Semaphorin CD100 from Activated T Lymphocytes Induces Process Extension Collapse in Oligodendrocytes and Death of Immature Neural Cells

Astrocyte endfoot formation controls the termination of oligodendrocyte precursor cell perivascular migration during development

Oligodendrocyte precursor cells (OPCs) undergo an extensive and coordinated migration in the developing CNS, using the pre-formed scaffold of developed blood vessels as their physical substrate for migration. While OPC association with vasculature is critical for dispersal, equally important for permitting differentiation and proper myelination of target axons is their appropriate and timely detachment, but regulation of this process remains unclear. Here we demonstrate a correlation between the developmental formation of astrocytic endfeet on vessels and the termination of OPC perivascular migration. Ex vivo and in vivo live imaging shows that astrocyte endfeet physically displace OPCs from vasculature, and genetic abrogation of endfoot formation hinders both OPC detachment from vessels and subsequent differentiation. Astrocyte-derived semaphorins 3a and 6a act to repel OPCs from blood vessels at the cessation of their perivascular migration and, in so doing, permit subsequent OPC differentiation by insulating them from a maturation inhibitory endothelial niche.

Pepinemab antibody blockade of SEMA4D in early Huntington's disease: a randomized, placebo-controlled, phase 2 trial

SIGNAL is a multicenter, randomized, double-blind, placebo-controlled phase 2 study (no. NCT02481674) established to evaluate pepinemab, a semaphorin 4D (SEMA4D)-blocking antibody, for treatment of Huntington's disease (HD). The trial enrolled a total of 265 HD gene expansion carriers with either early manifest (EM, n = 179) or late prodromal (LP, n = 86) HD, randomized (1:1) to receive 18 monthly infusions of pepinemab (n = 91 EM, 41 LP) or placebo (n = 88 EM, 45 LP). Pepinemab was generally well tolerated, with a relatively low frequency of serious treatment-emergent adverse events of 5% with pepinemab compared to 9% with placebo, including both EM and LP participants. Coprimary efficacy outcome measures consisted of assessments within the EM cohort of (1) a two-item HD cognitive assessment family comprising one-touch stockings of Cambridge (OTS) and paced tapping (PTAP) and (2) clinical global impression of change (CGIC). The differences between pepinemab and placebo in mean change (95% confidence interval) from baseline at month 17 for OTS were -1.98 (-4.00, 0.05) (one-sided P = 0.028), and for PTAP 1.43 (-0.37, 3.23) (one-sided P = 0.06). Similarly, because a significant treatment effect was not observed for CGIC, the coprimary endpoint, the study did not meet its prespecified primary outcomes. Nevertheless, a number of other positive outcomes and post hoc subgroup analyses-including additional cognitive measures and volumetric magnetic resonance imaging and fluorodeoxyglucose-positron-emission tomography imaging assessments-provide rationale and direction for the design of a phase 3 study and encourage the continued development of pepinemab in patients diagnosed with EM HD.

Semaphorin 4D is upregulated in neurons of diseased brains and triggers astrocyte reactivity

BACKGROUND

The close interaction and interdependence of astrocytes and neurons allows for the possibility that astrocyte dysfunction contributes to and amplifies neurodegenerative pathology. Molecular pathways that trigger reactive astrocytes may represent important targets to preserve normal homeostatic maintenance and modify disease progression.

METHODS

Semaphorin 4D (SEMA4D) expression in the context of disease-associated neuropathology was assessed in postmortem brain sections of patients with Huntington's (HD) and Alzheimer's disease (AD), as well as in mouse models of HD (zQ175) and AD (CVN; APPSwDI/NOS2^-/-) by immunohistochemistry. Effects of SEMA4D antibody blockade were assessed in purified astrocyte cultures and in the CVN mouse AD model. CVN mice were treated weekly from 26 to 38 weeks of age; thereafter mice underwent cognitive assessment and brains were collected for histopathology.

RESULTS

We report here that SEMA4D is upregulated in neurons during progression of neurodegenerative diseases and is a trigger of reactive astrocytes. Evidence of reactive astrocytes in close proximity to neurons expressing SEMA4D is detected in brain sections of patients and mouse models of HD and AD. We further report that SEMA4D-blockade prevents characteristic loss of GABAergic synapses and restores spatial memory and learning in CVN mice, a disease model that appears to reproduce many features of AD-like pathology including neuroinflammation. In vitro mechanistic studies demonstrate that astrocytes express cognate receptors for SEMA4D and that ligand binding triggers morphological variations, and changes in expression of key membrane receptors and enzymes characteristic of reactive astrocytes. These changes include reductions in EAAT-2 glutamate transporter and glutamine synthetase, key enzymes in neurotransmitter recycling, as well as reduced GLUT-1 glucose and MCT-4 lactate transporters, that allow astrocytes to couple energy metabolism with synaptic activity. Antibody blockade of SEMA4D prevented these changes and reversed functional deficits in glucose uptake.

CONCLUSIONS

Collectively, these results suggest that SEMA4D blockade may ameliorate disease pathology by preserving normal astrocyte function and reducing the negative consequences of reactive astrogliosis.

Neuroinflammation in Huntington's Disease: A Starring Role for Astrocyte and Microglia

Huntington's disease (HD) is a neurodegenerative genetic disorder caused by a CAG repeat expansion in the huntingtin gene. HD causes motor, cognitive, and behavioral dysfunction. Since no existing treatment affects the course of this disease, new treatments are needed. Inflammation is frequently observed in HD patients before symptom onset. Neuroinflammation, characterized by the presence of reactive microglia, astrocytes and inflammatory factors within the brain, is also detected early. However, in comparison to other neurodegenerative diseases, the role of neuroinflammation in HD is much less known. Work has been dedicated to altered microglial and astrocytic functions in the context of HD, but less attention has been given to glial participation in neuroinflammation. This review describes evidence of inflammation in HD patients and animal models. It also discusses recent knowledge on neuroinflammation in HD, highlighting astrocyte and microglia involvement in the disease and considering anti-inflammatory therapeutic approaches.

