miR-148a regulates osteoclastogenesis by targeting V-maf musculoaponeurotic fibrosarcoma oncogene homolog B

From oncogenes to tumor suppressors: The dual role of ncRNAs in fibrosarcoma

Fibrosarcoma is a challenging cancer originating from fibrous tissues, marked by aggressive growth and limited treatment options. The discovery of non-coding RNAs (ncRNAs), including long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and small interfering RNAs (siRNAs), has opened new pathways for understanding and treating this malignancy. These ncRNAs play crucial roles in gene regulation, cellular processes, and the tumor microenvironment. This review aims to explore the impact of ncRNAs on fibrosarcoma's pathogenesis, progression, and resistance to treatment, focusing on their mechanistic roles and therapeutic potential. A comprehensive review of literature from databases like PubMed and Google Scholar was conducted, focusing on the dysregulation of ncRNAs in fibrosarcoma, their contribution to tumor growth, metastasis, drug resistance, and their cellular pathway interactions. NcRNAs significantly influence fibrosarcoma, affecting cell proliferation, apoptosis, invasion, and angiogenesis. Their function as oncogenes or tumor suppressors makes them promising biomarkers and therapeutic targets. Understanding their interaction with the tumor microenvironment is essential for developing more effective treatments for fibrosarcoma. Targeting ncRNAs emerges as a promising strategy for fibrosarcoma therapy, offering hope to overcome the shortcomings of existing treatments. Further investigation is needed to clarify specific ncRNAs' roles in fibrosarcoma and to develop ncRNA-based therapies, highlighting the significance of ncRNAs in improving patient outcomes in this challenging cancer.

Exploring ncRNA-mediated regulation of EGFR signalling in glioblastoma: From mechanisms to therapeutics

Glioblastoma (GBM) is the most prevalent and deadly primary brain tumor type, with a discouragingly low survival rate and few effective treatments. An important function of the EGFR signalling pathway in the development of GBM is to affect tumor proliferation, persistence, and treatment resistance. Advances in molecular biology in the last several years have shown how important ncRNAs are for controlling a wide range of biological activities, including cancer progression and development. NcRNAs have become important post-transcriptional regulators of gene expression, and they may affect the EGFR pathway by either directly targeting EGFR or by modifying important transcription factors and downstream signalling molecules. The EGFR pathway is aberrantly activated in response to the dysregulation of certain ncRNAs, which has been linked to GBM carcinogenesis, treatment resistance, and unfavourable patient outcomes. We review the literature on miRNAs, circRNAs and lncRNAs that are implicated in the regulation of EGFR signalling in GBM, discussing their mechanisms of action, interactions with the signalling pathway, and implications for GBM therapy. Furthermore, we explore the potential of ncRNA-based strategies to overcome resistance to EGFR-targeted therapies, including the use of ncRNA mimics or inhibitors to modulate the activity of key regulators within the pathway.

Stem Cell and Regenerative Therapies for the Treatment of Osteoporotic Vertebral Compression Fractures

Osteoporotic vertebral compression fractures (OVCFs) significantly increase morbidity and mortality, presenting a formidable challenge in healthcare. Traditional interventions such as vertebroplasty and kyphoplasty, despite their widespread use, are limited in addressing the secondary effects of vertebral fractures in adjacent areas and do not facilitate bone regeneration. This review paper explores the emerging domain of regenerative therapies, spotlighting stem cell therapy's transformative potential in OVCF treatment. It thoroughly describes the therapeutic possibilities and mechanisms of action of mesenchymal stem cells against OVCFs, relying on recent clinical trials and preclinical studies for efficacy assessment. Our findings reveal that stem cell therapy, particularly in combination with scaffolding materials, holds substantial promise for bone regeneration, spinal stability improvement, and pain mitigation. This integration of stem cell-based methods with conventional treatments may herald a new era in OVCF management, potentially improving patient outcomes. This review advocates for accelerated research and collaborative efforts to translate laboratory breakthroughs into clinical practice, emphasizing the revolutionary impact of regenerative therapies on OVCF management. In summary, this paper positions stem cell therapy at the forefront of innovation for OVCF treatment, stressing the importance of ongoing research and cross-disciplinary collaboration to unlock its full clinical potential.

Epigenetic regulation of bone remodeling and its role in the pathogenesis of primary osteoporosis

Discovery of molecular mechanisms of primary osteoporosis development is fundamental to understand the pathogenesis of musculoskeletal diseases in general and for identifying key links in the genetic and epigenetic regulation of bone remodelling genes. The number of identified molecular genetic markers for osteoporosis is increasing but there is a need to describe their functional interactions. These interactions have been determined to be associated with the control of expression of a number of transcription factors and the differentiation of mesenchymal stem cells through the pathway of osteoblastogenesis or adipogenesis, and monocytic precursors through the pathway of osteoclastogenesis. The results of epigenetic studies have significantly increased the understanding of the role of post-translational modifications of histones, DNA methylation and RNA interference in the osteoporosis pathogenesis and in bone remodelling. However, the knowledge should be systematised and generalised according to the results of research on the role of epigenetic modifiers in the development of osteoporosis, and the influence of each epigenetic mechanism on the individual links of bone remodelling during ontogenesis of humans in general, including the elderly, should be described. Understanding which mechanisms and systems are involved in the development of this nosology is of interest for the development of targeted therapies, as the possibility of using microRNAs to regulate genes is now being considered. Systematisation of these data is important to investigate the differences in epigenetic marker arrays by race and ethnicity. The review article analyses references to relevant reviews and original articles, classifies information on current advances in the study of epigenetic mechanisms in osteoporosis and reviews the results of studies of epigenetic mechanisms on individual links of bone remodelling.

Fine-tuning osteoclastogenesis: An insight into the cellular and molecular regulation of osteoclastogenesis

Osteoclasts, the bone-resorbing cells, are essential for the bone remodeling process and are involved in the pathophysiology of several bone-related diseases. The extensive corpus of in vitro research and crucial mouse model studies in the 1990s demonstrated the key roles of monocyte/macrophage colony-stimulating factor, receptor activator of nuclear factor kappa B ligand (RANKL) and integrin αvβ3 in osteoclast biology. Our knowledge of the molecular mechanisms by which these variables control osteoclast differentiation and function has significantly advanced in the first decade of this century. Recent developments have revealed a number of novel insights into the fundamental mechanisms governing the differentiation and functional activity of osteoclasts; however, these mechanisms have not yet been adequately documented. Thus, in the present review, we discuss various regulatory factors including local and hormonal factors, innate as well as adaptive immune cells, noncoding RNAs (ncRNAs), etc., in the molecular regulation of the intricate and tightly regulated process of osteoclastogenesis. ncRNAs have a critical role as epigenetic controllers of osteoclast physiologic activities, including differentiation and bone resorption. The primary ncRNAs, which include micro-RNAs, circular RNAs, and long noncoding RNAs, form a complex network that affects gene transcription activities associated with osteoclast biological activity. Greater knowledge of the involvement of ncRNAs in osteoclast biological activities will contribute to the treatment and management of several skeletal diseases such as osteoporosis, osteoarthritis, rheumatoid arthritis, etc. Moreover, we further outline potential therapies targeting these regulatory pathways of osteoclastogenesis in distinct bone pathologies.

miRNAs as potential game-changers in bone diseases: Future medicinal and clinical uses

MicroRNAs (miRNAs), short, highly conserved non-coding RNA, influence gene expression by sequential mechanisms such as mRNA breakdown or translational repression. Many biological processes depend on these regulating substances, thus changes in their expression have an impact on the maintenance of cellular homeostasis and result in the emergence of a variety of diseases. Relevant studies have shown in recent years that miRNAs are involved in many stages of bone development and growth. Additionally, abnormal production of miRNA in bone tissues has been closely associated with the development of numerous bone disorders, such as osteonecrosis, bone cancer, and bone metastases. Many pathological processes, including bone loss, metastasis, the proliferation of osteosarcoma cells, and differentiation of osteoblasts and osteoclasts, are under the control of miRNAs. By bringing together the most up-to-date information on the clinical relevance of miRNAs in such diseases, this study hopes to further the study of the biological features of miRNAs in bone disorders and explore their potential as a therapeutic target.

