Molecular aspects of poliovirus pathogenesis

Abstract

The development of a transgenic mouse model carrying the human poliovirus receptor has made it possible to investigate the molecular mechanisms of the viral dissemination process in a whole organism. Studies on this have provided an insight into the mechanisms for viral permeation through the blood-brain barrier and retrograde axonal transport of the virus. In addition, strain-specific neurovirulence levels are shown to depend mainly on the replicating capacity of the virus in the central nervous system rather than the efficiency of the 2 dissemination pathways indicated above. Studies of poliovirus-induced cytopathic effects on neural cells revealed that neural cells possess anti-poliovirus characteristics that may offer a new avenue for investigating the molecular mechanisms of poliovirus neurovirulence.

Keywords: dissemination; neurovirulence; poliovirus; poliovirus receptor; transgenic mouse.

Fig. 1.

Dissemination pathways of poliovirus in humans.

Fig. 2.

Genome organization of poliovirus type 1. Genomic RNA and its gene organization are shown. VPg is a small protein attached to the 5′ end of the genome; poly(A) is 3′ terminal. Nucleotide numbers are shown over the genome RNA. P1 represents the protein region of viral capsid; P2 and P3 non-capsid protein. Gene products are indicated by wavy lines, and figures in parentheses are molecular mass of the corresponding viral gene products. IRES stands for internal ribosome entry site.

Fig. 3.

Schematic structure of human poliovirus receptor (hPVR). Three linked extracellular Ig-like domains (V, C2, and C2 types) are followed by a membrane-spanning domain and a cytoplasmic domain.

Fig. 4.

Restriction map of the human PVR gene and multiple splicing of its transcript. Structures of mRNAs for hPVRα, hPVRβ, and hPVRγ are shown by open (untranslated sequences) and shaded (translated sequences) boxes. Numbers of exons are indicated at the top of the figure. Receptor regions are connected by thin lines to exons contained on a gene map shown underneath. Restriction cleavage sites of BamHI and HindIII are indicated by vertical bars with closed circles and open boxes, respectively. Sequences of the human PVR gene cloned into cosmids HC3 and HC5 are indicated by bars. A scale for length of nucleotides of the PVR gene is shown by bar with arrowheads at both ends at the bottom of the figure. (quoted from ref. 2).

Fig. 5.

Amino acid sequences of cytoplasmic domains of hPVRα and hPVRδ. KXXR; Tctex-1 binding motif.

Fig. 6.

Conformational alteration of 160S (intact) poliovirus particle induced by the addition of soluble hPVR. Infectious poliovirus (160S) converts to 135S and 80S particles when the virus (160S) is incubated with the extracellular domain of hPVR in vitro.

Fig. 7.

Tissue distribution of poliovirus in mice after intravenous inoculation. (A) K_p,app values of [³⁵S]methionine-labeled MSM (a recombinant poliovirus Mahoney strain having the Sabin 1 derived capsid proteins) in various tissues were calculated in transgenic mice (vertical axis) and non-transgenic mice (horizontal axis) 5 h after the IV inoculation. (B) Transgenic mice were IV-injected with mAb p286 5 h before the IV inoculation of [³⁵S]methionine-labeled MSM.K_p,app values of MSM in various tissues were calculated (vertical axis) and transgenic mice pretreated with the mAb (horizontal axis) 5 h after the inoculation. (quoted from ref. 25).

Fig. 8.

Poliovirus antigens in axons. The sections of the sciatic nerves were prepared from a poliovirus-infected Tg mouse. The sections were immunostained with rabbit anti-poliovirus hyperimmune serum. (Left panel) Myelin sheaths can be seen. (Center panel) Bright fluorescence is visible. (Right panel) Merging picture of the left and center panels. Poliovirus antigens existing in axons surrounded by myelin sheath. Bar =50 μm. (modified from ref. 26).

Fig. 9.

Analysis of virus-related materials in the sciatic nerve. Tg mice with sciatic nerve ligation were intramuscularly inoculated with [³⁵S]methionine-labeled poliovirus Mahoney strain. Radioactive materials were recovered from the sciatic nerve and analyzed by sucrose density gradient centrifugation. (modified from ref. 26).

Fig. 10.

Possible mechanism for the retrograde axonal transport of poliovirus.

Fig. 11.

Genome structure of recombinant type 1 polioviruses. The expected genome structures of the recombinant viruses are shown as a combination of the Sabin 1 (open boxes) and Mahoney (closed boxes) sequences. The numbers over the genome RNAs are the nucleotide positions from the 5′ end of the genome. Nucleotide differences between the Mahoney and Sabin 1 strains are shown at the bottom of the figure. A small protein VPg is indicated by closed circles at the 5′ end of the genomes. Lesion scores obtained from monkey neurovirulence tests are shown on the right of the corresponding genome RNAs. (modified from refs. and 36).

Fig. 12.

Inhibition of the poliovirus-induced cytopathic effect in neural cells by mAb against poliovirus or hPVR. Neural cells (upper panels) or HeLa cells (lower panels) were infected with poliovirus type 1 Mahoney strain at an m.o.i. of 10. At 2 hpi, the cells were washed three times. Then, medium with or without mAb against poliovirus or hPVR was added to the culture. Poliovirus-infected or mock-infected cells were observed 24 hpi by microscope. (modified from ref. 43).