PLXNB1 mutations in the etiology of idiopathic hypogonadotropic hypogonadism

Idiopathic hypogonadotropic hypogonadism (IHH) comprises a group of rare genetic disorders characterized by pubertal failure caused by gonadotropin-releasing hormone (GnRH) deficiency. Genetic factors involved in semaphorin/plexin signaling have been identified in patients with IHH. PlexinB1, a member of the plexin family receptors, serves as the receptor for semaphorin 4D (Sema4D). In mice, perturbations in Sema4D/PlexinB1 signaling leads to improper GnRH development, highlighting the importance of investigating PlexinB1 mutations in IHH families. In total, 336 IHH patients (normosmic IHH, n = 293 and Kallmann syndrome, n = 43) from 290 independent families were included in the present study. Six PLXNB1 rare sequence variants (p.N361S, p.V608A, p.R636C, p.V672A, p.R1031H, and p.C1318R) are described in eight normosmic IHH patients from seven independent families. These variants were examined using bioinformatic modeling and compared to mutants reported in PLXNA1. Based on these analyses, the variant p.R1031H was assayed for alterations in cell morphology, PlexinB1 expression, and migration using a GnRH cell line and Boyden chambers. Experiments showed reduced membrane expression and impaired migration in cells expressing this variant compared to the wild-type. Our results provide clinical, genetic, molecular/cellular, and modeling evidence to implicate variants in PLXNB1 in the etiology of IHH.

Semaphorin-Plexin Signaling: From Axonal Guidance to a New X-Linked Intellectual Disability Syndrome

BACKGROUND

Semaphorins and plexins are ligands and cell surface receptors that regulate multiple neurodevelopmental processes such as axonal growth and guidance. PLXNA3 is a plexin gene located on the X chromosome that encodes the most widely expressed plexin receptor in fetal brain, plexin-A3. Plexin-A3 knockout mice demonstrate its role in semaphorin signaling in vivo. The clinical manifestations of semaphorin/plexin neurodevelopmental disorders have been less widely explored. This study describes the neurological and neurodevelopmental phenotypes of boys with maternally inherited hemizygous PLXNA3 variants.

METHODS

Data-sharing through GeneDx and GeneMatcher allowed identification of individuals with autism or intellectual disabilities (autism/ID) and hemizygous PLXNA3 variants in collaboration with their physicians and genetic counselors, who completed questionnaires about their patients. In silico analyses predicted pathogenicity for each PLXNA3 variant.

RESULTS

We assessed 14 boys (mean age, 10.7 [range 2 to 25] years) with maternally inherited hemizygous PLXNA3 variants and autism/ID ranging from mild to severe. Other findings included fine motor dyspraxia (92%), attention-deficit/hyperactivity traits, and aggressive behaviors (63%). Six patients (43%) had seizures. Thirteen boys (93%) with PLXNA3 variants showed novel or very low allele frequencies and probable damaging/disease-causing pathogenicity in one or more predictors. We found a genotype-phenotype correlation between PLXNA3 cytoplasmic domain variants (exons 22 to 32) and more severe neurodevelopmental disorder phenotypes (P < 0.05).

CONCLUSIONS

We report 14 boys with maternally inherited, hemizygous PLXNA3 variants and a range of neurodevelopmental disorders suggesting a novel X-linked intellectual disability syndrome. Greater understanding of PLXNA3 variant pathogenicity in humans will require additional clinical, computational, and experimental validation.

[Relapsing-remitting multiple sclerosis: clinical and immunological aspects of the pathology on the example of molecules Sema4D and CD72]

OBJECTIVE

To study the expression of Sema4D (CD100), receptor CD72 and a role of Sema4D-CD72-dependent signal in the control of the functions of immunocompetent cells in relapsing-remitting multiple sclerosis (RRMS).

MATERIAL AND METHODS

We studied 76 patients, including 52 with RRMS (41 in remission and 11 in exacerbation), 35 women (67.3%) and 17 men (32.7%) aged 18-55 years, who did not receive disease-modifying drugs, and 24 healthy donors. A controlled clinical and immunological examination of patients with RRMS was carried out proving the involvement of the Sema4D molecule and its CD72 receptor in pathological reactions in this autoimmune disease.

RESULTS AND CONCLUSION

The use of SemaD as a target in the treatment of RRMS is scientifically substantiated. In case of a positive decision on the use of anti-Sema4D drugs, it will be necessary to take into account the effects of semaphorin not only in the central nervous system, but also in the immune system of patients with RRMS.

Remyelination therapies for multiple sclerosis: optimizing translation from animal models into clinical trials

Introduction: Multiple sclerosis (MS) is the most common inflammatory disease of the central nervous system (CNS). Demyelination, the main pathology in MS, contributes to clinical symptoms and long-term neurological deficits if left untreated. Remyelination, the natural repair of damaged myelin by cells of the oligodendrocyte lineage, occurs in MS, but eventually fails in most patients as they age. Encouraging timely remyelination can restore axon conduction and minimize deficits.Areas covered: We discuss and correlate human MS pathology with animal models, propose methods to deplete resident oligodendrocyte progenitor cells (OPCs) to determine whether mature oligodendrocytes support remyelination, and review remyelinating agents, mechanisms of action, and available clinical trial data.Expert opinion: The heterogeneity of human MS may limit successful translation of many candidate remyelinating agents; some patients lack the biological targets necessary to leverage current approaches. Development of therapeutics for remyelination has concentrated almost exclusively on mobilization of innate OPCs. However, mature oligodendrocytes appear an important contributor to remyelination in humans. Limiting the contribution of OPC mediated repair in models of MS would allow the evaluation of remyelination-promoting agents on mature oligodendrocytes. Among remyelinating reagents reviewed, only rHIgM22 targets both OPCs and mature oligodendrocytes.

Semaphorins in Adult Nervous System Plasticity and Disease

Semaphorins, originally discovered as guidance cues for developing axons, are involved in many processes that shape the nervous system during development, from neuronal proliferation and migration to neuritogenesis and synapse formation. Interestingly, the expression of many Semaphorins persists after development. For instance, Semaphorin 3A is a component of perineuronal nets, the extracellular matrix structures enwrapping certain types of neurons in the adult CNS, which contribute to the closure of the critical period for plasticity. Semaphorin 3G and 4C play a crucial role in the control of adult hippocampal connectivity and memory processes, and Semaphorin 5A and 7A regulate adult neurogenesis. This evidence points to a role of Semaphorins in the regulation of adult neuronal plasticity. In this review, we address the distribution of Semaphorins in the adult nervous system and we discuss their function in physiological and pathological processes.

Myelin Repair: From Animal Models to Humans

It is widely thought that brain repair does not occur, but myelin regeneration provides clear evidence to the contrary. Spontaneous remyelination may occur after injury or in multiple sclerosis (MS). However, the efficiency of remyelination varies considerably between MS patients and between the lesions of each patient. Myelin repair is essential for optimal functional recovery, so a profound understanding of the cells and mechanisms involved in this process is required for the development of new therapeutic strategies. In this review, we describe how animal models and modern cell tracing and imaging methods have helped to identify the cell types involved in myelin regeneration. In addition to the oligodendrocyte progenitor cells identified in the 1990s as the principal source of remyelinating cells in the central nervous system (CNS), other cell populations, including subventricular zone-derived neural progenitors, Schwann cells, and even spared mature oligodendrocytes, have more recently emerged as potential contributors to CNS remyelination. We will also highlight the conditions known to limit endogenous repair, such as aging, chronic inflammation, and the production of extracellular matrix proteins, and the role of astrocytes and microglia in these processes. Finally, we will present the discrepancies between observations in humans and in rodents, discussing the relationship of findings in experimental models to myelin repair in humans. These considerations are particularly important from a therapeutic standpoint.

