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Bone marrow (BM) is a heterogeneous niche where bone marrow stromal cells (BMSCs), osteoblasts, osteoclasts, adipocytes, hematopoietic cells, and immune cells coexist. The cellular composition of BM changes with various pathophysiological states. A reduction in osteoblast number and a concomitant increase in adipocyte number in aging and pathological conditions put bone marrow adipose tissue (BMAT) into spotlight. Accumulating evidence strongly supports that an overwhelming production of BMAT is a major contributor to bone loss disorders. Therefore, BMAT-targeted therapy can be an efficient and feasible intervention for osteoporosis. However, compared to blocking bone-destroying molecules produced by BMAT, suppressing BMAT formation is theoretically a more effective and fundamental approach in treating osteoporotic bone diseases. Thus, a deep insight into the molecular basis underlying increased BM adiposity during pathologic bone loss is critical to formulate strategies for therapeutically manipulating BMAT. In this review, we comprehensively summarize the molecular mechanisms involved in adipocyte differentiation of BMSCs as well as the interaction between bone marrow adipocytes and osteoclasts. More importantly, we further discuss the potential clinical implications of therapeutically targeting the upstream of BMAT formation in bone loss diseases.

As the main cells in endochondral osteogenesis, chondrocytes have limited self-repair ability due to weak proliferation activity, low density, and dedifferentiation tendency. Here, a thorough inquiry about the effect and underlying mechanisms of methyltransferase like-3 (Mettl3) on chondrocytes was made. Functionally, it was indicated that Mettl3 promoted the proliferation and hypertrophic differentiation of chondrocytes. Mechanically, Dmp1 (dentin matrix protein 1) was proved to be the downstream direct target of Mettl3 for m

Statement of problem The internal connection is a widely used implant-abutment connection. However, a meta-analysis comparing the internal tapered and nontapered connection systems is lacking. Purpose The purpose of this systematic review and meta-analysis was to assess whether the internal tapered connection performs better than the internal nontapered connection in terms of implant survival, marginal bone loss, probing depths, and complications. Material and methods The following specific question was formulated based on the Population, Intervention, Control, and Outcome (PICO) model: Do patients receiving internal tapered connection implants show better prognosis than those receiving the internal nontapered connection in terms of implant survival, marginal bone loss, probing depths, and complications? An electronic systematic literature search was conducted in the Cochrane Library databases, MEDLINE (PubMed), and Embase for relevant studies published in English without time restrictions. A manual search was also conducted. In vivo randomized controlled trials (RCTs) and prospective cohort studies were included. Results A total of 592 studies were collected from the electronic and manual searches. After independent screening by 2 reviewers, 5 RCTs and 2 prospective cohort studies were included. No significant difference was observed in implant survival rates (P=.47; RR: 1.01; 95% CI: 0.98, 1.05). Regarding marginal bone loss, the internal tapered connection presented better results than the nontapered connection (P=.003; MD: −0.43 mm; 95% CI: −0.73, −0.14). The internal tapered connection also exhibited lower probing depths than the nontapered one (P=.002; MD: −0.24 mm; 95% CI: −0.39, −0.09). No significant difference was observed in complication rates (P=.47; RR: 1.21; 95% CI: 0.72, 2.04). Conclusions Within the limitations of this systematic review and meta-analysis, the internal tapered connection and nontapered connection were comparable in terms of implant survival rates and complication rates. In contrast to the internal nontapered connection, marginal bone loss and probing depths in the tapered connection were significantly lower.

Bone metastasis is the result of complex crosstalk between tumor cells and bone marrow cells. Bone marrow adipocytes (BMAs) are the most abundant cell type in adult bone marrow. Therefore, we explore the effects of BMAs on bone metastasis in lung cancer. RNA-seq was used to compare the mRNA expression level of bone metastatic SBC5 cells and non-bone metastatic SBC3 cells. Rosiglitazone-induced marrow adiposity and intra-femoral injection of SBC5 cells were used to demonstrate the relationship between BMAs and SBC5 cells in vivo. Co-culture system, gene co-expression, gene ontology (GO) enrichment analysis and protein–protein interaction (PPI) network were used to explore the potential mechanism. BMAs specially enhance the invasion of bone metastatic SBC5 instead of non-bone metastatic SBC3 in vitro. SBC5 instead of SBC3 promoted osteoblast and osteoclast differentiation as well as de-differentiation of mature BMAs. Rosiglitazone-induced marrow adiposity significantly enhanced osteolytic lesion induced by SBC5 in vivo. RNA-seq revealed that compared with SBC3, S100A9 and S100A8 genes were the most prominent genes up-regulated in SBC5 cells. High expression of S100A8/9 in SBC5 could be responsible for the crosstalk between lung cancer cells and BMAs. More importantly, interleukin 6 receptor (IL6R), which is adjacent to S100A8/A9 in 1q21.3, was significantly up-regulated by BMAs in vitro. S100A8/A9 (1 μg/ml) could obviously enhance the osteoblastic differentiation and inhibit adipogenic differentiation, whereas TLR4 inhibitor TAK242 (10 μmol/l) significantly attenuated this effect. Our study suggested that bone marrow adipocyte may communicate with lung cancer cells via 1q21.3 (S100A8/A9-IL6R)-TLR4 pathway to promote osteolytic bone destruction. 1q21.3 (S100A8/A9-IL6R) is a potential target for the treatment of lung cancer bone metastasis.

Background:Intercellular crosstalk among osteoblast, osteoclast, osteocyte and chondrocyte is involved in the precise control of bone homeostasis. Disruption of this cellular and molecular signaling would lead to metabolic bone diseases such as osteoporosis. Currently a number of anti-osteoporosis interventions are restricted by side effects, complications and long-term intolerance. This review aims to summarize the bone cellular communication involved in bone remodeling and its usage to develop new drugs for osteoporosis.Methods:We searched PubMed for publications from 1 January 1980 to 1 January 2018 to identify relevant and latest literatures, evaluation and prospect of osteoporosis medication were summarized. Detailed search terms were ‘osteoporosis’, ‘osteocyte’, ‘osteoblast’, ‘osteoclast’, ‘bone remodeling’, ‘chondrocyte’, ‘osteoporosis treatment’, ‘osteoporosis therapy’, ‘bisphosphonates’, ‘denosumab’, ‘Selective Estrogen Receptor Modulator (SERM)’, ‘PTH’, ‘romosozumab’, ‘dkk-1 antagonist’, ‘strontium ranelate’.Results:A total of 170 papers were included in the review. About 80 papers described bone cell interactions involved in bone remodeling. The remaining papers were focused on the novel advanced and new horizons in osteoporosis therapies.Conclusion:There exists a complex signal network among bone cells involved in bone remodeling. The disorder of cell-cell communications may be the underlying mechanism of osteoporosis. Current anti-osteoporosis therapies are effective but accompanied by certain drawbacks simultaneously. Restoring the abnormal signal network and individualized therapy are critical for ideal drug development.

