Beyond Antibodies: B Cells and the OPG/RANK-RANKL Pathway in Health, Non-HIV Disease and HIV-Induced Bone Loss

Bone marrow adipocytes and lung cancer bone metastasis: unraveling the role of adipokines in the tumor microenvironment

Bone is a common site of metastasis for lung cancer. The "seed and soil" hypothesis suggests that the bone marrow microenvironment ("soil") may provide a conducive survival environment for metastasizing tumor cells ("seeds"). The bone marrow microenvironment, comprising a complex array of cells, includes bone marrow adipocytes (BMAs), which constitute about 70% of the adult bone marrow volume and may play a significant role in tumor bone metastasis. BMAs can directly provide energy for tumor cells, promoting their proliferation and migration. Furthermore, BMAs participate in the tumor microenvironment's osteogenesis regulation, osteoclast(OC) regulation, and immune response through the secretion of adipokines, cytokines, and inflammatory factors. However, the precise mechanisms of BMAs in lung cancer bone metastasis remain largely unclear. This review primarily explores the role of BMAs and their secreted adipokines (leptin, adiponectin, Nesfatin-1, Resistin, chemerin, visfatin) in lung cancer bone metastasis, aiming to provide new insights into the mechanisms and clinical treatment of lung cancer bone metastasis.

Cooperation between T and B cells reinforce the establishment of bone metastases in a mouse model of breast cancer

Immune cells educated by the primary breast tumor and their secreted factors support the formation of bone pre-metastatic niche. Indeed, we showed that RANKL+ CD3+ T cells, specific for the 4T1 mammary carcinoma cell line, arrive at the bone marrow before metastatic cells and set the pre-metastatic niche. In the absence of RANKL expressed by T cells, there is no pre-metastatic osteolytic disease and bone metastases are completely blocked. Adding to the role of T cells, we have recently demonstrated that dendritic cells assist RANKL+ T cell activities at bone pre-metastatic niche, by differentiating into potent bone resorbing osteoclast-like cells, keeping their antigen-presenting cell properties, providing a positive feedback loop to the osteolytic profile. Here we are showing that bone marrow-derived CD19+ B cells, from 4T1 tumor-bearing mice, also express the pro-osteoclastogenic cytokine receptor activator of NFκB ligand (RANKL). Analysis of trabecular bone mineral density by conventional histomorphometry and X-ray microtomography (micro-CT) demonstrated that B cells expressing RANKL cooperate with 4T1-primed CD3+ T cells to induce bone loss. Moreover, RANKL expression by B cells depends on T cells activity, since experiments performed with B cells derived from 4T1 tumor-bearing nude BALB/c mice resulted in the maintenance of trabecular bone mass instead of bone loss. Altogether, we believe that 4T1-primed RANKL+ B cells alone are not central mediators of bone loss in vivo but when associated with T cells induce a strong decrease in bone mass, accelerating both breast cancer progression and bone metastases establishment. Although several studies performed in different pathological settings, showed that B cells, positively and negatively impact on osteoclastogenesis, due to their capacity to secret pro or anti-osteoclastogenic cytokines, as far as we know, this is the first report showing the role of RANKL expression by B cells on breast cancer-derived bone metastases scenario.

Global Publication Trends and Research Hotspots of the Immune System and Osteoporosis: A Bibliometric and Visualization Analysis from 2012 to 2022

BACKGROUND

Osteoporosis (OP) is a systemic bone metabolism disorder in which the immune system and bone metabolism interact.

OBJECTIVE

The purpose of this study was to explore the research status, hot spots and trends regarding the influence of the immune system on OP and to provide a basis for research directions and applications in this field.

METHODS

We searched and collected literature about the immune system and OP published from 2012 to 2022 in the Web of Science Core Collection database. All the included studies were subjected to bibliometrics analysis using Hiplot Pro, VOSviewer and CiteSpace software to produce statistics and visual analyses of the literature output, countries, institutions, authors, keywords and journals.

RESULTS

A total of 1201 papers were included, and the number of citations of these articles reached 31,776. The number of publications and citations on the immune system and OP has increased year by year. The top three countries with the greatest number of papers published were China, the United States of America (USA) and Italy. The two institutions with the largest number of papers published were Sichuan University and Soochow University, both located in China. De Martinis Massimo (Italy) and Ginaldi Lia (Italy) are prolific authors in this field. The representative academic journals are Osteoporosis International, Frontiers in Immunology, Journal of Bone and Mineral Research, PloS One and Bone. The results of the keyword cooccurrence analysis showed that the research topics in this field mainly focused on T cells, cytokines, signaling pathways, vitamin D, postmenopausal OP and immune diseases. The keyword burst results showed that zoledronic acid, chain fatty acids and gut microbiota are the frontiers and trends of future research on this topic.

CONCLUSION

The influence of the immune system on OP has been widely studied, and the current research in this field focuses on the effect or mechanism of immune-related cytokines, signaling pathways and vitamin D on OP. Future research trends in this field should focus on the immune regulation mechanism and clinical transformation of zoledronic acid, chain fatty acids and the gut microbiota in OP.

Evaluation of bone mineral density, microarchitecture, and detection of fractures on young patients living with human immunodeficiency virus: when and how to screen?

PURPOSE

People living with the human immunodeficiency virus (PLWH) developed higher life expectancy along with chronic bone disease over the past years. Our purpose is to evaluate bone mineral density, bone microarchitecture and fractures in young PLWH and understand the disease's contribution to bone derangements and fracture risk.

