three-dimensional-quantification-intestinal-mucus-using-whole-mount

Three-dimensional Quantification of Intestinal Mucus Using Whole-mount Tissue Imaging

Mucus plays a critical role in maintaining intestinal homeostasis by facilitating digestion, forming a barrier against microbes, and regulating immune ...

Chang Gung University

Chang Gung Memorial Hospital

Quorum-sensing systems that have been widely identified in bacteria play important roles in the regulation of bacterial multicellular behavior by which bacteria sense population density to control various biological functions, including virulence. One characteristic of the luxIR quorum-sensing genes is their diverse and discontinuous distribution among proteobacteria. Here we report that the spnIR quorum-sensing system identified in the enterobacterium Serratia marcescens strain SS-1 is carried in a transposon, TnTIR, which has common characteristics of Tn3 family transposons and is mobile between chromosomes and plasmids of different enterobacterial hosts. SpnIR functions in the new host and was shown to negatively regulate the TnTIR transposition frequency. This finding may help reveal the horizontal transfer and evolutionary mechanism of quorum-sensing genes and alter the way that we perceive regulation of bacterial multicellular behavior.

A mobile quorum-sensing system in Serratia marcescens.

Serratia marcescens has long been recognized as an important opportunistic pathogen, but the underlying pathogenesis mechanism is not completely clear. Here, we report a key pathogenesis pathway in S. marcescens comprising the RssAB two-component system and its downstream elements, FlhDC and the dominant virulence factor hemolysin ShlBA. Expression of shlBA is under the positive control of FlhDC, which is repressed by RssAB signaling. At 37°C, functional RssAB inhibits swarming, represses hemolysin production, and promotes S. marcescens biofilm formation. In comparison, when rssBA is deleted, S. marcescens displays aberrant multicellularity favoring motile swarming with unbridled hemolysin production. Cellular and animal infection models further demonstrate that loss of rssBA transforms this opportunistic pathogen into hypervirulent phenotypes, leading to extensive inflammatory responses coupled with destructive and systemic infection. Hemolysin production is essential in this context. Collectively, a major virulence regulatory pathway is identified in S. marcescens.

RssAB-FlhDC-ShlBA as a major pathogenesis pathway in Serratia marcescens.

Bacteria can coordinate several multicellular behaviors in response to environmental changes. Among these, swarming and biofilm formation have attracted significant attention for their correlation with bacterial pathogenicity. However, little is known about when and where the signaling occurs to trigger either swarming or biofilm formation. We have previously identified an RssAB two-component system involved in the regulation of swarming motility and biofilm formation in Serratia marcescens. Here we monitored the RssAB signaling status within single cells by tracing the location of the translational fusion protein EGFP-RssB following development of swarming or biofilm formation. RssAB signaling is specifically activated before surface migration in swarming development and during the early stage of biofilm formation. The activation results in the release of RssB from its cognate inner membrane sensor kinase, RssA, to the cytoplasm where the downstream gene promoters are located. Such dynamic localization of RssB requires phosphorylation of this regulator. By revealing the temporal activation of RssAB signaling following development of surface multicellular behavior, our findings contribute to an improved understanding of how bacteria coordinate their lifestyle on a surface.

RssAB signaling coordinates early development of surface multicellularity in Serratia marcescens.

The natural compound 2,3-BTD has diverse physiological effects in a range of organisms, including acting as a detoxifying product of liver alcohol metabolism in humans and ameliorating endotoxin-induced acute lung injury in rats. In this study, we reveal that 2,3-BTD enhances NK cell cytotoxic activity in human pNK cells and NK92 cells. Treatment of NK cells with 2,3-BTD increased perforin expression in a dose-dependent manner. This was accompanied by elevated JNK and ERK1/2 MAPK activities and enhanced expression of NKG2D/NCRs, upstream signaling molecules of the MAPK pathways. The 2,3-BTD effect was inhibited by pretreatment with inhibitors of JNK (SP) or ERK1/2 (PD) or by depleting NKG2D/NCRs or JNK1 or ERK2 with siRNA. These results indicate that 2,3-BTD activates NK cell cytotoxicity by NKG2D/NCR pathways and represent the first report of the 2,3-BTD effect on activation of innate immunity cells.

Activation of NK cell cytotoxicity by the natural compound 2,3-butanediol.

