liver cancer. In addition, challenges and opportunities in clinical applications of potential candidates for ferroptosis-driven therapeutic strategies will be summarized. Unraveling the role of ferroptosis in the immune response could benefit the development of promising anti-cancer therapies that overcome drug resistance and prevent tumor metastasis.

Sigma 1 Receptor Contributes to Astrocyte-Mediated Retinal Ganglion Cell Protection

Purpose

Sigma 1 receptor (S1R) is expressed in retinal ganglion cells (RGCs) and astrocytes, and its activation is neuroprotective. We evaluated the contribution of S1R within optic nerve head astrocytes (ONHAs) to growth and survival of RGCs in vitro.

Methods

Wild-type (WT) RGCs and WT or S1R knockout (S1R KO) ONHAs were cocultured for 2, 4, or 7 days. Total and maximal neurite length, neurite root, and extremity counts were measured. Cell death was measured using a TUNEL assay. Signal transducer and activator of transcription 3 phosphorylation levels were evaluated in ONHA-derived lysates by immunoblotting.

Results

The coculture of WT RGCs with WT or S1R KO ONHAs increased the total and maximal neurite length. Neurite root and extremity counts increased at 4 and 7 days when WT RGCs were cocultured with WT or S1R KO ONHAs. At all timepoints, the total and maximal neurite length decreased for WT RGCs in coculture with S1R KO ONHAs compared with WT ONHAs. Root and extremity counts decreased for WT RGCs in coculture with S1R KO ONHAs compared with WT ONHAs at 2 and 7, but not 4 days. RGC apoptosis increased in S1R KO ONHA coculture and S1R KO-conditioned medium, compared with WT ONHA coculture or WT-conditioned medium. S1R KO ONHA-derived lysates showed decreased phosphorylated signal transducer and activator of transcription 3 levels compared with WT ONHA-derived lysates.

Conclusions

The absence of S1R within ONHAs has a deleterious effect on RGC neurite growth and RGC survival, reflected in analysis of WT RGC + S1R KO ONHA indirect cocultures. The data suggest that S1R may enhance ganglion cell survival via glia-mediated mechanisms.

High glucose concentrations induce oxidative stress by inhibiting Nrf2 expression in rat Müller retinal cells in vitro

Diabetic retinopathy (DR) is a complication of diabetes. Several studies have implicated oxidative stress as a fundamental factor in the progression of the disease. The nuclear factor erythroid-2-related factor 2 (Nrf2) is one of the main regulators of redox homeostasis. Glia Müller cells (MC) maintain the structural and functional stability of the retina. The objective of this study was to evaluate the effect of high glucose concentrations on reactive oxygen species (ROS) production and Nrf2 expression levels in rat MC. MC were incubated with normal (NG; 5 mM) or high glucose (HG; 25 mM) for different times. Incubation with HG increased ROS levels from 12 to 48 h but did not affect cell viability. However, exposure to 3 h of HG caused a transient decrease Nrf2 levels. At that time, we also observed a decrease in the mRNA expression of Nrf2 target genes, glutathione levels, and catalase activity, all of which increased significantly beyond initial levels after 48 h of incubation. HG exposure leads to an increase in the p65 subunit of nuclear factor-κB (NF-kB) levels, and its target genes. These results suggest that high glucose concentrations lead to alteration of the redox regulatory capacity of Nrf2 mediated by NF-kB regulation.

Therapeutic Strategies Targeting Mitochondrial Calcium Signaling: A New Hope for Neurological Diseases?

Calcium (Ca²⁺) is a versatile secondary messenger involved in the regulation of a plethora of different signaling pathways for cell maintenance. Specifically, intracellular Ca²⁺ homeostasis is mainly regulated by the endoplasmic reticulum and the mitochondria, whose Ca²⁺ exchange is mediated by appositions, termed endoplasmic reticulum-mitochondria-associated membranes (MAMs), formed by proteins resident in both compartments. These tethers are essential to manage the mitochondrial Ca²⁺ influx that regulates the mitochondrial function of bioenergetics, mitochondrial dynamics, cell death, and oxidative stress. However, alterations of these pathways lead to the development of multiple human diseases, including neurological disorders, such as amyotrophic lateral sclerosis, Friedreich's ataxia, and Charcot-Marie-Tooth. A common hallmark in these disorders is mitochondrial dysfunction, associated with abnormal mitochondrial Ca²⁺ handling that contributes to neurodegeneration. In this work, we highlight the importance of Ca²⁺ signaling in mitochondria and how the mechanism of communication in MAMs is pivotal for mitochondrial maintenance and cell homeostasis. Lately, we outstand potential targets located in MAMs by addressing different therapeutic strategies focused on restoring mitochondrial Ca²⁺ uptake as an emergent approach for neurological diseases.

