The ALPK1 pathway drives the inflammatory response to Campylobacter jejuni in human intestinal epithelial cells

Fusobacterium nucleatum upregulates the immune inhibitory receptor PD-L1 in colorectal cancer cells via the activation of ALPK1

Fusobacterium nucleatum is a Gram-negative oncobacterium that is associated with colorectal cancer. The molecular mechanisms utilized by F. nucleatum to promote colorectal tumor development have largely focused on adhesin-mediated binding to the tumor tissue and on the pro-inflammatory capacity of F. nucleatum. However, the exact manner in which F. nucleatum promotes inflammation in the tumor microenvironment and subsequent tumor promotion remains underexplored. Here, we show that both living F. nucleatum and sterile F. nucleatum-conditioned medium promote CXCL8 release from the intestinal adenocarcinoma HT-29 cell line. We determined that the observed pro-inflammatory effect was ALPK1-dependent in both HEK293 and HT-29 cells and that the released F. nucleatum molecule had characteristics that match those of the pro-inflammatory ALPK1 ligand ADP-heptose or related heptose phosphates. In addition, we determined that not only F. nucleatum promoted an ALPK1-dependent pro-inflammatory environment but also other Fusobacterium species such as F. varium, F. necrophorum and F. gonidiaformans generated similar effects, indicating that ADP-heptose or related heptose phosphate secretion is a conserved feature of the Fusobacterium genus. By performing transcriptional analysis of ADP-heptose stimulated HT-29 cells, we found several inflammatory and cancer-related pathways to be differentially regulated, including DNA mismatch repair genes and the immune inhibitory receptor PD-L1. Finally, we show that stimulation of HT-29 cells with F. nucleatum resulted in an ALPK1-dependent upregulation of PD-L1. These results aid in our understanding of the mechanisms by which F. nucleatum can affect tumor development and therapy and pave the way for future therapeutic approaches.

ALPK1 signaling pathway activation by HMGB1 drives microglial pyroptosis and ferroptosis and brain injury after acute ischemic stroke

Pyroptosis and ferroptosis emerge as remarkable contributors to neuronal death and inflammation following ischemic stroke. High mobility group box 1 (HMGB1), a principal damage-associated molecular pattern (DAMP), is implicated in pyroptosis and ferroptosis post-stroke. Our previous research has demonstrated that alpha kinase 1 (ALPK1), a novel cytoplasmic pattern recognition receptor (PRR), plays an important role in mediating inflammatory damage following ischemic stroke. However, the interaction between ALPK1 and HMGB1, and their combined impact on pyroptosis and ferroptosis post-ischemic stroke remain unexplored, which is what this study aims to investigate. Initially, we observed that ALPK1 ablation attenuated ischemic brain injury of transient middle cerebral artery occlusion (tMCAO) mice. Moreover, recombinant HMGB1 (rHMGB1) stimulation induced the greatest upregulation of ALPK1 expression in microglia compared to astrocytes and neurons. Further investigation using co-immunofluorescence, co-immunoprecipitation, pull-down assay, and molecular docking revealed an interaction between HMGB1 and ALPK1. Additionally, the exacerbation of ischemic brain injury and the induction of microglial pyroptosis and ferroptosis by rHMGB1 treatment in tMCAO mice were significantly mitigated through ALPK1 deficiency by inhibiting the NLRP3/Caspase-1/GSDMD and JAK2/STAT3 signaling pathways. The inhibitory effects of ALPK1 deficiency on pyroptosis and ferroptosis induced by rHMGB1 in microglial cells were further substantiated. Finally, glycyrrhizic acid (GA), an inhibitor of HMGB1, exhibited significant neuroprotective effects in both tMCAO mice and BV2 cells subjected to oxygen-glucose deprivation/reperfusion (OGD/R) by downregulating ALPK1 expression and inhibiting microglial pyroptosis and ferroptosis. Collectively, these findings suggest that HMGB1 may interact with ALPK1 to drive microglial pyroptosis and ferroptosis via the activation of the ALPK1/NF-κB/NLRP3/GSDMD and JAK2/STAT3 signaling pathways, thereby exacerbating brain injury following acute ischemic stroke.