Iron availability affects swarming and biofilm formation in various bacterial species. However, how bacteria sense iron and coordinate swarming and biofilm formation remains unclear. Using Serratia marcescens as a model organism, we identify here a stage-specific iron-regulatory machinery comprising a two-component system (TCS) and the TCS-regulated iron chelator 2-isocyano-6,7-dihydroxycoumarin (ICDH-Coumarin) that directly senses and modulates environmental ferric iron (Fe) availability to determine swarming initiation and biofilm formation. We demonstrate that the two-component system RssA-RssB (RssAB) directly senses environmental ferric iron (Fe) and transcriptionally modulates biosynthesis of flagella and the iron chelator ICDH-Coumarin whose production requires the pvc cluster. Addition of Fe, or loss of ICDH-Coumarin due to pvc deletion results in prolonged RssAB signaling activation, leading to delayed swarming initiation and increased biofilm formation. We further show that ICDH-Coumarin is able to chelate Fe to switch off RssAB signaling, triggering swarming initiation and biofilm reduction. Our findings reveal a novel cellular system that senses iron levels to regulate bacterial surface lifestyle.

An iron detection system determines bacterial swarming initiation and biofilm formation.

Swarming motility is a mode of bacterial movement over a solid surface driven by rotating flagella in a coordinated manner. Bacteria can use two-component system (TCS), which typically comprises a sensor kinase and a specific cognate response regulator, to properly react to environmental changes. We previously showed that the TCS RssAB suppresses flagellar biosynthesis master regulator flhDC specifically in swarming lag phase to control surface migration timing without affecting expansion rate in Serratia marcescens swarming development. Here we demonstrate that the TCS QseBC, which has been found in several human pathogens involved in flagellar and virulence regulation, has cross-talk with RssAB. We demonstrate that the phosphorylated QseB repressed flhDC expression, reducing swarming migration rate with modest effect on migration initiation. Unexpectedly, the QseC can dephosphorylate non-cognate response regulator RssB. Deletion of qseC prolonged RssAB signaling, reduced flhDC expression, and delayed migration initiation. Our data suggest that QseC is a flagellar biosynthesis activator by de-repressing RssB ∼ P and QseB ∼ P respectively in lag and migration phases in a stage-specific manner in swarming development.

Cross-talk between bacterial two-component systems drives stepwise regulation of flagellar biosynthesis in swarming development.

Talaromyces marneffei causes life-threatening opportunistic infections, mainly in Southeast Asia and South China. T. marneffei mainly infects patients with human immunodeficiency virus (HIV) but also infects individuals without known immunosuppression. Here we investigated the involvement of anti-IFN-γ autoantibodies in severe T. marneffei infections in HIV-negative patients. We enrolled 58 HIV-negative adults with severe T. marneffei infections who were otherwise healthy. We found a high prevalence of neutralizing anti-IFN-γ autoantibodies (94.8%) in this cohort. The presence of anti-IFN-γ autoantibodies was strongly associated with HLA-DRB1*16:02 and -DQB1*05:02 alleles in these patients. We demonstrated that adult-onset acquired immunodeficiency due to autoantibodies against IFN-γ is the major cause of severe T. marneffei infections in HIV-negative patients in regions where this fungus is endemic. The high prevalence of anti-IFN-γ autoantibody-associated HLA class II DRB1*16:02 and DQB1*05:02 alleles may account for severe T. marneffei infections in Southeast Asia. Our findings clarify the pathogenesis of T. marneffei infection and pave the way for developing novel treatments.

Anti-IFN-γ autoantibodies underlie disseminated Talaromyces marneffei infections.

Anti-interferon (IFN)-γ autoantibodies (AIGAs) are a pathogenic factor in late-onset immunodeficiency with disseminated mycobacterial and other opportunistic infections. AIGAs block IFN-γ function, but their effects on IFN-γ signaling are unknown. Using a single-cell capture method, we isolated 19 IFN-γ-reactive monoclonal antibodies (mAbs) from patients with AIGAs. All displayed high-affinity (KD < 10-9 M) binding to IFN-γ, but only eight neutralized IFN-γ-STAT1 signaling and HLA-DR expression. Signal blockade and binding affinity were correlated and attributed to somatic hypermutations. Cross-competition assays identified three nonoverlapping binding sites (I-III) for AIGAs on IFN-γ. We found that site I mAb neutralized IFN-γ by blocking its binding to IFN-γR1. Site II and III mAbs bound the receptor-bound IFN-γ on the cell surface, abolishing IFN-γR1-IFN-γR2 heterodimerization and preventing downstream signaling. Site III mAbs mediated antibody-dependent cellular cytotoxicity, probably through antibody-IFN-γ complexes on cells. Pathogenic AIGAs underlie mycobacterial infections by the dual blockade of IFN-γ signaling and by eliminating IFN-γ-responsive cells.

