LncRNA MALAT1 inhibits osteogenic differentiation of mesenchymal stem cells in osteoporosis rats through MAPK signaling pathway

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.

Long non-coding RNA KCNQ1OT1 alleviates postmenopausal osteoporosis by modulating miR-421-3p/mTOR axis

The prevention and treatment of postmenopausal osteoporosis (PMOP) is a significant public health issue, and non-coding RNAs are of vital importance in this process. In this study, we find that the long non-coding RNA potassium voltage-gated channel subfamily Q member 1 overlapping transcript 1 (lncRNA KCNQ1OT1) can alleviate the ovariectomy-induced (OVX) PMOP in vivo. We determined that over-expression of KCNQ1OT1 could enhance functions of MC3T3-E1 cells, whereas an opposite trend was observed when KCNQ1OT1 was knocked down. Subsequently, miR-421-3p targeting KCNQ1OT1 was detected through a database search, and RNA fluorescent in situ hybridization, RNA immunoprecipitation, dual luciferase reporter assays all verified this relationship. Notably, KCNQ1OT1 stifled the miR-421-3p expression. The inhibition of proliferation, migration, and osteogenic differentiation caused by KCNQ1OT1 knock-down were reversed by an miR-421-3p inhibitor, further confirming the above findings. We verified that miR-421-3p specifically targeted the mammalian target of rapamycin (mTOR), and miR-421-3p inhibitor could reverse the negative effects of small interfering RNA of mTOR (si-mTOR) on MC3T3-E1 cells. Finally, osteoblasts isolated and cultured from OVX mice model and control mice also confirmed the observed trend. In combination, results mentioned above reveal that KCNQ1OT1 regulates MC3T3-E1 cell functions by regulating the miR-421-3p/mTOR axis.

Effect of LncRNA-MALAT1 on mineralization of dental pulp cells in a high-glucose microenvironment

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) belongs to the long non-coding RNA (LncRNA) family. LncRNA-MALAT1 is expressed in a variety of tissues and is involved in a variety of diseases and biological processes. Although LncRNA-MALAT1 is upregulated in a high-glucose microenvironment and may participate in odontogenic differentiation, the underlying mechanism is not yet well elucidated. Here, we show that MALAT1 was mainly expressed in the cytoplasm of dental pulp cells (DPCs) in situ hybridization. In addition, high levels of mineralization-related factors, namely, tumor growth factors β 1 and 2 (TGFβ-1 and TGFβ-2), bone morphogenetic proteins 2 and 4 (BMP2 and BMP4), bone morphogenetic protein receptor 1 (BMPR1), SMAD family member 2 (SMAD2), runt-related transcription factor 2 (RUNX2), Msh homeobox 2 (MSX2), transcription factor SP7 (SP7), alkaline phosphatase (ALP), dentin matrix acidic phosphoprotein 1 (DMP1), and dentin sialophosphoprotein (DSPP), were expressed, and MALAT1 was significantly overexpressed in DPCs 7 and 14 days after mineralization induction in a high-glucose microenvironment, but only TGFβ-1, BMP2, MSX2, SP7, ALP, and DSPP were significantly downregulated in DPCs after MALAT1 inhibition. MALAT1 may participate in the mineralization process of DPCs by regulating multiple factors (TGFβ-1, BMP2, MSX2, SP7, ALP, and DSPP).

A Quartet Network Analysis Identifying Mechanically Responsive Long Noncoding RNAs in Bone Remodeling