Revisiting the sigma-1 receptor as a biological target to treat affective and cognitive disorders

Depression and cognitive disorders are diseases with complex and not-fully understood etiology. Unfortunately, the COVID-19 pandemic dramatically increased the prevalence of both conditions. Since the current treatments are inadequate in many patients, there is a constant need for discovering new compounds, which will be more effective in ameliorating depressive symptoms and treating cognitive decline. Proteins attracting much attention as potential targets for drugs treating these conditions are sigma-1 receptors. Sigma-1 receptors are multi-functional proteins localized in endoplasmic reticulum membranes, which play a crucial role in cellular signal transduction by interacting with receptors, ion channels, lipids, and kinases. Changes in their functions and expression may lead to various diseases, including depression or memory impairments. Thus, sigma-1 receptor modulation might be useful in treating these central nervous system diseases. Importantly, two sigma-1 receptor ligands entered clinical trials, showing that this compound group possesses therapeutic potential. Therefore, based on preclinical studies, this review discusses whether the sigma-1 receptor could be a promising target for drugs treating affective and cognitive disorders.

Sigma-1 Receptor Activation Suppresses Microglia M1 Polarization via Regulating Endoplasmic Reticulum-Mitochondria Contact and Mitochondrial Functions in Stress-Induced Hypertension Rats

Exposure to stress plays a detrimental role in the pathogenesis of hypertension via neuroinflammation pathways. Microglial neuroinflammation in the rostral ventrolateral medulla (RVLM) exacerbates stress-induced hypertension (SIH) by increasing sympathetic hyperactivity. Mitochondria of microglia are the regulators of innate immune response. Sigma-1R (σ-1R) localizes to the mitochondria-associated membranes (MAMs) and regulates endoplasmic reticulum (ER) and mitochondria communication, in part through its chaperone activity. The present study aims to investigate the protective role of σ-1R on microglial-mediated neuroinflammation. Stress-induced hypertension (SIH) was induced in rats using electric foot shocks and intermittent noise. Arterial blood pressure (ABP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were measured to evaluate the sympathetic nervous system (SNS) activities. SKF10047 (100 µM), an agonist of σ-1R, was administrated to rats, then σ-1R localization and MAM alterations were detected by immuno-electron microscopy. Mitochondrial calcium homeostasis was examined in primary microglia and/or BV-2 microglia cells. The effect of SKF10047 treatment on the mitochondrial respiratory function of cultured microglia was measured using a Seahorse Extracellular Flux Analyzer. Confocal microscopic images were performed to indicate mitochondrial dynamics. Stress reduces σ-1R's localization at the MAMs, leading to decreased ER-mitochondria contact and IP3R-GRP75-VDAC calcium transport complexes expression in the RVLM of rats. SKF10047 promotes the length and coverage of MAMs in the prorenin-treated microglia. Prorenin treatment increases mitoROS levels, and inhibits Ca2+ signalling between the two organelles, therefore negatively affects ATP production in BV2 cells, and these effects are reversed by SKF10047 treatment. We found mitochondrial hyperfusion and microglial M1 polarization in prorenin-treated microglia. SKF10047 suppresses microglial M1 polarization and RVLM neuroinflammation, subsequently ameliorates sympathetic hyperactivity in stress-induced hypertensive rats. Sigma-1 receptor activation suppresses microglia M1 polarization and neuroinflammation via regulating endoplasmic reticulum-mitochondria contact and mitochondrial functions in stress-induced hypertension rats.

Proteomic Phenotyping of Stimulated Müller Cells Uncovers Profound Pro-Inflammatory Signaling and Antigen-Presenting Capacity

