Chlamydia evasion of neutrophil host defense results in NLRP3 dependent myeloid-mediated sterile inflammation through the purinergic P2X7 receptor

Exosomes secreted from adipose-derived stem cells inhibit M1 macrophage polarization ameliorate chronic endometritis by regulating SIRT2/NLRP3

Chronic endometritis (CE) is a key factor in adverse pregnancy outcomes such as miscarriage and infertility. Macrophages are an important immune cell type that secrete pro-inflammatory and anti-inflammatory cytokines that are essential for maintaining endometrial function. This study aimed to investigate the key mechanisms by which exosomes derived from adipose-derived mesenchymal stem cells (ADSCs) regulate macrophage polarization through the sirtuin 2 (SIRT2)/NOD-like receptor pyrin containing 3 (NLRP3) axis and exert a protective effect on CE. Exosomes were obtained from ADSCs (ADSCs-exo) using the classical ultracentrifugation method and characterized using transmission electron microscopy, nanoparticle tracking analysis, and western blotting. ADSCs-exo protective effects on CE mice and RAW 264.7 cells and its related molecular mechanisms were investigated using real-time quantitative polymerase chain reaction, western blotting, enzyme-linked immunosorbent assay, flow cytometry, immunofluorescence, immunoprecipitation, hematoxylin and eosin staining, and immunohistochemistry. ADSCs-exo significantly inhibited M1 macrophage polarization, as evidenced by a 54% reduction in tumor necrosis factor alfa (TNF-α), a 46% reduction in interleukin 1β (IL-1β), and a 36% reduction in interleukin 6 (IL-6) levels in LPS-induced RAW264.7 cells. In vivo, ADSCs-exo treatment reduced the expression of TNF-α by 50%, IL-1β by 58%, and IL-6 by 49% in the uterine tissues of CE mice. Moreover, ADSCs-exo upregulated the expression of SIRT2, promoted the deacetylation modification of NLRP3 to inhibit NLRP3 inflammasome activation, and further suppressed M1 macrophage polarization. However, these trends were reversed after SIRT2 silencing. Our experimental results demonstrate that ADSCs-exo alleviate CE by regulating the SIRT2/NLRP3 axis to inhibit M1 macrophage polarization. This provides a potential theoretical basis for the therapeutic role of stem cells in CE.

Development and Validation of Chlamydia muridarum Mouse Models for Studying Genital Tract Infection Pathogenesis

Animal infection models play significant roles in the study of bacterial pathogenic mechanisms and host-pathogen interactions, as well as in evaluating drug and vaccine efficacies. Chlamydia trachomatis is responsible for infections in various mucosal tissues, including the eyes and urogenital, respiratory, and gastrointestinal tracts. Chronic infections can result in severe consequences such as trachoma-induced blindness, ectopic pregnancy, and infertility. While intravaginal inoculation of C. muridarum mimics the natural route of sexual transmission between individuals, transcervical inoculation allows the organisms to directly infect endometrial epithelial cells without interference from host responses triggered by chlamydial contact or infection of vaginal and cervical cells. Therefore, in this study, we used mouse models to visualize pathologies in both the endometrium and oviduct following C. muridarum inoculation. Key features • This protocol develops the mouse-adapted Chlamydia muridarum model, ideal for visualizing pathologies in both the endometrium and oviduct genital tract. • Requires female mice and utilizes specific techniques for intravaginal and transcervical inoculation with chlamydial elementary body (EB) and a form specialized for intracellular replication. • The protocol necessitates specialized equipment, including a laminar flow hood, a micropipette, and a non-surgical embryo transfer device (NSET). Graphical overview.

Pathogenic and Protective Roles of Neutrophils in Chlamydia trachomatis Infection

Chlamydia trachomatis (Ct) is an obligate intracellular pathogen that causes the most commonly diagnosed bacterial sexually transmitted infection (STI) and is a leading cause of preventable blindness globally. Ct infections can generate a strong pro-inflammatory immune response, leading to immune-mediated pathology in infected tissues. Neutrophils play an important role in mediating both pathology and protection during infection. Excessive neutrophil activation, migration, and survival are associated with host tissue damage during Chlamydia infections. In contrast, neutrophils also perform phagocytic killing of Chlamydia in the presence of IFN-γ and anti-Chlamydia antibodies. Neutrophil extracellular traps (NETs) and many neutrophil degranulation products have also demonstrated strong anti-Chlamydia functions. To counteract this neutrophil-mediated protection, Chlamydia has developed several evasion strategies. Various Chlamydia proteins can limit potentially protective neutrophil responses by directly targeting receptors present on the surface of neutrophils or neutrophil degranulation products. In this review, we provide a survey of current knowledge regarding the role of neutrophils in pathogenesis and protection, including the ways that Chlamydia circumvents neutrophil functions, and we propose critical areas for future research.

