Pathologic conditions of hard tissue: role of osteoclasts in osteolytic lesion

Conjoined Free Fibula Transplantation and First Carpometacarpal Joint Prosthesis for Functional Thumb Reconstruction-A Case Report

BACKGROUND

Giant cell tumors grow locally invasive with osseous and soft tissue destruction, requiring wide resection to avoid recurrence. Stable reconstruction of the first carpometacarpal (CMC-1) joint remains a challenge due to its high range of mobility. The latter is of paramount for the functionality of the hand.

PURPOSE

Therefore, the aim of this study was to report our approach for a combined reconstruction of the first metacarpal and the CMC-1 joint.

METHODS

A 58-year-old woman underwent wide resection of a benign giant cell tumor at the base and shaft of the first metacarpal of the left thumb. Because of the loss of the CMC-1 joint and the instability of the thumb, an osseous reconstruction using a vascularized fibular graft combined with a TOUCH Dual Mobility CMC-1 prosthesis was performed to reconstruct the CMC-1 joint.

RESULTS

Osseous healing was observed after 3 months. No tumor recurrence and good joint function were documented at the follow-up investigation after 1 year. The patient reported only minor restrictions during activities of daily living. Thumb opposition was possible with a Kapandji score of 8/10. A slight pain while walking remained as a donor-side morbidity at the right lower leg.

CONCLUSION

Metacarpal reconstruction with vascularized fibula bone grafts allowed a combined joint reconstruction with a commercially available prosthesis, which is an approach to restore the complex range of motion of the thumb.

Inhibiting Osteolytic Breast Cancer Bone Metastasis by Bone-Targeted Nanoagent via Remodeling the Bone Tumor Microenvironment Combined with NIR-II Photothermal Therapy

Bone is one of the prone metastatic sites of patients with advanced breast cancer. The "vicious cycle" between osteoclasts and breast cancer cells plays an essential role in osteolytic bone metastasis from breast cancer. In order to inhibit bone metastasis from breast cancer, NIR-II photoresponsive bone-targeting nanosystems (CuP@PPy-ZOL NPs) are designed and synthesized. CuP@PPy-ZOL NPs can trigger the photothermal-enhanced Fenton response and photodynamic effect to enhance the photothermal treatment (PTT) effect and thus achieve synergistic anti-tumor effect. Meanwhile, they exhibit a photothermal enhanced ability to inhibit osteoclast differentiation and promote osteoblast differentiation, which reshaped the bone microenvironment. CuP@PPy-ZOL NPs effectively inhibited the proliferation of tumor cells and bone resorption in the in vitro 3D bone metastases model of breast cancer. In a mouse model of breast cancer bone metastasis, CuP@PPy-ZOL NPs combined with PTT with NIR-II significantly inhibited the tumor growth of breast cancer bone metastases and osteolysis while promoting bone repair to achieve the reversal of osteolytic breast cancer bone metastases. Furthermore, the potential biological mechanisms of synergistic treatment are identified by conditioned culture experiments and mRNA transcriptome analysis. The design of this nanosystem provides a promising strategy for treating osteolytic bone metastases.

Overexpression of PIK3R1 Promotes Bone Formation by Regulating Osteoblast Differentiation and Osteoclast Formation

In an effort to bolster our understanding of regulation of bone formation in the context of osteoporosis, we screened out differentially expressed genes in osteoporosis patients with high and low bone mineral density by bioinformatics analysis. PIK3R1 is increasingly being nominated as a pivotal mediator in the differentiation of osteoblasts and osteoclasts that is closely related to bone formation. However, the specific mechanisms underlying the way that PIK3R1 affects bone metabolism are not fully elucidated. We intended to examine the potential mechanism by which PIK3R1 regulates osteoblast differentiation. Enrichment analysis was therefore carried out for differentially expressed genes. We noted that the estrogen signaling pathway, TNF signaling pathway, and osteoclast differentiation were markedly associated with ossification, and they displayed enrichment in PIK3R1. Based on western blot, qRT-PCR, and differentiation analysis in vitro, we found that upregulation of PIK3R1 enhanced osteoblastic differentiation, as evidenced by increased levels of investigated osteoblast-related genes as well as activities of ALP and ARS, while it notably decreased levels of investigated osteoclast-related genes. On the contrary, downregulation of PIK3R1 decreased levels of osteoblast-related genes and increased levels of osteoclast-related genes. Besides, in vitro experiments revealed that PIK3R1 facilitated proliferation and repressed apoptosis of osteoblasts but had an opposite impact on osteoclasts. In summary, PIK3R1 exhibits an osteoprotective effect via regulating osteoblast differentiation, which can be represented as a promising therapeutic target for osteoporosis.