Müller cells are the main macroglial cells of the retina exerting a wealth of functions to maintain retinal homoeostasis. Upon pathological changes in the retina, they become gliotic with both protective and detrimental consequences. Accumulating data also provide evidence for a pivotal role of Müller cells in the pathogenesis of diabetic retinopathy (DR). While microglial cells, the resident immune cells of the retina are considered as main players in inflammatory processes associated with DR, the implication of activated Müller cells in chronic retinal inflammation remains to be elucidated. In order to assess the signaling capacity of Müller cells and their role in retinal inflammation, we performed in-depth proteomic analysis of Müller cell proteomes and secretomes after stimulation with INFγ, TNFα, IL-4, IL-6, IL-10, VEGF, TGFβ1, TGFβ2 and TGFβ3. We used both, primary porcine Müller cells and the human Müller cell line MIO-M1 for our hypothesis generating approach. Our results point towards an intense signaling capacity of Müller cells, which reacted in a highly discriminating manner upon treatment with different cytokines. Stimulation of Müller cells resulted in a primarily pro-inflammatory phenotype with secretion of cytokines and components of the complement system. Furthermore, we observed evidence for mitochondrial dysfunction, implying oxidative stress after treatment with the various cytokines. Finally, both MIO-M1 cells and primary porcine Müller cells showed several characteristics of atypical antigen-presenting cells, as they are capable of inducing MHC class I and MHC class II with co-stimulatory molecules. In line with this, they express proteins associated with formation and maturation of phagosomes. Thus, our findings underline the importance of Müller cell signaling in the inflamed retina, indicating an active role in chronic retinal inflammation.

Connection Lost, MAM: Errors in ER-Mitochondria Connections in Neurodegenerative Diseases

Mitochondria associated membranes (MAMs), as the name suggests, are the membranes that physically and biochemically connect mitochondria with endoplasmic reticulum. MAMs not only structurally but also functionally connect these two important organelles within the cell which were previously thought to exist independently. There are multiple points of communication between ER-mitochondria and MAMs play an important role in both ER and mitochondria functions such as Ca²⁺ homeostasis, proteostasis, mitochondrial bioenergetics, movement, and mitophagy. The number of disease-related proteins and genes being associated with MAMs has been continually on the rise since its discovery. There is an overwhelming overlap between the biochemical functions of MAMs and processes affected in neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). Thus, MAMs have received well-deserving and much delayed attention as modulators for ER-mitochondria communication and function. This review briefly discusses the recent progress made in this now fast developing field full of promise for very exciting future therapeutic discoveries.

Sigma-1 Receptor: A Potential Therapeutic Target for Traumatic Brain Injury

The sigma-1 receptor (Sig-1R) is a chaperone receptor that primarily resides at the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) and acts as a dynamic pluripotent modulator regulating cellular pathophysiological processes. Multiple pharmacological studies have confirmed the beneficial effects of Sig-1R activation on cellular calcium homeostasis, excitotoxicity modulation, reactive oxygen species (ROS) clearance, and the structural and functional stability of the ER, mitochondria, and MAM. The Sig-1R is expressed broadly in cells of the central nervous system (CNS) and has been reported to be involved in various neurological disorders. Traumatic brain injury (TBI)-induced secondary injury involves complex and interrelated pathophysiological processes such as cellular apoptosis, glutamate excitotoxicity, inflammatory responses, endoplasmic reticulum stress, oxidative stress, and mitochondrial dysfunction. Thus, given the pluripotent modulation of the Sig-1R in diverse neurological disorders, we hypothesized that the Sig-1R may affect a series of pathophysiology after TBI. This review summarizes the current knowledge of the Sig-1R, its mechanistic role in various pathophysiological processes of multiple CNS diseases, and its potential therapeutic role in TBI.

Ferroptosis as a new therapeutic opportunity for nonviral liver disease

Nonviral liver disease is a global public health problem due to its high mortality and morbidity. However, its underlying mechanism is unclear. Ferroptosis is a novel form of cell death that is involved in a variety of disease processes. Both abnormal iron metabolism (e.g., iron overload) and lipid peroxidation, which is induced by deletion of glutathione (GSH) or glutathione peroxidase 4 (GPX4), and the accumulation of polyunsaturated fatty acid-containing phospholipids (PUFA-PLs) trigger ferroptosis. Recently, ferroptosis has been involved in the pathological process of nonviral liver diseases [including alcohol-related liver disease (ALD); nonalcoholic fatty liver disease (NAFLD); hereditary hemochromatosis (HH); drug-, ischemia/reperfusion- or immune-induced liver injury; liver fibrosis; and liver cancer]. Hepatocyte ferroptosis is activated in ALD; NAFLD; HH; drug-, ischemia/reperfusion- or immune-induced liver injury; and liver fibrosis, whereas hepatic stellate cell and liver cancer cell ferroptosis are inhibited in liver fibrosis and liver cancer, respectively. Thus, ferroptosis is an ideal target for nonviral liver diseases. In the present review, we discuss the latest findings on ferroptosis and potential drugs targeting ferroptosis for nonviral liver diseases. This review will highlight further directions for the treatment and prevention of nonviral liver diseases.

