The correlation between the Th17/Treg cell balance and bone health

Regulatory T Cells promote osteogenic differentiation of periodontal ligament stem cells through the Jagged1-Notch2 signaling Axis

OBJECTIVES

This study aimed to elucidate the role of regulatory T cells (Tregs) in promoting the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) and to investigate the underlying mechanisms involving Notch signaling.

METHOD

Tregs were isolated via fluorescence-activated cell sorting (FACS) and co-cultured with PDLSCs. Osteogenic differentiation was assessed through in vitro assays and in vivo transplantation experiments. Gene expression profiles were quantified using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and Western blot analysis. A murine periodontitis model was used to validated therapeutic outcomes, with bone remodeling quantified by micro-CT and histology (H&E, Masson's staining). Immunophenotypic analysis of Jagged1 expression in Tregs and Notch2 receptor localization in PDLSCs were performed using flow cytometry and immunofluorescence microscopy, respectively. The role of immobilized Jagged1 in osteogenic differentiation was further evaluated, while Notch pathway inhibition was achieved via γ-secretase inhibitor DAPT in vitro.

RESULTS

Elevated levels of Th17 cells and Tregs were observed in peripheral blood samples from periodontitis patients, with a significantly increased Th17/Treg ratio (p < 0.01). In vitro, co-culturing Tregs with PDLSCs significantly enhanced PDLSC osteogenesis, as evidenced by increased ALP activity (p < 0.01), elevated expression of osteogenesis-related genes (Runx2 and Osterix; p < 0.01), and enhanced mineralization (Alizarin Red staining) (p < 0.01). In vivo, intravenous infusion of Tregs into a periodontitis mouse model reduced periodontal damage and promoted bone regeneration, as demonstrated by reduced CEJ-ABC distance and increased BV/TV ratio (p < 0.01). Mechanistically, Tregs expressed the Notch ligand Jagged1 and upregulated Notch2 receptor expression in PDLSCs, indicating activation of the Notch signaling pathway. Jagged1 promoted osteogenic differentiation of PDLSCs in a dose- and time-dependent manner. Inhibition of Notch signaling using DAPT reduced Tregs-mediated enhancement of PDLSC osteogenesis (p < 0.05).

CONCLUSION

These findings suggest that Tregs promote PDLSC osteogenic differentiation via Jagged1-Notch2 signaling, highlighting the therapeutic potential of modulating Tregs and Notch signaling for periodontal regeneration and bone tissue engineering.

CLINICAL SIGNIFICANCE

This study provides new insights into the complex interplay between immune modulation and stem cell differentiation, laying the foundation for potential Tregs-based therapeutic strategies for periodontal and bone tissue regeneration.

Osteogenesis imperfecta: exploring an autoimmune and immunotherapy perspective

Osteogenesis imperfecta (OI), also called brittle bone disease, is a genetic osteodysplasia characterized by a defect in type 1 collagen. Often diagnosed in infancy or early childhood, young patients are affected by frequent fractures. Osteogenesis imperfecta was first named almost 200 yr ago, yet there are still no FDA-approved treatments for OI, and existing treatments target only the skeletal defects of the disease. In this review, we briefly examine current treatments and ongoing clinical trials. Then, by analyzing OI with an osteoimmunological perspective, we have compiled evidence that OI has an autoimmune component. This autoimmune component of OI remains unconsidered, even though an immunology-based therapy has shown promise in treating OI. Acknowledging an autoimmune component of OI is critical to understanding its mechanisms and allowing for the development of more efficacious treatments and novel immunotherapies. Considering the existing literature and the growing impact of immunotherapeutic therapies in cancer and other autoimmune diseases, we believe it may be time to rethink the immune aspects of this genetic disorder and develop novel immunomodulating strategies to improve the quality of life for OI patients.

Progress of research on the gut microbiome and its metabolite short-chain fatty acids in postmenopausal osteoporosis: a literature review

Postmenopausal osteoporosis (PMOP) is a systemic metabolic bone disease caused by the decrease in estrogen levels after menopause. It leads to bone loss, microstructural damage, and an increased risk of fractures. Studies have found that the gut microbiota and its metabolites can regulate bone metabolism through the gut-bone axis and the gut-brain axis. As research progresses, PMOP has been found to be associated with gut microbiota dysbiosis and Th17/Treg imbalance. The gut microbiota is closely related to the development and differentiation of Treg and Th17 cells. Among them, the metabolites of the gut microbiota such as short-chain fatty acids (SCFAs) can regulate the differentiation of effector T cells by acting on molecular receptors on immune cells, thereby regulating the bone immune process. The multifaceted relationship among the gut microbiota, SCFAs, Th17/Treg cell-mediated bone immunity, and bone metabolism is eliciting attention from researchers. Through a review of existing literature, we have comprehensively summarized the effects of the gut microbiota and SCFAs on PMOP, especially from the perspective of Th17/Treg balance. Regulating this balance may provide new opportunities for PMOP treatment.

Gut Microbiota Modulation in Osteoporosis: Probiotics, Prebiotics, and Natural Compounds

Osteoporosis is a multifactorial bone metabolic disorder characterized by the deterioration of bone mass and microarchitecture, leading to increased fragility and fracture risk. Recent advances have revealed the critical role of the gut microbiota in the pathogenesis of osteoporosis, primarily mediated by metabolite-driven and immune-mediated interactions along the gut-bone axis. Dysbiosis, or microbial imbalance, can influence bone health by modulating host metabolism, immune function, and endocrine responses. While growing evidence suggests that gut microbiota modulation holds therapeutic potential for osteoporosis, the underlying mechanisms remain poorly understood. This review examines the latest findings on the role of prebiotics, probiotics, and natural bioactive substances in modulating the gut microbiota to improve bone health. We discuss how these interventions may restore microbial balance, enhance gut barrier function, and reduce systemic inflammation, thereby influencing bone metabolism. A deeper understanding of the gut-bone axis will pave the way for more targeted, effective, and personalized therapeutic strategies for osteoporosis prevention and treatment.

Modulation of the gut-bone axis: Lacticaseibacillus paracasei LC86 improves bone health via anti-inflammatory metabolic pathways in zebrafish models of osteoporosis and cartilage damage

Aim

Osteoporosis and cartilage injury are major health concerns with limited treatment options. This study investigates the therapeutic effects of Lacticaseibacillus paracasei LC86 (LC86) on osteoporosis and cartilage damage in a zebrafish (Danio rerio) model, focusing on its modulation of the gut-bone axis and its potential mechanisms for enhancing bone health.

Methods

A Dexamethasone-induced zebrafish model was used to mimic osteoporosis and cartilage injury. Zebrafish were divided into control, model, and LC86 treatment groups (3×107 CFU/mL). Bone and cartilage health were assessed using Alizarin red staining and fluorescence microscopy. Bone marker expression (sp7, runx2a, bmp2a, bmp4, and col2a1a) was quantified via qPCR. Metabolic alterations were analyzed using untargeted metabolomics, and changes in gut microbiota were examined through 16S rRNA gene sequencing.

Results

LC86 treatment significantly improved bone and cartilage health, as evidenced by increased fluorescence intensity in the skull, hard bone, and cartilage (p < 0.01, p < 0.05). qPCR results showed upregulation of key bone-related genes (sp7, runx2a, bmp2a, bmp4, and col2a1a), indicating enhanced bone and cartilage structure. Metabolomics analysis revealed alterations in over 300 metabolites, with changes in anti-inflammatory and energy pathways. Gut microbiota analysis demonstrated an increase in beneficial bacteria and a decrease in pathogenic genera.

Conclusions

LC86 significantly improved bone health, cartilage structure, and gut microbiota composition in a Dexamethasone-induced zebrafish model, supporting its potential as a therapeutic strategy for osteoporosis and cartilage injury via modulation of the gut-bone axis.

Nanomaterials-Based Drug Delivery Systems for Therapeutic Applications in Osteoporosis

The etiology of osteoporosis is rooted in the disruption of the intricate equilibrium between bone formation and bone resorption processes. Nevertheless, the conventional anti-osteoporotic medications and hormonal therapeutic regimens currently employed in clinical practice are associated with a multitude of adverse effects, thereby constraining their overall therapeutic efficacy and potential. Recently, nanomaterials have emerged as a promising alternative due to their minimal side effects, efficient drug delivery, and ability to enhance bone formation, aiding in restoring bone balance. This review delves into the fundamental principles of bone remodeling and the bone microenvironment, as well as current clinical treatment approaches for osteoporosis. It subsequently explores the research status of nanomaterial-based drug delivery systems for osteoporosis treatment, encompassing inorganic nanomaterials, organic nanomaterials, cell-mimicking carriers and exosomes mimics and emerging therapies targeting the osteoporosis microenvironment. Finally, the review discusses the potential of nanomedicine in treating osteoporosis and outlines the future trajectory of this burgeoning field. The aim is to provide a comprehensive reference for the application of nanomaterial-based drug delivery strategies in osteoporosis therapy, thereby fostering further advancements and innovations in this critical area of medical research.

