SEMA4D compromises blood–brain barrier, activates microglia, and inhibits remyelination in neurodegenerative disease

Infiltration by monocytes of the central nervous system and its role in multiple sclerosis: reflections on therapeutic strategies

Mononuclear macrophage infiltration in the central nervous system is a prominent feature of neuroinflammation. Recent studies on the pathogenesis and progression of multiple sclerosis have highlighted the multiple roles of mononuclear macrophages in the neuroinflammatory process. Monocytes play a significant role in neuroinflammation, and managing neuroinflammation by manipulating peripheral monocytes stands out as an effective strategy for the treatment of multiple sclerosis, leading to improved patient outcomes. This review outlines the steps involved in the entry of myeloid monocytes into the central nervous system that are targets for effective intervention: the activation of bone marrow hematopoiesis, migration of monocytes in the blood, and penetration of the blood-brain barrier by monocytes. Finally, we summarize the different monocyte subpopulations and their effects on the central nervous system based on phenotypic differences. As activated microglia resemble monocyte-derived macrophages, it is important to accurately identify the role of monocyte-derived macrophages in disease. Depending on the roles played by monocyte-derived macrophages at different stages of the disease, several of these processes can be interrupted to limit neuroinflammation and improve patient prognosis. Here, we discuss possible strategies to target monocytes in neurological diseases, focusing on three key aspects of monocyte infiltration into the central nervous system, to provide new ideas for the treatment of neurodegenerative diseases.

Asiaticoside alleviates lipopolysaccharide-induced acute lung injury by blocking Sema4D/CD72 and inhibiting mitochondrial dysfunction in RAW264.7 cell and mice

Acute lung injury (ALI) is a common disease with complex pathogenesis. However, the treatment is mainly symptomatic with limited clinical options. Asiaticoside (AS), a Chinese herbal extract, has protective effects against LPS-induced ALI in mice and inhibits nitric oxide and prostaglandin E2 synthesis; however, the specific mechanism of AS in the prevention and treatment of LPS-induced ALI needs further study. Sema4D/CD72 pathway, mitochondrial dysfunction, and miRNA-21 are closely associated with inflammation. Therefore, the present study aimed to explore whether AS exerts its therapeutic effect on ALI by influencing Sema4D/CD72 pathway and mitochondrial dysfunction, restoring the balance of inflammatory factors, and influencing miRNA-21 expression. Cell and animal experiments were performed to investigate the effect of AS on ALI. Lipopolysaccharide (LPS) was used to establish the ALI model. CCK8 and flow cytometry were used to detect the cell viability and apoptosis rate. HE staining and wet-to-dry weight ratio (W/D) of lung tissue were determined. The expressions of Sema4D, CD72, NF-κB p65, Bax, Bcl2, and caspase 3 in RAW264.7 cells and lung tissues were detected by western blot, and the levels of IL-10 and IL-1β induced by LPS in supernatant of RAW264.7 cells and BALF were measured by ELISA. And the expression of miRNA-21 in cells and lung tissues was detected by fluorescence quantitative PCR. The result shows that AS treatment suppressed LPS-induced cell damage and lung injury in mice. AS treatment could alleviate the pathological changes such as inflammatory infiltration and histopathological changes in the lungs caused by LPS, and reduce the ratio of W/D. AS significantly alleviated the decrease of mitochondrial membrane potential induced by LPS, inhibited the increase of ROS production, and reduced the expression of mitochondrial fission proteins Drp1 and Fis1. The high-dose AS group significantly downregulated the expression of Sema4D, CD72, phosphorylated NF-κB p65, and apoptosis-related proteins, decreased the pro-inflammatory factor IL-1β, and enhanced the level of anti-inflammatory factor IL-10. In addition, AS promoted miRNA-21 expression. These effects inhibited apoptosis and restored the balance between anti- and pro-inflammatory factors. This represents the inaugural report elucidating the mechanism by which AS inhibits the Sema4D/CD72 signaling pathway. These findings offer novel insights into the potential application of AS in both preventing and treating ALI.

Alzheimer's disease approaches - Focusing on pathology, biomarkers and clinical trial candidates

The strategy for the development of new drugs for Alzheimer's disease (AD) recognizes that an effective therapy requires early therapeutic intervention and a multifactorial approach that considers the individual initiators of AD development. Current knowledge of AD includes the understanding of pathophysiology, risk factors, biomarkers, and the evolving patterns of biomarker abnormalities. This knowledge is essential in identifying potential molecular targets for new drug development. This review summarizes promising AD drug candidates, many of which are currently in phase 2 or 3 clinical trials. New agents are classified according to the Common Alzheimer's Disease Research Ontology (CADRO). The main targets of new drugs for AD are processes related to amyloid beta and tau neurotoxicity, neurotransmission, inflammation, metabolism and bioenergetics, synaptic plasticity, and oxidative stress. These interventions are aimed at preventing disease onset and slowing or eliminating disease progression. The efficacy of pharmacotherapy may be enhanced by combining these drugs with other treatments, antioxidants, and dietary supplements. Ongoing research into AD pathophysiology, risk factors, biomarkers, and the dynamics of biomarker abnormalities may contribute to the understanding of AD and offer hope for effective therapeutic strategies in the near future.

Recent updates on immunotherapy in neurodegenerative diseases

Neurodegeneration is a progressive event leading to specific neuronal loss due to the accumulation of aberrant proteins. These pathologic forms of proteins further worsen and interfere with normal physiologic mechanisms, which can lead to abnormal proliferation of immune cells and subsequent inflammatory cascades and ultimately neuronal loss. Recently, immunotherapies targeting abnormal, pathologic forms of protein have shown a promising approach to modify the progression of neurodegeneration. Recent advances in immunotherapy have led to the development of novel antibodies against the proteinopathies which can eradicate aggregations of protein as evident from preclinical and clinical studies. Nonetheless, only a few of them have successfully received clinical approval, while others have been discontinued due to a lack of clinical efficacy endpoints. The current review discusses the status of investigational antibodies under clinical trials, their targets for therapeutic action, and evidence for failure or success.

Semaphorin heterodimerization in cis regulates membrane targeting and neocortical wiring

Disruption of neocortical circuitry and architecture in humans causes numerous neurodevelopmental disorders. Neocortical cytoarchitecture is orchestrated by various transcription factors such as Satb2 that control target genes during strict time windows. In humans, mutations of SATB2 cause SATB2 Associated Syndrome (SAS), a multisymptomatic syndrome involving epilepsy, intellectual disability, speech delay, and craniofacial defects. Here we show that Satb2 controls neuronal migration and callosal axonal outgrowth during murine neocortical development by inducing the expression of the GPI-anchored protein, Semaphorin 7A (Sema7A). We find that Sema7A exerts this biological activity by heterodimerizing in cis with the transmembrane semaphorin, Sema4D. We could also observe that heterodimerization with Sema7A promotes targeting of Sema4D to the plasma membrane in vitro. Finally, we report an epilepsy-associated de novo mutation in Sema4D (Q497P) that inhibits normal glycosylation and plasma membrane localization of Sema4D-associated complexes. These results suggest that neuronal use of semaphorins during neocortical development is heteromeric, and a greater signaling complexity exists than was previously thought.