The correlation between circulating growth differentiation factor 11 and the risk of osteopenia/osteoporosis in men

Our results suggest that the serum GDF11 concentration is significantly associated with the risk of bone metabolism dysfunction in men and may be a useful target for prediction of osteopenia/osteoporosis to enable prompt intervention for this common but invariably under- or misdiagnosed condition in men.

PURPOSE

Male osteopenia/osteoporosis remains a neglected subject or is under- or misdiagnosed. Many studies have confirmed the role of growth differentiation factor 11 (GDF11) in bone metabolism, although its role in bone metabolism remains controversial. In this study, we aimed to investigate the association between serum GDF11 levels and the prevalence of osteopenia/osteoporosis (OP) in a male cohort and explore the possibility of GDF11 to be a useful target for prediction of osteopenia/osteoporosis to enable prompt intervention for this disease.

METHODS

This cross-sectional study included 121 native Chinese men randomly aged 20-87 years, excluded the subjects who had the conditions of bone metabolism-related disease and administration of hormonal drugs, and grouped the subjects to OP and non-OP, based on the WHO definition and latest guidelines of OP. The serum GDF11 concentration was determined using a GDF11-specific immunoassay. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Tartrate-resistant acid phosphatase 5b (TRAP-5b) were measured in serum samples with ELISA method.

RESULTS

We observed a negative correlation between serum GDF11 levels and age, a positive correlation between serum GDF11 levels and the femoral neck BMD, and a negative correlation between serum GDF11 levels and TRAP-5b in men. The prevalence and risk of OP were significantly higher in men with low serum GDF11 levels.

CONCLUSIONS

The serum GDF11 concentration is significantly associated with the risk of bone metabolism dysfunction and may be a useful target for prediction of OP in male cohort.

MiR-148a deletion protects from bone loss in physiological and estrogen-deficient mice by targeting NRP1

Bone metabolic homeostasis is largely dependent on the dynamic balance between osteoblasts and osteoclasts. MicroRNAs (miRNAs) play critical roles in regulating bone metabolism. In this study, we explored the role of a new miRNA (miR-148a) in osteoporosis. We compared the bone phenotype between miR-148a knockout (KO) mice and the wild-type (WT) littermates. We found miR-148a KO mice exhibited an increased bone mass phenotype and decreased osteoclastogenesis compared to the WT group. In vitro, miR-148a overexpression promoted osteoclastogenesis and bone resorption function. Mechanistically, NRP1 was identified as a novel direct target of miR-148a, and NRP1 silencing reversed the effect of miR-148a knockout. In OVX and calvarial osteolysis models, miR-148a KO protects mice against excessive bone resorption, while miR-148a agomiR/AAV-shNRP1 accelerates pathologic bone loss. Finally, the miR-148a level was found to be positively correlated with β-CTX in postmenopausal osteoporosis (PMOP) serum specimens. In summary, our findings revealed that miR-148a genetic deletion ameliorates bone loss under physiological and pathological conditions by targeting NRP1. In osteoclast-related bone metabolic diseases such as PMOP, miR-148a may be an attractive therapeutic target in the future.

How Do Extracellular Vesicles Play a Key Role in the Maintenance of Bone Homeostasis and Regeneration? A Comprehensive Review of Literature

The maintenance of bone homeostasis includes both bone resorption by osteoclasts and bone formation by osteoblasts. These two processes are in dynamic balance to maintain a constant amount of bone for accomplishing its critical functions in daily life. Multiple cell type communications are involved in these two complex and continuous processes. In recent decades, an increasing number of studies have shown that osteogenic and osteoclastic extracellular vesicles play crucial roles in regulating bone homeostasis through paracrine, autosecretory and endocrine signaling. Elucidating the functional roles of extracellular vesicles in the maintenance of bone homeostasis may contribute to the design of new strategies for bone regeneration. Hence, we review the recent understandings of the classification, production process, extraction methods, structure, contents, functions and applications of extracellular vesicles in bone homeostasis. We highlight the contents of various bone-derived extracellular vesicles and their interactions with different cells in the bone microenvironment during bone homeostasis. We also summarize the recent advances in EV-loaded biomaterial scaffolds for bone regeneration and repair.

Milk Exosomal microRNAs: Postnatal Promoters of β Cell Proliferation but Potential Inducers of β Cell De-Differentiation in Adult Life

Pancreatic β cell expansion and functional maturation during the birth-to-weaning period is driven by epigenetic programs primarily triggered by growth factors, hormones, and nutrients provided by human milk. As shown recently, exosomes derived from various origins interact with β cells. This review elucidates the potential role of milk-derived exosomes (MEX) and their microRNAs (miRs) on pancreatic β cell programming during the postnatal period of lactation as well as during continuous cow milk exposure of adult humans to bovine MEX. Mechanistic evidence suggests that MEX miRs stimulate mTORC1/c-MYC-dependent postnatal β cell proliferation and glycolysis, but attenuate β cell differentiation, mitochondrial function, and insulin synthesis and secretion. MEX miR content is negatively affected by maternal obesity, gestational diabetes, psychological stress, caesarean delivery, and is completely absent in infant formula. Weaning-related disappearance of MEX miRs may be the critical event switching β cells from proliferation to TGF-β/AMPK-mediated cell differentiation, whereas continued exposure of adult humans to bovine MEX miRs via intake of pasteurized cow milk may reverse β cell differentiation, promoting β cell de-differentiation. Whereas MEX miR signaling supports postnatal β cell proliferation (diabetes prevention), persistent bovine MEX exposure after the lactation period may de-differentiate β cells back to the postnatal phenotype (diabetes induction).

Bilirubin increases viability and decreases osteoclast apoptosis contributing to osteoporosis in advanced liver diseases

Bilirubin and bile acids have deleterious effects on osteoblasts, which may explain the low bone formation of liver diseases with cholestasis. Although there is some clinical evidence of increased bone resorption in this condition, the effects of these substances on osteoclasts are unknown. The objective was to analyze the effects of bilirubin and bile acids -lithocholic acid (LCA) and ursodeoxycholic acid (UDCA)- on osteoclast viability and apoptosis, and on the expression of osteoclast-related microRNAs (miRNAs). RAW 264.7 cells and human PBMCs were differentiated into osteoclasts. Success in differentiation was assessed by TRAP stain and osteoclast-specific gene expression; osteoclast activity was detected by the resorption pits in Corning® Osteo Assay Surface Plates. Cells were treated with camptothecin (CAM) or with bilirubin, LCA or UDCA, at several concentrations and combinations, including non-treated cells as control. Cell viability was measured using WST-1 assay and apoptosis assessing Caspase-3 by Western blot. Expression of miR-21a, miR-29b, miR-31, miR-148a, miR-155 and miR-223 were analyzed by Real Time. Viability increased gradually in osteoclasts differentiated from RAW 264.7 cells, as the concentration of bilirubin increased, being particularly high with bilirubin 100 μM (61 %) as compared to the untreated control (p < 0.007). Viability decreased significantly with CAM, LCA and UDCA (80 %, 62 % and 27 %, respectively), effects which were abolished by bilirubin. Moreover, bilirubin increased viability in osteoclasts derived from human PBMCs (p < 0.03). Caspase-3 decreased by 46 % with bilirubin 50 μM and increased 10-fold with LCA 100 μM and CAM (p < 0.01). Bilirubin increased miR-21 and miR-148a expression as compared to controls (115 % and 59 %, respectively; p < 0.007). In conclusion, bilirubin increases viability and decreases apoptosis of osteoclasts, and overexpresses the osteoclastogenic miR-21 and miR-148a. The effects of bilirubin counteract the actions of LCA and UDCA. Therefore, bilirubin may contribute to the increased bone resorption and to the development of osteoporosis in advanced liver diseases.

