Targeting Schwann cells by nonlytic arenaviral infection selectively inhibits myelination

The underlying mechanisms of arenaviral entry through matriglycan

Matriglycan, a recently characterized linear polysaccharide, is composed of alternating xylose and glucuronic acid subunits bound to the ubiquitously expressed protein α-dystroglycan (α-DG). Pathogenic arenaviruses, like the Lassa virus (LASV), hijack this long linear polysaccharide to gain cellular entry. Until recently, it was unclear through what mechanisms LASV engages its matriglycan receptor to initiate infection. Additionally, how matriglycan is synthesized onto α-DG by the Golgi-resident glycosyltransferase LARGE1 remained enigmatic. Recent structural data for LARGE1 and for the LASV spike complex informs us about the synthesis of matriglycan as well as its usage as an entry receptor by arenaviruses. In this review, we discuss structural insights into the system of matriglycan generation and eventual recognition by pathogenic viruses. We also highlight the unique usage of matriglycan as a high-affinity host receptor compared with other polysaccharides that decorate cells.

Potential molecular mechanisms of chronic fatigue in long haul COVID and other viral diseases

Historically, COVID-19 emerges as one of the most devastating diseases of humankind, which creates an unmanageable health crisis worldwide. Until now, this disease costs millions of lives and continues to paralyze human civilization's economy and social growth, leaving an enduring damage that will take an exceptionally long time to repair. While a majority of infected patients survive after mild to moderate reactions after two to six weeks, a growing population of patients suffers for months with severe and prolonged symptoms of fatigue, depression, and anxiety. These patients are no less than 10% of total COVID-19 infected individuals with distinctive chronic clinical symptomatology, collectively termed post-acute sequelae of COVID-19 (PASC) or more commonly long-haul COVID. Interestingly, Long-haul COVID and many debilitating viral diseases display a similar range of clinical symptoms of muscle fatigue, dizziness, depression, and chronic inflammation. In our current hypothesis-driven review article, we attempt to discuss the molecular mechanism of muscle fatigue in long-haul COVID, and other viral diseases as caused by HHV6, Powassan, Epstein-Barr virus (EBV), and HIV. We also discuss the pathological resemblance of virus-triggered muscle fatigue with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

Design of a specific peptide against phenolic glycolipid-1 from Mycobacterium leprae and its implications in leprosy bacilli entry

BACKGROUND

Mycobacterium leprae, the causative agent of Hansen’s disease, causes neural damage through the specific interaction between the external phenolic glycolipid-1 (PGL-1) and laminin subunit alpha-2 (LAMA2) from Schwann cells.

OBJECTIVE

To design a LAMA2-based peptide that targets PGL-1 from M. leprae.

METHODS

We retrieved the protein sequence of human LAMA2 and designed a specific peptide using the Antimicrobial Peptide Database and physicochemical parameters for antimycobacterial peptide-lipid interactions. We used the AlphaFold2 server to predict its three-dimensional structure, AUTODOCK-VINA for docking, and GROMACS programs for molecular dynamics simulations.

FINDINGS

We analysed 52 candidate peptides from LAMA2, and subsequent screening resulted in a single 60-mer peptide. The mapped peptide comprises four β-sheets and a random coiled region. This peptide exhibits a 45% hydrophobic ratio, in which one-third covers the same surface. Molecular dynamics simulations show that our predicted peptide is stable in aqueous solution and remains stable upon interaction with PGL-1 binding. In addition, we found that PGL-1 has a preference for one of the two faces of the predicted peptide, which could act as the preferential binding site of PGL-1.

MAIN CONCLUSIONS

Our LAMA2-based peptide targeting PGL-1 might have the potential to specifically block this key molecule, suggesting that the preferential region of the peptide is involved in the initial contact during the attachment of leprosy bacilli to Schwann cells.

The role of primary infection of Schwann cells in the aetiology of infective inflammatory neuropathies

Numerous different pathogens are responsible for infective peripheral neuropathies and this is generally the result of the indirect effects of pathogen infection, namely anti pathogen antibodies cross reacting with epitopes on peripheral nerve, auto reactive T cells attacking myelin, circulating immune complexes and complement fixation. Primary infection of Schwann cells (SC) associated with peripheral nerve inflammation is rare requiring pathogens to cross the Blood Peripheral Nerve Barrier (BPNB) evade anti-pathogen innate immune pathways and invade the SC. Spirochetes Borrelia bourgdorferi and Trepomema pallidum are highly invasive, express surface lipo proteins, but despite this SC are rarely infected. However, Trypanosoma cruzi (Chaga's disease) and Mycobacterium leprae. Leprosy are two important causes of peripheral nerve infection and both demonstrate primary infection of SC. This is due to two novel strategies; T. cruzi express a trans-silalidase that mimics host neurotrophic factors and infects SC via tyrosine kinase receptors. M. leprae demonstrates multi receptor SC tropism and subsequent infection promotes nuclear reprogramming and dedifferentiation of host SC into progenitor stem like cells (pSLC) that are vulnerable to M. leprae infection. These two novel pathogen evasion strategies, involving stem cells and receptor mimicry, provide potential therapeutic targets relevant to the prevention of peripheral nerve inflammation by inhibiting primary SC infection.