Fluorescence-Based Real-Time Analysis of Osteoclast Development

Osteoclasts are multinucleated cells of hematopoietic origin which are critically involved in physiological and pathological bone resorption. They develop from myeloid progenitors through characteristic gene expression changes and intercellular fusion. This process is directed by M-CSF and RANKL which are also able to trigger osteoclast development from bone marrow cells in vitro. Osteoclasts are conventionally visualized by histochemical staining followed by manual counting, which hinders kinetic studies and automated quantification. Here we describe two fluorescence-based assays for the real-time analysis of myeloid cell to osteoclast development (FRAMCO) in primary mouse bone marrow cell cultures. Both assays rely on red-to-green fluorescence conversion of the membrane-targeted tdTomato/membrane-targeted eGFP (mTmG) transgene by Cre recombinase driven by the osteoclast-specific cathepsin K promoter (Ctsk-Cre). In the first assay (FRAMCO1.1), osteoclast-specific gene expression triggers red-to-green color conversion of cells carrying both the Ctsk-Cre and mTmG transgenes. In the second assay (FRAMCO1.2), red-to-green fluorescence conversion is triggered by fusion of neighboring co-cultured bone marrow cells separately carrying either the Ctsk-Cre or the mTmG transgenes. The two assays were tested using a high-content confocal fluorescence imaging system, followed by automated quantification. The FRAMCO1.1 assay showed robust red-to-green fluorescence conversion of more than 50% of the culture (including mononuclear cells) within 3 days under osteoclastogenic conditions. The FRAMCO1.2 assay showed a less robust but still readily measurable red-to-green color conversion in multinuclear cells within 5 days of differentiation. The assays required both the Ctsk-Cre and the mTmG transgenes and gave no signals in parallel macrophage cultures. The proper functioning of the two assays was also confirmed at the DNA, mRNA and bulk protein level. The assay systems were validated using lisophosphatidylcholine, a previously reported inhibitor of preosteoclast fusion. Taken together, our assays allow high-throughput automated real-time analysis of two critical aspects of osteoclast development, facilitating the screening for novel drug candidates for the pharmacological control of osteoclast-mediated bone resorption.

LncRNA X inactive-specific transcript promotes osteoclast differentiation through Tgif2 by acting as a ceRNA of miR-590-3p in a murine model

Aim: This study aims to investigate whether long noncoding RNA (lncRNA)  X-inactive specific transcript (Xist) can regulate osteoclast differentiation in osteoporosis and the mechanism. Materials & methods: The mouse model of osteoporosis was established by ovariectomy surgery. Osteoclast differentiation from RAW264.7 cells was induced in vitro. The relationships between associated genes were assessed. Results: Xist and Tgif2 were upregulated, but miR-590-3p was downregulated in ovariectomy mouse femurs and cell models. Xist knockdown or miR-590-3p overexpression inhibited Tgif2 expression and osteoclast differentiation. Tgif2 and Xist were the targets of miR-590-3p. Increased miR-590-3p expression inhibited Tgif2 level and osteoclast differentiation, while Xist overexpression reversed these effects. Conclusion: Xist serves as a ceRNA of miR-590-3p to promote Tgif2 level; thereby, contributing to osteoclast differentiation.