Mechanical force, being so ubiquitous that it is often taken for granted and overlooked, is now gaining the spotlight for reams of evidence corroborating their crucial roles in the living body. The bone, particularly, experiences manifold extraneous force like strain and compression, as well as intrinsic cues like fluid shear stress and physical properties of the microenvironment. Though sparkled in diversified background, long noncoding RNAs (lncRNAs) concerning the mechanotransduction process that bone undergoes are not yet detailed in a systematic way. Our principal goal in this research is to highlight the potential lncRNA-focused mechanical signaling systems which may be adapted by bone-related cells for biophysical environment response. Based on credible lists of force-sensitive mRNAs and miRNAs, we constructed a force-responsive competing endogenous RNA network for lncRNA identification. To elucidate the underlying mechanism, we then illustrated the possible crosstalk between lncRNAs and mRNAs as well as transcriptional factors and mapped lncRNAs to known signaling pathways involved in bone remodeling and mechanotransduction. Last, we developed combinative analysis between predicted and established lncRNAs, constructing a pathway–lncRNA network which suggests interactive relationships and new roles of known factors such as H19. In conclusion, our work provided a systematic quartet network analysis, uncovered candidate force-related lncRNAs, and highlighted both the upstream and downstream processes that are possibly involved. A new mode of bioinformatic analysis integrating sequencing data, literature retrieval, and computational algorithm was also introduced. Hopefully, our work would provide a moment of clarity against the multiplicity and complexity of the lncRNA world confronting mechanical input.

Role of lncRNAs into Mesenchymal Stromal Cell Differentiation

Currently, findings support that 75% of the human genome is actively transcribed, but only 2% is translated into a protein, according to databases such as ENCODE (Encyclopedia of DNA Elements) [1]. The development of high-throughput sequencing technologies, computational methods for genome assembly and biological models have led to the realization of the importance of the previously unconsidered non-coding fraction of the genome. Along with this, noncoding RNAs have been shown to be epigenetic, transcriptional and post-transcriptional regulators in a large number of cellular processes [2]. Within the group of non-coding RNAs, lncRNAs represent a fascinating field of study, given the functional versatility in their mode of action on their molecular targets. In recent years, there has been an interest in learning about lncRNAs in MSC differentiation. The aim of this review is to address the signaling mechanisms where lncRNAs are involved, emphasizing their role in either stimulating or inhibiting the transition to differentiated cell. Specifically, the main types of MSC differentiation are discussed: myogenesis, osteogenesis, adipogenesis and chondrogenesis. The description of increasingly new lncRNAs reinforces their role as players in the well-studied field of MSC differentiation, allowing a step towards a better understanding of their biology and their potential application in the clinic.

The management of bone defect using long non-coding RNA as a potential biomarker for regulating the osteogenic differentiation process

Tissue engineered bone brings hope to the treatment of bone defects, and the osteogenic differentiation of stem cells is the key link. Inducing osteogenic differentiation of stem cells may be a potential approach to promote bone regeneration. In recent years, lncRNA has been studied in the field increasingly, which is believed can regulate cell cycle, proliferation, metastasis, differentiation and immunity, participating in a variety of physiology and pathology processes. At present, it has been confirmed that certain lncRNAs regulate the osteogenesis of stem cells and take part in mediating signaling pathways including Wnt/β-catenin, MAPK, TGF-β/BMP, and Notch pathways. Here, we provided an overview of lncRNA, reviewed its researches in the osteogenic differentiation of stem cells, emphasized the importance of lncRNA in bone regeneration, and focused on the roles of lncRNA in signaling pathways, in order to make adequate preparations for applying lncRNA to bone tissue Engineering, letting it regulate the osteogenic differentiation of stem cells for bone regeneration.

The regulatory activities of MALAT1 in the development of bone and cartilage diseases

Long non-coding RNAs (lncRNAs) have been comprehensively implicated in various cellular functions by mediating transcriptional or post-transcriptional activities. MALAT1 is involved in the differentiation, proliferation, and apoptosis of multiple cell lines, including BMSCs, osteoblasts, osteoclasts, and chondrocytes. Interestingly, MALAT1 may interact with RNAs or proteins, regulating cellular processes. Recently, MALAT1 has been reported to be associated with the development of bone and cartilage diseases by orchestrating the signaling network. The involvement of MALAT1 in the pathological development of bone and cartilage diseases makes it available to be a potential biomarker for clinical diagnosis or prognosis. Although the potential mechanisms of MALAT1 in mediating the cellular processes of bone and cartilage diseases are still needed for further elucidation, MALAT1 shows great promise for drug development.

