MicroRNA-124 regulates osteoclast differentiation

A potential function for MicroRNA-124 in normal and pathological bone conditions

Cells produce short single-stranded non-coding RNAs (ncRNAs) called microRNAs (miRNAs), which actively regulate gene expression at the posttranscriptional level. Several miRNAs have been observed to exert significant impacts on bone health and bone-related disorders. One of these, miR-124, is observed in bone microenvironments and is conserved across species. It affects bone cell growth and differentiation by activating different transcription factors and signaling pathways. In-depth functional analyses of miR-124 have revealed several physiological and pathological roles exerted through interactions with other ncRNAs. Deciphering these RNA-mediated signaling networks and pathways is essential for understanding the potential impacts of dysregulated miRNA functions on bone biology. In this review, we aim to provide a comprehensive analysis of miR-124's involvement in bone physiology and pathology. We highlight the importance of miR-124 in controlling transcription factors and signaling pathways that promote bone growth. This review reveals therapeutic implications for the treatment of bone-related diseases.

The MicroRNAs in the Pathophysiology of Osteoporosis

Globally, osteoporosis is the most common systemic skeletal disease. There are many factors that influence osteoporosis' development and progression. During the pathogenesis of this disease, bone turnover is imbalanced between resorption and the formation of bone tissue. A growing interest has been devoted to the role that microRNA (miRNA) plays in osteoporosis regulation. A microRNA (miRNA) is a group of small single-stranded RNA molecules involved in regulating gene expression in eukaryotic organisms. As microRNAs (miRNAs) are key regulators of gene expression and can modulate processes related to bone metabolism, they have become increasingly important for studying osteoporosis pathogenesis. The available research suggests that miRNAs play an important role in regulating processes associated with bone metabolism, especially by influencing bone resorption and synthesis. Furthermore, microRNAs can also serve as potential therapeutic targets for osteoporosis, besides being a rapid and specific biomarker.

Epigenetic Regulation of Autophagy in Bone Metabolism

The skeletal system is crucial for supporting bodily functions, protecting vital organs, facilitating hematopoiesis, and storing essential minerals. Skeletal homeostasis, which includes aspects such as bone density, structural integrity, and regenerative processes, is essential for normal skeletal function. Autophagy, an intricate intracellular mechanism for degrading and recycling cellular components, plays a multifaceted role in bone metabolism. It involves sequestering cellular waste, damaged proteins, and organelles within autophagosomes, which are then degraded and recycled. Autophagy's impact on bone health varies depending on factors such as regulation, cell type, environmental cues, and physiological context. Despite being traditionally considered a cytoplasmic process, autophagy is subject to transcriptional and epigenetic regulation within the nucleus. However, the precise influence of epigenetic regulation, including DNA methylation, histone modifications, and non-coding RNA expression, on cellular fate remains incompletely understood. The interplay between autophagy and epigenetic modifications adds complexity to bone cell regulation. This article provides an in-depth exploration of the intricate interplay between these two regulatory paradigms, with a focus on the epigenetic control of autophagy in bone metabolism. Such an understanding enhances our knowledge of bone metabolism-related disorders and offers insights for the development of targeted therapeutic strategies.

Predictive and prognostic biomarkers of bone metastasis in breast cancer: current status and future directions

The most common site of metastasis in breast cancer is the bone, where the balance between osteoclast-mediated bone resorption and osteoblast-mediated bone formation is disrupted. This imbalance causes osteolytic bone metastasis in breast cancer, which leads to bone pain, pathological fractures, spinal cord compression, and other skeletal-related events (SREs). These complications reduce patients' quality of life significantly and have a profound impact on prognosis. In this review, we begin by providing a brief overview of the epidemiology of bone metastasis in breast cancer, including current diagnostic tools, treatment approaches, and existing challenges. Then, we will introduce the pathophysiology of breast cancer bone metastasis (BCBM) and the animal models involved in the study of BCBM. We then come to the focus of this paper: a discussion of several biomarkers that have the potential to provide predictive and prognostic value in the context of BCBM-some of which may be particularly compatible with more comprehensive liquid biopsies. Beyond that, we briefly explore the potential of new technologies such as single-cell sequencing and organoid models, which will improve our understanding of tumor heterogeneity and aid in the development of improved biomarkers. The emerging biomarkers discussed hold promise for future clinical application, aiding in the prevention of BCBM, improving the prognosis of patients, and guiding the implementation of personalized medicine.

