Itaconate is a metabolic regulator of bone formation in homeostasis and arthritis.

OBJECTIVES: Bone remodelling is a highly dynamic process dependent on the precise coordination of osteoblasts and haematopoietic-cell derived osteoclasts. Changes in core metabolic pathways during osteoclastogenesis, however, are largely unexplored and it is unknown whether and how these processes are involved in bone homeostasis. METHODS: We metabolically and transcriptionally profiled cells during osteoclast and osteoblast generation. Individual gene expression was characterised by quantitative PCR and western blot. Osteoblast function was assessed by Alizarin red staining. immunoresponsive gene 1 (Irg1)-deficient mice were used in various inflammatory or non-inflammatory models of bone loss. Tissue gene expression was analysed by RNA in situ hybridisation. RESULTS: We show that during differentiation preosteoclasts rearrange their tricarboxylic acid cycle, a process crucially depending on both glucose and glutamine. This rearrangement is characterised by the induction of Irg1 and production of itaconate, which accumulates intracellularly and extracellularly. While the IRG1-itaconate axis is dispensable for osteoclast generation in vitro and in vivo, we demonstrate that itaconate stimulates osteoblasts by accelerating osteogenic differentiation in both human and murine cells. This enhanced osteogenic differentiation is accompanied by reduced proliferation and altered metabolism. Additionally, supplementation of itaconate increases bone formation by boosting osteoblast activity in mice. Conversely, Irg1-deficient mice exhibit decreased bone mass and have reduced osteoproliferative lesions in experimental arthritis. CONCLUSION: In summary, we identify itaconate, generated as a result of the metabolic rewiring during osteoclast differentiation, as a previously unrecognised regulator of osteoblasts.

Bona fide dendritic cells are pivotal precursors for osteoclasts.

OBJECTIVES: Osteoclasts (OCs) are myeloid-derived multinucleated cells uniquely able to degrade bone. However, the exact nature of their myeloid precursors is not yet defined. METHODS: CD11c-diphtheria toxin receptor (CD11cDTR) transgenic mice were treated with diphtheria toxin (DT) or phosphate buffered saline (PBS) during serum transfer arthritis (STA) and human tumour necrosis factor transgenic (hTNFtg) arthritis and scored clinically and histologically. We measured cytokines in synovitis by quantitative polymerase chain reaction (qPCR). We performed ovariectomy in CD11cDTR mice treated with PBS or DT. We analysed CD11cDTR, CD11c-Cre/CX3CR1-STOP-DTR and Zbtb46-DTR-treated mice with DT using histomorphometry and OC of CD11c and Zbtb46 fate reporter mice by fluorescent imaging. We sorted murine and human OC precursors and stimulated them with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL) to generate OCs. RESULTS: Targeting CD11c+ cells in vivo in models of inflammatory arthritis (STA and hTNFtg) ameliorates arthritis by reducing inflammatory bone destruction and OC generation. Targeting CD11c-expressing cells in unchallenged mice removes all OCs in their long bones. OCs do not seem to be derived from CD11c+ cells expressing CX3CR1+, but from Zbtb46+conventional dendritic cells (cDCs) as all OCs in Zbtb46-Tomato fate reporter mice are Tomato+. In line, administration of DT in Zbtb46-DTR mice depletes all OCs in long bones. Finally, human CD1c-expressing cDCs readily differentiated into bone resorbing OCs. CONCLUSION: Taken together, we identify DCs as important OC precursors in bone homeostasis and inflammation, which might open new avenues for therapeutic interventions in OC-mediated diseases.

Amino Acids Fueling Fibroblast-Like Synoviocyte Activation and Arthritis By Regulating Chemokine Expression and Leukocyte Migration.