IFN-γ licenses normal and pathogenic ALPK1/TIFA pathway in human monocytes

Alpha-kinase 1 (ALPK1) is an immune receptor sensing the bacterial nucleotide sugar ADP-heptose. ALPK1 phosphorylates TIFA leading to its oligomerization and downstream NF-κB activation. Specific mutations in ALPK1 are associated with an autoinflammatory syndrome termed ROSAH and with spiradenoma (skin cancers with sweat gland differentiation). This study investigated ALPK1 responses in human mononuclear cells and demonstrates that human mononuclear cells have distinct abilities to respond to ADP-heptose. Notably, IFN-γ is required to license the ALPK1/TIFA pathway in monocytes, while it was dispensable for the responsiveness of B cells. IFN-γ induced TIFA upregulation in monocytes, and TIFA induction was sufficient to recapitulate the licensing effect of IFN-γ. IFN-γ treatment promoted the phenotypic expression of pathogenic ALPK1 mutations. The licensing effect of IFN-γ in monocytes was blocked by JAK inhibitors. These findings underscore the critical role of IFN-γ in ALPK1 function and suggest JAK inhibitors as potential therapies for ALPK1-related inflammatory conditions.

Actinobacteria: Smart Micro-Factories for The Health Sector

Antibiotics are considered "wonder drugs" due to the fact that they are the most extensively utilised medication in the world. They are used to cure a broad spectrum of diseases and lethal infections. A variety of bacteria and fungi produce antibiotics as a result of secondary metabolism; however, their production is dominated by a special class of bacteria, namely Actinobacteria. Actinobacteria are gram-positive bacteria with high G+C content and unparalleled antibiotic-producing ability. They produce numerous polyenes, tetracyclines, β-lactams, macrolides, and peptides. Actinobacteria are ubiquitous in nature and are isolated from various sources, such as marine and terrestrial endophytes of plants and air. They are studied for their relative antibiotic-producing ability along with the mechanism that the antibiotics follow to annihilate the pathogenic agents that include bacteria, fungi, protozoans, helminths, etc. Actinobacteria isolated from endophytes of medicinal plants have amassed significant attention as they interfere with the metabolism of medicinal plants and acquire enormous benefits from it in the form of conspicuous novel antibiotic-producing ability. Actinobacteria is not only an antibiotic but also a rich source of anticancer compounds that are widely used owing to its remarkable tumorigenic potential. Today, amongst Actinobacteria, class Streptomyces subjugates the area of antibiotic production, producing 70% of all known antibiotics. The uniqueness of bioactive Actinobacteria has turned the attention of scientists worldwide in order to explore its potentiality as effective "micronanofactories". This study provides a brief overview of the production of antibiotics from Actinobacteria inhabiting patent environments and the methods involved in the screening of antibiotics.

The β-d-manno-heptoses are immune agonists across kingdoms

Bacterial small molecule metabolites such as adenosine-diphosphate-d-glycero-β-d-manno-heptose (ADP-heptose) and their derivatives act as effective innate immune agonists in mammals. We show that functional nucleotide-diphosphate-heptose biosynthetic enzymes (HBEs) are distributed widely in bacteria, archaea, eukaryotes, and viruses. We identified a conserved STTR5 motif as a hallmark of heptose nucleotidyltransferases that can synthesize not only ADP-heptose but also cytidine-diphosphate (CDP)- and uridine-diphosphate (UDP)-heptose. Both CDP- and UDP-heptoses are agonists that trigger stronger alpha-protein kinase 1 (ALPK1)-dependent immune responses than ADP-heptose in human and mouse cells and mice. We also produced ADP-heptose in archaea and verified its innate immune agonist functions. Hence, the β-d-manno-heptoses are cross-kingdom, small-molecule, pathogen-associated molecular patterns that activate the ALPK1-dependent innate immune signaling cascade.

Campylobacter jejuni virulence factors: update on emerging issues and trends

Campylobacter jejuni is a very common cause of gastroenteritis, and is frequently transmitted to humans through contaminated food products or water. Importantly, C. jejuni infections have a range of short- and long-term sequelae such as irritable bowel syndrome and Guillain Barre syndrome. C. jejuni triggers disease by employing a range of molecular strategies which enable it to colonise the gut, invade the epithelium, persist intracellularly and avoid detection by the host immune response. The objective of this review is to explore and summarise recent advances in the understanding of the C. jejuni molecular factors involved in colonisation, invasion of cells, collective quorum sensing-mediated behaviours and persistence. Understanding the mechanisms that underpin the pathogenicity of C. jejuni will enable future development of effective preventative approaches and vaccines against this pathogen.