METHODS

Eighty-one HIV-infected and 54 control young (20-50 years) male and female subjects were enrolled in this study. Methods for patient evaluation included DXA-VFA (dual energy X-rays and vertebral fracture assessment), HR-pQCT (high resolution peripheral quantitative computed tomography), biochemistry and FRAX.

RESULTS

Fifty participants from each group completed all exams. Median age was 40 (25-49) vs. 36.5 (22-50) for the HIV and control groups, respectively (p 0.120). Ethnicity, body mass index, serum phosphorus, 25-hydroxyvitamin D, PTH and CTX were similar between groups, although ALP and OC suggested higher bone turnover in PLWH. VFA identified morphometric vertebral fractures in 12% of PLWH. PLWH had lower values for lumbar spine areal BMD and Z score, volumetric BMD, trabecular bone fraction (BV/TV) and trabecular number measured at the distal tibia by HR-pQCT; as a consequence, trabecular separation and heterogeneity were higher (all p < 0.05). The FRAX-estimated risk for hip and major osteoporotic fractures was statistically higher in PLWH (p < 0.001).

CONCLUSION

Our results confirm severe bone impairment and fractures associated with HIV in young patients. Thus, we developed a screening protocol for young PLWH to detect bone fragility, reduce skeletal disease progression and morbimortality, decrease fracture risk, and increase quality of life.

Distinct inflammation-related proteins associated with T cell immune recovery during chronic HIV-1 infection

Chronic inflammation and T cell dysregulation persist in individuals infected with human immunodeficiency virus type 1 (HIV-1), even after successful antiretroviral treatment. The mechanism involved is not fully understood. Here, we used Olink proteomics to comprehensively analyze the aberrant inflammation-related proteins (IRPs) in chronic HIV-1-infected individuals, including in 24 treatment-naïve individuals, 33 immunological responders, and 38 immunological non-responders. T cell dysfunction was evaluated as T cell exhaustion, activation, and differentiation using flow cytometry. We identified a cluster of IRPs (cluster 7), including CXCL11, CXCL9, TNF, CXCL10, and IL18, which was closely associated with T cell dysregulation during chronic HIV-1 infection. Interestingly, IRPs in cluster 5, including ST1A1, CASP8, SIRT2, AXIN1, STAMBP, CD40, and IL7, were negatively correlated with the HIV-1 reservoir size. We also identified a combination of CDCP1, CXCL11, CST5, SLAMF1, TRANCE, and CD5, which may be useful for distinguishing immunological responders and immunological non-responders. In conclusion, the distinct inflammatory milieu is closely associated with immune restoration of T cells, and our results provide insight into immune dysregulation during chronic HIV-1 infection.

Bone Health in People Living with HIV/AIDS: An Update of Where We Are and Potential Future Strategies

The developments in Human Immunodeficiency Virus (HIV) treatment and in the care of people living with HIV (PLWHIV) and Acquired Immunodeficiency Syndrome (AIDS) over the last three decades has led to a significant increase in life expectancy, on par with HIV-negative individuals. Aside from the fact that bone fractures tend to occur 10 years earlier than in HIV-negative individuals, HIV is, per se, an independent risk factor for bone fractures. A few available antiretroviral therapies (ARVs) are also linked with osteoporosis, particularly those involving tenofovir disoproxil fumarate (TDF). HIV and hepatitis C (HCV) coinfection is associated with a greater risk of osteoporosis and fracture than HIV monoinfection. Both the Fracture Risk Assessment Tool (FRAX) and measurement of bone mineral density (BMD) via a DEXA scan are routinely used in the assessment of fracture risk in individuals living with HIV, as bone loss is thought to start between the ages of 40 and 50 years old. The main treatment for established osteoporosis involves bisphosphonates. Supplementation with calcium and vitamin D is part of clinical practice of most HIV centers globally. Further research is needed to assess (i) the cut-off age for assessment of osteoporosis, (ii) the utility of anti-osteoporotic agents in PLWHIV and (iii) how concomitant viral infections and COVID-19 in PLWHIV can increase risk of osteoporosis.

Reduced bone formation and increased bone resorption drive bone loss in Eimeria infected broilers

Coccidiosis is an economically significant disease in the global poultry industry, but little is known about the mechanisms of bone defects caused by coccidiosis; thus, the study focused on effects of coccidiosis on the bone homeostasis of young broiler chickens. A total of 480 male Cobb500 broilers were randomly allocated into four treatment groups, including an uninfected control consuming diet ad libitum, two infected groups were orally gavaged with two different concentrations of sporulated Eimeria oocysts, and an uninfected pair-fed group fed the same amount of feed as the high Eimeria-infected group consumed. Growth performance and feed intake were recorded, and samples were collected on 6 days post infection. Results indicated that coccidiosis increased systemic oxidative status and elevated immune response in bone marrow, suppressing bone growth rate (P < 0.05) and increasing bone resorption (P < 0.05) which led to lower bone mineral density (P < 0.05) and mineral content (P < 0.05) under Eimeria infection. With the same amount of feed intake, the uninfected pair-fed group showed a distinguished bone formation rate and bone resorption level compared with the Eimeria infected groups. In conclusion, inflammatory immune response and oxidative stress in broilers after Eimeria infection were closely associated with altered bone homeostasis, highlighting the role of inflammation and oxidative stress in broiler bone homeostasis during coccidiosis.

