Project description:The host response of the primary intestinal epithelium to human astrovirus (HAstV infection has not been elucidated to date. In order to characterize the global effects of AstV infection on human intestinal tissue, we performed transcriptional profiling of VA1-infected human intestinal enteroids (HIE) by RNAseq. We used the D124 line for our studies since AstV infections are typically symptomatic in very young children, and our prior infection studies indicated rapid infection in D124. D124 HIE were mock-infected or infected with VA1 (MOI = 1) and harvested at 0 hpi (i.e., 1h post-adsorption), 12 hpi, and 24 hpi (Fig 4A). To monitor viral replication, VA1 genome copies were detected by RT-qPCR, revealing an approximately 1 and 2 log increase at 12 and 24 hpi, respectively (Fig 4B). Cellular RNA was extracted and analyzed by RNAseq. Genome copies as determined by RT-qPCR were correlated to the proportion of viral transcripts in the pool of sequenced RNA collected from the same HIE cultures, revealing an exceptionally strong correlation between the two measures of viral replication (r2 = 0.98, P = 2.5 x 10^-14. VA1 genome reads contributed 0.05 ± 0.02 x% of total RNAseq reads at 24 hpi, further confirming robust infection. Differential expression analysis was performed to identify genes associated with the HIE host response to VA1 infection. A total of 23,220 genes were detected. Differential expression of genes at each timepoint was graphed in a volcano plot. The log2 fold change in normalized expression (transcripts per million reads [TPM]) of all expressed host genes in VA1-infected HIEs relative to mock-infected HIE is shown on the x-axis. The -log10 transformed P-value is given on the y-axis. Genes that are significantly up-regulated (adjusted P < 0.05) in VA1-infected D124 HIE relative to mock-infected HIE are colored red, while significantly down-regulated genes are colored blue. Overall, after a 1 hour adsorption (0 hpi), 110 genes were significantly upregulated and 136 genes were downregulated , indicating changes due to viral attachment to cells. This number was reduced at 12 hpi, with 8 significantly upregulated and 5 downregulated genes. At 24 hpi, 154 upregulated and 49 downregulated genes compared to the mock-infected control were identified. We next identified the top 15 significantly up- and down-regulated genes at 24 hpi. This group of genes was used to generated a heatmap of the mean scaled fold-change (Z-score) in expression of each of them in virus-infected HIE relative to mock-infected HIE at each timepoint (Fig 4D). Most of the upregulated genes at 24 hpi were involved in type I and type III interferon (IFN) signaling. Of the IFN genes, IFNL1 was highly upregulated, with IFNA1 and IFNB1 upregulation being slightly lower (Fig S4B). No upregulation was observed for the genes encoding IFN-γ, or the type I and III IFN receptors (data not shown). The top 12 IFN-stimulated genes (ISGs) also positively correlated with VA1 infection (Fig S4C). Conversely, the top 12 downregulated genes, including fermitin family member 1 (FERMT1), signal peptide peptidase like 3 (SPPL3), and tetratricopeptide repeat domain 19 (TTC19) negatively correlated with VA1 infection (Fig S4D). Next, we evaluated lists of the top 100 up- and down-regulated genes at 24 hpi using an over-abundance test to identify significantly over-represented REACTOME pathways in these lists. These data revealed that the top four significantly enriched pathways among upregulated genes were all related to innate antiviral signaling (Fig 4E), which will be investigated in more detail below. For downregulated genes, the top two pathways were “neurexins and neuroligins”, which play signaling roles in synapse development, and “protein-protein interactions at synapses”. The biological significance of synapses during astrovirus infection remains to be elucidated. In order to evaluate the potential for coordinated and directional activation of genes in known signaling pathways, we applied gene set enrichment analysis (GSEA) to our RNAseq differential expression data. Based on the strong dominance of IFN signaling pathways, we focused our GSEA analysis on immune signaling (Fig 4F). During the adsorption phase, nucleic acid pattern recognition receptor signaling pathways (TLRs, STING) were upregulated, consistent with their early role in virus recognition and induction of IFN signaling. At 24 hpi, these early signaling events had been largely replaced by the later phase of IFN signaling and expression of ISGs. Taken together, these data indicate that VA1 infection predominantly elicited antiviral IFN signaling in HIE-derived fetal duodenum at the transcript level.

Project description:Astrovirus VA1/HMO-C (VA1; mamastrovirus 9) is a recently discovered astrovirus genotype that is divergent from the classic human astroviruses (mamastrovirus 1). The gastrointestinal tract is presumed to be the primary site of infection and pathogenicity for astroviruses. However, VA1 has been independently detected in brain tissue of five cases of human encephalitis. Studies of the pathogenicity of VA1 are currently impossible because there are no reported cell culture systems or in vivo models that support VA1 infection. Here, we describe successful propagation of VA1 in multiple human cell lines. The initial inoculum, a filtered clinical stool sample from the index gastroenteritis case cluster that led to the discovery of VA1, was first passaged in Vero cells. Serial blind passage in Caco-2 cells yielded increasing copies of VA1 RNA, and multistep growth curves demonstrated a >100-fold increase in VA1 RNA 72 h after inoculation. The full-length genomic and subgenomic RNA strands were detected by Northern blotting, and crystalline lattices of viral particles of ∼26-nm diameter were observed by electron microscopy in infected Caco-2 cells. Unlike other human astrovirus cell culture systems, which require addition of exogenous trypsin for continued propagation, VA1 could be propagated equally well with or without the addition of trypsin. Furthermore, VA1 was sensitive to the type I interferon (IFN-I) response, as VA1 RNA levels were reduced by pretreatment of Caco-2 cells with IFN-β1a. The ability to propagate VA1 in cell culture will facilitate studies of the neurotropism and neuropathogenesis of VA1.IMPORTANCE Astroviruses are an emerging cause of central nervous system infections in mammals, and astrovirus VA1/HMO-C is the most prevalent astrovirus in cases of human encephalitis. This virus has not been previously propagated, preventing elucidation of the biology of this virus. We describe the first cell culture system for VA1, a key step necessary for the study of its ability to cause disease.

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Human Astrovirus VA1 Infection on Small Bowel Enteroids

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