Callus γδ T cells and microbe-induced intestinal Th17 cells improve fracture healing in mice

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.

The role of hematopoiesis in bone repair: an update

PURPOSE OF REVIEW

The repair of bone after injury requires the participation of many different immune cell populations, which are derived from the hematopoietic lineage. The field of osteoimmunology, or the study of the interactions between bone and the immune system, is a growing field with emerging impact on both the basic science and clinical aspects of fracture healing.

RECENT FINDINGS

Despite previous focus on the innate immune system in fracture healing, recent studies have revealed an important role for the adaptive immune system in bone repair. The composition of adaptive and innate immune cell populations present at the fracture site is significantly altered during aging and diet-induced obesity, which may contribute to delayed healing. Recent data also suggest a complicated relationship between fracture repair and systemic inflammation, raising the possibility that immune populations from distant sites such as the gut can impact the bone repair process.

SUMMARY

These findings have important implications for the treatment of fracture patients with antibiotics or anti-inflammatory drugs. Furthermore, the effects of systemic inflammation on fracture repair in the contexts of aging or obesity should be carefully interpreted, as they may not be uniformly detrimental.

Immunoengineering Biomaterials for Musculoskeletal Tissue Repair across Lifespan

Musculoskeletal diseases and injuries are among the leading causes of pain and morbidity worldwide. Broad efforts have focused on developing pro-regenerative biomaterials to treat musculoskeletal conditions; however, these approaches have yet to make a significant clinical impact. Recent studies have demonstrated that the immune system is central in orchestrating tissue repair and that targeting pro-regenerative immune responses can improve biomaterial therapeutic outcomes. However, aging is a critical factor negatively affecting musculoskeletal tissue repair and immune function. Hence, understanding how age affects the response to biomaterials is essential for improving musculoskeletal biomaterial therapies. This review focuses on the intersection of the immune system and aging in response to biomaterials for musculoskeletal tissue repair. The article introduces the general impacts of aging on tissue physiology, the immune system, and the response to biomaterials. Then, it explains how the adaptive immune system guides the response to injury and biomaterial implants in cartilage, muscle, and bone and discusses how aging impacts these processes in each tissue type. The review concludes by highlighting future directions for the development and translation of personalized immunomodulatory biomaterials for musculoskeletal tissue repair.

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 Microbial Revolution in the World of Joint Replacement Surgery

Background

The prevalence of revision surgery due to aseptic loosening and periprosthetic joint infection (PJI) following total hip and knee arthroplasty is growing. Strategies to prevent the need for revision surgery and its associated health-care costs and patient morbidity are needed. Therapies that modulate the gut microbiota to influence bone health and systemic inflammation are a novel area of research.

Methods

A literature review of preclinical and clinical peer-reviewed articles relating to the role of the gut microbiota in bone health and PJI was performed.

Results

There is evidence that the gut microbiota plays a role in maintaining bone mineral density, which can contribute to osseointegration, osteolysis, aseptic loosening, and periprosthetic fractures. Similarly, the gut microbiota influences gut permeability and the potential for bacterial translocation to the bloodstream, increasing susceptibility to PJI.

Conclusions

Emerging evidence supports the role of the gut microbiota in the development of complications such as aseptic loosening and PJI after total hip or knee arthroplasty. There is a potential for microbial therapies such as probiotics or fecal microbial transplantation to moderate the risk of developing these complications. However, further investigation is required.

Clinical Relevance

Modulation of the gut microbiota may influence patient outcomes following total joint arthroplasty.