Roles of Gut Microbiome in Bone Homeostasis and Its Relationship with Bone-Related Diseases

Simple Summary

In recent years, there has been increasing evidence that communication between the skeletal system and the gut microbiome (GM) can influence bone health and that the GM is a key regulator of bone homeostasis. Here, we review the roles of GM in bone homeostasis. In addition, the relationship between GM composition and selected bone-related diseases (osteoporosis, osteoarthritis, rheumatoid arthritis, diabetes mellitus, obesity and bone cancer) is presented. It is also emphasized that a probiotic supplementation can play an important role in suppressing the symptoms of each of these diseases.

Abstract

The extended microbial genome—the gut microbiome (GM)—plays a significant role in host health and disease. It is able to influence a number of physiological functions. During dysbiosis, GM is associated with the development of various chronic diseases with impaired bone quality. In general, GM is important for bone homeostasis and can affect it via several mechanisms. This review describes the roles of GM in bone homeostasis through influencing the immune and endocrine functions, short-chain fatty acids production, calcium absorption and the gut–brain axis. The relationship between GM composition and several bone-related diseases, specifically osteoporosis, osteoarthritis, rheumatoid arthritis, diabetes mellitus, obesity and bone cancer, is also highlighted and summarized. GM manipulation may become a future adjuvant therapy in the prevention of many chronic diseases. Therefore, the beneficial effects of probiotic therapy to improve the health status of individuals with aforementioned diseases are provided, but further studies are needed to clearly confirm its effectiveness. Recent evidence suggests that GM is responsible for direct and indirect effects on drug efficacy. Accordingly, various GM alterations and interactions related to the treatment of bone-related diseases are mentioned as well.

Pattern recognition receptor ligand-induced differentiation of human transitional B cells

B cells represent a critical component of the adaptive immune response whose development and differentiation are determined by antigen-dependent and antigen-independent interactions. In this study, we explored the effects of IL-4 and pattern-recognition receptor (PRR) ligands on B cell development and differentiation by investigating their capacity to drive the in vitro maturation of human transitional B cells. In the presence of IL-4, ligands for TLR7/8, TLR9, and NOD1 were effective in driving the in vitro maturation of cord blood transitional B cells into mature, naïve B cells as measured by CD23 expression, ABCB1 transporter activation and upregulation of sIgM and sIgD. In addition, several stimulation conditions, including TLR9 ligand alone, favored an expansion of CD27⁺ IgM memory B cells. Transitional B cells stimulated with TLR7/8 ligand + IL-4 or TLR9 ligand, with or without IL-4, induced a significant subpopulation of CD23⁺CD27⁺ B cells expressing high levels of sIgM and sIgD, a minor B cell subpopulation found in human peripheral blood. These studies illustrate the heterogeneity of the B cell populations induced by cytokine and PRR ligand stimulation. A comparison of transitional and mature, naïve B cells transcriptomes to identify novel genes involved in B cell maturation revealed that mature, naïve B cells were less transcriptionally active than transitional B cells. Nevertheless, a subset of differentially expressed genes in mature, naïve B cells was identified including genes associated with the IL-4 signaling pathway, PI3K signaling in B lymphocytes, the NF-κB signaling pathway, and the TNFR superfamily. When transitional B cells were stimulated in vitro with IL-4 and PRR ligands, gene expression was found to be dependent on the nature of the stimulants, suggesting that exposure to these stimulants may alter the developmental fate of transitional B cells. The influence of IL-4 and PRR signaling on transitional B cell maturation illustrates the potential synergy that may be achieved when certain PRR ligands are incorporated as adjuvants in vaccine formulations and presented to developing B cells in the context of an inflammatory cytokine environment. These studies demonstrate the potential of the PRR ligands to drive transitional B cell differentiation in the periphery during infection or vaccination independently of antigen mediated BCR signaling.

Long-term implications of COVID-19 on bone health: pathophysiology and therapeutics

BACKGROUND

SARS-CoV-2 is a highly infectious respiratory virus associated with coronavirus disease (COVID-19). Discoveries in the field revealed that inflammatory conditions exert a negative impact on bone metabolism; however, only limited studies reported the consequences of SARS-CoV-2 infection on skeletal homeostasis. Inflammatory immune cells (T helper-Th17 cells and macrophages) and their signature cytokines such as interleukin (IL)-6, IL-17, and tumor necrosis factor-alpha (TNF-α) are the major contributors to the cytokine storm observed in COVID-19 disease. Our group along with others has proven that an enhanced population of both inflammatory innate (Dendritic cells-DCs, macrophages, etc.) and adaptive (Th1, Th17, etc.) immune cells, along with their signature cytokines (IL-17, TNF-α, IFN-γ, IL-6, etc.), are associated with various inflammatory bone loss conditions. Moreover, several pieces of evidence suggest that SARS-CoV-2 infects various organs of the body via angiotensin-converting enzyme 2 (ACE2) receptors including bone cells (osteoblasts-OBs and osteoclasts-OCs). This evidence thus clearly highlights both the direct and indirect impact of SARS-CoV-2 on the physiological bone remodeling process. Moreover, data from the previous SARS-CoV outbreak in 2002-2004 revealed the long-term negative impact (decreased bone mineral density-BMDs) of these infections on bone health.

METHODOLOGY

We used the keywords "immunopathogenesis of SARS-CoV-2," "SARS-CoV-2 and bone cells," "factors influencing bone health and COVID-19," "GUT microbiota," and "COVID-19 and Bone health" to integrate the topics for making this review article by searching the following electronic databases: PubMed, Google Scholar, and Scopus.