Huntington's Disease: Latest Frontiers in Therapeutics

PURPOSE OF REVIEW

Huntington's disease (HD) is an autosomal-dominant disorder caused by a pathological expansion of a trinucleotide repeat (CAG) on exon 1 of the huntingtin (HTT) gene. HD is characterized by the presence of chorea, alongside other hyperkinesia, parkinsonism and a combination of cognitive and behavioural features. Currently, there are no disease-modifying therapies (DMTs) for HD, and the only intervention(s) with approved indication target the treatment of chorea. This article reviews recent research on the clinical development of DMTs and newly developed tools that enhance clinical trial design towards a successful DMT in the future.

RECENT FINDINGS

HD is living in an era of target-specific drug development with emphasis on the mechanisms related to mutant Huntingtin (HTT) protein. Examples include antisense oligonucleotides (ASO), splicing modifiers and microRNA molecules that aim to reduce the levels of mutant HTT protein. After initial negative results with ASO molecules Tominersen and WVE-120101/ WVE-120102, the therapeutic landscape continues to expand, with various trials currently under development to document proof-of-concept and safety/tolerability. Immune-targeted therapies have also been evaluated in early-phase clinical trials, with promising preliminary findings. The possibility of quantifying mHTT in CSF, along with the development of an integrated biological staging system in HD are important innovations applicable to clinical trial design that enhance the drug development process. Although a future in HD with DMTs remains a hope for those living with HD, care partners and care providers, the therapeutic landscape is promising, with various drug development programs underway following a targeted approach supported by disease-specific biomarkers and staging frameworks.

Exploring cross-tissue DNA methylation patterns: blood-brain CpGs as potential neurodegenerative disease biomarkers

The difficulty of obtaining samples from certain human tissues has led to efforts to find accessible sources to analyze molecular markers derived from DNA. In this study, we look for DNA methylation patterns in blood samples and its association with the brain methylation pattern in neurodegenerative disorders. Using data from methylation databases, we selected 18,293 CpGs presenting correlated methylation levels between blood and brain (bb-CpGs) and compare their methylation level between blood samples from patients with neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, Multiple Sclerosis, and X Fragile Syndrome) and healthy controls. Sixty-four bb-CpGs presented significant distinct methylation levels in patients, being: nine for Alzheimer's disease, nine for Parkinson's disease, 28 for Multiple Sclerosis, and 18 for Fragile X Syndrome. Similar differences in methylation pattern for the nine Alzheimer's bb-CpGs was also observed when comparing brain tissue from patients vs. controls. The genomic regions of some of these 64 bb-CpGs are placed close to or inside genes previously associated with the respective condition. Our findings support the rationale of using blood DNA as a surrogate of brain tissue to analyze changes in CpG methylation level in patients with neurodegenerative diseases, opening the possibility for characterizing new biomarkers.

CCR2+ monocytes promote white matter injury and cognitive dysfunction after myocardial infarction

Survivors of myocardial infarction are at increased risk for vascular dementia. Neuroinflammation has been implicated in the pathogenesis of vascular dementia, yet little is known about the cellular and molecular mediators of neuroinflammation after myocardial infarction. Using a mouse model of myocardial infarction coupled with flow cytometric analyses and immunohistochemistry, we discovered increased monocyte abundance in the brain after myocardial infarction, which was associated with increases in brain-resident perivascular macrophages and microglia. Myeloid cell recruitment and activation was also observed in post-mortem brains of humans that died after myocardial infarction. Spatial and single cell transcriptomic profiling of brain-resident myeloid cells after experimental myocardial infarction revealed increased expression of monocyte chemoattractant proteins. In parallel, myocardial infarction increased crosstalk between brain-resident myeloid cells and oligodendrocytes, leading to neuroinflammation, white matter injury, and cognitive dysfunction. Inhibition of monocyte recruitment preserved white matter integrity and cognitive function, linking monocytes to neurodegeneration after myocardial infarction. Together, these preclinical and clinical results demonstrate that monocyte infiltration into the brain after myocardial infarction initiate neuropathological events that lead to vascular dementia.

Astrocyte-to-microglia communication via Sema4B-Plexin-B2 modulates injury-induced reactivity of microglia

After central nervous system injury, a rapid cellular and molecular response is induced. This response can be both beneficial and detrimental to neuronal survival in the first few days and increases the risk for neurodegeneration if persistent. Semaphorin4B (Sema4B), a transmembrane protein primarily expressed by cortical astrocytes, has been shown to play a role in neuronal cell death following injury. Our study shows that after cortical stab wound injury, cytokine expression is attenuated in Sema4B-/- mice, and microglia/macrophage reactivity is altered. In vitro, Sema4B enhances the reactivity of microglia following injury, suggesting astrocytic Sema4B functions as a ligand. Moreover, injury-induced microglia reactivity is attenuated in the presence of Sema4B-/- astrocytes compared to Sema4B+/- astrocytes. In vitro experiments indicate that Plexin-B2 is the Sema4B receptor on microglia. Consistent with this, in microglia/macrophage-specific Plexin-B2-/- mice, similar to Sema4B-/- mice, microglial/macrophage reactivity and neuronal cell death are attenuated after cortical injury. Finally, in Sema4B/Plexin-B2 double heterozygous mice, microglial/macrophage reactivity is also reduced after injury, supporting the idea that both Sema4B and Plexin-B2 are part of the same signaling pathway. Taken together, we propose a model in which following injury, astrocytic Sema4B enhances the response of microglia/macrophages via Plexin-B2, leading to increased reactivity.

YY1 Lactylation Aggravates Autoimmune Uveitis by Enhancing Microglial Functions via Inflammatory Genes

Activated microglia in the retina are essential for the development of autoimmune uveitis. Yin-Yang 1 (YY1) is an important transcription factor that participates in multiple inflammatory and immune-mediated diseases. Here, an increased YY1 lactylation in retinal microglia within in the experimental autoimmune uveitis (EAU) group is observed. YY1 lactylation contributed to boosting microglial activation and promoting their proliferation and migration abilities. Inhibition of lactylation suppressed microglial activation and attenuated inflammation in EAU. Mechanistically, cleavage under targets & tagmentation （CUT&Tag） analysis revealed that YY1 lactylation promoted microglial activation by regulating the transcription of a set of inflammatory genes, including STAT3, CCL5, IRF1, IDO1, and SEMA4D. In addition, p300 is identified as the writer of YY1 lactylation. Inhibition of p300 decreased YY1 lactylation and suppressed microglial inflammation in vivo and in vitro. Collectively, the results showed that YY1 lactylation promoted microglial dysfunction in autoimmune uveitis by upregulating inflammatory cytokine secretion and boosting cell migration and proliferation. Therapeutic effects can be achieved by targeting the lactate/p300/YY1 lactylation/inflammatory genes axis.