Potential regulation of artesunate on bone metabolism through suppressing inflammatory infiltration in type 2 diabetes mellitus

OBJECTIVE

Osteoimmunology is an emerging field that explores the interplay between bone and the immune system. The immune system plays a critical role in the pathogenesis of diabetes and significantly affects bone homeostasis. Artesunate, a first-line treatment for malaria, is known for its low toxicity and multifunctional properties. Increasing evidence suggests that artesunate possesses anti-inflammatory, immunoregulatory, and osteogenic effects. This review aims to explore the relationship between immune regulation and bone metabolism in type 2 diabetes (T2DM) and to investigate the potential therapeutic application of artesunate.

METHODS

This review systematically examines literature from PubMed/Medline, Elsevier, Web of Science, Embase, the International Diabetes Federation, and other relevant databases.

RESULTS

This review synthesizes evidence from multiple sources to delineate the relationship between T lymphocytes and T2DM, the regulation of T lymphocyte subsets in bone metabolism, and the effects of artesunate on both T lymphocytes and bone metabolism. Recent studies suggest a bidirectional regulatory relationship between T2DM and T lymphocytes (CD4+ T and CD8+ T) during the onset and progression of the disease, with inflammatory and anti-inflammatory cytokines serving as key mediators. T lymphocyte subsets and their cytokines play a pivotal role in regulating osteogenesis and osteoclastogenesis in pathological conditions. Furthermore, artesunate has shown promise in modulating inflammatory infiltration and bone metabolism.

CONCLUSION

The accumulated evidence indicates that artesunate exerts regulatory effects on bone metabolism in T2DM by influencing T lymphocyte differentiation.

Microbial Influences on Calcium-Phosphorus Homeostasis and Metabolic Bone Diseases: A Bidirectional Mendelian Randomisation Study on the Gut-Bone Axis

Observational studies have shown that the gut microbiota (GM) is associated with bone diseases, particularly calcium-phosphorus metabolic bone diseases, demonstrating the existence of a gut-bone axis. However, whether these associations are causal effects remains to be determined. This study employed bidirectional two-sample Mendelian randomisation (MR) using summary data from Genome-Wide Association Studies (GWAS) of 211 gut microbial taxa and six metabolic bone diseases (osteoporosis, Osteopenia, osteonecrosis, osteomyelitis, hypoparathyroidism and hyperparathyroidism) to explore causal relationships and their directionality. Comprehensive sensitivity analyses were conducted to ensure the robustness of the results, and a false discovery rate-corrected pFDR of < 0.05 was used as a threshold to support strong associations. Additionally, co-localisation analysis was conducted to consolidate the findings. We identified 35 causal relationships between GM and metabolic bone diseases, with 17 exhibiting positive and 18 negative correlations. Furthermore, reverse MR analysis indicated that osteomyelitis was associated with elevated abundance of two GMs (pFDR < 0.05, PP.H4 < 75%). No evidence of horizontal pleiotropy or heterogeneity was observed, and co-localisation analysis further strengthened the evidence for these causal relationships. The study underscores the critical role of GM in influencing bone health through the gut-bone axis, paving the way for future therapeutic interventions targeting the gut-bone axis and offering new directions for research in bone metabolism and diseases.

Modulation of biomaterial-induced foreign body response by regulating the differentiation and migration of Treg cells through the CXCL12-CXCR4/7 axis

Tissue exposure to implanted biomaterials triggers a foreign body response (FBR), which is a stepwise immunological process involving innate immune cells and tissue repair cells. Although the regulatory T (Treg) cells play a crucial role in inflammation and tissue repair, their function in the process of FBR has not been well investigated. In this study, as titanium (Ti) exhibits better biocompatibility and induces milder FBR than polymethyl methacrylate (PMMA), we analyzed the characteristics of Treg cells during FBR caused by the two types of biomaterials. In a rat femur implantation model, we found that the number of Treg cells around titanium implants was much more than that in the PMMA-implanted group. Meanwhile, the expression of CXCR4 in tissues around Ti implants was significantly higher, and the expression of CXCR7 was lower. When co-cultured with biomaterials and macrophages, the differentiation and migration of Treg cells in the Ti-implanted group were promoted, and this effect could be modulated by CXCR4/7 inhibitors. Moreover, targeting CXCR4/7 influenced the amount of Treg cells in vivo and then reversed the FBR induced by PMMA or Ti implants. In summary, our findings revealed the role of CXCR4/CXCR7 in regulating the migration and differentiation of Treg cells during FBR and suggested that the CXCL12-CXCR4/CXCR7 axis may serve as a potential therapeutic target for immunomodulating foreign body response.

Grem1 inhibits osteogenic differentiation of MBMSCs in OVX rats through BMP/Smad1/5 signaling pathway

Objective

This study aims to explore how Grem1 regulates the differentiation and signaling activity of mandibular bone marrow mesenchymal stem cells (MBMSCs), affecting their osteogenic differentiation capacity and participating in the pathophysiological mechanism of postmenopausal mandibular osteoporosis.

Materials and methods

A postmenopausal osteoporosis (POP) rat model was constructed via bilateral ovariectomy. Techniques such as Western Blot (WB) and Real-Time Quantitative PCR (RT-qPCR) were employed to determine changes in Grem1 expression in MBMSCs of postmenopausal rats and its effect on osteogenic differentiation. Plasmids for Grem1 overexpression and siRNA for Grem1 knockdown were transfected into MBMSCs, and WB was used to assess the regulatory role of Grem1 on MBMSCs osteogenic differentiation.

Results

Grem1 expression was significantly elevated in the MBMSCs and mandibular tissues of POP rats, accompanied by inhibited osteogenic differentiation. Grem1 levels were inversely proportional to osteogenic capacity and BMP/Smad1/5 signaling activity. BMP-2 alleviated Grem1's inhibitory effects on the BMP/Smad1/5 pathway, influencing MBMSCs' osteogenic differentiation. Upregulating Grem1 in MBMSCs suppressed BMP/Smad1/5 pathway activity and osteogenic differentiation, while Grem1 knockdown restored these processes in the OVX group.

Conclusion

Grem1 reduces osteogenic capacity in mandibular POP rats by inhibiting the BMP/Smad1/5 signaling pathway. Targeting Grem1 or enhancing BMP/Smad1/5 signaling activity may improve mandibular bone health in osteoporosis patients.

T cell related osteoimmunology in fracture healing: Potential targets for augmenting bone regeneration

Last decade has witnessed increasing evidence which highlights the roles of immune cells in bone regeneration. Numerous immune cell types, including macrophages, T cells, and neutrophils are involved in fracture healing by orchestrating a series of events that modulate bone formation and remodeling. In this review, the role of T cell immunity in fracture healing has been summarized, and the modulatory effects of T cell immunity in inflammation, bone formation and remodeling have been highlighted. The review also summarizes the specific roles of different T cell subsets, including CD4+ T cells, CD8+ T cells, regulatory T cells, T helper 17 cells, and γδ T cells in modulating fracture healing. The current therapeutics targeting T cell immunity to enhance fracture healing have also been reviewed, aiming to provide insights from a translational standpoint. Overall, this work discusses recent advances and challenges in the interdisciplinary research field of T cell related osteoimmunology and its implications in fracture healing.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Delayed unions or non-unions of bone fractures remain a challenge in clinical practice. Developing a deep understanding of the roles of immune cells, including T cells, in fracture healing will facilitate the advancement of novel therapeutics of fracture nonunion. This review summarizes the current understanding of different T cell subsets involved in various phases of fracture healing, providing insights for targeting T cells as an alternative strategy to enhance bone regeneration.

Single-cell transcriptomics identify a novel macrophage population associated with bone invasion in pituitary neuroendocrine tumors

BACKGROUND

Bone-invasive Pituitary Neuroendocrine Tumors (BI PitNETs) epitomize an aggressive subtype of pituitary tumors characterized by bone invasion, culminating in extensive skull base bone destruction and fragmentation. This infiltration poses a significant surgical risk due to potential damage to vital nerves and arteries. However, the mechanisms underlying bone invasion caused by PitNETs remain elusive, and effective interventions for PitNET-induced bone invasion are lacking in clinical practice.

METHODS

In this study, we performed single-cell (n = 87,287) RNA sequencing on 10 cases of bone-invasive PitNETs and 5 cases of non-bone-invasion PitNETs (Non-BI PitNETs). We identified various cell types and determined their interactions through cell-cell communication analysis, which was further validated experimentally.

