Inhibition of Notch signaling enhances tissue repair in an animal model of multiple sclerosis

DAPTA, a C-C Chemokine Receptor 5 (CCR5), Leads to the Downregulation of Notch/NF-κB Signaling and Proinflammatory Mediators in CD40+ Cells in Experimental Autoimmune Encephalomyelitis Model in SJL/J Mice

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system characterized by motor deficits, cognitive impairment, fatigue, pain, and sensory and visual dysfunction. CD40, highly expressed in B cells, plays a significant role in MS pathogenesis. The experimental autoimmune encephalomyelitis (EAE) mouse model of MS has been well established, as well as its relevance in MS patients. This study aimed to evaluate the therapeutic potential of DAPTA, a selective C-C chemokine receptor 5 (CCR5) antagonist in the murine model of MS, and to expand the knowledge of its mechanism of action. Following the induction of EAE, DAPTA was administrated (0.01 mg/kg, i.p.) daily from day 14 to day 42. We investigated the effects of DAPTA on NF-κB p65, IκBα, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α in CD40⁺ spleen B cells using flow cytometry. Furthermore, we also analyzed the effect of DAPTA on NF-κB p65, IκBα, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α mRNA expression levels using qRT-PCR in brain tissue. EAE mice treated with DAPTA showed substantial reductions in NF-κB p65, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α but an increase in the IκBα of CD40⁺ B lymphocytes. Moreover, EAE mice treated with DAPTA displayed decreased NF-κB p65, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α and but showed increased IκBα mRNA expression levels. This study showed that DAPTA has significant neuroprotective potential in EAE via the downregulation of inflammatory mediators and NF-κB/Notch signaling. Collectively, DAPTA might have potential therapeutic targets for use in MS treatment.

Signaling mechanisms involved in the regulation of remyelination in multiple sclerosis: a mini review

Multiple sclerosis is an autoimmune neurodegenerative disease of the CNS that causes progressive disabilities, owing to CNS axon degeneration as a late result of demyelination. In the search for the prevention of axonal loss, mitigating inflammatory attacks in the CNS and myelin restoration are two possible approaches. As a result, therapies that target diverse signaling pathways involved in neuroprotection and remyelination have the potential to overcome the challenges in the development of multiple sclerosis treatments. LINGO1 (Leucine rich repeat and Immunoglobulin domain containing, Nogo receptor- interaction protein), AKT/PIP3/mTOR, Notch, Wnt, RXR (Retinoid X receptor gamma), and Nrf2 (nuclear factor erythroid 2-related factor 2) signaling pathways are highlighted in this section. This article reviews the present knowledge regarding numerous signaling pathways and their functions in regulating remyelination in multiple sclerosis pathogenesis. These pathways are potential biomarkers and therapeutic targets in MS.

Endothelin-1–Endothelin receptor B complex contributes to oligodendrocyte differentiation and myelin deficits during preterm white matter injury

Preterm cerebral white matter injury (WMI), a major form of prenatal brain injury, may potentially be treated by oligodendrocyte (OL) precursor cell (OPC) transplantation. However, the defective differentiation of OPCs during WMI seriously hampers the clinical application of OPC transplantation. Thus, improving the ability of transplanted OPCs to differentiate is critical to OPC transplantation therapy for WMI. We established a hypoxia–ischemia-induced preterm WMI model in mice and screened the molecules affected by WMI using single-cell RNA sequencing. We revealed that endothelin (ET)-1 and endothelin receptor B (ETB) are a pair of signaling molecules responsible for the interaction between neurons and OPCs and that preterm WMI led to an increase in the number of ETB-positive OPCs and premyelinating OLs. Furthermore, the maturation of OLs was reduced by knocking out ETB but promoted by stimulating ET-1/ETB signaling. Our research reveals a new signaling module for neuron–OPC interaction and provides new insight for therapy targeting preterm WMI.

Promoting remyelination: A case study in regenerative medicine

Therapeutics that modulate regenerative mechanisms by targeting the activity of endogenous (adult) stem cell populations have the potential to revolutionize medicine. In many human disease states, capacity to repair damaged tissue underlies progressive decline and disease progression. Recent insights derived from efforts aimed at promoting remyelination for the treatment of multiple sclerosis (MS) highlight the importance of considering the limiting factors and underlying mechanisms associated with all aspects of disease onset, progression and recovery, during both the discovery and clinical stages of developing a regenerative medicine. This perspective presents general considerations for the development of regenerative therapies, using remyelination as a case study.

Nimodipine Exerts Beneficial Effects on the Rat Oligodendrocyte Cell Line OLN-93

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS). Therapy is currently limited to drugs that interfere with the immune system; treatment options that primarily mediate neuroprotection and prevent neurodegeneration are not available. Here, we studied the effects of nimodipine on the rat cell line OLN-93, which resembles young mature oligodendrocytes. Nimodipine is a dihydropyridine that blocks the voltage-gated L-type calcium channel family members Cav1.2 and Cav1.3. Our data show that the treatment of OLN-93 cells with nimodipine induced the upregulation of myelin genes, in particular of proteolipid protein 1 (Plp1), which was confirmed by a significantly greater expression of PLP1 in immunofluorescence analysis and the presence of myelin structures in the cytoplasm at the ultrastructural level. Whole-genome RNA sequencing additionally revealed the upregulation of genes that are involved in neuroprotection, remyelination, and antioxidation pathways. Interestingly, the observed effects were independent of Cav1.2 and Cav1.3 because OLN-93 cells do not express these channels, and there was no measurable response pattern in patch-clamp analysis. Taking into consideration previous studies that demonstrated a beneficial effect of nimodipine on microglia, our data support the notion that nimodipine is an interesting drug candidate for the treatment of MS and other demyelinating diseases.

Molecular mechanisms of developmental pathways in neurological disorders: a pharmacological and therapeutic review

Developmental signalling pathways such as Wnt/β-catenin, Notch and Sonic hedgehog play a central role in nearly all the stages of neuronal development. The term 'embryonic' might appear to be a misnomer to several people because these pathways are functional during the early stages of embryonic development and adulthood, albeit to a certain degree. Therefore, any aberration in these pathways or their associated components may contribute towards a detrimental outcome in the form of neurological disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and stroke. In the last decade, researchers have extensively studied these pathways to decipher disease-related interactions, which can be used as therapeutic targets to improve outcomes in patients with neurological abnormalities. However, a lot remains to be understood in this domain. Nevertheless, there is strong evidence supporting the fact that embryonic signalling is indeed a crucial mechanism as is manifested by its role in driving memory loss, motor impairments and many other processes after brain trauma. In this review, we explore the key roles of three embryonic pathways in modulating a range of homeostatic processes such as maintaining blood-brain barrier integrity, mitochondrial dynamics and neuroinflammation. In addition, we extensively investigated the effect of these pathways in driving the pathophysiology of a range of disorders such as Alzheimer's, Parkinson's and diabetic neuropathy. The concluding section of the review is dedicated to neurotherapeutics, wherein we identify and list a range of biological molecules and compounds that have shown enormous potential in improving prognosis in patients with these disorders.