Pathogenic autoantibodies to IFN-γ act through the impedance of receptor assembly and Fc-mediated response.

Candida albicans is a leading cause of intravascular catheter-related infections. The capacity for biofilm formation has been proposed to contribute to the persistence of this fungal pathogen on catheter surfaces. While efforts have been devoted to identifying microbial factors that modulate C. albicans biofilm formation in vitro, our understanding of the host factors that may shape C. albicans persistence in intravascular catheters is lacking. Here, we used multiphoton microscopy to characterize biofilms in intravascular catheters removed from candidiasis patients. We demonstrated that, NETosis, a type of neutrophil cell death with antimicrobial activity, was implicated in the interaction of immune cells with C. albicans in the catheters. The catheter isolates exhibited reduced filamentation and candidalysin gene expression, specifically in the total parenteral nutrition culture environment. Furthermore, we showed that the ablation of candidalysin expression in C. albicans reduced NETosis and conferred resistance to neutrophil-mediated fungal biofilm elimination. Our findings illustrate the role of neutrophil NETosis in modulating C. albicans biofilm persistence in an intravascular catheter, highlighting that C. albicans can benefit from reduced virulence expression to promote its persistence in an intravascular catheter.

Regulation of candidalysin underlies Candida albicans persistence in intravascular catheters by modulating NETosis.

TRPML2 is an endolysosomal calcium-permeable channel gated by phosphatidylinositol 3,5-bisphosphate (PI(3,5)P₂). However, its subcellular localization and functional contribution to compartment-specific vesicle trafficking remain incompletely defined. In this study, we identify Rab4-positive recycling endosomes as a key site of TRPML2 activity and regulation. We further examined a PI(3,5)P₂-insensitive TRPML2 mutant (R310A), which exhibited reduced channel activity, accumulated perinuclear vesicles, and impaired Rab4 + endosomal motility. To restore channel function, we employed two selective small-molecule TRPML2 agonists, ML2-SA1 and ML2-SA2. Endolysosomal patch-clamp recordings confirmed that both compounds activate wild-type TRPML2 and effectively restore channel activity in the R310A mutant. Functional imaging further demonstrated that ML2-SA2 treatment rescues vesicle redistribution, reduces Golgi accumulation, and promotes peripheral vesicle dynamics. Notably, these effects were observed even in the absence of functional PI(3,5)P₂ gating, indicating that small-molecule agonists can bypass endogenous lipid regulation to restore TRPML2 activity. Our findings identify TRPML2 as a druggable ion channel whose activity is essential for maintaining Rab4-dependent vesicle trafficking. This study establishes a mechanistic link between phosphoinositide sensitivity, TRPML2 activation, and endosomal motility, and highlights a potential therapeutic strategy for correcting trafficking defects caused by impaired lipid signaling in immune cells or other pathophysiological contexts involving endosomal stress.

Article	Year
A mobile quorum-sensing system in Serratia marcescens. Journal of bacteriology\| PubMed ID: 16452435	2006
RssAB-FlhDC-ShlBA as a major pathogenesis pathway in Serratia marcescens. Infection and immunity\| PubMed ID: 20713626	2010
RssAB signaling coordinates early development of surface multicellularity in Serratia marcescens. PloS one\| PubMed ID: 21887380	2011
Activation of NK cell cytotoxicity by the natural compound 2,3-butanediol. Journal of leukocyte biology\| PubMed ID: 22802446	2012
An iron detection system determines bacterial swarming initiation and biofilm formation. Scientific reports\| PubMed ID: 27845335	2016
Cross-talk between bacterial two-component systems drives stepwise regulation of flagellar biosynthesis in swarming development. Biochemical and biophysical research communications\| PubMed ID: 28522292	2017
Anti-IFN-γ autoantibodies underlie disseminated Talaromyces marneffei infections. The Journal of experimental medicine\| PubMed ID: 32880631	2020
Pathogenic autoantibodies to IFN-γ act through the impedance of receptor assembly and Fc-mediated response. The Journal of experimental medicine\| PubMed ID: 35833912	2022
Regulation of candidalysin underlies Candida albicans persistence in intravascular catheters by modulating NETosis. PLoS pathogens\| PubMed ID: 38885290	2024
TRPML2 channel modulation by PI(3,5)P₂ and small-molecule agonists controls endosomal vesicle dynamics. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie\| PubMed ID: 40664038	2025

Yu-Huan Tsai

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