The C-type lectin receptor Mincle is functionally expressed by murine bone cells and can mediate inflammatory responses to Staphylococcus aureus 2257334
Jul 2026· Journal of Immunology· Vol 215· 0 citations
TL;DR
It is shown that bone cells functionally express Mincle and indicated that this C-type lectin can mediate, at least in part, the inflammatory responses of OBs to SA challenge, which are attenuated following Mincle blockade.
Abstract
It is now apparent that osteoblasts (OBs) and osteoclasts (OCs) have immune functions that play a critical role in shaping host responses and the abnormal bone remodeling associated with Staphylococcus aureus (SA) infection. Both express pattern recognition receptors (PRR) to perceive pathogens and initiate the production of mediators that can exacerbate inflammatory bone loss. Macrophage-inducible C-type lectin (Mincle) is a tyrosine activation motif—coupled PRR for microbial glycolipids that has been suggested to play an important role in host responses against Gram positive bacteria in the lungs. However, the ability of Mincle to serve a similar function in bone tissue has not been investigated.
RNA sequence analysis was used to assess changes in the transcriptome of murine bone marrow-derived OCs and primary OBs following SA challenge. Additionally, bone cells were either treated with a Mincle-neutralizing antibody, an isotype control antibody, or were left untreated, prior to being stimulated with Mincle-specific ligands or SA infection. Cell supernatants and whole cell protein lysates were subsequently collected to quantify changes in the production of immune mediators by immunoblot analysis and ELISA.
RNA Tag-Seq analysis of SA infected OCs and OBs revealed elevated expression of mRNA encoding Mincle and its key downstream signaling components. We found robust levels of Mincle protein in murine OCs and OBs and demonstrated the inducible expression of this molecule in human OBs. The functional nature of Mincle expression by OCs and OBs was confirmed by the ability of Mincle agonists to elicit inflammatory cytokine production. Importantly, we showed that such responses to SA are attenuated following Mincle blockade.
These studies show that bone cells functionally express Mincle and indicate that this C-type lectin can mediate, at least in part, the inflammatory responses of OBs to SA challenge.
NIAID R01AI170012
Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)
It is found that fibroblast recognition of interleukin-1 is essential for immune response and fibroblasts actively participate in innate immunity and highlight an IL-1R1–dependent keratinocyte-fibroblast-neutrophil axis of communication.
Jared Simmons, T. Nakatsuji, Fengwu Li et al.· Science Advances· 0 citations
A novel function of Ecb is revealed, the activation of basophils to produce IL-4 in an IgE-independent manner, and a dual Ecb contribution to immune evasion-by interfering with complement activation and skewing Th2 immunity-and a role in the development of allergic inflammation-by inducing IL-4 production is suggested.
Haruka Sakakibara, Shion Kamada, Rikuto Iwata et al.· Microbiology and immunology· 0 citations
BACKGROUND
Toll-like receptor 4 (TLR4) activation within the bone marrow (BM) microenvironment regulates proinflammatory cytokines and chemokines, which influence immune activity and bone remodeling. However, the immune cell factors mediating TLR4-dependent cross-talk in the bone/BM microenvironment remain insufficiently defined.
METHODS
We provide a transcriptomic analysis of significant cellular and immune changes in total BM cells of wild-type mice following lipopolysaccharide (LPS)-induced TLR4 activation in vivo compared with TLR4 knockout (KO) mice. To obtain direct evidence that interleukin (IL)-22 contributes to TLR4-driven bone destruction, we analyzed their bone phenotypes following LPS injection into IL-22 KO mice. In addition, co-culture of pre-osteoblasts (OBs) and BM cells was conducted to evaluate the effect of IL-22 in osteoclast (OC) formation in a pre-OB-dependent manner.
RESULTS
Differentially expressed gene analysis from BM cells of wild-type (WT) mice revealed an increase in IL-22-producing cells, along with increased IL-22 production in a TLR4-dependent manner. Flow cytometry confirmed that LPS enhanced the number of CD4+IL-22+ cells in the BM and decreased in TLR4-deficient BM. LPS also enhanced the differentiation of CD4+IL-22+ T cells and promoted IL-22 induction in T cells. IL-22 KO mice showed minimal LPS-induced bone loss, whereas WT mice exhibited severe bone destruction with increased formation of tartrate-resistant acid phosphatase-positive OCs. Interestingly, while IL-22 did not directly affect OC differentiation, IL-22 enhanced OC differentiation only when BM cells were co-cultured with pre-OBs through the elevation of the receptor activator of nuclear factor-κB ligand (RANKL) in pre-OBs during osteogenesis. Mechanistically, IL-22 induced cyclooxygenase-2 in pre-OBs through extracellular signal-regulated kinase and p38 signaling, driving prostaglandin E2 production and subsequent RANKL induction.
CONCLUSIONS
TLR4 activation enhanced IL-22 production in T cells, which stimulates RANKL production in pre-OBs to further induce OC formation. These results support that IL-22 acts as a TLR4-driven mediator to shift bone remodeling toward catabolic bone degeneration.