Animal Model of Sensorineural Hearing Loss Associated with Lassa Virus Infection

Approximately one-third of Lassa virus (LASV)-infected patients develop sensorineural hearing loss (SNHL) in the late stages of acute disease or in early convalescence. With 500,000 annual cases of Lassa fever (LF), LASV is a major cause of hearing loss in regions of West Africa where LF is endemic. To date, no animal models exist that depict the human pathology of LF with associated hearing loss. Here, we aimed to develop an animal model to study LASV-induced hearing loss using human isolates from a 2012 Sierra Leone outbreak. We have recently established a murine model for LF that closely mimics many features of human disease. In this model, LASV isolated from a lethal human case was highly virulent, while the virus isolated from a nonlethal case elicited mostly mild disease with moderate mortality. More importantly, both viruses were able to induce SNHL in surviving animals. However, utilization of the nonlethal, human LASV isolate allowed us to consistently produce large numbers of survivors with hearing loss. Surviving mice developed permanent hearing loss associated with mild damage to the cochlear hair cells and, strikingly, significant degeneration of the spiral ganglion cells of the auditory nerve. Therefore, the pathological changes in the inner ear of the mice with SNHL supported the phenotypic loss of hearing and provided further insights into the mechanistic cause of LF-associated hearing loss.

IMPORTANCE

Sensorineural hearing loss is a major complication for LF survivors. The development of a small-animal model of LASV infection that replicates hearing loss and the clinical and pathological features of LF will significantly increase knowledge of pathogenesis and vaccine studies. In addition, such a model will permit detailed characterization of the hearing loss mechanism and allow for the development of appropriate diagnostic approaches and medical care for LF patients with hearing impairment.

Junín virus pathogenesis and virus replication

Junín virus, the etiological agent of Argentine hemorrhagic fever, causes significant morbidity and mortality. The virus is spread through the aerosolization of host rodent excreta and endemic to the humid pampas of Argentina. Recently, significant progress has been achieved with the development of new technologies (e.g. reverse genetics) that have expanded knowledge about the pathogenesis and viral replication of Junín virus. We will review the pathogenesis of Junín virus in various animal models and the role of innate and adaptive immunity during infection. We will highlight current research regarding the role of molecular biology of Junín virus in elucidating virus attenuation. We will also summarize current knowledge on Junín virus pathogenesis focusing on the recent development of vaccines and potential therapeutics.

Design and screening of a glial cell-specific, cell penetrating peptide for therapeutic applications in multiple sclerosis

Multiple Sclerosis (MS) is an autoimmune, neurodegenerative disease of the central nervous system (CNS) characterized by demyelination through glial cell loss. Current and proposed therapeutic strategies to arrest demyelination and/or promote further remyelination include: (i) modulation of the host immune system; and/or (ii) transplantation of myelinating/stem or progenitor cells to the circulation or sites of injury. However, significant drawbacks are inherent with both approaches. Cell penetrating peptides (CPP) are short amino acid sequences with an intrinsic ability to translocate across plasma membranes, and theoretically represent an attractive vector for delivery of therapeutic peptides or nanoparticles to glia to promote cell survival or remyelination. The CPPs described to date are commonly non-selective in the cell types they transduce, limiting their therapeutic application in vivo. Here, we describe a theoretical framework for design of a novel CPP sequence that selectively transduces human glial cells (excluding non-glial cell types), and conduct preliminary screens of purified, recombinant CPPs with immature and matured human oligodendrocytes and astrocytes, and two non-glial cell types. A candidate peptide, termed TD2.2, consistently transduced glial cells, was significantly more effective at transducing immature oligodendrocytes than matured progeny, and was virtually incapable of transducing two non-glial cell types: (i) human neural cells and (ii) human dermal fibroblasts. Time-lapse confocal microscopy confirms trafficking of TD2.2 (fused to EGFP) to mature oligodendrocytes 3-6 hours after protein application in vitro. We propose selectivity of TD2.2 for glial cells represents a new therapeutic strategy for the treatment of glial-related disease, such as MS.