Role and Regulation of Transcription Factors in Osteoclastogenesis

Bones serve mechanical and defensive functions, as well as regulating the balance of calcium ions and housing bone marrow.. The qualities of bones do not remain constant. Instead, they fluctuate throughout life, with functions increasing in some situations while deteriorating in others. The synchronization of osteoblast-mediated bone formation and osteoclast-mediated bone resorption is critical for maintaining bone mass and microstructure integrity in a steady state. This equilibrium, however, can be disrupted by a variety of bone pathologies. Excessive osteoclast differentiation can result in osteoporosis, Paget's disease, osteolytic bone metastases, and rheumatoid arthritis, all of which can adversely affect people's health. Osteoclast differentiation is regulated by transcription factors NFATc1, MITF, C/EBPα, PU.1, NF-κB, and c-Fos. The transcriptional activity of osteoclasts is largely influenced by developmental and environmental signals with the involvement of co-factors, RNAs, epigenetics, systemic factors, and the microenvironment. In this paper, we review these themes in regard to transcriptional regulation in osteoclastogenesis.

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.

Oxidative Stress and Inflammation in Osteoporosis: Molecular Mechanisms Involved and the Relationship with microRNAs

Osteoporosis is characterized by the alteration of bone homeostasis due to an imbalance between osteoclastic bone resorption and osteoblastic bone formation. Estrogen deficiency causes bone loss and postmenopausal osteoporosis, the pathogenesis of which also involves oxidative stress, inflammatory processes, and the dysregulation of the expression of microRNAs (miRNAs) that control gene expression at post-transcriptional levels. Oxidative stress, due to an increase in reactive oxygen species (ROS), proinflammatory mediators and altered levels of miRNAs enhance osteoclastogenesis and reduce osteoblastogenesis through mechanisms involving the activation of MAPK and transcription factors. The present review summarizes the principal molecular mechanisms involved in the role of ROS and proinflammatory cytokines on osteoporosis. Moreover, it highlights the interplay among altered miRNA levels, oxidative stress, and an inflammatory state. In fact, ROS, by activating the transcriptional factors, can affect miRNA expression, and miRNAs can regulate ROS production and inflammatory processes. Therefore, the present review should help in identifying targets for the development of new therapeutic approaches to osteoporotic treatment and improve the quality of life of patients.

Micro-RNA: A Future Approach to Personalized Diagnosis of Bone Diseases

Osteoporosis is a highly prevalent bone disease worldwide and the most studied bone-associated pathological condition. Although its diagnosis makes use of advanced and clinically relevant imaging and biochemical tools, the information suffers from several limitations and has little or no prognostic value. In this context, circulating micro-RNAs represent a potentially attractive alternative or a useful addition to the diagnostic arsenal and offer a greater prognostic potential than the conventional approaches. These short non-coding RNA molecules act as inhibitors of gene expression by targeting messenger RNAs with different degrees of complementarity, establishing a complex multilevel network, the basis for the fine modulation of gene expression that finally regulates every single activity of a cell. Micro-RNAs may passively and/or actively be released in the circulation by source cells, and being measurable in biological fluids, their concentrations may be associated to specific pathophysiological conditions. Mounting, despite debatable, evidence supports the use of micro-RNAs as markers of bone cell metabolic activity and bone diseases. Indeed, several micro-RNAs have been associated with bone mineral density, fractures and osteoporosis. However, concerns such as absence of comparability between studies and, the lack of standardization and harmonization of the methods, limit their application. In this review, we describe the pathophysiological bases of the association between micro-RNAs and the deregulation of bone cells activity and the processes that led to the identification of potential micro-RNA-based markers associated with metabolic bone diseases.

