De Novo Transcriptome Analysis Shows That SAV-3 Infection Upregulates Pattern Recognition Receptors of the Endosomal Toll-Like and RIG-I-Like Receptor Signaling Pathways in Macrophage/Dendritic Like TO-Cells.

Cheng Xu,Øystein Evensen,Hetron Munang’Andu

doi:10.3390/v8040114

Cheng Xu, Øystein Evensen + Show 1 more

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https://doi.org/10.3390/v8040114

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Journal: Viruses	Publication Date: Apr 21, 2016
Citations: 91	License type: CC BY 4.0

Affiliation: Norwegian University of Life Sciences

Abstract

A fundamental step in cellular defense mechanisms is the recognition of “danger signals” made of conserved pathogen associated molecular patterns (PAMPs) expressed by invading pathogens, by host cell germ line coded pattern recognition receptors (PRRs). In this study, we used RNA-seq and the Kyoto encyclopedia of genes and genomes (KEGG) to identify PRRs together with the network pathway of differentially expressed genes (DEGs) that recognize salmonid alphavirus subtype 3 (SAV-3) infection in macrophage/dendritic like TO-cells derived from Atlantic salmon (Salmo salar L) headkidney leukocytes. Our findings show that recognition of SAV-3 in TO-cells was restricted to endosomal Toll-like receptors (TLRs) 3 and 8 together with RIG-I-like receptors (RLRs) and not the nucleotide-binding oligomerization domain-like receptors NOD-like receptor (NLRs) genes. Among the RLRs, upregulated genes included the retinoic acid inducible gene I (RIG-I), melanoma differentiation association 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2). The study points to possible involvement of the tripartite motif containing 25 (TRIM25) and mitochondrial antiviral signaling protein (MAVS) in modulating RIG-I signaling being the first report that links these genes to the RLR pathway in SAV-3 infection in TO-cells. Downstream signaling suggests that both the TLR and RLR pathways use interferon (IFN) regulatory factors (IRFs) 3 and 7 to produce IFN-a2. The validity of RNA-seq data generated in this study was confirmed by quantitative real time qRT-PCR showing that genes up- or downregulated by RNA-seq were also up- or downregulated by RT-PCR. Overall, this study shows that de novo transcriptome assembly identify key receptors of the TLR and RLR sensors engaged in host pathogen interaction at cellular level. We envisage that data presented here can open a road map for future intervention strategies in SAV infection of salmon.

Highlights

A crucial step in cellular defense mechanisms against viral infection is recognition of danger signals that initiate signaling pathways aimed at protecting host cells against pathogen invasion [1].Apart from protecting host cells, recognition of microbial danger signals is a crucial step for targeted delivery of vaccine antigens into antigen presenting cells (APCs) as recently pointed out by Viruses 2016, 8, 114; doi:10.3390/v8040114 www.mdpi.com/journal/virusesMunang’andu and Evensen [2]
There are different pattern recognition receptors (PRRs) families identified in vertebrates that serve as immune sensors of pathogen associated molecular patterns” (PAMPs) and these include the Toll-like receptors (TLRs), retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), as well as the melanoma 2 (AIM2) like receptors (ALRs) and the cytoplasmic double stranded DNA sensors (CDSs) [5,6,7,8]
The TLR pathway had a marginal significance (p = 0.058), it was more significant than the NLR pathway (p = 0.91), while the RIG-I-like receptors (RLRs) pathway showed the highest significance (p = 0.024) of all the PRRs expressed in response to SAV-3 infection in TO-cells

Summary

Introduction

A crucial step in cellular defense mechanisms against viral infection is recognition of danger signals that initiate signaling pathways aimed at protecting host cells against pathogen invasion [1].Apart from protecting host cells, recognition of microbial danger signals is a crucial step for targeted delivery of vaccine antigens into antigen presenting cells (APCs) as recently pointed out by Viruses 2016, 8, 114; doi:10.3390/v8040114 www.mdpi.com/journal/virusesMunang’andu and Evensen [2]. A crucial step in cellular defense mechanisms against viral infection is recognition of danger signals that initiate signaling pathways aimed at protecting host cells against pathogen invasion [1]. The major players in recognition of microbial invasion are pattern recognition receptors (PRRs) made of germ line coded receptors that recognize conserved microbial features called “pathogen associated molecular patterns” (PAMPs) [3]. PRRs recognize endogenous host structures released after tissue damage called “damage associated molecular patterns”. There are different PRR families identified in vertebrates that serve as immune sensors of PAMPs and these include the Toll-like receptors (TLRs), retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), as well as the melanoma 2 (AIM2) like receptors (ALRs) and the cytoplasmic double stranded DNA sensors (CDSs) [5,6,7,8]. 17 members of the TLRs have been identified in different fish species [12,13]

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