RESULTS

We identified a novel TNF-α+ TAM macrophage subset. BI PitNETs showed increased IL-34 secretion, impacting TNF-α+ TAMs via the IL34/CSF1R axis, leading to TNF-α production. TNF-α+ TAMs, in turn, communicate with CD14+ monocytes to promote their differentiation into osteoclasts and leading to bone invasion. In addition, we defined a gene signature for TNF-α+ TAM to guide the clinical prognosis prediction of BI PitNETs.

CONCLUSIONS

Our study elucidates the tumor microenvironment changes in bone invasion and identifies the critical role of TNF-α+ TAMs in promoting bone invasion of PitNETs, laying a foundation for developing new molecular markers or therapeutic agents targeting BI PitNETs.

The ultimate microbial composition for correcting Th17/Treg cell imbalance and lipid metabolism disorders in osteoporosis

Osteoporosis is a systemic bone disease characterised by decreased bone mass and a deteriorated bone microstructure, leading to increased bone fragility and fracture risk. Disorders of the intestinal microbiota may be key inducers of osteoporosis. Furthermore, such disorders may contribute to osteoporosis by influencing immune function and lipid metabolism. Therefore, in this review, we aimed to summarise the molecular mechanisms through which the intestinal microbiota affect the onset and development of osteoporosis by regulating Th17/Treg imbalance and lipid metabolism disorders. We also discussed the regulatory mechanisms underlying the effect of intestinal microbiota-related modulators on Th17/Treg imbalance and lipid metabolism disorders in osteoporosis, to explore new molecular targets for its treatment and provide a theoretical basis for clinical management.

Gut-bone axis perturbation: Mechanisms and interventions via gut microbiota as a primary driver of osteoporosis

A growing number of studies have highlighted the significance of human gut microbiota (GM) as a potential target for osteoporosis. In this review, we discuss the effect of GM to bone metabolism focusing on two aspects: the local alterations of the human gut permeability that modify how the GM interact with the gut-bone axis (e.g., intestinal leakage, nutrient absorption), and the alterations of the GM itself (e.g., changes in microbiota metabolites, immune secretion, hormones) that modify the events of the gut-bone axis. We then classify these changes as possible therapeutic targets of bone metabolism and highlight some associated promising microbiome-based therapies. We also extend our discussions into combinatorial treatments that incorporate conservative treatments, such as exercise. We anticipate our review can provide an overview of the current pathophysiological and therapeutic paradigms of the gut-bone axis, as well as the prospects of ongoing clinical trials for readers to gain further insights into better microbiome-based treatments to osteoporosis and other bone-degenerative diseases. The translational potential of this article: This paper reviewed the potential links between gut microbiota and osteoporosis, as well as the prospective therapeutic avenues targeting gut microbiota for osteoporosis management, presenting a thorough and comprehensive literature review.

Immune Checkpoint Molecules as Biomarkers of Staphylococcus aureus Bone Infection and Clinical Outcome

Staphylococcus aureus prosthetic joint infections (PJIs) are broadly considered incurable, and clinical diagnostics that guide conservative vs. aggressive surgical treatments don't exist. Multi-omics studies in a humanized NSG-SGM3 BLT mouse model demonstrate human T cells: 1) are remarkably heterogenous in gene expression and numbers, and 2) exist as a mixed population of activated, progenitor-exhausted, and terminally-exhausted Th1/Th17 cells with increased expression of immune checkpoint proteins (LAG3, TIM-3). Importantly, these proteins are upregulated in the serum and the bone marrow of S. aureus PJI patients. A multiparametric nomogram combining high serum immune checkpoint protein levels with low proinflammatory cytokine levels (IFN-γ, IL-2, TNF-α, IL-17) revealed that TIM-3 was highly predictive of adverse disease outcomes (AUC=0.89). Hence, T cell impairment in the form of immune checkpoint expression and exhaustion could be a functional biomarker for S. aureus PJI disease outcome, and blockade of checkpoint proteins could potentially improve outcomes following surgery.

LPL-RH suppresses bone loss in ovariectomised rat models

BACKGROUND

Evidence has revealed that oestrogen deprivation-induced osteolysis is microbiota-dependent and can be treated by probiotics. However, the underlying mechanism require further investigation. This study aims to provide additional evidence supporting the use of probiotics as an adjuvant treatment and to explore the pathophysiology of oestrogen-deprived osteolysis.

METHODS

Forty-five SD rats were randomly divided into five groups (n = 9). Rats from four groups were ovariectomised and treated with NS, calcium, probiotics, or calcium + probiotics, while one group underwent a sham operation and was treated with NS. The osteometabolic effects were evaluated, and the mechanistic role of the probiotic supplement was explored.

RESULTS

Intragastric administration of Bifidobacterium animalis subsp. lactis LPL-RH (LPL-RH) markedly suppressed osteoclastic activation and bone calcium loss by downregulating TRAP enzymatic activity, the OPG/RANKL ratio, and the downstream signalling pathway RANKL/TRAF6/NF-κB/NFATc1/TRAP in ovariectomised SD rats. LPL-RH also reduced CD4+IL-17 A+ TH17 cells in the bone marrow, the pro-osteoclastogenic cytokine IL-17 A, pro-inflammatory molecules (LPS), and its binding protein (LBP) in the blood. LPL-RH restored intestinal ZO-1, occludin, claudin 2, claudin 12, and claudin 15, which improved ileal histopathology, reduced ileal oxidative stress, and attenuated the LPS-responsive TLR4/MyD88/NF-κB pathway. Furthermore, 16 S rRNA sequencing revealed that LPL-RH altered the faecal microbiome by reducing the relative abundance of S24-7 at the family level and promoting Prevotella and Bacteroides at the genus level.

CONCLUSION

Collectively, LPL-RH suppressed osteoclastogenesis and osteolysis by modulating type 17 immunity and gut microbiome.

Mechanisms of gut homeostasis regulating Th17/Treg cell balance in PMOP

Postmenopausal osteoporosis (PMOP) is a metabolic bone disease driven by estrogen deficiency, primarily manifesting as reduced bone mass and heightened fracture risk. Its development is intricately linked to the balance between Th17 and Treg cells. Recent studies have highlighted the significant role of gut homeostasis in PMOP. The gut microbiota profoundly impacts bone health by modulating the host's immune system, metabolic pathways, and endocrine functions. In particular, the regulation of Th17 and Treg cell balance by gut homeostasis plays a pivotal role in the onset and progression of PMOP. Th17 cells secrete pro-inflammatory cytokines that stimulate osteoclast activity, accelerating bone resorption, while Treg cells counteract this process through anti-inflammatory mechanisms, preserving bone mass. The gut microbiota and its metabolites can influence Th17/Treg equilibrium, thereby modulating bone metabolism. Furthermore, the integrity of the gut barrier is critical for systemic immune stability, and its disruption can lead to immune dysregulation and metabolic imbalances. Thus, targeting gut homeostasis to restore Th17/Treg balance offers a novel therapeutic avenue for the prevention and treatment of PMOP.

Mesenchymal stem cells and their exosomes mitigate osteoarthritis by restoring the balance between proinflammatory Teffs and Tregs

Osteoarthritis (OA) is a degenerative joint disease caused by chronic inflammation that damages articular cartilage. In addition to the wear and tear of joints, aberrant remodelling driven by a significant presence of inflammatory mediators within the joint is one of the key mechanisms in the pathogenesis of OA. Among these factors, hyperactivation of Teffs subsets plays a crucial role in promoting this pathological process. The immune imbalance between proinflammatory CD4+ effector T cells (proinflammatory Teffs) and Tregs could be a crucial factor in the pathogenesis of OA. Therefore, correcting the imbalance of Tregs/proinflammatory Teffs may slow or inhibit the occurrence and development of OA, which could be a potential target for the treatment of OA. Mesenchymal stem cells (MSCs) possess anti-inflammatory and immunomodulatory properties, regulating both adaptive and innate immunity through mechanisms involving soluble factors such as IDO, PGE2, and TGF-β, as well as cell-to-cell contact and exosomes. Correcting the imbalance between Tregs and proinflammatory Teffs may be one of the mechanisms of MSCs in the treatment of OA. Therefore, this review aims to summarize the relationship between OA and the immune imbalance between Tregs and proinflammatory Teffs, the immunoregulatory role of Tregs in OA, and the role of MSCs and their exosomes in correcting the imbalance between Tregs and proinflammatory Teffs.

Schistosoma antigens: A future clinical magic bullet for autoimmune diseases?

