NLRP6 controls pulmonary inflammation from cigarette smoke in a gut microbiota-dependent manner.

Chronic obstructive pulmonary disease (COPD) is a major health issue primarily caused by cigarette smoke (CS) and characterized by breathlessness and repeated airway inflammation. NLRP6 is a cytosolic innate receptor controlling intestinal inflammation and orchestrating the colonic host-microbial interface. However, its roles in the lungs remain largely unexplored. Using CS exposure models, our data show that airway inflammation is strongly impaired in Nlrp6-deficient mice with drastically fewer recruited neutrophils, a key cell subset in inflammation and COPD. We found that NLRP6 expression in lung epithelial cells is important to control airway and lung tissue inflammation in an inflammasome-dependent manner. Since gut-derived metabolites regulate NLRP6 inflammasome activation in intestinal epithelial cells, we investigated the link between NLRP6, CS-driven lung inflammation, and gut microbiota composition. We report that acute CS exposure alters gut microbiota in both wild-type (WT) and Nlrp6-deficient mice and that antibiotic treatment decreases CS-induced lung inflammation. In addition, gut microbiota transfer from dysbiotic Nlrp6-deficient mice to WT mice decreased airway lung inflammation in WT mice, highlighting an NLRP6-dependent gut-to-lung axis controlling pulmonary inflammation.

Homeostatic chemokines as putative therapeutic targets in idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a fatal chronic interstitial lung disease (ILD) that affects lung mechanical functions and gas exchange. IPF is caused by increased fibroblast activity and collagen deposition that compromise the alveolar-capillary barrier. Identifying an effective therapy for IPF remains a clinical challenge. Chemokines are key proteins in cell communication that have functions in immunity as well as in tissue homeostasis, damage, and repair. Chemokine receptor signaling induces the activation and proliferation of lung-resident cells, including alveolar macrophages (AMs) and fibroblasts. AMs are an important source of chemokines and cytokines during IPF. We highlight the complexity of this system and, based on insights from genetic and transcriptomic studies, propose a new role for homeostatic chemokine imbalance in IPF, with implications for putative therapeutic targets.

Lung inflammation and interstitial fibrosis by targeted alveolar epithelial type I cell death.

Introduction: The pathogenesis of chronic lung diseases is multifaceted with a major role of recurrent micro-injuries of the epithelium. While several reports clearly indicated a prominent role for surfactant-producing alveolar epithelial type 2 (AT2) cells, the contribution of gas exchange-permissive alveolar epithelial type 1 (AT1) cells has not been addressed yet. Here, we investigated whether repeated injury of AT1 cells leads to inflammation and interstitial fibrosis. Methods: We chose an inducible model of AT1 cell depletion following local diphtheria toxin (DT) administration using an iDTR flox/flox (idTRfl/fl) X Aquaporin 5CRE (Aqp5CRE) transgenic mouse strain. Results: We investigated repeated doses and intervals of DT to induce cell death of AT1 cells causing inflammation and interstitial fibrosis. We found that repeated DT administrations at 1ng in iDTRfl/fl X Aqp5CRE mice cause AT1 cell death leading to inflammation, increased tissue repair markers and interstitial pulmonary fibrosis. Discussion: Together, we demonstrate that depletion of AT1 cells using repeated injury represents a novel approach to investigate chronic lung inflammatory diseases and to identify new therapeutic targets.

Gasdermin D membrane pores orchestrate IL-1α secretion from necrotic macrophages after NFS-rich silica exposure.