Osteoporosis is the most common metabolic skeletal disease. It is characterized by the deterioration of the skeletal microarchitecture and bone loss, leading to ostealgia, and even bone fractures. Accumulating evidence has indicated that there is an inextricable relationship between the gut microbiota (GM) and bone homeostasis involving host-microbiota crosstalk. Any perturbation of the GM can play an initiating and reinforcing role in disrupting the bone remodeling balance during the development of osteoporosis. Although the GM is known to influence bone metabolism, the mechanisms associated with these effects remain unclear. Herein, we review the current knowledge of how the GM affects bone metabolism in health and disease, summarize the correlation between pathogen-associated molecular patterns of GM structural components and bone metabolism, and discuss the potential mechanisms underlying how GM metabolites regulate bone turnover. Deciphering the complicated relationship between the GM and bone health will provide new insights into the prevention and treatment of osteoporosis.

To review the pathological effects of cellular senescence in the occurrence and development of osteoarthritis (OA) and potential therapeutic targets.The role of chondrocyte senescence, synovial cell senescence, mesenchymal stem cells senescence in OA, and the biological mechanism and progress of chondrocyte senescence were summarized by consulting relevant domestic and abroad literature.The existing evidence has basically made clear that chondrocyte senescence, mesenchymal stem cells senescence, and cartilage repair abnormalities, and the occurrence and development of OA have a certain causal relationship, and the role of the senescence of synovial cells, especially synovial macrophages in OA is still unclear. Transcription factors and epigenetics are the main mechanisms that regulate the upstream pathways of cellular senescence. Signal communication between cells can promote the appearance of senescent phenotypes in healthy cells. Targeted elimination of senescent cells and promotion of mesenchymal stem cells rejuvenation can effectively delay the progress of OA.Cellular senescence is an important biological phenomenon and potential therapeutic target in the occurrence and development of OA. In-depth study of its biological mechanism is helpful to the early prevention and treatment of OA.综述细胞衰老在骨关节炎（osteoarthritis，OA）发生、发展中的病理作用及潜在治疗靶点。.查阅国内外相关文献，对软骨细胞衰老、滑膜细胞衰老、MSCs 衰老在 OA 中的作用及软骨细胞衰老发生的生物学机制和进展进行总结。.现有证据已基本明确软骨细胞衰老、MSCs 衰老与软骨修复异常及 OA 的发生、发展存在一定因果关系，而滑膜细胞衰老，特别是滑膜巨噬细胞衰老在 OA 中的作用尚不明确。转录因子、表观遗传是调控衰老上游通路的主要机制，细胞间的信号交流可促进健康细胞出现衰老表型。定向清除衰老细胞和促进 MSCs 年轻化可有效延缓 OA 的进展。.细胞衰老是 OA 发生、发展中的重要生物学现象及潜在治疗靶点，深入研究其生物学机制有助于 OA 的早期防治。.

Glucocorticoids are widely used to treat varieties of allergic and autoimmune diseases, however, long-term application results in glucocorticoid-induced osteoporosis (GIOP). Inflammatory cytokines: tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) play important regulatory roles in bone metabolism, but their roles in GIOP remain largely unknown. Osteocytes can modulate the formation and function of both osteoblasts and osteoclasts, directly via gap junctions, or indirectly by transferring molecule signaling. Apoptotic osteocytes release RANKL, HMGB1 and pro-inflammatory cytokines to stimulate osteoclastogenesis. Moreover, osteocytes can secrete FGF23 to regulate bone metabolism. Exposure to high levels of GCs can drive osteocyte apoptosis and influence gap junctions, leading to bone loss. GCs treatment is regarded to produce more FGF23 to inhibit bone mineralization. GCs also disrupt the vascular to decrease osteocyte feasibility and mineral appositional rate, resulting in a decline in bone strength. Apoptotic bodies from osteocytes induced by GCs treatment can enhance production of TNF-α and IL-6. On the other hand, TNF-α and IL-6 show synergistic effects by altering osteocytes signaling towards osteoclasts and osteoblasts. In addition, TNF-α can induce osteocyte apoptosis and attribute to a worsened bone quality in GCs. IL-6 and osteocytes may interact with each other. Therefore, we hypothesize that GCs regulate osteocyteogenesis through TNF-α and IL-6, which are highly expressed around osteocyte undergoing apoptosis. In the present review, we summarized the roles of osteocytes in regulating osteoblasts and osteoclasts. Furthermore, the mechanism of GCs altered relationship between osteocytes and osteoblasts/osteoclasts. In addition, we discussed the roles of TNF-α and IL-6 in GIOP by modulating osteocytes. Lastly, we discussed the possibility of using pro-inflammatory signaling pathway as therapeutic targets to develop drugs for GIOP.

The complex crosstalk between the immune and the skeletal systems plays an indispensable role in the maintenance of skeletal homeostasis. Various cytokines are involved, including interleukin (IL)-17A. A variety of immune and inflammatory cells produces IL-17A, especially Th17 cells, a subtype of CD4+ T cells. IL-17A orchestrates diverse inflammatory and immune processes. IL-17A induces direct and indirect effects on osteoclasts. The dual role of IL-17A on osteoclasts partly depends on its concentrations and interactions with other factors. Interestingly, IL-17A exerts a dual role in osteoblasts in vitro. IL-17A is a bone-destroying cytokine in numerous immune-mediated bone diseases including postmenopausal osteoporosis (PMOP), rheumatoid arthritis (RA), psoriatic arthritis (PsA) and axial spondylarthritis (axSpA). This review will summarize and discuss the pathophysiological roles of IL-17A on the skeletal system and its potential strategies for application in immune-mediated bone diseases.

Postmenopausal osteoporosis (PMOP) is a prevalent skeletal disorder associated with menopause-related estrogen withdrawal. PMOP is characterized by low bone mass, deterioration of the skeletal microarchitecture, and subsequent increased susceptibility to fragility fractures, thus contributing to disability and mortality. Accumulating evidence indicates that abnormal expansion of marrow adipose tissue (MAT) plays a crucial role in the onset and progression of PMOP, in part because both bone marrow adipocytes and osteoblasts share a common ancestor lineage. The cohabitation of MAT adipocytes, mesenchymal stromal cells, hematopoietic cells, osteoblasts and osteoclasts in the bone marrow creates a microenvironment that permits adipocytes to act directly on other cell types in the marrow. Furthermore, MAT, which is recognized as an endocrine organ, regulates bone remodeling through the secretion of adipokines and cytokines. Although an enhanced MAT volume is linked to low bone mass and fractures in PMOP, the detailed interactions between MAT and bone metabolism remain largely unknown. In this review, we examine the possible mechanisms of MAT expansion under estrogen withdrawal and further summarize emerging findings regarding the pathological roles of MAT in bone remodeling. We also discuss the current therapies targeting MAT in osteoporosis. A comprehensive understanding of the relationship between MAT expansion and bone metabolism in estrogen deficiency conditions will provide new insights into potential therapeutic targets for PMOP.

