IL-36γ Promotes Killing of Mycobacterium tuberculosis by Macrophages via WNT5A-Induced Noncanonical WNT Signaling

The role of interleukin-36 in health and disease states

The interleukin (IL)-1 superfamily upregulates immune responses and maintains homeostasis between the innate and adaptive immune systems. Within the IL-1 superfamily, IL-36 plays a pivotal role in both innate and adaptive immune responses. Of the four IL-36 isoforms, three have agonist activity (IL-36α, IL-36β, IL-36γ) and the fourth has antagonist activity (IL-36 receptor antagonist [IL-36Ra]). All IL-36 isoforms bind to the IL-36 receptor (IL-36R). Binding of IL-36α/β/γ to the IL-36R recruits the IL-1 receptor accessory protein (IL-1RAcP) and activates downstream signalling pathways mediated by nuclear transcription factor kappa B and mitogen-activated protein kinase signalling pathways. Antagonist binding of IL-36Ra to IL-36R inhibits recruitment of IL-1RAcP, blocking downstream signalling pathways. Changes in the balance within the IL-36 cytokine family can lead to uncontrolled inflammatory responses throughout the body. As such, IL-36 has been implicated in numerous inflammatory diseases, notably a type of pustular psoriasis called generalized pustular psoriasis (GPP), a chronic, rare, potentially life-threatening, multisystemic skin disease characterised by recurrent fever and extensive sterile pustules. In GPP, IL-36 is central to disease pathogenesis, and the prevention of IL-36-mediated signalling can improve clinical outcomes. In this review, we summarize the literature describing the biological functions of the IL-36 pathway. We also consider the evidence for uncontrolled activation of the IL-36 pathway in a wide range of skin (e.g., plaque psoriasis, pustular psoriasis, hidradenitis suppurativa, acne, Netherton syndrome, atopic dermatitis and pyoderma gangrenosum), lung (e.g., idiopathic pulmonary fibrosis), gut (e.g., intestinal fibrosis, inflammatory bowel disease and Hirschsprung's disease), kidney (e.g., renal tubulointerstitial lesions) and infectious diseases caused by a variety of pathogens (e.g., COVID-19; Mycobacterium tuberculosis, Pseudomonas aeruginosa, Streptococcus pneumoniae infections), as well as in cancer. We also consider how targeting the IL-36 signalling pathway could be used in treating inflammatory disease states.

Role of IL-1 Family Cytokines IL-36, IL-37, IL-38 in Osteoarthritis and Rheumatoid Arthritis: A Comprehensive Review

Inflammatory cytokines, interleukin-36 (IL-36), IL-37, IL-38 belong to IL-1 family. The IL-36 subfamily obtains pro- and anti-inflammatory effects on various immune responses. Cytokine IL-37, has anti-inflammatory functions in immunity, and the recently identified IL-38 negatively associated with disease pathogenesis. To date, expression of IL-36, IL-37, IL-38 is reported dysregulated in osteoarthritis (OA) and rheumatoid arthritis (RA), and may be disease markers for arthritis-related diseases. Interestingly, expression of IL-38 was different either in OA patients or animal models, and expression of IL-36Ra in synovium was different in OA and RA patients. Moreover, functional studies have demonstrated significant role of these cytokines in OA and RA progress. These processes were related to immune cells and non-immune cells, where the cytokines IL-36, IL-37, IL-38 may regulate downstream signalings in the cells, and then involve in OA, RA development. In this review, we comprehensively discuss recent advancements in cytokines and the development of OA, RA. We hope that targeting these cytokines will become a potential treatment option for OA and RA in the future.

ZNFX1 promotes AMPK-mediated autophagy against Mycobacterium tuberculosis by stabilizing Prkaa2 mRNA

Tuberculosis has the highest mortality rate worldwide for a chronic infectious disease caused by a single pathogen. RNA-binding proteins (RBPs) are involved in autophagy - a key defense mechanism against Mycobacterium tuberculosis (M. tuberculosis) infection - by modulating RNA stability and forming intricate regulatory networks. However, the functions of host RBPs during M. tuberculosis infection remain relatively unexplored. Zinc finger NFX1-type containing 1 (ZNFX1), a conserved RBP critically involved in immune deficiency diseases and mycobacterial infections, is significantly upregulated in M. tuberculosis-infected macrophages. Here, we aimed to explore the immunoregulatory functions of ZNFX1 during M. tuberculosis infection. We observed that Znfx1 knockout markedly compromised the multifaceted immune responses mediated by macrophages. This compromise resulted in reduced phagocytosis, suppressed macrophage activation, increased M. tuberculosis burden, progressive lung tissue injury, and chronic inflammation in M. tuberculosis-infected mice. Mechanistic investigations revealed that the absence of ZNFX1 inhibited autophagy, consequently mediating immune suppression. ZNFX1 critically maintained AMPK-regulated autophagic flux by stabilizing protein kinase AMP-activated catalytic subunit alpha 2 mRNA, which encodes a key catalytic α subunit of AMPK, through its zinc finger region. This process contributed to M. tuberculosis growth suppression. These findings reveal a function of ZNFX1 in establishing anti-M. tuberculosis immune responses, enhancing our understanding of the roles of RBPs in tuberculosis immunity and providing a promising approach to bolster antituberculosis immunotherapy.

