MicroRNAs in Bone Balance and Osteoporosis

Hypomethylation of the RUNX2 Gene Is a New Potential Biomarker of Primary Osteoporosis in Men and Women

The search for the molecular markers of osteoporosis (OP), based on the analysis of differential deoxyribonucleic acid (DNA) methylation in bone cells and peripheral blood cells, is promising for developments in the field of the early diagnosis and targeted therapy of the disease. The Runt-related transcription factor 2 (RUNX2) gene is one of the key genes of bone metabolism, which is of interest in the search for epigenetic signatures and aberrations associated with the risk of developing OP. Based on pyrosequencing, the analysis of the RUNX2 methylation profile from a pool of peripheral blood cells in men and women over 50 years of age of Russian ethnicity from the Volga-Ural region of Russia was carried out. The level of DNA methylation in three CpG sites of the RUNX2 gene was assessed and statistically significant hypomethylation was revealed in all three studied CpG sites in men (U = 746.5, p = 0.004; U = 784, p = 0.01; U = 788.5, p = 0.01, respectively) and in one CpG site in women (U = 537, p = 0.03) with primary OP compared with control. In the general sample, associations were preserved for the first CpG site (U = 2561, p = 0.0001766). The results were obtained for the first time and indicate the existence of potentially new epigenetic signatures of RUNX2 in individuals with OP.

Bioactives and Biomaterial Construction for Modulating Osteoclast Activities

Bone tissue constitutes 15-20% of human body weight and plays a crucial role in supporting the body, coordinating movement, regulating mineral homeostasis, and hematopoiesis. The maintenance of bone homeostasis relies on a delicate balance between osteoblasts and osteoclasts. Osteoclasts, as the exclusive "bone resorbers" in the human skeletal system, are of paramount significance yet often receive inadequate attention. When osteoclast activity becomes excessive, it frequently leads to various bone metabolic disorders, subsequently resulting in secondary bone injuries, such as fractures. This not only reduces life quality of patients, but also imposes a significant economic burden on society. In response to the pressing need for biomaterials in the treatment of osteoclast dysregulation, there is a surge of research and investigations aimed at osteoclast regulation. Promising progress is achieved in this domain. This review seeks to provide a comprehensive understanding of how to modulate osteoclast activities. It summarizes bioactive substances that influence osteoclasts and elucidates strategies for constructing related biomaterial systems. It offers practical insights and ideas for the development and application of biomaterials and tissue engineering, with the hope of guiding the clinical treatment of osteoclast-related bone diseases using biomaterials in the future.

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.

CX3CL1 deficiency ameliorates inflammation, apoptosis and accelerates osteogenic differentiation, mineralization in LPS-treated MC3T3-E1 cells via its receptor CX3CR1

BACKGROUND

Osteoporosis is a devastating skeletal disease responsible for bone fragility and fracture. CX3C chemokine ligand 1 (CX3CL1) is an inflammatory chemokine which has been identified to possess increased expression in the serum of postmenopausal osteoporotic patients. This paper was to illuminate the impacts of CX3CL1 on inflammation, apoptosis and osteogenic differentiation, mineralization in LPS-treated osteoblasts and investigate the regulatory mechanism.

METHODS

The viability of MC3T3-E1 cells exposed to elevating doses of LPS was detected by CCK-8 assay. CX3CL1 and C-X3-C motif chemokine receptor 1 (CX3CR1) expression were detected by RT-qPCR and western blot. CX3CR1 expression was examined again following CX3CL1 depletion. The binding of CX3CL1 with CX3CR1 was testified through Co-IP assay. In MC3T3-E1 cells co-transduced with CX3CL1 interference and CX3CR1 overexpression plasmids following LPS exposure, cell activity and inflammation were separately estimated via CCK-8 assay and RT-qPCR. Apoptosis was measured by TUNEL assay and western blot. Osteoblast differentiation was evaluated by ALP activity assay, RT-qPCR and western blot. Osteoblast mineralization was assessed by ARS staining, RT-qPCR and western blot. Results The experimental data presented that LPS attenuated the viability and enhanced CX3CL1 and CX3CR1 expression in MC3T3-E1 cells in a dose-dependent manner. CX3CR1 interacted with CX3CL1 and was positively modulated by CX3CL1. The suppressive role of CX3CL1 absence in LPS-evoked viability decrease, inflammation and apoptosis in MC3T3-E1 cells was reversed by CX3CR1 elevation. Besides, CX3CR1 reversed the promoted osteoblast differentiation and mineralization imposed by CX3CL1 interference.

CONCLUSIONS

CX3CL1 knockdown eased inflammation, apoptosis and promoted osteogenic differentiation, mineralization in MC3T3-E1 cells upon LPS exposure through down-regulating CX3CR1.

Emerging role of m6A modification in osteogenesis of stem cells

The differentiation of stem cells into osteoblasts is a key link in the treatment of bone defects and other orthopedic diseases. N6-methyladenosine (m6A) modification, an important post-transcriptional modification, is a methylation that occurs at the N6 site of RNA adenylate. The modification plays a regulatory role in the growth and development of biological individuals, the directional differentiation of stem cells and the occurrence of diseases. It is involved in various processes of the fate decision of stem cells. And it regulates the development and constant renewal of bone and keeps bone homeostasis by controlling and maintaining the balance between osteogenesis and adipogenesis. Meanwhile, it also affects the progress of orthopedic-associated diseases such as degenerative osteoporosis and bone tumor. In this review, we mainly summarize the new findings of three key molecules including Writers, Erasers and Readers which regulate m6A modification, and the emerging role of m6A modification in determining the fate and directed differentiation potential of stem cells, especially highlight the regulatory mechanism of osteogenic differentiation, the balance between osteogenesis and adipogenesis and the occurrence and development of bone-related diseases. It may provide some important ideas about finding new strategies to recover from bone defect and degenerative bone disease.

The Emerging Role of MicroRNAs in Bone Diseases and Their Therapeutic Potential

MicroRNAs (miRNAs) are a class of small (20-24 nucleotides), highly conserved, non-coding RNA molecules whose main function is the post-transcriptional regulation of gene expression through sequence-specific manners, such as mRNA degradation or translational repression. Since these key regulatory molecules are implicated in several biological processes, their altered expression affects the preservation of cellular homeostasis and leads to the development of a wide range of pathologies. Over the last few years, relevant investigations have elucidated that miRNAs participate in different stages of bone growth and development. Moreover, the abnormal expression of these RNA molecules in bone cells and tissues has been significantly associated with the progression of numerous bone diseases, including osteoporosis, osteosarcoma, osteonecrosis and bone metastasis, among others. In fact, miRNAs regulate multiple pathological mechanisms, including altering either osteogenic or osteoblast differentiation, metastasis, osteosarcoma cell proliferation, and bone loss. Therefore, in this present review, aiming to impulse the research arena of the biological implications of miRNA transcriptome in bone diseases and to explore their potentiality as a theragnostic target, we summarize the recent findings associated with the clinical significance of miRNAs in these ailments.

Advances in bone turnover markers

Bone fragility fractures remain an important worldwide health and economic problem due to increased morbidity and mortality. The current methods for predicting fractures are largely based on the measurement of bone mineral density and the utilization of mathematical risk calculators based on clinical risk factors for bone fragility. Despite these approaches, many bone fractures remain undiagnosed. Therefore, current research is focused on the identification of new factors such as bone turnover markers (BTM) for risk calculation. BTM are a group of proteins and peptides released during bone remodeling that can be found in serum or urine. They derive from bone resorptive and formative processes mediated by osteoclasts and osteoblasts, respectively. Potential use of BTM in monitoring these phenomenon and therefore bone fracture risk is limited by physiologic and pathophysiologic factors that influence BTM. These limitations in predicting fractures explain why their inclusion in clinical guidelines remains limited despite the large number of studies examining BTM.