IL-1α is an intracellular danger signal (DAMP) released by macrophages contributing to the development of silica-induced lung inflammation. The exact molecular mechanism orchestrating IL-1α extracellular release from particle-exposed macrophages is still unclear. To delineate this process, murine J774 and bone-marrow derived macrophages were exposed to increasing concentrations (1-40 cm2/ml) of a set of amorphous and crystalline silica particles with different surface chemical features. In particular, these characteristics include the content of nearly free silanols (NFS), a silanol population responsible for silica cytotoxicity recently identified. We first observed de novo stocks of IL-1α in macrophages after silica internalization regardless of particle physico-chemical characteristics and cell stress. IL-1α intracellular production and accumulation were observed by exposing macrophages to biologically-inert or cytotoxic crystalline and amorphous silicas. In contrast, only NFS-rich reactive silica particles triggered IL-1α release into the extracellular milieu from necrotic macrophages. We demonstrate that IL-1α is actively secreted through the formation of gasdermin D (GSDMD) pores in the plasma membrane and not passively released after macrophage plasma membrane lysis. Our findings indicate that the GSDMD pore-dependent secretion of IL-1α stock from macrophages solely depends on cytotoxicity induced by NFS-rich silica. This new regulated process represents a key first event in the mechanism of silica toxicity, suitable to refine the existing adverse outcome pathway (AOP) for predicting the inflammatory activity of silicas.

Butyrate: Connecting the gut-lung axis to the management of pulmonary disorders.

Short-chain fatty acids (SCFAs) are metabolites released by bacterial components of the microbiota. These molecules have a wide range of effects in the microbiota itself, but also in host cells in which they are known for contributing to the regulation of cell metabolism, barrier function, and immunological responses. Recent studies indicate that these molecules are important players in the gut-lung axis and highlight the possibility of using strategies that alter their intestinal production to prevent or treat distinct lung inflammatory diseases. Here, we review the effects of the SCFA butyrate and its derivatives in vitro and in vivo on murine models of respiratory disorders, besides discussing the potential therapeutic use of butyrate and the other SCFAs in lung diseases.

Cigarette smoke-induced gasdermin D activation in bronchoalveolar macrophages and bronchial epithelial cells dependently on NLRP3.

Chronic pulmonary inflammation and chronic obstructive pulmonary disease (COPD) are major health issues largely due to air pollution and cigarette smoke (CS) exposure. The role of the innate receptor NLRP3 (nucleotide-binding domain and leucine-rich repeat containing protein 3) orchestrating inflammation through formation of an inflammasome complex in CS-induced inflammation or COPD remains controversial. Using acute and subchronic CS exposure models, we found that Nlrp3-deficient mice or wild-type mice treated with the NLRP3 inhibitor MCC950 presented an important reduction of inflammatory cells recruited into the bronchoalveolar space and of pulmonary inflammation with decreased chemokines and cytokines production, in particular IL-1ß demonstrating the key role of NLRP3. Furthermore, mice deficient for Caspase-1/Caspase-11 presented also decreased inflammation parameters, suggesting a role for the NLRP3 inflammasome. Importantly we showed that acute CS-exposure promotes NLRP3-dependent cleavage of gasdermin D in macrophages present in the bronchoalveolar space and in bronchial airway epithelial cells. Finally, Gsdmd-deficiency reduced acute CS-induced lung and bronchoalveolar space inflammation and IL-1ß secretion. Thus, we demonstrated in our model that NLRP3 and gasdermin D are key players in CS-induced pulmonary inflammation and IL-1ß release potentially through gasdermin D forming-pore and/or pyroptoctic cell death.

Differential Regulation of Allergic Airway Inflammation by Acetylcholine.