Inflammation and Huntington's disease - a neglected therapeutic target?

INTRODUCTION

Huntington's Disease (HD) is a genetic neurodegenerative disease for which there is currently no disease-modifying treatment. One of several underlying mechanisms proposed to be involved in HD pathogenesis is inflammation; there is now accumulating evidence that the immune system may play an integral role in disease pathology and progression. As such, modulation of the immune system could be a potential therapeutic target for HD.

AREAS COVERED

To date, the number of trials targeting immune aspects of HD has been limited. However, targeting it, may have great advantages over other therapeutic areas, given that many drugs already exist that have actions in this system coupled to the fact that inflammation can be measured both peripherally and, to some extent, centrally using CSF and PET imaging. In this review, we look at evidence that the immune system and the newly emerging area of the microbiome are altered in HD patients, and then present and discuss clinical trials that have targeted different parts of the immune system.

EXPERT OPINION

We then conclude by discussing how this field might develop going forward, focusing on the role of imaging and other biomarkers to monitor central immune activation and response to novel treatments in HD.

A case for seeking sex-specific treatments in Alzheimer's disease

There is no satisfactory explanation for the sex-related differences in the incidence of many diseases and this is also true of Alzheimer's disease (AD), where females have a higher lifetime risk of developing the disease and make up about two thirds of the AD patient population. The importance of understanding the cause(s) that account for this disproportionate distribution cannot be overestimated, and is likely to be a significant factor in the search for therapeutic strategies that will combat the disease and, furthermore, potentially point to a sex-targeted approach to treatment. This review considers the literature in the context of what is known about the impact of sex on processes targeted by drugs that are in clinical trial for AD, and existing knowledge on differing responses of males and females to these drugs. Current knowledge strongly supports the view that trials should make assessing sex-related difference in responses a priority with a focus on exploring the sex-stratified treatments.

Passive immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by cognitive impairment with few therapeutic options. Despite many failures in developing AD treatment during the past 20 years, significant advances have been achieved in passive immunotherapy of AD very recently. Here, we review characteristics, clinical trial data, and mechanisms of action for monoclonal antibodies (mAbs) targeting key players in AD pathogenesis, including amyloid-β (Aβ), tau and neuroinflammation modulators. We emphasized the efficacy of lecanemab and donanemab on cognition and amyloid clearance in AD patients in phase III clinical trials and discussed factors that may contribute to the efficacy and side effects of anti-Aβ mAbs. In addition, we provided important information on mAbs targeting tau or inflammatory regulators in clinical trials, and indicated that mAbs against the mid-region of tau or pathogenic tau have therapeutic potential for AD. In conclusion, passive immunotherapy targeting key players in AD pathogenesis offers a promising strategy for effective AD treatment.

Association of Immune Semaphorins with COVID-19 Severity and Outcomes

Semaphorins have recently been recognized as crucial modulators of immune responses. In the pathogenesis of COVID-19, the activation of immune responses is the key factor in the development of severe disease. This study aimed to determine the association of serum semaphorin concentrations with COVID-19 severity and outcomes. Serum semaphorin concentrations (SEMA3A, -3C, -3F, -4D, -7A) were measured in 80 hospitalized adult patients with COVID-19 (moderate (n = 24), severe (n = 32), critical, (n = 24)) and 40 healthy controls. While SEMA3C, SEMA3F and SEMA7A serum concentrations were significantly higher in patients with COVID-19, SEMA3A was significantly lower. Furthermore, SEMA3A and SEMA3C decreased with COVID-19 severity, while SEMA3F and SEMA7A increased. SEMA4D showed no correlation with disease severity. Serum semaphorin levels show better predictive values than CRP, IL-6 and LDH for differentiating critical from moderate/severe COVID-19. SEMA3F and SEMA7A serum concentrations were associated with the time to recovery, requirement of invasive mechanical ventilation, development of pulmonary thrombosis and nosocomial infections, as well as with in-hospital mortality. In conclusion, we provide the first evidence that SEMA3A, SEMA3C, SEMA3F and SEMA7A can be considered as new biomarkers of COVID-19 severity.

Oligodendrocyte pathology in Huntington's disease: from mechanisms to therapeutics

Oligodendrocytes (OLGs), highly specialized glial cells that wrap axons with myelin sheaths, are critical for brain development and function. There is new recognition of the role of OLGs in the pathogenesis of neurodegenerative diseases (NDDs), including Huntington's disease (HD), a prototypic NDD caused by a polyglutamine tract expansion in huntingtin (HTT), which results in gain- and loss-of-function effects. Clinically, HD is characterized by a constellation of motor, cognitive, and psychiatric disturbances. White matter (WM) structures, representing myelin-rich regions of the brain, are profoundly affected in HD, and recent findings reveal oligodendroglia dysfunction as an early pathological event. Here, we focus on mechanisms that underlie oligodendroglial deficits and dysmyelination in the progression of the disease, highlighting the pathogenic contributions of mutant HTT (mHTT). We also discuss potential therapeutic implications involving these molecular pathways.

Knockout of Sema4D alleviates liver fibrosis by suppressing AOX1 expression

Liver fibrosis can occur in many chronic liver diseases, and no effective treatments are available due to the poorly characterized molecular pathogenesis. Semaphorin 4D (Sema4D) has immune functions and serves important roles in T cell priming. Here, we found that Sema4D was highly expressed in fibrotic liver, and the expression of Sema4D increased with hepatic stellate cells (HSCs) activation. Knockout of Sema4D alleviated liver fibrosis. Mechanistically, knockout of Sema4D alleviated liver fibrosis by suppressing the expression of AOX1 in retinol metabolism. Further investigation demonstrated that retinoic acid receptor α (RARA), an important nuclear receptor of retinoic acid, was reduced by Sema4D knockout during liver fibrogenesis. Sema4D knockout-mediated suppression of liver fibrosis was partly mediated by regulating the balance of Th1, Th2, Th17, and T-bet+Treg cells via inhibiting AOX1/RARA. Thus, targeting Sema4D may hold promise as a potential therapeutic approach for treating liver fibrosis.

