Endoplasmic reticulum stress in disorders of myelinating cells

Is age-related myelinodegenerative change an initial risk factor of neurodegenerative diseases?

Myelination, the continuous ensheathment of neuronal axons, is a lifelong process in the nervous system that is essential for the precise, temporospatial conduction of action potentials between neurons. Myelin also provides intercellular metabolic support to axons. Even minor disruptions in the integrity of myelin can impair neural performance and increase susceptibility to neurological diseases. In fact, myelin degeneration is a well-known neuropathological condition that is associated with normal aging and several neurodegenerative diseases, including multiple sclerosis and Alzheimer's disease. In the central nervous system, compact myelin sheaths are formed by fully mature oligodendrocytes. However, the entire oligodendrocyte lineage is susceptible to changes in the biological microenvironment and other risk factors that arise as the brain ages. In addition to their well-known role in action potential propagation, oligodendrocytes also provide intercellular metabolic support to axons by transferring energy metabolites and delivering exosomes. Therefore, myelin degeneration in the aging central nervous system is a significant contributor to the development of neurodegenerative diseases. Interventions that mitigate age-related myelin degeneration can improve neurological function in aging individuals. In this review, we investigate the changes in myelin that are associated with aging and their underlying mechanisms. We also discuss recent advances in understanding how myelin degeneration in the aging brain contributes to neurodegenerative diseases and explore the factors that can prevent, slow down, or even reverse age-related myelin degeneration. Future research will enhance our understanding of how reducing age-related myelin degeneration can be used as a therapeutic target for delaying or preventing neurodegenerative diseases.

Reduced White Matter Damage and Lower Neuroinflammatory Potential of Microglia and Macrophages in Hri/Eif2ak1 -/- Mice After Contusive Spinal Cord Injury

Cellular stressors inhibit general protein synthesis while upregulating stress response transcripts and/or proteins. Phosphorylation of the translation factor eIF2α by one of the several stress-activated kinases is a trigger for such signaling, known as the integrated stress response (ISR). The ISR regulates cell survival and function under stress. Here, germline knockout mice were used to determine contributions by three major ISR kinases, HRI/EIF2AK1, GCN2/EIF2AK4, and PKR//EIF2AK2, to pathogenesis of moderate contusive spinal cord injury (SCI) at the thoracic T9 level. One-day post-injury (dpi), reduced levels of peIF2α were found in Hri -/- and Gcn2 -/-, but not in Pkr -/- mice. In addition, Hri -/- mice showed attenuated expression of the downstream ISR transcripts, Atf4 or Chop. Such differential effects of SCI-activated ISR correlated with a strong or moderate enhancement of locomotor recovery in Hri -/- or Gcn2 -/- mice, respectively. Hri -/- mice also showed reduced white matter loss, increased content of oligodendrocytes (OL) and attenuated neuroinflammation, including decreased lipid accumulation in microglia/macrophages. Cultured neonatal Hri -/- OLs showed lower ISR cytotoxicity. Moreover, cell autonomous reduction in neuroinflammatory potential was observed in microglia and bone marrow-derived macrophages derived from Hri -/- mice. These data identify HRI as a major positive regulator of SCI-associated secondary injury. In addition, targeting HRI may enable multimodal neuroprotection to enhance functional recovery after SCI.

Clemastine Reduces post-stroke Neurodegeneration by Alleviating Endoplasmic Reticulum stress-mediated Demyelination and Cognitive Impairment Through PERK/ATF4/CHOP Signaling Pathway

The progressive brain damage following ischemic stroke is primarily due to oxidative stress and activation of inflammatory pathways. Post-stroke neurodegeneration can lead to the loss of neurons and glial cells, including oligodendrocytes, contributing to demyelination. Following ischemic stroke, reperfusion results in increased intracellular calcium, generation of free radicals, and inflammation culminating in accumulation of misfolded proteins in the endoplasmic reticulum (ER) lumen augmenting the ER stress. ER stress has been shown to aggravate post-stroke neurodegeneration by triggering neuronal apoptosis and also contributing towards demyelination of neurons. To address the limitations of current stroke therapies, repurposing of drugs as future adjunctive therapy may be promising. Clemastine, an antihistaminic drug, improves post stroke outcome as evident in the present study. Male Sprague Dawley (SD) rats were treated with clemastine following ischemic stroke. Harvested brain tissues were subjected to different biochemical assays, molecular assays, and histopathological analysis. Clemastine was able to reduce infarct size, alleviate oxidative stress, improve neuronal count, and functional outcomes. Clemastine downregulated genes and proteins responsible for ER stress, apoptosis and demyelination as shown by the western blot and qPCR results. Our study suggests that clemastine may alleviate endoplasmic reticulum stress-mediated demyelination by modulating PERK/ATF4/CHOP axis, and may be used as one of the adjunctive therapies for stroke in future.

Thinning of originally-existing, mature myelin represents a nondestructive form of myelin loss in the adult CNS

The main function of oligodendrocytes is to assemble and maintain myelin that wraps and insulates axons in the central nervous system (CNS). Traditionally, myelin structure, particularly its thickness, was believed to remain remarkably stable in adulthood (including early and middle adulthood, but not late adulthood or aging). However, emerging evidence reveals that the thickness of originally-existing, mature myelin (OEM) can undergo dynamic changes in the adult CNS. This overview highlights recent findings on the alteration of OEM thickness in the adult CNS, explores the underlying mechanisms, and proposes that progressive thinning of OEM represents a novel, nondestructive form of myelin loss in myelin disorders of the CNS.

Single-Cell RNA-Seq Uncovers Robust Glial Cell Transcriptional Changes in Methamphetamine-Administered Mice

Methamphetamine is a highly addictive stimulant known to cause neurotoxicity, cognitive deficits, and immune dysregulation in the brain. Despite significant research, the molecular mechanisms driving methamphetamine-induced neurotoxicity and glial cell dysfunction remain poorly understood. This study investigates how methamphetamine disrupts glial cell function and contributes to neurodevelopmental and neurodegenerative processes. Using single-cell RNA sequencing (scRNA-seq), we analyzed the transcriptomes of 4000 glial cell-associated genes from the cortical regions of mice chronically administered methamphetamine. Methamphetamine exposure altered the key pathways in astrocytes, including the circadian rhythm and cAMP signaling; in microglia, affecting autophagy, ubiquitin-mediated proteolysis, and mitophagy; and in oligodendrocytes, disrupting lysosomal function, cytoskeletal regulation, and protein processing. Notably, several transcription factors, such as Zbtb16, Hif3a, Foxo1, and Klf9, were significantly dysregulated in the glial cells. These findings reveal profound methamphetamine-induced changes in the glial transcriptomes, particularly in the cortical regions, highlighting potential molecular pathways and transcription factors as targets for therapeutic intervention. This study provides novel insights into the glial-mediated mechanisms of methamphetamine toxicity, contributing to our understanding of its effects on the central nervous system and laying the groundwork for future strategies to mitigate its neurotoxic consequences.

Multiple System Atrophy: Pathology, Pathogenesis, and Path Forward

Multiple system atrophy (MSA) is a fatal neurodegenerative disease characterized by autonomic failure and motor impairment. The hallmark pathologic finding in MSA is widespread oligodendroglial cytoplasmic inclusions rich in aggregated α-synuclein (αSyn). MSA is widely held to be an oligodendroglial synucleinopathy, and we outline lines of evidence to support this assertion, including the presence of early myelin loss. However, we also consider emerging data that support the possibility of neuronal or immune dysfunction as a primary driver of MSA. These hypotheses are placed in the context of a major recent discovery that αSyn is conformationally distinct in MSA versus other synucleinopathies such as Parkinson's disease. We outline emerging techniques in epidemiology, genetics, and molecular pathology that will shed more light on this mysterious disease. We anticipate a future in which cutting-edge developments in personalized disease modeling, including with pluripotent stem cells, bridge mechanistic developments at the bench and real benefits at the bedside.