Biological Functions of Let-7e-5p in Promoting the Differentiation of MC3T3-E1 Cells

MicroRNAs let-7c and let-7f, two members of the let-7 family, were involved in regulating osteoblast differentiation and have an important role in bone formation. Let-7e-5p, which also belonged to the let-7 family, presented in the differentiation of adipose-derived stem cells and mouse embryonic stem cells. However, the role of let-7e-5p in osteoblast differentiation was unclear. Thus, this study aimed to elucidate the function of let-7e-5p in osteoblast differentiation and its mechanism. Firstly, we found that the let-7e-5p mimic promoted osteoblast differentiation but not the proliferation of MC3T3-E1 cells by positively regulating the expression levels of osteogenic-associated genes (RUNX2, OCN, OPN, and OSX), the activity of ALP, and formation of mineralized nodules. Moreover, we ascertained that the let-7e-5p mimic downregulated the post-transcriptional expression of SOCS1 by specifically binding to the 3′ untranslated region of SOCS1 mRNA. Also, let-7e-5p-induced SOCS1 downregulation increased the protein levels of p-STAT5 and IGF-1, which were both modulated by SOCS1 molecules. Furthermore, let-7e-5p abrogated the inhibition of osteogenic differentiation mediated by SOCS1 overexpression. Therefore, these results suggested that let-7e-5p regulated the differentiation of MC3T3-E1 cells through the JAK2/STAT5 pathway to upregulate IGF-1 gene expression by inhibiting SOCS1. These findings may provide a new insight into the regulatory role of let-7e-5p in osteogenic differentiation and imply the existence of a novel mechanism underlying let-7e-5p-mediated osteogenic differentiation.

Mesenchymal stem cell conditioned medium attenuates oxidative stress injury in hepatocytes partly by regulating the miR-486-5p/PIM1 axis and the TGF-β/Smad pathway

This study investigated the role of microRNA (miRNA) miR-486-5p in oxidative stress injury in hepatocytes under the treatment of mesenchymal stem cell conditioned medium (MSC-CM). The oxidative stress injury in hepatocytes (L02) was induced by H₂O₂. Human umbilical cord blood MSC-CM (UCB-MSC-CM) was prepared. The effects of UCB-MSC-CM on the proliferation, apoptosis, and inflammatory response in L02 cells were detected by Cell Counting Kit-8 (CCK-8) assay, flow cytometry analysis, and enzyme-linked immunosorbent assay (ELISA). Subsequently, the target of miR-486-5p was predicted using bioinformatics analysis, and the possible signaling pathway addressed by miR-486-5p was explored using western blot. We found that miR-486-5p expression was elevated following oxidative stress injury and was reduced after UCB-MSC-CM treatment. UCB-MSC-CM protected L02 cells against H₂O₂-induced injury by downregulation of miR-486-5p. Proviral integration site for Moloney murine leukemia virus 1 (PIM1) was verified to be targeted by miR-486-5p. UCB-MSC-CM upregulated the expression of PIM1 reduced by H₂O₂ in L02 cells. Additionally, silencing PIM1 attenuated the protective effects of miR-486-5p downregulation against oxidative stress injury. We further demonstrated that UCB-MSC-CM inhibited the TGF-β/Smad signaling in H₂O_2-treated L02 cells by the miR-486-5p/PIM1 axis. Overall, UCB-MSC-CM attenuates oxidative stress injury in hepatocytes by downregulating miR-486-5p and upregulating PIM1, which may be related to the inhibition of TGF-β/Smad pathway.

Fluid shear stress regulates osteoblast proliferation and apoptosis via the lncRNA TUG1/miR-34a/FGFR1 axis

LncRNAs and microRNAs play critical roles in osteoblast differentiation and bone formation. However, their exact roles in osteoblasts under fluid shear stress (FSS) and the possible mechanisms remain unclear. The aim of this study was to explore whether and how miR‐34a regulates osteoblast proliferation and apoptosis under FSS. In this study, FSS down‐regulated miR‐34a levels of MC3T3‐E1 cells. MiR‐34a up‐regulation attenuated FSS‐induced promotion of proliferation and suppression of apoptosis. Luciferase reporter assay revealed that miR‐34a directly targeted FGFR1. Moreover, miR‐34a regulated osteoblast proliferation and apoptosis via FGFR1. Further, we validated that lncRNA TUG1 acted as a competing endogenous RNA (ceRNA) to interact with miR‐34a and up‐regulate FGFR1 protein expression. Furthermore, lncRNA TUG1 could promote proliferation and inhibit apoptosis. Taken together, our study revealed the key role of the lncRNA TUG1/miR‐34a/FGFR1 axis in FSS‐regulated osteoblast proliferation and apoptosis and may provide potential therapeutic targets for osteoporosis.

Current Status of MicroRNAs that Target the Wnt Signaling Pathway in Regulation of Osteogenesis and Bone Metabolism: A Review

The directional differentiation of bone mesenchymal stem cells (BMSCs) is regulated by a variety of transcription factors and intracellular signaling pathways. In the past, it was thought that the directional differentiation of BMSCs was related to transforming growth factors, such as bone morphogenetic protein (BMP) and MAPK pathway. However, in recent years, some scholars have pointed out that the Wnt signaling pathway, which is a necessary complex network of protein interactions for biological growth and development, takes a significant role in this process and plays a major part in regulating the development of osteoblasts by exerting signal transduction into cells. Also, they have proved the Wnt protein therapeutic truly have positive effects on the viability and osteogenic capacity of bone graft. Recent studies have shown that microRNAs (miRNAs) play an important regulatory role in this process. MiRNAs such as miRNA-218, miRNA-335, miRNA-29, microRNA-30 and other miRNAs exert negative or positive effects on some crucial molecules in the Wnt/β-catenin pathway, which in turn affect bone metabolism and osteopathy. Thus, miRNAs have been suggested as therapeutic targets for some metabolic bone diseases. This article aims to provide an update on the current status of microRNAs that target the Wnt signaling pathway in the regulation of osteogenesis and bone metabolism and includes a discussion of future areas of research, which can be a theoretical basis for bone metabolism-related diseases.

Circulating miRNAs in bone health and disease

microRNAs have evolved as important regulators of multiple biological pathways essential for bone homeostasis, and microRNA research has furthered our understanding of the mechanisms underlying bone health and disease. This knowledge, together with the finding that active or passive release of microRNAs from cells into the extracellular space enables minimal-invasive detection in biofluids (circulating miRNAs), motivated researchers to explore microRNAs as biomarkers in several pathologic conditions, including bone diseases. Thus, exploratory studies in cohorts representing different types of bone diseases have been performed. In this review, we first summarize important molecular basics of microRNA function and release and provide recommendations for best (pre-)analytical practices and documentation standards for circulating microRNA research required for generating high quality data and ensuring reproducibility of results. Secondly, we review how the genesis of bone-derived circulating microRNAs via release from osteoblasts and osteoclasts could contribute to the communication between these cells. Lastly, we summarize evidence from clinical research studies that have investigated the clinical utility of microRNAs as biomarkers in musculoskeletal disorders. While previous reviews have mainly focused on diagnosis of primary osteoporosis, we have also included studies exploring the utility of circulating microRNAs in monitoring anti-osteoporotic treatment and for diagnosis of other types of bone diseases, such as diabetic osteopathy, bone degradation in inflammatory diseases, and monogenetic bone diseases.