Alzheimer's disease and neuroinflammation: will new drugs in clinical trials pave the way to a multi-target therapy?

Despite extensive research, no disease-modifying therapeutic option, able to prevent, cure or halt the progression of Alzheimer's disease [AD], is currently available. AD, a devastating neurodegenerative pathology leading to dementia and death, is characterized by two pathological hallmarks, the extracellular deposits of amyloid beta (Aβ) and the intraneuronal deposits of neurofibrillary tangles (NFTs) consisting of altered hyperphosphorylated tau protein. Both have been widely studied and pharmacologically targeted for many years, without significant therapeutic results. In 2022, positive data on two monoclonal antibodies targeting Aβ, donanemab and lecanemab, followed by the 2023 FDA accelerated approval of lecanemab and the publication of the final results of the phase III Clarity AD study, have strengthened the hypothesis of a causal role of Aβ in the pathogenesis of AD. However, the magnitude of the clinical effect elicited by the two drugs is limited, suggesting that additional pathological mechanisms may contribute to the disease. Cumulative studies have shown inflammation as one of the main contributors to the pathogenesis of AD, leading to the recognition of a specific role of neuroinflammation synergic with the Aβ and NFTs cascades. The present review provides an overview of the investigational drugs targeting neuroinflammation that are currently in clinical trials. Moreover, their mechanisms of action, their positioning in the pathological cascade of events that occur in the brain throughout AD disease and their potential benefit/limitation in the therapeutic strategy in AD are discussed and highlighted as well. In addition, the latest patent requests for inflammation-targeting therapeutics to be developed in AD will also be discussed.

Semaphorins in immune cell function, inflammatory and infectious diseases

The Semaphorin family is a group of proteins studied broadly for their functions in nervous systems. They consist of eight subfamilies ubiquitously expressed in vertebrates, invertebrates, and viruses and exist in membrane-bound or secreted forms. Emerging evidence indicates the relevance of semaphorins outside the nervous system, including angiogenesis, cardiogenesis, osteoclastogenesis, tumour progression, and, more recently, the immune system. This review provides a broad overview of current knowledge on the role of semaphorins in the immune system, particularly its involvement in inflammatory and infectious diseases, including chlamydial infections.

Mediating immunosuppressive functions: a new perspective on the complex immunological properties of SEMA4D in the tumor microenvironment

Semaphorin 4D (SEMA4D) is considered a new antitumor target closely related to immune cells. However, understanding the role of SEMA4D in the tumor microenvironment (TME) is limited. In this study, we explored the expression and immune cell infiltration patterns of SEMA4D using multiple bioinformatics datasets and analyzed the relationship between SEMA4D expression with immune checkpoints, tumor mutational load (TMB), microsatellite instability (MSI) and immune function. We detected that SEMA4D is overexpressed in many tumors types, widely enriched in immune cells, and closely associated with TILs, MSI, TMB, as well as T-cell exhaustion-associated immune checkpoints, and thus can broadly affect the immune microenvironment. We further verified the overexpression of SEMA4D in tumor and its distribution in TME by immunohistochemistry, RT-qPCR and flow cytometry, and confirmed that decreased expression of SEMA4D can lead to recovery of T cell exhaustion. In conlusion, this study provides a more comprehensive perspective of SEMA4D regulation of tumor immunity, which provide a new option for cancer immunotherapy.

Insights into the Molecular Mechanisms Mediating Extravasation in Brain Metastasis of Breast Cancer, Melanoma, and Lung Cancer

Brain metastasis is an incurable end-stage of systemic cancer associated with poor prognosis, and its incidence is increasing. Brain metastasis occurs through a multi-step cascade where cancer cells spread from the primary tumor site to the brain. The extravasation of tumor cells through the blood-brain barrier (BBB) is a critical step in brain metastasis. During extravasation, circulating cancer cells roll along the brain endothelium (BE), adhere to it, then induce alterations in the endothelial barrier to transmigrate through the BBB and enter the brain. Rolling and adhesion are generally mediated by selectins and adhesion molecules induced by inflammatory mediators, while alterations in the endothelial barrier are mediated by proteolytic enzymes, including matrix metalloproteinase, and the transmigration step mediated by factors, including chemokines. However, the molecular mechanisms mediating extravasation are not yet fully understood. A better understanding of these mechanisms is essential as it may serve as the basis for the development of therapeutic strategies for the prevention or treatment of brain metastases. In this review, we summarize the molecular events that occur during the extravasation of cancer cells through the blood-brain barrier in three types of cancer most likely to develop brain metastasis: breast cancer, melanoma, and lung cancer. Common molecular mechanisms driving extravasation in these different tumors are discussed.

Synaptic degeneration in Alzheimer disease

Alzheimer disease (AD) is characterized by progressive cognitive decline in older individuals accompanied by the presence of two pathological protein aggregates - amyloid-β and phosphorylated tau - in the brain. The disease results in brain atrophy caused by neuronal loss and synapse degeneration. Synaptic loss strongly correlates with cognitive decline in both humans and animal models of AD. Indeed, evidence suggests that soluble forms of amyloid-β and tau can cause synaptotoxicity and spread through neural circuits. These pathological changes are accompanied by an altered phenotype in the glial cells of the brain - one hypothesis is that glia excessively ingest synapses and modulate the trans-synaptic spread of pathology. To date, effective therapies for the treatment or prevention of AD are lacking, but understanding how synaptic degeneration occurs will be essential for the development of new interventions. Here, we highlight the mechanisms through which synapses degenerate in the AD brain, and discuss key questions that still need to be answered. We also cover the ways in which our understanding of the mechanisms of synaptic degeneration is leading to new therapeutic approaches for AD.

Neuroinflammatory disease disrupts the blood-CNS barrier via crosstalk between proinflammatory and endothelial-to-mesenchymal-transition signaling

Breakdown of the blood-central nervous system barrier (BCNSB) is a hallmark of many neuroinflammatory disorders, such as multiple sclerosis (MS). Using a mouse model of MS, experimental autoimmune encephalomyelitis (EAE), we show that endothelial-to-mesenchymal transition (EndoMT) occurs in the CNS before the onset of clinical symptoms and plays a major role in the breakdown of BCNSB function. EndoMT can be induced by an IL-1β-stimulated signaling pathway in which activation of the small GTPase ADP ribosylation factor 6 (ARF6) leads to crosstalk with the activin receptor-like kinase (ALK)-SMAD1/5 pathway. Inhibiting the activation of ARF6 both prevents and reverses EndoMT, stabilizes BCNSB function, reduces demyelination, and attenuates symptoms even after the establishment of severe EAE, without immunocompromising the host. Pan-inhibition of ALKs also reduces disease severity in the EAE model. Therefore, multiple components of the IL-1β-ARF6-ALK-SMAD1/5 pathway could be targeted for the treatment of a variety of neuroinflammatory disorders.