Bisphosphonates are wildly used in breast cancer patients with bone metastasis and generally administrated every 4 weeks to lessen the risk of subsequent skeletal-related events. Bisphosphonates administration every 12 weeks is also recommended in some guidelines. Recent clinical trials suggested that bisphosphonate treatment with reduced frequency (every 12 weeks) to be non-inferior to standard therapy. The object of this analysis was to contrast the efficacy and safety of these two treatment strategies. We systematically retrieved databases such as MEDLINE, PubMed, Embase, and Cochrane library from 1947 to present for clinical trials comparing the efficacy between standard (every 4 weeks) and de-escalation (every 12 weeks) treatment of bisphosphates. We identified 4 articles with available data from 4 randomized clinical trials (n = 1721). Administration of bisphosphate every 12 weeks was non-inferior to administration every 4 weeks. There existed no significant difference in on-study skeletal-related events, renal dysfunction, and osteonecrosis of jaw. In the exploratory study, patients who received intravenous bisphosphates before enrollment experienced less on-study skeletal-related events and significant difference was observed between groups. This analysis suggested that de-escalation treatment with bisphosphates may be superior to standard treatment in terms of efficacy, safety, and economic costs. But it would be better that all the patients receive bisphosphates every 4 weeks for several months before de-escalation.

Background : Chronic consumption of alcohol has an adverse effect on the skeletal system, which may lead to osteoporosis, delayed fracture healing and osteonecrosis of the femoral head. Currently, the treatment is limited, therefore, there is an urgent need to determine the underline mechanism and develop a new treatment. It is well-known that normal bone remodeling relies on the balance between osteoclast-mediated bone resorption and - mediated bone formation. Various factors can destroy the balance, including the dysfunction of the immune system. In this review, we summarized the relevant research in the alcoholic osteopenia with a focus on the abnormal osteoimmunology signals. We provided a new theoretical basis for the prevention and treatment of the alcoholic bone. Methods: We searched PubMed for publications from 1 January 1980 to 1 February 2020 to identify relevant and recent literature, summarizing evaluation and the prospect of alcoholic osteopenia. Detailed search terms were ‘alcohol’, ‘alcoholic osteoporosis’, ‘alcoholic osteopenia’ ‘immune’, ‘osteoimmunology’, ‘bone remodeling’, ‘osteoporosis treatment’ and ‘osteoporosis therapy’. Results: A total of 135 papers are included in the review. About 60 papers described the mechanisms of alcohol involved in bone remodeling. Some papers were focused on the pathogenesis of alcohol on bone through osteoimmune mechanisms. Conclusion: There is a complex network of signals between alcohol and bone remodeling and intercellular communication of osteoimmune may be a potential mechanism for alcoholic bone. Studying the osteoimmune mechanism is critical for drug development specific to the alcoholic bone disorder.

XLαs, the extra-large isoform of alpha-subunit of the stimulatory guanine nucleotide-binding protein (Gsα), is paternally expressed. The significance of XLαs in humans remains largely unknown. Here, we report a patient who presented with increased bone mass, hypophosphatemia, and elevated parathyroid hormone (PTH) levels. His serum calcium was in the lower limit of the normal range. Whole exome sequencing of this subject found a novel non-sense variant c.424G>T (p. G142*) in the first exon of XLαs, which was inherited from his father and transmitted to his daughter. This variant was predicted to exclusively influence the expression of XLαs, while possibly having no significant effects on other gene products of this locus. Ellsworth-Howard test revealed normal renal response to PTH in proband. Human SaOS2 cells transfected with mutant XLαs failed to generate cyclic adenosine monophosphate under PTH stimulation, indicating skeletal resistance to this hormone. This subject showed higher circulating sclerostin, dickkopf1, and osteoprotegerin (OPG) levels, while lower receptor activator of nuclear factor kappa-B ligand/OPG ratio, leading to reduced bone resorption. Our findings indicate that XLαs plays a critical role in bone metabolism and GNAS locus should be considered as a candidate gene for high bone mass.

Background MiR-17-92 cluster is coded by MIR17HG in chromosome 13, which is highly conserved in vertebrates. Published literatures have proved that miR-17-92 cluster critically regulates tumorigenesis and metastasis. Recent researches showed that the miR-17-92 cluster also plays novel functions in the endocrine system. Objective To summarize recent findings on the physiological and pathological roles of miR-17-92 cluster in bone, lipid and glucose metabolisms. Results MiR-17-92 cluster plays significant regulatory roles in bone development and metabolism through regulating the differentiation and function of osteoblasts and osteoclasts. In addition, miR-17- 92 cluster is nearly involved in every aspect of lipid metabolism. Last but not the least, the miR-17-92 cluster is closely bound up with pancreatic beta cell function, development of type 1 diabetes and insulin resistance. However, whether miR-17-92 cluster is involved in the communication among bone, fat and glucose metabolisms remains unknown. Conclusion Growing evidence indicates that miR-17-92 cluster plays significant roles in bone, lipid and glucose metabolisms through a variety of signaling pathways. Fully understanding its modulating mechanisms may necessarily facilitate to comprehend the clinical and molecule features of some metabolic disorders such as osteoporosis, arthrosclerosis and diabetes mellitus. It may provide new drug targets to prevent and cure these disorders.

Cellular senescence is the inability of cells to proliferate, which has both beneficial and detrimental effects on tissue development and homeostasis. Chronic accumulation of senescent cells is associated with age-related disease, including osteoarthritis, a common joint disease responsible for joint pain and disability in older adults. The pathology of this disease includes loss of cartilage, synovium inflammation, and subchondral bone remodeling. Senescent cells are present in the cartilage of people with advanced osteoarthritis, but the link between cellular senescence and this disease is unclear. In this review, we summarize current evidence for the role of cellular senescence of different cell types in the onset and progression of osteoarthritis. We focus on the underlying mechanisms of senescence in chondrocytes, which maintain the cartilage in joints, and review the role of the Forkhead family of transcription factors, which are involved in cartilage maintenance and osteoarthritis. Finally, we discuss the potential therapeutic value and implications of targeting senescent cells using senolytic agents or immune therapies, targeting the senescence-associated secretory phenotype of these cells using senomorphic agents, and renewing the plasticity of stem cells and chondrocytes. Our review highlights current gaps in understanding of the mechanism of senescence that may, when addressed, provided new options for modifying and treating disease in osteoarthritis.

Mucopolysaccharidosis type I (MPSI) is a rare autosomal recessive disorder caused by mutations in alpha-L-iduronidase (

Osteoarthritis (OA) is the most common form of arthritic disease, leading to disability and impaired quality of life and no curative treatments exist. Increasing evidence indicates that low-grade inflammation plays a pivotal role in the onset and progression of OA. In this review, we summarize emerging findings on the pathological roles of synovial macrophages, adipose tissue macrophages, and osteoclasts in OA and their potential clinical implications from cell biology to preclinical and preliminary clinical trials. The failure of synovial macrophages to transition from pro-inflammatory M1 to anti-inflammatory M2 subtypes may contribute to the initiation and maintenance of synovitis in OA. M1 macrophages promote the inflammatory microenvironment and progression of OA through interactions with synovial fibroblasts and chondrocytes, thus increasing the secretion of matrix metalloproteinases. Direct inhibition of M1 or promotion of M2 polarization may be useful therapeutic interventions. Adipose tissue macrophages present in the infrapatella fat pad (IPFP) were involved in the progression of obesity-induced OA, which contributed to changes in the integrity of the IPFP. Furthermore, macrophages and osteoclasts in the subchondral bone were involved in bone remodeling and pain through uncoupled osteoclast/osteoblast activity and increased nociceptive signaling. Growing evidence has indicated an important role for macrophage-mediated low-grade inflammation in OA. Fully understanding the link between macrophages and other cells in joints will provide new insights into OA disease modification.