MiR-133b Modulates the Osteoblast Differentiation to Prevent Osteoporosis Via Targeting GNB4

MiR-133b is considered to be lowly expressed in osteoporosis patients. This study aimed to probe the role and in-depth mechanism of miR-133b in modulating osteoblast biological behavior and differentiation. The differential expressions of miR-133b and GNB4 in patients with osteoporosis and healthy control were analyzed based on the GEO database. Osteoblastic differentiation of hFOB 1.19 cells was induced in the culture medium containing 10 mM β-glycerophosphate, 50 nm dexamethasone, and 100 μg/ml ascorbic acid. The level of GNB4 was detected using quantitative real-time PCR (qRT-PCR) and Western blot. Cell viability and apoptosis were measured by Cell Counting Kit-8 (CCK-8) and flow cytometry assays, respectively. Western blot was also utilized to measure the levels of osteoblast-related proteins, including ALP, Runx2, Osterix, and OPN. GNB4 was identified and confirmed as a downstream target gene of miR-133b. The expression of miR-133b was declined while the expression of GNB4 was increased in osteoporosis patients. Importantly, up-regulation of miR-133b caused the increase of cell viability and the decrease of apoptosis, which could be blocked by overexpression of GNB4. Also, up-regulation of miR-133b promoted osteoblasts differentiation, as shown by the increase in the expression of ALP, Runx2, Osterix, and OPN. Similarly, this promoting impact resulted from miR-133b overexpression can be reversed via up-regulation of GNB4. These findings revealed that miR-133b can promote the viability and differentiation of osteoblasts by targeting GNB4, hoping to lay a feasible theoretical foundation for the clinical treatment of osteoporosis.

Synergistic effects of miR-708-5p and miR-708-3p accelerate the progression of osteoporosis

BACKGROUND

Bone homeostasis is a tightly orchestrated process maintained by osteoblasts and osteoclasts, and a disruption of their steady-state equilibrium can lead to the occurrence of osteoporosis (OP).

METHODS

We investigated the differential expression of micro (mi)RNAs in the bone tissues of a postmenopausal osteoporosis rat model induced by ovariectomy (OVX). Real-time PCR was used to verify the differentially expressed miRNAs in bone samples from OP patients and controls. The specific targets of two differentially expressed miRNAs in osteogenic or osteoclast differentiation were determined by bioinformatic prediction, and mRNA and protein detection.

RESULTS

miR-708-5p and miR-708-3p were highly expressed in the bone tissue of OVX rats and OP patients. miR-708-5p negatively regulated osteoblast differentiation in bone marrow mesenchymal stem cells by targeting SMAD specific E3 ubiquitin protein ligase 2, while miR-708-3p positively regulated osteoclast differentiation in bone marrow monocytes by targeting cerebellar degeneration associated protein 1 antisense RNA. miR-708-5p and miR-708-3p were shown to originate from the same precursor miRNA and to have a synergistic effect on the development of osteoporosis with different temporal and spatial patterns.

CONCLUSION

Our findings provide a referential theoretical basis and targets for the prevention and treatment of osteoporosis.

A validated miRNA signature for the diagnosis of osteoporosis related fractures using SVM algorithm classification

The aim of the present study was to develop a circulating microRNA expression signature for early prediction of osteoporotic fractures and to validate the results using Gene Expression Omnibus (GEO) datasets. The GSE70318 dataset was downloaded from GEO and used to build an osteoporotic fracture prediction model based on the receiver operating characteristic curve and support vector machine (SVM) classification index. The GSE74209 dataset was used as a validation dataset. Additionally, in vitro, alkaline phosphatase (ALP) activity was measured in the presence or absence of microRNA (miRNA/miR) treatments in human osteoblast cells. The expression of two selected genes was detected by western blotting. miR-188-3p, miR-942-3p, miR-576-3p and miR-135a-5p were differentially expressed between controls and osteoporotic patients with fractures. SVM classification using these four miRNAs provided better dichotomization. It was further confirmed that miR-576-3p and 135a-5p in the GSE74209 dataset could also significantly discriminate between the controls and fracture patients, the area under the curve of SVM2 was 0.9722 with 95% CI 0.8885-1.056. Further analysis indicated that the target genes of the two miRNAs participated in the Wingless-related integration site, Hedgehog and transforming growth factor-β signaling pathways and osteoclast differentiation. miR-576-3p and miR-135-5p transfection decreased ALP activity and ALP activity was increased in the presence of blocking antisense oligonucleotides. Western blotting indicated miR-576-3p and miR-135-5p decreased CSNK1A1L and LRP6 levels, respectively. In conclusion, two miRNA signatures were developed and validated for the prediction of osteoporotic fractures.

Geniposide promotes the proliferation and differentiation of MC3T3-E1 and ATDC5 cells by regulation of microRNA-214

The research plans to make sure how Geniposide (GEN) functions in osteoblast proliferation and differentiation. The MC3T3-E1 and ATDC5 cells were treated with the GEN, XAV-939 and/or transfected with microRNA (miR)-214 mimic or corresponding control. Cell viability was detected with the CCK-8. The CyclinD1, Runx2, Osx, Ocn, Wnt3a and β-catenin were individually quantified via western blot. The cell cycle was tested by cell cycle analysis assay. The ALP activity was tested by ALP assay. qRT-PCR was used to examine the miR-214 expression level. The cell viability and the expressions of the CyclinD1, Runx2, Osx, Ocn Wnt3a and β-catenin, as well as the ALP activity were individually and significantly promoted by the GEN. Besides, miR-214 was down-regulated by the GEN. The XAV-939 or the miR-214 mimic destroyed the promotional effect of GEN on these elements above. In conclusion, GEN induced the proliferation and differentiation of the MC3T3-E1 and ATDC5 cells by targeting the miR-214 through Wnt/β-catenin activation.

High-glucose-induced miR-214-3p inhibits BMSCs osteogenic differentiation in type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune insulin-dependent disease associated with destructive bone homeostasis. Accumulating evidence has proven that miRNAs are widely involved in the regulation of bone homeostasis. However, whether miRNAs also regulate osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in T1DM mice is under exploration. In this study, miRNA microarray was utilized to screen the differentially expressed miRNAs, which uncovered that miR-214-3p potentially inhibited BMSCs osteogenic differentiation in T1DM mice. We found that high glucose suppressed BMSCs osteogenic differentiation with significant elevation of the miR-214-3p expression. Further study found that the osteogenic differentiation of BMSCs was inhibited by AgomiR-214-3p while enhanced by AntagomiR-214-3p in BMSCs supplemented with high glucose. Moreover, we found that miR-214-3p knockout T1DM mice were resistant to high-glucose-induced bone loss. These results provide a novel insight into an inhibitory role of high-glucose-induced miR-214-3p in BMSCs osteogenic differentiation both in vitro and in vivo. Molecular studies revealed that miR-214-3p inhibits BMSCs osteogenic differentiation by targeting the 3′-UTR of β-catenin, which was further corroborated in human bone specimens and BMSCs of T1DM patients. Taken together, our study discovered that miR-214-3p is a pivotal regulator of BMSCs osteogenic differentiation in T1DM mice. Our findings also suggest that miR-214-3p could be a potential target in the treatment of bone disorders in patients with T1DM.

