Bone Microenvironment Research Articles

The Bone Microenvironment Soil in Prostate Cancer Metastasis: An miRNA Approach.

Bone metastatic prostate cancer (PCa) is associated with a high risk of mortality. Changes in the expression pattern of miRNAs seem to be related to early aspects of prostate cancer, as well as its establishment and proliferation, including the necessary steps for metastasis. Here we compiled, for the first time, the important roles of miRNAs in the development, diagnosis, and treatment of bone metastasis, focusing on recent in vivo and in vitro studies. PCa exosomes are proven to promote metastasis-related events, such as osteoblast and osteoclast differentiation and proliferation. Aberrant miRNA expression in PCa may induce abnormal bone remodeling and support tumor development. Furthermore, miRNAs are capable of binding to multiple mRNA targets, a dynamic property that can be harnessed for the development of treatment tools, such as antagomiRs and miRNA mimics, which have emerged as promising candidates in PCa treatment. Finally, miRNAs may serve as noninvasive biomarkers, as they can be detected in tissue and bodily fluids, are highly stable, and show differential expression between nonmetastatic PCa and bone metastatic samples. Taken together, the findings underscore the importance of miRNA expression profiles and miRNA-based tools as rational technologies to increase the quality of life and longevity of patients.

Substrate Stiffness of Bone Microenvironment Controls Functions of Pre-Osteoblasts and Fibroblasts In Vitro.

The formation of bone in a bone defect is accomplished by osteoblasts, while the over activation of fibroblasts promotes fibrosis. However, it is not clear how the extracellular matrix stiffness of the bone-regeneration microenvironment affects the function of osteoblasts and fibroblasts. This study aim to investigate the effect of bone-regeneration microenvironment stiffness on cell adhesion, cell proliferation, cell differentiation, synthesizing matrix ability and its potential mechanisms in mechanotransduction, in pre-osteoblasts and fibroblasts. Polyacrylamide substrates mimicking the matrix stiffness of different stages of the bone-healing process (15 kPa, mimic granulation tissue; 35 kPa, mimic osteoid; 150 kPa, mimic calcified bone matrix) were prepared. Mouse pre-osteoblasts MC3T3-E1 and mouse fibroblasts NIH3T3 were plated on three types of substrates, respectively. There were significant differences in the adhesion of pre-osteoblasts and fibroblasts on different polyacrylamide substrates. Runx2 expression increased with increasing substrate stiffness in pre-osteoblasts, while no statistical differences were found in the Acta2 expression in fibroblasts on three substrates. OPN expression in pre-osteoblasts, as well as Fn1 and Col1a1 expression in fibroblasts, decreased with increasing stiffness. The difference between the cell traction force generated by pre-osteoblasts and fibroblasts on substrates was also found. Our results indicated that substrate stiffness is a potent regulator of pre-osteoblasts and fibroblasts with the ability of promoting osteogenic differentiation of pre-osteoblasts, while having no effect on myofibroblast differentiation of fibroblasts.

Differential expression analysis of miRNAs in macrophage-derived exosomes in the tuberculosis-infected bone microenvironment.