Exosome mediated biological functions within skeletal microenvironment

Exosomes are membranous lipid vesicles fused with intracellular multicellular bodies that are released into the extracellular environment. They contain bioactive substances, including proteins, RNAs, lipids, and cytokine receptors. Exosomes in the skeletal microenvironment are derived from a variety of cells such as bone marrow mesenchymal stem cells (BMSCs), osteoblasts, osteoclasts, and osteocytes. Their biological function is key in paracrine or endocrine signaling. Exosomes play a role in bone remodeling by regulating cell proliferation and differentiation. Genetic engineering technology combined with exosome-based drug delivery can therapy bone metabolic diseases. In this review, we summarized the pathways of exosomes derived from different skeletal cells (i.e., BMSCs, osteoblasts, osteocytes, and osteoclasts) regulate the skeletal microenvironment through proteins, mRNAs, and non-coding RNAs. By exploring the role of exosomes in the skeletal microenvironment, we provide a theoretical basis for the clinical treatment of bone-related metabolic diseases, which may lay the foundation to improve bone tumor microenvironments, alleviate drug resistance in patients.

miR-134-5p inhibits osteoclastogenesis through a novel miR-134-5p/Itgb1/MAPK pathway

Osteoporosis affects approximately 200 million people and severely affects quality of life, but the exact pathological mechanisms behind this disease remain unclear. Various miRNAs have been shown to play a predominant role in the regulation of osteoclast formation. In this study, we explored the role of miR-134-5p in osteoclastogenesis both in vivo and in vitro. We constructed an ovariectomized (OVX) mouse model and performed microarray analysis using bone tissue from OVX mice and their control counterparts. Quantitative RT-PCR data from bone tissue and bone marrow macrophages (BMMs) confirmed the decreased expression of miR-134-5p in OVX mice observed in microarray analysis. In addition, a decrease in miR-134-5p was also observed during induced osteoclastogenesis of BMMs collected from C57BL/6N mice. Through transfection with miR-134-5p agomirs and antagomirs, we found that miR-134-5p knockdown significantly accelerated osteoclast formation and cell proliferation and inhibited apoptosis. Furthermore, a luciferase reporter assay showed that miR-134-5p directly targets the integrin surface receptor gene Itgb1. Cotransfection with Itgb1 siRNA reversed the effect of the miR-134-5p antagomir in promoting osteoclastogenesis. Moreover, the abundance levels of MAPK pathway proteins phosphorylated-p38 (p-p38) and phosphorylated-ERK (p-ERK) were significantly increased after transfection with the miR-134-5p antagomir but decreased after transfection with the miR-134-5p agomir or Itgb1 siRNA, which indicated a potential relationship between the miR-134-5p/Itgb1 axis and the MAPK pathway. Collectively, these results revealed that miR-134-5p inhibits osteoclast differentiation of BMMs both in vivo and in vitro and that the miR-134-5p/Itgb1/MAPK pathway might be a potential target for osteoporosis therapy.

Alcohol-induced inhibition of bone formation and neovascularization contributes to the failure of fracture healing via the miR-19a-3p/FOXF2 axis

Aims

Alcoholism is a well-known detrimental factor in fracture healing. However, the underlying mechanism of alcohol-inhibited fracture healing remains poorly understood.

Methods

MicroRNA (miR) sequencing was performed on bone mesenchymal stem cells (BMSCs). The effects of alcohol and miR-19a-3p on vascularization and osteogenic differentiation were analyzed in vitro using BMSCs and human umbilical vein endothelial cells (HUVECs). An in vivo alcohol-fed mouse model of femur fracture healing was also established, and radiological and histomorphometric analyses were used to evaluate the role of miR-19a-3p. The binding of miR-19a-3p to forkhead box F2 (FOXF2) was analyzed using a luciferase reporter assay.

Results

miR-19a-3p was identified as one of the key regulators in the osteogenic differentiation of BMSCs, and was found to be downregulated in the alcohol-fed mouse model of fracture healing. In vitro, miR-19a-3p expression was downregulated after ethanol administration in both BMSCs and HUVECs. Vascularization and osteogenic differentiation were independently suppressed by ethanol and reversed by miR-19a-3p. In addition, the luciferase reporter assay showed that FOXF2 is the direct binding target of miR-19a-3p. In vivo, miR-19a-3p agomir stimulated callus transformation and improved the alcohol-impaired fracture healing.

Conclusion

This study is the first to demonstrate that the miR-19a-3p/FOXF2 axis has a pivotal role in alcohol-impaired fracture healing, and may be a potential therapeutic target.

Cite this article: Bone Joint Res 2022;11(6):386–397.

Analysis of a miR-148a Targetome in B Cell Central Tolerance

A microRNA (miRNA) often regulates the expression of hundreds of target genes. A fundamental question in the field of miRNA research is whether a miRNA exerts its biological function through regulating a small number of key targets or through small changes in the expression of hundreds of target genes. We addressed this issue by performing functional analysis of target genes regulated by miR-148a. We previously identified miR-148a as a critical regulator of B cell central tolerance and found 119 target genes that may mediate its function. We selected 4 of them for validation and demonstrated a regulatory role for Bim, Pten, and Gadd45a in this process. In this study, we performed functional analysis of the other miR-148a target genes in in vitro and in vivo models of B cell central tolerance. Our results show that those additional target genes play a minimal role, if any, in miR-148a-mediated control of B cell central tolerance, suggesting that the function of miRNAs is mediated by a few key target genes. These findings have advanced our understanding of molecular mechanisms underlying miRNA regulation of gene expression and B cell central tolerance.

Regulation of osteoclast-mediated bone resorption by microRNA

Osteoclast-mediated bone resorption is responsible for bone metabolic diseases, negatively impacting people's health and life. It has been demonstrated that microRNA influences the differentiation of osteoclasts by regulating the signaling pathways during osteoclast-mediated bone resorption. So far, the involved mechanisms have not been fully elucidated. This review introduced the pathways involved in osteoclastogenesis and summarized the related microRNAs binding to their specific targets to mediate the downstream pathways in osteoclast-mediated bone resorption. We also discuss the clinical potential of targeting microRNAs to treat osteoclast-mediated bone resorption as well as the challenges of avoiding potential side effects and producing efficient delivery methods.

MicroRNA-1270 Inhibits Cell Proliferation, Migration, and Invasion via Targeting IRF8 in Osteoblast-like Cell Lines

Osteoporosis (OP) is the most common bone disease affecting elderly individuals. The diagnosis of this pathology is most commonly made on the basis of bone fractures. Several microRNAs (miRNAs/miRs) have been identified as possible biomarkers for the diagnosis and treatment of OP. miRNAs can regulate gene expression, and determining their functions can provide potential pharmacological targets for treating OP. A previous study showed that miR-1270 was upregulated in monocytes derived from postmenopausal women with OP. Therefore, the present study aimed to uncover the role of miR-1270 in regulating bone metabolism. To reveal the mechanism underlying the regulatory effect of miR-1270 on interferon regulatory factor 8 (IRF8) expression, luciferase assay, reverse transcription-quantitative PCR, and Western blot analysis were performed. The results suggest that miR-1270 could regulate the mRNA and protein expression levels of IRF8 by directly binding to its 3′-untranslated region. The effects of miR-1270 overexpression and IRF8 silencing on cell proliferation, migration, and invasion were also evaluated. To the best of our knowledge, the current study was the first to support the crucial role of miR-1270 in bone metabolism via modulation of IRF8 expression. In addition, miR-1270 overexpression could attenuate human osteoblast-like cells’ proliferation and migration ability.

Extracellular Vesicles Derived From Murine Cementoblasts Possess the Potential to Increase Receptor Activator of Nuclear Factor-κB Ligand-Induced Osteoclastogenesis

Cementum resorption, unlike bone resorption, is clinically known to occur only with limited pathological stimuli, such as trauma, orthodontic forces, and large apical periodontitis; however, the molecular mechanisms that control osteoclast formation on the cementum surface remain unclear. In this study, we focused on extracellular vesicles (EVs) secreted by cementoblasts and analyzed their effects on osteoclast differentiation. EVs were extracted from the conditioned medium (CM) of the mouse cementoblast cell line OCCM-30. Transmission electron microscopy (TEM) analysis confirmed the presence of EVs with a diameter of approximately 50–200 nm. The effect of the EVs on osteoclast differentiation was examined using the mouse osteoclast progenitor cell line RAW 264.7 with recombinant receptor activator of nuclear factor (NF)-κB ligand (rRANKL) stimulation. EVs enhanced the formation of tartrate-resistant acid phosphatase (TRAP) activity-positive cells upon rRANKL stimulation. EVs also enhanced the induction of osteoclast-associated gene and protein expression in this condition, as determined by real-time PCR and Western blotting, respectively. On the other hand, no enhancing effect of EVs was observed without rRANKL stimulation. A Western blot analysis revealed no expression of receptor activator of NF-κB ligand (RANKL) in EVs themselves. The effect on rRANKL-induced osteoclast differentiation was examined using the CM of cementoblasts in terms of TRAP activity-positive cell formation and osteoclast-associated gene expression. The conditioned medium partly inhibited rRANKL-induced osteoclast differentiation and almost completely suppressed its enhancing effect by EVs. These results indicate that cementoblasts secreted EVs, which enhanced RANKL-induced osteoclast differentiation, and simultaneously produced soluble factors that neutralized this enhancing effect of EVs, implicating this balance in the regulation of cementum absorption. A more detailed understanding of this crosstalk between cementoblasts and osteoclasts will contribute to the development of new therapies for pathological root resorption.