Therapeutic Targeting of Notch Signaling: From Cancer to Inflammatory Disorders

Over the past two decades, the Notch signaling pathway has been investigated as a therapeutic target for the treatment of cancers, and more recently in the context of immune and inflammatory disorders. Notch is an evolutionary conserved pathway found in all metazoans that is critical for proper embryonic development and for the postnatal maintenance of selected tissues. Through cell-to-cell contacts, Notch orchestrates cell fate decisions and differentiation in non-hematopoietic and hematopoietic cell types, regulates immune cell development, and is integral to shaping the amplitude as well as the quality of different types of immune responses. Depriving some cancer types of Notch signals has been shown in preclinical studies to stunt tumor growth, consistent with an oncogenic function of Notch signaling. In addition, therapeutically antagonizing Notch signals showed preclinical potential to prevent or reverse inflammatory disorders, including autoimmune diseases, allergic inflammation and immune complications of life-saving procedures such allogeneic bone marrow and solid organ transplantation (graft-versus-host disease and graft rejection). In this review, we discuss some of these unique approaches, along with the successes and challenges encountered so far to target Notch signaling in preclinical and early clinical studies. Our goal is to emphasize lessons learned to provide guidance about emerging strategies of Notch-based therapeutics that could be deployed safely and efficiently in patients with immune and inflammatory disorders.

The Notch Signaling Pathway Regulates Differentiation of NG2 Cells into Oligodendrocytes in Demyelinating Diseases

NG2 cells are highly proliferative glial cells that can self-renew or differentiate into oligodendrocytes, promoting remyelination. Following demyelination, the proliferative and differentiation potentials of NG2 cells increase rapidly, enhancing their differentiation into functional myelinating cells. Levels of the transcription factors Olig1 and Olig2 increase during the differentiation of NG2 cells and play important roles in the development and repair of oligodendrocytes. However, the ability to generate new oligodendrocytes is hampered by injury-related factors (e.g., myelin fragments, Wnt and Notch signaling components), leading to failed differentiation and maturation of NG2 cells into oligodendrocytes. Here, we review Notch signaling as a negative regulator of oligodendrocyte differentiation and discuss the extracellular ligands, intracellular pathways, and key transcription factors involved.

Ethyl Pyruvate-Derived Transdifferentiation of Astrocytes to Oligodendrogenesis in Cuprizone-Induced Demyelinating Model

Astrocytes redifferentiate into oligodendrogenesis, raising the possibility that astrocytes may be a potential target in the treatment of adult demyelinated lesion. Upon the basis of the improvement of behavior abnormality and demyelination by ethyl pyruvate (EP) treatment, we further explored whether EP affects the function of astrocytes, especially the transdifferentiation of astrocytes into oligodendrogenesis. The results showed that EP treatment increased the accumulation of astrocytes in myelin sheath and promoted the phagocytosis of myelin debris by astrocytes in vivo and in vitro. At the same time, EP treatment induced astrocytes to upregulate the expression of CNTF and BDNF in the corpus callosum and striatum as well as cultured astrocytes, accompanied by increased expression of nestin, Sox2, and β-catenin and decreased expression of Notch1 by astrocytes. As a result, EP treatment effectively promoted the generation of NG2+ and PDGF-Ra+ oligodendrocyte precursor cells (OPCs) that, in part, express astrocyte marker GFAP. Further confirmation was performed by intracerebral injection of primary astrocytes labeled with carboxyfluorescein diacetate succinimidyl ester (CFSE). As expected, NG2+ OPCs expressing CFSE and Sox2 were elevated in the corpus callosum of mice treated with EP following transplantation, revealing that EP can convert astrocytes into myelinating cells. Our results indicate the possibility that EP lead to effective myelin repair in patients suffering from myelination deficit.Graphical Abstract The diagram of EP action for promoting myelin regeneration in CPZ model. EP promoted migration and enrichment of astrocytes to demyelinated tissue and induced astrocytes to express neurotrophic CNTF and BDNF as well as translation factor nestin, Sox2, and β-catenin, which should contribute to astrocytes to differentiate of oligodendrogenesis. At the same time, EP promoted astrocytes to phagocytized myelin debris for removing the harmful substances of myelin regeneration.

The Notch pathway in CNS homeostasis and neurodegeneration

The role of the Notch signaling pathway in neural development has been well established over many years. More recent studies, however, have demonstrated that Notch continues to be expressed and active throughout adulthood in many areas of the central nervous system. Notch signals have been implicated in adult neurogenesis, memory formation, and synaptic plasticity in the adult organism, as well as linked to acute brain trauma and chronic neurodegenerative conditions. NOTCH3 mutations are responsible for the most common form of hereditary stroke, the progressive disorder cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. Notch has also been associated with several progressive neurodegenerative diseases, including Alzheimer's disease, multiple sclerosis, and amyotrophic lateral sclerosis. Although numerous studies link Notch activity with CNS homeostasis and neurodegenerative diseases, the data thus far are primarily correlative, rather than functional. Nevertheless, the evidence for Notch pathway activity in specific neural cellular contexts is strong, and certainly intriguing, and points to the possibility that the pathway carries therapeutic promise. This article is categorized under: Nervous System Development > Flies Signaling Pathways > Cell Fate Signaling Nervous System Development > Vertebrates: General Principles.

Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Neural tissue regeneration following traumatic injuries is often subpar. As a result, the field of neural tissue engineering has evolved to find therapeutic interventions and has seen promising outcomes. However, robust nerve and myelin regeneration remain elusive. One possible reason may be the fact that tissue regeneration often follows a complex sequence of events in a temporally-controlled manner. Although several other fields of tissue engineering have begun to recognise the importance of delivering two or more biomolecules sequentially for more complete tissue regeneration, such serial delivery of biomolecules in neural tissue engineering remains limited. This review aims to highlight the need for sequential delivery to enhance nerve regeneration and remyelination after traumatic injuries in the central nervous system, using spinal cord injuries as an example. In addition, possible methods to attain temporally-controlled drug/gene delivery are also discussed for effective neural tissue regeneration.

Astrocytes in multiple sclerosis and experimental autoimmune encephalomyelitis: Star-shaped cells illuminating the darkness of CNS autoimmunity

Neuropathology in the human autoimmune disease multiple sclerosis (MS) is considered to be mediated by autoreactive leukocytes, such as T cells, B cells, and macrophages. However, the inflammation and tissue damage in MS and its animal model experimental autoimmune encephalomyelitis (EAE) is also critically regulated by astrocytes, the most abundant cell population in the central nervous system (CNS). Under physiological conditions, astrocytes are integral to the development and function of the CNS, whereas in CNS autoimmunity, astrocytes influence the pathogenesis, progression, and recovery of the diseases. In this review, we summarize recent advances in astrocytic functions in the context of MS and EAE, which are categorized into two opposite aspects, one being detrimental and the other beneficial. Inhibition of the detrimental functions and/or enhancement of the beneficial functions of astrocytes might be favorable for the treatment of MS.