Exploring the Contribution of Campylobacter jejuni to Post-Infectious Irritable Bowel Syndrome: A Literature Review

This comprehensive review investigates the specific impact of the foodborne pathogen Campylobacter jejuni (C. jejuni) on gastrointestinal health, focusing on its connection to post-infectious irritable bowel syndrome (PI-IBS). This review examines the pathogen’s pathophysiology, clinical implications and epidemiological trends using recent research and data to highlight its prevalence and association with PI-IBS. A detailed literature analysis synthesizes current research to illuminate Campylobacter’s long-lasting effects on gut microbiota and intestinal function. It provides a detailed analysis of the literature to shed light on C. jejuni’s long-term impact on gut microbiota and intestinal function. The findings suggest the need for multifaceted prevention and treatment approaches considering individual, microbial and epidemiological factors, thus contributing to a more nuanced understanding of PI-IBS following C. jejuni infection.

The relationship of ALPK1, hyaluronic acid and M1 macrophage polarization in the temporomandibular joint synovitis

M1 macrophage polarization and synovitis play an important role in the pathogenesis of temporomandibular joint osteoarthritis (TMJOA). Reduced molecular weight of hyaluronic acid (HA) in synovial fluid of patients with TMJOA. In addition, high molecular weight hyaluronic acid (HMW-HA) is often used clinically to treat TMJ inflammation. As a pattern recognition receptor of the cytoplasm, ALPK1 was found to be pro-inflammatory in a variety of diseases. However, the relationship of ALPK1, HA and M1 macrophage polarization in TMJ synovitis remains unclear. We aimed to investigate the role of ALPK1 and HA in macrophage polarization and TMJ synovitis and the underlying mechanisms. The results demonstrated that ALPK1 was highly upregulated in the synovial macrophages in the inflamed TMJ synovium of patients. Low molecular weight hyaluronic acid (LMW-HA) promoted the expression of ALPK1 and M1 macrophage-associated genes. Besides, rhALPK1 promoted the expression of M1 macrophage-associated factors and the nuclear translocation of PKM2. Furthermore, ALPK1 knockout mice exhibited limited infiltration of macrophages and decreased expression levels of M1 macrophage-associated genes in CFA-induced TMJ synovitis. While HMW-HA inhibited the expression of ALPK1 and M1 macrophage polarization. Our results elucidated that ALPK1 promoted TMJ synovitis by promoting nuclear PKM2-mediated M1 macrophage polarization, whereas HMW-HA inhibited the expression of ALPK1 as well as M1 macrophage polarization.

Characterization of the ADP-β-D-manno-heptose biosynthetic enzymes from two pathogenic Vibrio strains

ADP-activated β-D-manno-heptoses (ADP-β-D-manno-heptoses) are precursors for the biosynthesis of the inner core of lipopolysaccharide in Gram-negative bacteria. Recently, ADP-D-glycero-β-D-manno-heptose (ADP-D,D-manno-heptose) and its C-6'' epimer, ADP-L-glycero-β-D-manno-heptose (ADP-L,D-manno-heptose), were identified as potent pathogen-associated molecular patterns (PAMPs) that can trigger robust innate immune responses. Although the production of ADP-D,D-manno-heptose has been studied in several different pathogenic Gram-negative bacteria, current knowledge of ADP-β-D-manno-heptose biosynthesis in Vibrio strains remains limited. Here, we characterized the biosynthetic enzymes of ADP-D,D-manno-heptose and the epimerase that converts it to ADP-L,D-manno-heptose from Vibrio cholerae (the causative agent of pandemic cholera) and Vibrio parahaemolyticus (non-cholera pathogen causing vibriosis with clinical manifestations of gastroenteritis and wound infections) in comparison with their isozymes from Escherichia coli. Moreover, we discovered that β-D-mannose 1-phosphate, but not α-D-mannose 1-phosphate, could be activated to its ADP form by the nucleotidyltransferase domains of bifunctional kinase/nucleotidyltransferases HldEVC (from V. cholerae) and HldEVP (from V. parahaemolyticus). Kinetic analyses of the nucleotidyltransferase domains of HldEVC and HldEVP together with the E. coli-derived HldEEC were thus carried out using β-D-mannose 1-phosphate as a mimic sugar substrate. Overall, our works suggest that V. cholerae and V. parahaemolyticus are capable of synthesizing ADP-β-D-manno-heptoses and lay a foundation for further physiological function explorations on manno-heptose metabolism in Vibrio strains. KEY POINTS: • Vibrio strains adopt the same biosynthetic pathway as E. coli in synthesizing ADP-β-D-manno-heptoses. • HldEs from two Vibrio strains and E. coli could activate β-D-mannose 1-phosphate to ADP-β-D-mannose. • Comparable nucleotidyltransfer efficiencies were observed in the kinetic studies of HldEs.