OBJECTIVE: We analyzed the impact of amino acid (AA) availability on the inflammatory response in arthritis. METHODS: We stimulated rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLSs) with tumor necrosis factor (TNF) in the presence or absence of proteinogenic AAs and measured their response by QuantSeq 3' messenger RNA sequencing, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay. Signal transduction events were determined by Western blot. We performed K/BxN serum transfer arthritis in mice receiving a normal and a low-protein diet and analyzed arthritis clinically and histologically. RESULTS: Deprivation of AAs decreased the expression of a specific subset of genes, including the chemokines CXCL10, CCL2, and CCL5 in TNF-stimulated FLSs. Mechanistically, the presence of AAs was required for the TNF-induced activation of an interferon regulatory factor 1 (IRF1)-STAT1 signaling circuit that drives the expression of chemotactic factors. The expression of IRF1 and the IRF1-dependent gene set in FLSs was highly correlated with the presence of inflammatory cells in human RA, emphasizing the important role of this AA-dependent pathway in inflammatory cell recruitment to the synovial tissue. Finally, we show that mice receiving a low-protein diet expressed less IRF1 in the inflamed synovium and consequently developed reduced clinical and histologic signs of arthritis. CONCLUSION: AA deprivation reduces the severity of arthritis by suppressing the expression of IRF1-STAT1-driven chemokines, which are crucial for leukocyte recruitment to the arthritic joint. Overall, our study provides novel insights into critical determinants of inflammatory arthritis and may pave the way for dietary intervention trials in RA.

Pharmacological targets at the lysosomal autophagy-NLRP3 inflammasome crossroads.

Many aspects of cell homeostasis and integrity are maintained by the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome. The NLRP3 oligomeric protein complex assembles in response to exogenous and endogenous danger signals. This inflammasome has also been implicated in the pathogenesis of a range of disease conditions, particularly chronic inflammatory diseases. Given that NLRP3 modulates autophagy, which is also a key regulator of inflammasome activity, excessive inflammation may be controlled by targeting this intersecting pathway. However, specific niche areas of NLRP3-autophagy interactions and their reciprocal regulatory mechanisms remain underexplored. Consequently, we lack treatment methods specifically targeting this pivotal axis. Here, we discuss the potential of such strategies in the context of autoimmune and metabolic diseases and propose some research avenues.

Measuring the transcriptome-wide effects of aging on murine adipocytes using RNAseq.

Adipose tissue plays a central role in age-related diseases. While RNAseq protocols exist for many tissues, few data have been generated with this technology to explore gene expression in adipocytes, particularly during aging. Here, we present a protocol to analyze the transcriptional changes that occur in adipose tissue during normal and accelerated aging in mouse models. We describe steps for genotyping, diet control, euthanasia, and dissection. We then detail RNA purification and genome-wide data generation and analysis. For complete details on the use and execution of this protocol, please refer to De Cauwer et al. (2022) iScience. Sep 16;25(10):105149.

Effects of the omega-3 fatty acid DHA on histone and p53 acetylation in diffuse large B cell lymphoma.

Diffuse large B cell lymphoma (DLBCL) often develops resistance and/or relapses in response to immunochemotherapy. Epigenetic modifiers are frequently mutated in DLBCL, i.e., the lysine (histone) acetyltransferases CREBBP and EP300. Mutations in CBP/p300 can prevent the proper acetylation and activation of (i) enhancer sequences of genes required for essential functions (e.g., germinal center exit and differentiation) and (ii) the tumor suppressor p53. Based on evidence that omega-3 fatty acids (ω-3 FAs) affect histone acetylation in various cancers, we investigated whether ω-3 FA docosahexaenoic acid (DHA) could modify levels of histone and p53 acetylation in three DLBCL cell lines (at different CREBBP/EP300 mutational status) versus normal B cells. Exposure to DHA at clinically attainable doses was shown to significantly alter the genome-wide levels of histone posttranslational modifications in a cell-line-dependent and dose-dependent manner. Although histone acetylation did not increase uniformly, as initially expected, levels of p53 acetylation increased consistently. Quantitative reverse transcription polymerase chain reaction results revealed significant changes in expression of multiple genes, including increased expression of CREBBP and of PRDM1 (required for differentiation into plasma cells or memory B cells). Taken together, our results provide (to our knowledge) the first characterization of the epigenetic effects of ω-3 FAs in DLBCL.

The Therapeutic Effect of Phosphopeptide P140 Attenuates Inflammation Induced by Uric Acid Crystals in Gout Arthritis Mouse Model.