TMEM97 ablation aggravates oxidant-induced retinal degeneration

The retinal pigment epithelium (RPE) is critical to the survival of the overlying photoreceptors. Subject to light exposure and active metabolism, the RPE and photoreceptors are particularly susceptible to oxidative damage that plays an important part in age-related macular degeneration (AMD). Recent meta-analyses identified TMEM97 as a new putative AMD risk locus, though it is yet to be functionally verified. The role of TMEM97 in the retina and RPE is not known. Here we investigated TMEM97 function using the sodium iodate model of oxidant-induced retinal degeneration in TMEM97 knockout (KO) mice. We found markedly increased reactive oxygen species (ROS) and loss of photoreceptos in TMEM97 KO mouse retinas relative to wild type (WT) controls. In vitro, sodium iodate treatment of CRISPR-mediated TMEM97 KO RPE cells resulted in diminished abundance of the master antioxidant transcription factor NRF2 and its target gene product SOD2, the mitochondrial superoxide dismutase, as well as elevated ROS and apoptosis markers. Moreover, TMEM97 KO affected proteins key to mitochondrial and lysosomal stability and impeded autophagy flux. These findings suggest that the absence of TMEM97 in RPE cells disturbs redox-balancing systems, thereby heightening oxidative stress. As TMEM97 is a druggable target, this study may inspire interest in basic and translational research in the context of retinal degeneration.

Sigma-1R Protects Retinal Ganglion Cells in Optic Nerve Crush Model for Glaucoma

Purpose

The purpose of this study was to determine the effects of the Sigma-1R (σ-1r) on retinal ganglion cell (RGC) survival following optic nerve crush (ONC) and the signaling mechanism involved in the σ-1r protection.

Methods

The overall strategy was to induce injury by ONC and mitigate RGC death by increasing σ-1r expression and/or activate σ-1r activity in σ-1r K/O mice and wild type (WT) mice. AAV2-σ-1r vector was used to increase σ-1r expression and σ-1r agonist used to activate the σ-1r and RGCs were counted. Immunohistochemical and Western blot analysis determined phosphorylated (p)-c-Jun, c-Jun, and Caspase-3. Pattern electroretinography (PERG) determined RGC activity.

Results

RGC counts and function were similar in pentazocine-treated WT mice when compared to untreated mice and in WT mice when compared with σ-1r K/O mice. Pentazocine-induced effects and the effects of σ-1r K/O were only observable after ONC. ONC resulted in decreased RGC counts and activity in both WT and σ-1r K/O mice, with σ-1r K/O mice experiencing significant decreases compared with WT mice. The σ-1r transgenic expression resulted in increased RGC counts and activity following ONC. In WT mice, treatment with σ-1r agonist pentazocine resulted in increased RGC counts and increased activity when compared with untreated WT mice. There were time-dependent increases in c-jun, p-c-jun, and caspase-3 expression in ONC mice that were mitigated with pentazocine-treatment.

Conclusions

These findings suggest that the apoptotic pathway is involved in RGC losses seen in an ONC model. The σ-1r offers neuroprotection, as activation and/or transgenic expression of σ-1r attenuated the apoptotic pathway and restored RGCs number and function following ONC.

Matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinases 1 (TIMP-1) are localized in the nucleus of retinal Müller glial cells and modulated by cytokines and oxidative stress

Matrix metalloproteinases (MMPs) are involved in the pathology of numerous inflammatory retinal degenerations, including retinitis pigmentosa (RP). Our previous work revealed that intravitreal injections with tissue inhibitor of metalloproteinases 1 (TIMP-1) reduce the progression of rod cell death and inhibit cone cell remodeling that involves reactive gliosis in retinal Müller glial cells (MGCs) in rodent models. The underlying cellular and molecular mechanisms of how TIMP-1 functions in the retina remain to be resolved; however, MGCs are involved in structural homeostasis, neuronal cell survival and death. In the present study, MMP-9 and TIMP-1 expression patterns were investigated in a human MGC line (MIO-M1) under inflammatory cytokine (IL-1β and TNF-α) and oxidative stress (H₂O₂) conditions. First, both IL-1β and TNF-α, but not H₂O_2, have a mild in vitro pro-survival effect on MIO-M1 cells. Treatment with either cytokine results in the imbalanced secretion of MMP-9 and TIMP-1. H₂O₂ treatment has little effect on their secretion. The investigation of their intracellular expression led to interesting observations. MMP-9 and TIMP-1 are both expressed, not only in the cytoplasm, but also inside the nucleus. None of the treatments alters the MMP-9 intracellular distribution pattern. In contrast to MMP-9, TIMP-1 is detected as speckles. Intracellular TIMP-1 aggregation forms in the cytoplasmic area with IL-1β treatment. With H₂O₂ treatments, the cell morphology changes from cobbles to spindle shapes and the nuclei become larger with increases in TIMP-1 speckles in an H₂O₂ dose-dependent manner. Two TIMP-1 cell surface receptors, low density lipoprotein receptor-related protein-1 (LRP-1) and cluster of differentiation 82 (CD82), are expressed within the nucleus of MIO-M1 cells. Overall, these observations suggest that intracellular TIMP-1 is a target of proinflammatory and oxidative insults in the MGCs. Given the importance of the roles for MGCs in the retina, the functional implication of nuclear TIMP-1 and MMP-9 in MGCs is discussed.