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.

It takes two to tango: Widening our understanding of the onset of schizophrenia from a neuro-angiogenic perspective

Schizophrenia is a chronic debilitating mental disorder characterized by perturbations in thinking, perception, and behavior, along with brain connectivity deficiencies, neurotransmitter dysfunctions, and loss of gray brain matter. To date, schizophrenia has no cure and pharmacological treatments are only partially efficacious, with about 30% of patients describing little to no improvement after treatment. As in most neurological disorders, the main descriptions of schizophrenia physiopathology have been focused on neural network deficiencies. However, to sustain proper neural activity in the brain, another, no less important network is operating: the vast, complex and fascinating vascular network. Increasing research has characterized schizophrenia as a systemic disease where vascular involvement is important. Several neuro-angiogenic pathway disturbances have been related to schizophrenia. Alterations, ranging from genetic polymorphisms, mRNA, and protein alterations to microRNA and abnormal metabolite processing, have been evaluated in plasma, post-mortem brain, animal models, and patient-derived induced pluripotent stem cell (hiPSC) models. During embryonic brain development, the coordinated formation of blood vessels parallels neuro/gliogenesis and results in the structuration of the neurovascular niche, which brings together physical and molecular signals from both systems conforming to the Blood-Brain barrier. In this review, we offer an upfront perspective on distinctive angiogenic and neurogenic signaling pathways that might be involved in the biological causality of schizophrenia. We analyze the role of pivotal angiogenic-related pathways such as Vascular Endothelial Growth Factor and HIF signaling related to hypoxia and oxidative stress events; classic developmental pathways such as the NOTCH pathway, metabolic pathways such as the mTOR/AKT cascade; emerging neuroinflammation, and neurodegenerative processes such as UPR, and also discuss non-canonic angiogenic/axonal guidance factor signaling. Considering that all of the mentioned above pathways converge at the Blood-Brain barrier, reported neurovascular alterations could have deleterious repercussions on overall brain functioning in schizophrenia.

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.

An antagonistic monoclonal anti-Plexin-B1 antibody exerts therapeutic effects in mouse models of postmenopausal osteoporosis and multiple sclerosis

Osteoporosis and multiple sclerosis are highly prevalent diseases with limited treatment options. In light of these unmet medical needs, novel therapeutic approaches are urgently sought. Previously, the activation of the transmembrane receptor Plexin-B1 by its ligand semaphorin 4D (Sema4D) has been shown to suppress bone formation and promote neuroinflammation in mice. However, it is unclear whether inhibition of this receptor–ligand interaction by an anti–Plexin-B1 antibody could represent a viable strategy against diseases related to these processes. Here, we raised and systematically characterized a monoclonal antibody directed against the extracellular domain of human Plexin-B1, which specifically blocks the binding of Sema4D to Plexin-B1. In vitro, we show that this antibody inhibits the suppressive effects of Sema4D on human osteoblast differentiation and mineralization. To test the therapeutic potential of the antibody in vivo, we generated a humanized mouse line, which expresses transgenic human Plexin-B1 instead of endogenous murine Plexin-B1. Employing these mice, we demonstrate that the anti–Plexin-B1 antibody exhibits beneficial effects in mouse models of postmenopausal osteoporosis and multiple sclerosis in vivo. In summary, our data identify an anti–Plexin-B1 antibody as a potential therapeutic agent for the treatment of osteoporosis and multiple sclerosis.

Current and Possible Future Therapeutic Options for Huntington's Disease

Huntington's disease (HD) is an autosomal neurodegenerative disease that is characterized by an excessive number of CAG trinucleotide repeats within the huntingtin gene (HTT). HD patients can present with a variety of symptoms including chorea, behavioural and psychiatric abnormalities and cognitive decline. Each patient has a unique combination of symptoms, and although these can be managed using a range of medications and non-drug treatments there is currently no cure for the disease. Current therapies prescribed for HD can be categorized by the symptom they treat. These categories include chorea medication, antipsychotic medication, antidepressants, mood stabilizing medication as well as non-drug therapies. Fortunately, there are also many new HD therapeutics currently undergoing clinical trials that target the disease at its origin; lowering the levels of mutant huntingtin protein (mHTT). Currently, much attention is being directed to antisense oligonucleotide (ASO) therapies, which bind to pre-RNA or mRNA and can alter protein expression via RNA degradation, blocking translation or splice modulation. Other potential therapies in clinical development include RNA interference (RNAi) therapies, RNA targeting small molecule therapies, stem cell therapies, antibody therapies, non-RNA targeting small molecule therapies and neuroinflammation targeted therapies. Potential therapies in pre-clinical development include Zinc-Finger Protein (ZFP) therapies, transcription activator-like effector nuclease (TALEN) therapies and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated system (Cas) therapies. This comprehensive review aims to discuss the efficacy of current HD treatments and explore the clinical trial progress of emerging potential HD therapeutics.

Engineered extracellular vesicles encapsulated Bryostatin-1 as therapy for neuroinflammation

Targeted and effective drug delivery to central nervous system (CNS) lesions is a major challenge in the treatment of multiple sclerosis (MS). Extracellular vesicles (EVs) have great promise as a drug delivery nanosystem given their unique characteristics, including a strong cargo-loading capacity, low immunogenicity, high biocompatibility, inherent stability, high delivery efficiency, ease of manipulation, and blood-brain barrier (BBB) penetration. Clinical applications are, however, limited by their insufficient targeting capability and "dilution effects" upon systemic administration. Neural stem cells (NSCs) provide an abundant source of EVs because of their remarkable capacity for self-renewal. Here, we developed a novel therapeutic strategy for local delivery and treatment using EVPs, which are derived from NSCs with the expression of the CNS lesion targeting ligand-PDGFRα. Furthermore, we used EVPs as a targeting carrier for encapsulating Bryostatin-1 (Bryo-1), a natural compound with remarkable anti-inflammation ability. Our data showed that Bryo-1 delivered by EVPs was more stable and concentrated in the CNS than native Bryo-1. Systemic injection of a low dosage (1 × 10⁸ particles) of EVPs + Bryo-1, versus only EVPs or Bryo-1 administration, significantly ameliorated clinical disease development, decreased the infiltration of pro-inflammatory cells, blocked myelin loss and astrogliosis, protected BBB integrity, and altered microglia pro-inflammatory phenotype in the CNS of EAE mice. Taken as a whole, our study showed that engineered EVs have a CNS targeting capacity, and it provides potentially powerful therapeutic effects for the treatment of various neuroinflammatory diseases.

