Largemouth Bass Virus Infection Induced Non-Apoptotic Cell Death in MsF Cells

Largemouth bass virus (LMBV), belonging to the genus Ranavirus, causes high mortality and heavy economic losses in largemouth bass aquaculture. In the present study, a novel cell line, designated as MsF, was established from the fin of largemouth bass (Micropterus salmoides), and applied to investigate the characteristics of cell death induced by LMBV. MsF cells showed susceptibility to LMBV, evidenced by the occurrence of a cytopathic effect (CPE), increased viral gene transcription, protein synthesis, and viral titers. In LMBV-infected MsF cells, two or more virus assembly sites were observed around the nucleus. Notably, no apoptotic bodies occurred in LMBV-infected MsF cells after nucleus staining, suggesting that cell death induced by LMBV in host cells was distinct from apoptosis. Consistently, DNA fragmentation was not detected in LMBV-infected MsF cells. Furthermore, only caspase-8 and caspase-3 were significantly activated in LMBV-infected MsF cells, suggesting that caspases were involved in non-apoptotic cell death induced by LMBV in host cells. In addition, the disruption of the mitochondrial membrane potential (ΔΨm) and reactive oxygen species (ROS) generation were detected in both LMBV-infected MsF cells and fathead minnow (FHM) cells. Combined with our previous study, we propose that cell death induced by LMBV infection was cell type dependent. Although LMBV-infected MsF cells showed the characteristics of non-apoptotic cell death, the signal pathways might crosstalk and interconnect between apoptosis and other PCD during LMBV infection. Together, our results not only established the in vitro LMBV infection model for the study of the interaction between LMBV and host cells but also shed new insights into the mechanisms of ranavirus pathogenesis.