Lung cancer still remains the leading cause of cancer-related mortality worldwide. Bone is one of preferred metastatic sites for lung cancer cells. So far, both accurate diagnosis and effective treatment of lung cancer bone metastases are difficult.This review aimed to evaluate roles of bone turnover markers (BTMs), microRNAs (miRNAs), dickkopf1 (DKK1) and insulin like growth factor binding protein 3 (IGFBP-3) in lung cancer bone metastases.We searched articles about these four biomarkers in lung cancer bone metastases mainly in PubMed.The levels of bone specific alkaline phosphatase (BALP), cross-linked carboxy-terminal telopeptide of type-I collagen (ICTP) and N-terminal telopeptides of type-I collagen (NTX) were reported to be significantly increased in lung cancer patients with bone metastases. ALP, NTX and bone sialoprotein were thought to be associated with prognosis of lung cancer patients with bone metastases. MiRNA-335, miRNA-33a, miRNA-21, DKK1 and IGFBP-3 were revealed to be novel biomarkers in lung cancer bone metastases.Current researches have revealed that BTMs, miRNAs, DKK1 and IGFBP-3 may be useful in diagnosis, prognosis evaluation or treatment of lung cancer bone metastases. More studies about these biomarkers in lung cancer bone metastases are needed.

MicroRNAs (miRNAs) are a new class of small noncoding RNAs of 19-25 nucleotides that function as negative posttranscriptional gene regulators. MiRNAs hybridize to the 3' untranslated region (UTR) of target mRNAs and repress translation or mediate mRNA cleavage. MiRNAs critically regulate tumorigenesis and progression by targeting oncogenes, tumor suppressor genes, or genes related to proliferation, angiogenesis, and apoptosis. Different tumor types and tumors at different stages exhibit unique miRNA profiles. MiRNAs show promise as potential biomarkers for cancer diagnostics, progression, and response to treatment. The role of miRNAs in promoting bone metastases is under investigated. We summarize recent findings on the mechanisms by which miRNAs may regulate bone metastatic spread of breast cancer, prostate cancer, lung cancer and multiple myeloma. We review similarities and differences in miRNA profiles that may explain the variety of molecular pathways underling metastatic spread to the skeleton in different cancers. Finally, we discuss the exciting potential of using miRNAs as diagnostics and therapeutic targets to reduce the risk of bone metastases in cancer, from the perspective of data provided by recent pre-clinical and clinical studies.

Lung cancer is the leading cause of malignancy-related mortality worldwide. Metastases, which account for 90% of lung cancer deaths, frequently target the skeleton, leading to rapid deterioration in quality of life and premature death. The molecular mechanism underlying this progression, especially the development of bone metastases, is largely unknown. MicroRNAs (miRNAs) are small, endogenous, noncoding RNAs that function as negatively posttranscriptional gene regulators. Changes in miRNAs, which may exhibit either oncogenic or tumor suppressive activity, are common in lung cancer. Over-expressed miRNAs may contribute to oncogenesis by down-regulating tumor suppressors, whereas the loss of selected miRNAs may negatively regulate oncogenes or factors related to tumorigenesis and progression. MiRNAs may activate or repress metastases. Specific miRNA expression profiles may correlate with the response in treatment. We summarize recent findings and patents in the pathological roles of miRNAs in the progression and bone metastases in lung cancer, and discuss the diagnostic and therapeutic options in the clinical management of lung cancer.

Background High bone mass (HBM) disorders are a group of clinically and genetically heterogeneous bone diseases characterized by increased bone density on radiographs, due to progressive bone overgrowth or impaired bone resorption, or both. Some HBM cases are secondary to other diseases, such as chronic hepatitis C virus infection. Despite the great advance in gene diagnostic technology, the majority of HBM individuals remain undiagnosed. Objective In this review, we will summarize the clinical, radiological and biochemical characteristics of HBM cases due to varying etiologies, since these features are helpful in the differential diagnosis of HBM. Results Each subgroup of HBM cases shows distinctive clinical, radiological and biochemical characteristics. HBM, due to bone overgrowth, was designated as sclerosteosis, as a result of mutations located in genes critically involved in the Wnt/beta-catenin signal pathway. Mutations in genes encoding factors relevant to the differentiation and maturation of osteoclasts, or critical for the acidification and resorption of osteoclasts may lead to osteopetrosis. Hepatitis C associated osteosclerosis is characterized by a generalized increase in bone mass and markedly elevated serum levels of bone specific alkaline phosphatase. Conclusion The clarification of the etiologies of HBM may have a breakthrough role in understanding the molecular mechanisms involved in bone metabolism and may provide new pathways for the intervention of osteoporosis.

Background: Bone metastasis is a common complication of certain types of cancer, and unfortunately, it is still incurable to date. Immune system is a major defence against tumor cells and bone metastasis. However, the immunodeficient mouse models are widely used in most researches of bone metastasis, thereby excluding the regulatory roles of the immune system in bone metastasis. Objective: To provide a comprehensive overview on the cellular and molecular mechanisms by which immune cells interact with tumor cells and bone cells, as well as recent related patents. Method: We performed a literature search of PubMed database for the current knowledge in the interaction between bone metastasis and immune system. Recent related patents were obtained from World Intellectual Property Organization (WIPO) website. Results: Immune cells in the bone-tumor microenvironment include dentritic cells, monocytes/macrophages, myeloid-derived suppressor cells, regulatory T cells, T helper cells, neutrophil, CD4+ T lyphocytes, CD8+cytotoxic T lymphocytes, and natural killer cells, et al. In addition to their well-known immunomodulatory function, recent studies revealed that immune cells could cooperate with tumor cells and bone cells to enhance bone metastasis and tumor progression. There are some patents targeted immune system to inhibit bone metastasis. Conclusion: Immune cells are instigated by tumor cells to enhance the occurrence and the development of bone metastasis. Taking full advantage of anti-tumor roles of immune cells may bring the promise of a possible cure for bone metastasis.

Postmenopausal osteoporosis (PMOP) is considered to be a well-defined subject that has caused high morbidity and mortality. In elderly women diagnosed with PMOP, low bone mass and fragile bone strength have been proven to significantly increase risk of fragility fractures. Currently, various anabolic and anti-resorptive therapies have been employed in an attempt to retain healthy bone mass and strength. Pulsed electromagnetic fields (PEMFs), first applied in treating patients with delayed fracture healing and nonunions, may turn out to be another potential and effective therapy for PMOP. PEMFs can enhance osteoblastogenesis and inhibit osteoclastogenesis, thus contributing to an increase in bone mass and strength. However, accurate mechanisms of the positive effects of PEMFs on PMOP remain to be further elucidated. This review attempts to summarize recent advances of PEMFs in treating PMOP based on clinical trials, and animal and cellular studies. Possible mechanisms are also introduced, and the future possibility of application of PEMFs on PMOP are further explored and discussed. Bioelectromagnetics. 38:406-424, 2017. © 2017 Wiley Periodicals, Inc.