Endoplasmic reticulum's role in multiple sclerosis, exploring potential biomarkers, and pioneering therapeutic strategies: a comprehensive review of literature

BACKGROUND

Multiple Sclerosis (MS) is a complex and chronic autoimmune disease that affects the central nervous system. Inflammation and demyelination characterize it, which results in a range of neurological impairments. The increasing worldwide occurrence of MS, affecting an estimated 2.8 million individuals in 2020, highlights the urgent requirement for further research to tackle the significant impact it has on individuals and healthcare systems globally.

OBJECTIVE

In this study, we wanted to explore the complex function of the endoplasmic reticulum (ER) in the origin, development, and resolution of MS, emphasizing its importance in neuroinflammatory illnesses. The ER has become a central focus in comprehending the pathogenesis of MS. Upon reviewing the literature, we observed a lack of thorough analysis that explores the involvement of endoplasmic reticulum stress in multiple sclerosis. Thus, we aimed through this research to examine the correlations between ER stress and its influence on immunological dysregulation, demyelination, and neurodegeneration in MS.

FINDINGS

Based on the latest clinical trials, we suggested theories that explore possible biomarkers linked to ER stress and the unfolded protein response. Identifying molecules that are suggestive of early stages of illness and can serve as prognostic tools for improving our understanding of the heterogeneity of MS and offering novel approaches for managing the disease. Finally, through our comprehensive search, we wanted to offer a plan for future research, suggesting new and creative methods for managing MS and encouraging the creation of specific treatments that aim to reduce the impact of MS on individuals worldwide.

Advances of traditional Chinese medicine preclinical mechanisms and clinical studies on diabetic peripheral neuropathy

CONTEXT

Diabetic peripheral neuropathy (DPN) results in an enormous burden and reduces the quality of life for patients. Considering there is no specific drug for the management of DPN, traditional Chinese medicine (TCM) has increasingly drawn attention of clinicians and researchers around the world due to its characteristics of multiple targets, active components, and exemplary safety.

OBJECTIVE

To summarize the current status of TCM in the treatment of DPN and provide directions for novel drug development, the clinical effects and potential mechanisms of TCM used in treating DPN were comprehensively reviewed.

METHODS

Existing evidence on TCM interventions for DPN was screened from databases such as PubMed, the Cochrane Neuromuscular Disease Group Specialized Register (CENTRAL), and the Chinese National Knowledge Infrastructure Database (CNKI). The focus was on summarizing and analyzing representative preclinical and clinical TCM studies published before 2023.

RESULTS

This review identified the ameliorative effects of about 22 single herbal extracts, more than 30 herbal compound prescriptions, and four Chinese patent medicines on DPN in preclinical and clinical research. The latest advances in the mechanism highlight that TCM exerts its beneficial effects on DPN by inhibiting inflammation, oxidative stress and apoptosis, endoplasmic reticulum stress and improving mitochondrial function.

CONCLUSIONS

TCM has shown the power latent capacity in treating DPN. It is proposed that more large-scale and multi-center randomized controlled clinical trials and fundamental experiments should be conducted to further verify these findings.

The physiological role of the unfolded protein response in the nervous system

The unfolded protein response (UPR) is a cellular stress response pathway activated when the endoplasmic reticulum, a crucial organelle for protein folding and modification, encounters an accumulation of unfolded or misfolded proteins. The UPR aims to restore endoplasmic reticulum homeostasis by enhancing protein folding capacity, reducing protein biosynthesis, and promoting protein degradation. It also plays a pivotal role in coordinating signaling cascades to determine cell fate and function in response to endoplasmic reticulum stress. Recent research has highlighted the significance of the UPR not only in maintaining endoplasmic reticulum homeostasis but also in influencing various physiological processes in the nervous system. Here, we provide an overview of recent findings that underscore the UPR's involvement in preserving the function and viability of neuronal and myelinating cells under physiological conditions, and highlight the critical role of the UPR in brain development, memory storage, retinal cone development, myelination, and maintenance of myelin thickness.

A novel missense variant in HIKESHI: Clinical phenotype, in vitro functional testing, and potential for gene therapy

A 7-month-old boy presented to our clinic with developmental delay, Magnetic Resonance Imaging (MRI) features of delayed myelination and diffusion restriction, and a homozygous variant of uncertain significance (c.4T>G, p.Phe2Val) in HIKESHI, a gene associated with autosomal-recessive hypomyelinating leukodystrophy 13. We hypothesized that the variant is disease-causing and aimed to rescue the cellular phenotype with vector-mediated gene replacement. HIKESHI mediates heat-induced nuclear accumulation of heat-shock proteins, including HSP70, to protect cells from stress. We generated skin fibroblasts from the proband and proband's mother (heterozygous) to compare protein expression and subcellular localization of HSP70 under heat stress conditions, and the effect of vector-mediated overexpression of HIKESHI in the proband's cells under the same heat stress conditions. Western blot analysis revealed absent HIKESHI protein from proband fibroblasts, contrasted with ample expression in parental cells. Under heat stress conditions, while the mother's cells displayed appropriate nuclear localization of HSP70, the proband's cells displayed impaired nuclear translocalization. When patient fibroblasts were provided exogenous HIKESHI, the transfected proband's cells showed restored heat-induced nuclear translocalization of HSP70 under conditions of heat stress. These functional data establish that the patient's variant is a pathogenic loss-of-function mutation, thus confirming a diagnosis of hypomyelinating leukodystrophy 13 and that vector-mediated gene replacement may be an effective treatment approach for patients with this disorder.

A deep phenotyping study in mouse and iPSC models to understand the role of oligodendroglia in optic neuropathy in Wolfram syndrome

Wolfram syndrome (WS) is a rare childhood disease characterized by diabetes mellitus, diabetes insipidus, blindness, deafness, neurodegeneration and eventually early death, due to autosomal recessive mutations in the WFS1 (and WFS2) gene. While it is categorized as a neurodegenerative disease, it is increasingly becoming clear that other cell types besides neurons may be affected and contribute to the pathogenesis. MRI studies in patients and phenotyping studies in WS rodent models indicate white matter/myelin loss, implicating a role for oligodendroglia in WS-associated neurodegeneration. In this study, we sought to determine if oligodendroglia are affected in WS and whether their dysfunction may be the primary cause of the observed optic neuropathy and brain neurodegeneration. We demonstrate that 7.5-month-old Wfs1∆exon8 mice display signs of abnormal myelination and a reduced number of oligodendrocyte precursor cells (OPCs) as well as abnormal axonal conduction in the optic nerve. An MRI study of the brain furthermore revealed grey and white matter loss in the cerebellum, brainstem, and superior colliculus, as is seen in WS patients. To further dissect the role of oligodendroglia in WS, we performed a transcriptomics study of WS patient iPSC-derived OPCs and pre-myelinating oligodendrocytes. Transcriptional changes compared to isogenic control cells were found for genes with a role in ER function. However, a deep phenotyping study of these WS patient iPSC-derived oligodendroglia unveiled normal differentiation, mitochondria-associated endoplasmic reticulum (ER) membrane interactions and mitochondrial function, and no overt signs of ER stress. Overall, the current study indicates that oligodendroglia functions are largely preserved in the WS mouse and patient iPSC-derived models used in this study. These findings do not support a major defect in oligodendroglia function as the primary cause of WS, and warrant further investigation of neurons and neuron-oligodendroglia interactions as a target for future neuroprotective or -restorative treatments for WS.