Marine-Fungi-Derived Gliotoxin Promotes Autophagy to Suppress Mycobacteria tuberculosis Infection in Macrophage

The Mycobacterium tuberculosis (MTB) infection causes tuberculosis (TB) and has been a long-standing public-health threat. It is urgent that we discover novel antitubercular agents to manage the increased incidence of multidrug-resistant (MDR) or extensively drug-resistant (XDR) strains of MTB and tackle the adverse effects of the first- and second-line antitubercular drugs. We previously found that gliotoxin (1), 12, 13-dihydroxy-fumitremorgin C (2), and helvolic acid (3) from the cultures of a deep-sea-derived fungus, Aspergillus sp. SCSIO Ind09F01, showed direct anti-TB effects. As macrophages represent the first line of the host defense system against a mycobacteria infection, here we showed that the gliotoxin exerted potent anti-tuberculosis effects in human THP-1-derived macrophages and mouse-macrophage-leukemia cell line RAW 264.7, using CFU assay and laser confocal scanning microscope analysis. Mechanistically, gliotoxin apparently increased the ratio of LC3-II/LC3-I and Atg5 expression, but did not influence macrophage polarization, IL-1β, TNF-a, IL-10 production upon MTB infection, or ROS generation. Further study revealed that 3-MA could suppress gliotoxin-promoted autophagy and restore gliotoxin-inhibited MTB infection, indicating that gliotoxin-inhibited MTB infection can be treated through autophagy in macrophages. Therefore, we propose that marine fungi-derived gliotoxin holds the promise for the development of novel drugs for TB therapy.

The diagnostic value of interleukin-36 cytokines in pleural effusions of varying etiologies

BACKGROUND

The clinical management of pleural effusion (PE) poses challenges due to its diverse etiologies. The objective of this research was to investigate the concentrations of interleukin-36 (IL-36) cytokines in pleural fluid (PF) from different etiologies and assess their diagnostic efficacy in distinguishing the causes of PE.

METHODS

This study enrolled 89 patients with confirmed PE, comprising 11 cases classified as transudate, 24 cases as malignant pleural effusion (MPE), 24 cases as tuberculous pleural effusion (TPE), and 30 cases as parapneumonic pleural effusion (PPE). The PPE group was further subdivided into 20 cases of uncomplicated parapneumonic effusion (UPPE) and 10 cases of complicated parapneumonic effusion (CPPE)/empyema. The concentrations of IL-36 cytokines in the PF of all 89 patients were quantified by the enzyme-linked immunosorbent assay (ELISA).

RESULTS

IL-36α exhibited excellent diagnostic accuracy in TPE, achieving a sensitivity of 91.7 % and specificity of 83.1 %, along with a cut-off value of 435.3 pg/ml. IL-36Ra also demonstrated relatively favorable diagnostic performance in PPE, with a sensitivity of 80.0 % and specificity of 76.3 %, along with a cut-off value of 390.8 pg/ml. Multivariable logistic regression models were successfully developed for both TPE and PPE, confirming their diagnostic utility. Furthermore, the levels of IL-36Ra were notably elevated in CPPE/empyema in comparison to UPPE. Moreover, in PF, IL-36γ exhibited positive associations with both IL-36α and IL-36Ra.

CONCLUSION

IL-36α and IL-36Ra may serve as novel biomarkers for diagnosing TPE and PPE, respectively. The multivariate models established significantly enhance the diagnostic efficacy of both TPE and PPE. Furthermore, IL-36Ra can function as an indicator for assessing the extent of pleural inflammation. Additionally, the interaction among IL-36 cytokines in PF may contribute to their expression modulation.

TFAP2C inhibits cell autophagy to alleviate myocardial ischemia/reperfusion injury by regulating miR-23a-5p/SFRP5/Wnt5a axis

Myocardial ischemia/reperfusion (MI/R) injury contributes to severe injury for cardiomyocytes. In this study, we aimed to explore the underlying mechanism of TFAP2C on cell autophagy in MI/R injury. MTT assay measured cell viability. The cells injury was evaluated by commercial kits. IF detected the level of LC3B. Dual luciferase reporter gene assay, ChIP or RIP assay were performed to verify the interactions between crucial molecules. We found that TFAP2C and SFRP5 expression were decreased while miR-23a-5p and Wnt5a increased in AC16 cells in response to H/R condition. H/R induction led to cell injury and induced autophagy, which were reversed by TFAP2C overexpression or 3-MA treatment (an autophagy inhibitor). Mechanistically, TFAP2C suppressed miR-23a expression through binding to miR-23a promoter, and SFRP5 was a target gene of miR-23a-5p. Moreover, miR-23a-5p overexpression or rapamycin reversed the protective impacts of TFAP2C overexpression on cells injury and autophagy upon H/R condition. In conclusion, TFAP2C inhibited autophagy to improve H/R-induced cells injury by mediating miR-23a-5p/SFRP5/Wnt5a axis.