The role of immune semaphorins in the pathogenesis of multiple sclerosis: Potential therapeutic targets

The immune and nervous systems possess a highly intricate network of synaptic connections, shared messenger molecules, and exquisite communication ways, allowing intercellular signal transduction. The semaphorins (Semas) were initially identified as axonal guidance molecules in the development of the nervous system but later were found to be implicated also in regulating the immune system, known in this case as the "immune Semas" or "immunoregulatory Semas". Increasingly, these molecules are involved in multiple aspects of both physiological and pathological immune responses and were recently indicated to take part in various immunological disorders, encompassing allergy, cancer, and autoimmunity. Semas transduce signals by connecting to their cognate receptors, namely, plexins and neuropilins. Some of them, like Sema-3F, have been found to function as the inducer of the remyelination process whereas some others, like Sema-3A and Sema-4D, act to inhibit this process, either directly or indirectly. Besides, Sema-4A is crucial to the differentiation of T helper type 1 (Th1) and Th17 cells that are potentially involved in the pathogenesis of multiple sclerosis (MS), an autoimmune disease of the central nervous system. This review aims to reveal the role of immune Semas in the pathogenesis of MS and its animal model, experimental autoimmune encephalomyelitis, focusing on the therapeutic usages of these molecules to treat this neurodegenerative disease.

Emerging myelin repair agents in preclinical and early clinical development for the treatment of multiple sclerosis

INTRODUCTION

Remyelination is a highly effective regenerative process that can restore axon function, prevent axonal loss, and reverse clinical deficits after demyelination. Hence, the promotion of remyelination is a logical goal in patients with multiple sclerosis (MS) in which remyelination is often insufficient. However, despite great progress regarding the development of immunomodulatory therapies for MS and an abundance of promising evidence from preclinical experiments so far, no therapy has convincingly demonstrated clinically significant remyelination properties. Therefore, enhancing myelin repair is an urgent and unmet need in MS.

AREAS COVERED

We searched clinicaltrials.gov and pubmed.ncbi.nlm.nih.gov and focused on therapeutic agents in development from the preclinical stage to clinical phase II. We selected agents for which data are available from in vitro experiments and at least one toxic demyelination animal model that reached at least phase I in clinical development in MS patients.

EXPERT OPINION

The evidence to promote remyelination is very promising for several agents, some of which possess anti-muscarinergic properties. Since remyelination is a complex process that involves various coordinated steps, a combination of different therapeutic approaches addressing different aspects of this regenerative mechanism may be reasonable. Furthermore, suitable surrogate markers of remyelination are necessary for proof-of-concept clinical trials.

[Relapsing-remitting multiple sclerosis: clinical and immunological aspects of the pathology on the example Sema4D and CD72]

AIM

To explore the expression of Sema4D, CD72 receptor and a role of Sema4D-CD72 signal in the control of immunocompetent cell function in remitting-relapsing multiple sclerosis (RRMS).

MATERIAL AND METHODS

Fifty-two patients with RRMS diagnosis according to 2010 revised McDonald's criteria were studied. The control group included 24 healthy people. A flow cytometry method was used to measure the expression of semaphorin Sema4D by T-lymphocytes of peripheral blood, expression of CD72 receptor by B-lymphocytes, percentage of cells containing pro- and anti-inflammatory cytokines. The level of soluble Sema4D (sSema4D) was evaluated by ELISA.

RESULTS

The level of Sema4D expression on T-lymphocytes (Mean Fluorescence Intensity - MFI) prevailed in cell subpopulations in patients with RRMS compared with the control group. Characteristics of membrane and sSema4D correlate with clinical presentations of the autoimmune disease. An increase in sSema4D level during cell cultivation was identified in RRMS patients. The results show the involvement of Sema4D in the hyperactivation of B-cell-mediated immunity through CD72 receptor and induction of proinflammatory cytokine synthesis.

CONCLUSION

RRMS is associated with elevated expression of Sema4D in the immune system. Membrane and sSema4D involved in the pathological process in RRMS. The authors suggest several mechanisms of the involvement of semaphorin and its receptor in the pathogenesis of RRMS: the direct damage of nervous tissues by sSema4D penetrated through the blood brain barrier disrupted in RRMS or by membrane Sema4D due to the infiltration of the central nervous system by T-lymphocytes and hyperactivation of B-cell-mediated immunity.

MMP2/MMP9-mediated CD100 shedding is crucial for inducing intrahepatic anti-HBV CD8 T cell responses and HBV clearance

BACKGROUND & AIMS

CD100 is constitutively expressed on T cells and can be cleaved from the cell surface by matrix metalloproteases (MMPs) to become soluble CD100 (sCD100). Both membrane-bound CD100 (mCD100) and sCD100 have important immune regulatory functions that promote immune cell activation and responses. This study investigated the expression and role of mCD100 and sCD100 in regulating antiviral immune responses during HBV infection.

METHODS

mCD100 expression on T cells, sCD100 levels in the serum, and MMP expression in the liver and serum were analysed in patients with chronic HBV (CHB) and in HBV-replicating mice. The ability of sCD100 to mediate antigen-presenting cell maturation, HBV-specific T cell activation, and HBV clearance were analysed in HBV-replicating mice and patients with CHB.

RESULTS

Patients with CHB had higher mCD100 expression on T cells and lower serum sCD100 levels compared with healthy controls. Therapeutic sCD100 treatment resulted in the activation of DCs and liver sinusoidal endothelial cells, enhanced HBV-specific CD8 T cell responses, and accelerated HBV clearance, whereas blockade of its receptor CD72 attenuated the intrahepatic anti-HBV CD8 T cell response. Together with MMP9, MMP2 mediated mCD100 shedding from the T cell surface. Patients with CHB had significantly lower serum MMP2 levels, which positively correlated with serum sCD100 levels, compared with healthy controls. Inhibition of MMP2/9 activity resulted in an attenuated anti-HBV T cell response and delayed HBV clearance in mice.

CONCLUSIONS

MMP2/9-mediated sCD100 release has an important role in regulating intrahepatic anti-HBV CD8 T cell responses, thus mediating subsequent viral clearance during HBV infection.

LAY SUMMARY

Chronic hepatitis B virus (HBV) infection is a major public health problem worldwide. The clearance of HBV relies largely on an effective T cell immune response, which usually becomes dysregulated in chronic HBV infection. Our study provides a new mechanism to elucidate HBV persistence and a new target for developing immunotherapy strategies in patients chronically infected with HBV.

