RNA-Seq Analysis Reveals Genes Underlying Different Disease Responses to Porcine Circovirus Type 2 in Pigs

Yanping Li,Shijin Jiang,Ping Zhang,Yunliang Jiang,Hao Liu,Liyuan Wang,Yi Sun,Pengfei Wang,Li Kang,Gen Liu

doi:10.1371/journal.pone.0155502

Abstract

Porcine circovirus type 2 (PCV2), an economically important pathogen, causes postweaning multisystemic wasting syndrome (PMWS) and other syndrome diseases collectively known as porcine circovirus-associated disease (PCVAD). Previous studies revealed breed-dependent differences in porcine susceptibility to PCV2; however, the genetic mechanism underlying different resistance to PCV2 infection remains largely unknown. In this study, we found that Yorkshire × Landrace (YL) pigs exhibited serious clinical features typifying PCV2 disease, while the Laiwu (a Chinese indigenous pig breed, LW) pigs showed little clinical symptoms of the disease during PCV2 infection. At 35 days post infection (dpi), the PCV2 DNA copy in YL pigs was significantly higher than that in LW pigs (P < 0.05). The serum level of IL-4, IL-6, IL-8, IL-12 and TGF-β1 in LW pigs and TNF-α in YL pigs increased significantly at the early infected stages, respectively; while that of IL-10 and IFN-γ in YL pigs was greatly increased at 35 dpi. RNA-seq analysis revealed that, at 35 dpi, 83 genes were up-regulated and 86 genes were down-regulated in the lung tissues of LW pigs, while in YL pigs, the numbers were 187 and 18, respectively. In LW pigs, the differentially expressed genes (DEGs) were mainly involved in complement and coagulation cascades, metabolism of xenobiotics by cytochrome P450, RIG-I-like receptor signaling and B cell receptor signaling pathways. Four up-regulated genes (TFPI, SERPNC1, SERPNA1, and SERPNA5) that are enriched in complement and coagulation cascades pathway were identified in the PCV2-infected LW pigs, among which the mRNA expression of SERPNA1, as well as three genes including TGF-β1, TGF-β2 and VEGF that are regulated by SERPNA1 was significantly increased (P < 0.05). We speculate that higher expression of SERPNA1 may effectively suppress excessive inflammation reaction and reduce the pathological degree of lung tissue in PCV2-infected pigs. Collectively, our findings indicate that the susceptibility to PCV2 infection depends on a genetic difference between LW and YL pigs, and SERPNA1 likely plays an important role in the resistance of LW pigs to PCV2 infection.

Highlights

Porcine circovirus (PCV) is a small, non-enveloped virus of the Circoviridae family, with a small, circular, single-stranded DNA molecule of approximately 1.7 kb in size [1,2,3,4]
We found that Porcine circovirus type 2 (PCV2) infection triggered an excessive immune and inflammatory response in the Yorkshire × Landrace (YL) pigs, and this contributed to severe tissue damage, lung damage but mild symptoms in LW pigs, and the higher expression of SERPINA1 in lung tissue was identified as an important mechanism preventing lung damage induced by PCV2 infection in LW pigs
During PCV2 infection, the trend of weight gain in PCV2-infected LW pigs were consistent with uninfected LW pigs (Fig 2A), while the PCV2-infected YL pigs had significantly lower average daily gain of body weight from 14 dpi to 35 dpi compared with uninfected pigs (P < 0.05) (Fig 2B)

Summary

Introduction

Porcine circovirus (PCV) is a small, non-enveloped virus of the Circoviridae family, with a small, circular, single-stranded DNA molecule of approximately 1.7 kb in size [1,2,3,4]. PCV2 virus alters the cytokine responses and leads to cytokine imbalance through targeting the lymphoid tissues and immune cells [15,16,17]. Studies revealed that IL-10, IL-1 and TNF-α in serum were up-regulated, while IL-2 and IL-4 were down-regulated in PCV2-infected pigs with PCVAD [14, 19]. Up-regulation of IL-10 expression in the thymus associated with thymic depletion and atrophy [20] and elevated IL-10 and serum PCV2 level [21,22,23] were reported in PCV2-infected pigs. PCV2 infection induces strong IL-1β and IL-8 responses in the peripheral blood mononuclear cells [24] and higher level of TNF-α, G-CSF, MCP-1, and IL-8 in alveolar macrophage [25, 26]

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