Development of a polarity-sensitive ratiometric fluorescent probe based on the intramolecular reaction of spiro-oxazolidine and its applications for in situ visualizing the fluctuations of polarity during ER stress

Polarity is a vital element in endoplasmic reticulum (ER) microenvironment, and its variation is closely related to many physiological and pathological activities of ER, so it is necessary to trace fluctuations of polarity in ER. However, most of fluorescent probes for detecting polarity dependent on the changes of single emission, which could be affected by many factors and cause false signals. Ratiometric fluorescent probe with "built-in calibration" can effectively avoid detection errors. Here, we have designed a ratiometric fluorescent probe HM for monitoring the ER polarity based on the intramolecular reaction of spiro-oxazolidine. It forms ring open/closed isomers driven by polarity to afford ratiometric sensing. Probe HM have manifested its ratiometric responses to polarity in spectroscopic results, which could offer much more precise information for the changes of polarity in living cells with the internal built-in correction. It also showed large emission shift ( 133 nm), high selectivity and photo-stability. In biological imaging, HM could selectively accumulate in ER with high photo-stability. Importantly, HM has ability for in situ tracing the changes of ER polarity with ratiometric behavior during the ER stress process with the stimulation of tunicamycin, dithiothreitol and hypoxia, suggesting that HM is an effective molecule tool for monitoring the variations of ER polarity.

Endoplasmic reticulum associated degradation preserves neurons viability by maintaining endoplasmic reticulum homeostasis

Endoplasmic reticulum-associated degradation (ERAD) is a principal quality-control mechanism responsible for targeting misfolded ER proteins for cytosolic degradation. Evidence suggests that impairment of ERAD contributes to neuron dysfunction and death in neurodegenerative diseases, many of which are characterized by accumulation and aggregation of misfolded proteins. However, the physiological role of ERAD in neurons remains unclear. The Sel1L-Hrd1 complex consisting of the E3 ubiquitin ligase Hrd1 and its adaptor protein Sel1L is the best-characterized ERAD machinery. Herein, we showed that Sel1L deficiency specifically in neurons of adult mice impaired the ERAD activity of the Sel1L-Hrd1 complex and led to disruption of ER homeostasis, ER stress and activation of the unfold protein response (UPR). Adult mice with Sel1L deficiency in neurons exhibited weight loss and severe motor dysfunction, and rapidly succumbed to death. Interestingly, Sel1L deficiency in neurons caused global brain atrophy, particularly cerebellar and hippocampal atrophy, in adult mice. Moreover, we found that cerebellar and hippocampal atrophy in these mice resulted from degeneration of Purkinje neurons and hippocampal neurons, respectively. These findings indicate that ERAD is required for maintaining ER homeostasis and the viability and function of neurons in adults under physiological conditions.

Reduced Expression of Oligodendrocyte Linage-Enriched Transcripts During the Endoplasmic Reticulum Stress/Integrated Stress Response

Endoplasmic reticulum (ER) stress in oligodendrocyte (OL) linage cells contributes to several CNS pathologies including traumatic spinal cord injury (SCI) and multiple sclerosis. Therefore, primary rat OL precursor cell (OPC) transcriptomes were analyzed using RNASeq after treatments with two ER stress-inducing drugs, thapsigargin (TG) or tunicamycin (TM). Gene ontology term (GO) enrichment showed that both drugs upregulated mRNAs associated with the general stress response. The GOs related to ER stress were only enriched for TM-upregulated mRNAs, suggesting greater ER stress selectivity of TM. Both TG and TM downregulated cell cycle/cell proliferation-associated transcripts, indicating the anti-proliferative effects of ER stress. Interestingly, many OL lineage-enriched mRNAs were downregulated, including those for transcription factors that drive OL identity such as Olig2. Moreover, ER stress-associated decreases of OL-specific gene expression were found in mature OLs from mouse models of white matter pathologies including contusive SCI, toxin-induced demyelination, and Alzheimer's disease-like neurodegeneration. Taken together, the disrupted transcriptomic fingerprint of OL lineage cells may facilitate myelin degeneration and/or dysfunction when pathological ER stress persists in OL lineage cells.

Pervasive environmental chemicals impair oligodendrocyte development

Exposure to environmental chemicals can impair neurodevelopment, and oligodendrocytes may be particularly vulnerable, as their development extends from gestation into adulthood. However, few environmental chemicals have been assessed for potential risks to oligodendrocytes. Here, using a high-throughput developmental screen in cultured cells, we identified environmental chemicals in two classes that disrupt oligodendrocyte development through distinct mechanisms. Quaternary compounds, ubiquitous in disinfecting agents and personal care products, were potently and selectively cytotoxic to developing oligodendrocytes, whereas organophosphate flame retardants, commonly found in household items such as furniture and electronics, prematurely arrested oligodendrocyte maturation. Chemicals from each class impaired oligodendrocyte development postnatally in mice and in a human 3D organoid model of prenatal cortical development. Analysis of epidemiological data showed that adverse neurodevelopmental outcomes were associated with childhood exposure to the top organophosphate flame retardant identified by our screen. This work identifies toxicological vulnerabilities for oligodendrocyte development and highlights the need for deeper scrutiny of these compounds' impacts on human health.

The Influence of Lysosomal Stress on Dental Pulp Stem Cell-Derived Schwann Cells

BACKGROUND

Dysregulation of the endo-lysosomal-autophagy pathway has been identified as a critical factor in the pathology of various demyelinating neurodegenerative diseases, including peripheral neuropathies. This pathway plays a crucial role in transporting newly synthesized myelin proteins to the plasma membrane in myelinating Schwann cells, making these cells susceptible to lysosome-related dysfunctions. Nevertheless, the specific impact of lysosomal dysfunction in Schwann cells and its contribution to neurodegeneration remain poorly understood.

METHODS

We aim to mimic lysosomal dysfunction in Schwann cells using chloroquine, a lysosomal dysfunction inducer, and to monitor lysosomal leakiness, Schwann cell viability, and apoptosis over time. Additionally, due to the ethical and experimental issues associated with cell isolation and the culturing of human Schwann cells, we use human dental pulp stem cell-derived Schwann cells (DPSC-SCs) as a model in our study.

RESULTS

Chloroquine incubation boosts lysosomal presence as demonstrated by an increased Lysotracker signal. Further in-depth lysosomal analysis demonstrated an increased lysosomal size and permeability as illustrated by a TEM analysis and GAL3-LAMP1 staining. Moreover, an Alamar blue assay and Caspase-3 staining demonstrates a reduced viability and increased apoptosis, respectively.

CONCLUSIONS

Our data indicate that prolonged lysosomal dysfunction leads to lysosomal permeability, reduced viability, and eventually apoptosis in human DPSC-SCs.

How to Use the Cuprizone Model to Study De- and Remyelination

Multiple sclerosis (MS) is an autoimmune and inflammatory disorder affecting the central nervous system whose cause is still largely unknown. Oligodendrocyte degeneration results in demyelination of axons, which can eventually be repaired by a mechanism called remyelination. Prevention of demyelination and the pharmacological support of remyelination are two promising strategies to ameliorate disease progression in MS patients. The cuprizone model is commonly employed to investigate oligodendrocyte degeneration mechanisms or to explore remyelination pathways. During the last decades, several different protocols have been applied, and all have their pros and cons. This article intends to offer guidance for conducting pre-clinical trials using the cuprizone model in mice, focusing on discovering new treatment approaches to prevent oligodendrocyte degeneration or enhance remyelination.

Claudin-11 in health and disease: implications for myelin disorders, hearing, and fertility

Claudin-11 plays a critical role in multiple physiological processes, including myelination, auditory function, and spermatogenesis. Recently, stop-loss mutations in CLDN11 have been identified as a novel cause of hypomyelinating leukodystrophy (HLD22). Understanding the multifaceted roles of claudin-11 and the potential pathogenic mechanisms in HLD22 is crucial for devising targeted therapeutic strategies. This review outlines the biological roles of claudin-11 and the implications of claudin-11 loss in the context of the Cldn11 null mouse model. Additionally, HLD22 and proposed pathogenic mechanisms, such as endoplasmic reticulum stress, will be discussed.