Role of Exosomal Non-Coding RNAs in Bone-Related Diseases

Bone-related diseases seriously affect the lives of patients and carry a heavy economic burden on society. Treatment methods cannot meet the diverse clinical needs of affected patients. Exosomes participate in the occurrence and development of many diseases through intercellular communication, including bone-related diseases. Studies have shown that exosomes can take-up and “package” non-coding RNAs and “deliver” them to recipient cells, thereby regulating the function of recipient cells. The exosomal non-coding RNAs secreted by osteoblasts, osteoclasts, chondrocytes, and other cells are involved in the regulation of bone-related diseases by inhibiting osteoclasts, enhancing chondrocyte activity and promoting angiogenesis. Here, we summarize the role and therapeutic potential of exosomal non-coding RNAs in the bone-related diseases osteoporosis, osteoarthritis, and bone-fracture healing, and discuss the clinical application of exosomes in patients with bone-related diseases.

MicroRNA-148a-3p is a candidate mediator of increased bone marrow adiposity and bone loss following spinal cord injury

Spinal cord injury is often followed by osteoporosis characterized by rapid and severe bone loss. This leads to an increased risk of osteoporotic fracture in people with spinal cord injury, resulting in increased healthcare costs, morbidity, and mortality. Though it is common, the mechanisms underlying this osteoporosis are not completely understood and treatment options are limited. No biomarkers have been identified for predicting fracture risk. In this study, we sought to investigate microRNA mediated mechanisms relating to osteoporosis following spinal cord injury. We studied subjects with acute SCI (n=12), chronic SCI (n=18), and controls with no SCI (n=23). Plasma samples from all subjects underwent transcriptomic analysis to quantify microRNA expression, after which miR-148a-3p was selected for further study. We performed CT scans of the knee on all subjects with SCI and analyzed these scans to quantify bone marrow adipose tissue volume. MiR-148a-3p was upregulated in subjects with acute SCI vs chronic SCI, as well as in acute SCI vs no SCI. Subjects with chronic SCI had greater levels of marrow adiposity in the distal femoral diaphysis compared to subjects with acute SCI. MiR-148a-3p levels were negatively associated with distal femoral diaphysis marrow adiposity. A multivariable model showed that miR-148a-3p and BMI explained 24% of variation in marrow adiposity. A literature search revealed that miR-148a-3p has multiple bone and fat metabolism related targets. Our findings suggest that miR-148a-3p is a mediator of osteoporosis following spinal cord injury and a potential future therapeutic target.

A systematic review of miRNAs as biomarkers in osteoporosis disease

Background

Osteoporosis is often considered to be a disease of the elderly, which is characterized by two characteristics: low bone mineral density (BMD) and increased risk of fracture. MicroRNAs (miRNAs) have been reported to play a potential role in bone formation and resorption, bone remodeling, bone homeostasis regulation, and bone cell differentiation. Therefore, altered expression of different miRNAs may impact the pathology of bone diseases such as osteoporosis. A systematic review was conducted to extract all miRNA found to be significantly dys-regulated in the peripheral blood.

Methods

This review was carried out using a systematically search on PubMed, Scopus, Embase, Web of Science (WoS), and Cochrane databases from 1990 to 2018 to explore the diagnostic value of miRNAs as a biomarker in osteoporosis.

Results

A total of 31 studies were identified in the systematic review that indicated more than 30 kinds of up-regulated and down-regulated miRNAs in three categories; postmenopausal osteoporosis, postmenopausal osteoporosis with fracture risk, and other types of osteoporosis and fracture risk.

Conclusion

The collective data presented in this review indicate that miRNAs could serve as biomarkers for the diagnosis (onset) and prognosis (progression of osteoporosis), while the clinical application of these findings has yet to be verified.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-021-00873-5.

Exosomes derived from PC-3 cells suppress osteoclast differentiation by downregulating miR-148a and blocking the PI3K/AKT/mTOR pathway

Prostate cancer is a leading malignancy in men that can also disrupt the bone tissue balance. Among all urological cancers, prostate cancer is associated with the highest rate of bone metastases, which can greatly reduce a patient's quality of life. In recent years, cell-derived exosomes, which can contain a wide range of biologically active molecules, have been reported as a novel method of communication among individual cells. However, the specific role that exosomes serve in this disease has not been fully elucidated. The prostate cancer cell line PC-3 were applied in the present study, where its exosomes were isolated to explore their potential effects on osteoclast differentiation. Exosomes are extracellular vesicles secreted by cells. The size of exosomes is 30-150 nm. They have double membrane structure and saucer-like morphology. They contain rich contents (including nucleic acid, protein and lipid) and participate in molecular transmission between cells. The combined results of tartrate-resistant acid phosphatase staining (to identify osteoclasts obtained from human peripheral blood mononuclear cells), reverse transcription-quantitative PCR and western blotting showed that PC-3-derived exosomes attenuated osteoclast differentiation by downregulating marker genes associated with osteoclastic maturation, including V-maf musculoaponeurotic fibrosarcoma oncogene homolog B, matrix metalloproteinase 9 and integrin β3. microRNA (miR)-148a expression was also found to be downregulated in osteoclasts by PC-3-derived exosomes. In addition, the mTOR and AKT signaling pathways were blocked after exposure to these PC-3 cell-derived exosomes. Therefore, results from the present study suggest that miR-148a mimics may be a new therapeutic approach for the prevention of prostate cancer bone metastases.

Circulating miR-122-5p and miR-375 as Potential Biomarkers for Bone Mass Recovery after Parathyroidectomy in Patients with Primary Hyperparathyroidism: A Proof-of-Concept Study

Primary hyperparathyroidism (PHPT) is the leading cause of secondary osteoporosis. Although bone mineral density (BMD) tends to recover after parathyroidectomy in PHPT patients, the degree of recovery varies. Circulating microRNAs (miRNAs) profiles are known to be correlated with osteoporosis and fracture. We aimed to investigate whether osteoporotic fracture-related miRNAs are associated with postoperative BMD recovery in PHPT. Here, 16 previously identified osteoporotic fracture-related miRNAs were selected. We analyzed the association between the preoperative level of each miRNA and total hip (TH) BMD change. All 12 patients (among the 18 patients enrolled) were cured of PHPT after parathyroidectomy as parathyroid hormone (PTH) and calcium levels were restored to the normal range. Preoperative miR-19b-3p, miR-122-5p, and miR-375 showed a negative association with the percent changes in TH BMD from baseline. The association remained robust for miR-122-5p and miR-375 even after adjusting for sex, age, PTH, and procollagen type 1 N-terminal propeptide levels in a multivariable model. In conclusion, preoperative circulating miR-122-5p and miR-375 levels were negatively associated with TH BMD changes after parathyroidectomy in PHPT patients. miRNAs have the potential to serve as predictive biomarkers of treatment response in PHPT patients, which merits further investigation.

Runx1/miR-26a/Jagged1 signaling axis controls osteoclastogenesis and alleviates orthodontically induced inflammatory root resorption

BACKGROUND

MicroRNAs (miRNAs) are involved in the regulation of osteoclast biology and several pathogenic progression. This study aimed to identify the role of miR-26a in osteoclastogenesis and orthodontically induced inflammatory root resorption(OIIRR).

