Induction of apoptosis in oral epithelial cells by Candida albicans

During infection, interactions between Candida albicans and oral epithelial cells result in oral epithelial cell death. This is clinically manifested by the development of oral mucosal ulcerations generally associated with discomfort. In vitro studies have shown that C. albicans induces early apoptotic alterations in oral epithelial cells; however, these studies have also shown that treatment of infected cells with caspase inhibitors does not prevent their death. The reasons for these contradictory results are unknown and it is still not clear if C. albicans stimulates oral epithelial signaling pathways that promote apoptotic cell death. Activation of specific death pathways in response to microbial organisms plays an essential role in modulating the pathogenesis of a variety of infectious diseases. The aim of this study was to (i) characterize C. albicans-induced apoptotic morphological alterations in oral epithelial cells, and (ii) investigate the activation of apoptotic signaling pathways and expression of apoptotic genes during infection. Candida albicans induced early apoptotic changes in over 50% of oral epithelial cells. However, only 15% of those showed mid-late apoptotic alterations. At the molecular level, C. albicans caused a loss of the mitochondrial transmembrane potential and translocation of mitochondrial cytochrome c. Caspase-3/9 activities increased only during the first hours of infection. Moreover, poly[ADP ribose] polymerase 1 was cleaved into apoptotic and necrotic-like fragments. Finally, five anti-apoptotic genes were significantly upregulated and two pro-apoptotic genes were downregulated during infection. Altogether, these findings indicate that epithelial apoptotic pathways are activated in response to C. albicans, but fail to progress and promote apoptotic cell death.