Candidalysin triggers epithelial cellular stresses that induce necrotic death.

Candida albicans is a common opportunistic fungal pathogen that causes a wide range of infections from superficial mucosal to hematogenously disseminated candidiasis. The hyphal form plays an important role in the pathogenic process by invading epithelial cells and causing tissue damage. Notably, the secretion of the hyphal toxin candidalysin is essential for both epithelial cell damage and activation of mucosal immune responses. However, the mechanism of candidalysin-induced cell death remains unclear. Here, we examined the induction of cell death by candidalysin in oral epithelial cells. Fluorescent imaging using healthy/apoptotic/necrotic cell markers revealed that candidalysin causes a rapid and marked increase in the population of necrotic rather than apoptotic cells in a concentration dependent manner. Activation of a necrosis-like pathway was confirmed since C. albicans and candidalysin failed to activate caspase-8 and -3, or the cleavage of poly (ADP-ribose) polymerase. Furthermore, oral epithelial cells treated with candidalysin showed rapid production of reactive oxygen species, disruption of mitochondria activity and mitochondrial membrane potential, ATP depletion and cytochrome c release. Collectively, these data demonstrate that oral epithelial cells respond to the secreted fungal toxin candidalysin by triggering numerous cellular stress responses that induce necrotic death. TAKE AWAYS: Candidalysin secreted from Candida albicans causes epithelial cell stress. Candidalysin induces calcium influx and oxidative stress in host cells. Candidalysin induces mitochondrial dysfunction, ATP depletion and epithelial necrosis. The toxicity of candidalysin is mediated from the epithelial cell surface.

Candida albicans and candidalysin in inflammatory disorders and cancer.

As our understanding of mycology progresses, the impact of fungal microbes on human health has become increasingly evident. Candida albicans is a common commensal fungus that gives rise to local and systemic infections, particularly in immunocompromised patients where it can result in mortality. However, C. albicans has also been quietly linked with a variety of inflammatory disorders, to which it has traditionally been considered incidental; recent studies may now provide new aspects of these relationships for further consideration. This review provides a novel perspective on the impact of C. albicans and its peptide toxin, candidalysin, on human health, exploring their contributions to pathology within a variety of diseases.

ß-Glucan-induced reprogramming of human macrophages inhibits NLRP3 inflammasome activation in cryopyrinopathies.

Exposure of mononuclear phagocytes to ß-glucan, a naturally occurring polysaccharide, contributes to the induction of innate immune memory, which is associated with long-term epigenetic, metabolic, and functional reprogramming. Although previous studies have shown that innate immune memory induced by ß-glucan confers protection against secondary infections, its impact on autoinflammatory diseases, associated with inflammasome activation and IL-1ß secretion, remains poorly understood. In particular, whether ß-glucan-induced long-term reprogramming affects inflammasome activation in human macrophages in the context of these diseases has not been explored. We found that NLRP3 inflammasome-mediated caspase-1 activation and subsequent IL-1ß production were reduced in ß-glucan-reprogrammed macrophages. ß-Glucan acted upstream of the NLRP3 inflammasome by preventing potassium (K+) efflux, mitochondrial ROS (mtROS) generation, and, ultimately, apoptosis-associated speck-like protein containing a CARD (ASC) oligomerization and speck formation. Importantly, ß-glucan-induced memory in macrophages resulted in a remarkable attenuation of IL-1ß secretion and caspase-1 activation in patients with an NLRP3-associated autoinflammatory disease, cryopyrin-associated periodic syndromes (CAPS). Our findings demonstrate that ß-glucan-induced innate immune memory represses IL-1ß-mediated inflammation and support its potential clinical use in NLRP3-driven diseases.

The Complexity of Fungal ß-Glucan in Health and Disease: Effects on the Mononuclear Phagocyte System.