METHODS

Rat orthodontic tooth movement (OTM) model was established by ligating a closed coil spring between maxillary first molar and incisor, and 50 g orthodontic force was applied to move upper first molar to middle for 7 days. Human periodontal ligament (hPDL) cells were isolated from periodontium of healthy donors, and then subjected to compression force (CF) for 24 h to mimic an in vitro OTM model. The levels of associated factors in vivo and in vitro were measured subsequently.

RESULT

The distance of tooth movement was increased and root resorption pits were occurred in rat OTM model. The expression of miR-26a was decreased in vivo and vitro experiments. CF treatment enhanced the secretion of inflammatory factors receptor activator of nuclear factor-kappa B ligand (RANKL) and IL-6, osteoclast marker levels, and the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, while miR-26a overexpression reversed these results. Furthermore, miR-26a overexpression inhibited the osteoclastogenesis and rescued the root resorption in OTM rats through inhibition of Jagged1. Additionally, Runx1 could bind to miR-26a promoter and promote its expression, thereby suppressing the osteoclastogenesis.

CONCLUSION

We concluded that Runx1/miR-26a/Jagged1 signaling axis restrained osteoclastogenesis and alleviated OIIRR.

Evaluation of the cargo contents and potential role of extracellular vesicles in osteoporosis

Osteoporosis is a common aging-related disease diagnosed primarily using bone mineral density (BMD). Extracellular vesicles (EVs) remain unexplored in the context of osteoporosis. Towards this, EVs were isolated from plasma of a discovery cohort with 8 non-osteoporotic and 8 osteoporotic individuals, and nanoparticle tracking analysis (NTA) revealed a significantly higher EV concentration in osteoporotic individuals (P = 0.003). Moreover, EVs concentration showed a linear correlation with bone mineral density (BMD) values (linear correlation coefficient r = 0.9542, deviation from zero, p < 0.001). Results using a mouse model of osteoporosis confirmed that the number of EVs in mice from hindlimb unloading group was significantly higher than that from the age-matched control group (p = 0.015). TaqMan Real-Time PCR demonstrated that miR-335-5p, -320a, -483-5p, and miR-21-5p, were significantly higher expressed in osteoporotic patients compared with non-osteoporotic individuals. Quantitative real-time PCR shown that Wnt1, Wnt5a, Wnt7a, and Wnt9a mRNAs were lower expressed in osteoporosis derived EVs. In vitro functional assay indicated that osteoporosis derived EVs resulted in reduced mineralization in SaOS-2 cells. In conclusion, these results suggest that osteoporosis increased the secretion of EVs which carry higher expression of miRNAs and decreased expression of Wnt signals, further decreased the mineralization capacity in human osteoblasts.

LncRNA Nron Inhibits Bone Resorption in Periodontitis

Periodontitis is the most common chronic oral disease and is characterized by active osteoclast activity and significant alveolar bone resorption. However, the key regulatory factors of periodontal bone loss have yet to be determined, and reasonable intervention methods for periodontitis have not been developed. Currently, long noncoding RNAs (lncRNAs) have shown a remarkable ability to maintain normal cell and tissue homeostasis. Interestingly, we recently found that the lncRNA Nron is negatively correlated with alveolar bone resorption in periodontitis model. To explore the role of Nron in periodontal bone loss, osteoclastic-specific Nron knockout mice and osteoclastic-specific Nron transgenic mice were generated. Nron effectively inhibited osteoclastogenesis and alveolar bone resorption. Mechanistically, Nron was found to effectively promote the nuclear transport of NF-κb repressing factor (NKRF). In addition, NKRF in the nucleus significantly repressed the transcription of Nfatc1, which is a major NF-κb signaling molecule. Importantly, local injection of the Nron overexpression vector significantly inhibited osteoclastogenesis and alveolar bone resorption, which indicated the translational application potential of lncRNAs in the treatment of bone resorption in periodontitis.

Exosome-Derived MicroRNAs of Human Milk and Their Effects on Infant Health and Development

Multiple biologically active components of human milk support infant growth, health and development. Milk provides a wide spectrum of mammary epithelial cell-derived extracellular vesicles (MEVs) for the infant. Although the whole spectrum of MEVs appears to be of functional importance for the growing infant, the majority of recent studies report on the MEV subfraction of milk exosomes (MEX) and their miRNA cargo, which are in the focus of this review. MEX and the dominant miRNA-148a play a key role in intestinal maturation, barrier function and suppression of nuclear factor-κB (NF-κB) signaling and may thus be helpful for the prevention and treatment of necrotizing enterocolitis. MEX and their miRNAs reach the systemic circulation and may impact epigenetic programming of various organs including the liver, thymus, brain, pancreatic islets, beige, brown and white adipose tissue as well as bones. Translational evidence indicates that MEX and their miRNAs control the expression of global cellular regulators such as DNA methyltransferase 1-which is important for the up-regulation of developmental genes including insulin, insulin-like growth factor-1, α-synuclein and forkhead box P3-and receptor-interacting protein 140, which is important for the regulation of multiple nuclear receptors. MEX-derived miRNA-148a and miRNA-30b may stimulate the expression of uncoupling protein 1, the key inducer of thermogenesis converting white into beige/brown adipose tissue. MEX have to be considered as signalosomes derived from the maternal lactation genome emitted to promote growth, maturation, immunological and metabolic programming of the offspring. Deeper insights into milk's molecular biology allow the conclusion that infants are both "breast-fed" and "breast-programmed". In this regard, MEX miRNA-deficient artificial formula is not an adequate substitute for breastfeeding, the birthright of all mammals.

Overexpression of miRNA-22-3p attenuates osteoporosis by targeting MAPK14

Osteoporosis (OP) results from an imbalance between bone formation, which is regulated by osteoblasts, and bone resorption, which is mediated by osteoclasts. MicroRNA-22-3p (miR-22-3p) expression is decreased during the process of osteoclast differentiation and p38α mitogen-activated protein kinase (MAPK)14 promotes the proliferation and differentiation of osteoclast progenitors. However, whether miR-22-3p could target MAPK14 to regulate the progression of OP remains unknown, which was the aim of the present study. CD14⁺ PBMCs were used for the establishment of osteoclastic differentiation in vitro. In the present study, reverse transcription quantitative PCR was used to determine the mRNA expression of MAPK14, tartrate resistant acid phosphatase (TRAP), nuclear factor of activated T-cells (NFATC1) and cathepsin K (CTSK). Western blotting was applied to determine the protein expression of MAPK14, TRAP, NFATC1, CTSK, p-p65 and p65. Dual luciferase reporter assay was applied to confirm the relation between miR-22-3p and MAPK14. Cell Counting Kit-8 assay and flow cytometry assays were used to determine the cell proliferation and cell apoptosis, respectively. The results demonstrated that miR-22-3p expression was lower while MAPK14 expression was higher in the serum from patients with OP compared with healthy volunteers. Furthermore, miR-22-3p expression was negatively correlated with MAPK14 expression in patients with OP. In addition, miR-22-3p expression was decreased and MAPK14 expression was increased during the progression of CD14⁺peripheral blood mononuclear cells (PBMCs) osteoclastic differentiation in a time-dependent manner. Furthermore, miR-22-3p inhibited the proliferation and differentiation and promoted the apoptosis of CD14⁺PBMCs by targeting MAPK14. In summary, the findings from the present study suggested that miR-22-3p may serve a potential therapeutic role in patients with OP.

Pasteurized non-fermented cow's milk but not fermented milk is a promoter of mTORC1-driven aging and increased mortality

Recent epidemiological studies in Sweden, a country with traditionally high milk consumption, revealed that the intake of non-fermented pasteurized milk increased all-cause mortality in a dose-dependent manner. In contrast, the majority of epidemiological and clinical studies report beneficial health effects of fermented milk products, especially of yogurt. It is the intention of this review to delineate potential molecular aging mechanisms related to the intake of non-fermented milk versus yogurt on the basis of mechanistic target of rapamycin complex 1 (mTORC1) signaling. Non-fermented pasteurized milk via its high bioavailability of insulinotropic branched-chain amino acids (BCAAs), abundance of lactose (glucosyl-galactose) and bioactive exosomal microRNAs (miRs) enhances mTORC1 signaling, which shortens lifespan and increases all-cause mortality. In contrast, fermentation-associated lactic acid bacteria metabolize BCAAs and degrade galactose and milk exosomes including their mTORC1-activating microRNAs. The Industrial Revolution, with the introduction of pasteurization and refrigeration of milk, restricted the action of beneficial milk-fermenting bacteria, which degrade milk's BCAAs, galactose and bioactive miRs that synergistically activate mTORC1. This unrecognized behavior change in humans after the Neolithic revolution increased aging-related over-activation of mTORC1 signaling in humans, who persistently consume large quantities of non-fermented pasteurized cow's milk, a potential risk factor for aging and all-cause mortality.