Copper regulates the host innate immune response against bacterial infection via activation of ALPK1 kinase

Copper is an essential trace element for the human body, and its requirement for optimistic immune functions has been recognized for decades. How copper is involved in the innate immune pathway, however, remains to be clarified. Here, we report that copper serves as a signal molecule to regulate the kinase activity of alpha-kinase 1 (ALPK1), a cytosolic pattern-recognition receptor (PRR), and therefore promotes host cell defense against bacterial infection. We show that in response to infection, host cells actively accumulate copper in the cytosol, and the accumulated cytosolic copper enhances host cell defense against evading pathogens, including intracellular and, unexpectedly, extracellular bacteria. Subsequently, we demonstrate that copper activates the innate immune pathway of host cells in an ALPK1-dependent manner. Further mechanistic studies reveal that copper binds to ALPK1 directly and is essential for the kinase activity of this cytosolic PRR. Moreover, the binding of copper to ALPK1 enhances the sensitivity of ALPK1 to the bacterial metabolite ADP-heptose and eventually prompts host cells to elicit an enhanced immune response during bacterial infection. Finally, using a zebrafish in vivo model, we show that a copper-treated host shows an increased production of proinflammatory cytokines, enhanced recruitment of phagosome cells, and promoted bacterial clearance. Our findings uncover a previously unrecognized role of copper in the modulation of host innate immune response against bacterial pathogens and advance our knowledge on the cross talk between cytosolic copper homeostasis and immune system.

Fusobacterium nucleatum promotes inflammatory and anti-apoptotic responses in colorectal cancer cells via ADP-heptose release and ALPK1/TIFA axis activation

The anaerobic bacterium Fusobacterium nucleatum is significantly associated with human colorectal cancer (CRC) and is considered a significant contributor to the disease. The mechanisms underlying the promotion of intestinal tumor formation by F. nucleatum have only been partially uncovered. Here, we showed that F. nucleatum releases a metabolite into the microenvironment that strongly activates NF-κB in intestinal epithelial cells via the ALPK1/TIFA/TRAF6 pathway. Furthermore, we showed that the released molecule had the biological characteristics of ADP-heptose. We observed that F. nucleatum induction of this pathway increased the expression of the inflammatory cytokine IL-8 and two anti-apoptotic genes known to be implicated in CRC, BIRC3 and TNFAIP3. Finally, it promoted the survival of CRC cells and reduced 5-fluorouracil chemosensitivity in vitro. Taken together, our results emphasize the importance of the ALPK1/TIFA pathway in Fusobacterium induced-CRC pathogenesis, and identify the role of ADP-H in this process.

The Role of ALPK1 in Inhibiting Hepatitis B Virus Replication Facilitates the Identification of ALPK1 P660L Variant for Predicting Response to Pegylated Interferon α Therapy

BACKGROUND

Alpha kinase 1 (ALPK1) agonist has recently been reported to demonstrate anti-hepatitis B virus (HBV) efficacy via activating NF-κB signaling, which is crucial for maximizing interferon (IFN) responses. Here, we investigated the impact of ALPK1 on HBV replication and explored ALPK1 variants for predicting the response to pegylated IFN-α (PegIFN-α) treatment.

METHODS

The potential anti-HBV effect of ALPK1 was evaluated in HBV-integrated and HBV-infected hepatoma cells. The potentially functional genetic variants of ALPK1 were screened out, and their correlations with PegIFN-α treatment response were assessed in 945 hepatitis B e antigen (HBeAg)-positive patients with chronic hepatitis B (CHB).

RESULTS

We revealed that ALPK1 inhibited HBV replication in hepatocytes via activating the JAK-STAT pathway. ALPK1 overexpression improved the anti-HBV effect of IFN-α in cell models. A missense variant, rs35389530 (P660L), of ALPK1 was strongly associated with combined response (CR; namely, HBeAg seroconversion and HBV DNA level <3.3log10 IU/mL) to PegIFN-α treatment in patients with CHB (P = 2.12 × 10-6). Moreover, a polygenic score integrating ALPK1_rs35389530 and 2 additional genetic variants was further significantly associated with CR (Ptrend = 9.28 × 10-7), hepatitis B surface antigen (HBsAg) level (Ptrend = .0002), and HBsAg loss (Ptrend = .025).