BBS genes are involved in accelerated proliferation and early differentiation of BBS-related tissues

Bardet-Biedl syndrome (BBS) is an inherited disorder primarily ciliopathy with pleiotropic multi-systemic phenotypic involvement, including adipose, nerve, retinal, kidney, Etc. Consequently, it is characterized by obesity, cognitive impairment and retinal, kidney and cutaneous abnormalities. Initial studies, including ours have shown that BBS genes play a role in the early developmental stages of adipocytes and β-cells. However, this role in other BBS-related tissues is unknown. We investigated BBS genes involvement in the proliferation and early differentiation of different BBS cell types. The involvement of BBS genes in cellular proliferation were studied in seven in-vitro and transgenic cell models; keratinocytes (hHaCaT) and Ras-transfected keratinocytes (Ras-hHaCaT), neuronal cell lines (hSH-SY5Y and rPC-12), silenced BBS4 neural cell lines (siBbs4 hSH-SY5Y and siBbs4 rPC-12), adipocytes (m3T3L1), and ex-vivo transformed B-cells obtain from BBS4 patients, using molecular and biochemical methodologies. RashHaCaT cells showed an accelerated proliferation rate in parallel to significant reduction in the transcript levels of BBS1, 2, and 4. BBS1, 2, and 4 transcripts linked with hHaCaT cell cycle arrest (G1 phase) using both chemical (CDK4 inhibitor) and serum deprivation methodologies. Adipocyte (m3T3-L1) Bbs1, 2 and 4 transcript levels corresponded to the cell cycle phase (CDK4 inhibitor and serum deprivation). SiBBS4 hSH-SY5Y cells exhibited early cell proliferation and differentiation (wound healing assay) rates. SiBbs4 rPC-12 models exhibited significant proliferation and differentiation rate corresponding to Nestin expression levels. BBS4 patients-transformed B-cells exhibited an accelerated proliferation rate (LPS-induced methodology). In conclusions, the BBS4 gene plays a significant, similar and global role in the cellular proliferation of various BBS related tissues. These results highlight the universal role of the BBS gene in the cell cycle, and further deepen the knowledge of the mechanisms underlying the development of BBS.

Increased activity of IRE1 improves the clinical presentation of EAE

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

Molecular cloning and characterization of endoplasmic reticulum stress related genes grp78 and atf6α from black seabream (Acanthopagrus schlegelii) and their expressions in response to nutritional regulation

Glucose-regulated protein 78 (grp78) and activating transcription factor 6α (atf6α) are considered vital endoplasmic reticulum (ER) molecular chaperones and ER stress (ERS) sensors, respectively. In the present study, the full cDNA sequences of these two ERS-related genes were first cloned and characterized from black seabream (Acanthopagrus schlegelii). The grp78 cDNA sequence is 2606 base pair (bp) encoding a protein of 654 amino acids (aa). The atf6α cDNA sequence is 2168 base pair (bp) encoding a protein of 645 aa. The predicted aa sequences of A. schlegelii grp78 and atf6α indicated that the proteins contain all the structural features, which were characteristic of the two genes in other species. Tissues transcript abundance analysis revealed that the mRNAs of grp78 and atf6α were expressed in all measured tissues, but the highest expression of these two genes was all recorded in the gill followed by liver/ brain. Moreover, in vivo experiment found that fish intake of a high lipid diet (HLD) can trigger ERS by activating grp78/Grp78 and atf6α/Atf6α. However, it can be alleviated by dietary betaine supplementation, similar results were also obtained by in vitro experiment using primary hepatocytes of A. schlegelii. These findings will be beneficial for us to evaluate the regulator effects of HLD supplemented with betaine on ERS at the molecular level, and thus provide some novel insights into the functions of betaine in marine fish fed with an HLD.

Potential Crosstalk between the PACAP/VIP Neuropeptide System and Endoplasmic Reticulum Stress-Relevance to Multiple Sclerosis Pathophysiology

Multiple sclerosis (MS) is an immune-mediated disorder characterized by focal demyelination and chronic inflammation of the central nervous system (CNS). Although the exact etiology is unclear, mounting evidence indicates that endoplasmic reticulum (ER) stress represents a key event in disease pathogenesis. Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) are two structurally related neuropeptides that are abundant in the CNS and are known to exert neuroprotective and immune modulatory roles. Activation of this endogenous neuropeptide system may interfere with ER stress processes to promote glial cell survival and myelin self-repair. However, the potential crosstalk between the PACAP/VIP system and ER stress remains elusive. In this review, we aim to discuss how these peptides ameliorate ER stress in the CNS, with a focus on MS pathology. Our goal is to emphasize the importance of this potential interaction to aid in the identification of novel therapeutic targets for the treatment of MS and other demyelinating disorders.

Proteostasis plays an important role in demyelinating Charcot Marie Tooth disease

Type 1 Charcot-Marie-Tooth disease (CMT1) is the most common demyelinating peripheral neuropathy. Patients suffer from progressive muscle weakness and sensory problems. The underlying disease mechanisms of CMT1 are still unclear and no therapy is currently available, hence patients completely rely on supportive care. Balancing protein levels is a complex multistep process fundamental to maintain cells in their healthy state and a disrupted proteostasis is a hallmark of several neurodegenerative diseases. When protein misfolding occurs, protein quality control systems are activated such as chaperones, the lysosomal-autophagy system and proteasomal degradation to ensure proper degradation. However, in pathological circumstances, these mechanisms are overloaded and thereby become inefficient to clear the load of misfolded proteins. Recent evidence strongly indicates that a disbalance in proteostasis plays an important role in several forms of CMT1. In this review, we present an overview of the protein quality control systems, their role in CMT1, and potential treatment strategies to restore proteostasis.

Insights into the mechanism of oligodendrocyte protection and remyelination enhancement by the integrated stress response

central nervous system (CNS) inflammation triggers activation of the integrated stress response (ISR). We previously reported that prolonging the ISR protects remyelinating oligodendrocytes and promotes remyelination in the presence of inflammation. However, the exact mechanisms through which this occurs remain unknown. Here, we investigated whether the ISR modulator Sephin1 in combination with the oligodendrocyte differentiation enhancing reagent bazedoxifene (BZA) is able to accelerate remyelination under inflammation, and the underlying mechanisms mediating this pathway. We find that the combined treatment of Sephin1 and BZA is sufficient to accelerate early-stage remyelination in mice with ectopic IFN-γ expression in the CNS. IFN-γ, which is a critical inflammatory cytokine in multiple sclerosis (MS), inhibits oligodendrocyte precursor cell (OPC) differentiation in culture and triggers a mild ISR. Mechanistically, we further show that BZA promotes OPC differentiation in the presence of IFN-γ, while Sephin1 enhances the IFN-γ-induced ISR by reducing protein synthesis and increasing RNA stress granule formation in differentiating oligodendrocytes. Finally, pharmacological suppression of the ISR blocks stress granule formation in vitro and partially lessens the beneficial effect of Sephin1 on disease progression in a mouse model of MS, experimental autoimmune encephalitis (EAE). Overall, our findings uncover distinct mechanisms of action of BZA and Sephin1 on oligodendrocyte lineage cells under inflammatory stress, suggesting that a combination therapy may effectively promote restoring neuronal function in MS patients.

The PERK pathway: beneficial or detrimental for neurodegenerative diseases and tumor growth and cancer

Protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK) is one of the three major sensors in the unfolded protein response (UPR). The UPR is involved in the modulation of protein synthesis as an adaptive response. Prolonged PERK activity correlates with the development of diseases and the attenuation of disease severity. Thus, the current debate focuses on the role of the PERK signaling pathway either in accelerating or preventing diseases such as neurodegenerative diseases, myelin disorders, and tumor growth and cancer. In this review, we examine the current findings on the PERK signaling pathway and whether it is beneficial or detrimental for the above-mentioned disorders.