Macrophages play an important role in regulating the course of spinal tuberculosis within the bone microenvironment. This study aimed to investigate the differential expression of miRNA in macrophage-derived exosomes within the tuberculosis-infected bone microenvironment, to identify miRNAs that hold potential as diagnostic markers and therapeutic targets. We established study cohorts for spinal tuberculosis, collected bone marrow blood samples, isolated macrophage exosomes, and performed exosome miRNA sequencing. A miRNA-mRNA co-expression network was constructed using WGCNA analysis. Gene GO analysis and KEGG pathway enrichment analysis were performed using KOBAS software. Target miRNAs were selected based on fold change, P-value, and false discovery rate, and their validation was carried out using qRT-PCR and ROC curve studies. Subsequently, we constructed a target gene network for these miRNAs and performed KEGG pathway enrichment analysis to explore the potential signaling mechanisms involved in regulating the disease course of spinal tuberculosis. Our findings revealed that macrophages from the tuberculosis-infected bone microenvironment exhibited an M1 phenotype. The successful extraction of exosomes from macrophage supernatants was confirmed through electron microscopy, particle size analysis, and protein blot analysis. Exosome miRNA-seq demonstrated that 28 miRNAs were up-regulated, while 34 miRNAs were down-regulated in individuals with spinal tuberculosis. GO analysis and KEGG pathway enrichment analysis indicated that the differentially expressed miRNAs were involved in various biological processes, cell components, molecular functions, and signaling pathways, which collectively contribute to the regulation of the disease course of spinal tuberculosis. Notably, miRNA-125b-5p was successfully selected based on fold change, p-value, and false discovery rate. qRT-PCR validation further confirmed the significant up-regulation of miRNA-125b-5p in spinal tuberculosis. The ROC curve revealed that miR-125b-5p is a potential diagnostic biomarker for spinal tuberculosis. Moreover, construction of the miRNA-125b-5p target gene network and subsequent KEGG enrichment analysis highlighted the importance of MAPK, TNF, Ras, Rap1, and the PI3K-Akt signaling pathways in the regulation of the disease course of spinal tuberculosis. Our study demonstrates differential expression of miRNAs in macrophage-derived exosomes in the tuberculosis-infected bone microenvironment. Specifically, MiRNA-125b-5p is significantly up-regulated in spinal tuberculosis and shows potential as a diagnostic biomarker for spinal tuberculosis.

Functional In Vivo Screening Identifies microRNAs Regulating Metastatic Dissemination of Prostate Cancer Cells to Bone Marrow.

Distant metastasis is the major cause of cancer-related deaths in men with prostate cancer (PCa). An in vivo functional screen was used to identify microRNAs (miRNAs) regulating metastatic dissemination of PCa cells. PC3 cells transduced with pooled miRZiP™ lentivirus library (anti-miRNAs) were injected intraprostatic to 13 NSG mice followed by targeted barcode/anti-miR sequencing. PCa cells in the primary tumours showed a homogenous pattern of anti-miRNAs, but different anti-miRNAs were enriched in liver, lung, and bone marrow, with anti-miR-379 highly enriched in the latter. The bone metastasis-promoting phenotype induced by decreased miR-379 levels was also confirmed in a less metastatic PCa cell line, 22Rv1, where all mice injected intracardially with anti-miR-379-22Rv1 cells developed bone metastases. The levels of miR-379 were found to be lower in bone metastases compared to primary tumours and non-cancerous prostatic tissue in a patient cohort. In vitro functional studies suggested that the mechanism of action was that reduced levels of miR-379 gave an increased colony formation capacity in conditions mimicking the bone microenvironment. In conclusion, our data suggest that specific miRNAs affect the establishment of primary tumours and metastatic dissemination, with a loss of miR-379 promoting metastases in bone.

A multifunctional polydopamine/genipin/alendronate nanoparticle licences fibrin hydrogels osteoinductive and immunomodulatory potencies for repairing bone defects

Here, we fabricated a hybrid nanoparticle composed of polydopamine nanoparticles (pNPs), alendronate (Al) and genipin (GP) for cranial bone defect repair. Al was crosslinked into pNPs via GP (Al@pNPs), after which hybrid nanoparticles were obtained. By embedding these Al@pNPs into the fibrin hydrogels, a multifunctional bone repair scaffold was fabricated (Al@pNPs/Fg). The Al@pNPs/Fg exhibited three synergistic effects on the bone microenvironment: i) enhanced ectomesenchymal stem cell (EMSC) osteogenic differentiation by activating the piezo 1 channel; ii) inhibited the formation and function of osteoclasts related to the NF-κB signaling pathways; and iii) promoted M2 polarization and anti-inflammatory factor expression under normal and simulated inflammatory conditions. Al@pNPs/Fg ultimately promoted cranial bone defect regeneration in an SD rat model. This simple and low-cost technology provides a new approach to constructing an efficient delivery system and has desirable biological properties, providing a tissue-committed niche for the repair of bone defects.

RAS‑stimulated release of exosomal miR‑494‑3p promotes the osteolytic bone metastasis of breast cancer cells.

