Membrane protective role of autophagic machinery during infection of epithelial cells by Candida albicans

Abstract

Candida albicans ( C. albicans ) is an opportunistic pathogen causing infections ranging from superficial to life-threatening disseminated infections. In a susceptible host, C. albicans is able to translocate through the gut barrier, promoting its dissemination into deeper organs. C. albicans hyphae can invade human epithelial cells by two well-documented mechanisms: epithelial-driven endocytosis and C. albicans -driven active penetration. One mechanism by which host cells protect themselves against intracellular C. albicans is termed autophagy. The protective role of autophagy during C. albicans infection has been investigated in myeloid cells; however, far less is known regarding the role of this process during the infection of epithelial cells. In the present study, we investigated the role of autophagy-related proteins during the infection of epithelial cells, including intestinal epithelial cells and gut explants, by C. albicans . Using cell imaging, we show that key molecular players of the autophagy machinery (LC3-II, PI3P, ATG16L1, and WIPI2) were recruited at Candida invasion sites. We deepened these observations by electron microscopy analyses that reveal the presence of autophagosomes in the vicinity of invading hyphae. Importantly, these events occur during active penetration of C. albicans into host cells and are associated with plasma membrane damage. In this context, we show that the autophagy-related key proteins ATG5 and ATG16L1 contribute to plasma membrane repair mediated by lysosomal exocytosis and participate in protecting epithelial cells against C. albicans -induced cell death. Our findings provide a novel mechanism by which epithelial cells, forming the first line of defense against C. albicans in the gut, can react to limit C. albicans invasion.

Trans-cellular tunnels induced by the fungal pathogen Candida albicans facilitate invasion through successive epithelial cells without host damage

“…5A). This result suggests that invasion in this cell type does not occur via induced endocytosis according to this distinguishing criterion, in agreement with previously published data 51 . However, another study in which endocytosis was directly monitored did determine a role for endocytosis in HeLa invasion 29 .…”

“…Thus, in our models, CaTCT as well as damaging invasion in HeLa is distinct from invasion by induced endocytosis, at least according to this distinguishing criterion. This result is consistent with studies suggesting that induced endocytosis does not play a major role in HeLa and Caco-2 invasion, though endocytosis was directly monitored in HeLa during C. albicans invasion, where it has been suggested to occur via an E-cadherin-independent mechanism 14,29,30,51 A schematic interpretation is also presented, corresponding to the hypothesis that host membranes extend from each invaded cell into the next host cell in the invasion sequence, resulting in progressive membrane layer accumulation. Insets show in detail inferred membrane organization in accordance with this hypothesis, with each layer derived from a plasma membrane deformed upon hypha entry or exit from each corresponding invaded cell.…”

“…Rather, the damage detected in this study is likely, at least in part, to be the result of other factors such as the mechanical strain on the host plasma membrane caused by hyphal extension. It has recently been shown that damage caused by mechanical strain during invasion may be repaired via lysosome exocytosis, mediated by the host autophagy machinery and by galectin-3 recruitment itself 51,61 . Overall, we cannot exclude the presence of host membrane damage not detected by Gal-3, as well as a role for host repair mechanisms, during both damaging and nondamaging invasion scenarios.…”

“…While invasion begins around one or two hours after attachment, host cell damage, measured by LDH or 51 Cr release assays, has been reported to occur at a later stage, usually after 6-24 h, depending on the epithelial tissue [14][15][16][17] . Indeed, the major cause of damage during C. albicans epithelial infection is thought not to be invasion per se, but other factors such as candidalysin, a fungal peptide toxin secreted during infection 18 .…”

Molecular docking: Bioactive compounds ofMimosa pudicaas an inhibitor ofCandida albicansSap 3

“…Invasive candidiasis is associated with a high mortality rate, ranging from 20 to 49%. C. albicans can be found to colonize various mucosal surfaces such as skin, mouth, and vagina; most studies consider the gastrointestinal tract as the main entry point for C. albicans to enter the bloodstream [5][6][7][8][9] . On the other hand, C. albicans is the most common causative agent of oral, vaginal, and disseminated candidiasis.…”