The intricate interactions between inflammasomes and bacterial pathogens: Roles, mechanisms, and therapeutic potentials

Inflammasomes are intracellular multiprotein complexes that consist of a sensor, an adaptor, and a caspase enzyme to cleave interleukin (IL)-1β and IL-18 into their mature forms. In addition, caspase-1 and -11 activation results in the cleavage of gasdermin D to form pores, thereby inducing pyroptosis. Activation of the inflammasome and pyroptosis promotes host defense against pathogens, whereas dysregulation of the inflammasome can result in various pathologies. Inflammasomes exhibit versatile microbial signal detection, directly or indirectly, through cellular processes, such as ion fluctuations, reactive oxygen species generation, and the disruption of intracellular organelle function; however, bacteria have adaptive strategies to manipulate the inflammasome by altering microbe-associated molecular patterns, intercepting innate pathways with secreted effectors, and attenuating inflammatory and cell death responses. In this review, we summarize recent advances in the diverse roles of the inflammasome during bacterial infections and discuss how bacteria exploit inflammasome pathways to establish infections or persistence. In addition, we highlight the therapeutic potential of harnessing bacterial immune subversion strategies against acute and chronic bacterial infections. A more comprehensive understanding of the significance of inflammasomes in immunity and their intricate roles in the battle between bacterial pathogens and hosts will lead to the development of innovative strategies to address emerging threats posed by the expansion of drug-resistant bacterial infections.

Cutaneous melanoma and purinergic modulation by phenolic compounds

Cutaneous melanoma is a complex pathology that still has only treatments that lack efficiency and offer many adverse effects. Due to this scenario emerges the need to analyze other possible treatments against this disease, such as the effect of phenolic compounds. These substances have proven antitumor effects, but still have not been fully explored as a form of therapy to combat melanoma. Also, the purinergic receptors, along with its system molecules, take part in the formation of tumors from many pathways, such as the actions of ectoenzymes and receptors activity, especially P2Rs family, and are formed by structures that can be modulated by the phenolic compounds. Therefore, more studies have to be made with the aim of explaining the purinergic system activity in carcinogenesis of cutaneous melanoma and the effects of its modulation by phenolic compound, in order to enable the development of new therapies to combat this aggressive and feared cancer.

Relationship between Chlamydia Trachomatis infection, infertility, and serum 25-hydroxyvitamin D: a cross-sectional study from NHANES 2013-2016

BACKGROUND

Chlamydia trachomatis is a common sexually transmitted disease that is associated with considerable morbidity and harmful sequelae, including pelvic inflammatory disease and infertility. Strategies for prevention and treatment of infertility in women with C. trachomatis infection require further investigation. There is evidence suggesting that vitamin D could be a potential treatment. This study aimed to investigate the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels, chlamydia seropositivity, and the risk of infertility in women.

METHODS

We conducted this cross-sectional study using 2013-2016 National Health and Nutrition Examination Survey data. Women aged 18-39 years with complete serum 25(OH)D and chlamydia Pgp3Ab multiplex bead/enzyme-linked immunosorbent assay data available were included. The correlation between 25(OH)D level, chlamydia seropositivity, and infertility was evaluated using the weighted chi-squared test and the t-test with multivariate logistic regression and moderation effect models.

RESULTS

Among the 1424 women who met our eligibility criteria, the weighted chlamydia seropositivity rate was 36.8%. The 25(OH)D level was significantly lower in the seropositive group compared with seronegative control. (P = 0.009). After adjusting for ethnicity, the effect of 25(OH)D was no longer significant (P = 0.693). Further analysis in the chlamydia-seropositive subset revealed that the vitamin D level was lower in the infertile group (P = 0.024). In an interaction model, 25(OH)D was found to antagonizes the positive relationship between chlamydia and infertility (OR = 0.985, 95% CI: 0.971-0.999, P = 0.040).

CONCLUSION

The serum vitamin D level may be more related to the prognosis in terms of infertility than to the risk of chlamydia infection. This finding may reveal a possible treatment strategy for chlamydia infection.