Extracellular Vesicle-Mediated Bone Remodeling and Bone Metastasis: Implications in Prostate Cancer

Bone metastasis is the tendency of certain primary tumors to spawn and dictate secondary neoplasia in the bone. The process of bone metastasis is regulated by the dynamic crosstalk between metastatic cancer cells, cellular components of the bone marrow microenvironment (osteoblasts, osteoclasts, and osteocytes), and the bone matrix. The feed-forward loop mechanisms governs the co-option of homeostatic bone remodeling by cancer cells in bone. Recent developments have highlighted the discovery of extracellular vesicles (EVs) and their diverse roles in distant outgrowths. Several studies have implicated EV-mediated interactions between cancer cells and the bone microenvironment in synergistically promoting pathological skeletal metabolism in the metastatic site. Nevertheless, the potential role that EVs serve in arbitrating intricate sequences of coordinated events within the bone microenvironment remains an emerging field. In this chapter, we review the role of cellular participants and molecular mechanisms in regulating normal bone physiology and explore the progress of current research into bone-derived EVs in directly triggering and coordinating the processes of physiological bone remodeling. In view of the emerging role of EVs in interorgan crosstalk, this review also highlights the multiple systemic pathophysiological processes orchestrated by the EVs to direct organotropism in bone in prostate cancer. Given the deleterious consequences of bone metastasis and its clinical importance, in-depth knowledge of the multifarious role of EVs in distant organ metastasis is expected to open new possibilities for prognostic evaluation and therapeutic intervention for advanced bone metastatic prostate cancer.

MicroRNA treatment modulates osteogenic differentiation potential of mesenchymal stem cells derived from human chorion and placenta

Mesenchymal stem cells (MSCs) are important in regenerative medicine because of their potential for multi-differentiation. Bone marrow, chorion and placenta have all been suggested as potential sources for clinical application. However, the osteogenic differentiation potential of MSCs derived from chorion or placenta is not very efficient. Bone morphogenetic protein-2 (BMP-2) plays an important role in bone development. Its effect on osteogenic augmentation has been addressed in several studies. Recent studies have also shown a relationship between miRNAs and osteogenesis. We hypothesized that miRNAs targeted to Runt-related transcription factor 2 (Runx-2), a major transcription factor of osteogenesis, are responsible for regulating the differentiation of MSCs into osteoblasts. This study examines the effect of BMP-2 on the osteogenic differentiation of MSCs isolated from chorion and placenta in comparison to bone marrow-derived MSCs and investigates the role of miRNAs in the osteogenic differentiation of MSCs from these sources. MSCs were isolated from human bone marrow, chorion and placenta. The osteogenic differentiation potential after BMP-2 treatment was examined using ALP staining, ALP activity assay, and osteogenic gene expression. Candidate miRNAs were selected and their expression levels during osteoblastic differentiation were examined using real-time RT-PCR. The role of these miRNAs in osteogenesis was investigated by transfection with specific miRNA inhibitors. The level of osteogenic differentiation was monitored after anti-miRNA treatment. MSCs isolated from chorion and placenta exhibited self-renewal capacity and multi-lineage differentiation potential similar to MSCs isolated from bone marrow. BMP-2 treated MSCs showed higher ALP levels and osteogenic gene expression compared to untreated MSCs. All investigated miRNAs (miR-31, miR-106a and miR148) were consistently downregulated during the process of osteogenic differentiation. After treatment with miRNA inhibitors, ALP activity and osteogenic gene expression increased over the time of osteogenic differentiation. BMP-2 has a positive effect on osteogenic differentiation of chorion- and placenta-derived MSCs. The inhibition of specific miRNAs enhanced the osteogenic differentiation capacity of various MSCs in culture and this strategy might be used to promote bone regeneration. However, further in vivo experiments are required to assess the validity of this approach.

MicroRNA function in craniofacial bone formation, regeneration and repair

Bone formation in the craniofacial complex is regulated by cranial neural crest (CNC) and mesoderm-derived cells. Different elements of the developing skull, face, mandible, maxilla (jaws) and nasal bones are regulated by an array of transcription factors, signaling molecules and microRNAs (miRs). miRs are molecular modulators of these factors and act to restrict their expression in a temporal-spatial mechanism. miRs control the different genetic pathways that form the craniofacial complex. By understanding how miRs function in vivo during development they can be adapted to regenerate and repair craniofacial genetic anomalies as well as bone diseases and defects due to traumatic injuries. This review will highlight some of the new miR technologies and functions that form new bone or inhibit bone regeneration.

MicroRNA-548-3p overexpression inhibits proliferation, migration and invasion in osteoblast-like cells by targeting STAT1 and MAFB

Osteoporosis is the most common bone disease and a public health issue with increasing prevalence in Mexico. This disease is caused by an imbalance in the bone remodelling process mediated by osteoclast and osteoblast. MicroRNAs have emerged as key players during the differentiation of both types of cells specialized involved in bone metabolism. We found high expression levels of miR-548x-3p in circulating monocytes derived from postmenopausal osteoporotic women. This study aimed to analyse the functional characterization of miR-548x-3p roles in the bone remodelling process. We validated by RT-qPCR, the elevated levels of miR-548x-3p in circulating monocytes derived from osteoporosis women. Through bioinformatics analysis, we identify MAFB and STAT1 as potential target genes for miR-548x-3p. Both genes showed low levels of expression in circulating monocytes derived from osteoporotic women. In addition, we demonstrated the binding of miR-548x-3p to the 3'-UTR of both mRNAs. MiR-548x-3p was overexpressed in osteoblasts-like cell lines decreasing the levels of MAFB and STAT1 mRNA and protein. We found that miR-548x-3p overexpression inhibits the proliferation, migration and invasion of the cell lines evaluated. Our results identified, by the first time, the potential role of miR-548x-3p as a modulator of the bone remodelling process by regulating the expression of MAFB and STAT1.

Role of Synovial Exosomes in Osteoclast Differentiation in Inflammatory Arthritis

This study aimed to investigate the characteristics of exosomes isolated from synovial fluid and their role in osteoclast differentiation in different types of inflammatory arthritis. Exosomes isolated from synovial fluid of rheumatoid arthritis (RA), ankylosing spondylitis (AS), gout, and osteoarthritis (OA) patients were co-incubated with CD14+ mononuclear cells from healthy donors without macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL). Osteoclast differentiation was evaluated via tartrate-resistant acid phosphatase (TRAP) staining and activity and F-actin ring formation. RANKL expression on synovial exosomes was assessed using flow cytometry and an enzyme-linked immunosorbent assay (ELISA). Synovial exosomes were the lowest in OA patients; these induced osteoclastogenesis in the absence of M-CSF and RANKL. Osteoclastogenesis was significantly higher with more exosomes in RA (p = 0.030) than in OA patients, but not in AS or gout patients. On treating macrophages with a specified number of synovial exosomes from RA/AS patients, exosomes induced greater osteoclastogenesis in RA than in AS patients. Synovial exosomal RANKL levels were significantly higher in RA (p = 0.035) than in AS patients. Synovial exosome numbers vary with the type of inflammatory arthritis. Synovial exosomes from RA patients may bear the disease-specific “synovial signature of osteoclastogenesis.”