RAS activation is a key determinant of breast cancer progression and metastasis. However, the role of the interaction among exosomes, RAS and microRNAs (miRNAs/miRs) in the osteolytic bone metastasis of breast cancer remains unclear. Therefore, the present study aimed to examine the role of activated RAS (KRAS, HRAS and NRAS) in the release of exosome‑mediated osteoclastogenic miRNAs and to elucidate their functional role in bone microenvironment remodeling invitro and invivo. Exosomes derived from RAS‑activated breast cancer cells promoted RANKL‑induced osteoclastogenesis; however, RAS inhibition abolished this effect. miR‑494‑3p, miR‑4508 and miR‑6869‑5p were identified as osteoclastogenic miRNAs in the exosomes secreted by RAS‑activated breast cancer cells. The levels of these osteoclastogenic miRNAs in the sera of patients with human epidermal growth factor receptor 2‑positive luminal breast cancer were significantly higher than those in the sera of patients with triple‑negative breast cancer. miR‑494‑3p exhibited both osteoclastogenic and anti‑osteoblastogenic activity. Treatment with a miR‑494‑3p inhibitor abolished the exosome‑mediated increase in RANKL‑induced osteoclastogenesis. Treatment with a miR‑494‑3p mimic enhanced RANKL‑induced osteoclast formation; however, treatment with its inhibitor suppressed this effect by targeting leucine‑rich repeat‑containing G‑protein coupled receptor 4 in osteoclast precursors. Furthermore, miR‑494‑3p inhibited bone morphogenetic protein 2‑induced osteoblast formation by targeting semaphorin 3A. In a mouse model, exosomes derived from breast cancer cells promoted osteolytic bone lesions; however, treatment with a miR‑494‑3p inhibitor significantly suppressed this effect. On the whole, the present study provides a novel mechanism, demonstrating that the RAS activation of breast cancer cells induces osteolytic bone metastasis by stimulating the exosome‑mediated transfer of osteoclastogenic miRNAs, including miR‑494‑3p to bone cells.

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

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

Radiation Induces Bone Microenvironment Disruption by Activating the STING-TBK1 Pathway.

Background and Objectives: Damage to normal bone tissue following therapeutic irradiation (IR) represents a significant concern, as IR-induced bone microenvironment disruption can cause bone loss and create a more favorable environment for tumor metastases. The aim of the present study was to explore the cellular regulatory mechanism of IR-induced bone microenvironment disruption to effectively prevent radiotherapy-associated adverse effects in the future. Materials and Methods: In this study, a mouse model of local IR was established via local irradiation of the left hind limb of BALB/c mice with 12 Gy X-rays, and an in vitro osteocyte (OCY) model was established by exposing osteocyte-like MLO-Y4 cells to 2, 4, and 8 Gy irradiation to analyze multicellular biological injuries and cellular senescence. Small interfering RNA (siRNA) transfection at the cellular level and a selective antagonist intervention C-176 at the animal level were used to explore the potential role of the stimulator of interferon genes (STING) on IR-induced bone microenvironment disruption. Results: The results showed that 12 Gy local IR induces multicellular dysfunction, manifested as ascension of OCYs exfoliation, activation of osteoclastogenesis, degeneration of osteogenesis and fate conversion of adipogenesis, as well as cellular senescence and altered senescence-associated secretory phenotype (SASP) secretion. Furthermore, the expression of STING was significantly elevated, both in the primary OCYs harvested from locally irradiated mice and in vitro irradiated MLO-Y4 cells, accompanied by the markedly upregulated levels of phosphorylated TANK-binding kinase 1 (P-TBK1), RANKL and sclerostin (SOST). STING-siRNA transfection in vitro restored IR-induced upregulated protein expression of P-TBK1 and RANKL, as well as the mRNA expression levels of inflammatory cytokines, such as IL-1α, IL-6 and NF-κB, accompanied by the alleviation of excessive osteoclastogenesis. Finally, administration of the STING inhibitor C-176 mitigated IR-induced activation of osteoclastogenesis and restraint of osteogenesis, ameliorating the IR-induced biological damage of OCYs, consistent with the inhibition of P-TBK1, RANKL and SOST. Conclusions: The STING-P-TBK1 signaling pathway plays a crucial role in the regulation of the secretion of inflammatory cytokines and osteoclastogenesis potential in IR-induced bone microenvironment disruption. The selective STING antagonist can be used to intervene to block the STING pathway and, thereby, repair IR-induced multicellular biological damage and mitigate the imbalance between osteoclastogenesis and osteoblastgenesis.