Effects of sulforaphane in the central nervous system

Sulforaphane (SFN) is an active component extracted from vegetables like cauliflower and broccoli. Activation of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling is a common mechanism for the anti-oxidative and anti-inflammatory activity of some herb-derived compounds, such as icariin and berberine. However, due to its peculiar ability in Nrf2 activation, SFN is recognized as an activator of Nrf2 and recommended as a supplementation for prevention and/or treatment of disorders like neoplasm and heart failure. In the central nervous system (CNS), the prophylactic and/or therapeutic effects of SFN have been revealed in recent years. For example, it has been reported to prevent the progression of Alzheimer's disease, Parkinson's disease, cerebral ischemia, Huntington's disease, multiple sclerosis, epilepsy, and psychiatric disorders via promotion of neurogenesis or inhibition of oxidative stress and neuroinflammation. SFN is also implicated in reversing cognition, learning, and memory impairment in rodents induced by scopolamine, lipopolysaccharide, okadaic acid, and diabetes. In models of neurotoxicity, SFN has been shown to suppress neurotoxicity induced by a wide range of toxic factors, such as hydrogen peroxide, prion protein, hyperammonemia, and methamphetamine. To date, no consolidated source of knowledge about the pharmacological effects of SFN in the CNS has been presented in the literature. In this review, we summarize and discuss the pharmacological effects of SFN as well as their possible mechanisms in prevention and/or therapy of disorders afflicting the CNS, aiming to get a further insight into how SFN affects the pathophysiological process of CNS disorders.

Current advancements in promoting remyelination in multiple sclerosis

Current multiple sclerosis (MS) therapies are effective in reducing relapse rate, short-term measures of disability, and magnetic resonance imaging (MRI) measures of inflammation in relapsing remitting MS (RRMS), whereas in progressive/degenerative disease phases these medications are of little or no benefit. Therefore, the development of new therapies aimed at reversing neurodegeneration is of great interest. Remyelination, which is usually a spontaneous endogenous process, is achieved when myelin-producing oligodendrocytes are generated from oligodendrocyte precursor cells (OPCs). Even though these precursor cells are abundant in MS brains, their regeneration capacity is limited. Enhancing the generation of myelin-producing cells is therefore a major focus of MS research. Here we present an overview of the different advancements in the field of remyelination, including suitable animal models for testing remyelination therapies, approved medications with a proposed role in regeneration, myelin repair treatments under investigation in clinical trials, as well as future therapeutics aimed at facilitating myelin repair.

Targeting Smoothened as a New Frontier in the Functional Recovery of Central Nervous System Demyelinating Pathologies

Myelin sheaths on vertebrate axons provide protection, vital support and increase the speed of neuronal signals. Myelin degeneration can be caused by viral, autoimmune or genetic diseases. Remyelination is a natural process that restores the myelin sheath and, consequently, neuronal function after a demyelination event, preventing neurodegeneration and thereby neuron functional loss. Pharmacological approaches to remyelination represent a promising new frontier in the therapy of human demyelination pathologies and might provide novel tools to improve adaptive myelination in aged individuals. Recent phenotypical screens have identified agonists of the atypical G protein-coupled receptor Smoothened and inhibitors of the glioma-associated oncogene 1 as being amongst the most potent stimulators of oligodendrocyte precursor cell (OPC) differentiation in vitro and remyelination in the central nervous system (CNS) of mice. Here, we discuss the current state-of-the-art of studies on the role of Sonic Hedgehog reactivation during remyelination, referring readers to other reviews for the role of Hedgehog signaling in cancer and stem cell maintenance.

Presenilin1 regulates Th1 and Th17 effector responses but is not required for experimental autoimmune encephalomyelitis

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) where pathology is thought to be regulated by autoreactive T cells of the Th1 and Th17 phenotype. In this study we sought to understand the functions of Presenilin 1 (PSEN1) in regulating T cell effector responses in the experimental autoimmune encephalomyelitis (EAE) murine model of MS. PSEN1 is the catalytic subunit of γ-secretase a multimolecular protease that mediates intramembranous proteolysis. γ-secretase is known to regulate several pathways of immune importance. Here we examine the effects of disrupting PSEN1 functions on EAE and T effector differentiation using small molecule inhibitors of γ-secretase (GSI) and T cell-specific conditional knockout mice (PSEN1 cKO). Surprisingly, blocking PSEN1 function by GSI treatment or PSEN1 cKO had little effect on the development or course of MOG35-55-induced EAE. In vivo GSI administration reduced the number of myelin antigen-specific T cells and suppressed Th1 and Th17 differentiation following immunization. In vitro, GSI treatment inhibited Th1 differentiation in neutral but not IL-12 polarizing conditions. Th17 differentiation was also suppressed by the presence of GSI in all conditions and GSI-treated Th17 T cells failed to induce EAE following adoptive transfer. PSEN cKO T cells showed reduced Th1 and Th17 differentiation. We conclude that γ-secretase and PSEN1-dependent signals are involved in T effector responses in vivo and potently regulate T effector differentiation in vitro, however, they are dispensable for EAE.

Effect of Notch1 gene on remyelination in multiple sclerosis in mouse models of acute demyelination

This study aims to explore the effects of Notch1 gene on remyelination in multiple sclerosis (MS). A mouse model of acute demyelination was successfully established and the model mice were grouped as cuprizone (CPZ) group, CPZ + small interfering RNA (siRNA)-Notch1 (siNotch1) group, and CPZ + siRNA negative control (NC) group. Meanwhile, another 3 groups (control, control + siNotch1, and control + siRNA NC) were established in normal mice. The changes of weight and maintenance time in rotating drum of mice were observed. Western blot analysis for the protein expressions related to Notch signaling pathway and oligodendrocyte (OL) differentiation in the corpus callosum of the mice. After model establishment, the weight of CPZ-induced demyelinated mice was decreased. During the repair period, the balance ability and movement of the mice was recovered, especially for those injected with siNotch1 plasmid. After model establishment, the number of myelinated axons was decreased. In comparison with the CPZ and CPZ siRNA NC groups, the CPZ + siNotch1 group had a decrease in the number of premature OLs, but increase in mature OLs, and a decrease in oligodendrocyte precursor cells and astrocytes. The expressions of proteins related to Notch signaling pathway, such as HES, Jagged-1 were decreased in the CPZ + siNotch1 group in contrast to the CPZ and CPZ + siRNA groups, but the OL-related transcription factor Sox10 was increased in the CPZ + siNotch1 group than in the CPZ + siRNA NC and CPZ groups, and Id2 was decreased. Our study provided evidence that the inhibition of Notch1 gene could accelerate remyelination in MS.

Potential role of the Jagged1/Notch1 signaling pathway in the endothelial-myofibroblast transition during BLM-induced pulmonary fibrosis

Endothelial cell myofibroblast transition (EndoMT) is found during the process of bleomycin (BLM)-induced pulmonary fibrosis in rats, and plays a very important role in sustaining inflammation and collagen secretion. Moreover, some studies have suggested that the Notch1 signaling pathway may be involved in the expression of α-smooth muscle actin (α-SMA) in pulmonary microvascular endothelial cells (PMVECs), a protein marker of EndoMT. Therefore, we aimed to investigate the expression level of α-SMA and Notch1-related signaling molecules in PMVECs from BLM-induced rats and determine the relationship between the Notch1 signaling pathway and the expression of α-SMA in PMVECs. We found that the expression levels of α-SMA, Notch1, and Jagged1 were upregulated, while the expression levels of Dll4 were downregulated. Furthermore, there was a positive correlation between the expression of Jagged1 and the α-SMA proteins in PMVECs, and NF-κB was downregulated by decreasing the expression of Jagged1. In conclusion, the Jagged1/Notch1 signaling pathway is activated in PMVECs during the pathogenesis of BLM-induced pulmonary fibrosis in rats, and it may induce α-SMA expression via a non-canonical pathway involving NF-κB as the target molecule. The precise mechanism and the molecules involved in this signaling pathway need to be further elucidated.