New insights on IL‑36 in intestinal inflammation and colorectal cancer (Review)

Interleukin (IL)-36 is a member of the IL-1 superfamily, which includes three receptor agonists and one antagonist and exhibits a familial feature of inflammatory regulation. Distributed among various tissues, such as the skin, lung, gut and joints, the mechanism of IL-36 has been most completely investigated in the skin and has been used in clinical treatment of generalized pustular psoriasis. Meanwhile, the role of IL-36 in the intestine has also been under scrutiny and has been shown to be involved in the regulation of various intestinal diseases. Inflammatory bowel disease and colorectal cancer are the most predominant inflammatory and neoplastic diseases of the intestine, and multiple studies have identified a complex role for IL-36 in both of them. Indeed, inhibiting IL-36 signaling is currently regarded as a promising therapeutic approach. Therefore, the present review briefly describes the composition and expression of IL-36 and focuses on the role of IL-36 in intestinal inflammation and colorectal cancer. The targeted therapies that are currently being developed for the IL-36 receptor are also discussed.

Cisatracurium besylate rescues Mycobacterium Tuberculosis-infected macrophages from necroptosis and enhances the bactericidal effect of isoniazid

OBJECTIVE

Tuberculosis is the leading killer among the chronic single-source infectious diseases. Mycobacterium tuberculosis can induce necrotic-dominant multiple modes of cell death in macrophages, which accelerates bacterium dissemination and expands tissue injury in host lungs. Mining drugs to counteract Mycobacterium tuberculosis-induced cell death would be beneficial to tuberculosis patients.

METHODS

In this study, the protective drug was screened out from the FDA-approved drug library in Mycobacterium tuberculosis-infected macrophages with CCK-8 assay. The death mode regulated by the drug was identified using transcriptomic sequencing, cytomorphological observation, and in the experimental mouse Mycobacterium tuberculosis-infection model. The functional mechanism was explored using western blot, co-immunoprecipitation, and DARTS assay. The intracellular bacterial survival was detected using colony forming unit assays.

RESULTS

Cisatracurium besylate was identified to be highly protective for the viability of macrophages during Mycobacterium tuberculosis infection via inhibiting necroptosis. Cisatracurium besylate prevented RIPK3 to be associated with the executive molecule MLKL for forming the necroptotic complex, resulting in the inhibition of MLKL phosphorylation and pore formation on cell membrane. However, Cisatracurium besylate did not interfere with the association between RIPK3 with its upstream kinase RIPK1 or ZBP1 but regulated RIPK3 autophosphorylation. Moreover, Cisatracurium besylate significantly inhibited the expansion of intracellular Mycobacterium tuberculosis both in vitro and in vivo, which also displayed a strong auxiliary bacteriostatic effect to support the therapeutic efficacy of isoniazid and rifampicin, the first-line anti-tubercular drugs.

CONCLUSION

Cisatracurium besylate performs anti-Mycobacterium tuberculosis and anti-necroptotic roles, which potentiates its application to be an adjuvant drug for antituberculosis therapy to assist the battle against drug-resistant tuberculosis.

Opposing Effects of Interleukin-36γ and Interleukin-38 on Trained Immunity

Trained immunity is the process of long-term functional reprogramming (a de facto innate immune memory) of innate immune cells such as monocytes and macrophages after an exposure to pathogens, vaccines, or their ligands. The induction of trained immunity is mediated through epigenetic and metabolic mechanisms. Apart from exogenous stimuli, trained immunity can be induced by endogenous compounds such as oxidized LDL, urate, fumarate, but also cytokines including IL-1α and IL-1β. Here, we show that also recombinant IL-36γ, a pro-inflammatory cytokine of the IL-1-family, is able to induce trained immunity in primary human monocytes, demonstrated by higher cytokine responses and an increase in cellular metabolic pathways both regulated by epigenetic histone modifications. These effects could be inhibited by the IL-36 receptor antagonist as well as by IL-38, an anti-inflammatory cytokine of the IL-1 family which shares its main receptor with IL-36 (IL-1R6). Further, we demonstrated that trained immunity induced by IL-36γ is mediated by NF-κB and mTOR signaling. The inhibitory effect of IL-38 on IL-36γ-induced trained immunity was confirmed in experiments using bone marrow of IL-38KO and WT mice. These results indicate that exposure to IL-36γ results in long-term pro-inflammatory changes in monocytes which can be inhibited by IL-38. Recombinant IL-38 could therefore potentially be used as a therapeutic intervention for diseases characterized by exacerbated trained immunity.