The Ins and Outs of Endosteal Niche Disruption in the Bone Marrow: Relevance for Myeloma Oncogenesis.

Multiple Myeloma (MM) and its preexisting stage, termed Monoclonal Gammopathy of Undetermined Significance (MGUS), have long been considered mainly as genomic diseases. However, the bone changes observed in both conditions have led to a reassessment of the role of the bone microenvironment, mainly the endosteal niche in their genesis. Here, we consider the disruption of the endosteal niche in the bone marrow, that is, the shift of the endosteal niche from an osteoblastic to an osteoclastic profile produced by bone senescence and inflammaging, as the key element. Thus, this disrupted endosteal niche is proposed to represent the permissive microenvironment necessary not only for the emergence of MM from MGUS but also for the emergence and maintenance of MGUS. Moreover, the excess of osteoclasts would favor the presentation of antigens (Ag) into the endosteal niche because osteoclasts are Ag-presenting cells. As such, they could significantly stimulate the presentation of some specific Ag and the clonal expansion of the stimulated cells as well as favor the expansion of such selected clones because osteoclasts are immunosuppressive. We also discuss this scenario in the Gaucher disease, in which the high incidence of MGUS and MM makes it a good model both at the bone level and the immunological level. Finally, we envisage that this endosteal niche disruption would increase the stochasticity (epigenetic and genetic instability) in the selected clones, according to our Tissue Disruption-induced cell Stochasticity (TiDiS) theory.

Incorporation/Enrichment of 3D Bioprinted Constructs by Biomimetic Nanoparticles: Tuning Printability and Cell Behavior in Bone Models.

Reproducing in vitro a model of the bone microenvironment is a current need. Preclinical in vitro screening, drug discovery, as well as pathophysiology studies may benefit from in vitro three-dimensional (3D) bone models, which permit high-throughput screening, low costs, and high reproducibility, overcoming the limitations of the conventional two-dimensional cell cultures. In order to obtain these models, 3D bioprinting offers new perspectives by allowing a combination of advanced techniques and inks. In this context, we propose the use of hydroxyapatite nanoparticles, assimilated to the mineral component of bone, as a route to tune the printability and the characteristics of the scaffold and to guide cell behavior. To this aim, both stoichiometric and Sr-substituted hydroxyapatite nanocrystals are used, so as to obtain different particle shapes and solubility. Our findings show that the nanoparticles have the desired shape and composition and that they can be embedded in the inks without loss of cell viability. Both Sr-containing and stoichiometric hydroxyapatite crystals permit enhancing the printing fidelity of the scaffolds in a particle-dependent fashion and control the swelling behavior and ion release of the scaffolds. Once Saos-2 cells are encapsulated in the scaffolds, high cell viability is detected until late time points, with a good cellular distribution throughout the material. We also show that even minor modifications in the hydroxyapatite particle characteristics result in a significantly different behavior of the scaffolds. This indicates that the use of calcium phosphate nanocrystals and structural ion-substitution is a promising approach to tune the behavior of 3D bioprinted constructs.

Insights into immuno-oncology drug development landscape with focus on bone metastasis.

Bone is among the main sites of metastasis in breast, prostate and other major cancers. Bone metastases remain incurable causing high mortality, severe skeletal-related effects and decreased quality of life. Despite the success of immunotherapies in oncology, no immunotherapies are approved for bone metastasis and no clear benefit has been observed with approved immunotherapies in treatment of bone metastatic disease. Therefore, it is crucial to consider unique features of tumor microenvironment in bone metastasis when developing novel therapies. The vicious cycle of bone metastasis, referring to crosstalk between tumor and bone cells that enables the tumor cells to grow in the bone microenvironment, is a well-established concept. Very recently, a novel osteoimmuno-oncology (OIO) concept was introduced to the scientific community. OIO emphasizes the significance of interactions between tumor, immune and bone cells in promoting tumor growth in bone metastasis, and it can be used to reveal the most promising targets for bone metastasis. In order to provide an insight into the current immuno-oncology drug development landscape, we used 1stOncology database, a cancer drug development resource to identify novel immunotherapies in preclinical or clinical development for breast and prostate cancer bone metastasis. Based on the database search, 24 immunotherapies were identified in preclinical or clinical development that included evaluation of effects on bone metastasis. This review provides an insight to novel immuno-oncology drug development in the context of bone metastasis. Bone metastases can be approached using different modalities, and tumor microenvironment in bone provides many potential targets for bone metastasis. Noting current increasing interest in the field of OIO, more therapeutic opportunities that primarily target bone metastasis are expected in the future.