Involvement of Degenerating 21.5 kDa Isoform of Myelin Basic Protein in the Pathogenesis of the Relapse in Murine Relapsing-Remitting Experimental Autoimmune Encephalomyelitis and MS Autopsied Brain

Multiple sclerosis (MS) is the chronic inflammatory demyelinating disease of the CNS. Relapsing-remitting MS (RRMS) is the most common type of MS. However, the mechanisms of relapse and remission in MS have not been fully understood. While SJL mice immunized with proteolipid protein (PLP) develop relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE), we have recently observed that some of these mice were resistant to the active induction of relapsing EAE after initial clinical and histological symptoms of EAE with a severity similar to the relapsing EAE mice. To clarify the mechanism of relapsing, we examined myelin morphology during PLP_139-151-induced RR-EAE in the SJL mice. While RR-EAE mice showed an increased EAE severity (relapse) with CNS inflammation, demyelination with abnormal myelin morphology in the spinal cord, the resistant mice exhibited a milder EAE phenotype with diminished relapse. Compared with the RR-EAE mice, the resistant mice showed less CNS inflammation, demyelination, and abnormalities of the myelin structure. In addition, scanning electron microscopic (SEM) analysis with the osmium-maceration method displayed ultrastructural abnormalities of the myelin structure in the white matter of the RR-EAE spinal cord, but not in that of the resistant mice. While the intensity of myelin staining was reduced in the relapsing EAE spinal cord, immunohistochemistry and immunoblot analysis revealed that the 21.5 kDa isoform of degenerating myelin basic protein (MBP) was specifically induced in the relapsing EAE spinal cord. Taken together, the neuroinflammation-induced degenerating 21 kDa isoform of MBP sheds light on the development of abnormal myelin on the relapse of MS pathogenesis.

Endoplasmic reticulum associated degradation is essential for maintaining the viability or function of mature myelinating cells in adults

Endoplasmic reticulum associated degradation (ERAD) is responsible for recognition and degradation of unfolded or misfolded proteins in the ER. Sel1L is essential for the ERAD activity of Sel1L-Hrd1 complex, the best-known ERAD machinery. Using a continuous Sel1L knockout mouse model (CNP/Cre; Sel1LloxP/loxP mice), our previous studies showed that Sel1L knockout in myelinating cells, oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS), leads to adult-onset myelin abnormalities in the CNS and PNS. Because Sel1L is deleted in myelinating cells of CNP/Cre; Sel1LloxP/loxP mice starting at very early stage of differentiation, it is impossible to rule out the possibility that the adult-onset myelin abnormalities in these mice results from developmental myelination defects caused by Sel1L knockout in myelinating cells during development. Thus, using an inducible Sel1L knockout mouse model (PLP/CreERT ; Sel1LloxP/loxP mice) that has normal, intact myelin and myelinating cells in the adult CNS and PNS prior to tamoxifen treatment, we sought to determine if Sel1L knockout in mature myelinating cells of adult mice leads to myelin abnormalities in the CNS and PNS. We showed that Sel1L knockout in mature myelinating cells caused ERAD impairment, ER stress and UPR activation. Interesting, Sel1L knockout in mature oligodendrocytes impaired their myelinating function by suppressing myelin protein translation, and resulted in progressive myelin thinning in the adult CNS. Conversely, Sel1L knockout in mature Schwann cells led to Schwann cell apoptosis and demyelination in the adult PNS. These findings demonstrate the essential roles of ERAD in mature myelinating cells in the adult CNS and PNS under physiological conditions.

Sensory deficit screen identifies nsf mutation that differentially affects SNARE recycling and quality control

The AAA+ NSF complex is responsible for SNARE complex disassembly both before and after membrane fusion. Loss of NSF function results in pronounced developmental and degenerative defects. In a genetic screen for sensory deficits in zebrafish, we identified a mutation in nsf, I209N, that impairs hearing and balance in a dosage-dependent manner without accompanying defects in motility, myelination, and innervation. In vitro experiments demonstrate that while the I209N NSF protein recognizes SNARE complexes, the effects on disassembly are dependent upon the type of SNARE complex and I209N concentration. Higher levels of I209N protein produce a modest decrease in binary (syntaxin-SNAP-25) SNARE complex disassembly and residual ternary (syntaxin-1A-SNAP-25-synaptobrevin-2) disassembly, whereas at lower concentrations binary disassembly activity is strongly reduced and ternary disassembly activity is absent. Our study suggests that the differential effect on disassembly of SNARE complexes leads to selective effects on NSF-mediated membrane trafficking and auditory/vestibular function.

Increased activity of IRE1 improves the clinical presentation of EAE

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

Immunomodulatory therapy with glatiramer acetate reduces endoplasmic reticulum stress and mitochondrial dysfunction in experimental autoimmune encephalomyelitis

Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are found in lesions of multiple sclerosis (MS) and animal models of MS such as experimental autoimmune encephalomyelitis (EAE), and may contribute to the neuronal loss that underlies permanent impairment. We investigated whether glatiramer acetate (GA) can reduce these changes in the spinal cords of chronic EAE mice by using routine histology, immunostaining, and electron microscopy. EAE spinal cord tissue exhibited increased inflammation, demyelination, mitochondrial dysfunction, ER stress, downregulation of NAD+ dependent pathways, and increased neuronal death. GA reversed these pathological changes, suggesting that immunomodulating therapy can indirectly induce neuroprotective effects in the CNS by mediating ER stress.

Update on Central Nervous System Effects of HIV in Adolescents and Young Adults

PURPOSE OF REVIEW

: Behaviorally acquired (non-perinatal) HIV infection during adolescence and young adulthood occurs in the midst of key brain developmental processes such as frontal lobe neuronal pruning and myelination of white matter, but we know little about the effects of new infection and therapy on the developing brain.

RECENT FINDINGS

Adolescents and young adults account for a disproportionately high fraction of new HIV infections each year. Limited data exist regarding neurocognitive performance in this age group, but suggest impairment is at least as prevalent as in older adults, despite lower viremia, higher CD4 + T cell counts, and shorter durations of infection in adolescents/young adults. Neuroimaging and neuropathologic studies specific to this population are underway. The full impact of HIV on brain growth and development in youth with behaviorally acquired HIV has yet to be determined; it must be investigated further to develop future targeted treatment and mitigation strategies.

Pervasive environmental chemicals impair oligodendrocyte development

Exposure to environmental chemicals can impair neurodevelopment1-4. Oligodendrocytes that wrap around axons to boost neurotransmission may be particularly vulnerable to chemical toxicity as they develop throughout fetal development and into adulthood5,6. However, few environmental chemicals have been assessed for potential risks to oligodendrocyte development. Here, we utilized a high-throughput developmental screen and human cortical brain organoids, which revealed environmental chemicals in two classes that disrupt oligodendrocyte development through distinct mechanisms. Quaternary compounds, ubiquitous in disinfecting agents, hair conditioners, and fabric softeners, were potently and selectively cytotoxic to developing oligodendrocytes through activation of the integrated stress response. Organophosphate flame retardants, commonly found in household items such as furniture and electronics, were non-cytotoxic but prematurely arrested oligodendrocyte maturation. Chemicals from each class impaired human oligodendrocyte development in a 3D organoid model of prenatal cortical development. In analysis of epidemiological data from the CDC's National Health and Nutrition Examination Survey, adverse neurodevelopmental outcomes were associated with childhood exposure to the top organophosphate flame retardant identified by our oligodendrocyte toxicity platform. Collectively, our work identifies toxicological vulnerabilities specific to oligodendrocyte development and highlights common household chemicals with high exposure risk to children that warrant deeper scrutiny for their impact on human health.