CONCLUSIONS

The anti-HBV effects of ALPK1 through activating JAK-STAT pathway provides a new perspective for CHB therapy. ALPK1_rs35389530 and polygenic score are potential biomarkers to predict PegIFN-α treatment response and may be used for optimizing CHB treatment.

Helicobacter pylori Modulates Heptose Metabolite Biosynthesis and Heptose-Dependent Innate Immune Host Cell Activation by Multiple Mechanisms

Heptose metabolites including ADP-d-glycero-β-d-manno-heptose (ADP-heptose) are involved in bacterial lipopolysaccharide and cell envelope biosynthesis. Recently, heptoses were also identified to have potent proinflammatory activity on human cells as novel microbe-associated molecular patterns. The gastric pathogenic bacterium Helicobacter pylori produces heptose metabolites, which it transports into human cells through its Cag type 4 secretion system. Using H. pylori as a model, we have addressed the question of how proinflammatory ADP-heptose biosynthesis can be regulated by bacteria. We have characterized the interstrain variability and regulation of heptose biosynthesis genes and the modulation of heptose metabolite production by H. pylori, which impact cell-autonomous proinflammatory human cell activation. HldE, a central enzyme of heptose metabolite biosynthesis, showed strong sequence variability between strains and was also variably expressed between strains. Amounts of gene transcripts in the hldE gene cluster displayed intrastrain and interstrain differences, were modulated by host cell contact and the presence of the cag pathogenicity island, and were affected by carbon starvation regulator A (CsrA). We reconstituted four steps of the H. pylori lipopolysaccharide (LPS) heptose biosynthetic pathway in vitro using recombinant purified GmhA, HldE, and GmhB proteins. On the basis of one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry, the structures of major reaction products were identified as β-d-ADP-heptose and β-heptose-1-monophosphate. A proinflammatory heptose-monophosphate variant was also identified for the first time as a novel cell-active product in H. pylori bacteria. Separate purified HldE subdomains and variant HldE allowed us to uncover additional strain variation in generating heptose metabolites. IMPORTANCE Bacterial heptose metabolites, intermediates of lipopolysaccharide (LPS) biosynthesis, are novel microbe-associated molecular patterns (MAMPs) that activate proinflammatory signaling. In the gastric pathogen Helicobacter pylori, heptoses are transferred into host cells by the Cag type IV secretion system, which is also involved in carcinogenesis. Little is known about how H. pylori, which is highly strain variable, regulates heptose biosynthesis and downstream host cell activation. We report here that the regulation of proinflammatory heptose production by H. pylori is strain specific. Heptose gene cluster activity is modulated by the presence of an active cag pathogenicity island (cagPAI), contact with human cells, and the carbon starvation regulator A. Reconstitution with purified biosynthesis enzymes and purified bacterial lysates allowed us to biochemically characterize heptose pathway products, identifying a heptose-monophosphate variant as a novel proinflammatory metabolite. These findings emphasize that the bacteria use heptose biosynthesis to fine-tune inflammation and also highlight opportunities to mine the heptose biosynthesis pathway as a potential therapeutic target against infection, inflammation, and cancer.

A Bittersweet Kiss of Gram-Negative Bacteria: The Role of ADP-Heptose in the Pathogenesis of Infection

Due to the global crisis caused by the dramatic rise of drug resistance among Gram-negative bacteria, there is an urgent need for a thorough understanding of the pathogenesis of infections of such an etiology. In light of the limited availability of new antibiotics, therapies aimed at host-pathogen interactions emerge as potential treatment modalities. Thus, understanding the mechanism of pathogen recognition by the host and immune evasion appear to be the key scientific issues. Until recently, lipopolysaccharide (LPS) was recognized as a major pathogen-associated molecular pattern (PAMP) of Gram-negative bacteria. However, recently, ADP-L-glycero-β-D-manno-heptose (ADP-heptose), an intermediate carbohydrate metabolite of the LPS biosynthesis pathway, was discovered to activate the hosts' innate immunity. Therefore, ADP-heptose is regarded as a novel PAMP of Gram-negative bacteria that is recognized by the cytosolic alpha kinase-1 (ALPK1) protein. The conservative nature of this molecule makes it an intriguing player in host-pathogen interactions, especially in the context of changes in LPS structure or even in its loss by certain resistant pathogens. Here, we present the ADP-heptose metabolism, outline the mechanisms of its recognition and the activation of its immunity, and summarize the role of ADP-heptose in the pathogenesis of infection. Finally, we hypothesize about the routes of the entry of this sugar into cytosol and point to emerging questions that require further research.