Sema4D/PlexinB1 promotes endothelial differentiation of dental pulp stem cells via activation of AKT and ERK1/2 signaling

Inducing of dental pulp stem cells (DPSCs) into endothelial cells (ECs) to prevascularize pulp tissue constructs may offer a novel and viable approach for enhancing pulp regeneration. However, there are numerous challenges in current methods for the acquisition of sufficient translational ECs. It was known that Sema4D/PlexinB1 signaling exerts profound effects on enhancing vascular endothelial growth factor (VEGF) secretion and angiogenesis. Whether Sema4D/PlexinB1 could regulate endothelial differentiation of DPSCs is not yet investigated. In this study, when DPSCs were treated with Sema4D (2 μg/mL), ECs-specific (VEGFR1, VEGFR2, CD31, and vWF), and angiogenic genes and proteins were significantly upregulated. The induced ECs exhibited similar endothelial vessel formation ability to that of human umbilical vein endothelial cells (HUVECs). Furthermore, phosphorylation of AKT increased dramatically within 5 minutes (from 0.93 to 21.8), while p-ERK1/2 was moderately elevated (from 0.94 to 2.65). In summary, our results demonstrated that Sema4D/PlexinB1 signaling induces endothelial differentiation of DPSCs. The interactions of Sema4D, VEGF, ANGPTL4, ANG1, and HIF-1α may play a crucial role in mediating the differentiation process.

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.

Therapeutic approaches to Huntington disease: from the bench to the clinic

The 25 years since the identification of the gene responsible for Huntington disease (HD) have stood witness to profound discoveries about the nature of the disease and its pathogenesis. Despite this progress, however, the development of disease-modifying therapies has thus far been slow. Preclinical validation of the therapeutic potential of disrupted pathways in HD has led to the advancement of pharmacological agents, both novel and repurposed, for clinical evaluation. The most promising therapeutic approaches include huntingtin (HTT) lowering and modification as well as modulation of neuroinflammation and synaptic transmission. With clinical trials for many of these approaches imminent or currently ongoing, the coming years are promising not only for HD but also for more prevalent neurodegenerative disorders, such as Alzheimer and Parkinson disease, in which many of these pathways have been similarly implicated.

Effects of CD100 promote wound healing in diabetic mice

Diabetes is a condition that causes delayed wound healing and results in chronic wounds. CD100 has been reported to promote and induce potent and obvious angiogenesis both in vivo and in vitro studies, the absence of which are a main cause of the diabetic chronic wound. In the present study, we investigated the effects of application of soluble CD100 on wound healing in diabetic mice. Four 5-mm full-thickness dermal wounds were made on each male db/db mouse. 12 mice from CD100 group were subcutaneously injected with 250 ng of CD100 (50 µl) per wound, in addition, 12 mice were injected with the same volume phosphate-balanced solution as the control. The animals were treated every other day until the wounds healed completely. Images were obtained to calculate the area ratio of the original area. HE and Masson's trichrome staining were used for histological examination. Collagen remodeling, angiogenesis and wound bed inflammation were evaluated by immunohistochemical staining and western blot. We demonstrated that CD100 had distinct functions during the wound healing process. Histological and western blotting analysis showed a more organized epithelium and dermis, more collagen fibers, higher angiogenesis and lower inflammation in the CD100 group than in the PBS group. These findings suggest that CD100 may accelerate wound healing in diabetic mice by promoting angiogenesis in the wound and by reducing the inflammatory response.

Recent achievements in stem cell-mediated myelin repair

PURPOSE OF REVIEW

Following the establishment of a number of successful immunomodulatory treatments for multiple sclerosis, current research focuses on the repair of existing damage.

RECENT FINDINGS

Promotion of regeneration is particularly important for demyelinated areas with degenerated or functionally impaired axons of the central nervous system's white and gray matter. As the protection and generation of new oligodendrocytes is a key to the re-establishment of functional connections, adult oligodendrogenesis and myelin reconstitution processes are of primary interest. Moreover, understanding, supporting and promoting endogenous repair activities such as mediated by resident oligodendroglial precursor or adult neural stem cells are currently thought to be a promising approach toward the development of novel regenerative therapies.

SUMMARY

This review summarizes recent developments and findings related to pharmacological myelin repair as well as to the modulation/application of stem cells with the aim to restore defective myelin sheaths.

Determinants of Axon Growth, Plasticity, and Regeneration in the Context of Spinal Cord Injury

The mechanisms that underlie recovery after injury of the central nervous system have rarely been definitively established. Axon regrowth remains the major prerequisite for plasticity, regeneration, circuit formation, and eventually functional recovery. The attributed functional relevance of axon regrowth, however, will depend on several subsequent conditional neurobiological modifications, including myelination and synapse formation, but also pruning of aberrant connectivity. Despite the ability to revamp axon outgrowth by altering an increasing number of extracellular and intracellular targets, disentangling which axons are responsible for the recovery of function from those that are functionally silent, or even contributing to aberrant functions, represents a pertinent void in our understanding, challenging the intuitive translational link between anatomical and functional regeneration. Anatomic hallmarks of regeneration are not static and are largely activity dependent. Herein, we survey mechanisms leading to the formation of dystrophic growth cone at the injured axonal tip, the subsequent axonal dieback, and the molecular determinants of axon growth, plasticity, and regeneration in the context of spinal cord injury.

Semaphorin 3A is a retrograde cell death signal in developing sympathetic neurons

During development of the peripheral nervous system, excess neurons are generated, most of which will be lost by programmed cell death due to a limited supply of neurotrophic factors from their targets. Other environmental factors, such as 'competition factors' produced by neurons themselves, and axon guidance molecules have also been implicated in developmental cell death. Semaphorin 3A (Sema3A), in addition to its function as a chemorepulsive guidance cue, can also induce death of sensory neurons in vitro The extent to which Sema3A regulates developmental cell death in vivo, however, is debated. We show that in compartmentalized cultures of rat sympathetic neurons, a Sema3A-initiated apoptosis signal is retrogradely transported from axon terminals to cell bodies to induce cell death. Sema3A-mediated apoptosis utilizes the extrinsic pathway and requires both neuropilin 1 and plexin A3. Sema3A is not retrogradely transported in older, survival factor-independent sympathetic neurons, and is much less effective at inducing apoptosis in these neurons. Importantly, deletion of either neuropilin 1 or plexin A3 significantly reduces developmental cell death in the superior cervical ganglia. Taken together, a Sema3A-initiated apoptotic signaling complex regulates the apoptosis of sympathetic neurons during the period of naturally occurring cell death.