Targeting macrophage autophagy for inflammation resolution and tissue repair in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, non-specific, recurrent inflammatory disease, majorly affecting the gastrointestinal tract. Due to its unclear pathogenesis, the current therapeutic strategy for IBD is focused on symptoms alleviation. Autophagy is a lysosome-mediated catabolic process for maintaining cellular homeostasis. Genome-wide association studies and subsequent functional studies have highlighted the critical role of autophagy in IBD via a number of mechanisms, including modulating macrophage function. Macrophages are the gatekeepers of intestinal immune homeostasis, especially involved in regulating inflammation remission and tissue repair. Interestingly, many autophagic proteins and IBD-related genes have been revealed to regulate macrophage function, suggesting that macrophage autophagy is a potentially important process implicated in IBD regulation. Here, we have summarized current understanding of macrophage autophagy function in pathogen and apoptotic cell clearance, inflammation remission and tissue repair regulation in IBD, and discuss how this knowledge can be used as a strategy for IBD treatment.

A novel biomarker for pleural effusion diagnosis: Interleukin-36γ in pleural fluid

BACKGROUND

Numerous studies have described the critical importance of interleukin (IL) -36γ in host defense against lung infections, but it is unknown whether it plays a role in infectious pleural effusion (IPE). This study aimed to examine the levels of IL-36γ in pleural effusions of different etiologies and evaluate the diagnostic accuracy of IL-36γ in the differential diagnosis of IPE.

METHODS

A total of 112 individuals was enrolled in this research. IL-36γ levels in pleural fluids of all 112 patients were measured by enzyme-linked immunosorbent assay (ELISA). We also characterized these markers' diagnostic values across various groups.

RESULTS

Patients with tuberculous pleural effusion (TPE) and parapneumonic effusion (PPE) had exhibited markedly higher IL-36γ levels in their pleural fluid than the malignant pleural effusion (MPE) and transudative effusion patients. Furthermore, the IL-36γ concentrations in TPE patients were evidently higher than in uncomplicated parapneumonic effusion (UPPE) patients but significantly lower than in complicated parapneumonic effusion (CPPE)/empyema patients. Pleural fluid IL-36γ is a useful marker to differentiate TPE from UPPE, at a cut-off value for 657.5 pg/ml (area under the curve = 0.904, p < 0.0001) with 70.0% sensitivity and 95.7% specificity.

CONCLUSIONS

The elevated IL-36γ in pleural effusion may be used as a novel biomarker for infectious pleural effusion diagnosis, particularly in patients with CPPE/empyema, and is a potentially promising biomarker to differentiate between TPE and UPPE.

Wnt5a regulates autophagy in Bacille Calmette-Guérin (BCG)-Infected pulmonary epithelial cells

Autophagy functions as a critical process that can suppress the proliferation of Mycobacterium tuberculosis (Mtb) within infected host cells. Wnt5a is a secreted protein that plays a range of physiological functions, activating several signaling pathways and thereby controlling cellular responses to particular stimuli. The importance of Wnt5a as a regulator of protection against Mtb infection, however, has yet to be fully characterized. Here, changes in murine pulmonary epithelial-like TC-1 cell morphology, autophagy, the Wnt/Ca²⁺ signaling pathway, and the mTOR autophagy pathway were analyzed following infection with the Mtb model pathogen Bacille Calmette-Guerin (BCG) in order to understand the regulatory role of Wnt5a in this context. These experiments revealed that Wnt5a was upregulated and autophagy was enhanced in TC-1 cells infected with BCG, and Wnt5a overexpression was found to drive BCG-induced autophagy in these cells upon infection, whereas the inhibition or knockdown of Wnt5a yielded the opposite effect. At the mechanistic level, Wnt5a was found to mediate non-canonical Wnt/Ca²⁺ signaling and thereby inhibit mTOR-dependent pathway activation, promoting autophagic induction within BCG-infected TC-1 cells. These data offer new insight regarding how Wnt5a influences Mtb-induced autophagy within pulmonary epithelial cells, providing a foundation for further research exploring the immunological control of this infection through the modulation of autophagy.