BACKGROUND Obesity was traditionally considered as a positive regulator on the strength of bone. With the in-depth study, obesity is considered as a major risk factor for osteoporosis. Some proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) are the factors that fat uses to negatively regulate bone metabolism. OBJECTIVE This review was aimed to summarize and critically discuss the convincing evidence for the therapeutic effectiveness of pro-inflammatory cytokines for the treatment of obesity-related bone disorders. RESULTS Obese people and animals show a higher level of serum TNF-α and IL-6, which are produced by macrophages derived from adipose tissue. These pro-inflammatory cytokines regulate the proliferation and apoptosis of adipocyte, promote lipolysis, inhibit lipid synthesis and decrease blood lipids through autocrine and paracrine way. On the other hand, TNF-α and IL-6 regulate bone metabolism through the endocrine way. Several reports suggest that TNF-α is a negative regulator of osteoblast at some stages of differentiation and positively regulates osteoclast proliferation and differentiation. In contrast, IL-6 influences osteoblasts and osteoclasts through complex mechanisms, which reflect dual effects. In addition, TNF-α and IL-6 may regulate bone metabolism indirectly by regulating adiponectin and leptin released from adipocytes. CONCLUSION In this review, we first summarize the role of TNF-α and IL-6 in lipid and bone metabolisms. We further discuss how TNF-α and IL-6 regulate the communication between fat and bone, and their pathological roles in obesity-related bone disorders. Lastly, we discuss the possibility of using pro-inflammatory signaling pathway as a therapeutic target to develop drug for obesity-related bone disorders.

The skeleton is frequently affected in individuals with neurofibromatosis type 1, and some of these bone manifestations can result in significant morbidity. The natural history and pathogenesis of the skeletal abnormalities of this disorder are poorly understood and consequently therapeutic options for these manifestations are currently limited. The Children's Tumor Foundation convened an International Neurofibromatosis Type 1 Bone Abnormalities Consortium to address future directions for clinical trials in skeletal abnormalities associated with this disorder. This report reviews the clinical skeletal manifestations and available preclinical mouse models and summarizes key issues that present barriers to optimal clinical management of skeletal abnormalities in neurofibromatosis type 1. These concepts should help advance optimal clinical management of the skeletal abnormalities in this disease and address major difficulties encountered for the design of clinical trials.

Unique among fibroblast growth factors (FGFs), FGF19, -21, and -23 act in an endocrine fashion to regulate energy, bile acid, glucose, lipid, phosphate, and vitamin D homeostasis. These FGFs require the presence of Klotho/betaKlotho in their target tissues. Here, we present the crystal structures of FGF19 alone and FGF23 in complex with sucrose octasulfate, a disaccharide chemically related to heparin. The conformation of the heparin-binding region between beta strands 10 and 12 in FGF19 and FGF23 diverges completely from the common conformation adopted by paracrine-acting FGFs. A cleft between this region and the beta1-beta2 loop, the other heparin-binding region, precludes direct interaction between heparin/heparan sulfate and backbone atoms of FGF19/23. This reduces the heparin-binding affinity of these ligands and confers endocrine function. Klotho/betaKlotho have evolved as a compensatory mechanism for the poor ability of heparin/heparan sulfate to promote binding of FGF19, -21, and -23 to their cognate receptors.

Individuals with neurofibromatosis type 1 (NF1) have a high incidence of osteoporosis and osteopenia. However, understanding of the cellular and molecular basis of these sequelae is incomplete. Osteoclasts are specialized myeloid cells that are the principal bone-resorbing cells of the skeleton. We found that Nf1(+/-) mice contain elevated numbers of multinucleated osteoclasts. Both osteoclasts and osteoclast progenitors from Nf1(+/-) mice were hyperresponsive to limiting concentrations of M-CSF and receptor activator of NF-kappaB ligand (RANKL) levels. M-CSF-stimulated p21(ras)-GTP and Akt phosphorylation was elevated in Nf1(+/-) osteoclasts associated with gains of function in survival, proliferation, migration, adhesion, and lytic activity. These gains of function are associated with more severe bone loss following ovariectomy as compared with that in syngeneic WT mice. Intercrossing Nf1(+/-) mice and mice deficient in class 1(A) PI3K (p85alpha) restored elevated PI3K activity and Nf1(+/-) osteoclast functions to WT levels. Furthermore, in vitro-differentiated osteoclasts from NF1 patients also displayed elevated Ras/PI3K activity and increased lytic activity analogous to those in murine Nf1(+/-) osteoclasts. Collectively, our results identify a what we believe to be a novel cellular and biochemical NF1-haploinsufficient phenotype in osteoclasts that has potential implications for the pathogenesis of NF1 bone disease.

The osteocyte, a terminally differentiated cell comprising 90%–95% of all bone cells1,2, may have multiple functions, including acting as a mechanosensor in bone (re)modeling3. Dentin matrix protein 1 (encoded by DMP1) is highly expressed in osteocytes4 and, when deleted in mice, results in a hypomineralized bone phenotype5. We investigated the potential for this gene not only to direct skeletal mineralization but also to regulate phosphate (Pi) homeostasis. Both Dmp1- null mice and individuals with a newly identified disorder, autosomal recessive hypophosphatemic rickets, manifest rickets and osteomalacia with isolated renal phosphate-wasting associated with elevated fibroblast growth factor 23 (FGF23) levels and normocalciuria. Mutational analyses showed that autosomal recessive hypophosphatemic rickets family carried a mutation affecting the DMP1 start codon, and a second family carried a 7-bp deletion disrupting the highly conserved DMP1 C terminus. Mechanistic studies using Dmp1-null mice demonstrated that absence of DMP1 results in defective osteocyte maturation and increased FGF23 expression, leading to pathological changes in bone mineralization. Our findings suggest a bone-renal axis that is central to guiding proper mineral metabolism.

Fibroblast growth factor (FGF)-23 has emerged as an endocrine regulator of phosphate and of vitamin D metabolism. It is produced in bone and, unlike other FGFs, circulates in the bloodstream to ultimately regulate phosphate handling and vitamin D production in the kidney. Presently, it is unknown which of the seven principal FGF receptors (FGFRs) transmits FGF23 biological activity. Furthermore, the molecular basis for the endocrine mode of FGF23 action is unclear. Herein, we performed surface plasmon resonance and mitogenesis experiments to comprehensively characterize receptor binding specificity. Our data demonstrate that FGF23 binds and activates the c splice isoforms of FGFR1–3, as well as FGFR4, but not the b splice isoforms of FGFR1–3. Interestingly, highly sulfated and longer glycosaminoglycan (GAG) species were capable of promoting FGF23 mitogenic activity. We also show that FGF23 induces tyrosine phosphorylation and inhibits sodium-phosphate cotransporter Npt2a mRNA expression using opossum kidney cells, a model kidney proximal tubule cell line. Removal of cell surface GAGs abolishes the effects of FGF23, and exogenous highly sulfated GAG is capable of restoring FGF23 activity, suggesting that proximal tubule cells naturally express GAGs that are permissive for FGF23 action. We propose that FGF23 signals through multiple FGFRs and that the unique endocrine actions of FGF23 involve escape from FGF23-producing cells and circulation to the kidney, where highly sulfated GAGs most likely act as cofactors for FGF23 activity. Our biochemical findings provide important insights into the molecular mechanisms by which dysregulated FGF23 signaling leads to disorders of hyper- and hypophosphatemia. (Endocrinology 146: 4647–4656, 2005)