Anti-Semaphorin 4D Rescues Motor, Cognitive, and Respiratory Phenotypes in a Rett Syndrome Mouse Model

Rett syndrome is a neurodevelopmental disorder caused by mutations of the methyl-CpG binding protein 2 gene. Abnormal physiological functions of glial cells contribute to pathogenesis of Rett syndrome. Semaphorin 4D (SEMA4D) regulates processes central to neuroinflammation and neurodegeneration including cytoskeletal structures required for process extension, communication, and migration of glial cells. Blocking SEMA4D-induced gliosis may preserve normal glial and neuronal function and rescue neurological dysfunction in Rett syndrome. We evaluated the pre-clinical therapeutic efficacy of an anti-SEMA4D monoclonal antibody in the Rett syndrome Mecp2T158A transgenic mouse model and investigated the contribution of glial cells as a proposed mechanism of action in treated mice and in primary glial cultures isolated from Mecp2T158A/y mutant mice. SEMA4D is upregulated in neurons while glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1-positive cells are upregulated in Mecp2T158A/y mice. Anti-SEMA4D treatment ameliorates Rett syndrome-specific symptoms and improves behavioural functions in both pre-symptomatic and symptomatic cohorts of hemizygous Mecp2T158A/y male mice. Anti-SEMA4D also reduces astrocyte and microglia activation in vivo. In vitro experiments demonstrate an abnormal cytoskeletal structure in mutant astrocytes in the presence of SEMA4D, while anti-SEMA4D antibody treatment blocks SEMA4D–Plexin B1 signaling and mitigates these abnormalities. These results suggest that anti-SEMA4D immunotherapy may be an effective treatment option to alleviate symptoms and improve cognitive and motor function in Rett syndrome.

The emerging roles of semaphorin4D/CD100 in immunological diseases

In vertebrates, the semaphorin family of proteins is composed of 21 members that are divided into five subfamilies, i.e. classes 3 to 7. Semaphorins play crucial roles in regulating multiple biological processes, such as neural remodeling, tissue regeneration, cancer progression, and, especially, in immunological regulation. Semaphorin 4D (SEMA4D), also known as CD100, is an important member of the semaphorin family and was first characterized as a lymphocyte-specific marker. SEMA4D has diverse effects on immunologic processes, including immune cell proliferation, differentiation, activation, and migration, through binding to its specific membrane receptors CD72, PLXNB1, and PLXNB2. Furthermore, SEMA4D and its underlying signaling have been increasingly linked with several immunological diseases. This review focuses on the significant immunoregulatory role of SEMA4D and the associated underlying mechanisms, as well as the potential application of SEMA4D as a diagnostic marker and therapeutic target for the treatment of immunological diseases.

Unraveling Axon Guidance during Axotomy and Regeneration

During neuronal development and regeneration axons extend a cytoskeletal-rich structure known as the growth cone, which detects and integrates signals to reach its final destination. The guidance cues “signals” bind their receptors, activating signaling cascades that result in the regulation of the growth cone cytoskeleton, defining growth cone advance, pausing, turning, or collapse. Even though much is known about guidance cues and their isolated mechanisms during nervous system development, there is still a gap in the understanding of the crosstalk between them, and about what happens after nervous system injuries. After neuronal injuries in mammals, only axons in the peripheral nervous system are able to regenerate, while the ones from the central nervous system fail to do so. Therefore, untangling the guidance cues mechanisms, as well as their behavior and characterization after axotomy and regeneration, are of special interest for understanding and treating neuronal injuries. In this review, we present findings on growth cone guidance and canonical guidance cues mechanisms, followed by a description and comparison of growth cone pathfinding mechanisms after axotomy, in regenerative and non-regenerative animal models.

Potential crosstalk between sonic hedgehog-WNT signaling and neurovascular molecules: Implications for blood-brain barrier integrity in autism spectrum disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disease originating from combined genetic and environmental factors. Post-mortem human studies and some animal ASD models have shown brain neuroinflammation, oxidative stress, and changes in blood-brain barrier (BBB) integrity. However, the signaling pathways leading to these inflammatory findings and vascular alterations are currently unclear. The BBB plays a critical role in controlling brain homeostasis and immune response. Its dysfunction can result from developmental genetic abnormalities or neuroinflammatory processes. In this review, we explore the role of the Sonic Hedgehog/Wingless-related integration site (Shh/Wnt) pathways in neurodevelopment, neuroinflammation, and BBB development. The balance between Wnt-β-catenin and Shh pathways controls angiogenesis, barriergenesis, neurodevelopment, central nervous system (CNS) morphogenesis, and neuronal guidance. These interactions are critical to maintain BBB function in the mature CNS to prevent the influx of pathogens and inflammatory cells. Genetic mutations of key components of these pathways have been identified in ASD patients and animal models, which correlate with the severity of ASD symptoms. Disruption of the Shh/Wnt crosstalk may therefore compromise BBB development and function. In turn, impaired Shh signaling and glial activation may cause neuroinflammation that could disrupt the BBB. Elucidating how ASD-related mutations of Shh/Wnt signaling could cause BBB leaks and neuroinflammation will contribute to our understanding of the role of their interactions in ASD pathophysiology. These observations may provide novel targeted therapeutic strategies to prevent or alleviate ASD symptoms while preserving normal developmental processes. Cover Image for this issue: https://doi.org/10.1111/jnc.15081.

Potential crosstalk between sonic hedgehog-WNT signaling and neurovascular molecules: Implications for blood-brain barrier integrity in autism spectrum disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disease originating from combined genetic and environmental factors. Post-mortem human studies and some animal ASD models have shown brain neuroinflammation, oxidative stress, and changes in blood-brain barrier (BBB) integrity. However, the signaling pathways leading to these inflammatory findings and vascular alterations are currently unclear. The BBB plays a critical role in controlling brain homeostasis and immune response. Its dysfunction can result from developmental genetic abnormalities or neuroinflammatory processes. In this review, we explore the role of the Sonic Hedgehog/Wingless-related integration site (Shh/Wnt) pathways in neurodevelopment, neuroinflammation, and BBB development. The balance between Wnt-β-catenin and Shh pathways controls angiogenesis, barriergenesis, neurodevelopment, central nervous system (CNS) morphogenesis, and neuronal guidance. These interactions are critical to maintain BBB function in the mature CNS to prevent the influx of pathogens and inflammatory cells. Genetic mutations of key components of these pathways have been identified in ASD patients and animal models, which correlate with the severity of ASD symptoms. Disruption of the Shh/Wnt crosstalk may therefore compromise BBB development and function. In turn, impaired Shh signaling and glial activation may cause neuroinflammation that could disrupt the BBB. Elucidating how ASD-related mutations of Shh/Wnt signaling could cause BBB leaks and neuroinflammation will contribute to our understanding of the role of their interactions in ASD pathophysiology. These observations may provide novel targeted therapeutic strategies to prevent or alleviate ASD symptoms while preserving normal developmental processes.