Comprehensive overview of microRNA function in rheumatoid arthritis

MicroRNAs (miRNAs), a class of endogenous single-stranded short noncoding RNAs, have emerged as vital epigenetic regulators of both pathological and physiological processes in animals. They direct fundamental cellular pathways and processes by fine-tuning the expression of multiple genes at the posttranscriptional level. Growing evidence suggests that miRNAs are implicated in the onset and development of rheumatoid arthritis (RA). RA is a chronic inflammatory disease that mainly affects synovial joints. This common autoimmune disorder is characterized by a complex and multifaceted pathogenesis, and its morbidity, disability and mortality rates remain consistently high. More in-depth insights into the underlying mechanisms of RA are required to address unmet clinical needs and optimize treatment. Herein, we comprehensively review the deregulated miRNAs and impaired cellular functions in RA to shed light on several aspects of RA pathogenesis, with a focus on excessive inflammation, synovial hyperplasia and progressive joint damage. This review also provides promising targets for innovative therapies of RA. In addition, we discuss the regulatory roles and clinical potential of extracellular miRNAs in RA, highlighting their prospective applications as diagnostic and predictive biomarkers.

Application of exosome-derived noncoding RNAs in bone regeneration: Opportunities and challenges

With advances in the fields of regenerative medicine, cell-free therapy has received increased attention. Exosomes have a variety of endogenous properties that provide stability for molecular transport across biological barriers to cells, as a form of cell-to-cell communication that regulates function and phenotype. In addition, exosomes are an important component of paracrine signaling in stem-cell-based therapy and can be used as a stand-alone therapy or as a drug delivery system. The remarkable potential of exosomes has paved the pathway for cell-free treatment in bone regeneration. Exosomes are enriched in distinct noncoding RNAs (ncRNAs), including microRNAs, long ncRNAs and circular RNAs. Different ncRNAs have multiple functions. Altered expression of ncRNA in exosomes is associated with the regenerative potential and development of various diseases, such as femoral head osteonecrosis, myocardial infarction, and cancer. Although there is increasing evidence that exosome-derived ncRNAs (exo-ncRNAs) have the potential for bone regeneration, the detailed mechanisms are not fully understood. Here, we review the biogenesis of exo-ncRNA and the effects of ncRNAs on angiogenesis and osteoblast- and osteoclast-related pathways in different diseases. However, there are still many unsolved problems and challenges in the clinical application of ncRNA; for instance, production, storage, targeted delivery and therapeutic potency assessment. Advancements in exo-ncRNA methods and design will promote the development of therapeutics, revolutionizing the present landscape.

Babam2 negatively regulates osteoclastogenesis by interacting with Hey1 to inhibit Nfatc1 transcription

Osteoclast-mediated excessive bone resorption was highly related to diverse bone diseases including osteoporosis. BRISC and BRCA1-A complex member 2 (Babam2) was an evolutionarily conserved protein that is highly expressed in bone tissues. However, whether Babam2 is involved in osteoclast formation is still unclear. In this study, we identify Babam2 as an essential negative regulator of osteoclast formation. We demonstrate that Babam2 knockdown significantly accelerated osteoclast formation and activity, while Babam2 overexpression blocked osteoclast formation and activity. Moreover, we demonstrate that the bone resorption activity was significantly downregulated in Babam2-transgenic mice as compared with wild-type littermates. Consistently, the bone mass of the Babam2-transgenic mice was increased. Furthermore, we found that Babam2-transgenic mice were protected from LPS-induced bone resorption activation and thus reduced the calvarial bone lesions. Mechanistically, we demonstrate that the inhibitory effects of Babam2 on osteoclast differentiation were dependent on Hey1. As silencing Hey1 largely diminished the effects of Babam2 on osteoclastogenesis. Finally, we show that Babam2 interacts with Hey1 to inhibit Nfatc1 transcription. In sum, our results suggested that Babam2 negatively regulates osteoclastogenesis and bone resorption by interacting with Hey1 to inhibit Nfatc1 transcription. Therefore, targeting Babam2 may be a novel therapeutic approach for osteoclast-related bone diseases.

Regulation of osteoclast-mediated bone resorption by microRNA

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

The effect of pharmacological cessation and restoration of menstrual cycle on bone metabolism in premenopausal women with endometriosis

INTRODUCTION

GnRH-analogs induce bone loss. We aimed to investigate the effects of goserelin-induced menstrual cessation (MC) and subsequent menstrual restoration (MR) on bone metabolism (BM).

