Regulation of pro-apoptotic bax and trail gene expressions by H5N1 in madin-darby canine kidney (mdck) cell line

Avian influenza virus (AIV) A H5N1 is able to cause zoonosis with high morbidity and mortality. Several studies suggested the regulation of cellular apoptosis for virus survival by influenza viruses. This sheds light on the development of antivirals that can improve cellular apoptosis to fight influenza infections. This study aimed to investigate the regulation of pro-apoptotic gene expressions by H5N1 in MDCK cells. The H5N1 infection (10^2.67TCID50/ml) was performed for 8, 24, 48, 72, 96 and 120 hours. Upon incubation, the percentage of cell death, DNA fragmentation and pro-apoptotic gene expressions i.e. Bax, TRAIL, Caspase 3 (Cas3) and 8 (Cas8), and Fas-ligand (FasL) were determined. The degree of DNA laddering and pro-apoptotic gene expressions were determined on agarose gels. The results indicated that severe cytopathic effects (CPE) caused by H5N1 appeared as early as 24 hour post-infection (hpi) meanwhile a significant cell death was observed starting at 48 hpi. However, DNA laddering was not observed in both of the control and infected DNA samples. Downregulation of Bax gene expression was recorded at 24 -72 hpi and a total suppression was observed at 96 and 120 hpi. Similarly, a significant decrease in the TRAIL gene expression was observed at 48-120 hpi. On the contrary, the expressions of Cas3, Cas8 and FasL genes were not detected in the mock and infected samples. Conclusively, this study suggested that H5N1 might downregulate cellular apoptosis prematurely for viral survival which can be a target cellular mechanism for newly developed antivirals to combat H5N1 infections.