Project description:To screen for altered gene expression during osteoclastogenesis, BMM cells depleted of TMBIM6 with or without RANKL were subjected to gene expression profiling.
Project description:Osteoclastogenesis is an essential process during bone metabolism which can also be promoted by inflammatory signals. Thrombomodulin (TM), a transmembrane glycoprotein, exerts anti-inflammatory activities such as neutralization of proinflammatory high-mobility group box 1 (HMGB1) through TM lectin-like domain. This study aimed to identify the role of myeloid TM (i.e., endogenous TM expression on the myeloid lineage) in osteoclastogenesis and inflammatory bone loss. Using human peripheral blood mononuclear cells and mouse bone marrow-derived macrophages, we observed that the protein levels of TM were dramatically reduced as these cells differentiated into osteoclasts. In addition, osteoclastogenesis and extracellular HMGB1 accumulation were enhanced in primary cultured monocytes from myeloid-specific TM-deficient mice (LysMcre/TM(flox/flox)) and from TM lectin-like domain deleted mice (TM(LeD/LeD)) compared with their respective controls. Micro-computerized tomography scans showed that ovariectomy-induced bone loss was more pronounced in TM(LeD/LeD) mice compared with controls. Finally, the inhibiting effects of recombinant TM lectin-like domain (rTMD1) on bone resorption in vitro, and bone loss in both the ovariectomized model and collagen antibody-induced arthritis model has been detected. These findings suggested that the myeloid TM lectin-like domain may inhibit osteoclastogenesis by reducing HMGB1 signaling, and rTMD1 may hold therapeutic potential for inflammatory bone loss.
Project description:Training and priming of innate immune cells involve preconditioning by PAMPs, DAMPs and/or cytokines that elicits stronger induction of inflammatory genes upon secondary challenge. Previous models distinguish training and priming based upon whether immune activation returns to baseline prior to secondary challenge. Tolerance is a protective mechanism whereby potent stimuli induce refractoriness to secondary challenge. Training and priming are important for innate memory responses that protect against infection, efficacy of vaccines, and maintaining innate immune cells in a state of readiness; tolerance prevents toxicity from excessive immune activation. Dysregulation of these processes can contribute to pathogenesis of autoimmune/inflammatory conditions, post-COVID-19 hyperinflammatory states, or sepsis- associated immunoparalysis. Training, priming and tolerance regulate similar ‘signature’ inflammatory genes such as TNF, IL6 and IL1B and utilize overlapping epigenetic mechanisms. We review how interferons (IFNs), best known for activating Jak-STAT signaling and interferon- stimulated genes, also play a key role regulating training, priming and tolerance via chromatin- mediated mechanisms. We present new data on how monocyte-to-macrophage differentiation modulates IFN-g-mediated priming, changes AP-1 and CEBP activity, and attenuates superinduction of inflammatory genes. We present a ‘training-priming continuum’ model that integrates IFN-mediated priming into current concepts about training and tolerance and proposes a central role for STAT1 and IRF1.
Project description:Training and priming of innate immune cells involve preconditioning by PAMPs, DAMPs and/or cytokines that elicits stronger induction of inflammatory genes upon secondary challenge. Previous models distinguish training and priming based upon whether immune activation returns to baseline prior to secondary challenge. Tolerance is a protective mechanism whereby potent stimuli induce refractoriness to secondary challenge. Training and priming are important for innate memory responses that protect against infection, efficacy of vaccines, and maintaining innate immune cells in a state of readiness; tolerance prevents toxicity from excessive immune activation. Dysregulation of these processes can contribute to pathogenesis of autoimmune/inflammatory conditions, post-COVID-19 hyperinflammatory states, or sepsis- associated immunoparalysis. Training, priming and tolerance regulate similar ‘signature’ inflammatory genes such as TNF, IL6 and IL1B and utilize overlapping epigenetic mechanisms. We review how interferons (IFNs), best known for activating Jak-STAT signaling and interferon- stimulated genes, also play a key role regulating training, priming and tolerance via chromatin- mediated mechanisms. We present new data on how monocyte-to-macrophage differentiation modulates IFN-g-mediated priming, changes AP-1 and CEBP activity, and attenuates superinduction of inflammatory genes. We present a ‘training-priming continuum’ model that integrates IFN-mediated priming into current concepts about training and tolerance and proposes a central role for STAT1 and IRF1.