METHODS

In this prospective cohort study, premenopausal women (PMW) with histologically verified endometriosis (n = 21) received goserelin monthly for 6 months (6 m) resulting in MC and were followed up for another 6 m after MR (12 m). Age- and BMI-matched healthy PMW (n = 20) served as controls for bone mineral density (BMD) measurements. The primary endpoint was changes in lumbar spine (LS)-BMD at 6 m and 12 m; Secondary endpoints were changes in femoral neck (FN)-BMD, bone turnover markers (P1NP and CΤx), sclerostin, and expression of bone-related circulating microRNAs (miRNAs) at 6 m and 12 m.

RESULTS

Goserelin-induced MC reduced LS- and FN-BMD at 6 m (both p < 0.001). From 6 m to 12 m, LS-BMD increased (p < 0.001) but remained below baseline values (p = 0.012), whereas FN-BMD remained stable (p = 1.000). CTx and P1NP levels increased at 6 m (both p < 0.001) and decreased at 12 m (p < 0.001 and p = 0.013, respectively), while CTx (p = 1.000) alone and not P1NP (p = 0.020) returned to baseline. Sclerostin levels did not change. Relative expression of miRNAs targeting RUNX 2 and beta-catenin was significantly downregulated at 6 m compared to baseline (p < 0.001), while the expression of miRNAs targeting osteoblast and osteoclast function at both directions demonstrated a robust increase (up to 400fold) at 12 m (p < 0.001).

CONCLUSIONS

Six months of goserelin-induced MC lead to significant bone loss associated with increased bone turnover and changes in the expression of bone-related miRNAs, changes that are only partially reversed at 6 m after MR.

miRNAs Related to Different Processes of Fracture Healing: An Integrative Overview

Fracture healing is a complex, dynamic process that is directed by cellular communication and requires multiple cell types, such as osteoblasts, osteoclasts, and immune cells. Physiological fracture healing can be divided into several phases that consist of different processes, such as angiogenesis, osteogenesis, and bone resorption/remodelling. This is needed to guarantee proper bone regeneration after fracture. Communication and molecular regulation between different cell types and within cells is therefore key in successfully orchestrating these processes to ensure adequate bone healing. Among others, microRNAs (miRNAs) play an important role in cellular communication. microRNAs are small, non-coding RNA molecules of ~22 nucleotides long that can greatly influence gene expression by post-transcriptional regulation. Over the course of the past decade, more insights have been gained in the field of miRNAs and their role in cellular signalling in both inter- and intracellular pathways. The interplay between miRNAs and their mRNA targets, and the effect thereof on different processes and aspects within fracture healing, have shown to be interesting research topics with possible future diagnostic and therapeutic potential. Considering bone regeneration, research moreover focusses on specific microRNAs and their involvement in individual pathways. However, it is required to combine these data to gain more understanding on the effects of miRNAs in the dynamic process of fracture healing, and to enhance their translational application in research, as well as in the clinic. Therefore, this review aims to provide an integrative overview on miRNAs in fracture healing, related to several key aspects in the fracture healing cascade. A special focus will be put on hypoxia, angiogenesis, bone resorption, osteoclastogenesis, mineralization, osteogenesis, osteoblastogenesis, osteocytogenesis, and chondrogenesis.

MiRNAs Expression Profiling in Raw264.7 Macrophages after Nfatc1-Knockdown Elucidates Potential Pathways Involved in Osteoclasts Differentiation

Differentiation of macrophages toward osteoclasts is crucial for bone homeostasis but can be detrimental in disease states, including osteoporosis and cancer. Therefore, understanding the osteoclast differentiation process and the underlying regulatory mechanisms may facilitate the identification of new therapeutic targets. Hereby, we tried to reveal new miRNAs potentially involved in the regulation of early steps of osteoclastogenesis, with a particular focus on those possibly correlated with NFATc1 expression, by studying miRNAs profiling. During the first 24 h of osteoclastogenesis, 38 miRNAs were differentially expressed between undifferentiated and RANKL-stimulated RAW264.7 cells, while 10 miRNAs were differentially expressed between RANKL-stimulated cells transfected with negative control or NFATc1-siRNAs. Among others, the expression levels of miR-411, miR-144 and members of miR-29, miR-30, and miR-23 families changed after RANKL stimulation. Moreover, the potential role of miR-124 during osteoclastogenesis was explored by transient cell transfection with anti-miR-124 or miR-124-mimic. Two relatively unknown miRNAs, miR-880-3p and miR-295-3p, were differentially expressed between RANKL-stimulated/wild-type and RANKL-stimulated/NFATc1-silenced cells, suggesting their possible correlation with NFATc1. KEGG enrichment analyses showed that kinase and phosphatase enzymes were among the predicted targets for many of the studied miRNAs. In conclusion, our study provides new data on the potential role and possible targets of new miRNAs during osteoclastogenesis.