Comprehensive In Vitro Testing of Calcium Phosphate-Based Bioceramics with Orthopedic and Dentistry Applications

Recently, a large spectrum of biomaterials emerged, with emphasis on various pure, blended, or doped calcium phosphates (CaPs). Although basic cytocompatibility testing protocols are referred by International Organization for Standardization (ISO) 10993 (parts 1-22), rigorous in vitro testing using cutting-edge technologies should be carried out in order to fully understand the behavior of various biomaterials (whether in bulk or low-dimensional object form) and to better gauge their outcome when implanted. In this review, current molecular techniques are assessed for the in-depth characterization of angiogenic potential, osteogenic capability, and the modulation of oxidative stress and inflammation properties of CaPs and their cation- and/or anion-substituted derivatives. Using such techniques, mechanisms of action of these compounds can be deciphered, highlighting the signaling pathway activation, cross-talk, and modulation by microRNA expression, which in turn can safely pave the road toward a better filtering of the truly functional, application-ready innovative therapeutic bioceramic-based solutions.

miR-203a-3p.1 is involved in the regulation of osteogenic differentiation by directly targeting Smad9 in MM-MSCs

MicroRNAs (miRNAs) have emerged as important regulators of bone development and regeneration. The aim of the present study was to determine whether miR-203a-3p.1 is involved in osteogenic differentiation of multiple myeloma (MM)-mesenchymal stem cells (MSCs) and the potential underlying mechanism. MSCs were isolated from patients with MM and normal subjects and confirmed by flow cytometry using specific surface markers. The osteogenic differentiation capacity of MM-MSCs was identified by Alizarin Red S calcium deposition staining and reverse transcription-quantitative PCR (RT-qPCR) of typical osteoblast differentiation markers. The role of miR-203a-3p.1 in the osteoblast differentiation of MM-MSCs was determined by gain or loss of function experiments. The target of miR-203a-3p.1 was identified using bioinformatics (including the miRNA target prediction database TargetScan, miRDB, DIANA TOOLS and venny 2.1.0), luciferase reporter assay, RT-qPCR and western blotting. The expression levels of proteins involved in the Wnt3a/β-catenin signaling pathway were detected by western blot analysis. The results revealed that the osteogenic differentiation capacity of MM-MSCs was reduced when compared with normal (N)-MSCs, as demonstrated by a decrease in calcium deposition and mRNA expression of typical osteoblast differentiation markers, including ALP, OPN and OC. In addition, miR-203a-3p.1 was downregulated in N-MSCs following osteoblast induction, whereas no changes were observed in MM-MSCs. The downregulation of miR-203a-3p.1 resulted in increased osteogenic potential, as indicated by the increase in the mRNA expression levels of the typical osteoblast differentiation markers, including alkaline phosphatase (ALP), osteopontin (OPN) and osteocalcin (OC). Bioinformatics and luciferase reporter assay analysis indicated that mothers against decapentaplegic homolog 9 (Smad9) may be a direct target of miR-203a-3p.1 in N-MSCs. The RT-qPCR and western blot assays revealed that overexpression of smad9 significantly enhanced the effect of miR-203a-3p.1 inhibitors on osteoblast markers, which indicated that miR-203a-3p.1 inhibitors may regulate the osteogenic differentiation of MM-MSCs by upregulating Smad9. In addition, the Wnt3a/β-catenin signaling pathway was activated following miR-203a-3p.1 inhibition. These results suggest that miR-203a-3p.1 may serve an important role in the osteogenic differentiation of MM-MSCs by regulating Smad9 expression.

Extracellular vesicles from human umbilical cord blood ameliorate bone loss in senile osteoporotic mice

OBJECTIVE

Senile osteoporosis is one of the most common age-related diseases worldwide. Accumulating evidences have indicated that young blood can reverse age-related impairments. Extracellular vesicles (EVs) exert therapeutic effects in a variety of diseases by delivering bioactive molecules such as microRNAs (miRNAs). The aim of the study is to evaluate the therapeutic potential of EVs from human umbilical cord blood plasma (UCB-EVs) on senile osteoporosis and to preliminarily clarify the underlying mechanism.

METHODS

UCB-EVs were injected into the tail vein of aged (16 months old) male C57BL/6 mice. Microcomputed tomography was performed to evaluate bone mass and microarchitecture of mice. The osteogenic and osteoclastic activities were determined by quantitative real-time PCR (qRT-PCR), histological examination and western blot analysis. In vitro, qRT-PCR assay was undertaken to explore the enrichment levels of a number of miRNAs that have positive effects in reducing bone loss. The efficacy of UCB-EVs on osteoblastic differentiation of bone marrow mesenchymal stromal cells (BMSCs) and osteoclastogenesis of RAW264.7 cells were assessed by cytochemical staining. Gene and protein expression changes were detected by qRT-PCR and western blotting respectively. Meanwhile, the roles of the selected miRNA in the regulatory effects of UCB-EVs on BMSCs and RAW264.7 cells were evaluated by using specific miRNA inhibitor.

RESULTS

The intravenous injection of UCB-EVs for two months attenuated bone loss in old mice, as defined by increased trabecular and cortical bone mass, enhanced osteoblast formation and reduced osteoclast formation compared to the control mice. In vitro, UCB-EVs could promote the osteogenic differentiation of BMSCs and inhibit the osteoclastogenesis of RAW264.7 cells. Moreover, it was confirmed that miR-3960 was highly enriched in UCB-EVs and miR-3960 inhibitor reversed the stimulatory effect of UCB-EVs on osteoblastic differentiation of BMSCs.

CONCLUSION

Our findings indicate that UCB-EVs ameliorate age-related bone loss by stimulating bone formation and inhibiting bone resorption, and miR-3960 mediated the osteogenic effect of UCB-EVs on BMSCs. Thus, UCB-EVs may represent a promising agent for prevention of senile osteoporosis.

Extracellular vesicles: Squeezing every drop of regenerative potential of umbilical cord blood

Collection, cryopreservation and transplantation of umbilical cord blood (UCB)-derived cells have become a popular option for regenerative medicine, not limited to the transplantation of hematopoietic cell progenitors only. Indeed, increasing evidence shows that extracellular vesicles (EV), which include a heterogeneous pool of membranous structures secreted by the vast majority of cells, can serve as powerful tools for cell-free therapy due to precise multifunctional molecular cargoes. In this issue, Hu et al. [1] described that EV extracted from UCB (UCB-EV) ameliorate bone loss in senile osteoporotic mice and promote in vitro osteoblast differentiation of bone marrow-derived Mesenchymal Stromal Cells through miR-3960-mediated signaling. These results envision the capability of UCB-EV of priming multipotent stem cells toward the osteogenic cell lineage and interfering on bone resorption processes. Although processing and manufacturing of EV-based products have to further develop major issues, we foresee that EV will soon become new therapeutic products supplied by UCB banks for treating human diseases, including bone-related conditions.

Suppressing MicroRNA-30b by Estrogen Promotes Osteogenesis in Bone Marrow Mesenchymal Stem Cells

MicroRNAs (miRNAs) have been widely demonstrated to interact with multiple cellular signaling pathways and to participate in a wide range of physiological processes. Estradiol-17β (E2) is the most potent and prevalent endogenous estrogen that plays a vital role in promoting bone formation and reducing bone resorption. Currently, little is known about the regulation of miRNAs in E2-induced osteogenic differentiation. In the present study, the primary bone marrow mesenchymal stem cells from rats (rBMSCs) were isolated and incubated with E2, followed by miRNA profiling. The microarray showed that 29 miRNAs were differentially expressed in response to E2 stimulation. Further verification by real-time reverse-transcriptase polymerase chain reaction revealed that E2 enhanced the expression of let-7b and miR-25 but suppressed the miR-30b expression. Moreover, a gain-of-function experiment confirmed that miR-30b negatively regulated the E2-induced osteogenic differentiation. These data suggest an important role of miRNAs in osteogenic differentiation.

MicroRNAs: Key Regulators to Understand Osteoclast Differentiation?

MicroRNAs (miRNAs) are small non-coding single-stranded RNAs that represent important posttranscriptional regulators of protein-encoding genes. In particular, miRNAs play key roles in regulating cellular processes such as proliferation, migration, and cell differentiation. Recently, miRNAs emerged as critical regulators of osteoclasts (OCs) biology and have been involved in OCs pathogenic role in several disorders. OCs are multinucleated cells generated from myeloid precursors in the bone marrow, specialized in bone resorption. While there is a growing number of information on the cytokines and signaling pathways that are critical to control the differentiation of osteoclast precursors (OCPs) into mature OCs, the connection between OC differentiation steps and miRNAs is less well-understood. The present review will first summarize our current understanding of the miRNA-regulated pathways in the sequential steps required for OC formation, from the motility and migration of OCPs to the cell-cell fusion and the final formation of the actin ring and ruffled border in the functionally resorbing multinucleated OCs. Then, considering the difficulty of working on primary OCs and on the generation of robust data we will give an update on the most recent advances in the detection technologies for miRNAs quantification and how these are of particular interest for the understanding of OC biology and their use as potential biomarkers.