Host cell transcriptomic response to the multidrug-resistant Mycobacterium tuberculosis clonal outbreak Beijing strain reveals its pathogenic features

The upsurge of multidrug-resistant infections has rendered tuberculosis the principal cause of death among infectious diseases. A clonal outbreak multidrug-resistant triggering strain of Mycobacterium tuberculosis was identified in Kanchanaburi Province, labelled "MKR superspreader," which was found to subsequently spread to other regions, as revealed by prior epidemiological reports in Thailand. Herein, we showed that the MKR displayed a higher growth rate upon infection into host macrophages in comparison with the H37Rv reference strain. To further elucidate MKR's biology, we utilized RNA-Seq and differential gene expression analyses to identify host factors involved in the intracellular viability of the MKR. A set of host genes function in the cellular response to lipid pathway was found to be uniquely up-regulated in host macrophages infected with the MKR, but not those infected with H37Rv. Within this set of genes, the IL-36 cytokines which regulate host cell cholesterol metabolism and resistance against mycobacteria attracted our interest, as our previous study revealed that the MKR elevated genes associated with cholesterol breakdown during its growth inside host macrophages. Indeed, when comparing macrophages infected with the MKR to H37Rv-infected cells, our RNA-Seq data showed that the expression ratio of IL-36RN, the negative regulator of the IL-36 pathway, to that of IL-36G was greater in macrophages infected with the MKR. Furthermore, the MKR's intracellular survival and increased intracellular cholesterol level in the MKR-infected macrophages were diminished with decreased IL-36RN expression. Overall, our results indicated that IL-36RN could serve as a new target against this emerging multidrug-resistant M. tuberculosis strain.

IL-36 Cytokines: Their Roles in Asthma and Potential as a Therapeutic

Interleukin (IL)-36 cytokines are members of the IL-1 superfamily, which consists of three agonists (IL-36α, IL-36β and IL-36γ) and an IL-36 receptor antagonist (IL-36Ra). IL-36 cytokines are crucial for immune and inflammatory responses. Abnormal levels of IL-36 cytokine expression are involved in the pathogenesis of inflammation, autoimmunity, allergy and cancer. The present study provides a summary of recent reports on IL-36 cytokines that participate in the pathogenesis of inflammatory diseases, and the potential mechanisms underlying their roles in asthma. Abnormal levels of IL-36 cytokines are associated with the pathogenesis of different types of asthma through the regulation of the functions of different types of cells. Considering the important role of IL-36 cytokines in asthma, these may become a potential therapeutic target for asthma treatment. However, existing evidence is insufficient to fully elucidate the specific mechanism underlying the action of IL-36 cytokines during the pathological process of asthma. The possible mechanisms and functions of IL-36 cytokines in different types of asthma require further studies.

The role of IL-36 subfamily in intestinal disease

Interleukin (IL)-36 is a subfamily, of the IL-1 super-family and includes IL-36α, IL-36β, IL-36γ, IL-38 and IL-36Ra. IL-36 cytokines are involved in the pathology of multiple tissues, including skin, lung, oral cavity, intestine, kidneys and joints. Recent studies suggest that IL-36 signaling regulates autoimmune disease in addition to antibacterial and antiviral responses. Most research has focused on IL-36 in skin diseases such as psoriasis, however, studies on intestinal diseases are also underway. This review outlines what is known about the bioactivity of the IL-36 subfamily and its role in the pathogenesis of intestinal diseases such as inflammatory bowel disease, colorectal cancer, gut dysbacteriosis and infection, and proposes that IL-36 may be a target for novel therapeutic strategies to prevent or treat intestinal diseases.

IL-36α and Lipopolysaccharide Cooperatively Induce Autophagy by Triggering Pro-Autophagic Biased Signaling

Autophagy is an intracellular catabolic process that controls infections both directly and indirectly via its multifaceted effects on the innate and adaptive immune responses. It has been reported that LPS stimulates this cellular process, whereas the effect of IL-36α on autophagy remains largely unknown. We therefore investigated how IL-36α modulates the endogenous and LPS-induced autophagy in THP-1 cells. The levels of LC3B-II and autophagic flux were determined by Western blotting. The intracellular localization of LC3B was measured by immunofluorescence assay. The activation levels of signaling pathways implicated in autophagy regulation were evaluated by using a phosphokinase array. Our results showed that combined IL-36α and LPS treatment cooperatively increased the levels of LC3B-II and Beclin-1, stimulated the autophagic flux, facilitated intracellular redistribution of LC3B, and increased the average number of autophagosomes per cell. The IL36α/LPS combined treatment increased phosphorylation of STAT5a/b, had minimal effect on the Akt/PRAS40/mTOR pathway, and reduced the levels of phospho-Yes, phospho-FAK, and phospho-WNK1. Thus, this cytokine/PAMP combination triggers pro-autophagic biased signaling by several mechanisms and thus cooperatively stimulates the autophagic cascade. An increased autophagic activity of innate immune cells simultaneously exposed to IL-36α and LPS may play an important role in the pathogenesis of Gram-negative bacterial infections.

IL-36 in chronic inflammation and fibrosis - bridging the gap?