Autoimmune diseases are characterized by dysregulated immunity against self-antigens. Current treatment of autoimmune diseases largely relies on suppressing host immunity to prevent excessive inflammation. Other immunotherapy options, such as cytokine or cell-targeted therapies, have also been used. However, most patients do not benefit from these therapies as recurrence of the disease usually occurs. Therefore, more effort is needed to find alternative immune therapeutics. Schistosoma infection has been a significant public health problem in most developing countries. Schistosoma parasites produce eggs that continuously secrete soluble egg antigen (SEA), which is a known modulator of host immune responses by enhancing Th2 immunity and alleviating outcomes of Th1 and Th17 responses. Recently, SEA has shown promise in treating autoimmune disorders due to their substantial immune-regulatory effects. Despite this interest, how these antigens modulate human immunity demonstrates only limited pieces of evidence, and whether there is potential for Schistosoma antigens in other diseases in the future remains an unsolved question. This review discusses how SEA modulates human immune responses and its potential for development as a novel immunotherapeutic for autoimmune diseases. We also discuss the immune modulatory effects of other non-SEA schistosome antigens at different stages of the parasite's life cycle.

Alleviated diabetic osteoporosis and peripheral neuropathic pain by Rehmannia glutinosa Libosch polysaccharide via increasing regulatory T cells

Diabetic peripheral neuropathy (DPN) and diabetic osteoporosis (DOP) are conditions that significantly impact the quality of life of patients worldwide. Rehmanniae Radix Preparata, a component of traditional Chinese medicine with a history spanning thousands of years, has been utilized in the treatment of osteoporosis and diabetes. Specifically, Rehmannia glutinosa Libosch polysaccharide (RGP), a key bioactive compound of Rehmanniae Radix Preparata, has demonstrated immune-modulating properties and beneficial effects on hyperglycemia, hyperlipidemia, and vascular inflammation in diabetic mice. Despite these known actions, the precise mechanisms of RGP in addressing DOP and DPN remain unclear. Our study aimed to explore the impact of RGP on osteoporosis and peripheral neuropathic pain in diabetic mice induced by streptozotocin (STZ). The findings revealed that RGP not only improved hyperglycemia and osteoporosis in STZ-induced diabetic mice but also enhanced osteogenesis, insulin production, and nerve health. Specifically, RGP alleviated distal pain, improved nerve conduction velocity, nerve fiber integrity, and immune cell balance in the spleen. Mechanistically, RGP was found to upregulate HDAC6 mRNA expression in regulatory T cells, potentially shedding light on novel pathways for preventing DOP and DPN. These results offer promising insights for the development of new therapeutic approaches for diabetic complications.

The role of Th/Treg immune cells in osteoarthritis

Osteoarthritis (OA) is a prevalent clinical condition affecting the entire joint, characterized by its multifactorial etiology and complex pathophysiology. The onset of OA is linked to inflammatory mediators produced by the synovium, cartilage, and subchondral bone, all of which are closely tied to cartilage degradation. Consequently, OA may also be viewed as a systemic inflammatory disorder. Emerging studies have underscored the significance of T cells in the development of OA. Notably, imbalances in Th1/Th2 and Th17/Treg immune cells may play a crucial role in the pathogenesis of OA. This review aims to compile recent advancements in understanding the role of T cells and their Th/Treg subsets in OA, examines the immune alterations and contributions of Th/Treg cells to OA progression, and proposes novel directions for future research, including potential therapeutic strategies for OA.

The interactions of macrophages, lymphocytes, and mesenchymal stem cells during bone regeneration

Bone regeneration and repair are crucial to ambulation and quality of life. Factors such as poor general health, serious medical comorbidities, chronic inflammation, and ageing can lead to delayed healing and nonunion of fractures, and persistent bone defects. Bioengineering strategies to heal bone often involve grafting of autologous bone marrow aspirate concentrate (BMAC) or mesenchymal stem cells (MSCs) with biocompatible scaffolds. While BMAC shows promise, variability in its efficacy exists due to discrepancies in MSC concentration and robustness, and immune cell composition. Understanding the mechanisms by which macrophages and lymphocytes - the main cellular components in BMAC - interact with MSCs could suggest novel strategies to enhance bone healing. Macrophages are polarized into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, and influence cell metabolism and tissue regeneration via the secretion of cytokines and other factors. T cells, especially helper T1 (Th1) and Th17, promote inflammation and osteoclastogenesis, whereas Th2 and regulatory T (Treg) cells have anti-inflammatory pro-reconstructive effects, thereby supporting osteogenesis. Crosstalk among macrophages, T cells, and MSCs affects the bone microenvironment and regulates the local immune response. Manipulating the proportion and interactions of these cells presents an opportunity to alter the local regenerative capacity of bone, which potentially could enhance clinical outcomes.

An Osteoimmunomodulatory Biopatch Potentiates Stem Cell Therapies for Bone Regeneration by Simultaneously Regulating IL-17/Ferroptosis Signaling Pathways

Currently, there are still great challenges in promoting bone defect healing, a common health problem affecting millions of people. Herein an osteoimmunity-regulating biopatch capable of promoting stem cell-based therapies for bone regeneration is developed. A totally biodegradable conjugate is first synthesized, which can self-assemble into bioactive nano micelles (PPT NMs). This nanotherapy effectively improves the osteogenesis of periodontal ligament stem cells (PDLSCs) under pathological conditions, by simultaneously regulating IL-17 signaling and ferroptosis pathways. Incorporation of PPT NMs into biodegradable electrospun nanofibers affords a bioactive patch, which notably improves bone formation in two rat bone defect models. A Janus bio patch is then engineered by integrating the bioactive patch with a stem cell sheet of PDLSCs. The obtained biopatch shows additionally potentiated bone regeneration capacity, by synergistically regulating osteoimmune microenvironment and facilitating stem cell differentiation. Further surface functionalization of the biopatch with tannic acid considerably increases its adhesion to the bone defect, prolongs local retention, and sustains bioactivities, thereby offering much better repair effects in rats with mandibular or cranial bone defects. Moreover, the engineered bioactive patches display good safety. Besides bone defects, this osteoimmunity-regulating biopatch strategy can be applied to promote stem cell therapies for spinal cord injury, wound healing, and skin burns.

The balance between helper T 17 and regulatory T cells in osteoimmunology and relevant research progress on bone tissue engineering

BACKGROUND

Bone regeneration is a well-regulated dynamic process, of which the prominent role of the immune system on bone homeostasis is more and more revealed by recent research. Before fully activation of the bone remodeling cells, the immune system needs to clean up the microenvironment in facilitating the bone repair initiation. Furthermore, this microenvironment must be maintained properly by various mechanisms over the entire bone regeneration process.

OBJECTIVE

This review aims to summarize the role of the T-helper 17/Regulatory T cell (Th17/Treg) balance in bone cell remodeling and discuss the relevant progress in bone tissue engineering.

RESULTS

The role of the immune response in the early stages of bone regeneration is crucial, especially the impact of the Th17/Treg balance on osteoclasts, mesenchymal stem cells (MSCs), and osteoblasts activity. By virtue of these knowledge advancements, innovative approaches in bone tissue engineering, such as nano-structures, hydrogel, and exosomes, are designed to influence the Th17/Treg balance and thereby augment bone repair and regeneration.

CONCLUSION

Targeting the Th17/Treg balance is a promising innovative strategy for developing new treatments to enhance bone regeneration, thus offering potential breakthroughs in bone injury clinics.

Advances on T cell immunity in bone remodeling and bone regeneration

Bone remodeling and bone regeneration are essential for preserving skeletal integrity and maintaining mineral homeostasis. T cells, as key members of adaptive immunity, play a pivotal role in bone remodeling and bone regeneration by producing a range of cytokines and growth factors. In the physiological state, T cells are involved in the maintenance of bone homeostasis through interactions with mesenchymal stem cells, osteoblasts, and osteoclasts. In pathological states, T cells participate in the pathological process of different types of osteoporosis through interaction with estrogen, glucocorticoids, and parathyroid hormone. During fracture healing for post-injury repair, T cells play different roles during the inflammatory hematoma phase, the bone callus formation phase and the bone remodeling phase. Targeting T cells thus emerges as a potential strategy for regulating bone homeostasis. This article reviews the research progress on related mechanisms of T cells immunity involved in bone remodeling and bone regeneration, with a view to providing a scientific basis for targeting T cells to regulate bone remodeling and bone regeneration.

Nlrp3 inflammasome drives regulatory T cell depletion to accelerate periapical bone erosion

AIM

Apical periodontitis is an inflammatory disorder triggered by an immune response to bacterial infection, leading to the periapical tissue damage and alveolar resorption. However, the underlying mechanisms driving this process remain elusive, due to the complex and interconnected immune microenvironment within the local lesion site. In this study, the influence of Nlrp3 inflammasome-mediated immune response on the apical periodontitis was investigated.