The Role of Microbiota-Derived Metabolites in Colorectal Cancer

The impact of bacterial members of the microbiota on the development of colorectal cancer (CRC) has become clear in recent years. However, exactly how bacteria contribute to the development of cancer is often still up for debate. The impact of bacteria-derived metabolites, which can influence the development of CRC either in a promoting or inhibiting manner, is undeniable. Here, we discuss the effects of the most well-studied bacteria-derived metabolites associated with CRC, including secondary bile acids, short-chain fatty acids, trimethylamine-N-oxide and indoles. We show that the effects of individual metabolites on CRC development are often nuanced and dose- and location-dependent. In the coming years, the array of metabolites involved in CRC development will undoubtedly increase further, which will emphasize the need to focus on causation and mechanisms and the clearly defined roles of bacterial species within the microbiota.

Epithelial immune activation and intracellular invasion by non-typeable Haemophilus influenzae

Type-2 low asthma affects 30-50% of people with severe asthma and includes a phenotype characterized by sputum neutrophilia and resistance to corticosteroids. Airways inflammation in type-2 low asthma or COPD is potentially driven by persistent bacterial colonization of the lower airways by bacteria such as non-encapsulated Haemophilus influenzae (NTHi). Although pathogenic in the lower airways, NTHi is a commensal of the upper airways. It is not known to what extent these strains can invade airway epithelial cells, persist intracellularly and activate epithelial cell production of proinflammatory cytokines, and how this differs between the upper and lower airways. We studied NTHi infection of primary human bronchial epithelial cells (PBECs), primary nasal epithelial cells (NECs) and epithelial cell lines from upper and lower airways. NTHi strains differed in propensity for intracellular and paracellular invasion. We found NTHi was internalized within PBECs at 6 h, but live intracellular infection did not persist at 24 h. Confocal microscopy and flow cytometry showed NTHi infected secretory, ciliated and basal PBECs. Infection of PBECs led to induction of CXCL8, interleukin (IL)-1β, IL-6 and TNF. The magnitude of cytokine induction was independent of the degree of intracellular invasion, either by differing strains or by cytochalasin D inhibition of endocytosis, with the exception of the inflammasome-induced mediator IL-1β. NTHi-induced activation of TLR2/4, NOD1/2 and NLR inflammasome pathways was significantly stronger in NECs than in PBECs. These data suggest that NTHi is internalized transiently by airway epithelial cells and has capacity to drive inflammation in airway epithelial cells.

In vitro kinase assay reveals ADP-heptose-dependent ALPK1 autophosphorylation and altered kinase activity of disease-associated ALPK1 mutants

Alpha-protein kinase 1 (ALPK1) is a pathogen recognition receptor that detects ADP-heptose (ADPH), a lipopolysaccharide biosynthesis intermediate, recently described as a pathogen-associated molecular pattern in Gram-negative bacteria. ADPH binding to ALPK1 activates its kinase domain and triggers TIFA phosphorylation on threonine 9. This leads to the assembly of large TIFA oligomers called TIFAsomes, activation of NF-κB and pro-inflammatory gene expression. Furthermore, mutations in ALPK1 are associated with inflammatory syndromes and cancers. While this kinase is of increasing medical interest, its activity in infectious or non-infectious diseases remains poorly characterized. Here, we use a non-radioactive ALPK1 in vitro kinase assay based on the use of ATPγS and protein thiophosphorylation. We confirm that ALPK1 phosphorylates TIFA T9 and show that T2, T12 and T19 are also weakly phosphorylated by ALPK1. Interestingly, we find that ALPK1 itself is phosphorylated in response to ADPH recognition during Shigella flexneri and Helicobacter pylori infection and that disease-associated ALPK1 mutants exhibit altered kinase activity. In particular, T237M and V1092A mutations associated with ROSAH syndrome and spiradenoma/spiradenocarcinoma respectively, exhibit enhanced ADPH-induced kinase activity and constitutive assembly of TIFAsomes. Altogether, this study provides new insights into the ADPH sensing pathway and disease-associated ALPK1 mutants.