IL-36 is a member of the IL-1 superfamily and consists of three agonists and one receptor antagonist (IL-36Ra). The three endogenous agonists, IL-36α, -β, and -γ, act primarily as proinflammatory cytokines, and their signaling through the IL-36 receptor (IL-36R) promotes immune cell infiltration and secretion of inflammatory and chemotactic molecules. However, IL-36 signaling also fosters secretion of profibrotic soluble mediators, suggesting a role in fibrotic disorders. IL-36 isoforms and IL-36 have been implicated in inflammatory diseases including psoriasis, arthritis, inflammatory bowel diseases, and allergic rhinitis. Moreover, IL-36 has been connected to fibrotic disorders affecting the kidney, lung, and intestines. This review summarizes the expression, cellular source, and function of IL-36 in inflammation and fibrosis in various organs, and proposes that IL-36 modulation may prove valuable in preventing or treating inflammatory and fibrotic diseases and may reveal a mechanistic link between inflammation and fibrosis.

Long-Term Hypoxia Maintains a State of Dedifferentiation and Enhanced Stemness in Fetal Cardiovascular Progenitor Cells

Early-stage mammalian embryos survive within a low oxygen tension environment and develop into fully functional, healthy organisms despite this hypoxic stress. This suggests that hypoxia plays a regulative role in fetal development that influences cell mobilization, differentiation, proliferation, and survival. The long-term hypoxic environment is sustained throughout gestation. Elucidation of the mechanisms by which cardiovascular stem cells survive and thrive under hypoxic conditions would benefit cell-based therapies where stem cell survival is limited in the hypoxic environment of the infarcted heart. The current study addressed the impact of long-term hypoxia on fetal Islet-1+ cardiovascular progenitor cell clones, which were isolated from sheep housed at high altitude. The cells were then cultured in vitro in 1% oxygen and compared with control Islet-1+ cardiovascular progenitor cells maintained at 21% oxygen. RT-PCR, western blotting, flow cytometry, and migration assays evaluated adaptation to long term hypoxia in terms of survival, proliferation, and signaling. Non-canonical Wnt, Notch, AKT, HIF-2α and Yap1 transcripts were induced by hypoxia. The hypoxic niche environment regulates these signaling pathways to sustain the dedifferentiation and survival of fetal cardiovascular progenitor cells.

IL-36 cytokines in inflammatory and malignant diseases: not the new kid on the block anymore

The IL-36 family of cytokines were first identified in 2000 based on their sequence homology to IL-1 cytokines. Over subsequent years, the ability of these cytokines to either agonise or antagonise an IL-1R homologue, now known as the IL-36 Receptor (IL-36R), was identified and these cytokines went through several cycles of renaming with the current nomenclature being proposed in 2010. Despite being identified over 20 years ago, it is only during the last decade that the function of these cytokines in health and disease has really begun to be appreciated, with both homeostatic functions in wound healing and response to infection, as well as pathological functions now ascribed. In the disease context, over activation of IL-36 has now been associated with many inflammatory diseases including Psoriasis and inflammatory bowel diseases, with roles in cancer also now being investigated. This review summarises the current knowledge of IL-36 biology, its role in inflammatory diseases and focuses on an emerging role for IL-36 in cancer.

β-Arrestin 2 Regulates Inflammatory Responses against Mycobacterium tuberculosis Infection through ERK1/2 Signaling

Mycobacterium tuberculosis, the pathogen that causes tuberculosis, exhibits complex host-pathogen interactions. Pattern recognition receptors and their downstream signaling pathways play crucial roles in determining the outcome of infection. In particular, the scaffold protein β-arrestin 2 mediates downstream signaling of G protein-coupled receptors. However, the role of β-arrestin 2 in conferring immunity against M. tuberculosis has not yet been explored. We found that β-arrestin 2 was upregulated in the lesioned regions of lung tissues in patients with tuberculosis. M. tuberculosis infection upregulated β-arrestin 2 expression in human macrophages, and silencing of β-arrestin 2 significantly enhanced bactericidal activity by enhancing the expression of proinflammatory cytokines such as TNF-α. β-Arrestin 2 was shown to inhibit the activation of the TLR2/ERK1/2 pathway and its transcriptional regulation activity upon M. tuberculosis infection. Furthermore, β-arrestin 2 transcriptionally regulates TNF-α by binding to CREB1. These observations revealed that the upregulation of β-arrestin 2 is critical for M. tuberculosis to escape immune surveillance through an unknown mechanism. Our research offers a novel interference modality to enhance the immune response against tuberculosis by targeting β-arrestin 2 to modulate the TLR2-β-arrestin 2-ERK1/2-CREB1-TNF-α regulatory axis.

The Role of IL-36 in Infectious Diseases: Potential Target for COVID-19?

IL-36 is a member of the interleukin 1 cytokine family, which is currently experiencing a renaissance due to the growing understanding of its context-dependent roles and advances in our understanding of the inflammatory response. The immunological role of IL-36 has revealed its profound and indispensable functional roles in psoriasis, as well as in several inflammatory diseases, including inflammatory bowel disease (IBD), systemic lupus erythematosus, rheumatoid arthritis (RA) and cancer. More recently, an increasing body of evidence suggests that IL-36 plays a crucial role in viral, bacterial and fungal infections. There is a growing interest as to whether IL-36 contributes to host protective immune responses against infection as well as the potential implications of IL-36 for the development of new therapeutic strategies. In this review, we summarize the recent progress in understanding cellular expression, regulatory mechanisms and biological roles of IL-36 in infectious diseases, which suggest more specific strategies to maneuver IL-36 as a diagnostic or therapeutic target, especially in COVID-19.