METHODOLOGY

RNA sequencing, immunohistochemistry and ELISA assay were performed to investigate the activation of Nlrp3 inflammasome signalling pathways in the human periapical tissues, including radicular cysts, periapical granulomas and healthy oral mucosa. A mouse model of apical periodontitis was established to study the role of Nlrp3 knockout in periapical bone resorption and Treg cell stability, and the underlying mechanism was explored through in vitro experiments. In vivo Treg cell adoptive transfer was performed to investigate the effects of Treg cells on the progression of apical periodontitis.

RESULTS

Our findings find that the hyperactivated Nlrp3 inflammasome is present in human periapical lesions and plays a vital role in the immune-related periapical bone loss. Using a mouse model of apical periodontitis, we observe that Nlrp3 deficiency is resistant to bone resorption. This protection was accompanied by elevated generation and infiltration of local Treg cells that displayed a notable ability to suppress RANKL-dependent osteoclast differentiation. In terms of the mechanism of action, Nlrp3 deficiency directly inhibits the osteoclast differentiation and bone loss through JNK/MAPK and NF-κB pathways. In addition, Nlrp3 induces pyroptosis in the stem cells from apical papilla (SCAPs), and the subsequent release of cytokines affects the stability of Treg cell in periapical lesions, leading indirectly to enhanced bone resorption. In turn, adoptive transfer of both Nlrp3-deficient and wild-type Treg cells effectively prevent the bone erosion during apical periodontitis.

CONCLUSIONS

Together, our data identify that the Nlrp3 inflammasome modulates the Treg cell stability and osteoclastogenesis in the periapical inflammatory microenvironment, thus determining the progression of bone erosion.

The combination of Butyricicoccus pullicaecorum and 3-hydroxyanthranilic acid prevents postmenopausal osteoporosis by modulating gut microbiota and Th17/Treg

BACKGROUND

Postmenopausal osteoporosis (PMO) is a chronic condition characterized by decreased bone strength. This study aims to investigate the effects and mechanisms of the combination of Butyricicoccus pullicaecorum (Bp) and 3-hydroxyanthranilic acid (3-HAA) on PMO.

METHODS

The effects of Bp and 3-HAA on PMO were evaluated in ovariectomized (OVX) rats by assessing stereological parameters, femur microstructure, and autophagy levels. The T helper (Th) 17/Regulatory T (Treg) cells of rats were detected using flow cytometric analysis. Furthermore, the impact of Bp and 3-HAA on the gut microbiota of rats was assessed using 16S rRNA gene sequencing. The correlation between the gut microbiota of rats and Th17/Treg immune factors, as well as femoral stereo parameters, was separately assessed using Spearman rank correlation analysis.

RESULTS

Bp and 3-HAA treatments protected OVX rats by promoting osteogenesis and inhibiting autophagy. Compared to the Sham group, OVX rats showed an increase in Th17 cells and a decrease in Treg cells. Bp and 3-HAA reversed these changes. Enterorhabdus and Pseudomonas were significantly enriched in OVX rats. Bp and 3-HAA regulated the gut microbiota of OVX rats, enriching pathways related to nutrient metabolism and immune function. There was a correlation between the gut microbiota and the Th17/Treg, as well as femoral stereo parameters. The concurrent administration of Bp and 3-HAA medication facilitated the enrichment of gut microbiota associated with the improvement of PMO.

CONCLUSION

The combination therapy of Bp and 3-HAA can prevent PMO by modulating the gut microbiota and restoring Th17/Treg immune homeostasis.

Halofuginone Inhibits Osteoclastogenesis and Enhances Osteoblastogenesis by Regulating Th17/Treg Cell Balance in Multiple Myeloma Mice with Bone Lesions

Evidences shows that T helper 17 (Th17) and regulatory T (Treg) cells imbalance plays a critical role in bone lesions of MM patients. Therefore, regulating the Th17/Treg imbalance may be beneficial for bone lesions in MM. Ten MM mice complicated with bone lesions were established and divided into the halofuginone (HF) group and the PBS group. After treatment, tibia and fibula from both groups were scanned by micro-CT. Osteoclasts and osteoblasts were validated by histochemical staining and ELISA. Th17 and Treg cells were tested by flow cytometry. The correlations between Th17/Treg cell ratio and osteoclasts, osteoblasts and bone remodeling were analyzed using the Spearman relative analysis. After treatment, mice in the HF group had an increase in trabecular bone volume fraction and thickened cortex, but a decrease in trabecular separation compared to mice in the PBS group.Tartrate-resistant acid phosphase (TRAP) + osteoclasts and its biomarker TRACP5b in serum were reduced, while alkaline phosphatase (ALP) + osteoblasts and its biomarker N-terminal propeptide of type 1precollagen (P1NP) in serum were accreted in the HF group. Th17/Treg cell ratio in halofuginone-treated mice was 0.85 ± 0.05, and was significantly lower than that in PBS-treated mice, which was 1.51 ± 0.03. In addition, it showed that the Th17/Treg cell ratio was significantly and positively associated with osteoclasts, but was significantly and negatively associated with osteoblasts and bone remodeling. Halofuginone plays a critical role in the amelioration bone lesions in MM, as it can inhibit osteoclastogenesis and enhance osteoblastogenesis by regulating the Th17/Treg cell balance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-024-01756-4.

Osteoimmunology of Fracture Healing

PURPOSE OF REVIEW

The purpose of this review is to summarize what is known in the literature about the role inflammation plays during bone fracture healing. Bone fracture healing progresses through four distinct yet overlapping phases: formation of the hematoma, development of the cartilaginous callus, development of the bony callus, and finally remodeling of the fracture callus. Throughout this process, inflammation plays a critical role in robust bone fracture healing.

RECENT FINDINGS

At the onset of injury, vessel and matrix disruption lead to the generation of an inflammatory response: inflammatory cells are recruited to the injury site where they differentiate, activate, and/or polarize to secrete cytokines for the purposes of cell signaling and cell recruitment. This process is altered by age and by sex. Bone fracture healing is heavily influenced by the presence of inflammatory cells and cytokines within the healing tissue.

The role of neuropilin in bone/cartilage diseases

Bone remodeling is the balance between osteoblasts and osteoclasts. Bone diseases such as osteoporosis and osteoarthritis are associated with imbalanced bone remodeling. Skeletal injury leads to limited motor function and pain. Neurophilin was initially identified in axons, and its various ligands and roles in bone remodeling, angiogenesis, neuropathic pain and immune regulation were later discovered. Neurophilin promotes osteoblast mineralization and inhibits osteoclast differentiation and its function. Neuropolin-1 provides channels for immune cell chemotaxis and cytokine diffusion and leads to pain. Neuropolin-1 regulates the proportion of T helper type 17 (Th17) and regulatory T cells (Treg cells), and affects bone immunity. Vascular endothelial growth factors (VEGF) combine with neuropilin and promote angiogenesis. Class 3 semaphorins (Sema3a) compete with VEGF to bind neuropilin, which reduces angiogenesis and rejects sympathetic nerves. This review elaborates on the structure and general physiological functions of neuropilin and summarizes the role of neuropilin and its ligands in bone and cartilage diseases. Finally, treatment strategies and future research directions based on neuropilin are proposed.

The immune cells in modulating osteoclast formation and bone metabolism

Osteoclasts are pivotal in regulating bone metabolism, with immune cells significantly influencing both physiological and pathological processes by modulating osteoclast functions. This is particularly evident in conditions of inflammatory bone resorption, such as rheumatoid arthritis and periodontitis. This review summarizes and comprehensively analyzes the research progress on the regulation of osteoclast formation by immune cells, aiming to unveil the underlying mechanisms and pathways through which diseases, such as rheumatoid arthritis and periodontitis, impact bone metabolism.

