Autophagy gene ATG5 knockdown upregulates apoptotic cell death during Candida albicans infection in human vaginal epithelial cells.

PROBLEM: Candida albicans infection induces damage in host cells that results in the activation of cell death pathways such as apoptosis and necrosis. Autophagy acts as a pro-survival mechanism during various infections and has cross talks with apoptosis. The objective of our study was to delineate the effect of autophagy knockdown in human vaginal epithelial cells (VECs) during Candida infection-induced apoptosis. METHOD OF STUDY: We overexpressed wild-type or mutant form of autophagy-related gene 5 (ATG5) in human VECs and determined the levels of autophagy and lysosome marker genes upon C. albicans infection. We analyzed the expression of apoptosis and necrosis markers using confocal microscopy and flow cytometry.
RESULTS: Mutant ATG5 overexpressing VECs were unable to form Atg5-Atg12 complex, which is required for functional autophagy pathway. Upon Candida albicans infection, wild-type ATG5 overexpressing cells showed upregulation of autophagy marker genes, ATG5, LC3-I, LC3-II, and LAMP-1. Mutant ATG5 overexpressing cells could not upregulate LC3-II and LAMP-1 expression, indicating a defective autophagy pathway. Confocal microscopy and flow cytometry results revealed that wild-type ATG5 overexpressing VECs showed significantly lower number of apoptotic and necrotic cells as compared to mutant ATG5 overexpressing cells.
CONCLUSION: Vaginal epithelial cells with active autophagy were able to survive the damage caused by C. albicans infection, whereas those with defective autophagy succumbed to the infection. This suggests that autophagy plays a critical role in human VECs survival during C. albicans infection.