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

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

Novel Nanohydroxyapatite (nHAp)-Based Scaffold Doped with Iron Oxide Nanoparticles (IO), Functionalized with Small Non-Coding RNA (miR-21/124) Modulates Expression of Runt-Related Transcriptional Factor 2 and Osteopontin, Promoting Regeneration of Osteoporotic Bone in Bilateral Cranial Defects in a Senescence-Accelerated Mouse Model (SAM/P6). PART 2

Purpose

Healing of osteoporotic defects is challenging and requires innovative approaches to elicit molecular mechanisms promoting osteoblasts-osteoclasts coupling and bone homeostasis.

Methods

Cytocompatibility and biocompatibility of previously characterised nanocomposites, i.e Ca₅(PO₄)₃OH/Fe₃O₄ (later called nHAp/IO) functionalised with microRNAs (nHAp/IO@miR-21/124) was tested. In vitro studies were performed using a direct co-culture system of MC3T3-E1 pre-osteoblast and 4B12 pre-osteoclasts. The analysis included determination of nanocomposite influence on cultures morphology (confocal imaging), viability and metabolic activity (Alamar Blue assay). Pro-osteogenic signals were identified at mRNA, miRNA and protein level with RT-qPCR, Western blotting and immunocytochemistry. Biocompatibility of biomaterials was tested using bilateral cranial defect performed on a senescence-accelerated mouse model, ie SAM/P6 and Balb/c. The effect of biomaterial on the process of bone healing was monitored using microcomputed tomography.

Results

The nanocomposites promoted survival and metabolism of bone cells, as well as enhanced functional differentiation of pre-osteoblasts MC3T3-E1 in co-cultures with pre-osteoclasts. Differentiation of MC3T3-E1 driven by nHAp/IO@miR-21/124 nanocomposite was manifested by improved extracellular matrix differentiation and up-regulation of pro-osteogenic transcripts, ie late osteogenesis markers. The nanocomposite triggered bone healing in a cranial defect model in SAM/P6 mice and was replaced by functional bone in Balb/c mice.

Conclusion

This study demonstrates that the novel nanocomposite nHAp/IO can serve as a platform for therapeutic miRNA delivery. Obtained nanocomposite elicit pro-osteogenic signals, decreasing osteoclasts differentiation, simultaneously improving osteoblasts metabolism and their transition toward pre-osteocytes and bone mineralisation. The proposed scaffold can be an effective interface for in situ regeneration of osteoporotic bone, especially in elderly patients.

The role of stem cell-derived exosomes in the repair of cutaneous and bone tissue

Exosomes are extracellular vesicles secreted by various cell types, which play important roles in physiological processes. In particular, stem cell-derived exosomes have been shown to play crucial functions in intercellular communication during the tissue healing process. This review summarizes the effects of exosomes derived from different stem cell sources on the repair of cutaneous and bone tissue, focusing on the different pathways that could be involved in the regeneration process. The biogenesis, isolation, and content of exosomes have also been discussed. The effectiveness of exosomes is broadly demonstrated for skin and bone regeneration in animal models, supporting the basis for clinical translation of exosomes as a ready-to-use cell-free therapeutic for skin and bone regeneration.

miR-143-3p Inhibits the Differentiation of Osteoclast Induced by Synovial Fibroblast and Monocyte Coculture in Adjuvant-Induced Arthritic Rats

Osteoclast, which mediates overactive bone resorption, is one of the key factors for bone destruction in rheumatoid arthritis (RA). Existing studies have shown that abnormal miR-143-3p expression was observed in both RA patients and arthritis animals, which can participate in osteoclast differentiation, and mitogen-activated protein kinase (MAPK) signaling pathway was closely related to osteoclast differentiation. The primary objective of the current study was to determine the role of miR-143-3p in the progression of osteoclast differentiation and its relationship with MAPK signaling pathways. The results showed that miR-143-3p inhibited osteoclast differentiation and decreased the levels of M-CSF and RANKL during osteoclast differentiation. miR-143-3p inhibited the expression of MAPK signaling proteins, which is ERK1/2 in the early stage and JNK in the later stage of osteoclast differentiation. It was also observed that MAPK inhibitors upregulated miR-143-3p expression in osteoclast differentiation. Taken together, our results suggested that miR-143-3p could inhibit the differentiation of osteoclast, which was related to inhibiting MAPK signaling pathways. This may provide a novel strategy for curing RA.