Tissue adaptation of CD4 T lymphocytes in homeostasis and cancer

The immune system is traditionally classified as a defense system that can discriminate between self and non-self or dangerous and non-dangerous situations, unleashing a tolerogenic reaction or immune response. These activities are mainly coordinated by the interaction between innate and adaptive cells that act together to eliminate harmful stimuli and keep tissue healthy. However, healthy tissue is not always the end point of an immune response. Much evidence has been accumulated over the years, showing that the immune system has complex, diversified, and integrated functions that converge to maintaining tissue homeostasis, even in the absence of aggression, interacting with the tissue cells and allowing the functional maintenance of that tissue. One of the main cells known for their function in helping the immune response through the production of cytokines is CD4+ T lymphocytes. The cytokines produced by the different subtypes act not only on immune cells but also on tissue cells. Considering that tissues have specific mediators in their architecture, it is plausible that the presence and frequency of CD4+ T lymphocytes of specific subtypes (Th1, Th2, Th17, and others) maintain tissue homeostasis. In situations where homeostasis is disrupted, such as infections, allergies, inflammatory processes, and cancer, local CD4+ T lymphocytes respond to this disruption and, as in the healthy tissue, towards the equilibrium of tissue dynamics. CD4+ T lymphocytes can be manipulated by tumor cells to promote tumor development and metastasis, making them a prognostic factor in various types of cancer. Therefore, understanding the function of tissue-specific CD4+ T lymphocytes is essential in developing new strategies for treating tissue-specific diseases, as occurs in cancer. In this context, this article reviews the evidence for this hypothesis regarding the phenotypes and functions of CD4+ T lymphocytes and compares their contribution to maintaining tissue homeostasis in different organs in a steady state and during tumor progression.

Immunomodulatory nanomedicine for osteoporosis: Current practices and emerging prospects

Osteoporosis results from the disruption of the balance between bone resorption and bone formation. However, classical anti-osteoporosis drugs exhibit several limitations in clinical applications, such as multiple adverse reactions and poor therapeutic effects. Therefore, there is an urgent need for alternative treatment strategies. With the evolution of immunomodulatory nanomedicine, a variety of nanomaterials have been designed for anti-osteoporosis treatment, offering prospects of minimal adverse reactions, enhanced bone induction, and high osteogenic activity. This review initially provides a brief overview of the fundamental principles of bone reconstruction, current osteogenic clinical methods in osteoporosis treatment, and the significance of osteogenic-angiogenic coupling, laying the groundwork for understanding the pathophysiology and therapeutics of osteoporosis. Subsequently, the article emphasizes the relationship between bone immunity and osteogenesis-angiogenesis coupling and provides a detailed analysis of the application of immunomodulatory nanomedicines in the treatment of osteoporosis, including various types of nanomaterials and their integration with carrier biomaterials. Importantly, we discuss the potential of some emerging strategies in immunomodulatory nanomedicine for osteoporosis treatment. This review introduces the innovative applications of immunomodulatory nanomedicine in the treatment of osteoporosis, aiming to serve as a reference for the application of immunomodulatory nanomedicine strategies in osteoporosis treatment. STATEMENT OF SIGNIFICANCE: Osteoporosis, as one of the most prevalent skeletal disorders, poses a significant threat to public health. To date, conventional anti-osteoporosis strategies have been limited in efficacy and plagued with numerous side effects. Fortunately, with the advancement of research in osteoimmunology and nanomedicine, strategies integrating these two fields show great promise in combating osteoporosis. Nanomedicine with immunomodulatory properties exhibits enhanced efficiency, prolonged effectiveness, and increased safety. However, as of now, there exists no comprehensive review amalgamating immunomodulation with nanomedicine to delineate the progress of immunomodulatory nanomedicine in osteoporosis treatment, as well as the future direction of this strategy.

CD4+ and CD8+ T cells reduce inflammation and promote bone healing in response to titanium implants

T cells are adaptive immune cells essential in pathogenic response, cancer, and autoimmune disorders. During the integration of biomaterials with host tissue, T cells modify the local inflammatory environment by releasing cytokines that promote inflammatory resolution following implantation. T cells are vital for the modulation of innate immune cells, recruitment and proliferation of mesenchymal stem cells (MSCs), and formation of functional tissue around the biomaterial implant. We have demonstrated that deficiency of αβ T cells promotes macrophage polarization towards a pro-inflammatory phenotype and attenuates MSC recruitment and proliferation in vitro and in vivo. The goal of this study was to understand how CD4+ and CD8+ T cells, subsets of the αβ T cell family, impact the inflammatory response to titanium (Ti) biomaterials. Deficiency of either CD4+ or CD8+ T cells increased the proportion of pro-inflammatory macrophages, lowered anti-inflammatory macrophages, and diminished MSC recruitment in vitro and in vivo. In addition, new bone formation at the implantation site was significantly reduced in T cell-deficient mice compared to T cell-competent mice. Deficiency of CD4+ T cells exacerbated these effects compared to CD8+ T cell deficiency. Our results show the importance of CD4+ and CD8+ T cells in modulating the inflammatory response and promoting new bone formation in response to modified Ti implants. STATEMENT OF SIGNIFICANCE: CD4+ and CD8+ T cells are essential in modulating the peri-implant microenvironment during the inflammatory response to biomaterial implantation. This study shows that deficiency of either CD4+ or CD8+ T cell subsets altered macrophage polarization and reduced MSC recruitment and proliferation at the implantation site.

Zinc based biodegradable metals for bone repair and regeneration: Bioactivity and molecular mechanisms

Bone fractures and critical-size bone defects are significant public health issues, and clinical treatment outcomes are closely related to the intrinsic properties of the utilized implant materials. Zinc (Zn)-based biodegradable metals (BMs) have emerged as promising bioactive materials because of their exceptional biocompatibility, appropriate mechanical properties, and controllable biodegradation. This review summarizes the state of the art in terms of Zn-based metals for bone repair and regeneration, focusing on bridging the gap between biological mechanism and required bioactivity. The molecular mechanism underlying the release of Zn ions from Zn-based BMs in the improvement of bone repair and regeneration is elucidated. By integrating clinical considerations and the specific bioactivity required for implant materials, this review summarizes the current research status of Zn-based internal fixation materials for promoting fracture healing, Zn-based scaffolds for regenerating critical-size bone defects, and Zn-based barrier membranes for reconstituting alveolar bone defects. Considering the significant progress made in the research on Zn-based BMs for potential clinical applications, the challenges and promising research directions are proposed and discussed.

Lilrb4 ameliorates ileal injury in rats with hemorrhagic shock and suppresses the activation of NF-κB signaling pathway

Hemorrhagic shock (HS) leads to intestinal damage and subsequent multiple organ dysfunction syndrome. Intestinal barrier dysfunction is the main cause of multiple organ failure associated with HS. Leukocyte immunoglobulin-like receptor B4 (Lilrb4) belongs to the Ig superfamily and is a vital natural immunomodulatory receptor. The purpose of this study was to identify the role and molecular mechanism of Lilrb4 in HS-induced ileal injury. In this work, HS was established by femoral artery cannula and 90 min of HS (blood pressure, 35-40 mmHg), followed by resuscitation. RNA sequencing analysis showed that Lilrb4 was highly expressed in the ileum of HS rats. As observed, HS rats exhibited severe ileal injury, characterized by enlarged subepithelial space, edema, exfoliation and extensive loss of villi. Whereas, lentivirus system-mediated Lilrb4 overexpression considerably mitigated these alterations. HS led to increased release of markers associated with intestinal injury, which was effectively reversed by Lilrb4 overexpression. In addition, after resuscitation, Lilrb4 overexpression inhibited HS-triggered inflammatory response, as evidenced by decreased levels of proinflammatory cytokines. Lilrb4 also inhibited the activation of NF-κB signal induced by HS. Notably, Lilrb4 modulated the balance of regulatory T (Treg)-T helper 17 (Th17) cells in the mesenteric lymph node (MLN), which may also contribute to its protective role in HS progression. In aggregate, these findings confirmed that Lilrb4 overexpression protected against ileal injury caused by HS, indicating that Lilrb4 may be a potential candidate for the treatment of HS.

Comparison of the therapeutic effects of mesenchymal stem cells derived from human dental pulp (DP), adipose tissue (AD), placental amniotic membrane (PM), and umbilical cord (UC) on postmenopausal osteoporosis

Background: Osteoporosis is a systemic bone disease characterized by bone loss and microstructural degeneration. Recent preclinical and clinical trials have further demonstrated that the transplantation of mesenchymal stem cells (MSCs) derived from human adipose tissue (AD), dental pulp (DP), placental amniotic membrane (AM), and umbilical cord (UC) tissues can serve as an effective form of cell therapy for osteoporosis. However, MSC-mediated osteoimmunology and the ability of these cells to regulate osteoclast-osteoblast differentiation varies markedly among different types of MSCs. Methods: In this study, we investigated whether transplanted allogeneic MSCs derived from AD, DP, AM, and UC tissues were able to prevent osteoporosis in an ovariectomy (OVX)-induced mouse model of osteoporosis. The homing and immunomodulatory ability of these cells as well as their effects on osteoblastogenesis and the maintenance of bone formation were compared for four types of MSCs to determine the ideal source of MSCs for the cell therapy-based treatment of OVX-induced osteoporosis. The bone formation and bone resorption ability of these four types of MSCs were analyzed using micro-computed tomography analyses and histological staining. In addition, cytokine array-based analyses of serological markers and bioluminescence imaging assays were employed to evaluate cell survival and homing efficiency. Immune regulation was determined by flow cytometer assay to reflect the mechanisms of osteoporosis treatment. Conclusion: These analyses demonstrated that MSCs isolated from different tissues have the capacity to treat osteoporosis when transplanted in vivo. Importantly, DP-MSCs infusion was able to maintain trabecular bone mass more efficiently with corresponding improvements in trabecular bone volume, mineral density, number, and separation. Among the tested MSC types, DP-MSCs were also found to exhibit greater immunoregulatory capabilities, regulating the Th17/Treg and M1/M2 ratios. These data thus suggest that DP-MSCs may represent an effective tool for the treatment of osteoporosis.