The expression levels of Notch-related signaling molecules in pulmonary microvascular endothelial cells in bleomycin-induced rat pulmonary fibrosis

Previous studies have suggested that the Notch signaling pathway plays a very important role in the proliferation and differentiation of pulmonary microvascular endothelial cells (PMVECs). Therefore, we aimed to investigate the expression level of Notch-related signaling molecules in PMVECs in bleomycin (BLM)-induced rat pulmonary fibrosis. Immunohistochemistry, immunofluorescence, Western blotting, and real-time PCR were used to analyze the differences in protein and mRNA expression levels of Notch-related signaling molecules, i.e. Notch1, Jagged1, Delta-like ligand 4 (Dll4), and hairy and enhancer of split homolog 1 (Hes1), between a control group treated with intratracheal instillation of saline and a study group treated with intratracheal instillation of BLM solution. Expression levels of the receptor Notch1 and one of its ligands, Jagged1, were upregulated, while the expression levels of the ligand Dll4 and the target molecule of the Notch signaling pathway, Hes1, were downregulated. The differences in protein and mRNA expression levels between the control and study groups were significant (p<0.001). The Jagged1/Notch1 signaling pathway is activated in the pathogenesis of BLM-induced rat pulmonary fibrosis, while the Dll4/Notch1 signaling pathway is inhibited, which inhibits the suppressive effect of Dll4/Notch1 signaling on PMVEC overproliferation, further causing PMVEC dysfunction in cell sprouting and maturation as well as abnormal differentiation of the cell phenotype. Conversely, the down-expression of Hes1 indicates that the Jagged1/Notch1 signaling pathway could be a non-canonical Notch signaling pathway independent of Hes1 activation, which differs from the canonical Dll4/Notch1 signaling pathway.

Pharmacological approaches to intervention in hypomyelinating and demyelinating white matter pathology

White matter disease afflicts both developing and mature central nervous systems. Both cell intrinsic and extrinsic dysregulation result in profound changes in cell survival, axonal metabolism and functional performance. Experimental models of developmental white matter (WM) injury and demyelination have not only delineated mechanisms of signaling and inflammation, but have also paved the way for the discovery of pharmacological approaches to intervention. These reagents have been shown to enhance protection of the mature oligodendrocyte cell, accelerate progenitor cell recruitment and/or differentiation, or attenuate pathological stimuli arising from the inflammatory response to injury. Here we highlight reports of studies in the CNS in which compounds, namely peptides, hormones, and small molecule agonists/antagonists, have been used in experimental animal models of demyelination and neonatal brain injury that affect aspects of excitotoxicity, oligodendrocyte development and survival, and progenitor cell function, and which have been demonstrated to attenuate damage and improve WM protection in experimental models of injury. The molecular targets of these agents include growth factor and neurotransmitter receptors, morphogens and their signaling components, nuclear receptors, as well as the processes of iron transport and actin binding. By surveying the current evidence in non-immune targets of both the immature and mature WM, we aim to better understand pharmacological approaches modulating endogenous oligodendroglia that show potential for success in the contexts of developmental and adult WM pathology. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Clobetasol promotes remyelination in a mouse model of neuromyelitis optica

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the central nervous system that can produce marked neurological deficit. Current NMO therapies include immunosuppressants, plasma exchange and B-cell depletion. Here, we evaluated 14 potential remyelinating drugs emerging from prior small molecule screens done to identify drugs for repurposing in multiple sclerosis and other demyelinating neurological diseases. Compounds were initially evaluated in oligodendrocyte precursor cell (OPC) and cerebellar slice cultures, and then in a mouse model of NMO produced by intracerebral injection of anti-AQP4 autoantibody (AQP4-IgG) and human complement characterized by demyelination with minimal axonal damage. The FDA-approved drug clobetasol promoted differentiation in OPC cultures and remyelination in cerebellar slice cultures and in mice. Intraperitoneal administration of 2 mg/kg/day clobetasol reduced myelin loss by ~60 %, even when clobetasol was administered after demyelination occurred. Clobetasol increased the number of mature oligodendrocytes within lesions without significantly altering initial astrocyte damage or inflammation. These results provide proof-of-concept for the potential utility of a remyelinating approach in the treatment of NMO.

Development of a central nervous system axonal myelination assay for high throughput screening

Background

Regeneration of new myelin is impaired in persistent multiple sclerosis (MS) lesions, leaving neurons unable to function properly and subject to further degeneration. Current MS therapies attempt to ameliorate autoimmune-mediated demyelination, but none directly promote the regeneration of lost and damaged myelin of the central nervous system (CNS). Development of new drugs that stimulate remyelination has been hampered by the inability to evaluate axonal myelination in a rapid CNS culture system.

Results

We established a high throughput cell-based assay to identify compounds that promote myelination. Culture methods were developed for initiating myelination in vitro using primary embryonic rat cortical cells. We developed an immunofluorescent phenotypic image analysis method to quantify the morphological alignment of myelin characteristic of the initiation of myelination. Using γ-secretase inhibitors as promoters of myelination, the optimal growth, time course and compound treatment conditions were established in a 96 well plate format. We have characterized the cortical myelination assay by evaluating the cellular composition of the cultures and expression of markers of differentiation over the time course of the assay. We have validated the assay scalability and consistency by screening the NIH clinical collection library of 727 compounds and identified ten compounds that promote myelination. Half maximal effective concentration (EC₅₀) values for these compounds were determined to rank them according to potency.

Conclusions

We have designed the first high capacity in vitro assay that assesses myelination of live axons. This assay will be ideal for screening large compound libraries to identify new drugs that stimulate myelination. Identification of agents capable of promoting the myelination of axons will likely lead to the development of new therapeutics for MS patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-016-0250-2) contains supplementary material, which is available to authorized users.

Pushing Forward: Remyelination as the New Frontier in CNS Diseases

The evolutionary acquisition of myelin sheaths around large caliber axons in the central nervous system (CNS) represented a milestone in the development of vertebrate higher brain function. Myelin ensheathment of axons enabled saltatory conduction and thus accelerated information processing. However, a number of CNS diseases harm or destroy myelin and oligodendrocytes (myelin-producing cells), ultimately resulting in demyelination. In the adult CNS, new oligodendrocytes can be generated from a quiescent pool of precursor cells, which - upon differentiation - can replace lost myelin sheaths. The efficiency of this spontaneous regeneration is limited, which leads to incomplete remyelination and residual clinical symptoms. Here, we discuss CNS pathologies characterized by white matter degeneration and regeneration and highlight drugs that could potentially serve as remyelination therapies.