LncRNA MALAT1 mediates osteogenic differentiation in osteoporosis by regulating the miR-485-5p/WNT7B axis

INTRODUCTION

Accumulating evidence demonstrates that long non-coding RNAs (lncRNAs) are associated with the development of osteoporosis.

METHODS

This study aimed to investigate the effects of MALAT1 on osteogenic differentiation and cell apoptosis in osteoporosis. MALAT1 level, detected by RT-qPCR, was downregulated in hindlimb unloading (HU) mice and simulated microgravity (MG)-treated MC3T3-E1 cells. Moreover, osteogenic differentiation-related factor (Bmp4, Col1a1, and Spp1) levels were measured by RT-qPCR and Western blot. ALP activity was detected, and ALP staining was performed. Cell apoptosis was assessed by flow cytometry.

RESULTS

The results revealed that MALAT1 upregulated the expression of Bmp4, Col1a1, and Spp1, and enhanced ALP activity. Knockdown of MALAT1 suppressed their expression and ALP activity, suggesting that MALAT1 promoted osteogenic differentiation. Additionally, MALAT1 inhibited apoptosis, increased Bax and caspase-3 levels, and decreased Bcl-2 level. However, knockdown of MALAT1 had opposite results. In MG cells, MALAT1 facilitated osteogenic differentiation and suppressed apoptosis. Furthermore, miR-485-5p was identified as a target of MALAT1, and WNT7B was verified as a target of miR-485-5p. Overexpression of miR-485-5p rescued the promotion of osteogenic differentiation and the inhibition of apoptosis induced by MALAT1. Knockdown of WNT7B abolished the facilitation of osteogenic differentiation and the suppression of apoptosis induced by downregulation of miR-485-5p.

DISCUSSION

In conclusion, MALAT1 promoted osteogenic differentiation and inhibited cell apoptosis through the miR-485-5p/WNT7B axis, which suggested that MALAT1 is a potential target to alleviate osteoporosis.

Comprehensive analysis of the m6A-related molecular patterns and diagnostic biomarkers in osteoporosis

BACKGROUND

N6-methyladenosine (m6A) modification is a critical epigenetic modification in eukaryotes and involves several biological processes and occurrences of diseases. However, the roles and regulatory mechanisms of m6A regulators in osteoporosis (OP) remain unclear. Thus, the purpose of this study is to explore the roles and mechanisms of m6A regulators in OP.

METHODS

The mRNA and microRNA (miRNA) expression profiles were respectively obtained from GSE56815, GSE7158, and GSE93883 datasets in Gene Expression Omnibus (GEO). The differential expression of 21 m6A regulators between high-bone mineral density (BMD) and low-BMD women was identified. Then, a consensus clustering of low-BMD women was performed based on differentially expressed (DE)-m6A regulators. The m6A-related differentially expressed genes (DEGs), the differentially expressed miRNAs (DE-miRNAs), and biological functions were investigated. Moreover, a weighted gene co-expression network analysis (WGCNA) was constructed to identify the OP-related hub modules, hub genes, and the functional pathways. Then, an m6A regulator-target-pathway network and the competing endogenous RNA (ceRNA) network in key modules were constructed. A least absolute shrinkage and selection operation (LASSO) Cox regression model and a Support Vector Machine-Recursive Feature Elimination (SVM-RFE) model were constructed to identify the candidate genes for OP prediction. The receiver operator characteristic (ROC) curves were used to validate the performances of predictive models and candidate genes.

RESULTS

A total of 10,520 DEGs, 13 DE-m6A regulators, and 506 DE-miRNAs between high-BMD and low-BMD women were identified. Two m6A-related subclusters with 13 DE-m6A regulators were classified for OP. There were 5,260 m6A-related DEGs identified between two m6A-related subclusters, the PI3K-Akt, MAPK, and immune-related pathways, and bone metabolism was mainly enriched in cluster 2. Cell cycle-related pathways, RNA methylation, and cell death-related pathways were significantly involved in cluster 1. Five modules were identified as key modules based on WGCNA, and an m6A regulator-target gene-pathway network and the ceRNA network were constructed in module brown. Moreover, three m6A regulators (FTO, YTHDF2, and CBLL1) were selected as the candidate genes for OP.