Gain-of-function mutations in fibroblast growth factor-23 (FGF23) are responsible for autosomal dominant hypophosphatemic rickets, a disorder of isolated renal phosphate wasting. Patients with the disorder display hypophosphatemia with normocalcemia as well as inappropriately normal 1,25-dihydroxyvitamin D [1,25(OH)2D3] concentrations. Reciprocally tumoral calcinosis (TC) patients are often hyperphosphatemic with inappropriately normal or elevated serum 1,25(OH)2D3 levels and have ectopic and vascular calcifications, a phenotype similar to that of Fgf23 null mice. Therefore, the goal of the present studies was to test whether FGF23 was a candidate gene for TC. Two sisters in a consanguineous TC family had hyperphosphatemia and normal 1,25(OH)2D3 levels with characteristic ectopic and vascular calcifications. Interestingly, these patients had low-normal intact serum FGF23 levels but demonstrated FGF23 concentrations approximately 40 times normal when assessed with a C-terminal FGF23 serum assay. Mutational analyses identified a homozygous S71G mutation in FGF23 in the TC patients, which was not found in control alleles. Finally, modeling demonstrated that the S71G mutation most likely destabilizes full-length FGF23. In summary, recessive FGF23 mutations can lead to TC. Additionally, our findings indicate that FGF23 may adopt an unstable conformation in some TC patients, possibly leading to nonfunctional FGF23 protein.

The association between lipid and bone metabolism has become an increasing focus of interest in recent years, and accumulating evidence has shown that atherosclerosis (AS) and osteoporosis (OP), a disorder of bone metabolism, frequently co-exist. Fat and bone are known to share a common progenitor cell: Multipotent mesenchymal stem cells (MSC) in the bone marrow (BM), which are able to differentiate into various cell phenotypes, including osteoblasts, adipocytes and chondrocytes. Laboratory-based and clinical trials have shown that increasing adipocytes are accompanied by a decrease in bone mineral density (BMD) and bone mass. Statins, lipid-lowering drugs used to treat hyperlipidemia, also provide benefit in the treatment of OP. There is thus evidence that the metabolism of lipids is correlated with that of bone, and that the two are mutually regulated. The present review primarily focuses on the potential association between lipid metabolism disturbance and OP, based on biological metabolism, pathophysiological processes, results from clinical and experimental animal studies, processes involved in the differentiation of adipocytes and osteoblasts, as well as pharmacological treatments of these diseases.

Research on the characteristics and mechanisms of diabetes in Tibetans is scant. Especially, there is no study on the relationship between osteocalcin and glucose metabolism. The objective of this study was to investigate the associations of serum total osteocalcin (tOC) and undercarboxylated osteocalcin (ucOC) with glucose and lipid metabolism in Chinese indigenous Tibetans with different degrees of glucose tolerance.In this study, 160 middle-aged Tibetan men were involved, including 46 subjects with normal glucose tolerance (NGT), 52 subjects with impaired glucose regulation (IGR) and 62 subjects with type 2 diabetes. The homeostasis model assessment (HOMA) parameters, including HOMA-IR and HOMA-B, were used to estimate insulin resistance and β-cell function, respectively. Adiponectin, leptin, testosterone, 1,25-dihydroxyvitamin D, tOC and ucOC were measured using ELISA kits.After adjustment for age and body mass index, plasma tOC level was correlated negatively with fasting and 30-min post-OGTT glucose, HOMA-IR, leptin and testosterone; plasma ucOC level was correlated negatively with 30-min post-OGTT glucose, total cholesterol and 1,25-dihydroxyvitamin D; ucOC : tOC was correlated positively with leptin. The negative association between HOMA-IR and tOC remained significant after correcting for adiponectin; however, the association disappeared after correcting for leptin. HOMA-IR was correlated negatively with age, adiponectin and tOC, and positively with total cholesterol, triglyceride and leptin. Stepwise linear regression analysis revealed that total cholesterol, leptin and adiponectin were independent predictors for HOMA-IR in all subjects.Our data support a link between osteocalcin and glucose metabolism in middle-aged Tibetan men. The improved glucose tolerance exerted by tOC may be related to improved insulin sensitivity rather than improved β-cell function.

Small cell lung cancer (SCLC) is a rapidly progressing, incurable cancer that frequently spreads to bone. New insights are needed to identify therapeutic targets to prevent or retard SCLC metastatic progression. Human SCLC SBC-5 cells in mouse xenograft models home to skeletal and nonskeletal sites, whereas human SCLC SBC-3 cells only pervade nonskeletal sites. Because microRNAs (miRNA) often act as tumor regulators, we investigated their role in preclinical models of SCLC. miRNA expression profiling revealed selective and reduced expression of miRNA (miR)-335 and miR-29a in SBC-5 cells, compared with SBC-3 cells. In SBC-5 cells, miR-335 expression correlated with bone osteolytic lesions, whereas miR-29a expression did not. Overexpression of miR-335 in SBC-5 cells significantly reduced cell migration, invasion, proliferation, colony formation, and osteoclast induction in vitro. Importantly, in miR-335 overexpressing SBC-5 cell xenografts (n = 10), there were minimal osteolytic lesions in the majority of mice and none in three mice. Expression of RANK ligand (RANKL) and insulin-like growth factor-I receptor (IGF-IR), key mediators of bone metastases, were elevated in SBC-5 as compared with SBC-3 cells. Mechanistically, overexpression of miR-335 in SBC-5 cells reduced RANKL and IGF-IR expression. In conclusion, loss of miR-335 promoted SCLC metastatic skeletal lesions via deregulation of IGF-IR and RANKL pathways and was associated with metastatic osteolytic skeletal lesions. Implications: These preclinical findings establish a need to pursue the role of miR-335 in human SCLC with metastatic skeletal disease. Mol Cancer Res; 12(1); 101–10. ©2013 AACR.

Abnormal osteoclast formation and resorption play a fundamental role in osteoporosis pathogenesis. Over the past two decades, much progress has been made to target osteoclasts. The existing therapeutic drugs include bisphosphonates, hormone replacement therapy, selective estrogen receptor modulators, calcitonin and receptor activator of nuclear factor NF-κB ligand (RANKL) inhibitor (denosumab), etc. Among them, bisphosphonates are most widely used due to their low price and high efficiency in reducing the risk of fracture. However, bisphosphonates still have their limitations, such as the gastrointestinal side-effects, osteonecrosis of the jaw, and atypical subtrochanteric fracture. Based on the current situation, research for new drugs to regulate bone resorption remains relevant. MicroRNAs (miRNAs) are a new group of small, noncoding RNAs of 19–25 nucleotides, which negatively regulate gene expression after transcription. Recent studies discovered miRNAs play a considerable function in bone remodeling by regulating osteoblast and osteoclast differentiation and function. An increasing number of miRNAs have been identified to participate in osteoclast formation, differentiation, apoptosis, and resorption. miRNAs show great promise to serve as biomarkers and potential therapeutic targets for osteoporosis. In this review, we will summarize our current understanding of how miRNAs regulate osteoclastogenesis and function. We will further discuss the approach to develop drugs for osteoporosis based on these miRNA networks.