The effect of cytokines on osteoblasts and osteoclasts in bone remodeling in osteoporosis: a review.

The complicated connections and cross talk between the skeletal system and the immune system are attracting more attention, which is developing into the field of Osteoimmunology. In this field, cytokines that are among osteoblasts and osteoclasts play a critical role in bone remodeling, which is a pathological process in the pathogenesis and development of osteoporosis. Those cytokines include the tumor necrosis factor (TNF) family, the interleukin (IL) family, interferon (IFN), chemokines, and so on, most of which influence the bone microenvironment, osteoblasts, and osteoclasts. This review summarizes the effect of cytokines on osteoblasts and osteoclasts in bone remodeling in osteoporosis, aiming to providing the latest reference to the role of immunology in osteoporosis.

Precision of bone mechanoregulation assessment in humans using longitudinal high-resolution peripheral quantitative computed tomography in vivo.

Local mechanical stimuli in the bone microenvironment are essential for the homeostasis and adaptation of the skeleton, with evidence suggesting that disruption of the mechanically-driven bone remodelling process may lead to bone loss. Longitudinal clinical studies have shown the combined use of high-resolution peripheral quantitative computed tomography (HR-pQCT) and micro-finite element analysis can be used to measure load-driven bone remodelling in vivo; however, quantitative markers of bone mechanoregulation and the precision of these analyses methods have not been validated in human subjects. Therefore, this study utilised participants from two cohorts. A same-day cohort (n=33) was used to develop a filtering strategy to minimise false detections of bone remodelling sites caused by noise and motion artefacts present in HR-pQCT scans. A longitudinal cohort (n=19) was used to develop bone imaging markers of trabecular bone mechanoregulation and characterise the precision for detecting longitudinal changes in subjects. Specifically, we described local load-driven formation and resorption sites independently using patient-specific odds ratios (OR) and 99% confidence intervals. Conditional probability curves were computed to link the mechanical environment to the remodelling events detected on the bone surface. To quantify overall mechanoregulation, we calculated a correct classification rate measuring the fraction of remodelling events correctly identified by the mechanical signal. Precision was calculated as root-mean-squared averages of the coefficient of variation (RMS-SD) of repeated measurements using scan-rescan pairs at baseline combined with a one-year follow-up scan. We found no significant mean difference (p<0.01) between scan-rescan conditional probabilities. RMS-SD was 10.5% for resorption odds, 6.3% for formation odds, and 1.3% for correct classification rates. Bone was most likely to be formed in high-strain and resorbed in low-strain regions for all participants, indicating a consistent, regulated response to mechanical stimuli. For each percent increase in strain, the likelihood of bone resorption decreased by 2.0±0.2%, and the likelihood of bone formation increased by 1.9±0.2%, totalling 38.3±1.1% of strain-driven remodelling events across the entire trabecular compartment. This work provides novel robust bone mechanoregulation markers and their precision for designing future clinical studies.

Cell-Instructive Mineralized Microenvironment Regulates Osteogenesis: A Growing SYMBIOSIS of Cell Biology and Biomaterials Engineering in Bone Tissue Regeneration.