CONCLUSION

M6A regulators play an important role in the occurrences and diagnosis of OP.

FGD5-AS1 facilitates the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells via targeting the miR-506-3p/BMP7 axis

BACKGROUND

Osteoporosis is a systemic disease characterized by impaired bone formation, increased bone resorption, and brittle bone fractures. The osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) is considered to be a vital process for bone formation. Numerous studies have reported that long non-coding RNAs (lncRNAs) are involved in the osteogenic differentiation of hBMSCs. The present study aimed to investigate the effect of FGD5 antisense RNA 1 (FGD5-AS1) on osteogenic differentiation.

METHODS

RT-qPCR was performed to detect the expression of FGD5-AS1, miR-506-3p, and osteogenesis-related genes OCN, OPN, OSX, and RUNX2. Western blotting was carried out to detect the protein levels of osteogenesis-related markers. In addition, the regulatory effect of FGD5-AS1 on osteogenic differentiation was detected through alkaline phosphatase (ALP) activity, Alizarin Red S (ARS) staining, and Cell Counting Kit-8 (CCK-8). Bioinformatics analysis and luciferase reporter assay were used to predict and validate the interaction between FGD5-AS1 and miR-506-3p as well as miR-506-3p and bone morphogenetic protein 7 (BMP7).

RESULTS

The RT-qPCR analysis revealed that FGD5-AS1 was upregulated in hBMSCs following induction of osteogenic differentiation. In addition, FGD5-AS1 knockdown attenuated hBMSC viability and osteogenic differentiation. Bioinformatics analysis and luciferase reporter assays verified that FGD5-AS1 could directly interact with microRNA (miR)-506-3p. Furthermore, miR-506-3p could directly target the 3'-untranslated region (3'-UTR) of BMP7. Additionally, functional assays demonstrated that miR-506-3p silencing could restore the suppressive effect of FGD5-AS1 knockdown on osteogenic differentiation and viability of hBMSCs, and miR-506-3p could attenuate osteogenic differentiation via targeting BMP7.

CONCLUSIONS

Taken together, the results of the present study suggested that FGD5-AS1 could positively regulate the osteogenic differentiation of hBMSCs via targeting the miR-506-3p/BMP7 axis.

METTL3-Mediated lncRNA m6A Modification in the Osteogenic Differentiation of Human Adipose-Derived Stem Cells Induced by NEL-Like 1 Protein

OBJECTIVES

This study aimed to explore the regulatory mechanism of methyltransferase3 (METTL3) -mediated long non-coding RNA (lncRNA) N6-methyladenosine (m⁶A) modification in the osteogenic differentiation of human adipose-derived stem cells (hASCs) induced by NEL-like 1 protein (NELL-1).

MATERIALS AND METHODS

Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and high- throughput sequencing for RNA (RNA-seq) were performed on hASCs. Osteogenic ability was detected by alkaline phosphatase (ALP) staining, Alizarin Red S(ARS) staining, ALP quantification and Quantitative real-time polymerase chain reaction analysis (qRT-PCR). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis predicted the osteogenesis-related pathways enriched for the lncRNAs and identified the target lncRNAs. After overexpression and knockdown of METTL3, methylated RNA immunoprecipitation-qPCR (MeRIP-qPCR) and qRT-PCR were used to detect the levels of m⁶A modification and the expression of the target lncRNA, and the binding of both was confirmed by RNA binding protein immunoprecipitation (RIP) assay. The effects of lncRNA and METTL3 on phosphorylation of the key proteins of the pathway were detected by western blot analysis.

