Mechanism of cell death during infectious salmon anemia virus infection is cell type-specific

Abstract

Infectious salmon anemia virus (ISAV) is a very important fish virus in the Northern hemisphere and there is continued interest in understanding the mechanisms of its pathogenesis and persistence in fish. In this study, the permissive fish cell lines SHK-1, CHSE-214 and TO were used to determine whether ISAV-induced cytopathic effect (CPE) is due to apoptosis or necrosis. Characteristic apoptotic DNA fragmentation was observed only in ISAV-infected SHK-1 and CHSE-214 cells. Apoptosis in ISAV-infected SHK-1 cells was confirmed by fragment end-labelling assay, suggesting that CPE in these cells is associated with apoptosis. ISAV-infected TO cells did not undergo apoptosis, but showed leakage of high-mobility group 1 (HMGB1) protein from the nucleus, which is characteristic of cells undergoing necrosis; this suggests that CPE in these cells is associated with necrosis. ISAV-infected SHK-1 cells did not show leakage of HMGB1 protein. Infection with two different strains of ISAV showed that induction of apoptosis was correlated with the appearance of CPE in SHK-1 cells. ISAV-induced apoptosis was inhibited by a pan-caspase inhibitor, Z-VAD-fmk, indicating a caspase-activation pathway. The ISAV putative PB2 protein and proteins encoded by RNA segment 7 bound caspase-8 specifically in vitro, suggesting that these viral proteins may have a role in ISAV-induced apoptosis. These findings demonstrate for the first time that the mechanism of cell death during ISAV infection is dependent on the cell type, which may have implications for ISAV pathogenesis and persistence. INTRODUCTIONInfectious salmon anemia (ISA) virus (ISAV) is the causative agent of ISA, which is a highly infectious disease of farmed Atlantic salmon in the Northern hemisphere. This virus is a member of the family Orthomyxoviridae, genus Isavirus (Falk et al., 1997;Krossøy et al., 1999; www. ncbi.nlm.nih.gov/ICTVdb/Ictv/index.htm). The clinical disease in farmed Atlantic salmon is characterized by high mortality with exophthalmia, pale gills, ascites, haemorrhagic liver necrosis, renal interstitial haemorrhage and tubular nephrosis. ISAV is known to cause overt and fatal systemic infection in farmed Atlantic salmon and asymptomatic infection in feral fish, a situation analogous to that caused by avian influenza viruses in domestic poultry and feral birds (reviewed by Kibenge et al., 2004). ISAV may infect and replicate in sea trout, brown trout, rainbow trout, eels, herring and Arctic char, resulting in asymptomatic, probably lifelong carriers of the virus (reviewed by Kibenge et al., 2004). In Atlantic salmon, ISAV targets leukocytic cells and endothelial cells , or endothelial-associated cells (Falk et al., 2001) and macrophages (Moneke et al., 2003). Permissive fish cell lines for ISAV include salmon head kidney (SHK-1) cells ; TO cells (Wergeland & Jakobsen, 2001); and Atlantic salmon kidney (ASK-2) cells (Rolland et al., 2002), which are macrophage-like cell lines Wergeland & Jakobsen, 2001;Rolland et al., 2002) in which virus replicates with produc...

The Role of IFN-α and Nitric Oxide in the Release of HMGB1 by RAW 264.7 Cells Stimulated with Polyinosinic-Polycytidylic Acid or Lipopolysaccharide

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Systemic Release of High Mobility Group Box 1 Protein during Severe Murine Influenza

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