Acetylcholine (ACh) from neuronal and non-neuronal sources plays an important role in the regulation of immune responses and is associated with the development of several disease pathologies. We have previously demonstrated that group 2 innate lymphoid cell (ILC2)-derived ACh is required for optimal type 2 responses to parasitic infection and therefore sought to determine whether this also plays a role in allergic inflammation. RoraCre+ChatLoxP mice (in which ILC2s cannot synthesize ACh) were exposed to an allergenic extract of the fungus Alternaria alternata, and immune responses in the airways and lung tissues were analyzed. Airway neutrophilia and expression of the neutrophil chemoattractants CXCL1 and CXCL2 were enhanced 24 h after exposure, suggesting that ILC2-derived ACh plays a role in limiting excessive pulmonary neutrophilic inflammation. The effect of non-selective depletion of ACh was examined by intranasal administration of a stable parasite-secreted acetylcholinesterase. Depletion of airway ACh in this manner resulted in a more profound enhancement of neutrophilia and chemokine expression, suggesting multiple cellular sources for the release of ACh. In contrast, depletion of ACh inhibited Alternaria-induced activation of ILC2s, suppressing the expression of IL-5, IL-13, and subsequent eosinophilia. Depletion of ACh reduced macrophages with an alternatively activated M2 phenotype and an increase in M1 macrophage marker expression. These data suggest that ACh regulates allergic airway inflammation in several ways, enhancing ILC2-driven eosinophilia but suppressing neutrophilia through reduced chemokine expression.

NLRP6 negatively regulates type 2 immune responses in mice.

BACKGROUND: Inflammasomes are large protein complexes that assemble in the cytosol in response to danger such as tissue damage or infection. Following activation, inflammasomes trigger cell death and the release of biologically active forms of pro-inflammatory cytokines interleukin (IL)-1ß and IL-18. NOD-like receptor family pyrin domain containing 6 (NLRP6) inflammasome is required for IL-18 secretion by intestinal epithelial cells, macrophages, and T cells, contributing to homeostasis and self-defense against pathogenic microbes. However, the involvement of NLRP6 in type 2 lung inflammation remains elusive. METHODS: Wild-type (WT) and Nlrp6-/- mice were used. Birch pollen extract (BPE)-induced allergic lung inflammation, eosinophil recruitment, Th2-related cytokine and chemokine production, airway hyperresponsiveness, and lung histopathology, Th2 cell differentiation, GATA3, and Th2 cytokines expression, were determined. Nippostrongylus brasiliensis (Nb) infection, worm count in intestine, type 2 innate lymphoid cell (ILC2), and Th2 cells in lungs were evaluated. RESULTS: We demonstrate in Nlrp6-/- mice that a mixed Th2/Th17 immune responses prevailed following birch pollen challenge with increased eosinophils, ILC2, Th2, and Th17 cell induction and reduced IL-18 production. Nippostrongylus brasiliensis infected Nlrp6-/- mice featured enhanced early expulsion of the parasite due to enhanced type 2 immune responses compared to WT hosts. In vitro, NLRP6 repressed Th2 polarization, as shown by increased Th2 cytokines and higher expression of the transcription factor GATA3 in the absence of NLRP6. Exogenous IL-18 administration partially reduced the enhanced airways inflammation in Nlrp6-/- mice. CONCLUSIONS: In summary, our data identify NLRP6 as a negative regulator of type 2 immune responses.

Natterin-Induced Neutrophilia Is Dependent on cGAS/STING Activation via Type I IFN Signaling Pathway.

Natterin is a potent pro-inflammatory fish molecule, inducing local and systemic IL-1ß/IL-1R1-dependent neutrophilia mediated by non-canonical NLRP6 and NLRC4 inflammasome activation in mice, independent of NLRP3. In this work, we investigated whether Natterin activates mitochondrial damage, resulting in self-DNA leaks into the cytosol, and whether the DNA sensor cGAS and STING pathway participate in triggering the innate immune response. Employing a peritonitis mouse model, we found that the deficiency of the tlr2/tlr4, myd88 and trif results in decreased neutrophil influx to peritoneal cavities of mice, indicative that in addition to MyD88, TRIF contributes to neutrophilia triggered by TLR4 engagement by Natterin. Next, we demonstrated that gpcr91 deficiency in mice abolished the neutrophil recruitment after Natterin injection, but mice pre-treated with 2-deoxy-d-glucose that blocks glycolysis presented similar infiltration than WT Natterin-injected mice. In addition, we observed that, compared with the WT Natterin-injected mice, DPI and cyclosporin A treated mice had a lower number of neutrophils in the peritoneal exudate. The levels of dsDNA in the supernatant of the peritoneal exudate and processed IL-33 in the supernatant of the peritoneal exudate or cytoplasmic supernatant of the peritoneal cell lysate of WT Natterin-injected mice were several folds higher than those of the control mice. The recruitment of neutrophils to peritoneal cavity 2 h post-Natterin injection was intensely impaired in ifnar KO mice and partially in il-28r KO mice, but not in ifnγr KO mice. Finally, using cgas KO, sting KO, or irf3 KO mice we found that recruitment of neutrophils to peritoneal cavities was virtually abolished in response to Natterin. These findings reveal cytosolic DNA sensors as critical regulators for Natterin-induced neutrophilia.

