Dectin-1 is the critical sensor for β-glucan from Candida which is the most common human fungal pathogen and cause superficial and system infection. MicroRNAs (miRNAs) play crucial roles in regulating innate immunity. However, the functional role of miRNAs in inflammatory response dependent on the activation of dectin-1 pathway has not been defined. In the present study, we found insoluble β-glucan from the cell wall of Candida albicans (CaIG) was able to increase the production of of IL-6 and TNFα through Dectin-1-Syk-NF-κB and p38MAPK pathway. MiRNAs profiles combined with real-time PCR validation revealed that miR-146a, miR-30-5p, miR-210-3p expression level were increased in THP-1 cells treated with CaIG. The interaction between Dectin-1 and CaIG resulted in an long lasting increase of miR-146a expression dependent on Dectin-1-Syk-NF-κB, p38MAPK, contrasting with a rapid and transient increase of IL-6 and TNFα. Overexpression of miR-146a significantly suppressed the production of IL-6 and TNFα. MiR-146a mimics inhibited CaIG-induced activity of p-IκBα and translocation of NF-κB p65. Luciferase reporter assays showed miR-146a inhibited NF-κB promoter-binding activity. Together, our data suggest miR-146a may play the potent negative feedback regulator in inflammatory response following Dectin-1 stimulation.
Acne is a chronic inflammatory skin disorder that often involves the formation of Cutibacterium acnes (C. acnes) biofilms. Several microRNAs (miRNAs) are known to be involved in inflammatory responses. However, it is unknown whether miRNAs play a role in the inflammatory reaction triggered by C. acnes biofilm. In this study, we investigated the role of miR-146a in biofilm-derived C. acneseinduced inflammatory responses. Increased expressions of miR-146a and toll-like receptor (TLR) 2 were detected in acne lesions. In the presence of biofilm-derived C. acnes, TLR2 and its downstream NF-kB and MAPK pathways were activated in keratinocytes. Subsequently, miR-146a was upregulated in these cells along with the induction of IL-6, IL-8, and tumor necrosis factor (TNF)-a. Furthermore, our data indicates that miR-146a could directly bind the 3 0-untranslated region of IRAK1 and TNF receptor-associated factor 6 (TRAF6) and suppress their expression, leading to an inhibition of biofilm-derived C. acneseinduced activation of NF-kB, p38, and ERK1/2 pathways. Overall, our results indicate that biofilm-derived C. acnes induces miR-146a, which can downregulate the production of IL-6,-8, and TNF-a in acne inflammation by inhibiting the TLR2/IRAK1/TRAF6/NF-kB and MAPK pathways.
Autophagy machinery has roles in the defense against microorganisms such as Candida albicans. Lipidated LC3, the marker protein of autophagy, participates in the elimination of C. albicans by forming a single-membrane phagosome; this process is called LC3-associated phagocytosis (LAP). However, the influence of C. albicans on autophagic flux is not clear. In this study, we found that C. albicans inhibited LC3 turnover in macrophages. After the phagocytosis of C. albicans in macrophages, we observed fewer acridine orange-positive vacuoles and RFP-GFP-LC3 puncta without colocalization with phagocytized C. albicans. However, phagocytosis of C. albicans led to LC3 recruitment, but p62 and ATG9A did not colocalize with LC3 or C. albicans. These effects are due to an MTOR-independent pathway. Nevertheless, we found that the C. albicans pattern-associated molecular pattern β-glucan increased LC3 turnover. In addition, phagocytosis of C. albicans caused a decrease in BrdU incorporation. Blocking autophagic flux aggravated this effect. Our findings suggest that phagocytosis of C. albicans decreases autophagic flux but induces LAP in an MTOR-independent manner in macrophages. Occupation of LC3 by recruiting engulfed C. albicans might contribute to the inhibition of autophagic flux. Our study highlights the coordinated machinery between canonical autophagy and LAP that defends against C. albicans challenge.
Candida parapsilosis is one of the most prevalent Candida species; however, the inflammation response induced by C. parapsilosis and related mechanism received few studies. In this study, we analyzed the pro-inflammatory cytokine responses evoked by C. parapsilosis in human peripheral blood mononuclear cells (PBMCs) and THP-1 cells, determined the signal pathways related to the inflammation response and investigated the expression of dectin-1 modified with C. parapsilosis. Exposure of PBMCs and THP-1 cells to C. parapsilosis led to the increased gene expression and production of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). C. parapsilosis induced TNF-α and IL-6 release in a time- and dose-dependent manner. Western blotting was used to analyze p38, ERK1/2 mitogen-activated protein kinases (MAPKs) and IκB-α phosphorylation and degradation. Nuclear translocation of NF-κB was detected by confocal microscopy. THP-1 cells challenged by C. parapsilosis resulted in the activation of NF-κB and phosphorylation of p38 and ERK1/2 MAPKs. The expression of dectin-1 was up-regulated after the stimulation of C. parapsilosis. Our results suggest that C. parapsilosis could stimulate the inflammatory response, increase the expression of dectin-1 and activate NF-κB and MAPKs signaling pathways in macrophages.
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