Molecular alterations of the blood-brain barrier under inflammatory conditions: The role of endothelial to mesenchymal transition

Impairment of the protective properties of the blood-brain barrier (BBB) is a key event during numerous neurological diseases, including multiple sclerosis (MS). Under these pathological conditions, the specialized brain endothelial cells (BECs) lose their protective function leading to neuroinflammation and neurodegeneration. To date, underlying mechanisms for this loss of function remain unclear. Endothelial to mesenchymal transition (EndoMT) is a dynamic process by which endothelial cells (ECs) dedifferentiate into mesenchymal cells and as a result lose their specific phenotype and function. As yet, little is known about the involvement of this process in the impaired function of the BECs under pathological conditions such as MS. Interestingly, several signaling pathways that can induce EndoMT are also involved in different central nervous system (CNS) pathologies associated with BBB dysfunction. In this review, we first discuss the structure and function of the BBB highlighting the changes that occur during MS. Next, we will summarize recent findings on the pathways underlying EndoMT, and finally, we will discuss the potential role of EndoMT during BBB dysfunction in neurological disorders. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

Heat shock protein 70 (Hsp70) interacts with the Notch1 intracellular domain and contributes to the activity of Notch signaling in myelin-reactive CD4 T cells

Notch receptors (Notch1-4) are involved in the differentiation of CD4 T cells and the development of autoimmunity. Mechanisms regulating Notch signaling in CD4 T cells are not fully elucidated. In this study we investigated potential crosstalk between Notch pathway molecules and heat shock protein 70 (Hsp70), the major intracellular chaperone involved in the protein transport during immune responses and other stress conditions. Using Hsp70(-/-) mice we found that Hsp70 is critical for up-regulation of NICD1 and induction of Notch target genes in Jagged1- and Delta-like1-stimulated CD4 T cells. Co-immunoprecipitation analysis of wild-type CD4 T cells stimulated with either Jagged1 or Delta-like1 showed a direct interaction between NICD1 and Hsp70. Both molecules co-localized within the nucleus of CD4 T cells stimulated with Notch ligands. Molecular interaction and nuclear colocalization of NICD1 and Hsp70 were also detected in CD4 T cells reactive against myelin oligodendrocyte glycoprotein (MOG)35-55, which showed Hsp70-dependent up-regulation of both NICD1 and Notch target genes. In conclusion, we demonstrate for the first time that Hsp70 interacts with NICD1 and contributes to the activity of Notch signaling in CD4 T cells. Interaction between Hsp70 and NICD1 may represent a novel mechanism regulating Notch signaling in activated CD4 T cells.

Quetiapine Ameliorates Schizophrenia-Like Behaviors and Protects Myelin Integrity in Cuprizone Intoxicated Mice: The Involvement of Notch Signaling Pathway

BACKGROUND

White matter disturbances and myelin impairment are key features of schizophrenia. The antipsychotic drug quetiapine can promote the maturation of oligodendrocytes, but the molecular mechanisms remain largely unknown.

METHODS

The schizophrenia-like behaviors, degrees of demyelination, and levels of Notch signaling molecules in forebrains of adult male C57BL/6 mice were examined after fed with cuprizone (0.2% wt/wt) in the presence or absence of 10mg/kg/d quetiapine for 6 weeks. These parameters were also observed after the transcranial injection of Notch signaling inhibitor MW167 (1mM) daily during the last week of the treatment period.

RESULTS

Quetiapine ameliorated the schizophrenia-like behaviors and decreased expression of myelin basic protein and inhibition of Notch signaling molecules, such as Notch1, Hes1, and Hes5, in the forebrain that induced by cuprizone. These beneficial effects of quetiapine were abolished by MW167.

CONCLUSIONS

The antipsychotic and myelin protective effects of quetiapine are mediated by Notch signaling in a mouse model of cuprizone-induced demyelination associated with schizophrenia-like behaviors. The Notch pathway might therefore be a novel target for the development of antipsychotic drugs.

[New therapeutic strategies for remyelination in multiple sclerosis]

Multiple sclerosis (MS) is characterized by oligodendrocyte death and myelin sheath destruction of the central nervous system (CNS) in response to autoinflammatory processes. Besides demyelination axonal degeneration constitutes the second histopathological hallmark of this disease. A large number of immunomodulatory and targeted immunosuppression treatments have been approved for relapsing remitting (RR) MS where they effectively reduce relapse rates; however, currently no treatment options exist to repair injured axonal tracts or myelin damage that accumulates over time particularly in progressive MS. In light of the growing available therapeutic repertoire of highly potent immunomodulatory medications there is an increasing interest in the development of therapies aimed at neutralizing neurodegenerative damage. Endogenous remyelination processes occur mainly as a result of oligodendrocyte precursor cell (OPC) activation, recruitment and maturation; however, this repair activity appears to be limited and increasingly fails during disease progression. Based on these observations OPCs are considered as promising targets for the regenerative treatment of all stages of MS. This article presents an overview of approved medications with a suggested role in regeneration, regenerative treatments that are currently being tested in clinical trials, as well as promising future therapeutic approaches derived from basic glial cell research aiming at the promotion of the endogenous repair activity of the brain.

Electroacupuncture Pretreatment Attenuates Cerebral Ischemic Injury via Notch Pathway-Mediated Up-Regulation of Hypoxia Inducible Factor-1α in Rats

We have reported electroacupuncture (EA) pretreatment induced the tolerance against focal cerebral ischemia through activation of canonical Notch pathway. However, the underlying mechanisms have not been fully understood. Evidences suggest that up-regulation of hypoxia inducible factor-1α (HIF-1α) contributes to neuroprotection against ischemia which could interact with Notch signaling pathway in this process. Therefore, the current study is to test that up-regulation of HIF-1α associated with Notch pathway contributes to the neuroprotection of EA pretreatment. Sprague–Dawley rats were treated with EA at the acupoint “Baihui (GV 20)” 30 min per day for successive 5 days before MCAO. HIF-1α levels were measured before and after reperfusion. Then, HIF-1α antagonist 2ME2 and γ-secretase inhibitor MW167 were used. Neurologic deficit scores, infarction volumes, neuronal apoptosis, and Bcl2/Bax were evaluated. HIF-1α and Notch1 intracellular domain (NICD) were assessed. The results showed EA pretreatment enhanced the neuronal expression of HIF-1α, reduced infarct volume, improved neurological outcome, inhibited neuronal apoptosis, up-regulated expression of Bcl-2, and down-regulated expression of Bax after reperfusion in the penumbra, while the beneficial effects were attenuated by 2ME2. Furthermore, intraventricular injection with MW167 efficiently suppressed both up-regulation of NICD and HIF-1α after reperfusion. However, administration with 2ME2 could only decrease the expression of HIF-1α in the penumbra. In conclusion, EA pretreatment exerts neuroprotection against ischemic injury through Notch pathway-mediated up-regulation of HIF-1α.

Differential roles of Aβ processing in hypoxia-induced axonal damage

Axonopathy is a common and early phase in neurodegenerative and traumatic CNS diseases. Recent work suggests that amyloid β (Aβ) produced from amyloid precursor protein (APP) may be a critical downstream mediator of CNS axonopathy in CNS diseases, particularly those associated with hypoxia. We critically tested this hypothesis in an adult retinal explant system that preserves the three-dimensional organization of the retina while permitting direct imaging of two cardinal features of early-stage axonopathy: axonal structural integrity and axonal transport capacity. Using this system, we found via pharmacological inhibition and genetic deletion of APP that production of Aβ is a necessary step in structural compromise of retinal ganglion cell (RGC) axons induced by the disease-relevant stressor hypoxia. However, identical blockade of Aβ production was not sufficient to protect axons from associated hypoxia-induced reduction in axonal transport. Thus, Aβ mediates distinct facets of hypoxia-induced axonopathy and may represent a functionally selective pharmacological target for therapies directed against early-stage axonopathy in CNS diseases.

