Exposure of Keratinocytes to Candida Albicans in the Context of Atopic Milieu Induces Changes in the Surface Glycosylation Pattern of Small Extracellular Vesicles to Enhance Their Propensity to Interact With Inhibitory Siglec Receptors

Abstract

Candida albicans (C. albicans) infection is a potential complication in the individuals with atopic dermatitis (AD) and can affect clinical course of the disease. Here, using primary keratinocytes we determined that atopic milieu promotes changes in the interaction of small extracellular vesicles (sEVs) with dendritic cells and that this is further enhanced by the presence of C. albicans. sEV uptake is largely dependent on the expression of glycans on their surface; modelling of the protein interactions indicated that recognition of this pathogen through C. albicans-relevant pattern recognition receptors (PRRs) is linked to several glycosylation enzymes which may in turn affect the expression of sEV glycans. Here, significant changes in the surface glycosylation pattern, as determined by lectin array, could be observed in sEVs upon a combined exposure of keratinocytes to AD cytokines and C. albicans. This included enhanced expression of multiple types of glycans, for which several dendritic cell receptors could be proposed as binding partners. Blocking experiments showed predominant involvement of the inhibitory Siglec-7 and -9 receptors in the sEV-cell interaction and the engagement of sialic acid-containing carbohydrate moieties on the surface of sEVs. This pointed on ST6 β-Galactoside α-2,6-Sialyltransferase 1 (ST6GAL1) and Core 1 β,3-Galactosyltransferase 1 (C1GALT1) as potential enzymes involved in the process of remodelling of the sEV surface glycans upon C. albicans exposure. Our results suggest that, in combination with atopic dermatitis milieu, C. albicans promotes alterations in the glycosylation pattern of keratinocyte-derived sEVs to interact with inhibitory Siglecs on antigen presenting cells. Hence, a strategy aiming at this pathway to enhance antifungal responses and restrict pathogen spread could offer novel therapeutic options for skin candidiasis in AD.

Excess filaggrin in keratinocytes is removed by extracellular vesicles to prevent premature death and this mechanism can be hijacked by Staphylococcus aureus in a TLR2‐dependent fashion

“…It would be interesting to investigate the secretion of profilaggrin/filaggrin cargo within sEVs in real time, also in patients heavily colonised with S. aureus , for example, by open flow microperfusion on human skin, which would provide additional in vivo data; this unfortunately was not possible in the current study. Recently, we demonstrated that the exposure of keratinocytes to Candida albicans in the context of AD inflammatory milieu leads to re‐programming of the surface glycosylation pattern on secreted sEVs; sEVs released under these conditions increased their capacity to interact with dendritic cells (DCs) via inhibitory Siglec receptors (Kobiela et al., 2022 ), activation of which has been shown to reduce innate responses to pathogens (Alef et al., 2009 ; Rasheed et al., 2018 ). To our knowledge, no extracellular vesicle‐assisted mechanism to reduce host control measures by removal of proteins or compounds with antimicrobial properties from the cells or tissue has been described to date; whether this is a broadly pathogen‐utilised mechanism or S. aureus ‐specific phenomenon remains to be clarified.…”

Excess filaggrin in keratinocytes is removed by extracellular vesicles to prevent premature death and this mechanism can be hijacked by Staphylococcus aureus in a TLR2-dependent fashion

“…Such intensified filaggrin removal process could support bacterial growth and colonisation and contribute to the increased amount of filaggrin-related sEV cargo in the circulation of AD patients. Recently, we demonstrated that the exposure of keratinocytes to Candida albicans in the context of AD inflammatory milieu leads to re-programming of the surface glycosylation pattern on secreted sEVs; sEVs released under these conditions increased their capacity to interact with dendritic cells (DCs) via inhibitory Siglec receptors 59 , activation of which has been shown to reduce innate responses to pathogens 53,54 . To our knowledge, no extracellular vesicle-assisted mechanism to reduce host control measures by removal of proteins or compounds with antimicrobial properties from the cells or tissue has been described to date; whether this is a broadly pathogen-utilised mechanism or S. aureusspecific phenomenon remains to be clarified.…”

The emerging role of extracellular vesicles in fungi: a double-edged sword

“…Under an atopic dermatitis (AD) setting, Candida albicans promoted altered glycosylation patterns in keratinocyte-derived EVs, to interact with inhibitory Siglecs on antigen-presenting cells. Strategies that target this pathway to enhance antifungal responses and limit pathogen transmission may provide new therapeutic options for AD cutaneous candidiasis ( Kobiela et al, 2022 ). In Candida albicans EVs, the plasma membrane proteins Sur7 and EVp1 could be fungal equivalents of four transmembrane protein tags for EV studies ( Dawson et al, 2020 ).…”