GATA4-driven miR-206-3p signatures control orofacial bone development by regulating osteogenic and osteoclastic activity

Growth disorders in the orofacial bone development process may lead to orofacial deformities. The balance between bone matrix formation by mesenchymal lineage osteoblasts and bone resorption by osteoclasts is vital for orofacial bone development. Although the mechanisms of orofacial mesenchymal stem cells (OMSCs) in orofacial bone development have been studied intensively, the communication between OMSCs and osteoclasts remains largely unclear. Methods: We used a neural crest cell-specific knockout mouse model to investigate orofacial bone development in GATA-binding protein 4 (GATA4) morphants. We investigated the underlying mechanisms of OMSCs-derived exosomes (OMExos) on osteoclastogenesis and bone resorption activity in vitro. miRNAs were extracted from OMExos, and differences in miRNA abundances were determined using an Affymetrix miRNA array. Luciferase reporter assays were used to validate the binding between GATA4 and miR-206-3p in OMSCs and to confirm the putative binding of miR-206-3p and its target genes in OMSCs and osteoclasts. The regulatory mechanism of the GATA4-miR-206-3p axis in OMSC osteogenic differentiation and osteoclastogenesis was examined in vitro and in vivo. Results: Wnt1-Cre;Gata4^fl/fl mice (cKO) not only presented inhibited bone formation but also showed active bone resorption. Osteoclasts cocultured in vitro with cKO OMSCs presented an increased capacity for osteoclastogenesis, which was exosome-dependent. Affymetrix miRNA array analysis showed that miR-206-3p was downregulated in exosomes from shGATA4 OMSCs. Moreover, the transcriptional activity of miR-206-3p was directly regulated by GATA4 in OMSCs. We further demonstrated that miR-206-3p played a key role in the regulation of orofacial bone development by directly targeting bone morphogenetic protein-3 (Bmp3) and nuclear factor of activated T -cells, cytoplasmic 1 (NFATc1). OMExos and agomiR-206-3p enhanced bone mass in Wnt1-cre;Gata4^fl/fl mice by augmenting trabecular bone structure and decreasing osteoclast numbers. Conclusion: Our findings confirm that miR-206-3p is an important downstream factor of GATA4 that regulates the functions of OMSCs and osteoclasts. These results demonstrate the efficiency of OMExos and microRNA agomirs in promoting bone regeneration, which provide an ideal therapeutic tool for orofacial bone deformities in the future.

LncRNA Nron Inhibits Bone Resorption in Periodontitis

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

Regulation of Osteoclastogenesis and Bone Resorption by miRNAs

Osteoclasts are specialized bone-resorbing cells that contribute to physiological bone development and remodeling in bone metabolism throughout life. Abnormal production and activation of osteoclasts lead to excessive bone resorption in pathological conditions, such as in osteoporosis and in arthritic diseases with bone destruction. Recent epigenetic studies have shed novel insight into the dogma of the regulation of gene expression. microRNAs belong to a category of epigenetic regulators, which post-transcriptionally regulate and silence target gene expression, and thereby control a variety of biological events. In this review, we discuss miRNA biogenesis, the mechanisms utilized by miRNAs, several miRNAs that play important roles in osteoclast differentiation, function, survival and osteoblast-to-osteoclast communication, and their translational potential and challenges in bone biology and skeletal diseases.

Nanohydroxyapatite (nHAp) Doped with Iron Oxide Nanoparticles (IO), miR-21 and miR-124 Under Magnetic Field Conditions Modulates Osteoblast Viability, Reduces Inflammation and Inhibits the Growth of Osteoclast - A Novel Concept for Osteoporosis Treatment: Part 1

Purpose

Osteoporosis results in a severe decrease in the life quality of many people worldwide. The latest data shows that the number of osteoporotic fractures is becoming an increasing international health service problem. Therefore, a new kind of controllable treatment methods for osteoporotic fractures is extensively desired. For that reason, we have manufactured and evaluated nanohydroxyapatite (nHAp)-based composite co-doped with iron oxide (IO) nanoparticles. The biomaterial was used as a matrix for the controlled delivery of miR-21-5p and miR-124-3p, which have a proven impact on bone cell metabolism.