STING agonist diABZI induces PANoptosis and DNA mediated acute respiratory distress syndrome (ARDS).

Stimulator of interferon genes (STING) contributes to immune responses against tumors and may control viral infection including SARS-CoV-2 infection. However, activation of the STING pathway by airway silica or smoke exposure leads to cell death, self-dsDNA release, and STING/type I IFN dependent acute lung inflammation/ARDS. The inflammatory response induced by a synthetic non-nucleotide-based diABZI STING agonist, in comparison to the natural cyclic dinucleotide cGAMP, is unknown. A low dose of diABZI (1 µg by endotracheal route for 3 consecutive days) triggered an acute neutrophilic inflammation, disruption of the respiratory barrier, DNA release with NET formation, PANoptosis cell death, and inflammatory cytokines with type I IFN dependent acute lung inflammation. Downstream upregulation of DNA sensors including cGAS, DDX41, IFI204, as well as NLRP3 and AIM2 inflammasomes, suggested a secondary inflammatory response to dsDNA as a danger signal. DNase I treatment, inhibition of NET formation together with an investigation in gene-deficient mice highlighted extracellular DNA and TLR9, but not cGAS, as central to diABZI-induced neutrophilic response. Therefore, activation of acute cell death with DNA release may lead to ARDS which may be modeled by diABZI. These results show that airway targeting by STING activator as a therapeutic strategy for infection may enhance lung inflammation with severe ARDS. STING agonist diABZI induces neutrophilic lung inflammation and PANoptosis A, Airway STING priming induce a neutrophilic lung inflammation with epithelial barrier damage, double-stranded DNA release in the bronchoalvelolar space, cell death, NETosis and type I interferon release. B, 1. The diamidobenzimidazole (diABZI), a STING agonist is internalized into the cytoplasm through unknown receptor and induce the activation and dimerization of STING followed by TBK1/IRF3 phosporylation leading to type I IFN response. STING activation also leads to NF-kB activation and the production of pro-inflammatory cytokines TNFα and IL-6. 2. The activation of TNFR1 and IFNAR1 signaling pathway results in ZBP1 and RIPK3/ASC/CASP8 activation leading to MLKL phosphorylation and necroptosis induction. 3. This can also leads to Caspase-3 cleavage and apoptosis induction. 4. Self-dsDNA or mtDNA sensing by NLRP3 or AIM2 induces inflammsome formation leading to Gasdermin D cleavage enabling Gasdermin D pore formation and the release mature IL-1ß and pyroptosis. NLRP3 inflammasome formation can be enhanced by the ZBP1/RIPK3/CASP8 complex. 5. A second signal of STING activation with diABZI induces cell death and the release of self-DNA which is sensed by cGAS and form 2'3'-cGAMP leading to STING hyper activation, the amplification of TBK1/IRF3 and NF-kB pathway and the subsequent production of IFN-I and inflammatory TNFα and IL-6. This also leads to IFI204 and DDX41 upregulation thus, amplifying the inflammatory loop. The upregulation of apoptosis, pyroptosis and necroptosis is indicative of STING-dependent PANoptosis.