Campylobacter jejuni: targeting host cells, adhesion, invasion, and survival

Campylobacter jejuni, causing strong enteritis, is an unusual bacterium with numerous peculiarities. Chemotactically controlled motility in viscous milieu allows targeted navigation to intestinal mucus and colonization. By phase variation, quorum sensing, extensive O-and N-glycosylation and use of the flagellum as type-3-secretion system C. jejuni adapts effectively to environmental conditions. C. jejuni utilizes proteases to open cell-cell junctions and subsequently transmigrates paracellularly. Fibronectin at the basolateral side of polarized epithelial cells serves as binding site for adhesins CadF and FlpA, leading to intracellular signaling, which again triggers membrane ruffling and reduced host cell migration by focal adhesion. Cell contacts of C. jejuni results in its secretion of invasion antigens, which induce membrane ruffling by paxillin-independent pathway. In addition to fibronectin-binding proteins, other adhesins with other target structures and lectins and their corresponding sugar structures are involved in host-pathogen interaction. Invasion into the intestinal epithelial cell depends on host cell structures. Fibronectin, clathrin, and dynein influence cytoskeletal restructuring, endocytosis, and vesicular transport, through different mechanisms. C. jejuni can persist over a 72-h period in the cell. Campylobacter-containing vacuoles, avoid fusion with lysosomes and enter the perinuclear space via dynein, inducing signaling pathways. Secretion of cytolethal distending toxin directs the cell into programmed cell death, including the pyroptotic release of proinflammatory substances from the destroyed cell compartments. The immune system reacts with an inflammatory cascade by participation of numerous immune cells. The development of autoantibodies, directed not only against lipooligosaccharides, but also against endogenous gangliosides, triggers autoimmune diseases. Lesions of the epithelium result in loss of electrolytes, water, and blood, leading to diarrhea, which flushes out mucus containing C. jejuni. Together with the response of the immune system, this limits infection time. Based on the structural interactions between host cell and bacterium, the numerous virulence mechanisms, signaling, and effects that characterize the infection process of C. jejuni, a wide variety of targets for attenuation of the pathogen can be characterized. The review summarizes strategies of C. jejuni for host-pathogen interaction and should stimulate innovative research towards improved definition of targets for future drug development. KEY POINTS: • Bacterial adhesion of Campylobacter to host cells and invasion into host cells are strictly coordinated processes, which can serve as targets to prevent infection. • Reaction and signalling of host cell depend on the cell type. • Campylobacter virulence factors can be used as targets for development of antivirulence drug compounds.

In vitro and ex vivo modeling of enteric bacterial infections

Enteric bacterial infections contribute substantially to global disease burden and mortality, particularly in the developing world. In vitro 2D monolayer cultures have provided critical insights into the fundamental virulence mechanisms of a multitude of pathogens, including Salmonella enterica serovars Typhimurium and Typhi, Vibrio cholerae, Shigella spp., Escherichia coli and Campylobacter jejuni, which have led to the identification of novel targets for antimicrobial therapy and vaccines. In recent years, the arsenal of experimental systems to study intestinal infections has been expanded by a multitude of more complex models, which have allowed to evaluate the effects of additional physiological and biological parameters on infectivity. Organoids recapitulate the cellular complexity of the human intestinal epithelium while 3D bioengineered scaffolds and microphysiological devices allow to emulate oxygen gradients, flow and peristalsis, as well as the formation and maintenance of stable and physiologically relevant microbial diversity. Additionally, advancements in ex vivo cultures and intravital imaging have opened new possibilities to study the effects of enteric pathogens on fluid secretion, barrier integrity and immune cell surveillance in the intact intestine. This review aims to present a balanced and updated overview of current intestinal in vitro and ex vivo methods for modeling of enteric bacterial infections. We conclude that the different paradigms are complements rather than replacements and their combined use promises to further our understanding of host-microbe interactions and their impacts on intestinal health.

Gain-of-function mutations in ALPK1 cause an NF-κB-mediated autoinflammatory disease: functional assessment, clinical phenotyping and disease course of patients with ROSAH syndrome

OBJECTIVES

To test the hypothesis that ROSAH (retinal dystrophy, optic nerve oedema, splenomegaly, anhidrosis and headache) syndrome, caused by dominant mutation in ALPK1, is an autoinflammatory disease.

