AZT inhibits Visna/maedi virus-induced apoptosis

Visna/maedi virus (VMV) causes severe encephalitis and a progressive demyelinating disease in sheep. Previous in vitro studies have demonstrated that VMV-infection leads to apoptosis in sheep choroid plexus cells (SCPC) via induction of both intrinsic and extrinsic pathways with subsequent activation of caspases. 3' azido-2',3'-deoxythymidine (AZT) is a potent and selective Human immunodeficiency virus 1 (HIV-1) reverse transcriptase inhibitor, widely used in antiretroviral therapy; however its effects on retrovirus-induced apoptosis are unknown. Using diverse strategies to detect apoptosis, we analysed the broad range effect of AZT treatment on inhibition of VMV-induced apoptosis. First, we found that AZT treatment inhibited the appearance of characteristic apoptotic morphologic changes documented by DAPI staining and oligonucleosomal DNA laddering. Secondly, AZT treatment inhibited caspase cascade and resulted in (i) diminished caspase-3, -8 and -9 activities and (ii) no fluorescein isothiocynate-[VAD]-fluoromethylketone (FITC-VAD-FMK) in situ labelling in VMV-infected cells treated with AZT. Finally, immunocytochemistry indicated that VMV-infection of SCPC induced the subsequent release of apoptosis inducing factor (AIF), whereas AZT treatment inhibited AIF leakage. Consequently, the anti-apoptotic effects of AZT are not restricted, since AZT treatment blocks all the apoptotic pathways induced during VMV-infection.