Sigmar1's Molecular, Cellular, and Biological Functions in Regulating Cellular Pathophysiology

The Sigma 1 receptor (Sigmar1) is a ubiquitously expressed multifunctional inter-organelle signaling chaperone protein playing a diverse role in cellular survival. Recessive mutation in Sigmar1 have been identified as a causative gene for neuronal and neuromuscular disorder. Since the discovery over 40 years ago, Sigmar1 has been shown to contribute to numerous cellular functions, including ion channel regulation, protein quality control, endoplasmic reticulum-mitochondrial communication, lipid metabolism, mitochondrial function, autophagy activation, and involved in cellular survival. Alterations in Sigmar1’s subcellular localization, expression, and signaling has been implicated in the progression of a wide range of diseases, such as neurodegenerative diseases, ischemic brain injury, cardiovascular diseases, diabetic retinopathy, cancer, and drug addiction. The goal of this review is to summarize the current knowledge of Sigmar1 biology focusing the recent discoveries on Sigmar1’s molecular, cellular, pathophysiological, and biological functions.

Sigma 1 Receptor Co-Localizes with NRF2 in Retinal Photoreceptor Cells

Sigma 1 receptor (Sig1R), a modulator of cell survival, has emerged as a novel target for retinal degenerative disease. Studies have shown that activation of Sig1R, using the high affinity ligand (+)-pentazocine ((+)-PTZ), improves cone function in a severe retinopathy model. The rescue is accompanied by normalization of levels of NRF2, a key transcription factor that regulates the antioxidant response. The interaction of Sig1R with a number of proteins has been investigated; whether it interacts with NRF2, however, is not known. We used co-immunoprecipitation (co-IP), proximity ligation assay (PLA), and electron microscopy (EM) immunodetection methods to investigate this question in the 661W cone photoreceptor cell line. For co-IP experiments, immune complexes were precipitated by protein A/G agarose beads and immunodetected using anti-NRF2 antibody. For PLA, cells were incubated with anti-Sig1R polyclonal and anti-NRF2 monoclonal antibodies, then subsequently with (−)-mouse and (+)-rabbit PLA probes. For EM analysis, immuno-EM gold labeling was performed using nanogold-enhanced labeling with anti-NRF2 and anti-Sig1R antibodies, and data were confirmed using colloidal gold labeling. The co-IP experiment suggested that NRF2 was bound in a complex with Sig1R. The PLA assays detected abundant orange fluorescence in cones, indicating that Sig1R and NRF2 were within 40 nm of each other. EM immunodetection confirmed co-localization of Sig1R with NRF2 in cells and in mouse retinal tissue. This study is the first to report co-localization of Sig1R-NRF2 and supports earlier studies implicating modulation of NRF2 as a mechanism by which Sig1R mediates retinal neuroprotection.

Mitophagy, Ferritinophagy and Ferroptosis in Retinal Pigment Epithelial Cells Under High Glucose Conditions: Implications for Diabetic Retinopathy and Age-Related Retinal Diseases

Diabetic retinopathy (DR) is a devastating disease leading to blindness among majority of working adults around the globe. Nonetheless, an effective treatment or cure for the disease is still to be achieved. This is because the cellular and molecular mechanisms of DR are complex and not fully understood yet. In this article, we describe how high glucose induced TXNIP upregulation and associated redox stress may cause mitochondrial dysfunction, mitophagy, ferritinophagy (iron release by autophagy) and lysosome destabilization. Labile irons react with hydrogen peroxide (H2O2) to generate hydroxyl radicals (.OH) by the Fenton reaction and cause membrane phospholipid peroxidation due to reduction in glutathione (GSH) level and glutathione peroxidase 4 (GPX4) activity, which cause ferroptosis, a recently identified non-apoptotic cell death mechanism. We used in this study a retinal pigment epithelial cell line, ARPE- 19 and exposed it to high glucose in in vitro cultures to highlight some of the intricacies of these cellular processes, which may be relevant to the pathogenesis of DR and age-related retinal neurodegenerative diseases, such as age-related macular degeneration, AMD.