Epigenetic therapies of osteoporosis

The study of epigenetics reaches its 50th anniversary, however, its clinical application is gradually coming into the clinical setting. Osteoporosis is one of the major and widely diffused bone diseases. Pathogenic mechanisms at the epigenetic level may interfere with bone remodeling occurring during osteoporosis. Preclinical models were used to understand whether such events may interfere with the disease. Besides, observational clinical trials investigated epigenetic-related biomarkers. This effort leads to some epigenetic-related therapies in clinical trials for the treatment of osteoporosis. Bisphosphonates (BPs), target therapy blocking RANK/RANKL pathway, and anti-sclerostin antibody (SOST) are the main therapeutic approaches. However, future large trials will reveal whether epigenetic therapies of osteoporosis will remain a work in progress or data will become more robust in the real-world management of these frailty patients.

Exosomes: A Friend or Foe for Osteoporotic Fracture?

The clinical need for effective osteoporotic fracture therapy and prevention remains urgent. The occurrence and healing of osteoporotic fracture are closely associated with the continuous processes of bone modeling, remodeling, and regeneration. Accumulating evidence has indicated a prominent role of exosomes in mediating multiple pathophysiological processes, which are essential for information and materials exchange and exerting pleiotropic effects on neighboring or distant bone-related cells. Therefore, the exosomes are considered as important candidates both in the occurrence and healing of osteoporotic fracture by accelerating or suppressing related processes. In this review, we collectively focused on recent findings on the diagnostic and therapeutic applications of exosomes in osteoporotic fracture by regulating osteoblastogenesis, osteoclastogenesis, and angiogenesis, providing us with novel therapeutic strategies for osteoporotic fracture in clinical practice.

Mesenchymal stem cells secretome: The cornerstone of cell-free regenerative medicine

Mesenchymal stem cells (MSCs) are the most frequently used stem cells in clinical trials due to their easy isolation from various adult tissues, their ability of homing to injury sites and their potential to differentiate into multiple cell types. However, the realization that the beneficial effect of MSCs relies mainly on their paracrine action, rather than on their engraftment in the recipient tissue and subsequent differentiation, has opened the way to cell-free therapeutic strategies in regenerative medicine. All the soluble factors and vesicles secreted by MSCs are commonly known as secretome. MSCs secretome has a key role in cell-to-cell communication and has been proven to be an active mediator of immune-modulation and regeneration both in vitro and in vivo. Moreover, the use of secretome has key advantages over cell-based therapies, such as a lower immunogenicity and easy production, handling and storage. Importantly, MSCs can be modulated to alter their secretome composition to better suit specific therapeutic goals, thus, opening a large number of possibilities. Altogether these advantages now place MSCs secretome at the center of an important number of investigations in different clinical contexts, enabling rapid scientific progress in this field.

Osteosarcoma cell-derived exosomes affect tumor microenvironment by specific packaging of microRNAs

Bone microenvironment provides growth and survival signals essential for osteosarcoma (OS) initiation and progression. OS cells regulate communications inside tumor microenvironment through different ways and, among all, tumor-derived exosomes support cancer progression and metastasis. To define the contribution of OS-derived exosomes inside the microenvironment, we investigated the effects induced in bone remodeling mechanism and tumor angiogenesis. We demonstrated that exosomes promoted osteoclasts differentiation and bone resorption activity. Furthermore, exosomes potentiated tube formation of endothelial cells and increased angiogenic markers expression. We therefore investigated the micro RNA (miRNA) cargo from exosomes and their parental cells by performing small RNA sequencing through NGS Illumina platform. Hierarchical clustering highlighted a unique molecular profile of exosomal miRNA; bioinformatic analysis by DIANA-mirPath revealed that miRNAs identified take part in various biological processes and carcinogenesis. Among these miRNAs, some were already known for their involvement in the tumor microenvironment establishment, as miR-148a and miR-21-5p. Enforced expression of miR-148a and miR-21-5p in Raw264.7 and hTert immortalized umbilical vein endothelial cells recapitulated the effects induced by exosomes. Overall, our study highlighted the importance of OS exosomes in tumor microenvironment also by a specific packaging of miRNAs.

Role of MicroRNAs in Bone Pathology during Chikungunya Virus Infection

Chikungunya virus (CHIKV) is an alphavirus, transmitted by mosquitoes, which causes Chikungunya fever with symptoms of fever, rash, headache, and joint pain. In about 30%-40% of cases, the infection leads to polyarthritis and polyarthralgia. Presently, there are no treatment strategies or vaccine for Chikungunya fever. Moreover, the mechanism of CHIKV induced bone pathology is not fully understood. The modulation of host machinery is known to be essential in establishing viral pathogenesis. MicroRNAs (miRNAs) are small non-coding RNAs that regulate major cellular functions by modulating gene expression. Fascinatingly, recent reports have indicated the role of miRNAs in regulating bone homeostasis and altered expression of miRNAs in bone-related pathological diseases. In this review, we summarize the altered expression of miRNAs during CHIKV pathogenesis and the possible role of miRNAs during bone homeostasis in the context of CHIKV infection. A holistic understanding of the different signaling pathways targeted by miRNAs during bone remodeling and during CHIKV-induced bone pathology may lead to identification of useful biomarkers or therapeutics.

Epigenetic Regulators Involved in Osteoclast Differentiation

Age related changes to the skeleton, such as osteoporosis, increase the risk of fracture and morbidity in the elderly population. In osteoporosis, bone remodeling becomes unbalanced with an increase in bone resorption and a decrease in bone formation. Osteoclasts are large multinucleated cells that secrete acid and proteases to degrade and resorb bone. Understanding the molecular mechanisms that regulate osteoclast differentiation and activity will provide insight as to how hyper-active osteoclasts lead to pathological bone loss, contributing to diseases such as osteoporosis. Reversible modifications to the DNA such as histone acetylation, methylation, phosphorylation and ubiquitylation alters the access of transcriptional machinery to DNA and regulates gene expression and osteoclast differentiation and activity. It is critical for the management of bone related diseases to understand the role of these chromatin modifying proteins during osteoclast differentiation, as potential therapies targeting these proteins are currently under development.

Involvement of Noncoding RNAs in the Differentiation of Osteoclasts

As the most important bone-resorbing cells, osteoclasts play fundamental roles in bone remodeling and skeletal health. Much effort has been focused on identifying the regulators of osteoclast metabolism. Noncoding RNAs (ncRNAs) reportedly regulate osteoclast formation, differentiation, survival, and bone-resorbing activity to participate in bone physiology and pathology. The present review intends to provide a general framework for how ncRNAs and their targets regulate osteoclast differentiation and the important events of osteoclastogenesis they are involved in, including osteoclast precursor generation, early differentiation, mononuclear osteoclast fusion, and multinucleated osteoclast function and survival. This framework is beneficial for understanding bone biology and for identifying the potential biomarkers or therapeutic targets of bone diseases. The review also summarizes the results of in vivo experiments and classic experiment methods for osteoclast-related researches.

Circulating fractures-related microRNAs distinguish primary hyperparathyroidism-related from estrogen withdrawal-related osteoporosis in postmenopausal osteoporotic women: A pilot study

Primary hyperparathyroidism (PHPT) represents a common cause of secondary osteoporosis in postmenopausal women, where the negative effect of estrogen withdrawal and that of hyperparathyroidism on bone mineralization coexist. Circulating microRNAs (miRNAs) expression profile has been correlated to both osteoporosis and fragility fractures. The study aimed to profile a set of miRNAs associated with osteoporotic fractures, namely miR-21-5p, miR-23a-5p, miR-24-2-5p, miR-24-3p, miR-93-5p, miR-100-5p, miR-122-5p, miR-124-3p, miR-125b-5p and miR-148-3p, in the plasma of 20 postmenopausal PHPT women. PHPT miRNAs profiles were compared with those detected in 10 age-matched postmenopausal non-PHPT osteoporotic women (OP). All the 10 miRNAs were detected in the plasma samples of both PHPT and OP women. The miRNA profiles clearly distinguished PHPT from OP samples, and identified within the PHPT group, two clusters differing for the PHPT severity, in term of ionized calcium and bone mineralization. In particular, miR-93-5p was significantly downregulated in PHPT samples, while miR-24-3p negatively correlated with the T-score at lumbar, femur neck and total hip sites. PHPT women who experienced osteoporotic fractures had plasma miR-24-3p levels higher than those detected in unfractured PHPT women. In conclusion, PHPT may modulate circulating fractures-related miRNAs, in particular, miR-93-5p, which may distinguish estrogen-related from PHPT-related osteoporosis.