Promoting remyelination in multiple sclerosis: current drugs and future prospects

Myelin destruction due to inflammatory oligodendrocyte cell damage or death in conjunction with axonal degeneration are among the major histopathological hallmarks of multiple sclerosis (MS). The majority of available immunomodulatory medications for MS are approved for relapsing-remitting (RR) MS, for which they reduce relapse rate, MRI measures of inflammation, and the accumulation of disability. These medications are, however, of little benefit during progressive MS where axonal degeneration following demyelination outweighs inflammation. This has sparked great interest in the development of new remyelination therapies aimed at reversing the neurodegenerative damage observed in this disease. Remyelination as a result of oligodendrocyte production from oligodendrocyte precursor cells (OPCs) is considered a promising potential target for the treatment of all stages of MS. In this review we present an overview of a) approved medications (some of them FDA-and EMA-approved for other diseases) with a proposed role in regeneration, b) regenerative treatments under investigation in clinical trials, and c) promising future therapeutic approaches aiming specifically at facilitating endogenous repair.

Emerging roles of the γ-secretase-notch axis in inflammation

γ-Secretase is a distinct proteolytic complex required for the activation of many transmembrane proteins. The cleavage of substrates by γ-secretase plays diverse biological roles in producing essential products for the organism. More than 90 transmembrane proteins have been reported to be substrates of γ-secretase. Two of the most widely known and studied of these substrates are the amyloid precursor protein (APP) and the Notch receptor, which are precursors for the generation of amyloid-β (Aβ) and the Notch intracellular domain (NICD), respectively. The wide spectrum of γ-secretase substrates has made analyses of the pathology of γ-secretase-related diseases and underlying mechanisms challenging. Inflammation is an important aspect of disease pathology that requires an in-depth analysis. γ-Secretase may contribute to disease development or progression by directly increasing and regulating production of pro-inflammatory cytokines. This review summarizes recent evidence for a role of γ-secretase in inflammatory diseases, and discusses the potential use of γ-secretase inhibitors as an effective future treatment option.

Parent-of-origin effects implicate epigenetic regulation of experimental autoimmune encephalomyelitis and identify imprinted Dlk1 as a novel risk gene

Parent-of-origin effects comprise a range of genetic and epigenetic mechanisms of inheritance. Recently, detection of such effects implicated epigenetic mechanisms in the etiology of multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system. We here sought to dissect the magnitude and the type of parent-of-origin effects in the pathogenesis of experimental neuroinflammation under controlled environmental conditions. We investigated inheritance of an MS-like disease in rat, experimental autoimmune encephalomyelitis (EAE), using a backcross strategy designed to identify the parental origin of disease-predisposing alleles. A striking 37–54% of all detected disease-predisposing loci depended on parental transmission. Additionally, the Y chromosome from the susceptible strain contributed to disease susceptibility. Accounting for parent-of-origin enabled more powerful and precise identification of novel risk factors and increased the disease variance explained by the identified factors by 2-4-fold. The majority of loci displayed an imprinting–like pattern whereby a gene expressed only from the maternal or paternal copy exerts an effect. In particular, a locus on chromosome 6 comprises a well-known cluster of imprinted genes including the paternally expressed Dlk1, an atypical Notch ligand. Disease-predisposing alleles at the locus conferred lower Dlk1 expression in rats and, together with data from transgenic overexpressing Dlk1 mice, demonstrate that reduced Dlk1 drives more severe disease and modulates adaptive immune reactions in EAE. Our findings suggest a significant epigenetic contribution to the etiology of EAE. Incorporating these effects enables more powerful and precise identification of novel risk factors with diagnostic and prognostic implications for complex disease.

Even with recent progress in determining the genetic basis of complex diseases, the issue of ‘missing heritability’ remains and its potential sources are frequently speculated about but rarely explained. Parent-of-origin effects might contribute to the ‘missing heritability’ and involve genetic and epigenetic mechanisms of inheritance. Our study is the first that establishes (i) the magnitude and (ii) the type of parent-of-origin effects in the pathogenesis of a multiple sclerosis-like disease, experimental autoimmune encephalomyelitis (EAE) in rat, using a strategy designed to identify genes that confer risk only when inherited from either mother or father. A striking 37-54% of all risk loci depended on parental origin. Accounting for parent-of-origin enabled more powerful and precise identification of novel risk factors for EAE, such as the imprinted Dlk1gene. Disease-predisposing alleles conferred lower Dlk1 expression in rats and transgenic Dlk1 mice demonstrated that lower Dlk1 drives more severe EAE and modulates adaptive immune responses. Because parental-origin effects are epigenetically regulated, our data implicate a contributory role for epigenetic mechanisms in complex diseases. Considering parent-of-origin effects in complex disease has enabled more powerful and precise identification of novel risk factors.

Tocopherol derivative TFA-12 promotes myelin repair in experimental models of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the CNS that is associated with demyelination and axonal loss, resulting in severe neurological handicap. Current MS therapies mostly target neuroinflammation but have only a little impact on CNS myelin repair. Progress toward treatments that enhance remyelination would therefore represent major advances in MS treatment. Here, we examined the ability of TFA-12, a new synthetic compound belonging to tocopherol long-chain fatty alcohols, to promote oligodendrocyte regeneration and remyelination in experimental models of MS. We showed that TFA-12 significantly ameliorates neurological deficit and severity of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) in mice. Histological evaluation of mouse EAE spinal cords showed that TFA-12 treatment reduces inflammation, astrogliosis, and myelin loss. Additionally, we demonstrated that TFA-12 accelerates remyelination of focal demyelinated lesions induced by lysolecithin injections. We also found that this compound induces the differentiation of oligodendrocyte precursor cells into mature oligodendrocytes through the inhibition of the Notch/Jagged1 signaling pathway. Altogether, our data provide important proof of principle indicating that TFA-12 could be a potential therapeutic compound for myelin repair in MS.

Notch signaling regulates T cell accumulation and function in the central nervous system during experimental autoimmune encephalomyelitis

Systemic inhibition of Notch signaling was previously shown to attenuate experimental autoimmune encephalomyelitis (EAE), a disease model of multiple sclerosis in mice. Different studies attributed these effects to decreased T-bet and IFN-γ expression, enhanced regulatory T cell function, reduced T cell chemotaxis to the CNS, or impaired Th9 cell differentiation. Interpretation of these heterogeneous findings is difficult because past experimental strategies did not ensure complete Notch inhibition in T cells and because many cell populations could be affected by systemic Notch blockade. To resolve the role of Notch in T cells during EAE, we used the pan-Notch inhibitor dominant-negative form of Mastermind-like 1 (DNMAML), as well as several complementary loss-of-function approaches specifically in myelin-reactive T cells. Notch inhibition in T cells profoundly decreased EAE incidence and severity. Notch-deprived myelin-reactive T cells had preserved activation and effector differentiation in secondary lymphoid tissues. However, Notch-deprived T cells failed to accumulate in the CNS after immunization. Parking wild-type and DNMAML T cells together in bone marrow chimeras increased accumulation of Notch-deprived T cells in the CNS after immunization but did not prevent EAE, indicating the absence of dominant suppression by DNMAML T cells. Analysis of CNS-infiltrating DNMAML T cells revealed markedly defective IL-17A and IFN-γ production, despite preserved T-bet expression. Collectively, our findings capture the profound overall effects of Notch signaling in myelin-reactive T cells and demonstrate that Notch controls the accumulation and pathogenic functions of CD4(+) T cells within their target organ but not in lymphoid tissues during EAE.