MicroRNA-672-5p Identified during Weaning Reverses Osteopenia and Sarcopenia in Ovariectomized Mice

Post-menopausal condition augments the biological aging process, characterized by multiple metabolic disorders in which bone loss is the most prevalent outcome and usually coupled with sarcopenia. Coexistence of such associated pathogenesis have much worse health outcomes, compared to individuals with osteoporosis only. Pre- and post-natal bone development demands calcium from mother to fetus during pregnancy and lactation leading to a significant maternal skeletal loss. It follows an anabolic phase around weaning during which there is a notable recovery of the maternal skeleton. Here, we have studied the therapeutic effect of microRNA-672-5p identified during weaning when it is predominantly expressed, in ovariectomized mice for both osteopenia and sarcopenia. miR-672-5p induced osteoblast differentiation and mineralization. These actions were mediated through inhibition of Smurf1 with enhanced Runx2 transcriptional activation. In vivo, miR-672-5p significantly increased osteoblastogenesis and mineralization, thus reversing bone loss caused by ovariectomy. It also improved bone-mineral density, load-bearing capacity, and bone quality. Sarcopenia was also alleviated by miR-672-5p, as we observed increased cross-sectional area and Feret's diameter of muscle fibers. We hypothesize that elevated miR-672-5p expression has therapeutic efficacy in estrogen-deficiency-induced osteopenia along with sarcopenia.

Micrornas at the Interface between Osteogenesis and Angiogenesis as Targets for Bone Regeneration

Bone formation and regeneration is a multistep complex process crucially determined by the formation of blood vessels in the growth plate region. This is preceded by the expression of growth factors, notably the vascular endothelial growth factor (VEGF), secreted by osteogenic cells, as well as the corresponding response of endothelial cells, although the exact mechanisms remain to be clarified. Thereby, coordinated coupling between osteogenesis and angiogenesis is initiated and sustained. The precise interplay of these two fundamental processes is crucial during times of rapid bone growth or fracture repair in adults. Deviations in this balance might lead to pathologic conditions such as osteoarthritis and ectopic bone formation. Besides VEGF, the recently discovered important regulatory and modifying functions of microRNAs also support this key mechanism. These comprise two principal categories of microRNAs that were identified with specific functions in bone formation (osteomiRs) and/or angiogenesis (angiomiRs). However, as hypoxia is a major driving force behind bone angiogenesis, a third group involved in this process is represented by hypoxia-inducible microRNAs (hypoxamiRs). This review was focused on the identification of microRNAs that were found to have an active role in osteogenesis as well as angiogenesis to date that were termed "CouplingmiRs (CPLGmiRs)". Outlined representatives therefore represent microRNAs that already have been associated with an active role in osteogenic-angiogenic coupling or are presumed to have its potential. Elucidation of the molecular mechanisms governing bone angiogenesis are of great relevance for improving therapeutic options in bone regeneration, tissue-engineering, and the treatment of bone-related diseases.

MicroRNAs and long noncoding RNAs: new regulators in cell fate determination of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells that are able to differentiate into numerous cell types, including well-known inherent osteoblasts, adipocytes, and chondrocytes, and other cell types, such as hepatocytes, cardiomyocytes and nerve cells. They have become a favorite source of cell-based therapy. Therefore, knowing the mechanism that determines the cell fate of MSCs is important not only for deep understanding of the MSC function but also for the manipulation of MSCs for clinical application. Recently, studies have demonstrated that microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), the two best studied noncoding RNAs, show key roles in cell fate determination of MSCs by functioning as vital regulators of their target gene expression or signaling transduction. Here, we summarize the characteristics of miRNAs and lncRNAs, and review the recent advances proving their profound involvement in determining the cell fate of MSCs to inherent osteoblast, adipocyte, and chondrocyte cells, and to several key cell types including hepatocytes, cardiomyocytes and nerve cells. This will provide researchers with a deep understanding of the role of miRNAs and lncRNAs in MSCs and provide guidance for future research.

The recent advances of miRNAs and lncRNAs in determining the cell fate of MSCs.

MicroRNA-139-3p regulates osteoblast differentiation and apoptosis by targeting ELK1 and interacting with long noncoding RNA ODSM

Recent studies have confirmed that microRNAs and lncRNAs can affect bone cell differentiation and bone formation. In this study, miR-139-3p was upregulated in the femurs of hindlimb unloading mice and MC3T3-E1 cells under simulated microgravity; this effect was related to osteoblast differentiation and apoptosis. Silencing miR-139-3p attenuated the suppression of differentiation and the promotion of MC3T3-E1 cell apoptosis induced by simulated microgravity. ELK1 is a target of miR-139-3p and is essential for miR-139-3p to regulate osteoblast differentiation and apoptosis. An osteoblast differentiation-related lncRNA that could interact with miR-139-3p (lncRNA ODSM) was identified in MC3T3-E1 cells under simulated microgravity. Further investigations demonstrated that lncRNA ODSM could promote MC3T3-E1 cell differentiation. Therefore, this research was the first to reveal the critical role of the lncRNA ODSM/miR-139-3p/ELK1 pathway in osteoblasts, and these findings suggest the potential value of miR-139-3p in osteoporosis diagnosis and therapy.

Downregulation of microRNA-149 in retinal ganglion cells suppresses apoptosis through activation of the PI3K/Akt signaling pathway in mice with glaucoma

Glaucoma represents a major cause of blindness, generally associated with elevated intraocular pressure (EIOP). The aim of the present study was to investigate whether microRNA-149 (miR-149) affects retinal ganglion cells (RGCs) and the underlying mechanism based on a mouse model of chronic glaucoma with EIOP. The successfully modeled mice were administered with mimics or inhibitors of miR-149. Next, the number of RGCs, ultrastructural changes of RGCs, and purity of RGCs in the retinal tissues were detected. Moreover, the RGCs were collected and subsequently treated with 60 mmHg pressure and transfected with a series of plasmids aiding in the regulation of the expression of miR-149 and betacellulin (BTC). The levels of miR-149, BTC, phosphatidylinositol 3-kinase (PI3K), and Akt were subsequently determined. Finally, RGC viability and apoptosis were detected accordingly. Dual luciferase reporter gene assay provided validation, highlighting BTC was indeed a target gene of miR-149. The downregulation of miR-149 is accompanied by an increased number of RGCs and decreased ultrastructural RGC alterations. Additionally, downregulated miR-149 was noted to increase the levels of BTC, PI3K, and Akt in both the retinal tissues and RGCs, whereas the silencing of miR-149 was observed to promote the viability of RGC and inhibit RGC apoptosis. Taken together, the results of the current study provided validation suggesting that the downregulation of miR-149 confers protection to RGCs by means of activating the PI3K/Akt signaling pathway via upregulation of BTC in mice with glaucoma. Evidence presented indicated the promise of miR-149 inhibition as a potential therapeutic strategy for glaucoma treatment.