Oxygen treatment reduces neurological deficits and demyelination in two animal models of multiple sclerosis

AIMS

The objective of the study is to explore the importance of tissue hypoxia in causing neurological deficits and demyelination in the inflamed CNS, and the value of inspiratory oxygen treatment, using both active and passive experimental autoimmune encephalomyelitis (EAE).

METHODS

Normobaric oxygen treatment was administered to Dark Agouti rats with either active or passive EAE, compared with room air-treated, and naïve, controls.

RESULTS

Severe neurological deficits in active EAE were significantly improved after just 1 h of breathing approximately 95% oxygen. The improvement was greater and more persistent when oxygen was applied either prophylactically (from immunisation for 23 days), or therapeutically from the onset of neurological deficits for 24, 48, or 72 h. Therapeutic oxygen for 72 h significantly reduced demyelination and the integrated stress response in oligodendrocytes at the peak of disease, and protected from oligodendrocyte loss, without evidence of increased oxidative damage. T-cell infiltration and cytokine expression in the spinal cord remained similar to that in untreated animals. The severe neurological deficit of animals with passive EAE occurred in conjunction with spinal hypoxia and was significantly reduced by oxygen treatment initiated before their onset.

CONCLUSIONS

Severe neurological deficits in both active and passive EAE can be caused by hypoxia and reduced by oxygen treatment. Oxygen treatment also reduces demyelination in active EAE, despite the autoimmune origin of the disease.

Insights into the mechanism of oligodendrocyte protection and remyelination enhancement by the integrated stress response

CNS inflammation triggers activation of the integrated stress response (ISR). We previously reported that prolonging the ISR protects remyelinating oligodendrocytes and promotes remyelination in the presence of inflammation (Chen et al., eLife , 2021). However, the exact mechanisms through which this occurs remain unknown. Here, we investigated whether the ISR modulator Sephin1 in combination with the oligodendrocyte differentiation enhancing reagent bazedoxifene (BZA) is able to accelerate remyelination under inflammation, and the underlying mechanisms mediating this pathway. We find that the combined treatment of Sephin1 and BZA is sufficient to accelerate early-stage remyelination in mice with ectopic IFN-γ expression in the CNS. IFN-γ, which is a critical inflammatory cytokine in multiple sclerosis (MS), inhibits oligodendrocyte precursor cell (OPC) differentiation in culture and triggers a mild ISR. Mechanistically, we further show that BZA promotes OPC differentiation in the presence of IFN-γ, while Sephin1 enhances the IFN-γ-induced ISR by reducing protein synthesis and increasing RNA stress granule formation in differentiating oligodendrocytes. Finally, the ISR suppressor 2BAct is able to partially lessen the beneficial effect of Sephin1 on disease progression, in an MS mouse model of experimental autoimmune encephalitis (EAE). Overall, our findings uncover distinct mechanisms of action of BZA and Sephin1 on oligodendrocyte lineage cells under inflammatory stress, suggesting that a combination therapy may effectively promote restoring neuronal function in MS patients.

Leukoencephalopathy hypomyelination with brainstem and spinal cord involvement and leg spasticity caused by DARS1 mutations

Hypomyelination with brainstem and spinal cord involvement and leg spasticity (HBSL), caused by aspartyl-tRNA synthetase (DARS1) gene mutations, is extremely rare, with only a few cases reported worldwide; thus, reports on HBSL treatment are few. In this review, we summarized the clinical manifestations, imaging features, treatment methods, and gene mutations responsible for HBSL based on relevant studies and cases.

Autophagy collaborates with apoptosis pathways to control myelination specificity and function

Oligodendrocytes are the sole myelin producing cells in the central nervous system. Oligodendrocyte numbers are tightly controlled across diverse brain regions to match local axon type and number, but the underlying mechanisms and functional significance remain unclear. Here, we show that autophagy, an evolutionarily conserved cellular process that promotes cell survival under canonical settings, elicits premyelinating oligodendrocyte apoptosis during development and regulates critical aspects of nerve pulse propagation. Autophagy flux is increased in premyelinating oligodendrocytes, and its genetic blockage causes ectopic oligodendrocyte survival throughout the entire brain. Autophagy acts in the TFEB-Bax/Bak pathway and elevates PUMA mRNA levels to trigger premyelinating oligodendrocyte apoptosis cell-autonomously. Autophagy continuously functions in the myelinating oligodendrocytes to limit myelin sheath numbers and fine-tune nerve pulse propagation. Our results provide in vivo evidence showing that autophagy promotes apoptosis in mammalian cells under physiological conditions and reveal key intrinsic mechanisms governing oligodendrocyte number.

HIGHLIGHTS

Autophagy flux increases in the premyelinating and myelinating oligodendrocytesAutophagy promotes premyelinating oligodendrocyte (pre-OL) apoptosis to control myelination location and timing Autophagy acts in the TFEB-PUMA-Bax/Bak pathway and elevates PUMA mRNA levels to determine pre-OL fate Autophagy continuously functions in the myelinating oligodendrocytes to limit myelin sheath thickness and finetune nerve pulse propagation.

Endoplasmic reticulum as a therapeutic target in type 2 diabetes: Role of phytochemicals

Type 2 diabetes mellitus (T2DM) is a metabolic disorders characterized by insulin resistance and β-cell dysfunction with an increasing worldwide incidence. Several studies have revealed that long-term glucotoxicity results in β-cell failure and death through induction of endoplasmic reticulum (ER) stress. Owing to the chronic progression of T2DM and the low effectiveness of antidiabetic drugs in long-term use, medicinal plants and their secondary metabolites seem to be the promising alternatives. Here we have provided a comprehensive review regarding the role of phytochemicals to alleviate ER stress in T2DM. Ginsenoside compound K, baicalein, quercetin, isopulegol, kaempferol, liquiritigenin, aspalathin, and tyrosol have demonstrated remarkable improvement of T2DM via modulation of ER stress. Arctigenin and total glycosides of peony have been shown to be effective in the treatment of diabetic retinopathy through modulation of ER stress. The effectiveness of grape seed proanthocyanidins and wolfberry is also shown in the relief of diabetic neuropathy and retinopathy. Resveratrol is involved in the prevention of atherosclerosis via ER stress modulation. Taken together, the data described herein revealed the capability of herbal constituents to prevent different complications of T2DM via a decrease in ER stress which open new doors to the treatment of diabetes.

tRNA dysregulation and disease

tRNAs are key adaptor molecules that decipher the genetic code during translation of mRNAs in protein synthesis. In contrast to the traditional view of tRNAs as ubiquitously expressed housekeeping molecules, awareness is now growing that tRNA-encoding genes display tissue-specific and cell type-specific patterns of expression, and that tRNA gene expression and function are both dynamically regulated by post-transcriptional RNA modifications. Moreover, dysregulation of tRNAs, mediated by alterations in either their abundance or function, can have deleterious consequences that contribute to several distinct human diseases, including neurological disorders and cancer. Accumulating evidence shows that reprogramming of mRNA translation through altered tRNA activity can drive pathological processes in a codon-dependent manner. This Review considers the emerging evidence in support of the precise control of functional tRNA levels as an important regulatory mechanism that coordinates mRNA translation and protein expression in physiological cell homeostasis, and highlights key examples of human diseases that are linked directly to tRNA dysregulation.