Natterin-induced neutrophilia is dependent on cGAS/STING activation via type i IFN signaling pathway

Natterin is a potent pro-inflammatory fish molecule, inducing local and systemic IL-1β/IL-1R1-dependent neutrophilia mediated by non-canonical NLRP6 and NLRC4 inflammasome activation in mice, independent of NLRP3. In this work, we investigated whether Natterin activates mitochondrial damage, resulting in self-DNA leaks into the cytosol, and whether the DNA sensor cGAS and STING pathway participate in triggering the innate immune response. Employing a peritonitis mouse model, we found that the deficiency of the tlr2/tlr4, myd88 and trif results in decreased neutrophil influx to peritoneal cavities of mice, indicative that in addition to MyD88, TRIF contributes to neutrophilia triggered by TLR4 engagement by Natterin. Next, we demonstrated that gpcr91 deficiency in mice abolished the neutrophil recruitment after Natterin injection, but mice pre-treated with 2-deoxy-d-glucose that blocks glycolysis presented similar infiltration than WT Natterin-injected mice. In addition, we observed that, compared with the WT Natterin-injected mice, DPI and cyclosporin A treated mice had a lower number of neutrophils in the peritoneal exudate. The levels of dsDNA in the supernatant of the peritoneal exudate and processed IL-33 in the supernatant of the peritoneal exudate or cytoplasmic supernatant of the peritoneal cell lysate of WT Natterin-injected mice were several folds higher than those of the control mice. The recruitment of neutrophils to peritoneal cavity 2 h post-Natterin injection was intensely impaired in ifnar KO mice and partially in il-28r KO mice, but not in ifnγr KO mice. Finally, using cgas KO, sting KO, or irf3 KO mice we found that recruitment of neutrophils to peritoneal cavities was virtually abolished in response to Natterin. These findings reveal cytosolic DNA sensors as critical regulators for Natterin-induced neutrophilia.

Sepsis expands a CD39+ plasmablast population that promotes immunosuppression via adenosine-mediated inhibition of macrophage antimicrobial activity.

Sepsis results in elevated adenosine in circulation. Extracellular adenosine triggers immunosuppressive signaling via the A2a receptor (A2aR). Sepsis survivors develop persistent immunosuppression with increased risk of recurrent infections. We utilized the cecal ligation and puncture (CLP) model of sepsis and subsequent infection to assess the role of adenosine in post-sepsis immune suppression. A2aR-deficient mice showed improved resistance to post-sepsis infections. Sepsis expanded a subset of CD39hi B cells and elevated extracellular adenosine, which was absent in mice lacking CD39-expressing B cells. Sepsis-surviving B cell-deficient mice were more resistant to secondary infections. Mechanistically, metabolic reprogramming of septic B cells increased production of ATP, which was converted into adenosine by CD39 on plasmablasts. Adenosine signaling via A2aR impaired macrophage bactericidal activity and enhanced interleukin-10 production. Septic individuals exhibited expanded CD39hi plasmablasts and adenosine accumulation. Our study reveals CD39hi plasmablasts and adenosine as important drivers of sepsis-induced immunosuppression with relevance in human disease.

Bromodomain and extraterminal (BET) protein inhibition of IgG/IgE production in murine B cells is counter-balanced by a strong Th2 bias.

OBJECTIVES: Inhibitors of bromodomain and extra terminal domain (BET) proteins are a new and growing class of anti-cancer drugs, which decrease oncogene expression by targeting superenhancers. Antibody production is another physiological process relying on superenhancers, and it remains to be clarified whether potential immunomodulatory properties of BET inhibitors might impact humoral immunity and allergy. METHODS: We thus evaluated humoral immune responses and their Th2 context in vitro and in vivo in mice following treatment with the classical BET-inhibitor JQ1. We quantified immunoglobulin (Ig) and antibody production by B cells either stimulated in vitro or obtained from immunised mice. JQ1 effects on class switching and activation-induced deaminase loading were determined, together with modifications of B, T follicular helper (Tfh) and T helper 2 (Th2) populations. JQ1 was finally tested in B-cell-dependent models of immune disorders. RESULTS: Bromodomain and extra terminal domain inhibition reduced class switching, Ig expression on B cells and antibody secretion and was correlated with decreased numbers of Tfh cells. However, JQ1 strongly increased the proportion of GATA3+ Th2 cells and the secretion of corresponding cytokines. In a mouse allergic model of lung inflammation, JQ1 did not affect eosinophil infiltration or mucus production but enhanced Th2 cytokine production and aggravated clinical manifestations. CONCLUSION: Altogether, BET inhibition thus interweaves intrinsic negative effects on B cells with a parallel complex reshaping of T-cell polarisation which can increase type 2 cytokines and eventually promote B-cell-dependent immunopathology. These opposite and potentially hazardous immunomodulatory effects raise concerns for clinical use of BET inhibitors in patients with immune disorders.