RESULTS

In vitro experiments showed that METTL3 can promote osteogenic differentiation and that its expression level is upregulated. KEGG pathway analysis predicted that lncRNAs with differentially upregulated methylated peaks were enriched mostly in the mitogen-activated protein kinase (MAPK) signaling pathway, in which Serine/threonine protein kinase 3 (STK3) was the predicted target gene of the lncRNA RP11-44 N12.5. The m⁶A modification and expression of RP11-44 N12.5 were both regulated by METTL3. Subsequently, lncRNA RP11-44 N12.5 and METTL3 were found to regulate the phosphorylation levels of three key proteins in the MAPK signaling pathway, ERK, JNK and p38.

CONCLUSIONS

This study shows, for the first time, that METTL3 can activate the MAPK signaling pathway by regulating the m⁶A modification and expression of a lncRNA, thereby enhancing the osteogenic differentiation of hASCs.

The potential role of lncRNAs in osteoporosis

Osteoporosis is a common bone disease characterized by low bone mass and deterioration of bone microstructure, which predisposes to higher risks of bone fragility and bone fracture. Long non-coding RNAs (lncRNAs) are a class of RNAs with a length of > 200 nucleotides without protein-coding function, which control the expression of genes and affect multiple biological processes. Accumulating evidence suggests that lncRNAs are widely involved in the molecular mechanisms of osteoporosis. This review aims to summarize the function and underlying mechanism of lncRNAs involved in the development of osteoporosis, and how it contributes to osteoblast and osteoclast function. This knowledge will shed new light on the modulation and potential treatment of osteoporosis.

The Involvement of Long Non-Coding RNAs in Bone

A harmonious balance between osteoblast and osteoclast activity guarantees optimal bone formation and resorption, pathological conditions affecting the bone may arise. In recent years, emerging evidence has shown that epigenetic mechanisms play an important role during osteoblastogenesis and osteoclastogenesis processes, including long non-coding RNAs (lncRNAs). These molecules are a class of ncRNAs with lengths exceeding 200 nucleotides not translated into protein, that have attracted the attention of the scientific community as potential biomarkers to use for the future development of novel diagnostic and therapeutic approaches for several pathologies, including bone diseases. This review aims to provide an overview of the lncRNAs and their possible molecular mechanisms in the osteoblastogenesis and osteoclastogenesis processes. The deregulation of their expression profiles in common diseases associated with an altered bone turnover is also described. In perspective, lncRNAs could be considered potential innovative molecular biomarkers to help with earlier diagnosis of bone metabolism-related disorders and for the development of new therapeutic strategies.

The Roles of Epigenetics Regulation in Bone Metabolism and Osteoporosis

Osteoporosis is a metabolic disease characterized by decreased bone mineral density and the destruction of bone microstructure, which can lead to increased bone fragility and risk of fracture. In recent years, with the deepening of the research on the pathological mechanism of osteoporosis, the research on epigenetics has made significant progress. Epigenetics refers to changes in gene expression levels that are not caused by changes in gene sequences, mainly including DNA methylation, histone modification, and non-coding RNAs (lncRNA, microRNA, and circRNA). Epigenetics play mainly a post-transcriptional regulatory role and have important functions in the biological signal regulatory network. Studies have shown that epigenetic mechanisms are closely related to osteogenic differentiation, osteogenesis, bone remodeling and other bone metabolism-related processes. Abnormal epigenetic regulation can lead to a series of bone metabolism-related diseases, such as osteoporosis. Considering the important role of epigenetic mechanisms in the regulation of bone metabolism, we mainly review the research progress on epigenetic mechanisms (DNA methylation, histone modification, and non-coding RNAs) in the osteogenic differentiation and the pathogenesis of osteoporosis to provide a new direction for the treatment of bone metabolism-related diseases.