Osteoimmunology: The Crosstalk between T Cells, B Cells, and Osteoclasts in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an ongoing inflammatory condition that affects the joints and can lead to severe damage to cartilage and bones, resulting in significant disability. This condition occurs when the immune system becomes overactive, causing osteoclasts, cells responsible for breaking down bone, to become more active than necessary, leading to bone breakdown. RA disrupts the equilibrium between osteoclasts and osteoblasts, resulting in serious complications such as localized bone erosion, weakened bones surrounding the joints, and even widespread osteoporosis. Antibodies against the receptor activator of nuclear factor-κB ligand (RANKL), a crucial stimulator of osteoclast differentiation, have shown great effectiveness both in laboratory settings and actual patient cases. Researchers are increasingly focusing on osteoclasts as significant contributors to bone erosion in RA. Given that RA involves an overactive immune system, T cells and B cells play a pivotal role by intensifying the immune response. The imbalance between Th17 cells and Treg cells, premature aging of T cells, and excessive production of antibodies by B cells not only exacerbate inflammation but also accelerate bone destruction. Understanding the connection between the immune system and osteoclasts is crucial for comprehending the impact of RA on bone health. By delving into the immune mechanisms that lead to joint damage, exploring the interactions between the immune system and osteoclasts, and investigating new biomarkers for RA, we can significantly improve early diagnosis, treatment, and prognosis of this condition.

The Role of Breast Cancer Cells in Bone Metastasis: Suitable Seeds for Nourishing Soil

PURPOSE OF REVIEW

The purpose of this review was to describe the characteristics of breast cancer cells prone to developing bone metastasis and determine how they are regulated by the bone microenvironment.

RECENT FINDINGS

The bone is a site of frequent breast cancer metastasis. Bone metastasis accounts for 70% of advanced breast cancer cases and remains incurable. It can lead to skeletal-related events, such as bone fracture and pain, and seriously affect the quality of life of patients. Breast cancer cells escape from the primary lesion and spread to the bone marrow in the early stages. They can then enter the dormant state and restore tumourigenicity after several years to develop overt metastasis. In the last few years, an increasing number of studies have reported on the factors promoting bone metastasis of breast cancer cells, both at the primary and metastatic sites. Identifying factors associated with bone metastasis aids in the early recognition of bone metastasis tendency. How to target these factors and minimize the side effects on the bone remains to be further explored.

Research progress of targeted therapy regulating Th17/Treg balance in bone immune diseases

Rheumatoid arthritis (RA) and postmenopausal osteoporosis (PMOP) are common bone-immune diseases. The imbalance between helper (Th17) and regulatory T cells (Tregs) produced during differentiation of CD4+ T cells plays a key regulatory role in bone remodelling disorders in RA and PMOP. However, the specific regulatory mechanism of this imbalance in bone remodelling in RA and PMOP has not been clarified. Identifying the regulatory mechanism underlying the Th17/Treg imbalance in RA and PMOP during bone remodelling represents a key factor in the research and development of new drugs for bone immune diseases. In this review, the potential roles of Th17, Treg, and Th17/Treg imbalance in regulating bone remodelling in RA and PMOP have been summarised, and the potential mechanisms by which probiotics, traditional Chinese medicine compounds, and monomers maintain bone remodelling by regulating the Th17/Treg balance are expounded. The maintenance of Th17/Treg balance could be considered as an therapeutic alternative for the treatment of RA and PMOP. This study also summarizes the advantages and disadvantages of conventional treatments and the quality of life and rehabilitation of patients with RA and PMOP. The findings presented her will provide a better understanding of the close relationship between bone immunity and bone remodelling in chronic bone diseases and new ideas for future research, prevention, and treatment of bone immune diseases.

Impact of inflammation and Treg cell regulation on neuropathic pain in spinal cord injury: mechanisms and therapeutic prospects

Spinal cord injury is a severe neurological trauma that can frequently lead to neuropathic pain. During the initial stages following spinal cord injury, inflammation plays a critical role; however, excessive inflammation can exacerbate pain. Regulatory T cells (Treg cells) have a crucial function in regulating inflammation and alleviating neuropathic pain. Treg cells release suppressor cytokines and modulate the function of other immune cells to suppress the inflammatory response. Simultaneously, inflammation impedes Treg cell activity, further intensifying neuropathic pain. Therefore, suppressing the inflammatory response while enhancing Treg cell regulatory function may provide novel therapeutic avenues for treating neuropathic pain resulting from spinal cord injury. This review comprehensively describes the mechanisms underlying the inflammatory response and Treg cell regulation subsequent to spinal cord injury, with a specific focus on exploring the potential mechanisms through which Treg cells regulate neuropathic pain following spinal cord injury. The insights gained from this review aim to provide new concepts and a rationale for the therapeutic prospects and direction of cell therapy in spinal cord injury-related conditions.

Osteo-immunological impact of radon spa treatment: due to radon or spa alone? Results from the prospective, thermal bath placebo-controlled RAD-ON02 trial

Musculoskeletal disorders (MSDs) are associated with pain and lead to reduced mobility and quality of life for patients. Radon therapy is used as alternative or complementary to pharmaceutical treatments. According to previous reports, radon spa leads to analgesic and anti-inflammatory effects, but the cellular and molecular mechanisms are widely unknown. A previous study (RAD-ON01) revealed, that bone erosion markers like collagen fragments (C-terminal telopeptide, CTX) are reduced after radon spa treatment in serum of patients with degenerative MSDs. Within the scope of the prospective, placebo-controlled RAD-ON02 trial presented here, we analyzed the influence of radon and thermal spa treatment on osteoclastogenesis. From patient blood, we isolate monocytes, seeded them on bone slices and differentiated them in the presence of growth factors into mature osteoclasts (mOCs). Subsequent analysis showed a smaller fraction of mOCs after both treatments, which was even smaller after radon spa treatment. A significantly reduced resorbed area on bone slices reflects this result. Only after radon spa treatment, we detected in the serum of patients a significant decrease of receptor activator of NF-κB ligand (RANKL), which indicates reduced differentiation of OCs. However, other markers for bone resorption (CTX) and bone formation (OPG, OCN) were not altered after both treatments. Adipokines, such as visfatin and leptin that play a role in some MSD-types by affecting osteoclastogenesis, were not changed after both treatments. Further, also immune cells have an influence on osteoclastogenesis, by inhibiting and promoting terminal differentiation and activation of OCs, respectively. After radon treatment, the fraction of Treg cells was significantly increased, whereas Th17 cells were not altered. Overall, we observed that both treatments had an influence on osteoclastogenesis and bone resorption. Moreover, radon spa treatment affected the Treg cell population as well as the Th17/Treg ratio were affected, pointing toward a contribution of the immune system after radon spa. These data obtained from patients enrolled in the RAD-ON02 trial indicate that radon is not alone responsible for the effects on bone metabolism, even though they are more pronounced after radon compared to thermal spa treatment.

Inflammatory Processes Affecting Bone Health and Repair

PURPOSE OF REVIEW

The purpose of this article is to review the current understanding of inflammatory processes on bone, including direct impacts of inflammatory factors on bone cells, the effect of senescence on inflamed bone, and the critical role of inflammation in bone pain and healing.

RECENT FINDINGS

Advances in osteoimmunology have provided new perspectives on inflammatory bone loss in recent years. Characterization of so-called inflammatory osteoclasts has revealed insights into physiological and pathological bone loss. The identification of inflammation-associated senescent markers in bone cells indicates that therapies that reduce senescent cell burden may reverse bone loss caused by inflammatory processes. Finally, novel studies have refined the role of inflammation in bone healing, including cross talk between nerves and bone cells. Except for the initial stages of fracture healing, inflammation has predominately negative effects on bone and increases fracture risk. Eliminating senescent cells, priming the osteo-immune axis in bone cells, and alleviating pro-inflammatory cytokine burden may ameliorate the negative effects of inflammation on bone.

