Genetic Determinants of Reovirus Pathogenesis in a Murine Model of Respiratory Infection

Abstract

Many viruses invade mucosal surfaces to establish infection in the host. Some viruses are restricted to mucosal surfaces, whereas others disseminate to sites of secondary replication. Studies of strain-specific differences in reovirus mucosal infection and systemic dissemination have enhanced an understanding of viral determinants and molecular mechanisms that regulate viral pathogenesis. After peroral inoculation, reovirus strain type 1 Lang replicates to high titers in the intestine and spreads systemically, whereas strain type 3 Dearing (T3D) does not. These differences segregate with the viral S1 gene segment, which encodes attachment protein 1 and nonstructural protein 1s. In this study, we define genetic determinants that regulate reovirus-induced pathology following intranasal inoculation and respiratory infection. We report that two laboratory isolates of T3D, T3D C and T3D F , differ in the capacity to replicate in the respiratory tract and spread systemically; the T3D C isolate replicates to higher titers in the lungs and disseminates, while T3D F does not. Two nucleotide polymorphisms in the S1 gene influence these differences, and both S1 gene products are involved. T3D C amino acid polymorphisms in the tail and head domains of 1 protein influence the sensitivity of virions to protease-mediated loss of infectivity. The T3D C polymorphism at nucleotide 77, which leads to coding changes in both S1 gene products, promotes systemic dissemination from the respiratory tract. A 1s-null virus produces lower titers in the lung after intranasal inoculation and disseminates less efficiently to sites of secondary replication. These findings provide new insights into mechanisms underlying reovirus replication in the respiratory tract and systemic spread from the lung. Many viruses enter host organisms by invading mucosal surfaces, including those that line the respiratory tract. Infection by some pneumotropic viruses is restricted to the respiratory tract, whereas others replicate in the lung and disseminate to sites of secondary replication. Mammalian orthoreoviruses (reoviruses) naturally infect both the respiratory and gastrointestinal tracts (1). Reovirus strains differ in the capacity to replicate at mucosal sites and disseminate systemically. Studies of strain-specific differences in reovirus mucosal infection and systemic spread have enhanced an understanding of viral determinants and molecular mechanisms that regulate reovirus pathogenesis. For example, after peroral or intratracheal inoculation, reovirus strain type 1 Lang (T1L) replicates to higher titers than does strain type 3 Dearing (T3D) (2). This difference in replication efficiency at the site of primary replication segregates with the reovirus S1 gene segment (2, 3). Like T1L, reassortant virus 3HA1, with nine gene segments from T3D and an S1 gene from T1L, replicates to high titers in mucosal tissues (2). In contrast, reassortant virus 1HA3, with nine gene segments from T1L and an S1 gene from T3D, fails to replicate to high titers at those sit...

Amino acids substitutions in σ1 and μ1 outer capsid proteins of a Vero cell-adapted mammalian orthoreovirus are required for optimal virus binding and disassembly

“…The exact significance of these variations in the amount of virion-incorporated σ1, if any, remains to be established but is likely due to differences in the structural stability of the capsid (Coombs, 1998). This is also supported by the observation that the loss of σ1 upon long-term storage of the virion at 4ºC is more drastic in strains that already have a lower amount of σ1 per virion (Nygaard et al, 2013).…”

“…It is interesting to note that reducing trimers to only three copies does not seem to affect infectivity, at least in L929 cells (Larson et al, 1994); the lack of effect on viral infectivity on Vero cells when the number of wild-type σ1 trimers increased is also consistent with this idea. Interestingly, an approximately 3-fold difference in σ1 incorporation between two viral clones of reovirus type 3 Dearing was also recently reported (Nygaard et al, 2013) and attributed to an amino acid substitution in the virion-anchoring region of σ1. In VeroAV, the substitution at position 78 is outside the critical 28 amino acid amino-terminal anchoring region; although it cannot be excluded that this substitution in the adjacent region may influence incorporation (Leone et al, 1991).…”

“…The σ1 protein forms the surface-exposed spikes at the surface of the virion and binds to both sialic acid and the JAM receptor at the cell surface (Danthi et al, 2010;Dermody et al, 2013), σ1 is also retained in infectious subviral particles (ISVPs) that are generated by proteolytic cleavage of the outer capsid proteins; in fact, reovirus uncoating has been shown to increase the binding of the resulting ISVPs to the cell surface (Chappell et al, 1998;Nibert et al, 1995). The proteolytic cleavage of the outer capsid, referred to as "uncoating", takes place in endosomes following endocytosis of the viral particles or in the extracellular milieu where proteases are present.…”

“…Uncoating can also be achieved in the laboratory by chymotrypsin treatment of virions and this facilitates infection of certain cell types, such as the Vero cells used in the present study, that are inefficient in their ability to uncoat the virus (Golden et al, 2002). During uncoating, the σ3 protein is first removed, followed by proteolytic cleavage of the μ1 protein, allowing the viral particles to cross the cellular or endosomal membrane (Danthi et al, 2010;Dermody et al, 2013). Together, the three outer capsid proteins σ1, σ3 and μ1, are thus critical in infectivity of the viral particles and initiation of the viral replication cycle.…”

Reduction of Virion-Associated σ1 Fibers on Oncolytic Reovirus Variants Promotes Adaptation toward Tumorigenic Cells

“…The finding by Larson et al that reovirus preparations consist of particles with 0 to 12 1 trimers was the first indication (to our knowledge) that 1 levels can vary on particles. Recently, Nygaard et al thoroughly compared the pathogeneses of two reovirus isolates in a murine model of respiratory infection (68). Differences in pathogenesis were attributed to two polymorphisms in 1: one in the tail region (nucleotide 77) that produces an amino acid change in both 1 and the second overlapping nonstructural protein 1-small (1s) and one in the head domain of 1.…”