Integrative multiomic analyses of dorsal root ganglia in diabetic neuropathic pain using proteomics, phospho-proteomics, and metabolomics

Diabetic peripheral neuropathy (DPN) is characterized by spontaneous pain in the extremities. Incidence of DPN continues to rise with the global diabetes epidemic. However, there remains a lack of safe, effective analgesics to control this chronic painful condition. Dorsal root ganglia (DRG) contain soma of sensory neurons and modulate sensory signal transduction into the central nervous system. In this study, we aimed to gain a deeper understanding of changes in molecular pathways in the DRG of DPN patients with chronic pain. We recently reported transcriptomic changes in the DRG with DPN. Here, we expand upon those results with integrated metabolomic, proteomic, and phospho-proteomic analyses to compare the molecular profiles of DRG from DPN donors and DRG from control donors without diabetes or chronic pain. Our analyses identified decreases of select amino acids and phospholipid metabolites in the DRG from DPN donors, which are important for cellular maintenance. Additionally, our analyses revealed changes suggestive of extracellular matrix (ECM) remodeling and altered mRNA processing. These results reveal new insights into changes in the molecular profiles associated with DPN.

Oxalate-induced apoptosis through ERS-ROS-NF-κB signalling pathway in renal tubular epithelial cell

Background

Kidney stones are composed of approximately 70–80% calcium oxalate. However, the exact mechanism of formation of calcium oxalate kidney stones remains unclear. In this study, we investigated the roles of endoplasmic reticulum stress (ERS), reactive oxygen species (ROS), and the NF-κB signalling pathway in the pathogenesis of oxalate-induced renal tubular epithelial cell injury and its possible molecular mechanisms.

Methods

We established a model to evaluate the formation of kidney stones by intraperitoneal injection of glyoxylic acid solution into mice and assessed cell morphology, apoptosis, and the expression levels of ERS, ROS, and NF-κB signalling pathway-related proteins in mouse renal tissues. Next, we treated HK-2 cells with potassium oxalate to construct a renal tubular epithelial cell injury model. We detected the changes in autophagy, apoptosis, and mitochondrial membrane potential and investigated the ultrastructure of the cells by transmission electron microscopy. Western blotting revealed the expression levels of apoptosis and autophagy proteins; mitochondrial structural and functional proteins; and ERS, ROS, and NF-κB (p65) proteins. Lastly, we studied the downregulation of NF-κB activity in HK-2 cells by lentivirus interference and confirmed the interaction between the NF-κB signalling and ERS/ROS pathways.

Results

We observed swelling of renal tissues, increased apoptosis of renal tubular epithelial cells, and activation of the ERS, ROS, and NF-κB signalling pathways in the oxalate group. We found that oxalate induced autophagy, apoptosis, and mitochondrial damage in HK-2 cells and activated the ERS/ROS/NF-κB pathways. Interestingly, when the NF-κB signalling pathway was inhibited, the ERS/ROS pathway was also inhibited.

Conclusion

Oxalate induces HK-2 cell injury through the interaction between the NF-κB signalling and ERS/ROS pathways.

Curcumin protect Schwann cells from inflammation response and apoptosis induced by high glucose through the NF-κB pathway

Demyelination disease as diabetes mellitus (DM) complication is characterized by apoptosis of Schwann cells (SCs) and several reports have demonstrated that high glucose content can induce an inflammation response and lead to the apoptosis of SCs. For NF-κB plays a pivotal role in the inflammatory response, hence we hypothesized that high glucose content can induce inflammation though the NF-κB pathway. First we verified that 150 mM high glucose can increase the expression of cleaved caspase 3, interleukin (IL)- 1β, Cyto-C and NF-κB with time through Western blot and increase the apoptosis of RSC96s through Flow Cytometry. Then we found that high glucose can increase the nuclear translocation NF-κB through confocal system which can promote the expression of inflammation genes such as IL-1β. Curcumin has been reported to possess anti-inflammation activities to protect cells. In this study, we found that application with 25 μM curcumin could alleviate the inflammation response and protect the cells from apoptosis. We revealed that the expression of NF-κB and p-NF-κB was decreased and the translocation was also inhibited after curcumin application. Accordingly, the secretion of IL-1β and the apoptosis of RSC96s induce by high glucose was suppressed. Our cumulative findings suggest that curcumin can protect SCs from apoptosis through the inhibition of the inflammatory response though the NF-κB pathway.

Developmental delay and late onset HBSL pathology in hypomorphic Dars1M256L mice

The leukodystrophy Hypomyelination with Brainstem and Spinal cord involvement and Leg spasticity (HBSL) is caused by recessive mutations of the DARS1 gene, which encodes the cytoplasmic aspartyl-tRNA synthetase. HBSL is a spectrum disorder with disease onset usually during early childhood and no available treatment options. Patients display regression of previously acquired motor milestones, spasticity, ataxia, seizures, nystagmus, and intellectual disabilities. Gene-function studies in mice revealed that homozygous Dars1 deletion is embryonically lethal, suggesting that successful modelling of HBSL requires the generation of disease-causing genocopies in mice. In this study, we introduced the pathogenic DARS1 M256L mutation located on exon nine of the murine Dars1 locus. Despite causing severe illness in humans, homozygous Dars1 M256L mice were only mildly affected. To exacerbate HBSL symptoms, we bred Dars1 M256L mice with Dars1-null 'enhancer' mice. The Dars1 M256L/- offspring displayed increased embryonic lethality, severe developmental delay, reduced body weight and size, hydrocephalus, anophthalmia, and vacuolization of the white matter. Remarkably, the Dars1 M256L/- genotype affected energy metabolism and peripheral organs more profoundly than the nervous system and resulted in reduced body fat, increased respiratory exchange ratio, reduced liver steatosis, and reduced hypocellularity of the bone marrow. In summary, homozygous Dars1 M256L and compound heterozygous Dars1 M256L/- mutation genotypes recapitulate some aspects of HBSL and primarily manifest in developmental delay as well as metabolic and peripheral changes. These aspects of the disease might have been overlooked in HBSL patients with severe neurological deficits but could be included in the differential diagnosis of HBSL in the future.

T-cell-specific Sel1L deletion exacerbates EAE by promoting Th1/Th17-cell differentiation

Multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) are demyelinating neuroinflammatory diseases identified by the accumulation and aggregation of misfolded proteins in the brain. The Sel1L-Hrd1 complex comprising endoplasmic reticulum associated degradation (ERAD) is an ER-protein quality control system (ERQC) in the cell. Unfortunately, the contribution of ERAD to the development of these diseases has not been well explored. In this study, we used mice with a conditional deletion (KO) of Sel1L in T cells to dissect the role of ERAD on T cells and its contribution to the development of EAE. The results showed that Sel1L KO mice developed more severe EAE than the control wild type (WT) mice. Although, no obvious effects on peripheral T cells in steady state, more CD44-CD25+ double-negative stage 3 (DN3) cells were detected in the thymus. Moreover, Sel1L deficiency promoted the differentiation of Th1 and Th17 cells and upregulated the proliferation and apoptosis of CD4 T cells in vitro. Regarding the mechanism analyzed by RNA sequencing, 437 downregulated genes and 271 upregulated genes were detected in Sel1L deletion CD4 T cells, which covered the activation, proliferation, differentiation and apoptosis of these T cells. Thus, this study declared that the dysfunction of Sel1L in ERAD in T cells exacerbated the severity of EAE and indicated the important role of ERQC in maintaining immune homeostasis in the central nervous system.

Long Noncoding RNAs in CNS Myelination and Disease

Myelination by oligodendrocytes is crucial for neuronal survival and function, and defects in myelination or failure in myelin repair can lead to axonal degeneration and various neurological diseases. At present, the factors that promote myelination and overcome the remyelination block in demyelinating diseases are poorly defined. Although the roles of protein-coding genes in oligodendrocyte differentiation have been extensively studied, the majority of the mammalian genome is transcribed into noncoding RNAs, and the functions of these molecules in myelination are poorly characterized. Long noncoding RNAs (lncRNAs) regulate transcription at multiple levels, providing spatiotemporal control and robustness for cell type-specific gene expression and physiological functions. lncRNAs have been shown to regulate neural cell-type specification, differentiation, and maintenance of cell identity, and dysregulation of lncRNA function has been shown to contribute to neurological diseases. In this review, we discuss recent advances in our understanding of the functions of lncRNAs in oligodendrocyte development and myelination as well their roles in neurological diseases and brain tumorigenesis. A more systematic characterization of lncRNA functional networks will be instrumental for a better understanding of CNS myelination, myelin disorders, and myelin repair.