ß-glucan, the most abundant fungal cell wall polysaccharide, has gained much attention from the scientific community in the last few decades for its fascinating but not yet fully understood immunobiology. Study of this molecule has been motivated by its importance as a pathogen-associated molecular pattern upon fungal infection as well as by its promising clinical utility as biological response modifier for the treatment of cancer and infectious diseases. Its immune effect is attributed to the ability to bind to different receptors expressed on the cell surface of phagocytic and cytotoxic innate immune cells, including monocytes, macrophages, neutrophils, and natural killer cells. The characteristics of the immune responses generated depend on the cell types and receptors involved. Size and biochemical composition of ß-glucans isolated from different sources affect their immunomodulatory properties. The variety of studies using crude extracts of fungal cell wall rather than purified ß-glucans renders data difficult to interpret. A better understanding of the mechanisms of purified fungal ß-glucan recognition, downstream signaling pathways, and subsequent immune regulation activated, is, therefore, essential not only to develop new antifungal therapy but also to evaluate ß-glucan as a putative anti-infective and antitumor mediator. Here, we briefly review the complexity of interactions between fungal ß-glucans and mononuclear phagocytes during fungal infections. Furthermore, we discuss and present available studies suggesting how different fungal ß-glucans exhibit antitumor and antimicrobial activities by modulating the biologic responses of mononuclear phagocytes, which make them potential candidates as therapeutic agents.

Regulation and trafficking of the HLA-E molecules during monocyte-macrophage differentiation.

HLA-E is a nonclassical HLA-class I molecule whose best known role is to protect from the natural killer cells. More recently, an additional function more similar to that of classical HLA-class I molecules, i.e., antigen presentation to T cells, is emerging. However, much remains to be explored about the intracellular trafficking of the HLA-E molecules. With the use of 3 different cellular contexts, 2 monocytic cell lines, U937 and THP1, and peripheral blood monocytes, we show here a remarkable increase of HLA-E during monocyte-macrophage differentiation. This goes independently from the classical HLA-class I, the main source of HLA-E-specific peptides, which is found strongly up-regulated upon differentiation of peripheral blood monocytes but not at all in the case of U937 and THP1 cell lines. Although in all cases, there was a moderate increase of HLA-E expressed in the cell surface, lysis by natural killer cells is comparably restored by an anti-NKG2A antibody in untreated as well as in PMA-differentiated U937 cells. Instead, the great majority of the HLA-E is retained in the vesicles of the autophagy-lysosome network, where they colocalize with the microtubule-associated protein light chain 3, as well as with the lysosomal-associated membrane protein 1. We conclude that differently from the classical HLA-class I molecules, the primary destination of the newly synthesized HLA-E molecules in macrophages is, rather than the cell membrane, the intracellular autophagy-lysosomal vesicles where they are stored and where they can encounter the exogenous antigens.

Single nucleotide polymorphisms in the 3'UTR of VPAC-1 cooperate in modulating gene expression and impact differently on the interaction with miR525-5p.

Complex immune and neurodegenerative disorders are the result of multiple interactions between common genetic variations having, individually, a weak effect on the disease susceptibility or resistance. Interestingly, some genes have been found to be associated with more than one disease although not necessarily the same SNPs are involved. In this context, single nucleotide polymorphisms in the 3'UTR region of type 1 receptor (VPAC-1) for vasoactive intestinal peptide (VIP) have been reported to be associated with some immune-mediated as well as with neurodegenerative diseases such as Alzheimer's Disease (AD). Here, we demonstrate that variations at the 3'UTR of the VPAC-1 gene act synergistically to affect the expression of the luciferase as well as of the GFP reporter genes expressed in HEK293T cells. Moreover, the miRNA 525-5p, previously shown by us to target the 3'UTR of VPAC-1, is more efficient in decreasing GFP expression when co-expressed with constructs carrying the allele C at rs896 (p<10(-3)) suggesting that this miRNA regulates VPAC-1 expression at different levels depending on rs896 polymorphism and thus adding complexity to the network of disease susceptibility.