Effect of zileuton on osteoporotic bone and its healing, expression of bone, and brain genes in rats

Estrogen deficiency and aging are associated with osteoporosis, impaired bone healing, and lower cognitive performance. Close functional and physical connections occur between bone and the central nervous system. An anti-inflammatory drug, zileuton (which is an inhibitor of arachidonate 5-lipoxygenase), is known to have a positive effect on bone tissue repair and brain ischemia. We studied the effect of zileuton on osteopenic bone and its healing and on the genes considered to be crucial for the cross talks between bone and brain. Three-month-old Sprague-Dawley rats were ovariectomized or left untreated. After 8 wk, bilateral metaphyseal tibia osteotomy with plate osteosynthesis was performed in all rats. Ovariectomized rats were fed with food containing zileuton (1, 10, or 100 mg/kg body wt) for 5 wk. In tibiae, bone volume, callus and cortical volume, and gene expression of osteocalcin and alkaline phosphatase were enhanced by zileuton (10 or 100 mg); biomechanical properties and bone density were not changed. In femur, zileuton enlarged cortical volume distal and trabecular volume proximal, decreasing their density. The expression level of brain Sema3a, known to regulate bone mass positively, was downregulated after ovariectomy. In contrast, bone Sema4d, a negative regulator of bone mass, was upregulated in the tibia callus after ovariectomy, whereas zileuton treatment (10 or 100 mg) resulted in reverse effects. Here, we describe for the first time the expression of Rbbp4 mRNA and its increase in tibia after ovariectomy. Zileuton caused downregulation of Rbbp4 in the hippocampus and had an effect on bone healing, changed the expression of genes involved in cross talk between bones and brain, and may be a potent drug for further examination in estrogen deficiency-related dysfunction(s). NEW & NOTEWORTHY Zileuton, a 5-lipoxygenase inhibitor, increased bone volume, callus and cortical volume in osteotomized tibia, and trabecular and cortical volume in femur. Although the expression of Sema3a (positively regulating bone mass) in brain was downregulated and Sema4d (negatively regulating bone mass) was upregulated in tibia callus after ovariectomy, zileuton could counteract these effects. Rbbp4 (involved in age-related memory loss) was increased in tibia callus after ovariectomy.

Remyelination therapies: a new direction and challenge in multiple sclerosis

Multiple sclerosis is characterized by inflammatory activity that results in destruction of the myelin sheaths that enwrap axons. The currently available medications for multiple sclerosis are predominantly immune-modulating and do not directly promote repair. White matter regeneration, or remyelination, is a new and exciting potential approach to treating multiple sclerosis, as remyelination repairs the damaged regions of the central nervous system. A wealth of new strategies in animal models that promote remyelination, including the repopulation of oligodendrocytes that produce myelin, has led to several clinical trials to test new reparative therapies. In this Review, we highlight the biology of, and obstacles to, remyelination. We address new strategies to improve remyelination in preclinical models, highlight the therapies that are currently undergoing clinical trials and discuss the challenges of objectively measuring remyelination in trials of repair in multiple sclerosis.

Safety/tolerability of the anti-semaphorin 4D Antibody VX15/2503 in a randomized phase 1 trial

Objective:

To evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of VX15/2503 in a randomized, single-dose, dose-escalation, double-blind, placebo-controlled study enrolling adult patients with MS.

Methods:

Single IV doses of VX15/2503 or placebo were administered. Ten patients each were randomized (4:1 randomization ratio) into 5 ascending dose cohorts of 1, 3, 6, 10, or 20 mg/kg. Safety, immunogenicity, PK/PD, MRI, ECG, and lymphocyte subset levels were evaluated. A Dose Escalation Safety Committee (DESC) approved each dose escalation.

Results:

VX15/2503 was well tolerated, and all participants completed the study. Antibody treatment–related adverse events were primarily grade 1 or 2 and included urinary tract infection (12.5%) and muscle weakness, contusion, and insomnia (each 7.5%). No dose-limiting toxicities were observed, and no maximum tolerated dose was determined. One subject (20 mg/kg) experienced disease relapse 3 months before study entry and exhibited a grade 3 (nonserious) increase in brain lesions by day 29, possibly related to VX15/2503. Twenty-nine patients exhibited human anti-humanized antibody responses; 5 with titer ≥100. No anti-VX15/2503 antibody responses were fully neutralizing. VX15/2503 C_max, area under the time-concentration curve, and mean half-life increased with dose level; at 20 mg/kg, the T_1/2 was 20 days. Cellular SEMA4D saturation occurred at serum antibody concentrations ≤0.3 μg/mL, resulting in decreased cSEMA4D expression. At 20 mg/kg, cSEMA4D saturation persisted for ≥155 days. Total sSEMA4D levels increased with dose level and declined with antibody clearance.

Conclusions:

These results support the continued investigation of VX15/2503 in neurodegenerative diseases.

ClinicalTrials.gov identifier:

NCT01764737.

Classification of evidence:

This study provides Class III evidence that anti-semaphorin 4D antibody VX15/2503 at various doses was safe and well tolerated vs placebo, although an increase in treatment-emergent adverse events in the treatment group could not be excluded (risk difference −0.7%, 95% CI −28.0% to 32.7%).

Recruitment of endogenous CNS stem cells for regeneration in demyelinating disease

Demyelinating diseases, such as multiple sclerosis (MS), are responsible for a significant portion of the neurological disability burden worldwide, especially in young adults. Demyelination can be followed by a spontaneous regenerative process called remyelination, in which new myelin sheaths are restored to denuded axons. However, in chronic demyelinating disease such as MS, this process becomes progressively less efficient. This chapter reviews the biology of remyelination and the rationale and strategies by which it can be enhanced therapeutically in acquired demyelinating disease.