IL-36 cytokines and gut immunity

Interleukin 36 (IL-36) constitutes a group of cytokines that belong to the IL-1 superfamily. Emerging evidence has suggested a role of IL-36 in the pathogenesis of many inflammatory disorders. Intriguingly, in the gastrointestinal tract, IL-36 has a rather complex function. IL-36 receptor ligands are overexpressed in both animal colitis models and human IBD patients and may play both pathogenic and protective roles, depending on the context. IL-36 cytokines comprise three receptor agonists: IL-36α, IL-36β and IL-36γ, and two receptor antagonists: IL-36Ra and IL-38. All IL-36 receptor agonists bind to the IL-36R complex and exert pleiotropic effects during inflammatory settings. Here, we first briefly review the processing and secretion of IL-36 cytokines. We then focus on the current understanding of the immunology effects of IL-36 in gut immunity. In addition, we also discuss the ongoing trials that aim to blockage IL-36R signalling for treating chronic intestinal inflammation and present some unexplored questions regarding IL-36 research.

Wnt5A-Mediated Actin Organization Regulates Host Response to Bacterial Pathogens and Non-Pathogens

Wnt5A signaling facilitates the killing of several bacterial pathogens, but not the non-pathogen E. coli DH5α. The basis of such pathogen vs. non-pathogen distinction is unclear. Accordingly, we analyzed the influence of Wnt5A signaling on pathogenic E. coli K1 in relation to non-pathogenic E. coli K12-MG1655 and E. coli DH5α eliminating interspecies variability from our study. Whereas cell internalized E. coli K1 disrupted cytoskeletal actin organization and multiplied during Wnt5A depletion, rWnt5A mediated activation revived cytoskeletal actin assembly facilitating K1 eradication. Cell internalized E. coli K12-MG1655 and E. coli DH5α, which did not perturb actin assembly appreciably, remained unaffected by rWnt5A treatment. Phagosomes prepared separately from Wnt5A conditioned medium treated K1 and K12-MG1655 infected macrophages revealed differences in the relative levels of actin and actin network promoting proteins, upholding that the Wnt5A-Actin axis operates differently for internalized pathogen and non-pathogen. Interestingly, exposure of rWnt5A treated K1 and K12-MG1655/DH5α infected macrophages to actin assembly inhibitors reversed the scenario, blocking killing of K1, yet promoting killing of both K12-MG1655 and DH5α. Taken together, our study illustrates that the state of activation of the Wnt5A/Actin axis in the context of the incumbent bacteria is crucial for directing host response to infection.

Role of Wnt5a in periodontal tissue development, maintenance, and periodontitis: Implications for periodontal regeneration (Review)

The periodontium is a highly dynamic microenvironment constantly adapting to changing external conditions. In the processes of periodontal tissue formation and remodeling, certain molecules may serve an essential role in maintaining periodontal homeostasis. Wnt family member 5a (Wnt5a), as a member of the Wnt family, has been identified to have extensive biological roles in development and disease, predominantly through the non‑canonical Wnt signaling pathway or through interplay with the canonical Wnt signaling pathway. An increasing number of studies has also demonstrated that it serves crucial roles in periodontal tissues. Wnt5a participates in the development of periodontal tissues, maintains a non‑mineralized state of periodontal ligament, and regulates bone homeostasis. In addition, Wnt5a is involved in the pathogenesis of periodontitis. Recently, it has been shown to serve a positive role in the regeneration of integrated periodontal complex. The present review article focuses on recent research studies of Wnt5a and its functions in development, maintenance, and pathological disorders of periodontal tissues, as well as its potential effect on periodontal regeneration.

Regulatory Mechanisms of Autophagy-Targeted Antimicrobial Therapeutics Against Mycobacterial Infection

Mycobacterium tuberculosis (Mtb) is an intracellular pathogen causing human tuberculosis, an infectious disease that still remains as a global health problem. Autophagy, a lysosomal degradative process, has emerged as a critical pathway to restrict intracellular Mtb growth through enhancement of phagosomal maturation. Indeed, several autophagy-modulating agents show promise as host-directed therapeutics for Mtb infection. In this Review, we discuss recent progress in our understanding the molecular mechanisms underlying the action of autophagy-modulating agents to overcome the immune escape strategies mediated by Mtb. The factors and pathways that govern such mechanisms include adenosine 5'-monophosphate-activated protein kinase, Akt/mammalian TOR kinase, Wnt signaling, transcription factor EB, cathelicidins, inflammation, endoplasmic reticulum stress, and autophagy-related genes. A further understanding of these mechanisms will facilitate the development of host-directed therapies against tuberculosis as well as infections with other intracellular bacteria targeted by autophagic degradation.