CONCLUSION

Current evidence and reports indicate the direct relation between SARS-CoV-2 infection and bone health and thus warrant future research in this field. It would be imperative to assess the post-COVID-19 fracture risk of SARS-CoV-2-infected individuals by simultaneously monitoring them for bone metabolism/biochemical markers. Importantly, several emerging research suggest that dysbiosis of the gut microbiota-GM (established role in inflammatory bone loss conditions) is further involved in the severity of COVID-19 disease. In the present review, we thus also highlight the importance of dietary interventions including probiotics (modulating dysbiotic GM) as an adjunct therapeutic alternative in the treatment and management of long-term consequences of COVID-19 on bone health.

Effects of Biological/Targeted Therapies on Bone Mineral Density in Inflammatory Arthritis

Inflammatory arthritis has been reported to be associated with the development of osteoporosis. Recent research has investigated the mechanisms of bone metabolism in chronic inflammatory arthritis such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). Progress in both animal and clinical studies has provided a better understanding of the osteoclastogenesis-related pathways regarding the receptor activator of nuclear factor-κB ligand (RANKL), anti-citrullinated protein antibodies (ACPAs), and Wnt signaling and Dickkopf-related protein 1 (Dkk-1). The complex interplay between inflammatory cytokines and bone destruction has been elucidated, especially that in the interleukin-17/23 (IL-17/23) axis and Janus kinase and signal transducer and activator of transcription (JAK-STAT) signaling. Moreover, advances in biological and targeted therapies have achieved essential modifications to the bone metabolism of these inflammatory arthritis types. In this narrative review, we discuss recent findings on the pathogenic effects on bone in RA and SpA. Proinflammatory cytokines, autoantibodies, and multiple signaling pathways play an essential role in bone destruction in RA and SpA patients. We also reviewed the underlying pathomechanisms of bone structure in biological and targeted therapies of RA and SpA. The clinical implications of tumor necrosis factor inhibitors, abatacept, rituximab, tocilizumab, Janus kinase inhibitors, and inhibitors of the IL-17/23 axis are discussed. Since these novel therapeutics provide new options for disease improvement and symptom control in patients with RA and SpA, further rigorous evidence is warranted to provide a clinical reference for physicians and patients.

Estrogen-mediated downregulation of HIF-1α signaling in B lymphocytes influences postmenopausal bone loss

In the bone marrow, B cells and bone-resorbing osteoclasts colocalize and form a specific microenvironment. How B cells functionally influence osteoclasts and bone architecture is poorly understood. Using genetically modified mice and high-throughput analyses, we demonstrate that prolonged HIF-1α signaling in B cells leads to enhanced RANKL production and osteoclast formation. In addition, deletion of HIF-1α in B cells prevents estrogen deficiency-induced bone loss in mice. Mechanistically, estrogen controls HIF-1α protein stabilization through HSP70-mediated degradation in bone marrow B cells. The stabilization of HIF-1α protein in HSP70-deficient bone marrow B cells promotes RANKL production and osteoclastogenesis. Induction of HSP70 expression by geranylgeranylacetone (GGA) administration alleviates ovariectomy-induced osteoporosis. Moreover, RANKL gene expression has a positive correlation with HIF1A expression in human B cells. In conclusion, HIF-1α signaling in B cells is crucial for the control of osteoclastogenesis, and the HSP70/HIF-1α axis may serve as a new therapeutic target for osteoporosis.

RSPO2/RANKL-LGR4 signaling regulates osteoclastic pre-metastatic niche formation and bone metastasis

Therapeutics targeting osteoclasts are commonly used treatments for bone metastasis; however, whether and how osteoclasts regulate pre-metastatic niche and bone tropism is largely unknown. In this study, we report that osteoclast precursors (OPs) can function as a pre-metastatic niche component that facilitates breast cancer (BCa) bone metastasis at early stages. At the molecular level, unbiased GPCR ligand/agonist screening in BCa cells suggested that R-spondin 2 (RSPO2) and RANKL, through interacting with their receptor LGR4, promoted osteoclastic pre-metastatic niche formation and enhanced BCa bone metastasis. This was achieved by RSPO2/RANKL-LGR4 signal modulating WNT inhibitor DKK1 through Gαq and β-catenin signaling. DKK1 directly facilitated OP recruitment through suppressing its receptor low-density lipoprotein-related receptors 5 (LRP5) but not LRP6, upregulating Rnasek expression via inhibiting canonical WNT signaling. In clinical samples, RSPO2, LGR4 and DKK1 expression showed positive correlation with BCa bone metastasis. Furthermore, soluble LGR4 extracellular domain (ECD) protein, acting as a decoy receptor for RSPO2 and RANKL, significantly alleviated bone metastasis and osteolytic lesions in mouse bone metastasis model. These findings provide unique insights into the functional role of OPs as key components of pre-metastatic niche for BCa bone metastasis, indicate RSPO2/RANKL-LGR4 signaling as a promising target for inhibiting BCa bone metastasis.