One of the objectives of bone tissue engineering is to produce scaffolds that are biocompatible, osteoinductive, and mechanically equivalent to the natural extracellular matrix of bone in terms of structure and function. Reconstructing the osteoconductive bone microenvironment into a scaffold can attract native mesenchymal stem cells and differentiate them into osteoblasts at the defect site. The symbiotic relationship between cell biology and biomaterial engineering could result in composite polymers containing the necessary signals to recreate tissue- and organ-specific differentiation. In the current work, drawing inspiration from the natural stem cell niche to govern stem cell fate, the cell-instructive hydrogel platforms were constructed by engineering the mineralized microenvironment. This work employed two different hydroxyapatite delivery strategies to create a mineralized microenvironment in an alginate-PEGDA interpenetrating network (IPN) hydrogel. The first approach involved coating of nano-hydroxyapatite (nHAp) on poly(lactide-co-glycolide) microspheres and then encapsulating the coated microspheres in an IPN hydrogel for a sustained release of nHAp, whereas the second approach involved directly loading nHAp into the IPN hydrogel. This study demonstrate that both direct encapsulation and a sustained release approach showed enhanced osteogenesis in target-encapsulated cells; however, direct loading of nHAp into the IPN hydrogel increased the mechanical strength and swelling ratio of the scaffold by 4.6-fold and 1.14-fold, respectively. In addition, the biochemical and molecular studies revealed improved osteoinductive and osteoconductive potential of encapsulated target cells. Being less expensive and simple to perform, this approach could be beneficial in clinical settings.

Induction of Reactive Bone Stromal Fibroblasts in 3D Models of Prostate Cancer Bone Metastases.

A dynamic interplay between prostate cancer (PCa) cells and reactive bone stroma modulates the growth of metastases within the bone microenvironment. Of the stromal cells, metastasis-associated fibroblasts (MAFs) are known to contribute but are the least studied cell type in PCa tumour progression. It is the aim of the current study to establish a biologically relevant 3D in vitro model that mimics the cellular and molecular profiles of MAFs found in vivo. Using 3D in vitro cell culture models, the bone-derived fibroblast cell line, HS-5, was treated with conditioned media from metastatic-derived PCa cell lines, PC3 and MDA-PCa 2b, or mouse-derived fibroblasts 3T3. Two corresponding reactive cell lines were propagated: HS5-PC3 and HS5-MDA, and evaluated for alterations in morphology, phenotype, cellular behaviour, plus protein and genomic profiles. HS5-PC3 and HS5-MDA displayed distinct alterations in expression levels of N-Cadherin, non-functional E-Cadherin, alpha-smooth muscle actin (α-SMA), Tenascin C, and vimentin, along with transforming growth factor receptor expression (TGF β R1 and R2), consistent with subpopulations of MAFs reported in vivo. Transcriptomic analysis revealed a reversion of HS5-PC3 towards a metastatic phenotype with an upregulation in pathways known to regulate cancer invasion, proliferation, and angiogenesis. The exploitation of these engineered 3D models could help further unravel the novel biology regulating metastatic growth and the role fibroblasts play in the colonisation process.

Intravital imaging of osteocyte integrin dynamics with locally injectable fluorescent nanoparticles

Osteocytes are the resident mechanosensory cells in bone. They are responsible for skeletal homeostasis and adaptation to mechanical cues. Integrin proteins play a prominent role in osteocyte mechanotransduction, but the details are not well stratified. Intravital imaging with multiphoton microscopy presents an opportunity to study molecular level mechanobiological events in vivo and presents an opportunity to study integrin dynamics in osteocytes. However, fluorescent imaging limitations with respect to excessive optical scattering and low signal to noise ratio caused by mineralized bone matrix make such investigations non-trivial. Here, we demonstrate that ultra-small and bright fluorescent core-shell silica nanoparticles (<7 nm diameter), known as Cornell Prime Dots (C'Dots), are well-suited for the in vivo bone microenvironment and can improve intravital imaging capabilities. We report validation studies for C'Dots as a novel, locally injectable in vivo osteocyte imaging tool for both non-specific cellular uptake and for targeting integrins. The pharmacokinetics of C'Dots reveal distinct sex differences in nanoparticle intracellular dynamics and clearance in osteocytes, which represents a novel topic of study in bone biology. Integrin-targeted C'Dots were used to study osteocyte integrin dynamics. To the best of our knowledge, we report here the first evidence of osteocyte integrin endocytosis and recycling in vivo. Our results provide novel insights in osteocyte biology and will open up new lines of investigation that were previously unavailable in vivo.

Targeting c-Jun Is a Potential Therapy for Luminal Breast Cancer Bone Metastasis.

c-Jun expression mediates bone metastasis in luminal breast cancer by forming a vicious cycle in the bone microenvironment, which reveals potential strategies for subtype-specific bone metastasis therapy.