Tannins in the Treatment of Diabetic Neuropathic Pain: Research Progress and Future Challenges

Diabetes mellitus and its consequences continue to put a significant demand on medical resources across the world. Diabetic neuropathic pain (DNP) is a frequent diabetes mellitus chronic microvascular outcome. Allodynia, hyperalgesia, and aberrant or lack of nerve fibre sensation are all symptoms of DNP. These clinical characteristics will lead to worse quality of life, sleep disruption, depression, and increased mortality. Although the availability of numerous medications that alleviate the symptoms of DNP, the lack of long-term efficacy and unfavourable side effects highlight the urgent need for novel treatment strategies. This review paper systematically analysed the preclinical research on the treatment of DNP using plant phytochemicals that contain only tannins. A total of 10 original articles involved in in-vivo and in-vitro experiments addressing the promising benefits of phytochemical tannins on DNP were examined between 2008 and 2021. The information given implies that these phytochemicals may have relevant pharmacological effects on DNP symptoms through their antihyperalgesic, anti-inflammatory, and antioxidant properties; however, because of the limited sample size and limitations of the studies conducted so far, we were unable to make definitive conclusions. Before tannins may be employed as therapeutic agents for DNP, more study is needed to establish the specific molecular mechanism for all of these activities along the pain pathway and examine the side effects of tannins in the treatment of DNP.

Detection of PERK Signaling in the Central Nervous System

In response to endoplasmic reticulum (ER) stress, activation of pancreatic ER kinase (PERK) signaling adapts cells to stressful conditions by phosphorylating eukaryotic translation initiation factor 2α (eIF2α). Phosphorylation of eIF2α inhibits global protein translation but stimulates the expression of numerous stress-responsive genes by inducing the transcription factor ATF4. A large number of studies have shown that activation of PERK signaling has beneficial or detrimental effects in various diseases of the central nervous system (CNS), including neurodegenerative diseases, myelin disorders, CNS injuries, among others. This chapter is devoted to describing the practical methods for the detection of PERK signaling in CNS diseases.

GANAB as a Novel Biomarker in Multiple Sclerosis: Correlation with Neuroinflammation and IFI35

Multiple sclerosis (MS) still lacks reliable biomarkers of neuroinflammation predictive for disease activity and treatment response. Thus, in a prospective study we assessed 55 MS patients (28 interferon (IFN)-treated, 10 treated with no-IFN therapies, 17 untreated) and 20 matched healthy controls (HCs) for the putative correlation of the densitometric expression of glucosidase II alpha subunit (GANAB) with clinical/paraclinical parameters and with interferon-induced protein 35 (IFI35). We also assessed the disease progression in terms of the Rio Score (RS) in order to distinguish the responder patients to IFN therapy (RS = 0) from the non-responder ones (RS ≥ 1). We found GANAB to be 2.51-fold downregulated in the IFN-treated group with respect to the untreated one (p < 0.0001) and 3.39-fold downregulated in responder patients compared to the non-responders (p < 0.0001). GANAB correlated directly with RS (r = 0.8088, p < 0.0001) and lesion load (LL) (r = 0.5824, p = 0.0014) in the IFN-treated group and inversely with disease duration (DD) (r = −0.6081, p = 0.0096) in the untreated one. Lower mean values were expressed for GANAB than IFI35 in IFN responder (p < 0.0001) and higher mean values in the non-responder patients (p = 0.0022). Inverse correlations were also expressed with IFI35 in the overall patient population (r = −0.6468, p < 0.0001). In conclusion, the modular expression of GANAB reflects IFI35, RS, DD, and LL values, making it a biomarker of neuroinflammation that is predictive for disease activity and treatment response in MS.

Farnesol Ameliorates Demyelinating Phenotype in a Cellular and Animal Model of Charcot-Marie-Tooth Disease Type 1A

Charcot-Marie-Tooth disease (CMT) is a genetically heterogeneous disease affecting the peripheral nervous system that is caused by either the demyelination of Schwann cells or degeneration of the peripheral axon. Currently, there are no treatment options to improve the degeneration of peripheral nerves in CMT patients. In this research, we assessed the potency of farnesol for improving the demyelinating phenotype using an animal model of CMT type 1A. In vitro treatment with farnesol facilitated myelin gene expression and ameliorated the myelination defect caused by PMP22 overexpression, the major causative gene in CMT. In vivo administration of farnesol enhanced the peripheral neuropathic phenotype, as shown by rotarod performance in a mouse model of CMT1A. Electrophysiologically, farnesol-administered CMT1A mice exhibited increased motor nerve conduction velocity and compound muscle action potential compared with control mice. The number and diameter of myelinated axons were also increased by farnesol treatment. The expression level of myelin protein zero (MPZ) was increased, while that of the demyelination marker, neural cell adhesion molecule (NCAM), was reduced by farnesol administration. These data imply that farnesol is efficacious in ameliorating the demyelinating phenotype of CMT, and further elucidation of the underlying mechanisms of farnesol’s effect on myelination might provide a potent therapeutic strategy for the demyelinating type of CMT.

TREM2-dependent lipid droplet biogenesis in phagocytes is required for remyelination

Upon demyelinating injury, microglia orchestrate a regenerative response that promotes myelin repair, thereby restoring rapid signal propagation and protecting axons from further damage. Whereas the essential phagocytic function of microglia for remyelination is well known, the underlying metabolic pathways required for myelin debris clearance are poorly understood. Here, we show that cholesterol esterification in male mouse microglia/macrophages is a necessary adaptive response to myelin debris uptake and required for the generation of lipid droplets upon demyelinating injury. When lipid droplet biogenesis is defective, innate immune cells do not resolve, and the regenerative response fails. We found that triggering receptor expressed on myeloid cells 2 (TREM2)-deficient mice are unable to adapt to excess cholesterol exposure, form fewer lipid droplets, and build up endoplasmic reticulum (ER) stress. Alleviating ER stress in TREM2-deficient mice restores lipid droplet biogenesis and resolves the innate immune response. Thus, we conclude that TREM2-dependent formation of lipid droplets constitute a protective response required for remyelination to occur.

Mechanisms and Treatments in Demyelinating CMT

Demyelinating forms of Charcot-Marie-Tooth disease (CMT) are genetically and phenotypically heterogeneous and result from highly diverse biological mechanisms including gain of function (including dominant negative effects) and loss of function. While no definitive treatment is currently available, rapid advances in defining the pathomechanisms of demyelinating CMT have led to promising pre-clinical studies, as well as emerging clinical trials. Especially promising are the recently completed pre-clinical genetic therapy studies in PMP-22, GJB1, and SH3TC2-associated neuropathies, particularly given the success of similar approaches in humans with spinal muscular atrophy and transthyretin familial polyneuropathy. This article focuses on neuropathies related to mutations in PMP-22, MPZ, and GJB1, which together comprise the most common forms of demyelinating CMT, as well as on select rarer forms for which promising treatment targets have been identified. Clinical characteristics and pathomechanisms are reviewed in detail, with emphasis on therapeutically targetable biological pathways. Also discussed are the challenges facing the CMT research community in its efforts to advance the rapidly evolving biological insights to effective clinical trials. These considerations include the limitations of currently available animal models, the need for personalized medicine approaches/allele-specific interventions for select forms of demyelinating CMT, and the increasing demand for optimal clinical outcome assessments and objective biomarkers.