Decoding arenavirus pathogenesis: essential roles for alpha-dystroglycan-virus interactions and the immune response

Pathogenesis following a virus infection results from interactions between the virus and its host. The outcome is determined by tipping the balance between virulence of the virus or susceptibility/resistance of the host to favor one or the other. This review focuses on two important members of the Old World arenavirus family: Lassa fever virus (LFV), a robust human pathogen that causes a severe acute hemorrhagic disease; and lymphocytic choriomeningitis virus (LCMV), also a human pathogen but better known in the context of its rodent model. Research with this model has uncovered and illuminated many of our current concepts in immunobiology and viral pathogenesis. Presented here are recent advances that form the framework for a better understanding of how viruses induce and maintain persistent infection as well as for the pathogenesis associated with acute LFV infection. A major component for understanding the pathogenesis of these arenaviruses revolves around study of the interaction of virus with its receptor, alpha-dystroglycan (α-DG).

Biological role of dystroglycan in Schwann cell function and its implications in peripheral nervous system diseases

Dystroglycan is a central component of the dystrophin-glycoprotein complex (DGC) that links extracellular matrix with cytoskeleton, expressed in a variety of fetal and adult tissues. Dystroglycan plays diverse roles in development and homeostasis including basement membrane formation, epithelial morphogenesis, membrane stability, cell polarization, and cell migration. In this paper, we will focus on biological role of dystroglycan in Schwann cell function, especially myelination. First, we review the molecular architecture of DGC in Schwann cell abaxonal membrane. Then, we will review the loss-of-function studies using targeted mutagenesis, which have revealed biological functions of each component of DGC in Schwann cells. Based on these findings, roles of dystroglycan in Schwann cell function, in myelination in particular, and its implications in diseases will be discussed in detail. Finally, in view of the fact that understanding the role of dystroglycan in Schwann cells is just beginning, future perspectives will be discussed.

Laminin isoforms in development and disease

The members of the laminin family of heterotrimers are major constituents of all basement membranes, sheet-like extracellular structures, present in almost all organs. The laminins bind to cell surface receptors and thereby tightly connect the basement membrane to the adjacent cell layer. This provides for the specific basement membrane functions to stabilize cellular structures, to serve as effective physical barriers, and furthermore, to govern cell fate by inducing intracellular signalling cascades. Many different types of diseases involve basement membranes and laminins. Metastasizing solid tumors must pass through basement membranes to reach the vascular system, and various microbes and viruses enter the cells through direct interaction with laminins. Furthermore, whereas mutations in one specific laminin chain lead to a muscular disorder, mutations of other laminin chains cause skin blistering and kidney defects, respectively. This review summarizes recent progress concerning the molecular mechanisms of laminins in development and disease. The current knowledge may lead to clinical treatment of lamininopathies and may include stem-cell approaches as well as gene therapy.

Viral persistence: parameters, mechanisms and future predictions

For a virus to persist, it must actively curtail the host's antiviral immune response. Here, we review the conceptual basis by which this can occur and discuss the subsequent fate of differentiated cells infected over long periods of time. We also consider how the compromised antiviral immune response can be revigorated or replaced with a potent response that purges the virus and thereby terminates persistent infection.

Posttranslational modification of alpha-dystroglycan, the cellular receptor for arenaviruses, by the glycosyltransferase LARGE is critical for virus binding

The receptor for lymphocytic choriomeningitis virus (LCMV), the human pathogenic Lassa fever virus (LFV), and clade C New World arenaviruses is alpha-dystroglycan (alpha-DG), a cell surface receptor for proteins of the extracellular matrix (ECM). Specific posttranslational modification of alpha-DG by the glycosyltransferase LARGE is critical for its function as an ECM receptor. In the present study, we show that LARGE-dependent modification is also crucial for alpha-DG's function as a cellular receptor for arenaviruses. Virus binding involves the mucin-type domain of alpha-DG and depends on modification by LARGE. A crucial role of the LARGE-dependent glycosylation of alpha-DG for virus binding is found for several isolates of LCMV, LFV, and the arenaviruses Mobala and Oliveros. Since the posttranslational modification by LARGE is crucial for alpha-DG recognition by both arenaviruses and the host-derived ligand laminin, it also influences competition between virus and laminin for alpha-DG. Hence, LARGE-dependent glycosylation of alpha-DG has important implications for the virus-host cell interaction and the pathogenesis of LFV in humans.