Bone-sparing effects of rituximab and body composition analysis in a cohort of postmenopausal women affected by rheumatoid arthritis - retrospective study

Objective

Osteoporosis is the most common bone tissue disease and it is characterized by a reduced bone mineral density (BMD). The main physiopathological mechanisms converge on the uncoupling between bone formation and resorption, thus leading to an enhanced risk of fractures. Several papers have documented the inverse relationships linking high inflammatory cytokines, anti-citrullinated protein antibodies, rheumatoid factor, and BMD in rheumatoid arthritis (RA). Rituximab (RTX) is a chimeric monoclonal antibody directed against the CD20 receptor of B cells. Since the Food and Drug Administration approved it for RA in 2006, there have been many clinical experiences regarding its use. Nevertheless, few studies evaluate the effect of rituximab on BMD. RA is a disease characterized by immune dysfunction with high levels of inflammatory cytokines, autoantibodies, and it is reasonable that a B cell depleting therapy could restore a physiological cytokine balance, thus exerting an osteoprotective effect on the bone tissue. The purpose of this paper is to highlight any difference in BMD and to assess differences in body composition over a retrospective 18-month follow-up period after RTX treatment with a B cell depleting therapy.

Material and methods

We analyzed by dual energy X-ray absorptiometry BMD expressed as g/cm² and body composition modifications over 18 months with RTX treatment of 20 postmenopausal RA patients.

Results

After eighteen months of therapy with RTX, a statistically significant increase in vertebral (L1–L4) BMD and the stability of femoral BMD were documented.

Conclusions

Rituximab is associated with an improvement of vertebral and preservation of femoral BMD, suggesting a bone-sparing effect due to B cell depletion. Furthermore, patients displayed a redistribution of fat masses toward the hip region.

Patterns of Immune Activation in HIV and Non HIV Subjects and Its Relation to Cardiovascular Disease Risk

Introduction

Insight into inflammation patterns is needed to understand the pathophysiology of HIV and related cardiovascular disease (CVD). We assessed patterns of inflammation related to HIV infection and CVD risk assessed with carotid intima media thickness (CIMT).

Methods

A cross-sectional study was performed in Johannesburg, South Africa, including participants with HIV who were virally suppressed on anti-retroviral therapy (ART) as well as HIV-negative participants who were family members or friends to the HIV-positive participants. Information was collected on CVD risk factors and CIMT. Inflammation was measured with the Olink panel ‘inflammation’, allowing to simultaneously assess 92 inflammation markers. Differences in inflammation patterns between HIV-positive and HIV-negative participants were explored using a principal component analysis (PCA) and ANCOVA. The impact of differentiating immune markers, as identified by ANCOVA, on CIMT was assessed using linear regression while adjusting for classic CVD risk factors.

Results

In total, 185 HIV-positive and 104 HIV negative participants, 63% females, median age 40.7 years (IQR 35.4 – 47.7) were included. HIV-positive individuals were older (+6 years, p <0.01) and had a higher CIMT (p <0.01). No clear patterns of inflammation were identified by use of PCA. Following ANCOVA, nine immune markers differed significantly between HIV-positive and HIV-negative participants, including PDL1. PDL1 was independently associated with CIMT, but upon stratification this effect remained for HIV-negative individuals only.

Conclusion

HIV positive patients on stable ART and HIV negative controls had similar immune activation patterns. CVD risk in HIV-positive participants was mediated by inflammation markers included in this study.

The microbiota-gut-bone axis and bone health

The gastrointestinal tract is colonized by trillions of microorganisms, consisting of bacteria, fungi, and viruses, known as the "second gene pool" of the human body. In recent years, the microbiota-gut-bone axis has attracted increasing attention in the field of skeletal health/disorders. The involvement of gut microbial dysbiosis in multiple bone disorders has been recognized. The gut microbiota regulates skeletal homeostasis through its effects on host metabolism, immune function, and hormonal secretion. Owing to the essential role of the gut microbiota in skeletal homeostasis, novel gut microbiota-targeting therapeutics, such as probiotics and prebiotics, have been proven effective in preventing bone loss. However, more well-controlled clinical trials are still needed to evaluate the long-term efficacy and safety of these ecologic modulators in the treatment of bone disorders.

Development of a method for the identification of receptor activator of nuclear factor-κB+ populations in vivo

OBJECTIVES

Osteoclasts are induced by macrophage colony-stimulating factor-1 (CSF-1) and receptor activator of nuclear factor-κB (RANK) ligand (RANKL). Monocyte/macrophage lineages are thought to be osteoclast precursors; however, such cells have not been fully characterized owing to a lack of tools for their identification. Osteoclast precursors express colony-stimulating factor-1 receptor (CSF-1R) and RANK. However, the capacity of conventional methods using anti-RANK antibodies to detect RANK⁺ cells by flow cytometry is insufficient. Here, we developed a high-sensitivity method for detecting RANK⁺ cells using biotinylated recombinant glutathione S-transferase-RANKL (GST-RANKL-biotin).

METHODS

We sorted sub-populations of mouse bone marrow (BM) or peripheral blood (PB) cells using GST-RANKL-biotin, anti-CSF1R, and anti-B220 antibodies and induced osteoclastogenesis in vitro.

RESULTS

The frequency of the RANK⁺ population in BM detected by GST-RANKL-biotin was significantly higher than that detected by anti-RANK antibodies. Although RANK⁺ cells were detected in both the B220⁺ and B220^- populations, the macrophage lineage was present only in B220^-. Unexpectedly, a significantly higher number of osteoclasts was induced in RANK^-CSF-1R⁺ cells than in RANK⁺CSF-1R⁺ cells contained in the B220^- population. In contrast, the PB-derived B220^-RANK⁺CSF-1R⁺ population contained a significantly higher frequency of osteoclast precursors than the B220^-RANK^-CSF-1R⁺ population.