Gout is a painful form of inflammatory arthritis characterized by the deposition of monosodium urate (MSU) crystals in the joints. The aim of this study was to investigate the effect of peptide P140 on the inflammatory responses in crystal-induced mouse models of gout and cell models including MSU-treated human cells. Injection of MSU crystals into the knee joint of mice induced neutrophil influx and inflammatory hypernociception. Injection of MSU crystals subcutaneously into the hind paw induced edema and increased pro-inflammatory cytokines levels. Treatment with P140 effectively reduced hypernociception, the neutrophil influx, and pro-inflammatory cytokine levels in these experimental models. Furthermore, P140 modulated neutrophils chemotaxis in vitro and increased apoptosis pathways through augmented caspase 3 activity and reduced NFκB phosphorylation. Moreover, P140 increased the production of the pro-resolving mediator annexin A1 and decreased the expression of the autophagy-related ATG5-ATG12 complex and HSPA8 chaperone protein. Overall, these findings suggest that P140 exerts a significant beneficial effect in a neutrophilic inflammation observed in the model of gout that can be of special interest in the design of new therapeutic strategies.

Dicer1 deficient mice exhibit premature aging and metabolic perturbations in adipocytes.

Age-related diseases are major concern in developed countries. To avoid disabilities that accompany increased lifespan, pharmaceutical approaches are considered. Therefore, appropriate animal models are required for a better understanding of aging processes and potential in vivo assays to evaluate the impact of molecules that may delay the occurrence of age-related diseases. Few mouse models exhibiting pathological aging exist, but currently, none of them reproducibly mimics human diseases like osteoporosis, cognitive dysfunctions or sarcopenia that can be seen in some, but not all, elders. Here, we describe the premature aging phenotypes of Dicer-deficient mature animals, which exhibit an overall deterioration of many organs and tissues (skin, heart, and adipose tissue) ultimately leading to a significant reduction of their lifespan. Molecular characterization of transcriptional responses focused on the adipose tissue suggested that both canonical and non-canonical functions of DICER are involved in this process and highlight potential actionable pathways to revert it.

Contrasting role of NLRP12 in autoinflammation: evidence from a case report and mouse models.

OBJECTIVE: To explore at the molecular level the phenotype of a patient suffering an autoinflammatory syndrome which was diagnosed as familial cold autoinflammatory syndrome type 2 (FCAS-2). To explore the functions of Nlrp12 in inflammation using mouse models. METHODS: Whole exome sequencing and Nlrp12 targeted resequencing were performed on DNA isolated from the patient and her family members. In vivo and ex vivo models of inflammation (urate crystals-dependent acute joint inflammation and urate crystals-induced peritonitis) were analysed in Nlrp12-deficient and Nlrp12-competent mice. RESULTS: A rare missense NLRP12 variant (c.857C>T, p.P286L) was identified in the patient and her healthy relatives. Nlrp12-deficient mice exhibit reduced systemic inflammation and neutrophilic infiltration. CONCLUSION: Nlrp12 mediates proinflammatory functions in mice. In humans, the identification of Nlrp12 variants must be cautiously interpreted depending on clinical and paraclinical data to diagnose FCAS-2.

Where Epigenetics Meets Food Intake: Their Interaction in the Development/Severity of Gout and Therapeutic Perspectives.

Gout is the most frequent form of inflammatory arthritis in the world. Its prevalence is particularly elevated in specific geographical areas such as in the Oceania/Pacific region and is rising in the US, Europe, and Asia. Gout is a severe and painful disease, in which co-morbidities are responsible for a significant reduction in life expectancy. However, gout patients remain ostracized because the disease is still considered "self-inflicted", as a result of unhealthy lifestyle and excessive food and alcohol intake. While the etiology of gout flares is clearly associated with the presence of monosodium urate (MSU) crystal deposits, several major questions remain unanswered, such as the relationships between diet, hyperuricemia and gout flares or the mechanisms by which urate induces inflammation. Recent advances have identified gene variants associated with gout incidence. Nevertheless, genetic origins of gout combined to diet-related possible uric acid overproduction account for the symptoms in only a minor portion of patients. Hence, additional factors must be at play. Here, we review the impact of epigenetic mechanisms in which nutrients (such as ω-3 polyunsaturated fatty acids) and/or dietary-derived metabolites (like urate) trigger anti/pro-inflammatory responses that may participate in gout pathogenesis and severity. We propose that simple dietary regimens may be beneficial to complement therapeutic management or contribute to the prevention of flares in gout patients.