Optimal timing for activation of sigma 1 receptor in the Pde6brd10/J (rd10) mouse model of retinitis pigmentosa

Sigma 1 Receptor (Sig1R), a pluripotent modulator of cell survival, is a promising target for treatment of retinal degenerative diseases. Previously, we reported that administration of the high-affinity, high-specificity Sig1R ligand (+)-pentazocine, ((+)-PTZ) beginning at post-natal day 14 (P14) and continuing every other day improves visual acuity and delays loss of photoreceptor cells (PRCs) in the Pde6βrd10/J (rd10) mouse model of retinitis pigmentosa. Whether administration of (+)-PTZ, at time points concomitant with (P18) or following (P21, P24) onset of PRC death, would prove neuroprotective was investigated in this study. Rd10 mice were administered (+)-PTZ intraperitoneally [0.5 mg/kg], starting at either P14, P18, P21 or P24. Injections continued every other day through P42. Visual acuity was assessed using the optokinetic tracking response (OKR). Rd10 mice treated with (+)-PTZ beginning at P14 retained visual acuity for the duration of the study (~0.33 c/d at P21, ~0.38 c/d at P28, ~0.32 c/d at P35, ~0.32 c/d at P42), whereas mice injected beginning at P18, P21, P24 showed a decline in acuity when tested at P35 and P42. Their acuity was only slightly better than rd10-non-treated mice. Electrophysiologic function was assessed using scotopic and photopic electroretinography (ERG) to assess rod and cone function, respectively. Photopic a- and b-wave amplitudes were significantly greater in rd10 mice treated with (+)-PTZ beginning at P14 compared with non-treated mice and those in the later-onset (+)-PTZ injection groups. Retinal architecture was visualized in living mice using spectral domain-optical coherence tomography (SD-OCT) allowing measurement of the total retinal thickness, the inner retina and the outer retina (the area most affected in rd10 mice). The outer retina measured ~35 μm in rd10 mice treated with (+)-PTZ beginning at P14, which was significantly greater than mice in the later-onset (+)-PTZ injection groups (~25 μm) and non-treated rd10 mice (~25 μm). Following the visual function studies performed in the living mice, eyes were harvested at P42 for histologic analysis. While the inner retina was largely intact in all (+)-PTZ-injection groups, there was a marked reduction in the outer retina of non-treated rd10 mice (e.g. in the outer nuclear layer there were ~10 PRCs/100 μm retinal length). The rd10 mice treated with (+)-PTZ beginning at P14 had ~20 PRCs/100 μm retinal length, whereas the mice in groups beginning P18, P21 and P24 had ~16 PRCs/100 μm retinal length. In conclusion, the data indicate that delaying (+)-PTZ injection past the onset of PRC death in rd10 mice - even by a few days - can negatively impact the long-term preservation of retinal function. Our findings suggest that optimizing the administration of Sig1R ligands is critical for retinal neuroprotection.

Matrine Can Inhibit the Growth of Colorectal Cancer Cells by Inducing Ferroptosis

Colorectal cancer (CRC) is a common malignant tumor of the digestive system that can seriously threaten human health. Chinese matrine is known to have a wide range of antiviral and immunomodulatory effects. In this study, we evaluated the effect of matrine on ferroptosis using the HCT116 human colon cancer cell line. We evaluated cell viability and proliferation using the cell counting kit-8 assay and carried out cell clone formation experiment by measuring reactive oxygen species (ROS) production, as well as levels of glutathione (GSH), lipid peroxide (MDA), Fe2+, glutathione peroxidase 4 (GPX4), activating transcription factor 4 (ATF4), solute carrier family 7 member 11 (SLC7A11), transferrin receptor protein 2 (TFR2), and Sigma-1 receptor (Sigma-1R) in order to evaluate the redox status of cells. These results indicate that matrine can significantly reduce the cell viability of HCT116 and decrease cell proliferation. After treatment with matrine, ROS, Fe2+, and MDA levels increased significantly, while the GSH content decreased. In addition, the expression of GPX4, SLC7A11, and Sigma-1R decreased significantly, while the expression of ATF4 and TFR2 increased significantly. These results indicate that matrine can induce ferroptosis in CRC, which can provide new clues for further pharmacological research of matrine and provide experimental evidence for understanding its mechanism of inhibiting CRC.