Identification of Serum Exosomal MicroRNA Expression Profiling in Menopausal Females with Osteoporosis by High-throughput Sequencing

Estrogen deficiency, which mainly occurs in postmenopausal women, is a primary reason for osteoporosis in clinical diagnosis. However, the molecular regulation of osteoporosis in menopausal females is still not adequately explained in the literature, with the diagnosis and treatment for osteoporosis being limited. Herein, exosomal microRNAs (miRNAs) were used to evaluate their diagnosis and prediction effects in menopausal females with osteoporosis. In this study, 6 menopausal females without osteoporosis and 12 menopausal females with osteoporosis were enrolled. The serum exosomes were isolated, and the miRNA expression was detected by miRNA high-throughput sequencing. Exosomal miRNA effects were analyzed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses. The miRNA-targeted genes were evaluated by Targetscan 7.2 and the protein-protein interactions (PPI) by STRING. Hub genes were analyzed by the CytoHubba app of Cytoscape. The results showed that 191 aberrant miRNAs were found in the group of menopausal females with osteoporosis, including 72 upregulated miRNAs and 121 downregulated miRNAs. Aberrant miRNAs were involved in many signaling pathways, such as the Wnt, MAPK, and Hippo pathways. Based on PPI network analysis, FBXL3, FBXL13, COPS2, UBE2D3, DCUN1D1, DCUN1D4, CUL3, FBXO22, ASB6, and COMMD2 were the 10 most notable genes in the PPI network. In conclusion, aberrant serum exosomal miRNAs were associated with an altered risk of osteoporosis in menopausal females and may act as potential biomarkers for the prediction of risk of osteoporosis in menopausal females.

Role of LncRNAs and CircRNAs in Bone Metabolism and Osteoporosis

Bone is a mechanosensitive organ that provides strength and support. Many bone cells, various pathways, and signaling molecules coordinate bone metabolism and also determine the course of bone diseases, such as osteoporosis, osteonecrosis, osteopenia, etc. Osteoporosis is caused by increased bone resorption and reduced bone formation due to the changes in the level of different proteins and RNAs in osteoclast or/and osteoblasts. The available therapeutic interventions can significantly reduce bone resorption or enhance bone formation, but their prolonged use has deleterious side effects. Therefore, the use of non-coding RNAs as therapeutics has emerged as an interesting field of research. Despite advancements in the molecular field, not much is known about the role of long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) in bone homeostasis and osteoporosis. Therefore, in this article, we summarize the role of lncRNAs and circRNAs in different bone cells and osteoporosis so that it might help in the development of osteoporotic therapeutics.

Comprehensive Analysis of Differentially Expressed Circular RNAs in Patients with Senile Osteoporotic Vertebral Compression Fracture

Aim

Circular RNAs (circRNAs) have been found to contribute to the regulation of many diseases and are abundantly expressed in various organisms. The present study is aimed at systematically characterizing the circRNA expression profiles in patients with senile osteoporotic vertebral compression fracture (OVCF) and predicting the potential functions of the regulatory networks correlated with these differentially expressed circRNAs.

Methods

The circRNA expression profile in patients with senile OVCF was explored by using RNA sequencing. The prediction of the enriched signaling pathways and circRNA-miRNA networks was conducted by bioinformatics analysis. Real-time quantitative PCR was used to validate the selected differentially expressed circRNAs from 20 patients with senile OVCF relative to 20 matched healthy controls.

Results

A total of 884 differentially expressed circRNAs were identified, of which 554 were upregulated and 330 were downregulated. The top 15 signaling pathways associated with these differentially expressed circRNAs were predicted. The result of qRT-PCR of the selected circRNAs was consistent with RNA sequencing.

Conclusions

CircRNAs are differentially expressed in patients with senile OVCF, which might contribute to the pathophysiological mechanism of senile osteoporosis.