Recognition of Chlamydia trachomatis by Toll-like receptor 9 is altered during persistence

Toll-like receptor 9 (TLR9) is an innate immune receptor that localizes to endosomes in antigen presenting cells and recognizes single stranded unmethylated CpG sites on bacterial genomic DNA (gDNA). Previous bioinformatic studies have demonstrated that the genome of the human pathogen Chlamydia trachomatis contains TLR9 stimulatory motifs, and correlative studies have implied a link between human TLR9 (hTLR9) genotype variants and susceptibility to infection. Here, we present our evaluation of the stimulatory potential of C. trachomatis gDNA and its recognition by hTLR9- and murine TLR9 (mTLR9)-expressing cells. Utilizing reporter cell lines, we demonstrate that purified gDNA from C. trachomatis can stimulate hTLR9 signaling, albeit at lower levels than gDNA prepared from other Gram-negative bacteria. Interestingly, we found that while C. trachomatis is capable of signaling through hTLR9 and mTLR9 during live infections in HEK293 reporter cell lines, signaling only occurs at later developmental time points. Chlamydia-specific induction of hTLR9 is blocked when protein synthesis is inhibited prior to the RB-to-EB conversion, exacerbated by the inhibition of lipooligosaccharide biosynthesis, and is significantly altered during the induction of aberrance/persistence. Our observations support the hypothesis that chlamydial gDNA is released during the conversion between the pathogen's replicative and infectious forms and during treatment with antibiotics targeting peptidoglycan assembly. Given that C. trachomatis inclusions do not co-localize with TLR9-containing vacuoles in the pro-monocytic cell line U937, our findings also hint that chlamydial gDNA is capable of egress from the inclusion, and traffics to TLR9-containing vacuoles via an as yet unknown pathway.

CT135 mediates the resistance of Chlamydia trachomatis to primate interferon gamma stimulated immune defenses

Evading host innate immune defenses is a critical feature of Chlamydia trachomatis infections, and the mechanisms used by C. trachomatis to subvert these pathways are incompletely understood. We screened a library of chimeric C. trachomatis mutants for genetic factors important for interference with cell-autonomous immune defenses. Mutant strains with predicted truncations of the inclusion membrane protein CT135 were susceptible to interferon gamma-activated immunity in human cells. CT135 functions to prevent host-driven recruitment of ubiquitin and p62/SQSTM to the inclusion membrane. In a nonhuman primate model of C. trachomatis infection, a CT135-deficient strain was rapidly cleared, highlighting the importance of this virulence factor for C. trachomatis pathogenesis. Analysis of CT135 phenotypes in primary macaque cells revealed that cell-autonomous immune defenses against C. trachomatis are conserved between humans and nonhuman primates and connects mechanistic findings with in vivo infection outcomes.

ATP and Formyl Peptides Facilitate Chemoattractant Leukotriene-B4 Synthesis and Drive Calcium Fluxes, Which May Contribute to Neutrophil Swarming at Sites of Cell Damage and Pathogens Invasion

Here, we demonstrate that human neutrophil interaction with the bacterium Salmonella typhimurium fuels leukotriene B4 synthesis induced by the chemoattractant fMLP. In this work, we found that extracellular ATP (eATP), the amount of which increases sharply during tissue damage, can effectively regulate fMLP-induced leukotriene B4 synthesis. The vector of influence strongly depends on the particular stage of sequential stimulation of neutrophils by bacteria and on the stage at which fMLP purinergic signaling occurs. Activation of 5-lipoxygenase (5-LOX), key enzyme of leukotriene biosynthesis, depends on an increase in the cytosolic concentration of Ca2+. We demonstrate that eATP treatment prior to fMLP, by markedly reducing the amplitude of the fMLP-induced Ca2+ transient jump, inhibits leukotriene synthesis. At the same time, when added with or shortly after fMLP, eATP effectively potentiates arachidonic acid metabolism, including by Ca2+ fluxes stimulation. Flufenamic acid, glibenclamide, and calmodulin antagonist R24571, all of which block calcium signaling in different ways, all suppressed 5-LOX product synthesis in our experimental model, indicating the dominance of calcium-mediated mechanisms in eATP regulatory potential. Investigation into the adhesive properties of neutrophils revealed the formation of cell clusters when adding fMLP to neutrophils exposed to the bacterium Salmonella typhimurium. eATP added simultaneously with fMLP supported neutrophil polarization and clustering. A cell-derived chemoattractant such as leukotriene B4 plays a crucial role in the recruitment of additional neutrophils to the foci of tissue damage or pathogen invasion, and eATP, through the dynamics of changes in [Ca2+]i, plays an important decisive role in fMLP-induced leukotrienes synthesis during neutrophil interactions with the bacterium Salmonella typhimurium.