Remyelination therapy for multiple sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system characterized by infiltration of immune cells and progressive damage to myelin and axons. All therapeutics used to treat MS have been developed to target an overactive immune response, with aims to reduce disease activity. Chronic demyelinated axons are further prone to irreversible damage and death, and it is imperative that new therapies address this critical issue. Remyelination, the generation of new myelin in the adult nervous system, is an endogenous repair mechanism that restores function of denuded axons and delays their deterioration. Although remyelination can be extensive in some patients, the majority of cases limit repair only to the acute phase of disease. A significant current drive in new MS therapeutics is to identify targets that can promote remyelination by boosting endogenous oligodendrocyte precursor cells to form new myelin. Also, a number of inhibitory pathways have been identified in chronic MS lesions that prevent oligodendrocyte precursor cells from being properly recruited to demyelinated lesions or interfere with their differentiation to myelin-forming oligodendrocytes. In this review, we introduce the phenomenon of remyelination from the view of experimental models and studies in MS patients, describe a potential role in remyelination for currently available MS mediations, and discuss many avenues that are being actively studied to promote remyelination. The next frontier in MS therapeutics will supplement immunomodulation with agents that directly foster myelin repair, with aims to delay disease progression and recover lost neurological functions.

Electroacupuncture pretreatment induces tolerance against focal cerebral ischemia through activation of canonical Notch pathway

Background

Electroacupuncture (EA) pretreatment can induce the tolerance against focal cerebral ischemia. However, the underlying mechanisms have not been fully understood. Emerging evidences suggest that canonical Notch signaling may be involved in ischemic brain injury. In the present study, we tested the hypothesis that EA pretreatment-induced tolerance against focal cerebral ischemia is mediated by Notch signaling.

Results

EA pretreatment significantly enhanced Notch1, Notch4 and Jag1 gene transcriptions in the striatum, except Notch1 intracellular domain level, which could be increased evidently by ischemia. After ischemia and reperfusion, Hes1 mRNA and Notch1 intracellular domain level in ischemic striatum in EA pretreatment group were increased and reached the peak at 2 h and 24 h, respectively, which were both earlier than the peak achieved in control group. Intraventricular injection with the γ-secretase inhibitor MW167 attenuated the neuroprotective effect of EA pretreatment.

Conclusions

EA pretreatment induces the tolerance against focal cerebral ischemia through activation of canonical Notch pathway.

Emerging strategies for the treatment of multiple sclerosis

Despite extraordinary advances in the field of neuroimmunology, ideal treatment for patients with multiple sclerosis remains an unmet need. Existing treatments are only partially effective in preventing multiple sclerosis relapses, have a limited impact on the accrual of disability, have not been effective in progressive forms of the disease, and treatment remains preventive rather than restorative. This review provides an overview of emerging therapies and targets, and incorporates strategies for two different approaches to multiple sclerosis: prevention, through immune modulation; and repair, through neuroprotection and remyelination. Agents at all stages of development, from late-stage clinical trials of BG-12, teriflunomide, alemtuzumab, daclizumab and anti-CD20 agents, to novel approaches in preclinical testing, are discussed.

Myelin regeneration in multiple sclerosis: targeting endogenous stem cells

Regeneration of myelin sheaths (remyelination) after central nervous system demyelination is important to restore saltatory conduction and to prevent axonal loss. In multiple sclerosis, the insufficiency of remyelination leads to the irreversible degeneration of axons and correlated clinical decline. Therefore, a regenerative strategy to encourage remyelination may protect axons and improve symptoms in multiple sclerosis. We highlight recent studies on factors that influence endogenous remyelination and potential promising pharmacological targets that may be considered for enhancing central nervous system remyelination.

Regenerative medicine in multiple sclerosis: identifying pharmacological targets of adult neural stem cell differentiation

Progressive axonal loss from chronic demyelination in multiple sclerosis (MS) is the key contributor to clinical decline. Failure to regenerate myelin by adult oligodendrocyte precursor cells (OPCs), a widely distributed neural stem cell population in the adult brain, is one of the major causes of axonal degeneration. In order to develop successful therapies to protect the integrity of axons in MS, it is important to identify and understand the key molecular pathways involved in myelin regeneration (remyelination) by adult OPCs. This review highlights recent findings on the critical signaling pathways associated with OPC differentiation following CNS demyelination. We discuss the role of LINGO-1, Notch, Wnt, and retinoid X receptor (RXR) signaling, and how they might be useful pharmacological targets to overcoming remyelination failure in MS.

Enhancing remyelination in disease--can we wrap it up?

Demyelinating disorders of the central nervous system are among the most crippling neurological diseases affecting patients at various stages of life. In the most prominent demyelinating disease, multiple sclerosis, the regeneration of myelin sheaths often fails due to a default of the resident stem/precursor cells (oligodendrocyte precursor cells) to differentiate into mature myelin forming cells. Significant advances have been made in our understanding of the molecular and cellular processes involved in remyelination. Furthermore, important insight has been gained from studies investigating the interaction of stem/precursor cells with the distinct environment of demyelinating lesions. These suggest that successful regeneration depends on a signalling environment conducive to remyelination, which is provided in the context of acute inflammation. However, multiple sclerosis lesions also contain factors that inhibit the differentiation of oligodendrocyte precursor cells into myelinating oligodendrocytes. The pattern by which remyelination inducers and inhibitors are expressed in multiple sclerosis lesions may determine a window of opportunity during which oligodendrocyte precursor cells can successfully differentiate. As the first molecules aiming at promoting remyelination are about to enter clinical trials, this review critically evaluates recent advances in our understanding of the biology of oligodendrocyte precursor cells and of the stage-dependent molecular pathology of multiple sclerosis lesions relevant to the regeneration of myelin sheaths. We propose a model that may help to provide cues for how remyelination can be therapeutically enhanced in clinical disease.

Notch signaling: key role in intrauterine infection/inflammation, embryonic development, and white matter damage?

The mechanisms or pathophysiologies that lead to cerebral white matter damage during development are complex and not fully understood. It is postulated that exposure of the preterm brain to inflammatory cytokines during intrauterine infection/inflammation contributes to brain white matter damage, and this damage may affect the function and differentiation of progenitor oligodendrocyte cells under physiological conditions. The Notch pathway, an important signaling pathway controlling various cells' differentiation, functions in the timing of oligodendrocyte differentiation, and Notch signaling may contribute to white matter damage and may mediate neurogenesis in a pathophysiological phase. Recent studies have led to recognition of the role of the Notch pathway in neurogenesis in cerebral ischemic damage and in myelination and axonal damage of neurodegenerative diseases. Moreover, Notch plays a critical role in steering an immune response toward inflammation by regulating expression of various cytokines and proinflammatory cytokines resulting in the activation of Notch signaling. Thus, the Notch signaling pathway likely plays a key role in intrauterine infection/inflammation, brain development, and white matter damage, and future research directed toward understanding its role will be important. Insofar as Notch signaling could have an important effect on neurogenesis, mobilization of progenitor cells is one strategy for compensating for the neuronal losses seen in white matter damage after intrauterine infection/inflammation.

gamma-secretases: from cell biology to therapeutic strategies

Presenilins form the catalytic part of the gamma-secretases, protein complexes that are responsible for the intramembranous cleavage of transmembrane proteins. The presenilins are involved in several biological functions, but are best known for their role in the generation of the beta-amyloid (Abeta) peptide in Alzheimer's disease and are therefore thought to be important drug targets for this disorder. Mutations in the presenilin genes cause early-onset familial Alzheimer's disease, but mutation carriers have substantial phenotypic heterogeneity. Recent evidence implicating presenilin mutations in non-Alzheimer's dementias, including frontotemporal dementia and Lewy body dementia, warrants further investigation. An increased understanding of the diversity of the molecular cell biology of the gamma-secretase complex and the effects of clinical mutations in the presenilin genes might help pave the way for improved development of drugs that are designed to target gamma-secretase enzymatic activity in Alzheimer's disease and potentially in other neurological diseases.