Chronic Pseudomonas aeruginosa Lung Infection Is IL-1R Independent, but Relies on MyD88 Signaling.

Cystic fibrosis is associated with chronic Pseudomonas aeruginosa colonization and inflammation. The role of MyD88, the shared adapter protein of the proinflammatory TLR and IL-1R families, in chronic P. aeruginosa biofilm lung infection is unknown. We report that chronic lung infection with the clinical P. aeruginosa RP73 strain is associated with uncontrolled lung infection in complete MyD88-deficient mice with epithelial damage, inflammation, and rapid death. Then, we investigated whether alveolar or myeloid cells contribute to heightened sensitivity to infection. Using cell-specific, MyD88-deficient mice, we uncover that the MyD88 pathway in myeloid or alveolar epithelial cells is dispensable, suggesting that other cell types may control the high sensitivity of MyD88-deficient mice. By contrast, IL-1R1-deficient mice control chronic P. aeruginosa RP73 infection and IL-1ß Ab blockade did not reduce host resistance. Therefore, the IL-1R1/MyD88 pathway is not involved, but other IL-1R or TLR family members need to be investigated. Our data strongly suggest that IL-1 targeted neutralizing therapies used to treat inflammatory diseases in patients unlikely reduce host resistance to chronic P. aeruginosa infection.

Acetylcholine production by group 2 innate lymphoid cells promotes mucosal immunity to helminths.

Innate lymphoid cells (ILCs) are critical mediators of immunological and physiological responses at mucosal barrier sites. Whereas neurotransmitters can stimulate ILCs, the synthesis of small-molecule neurotransmitters by these cells has only recently been appreciated. Group 2 ILCs (ILC2s) are shown here to synthesize and release acetylcholine (ACh) during parasitic nematode infection. The cholinergic phenotype of pulmonary ILC2s was associated with their activation state, could be induced by in vivo exposure to extracts of Alternaria alternata or the alarmin cytokines interleukin-33 (IL-33) and IL-25, and was augmented by IL-2 in vitro. Genetic disruption of ACh synthesis by murine ILC2s resulted in increased parasite burdens, lower numbers of ILC2s, and reduced lung and gut barrier responses to Nippostrongylus brasiliensis infection. These data demonstrate a functional role for ILC2-derived ACh in the expansion of ILC2s for maximal induction of type 2 immunity.

NOD1 sensing of house dust mite-derived microbiota promotes allergic experimental asthma.