Radiological findings of denosumab treatment for giant cell tumours of bone

Giant cell tumours of bone (GCTB) are benign giant cell-rich tumours typically occurring in the epi-metaphysis of skeletally mature patients. Despite their benign classification, GCTB may be locally aggressive with local recurrence as a challenging issue. Denosumab is a human monoclonal antibody that inhibits osteolysis via the RANK-RANK ligand pathway. There is currently no consensus on optimal treatment duration or imaging modality for monitoring patients on denosumab therapy. This review illustrates the radiological findings of GCTB on denosumab treatment seen on plain radiographs, CT, MRI, PET-CT and DEXA, with reference to the current literature. Recognizing imaging features indicative of a positive response to denosumab is important for therapeutic decision-making. Imaging findings with respect to duration of denosumab treatment, tumour upregulation during treatment, tumour recurrence and malignant transformation are discussed. The development of a sclerotic neocortex and varying degrees of matrix osteosclerosis are seen on plain radiographs. Reconstitution of subarticular bone and articular surface irregularity are optimally evaluated on CT which can also quantify tumour density. MRI demonstrates heterogeneous low signal matrix and is useful to assess decrease in size of cystic and/or soft tissue components of GCTB. A fat-suppressed fluid-sensitive MR sequence is important to detect tumour reactivation. Reduction in 18F-FDG-PET avidity represents an early sensitive sign of response to denosumab treatment. Regardless of imaging modality, close follow-up in a specialist centre and careful evaluation of nonresponders is necessary as local recurrence after cessation of denosumab treatment and malignant transformation of GCTB have been described.

miR-346-3p promotes osteoclastogenesis via inhibiting TRAF3 gene

MicroRNAs (miRNAs) modulate gene expression and regulate many physiological and pathological conditions. However, their modulation and effect in osteoclastogenesis remain unknown. In this study, we investigated the role of miR-346-3p in regulating the osteoclast differentiation from RAW264.7 cells. We used the miRNA microarray assay, miR-346-3p mimic transfection, tartrate resistant acid phosphatase (TRAP) staining, bone resorption assay, qRT-PCR, and western blot. Our results showed that the expression of miR-346-3p was significantly upregulated during osteoclast differentiation. Further, by transfecting cells with miR-346-3p mimic, we observed an increased number of TRAP-positive multinucleated cells, increased pit area caused by bone resorption, and enhanced expression of osteoclast-specific genes and proteins. Conversely, miR-346-3p inhibition attenuated the osteoclast differentiation and function. Software-mediated prediction and validation using luciferase reporter assay showed that TRAF3, a negative regulator of osteoclast differentiation, was inhibited by miR-346-3p overexpression. Our results showed that miR-346-3p directly targeted TRAF3 mRNA via binding to its 3'-UTR and inhibited the expression of TRAF3 protein. Taken together, our results revealed that miR-346-3p promotes the regulation of osteoclastogenesis by suppressing the TRAF3 gene. In conclusion, miR-346-3p could be a novel therapeutic target for bone loss-related pathogenesis.

Sema6A-plexin-A2 axis stimulates RANKL-induced osteoclastogenesis through PLCγ-mediated NFATc1 activation

Recently, several plexins and semaphorins have been associated with osteoclastogenesis, a vital process for bone remodeling. Plexin-A2 is implicated in bone homeostasis, however, whether it plays a role in osteoclastogenesis and the underlying mechanism remain unknown. We show that plexin-A2 expression is upregulated during RANKL-induced osteoclastogenesis. In addition, the soluble Sema6A fused with IgG1 Fc region (Fc-Sema6A) interacts with plexin-A2 from cell lysates of osteoclasts, suggesting that plexin-A2 acts as a receptor of Sema6A in osteoclasts. Moreover, Sema6A treatment stimulates RANKL-induced osteoclastogenesis, and this effect is abolished when plexin-A2 is neutralized, which illustrates an indispensable role of plexin-A2 in mediating Sema6A effect on osteoclastogenesis. Mechanistically, Sema6A-plexin-A2 axis enhances RANKL-induced activation of PLCγ as well as downstream target NFATc1, one master transcriptional factor of osteoclastogenesis. Lastly, inhibition of PLCγ by pharmacological inhibitor U73122 abrogates Sema6A-stimulated NFATc1 activation and RANKL-induced osteoclastogenesis, thus demonstrating that the PLCγ-mediated NFATc1 activation accounts for the promotive role of Sema6A-plexin-A2 axis in RANKL-induced osteoclastogenesis. Taken together, this study uncovers a novel role of Sema6A and plexin-A2 in osteoclastogenesis, and also offers them as possible therapeutic targets in the intervention of osteolytic diseases.