OBJECTIVE To summary the functional roles and molecular mechanisms of microRNA (miRNA) in osteoblast differentiation so as to supply information for basic and clinical researches.Recent literature concerning miRNA in osteoblast differentiation was reviewed. The information was classified and summarized.miRNAs critically regulate bone morphogenetic protein, transforming growth factor beta, and Wnt/beta-catenin signaling pathways during osteoblast differentiation. In pathological conditions, especially in some disorders of abnormal osteoblast differentiation, down-regulated miRNA expression has been observed.miRNA may represent a novel biomarker for diagnosis, and a candidate target therapies for the disorders with abnormal osteoblast differentiation.

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue sarcomas accounting for 3%–10% of all soft tissue sarcomas. Neurofibromatosis type 1 (NF1) is the most important known risk factor. MPNSTs are often diagnosed at an advanced stage when distant metastases have developed. Although surgical resection remains the main treatment for MPNSTs, complete surgical resection is rarely possible. The prognosis for patients with MPNSTs is poor. There is an urgent need for improved therapies. To this end, we investigated whether microRNA (miR), specifically miR-204, might be implicated in MPNSTs because it is located at a cancer-associated genomic region exhibiting high frequency of loss of heterozygosity in tumors. We show that miR-204 expression is downregulated in NF1 and non-NF1 MPNST tumor tissues and in tumor cell lines. Restoring miR-204 expression in MPNST cell lines STS26T (non-NF1), ST88-14 (NF1), and T265p21 (NF1) significantly reduces cellular proliferation, migration, and invasion in vitro. Restoring miR-204 expression in STS26T decreases tumor growth and malignant progression in vivo. We also report that miR-204 inhibits Ras signaling and expression of high mobility group gene A2. These findings support the hypothesis that miR-204 plays critical roles in MPNST development and tumor progression. miR-204 may represent a novel biomarker for diagnosis and a candidate target with which to develop effective therapies for MPNSTs.

MicroRNAs (miRNAs) are frequently deregulated in human tumors, and play important roles in tumor development and progression. The pathological roles of miRNAs in neurofibromatosis type 1 (NF1) tumorigenesis are largely unknown. We demonstrated that miR-10b was up-regulated in primary Schwann cells isolated from NF1 neurofibromas and in cell lines and tumor tissues from malignant peripheral nerve sheath tumors (MPNSTs). Intriguingly, a significantly high level of miR-10b correlated with low neurofibromin expression was found in a neuroectodermal cell line: Ewing's sarcoma SK-ES-1 cells. Antisense inhibiting miR-10b in NF1 MPNST cells reduced cell proliferation, migration and invasion. Furthermore, we showed that NF1 mRNA was the target for miR-10b. Overexpression of miR-10b in 293T cells suppressed neurofibromin expression and activated RAS signaling. Antisense inhibition of miR-10b restored neurofibromin expression in SK-ES-1 cells, and decreased RAS signaling independent of neurofibromin in NF1 MPNST cells. These results suggest that miR-10b may play an important role in NF1 tumorigenesis through targeting neurofibromin and RAS signaling.

Fibroblast growth factor 23 (FGF23) is a hormone required for normal renal phosphate reabsorption. FGF23 gain-of-function mutations result in autosomal dominant hypophosphatemic rickets (ADHR), and FGF23 loss-of-function mutations cause familial hyperphosphatemic tumoral calcinosis (TC). In this study, we identified a novel recessive FGF23 TC mutation, a lysine (K) substitution for glutamine (Q) (160 C > A) at residue 54 (Q54K). To understand the molecular consequences of all known FGF23-TC mutants (H41Q, S71G, M96T, S129F, and Q54K), these proteins were stably expressed in vitro. Western analyses revealed minimal amounts of secreted intact protein for all mutants, and ELISA analyses demonstrated high levels of secreted COOH-terminal FGF23 fragments but low amounts of intact protein, consistent with TC patients' FGF23 serum profiles. Mutant protein function was tested and showed residual, yet decreased, bioactivity compared with wild-type protein. In examining the role of the FGF23 COOH-terminal tail (residues 180–251) in protein processing and activity, truncated mutants revealed that the majority of the residues downstream from the known FGF23 SPC protease site (176RXXR179/S180) were not required for protein secretion. However, residues adjacent to the RXXR site (between residues 188 and 202) were required for full bioactivity. In summary, we report a novel TC mutation and demonstrate a common defect of reduced FGF23 stability for all known FGF23-TC mutants. Finally, the majority of the COOH-terminal tail of FGF23 is not required for protein secretion but is required for full bioactivity.

Familial tumoral calcinosis is characterized by ectopic calcifications and hyperphosphatemia due to inactivating mutations in FGF23 or UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 3 (GALNT3). Herein we report a homozygous missense mutation (H193R) in the KLOTHO (KL) gene of a 13-year-old girl who presented with severe tumoral calcinosis with dural and carotid artery calcifications. This patient exhibited defects in mineral ion homeostasis with marked hyperphosphatemia and hypercalcemia as well as elevated serum levels of parathyroid hormone and FGF23. Mapping of H193R mutation onto the crystal structure of myrosinase, a plant homolog of KL, revealed that this histidine residue was at the base of the deep catalytic cleft and mutation of this histidine to arginine should destabilize the putative glycosidase domain (KL1) of KL, thereby attenuating production of membrane-bound and secreted KL. Indeed, compared with wild-type KL, expression and secretion of H193R KL were markedly reduced in vitro, resulting in diminished ability of FGF23 to signal via its cognate FGF receptors. Taken together, our findings provide what we believe to be the first evidence that loss-of-function mutations in human KL impair FGF23 bioactivity, underscoring the essential role of KL in FGF23-mediated phosphate and vitamin D homeostasis in humans.

Approximately 50% of neurofibromatosis type 1 (NF1) patients exhibit skeletal pathology, such as premature osteoporosis or pseudoarthroses. Loss of neurofibromin deregulates Ras signal transduction to affect generation of mitogen-activated protein kinase and Akt, both of which have been implicated in parathyroid hormone (PTH) anabolic mechanisms. Our aim was to determine if loss of neurofibromin impaired the anabolic effect of PTH on bone mass. Nf1 heterozygote (Nf1+/−) and wild type (Nf1 +/+ ) mice were treated with recombinant human PTH1–34 or vehicle once daily for 3–28 days. PTH enhanced mRNA expression of c-fos, junB, and fra2 in the distal femur metaphyses of both genotypes; expression of these transcripts was consistently lower in PTH-treated Nf1+/− mice. Despite lowered c-fos expression in Nf1+/− mice, PTH increased bone mass equivalently in both genotypes by 28 days. Ex vivo, Nf1 heterozygosity was associated with increased inducible osteoclasts in PTH-treated bone marrow cells and impairment of the actin stress fiber and cyclic adenosine monophosphate response to PTH in osteoprogenitors. Lower c-fos expression was previously thought to abrogate PTH responsiveness. Our results suggest crosstalk might occur between Ras signal transduction and the protein kinase A pathway in Nf1+/− mice. Ras signal transduction does not appear to be essential for the anabolic actions of PTH on bone. Because PTH was effective in the absence of Nf1, it may offer a useful approach to treat osteoporosis in NF1 patients.