IL-17RA Signaling in Prx1+ Mesenchymal Cells Influences Fracture Healing in Mice

Fracture healing is a complex series of events that requires a local inflammatory reaction to initiate the reparative process. This inflammatory reaction is important for stimulating the migration and proliferation of mesenchymal progenitor cells from the periosteum and surrounding tissues to form the cartilaginous and bony calluses. The proinflammatory cytokine interleukin (IL)-17 family has gained attention for its potential regenerative effects; however, the requirement of IL-17 signaling within mesenchymal progenitor cells for normal secondary fracture healing remains unknown. The conditional knockout of IL-17 receptor a (Il17ra) in mesenchymal progenitor cells was achieved by crossing Il17raF/F mice with Prx1-cre mice to generate Prx1-cre; Il17raF/F mice. At 3 months of age, mice underwent experimental unilateral mid-diaphyseal femoral fractures and healing was assessed by micro-computed tomography (µCT) and histomorphometric analyses. The effects of IL-17RA signaling on the osteogenic differentiation of fracture-activated periosteal cells was investigated in vitro. Examination of the intact skeleton revealed that the conditional knockout of Il17ra decreased the femoral cortical porosity but did not affect any femoral trabecular microarchitectural indices. After unilateral femoral fractures, Il17ra conditional knockout impacted the cartilage and bone composition of the fracture callus that was most evident early in the healing process (day 7 and 14 post-fracture). Furthermore, the in vitro treatment of fracture-activated periosteal cells with IL-17A inhibited osteogenesis. This study suggests that IL-17RA signaling within Prx1+ mesenchymal progenitor cells can influence the early stages of endochondral ossification during fracture healing.

Analysis of Infiltrating Immune Cells Following Intervertebral Disc Injury Reveals Recruitment of Gamma-Delta (γδ) T cells in Female Mice

Inadequate repair of injured intervertebral discs (IVD) leads to degeneration and contributes to low back pain. Infiltrating immune cells into damaged musculoskeletal tissues are critical mediators of repair, yet little is known about their identities, roles, and temporal regulation following IVD injury. By analyzing longitudinal changes in gene expression, tissue morphology, and the dynamics of infiltrating immune cells following injury, we characterize sex-specific differences in immune cell populations and identify the involvement of previously unreported immune cell types, γδ and NKT cells. Cd3+Cd4-Cd8- T cells are the largest infiltrating lymphocyte population with injury, and we identified the presence of γδ T cells in this population in female mice specifically, and NKT cells in males. Injury-mediated IVD degeneration was prevalent in both sexes, but more severe in males. Sex-specific degeneration may be associated with the differential immune response since γδ T cells have potent anti-inflammatory roles and may mediate IVD repair.

Periosteum Containing Implicit Stem Cells: A Progressive Source of Inspiration for Bone Tissue Regeneration

The periosteum is known as the thin connective tissue covering most bone surfaces. Its extrusive bone regeneration capacity was confirmed from the very first century-old studies. Recently, pluripotent stem cells in the periosteum with unique physiological properties were unveiled. Existing in dynamic contexts and regulated by complex molecular networks, periosteal stem cells emerge as having strong capabilities of proliferation and multipotential differentiation. Through continuous exploration of studies, we are now starting to acquire more insight into the great potential of the periosteum in bone formation and repair in situ or ectopically. It is undeniable that the periosteum is developing further into a more promising strategy to be harnessed in bone tissue regeneration. Here, we summarized the development and structure of the periosteum, cell markers, and the biological features of periosteal stem cells. Then, we reviewed their pivotal role in bone repair and the underlying molecular regulation. The understanding of periosteum-related cellular and molecular content will help enhance future research efforts and application transformation of the periosteum.

SARS-CoV-2 and its Multifaceted Impact on Bone Health: Mechanisms and Clinical Evidence

PURPOSE OF REVIEW

SARS-CoV-2 infection, the culprit of the COVID-19 pandemic, has been associated with significant long-term effects on various organ systems, including bone health. This review explores the current understanding of the impacts of SARS-CoV-2 infection on bone health and its potential long-term consequences.

RECENT FINDINGS

As part of the post-acute sequelae of SARS-CoV-2 infection, bone health changes are affected by COVID-19 both directly and indirectly, with multiple potential mechanisms and risk factors involved. In vitro and preclinical studies suggest that SARS-CoV-2 may directly infect bone marrow cells, leading to alterations in bone structure and osteoclast numbers. The virus can also trigger a robust inflammatory response, often referred to as a "cytokine storm", which can stimulate osteoclast activity and contribute to bone loss. Clinical evidence suggests that SARS-CoV-2 may lead to hypocalcemia, altered bone turnover markers, and a high prevalence of vertebral fractures. Furthermore, disease severity has been correlated with a decrease in bone mineral density. Indirect effects of SARS-CoV-2 on bone health, mediated through muscle weakness, mechanical unloading, nutritional deficiencies, and corticosteroid use, also contribute to the long-term consequences. The interplay of concurrent conditions such as diabetes, obesity, and kidney dysfunction with SARS-CoV-2 infection further complicates the disease's impact on bone health. SARS-CoV-2 infection directly and indirectly affects bone health, leading to potential long-term consequences. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

Interleukin-17 alleviates erastin-induced alveolar bone loss by suppressing ferroptosis via interaction between NRF2 and p-STAT3

AIM

To investigate the relationship between interleukin-17 (IL-17), ferroptosis and osteogenic differentiation.

