Azadirachta indica A. Juss Ameliorates Mouse Hepatitis Virus-Induced Neuroinflammatory Demyelination by Modulating Cell-to-Cell Fusion in an Experimental Animal Model of Multiple Sclerosis.

Lucky Sarkar,Ravi Kiran Putchala,Abass Alao Safiriyu,Jayasri Das Sarma

doi:10.3389/fncel.2020.00116

Abstract

Mouse hepatitis virus (MHV)-induced murine neuroinflammation serves as a model to study acute meningoencephalomyelitis, hepatitis, and chronic neuroinflammatory demyelination; which mimics certain pathologies of the human neurologic disease, multiple sclerosis (MS). MHV-induced acute neuroinflammation occurs due to direct glial cell dystrophy instigated by central nervous system (CNS)-resident microglia and astrocytes, in contrast to peripheral CD4+T cell-mediated myelin damage prevalent in the experimental autoimmune encephalomyelitis (EAE) model of MS. Viral envelope Spike glycoprotein-mediated cell-to-cell fusion is an essential mechanistic step for MHV-induced CNS pathogenicity. Although Azadirachta indica (Neem), a traditional phytomedicine, is known for its anti-inflammatory, anti-fungal, and spermicidal activities, not much is known about anti-neuroinflammatory properties of its bark (NBE) in MHV-induced acute neuroinflammation and chronic demyelination. Recombinant demyelinating MHV strain (RSA59) was preincubated with NBE to arrest the infection-initiation event, and its effect on viral replication, viral transcription, cytokine expression, and successive pathogenicity were investigated in vitro and in vivo. Virus-free Luciferase assay explained NBE’s anti-virus-to-cell fusion activity in vitro. Intracranial inoculation of RSA59 preincubated with NBE into the mouse brain significantly reduces acute hepatitis, meningoencephalomyelitis, and chronic progressive demyelination. Additionally, NBE effectively restricts viral entry, dissemination in CNS, viral replication, viral transcription, and expression of the viral nucleocapsid and inflammatory cytokines. From mechanistic standpoints, RSA59 preincubated with NBE reduced viral entry, viral replication and cell-to-cell fusion, as a mode of viral dissemination. Moreover, intraperitoneal injection with NBE (25 mg/kg B.W.) into mice revealed a significant reduction in viral Nucleocapsid protein expression in vivo. Conclusively, A. indica bark extract may directly bind to the virus-host attachment Spike glycoprotein and suppresses MHV-induced neuroinflammation and neuropathogenesis by inhibiting cell-to-cell fusion and viral replication. Further studies will focus on combining bioanalytical assays to isolate potential NBE bioactive compound(s) that contribute towards the anti-viral activity of NBE.

Highlights

Neuroinflammatory cascades play an important defensive role against various pathogenic stimuli, toxins, ischemic injury, and protein accumulation that induce neurodegeneration and can challenge the host immune system
Neuro-2A cells post-incubated with Neem bark extract (NBE) following viral infection at MOI of 1 showed that NBE inhibited enhanced green fluorescence protein (EGFP) expressing syncytia formation and restricted viral spread entirely at 12 h p.i. (Figures 1D–I)
A top-down experimental approach was applied by using Azadirachta indica crude bark extract (NBE) to assess its potential neuroprotective effect and avoid bias

Summary

Introduction

Neuroinflammatory cascades play an important defensive role against various pathogenic stimuli, toxins, ischemic injury, and protein accumulation that induce neurodegeneration and can challenge the host immune system. MHV (m-CoV) mainly infects mouse and induces acute hepatitis, meningitis, encephalitis, myelitis, and chronic phase progressive demyelination concurrent with axonal loss and serves as an experimental model for human neurological disease multiple sclerosis (MS; Bjartmar et al, 2003). MS is commonly studied in experimental autoimmune encephalitis (EAE) models which demonstrate that myelinspecific CD4+T cells cause neuroinflammation and subsequent demyelination Though this model is well-established, it is unable to dissect direct viral infection-induced myelin damage as opposed to CD4+T cell-mediated pathology. In this context, MHV-induced neuroinflammatory demyelination is considered a unique experimental animal model to study the role of direct neural cell death and damage, which may contribute to axonal loss and myelin damage as an inside-out model of demyelination (Weiner, 1973; Lavi et al, 1984a)

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