Limits...
Candida albicans-epithelial interactions: dissecting the roles of active penetration, induced endocytosis and host factors on the infection process.

Wächtler B, Citiulo F, Jablonowski N, Förster S, Dalle F, Schaller M, Wilson D, Hube B - PLoS ONE (2012)

Bottom Line: Here we investigated the contributions of the two invasion routes of C. albicans to epithelial invasion.Using selective cellular inhibition approaches and differential fluorescence microscopy, we demonstrate that induced endocytosis contributes considerably to the early time points of invasion, while active penetration represents the dominant epithelial invasion route.Although induced endocytosis depends mainly on Als3-E-cadherin interactions, we observed E-cadherin independent induced endocytosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbial Pathogenicity Mechanisms, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knoell Institute Jena (HKI), Jena, Germany.

ABSTRACT
Candida albicans frequently causes superficial infections by invading and damaging epithelial cells, but may also cause systemic infections by penetrating through epithelial barriers. C. albicans is a remarkable pathogen because it can invade epithelial cells via two distinct mechanisms: induced endocytosis, analogous to facultative intracellular enteropathogenic bacteria, and active penetration, similar to plant pathogenic fungi. Here we investigated the contributions of the two invasion routes of C. albicans to epithelial invasion. Using selective cellular inhibition approaches and differential fluorescence microscopy, we demonstrate that induced endocytosis contributes considerably to the early time points of invasion, while active penetration represents the dominant epithelial invasion route. Although induced endocytosis depends mainly on Als3-E-cadherin interactions, we observed E-cadherin independent induced endocytosis. Finally, we provide evidence of a protective role for serum factors in oral infection: human serum strongly inhibited C. albicans adhesion to, invasion and damage of oral epithelial cells.

Show MeSH

Related in: MedlinePlus

Transmission electron microscopy of C. albicans epithelial invasion. Induced endocytosis of thimerosal killed hyphae (A), invasion of cytochalasin D treated epithelial cells by viable hyphae (B), invasion of untreated epithelial cells by viable hyphae (C), invasion of inactivated epithelial cells by viable hyphae (D).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3351431&req=5

pone-0036952-g001: Transmission electron microscopy of C. albicans epithelial invasion. Induced endocytosis of thimerosal killed hyphae (A), invasion of cytochalasin D treated epithelial cells by viable hyphae (B), invasion of untreated epithelial cells by viable hyphae (C), invasion of inactivated epithelial cells by viable hyphae (D).

Mentions: Previous scanning electron microscopy (SEM) studies of viable hyphae invading oral epithelial cells have demonstrated both depressions of epithelial cell surfaces (indicative of active penetration) and membrane ruffling and epithelial cell protrusions (indicative of induced endocytosis) [8], [9]. To further dissect the cellular events associated with these two invasion mechanisms, we employed transmission electron microscopy (TEM) of (1) oral epithelial cells co-incubated with thimerosal killed C. albicans hyphae (induced endocytosis only), (2) cytD treated epithelial cells co-incubated with viable C. albicans (active penetration only) and (3) untreated epithelial cells co-incubated with viable C. albicans (both invasion mechanisms). Thimerosal killed hyphae (induced endocytosis only) were engulfed by oral epithelial cells and tightly surrounded by the host membrane (Fig. 1A, upper panel). Membrane ruffling was visible around engulfed hyphae (Fig. 1A, lower panel). In contrast, oral epithelial cells treated with cytD (active penetration only) did not exhibit filopod formation or membrane ruffling (Fig. 1B). Invasion of hyphae occurred not only vertically (tip-first), but also laterally, with few direct physical contacts between hyphae and epithelial surface structures (Fig. 1B upper picture). Furthermore, invading hyphae were not tightly surrounded by host membranes in the presence of cytD. Rather we observed invaginations and broader spaces between penetrating hyphae and host membranes (Fig. 1B, lower pictures). Untreated oral epithelial cells invaded by viable hyphae (both invasion routes possible) generally reflected that of active penetration (invaginations and broader spaces between hyphae and host membranes). However, we also observed intermediate examples, with filopod-like structures and membrane ruffling on epithelial surfaces, but also the presence of broader spaces between hyphae and host membrane (Fig. 1C) similar to pictures shown previously [8]. We also tested the effect of complete epithelial inactivation on invasion by killing the epithelial cells with paraformaldehyde. In contrast to invasion of living cells by viable C. albicans, where we observed defined spaces between the fungal cell wall and the host membrane, invasion of killed epithelial cells was characterized by disrupted cellular structures around the invading hypha, with no evidence of an intact host membrane (Fig. 1D).