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.

Molecular signature of extracellular matrix pathology in schizophrenia

Growing evidence points to a critical involvement of the extracellular matrix (ECM) in the pathophysiology of schizophrenia (SZ). Decreases of perineuronal nets (PNNs) and altered expression of chondroitin sulphate proteoglycans (CSPGs) in glial cells have been identified in several brain regions. GWAS data have identified several SZ vulnerability variants of genes encoding for ECM molecules. Given the potential relevance of ECM functions to the pathophysiology of this disorder, it is necessary to understand the extent of ECM changes across brain regions, their region- and sex-specificity and which ECM components contribute to these changes. We tested the hypothesis that the expression of genes encoding for ECM molecules may be broadly disrupted in SZ across several cortical and subcortical brain regions and include key ECM components as well as factors such as ECM posttranslational modifications and regulator factors. Gene expression profiling of 14 neocortical brain regions, caudate, putamen and hippocampus from control subjects (n = 14/region) and subjects with SZ (n = 16/region) was conducted using Affymetrix microarray analysis. Analysis across brain regions revealed widespread dysregulation of ECM gene expression in cortical and subcortical brain regions in SZ, impacting several ECM functional key components. SRGN, CD44, ADAMTS1, ADAM10, BCAN, NCAN and SEMA4G showed some of the most robust changes. Region-, sex- and age-specific gene expression patterns and correlation with cognitive scores were also detected. Taken together, these findings contribute to emerging evidence for large-scale ECM dysregulation in SZ and point to molecular pathways involved in PNN decreases, glial cell dysfunction and cognitive impairment in SZ.

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.

Downregulation of miR-125a-5p and miR-218-5p in Peripheral Blood Mononuclear Cells of Patients with Relapsing-Remitting Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the brain and spinal cord. Evidences have demonstrated that microRNAs (miRNAs) are involved in the pathological process of MS that may confer a valuable diagnostic biomarker for disease diagnosis, prognosis, and treatment. Hence, we assessed the expression pattern of miR-125a-5p and miR-218-5p in the peripheral blood mononuclear cells (PBMCs) of subjects with relapsing-remitting multiple sclerosis (RRMS). We recruited 50 RRMS patients and 50 age- and sex-matched healthy control subjects. PBMCs were isolated from the peripheral blood samples, RNA content was extracted, cDNA was synthesized, and finally expression level of miRNAs was determined using quantitative real-time PCR. Our data indicate significant downregulation of both miR-125a-5p and miR-218-5p in RRMS patients compared to healthy controls (P< .0001). The levels of both miRNAs were significantly downregulated in an age-dependent manner compared with consistent healthy control groups (30-40 years old P< .0001). Expression level of miR-218-5p was significantly changed in only female patients (Female group P< .0001; Male group P= .12). Receiver operating characteristic (ROC) curve data indicated that the expression levels of both miRNAs were able to discriminate RRMS patients from healthy subjects (P< .05). Moreover, bioinformatic enrichment analysis revealed that the target genes of these miRNAs had cardinal roles in the regulation of key biological pathways involved in the clinical course and pathogenesis of MS. Collectively, our results suggested that miR-125a-5p and miR-218-5p play a role in RRMS pathogenesis and have an age- and sex-dependent expression pattern in these patients.

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.

Interaction between Neurons and the Oligodendroglial Lineage in Multiple Sclerosis and Its Preclinical Models

Multiple sclerosis (MS) is a complex central nervous system inflammatory disease leading to demyelination and associated functional deficits. Though endogenous remyelination exists, it is only partial and, with time, patients can enter a progressive phase of the disease, with neurodegeneration as a hallmark. Though major therapeutic advances have been made, with immunotherapies reducing relapse rate during the inflammatory phase of MS, there is presently no therapy available which significantly impacts disease progression. Remyelination has been shown to favor neuroprotection, and it is thus of major importance to better understand remyelination mechanisms in order to promote them and hence preserve neurons. A crucial point is how this process is regulated through the neuronal crosstalk with the oligodendroglial lineage. In this review, we present the current knowledge on neuron interaction with the oligodendroglial lineage, in physiological context as well as in MS and its experimental models. We further discuss the therapeutic possibilities resulting from this research field, which might allow to support remyelination and neuroprotection and thus limit MS progression.

Signaling from membrane semaphorin 4D in T lymphocytes

Semaphorin 4D (Sema4D) is widely represented in the immune system in both membrane and soluble form, and controls immune processes through the specific receptors - these are generally accepted views. Here, an alternative way of Sema4D-dependent immunoregulation is presented, suggesting its functioning as a receptor. We have shown that activation of membrane Sema4D induces phosphorylation of Lck/ZAP-70 in intact T lymphocytes and enhances it in stimulated T cells. Since Sema4D is constitutively presented on the membrane of T lymphocytes, and classical Sema4D receptors are highly expressed by antigen-presenting cells, the membrane Sema4D can serve as an obligate costimulatory molecule in T lymphocyte priming or T-dependent B cell activation.

Discontinued disease-modifying therapies for Alzheimer's disease: status and future perspectives

INTRODUCTION

Alzheimer's disease (AD) is the main cause of dementia and represents a huge burden for patients, carers, and healthcare systems. Extensive efforts for over 20 years have failed to find effective disease-modifying drugs. Although amyloid-β (Aβ) accumulation in the brain predicts cognitive decline, effective reduction of plaque load by numerous drug candidates has not yielded significant clinical benefits. A similar pattern is now emerging for drugs which target hyperphosphorylated tau, and trials with anti-inflammatory drugs have been negative despite neuroinflammation appearing to have a crucial role in AD pathogenesis.

AREAS COVERED

This article reviews key drugs that have been discontinued while in development for AD and delineates the future landscape for present and alternative approaches.

EXPERT OPINION

Anti-Aβ drugs have failed to validate the Aβ cascade hypothesis of AD. Early findings suggest that the same is happening with therapeutics targeting tau and focussing future research solely on anti-tau drugs is inappropriate. Alternative targets should be pursued, including apolipoprotein E, immunomodulation, plasma exchange, protein autophagy and clearance, mitochondrial dysfunction, abnormal glucose metabolism, neurovascular unit support, epigenetic dysregulation, synaptic loss and dysfunction, microbiota dysbiosis, and combination therapies. Meanwhile, repurposing of drugs approved for other indications is justified where scientific rationale and robust preclinical evidence exist.