Exploring Bone Cell Research Using Bone-on-a-Chip Models and Microfluidics: A Literature Review

Introduction: Organ-on-a-chip models are becoming popular due to its success in modeling human tissues and organs, to mimic human physiology and understand how diseases or drugs affect organs. Traditional 2-dimensional in vitro models are limited in recreating complicated bone structure and examining cell-cell interactions. Alternatively, bone-on-a-chip models establish biomimetic conditions to accurately recapitulate the complexity of the bone. However, bone-on-a-chip models as 3D culture systems do not accurately replicate the bone microenvironment. Rather, microfluidic devices allow for fluid control on a microscale or nanoscale level and the incorporation of fluid shear stress normally experienced by bone cells. The goal of this review paper is to summarize advancements to bone-on-a-chip models. Methods: Relevant articles were selected through a computerized search using GEOBASE and PubMED. Search terms included ‘microfluidic devices AND bones’, ‘organ-on-a-chip models’, ‘bone-on-a-chip models’, ‘PDMS AND bone regeneration’, ‘PolyHIPE AND bone regeneration’ and ‘bone scaffolds’. Results: Microfluidic chips are fabricated using soft lithography and poly-di-methyl siloxane (PDMS) which is a biocompatible, synthetic polymer that is used as a cell culture substrate but is too stiff to facilitate bone regeneration. Hydroxyapatite (HA), lined with PDMS, is commonly used, but the substrate degrades at a much slower rate. Moreover, β-tricalcium-phosphate (β-TCP) as a bone scaffold is both porous and degrades faster hence existing studies have used it to generate a dense extracellular matrix. Discussion: The studies examined in this paper highlight contributions made to scaffolds and microfluidics using bone-on-a-chip models. Notably, scaffolds must be osteoconductive to allow bone cells to adhere, proliferate and form an extracellular matrix on its surface and pore. While PDMS is both osteoconductive and biocompatible, its rigidity poses a concern. Both β-TCP and HA have capabilities for cell-mediated resorption and are more favourable substrates. Additionally, by incorporating microfluidics with bone-on-a-chip models, cells experience greater fluid shear stress similar to that of loading within the bone. Conclusion: In sum, advancements to bone-on-a-chip platforms are ongoing and the many published studies discussed in this paper aim to optimize both the design and materials used to create long lasting impacts on the rapidly growing field of cell and tissue engineering.

Checkpoint Inhibitors in Bone Metastatic Disease in Solid Tumors.

Bone is a common site of metastatic spread for solid tumors. Bone as an organ serves unique roles in the body's structural integrity, hematopoiesis, and the development of immune modulating cells. With the increasing use of immunotherapy, specifically immune checkpoint inhibitors, understanding the response of bone metastases is necessary. The data on checkpoint inhibitors used for managing solid tumors are reviewed here with a focus on bone metastases. Albeit with limited available data, there is a trend toward poorer outcomes in this setting, presumably due to the unique immune microenvironment within bone and bone marrow. Despite the potential to improve cancer outcomes with use of ICIs, bone metastases remain challenging to manage and may have different responses to ICIs than other disease sites. Areas for future investigation include a nuanced understanding of the bone microenvironment and dedicated research aimed at specific bone metastases outcomes.

Hydrogels provide microenvironments to mesenchymal stem cells for craniofacial bone regeneration: Review.

The anatomical and physiological architecture of the craniofacial bone is intricate. Hence, the exact management of osteogenesis is necessary for the regeneration of the deficiencies that present in this area. Stem-based tissue engineering approaches, as opposed to conventional surgical intervention, induce bone growth with minimal postoperative risk and expense. Mesenchymal stem/stromal cells (MSC)'s pluripotent differentiation potential, anti-inflammatory and immunomodulatory properties underpin its versatility as a therapeutic agent in bone tissues. Inspired by the native stem cell niche, hydrogels are preferred choices to mediate cells and adapt to 3-D environment because of their outstanding swelling capabilities and similarity to natural extracellular matrices (ECMs). Due to their remarkable biocompatibility and capacity for stimulating bone regeneration, bone regeneration hydrogels have also received a great deal of interest. This review explores the opportunities of MSC based regenerative skeletal therapies, introduces the application of hydrogel scaffolds as artificial bone microenvironments for stem cells to explore its usage in craniofacial bone tissue engineering.