Long non-coding RNA MIR22HG promotes osteogenic differentiation of bone marrow mesenchymal stem cells via PTEN/ AKT pathway

Osteoporosis is a prevalent metabolic bone disease characterized by low bone mineral density and degenerative disorders of bone tissues. Previous studies showed the abnormal osteogenic differentiation of endogenous bone marrow mesenchymal stem cells (BMSCs) contributes to the development of osteoporosis. However, the underlying mechanisms by which BMSCs undergo osteogenic differentiation remain largely unexplored. Recently, long non-coding RNAs have been discovered to play important roles in regulating BMSC osteogenesis. In this study, we first showed MIR22HG, which has been demonstrated to be involved in the progression of several cancer types, played an important role in regulating BMSC osteogenesis. We found the expression of MIR22HG was significantly decreased in mouse BMSCs from the osteoporotic mice and it was upregulated during the osteogenic differentiation of human BMSCs. Overexpression of MIR22HG in human BMSCs enhanced osteogenic differentiation, whereas MIR22HG knockdown inhibited osteogenic differentiation both in vitro and in vivo. Mechanistically, MIR22HG promoted osteogenic differentiation by downregulating phosphatase and tensin homolog (PTEN) and therefore activating AKT signaling. Moreover, we found MIR22HG overexpression promoted osteoclastogenesis of RAW264.7 cells, which indicated that MIR22HG played a significant role in bone metabolism and could be a therapeutic target for osteoporosis and other bone-related diseases.

The Role of Micro RNA and Long-Non-Coding RNA in Osteoporosis

Osteoporosis is a major concern worldwide and can be attributed to an imbalance between osteoblastic bone formation and osteoclastic bone resorption due to the natural aging process. Heritable factors account for 60-80% of optimal bone mineralization; however, the finer details of pathogenesis remain to be elucidated. Micro RNA (miRNA) and long-non-coding RNA (lncRNA) are two targets that have recently come into the spotlight due to their ability to control gene expression at the post-transcriptional level and provide epigenetic modification. miRNAs are a class of non-coding RNAs that are approximately 18-25 nucleotides long. It is thought that up to 60% of human protein-coding genes may be regulated by miRNAs. They have been found to regulate gene expression that controls osteoblast-dependent bone formation and osteoclast-related bone remodeling. lncRNAs are highly structured RNA transcripts longer than 200 nucleotides that do not translate into proteins. They have very complex secondary and tertiary structures and the same degradation processes as messenger RNAs. The fact that they have a rapid turnover is due to their sponge function in binding the miRNAs that lead to a degradation of the lncRNA itself. They can act as signaling, decoy, and framework molecules, or as primers. Current evidence suggests that lncRNAs can act as chromatin and transcriptional as well as post-transcriptional regulators. With regards to osteoporosis, lncRNA is thought to be involved in the proliferation, apoptosis, and inflammatory response of the bone. This review, which is based on a systematic appraisal of the current literature, provides current molecular and genetic opinions on the roles of miRNAs and lncRNAs in osteoporosis. Further research into the epigenetic modification and the regulatory roles of these molecules will bring us closer to potential disease-modifying treatment for osteoporosis. However, more issues regarding the detailed actions of miRNAs and lncRNAs in osteoporosis remain unknown and controversial and warrant future investigation.

Identification of circRNA-associated ceRNA network in BMSCs of OVX models for postmenopausal osteoporosis

Circular RNAs (circRNAs) serve as competing endogenous RNAs (ceRNAs) and indirectly regulate gene expression through shared microRNAs (miRNAs). However, the potential circRNAs functioning as ceRNAs in osteoporosis remain unclear. The bone marrow mesenchymal stem cells (BMSCs) were isolated from ovariectomy (OVX) mice and controls. We systematically analyzed RNA‐seq and miRNA‐microarray data, miRNA‐target interactions, and prominently coexpressed gene pairs to identify aberrantly expressed circRNAs, miRNAs, and messenger RNAs (mRNAs) between the OVX mice and controls. A total of 45 circRNAs, 22 miRNAs, and 548 mRNAs were significantly dysregulated (fold change > 1.5; p < 0.05). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses were conducted for differentially expressed mRNAs, and subsequently a circRNA‐associated ceRNA network involved in osteoporosis was constructed. We identified two ceRNA regulatory pathways in this osteoporosis mouse model—novel circRNA 0020/miR-206-3p/Nnmt and circRNA 3832/miR-3473e/Runx3, which were validated by real-time PCR. This is the first study to elucidate the circRNA-associated ceRNA network in OVX and control mice using deep RNA-seq and RNA-microarray analysis. The data further expanded the understanding of circRNA-associated ceRNA networks, and the regulatory functions of circRNAs, miRNAs and mRNAs in the pathogenesis and pathology of osteoporosis.