Comparison of Sigma 1 Receptor Ligands SA4503 and PRE084 to (+)-Pentazocine in the rd10 Mouse Model of RP

Purpose

Sigma 1 receptor is a novel therapeutic target for retinal disease. Its activation, using a high-affinity, high-specificity ligand (+)-pentazocine ((+)-PTZ), rescues photoreceptor cells in the rd10 mouse model of RP. Here, we asked whether the robust retinal neuroprotective properties of (+)-PTZ are generalizable to SA4503 and PRE084, two other high-affinity sigma 1 receptor ligands.

Methods

We treated 661W cells with SA4503 or PRE084. Cell viability, oxidative stress, and expression of Nrf2 and NRF2-regulated antioxidant genes (Nqo1, Cat, and Sod1) were assessed. Rd10 mice were administered SA4503 (1 mg/kg), PRE084 (0.5 mg/kg), or (+)-PTZ (0.5 mg/kg). Visual acuity, retinal architecture, and retinal electrophysiologic function were measured in vivo and retinal structure was assessed histologically.

Results

Similar to (+)-PTZ, SA4503 and PRE084 improved cell viability, attenuated oxidative stress, and increased Nrf2, Nqo1 and Cat expression. Although treatment of rd10 mice with (+)-PTZ improved visual acuity, increased outer retinal thickness, and improved photopic a- and b-wave responses compared with nontreated rd10 mice, treatment with SA4503 or PRE084 did not. The number of photoreceptor nuclei/100 µm retinal length in SA4503- and PRE084-treated rd10 mice (approximately 11/100) did not differ significantly from nontreated rd10 mice, whereas (+)-PTZ-treated mice had significantly more nuclei (approximately 22/100 µm).

Conclusions

Cell survival and gene regulation experiments yielded similar outcomes when SA4503, PRE084, or (+)-PTZ were conducted in vitro, however neither SA4503 or PRE084 afforded in vivo protection in the severe rd10 retinopathy model comparable to (+)-PTZ. Despite all three compounds demonstrating the potential to activate sigma 1 receptor, the retinal neuroprotective properties of the three ligands differ significantly.

Glutathione peroxidase-1 knockout potentiates behavioral sensitization induced by cocaine in mice via σ-1 receptor-mediated ERK signaling: A comparison with the case of glutathione peroxidase-1 overexpressing transgenic mice

We demonstrated that the gene of glutathione peroxidase-1 (GPx-1), a major antioxidant enzyme, is a potential protectant against the neurotoxicity and conditioned place preference induced by cocaine. Because the sigma (σ)-1 receptor is implicated in cocaine-induced drug dependence, we investigated whether the GPx-1 gene modulates the σ-1 receptor in the behavioral sensitization induced by cocaine. Cocaine-induced behavioral sensitization was more pronounced in GPx-1 knockout (KO) than wild-type (WT) mice and was less pronounced in GPx-1 overexpressing transgenic (GPx-1 TG) than non-TG mice. Cocaine treatment significantly enhanced the oxidative burden and reduced the GSH levels in the striatum of WT, GPx-1 KO, and non-TG mice but not in that of GPx-1 TG mice. In addition, cocaine significantly increased the nuclear translocation, its DNA binding activity of nuclear factor erythroid-2-related factor 2 (Nrf2) as well as the mRNA expression of γ-glutamylcysteine (GCL). The genetic depletion of GPx-1 inhibited the Nrf2-related glutathione system, whereas the genetic overexpression of GPx-1 activated this system against behavioral sensitization. BD1047, a σ-1 receptor antagonist, and U0126, an ERK inhibitor significantly induced the Nrf2-related antioxidant potential against behavioral sensitization. Unlike BD1047, U0126 did not affect the cocaine-induced σ-1 receptor immunoreactivity, suggesting that the σ-1 receptor is an upstream molecule for ERK signaling. Importantly, BD1047 and U0126 failed to affect the σ-1 receptor immunoreactivity and ERK phosphorylation induced by cocaine in GPx-1 TG mice. Our results suggest that GPx-1 is a critical mediator for the attenuation of cocaine-induced behavioral sensitization via modulating σ-1 receptor-mediated ERK activation by the induction of the Nrf2-related system.