A potential therapeutic target for regulating osteoporosis via suppression of osteoclast differentiation

OBJECTIVES

Osteoclast differentiation is regulated by transcriptional, post-transcriptional and post-translational mechanisms. Micro-ribonucleic acids (miRNAs) are 20-24 nucleotides long non-coding RNAs involved in post-translational regulation of gene expressions during osteoclast differentiation. The objective of the present study was to investigate the role played by the miRNA, miR-338-3p, in osteoclastogenesis.

METHODS

Osteoclastogenesis was induced in murine RAW264.7 cells using M-CSF and RANKL. The differentiated cells were harvested at designated times for TRAP staining and detection of designated gene expressions. A synthetic miR-338-3p mimic or its inhibitor was transfected into RAW264.7 cells prior to the induction of osteoclastogenesis. The effects of mimic or inhibitor on osteoclastogenesis were examined by qRT-PCR and TRAP staining. Bioinformatic analysis and luciferase activity were performed to identify the relationship between miR-338-3p and the transcription factor MafB. The miR-338-3p mimic and MafB siRNA were co-transfected into RAW264.7 cells to evaluate the cross-talk between miR-338-3p and MafB.

RESULTS

miR-338-3p was increased significantly during osteoclast differentiation. Overexpression of miR-338-3p promoted osteoclastogenesis while its inhibition had the opposite effect. Bioinformatic analysis and dual luciferase assays indicated that miR-338-3p targeted MafB to repress its gene expression. MafB knockdown by RNA silencing blocked the promotional effect of miR-338-3p on osteoclast differentiation.

CONCLUSION

Because miR-338-3p is crucial for osteoclastic differentiation via targeting of the transcription factor MafB, inhibition of this miRNA represents a potential strategy for modulating osteoporosis in an aging population. CLINICAL SIGNIfiCANCE: Understanding the role played by miR-338-3p in osteoclast differentiation bridges the gap between the pathogenesis of osteoporosis and the quest for novel therapeutics to reduce the risk of bone fracture associated with this global disease.

From the Clinical Problem to the Basic Research-Co-Culture Models of Osteoblasts and Osteoclasts

Bone tissue undergoes constant remodeling and healing when fracture happens, in order to ensure its structural integrity. In order to better understand open biological and clinical questions linked to various bone diseases, bone cell co-culture technology is believed to shed some light into the dark. Osteoblasts/osteocytes and osteoclasts dominate the metabolism of bone by a multitude of connections. Therefore, it is widely accepted that a constant improvement of co-culture models with both cell types cultured on a 3D scaffold, is aimed to mimic an in vivo environment as closely as possible. Although in recent years a considerable knowledge of bone co-culture models has been accumulated, there are still many open questions. We here try to summarize the actual knowledge and address open questions.

Morphology-oriented epigenetic research

Cytosine methylation plays a major role in the regulation of sequential and tissue-specific expression of genes. De novo aberrant DNA methylation and demethylation are also crucial processes in tumorigenesis and tumor progression. The mechanisms of how and when such aberrant methylation and demethylation occur in tumor cells are still obscure, however. To evaluate subtle epigenetic alteration among minor subclonal populations, morphology-oriented epigenetic analysis is requisite, especially where heterogeneity and flexibility are as notable as in the process of cancer progression and cellular differentiation at critical stages. Therefore, establishment of reliable morphology-oriented epigenetic studies has become increasingly important in not only the experimental but also the diagnostic field. By selecting a subset of cells based on characteristic morphological features disclosed by microdissection or in situ hybridization, we discovered how methylation at certain CpG sites outside of CpG islands would play a crucial epigenetic role in the versatility and flexibility of gene expression during cancer progression. In this review, we first introduce technical aspects of two morphology-oriented epigenetic studies: (1) histoendonuclease-linked detection of methylated sites of DNA (HELMET), and (2) padlock probe and rolling circle amplification (RCA) for in situ identification of methylated cytosine in a sequence-dependent manner. We then present our observation of a novel MeCP2-mediated gene-silencing mechanism through the addition of methylation to a single-CpG-locus upstream of the TATA-box of the receptor activator of NF-κB ligand (RANKL) and of secreted frizzled-related protein 4 (SFRP4) gene promoters.