Disruption of the mouse Large gene in the enr and myd mutants results in nerve, muscle, and neuromuscular junction defects

The autosomal recessive neuromuscular disorder associated with the enervated (enr) mouse transgene insertion manifests impaired peripheral nerve regeneration due to defects in Schwann cells and resembles the myodystrophy (Large(myd)) phenotype. Here we show that the enr transgene has integrated into Chr 8 approximately 160 kb downstream from the 3' end of the Large gene disrupting its expression as confirmed by the lack of genetic complementation between Large(myd) and enr mice, the very low Large mRNA levels in enr tissues and hypoglycosylation of alpha-dystroglycan, a known substrate of LARGE. Mutant nerve conduction and grip strength were impaired whereas sodium channel clustering at the nodes of Ranvier was unaffected. Interestingly, the mutant neuromuscular junctions displayed abnormal acetylcholine receptor clustering with reduced immunostaining for beta-dystroglycan, laminin, agrin, MuSK, and to a lesser extent acetylcholinesterase and rapsyn. These data implicate LARGE in nerve, muscle, and neuromuscular junction function.

Type I interferons act directly on CD8 T cells to allow clonal expansion and memory formation in response to viral infection

T cell expansion and memory formation are generally more effective when elicited by live organisms than by inactivated vaccines. Elucidation of the underlying mechanisms is important for vaccination and therapeutic strategies. We show that the massive expansion of antigen-specific CD8 T cells that occurs in response to viral infection is critically dependent on the direct action of type I interferons (IFN-Is) on CD8 T cells. By examining the response to infection with lymphocytic choriomeningitis virus using IFN-I receptor–deficient (IFN-IR⁰) and –sufficient CD8 T cells adoptively transferred into normal IFN-IR wild-type hosts, we show that the lack of direct CD8 T cell contact with IFN-I causes >99% reduction in their capacity to expand and generate memory cells. The diminished expansion of IFN-IR⁰ CD8 T cells was not caused by a defect in proliferation but by poor survival during the antigen-driven proliferation phase. Thus, IFN-IR signaling in CD8 T cells is critical for the generation of effector and memory cells in response to viral infection.

Characterization of the interaction of lassa fever virus with its cellular receptor alpha-dystroglycan

The cellular receptor for the Old World arenaviruses Lassa fever virus (LFV) and lymphocytic choriomeningitis virus (LCMV) has recently been identified as alpha-dystroglycan (alpha-DG), a cell surface receptor that provides a molecular link between the extracellular matrix and the actin-based cytoskeleton. In the present study, we show that LFV binds to alpha-DG with high affinity in the low-nanomolar range. Recombinant vesicular stomatitis virus pseudotyped with LFV glycoprotein (GP) adopted the receptor binding characteristics of LFV and depended on alpha-DG for infection of cells. Mapping of the binding site of LFV on alpha-DG revealed that LFV binding required the same domains of alpha-DG that are involved in the binding of LCMV. Further, LFV was found to efficiently compete with laminin alpha1 and alpha2 chains for alpha-DG binding. Together with our previous studies on receptor binding of the prototypic immunosuppressive LCMV isolate LCMV clone 13, these findings indicate a high degree of conservation in the receptor binding characteristics between the highly human-pathogenic LFV and murine-immunosuppressive LCMV isolates.

In vitro and other alternative approaches to developmental neurotoxicity testing (DNT)

To address the growing need for scientifically valid and humane alternatives to developmental neurotoxicity testing (DNT), we propose that basic research scientists in developmental neurobiology be brought together with mechanistic toxicologists and policy analysts to develop the science and policy for DNT alternatives that are based on evolutionarily conserved mechanisms of neurodevelopment. In this article we briefly review in vitro and other alternative models and present our rationale for proposing that resources be focused on adapting alternative simple organism systems for DNT. We recognize that alternatives to DNT will not completely replace a DNT paradigm that involves in vivo testing in mammals. However, we believe that alternatives will be of great value in prioritizing chemicals and in identifying mechanisms of developmental neurotoxicity, which in turn will be useful in refining and reducing in vivo mammalian tests for exposures most likely to be hazardous to the developing human nervous system.

Mycobacterium leprae-induced demyelination: a model for early nerve degeneration

The molecular events that occur at the early phase of many demyelinating neurodegenerative diseases are unknown. A recent demonstration of rapid demyelination and axonal injury induced by Mycobacterium leprae provides a model for elucidating the molecular events of early nerve degeneration which might be common to neurodegenerative diseases of both infectious origin and unknown etiology. The identification of the M. leprae-targeted Schwann cell receptor, dystroglycan, and its associated molecules in myelination, demyelination and axonal functions suggests a role for these molecules in early nerve degeneration.