High Expression of IL-36γ in Influenza Patients Regulates Interferon Signaling Pathway and Causes Programmed Cell Death During Influenza Virus Infection

As a severe complication of influenza infection, acute respiratory distress syndrome (ARDS) has higher morbidity and mortality. Although IL-36γ has been proven to promote inflammation at epithelial sites and protect against specific pathogen infection, the detailed roles in severe influenza infection remain poorly understood. In this study, we have found that the expression of IL-36γ is higher in influenza-induced ARDS patients than healthy individuals. IL-36γ was induced in human lung epithelial cells and peripheral blood mononuclear cells by Influenza A virus (IAV) infection, and its induction was synergistically correlated with initiation of the cyclooxygenase-2 (COX-2)/Prostaglandin E2 (PGE2) axis. We also have found that expression of superficial IL-36R was elevated in severe influenza patients and in IAV-stimulated cells. Furthermore, although IL-36γ enhanced the induction of type I and III interferons (IFNs), which promoted IAV-mediated IFN-stimulated STAT1 and STAT2 phosphorylated inhibition in lung epithelial cells, the downstream interferon-stimulated genes (ISGs) were not affected. Finally, we have revealed that IL-36γ treatment could promote apoptosis and inhibit autophagy in the early stages of IAV infection. Overall, these findings demonstrated IL-36γ is a critical host immune factor in response to IAV infection. It has potential activity in the regulation of the interferon signaling pathway and was involved in different types of programmed cell death in human airway epithelial cells as well.

IL-36 family cytokines in protective versus destructive inflammation

The IL-1 family of cytokines and receptors are critical regulators of inflammation. Within the IL-1 family and in contrast to its IL-1 and IL-18 subfamilies, the IL-36 subfamily is still poorly characterized. Three pro-inflammatory agonists IL-36α, IL-36β, IL-36γ, one IL-36 receptor (IL-1R6) antagonist, IL-36RA, and one putative IL-1R6 antagonist, IL-38, have been grouped into the IL-36 cytokine subfamily. IL-36 agonists signal through a common receptor complex to serve as early triggers of inflammatory responses by activating and cross-regulating a number of inflammatory pathways including NF-κB, MAPK and IFN signaling. IL-36RA binds to IL-1R6 to limit inflammatory signaling, while IL-38 may be an antagonist of more than one IL-1 family receptor. Expression patterns of IL-36 family cytokines, being most prominently expressed in epithelial barrier tissues such as the skin and intestines as well as in immune cells, suggest a role in protecting these barriers from infection. Dysregulation of IL-36 family cytokine signaling at physiological barriers, most prominently the skin, induces autoimmune inflammation. However, transferring the potential of IL-36 to induce tissue damage to tumors might benefit cancer patients. Here we summarize signaling pathways regulated by IL-36 family cytokines, including IL-38, and the consequences for physiological protective and pathophysiological destructive inflammation. Moreover, we discuss the limits of current knowledge on IL-36 family function to open potential avenues for research in the future.

Functions of the WNT Signaling Network in Shaping Host Responses to Infection

It is well-established that aberrant WNT expression and signaling is associated with developmental defects, malignant transformation and carcinogenesis. More recently, WNT ligands have emerged as integral components of host responses to infection but their functions in the context of immune responses are incompletely understood. Roles in the modulation of inflammatory cytokine production, host cell intrinsic innate defense mechanisms, as well as the bridging of innate and adaptive immunity have been described. To what degree WNT responses are defined by the nature of the invading pathogen or are specific for subsets of host cells is currently not well-understood. Here we provide an overview of WNT responses during infection with phylogenetically diverse pathogens and highlight functions of WNT ligands in the host defense against infection. Detailed understanding of how the WNT network orchestrates immune cell functions will not only improve our understanding of the fundamental principles underlying complex immune response, but also help identify therapeutic opportunities or potential risks associated with the pharmacological targeting of the WNT network, as currently pursued for novel therapeutics in cancer and bone disorders.

Wnt Signaling: Pathogen Incursion and Immune Defense

Wnt ligands interact with the transmembrane cell surface receptors Frizzled and ROR/RYK to initiate complex signaling cascades that are crucial for cell physiology and the proper functioning of the immune system. Wnt signaling is instrumental in maintaining immune surveillance and during infections by pathogenic microbes helps mount host resistance to infection. Some pathogens, however, utilize Wnt signaling to build a niche for their survival. The goal of this review is to summarize current and developing concepts about the tug of war between Wnt signaling and pathogens for deployment of host resources, focusing mostly on macrophages and cytoskeletal actin dynamics. An additional objective is to outline the interrelation between Wnt signaling and the host microbiota, which is vital for immune defense, discussing in the same perspective, how Wnt signaling could be differentiating pathogen from non-pathogen.