CONCLUSIONS

These results suggest that GST-RANKL-biotin is useful for the detection of RANK⁺ cells and that RANK and CSF-1R may be helpful indicators of osteoclast precursors in PB.

PKC-δ deficiency in B cells displays osteopenia accompanied with upregulation of RANKL expression and osteoclast-osteoblast uncoupling

PKC-δ is an important molecule for B-cell proliferation and tolerance. B cells have long been recognized to play a part in osteoimmunology and pathological bone loss. However, the role of B cells with PKC-δ deficiency in bone homeostasis and the underlying mechanisms are unknown. We generated mice with PKC-δ deletion selectively in B cells by crossing PKC-δ-loxP mice with CD19-Cre mice. We studied their bone phenotype using micro-CT and histology. Next, immune organs were obtained and analyzed. Western blotting was used to determine the RANKL/OPG ratio in vitro in B-cell cultures, ELISA assay and immunohistochemistry were used to analyze in vivo RANKL/OPG balance in serum and bone sections respectively. Finally, we utilized osteoclastogenesis to study osteoclast function via hydroxyapatite resorption assay, and isolated primary calvaria osteoblasts to investigate osteoblast proliferation and differentiation. We also investigated osteoclast and osteoblast biology in co-culture with B-cell supernatants. We found that mice with PKC-δ deficiency in B cells displayed an osteopenia phenotype in the trabecular and cortical compartment of long bones. In addition, PKC-δ deletion resulted in changes of trabecular bone structure in association with activation of osteoclast bone resorption and decrease in osteoblast parameters. As expected, inactivation of PKC-δ in B cells resulted in changes in spleen B-cell number, function, and distribution. Consistently, the RANKL/OPG ratio was elevated remarkably in B-cell culture, in the serum and in bone specimens after loss of PKC-δ in B cells. Finally, in vitro analysis revealed that PKC-δ ablation suppressed osteoclast differentiation and function but co-culture with B-cell supernatant reversed the suppression effect, as well as impaired osteoblast proliferation and function, indicative of osteoclast–osteoblast uncoupling. In conclusion, PKC-δ plays an important role in the interplay between B cells in the immune system and bone cells in the pathogenesis of bone lytic diseases.

Profiling of Inflammatory Proteins in Plasma of HIV-1-Infected Children Receiving Antiretroviral Therapy

Treatment of HIV-1-infected patients results in improved clinical and immunological conditions, but severe non-AIDS-related conditions still persist. Novel proteomic platforms have identified inflammatory proteins where abundance is dysregulated in adult treated patients, whereas limited data are available in treated HIV-1 infection of children. Using a proteomic plasma profiling approach comprising 92 inflammation-related molecules, we analyzed specimens from 43 vertically HIV-1-infected children receiving antiretroviral treatment (ART) and matched controls in Ethiopia. The infected children were analyzed as a group and separately, according to age of treatment initiation. Proteins displaying a significantly different abundance between groups were hierarchically clustered and presented in heat maps. Random forest analysis was performed to pin-point proteins discriminating between groups; five proteins (STAMBP, CD5, TFG-α, TRANCE, AXIN1) were the strongest prediction factors for treated HIV-1 infection. TRANCE was previously linked to reduced bone mass levels in HIV-1-infected children. CCL4 chemokine, ligand to HIV-1 co-receptor CCR5, was the most critical protein for successful classification between children who initiated ART at different time points. Our data provide evidence that a dysregulated expression of proteins linked to immunological abnormalities and bone metabolism can be found in HIV-1-infected children with prolonged exposure to ART.

People living with HIV and fracture risk

PLHIV have an increased risk of osteoporosis and fractures when compared with people of the same age and sex. In this review, we address the epidemiology and the pathophysiology of bone disease and fractures in PLHIV. The assessment of fracture risk and fracture prevention in these subjects is also discussed. The spectrum of HIV-associated disease has changed dramatically since the introduction of potent antiretroviral drugs. Today, the survival of people living with HIV (PLHIV) is close to that of the general population. However, the longer life-span in PLHIV is accompanied by an increased prevalence of chronic diseases. Detrimental effects on bone health are well recognised, with an increased risk of osteoporosis and fractures, including vertebral fractures, compared to the general population. The causes of bone disease in PLHIV are not fully understood, but include HIV-specific risk factors such as use of antiretrovirals and the presence of chronic inflammation, as well as traditional risk factors for fracture. Current guidelines recommend the use of FRAX to assess fracture probability in PLHIV age ≥ 40 years and measurement of bone mineral density in those at increased fracture risk. Vitamin D deficiency, if present, should be treated. Bisphosphonates have been shown to increase bone density in PLHIV although fracture outcomes are not available.

Immature/transitional B-cell expansion is associated with bone loss in HIV-infected individuals with severe CD4+ T-cell lymphopenia

BACKGROUND

Antiretroviral therapy (ART) has led to a significant decline in HIV-related morbidity and mortality in people living with HIV (PLWH). PLWH however experience non-AIDS ageing-associated comorbidities, including decreased bone mass and osteoporosis, earlier and more severely, than uninfected people. We previously reported that total B-cell production of the key osteoclastogenic cytokine receptor activator of NF-κB ligand (RANKL) was elevated in PLWH, concurrent with a decrease in total B-cell production of RANKL's physiological moderator Osteoprotegerin (OPG). The resulting increased total B-cell RANKL/OPG ratio was significantly associated with bone loss in the appendicular (long bones), but not axial (spine) skeletons of PLWH. A role for immature/transitional B cells (BImm) in HIV-induced bone loss has not been reported.

