Coxsackievirus infection in skeletal muscles of mice. An electron microscopic study. I. Cell- and nucleus alterations

Two membrane-associated regions within the Nodamura virus RNA-dependent RNA polymerase are critical for both mitochondrial localization and RNA replication

Viruses with positive-strand RNA genomes amplify their genomes in replication complexes associated with cellular membranes. Little is known about the mechanism of replication complex formation in cells infected with Nodamura virus. This virus is unique in its ability to lethally infect both mammals and insects. In mice and in larvae of the greater wax moth (Galleria mellonella), Nodamura virus-infected muscle cells exhibit mitochondrial aggregation and membrane rearrangement, leading to disorganization of the muscle fibrils on the tissue level and ultimately in hind limb/segment paralysis. However, the molecular basis for this pathogenesis and the role of mitochondria in Nodamura virus infection remains unclear. Here, we tested the hypothesis that Nodamura virus establishes RNA replication complexes that associate with mitochondria in mammalian cells. Our results showed that Nodamura virus replication complexes are targeted to mitochondria, as evidenced in biochemical, molecular, and confocal microscopy studies. More specifically, we show that the Nodamura virus RNA-dependent RNA polymerase interacts with the outer mitochondrial membranes as an integral membrane protein and ultimately becomes associated with functional replication complexes. These studies will help us to understand the mechanism of replication complex formation and the pathogenesis of Nodamura virus for mammals.

IMPORTANCE

This study will further our understanding of Nodamura virus (NoV) genome replication and its pathogenesis for mice. NoV is unique among the Nodaviridae in its ability to infect mammals. Here we show that NoV establishes RNA replication complexes (RCs) in association with mitochondria in mammalian cells. These RCs contain newly synthesized viral RNA and feature a physical interaction between mitochondrial membranes and the viral RNA-dependent RNA polymerase (RdRp), which is mediated by two membrane-associated regions. While the nature of the interaction needs to be explored further, it appears to occur by a mode distinct from that described for the insect nodavirus Flock House virus (FHV). The interaction of the NoV RdRp with mitochondrial membranes is essential for clustering of mitochondria into networks that resemble those described for infected mouse muscle and that are associated with fatal hind limb paralysis. This work therefore provides the first link between NoV RNA replication complex formation and the pathogenesis of this virus for mice.

Morphogenesis of the nodamura virus in the larbae of the lepidopteran Galleria mellonella (L.)

The pathogenesis and morphogenesis of the Nodamura virus, an insect picorna- virus which can also infect vertebrates such as newborn mice, are described in the larvae of G. mellonella. Examination of thin sections of muscle, salivary and moulting glands, hemocytes adipose tissue and hypodermis of the infected larvae of G. mellonella shows in the cytoplasm the accumulation of viral particles either dispersed or in a stringlike or paracrystalline array. These arrays of virions can be within membrane- bound vesicles. Helical filaments of 110 A of diameter can be observed inside the basal membranes and later in the cytoplasm, in relation to the infection of muscular or adipose tissues. The morphogenesis of Nodamura virus in G. mellonella or in suckling mice is very similar to that of the Coxsackie A virus observed in the mouse.

Effects of viral and mycoplasma infections on ultrastructure and enzyme activities in human skeletal muscle

The effect on skeletal muscle of acute viral and mycoplasma infections in thirteen men of ages ranging between 20-42 years has been studied. Comparisons are made with eight healthy men in the age group 22-29 years who were confined to bed for periods of time of lengths similar to the confinement to bed of the patients. Muscle samples were taken from the thigh. Glyceraldehyde-3-phosphate (triosephosphate) dehydrogenase (TPD), lactate dehydrogenase (LDH), citrate synthetase (CS) and cytochrome oxidase (cytox) activities were measured and the ultrastructure of the muscle specimens was studied by electron microscopy. Immobilization of the healthy persons induced decreased activities of CS, but those of TPD, LDH and cytox remained unaffected. Return to normal life restored the CS activity. The activities of the four enzymes were lower in the patients than in the healthy subjects after immobilization. During normal life, the activities slowly rose to levels as those seen in the healthy subjects. In connection with the acute disease, focal ultrastructural changes within the muscle were found. The changes were similar to those reported to occur in other, more specific muscle diseases.