Effects of Essential Trace Elements and Oxidative Stress on Endemic Arsenism Caused by Coal Burning in PR China

Few studies have investigated the association between essential trace elements and oxidative stress in environmental media and populations with endemic arsenism caused by coal burning. Element contents and oxidative stress indicators were measured. Moreover, the expression of genes related to the nuclear factor E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1)-antioxidant response element (ARE) signaling pathway and Nrf2-ARE binding ability is detected. The results show that the contents of arsenic, copper, iron, and chromium were increased in environmental media from the arsenism area compared with the control area; however, the selenium content decreased. The arsenic, iron, chromium, and copper contents and the copper/zinc ratio were also increased in the arsenic-exposed population; however, the selenium content decreased. The results also show that the concentrations of arsenic, iron, and chromium and the copper/zinc ratio increased gradually with the severity of arsenism. However, selenium concentrations decreased gradually with the severity of arsenism. The contents of malondialdehyde, 8-hydroxyldeoxyguanosine, and protein carbonyl in plasma increased, while the levels of sulfhydryl, thioredoxin reductase (TrxR), glutathione peroxidase (Gpx), and superoxide dismutase 1 (SOD1) decreased. The mRNA expression of Keap1 and TrxR1 decreased in the blood, while the mRNA expression of Nrf2, GPx1, and SOD1 increased. Moreover, the Nrf2 protein content and Nrf2-ARE binding ability increased, and the Keap1 protein content decreased. In conclusion, our data suggest that the increased arsenic content in environmental media and populations was accompanied by abnormal levels of essential trace elements. Insufficient selenium intake, copper, and chromium overload and a high copper/zinc ratio might be some of the causes of arsenism, which might be related to the Nrf2/Keap1-ARE signaling pathway.

xCT regulates redox homeostasis and promotes photoreceptor survival after retinal detachment

BACKGROUNDS

Photoreceptor degeneration underlies various retinal disorders that lead to vision impairment. Currently, no effective medication is available to rescue photoreceptors under disease conditions. Elucidation of the molecular pathways involved in photoreceptor degeneration is a prerequisite for the rational design of therapeutic interventions. Photoreceptors are among the most energy-demanding tissues that require highly active oxidative phosphorylation. Therefore, disruption of metabolic support to photoreceptors results in a redox imbalance and subsequent cell death. We hypothesize that the redox regulatory pathway could be a potential therapeutic target to rescue photoreceptors under disease conditions.

METHODS

Experimental retinal detachment was induced in mice. A murine photoreceptor-derived 661w cell line treated with H₂O₂ was employed as an in vitro model to study the cellular response to oxidative stress. The expression and functional role of xCT, an upstream regulator of redox homeostasis, was assessed in vivo and in vitro. An xCT expression vector was constructed for an in vivo study to evaluate the therapeutic potential of this molecule.

RESULTS

xCT expression was upregulated in detached retina and H₂O₂-stimulated 661w cells compared to the control cells. Pharmacological inhibition of xCT by sulfasalazine (SAS) promoted photoreceptor degeneration after retinal detachment and 661w cell death upon H₂O₂ treatment. Additionally, SAS treatment induced reactive oxidative species (ROS) accumulation, glutathione (GSH) depletion, and glutamate release in 661w cells. In contrast, xCT overexpression via viral infection protected photoreceptors from degeneration after retinal detachment.

CONCLUSION

We conclude that xCT expression is upregulated in photoreceptors after retinal detachment and plays a neuroprotective role in preserving photoreceptors. Mechanistically, xCT promotes cellular homeostasis by regulating intracellular ROS and GSH levels, which are critical to photoreceptor survival after retinal detachment. Collectively, our findings identify xCT as a potential therapeutic target for protection of photoreceptors under disease conditions.

Identification, Expression, and Roles of the Cystine/Glutamate Antiporter in Ocular Tissues

The cystine/glutamate antiporter (system x _c ^-) is composed of a heavy chain subunit 4F2hc linked by a disulphide bond to a light chain xCT, which exchanges extracellular cystine, the disulphide form of the amino acid cysteine, for intracellular glutamate. In vitro research in the brain, kidney, and liver have shown this antiporter to play a role in minimising oxidative stress by providing a source of intracellular cysteine for the synthesis of the antioxidant glutathione. In vivo studies using the xCT knockout mouse revealed that the plasma cystine/cysteine redox couple was tilted to a more oxidative state demonstrating system x_c ^- to also play a role in maintaining extracellular redox balance by driving a cystine/cysteine redox cycle. In addition, through import of cystine, system x_c ^- also serves to export glutamate into the extracellular space which may influence neurotransmission and glutamate signalling in neural tissues. While changes to system x_c ^- function has been linked to cancer and neurodegenerative disease, there is limited research on the roles of system x_c ^- in the different tissues of the eye, and links between the antiporter, aging, and ocular disease. Hence, this review seeks to consolidate research on system x_c ^- in the cornea, lens, retina, and ocular humours conducted across several species to shed light on the in vitro and in vivo roles of xCT in the eye and highlight the utility of the xCT knockout mouse as a tool to investigate the contribution of xCT to age-related ocular diseases.