Ji-Eun Kim, Jinyoung Go, Eun-Jin Lee et al.· Cellular & Molecular Biology...· 0 citations
Lymphocytes play a central role in adaptive immunity and represent the primary source of RANKL in periodontitis. Understanding their organization and activation within gingiva is therefore essential. This study investigates the role of tertiary lymphoid structures (TLSs), ectopic lymphoid aggregates that orchestrate local immune responses. Using multiplex immunohistochemistry staining, we found that TLSs form and mature with increasing inflammatory severity. These structures function as hubs for B cell activation and were associated with poorer surgical outcomes. Given the known role of fibroblasts in initiating TLS assembly, we explored the underlying mechanism. Using single-cell RNA sequencing and in vitro assays, we identified that oral pathogens activate the IFN-I–IRF7 axis in gingival fibroblasts, leading to overproduction of IFNβ and driving their differentiation into a CXCL13-producing subtype that facilitates TLS organization. Furthermore, in a mouse periodontitis model, we demonstrated that activated IgD+CD80+ B cells within TLSs promote osteoclastogenesis and bone resorption via RANKL secretion. Therapeutically, inhibition of IFN-I signaling disrupted this pathogenic cascade by suppressing TLS formation and subsequent RANKL production, thereby mitigating periodontitis bone loss. In conclusion, our findings establish TLSs as pathological hubs that coordinate B cell-mediated bone destruction in periodontitis and highlight the IFN-I signaling pathway as a promising target for therapeutic intervention.
Jiawei Lu, Xiao Wu, Zehui Xiong et al.· International Journal of Ora...· 0 citations
Macrophages in bone possess a unique bi-potential capacity. Different from their primary roles in inflammation and immunity, these cells can differentiate into bone-resorbing osteoclasts. However, it remains unclear how macrophages determine which function to engage in bone, especially when exposed to the same stimulus, such as TNF, which can drive both pathways. Understanding these mechanisms is particularly important in inflammatory bone diseases, such as rheumatoid arthritis, where inflammation and bone resorption are hallmarks. Here, we identified an RBP-J–Hs2st1–2-O-sulfated heparan sulfate (HS)–IFNβ dependent molecular network that acts as a gatekeeper balancing macrophage fate inclinations in response to TNF. This network integrates cellular outside-in, inside-out, and relayed outside-in pathways. RBP-J deficiency in macrophages shifts TNF action from inflammatory regulation to osteoclastogenesis. Hs2st1, the exclusive biosynthetic enzyme for 2-O sulfation of HS, is a key target suppressed by RBP-J. Loss of Hs2st1 significantly reduces inflammatory osteoclastogenesis and arthritic bone erosion without affecting physiological bone mass. Elevated Hs2st1 expression and 2-O sulfation shift macrophages toward an osteoclastogenic fate, and vice versa. We further identified residues in IFNβ that are responsible for binding HS. Mutation of these sites diminished HS binding, augmented type I IFN response, and more strongly suppressed osteoclastogenesis. Our findings reveal a previously unrecognized molecular program fine-tuning macrophage fate and function, and highlight potential therapeutic strategies for inflammatory diseases with bone defects.
The impact of the systemic commensal microbiome on the lung microenvironment and alveolar macrophage (AM) polarization is largely unexplored. We find that AMs from mice lacking commensal microbiota (germ-fee) have heightened inflammatory function and that this is coincident with a reduction in IGF-1 protein in the germ-free lungs. The IGF-1 receptor gene (Igf1r) is highly expressed in alveolar epithelial cells (AECs), which are critical for mediating AM anti-inflammatory programming.
To define how microbe-dependent IGF-1 shapes AM function, we generated two lines of conditional knockout mice that are Igf1rfl/fl, and with either LysMCre for the conditional deletion in myeloid cells, or Nkx2.1Cre for the conditional deletion in AECs. For both steady-state and after LPS stimulation, AMs from these mice were phenotypically evaluated by flow cytometry and assessed for functional capability such as cytokine secretion and phagocytosis. We also performed RNAseq analysis of AMs isolated from Igf1r deficient mice and germ-free mice.
We find that IGF1R deficiency in AECs largely recapitulates AM phenotypes overserved in germ-free mice, with increased phagocytic capacity and enhanced inflammatory cytokine production in response to microbial stimuli. RNAseq analysis of germ-free AMs revealed 1639 differentially expressed genes, and protein interaction networks allowed us to identify a microbiota-dependent subnetwork of transcription factors including CEBPβ, PU.1, and Smad3. We are analyzing RNAseq from Igf1r deficient mice to identify AM programs regulated by IGF-1-dependent transcription factors.
Next steps include spatial transcriptomics analysis of lungs from conditional Igf1r knockout mice to interrogate IGF-1 dependent AM-AEC crosstalk via ligand-receptor analysis and gene regulatory networks. This work will determine how microbiota-dependent IGF-1 stabilizes cell-cell communication to support lung homeostasis and regulate inflammation.
n/a
Mucosal and Regional Immunology (MUC)
Sonia M. Kruszelnicki, Devon Colby, Kay Bajpai et al.· Journal of Immunology· 0 citations
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