Metabolism and physiology of pathogenic bacterial obligate intracellular parasites

Bacterial obligate intracellular parasites (BOIPs) represent an exclusive group of bacterial pathogens that all depend on invasion of a eukaryotic host cell to reproduce. BOIPs are characterized by extensive adaptation to their respective replication niches, regardless of whether they replicate within the host cell cytoplasm or within specialized replication vacuoles. Genome reduction is also a hallmark of BOIPs that likely reflects streamlining of metabolic processes to reduce the need for de novo biosynthesis of energetically costly metabolic intermediates. Despite shared characteristics in lifestyle, BOIPs show considerable diversity in nutrient requirements, metabolic capabilities, and general physiology. In this review, we compare metabolic and physiological processes of prominent pathogenic BOIPs with special emphasis on carbon, energy, and amino acid metabolism. Recent advances are discussed in the context of historical views and opportunities for discovery.

Recognition of Chlamydia trachomatis by Toll-Like Receptor 9 is altered during persistence

Toll-like receptor 9 (TLR9) is an innate immune receptor that localizes to endosomes in antigen presenting cells and recognizes single stranded unmethylated CpG sites on bacterial genomic DNA. Previous bioinformatic studies have indicated that the genome of the human pathogen Chlamydia trachomatis contains TLR9 stimulatory motifs, and correlative studies have implied a link between human TLR9 (hTLR9) genotype variants and susceptibility to infection. Here we present our evaluation of the stimulatory potential of C. trachomatis gDNA and its recognition by hTLR9- and murine TLR9 (mTLR9)-expressing cells. We confirm that hTLR9 colocalizes with chlamydial inclusions in the pro-monocytic cell line, U937. Utilizing HEK293 reporter cell lines, we demonstrate that purified genomic DNA from C. trachomatis can stimulate hTLR9 signaling, albeit at lower levels than gDNA prepared from other Gram-negative bacteria. Interestingly, we found that while C. trachomatis is capable of signaling through hTLR9 and mTLR9 during live infections in non-phagocytic HEK293 reporter cell lines, signaling only occurs at later developmental time points. Chlamydia-specific induction of hTLR9 is blocked when protein synthesis is inhibited prior to the RB-to-EB conversion and exacerbated by the inhibition of lipooligosaccharide biosynthesis. The induction of aberrance / persistence also significantly alters Chlamydia-specific TLR9 signaling. Our observations support the hypothesis that chlamydial gDNA is released at appreciable levels by the bacterium during the conversion between its replicative and infectious forms and during treatment with antibiotics targeting peptidoglycan assembly.

Insights into innate immune cell evasion by Chlamydia trachomatis

Chlamydia trachomatis, is a kind of obligate intracellular pathogen. The removal of C. trachomatis relies primarily on specific cellular immunity. It is currently considered that CD4+ Th1 cytokine responses are the major protective immunity against C. trachomatis infection and reinfection rather than CD8+ T cells. The non-specific immunity (innate immunity) also plays an important role in the infection process. To survive inside the cells, the first process that C. trachomatis faces is the innate immune response. As the "sentry" of the body, mast cells attempt to engulf and remove C. trachomatis. Dendritic cells present antigen of C. trachomatis to the "commanders" (T cells) through MHC-I and MHC-II. IFN-γ produced by activated T cells and natural killer cells (NK) further activates macrophages. They form the body's "combat troops" and produce immunity against C. trachomatis in the tissues and blood. In addition, the role of eosinophils, basophils, innate lymphoid cells (ILCs), natural killer T (NKT) cells, γδT cells and B-1 cells should not be underestimated in the infection of C. trachomatis. The protective role of innate immunity is insufficient, and sexually transmitted diseases (STDs) caused by C. trachomatis infections tend to be insidious and recalcitrant. As a consequence, C. trachomatis has developed a unique evasion mechanism that triggers inflammatory immunopathology and acts as a bridge to protective to pathological adaptive immunity. This review focuses on the recent advances in how C. trachomatis evades various innate immune cells, which contributes to vaccine development and our understanding of the pathophysiologic consequences of C. trachomatis infection.