Candida albicans-epithelial interactions: dissecting the roles of active penetration, induced endocytosis and host factors on the infection process.

Wächtler B, Citiulo F, Jablonowski N, Förster S, Dalle F, Schaller M, Wilson D, Hube B - PLoS ONE (2012)

Transmission electron microscopy of C. albicans epithelial invasion. Induced endocytosis of thimerosal killed hyphae (A), invasion of cytochalasin D treated epithelial cells by viable hyphae (B), invasion of untreated epithelial cells by viable hyphae (C), invasion of inactivated epithelial cells by viable hyphae (D).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3351431&req=5

pone-0036952-g001: Transmission electron microscopy of C. albicans epithelial invasion. Induced endocytosis of thimerosal killed hyphae (A), invasion of cytochalasin D treated epithelial cells by viable hyphae (B), invasion of untreated epithelial cells by viable hyphae (C), invasion of inactivated epithelial cells by viable hyphae (D).
Mentions: Previous scanning electron microscopy (SEM) studies of viable hyphae invading oral epithelial cells have demonstrated both depressions of epithelial cell surfaces (indicative of active penetration) and membrane ruffling and epithelial cell protrusions (indicative of induced endocytosis) [8], [9]. To further dissect the cellular events associated with these two invasion mechanisms, we employed transmission electron microscopy (TEM) of (1) oral epithelial cells co-incubated with thimerosal killed C. albicans hyphae (induced endocytosis only), (2) cytD treated epithelial cells co-incubated with viable C. albicans (active penetration only) and (3) untreated epithelial cells co-incubated with viable C. albicans (both invasion mechanisms). Thimerosal killed hyphae (induced endocytosis only) were engulfed by oral epithelial cells and tightly surrounded by the host membrane (Fig. 1A, upper panel). Membrane ruffling was visible around engulfed hyphae (Fig. 1A, lower panel). In contrast, oral epithelial cells treated with cytD (active penetration only) did not exhibit filopod formation or membrane ruffling (Fig. 1B). Invasion of hyphae occurred not only vertically (tip-first), but also laterally, with few direct physical contacts between hyphae and epithelial surface structures (Fig. 1B upper picture). Furthermore, invading hyphae were not tightly surrounded by host membranes in the presence of cytD. Rather we observed invaginations and broader spaces between penetrating hyphae and host membranes (Fig. 1B, lower pictures). Untreated oral epithelial cells invaded by viable hyphae (both invasion routes possible) generally reflected that of active penetration (invaginations and broader spaces between hyphae and host membranes). However, we also observed intermediate examples, with filopod-like structures and membrane ruffling on epithelial surfaces, but also the presence of broader spaces between hyphae and host membrane (Fig. 1C) similar to pictures shown previously [8]. We also tested the effect of complete epithelial inactivation on invasion by killing the epithelial cells with paraformaldehyde. In contrast to invasion of living cells by viable C. albicans, where we observed defined spaces between the fungal cell wall and the host membrane, invasion of killed epithelial cells was characterized by disrupted cellular structures around the invading hypha, with no evidence of an intact host membrane (Fig. 1D).

Bottom Line: Here we investigated the contributions of the two invasion routes of C. albicans to epithelial invasion.Using selective cellular inhibition approaches and differential fluorescence microscopy, we demonstrate that induced endocytosis contributes considerably to the early time points of invasion, while active penetration represents the dominant epithelial invasion route.Although induced endocytosis depends mainly on Als3-E-cadherin interactions, we observed E-cadherin independent induced endocytosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbial Pathogenicity Mechanisms, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knoell Institute Jena (HKI), Jena, Germany.

ABSTRACT
Candida albicans frequently causes superficial infections by invading and damaging epithelial cells, but may also cause systemic infections by penetrating through epithelial barriers. C. albicans is a remarkable pathogen because it can invade epithelial cells via two distinct mechanisms: induced endocytosis, analogous to facultative intracellular enteropathogenic bacteria, and active penetration, similar to plant pathogenic fungi. Here we investigated the contributions of the two invasion routes of C. albicans to epithelial invasion. Using selective cellular inhibition approaches and differential fluorescence microscopy, we demonstrate that induced endocytosis contributes considerably to the early time points of invasion, while active penetration represents the dominant epithelial invasion route. Although induced endocytosis depends mainly on Als3-E-cadherin interactions, we observed E-cadherin independent induced endocytosis. Finally, we provide evidence of a protective role for serum factors in oral infection: human serum strongly inhibited C. albicans adhesion to, invasion and damage of oral epithelial cells.

Show MeSH
Related in: MedlinePlus