The Emerging Role of Exosomal Non-coding RNAs in Musculoskeletal Diseases

Exosomes are phospholipid bilayer-enclosed membrane vesicles derived and constitutively secreted by various metabolically active cells. They are capable of mediating hetero- and homotypic intercellular communication by transferring multiple cargos from donor cells to recipient cells. Nowadays, non-coding RNAs (ncRNAs) have emerged as novel potential biomarkers or disease-targeting agents in a variety of diseases. However, the lack of effective delivery systems may impair their clinical application. Recently, accumulating evidence demonstrated that ncRNAs could be efficiently delivered to recipient cells using exosomes as a carrier, and therefore can exert a critical role in musculoskeletal diseases including osteoarthritis, rheumatoid arthritis, osteoporosis, muscular dystrophies, osteosarcoma and other diseases. Herein, we present an extensive review of biogenesis, physiological relevance and clinical implication of exosome-derived ncRNAs in musculoskeletal diseases.

Progress of orthopaedic research in China over the last decade

Objective

To summarize the representative scientific achievements in the past decade, and discuss the future challenges and directions for orthopaedic research in China.

Methods

In this review, we used the data provided by National Natural Science Foundation of China (NSFC) for analysis.

Results

Over the last decade, NSFC has initiated various research programs with a total funding of over 1149 million RMB to support orthopaedic exploration. Under the strong support of NSFC, great progresses have been made in basic research, talent training, platform construction and the clinical translation in the field of orthopaedics in China.

Conclusion

In general, since the establishment of the Department of Health Sciences of NSFC 10 years ago, both the amount of funding and the scale of researchers in the field of orthopaedic research have increased substantially. Despite of several shortcomings in orthopaedic research, with continuous support from NSFC both in funding and in policy, we believe that the orthopaedic research in China will surely make steady and significant progress.

The translational potential of this article

This article summarizes the representative scientific achievements in the past decade and puts forward the future challenges and directions for orthopaedic research in China.

MicroRNAs-containing extracellular vesicles in bone remodeling: An emerging frontier

Bone remodeling is a complex and constant process, which is maintained by well-regulated communication among various cells. Extracellular vesicles (EVs) are small vesicles, which could provide a protective environment for the transportation of various functional molecules. It has been shown that EVs could dock with distant and/or neighboring target cells, deliver cargoes to these specific cells and alter their fates. MicroRNAs (miRNAs), single-stranded non-coding RNAs with 22-26 nucleotides, could bind to mRNAs and repress the translation or stimulate the degradation of mRNAs. It is reported that EVs could serve as the mail carriers, which could cargo miRNAs to exchange information between different cells and act through a novel way to regulate signaling pathways during bone remodeling. In this review, we summarize the function of EV-miRNAs in the communication among mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, osteocytes, and myoblasts during bone remodeling, as well as the key signaling molecules which are involved in this process. The roles of EV-miRNAs in sending intercellular messages in the microenvironment of bone remodeling could shed new light on the development of tissue engineering, and provide novel diagnostic markers and therapeutic targets of bone-related diseases.

LncRNA Nron regulates osteoclastogenesis during orthodontic bone resorption

Activation of osteoclasts during orthodontic tooth treatment is a prerequisite for alveolar bone resorption and tooth movement. However, the key regulatory molecules involved in osteoclastogenesis during this process remain unclear. Long noncoding RNAs (lncRNAs) are a newly identified class of functional RNAs that regulate cellular processes, such as gene expression and translation regulation. Recently, lncRNAs have been reported to be involved in osteogenesis and bone formation. However, as the most abundant noncoding RNAs in vivo, the potential regulatory role of lncRNAs in osteoclast formation and bone resorption urgently needs to be clarified. We recently found that the lncRNA Nron (long noncoding RNA repressor of the nuclear factor of activated T cells) is highly expressed in osteoclast precursors. Nron is downregulated during osteoclastogenesis and bone ageing. To further determine whether Nron regulates osteoclast activity during orthodontic treatment, osteoclastic Nron transgenic (Nron cTG) and osteoclastic knockout (Nron CKO) mouse models were generated. When Nron was overexpressed, the orthodontic tooth movement rate was reduced. In addition, the number of osteoclasts decreased, and the activity of osteoclasts was inhibited. Mechanistically, Nron controlled the maturation of osteoclasts by regulating NFATc1 nuclear translocation. In contrast, by deleting Nron specifically in osteoclasts, tooth movement speed increased in Nron CKO mice. These results indicate that lncRNAs could be potential targets to regulate osteoclastogenesis and orthodontic tooth movement speed in the clinic in the future.

Circulating MicroRNA-19b Identified From Osteoporotic Vertebral Compression Fracture Patients Increases Bone Formation

Circulating microRNAs (miRNAs) play important roles in regulating gene expression and have been reported to be involved in various metabolic diseases, including osteoporosis. Although the transcriptional regulation of osteoblast differentiation has been well characterized, the role of circulating miRNAs in this process is poorly understood. Here we discovered that the level of circulating miR-19b was significantly lower in osteoporotic patients with vertebral compression fractures than that of healthy controls. The expression level of miR-19b was increased during osteoblastic differentiation of human mesenchymal stem cells (hMSCs) and MC3T3-E1 cells, and transfection with synthetic miR-19b could promote osteoblastic differentiation of hMSCs and MC3T3-E1 cells. PTEN (phosphatase and tensin homolog deleted from chromosome 10) was found to be directly repressed by miR-19b, with a concomitant increase in Runx2 expression and increased phosphorylation of AKT (protein kinase B, PKB). The expression level of circulating miR-19b in aged ovariectomized mice was significantly lower than in young mice. Moreover, the osteoporotic bone phenotype in aged ovariectomized mice was alleviated by the injection of chemically modified miR-19b (agomiR-19b). Taken together, our results show that circulating miR-19b plays an important role in enhancing osteoblastogenesis, possibly through regulation of the PTEN/pAKT/Runx2 pathway, and may be a useful therapeutic target in bone loss disorders, such as osteoporosis. © 2019 American Society for Bone and Mineral Research.

miR‑21 promotes osteoclastogenesis through activation of PI3K/Akt signaling by targeting Pten in RAW264.7 cells

The present study aimed to investigate the effects of microRNA (miR)-21 on osteoclastogenesis and its underlying molecular mechanisms. The expression levels of tartrate-resistant acid phosphatase (TRAP) and miR-21 were detected during osteoclastogenesis in receptor activator of NF-κB ligand (RANKL)-induced RAW264.7 cells via reverse transcription-quantitative PCR. Bioinformatics and dual luciferase reporter assays were performed to analyze the association between miR-21 and Pten. RANKL-induced RAW264.7 cells were divided into the following groups: MiR-negative control (NC), miR-21 mimic, miR-21 inhibitor and miR-21 mimic + LY294002. The effects of miR-21 on osteoclastogenesis and bone resorption were then detected using TRAP staining and a bone resorption assay. Pten, phosphorylated-Akt and nuclear factor of activated T cell (NFATc1) expression levels were measured by western blotting to analyze the effects of miR-21 on the PI3K/Akt signaling pathway. The present study revealed that miR-21 was upregulated during osteoclastogenesis in RANKL-induced RAW264.7 cells. Furthermore, miR-21 negatively regulated Pten. Compared with the miR-negative control (NC) group, the number of osteoclasts and the percentage of bone resorption were increased in the miR-21 mimic group, whereas they were decreased in the miR-21 inhibitor group. The number of osteoclasts and the percentage of bone resorption in the miR-21 mimic + LY294002 group were lower than in the miR-21 mimic group. Compared with the miR-NC group, the protein expression levels of Pten were decreased, whereas p-Akt and NFATc1 were increased in the miR-21 mimic group. Conversely, Pten protein expression was increased, whereas p-Akt and NFATc1 were decreased in the miR-21 inhibitor group. In the miR-21 mimic + LY294002 group, Pten protein expression was higher, and p-Akt and NFATc1 were lower than in the miR-21 mimic group. In conclusion, miR-21 is upregulated during osteoclastogenesis, and may promote osteoclastogenesis and bone resorption through activating the PI3K/Akt signaling pathway via targeting Pten.