Neisseria gonorrhoeae drives Chlamydia trachomatis into a persistence-like state during in vitro co-infection

Chlamydia trachomatis and Neisseria gonorrhoeae are the most prevalent bacterial sexually transmitted infections (STIs) globally. Despite frequent co-infections in patients, few studies have investigated how mono-infections may differ from co-infections. We hypothesized that a symbiotic relationship between the pathogens could account for the high rates of clinical co-infection. During in vitro co-infection, we observed an unexpected phenotype where the C. trachomatis developmental cycle was impaired by N. gonorrhoeae. C. trachomatis is an obligate intracellular pathogen with a unique biphasic developmental cycle progressing from infectious elementary bodies (EB) to replicative reticulate bodies (RB), and back. After 12 hours of co-infection, we observed fewer EBs than in a mono-infection. Chlamydial genome copy number remained equivalent between mono- and co-infections. This is a hallmark of Chlamydial persistence. Chlamydial persistence alters inclusion morphology but varies depending on the stimulus/stress. We observed larger, but fewer, Chlamydia during co-infection. Tryptophan depletion can induce Chlamydial persistence, but tryptophan supplementation did not reverse the co-infection phenotype. Only viable and actively growing N. gonorrhoeae produced the inhibition phenotype in C. trachomatis. Piliated N. gonorrhoeae had the strongest effect on C. trachomatis, but hyperpiliated or non-piliated N. gonorrhoeae still produced the phenotype. EB development was modestly impaired when N. gonorrhoeae were grown in transwells above the infected monolayer. C. trachomatis serovar L2 was not impaired during co-infection. Chlamydial impairment could be due to cytoskeletal or osmotic stress caused by an as-yet-undefined mechanism. We conclude that N. gonorrhoeae induces a persistence-like state in C. trachomatis that is serovar dependent.

Endometrial responses to bacterial and viral infection: a scoping review

BACKGROUND

The endometrium is a highly dynamic tissue that undergoes dramatic proliferation and differentiation monthly in order to prepare the uterus for implantation and pregnancy. Intrauterine infection and inflammation are being increasingly recognized as potential causes of implantation failure and miscarriage, as well as obstetric complications later in gestation. However, the mechanisms by which the cells of the endometrium respond to infection remain understudied and recent progress is slowed in part owing to similar overlapping studies being performed in different species.

OBJECTIVE AND RATIONALE

The aim of this scoping review is to systematically summarize all published studies in humans and laboratory animals that have investigated the innate immune sensing and response of the endometrium to bacteria and viruses, and the signaling mechanisms involved. This will enable gaps in our knowledge to be identified to inform future studies.

SEARCH METHODS

The Cochrane Library, Ovid Embase/Medline, PubMed, Scopus, Google Scholar, and Web of Science databases were searched using a combination of controlled and free text terms for uterus/endometrium, infections, and fertility to March 2022. All primary research papers that have reported on endometrial responses to bacterial and viral infections in the context of reproduction were included. To focus the scope of the current review, studies in domesticated animals, included bovine, porcine, caprine, feline, and canine species were excluded.

OUTCOMES

This search identified 42 728 studies for screening and 766 full-text studies were assessed for eligibility. Data was extracted from 76 studies. The majority of studies focused on endometrial responses to Escherichia coli and Chlamydia trachomatis, with some studies of Neisseria gonorrhea, Staphylococcus aureus, and the Streptococcus family. Endometrial responses have only been studied in response to three groups of viruses thus far: HIV, Zika virus, and the herpesvirus family. For most infections, both cellular and animal models have been utilized in vitro and in vivo, focusing on endometrial production of cytokines, chemokines, and antiviral/antimicrobial factors, and the expression of innate immune signaling pathway mediators after infection. This review has identified gaps for future research in the field as well as highlighted some recent developments in organoid systems and immune cell co-cultures that offer new avenues for studying endometrial responses to infection in more physiologically relevant models that could accelerate future findings in this area.

WIDER IMPLICATIONS

This scoping review provides an overarching summary and benchmark of the current state of research on endometrial innate immune responses to bacterial and viral infection. This review also highlights some exciting recent developments that enable future studies to be designed to deepen our understanding of the mechanisms utilized by the endometrium to respond to infection and their downstream effects on uterine function.

In Silico Identification and Validation of Pyroptosis-Related Genes in Chlamydia Respiratory Infection

The incidence of Chlamydia trachomatis respiratory infection is increasing, and its pathogenesis is still unclear. Pyroptosis, as a mode of inflammatory cell death, plays a vital role in the occurrence and development of Chlamydia trachomatis respiratory infection. In this study, the potential pyroptosis-related genes involved in Chlamydia trachomatis respiratory infection were identified by constructing a mouse model of C. muridarum infection combined with bioinformatics analysis. Through in-depth analysis of the RNA sequencing data, 13 differentially expressed pyroptosis-related genes were screened, including 1 downregulated gene and 12 upregulated genes. Gene ontology (GO) analysis showed that these genes mainly regulate inflammatory responses and produce IL-1β. Protein-protein interaction network analysis identified eight hub genes of interest: Tnf, Tlr2, Il1b, Nlrp3, Tlr9, Mefv, Zbp1 and Tnfaip3. Through quantitative real-time PCR (qPCR) analysis, we found that the expression of these genes in the lungs of C. muridarum-infected mice was significantly reduced, consistent with the bioinformatics results. At the same time, we detected elevated levels of caspase-3, gasdermin D and gasdermin E proteins in the lungs of C. muridarum-infected mice, demonstrating that Chlamydia trachomatis infection does induce pyroptosis. We then predicted nine miRNAs targeting these hub genes and constructed a key competitive endogenous RNA (ceRNA) network. In summary, we identified six key pyroptosis-related genes involved in Chlamydia trachomatis respiratory infection and constructed a ceRNA network associated with these genes. These findings will improve understanding of the molecular mechanisms underlying pyroptosis in Chlamydia trachomatis respiratory infections.