Long noncoding RNA MALAT1 promotes osterix expression to regulate osteogenic differentiation by targeting miRNA-143 in human bone marrow-derived mesenchymal stem cells

Osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) is essential for the human bone formation, and emerging evidence shows that long non-coding RNAs (lncRNAs) play important roles in hBMSC osteogenic differentiation. MALAT1 is often regarded as a tumor-related lncRNA, but its function in mesenchymal stem cell differentiation remains to be defined. In this study, we aimed to investigate whether MALAT1 regulates Osterix (Osx) expression by sponging miR-143 to promote hBMSC osteogenic differentiation. Firstly, we found that the expression of MALAT1 was much lower in hBMSCs from osteoporosis patients and miR-143 was contrarily higher. In addition, MALAT1 expression increased, and miR-143 decreased when hBMSCs were treated with osteogenic induction. Then, we used short hairpin RNAs to knockdown MALAT1, and the results showed that hBMSC osteogenic differentiation decreased significantly, indicating that MALAT1 is a positive regulator of osteogenic differentiation in hBMSCs. Furthermore, by luciferase assays, we found that MALAT1 could directly bind to miR-143 and negatively regulate its expression. Similarly, miR-143 could directly bind to the target site on the Osx 3'-UTR and then inhibit Osx expression. Knockdown of MALAT1 decreased Osx expression, and co-transfection of miR-143 inhibitor could rescue Osx mRNA expression. While Osx expression was increased in MALAT1-overexpressing hBMSCs, it was reversed by the miR-143 mimics. Moreover, Osx silencing decreased ALP, OCN, and OPN mRNA expression induced by the miR-143 inhibitor. Altogether, our findings suggest that MALAT1 acts to regulate Osx expression through targeting miR-143; thus, it is considered as a positive regulator in hBMSC osteogenic differentiation.

MicroRNA-539 promotes osteoblast proliferation and differentiation and osteoclast apoptosis through the AXNA-dependent Wnt signaling pathway in osteoporotic rats

This study aims to explore the effects of miR-539 on osteoblast proliferation and differentiation and osteoclast apoptosis in a rat model of osteoporosis, and its mechanism involving the regulation of the AXIN1-mediated wingless-Int (Wnt) signaling pathway. A rat model of osteoporosis was successfully established by ovariectomy. With osteoblasts and osteoclasts of rats not receiving ovariectomy in the sham group as control, those of osteoporotic rats were treated with miR-539 inhibitor, miR-539 mimic, and AXIN1 shRNA. The expression of miR-53, AXIN1, the Wnt pathway related-genes, apoptosis related-genes, and osteogenic markers were measured by RT-qPCR and Western blot analysis, respectively. Alkaline phosphatase (ALP) activity in osteoblast and tartrate-resistant acid phosphatase (TRAP) activity in osteoclasts were determined after cell transfection. Osteoblast and osteoclast viability was assayed by CCK-8 assay. Cell cycle and apoptosis of osteoblasts and osteoclasts were detected by flow cytometry. Lastly, alizarin red S staining was used to detect mineralized nodules of osteoblasts. Firstly, we determined that miR-539 was down-regulated in osteoblast and osteoclast of osteoporotic rats and AXIN1 was negatively regulated by miR-539. Additionally, overexpression of miR-539 increased the expressions of β-catenin, LEF1, c-myc, cyclin D1, RUNX2, BGP, BMP-2 in osteoblast as well as β-catenin, RhoA, caspase-3, and Bcl-2 in osteoclasts. Finally, overexpression of miR-539 elevated ALP activity, proliferation, and mineralized nodules in osteoblast and osteoclast apoptosis, with reduced TRAP activity in osteoclasts. Our results demonstrate that miR-539 promotes osteoblast proliferation and differentiation as well as osteoclast apoptosis through the AXIN1-dependent Wnt signaling pathway in osteoporotic rats.

Effects of repeated sprints training on fracture risk-associated miRNA

Repeated-sprint training (RS, short-duration sprints at supramaximal intensities interspersed with brief recoveries) is a time-saving metabolically effective strategy whose effects on bone are unknown. Bone metabolism is a finely regulated process profoundly affected by exercise as assayable by studying specific systemic (e.g., hormones, cytokines) and bone-derived molecules (e.g., bone markers, miRNAs). Aim of this study was to determine the effect of a 8-week repeated-sprint on circulating levels of fracture risk-associated miRNA. Blood was collected from 9 subjects performing RS 3 times/week (EXP) and 9 age-matched inactive controls (CTRL) before the start of the protocol (T0) and after 4 (T1) and 8 weeks (T2). The relative expression of miR-21-5p, miR-23a-3p, miR-24-3p, miR93-5p, miR-100-5p, miR-122-5p, miR-124-3p, miR-125b-5p, miR-148a-3p, miR-637 was assayed by real-time PCR by the 2^−ΔΔCT method (housekeeping: miR-425-5p, miR-484). Serum concentrations of bone markers (DKK1, sclerostin, osteoprotegerin, osteocalcin, osteopontin), cytokines (IL-1β, TNFα), and metabolic hormones (leptin, insulin, PTH) were assayed by multiplex assay. miR-637 and miR-124-3p were undetectable. In CTRL miRNA levels remained unchanged. In EXP miR-21-5p remained unchanged. Compared to T0 miR-23a-3p and miR-24-3p were significantly decreased at T1 and T2, also compared to CTRL, miR-100 was significantly decreased at T2, miR-122-5p, miR-125-5p, and miR148a-3p were significantly decreased at T1, while miR-93-5p was significantly increased at T1. None of the metabolic hormones was affected by the intervention while, among the bone markers, DKK1, osteocalcin and sclerostin were slightly but significantly decreased. In conclusion, an 8-week repeated-sprint training downregulates the expression of circulating miRNA associated with fracture risk.

MicroRNA‑148a inhibition protects against ovariectomy‑induced osteoporosis through PI3K/AKT signaling by estrogen receptor α

The present study aimed to investigate the effect of microRNA‑148a downregulation on osteoporosis by using an ovariectomized rat model. Reverse transcription‑quantitative polymerase chain reaction was used to analyze microRNA‑148a expression levels, MTT and flow cytometry assays were used to examine cytotoxicity and apoptosis, respectively. The gap‑associated proteins were quantified using western blotting. The expression of microRNA‑148a was significantly increased in osteoporosis rat following ovariectomy. Overexpression of microRNA‑148a significantly promoted apoptosis and inhibited cell growth, whereas downregulation of microRNA‑148a significantly reduced apoptosis and increased cell growth. Overexpression of microRNA‑148a significantly reduced estrogen receptor a (ERα) protein expression and suppressed phosphoinositide‑3‑kinase regulatory subunit 1 (PI3K) and phosphorylated‑protein kinase B (AKT) protein expression in osteoblasts in vitro. The inhibition of ERα increased the microRNA‑148a effect on apoptosis in osteoblasts in vitro. Subsequently, LY294002, an PI3K inhibitor, significantly increased the effect of microRNA‑148a on apoptosis in osteoblasts in vitro. The findings of the present study revealed that anti‑microRNA‑148a protected cells against ovariectomy‑induced osteoporosis through ERα by PI3K/AKT signaling.

miRNA-133a-5p Inhibits the Expression of Osteoblast Differentiation-Associated Markers by Targeting the 3' UTR of RUNX2

Recent studies have recognized the involvement of microRNAs (miRNAs) in the development of osteoporosis, which regulate the balance between osteogenesis and osteoclasis. In this study, we investigated the regulation by miRNA-133a-5p on the osteoblast differentiation-associated markers in the mouse osteoblast-like MC3T3-E1 cells by RUNX2. First, we manipulated the miRNA-133a level in the MC3T3-E1 cells with 20 or 40 nM miR-133a-5p mimics, miR-133a-5p inhibitor, or scramble miRNA. Then, we quantified with real-time polymerase chain reaction (qRT-PCR) the expression of Collagen I, osteocalcin (OCN), and osteopontin (OPN) in the miR-133a-5p-manipulated MC3T3-E1 cells. And the confocal microscopy was also utilized to confirm the regulation by miR-133a-5p on the expression of the three molecules. We also investigated the extracellular matrix (ECM) mineralization and the alkaline phosphatase (ALP) activity in the miR-133a-5p-manipulated MC3T3-E1 cells. In addition, we explored the possible targeting by miR-133a-5p on RUNX2, which was a well-recognized promoter to osteoblast differentiation, with luciferase reporter, qRT-PCR, and Western blotting assay. Results demonstrated that the miRNA-133a-5p mimics markedly reduced, whereas the miRNA-133a-5p inhibitor significantly promoted the expression of Collagen I, OCN, and OPN, the ECM mineralization, and the ALP activity in MC3T3-E1 cells. The alignment analysis demonstrated a high homology between miRNA-133a-5p and the 3' UTR of RUNX2. Moreover, the luciferase reporter assay demonstrated that miRNA-133a-5p targeted the 3' UTR of RUNX2, and inhibited the expression of RUNX2 in both mRNA and protein levels. In conclusion, we identified the inhibition by miRNA-133a-5p to the expression of osteoblast differentiation markers, to the ECM mineralization, and to the ALP activity in MC3T3-E1 cells, by targeting the 3' UTR of RUNX2. Our study suggests that miRNA-133a-5p might be an important target to inhibit osteoblast differentiation in osteoporosis.