Oligodendrocyte regeneration: Its significance in myelin replacement and neuroprotection in multiple sclerosis

Oligodendrocytes readily regenerate and replace myelin membranes around axons in the adult mammalian central nervous system (CNS) following injury. The ability to regenerate oligodendrocytes depends on the availability of neural progenitors called oligodendrocyte precursor cells (OPCs) in the adult CNS that respond to injury-associated signals to induce OPC expansion followed by oligodendrocyte differentiation, axonal contact and myelin regeneration (remyelination). Remyelination ensures the maintenance of axonal conduction, and the oligodendrocytes themselves provide metabolic factors that are necessary to maintain neuronal integrity. Recent advances in oligodendrocyte regeneration research are beginning to shed light on critical intrinsic signals, as well as extrinsic, environmental factors that regulate the distinct steps of oligodendrocyte lineage progression and myelin replacement under CNS injury. These studies may offer novel pharmacological targets for regenerative medicine in inflammatory demyelinating disorders in the CNS such as multiple sclerosis. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Extracellular cues influencing oligodendrocyte differentiation and (re)myelination

There is an increasing number of neurologic disorders found to be associated with loss and/or dysfunction of the CNS myelin sheath, ranging from the classic demyelinating disease, multiple sclerosis, through CNS injury, to neuropsychiatric diseases. The disabling burden of these diseases has sparked a growing interest in gaining a better understanding of the molecular mechanisms regulating the differentiation of the myelinating cells of the CNS, oligodendrocytes (OLGs), and the process of (re)myelination. In this context, the importance of the extracellular milieu is becoming increasingly recognized. Under pathological conditions, changes in inhibitory as well as permissive/promotional cues are thought to lead to an overall extracellular environment that is obstructive for the regeneration of the myelin sheath. Given the general view that remyelination is, even though limited in human, a natural response to demyelination, targeting pathologically 'dysregulated' extracellular cues and their downstream pathways is regarded as a promising approach toward the enhancement of remyelination by endogenous (or if necessary transplanted) OLG progenitor cells. In this review, we will introduce the extracellular cues that have been implicated in the modulation of (re)myelination. These cues can be soluble, part of the extracellular matrix (ECM) or mediators of cell-cell interactions. Their inhibitory and permissive/promotional roles with regard to remyelination as well as their potential for therapeutic intervention will be discussed.

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.

Tax and Semaphorin 4D Released from Lymphocytes Infected with Human Lymphotropic Virus Type 1 and Their Effect on Neurite Growth

Human lymphotropic virus type 1 (HTLV-1) is a retrovirus causing HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a neurodegenerative central nervous system (CNS) axonopathy. This virus mainly infects CD4(+) T lymphocytes without evidence of neuronal infection. Viral Tax, secreted from infected lymphocytes infiltrated in the CNS, is proposed to alter intracellular pathways related to axonal cytoskeleton dynamics, producing neurological damage. Previous reports showed a higher proteolytic release of soluble Semaphorin 4D (sSEMA-4D) from CD4(+) T cells infected with HTLV-1. Soluble SEMA-4D binds to its receptor Plexin-B1, activating axonal growth collapse pathways in the CNS. In the current study, an increase was found in both SEMA-4D in CD4(+) T cells and sSEMA-4D released to the culture medium of peripheral blood mononuclear cells (PBMCs) from HAM/TSP patients compared to asymptomatic carriers and healthy donors. After a 16-h culture, infected PBMCs showed significantly higher levels of CRMP-2 phosphorylated at Ser(522). The effect was blocked either with anti-Tax or anti-SEMA-4D antibodies. The interaction of Tax and sSEMA-4D was found in secreted medium of PBMCs in patients, which might be associated with a leading role of Tax with the SEMA-4D-Plexin-B1 signaling pathway. In infected PBMCs, the migratory response after transwell assay showed that sSEMA-4D responding cells were CD4(+)Tax(+) T cells with a high CRMP-2 pSer(522) content. In the present study, the participation of Tax-sSEMA-4D in the reduction in neurite growth in PC12 cells produced by MT2 (HTLV-1-infected cell line) culture medium was observed. These results lead to the participation of plexins in the reported effects of infected lymphocytes on neuronal cells.

Soluble SEMA4D/CD100: A novel immunoregulator in infectious and inflammatory diseases

SEMA4D/CD100 is a homodimeric protein belonging to the semaphorin family of axonal guidance proteins. Semaphorin family members have received increased attention lately due to their diverse functions in the immune system. SEMA4D was the first semaphorin described to have immune functions and serves important roles in T cell priming, antibody production, and cell-to-cell adhesion. Proteolytic cleavage of SEMA4D from the cell surface gives rise to a soluble fragment of SEMA4D (sSEMA4D). Similar to the transmembranal form, sSEMA4D is thought to have immunoregulatory properties. While the exact mechanisms responsible for SEMA4D shedding remain to be elucidated, emerging data have revealed associations between elevated systemic sSEMA4D levels and severity of infectious and inflammatory diseases. This review summarizes the literature concerning sSEMA4D and discusses its potential as a novel prognostic immune-biomarker and potential target for immunotherapy.

Saturation monitoring of VX15/2503, a novel semaphorin 4D-specific antibody, in clinical trials

Background

Receptor occupancy, or saturation, assays are often utilized in preclinical and clinical development programs to evaluate the binding of a biologic to a cellular target. These assays provide critical information regarding the dose of drug required to “saturate” the target as well as important pharmacodymamic (PD) data. A flow cytometric method was developed to measure the degree of Semaphorin 4D (SEMA4D; CD100) saturation by VX15/2303, an investigational monoclonal antibody specific for SEMA4D.

Methods

The assay detects VX15/2503, a human IgG₄ specific for SEMA4D, with an IgG₄‐specific monoclonal antibody.

Results

Data generated allowed assessment of two related SEMA4D‐specific pharmacodynamic (PD) markers: (1) The measurement of cellular SEMA4D (cSEMA4D) saturation by VX15/2503, and (2) the cell membrane expression levels of cSEMA4D.

Conclusions

This assay specifically and reproducibly measured cSEMA4D saturation and expression levels. Evaluation of the SEMA4D‐specific PD markers were critical in determining the clinical saturation threshold of cSEMA4D by VX15/2503. © 2015 he Authors Cytometry Part B: Clinical Cytometry Published by Wiley Periodicals, Inc.

Generation and preclinical characterization of an antibody specific for SEMA4D

Semaphorin 4D (SEMA4D or CD100) is a member of the semaphorin family of proteins and an important mediator of the movement and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. Blocking the binding of SEMA4D to its receptors can result in physiologic changes that may have implications in cancer, autoimmune, and neurological disease. To study the effects of blocking SEMA4D, we generated, in SEMA4D-deficient mice, a panel of SEMA4D-specific hybridomas that react with murine, primate, and human SEMA4D. Utilizing the complementarity-determining regions from one of these hybridomas (mAb 67-2), we generated VX15/2503, a humanized IgG4 monoclonal antibody that is currently in clinical development for the potential treatment of various malignancies and neurodegenerative disorders, including multiple sclerosis and Huntington's disease. This work describes the generation and characterization of VX15/2503, including in vitro functional testing, epitope mapping, and an in vivo demonstration of efficacy in an animal model of rheumatoid arthritis.

[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.