Nitric Oxide-Producing Polymorphonuclear Neutrophils Confer Protection Against Chlamydia psittaci in Mouse Lung Infection

BACKGROUND

Whether polymorphonuclear neutrophils (PMN) exert a protective role upon chlamydial infection by expressing inducible nitric oxide (NO) synthase (iNOS) and producing NO remains unclear.

METHODS

This issue was addressed using BALB/c mice infected with Chlamydia psittaci 6BC strain. Methods included flow cytometry, immunofluorescence, qRT-PCR, and western blot.

RESULTS

The number of PMN was significantly increased during C. psittaci infection, which was accompanied by increased iNOS expression and NO production in the mouse lungs. PMN were the major source of NO during pulmonary C. psittaci infection and inhibited C. psittaci multiplication in an iNOS/NO-dependent manner. Depletion of PMN aggravated C. psittaci-induced disease and increased C. psittaci burden. Nuclear factor-κB (NF-κB) and STAT1 signaling pathways, but not MAPK signaling pathways, were required for the induction of iNOS expression and NO production in PMN by C. psittaci infection. Thus, our findings highlight the protective role of NO-producing PMN in C. psittaci infection.

CONCLUSIONS

NO-producing PMN confer a protective role during pulmonary C. psittaci infection in mice, and thus our study sheds new light on PMN function during Chlamydia infection.

Intragraft immune cells: accomplices or antagonists of recipient-derived macrophages in allograft fibrosis?

Organ fibrosis caused by chronic allograft rejection is a major concern in the field of transplantation. Macrophage-to-myofibroblast transition plays a critical role in chronic allograft fibrosis. Adaptive immune cells (such as B and CD4⁺ T cells) and innate immune cells (such as neutrophils and innate lymphoid cells) participate in the occurrence of recipient-derived macrophages transformed to myofibroblasts by secreting cytokines, which eventually leads to fibrosis of the transplanted organ. This review provides an update on the latest progress in understanding the plasticity of recipient-derived macrophages in chronic allograft rejection. We discuss here the immune mechanisms of allograft fibrosis and review the reaction of immune cells in allograft. The interactions between immune cells and the process of myofibroblast formulation are being considered for the potential therapeutic targets of chronic allograft fibrosis. Therefore, research on this topic seems to provide novel clues for developing strategies for preventing and treating allograft fibrosis.

Pyroptosis-triggered pathogenesis: New insights on antiphospholipid syndrome

APS (antiphospholipid syndrome) is a systematic autoimmune disease presenting with the high levels of aPLs (antiphospholipid antibodies). These autoantibodies are involved in various clinical manifestations, mainly including arterial or venous thrombosis formation, proinflammatory response, and recurrent pregnant loss. Pyroptosis is a form of lytic programmed cell death, and it aggravates autoimmune diseases progression via activating NOD-like receptors, especially the NLRP3 inflammasome and its downstream inflammatory factors IL (interleukin)-1β and IL-18. However, the underlying mechanisms of pyroptosis-induced APS progression remain to be elucidated. ECs (endothelial cells), monocytes, platelets, trophoblasts, and neutrophils are prominent participants in APS development. Of significance, pyroptosis of APS-related cells leads to the excessive release of proinflammatory and prothrombotic factors, which are the primary contributors to APOs (adverse pregnancy outcomes), thrombosis formation, and autoimmune dysfunction in APS. Furthermore, pyroptosis-associated medicines have made encouraging advancements in attenuating inflammation and thrombosis. Given the potential of pyroptosis in regulating APS development, this review would systematically expound the molecular mechanisms of pyroptosis, and elaborate the role of pyroptosis-mediated cellular effects in APS progression. Lastly, the prospective therapeutic approaches for APS would be proposed based on the regulation of pyroptosis.