MATERIALS AND METHODS

We first analysed the changes in ferroptosis-related molecules in experimental periodontitis models. The effects of erastin, a small-molecule ferroptosis inducer, and IL-17 on alveolar bone loss and repair in animal models were then investigated. Primary mouse mandibular osteoblasts were exposed to erastin and IL-17 in vitro. Ferroptosis- and osteogenesis-related genes and proteins were detected. Further, siRNA, immunofluorescence co-localization and immunoprecipitation were used to confirm the roles of the nuclear factor erythroid-2-related factor 2 (NRF2) and phosphorylated signal transducer and activator of transcription 3 (p-STAT3), as well as their interaction.

RESULTS

The levels of NRF2, glutathione peroxidase 4 and solute carrier family 7 member 11 were lower in the ligated tissues than in normal periodontal tissues. Alveolar bone loss in an in vivo experimental periodontitis model was aggravated by erastin and alleviated by IL-17. In vitro, IL-17 ameliorated erastin-inhibited osteogenic differentiation by reversing ferroptosis. Altered NRF2 expression correlated with changes in ferroptosis-related molecules and osteogenesis. Furthermore, the physical interaction between NRF2 and p-STAT3 was confirmed in the nucleus. In IL-17 + erastin-stimulated osteoblasts, the p-STAT3-NRF2 complex might actively participate in the downstream transcription of ferroptosis- and osteogenesis-related genes.

CONCLUSIONS

IL-17 administration conferred resistance to erastin-induced osteoblast ferroptosis and osteogenesis. The possible mechanism may involve p-STAT3 directly interacting with NRF2.

The Role of the Gut Microbiome in Orthopedic Surgery-a Narrative Review

PURPOSE OF REVIEW

The importance of the gut microbiome has received increasing attention in recent years. New literature has revealed significant associations between gut health and various orthopedic disorders, as well as the potential for interventions targeting the gut microbiome to prevent disease and improve musculoskeletal outcomes. We provide a broad overview of available literature discussing the links between the gut microbiome and pathogenesis and management of orthopedic disorders.

RECENT FINDINGS

Human and animal models have characterized the associations between gut microbiome dysregulation and diseases of the joints, spine, nerves, and muscle, as well as the physiology of bone formation and fracture healing. Interventions such as probiotic supplementation and fecal transplant have shown some promise in ameliorating the symptoms or slowing the progression of these disorders. We aim to aid discussions regarding optimization of patient outcomes in the field of orthopedic surgery by providing a narrative review of the available evidence-based literature involving gut microbiome dysregulation and its effects on orthopedic disease. In general, we believe that the gut microbiome is a viable target for interventions that can augment current management models and lead to significantly improved outcomes for patients under the care of orthopedic surgeons.

COVID-19 and Bone Loss: A Review of Risk Factors, Mechanisms, and Future Directions

PURPOSE OF REVIEW

SARS-CoV-2 drove the catastrophic global phenomenon of the COVID-19 pandemic resulting in a multitude of systemic health issues, including bone loss. The purpose of this review is to summarize recent findings related to bone loss and potential mechanisms.

RECENT FINDINGS

The early clinical evidence indicates an increase in vertebral fractures, hypocalcemia, vitamin D deficiencies, and a loss in BMD among COVID-19 patients. Additionally, lower BMD is associated with more severe SARS-CoV-2 infection. Preclinical models have shown bone loss and increased osteoclastogenesis. The bone loss associated with SARS-CoV-2 infection could be the result of many factors that directly affect the bone such as higher inflammation, activation of the NLRP3 inflammasome, recruitment of Th17 cells, the hypoxic environment, and changes in RANKL/OPG signaling. Additionally, SARS-CoV-2 infection can exert indirect effects on the skeleton, as mechanical unloading may occur with severe disease (e.g., bed rest) or with BMI loss and muscle wasting that has also been shown to occur with SARS-CoV-2 infection. Muscle wasting can also cause systemic issues that may influence the bone. Medications used to treat SARS-CoV-2 infection also have a negative effect on the bone. Lastly, SARS-CoV-2 infection may also worsen conditions such as diabetes and negatively affect kidney function, all of which could contribute to bone loss and increased fracture risk. SARS-CoV-2 can negatively affect the bone through multiple direct and indirect mechanisms. Future work will be needed to determine what patient populations are at risk of COVID-19-related increases in fracture risk, the mechanisms behind bone loss, and therapeutic options. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