METHODS

This cohort study systematically evaluated 27 patients with ROSAH syndrome for inflammatory features and investigated the effect of ALPK1 mutations on immune signalling. Clinical, immunologic and radiographical examinations were performed, and 10 patients were empirically initiated on anticytokine therapy and monitored. Exome sequencing was used to identify a new pathogenic variant. Cytokine profiling, transcriptomics, immunoblotting and knock-in mice were used to assess the impact of ALPK1 mutations on protein function and immune signalling.

RESULTS

The majority of the cohort carried the p.Thr237Met mutation but we also identified a new ROSAH-associated mutation, p.Tyr254Cys.Nearly all patients exhibited at least one feature consistent with inflammation including recurrent fever, headaches with meningeal enhancement and premature basal ganglia/brainstem mineralisation on MRI, deforming arthritis and AA amyloidosis. However, there was significant phenotypic variation, even within families and some adults lacked functional visual deficits. While anti-TNF and anti-IL-1 therapies suppressed systemic inflammation and improved quality of life, anti-IL-6 (tocilizumab) was the only anticytokine therapy that improved intraocular inflammation (two of two patients).Patients' primary samples and in vitro assays with mutated ALPK1 constructs showed immune activation with increased NF-κB signalling, STAT1 phosphorylation and interferon gene expression signature. Knock-in mice with the Alpk1 T237M mutation exhibited subclinical inflammation.Clinical features not conventionally attributed to inflammation were also common in the cohort and included short dental roots, enamel defects and decreased salivary flow.

CONCLUSION

ROSAH syndrome is an autoinflammatory disease caused by gain-of-function mutations in ALPK1 and some features of disease are amenable to immunomodulatory therapy.

Tnfaip2 promotes atherogenesis by enhancing oxidative stress induced inflammation

The inflammation is considered to be the crucial determinants of lesion progression and plaque stability during atherogenesis. Tnfaip2 appears to be a regulator for carcinogenesis and infectious diseases. But its role in atherosclerosis is not clear. Here we first report that Tnfaip2 promotes the formation of atherosclerosis through enhancing the inflammation under oxidative stress condition. Although the endogenous expression of Tnfaip2 was upregulated under oxidative stress condition, the overexpressed Tnfaip2 could promote cells proliferation. This might result from the ability of promoting cells entering G₂/M phase. Conversely, the cells proliferation and migration were significantly reduced in Tnfaip2 knockdown cells through inhibiting the activation of NF-κB/MAPK/Akt signaling pathways. However, the efferocytosis increased markedly due to the upregulation of "eat me" receptors, such as CD36, SR-A, and SR-B1, and the downregulation of "don't eat me" signal CD47. As a consequence, Tnfaip2 deficiency in bone marrow-derived cells inhibited atherosclerosis development in Ldlr^-/- mice fed a high-fat diet accompanied by decreased inflammatory cytokines and shTnfaip2 could reduce the plaque lesions in ApoE^-/- mice. These results indicate that Tnfaip2 might play an important role during atherogenesis.

Akkermansia muciniphila upregulates genes involved in maintaining the intestinal barrier function via ADP-heptose-dependent activation of the ALPK1/TIFA pathway

The commensal bacteria that make up the gut microbiota impact the health of their host on multiple levels. In particular, the interactions taking place between the microbe-associated molecule patterns (MAMPs) and pattern recognition receptors (PRRs), expressed by intestinal epithelial cells (IECs), are crucial for maintaining intestinal homeostasis. While numerous studies showed that TLRs and NLRs are involved in the control of gut homeostasis by commensal bacteria, the role of additional innate immune receptors remains unclear. Here, we seek for novel MAMP-PRR interactions involved in the beneficial effect of the commensal bacterium Akkermansia muciniphila on intestinal homeostasis. We show that A. muciniphila strongly activates NF-κB in IECs by releasing one or more potent activating metabolites into the microenvironment. By using drugs, chemical and gene-editing tools, we found that the released metabolite(s) enter(s) epithelial cells and activate(s) NF-κB via an ALPK1, TIFA and TRAF6-dependent pathway. Furthermore, we show that the released molecule has the biological characteristics of the ALPK1 ligand ADP-heptose. Finally, we show that A. muciniphila induces the expression of the MUC2, BIRC3 and TNFAIP3 genes involved in the maintenance of the intestinal barrier function and that this process is dependent on TIFA. Altogether, our data strongly suggest that the commensal A. muciniphila promotes intestinal homeostasis by activating the ALPK1/TIFA/TRAF6 axis, an innate immune pathway exclusively described so far in the context of Gram-negative bacterial infections.