Virulence Protein Pgp3 Is Insufficient To Mediate Plasmid-Dependent Infectivity of Chlamydia trachomatis

Chlamydia trachomatis is the most common cause of infectious blindness and sexually transmitted bacterial infection globally. C. trachomatis contains a conserved chlamydial plasmid with eight coding sequences. Plasmid-cured Chlamydia strains are attenuated and display reduced infectivity in cell culture and in vivo genital infection of female mice. Mutants that do not express the plasmid-encoded proteins Pgp3, a secreted protein with unknown function, or Pgp4, a putative regulator of pgp3 and other chromosomal loci, display an infectivity defect similar to plasmid-deficient strains. Our objective was to determine the combined and individual contributions of Pgp3 and Pgp4 to this phenotype. Deletion of pgp3 and pgp4 resulted in an infectivity defect detected by competition assay in cell culture and in mice. The pgp3 locus was placed under the control of an anhydrotetracycline-inducible promoter to examine the individual contributions of Pgp3 and Pgp4 to infectivity. Expression of pgp3 was induced 100- to 1,000-fold after anhydrotetracycline administration, regardless of the presence or absence of pgp4. However, secreted Pgp3 was not detected when pgp4 was deleted, confirming a role for Pgp4 in Pgp3 secretion. We discovered that expression of pgp3 or pgp4 alone was insufficient to restore normal infectivity, which required expression of both Pgp3 and Pgp4. These results suggest Pgp3 and Pgp4 are both required for infectivity during C. trachomatis infection. Future studies are required to determine the mechanism by which Pgp3 and Pgp4 influence chlamydial infectivity as well as the potential roles of Pgp4-regulated loci.

Intracellular lifestyle of Chlamydia trachomatis and host-pathogen interactions

In recent years, substantial progress has been made in the understanding of the intracellular lifestyle of Chlamydia trachomatis and how the bacteria establish themselves in the human host. As an obligate intracellular pathogenic bacterium with a strongly reduced coding capacity, C. trachomatis depends on the provision of nutrients from the host cell. In this Review, we summarize the current understanding of how C. trachomatis establishes its intracellular replication niche, how its metabolism functions in the host cell, how it can defend itself against the cell autonomous and innate immune response and how it overcomes adverse situations through the transition to a persistent state. In particular, we focus on those processes for which a mechanistic understanding has been achieved.

Human umbilical cord mesenchymal stem cells derived extracellular vesicles alleviate salpingitis by promoting M1-to-M2 transformation

Background: With an increasing number of patients experiencing infertility due to chronic salpingitis after Chlamydia trachomatis (CT) infection, there is an unmet need for tissue repair or regeneration therapies. Treatment with human umbilical cord mesenchymal stem cell-derived extracellular vesicles (hucMSC-EV) provides an attractive cell-free therapeutic approach. Methods: In this study, we investigated the alleviating effect of hucMSC-EV on tubal inflammatory infertility caused by CT using in vivo animal experiments. Furthermore, we examined the effect of hucMSC-EV on inducing macrophage polarization to explore the molecular mechanism. Results: Our results showed that tubal inflammatory infertility caused by Chlamydia infection was significantly alleviated in the hucMSC-EV treatment group compared with the control group. Further mechanistic experiments showed that the application of hucMSC-EV induced macrophage polarization from the M1 to the M2 type via the NF-κB signaling pathway, improved the local inflammatory microenvironment of fallopian tubes and inhibited tube inflammation. Conclusion: We conclude that this approach represents a promising cell-free avenue to ameliorate infertility due to chronic salpingitis.

The bacterial effector GarD shields Chlamydia trachomatis inclusions from RNF213-mediated ubiquitylation and destruction

Chlamydia trachomatis is the leading cause of sexually transmitted bacterial infections and a major threat to women's reproductive health in particular. This obligate intracellular pathogen resides and replicates within a cellular compartment termed an inclusion, where it is sheltered by unknown mechanisms from gamma-interferon (IFNγ)-induced cell-autonomous host immunity. Through a genetic screen, we uncovered the Chlamydia inclusion membrane protein gamma resistance determinant (GarD) as a bacterial factor protecting inclusions from cell-autonomous immunity. In IFNγ-primed human cells, inclusions formed by garD loss-of-function mutants become decorated with linear ubiquitin and are eliminated. Leveraging cellular genome-wide association data, we identified the ubiquitin E3 ligase RNF213 as a candidate anti-Chlamydia protein. We demonstrate that IFNγ-inducible RNF213 facilitates the ubiquitylation and destruction of GarD-deficient inclusions. Furthermore, we show that GarD operates as a cis-acting stealth factor barring RNF213 from targeting inclusions, thus functionally defining GarD as an RNF213 antagonist essential for chlamydial growth during IFNγ-stimulated immunity.