Semaphorin4A Is Cytotoxic to Oligodendrocytes and Is Elevated in Microglia and Multiple Sclerosis

We have previously established that T cell immunoglobulin and mucin domain containing 2 (Tim2) is an H-ferritin receptor on oligodendrocytes (OLs). Tim2 also binds Semaphorin4A (Sema4A). Sema4A is expressed by lymphocytes, and its role in immune activation is known; however, its relationship to diseases that are known to have myelin damage has not been studied. In this study, we demonstrate that Sema4A is cytotoxic to OLs in culture: an effect accompanied by process collapse, membrane blebbing, and phosphatidylserine inversion. We further demonstrate that Sema4A preferentially binds to primary OLs but not astrocytes: an observation consistent with the lack of expression of Tim2 on astrocytes. We found that Sema4A protein levels are increased within multiple sclerosis plaques compared with normal-appearing white matter and that Sema4A induces lactate dehydrogenase release in a human OL cell line. The chief cellular source of Sema4A within the multiple sclerosis plaques appears to be infiltrating lymphocytes and microglia. Macrophages are known to express Sema4A, so we interrogated microglia as a potential source of Sema4A in the brain. We found that rat primary microglia express Sema4A which increased after lipopolysaccharide activation. Because activated microglia accumulate iron, we determined whether iron status influenced Sema4A and found that iron chelation decreased Sema4A and iron loading increased Sema4A in activated microglia. Overall, our data implicate Sema4A in the destruction of OLs and reveal that its expression is sensitive to iron levels.

Nonclinical Safety Evaluation of VX15/2503, a Humanized IgG4 Anti-SEMA4D Antibody

The humanized IgG4 monoclonal antibody VX15/2503 bound with 1 to 5 nmol/L affinity to purified recombinant semaphorin 4D (SEMA4D; CD100) produced using murine, rat, cynomolgus macaque, and human sequences. The affinity for native SEMA4D expressed on macaque T lymphocytes was approximately 0.6 nmol/L. Tissues from rats and cynomolgus macaques demonstrated specific staining only with resident lymphocytes. Single-dose and one-month toxicology/PK studies used VX15/2503 dose levels of 0 to 100 mg/kg. No toxicity was observed with either species in these studies, thus the no observed adverse effect level (NOAEL) was 100 mg/kg. Cmax, exposure, and half-life values were similar for both rats and macaques. The NOAEL in a primate maximum feasible dose study was 200 mg/kg. Saturation of T-cell-associated SEMA4D occurred following administration of single doses of 0.1 mg/kg and above; five weekly injections of VX15/2503 at a dose level of 100 mg/kg produced saturation lasting for more than 120 and 130 days, respectively, for rats and primates. Macaques administered five weekly doses of VX15/2503 showed dose-dependent reductions of 2- to 3-fold in T-cell SEMA4D (cSEMA4D) expression levels compared with controls. Reduced cSEMA4D expression levels continued until serum antibody concentrations were 2 to 5 μg/mL, and thereafter normal cSEMA4D levels were restored. On the basis of these data, a phase I clinical study of the safety and tolerability of VX15/2503 was conducted, enrolling adult patients with advanced solid tumor diseases; a single-dose, dose escalation, phase I safety study was also initiated with subjects with multiple sclerosis.

Anti-semaphorin 4D immunotherapy ameliorates neuropathology and some cognitive impairment in the YAC128 mouse model of Huntington disease

Huntington disease (HD) is an inherited, fatal neurodegenerative disease with no disease-modifying therapy currently available. In addition to characteristic motor deficits and atrophy of the caudate nucleus, signature hallmarks of HD include behavioral abnormalities, immune activation, and cortical and white matter loss. The identification and validation of novel therapeutic targets that contribute to these degenerative cellular processes may lead to new interventions that slow or even halt the course of this insidious disease. Semaphorin 4D (SEMA4D) is a transmembrane signaling molecule that modulates a variety of processes central to neuroinflammation and neurodegeneration including glial cell activation, neuronal growth cone collapse and apoptosis of neural precursors, as well as inhibition of oligodendrocyte migration, differentiation and process formation. Therefore, inhibition of SEMA4D signaling could reduce CNS inflammation, increase neuronal outgrowth and enhance oligodendrocyte maturation, which may be of therapeutic benefit in the treatment of several neurodegenerative diseases, including HD. To that end, we evaluated the preclinical therapeutic efficacy of an anti-SEMA4D monoclonal antibody, which prevents the interaction between SEMA4D and its receptors, in the YAC128 transgenic HD mouse model. Anti-SEMA4D treatment ameliorated neuropathological signatures, including striatal atrophy, cortical atrophy, and corpus callosum atrophy and prevented testicular degeneration in YAC128 mice. In parallel, a subset of behavioral symptoms was improved in anti-SEMA4D treated YAC128 mice, including reduced anxiety-like behavior and rescue of cognitive deficits. There was, however, no discernible effect on motor deficits. The preservation of brain gray and white matter and improvement in behavioral measures in YAC128 mice treated with anti-SEMA4D suggest that this approach could represent a viable therapeutic strategy for the treatment of HD. Importantly, this work provides in vivo demonstration that inhibition of pathways initiated by SEMA4D constitutes a novel approach to moderation of neurodegeneration.

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.

Semaphorin 4D induces vaginal epithelial cell apoptosis to control mouse postnatal vaginal tissue remodeling

The opening of the mouse vaginal cavity to the skin is a postnatal tissue remodeling process that occurs at approximately five weeks of age for the completion of female genital tract maturation at puberty. The tissue remodeling process is primarily composed of a hormonally triggered apoptotic process predominantly occurring in the epithelium of the distal section of the vaginal cavity. However, the detailed mechanism underlying the apoptotic induction remains to be elucidated. In the present study, it was observed that the majority of BALB/c mice lacking the class 4 semaphorin, semaphorin 4D (Sema4D), developed imperforate vagina and hydrometrocolpos resulting in a perpetually unopened vaginal cavity regardless of a normal estrogen level comparable with that in wild-type (WT) mice. Administration of β-estradiol to infant Sema4D-deficient (Sema4D^−/−) mice did not induce precocious vaginal opening, which was observed in WT mice subjected to the same β-estradiol administration, excluding the possibility that the closed vaginal phenotype was due to insufficient estrogen secretion at the time of vaginal opening. In order to assess the role of Sema4D in the postnatal vaginal tissue remodeling process, the expression of Sema4D and its receptor, plexin-B1, was examined as well as the level of apoptosis in the vaginal epithelia of five-week-old WT and Sema4D^−/− mice. Immunohistochemical analyses confirmed the localization of Sema4D and plexin-B1 in the mouse vaginal epithelia. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay and immunohistochemistry detecting activated caspase-3 revealed significantly fewer apoptotic cells in situ in the vaginal mucosa of five-week-old Sema4D^−/− mice compared with WT mice. The addition of recombinant Sema4D to Sema4D^−/− vaginal epithelial cells in culture significantly enhanced apoptosis of the vaginal epithelial cells, demonstrating the apoptosis-inducing activity of Sema4D. The experimental reduction of plexin-B1 expression in vaginal epithelial cells demonstrated the integral role of plexin-B1 in Sema4D-induced apoptotic cell death. These results suggest a non-redundant role of Sema4D in the postnatal tissue remodeling process in five-week-old BALB/c mice, which involves the induction of vaginal epithelial cell apoptosis through Sema4D binding to plexin-B1.