White matter alterations in Williams syndrome related to behavioral and motor impairments

Myelin is the electrical insulator surrounding the neuronal axon that makes up the white matter (WM) of the brain. It helps increase axonal conduction velocity (CV) by inducing saltatory conduction. Damage to the myelin sheath and WM is associated with many neurological and psychiatric disorders. Decreasing myelin deficits, and thus improving axonal conduction, has the potential to serve as a therapeutic mechanism for reducing the severity of some of these disorders. Myelin deficits have been previously linked to abnormalities in social behavior, suggesting an interplay between brain connectivity and sociability. This review focuses on Williams syndrome (WS), a genetic disorder characterized by neurocognitive characteristics and motor abnormalities, mainly known for its hypersociability characteristic. We discuss fundamental aspects of WM in WS and how its alterations can affect motor abilities and social behavior. Overall, findings regarding changes in myelin genes and alterations in WM structure in WS suggest new targets for drug therapy aimed at improving conduction properties and altering brain-activity synchronization in this disorder.

Neuroinflammation in Demyelinating Diseases: Oxidative Stress as a Modulator of Glial Cross-Talk

Myelin is a specialized membrane allowing for saltatory conduction of action potentials in neurons, an essential process to achieve the normal communication across the nervous system. Accordingly, in diseases characterized by the loss of myelin and myelin forming cells -oligodendrocytes in the CNS-, patients show severe neurological disabilities. After a demyelinated insult, microglia, astrocytes and oligodendrocyte precursor cells invade the lesioned area initiating a spontaneous process of myelin repair (i.e. remyelination). A preserved hallmark of this neuroinflammatory scenario is a local increase of oxidative stress, where several cytokines and chemokines are released by glial and other cells. This generates an environment that determines cell interaction resulting in oligodendrocyte maturity and the ability to synthesize new myelin. Herein we review the main features of the regulatory aspect of these molecules based on recent findings and propose new putative signal molecules involved in the remyelination process, focused in the etiology of Multiple Sclerosis, one of the main demyelinating diseases causing disabilities in the population.

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.

Genes that Mediate Metastasis across the Blood-Brain Barrier

Brain metastasis is an important cause of mortality in patients with cancer and represents the majority of all intracranial tumors. A key step during the metastatic journey of the cancer cell to the brain is the invasion through the blood-brain barrier (BBB). Nevertheless, the molecular mechanisms that govern this process remain unknown. The BBB has been blamed for limiting the access of therapeutic drugs to the brain, which provides a safe haven for cancer cells in the brain and confers poor prognosis for the patient. Here, we explore the genes that control the transmigration of metastatic cancer cells across the BBB, offering new targets for the development of gene and cell therapies against brain metastases.

Sema4D Aggravated LPS-Induced Injury via Activation of the MAPK Signaling Pathway in ATDC5 Chondrocytes

Osteoarthritis (OA) is the most common chronic degenerative joint disease, and it remains the main cause of chronic disability in elderly individuals. Sema4D (semaphorin 4D) is involved in the immune system and related to bone injury, osteoporosis, osteoblast differentiation, and rheumatoid arthritis. However, the role of Sema4D in OA remains unclear. Hence, the LPS-stimulated chondrocyte cell injury model was constructed in this study to investigate the role of Sema4D in OA development. The results showed that Sema4D was increased in LPS-treated ATDC5 cells, and the knockdown of Sema4D suppressed the decline of cell viability, the increase of cell apoptosis, and the increase of IL-6, IL-1β, and TNF-α secretion in ATDC5 cells induced by LPS. Meanwhile, Sema4D overexpression aggravated the cell injury triggered by LPS, and inhibiting Plexin B1 partly abolished the effect of Sema4D overexpression on LPS-induced chondrocyte injury. Furthermore, silencing of Sema4D blocked the activation of the MAPK pathway in LPS-stimulated ATDC5 cells. Enhanced Sema4D promoted the activation of the MAPK pathway in LPS-stimulated ATDC5 cells. What is more, inhibiting the MAPK signaling pathway abolished the promoting effect of Sema4D overexpression on LPS-induced chondrocyte injury. Therefore, our study suggested that the knockdown of Sema4D protects ATDC5 cells against LPS-induced injury through inactivation of the MAPK signaling pathway via interacting with Plexin B1.

Semaphorin 4A, 4C, and 4D: Function comparison in the autoimmunity, allergy, and cancer

Semaphorins are a group of proteins that are divided into eight subclasses and identified by a conserved Sema domain on their carboxyl terminus. Sema4A, 4C, and 4D are the members of the fourth class of semaphorin family, which are known as membrane semaphorins; however, these molecules can be altered to soluble semaphorins by proteolytic cleavage. Semaphorins have various roles in the immune, nervous, and metabolic systems. In the immune system, these molecules contribute to the formation of cellular, humoral, and innate immune responses, such as inflammation, leukocyte migration, immunological synapse formation, and germinal center events. Given the diverse roles of semaphorins in the immune system, in this review, we have tried to give a comprehensive look at the role of these molecules in autoimmunity, allergy, and cancer. Sema4D and 4A seem to play a critical role in the pathogenesis of some autoimmune diseases, such as multiple sclerosis. In contrast, it has been shown that Sema4A and 4C have beneficial effects on allergies, and their absence can exacerbate the severity of the disease. In the case of cancer, an increase in all three of these molecules has been reported. Sema4D and 4C can contribute to tumor progression in human patients or experimental models, while the role of Sema4A has not yet been fully understood. In conclusion, semaphorins seem to be a favorable therapeutic target for autoimmune diseases and allergies. However, in cancer, studies have not yet been able to identify the exact role of semaphorins, and further studies are needed.

Modulation of in vitro Brain Endothelium by Mechanical Trauma: Structural and Functional Restoration by Poloxamer 188

Brain injuries caused by an explosive blast or blunt force is typically presumed to associate with mechanical trauma to the brain tissue. Recent findings from our laboratory suggest that shockwaves produced by a blast can generate micron-sized bubbles in the tissue. The collapse of microbubbles (i.e., microcavitation) may induce a mechanical trauma and compromise the integrity of the blood-brain endothelium (BBE). To test our hypothesis, we engineered a BBE model to determine the effect of microbubbles on the structural and functional changes in the BBE. Using monolayers of mouse primary brain microvascular endothelial cells, the permeability coefficient was measured following simulated blast-induced microcavitation. This event down-regulated the expression of tight junction markers, disorganized the cell-cell junction, and increased permeability. Since poloxamers have been shown to rescue damaged cells, the cells were treated with the FDA-approved poloxamer 188 (P188). The results indicate P188 recovered the permeability, restored the tight junctions, and suppressed the expressions of matrix metalloproteinases. The biomimetic interface we developed appears to provide a systematic approach to replicate the structure and function of BBE, determine its alteration in response to traumatic brain injury, and test potential therapeutic treatments to repair the damaged brain endothelium.