Crosstalk between Interleukin-1ß and Type I Interferons Signaling in Autoinflammatory Diseases.

Interleukin-1ß (IL-1ß) and type I interferons (IFNs) are major cytokines involved in autoinflammatory/autoimmune diseases. Separately, the overproduction of each of these cytokines is well described and constitutes the hallmark of inflammasomopathies and interferonopathies, respectively. While their interaction and the crosstalk between their downstream signaling pathways has been mostly investigated in the frame of infectious diseases, little information on their interconnection is still available in the context of autoinflammation promoted by sterile triggers. In this review, we will examine the respective roles of IL-1ß and type I IFNs in autoinflammatory/rheumatic diseases and analyze their potential connections in the pathophysiology of some of these diseases, which could reveal novel therapeutic opportunities.

Epigenetic Reprogramming Mediated by Maternal Diet Rich in Omega-3 Fatty Acids Protects From Breast Cancer Development in F1 Offspring.

Diets rich in omega-3 fatty acids (FA) have been associated with lowered risks of developing certain types of cancers. We earlier reported that in transgenic mice prone to develop breast cancer (BCa), a diet supplemented with canola oil, rich in omega-3-rich FA (as opposed to an omega-6-rich diet containing corn oil), reduced the risk of developing BCa, and also significantly reduced the incidence of BCa in F1 offspring. To investigate the underlying mechanisms of the cancer protective effect of canola oil in the F1 generation, we designed and performed the present study with the same diets using BALB/c mice to remove any possible effect of the transgene. First, we observed epigenetic changes at the genome-wide scale in F1 offspring of mothers fed diets containing omega-3 FAs, including a significant increase in acetylation of H3K18 histone mark and a decrease in H3K4me2 mark on nucleosomes around transcription start sites. These epigenetic modifications contribute to differential gene expressions associated with various pathways and molecular mechanisms involved in preventing cancer development, including p53 pathway, G2M checkpoint, DNA repair, inflammatory response, and apoptosis. When offspring mice were exposed to 7,12-Dimethylbenz(a)anthracene (DMBA), the group of mice exposed to a canola oil (with omega 3 FAs)-rich maternal diet showed delayed mortality, increased survival, reduced lateral tumor growth, and smaller tumor size. Remarkably, various genes, including BRCA genes, appear to be epigenetically re-programmed to poise genes to be ready for a rapid transcriptional activation due to the canola oil-rich maternal diet. This ability to respond rapidly due to epigenetic potentiation appeared to contribute to and promote protection against breast cancer after carcinogen exposure.

A Translational Investigation of IFN-α and STAT1 Signaling in Endothelial Cells during Septic Shock Provides Therapeutic Perspectives.

Septic shock and disseminated intravascular coagulation (DIC) are known to be characterized by an endothelial cell dysfunction. The molecular mechanisms underlying this relationship are, however, poorly understood. In this work, we aimed to investigate human circulating IFN-α in patients with septic shock-induced DIC and tested the potential role of endothelial Stat1 (signal transducer and activator of transcription 1) as a therapeutic target in a mouse model of sepsis. For this, circulating type I, type II, and type III IFNs and procoagulant microvesicles were quantified in a prospective cohort of patients with septic shock. Next, we used a septic shock model induced by cecal ligation and puncture in wild-type mice, in Ifnar1 (type I IFN receptor subunit 1)-knockout mice, and in Stat1 conditional knockout mice. In human samples, we observed higher concentrations of circulating IFN-α and IFN-α1 in patients with DIC compared with patients without DIC, whereas concentrations of IFN-ß, IFN-γ, IFN-λ1, IFN-λ2, and IFN-λ3 were not different. IFN-α concentration was positively correlated with CD105 microvesicle concentrations, reflecting endothelial injury. In Ifnar1-/- mice, cecal ligation and puncture did not induce septic shock and was characterized by lesser endothelial cell injury, with lower aortic inflammatory cytokine expression, endothelial inflammatory-related gene expression, and fibrinolysis. In mice in which Stat1 was specifically ablated in endothelial cells, a marked protection against sepsis was also observed, suggesting the relevance of an endothelium-targeted strategy. Our work highlights the key roles of type I IFNs as pathogenic players in septic shock-induced DIC and the potential pertinence of endothelial STAT1 as a therapeutic target.