The Chlamydia trachomatis Inclusion Membrane Protein CTL0390 Mediates Host Cell Exit via Lysis through STING Activation

The obligate intracellular bacterium Chlamydia trachomatis is the causative agent of the most frequently reported bacterial sexually transmitted disease. Upon internalization into host cells, C. trachomatis remains within a membrane-bound compartment known as an inclusion, where it undergoes its developmental cycle. After completion of this cycle, bacteria exit the host cell. One mechanism of exit is lysis, whereby the inclusion and host cell rupture to release bacteria; however, the mechanism of lysis is not well characterized. A subset of C. trachomatis effectors, known as inclusion membrane proteins (Inc), are embedded within the inclusion membrane to facilitate host cell manipulation. The functions of many Inc proteins are unknown. We sought to characterize the Inc protein CTL0390. We determined that CTL0390 is expressed throughout the developmental cycle and that its C-terminal tail is exposed to the cytosol. To investigate the function of CTL0390, we generated a ctl0390 mutant complemented with ctl0390 on a plasmid. Loss of CTL0390 did not affect infectious progeny production but resulted in a reduction in lysis. Overexpression of CTL0390 induced premature lysis and host nuclear condensation, the latter of which could be reduced upon inhibition of the cGAS-STING DNA sensing pathway. Infection with the clt0390 mutant led to reduced Golgi translocation of STING, and chemical and genetic approaches to inactivate STING revealed that STING plays a role in lysis in a CTL0390-dependent manner. Together, these results reveal a role for CTL0390 in bacterial exit via lysis at late stages of the Chlamydia developmental cycle and through STING activation.

Noise exposure and its relationship with postinfarction cardiac remodeling: implications for NLRP3 inflammasome activation

In recent years, high-decibel noise has emerged as a causative risk factor for ischemic heart disease. Massive noise overdose is associated with increased endocrine, neural, and immune stress responses. The NLRP3 (nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 3) inflammasome, the most characterized supramolecular complex and a potent mediator of inflammatory signaling, has been reported to be a marker of increased ischemic heart disease vulnerability. Our study evaluated the association of noise exposure with postinfarction cardiac remodeling and its effect on NLRP3 inflammasome activation. Rats were exposed to a noisy environment (14 days, 24 h/per day, 70 ± 5 dB), and speck formation by the NLRP3 inflammasome scaffold protein ASC (apoptosis-associated speck-like protein) was assessed by confocal immunofluorescence. Echocardiography, pathological analysis, and in vivo electrophysiology were performed. Our results revealed the improved postinfarction cardiac function, mitigated fibrosis, and decreased arrhythmia vulnerability and sympathetic sprouting in low-environment noise groups. Moreover, western blotting of NLRP3, caspase-1, ASC, IL-1β, and IL-18 and confocal microscopy of ASC speck showed that the priming and activation of NLRP3 inflammasome were higher in the NE group than in the NI group. In conclusion, our findings reveal a previously unidentified association between NLRP3 inflammasome activation and noise exposure, underscoring the significance of effective noise prevention in improving postinfarction prognosis.

Fracture healing is delayed in the absence of gasdermin - interleukin-1 signaling

Amino-terminal fragments from proteolytically cleaved gasdermins (GSDMs) form plasma membrane pores that enable the secretion of interleukin-1β (IL-1β) and IL-18. Excessive GSDM-mediated pore formation can compromise the integrity of the plasma membrane thereby causing the lytic inflammatory cell death, pyroptosis. We found that GSDMD and GSDME were the only GSDMs that were readily expressed in bone microenvironment. Therefore, we tested the hypothesis that GSDMD and GSDME are implicated in fracture healing owing to their role in the obligatory inflammatory response following injury. We found that bone callus volume and biomechanical properties of injured bones were significantly reduced in mice lacking either GSDM compared with wild-type (WT) mice, indicating that fracture healing was compromised in mutant mice. However, compound loss of GSDMD and GSDME did not exacerbate the outcomes, suggesting shared actions of both GSDMs in fracture healing. Mechanistically, bone injury induced IL-1β and IL-18 secretion in vivo, a response that was mimicked in vitro by bone debris and ATP, which function as inflammatory danger signals. Importantly, the secretion of these cytokines was attenuated in conditions of GSDMD deficiency. Finally, deletion of IL-1 receptor reproduced the phenotype of Gsdmd or Gsdme deficient mice, implying that inflammatory responses induced by the GSDM-IL-1 axis promote bone healing after fracture.