Bone Involvement in Rheumatoid Arthritis and Spondyloartritis: An Updated Review

Several rheumatologic diseases are primarily distinguished by their involvement of bone tissue, which not only serves as a mere target of the condition but often plays a pivotal role in its pathogenesis. This scenario is particularly prominent in chronic inflammatory arthritis such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). Given the immunological and systemic nature of these diseases, in this review, we report an overview of the pathogenic mechanisms underlying specific bone involvement, focusing on the complex interactions that occur between bone tissue's own cells and the molecular and cellular actors of the immune system, a recent and fascinating field of interest defined as osteoimmunology. Specifically, we comprehensively elaborate on the distinct pathogenic mechanisms of bone erosion seen in both rheumatoid arthritis and spondyloarthritis, as well as the characteristic process of aberrant bone formation observed in spondyloarthritis. Lastly, chronic inflammatory arthritis leads to systemic bone involvement, resulting in systemic bone loss and consequent osteoporosis, along with increased skeletal fragility.

CARM1 deficiency inhibits osteoblastic differentiation of bone marrow mesenchymal stem cells and delays osteogenesis in mice

Bone repair remains a clinical challenge due to low osteogenic capacity. Coactivator associated arginine methyltransferase 1 (CARM1) is a protein arginine methyltransferase that mediates arginine methylation and endochondral ossification. However, the roles of CARM1 in osteoblastic differentiation and bone remodeling have not been explored. In our study, heterozygous CARM1-knockout (KO) mice were generated using the CRISPR-Cas9 system and a model of femoral defect was created. At day 7 postsurgery, CARM1-KO mice exhibited obvious bone loss compared with wild type (WT) mice, as evidenced by reduced bone mineral density (BMD), bone volume/total volume (BV/TV), trabecular thickness (Tb.Th), and trabecular number (Tb.N), and increased trabecular separation (Tb.Sp). Deletion of CARM1 in mice lowered synthesis and accumulation of collagen at the injury sites. The alkaline phosphatase (ALP) activity and osteogenic-related gene expression were declined in CARM1-KO mice. To further understand the role of CARM1 in osteoblastic differentiation, bone marrow mesenchymal stem cells (BMSCs) were isolated from the tibia and femur of WT or CARM1-KO mice. CARM1 deletion decreased histone arginine methylation and inhibited osteoblastic differentiation and mineralization. The mRNA sequencing of CARM1-KO BMSCs revealed the possible regulatory molecules by CARM1, which could deepen our understanding of CARM1 regulatory mechanisms. These data could be of interest to basic researchers and provide the direction for future research into bone-related disorders.

Contribution of αβ T cells to macrophage polarization and MSC recruitment and proliferation on titanium implants

Physiochemical cues like topography and wettability can impact the inflammatory response and tissue integration after biomaterial implantation. T cells are essential for immunomodulation of innate immune cells and play an important role in the host response to biomaterial implantation. This study aimed to understand how CD4+ and CD8+ T cell subsets, members of the αβ T cell family, polarize in response to smooth, rough, or rough-hydrophilic titanium (Ti) implants and whether their presence modulates immune cell crosstalk and mesenchymal stem cell (MSC) recruitment following biomaterial implantation. Post-implantation in mice, we found that CD4+ and CD8+ T cell subsets polarized differentially in response to modified Ti surfaces. Additionally, mice lacking αβ T cells had significantly more pro-inflammatory macrophages, fewer anti-inflammatory macrophages, and reduced MSC recruitment in response to modified Ti post-implantation than αβ T cell -competent mice. Our results demonstrate that T cell activation plays a significant role during the inflammatory response to implanted biomaterials, contributing to macrophage polarization and MSC recruitment and proliferation, and the absence of αβ T cells compromises new bone formation at the implantation site. STATEMENT OF SIGNIFICANCE: T cells are essential for immunomodulation and play an important role in the host response to biomaterial implantation. Our results demonstrate that T cells actively participate during the inflammatory response to implanted biomaterials, controlling macrophage phenotype and recruitment of MSCs to the implantation site.

Low-Dose Staphylococcal Enterotoxin C2 Mutant Maintains Bone Homeostasis via Regulating Crosstalk between Bone Formation and Host T-Cell Effector Immunity

Studies in recent years have highlighted an elaborate crosstalk between T cells and bone cells, suggesting that T cells may be alternative therapeutic targets for the maintenance of bone homeostasis. Here, it is reported that systemic administration of low-dose staphylococcal enterotoxin C2 (SEC2) 2M-118, a form of mutant superantigen, dramatically alleviates ovariectomy (OVX)-induced bone loss via modulating T cells. Specially, SEC2 2M-118 treatment increases trabecular bone mass significantly via promoting bone formation in OVX mice. These beneficial effects are largely diminished in T-cell-deficient nude mice and can be rescued by T-cell reconstruction. Neutralizing assays determine interferon gamma (IFN-γ) as the key factor that mediates the beneficial effects of SEC2 2M-118 on bone. Mechanistic studies demonstrate that IFN-γ stimulates Janus kinase/signal transducer and activator of transcription (JAK-STAT) signaling, leading to enhanced production of nitric oxide, which further activates p38 mitogen-activated protein kinase (MAPK) and Runt-related transcription factor 2 (Runx2) signaling and promotes osteogenic differentiation. IFN-γ also directly inhibits osteoclast differentiation, but this effect is counteracted by proabsorptive factors tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) secreted from IFN-γ-stimulated macrophages. Taken together, this work provides clues for developing innovative approaches which target T cells for the prevention and treatment of osteoporosis.

Immune homeostasis modulation by hydrogel-guided delivery systems: a tool for accelerated bone regeneration

Immune homeostasis is delicately mediated by the dynamic balance between effector immune cells and regulatory immune cells. Local deviations from immune homeostasis in the microenvironment of bone fractures, caused by an increased ratio of effector to regulatory cues, can lead to excessive inflammatory conditions and hinder bone regeneration. Therefore, achieving effective and localized immunomodulation of bone fractures is crucial for successful bone regeneration. Recent research has focused on developing localized and specific immunomodulatory strategies using local hydrogel-based delivery systems. In this review, we aim to emphasize the significant role of immune homeostasis in bone regeneration, explore local hydrogel-based delivery systems, discuss emerging trends in immunomodulation for enhancing bone regeneration, and address the limitations of current delivery strategies along with the challenges of clinical translation.

Nociceptor-Macrophage Interactions in Apical Periodontitis: How Biomolecules Link Inflammation with Pain

Periradicular tissues have a rich supply of peripheral afferent neurons, also known as nociceptive neurons, originating from the trigeminal nerve. While their primary function is to relay pain signals to the brain, these are known to be involved in modulating innate and adaptive immunity by initiating neurogenic inflammation (NI). Studies have investigated neuroanatomy and measured the levels of biomolecules such as cytokines and neuropeptides in human saliva, gingival crevicular fluid, or blood/serum samples in apical periodontitis (AP) to validate the possible role of trigeminal nociceptors in inflammation and tissue regeneration. However, the contributions of nociceptors and the mechanisms involved in the neuro-immune interactions in AP are not fully understood. This narrative review addresses the complex biomolecular interactions of trigeminal nociceptors with macrophages, the effector cells of the innate immune system, in the clinical manifestations of AP.

The Relationship between Renin-Angiotensin-Aldosterone System (RAAS) Activity, Osteoporosis and Estrogen Deficiency in Type 2 Diabetes

Type 2 diabetes (T2D) is associated with a plethora of comorbidities, including osteoporosis, which occurs due to an imbalance between bone resorption and formation. Numerous mechanisms have been explored to understand this association, including the renin-angiotensin-aldosterone system (RAAS). An upregulated RAAS has been positively correlated with T2D and estrogen deficiency in comorbidities such as osteoporosis in humans and experimental studies. Therefore, research has focused on these associations in order to find ways to improve glucose handling, osteoporosis and the downstream effects of estrogen deficiency. Upregulation of RAAS may alter the bone microenvironment by altering the bone marrow inflammatory status by shifting the osteoprotegerin (OPG)/nuclear factor kappa-Β ligand (RANKL) ratio. The angiotensin-converting-enzyme/angiotensin II/Angiotensin II type 1 receptor (ACE/Ang II/AT1R) has been evidenced to promote osteoclastogenesis and decrease osteoblast formation and differentiation. ACE/Ang II/AT1R inhibits the wingless-related integration site (Wnt)/β-catenin pathway, which is integral in bone formation. While a lot of literature exists on the effects of RAAS and osteoporosis on T2D, the work is yet to be consolidated. Therefore, this review looks at RAAS activity in relation to osteoporosis and T2D. This review also highlights the relationship between RAAS activity, osteoporosis and estrogen deficiency in T2D.