Aryl hydrocarbon receptor (Ahr)-dependent Il-22 expression by type 3 innate lymphoid cells control of acute joint inflammation.

The aryl hydrocarbon receptor (AHR) controls several inflammatory and metabolic pathways involved in various diseases, including the development of arthritis. Here, we investigated the role of AHR activation in IL-22-dependent acute arthritis using the K/BxN serum transfer model. We observed an overall reduction of cytokine expression in Ahr-deficient mice, along with decreased signs of joint inflammation. Conversely, we report worsened arthritis symptoms in Il-22 deficient mice. Pharmacological stimulation of AHR with the agonist VAG539, as well as injection of recombinant IL-22, given prior arthritogenic triggering, attenuated inflammation and reduced joint destruction. The protective effect of VAG539 was abrogated in Il-22 deficient mice. Finally, conditional Ahr depletion of Rorc-expressing cells was sufficient to attenuate arthritis, thereby uncovering a previously unsuspected role of AHR in type 3 innate lymphoid cells during acute arthritis.

NKG2D ligands in inflammatory joint diseases: analysis in human samples and mouse models.

OBJECTIVES: NKG2D ligands (NKG2DLs) are stress-inducible molecules involved in multiple inflammatory settings. In this work, we quantified MICA, an NKG2DL, in the synovial fluid of patients suffering various arthritides and measured Nkg2dLs gene expression in murine models of acute joint inflammation. METHODS: Soluble MICA (sMICA) was quantified by ELISA is synovial fluids harvested from patients suffering osteoarthritis, rheumatoid arthritis, psoriatic arthritis, calcium pyrophosphate crystal arthritis, urate crystal arthritis and reactive arthritis. Transcripts encoding murine NKG2DLs were quantified by RT-qPCR in the joints of mouse models of rheumatoid arthritis, urate crystal arthritis and osteoarthritis. RESULTS: Marked overproduction of sMICA was observed in the synovial fluid of RA patients. Mouse studies highlighted the complex transcriptional regulation of Nkg2d ligands encoding genes depending on the inflammatory setting and microenvironment CONCLUSIONS: sMICA quantification could be an interesting biomarker to identify acute inflammation in RA patients in whom classical markers (i.e. anti-citrullinated protein antibodies, ACPA) are undetectable.

Genetic and epigenetic determinants of diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma and is notorious for its heterogeneity, aggressive nature, and the frequent development of resistance and/or relapse after treatment with standard chemotherapy. To address these problems, a strong emphasis has been placed on researching the molecular origins and mechanisms of DLBCL to develop effective treatments. One of the major insights produced by such research is that DLBCL almost always stems from genetic damage that occurs during the germinal center (GC) reaction, which is required for the production of high-affinity antibodies. Indeed, there is significant overlap between the mechanisms that govern the GC reaction and those that drive the progression of DLBCL. A second important insight is that some of the most frequent genetic mutations that occur in DLBCL are those related to chromatin and epigenetics, especially those related to proteins that "write" histone post-translational modifications (PTMs). Mutation or deletion of these epigenetic writers often renders cells unable to epigenetically "switch on" critical gene sets that are required to exit the GC reaction, differentiate, repair DNA, and other essential cellular functions. Failure to activate these genes locks cells into a genotoxic state that is conducive to oncogenesis and/or relapse.

JAK-STAT Targeting Offers Novel Therapeutic Opportunities in Sepsis.

Sepsis is a life-threatening condition caused by exaggerated host responses to infections taking place in two phases: (i) a systemic (hyper)inflammatory response syndrome (SIRS), participating in multiple organ failure (MOF), a major complication of septic shock, followed by (ii) a compensatory anti-inflammatory response syndrome (CARS), leading to sepsis-induced immunosuppression and resulting in late infections and long-term mortality. The Janus kinase-signal transducer and activator of transcription (JAK-STAT)-dependent signaling pathway is involved in both manifestations, hence playing a key role during sepsis. It is also involved in emergency myelopoiesis, which participates in host defense. The aim of this review is to highlight and refine the recent implications of this signaling pathway in sepsis and illustrate why its central position makes it a potential biomarker and therapeutic target.