African horse sickness virus induces apoptosis in cultured mammalian cells

Abstract

Infection of mammalian cell cultures with African horse sickness virus (AHSV) is known to result in dramatic cytopathic effects (CPE), but no CPE is observed in infected insect cell cultures despite productive virus replication. The basis for this phenomenon has not yet been investigated, but is suggestive of apoptosis being induced following virus infection of the mammalian cells. To investigate whether AHSV can induce apoptosis in infected mammalian cells, Culicoides variipennis (KC) insect cells and BHK-21 mammalian cells were infected with AHSV-9 and analyzed for morphological and biochemical hallmarks of apoptosis. In contrast to KC cells, infection of BHK-21 cells with AHSV-9 resulted in ultrastructural changes and nuclear DNA fragmentation, both of which are associated with the induction of apoptosis. Results also indicated that AHSV-9 infection of BHK-21 cells resulted in activation of caspase-3, a key agent in apoptosis, and in mitochondrial membrane depolarization. Cumulatively, the data indicate that the intrinsic pathway is activated in AHSVinduced apoptosis.Keywords: African horse sickness virus; Apoptosis; BHK-21 cells; Culicoides variipennis cells; Caspases; Intrinsic pathwayAfrican horse sickness virus (AHSV) is a species in the genus Orbivirus, family Reoviridae (Calisher and Mertens, 1998), and is the causative agent of African horse sickness (AHS), a highly infectious arthropod-borne (Culicoides spp.) disease of equids, of which the mortality rate in horses may exceed 90% (Coetzer and Erasmus, 1994;Guthrie, 2007). Although African horse sickness virus (AHSV) causes severe oedema and haemorrhages in horses, it is asymptomatic in the insect host (Mellor and Hamblin, 2004;Wilson et al., 2009). This is also reflected in tissue culture where AHSV causes rapid cell death in infected mammalian cells in culture, whereas infection of insect cells are unapparent and show no CPE (Mirchamsy et al., 1970;Osawa and Hazrati, 1965). The basis for this differential host response is not known, but may be due to the induction of apoptosis in infected mammalian cells. Indeed, analyses of endothelial cells of animals infected with AHSV indicated ultrastructural changes that could be suggestive of apoptosis (Gómez-Villamandos et al., 1999).Apoptosis is a selective process of physiological cell deletion in response to numerous developmental and environmental stimuli (Kerr et al., 1972). There are two common pathways for the induction of apoptosis, i.e. the extrinsic pathway, which is primarily initiated by virus attachment to receptors, and the intrinsic pathway, which is mediated by damage to the mitochondria (Duprez et al., 2009). Various reports have indicated that infection of mammalian cells by viruses induces apoptosis (Roulston et al., 1999) and in some virus-induced diseases, apoptosis is a pathogenic mechanism that contributes in vivo to cell death, tissue injury and disease severity Samuel et al., 2007). Indeed, the induction of apoptosis has recently been implicated in the pathogenesis of bluetong...

Epizootic Hemorrhagic Disease Virus Induces and Benefits from Cell Stress, Autophagy, and Apoptosis

“…The present study mainly employs the Ibaraki strain of EHDV2 (EHDV2-IBA), originally isolated from infected cattle in 1959, in Ibaraki, Japan (8). Selected experiments were also carried out with EHDV7-Israel (EHDV7-ISR), isolated from infected cattle in 2006 in Israel (1).For different types of reoviruses, including BTV, apoptosis is integral to the cellular pathogenesis they induce (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Yet the molecular mechanisms that govern reovirus-mediated induction of apoptosis are a contentious matter (10,17,19,20).…”

African horse sickness virus infects BSR cells through macropinocytosis

“…The mechanism by which AHSV-4 triggers macropinocytosis in BSR cells is currently unknown, but likely involves interaction between its surface protein (VP2) and cellular receptors. Considering that AHSV infects and replicates in a wide range of cells (Meiring et al, 2009;Clift and Penrith, 2010;Stassen et al, 2012), it is plausible that its entry into cells is mediated by the binding of VP2…”

Virus uncoating is required for apoptosis induction in cultured mammalian cells infected with African horse sickness virus

“…Although it has been reported that AHSV infection of cultured mammalian cells induces apoptosis and results in the activation of caspase-3, these studies have characterized apoptosis mainly in terms of morphological markers of apoptosis (Stassen et al, 2012;Venter, 2014). During the course of the viral life cycle, there are several obligate interactions between viruses and cells capable of triggering apoptosis, including virus-receptor engagement, fusion with or penetration of cellular membranes, and disruption of host cell transcriptional and translational machineries (Roulston et al, 1999;Danthi, 2011).…”

“…The proapoptotic activity of AHSV appears to be a general feature of these viruses, as it is not specific for a particular virus serotype or to the infection of a specific type of cell (Osawa & Hazrati, 1965;Stassen et al, 2012;Venter, 2014). However, the initiators of the apoptotic response, the nature of the caspase cascades activated and the functional consequences of their activation on the virus replication cycle are unknown.…”