BACKGROUND: Asthma severity has been linked to exposure to gram-negative bacteria from the environment that are recognized by NOD1 receptor and are present in house dust mite (HDM) extracts. NOD1 polymorphism has been associated with asthma. OBJECTIVE: We sought to evaluate whether either host or HDM-derived microbiota may contribute to NOD1-dependent disease severity. METHODS: A model of HDM-induced experimental asthma was used and the effect of NOD1 deficiency was evaluated. Contribution of host microbiota was evaluated by fecal transplantation. Contribution of HDM-derived microbiota was assessed by 16S ribosomal RNA sequencing, mass spectrometry analysis, and peptidoglycan depletion of the extracts. RESULTS: In this model, loss of the bacterial sensor NOD1 and its adaptor RIPK2 improved asthma features. Such inhibitory effect was not related to dysbiosis caused by NOD1 deficiency, as shown by fecal transplantation of Nod1-deficient microbiota to wild-type germ-free mice. The 16S ribosomal RNA gene sequencing and mass spectrometry analysis of HDM allergen, revealed the presence of some muropeptides from gram-negative bacteria that belong to the Bartonellaceae family. While such HDM-associated muropeptides were found to activate NOD1 signaling in epithelial cells, peptidoglycan-depleted HDM had a decreased ability to instigate asthma in vivo. CONCLUSIONS: These data show that NOD1-dependent sensing of HDM-associated gram-negative bacteria aggravates the severity of experimental asthma, suggesting that inhibiting the NOD1 signaling pathway may be a therapeutic approach to treating asthma.

Deletion of Mocos Induces Xanthinuria with Obstructive Nephropathy and Major Metabolic Disorders in Mice.

Background: Xanthinuria type II is a rare autosomal purine disorder. This recessive defect of purine metabolism remains an under-recognized disorder. Methods: Mice with targeted disruption of the molybdenum cofactor sulfurase (Mocos) gene were generated to enable an integrated understanding of purine disorders and evaluate pathophysiologic functions of this gene which is found in a large number of pathways and is known to be associated with autism. Results: Mocos-deficient mice die with 4 weeks of age due to renal failure of distinct obstructive nephropathy with xanthinuria, xanthine deposits, cystic tubular dilation, Tamm-Horsfall (uromodulin) protein (THP) deposits, tubular cell necrosis with neutrophils, and occasionally hydronephrosis with urolithiasis. Obstructive nephropathy is associated with moderate interstitial inflammatory and fibrotic responses, anemia, reduced detoxification systems, and important alterations of the metabolism of purines, amino acids, and phospholipids. Conversely, heterozygous mice expressing reduced MOCOS protein are healthy with no apparent pathology. Conclusions: Mocos-deficient mice develop a lethal obstructive nephropathy associated with profound metabolic changes. Studying MOCOS functions may provide important clues about the underlying pathogenesis of xanthinuria and other diseases requiring early diagnosis.

Hippocampal interleukin-33 mediates neuroinflammation-induced cognitive impairments.

BACKGROUND: Interleukin (IL)-33 is expressed in a healthy brain and plays a pivotal role in several neuropathologies, as protective or contributing to the development of cerebral diseases associated with cognitive impairments. However, the role of IL-33 in the brain is poorly understood, raising the question of its involvement in immunoregulatory mechanisms. METHODS: We administered recombinant IL-33 (rmIL-33) by intra-hippocampal injection to C57BL/6 J (WT) and IL-1αß deficient mice. Chronic minocycline administration was performed and cognitive functions were examined trough spatial habituation test. Hippocampal inflammatory responses were investigated by RT-qPCR. The microglia activation was assessed using immunohistological staining and fluorescence-activated cell sorting (FACS). RESULTS: We showed that IL-33 administration in mice led to a spatial memory performance defect associated with an increase of inflammatory markers in the hippocampus while minocycline administration limited the inflammatory response. Quantitative assessment of glial cell activation in situ demonstrated an increase of proximal intersections per radius in each part of the hippocampus. Moreover, rmIL-33 significantly promoted the outgrowth of microglial processes. Fluorescence-activated cell sorting analysis on isolated microglia, revealed overexpression of IL-1ß, 48 h post-rmIL-33 administration. This microglial reactivity was closely related to the onset of cognitive disturbance. Finally, we demonstrated that IL-1αß deficient mice were resistant to cognitive disorders after intra-hippocampal IL-33 injection. CONCLUSION: Thus, hippocampal IL-33 induced an inflammatory state, including IL-1ß overexpression by microglia cells, being causative of the cognitive impairment. These results highlight the pathological role for IL-33 in the central nervous system, independently of a specific neuropathological model.