Systematic analysis of lncRNAs, miRNAs and mRNAs for the identification of biomarkers for osteoporosis in the mandible of ovariectomized mice

Osteoporosis is a complex and multifactorial disease caused by an imbalance between bone formation and resorption. Post-menopausal women with endogenous estrogen deficiency suffer from systemic bone loss and osteoporosis, and are at high risk of this affecting the jaw bones. MicroRNAs (miRNAs or miRs) have been implicated in the mechanisms of metabolic bone diseases and are expressed at differential levels in alveolar bone following ovariectomy. In the present study, we systematically analyzed the expression profiles of miRNAs, mRNAs and long non-coding RNA (lncRNAs) in the mandible of ovariectomized (OVX) mice. A complex miRNA-mRNA-lncRNA regulatory network was constructed based on differentially expressed RNAs. Two core differentially expressed genes (DEGs), namely, LRP2 binding protein (Lrp2bp) and perilipin 4 (Plin4), significantly influenced the network targeted by differentially expressed miRNAs. Moreover, peroxisome proliferator-activated receptor (PPAR) and insulin signaling pathways were significantly dysregulated in the mandible of OVX mice. Several differentially expressed lncRNAs were also implicated in the two signaling pathways, which influenced mandible development by forming competing endogenous RNA. On the whole, our data indicate that the comprehensive analysis of miRNAs, mRNAs and lncRNAs provides insight into the pathogenesis of estrogen deficiency-induced osteoporosis in the mandible. This study proposes potential biomarkers for diagnosis or therapeutic targets for osteoporosis which may aid in the development of novel drugs for the treatment of osteoporosis.

Aluminum Trichloride Inhibited Osteoblastic Proliferation and Downregulated the Wnt/β-Catenin Pathway

Aluminum (Al) exposure inhibits bone formation. Osteoblastic proliferation promotes bone formation. Therefore, we inferred that Al may inhibit bone formation by the inhibition of osteoblastic proliferation. However, the effects and molecular mechanisms of Al on osteoblastic proliferation are still under investigation. Osteoblastic proliferation can be regulated by Wnt/β-catenin signaling pathway. To investigate the effects of Al on osteoblastic proliferation and whether Wnt/β-catenin signaling pathway is involved in it, osteoblasts from neonatal rats were cultured and exposed to 0, 0.4 mM (1/20 IC₅₀), 0.8 mM (1/10 IC₅₀), and 1.6 mM (1/5 IC₅₀) of aluminum trichloride (AlCl₃) for 24 h, respectively. The osteoblastic proliferation rates; Wnt3a, lipoprotein receptor-related protein 5 (LRP-5), T cell factor 1 (TCF-1), cyclin D1, and c-Myc messenger RNA (mRNA) expressions; and p-glycogen synthase kinase 3β (GSK3β), GSK3β, and β-catenin protein expressions indicated that AlCl₃ inhibited osteoblastic proliferation and downregulated Wnt/β-catenin signaling pathway. In addition, the AlCl₃ concentration was negatively correlated with osteoblastic proliferation rates and the mRNA expressions of Wnt3a, c-Myc, and cyclin D1, while the osteoblastic proliferation rates were positively correlated with mRNA expressions of Wnt3a, c-Myc, and cyclin D1. Taken together, these findings indicated that AlCl₃ inhibits osteoblastic proliferation may be associated with the inactivation of Wnt/β-catenin signaling pathway.

MicroRNA-34c promotes osteoclast differentiation through targeting LGR4

MicroRNAs have emerged as important regulators of osteoclast differentiation in recent years. Of these, miR-34c has been reported to play an important role in bone development. However, its role and the underlying mechanism in osteoclast differentiation remains poorly understood. In this study, we aimed to investigate the precise role and molecular mechanism of miR-34c in osteoclast differentiation. We found an obvious increase in miR-34c expression during osteoclast differentiation in osteoclast precursors induced by receptor activator of nuclear factor κB (NF-κB) ligand and macrophage colony-stimulating factor in vitro. Further experiments showed that overexpression of miR-34c significantly promoted osteoclast differentiation while suppression of miR-34c showed the opposite effect. Interestingly, bioinformatics analysis and dual-luciferase reporter assays showed that miR-34c targets the 3'-untranslated region of leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4). The expression of LGR4 was regulated by miR-34c in osteoclasts. Moreover, miR-34c regulated NF-κB and glycogen synthase kinase 3-β signaling during osteoclast differentiation. Overexpression of LGR4 partially reversed the promoting effect of miR-34c overexpression on osteoclast differentiation. Taken together, our study suggests that miR-34c contributes to osteoclast differentiation by targeting LGR4, providing novel insights into understanding the molecular mechanism underlying osteoclast differentiation.

Exosome-Mediated Genetic Information Transfer, a Missing Piece of Osteoblast-Osteoclast Communication Puzzle

The skeletal system functions and maintains itself based on communication between cells of diverse origins, especially between osteoblasts (OBs) and osteoclasts (OCs), accounting for bone formation and resorption, respectively. Previously, protein-level information exchange has been the research focus, and this has been discussed in detail. The regulative effects of microRNAs (miRNAs) on OB and OC ignite the question as to whether genetic information could be transferred between bone cells. Exosomes, extracellular membrane vesicles 30-100 nm in diameter, have recently been demonstrated to transfer functional proteins, mRNAs, and miRNAs, and serve as mediators of intercellular communication. By reviewing the distinguishing features of exosomes, a hypothesis was formulated and evaluated in this article that exosome-mediated genetic information transfer may represent a novel strategy for OB-OC communication. The exosomes may coordinately regulate these two cells under certain physiological conditions by transferring genetic information. Further research in exosome-shuttered miRNAs in OB-OC communication may add a missing piece to the bone cells communication "puzzle."