Involvement of Notch1 inhibition in serum-stimulated glia and oligodendrocyte differentiation from human mesenchymal stem cells

The use of in vitro oligodendrocyte differentiation for transplantation of stem cells to treat demyelinating diseases is an important consideration. In this study, we investigated the effects of serum on glia and oligodendrocyte differentiation from human mesenchymal stem cells (KP-hMSCs). We found that serum deprivation resulted in a reversible downregulation of glial- and oligodendrocyte-specific markers. Serum stimulated expression of oligodendrocyte markers, such as galactocerebroside, as well as Notch1 and JAK1 transcripts. Inhibition of Notch1 activation by the Notch inhibitor, MG132, led to enhanced expression of a serum-stimulated oligodendrocyte marker. This marker was undetectable in serum-deprived KP-hMSCs treated with MG132, suggesting that inhibition of Notch1 function is additive to serum-stimulated oligodendrocyte differentiation. Furthermore, a dominant-negative mutant RBP-J protein also inhibited Notch1 function and led to upregulation of oligodendrocyte-specific markers. Our results demonstrate that serum-stimulated oligodendrocyte differentiation is enhanced by the inhibition of Notch1-associated functions.

Notch: a new player in MS mechanisms

Notch is a family of four transmembrane receptors (Notch1-4) that orchestrate differentiation of various cell types, tissues and organs. Recent studies have revealed that Notch, among other processes, regulates immune responses of peripheral T cells, controls oligodendrocyte maturation and myelination of axons and under inflammatory conditions affects activation of macrophages and microglia. Therefore, Notch signaling has been implicated in the differentiation and function of all cell types considered crucial for the development and clinical progression of multiple sclerosis (MS). Importantly, inflammatory/demyelinating lesions in MS and its animal model, autoimmune experimental encephalomyelitis (EAE), abundantly express Notch receptors, their ligands and downstream activation targets. In EAE, in vivo modulation of Notch signaling affects immune responses of myelin-reactive T cells, enhances tissue repair and reduces clinical severity of the disease. In this review, we present recent findings on how Notch signaling may affect function of both immune and glial cells, analyze data implicating the Notch pathway in MS and EAE, and discuss the therapeutic potential of manipulating Notch signaling in MS patients.

p57kip2 is dynamically regulated in experimental autoimmune encephalomyelitis and interferes with oligodendroglial maturation

The mechanisms preventing efficient remyelination in the adult mammalian central nervous system after demyelinating inflammatory diseases, such as multiple sclerosis, are largely unknown. Partial remyelination occurs in early disease stages, but repair capacity diminishes over time and with disease progression. We describe a potent candidate for the negative regulation of oligodendroglial differentiation that may underlie failure to remyelinate. The p57kip2 gene is dynamically regulated in the spinal cord during MOG-induced experimental autoimmune encephalomyelitis. Transient down-regulation indicated that it is a negative regulator of post-mitotic oligodendroglial differentiation. We then applied short hairpin RNA-mediated gene suppression to cultured oligodendroglial precursor cells and demonstrated that down-regulation of p57kip2 accelerates morphological maturation and promotes myelin expression. We also provide evidence that p57kip2 interacts with LIMK-1, implying that p57kip2 affects cytoskeletal dynamics during oligodendroglial maturation. These data suggest that sustained down-regulation of p57kip2 is important for oligodendroglial maturation and open perspectives for future therapeutic approaches to overcome the endogenous remyelination blockade in multiple sclerosis.

Notch1 signaling in FIZZ1 induction of myofibroblast differentiation

Notch1 is an evolutionarily conserved receptor that regulates cell fate, including such events as differentiation, proliferation, and apoptosis. Myofibroblast differentiation is a key feature of lung fibrosis. Found in inflammatory zone 1 (FIZZ1) has direct fibrogenic properties because of its ability to induce myofibroblast differentiation. However, the downstream signaling pathway that mediates FIZZ1 induction of myofibroblast differentiation remains unknown. The objective of this study was to investigate the involvement of Notch signaling in FIZZ1 induction of lung myofibroblast differentiation and thus explore the potential role of Notch1 in pulmonary fibrosis. The results showed that FIZZ1 increased the expression levels of activated intracellular domain of Notch1 (NIC), its ligand Jagged1, and its target gene Hes1, which were associated with elevated alpha-smooth muscle actin expression levels. Fibroblast alpha-smooth muscle actin expression is induced by the overexpression of NIC but is suppressed by the inhibition of NIC. Moreover, lung fibroblasts that were isolated from mice lacking the GDP-4-keto-6-deoxymannose3,5-epimerase-4-reductase enzyme (FX knockout) exhibited significantly reduced responsiveness to FIZZ1, which was reversed by fucose supplementation. In the absence of exogenous fucose, these FX-deficient cells exhibited defective fucosylation, which is required for Notch signaling. These knockout mice also showed impaired lung fibrosis. These findings suggest that Notch1 signaling in response to FIZZ1 may play a significant role in myofibroblast differentiation during lung fibrosis.

Disease-modifying agents for multiple sclerosis: recent advances and future prospects

Multiple sclerosis (MS) is a chronic autoimmune disease of the CNS. Currently, six medications are approved for immunmodulatory and immunosuppressive treatment of the relapsing disease course and secondary-progressive MS. In the first part of this review, the pathogenesis of MS and its current treatment options are discussed. During the last decade, our understanding of autoimmunity and the pathogenesis of MS has advanced substantially. This has led to the development of a number of compounds, several of which are currently undergoing clinical testing in phase II and III studies. While current treatment options are only available for parenteral administration, several oral compounds are now in clinical trials, including the immunosuppressive agents cladribine and laquinimod. A novel mode of action has been described for fingolimod, another orally available agent, which inhibits egress of activated lymphocytes from draining lymph nodes. Dimethylfumarate exhibits immunomodulatory as well as immunosuppressive activity when given orally. All of these compounds have successfully shown efficacy, at least in regards to the surrogate marker contrast-enhancing lesions on magnetic resonance imaging. Another class of agents that is highlighted in this review are biological agents, namely monoclonal antibodies (mAb) and recombinant fusion proteins. The humanized mAb daclizumab inhibits T-lymphocyte activation via blockade of the interleukin-2 receptor. Alemtuzumab and rituximab deplete leukocytes and B cells, respectively; the fusion protein atacicept inhibits specific B-cell growth factors resulting in reductions in B-cells and plasma cells. These compounds are currently being tested in phase II and III studies in patients with relapsing MS. The concept of neuro-protection and -regeneration has not advanced to a level where specific compounds have entered clinical testing. However, several agents approved for conditions other than MS are highlighted. Finally, with the advent of these highly potent novel therapies, rare, but potentially serious adverse effects have been noted, namely infections and malignancies. These are critically reviewed and put into perspective.