LncRNA LOC100506178 promotes osteogenic differentiation via regulating miR-214-5p-BMP2 axis in human bone marrow mesenchymal stem cells

Osteogenic differentiation is an important role in dental implantation. Long no coding RNAs (lncRNAs) are a novel class of noncoding RNAs that have significant effects in a variety of diseases. However, the function and mechanisms of LOC100506178 in osteogenic differentiation and migration of bone morphogenetic protein 2 (BMP2)-induced osteogenic differentiation of human bone marrow mesenchymalstem cells (hBMSCs) remain largely unclear. BMP2 was used to induce osteogenic differentiation of hBMSCs. Quantitative real time PCR (qRT-PCR) was used to examine the expression of LOC100506178, miR-214-5p, Runt-related transcription factor 2 (RUNX2), Osterix (Osx), and Alkaline Phosphatase (ALP) in BMP2-induced osteogenic differentiation of hBMSCs. The function of LOC100506178 and miR-214-5p was explored in vitro using Alizarin Red S Staining, ALP activity, as well as in vivo ectopic bone formation. Luciferase reporter assay was performed to assess the association between LOC100506178 and miR-214-5p, as well as miR-214-5p and BMP2. The miR-214-5p sponging potential of LOC100506178 was evaluated by RNA immunoprecipitation. In the present study, the expression of LOC100506178 was found to be increased in BMP2-induced osteogenic differentiation of hBMSCs, accompanied with decreased miR-214-5p expression and increased RUNX2, Osx and ALP expression. LOC100506178 significantly induced, while miR-214-5p suppressed the BMP2-induced osteogenic differentiation of hBMSCs. Mechanistically, LOC100506178 was directly bound to miR-214-5p and miR-214-5p targeted the 3′-untranslated region of BMP2 to negatively regulate its expression. In conclusion, our data indicate a novel molecular pathway LOC100506178/miR-214-5p/BMP2 in relation to hBMSCs differentiation into osteoblasts, which may facilitate bone anabolism.

LncRNA TUG1 was upregulated in osteoporosis and regulates the proliferation and apoptosis of osteoclasts

Background

Long non-coding RNA (LncRNA) TUG1 plays critical roles in the development of human cancers. Its inhibition has been proved to participate in ankylosing spondylitis, which is an inverse pathological procedure of osteoporosis. In the present study, we aim to investigate the role of lncRNA TUG1 in ankylosing spondylitis.

Materials and methods

Expressions of lncRNA TUG1 in plasma of 98 patients with osteoporosis and 60 healthy participants were detected by real-time quantitative PCR (RT-qPCR). Diagnostic values of lncRNA CASC11 for osteoclasts were performed by the ROC curve with osteoporosis patients as positive and healthy participants as negative. All experiments were repeated 3 times. Mean ± standard deviation was calculated.

Results

We found that plasma lncRNA TUG1 was upregulated in osteoporosis patients than in healthy participants. Upregulation of plasma lncRNA TUG1 distinguished osteoporosis patients from healthy participants. LncRNA TUG1 level increased with the advances of clinical stages. Over-expression of lncRNA TUG1 promoted the proliferation and inhibited the apoptosis of mice osteoclasts, while lncRNA TUG1 siRNA silencing played an opposite role. In addition, lncRNA TUG1 over-expression led to downregulated PTEN, while lncRNA TUG1 siRNA silencing played an opposite role.

Conclusion

Therefore, lncRNA TUG1 is upregulated in osteoporosis and regulates the proliferation and apoptosis of osteoclasts. lncRNA TUG1 knockdown may serve as a promising therapeutic target for osteoporosis by inhibiting the proliferation and promoting the apoptosis of osteoclasts through PTEN.