Project description:TNF plays a key role in inflammation and bone resorption. However, the mechanisms regulating TNF-mediated osteoclastogenesis remain largely unclear because its direct osteoclastogenic ability is weak. Here, we found that TGFβ priming enables TNF to effectively induce osteoclastogenesis from macrophages, independently of the osteoclastogenic action of RANKL. Lack of TGFβ signaling in macrophages suppresses inflammatory, but not physiological, osteoclastogenesis and bone resorption in vivo. Mechanistically, TGFβ priming reprograms macrophage response to TNF towards osteoclastogenesis by remodeling chromatin accessibility and histone modification. TGFβ and TNF induce an unconventional osteoclastogenic program, which includes the suppression of the TNF-induced IRF1-IFNβ-IFN stimulated gene (ISG) axis, promotion of IRF8 degradation and B-Myb induction. These mechanisms are present in RA, in which TGFβ level is elevated and correlated with osteoclast activity. Our findings identify a function and mechanism of action for TGFβ in TNF-mediated inflammatory osteoclastogenesis, and open avenues for selective treatment of inflammatory bone loss.
Project description:TNF plays a key role in inflammation and bone resorption. However, the mechanisms regulating TNF-mediated osteoclastogenesis remain largely unclear because its direct osteoclastogenic ability is weak. Here, we found that TGFβ priming enables TNF to effectively induce osteoclastogenesis from macrophages, independently of the osteoclastogenic action of RANKL. Lack of TGFβ signaling in macrophages suppresses inflammatory, but not physiological, osteoclastogenesis and bone resorption in vivo. Mechanistically, TGFβ priming reprograms macrophage response to TNF towards osteoclastogenesis by remodeling chromatin accessibility and histone modification. TGFβ and TNF induce an unconventional osteoclastogenic program, which includes the suppression of the TNF-induced IRF1-IFNβ-IFN stimulated gene (ISG) axis, promotion of IRF8 degradation and B-Myb induction. These mechanisms are present in RA, in which TGFβ level is elevated and correlated with osteoclast activity. Our findings identify a function and mechanism of action for TGFβ in TNF-mediated inflammatory osteoclastogenesis, and open avenues for selective treatment of inflammatory bone loss.
Project description:TNF plays a key role in inflammation and bone resorption. However, the mechanisms regulating TNF-mediated osteoclastogenesis remain largely unclear because its direct osteoclastogenic ability is weak. Here, we found that TGFβ priming enables TNF to effectively induce osteoclastogenesis from macrophages, independently of the osteoclastogenic action of RANKL. Lack of TGFβ signaling in macrophages suppresses inflammatory, but not physiological, osteoclastogenesis and bone resorption in vivo. Mechanistically, TGFβ priming reprograms macrophage response to TNF towards osteoclastogenesis by remodeling chromatin accessibility and histone modification. TGFβ and TNF induce an unconventional osteoclastogenic program, which includes the suppression of the TNF-induced IRF1-IFNβ-IFN stimulated gene (ISG) axis, promotion of IRF8 degradation and B-Myb induction. These mechanisms are present in RA, in which TGFβ level is elevated and correlated with osteoclast activity. Our findings identify a function and mechanism of action for TGFβ in TNF-mediated inflammatory osteoclastogenesis, and open avenues for selective treatment of inflammatory bone loss.
Project description:Under physiological conditions, osteoclasts (OCs) are generated from monocytic osteoprecursors under the stimulation of RANKL and M-CSF, requiring co-stimulatory signals from Fc receptor common γ chain (FcRγ) or DNAX-activated protein 12. It has been proposed that immune complexes (ICs) directly potentiate RANKL-mediated osteoclastogenesis by triggering FcγR-coupled Fcγ receptors (FcγRs), thereby linking IC accumulation and pathological osteolysis under various disease conditions. However, whether ICs possess pro-osteoclastogenic potential independent of RANKL is unknown. Here we demonstrate that IgG ICs alone can drive the differentiation of human blood monocytes into nonclassical OCs (NOCs) phenotypically and functionally distinguishable from RANKL-induced classical OCs (COCs). This novel noncanonical osteoclastogenesis pathway is triggered by full crosslinking of human FcγRIIa (hFcγRIIa), or co-ligation of hFcγRIIa and TLR4, and signals through the Src family kinase-STAT5 axis without inducing the expression of NFATc1, a master transcription factor for the previously described osteoclastogenesis pathways. Surprisingly, IgG ICs strongly overrule the generation of COCs driven by RANKL in vitro. More importantly, TRAP+ OCs found in the inflammatory joint tissues of hFcγRIIa-transgenic mice with collagen-induced arthritis bear the NFATc1- phenotype. Our results unmask the “double faces” of IgG ICs in health and disease, and suggest a novel and important pathway for ICs contributing to pathological bone erosion in inflammatory arthritis.