The Signaling Pathways Involved in Chondrocyte Differentiation and Hypertrophic Differentiation

Chondrocytes communicate with each other mainly via diffusible signals rather than direct cell-to-cell contact. The chondrogenic differentiation of mesenchymal stem cells (MSCs) is well regulated by the interactions of varieties of growth factors, cytokines, and signaling molecules. A number of critical signaling molecules have been identified to regulate the differentiation of chondrocyte from mesenchymal progenitor cells to their terminal maturation of hypertrophic chondrocytes, including bone morphogenetic proteins (BMPs), SRY-related high-mobility group-box gene 9 (Sox9), parathyroid hormone-related peptide (PTHrP), Indian hedgehog (Ihh), fibroblast growth factor receptor 3 (FGFR3), and β-catenin. Except for these molecules, other factors such as adenosine, O₂ tension, and reactive oxygen species (ROS) also have a vital role in cartilage formation and chondrocyte maturation. Here, we outlined the complex transcriptional network and the function of key factors in this network that determine and regulate the genetic program of chondrogenesis and chondrocyte differentiation.

miR-195 inhibits the proliferation and migration of chondrocytes by targeting GIT1

Previous studies have demonstrated that G-protein coupled receptor kinase interacting protein-1 (GIT1) and microRNAs (miRNAs) serve an important role in chondrocyte proliferation and migration. However, a limited number of studies conducted thus far have investigated the association between GIT1 and miRNAs. In the present study, putative miR‑195 binding sites in the GIT1 3'‑untranslated region were identified using common bioinformatic algorithms (miRanda, TargetScan, miRBase and miRWalk), and it was demonstrated that they may be involved in regulating GIT1 expression. Following transfection of miR‑195 mimics in chondrocytes, the expression of GIT1 was significantly reduced, whereas the expression was significantly increased following transfection with miR‑195 inhibitors. In addition, the results of the current study demonstrated that increased miR‑195 expression may downregulate chondrocyte proliferation and reduce cell migration. However, chondrocyte proliferation and migration was enhanced following suppression of miR‑195 expression. Furthermore, upon co‑transfection of miR‑195 and GIT1 expression vectors, the inhibitory effect of miR‑195 on chondrocyte proliferation and migration was attenuated. Therefore, miR‑195 may affect chondrocyte proliferation and migration via targeted regulation of GIT1 expression. The results of the current study provide novel evidence for the regulatory mechanisms of miRNAs in bone and cartilage tissues, which may facilitate further research and provide a greater understanding of different osteoarticular diseases.

Circulating miRNA as fine regulators of the physiological responses to physical activity: Pre-analytical warnings for a novel class of biomarkers

MicroRNAs are endogenous non-coding RNAs that post-transcriptionally regulate gene expression by specifically binding the target mRNA and by consequently inducing its degradation. miRNAs can be released into the circulation where they remain stable and they can be measured. Their changes reflect individual biologic adaptation to exposures to specific environmental conditions. As such, measurement of circulating microRNAs represents an opportunity to evaluate biologic changes associated with interventions such as exercise and diet. Physical activity is, indeed, a very important modifying factor for circulating miRNAs. Toward their use in clinical settings several issues should be still solved. Their clinical application is hindered by the high heterogeneity of the analytical procedures used for their measurements. Furthermore, several pre-analytical concerns equally reduce the clinical applicability of miRNA. Pre-analytical phase in sports medicine is an important issue both because, often the conditions in which sampling are performed are peculiar (and not always canonical) and because some of the tested parameters, in the case of professional athletes, enters in routine anti-doping testing and, as such, they should be treated according to precise rules in order to avoid any false positive results. Aim of this review is to give an overview of the main available knowledges about the pre-analytical management of the sample for circulating miRNA evaluation along with the importance of miRNA as regulators of the response to physical activity and their possible future use in anti-doping settings.

Epigenetic Regulation of Bone Remodeling and Its Impacts in Osteoporosis

Epigenetics describes mechanisms which control gene expression and cellular processes without changing the DNA sequence. The main mechanisms in epigenetics are DNA methylation in CpG-rich promoters, histone modifications and non-coding RNAs (ncRNAs). DNA methylation modifies the function of the DNA and correlates with gene silencing. Histone modifications including acetylation/deacetylation and phosphorylation act in diverse biological processes such as transcriptional activation/inactivation and DNA repair. Non-coding RNAs play a large part in epigenetic regulation of gene expression in addition to their roles at the transcriptional and post-transcriptional level. Osteoporosis is the most common skeletal disorder, characterized by compromised bone strength and bone micro-architectural deterioration that predisposes the bones to an increased risk of fracture. It is most often caused by an increase in bone resorption that is not sufficiently compensated by a corresponding increase in bone formation. Nowadays it is well accepted that osteoporosis is a multifactorial disorder and there are genetic risk factors for osteoporosis and bone fractures. Here we review emerging evidence that epigenetics contributes to the machinery that can alter DNA structure, gene expression, and cellular differentiation during physiological and pathological bone remodeling.

MiR-9 promotes osteoblast differentiation of mesenchymal stem cells by inhibiting DKK1 gene expression

The aim of this study is to investigate the role of miR-9 and its mechanism on the osteoblast differentiation of mesenchymal stem cells. Real-time PCR and western blotting were used to study gene expression. Assay of Alkaline phosphatase activity and alizarin red staining were used to examine osteoblast differentiation. Transfection of miR-9 mimics or lent-shmiR-9 was used to modulate the level of miR-9 in C2C12. Overexpression of miR-9 in C2C12 cells stimulated alkaline phosphatase activity and osteoblast mineralization, as well as the expression of osteoblast marker genes Col I, Ocn and Bsp. Gene silencing of miR-9 in C2C12 resulted in the suppression of alkaline phosphatase activity and osteoblast mineralization, as well as the expression of Col I, Ocn and Bsp. DKK1 mRNA was not affected by miR-9 overexpression, however, DKK1 protein was significantly decreased. Moreover, DKK1 3'-UTR mediated transcriptional luciferase activity was also significantly suppressed by miR-9 overexpression. DKK1 mRNA was not affected by miR-9 gene silencing, however, DKK1 protein was significantly stimulated. Moreover, DKK1 3'-UTR mediated transcriptional luciferase activity was significantly stimulated by miR-9 gene silencing, and suppressed by miR-9 overexpression, however, DKK1 3'-UTR mutant mediated luciferase activity was unaffected. The siRNA derived gene silencing of DKK1 blocked the inhibiting effect of shmiR-9 on the expression of alkaline phosphatase; and blocked the inhibiting effect of shmiR-9 on the expression of ColI, Ocn and Bsp. MiR-9 promotes osteoblast differentiation of mesenchymal cell C2C12 by suppressing the gene expression of DKK1.

DC-STAMP: A Key Regulator in Osteoclast Differentiation

Osteoimmunology research is a new emerging research field that investigates the links between the bone and immune responses. Results from osteoimmunology studies suggest that bone is not only an essential component of the musculoskeletal system, but is also actively involved in immune regulation. Many important factors involved in immune regulation also participate in bone homeostasis. Bone homeostasis is achieved by a coordinated action between bone-synthesizing osteoblasts and bone-degrading osteoclasts. An imbalanced action between osteoblasts and osteoclasts often results in pathological bone diseases: osteoporosis is caused by an excessive osteoclast activity, whereas osteopetrosis results from an increased osteoblast activity. This review focuses on dendritic cell-specific transmembrane protein (DC-STAMP), an important protein currently considered as a master regulator of osteoclastogenesis. Of clinical relevance, the frequency of circulating DC-STAMP+ cells is elevated during the pathogenesis of psoriatic diseases. Intriguingly, recent results suggest that DC-STAMP also plays an imperative role in bone homeostasis by regulating the differentiation of both osteoclasts and osteoblasts. This article summarizes our current knowledge on DC-STAMP by focusing on its interacting proteins, its regulation on osteoclastogenesis-related genes, its possible involvement in immunoreceptor tyrosine-based inhibitory motif (ITIM)-mediated signaling cascade, and its potential of developing therapeutics for clinical applications. J. Cell. Physiol. 231: 2402-2407, 2016. © 2016 Wiley Periodicals, Inc.

The impact of microgravity on bone in humans

Experiencing real weightlessness in space is a dream for many of us who are interested in space research. Although space traveling fascinates us, it can cause both short-term and long-term health problems. Microgravity is the most important influence on the human organism in space. The human body undergoes dramatic changes during a long-term spaceflight. In this review, we will mainly focus on changes in calcium, sodium and bone metabolism of space travelers. Moreover, we report on the current knowledge on the mechanisms of bone loss in space, available models to simulate the effects of microgravity on bone on Earth as well as the combined effects of microgravity and cosmic radiation on bone. The available countermeasures applied in space will also be evaluated.

MicroRNAs in Osteoclastogenesis and Function: Potential Therapeutic Targets for Osteoporosis

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