Cell-to-Cell Measles Virus Spread between Human Neurons Is Dependent on Hemagglutinin and Hyperfusogenic Fusion Protein

Abstract

Measles virus (MV) usually causes acute infection but in rare cases persists in the brain, resulting in subacute sclerosing panencephalitis (SSPE). Since human neurons, an important target affected in the disease, do not express the known MV receptors (signaling lymphocyte activation molecule [SLAM] and nectin 4), how MV infects neurons and spreads between them is unknown. Recent studies have shown that many virus strains isolated from SSPE patients possess substitutions in the extracellular domain of the fusion (F) protein which confer enhanced fusion activity. Hyperfusogenic viruses with such mutations, unlike the wild-type MV, can induce cell-cell fusion even in SLAM- and nectin 4-negative cells and spread efficiently in human primary neurons and the brains of animal models. We show here that a hyperfusogenic mutant MV, IC323-F(T461I)-EGFP (IC323 with a fusion-enhancing T461I substitution in the F protein and expressing enhanced green fluorescent protein), but not the wild-type MV, spreads in differentiated NT2 cells, a widely used human neuron model. Confocal time-lapse imaging revealed the cell-to-cell spread of IC323-F(T461I)-EGFP between NT2 neurons without syncytium formation. The production of virus particles was strongly suppressed in NT2 neurons, also supporting cell-to-cell viral transmission. The spread of IC323-F(T461I)-EGFP was inhibited by a fusion inhibitor peptide as well as by some but not all of the anti-hemagglutinin antibodies which neutralize SLAM- or nectin-4-dependent MV infection, suggesting the presence of a distinct neuronal receptor. Our results indicate that MV spreads in a cell-to-cell manner between human neurons without causing syncytium formation and that the spread is dependent on the hyperfusogenic F protein, the hemagglutinin, and the putative neuronal receptor for MV. Measles virus (MV), in rare cases, persists in the human central nervous system (CNS) and causes subacute sclerosing panencephalitis (SSPE) several years after acute infection. This neurological complication is almost always fatal, and there is currently no effective treatment for it. Mechanisms by which MV invades the CNS and causes the disease remain to be elucidated. We have previously shown that fusion-enhancing substitutions in the fusion protein of MVs isolated from SSPE patients contribute to MV spread in neurons. In this study, we demonstrate that MV bearing the hyperfusogenic mutant fusion protein spreads between human neurons in a cell-to-cell manner. Spread of the virus was inhibited by a fusion inhibitor peptide and antibodies against the MV hemagglutinin, indicating that both the hemagglutinin and hyperfusogenic fusion protein play important roles in MV spread between human neurons. The findings help us better understand the disease process of SSPE.

Subacute sclerosing panencephalitis

“…The hyperfusogenic properties facilitate the virus for cell‐cell fusion with SLAM and nectin‐4 deficient neuronal cells. H protein and its interaction with a specific neuronal receptor is also important for viral spread between neurons . F protein–mediated transmission of the virus across synapse to another neuronal cell can potentially be inhibited by a fusion inhibitor peptide and antibodies against the measles virus H protein.…”

“…F protein–mediated transmission of the virus across synapse to another neuronal cell can potentially be inhibited by a fusion inhibitor peptide and antibodies against the measles virus H protein. Both hyperfusogenic F protein and the H protein are crucial for transneuronal spread of measles virus …”

Subacute sclerosing panencephalitis: clinical phenotype, epidemiology, and preventive interventions

“…2 In cases of SSPE that developed in children or adults with no history of prior measles infection, but who did have a history of vaccination against measles virus, analysis of measles virus sequences confirmed the presence of the wild-type genome, indicating that the individuals had suffered an undiagnosed measles virus infection. 24,25 Measles virus is believed to enter the brain during the primary infection. 24,25 Measles virus is believed to enter the brain during the primary infection.…”

“…3 Recent evidence suggests that mutations that alter viral envelope glycoproteins, in particular the F protein, are responsible for neurovirulence. 24,25 Strong antiviral immune responses in the host are evidenced by high levels of specific antibody in blood and cerebrospinal fluid (CSF) and are a characteristic feature of this condition. By remaining in cells, the virus evades the host's immune response.…”

“…By remaining in cells, the virus evades the host's immune response. 24,25 Strong antiviral immune responses in the host are evidenced by high levels of specific antibody in blood and cerebrospinal fluid (CSF) and are a characteristic feature of this condition. 23 Clinical course of SSPE SSPE typically begins with behavioural and intellectual disability followed by paroxysmal movements, myoclonic jerks, and/or negative myoclonia (head drops).…”