METHODS

BImm frequency was determined by flow cytometry; plasma IL-7 was quantified by ELISA and bone mineral density (BMD) measured by dual X-ray absorptiometry (DXA) in a cross-sectional study of 62 ART-naive HIV-infected and 58 HIV-negative individuals.

RESULTS

BImm expansion correlated with the total B-cell RANKL/OPG ratio in HIV-infected individuals and inversely with BMD at the total hip, femoral neck and the lumbar spine, and with IL-7.

CONCLUSION

These data suggest that BImm contribute to the increased B-cell RANKL/OPG ratio in PLWH, and reveal a previously unrecognized link between BImm expansion and HIV-induced bone loss in the axial and appendicular skeletons of severely immunocompromised HIV-infected individuals. BImm expansion may be a novel biomarker for screening patients at risk of osteoporosis.

Erythropoietin receptor in B cells plays a role in bone remodeling in mice

Erythropoietin (EPO) is a key regulator of erythropoiesis. However, EPO receptors (EPO-Rs) are also expressed on non-erythroid cell types, including myeloid and bone cells. Immune cells also participate in bone homeostasis. B cells produce receptor activator of nuclear factor kappa-Β ligand (RANKL) and osteoprotegerin (OPG), two pivotal regulators of bone metabolism. Here we explored the ability of B cells to transdifferentiate into functional osteoclasts and examined the role of EPO in this process in a murine model.

Methods: We have combined specifically-designed experimental mouse models and in vitro based osteoclastogenesis assays, as well as PCR analysis of gene expression.

Results: (i) EPO treatment in vivo increased RANKL expression in bone marrow (BM) B cells, suggesting a paracrine effect on osteoclastogenesis; (ii) B cell-derived osteoclastogenesis occured in vivo and in vitro, as demonstrated by B cell lineage tracing in murine models; (iii) B-cell-derived osteoclastogenesis in vitro was restricted to Pro-B cells expressing CD115/CSF1-R and is enhanced by EPO; (iv) EPO treatment increased the number of B-cell-derived preosteoclasts (β3⁺CD115⁺), suggesting a physiological rationale for B cell derived osteoclastogenesis; (v) finally, mice with conditional EPO-R knockdown in the B cell lineage (cKD) displayed a higher cortical and trabecular bone mass. Moreover, cKD displayed attenuated EPO-driven trabecular bone loss, an effect that was observed despite the fact that cKD mice attained higher hemoglobin levels following EPO treatment.

Conclusions: Our work highlights B cells as an important extra-erythropoietic target of EPO-EPO-R signaling and suggests their involvement in the regulation of bone homeostasis and possibly in EPO-stimulated erythropoietic response. Importantly, we present here for the first time, histological evidence for B cell-derived osteoclastogenesis in vivo.

Osteocalcin and regulatory cytokine imbalance in children with congenital cleft lip and palate

The aim of the work was a comprehensive assessment of the cytokine system and peripheral blood osteocalcin with the establishment of features of their interconnections in children with congenital cleft lip and palate (CCLP) in comparison with corresponding controls at different age periods. Levels of IL17, IL4, IL6, IL1β, IFNγ and osteocalcin were analyzed by enzyme immunoassay in the peripheral blood of 80 children (0-12 months, 1-3 years, 4-9 years, 10-15 years) with CCLP and age-appropriate control of healthy individuals (40 people). An analysis of the obtained data shows that in children with CCLP we revealed significant differences between pro-inflammatory (IL1β, IL6, IL17), regulatory (IFNγ), anti-inflammatory (IL4) cytokines and osteocalcin compared with controls. Differences were found in the content of IL17, IFNγ, IL4 and osteocalcin in healthy children and in children with CCLP in postnatal ontogenesis. Cytokine deregulation of immunosteogenesis in CCLP, leading to a significant deficit of osteocalcin in the first year of life due to imbalance of the cytokine profile: discordant IL17, IFNγ and IL4 were detected. Obtained data are undoubtedly important in the future for developing new strategies for targeted therapy aimed at normalizing osteocalcin levels at different age periods in children with CCLP.

D-mannose attenuates bone loss in mice via Treg cell proliferation and gut microbiota-dependent anti-inflammatory effects

Background:

D-mannose exhibits strong anti-inflammatory properties, but whether it has beneficial effects on preventing and treating osteoporosis remains unknown.

Methods:

Female, 12-month-old senile C57BL6/J mice (s-Man group) and 8-week-old ovariectomized C57BL6/J mice (OVX-Man group) were treated with D-mannose in drinking water for 2 months (six mice/group). Microcomputed tomography analysis and hematoxylin and eosin staining were performed to investigate the effect of D-mannose on attenuation of bone loss. Tartrate-resistant acid phosphatase staining of tissue sections, flow cytometry, enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, and gut microbiome biodiversity tests were used to explore the underlying mechanisms.

Results:

D-mannose-induced marked increases in cortical bone volume and trabecular bone microarchitecture in the s-Man and OVX-Man group compared with that in the s-CTRL (senile control) and OVX group, respectively. Moreover, D-mannose downregulated osteoclastogenesis-related cytokines in the bone marrow and expanded regulatory T cells in the spleen of mice. Furthermore, D-mannose reconstructed the gut microbiota and changed the metabolite composition.