Semaforin Sema4D in the immune system in multiple sclerosis

The expression of class IV semaforin Sema4D and its CD72 receptor on lymphocytes was studied in patients with multiple sclerosis. The disease was associated with an increase in Sema4D level on intact T lymphocytes and with its more intense shedding from the membrane of activated cell. Multiple sclerosis was also associated with a decrease of CD72 receptor expression by B lymphocytes. Possible contribution of Sema4D to the disease development via the direct effects in the CNS and the immunomodulatory effect, specifically, B cell activity regulation, was discussed.

Immunological functions of the neuropilins and plexins as receptors for semaphorins

Semaphorins were originally identified as axon-guidance molecules that function during neuronal development. However, cumulative evidence indicates that semaphorins also participate in immune responses, both physiological and pathological, and they are now considered to be potential diagnostic and/or therapeutic targets for a range of diseases. The primary receptors for semaphorins are neuropilins and plexins, which have cell type-specific patterns of expression and are involved in multiple signalling responses. In this Review, we focus on the roles of neuropilin 1 (NRP1) and plexins in the regulation of the immune system, and we summarize recent advances in our understanding of their pathological implications.

Novel therapeutic options for multiple sclerosis

Multiple sclerosis (MS) is considered as an autoimmune disorder of the CNS with neuro-inflammatory and neurodegenerative components. We review here the innovative drugs recently registered and those in clinical development for MS. Immunomodulation has been the preferred therapeutic approach for MS since the first IFN-β was registered in the 1990s. Several immunomodulators are now available, which show a high efficacy in reducing the number of relapses in patients with the relapsing-remitting form of MS (RRMS). The high efficacy of most immunomodulators is, however, associated with substantial safety risks, notably concerning infections or cancers. Recently oral drugs have been approved for RRMS; however, biologics, and notably, monoclonal antibodies are still well represented in the development pipelines. An unmet medical need remains the treatment of the primary and secondary forms of MS or chronic progressive MS (CPMS). Half a dozen immunomodulators with proven efficacy in RRMS are now undergoing evaluation in Phase III trials in the CPMS indication. Neuroprotective drugs that prevent demyelination and/or improve remyelination would be interesting for CPMS, but these drugs are currently in the early development phase and their efficacy has not been demonstrated yet.

Elevated plasma soluble Sema4D/CD100 levels are associated with disease severity in patients of hemorrhagic fever with renal syndrome

Background

Hantaan virus (HTNV) could cause a severe lethal hemorrhagic fever with renal syndrome (HFRS) in humans. Despite a limited understanding of the pathogenesis of HFRS, the importance of host-related immune responses in the pathogenesis of HFRS has been widely recognized. CD100/Sema4D has been demonstrated to play an important role in physiological and pathological immune responses, but the functional role of CD100 in infectious diseases has only been inadequately reported. The aim of this study was to investigate the pathological significance of CD100 in patients after HTNV infection.

Methodology/Principal Findings

Blood samples were collected from 99 hospitalized patients in Tangdu Hospital and 27 health controls. The level of soluble CD100 (sCD100) in plasma were quantified by ELISA and the relationship between sCD100 and the disease course or severity were analyzed. The expressions of membrane CD100 on various subpopulations of peripheral blood mononuclear cell (PBMC) were analyzed by flow cytometry. The results showed that sCD100 level in acute phase of HFRS was significantly higher in patients than that in healthy controls (P<0.0001) and the sCD100 level declined in convalescent phase. Multivariate model analysis showed that platelet count, white blood cell count, serum creatinine level and blood urea nitrogen level were associated with sCD100 levels and contributed independently to the elevated sCD100 levels. The expression of membrane CD100 on PBMCs decreased in the acute phase of HFRS patients compared with that of the normal controls and recovered in the convalescent phase.

Conclusions

We reported the elevated level of plasma sCD100 in HFRS patients and the elevated level might be a result from the shedding of membrane CD100 on PBMC. The elevated level of sCD100 was associated with disease severity, suggesting that sCD100 might be a cause or a consequence of progression of HFRS. The underlying mechanisms should be explored further.

Myelin-based inhibitors of oligodendrocyte myelination: clues from axonal growth and regeneration

The differentiation of and myelination by oligodendrocytes (OLs) are exquisitely regulated by a series of intrinsic and extrinsic mechanisms. As each OL can make differing numbers of myelin segments with variable lengths along similar axon tracts, myelination can be viewed as a graded process shaped by inhibitory/inductive cues during development. Myelination by OLs is a prime example of an adaptive process determined by the microenvironment and architecture of the central nervous system (CNS). in this review, we discuss how myelin formation by OLs may be controlled by the heterogeneous microenvironment of the CNS. Then we address recent findings demonstrating that neighboring OLs may compete for available axon space, and highlight our current understanding of myelin-based inhibitors of axonal regeneration that are potentially responsible for the reciprocal dialogue between OLs and determine the numbers and lengths of myelin internodes. Understanding the mechanisms that control the spatiotemporal regulation of myelinogenic potential during development may provide valuable insight into therapeutic strategies for promoting remyelination in an inhibitory microenvironment.

Plexin-B1: a potential diagnostic biomarker for glioma and a future target for glioma immunotherapy

Gliomas are the most common tumors in the central nervous system. Plexin-B1 is abundantly expressed in the nervous system as an axonal guidance molecule during neuronal development. However, the correlation between its expression and the clinical characteristics of gliomas, and its therapeutic significance, remain largely unexplored. In this study, we detected the expression of Plexin-B1 in clinical glioma tissue samples. Plexin-B1 was highly expressed in the cytoplasm and on the membrane of glioma tissues, while only trace levels of Plexin-B1 were present in normal brain tissue. The expression level of Plexin-B1 in glioma tissue was associated with the pathological grade of the glioma. In addition, we used flow cytometry to analyze the expression of Plexin-B1 in glioma cell lines and its ligand, semaphorin 4D (Sema4D), in natural killer (NK) cell lines. Cytotoxicity assays showed cytolysis of the U251 glioma cell line by the NK cell line, NK92, and this was markedly downregulated when the neutralizing antibody to Plexin-B1 was added. This study demonstrates that Plexin-B1 could be used as a diagnostic biomarker, and also suggests that it may be involved in the cytotoxicity of NK cells to glioma cells. Plexin-B1 could be a useful future target for glioma immunotherapy.