Fibroblast growth factor 23 (FGF23) is a circulating factor that plays critical roles in phosphate and vitamin D metabolism, as evidenced by the fact that FGF23 missense mutations cause autosomal dominant hypophosphatemic rickets (ADHR). Autosomal dominant hypophosphatemic rickets is characterized by hypophosphatemia with inappropriately normal 1,25-dihydroxyvitamin D concentrations, as well as bone pain, fracture and rickets. This phenotype parallels that of patients with tumor induced osteomalacia (TIO), X-linked hypophosphatemic rickets (XLH), and fibrous dysplasia (FD), in whom elevated serum FGF23 levels are often observed. The fibroblast growth factor receptors (FGFR1-4) play key roles in skeletal development, as well as in normal metabolic processes. Several FGFR isoforms that potentially mediate the activity of FGF23 have been implicated. In the short term, these findings will lead to further understanding of FGF23 function, and potentially in the long term, to targeted therapies in disorders of hypo- and hyperphosphatemia that involve FGF23.

It is well known that fibroblast growth factor (FGF) family members are associated with embryonic development and are critical for basic metabolic functions. This review will focus upon fibroblast growth factor-23 (FGF23) and its roles in disorders associated with phosphate handling. The discovery that mutations in FGF23 were responsible for the isolated renal phosphate wasting disorder autosomal dominant hypophosphatemic rickets (ADHR) has ascribed novel functions to the FGF family. FGF23 circulates in the bloodstream, and animal models demonstrate that FGF23 controls phosphate and Vitamin D homeostasis through the regulation of specific renal proteins. The ADHR mutations in FGF23 produce a protein species less susceptible to proteolytic processing. X-linked hypophosphatemic rickets (XLH), tumor-induced osteomalacia (TIO), and fibrous dysplasia of bone (FD) are disorders involving phosphate homeostasis that share phenotypes with ADHR, indicating that FGF23 may be a common denominator for the pathophysiology of these syndromes. Our understanding of FGF23 will help to develop novel therapies for phosphate wasting disorders, as well as for disorders of increased serum phosphate, such as tumoral calcinosis, a rare disorder, and renal failure, a common disorder.

Activating mutations in the genes for fibroblast growth factor receptors 1-3 (FGFR1-3) are responsible for a diverse group of skeletal disorders. In general, mutations in FGFR1 and FGFR2 cause the majority of syndromes involving craniosynostosis, whereas the dwarfing syndromes are largely associated with FGFR3 mutations. Osteoglophonic dysplasia (OD) is a "crossover" disorder that has skeletal phenotypes associated with FGFR1, FGFR2, and FGFR3 mutations. Indeed, patients with OD present with craniosynostosis, prominent supraorbital ridge, and depressed nasal bridge, as well as the rhizomelic dwarfism and nonossifying bone lesions that are characteristic of the disorder. We demonstrate here that OD is caused by missense mutations in highly conserved residues comprising the ligand-binding and transmembrane domains of FGFR1, thus defining novel roles for this receptor as a negative regulator of long-bone growth.

Skeletal problems and osteoporosis occur in up to 50% affected neurofibromatosis type 1 (NF1) humans. Inactivation of neurofibromin results in deregulation of Ras signal transduction. Little is known of bone biology in humans with NF1. The goal of our work was to determine if loss-of-function of Nf1 gene was associated with altered bone homeostasis and Ras signal transduction. Because homozygous Nf1 mice are embryonically lethal, heterozygote Nf1 (Nf1+/-) male mice were used to investigate skeletal phenotypes and osteoprogenitor functions, using standard in vivo and in vitro assays. We found that bone mass and geometry of Nf1+/- mice did not differ from wild type controls, despite a trend to less bone formation. Nf1+/- committed osteoprogenitors from femur metaphysis exhibited premature apoptosis and higher proliferation. Ras signaling was activated in primary Nf1+/- bone marrow-inducible osteoprogenitors. Inducible osteoprogenitors exhibited lower induction of osteoblast differentiation, assessed as alkaline phosphatase positive CFU-f. A screen of osteoblast marker genes showed a selective increase in osteopontin (OPN) mRNA and protein expression in these cells. OPN protein was increased in Nf1+/- bone, especially in cortical bone matrix. Because bone cell abnormalities in Nf1 haploinsufficiency were detected in vitro, redundant pathways must compensate for the deregulation of Ras signaling in vivo to maintain normal bone mass and function in vivo. Our in vitro data revealed that neurofibromin and its control of Ras signaling are required for osteoprogenitor homeostasis.

To construct the adenoviral vector bringing hVEGF(121) cDNA for evaluation of the possibility of VEGF gene therapy in ischemic bone disease.Human vascular endothelial growth factor (hVEGF(121)) cDNA obtained from the plasmid pCDI/VEGF(121) was cloned into plasmid pshuttle and further cloned to Adeno-X Viral DNA. The recombinant adenoviral plasmid was identified and then transferred to the adenoviral packaging cell HEK293 by lipofectamine mediated gene transfer method to pack the virus. After titilating the virus, the mouse bone marrow stromal cells (MSC) were transfected by the adenovirus and the expression of VEGF gene was detected.The recombinant Adeno-VEGF(121) was correctly constructed and confirmed by restriction endonuclease analysis and DNA sequencing analysis. After MSCs were tranfected by the virus, RT-PCR showed that hVEGF(121) mRNA was transcripted from the hVEGF(121) gene. Western blot and immune histochemistry showed VEGF(121) protein was expressed in transgene MSCs.The recombinant adenoviral vector bringing hVEGF(121) cDNA was successfully constructed and the transgene MSC expressed hVEGF gene in vitro, it provided the further foundation of VEGF gene therapy for bone ischemic diseases.

To construct a retroviral vector carrying human vascular endothelial growth factor (hVEGF (121)) cDNA for evaluation of the possibility of VEGF gene therapy in ischemic bone disease.hVEGF(121) cDNA was obtained from the plasmid pCDI/VEGF(121) and cloned into retroviral plasmid pLXSN. Recombinant plasmid was transferred to the retro virus packaging cell, PT-67, by lipofectamine mediated gene transfer. Mouse bone marrow stromal cells (MSCs) were transfected by the retrovirus. The integration of the hVEGF(121) cDNA into MSC genomic DNA and expression of the VEGF gene was detected. Proliferation assays of human umbilical vein endothelial cells (HUVECs) by VEGF(121) in culture medium were performed.Recombinant pLXSN/VEGF(121) was correctly constructed and confirmed by restriction endonuclease analysis and DNA sequencing analysis. hVEGF(121) gene was integrated into MSC genomic DNA after transfection, and the VEGF(121) protein was expressed. Proliferation assays showed VEGF(121) in culture medium was a biologically active protein and had a mitogenic effect on HUVEC.Recombinant retroviral vector carrying hVEGF(121) cDNA was successfully constructed. VEGF (121) protein expressed by MSCs had mitogenic effect biologically. This provides a further foundation for VEGF gene therapy for bone ischemic disease and bone tissue engineering.