Conclusion:

D-mannose attenuated bone loss induced by senility and estrogen deficiency in mice, and this effect may be mediated by D-mannose-induced proliferation of regulatory T cells and gut microbiota-dependent anti-inflammatory effects.

[The impact of disbalance of regulatory cytokines and osteocalcin on osteogenesis in children with congenital cleft lip and palate in postnatal ontogenesis]

The aim of the work was a comprehensive assessment of the system of cytokines and peripheral blood osteocalcin with the establishment of features of their interconnections in children with congenital cleft lip and palate (CCLP) in comparison with the corresponding controls at different age periods. In the peripheral blood of 80 children (0-12 months, 1-3 years, 4-9 years, 10-15 years) with osteocalcin and IL17, IL4, congenital cleft lip and palate and age-appropriate control of healthy individuals (40 people) IL6, IL1β, IFNγ by enzyme immunoassay. An analysis of the data obtained with CCLP revealed significant differences in the dynamics of the relationship between pro-inflammatory (IL1β, IL6, IL17), regulatory (IFNγ), anti-inflammatory (IL4) cytokines and osteocalcin compared with controls. The patterns of changes and effects of IL17, IFNγ, IL4 and osteocalcin in healthy children and in children with congenital cleft lip and palate in postnatal ontogenesis were established. Cytokine dysregulation of immunosteogenesis in CCLP, leading to a significant deficit of osteocalcin in the first year of life due to an imbalance of the cytokine profile: discordant IL17, IFNγ and IL4 were detected. Thus, the data obtained are undoubtedly important in the future for developing new strategies for targeted therapy aimed at normalizing osteocalcin levels at different age periods in children with congenital cleft lip and palate.

Bone Diseases in Patients with Chronic Liver Disease

Osteoporosis is a frequently observed complication in patients with chronic liver disease, particularly liver cirrhosis and cholestatic liver diseases. In addition, osteoporosis is critical in patients receiving a liver transplant. Nevertheless, few studies have evaluated bone diseases in patients with more frequently observed chronic liver disease, such as chronic viral hepatitis, nonalcoholic fatty liver disease and alcoholic liver disease. Osteoporosis is a disease caused by an imbalance in the activities of osteoblasts and osteoclasts. Over the last few decades, many advances have improved our knowledge of the pathogenesis of osteoporosis. Importantly, activated immune cells affect the progression of osteoporosis, and chronic inflammation may exert an additional effect on the existing pathophysiology of osteoporosis. The microbiota of the intestinal tract may also affect the progression of bone loss in patients with chronic liver disease. Recently, studies regarding the effects of chronic inflammation on dysbiosis in bone diseases have been conducted. However, mechanisms underlying osteoporosis in patients with chronic liver disease are complex and precise mechanisms remain unknown. The following special considerations in patients with chronic liver disease are reviewed: bone diseases in patients who underwent a liver transplant, the association between chronic hepatitis B virus infection treatment and bone diseases, the association between sarcopenia and bone diseases in patients with chronic liver disease, and the association between chronic liver disease and avascular necrosis of the hip. Few guidelines are currently available for the management of low bone mineral density or bone diseases in patients with chronic liver disease. Due to increased life expectancy and therapeutic advances in chronic liver disease, the importance of managing osteoporosis and other bone diseases in patients with chronic liver disease is expected to increase. Consequently, specific guidelines need to be established in the near future.

Transcriptome Sequencing Identifies Novel Immune Response Genes Highly Related to the Severity of Human Adenovirus Type 55 Infection

Human adenovirus type 55 (HAdV-55) is considered a highly virulent pathogen causing severe and even deadly pneumonia in immunocompetent people. The mechanisms of HAdV-55-induced initiation and progression of severe pneumonia remain ambiguous. In the current study, we endeavored to identify novel immune response genes which are substantially involved in the pathogenesis of severe inflammation in HAdV-55-infected patients. HAdV-55-infected patients with upper respiratory tract symptoms (minor patients) and pneumonia (severe patients) were enrolled. Through transcriptome sequencing and quantitative real-time PCR, the peripheral blood mononuclear cells of the patients were analyzed. We found that the expression of eight genes, including Il18, Il36b, Il17rc, Tnfsf10, Tnfsf11, Tnfsf14, Tnfsf15, and Il1a, were closely correlated with the severity of HAdV-55 infection. Most of these genes belong to interleukin-1 family or tumor necrosis factor (TNF) superfamily, respectively. The changes in gene expression were confirmed by Western blot assay. Our data will be crucial for deepening the understanding of the pathogenic mechanisms of severe pneumonia in HAdV-55 infection.

Interferon-Gamma-Mediated Osteoimmunology

Osteoimmunology is the interdiscipline that focuses on the relationship between the skeletal and immune systems. They are interconnected by shared signal pathways and cytokines. Interferon-gamma (IFN-γ) plays important roles in immune responses and bone metabolism. IFN-γ enhances macrophage activation and antigen presentation. It regulates antiviral and antibacterial immunity as well as signal transduction. IFN-γ can promote osteoblast differentiation and inhibit bone marrow adipocyte formation. IFN-γ plays dual role in osteoclasts depending on its stage. Furthermore, IFN-γ is an important pathogenetic factor in some immune-mediated bone diseases including rheumatoid arthritis, postmenopausal osteoporosis, and acquired immunodeficiency syndrome. This review will discuss the contradictory findings of IFN-γ in osteoimmunology and its clinical application potential.