Diets intervene osteoporosis via gut-bone axis

Osteoporosis is a systemic skeletal disease that seriously endangers the health of middle-aged and older adults. Recently, with the continuous deepening of research, an increasing number of studies have revealed gut microbiota as a potential target for osteoporosis, and the research concept of the gut-bone axis has gradually emerged. Additionally, the intake of dietary nutrients and the adoption of dietary patterns may affect the gut microbiota, and alterations in the gut microbiota might also influence the metabolic status of the host, thus adjusting bone metabolism. Based on the gut-bone axis, dietary intake can also participate in the modulation of bone metabolism by altering abundance, diversity, and composition of gut microbiota. Herein, combined with emerging literatures and relevant studies, this review is aimed to summarize the impacts of different dietary components and patterns on osteoporosis by acting on gut microbiota, as well as underlying mechanisms and proper dietary recommendations.

IL-17A functions and the therapeutic use of IL-17A and IL-17RA targeted antibodies for cancer treatment

Interleukin 17A (IL-17A) is a major member of the IL-17 cytokine family and is produced mainly by T helper 17 (Th17) cells. Other cells such as CD8+ T cells, γδ T cells, natural killer T cells and innate lymphoid-like cells can also produce IL-17A. In healthy individuals, IL-17A has a host-protective capacity, but excessive elevation of IL-17A is associated with the development of autoimmune diseases and cancer. Monoclonal antibodies (mAbs) targeting IL-17A (e.g., ixekizumab and secukinumab) or IL-17A receptor (IL-17RA) (e.g., brodalumab) would be investigated as potential treatments for these diseases. Currently, the application of IL-17A-targeted drugs in autoimmune diseases will provide new ideas for the treatment of tumors, and its combined application with immune checkpoint inhibitors has become a research hotspot. This article reviews the mechanism of action of IL-17A and the application of anti-IL-17A antibodies, focusing on the research progress on the mechanism of action and therapeutic blockade of IL-17A in various tumors such as colorectal cancer (CRC), lung cancer, gastric cancer and breast cancer. Moreover, we also include the results of therapeutic blockade in the field of cancer as well as recent advances in the regulation of IL-17A signaling.

The intestinal γδ T cells: functions in the gut and in the distant organs

Located in the frontline against the largest population of microbiota, the intestinal mucosa of mammals has evolved to become an effective immune system. γδ T cells, a unique T cell subpopulation, are rare in circulation blood and lymphoid tissues, but rich in the intestinal mucosa, particularly in the epithelium. Via rapid production of cytokines and growth factors, intestinal γδ T cells are key contributors to epithelial homeostasis and immune surveillance of infection. Intriguingly, recent studies have revealed that the intestinal γδ T cells may play novel exciting functions ranging from epithelial plasticity and remodeling in response to carbohydrate diets to the recovery of ischemic stroke. In this review article, we update regulatory molecules newly defined in lymphopoiesis of the intestinal γδ T cells and their novel functions locally in the intestinal mucosa, such as epithelial remodeling, and distantly in pathological setting, e.g., ischemic brain injury repair, psychosocial stress responses, and fracture repair. The challenges and potential revenues in intestinal γδ T cell studies are discussed.

Gut Microbiota and Microbial Metabolism in Early Risk of Cardiometabolic Disease

Cardiometabolic disease comprises cardiovascular and metabolic dysfunction and underlies the leading causes of morbidity and mortality, both within the United States and worldwide. Commensal microbiota are implicated in the development of cardiometabolic disease. Evidence suggests that the microbiome is relatively variable during infancy and early childhood, becoming more fixed in later childhood and adulthood. Effects of microbiota, both during early development, and in later life, may induce changes in host metabolism that modulate risk mechanisms and predispose toward the development of cardiometabolic disease. In this review, we summarize the factors that influence gut microbiome composition and function during early life and explore how changes in microbiota and microbial metabolism influence host metabolism and cardiometabolic risk throughout life. We highlight limitations in current methodology and approaches and outline state-of-the-art advances, which are improving research and building toward refined diagnosis and treatment options in microbiome-targeted therapies.