Methods

The nanocomposite Ca₅(PO₄)₃OH/Fe₃O₄ (later called nHAp/IO) was obtained by the wet chemistry method and functionalised with microRNAs (nHAp/IO@miR-21/124). Its physicochemical characterization was performed using XRPD, FT-IR, SEM-EDS and HRTEM and SAED methods. The modulatory effect of the composite was tested in vitro using murine pre-osteoblasts MC3T3-E1 and pre-osteoclasts 4B12. Moreover, the anti-inflammatory effects of biomaterial were analysed using a model of LPS-treated murine macrophages RAW 264.7. We have analysed the cells’ viability, mitochondria membrane potential and oxidative stress under magnetic field (MF+) and without (MF-). Moreover, the results were supplemented with RT-qPCR and Western blot assays to evaluate the expression profile for master regulators of bone metabolism.

Results

The results indicated pro-osteogenic effects of nHAp/IO@miR-21/124 composite enhanced by exposure to MF. The enhanced osteogenesis guided by nHAp/IO@miR-21/124 presence was associated with increased metabolism of progenitor cells and activation of osteogenic markers (Runx-2, Opn, Coll-1). Simultaneously, nanocomposite decreased metabolism and differentiation of pre-osteoclastic 4B12 cells accompanied by reduced expression of CaII and Ctsk. Obtained composite regulated viability of bone progenitor cells and showed immunomodulatory properties inhibiting the expression of inflammatory markers, ie, TNF-α, iNOs or IL-1β, in LPS-stimulated RAW 264.7 cells.

Conclusion

We have described for the first time a new concept of osteoporosis treatment based on nHAp/IO@miR-21/124 application. Obtained results indicated that fabricated nanocomposite might impact proper regeneration of osteoporotic bone, restoring the balance between osteoblasts and osteoclast.

Osteosarcoma-Derived Small Extracellular Vesicles Enhance Tumor Metastasis and Suppress Osteoclastogenesis by miR-146a-5p

Osteosarcoma is the most frequent type of primary bone tumor in children and adolescents, thus care for patients with malignant osteosarcoma is strongly required. The roles of small extracellular vesicles (SEVs) in enhancing metastases have been demonstrated in multiple tumors, but they are still poorly understood in osteosarcoma. Hence, this study investigated the effects of SEVs on progression and the tumor microenvironment in mice and patients. In an orthotopic implantation study, we found that osteosarcoma-derived SEVs had the potential to enhance metastases and angiogenesis. In addition, osteosarcoma-derived SEVs decreased the number of mature osteoclasts in vivo. In vitro osteoclastogenesis studies revealed that the inhibition of osteoclast maturation by osteosarcoma-derived SEVs was mediated by suppressing the NF-κB signal pathway. MicroRNA analysis of SEVs from different malignant human osteosarcomas revealed that miR-146a-5p was involved in the inhibition of osteoclastogenesis. In osteosarcoma patients, lower numbers of osteoclasts in biopsy specimens at the first visits were correlated with higher malignancy. These findings indicated that osteosarcoma-derived SEVs enhance distant metastasis of osteosarcomas by inhibiting osteoclast maturation, which may be a useful prognostic marker. This diagnostic method may enable to predict malignancy at early stage, and help to provide optimal care to patients with risk of high malignancy.

Circulating microRNAs Related to Bone Metabolism in HIV-Associated Bone Loss

The pathophysiology of human immunodeficiency virus (HIV)-associated bone loss is complex and to date largely unknown. In this study, we investigated serum expression of microRNAS (miRNAs) linked to bone metabolism in HIV-associated bone loss. This was a case-control study. Thirty male individuals with HIV infection (HIV+) and osteoporosis/osteopenia (HIV+/OP+) (cases) and 30 age-matched male HIV+ individuals with normal bone mass (HIV+/OP-) (controls) were included in the analysis. Thirty male individuals matched for age without HIV infection (HIV-), were also included as second controls. The selected panel of miRNAs was as follows: hsa-miRNA-21-5p; hsa-miRNA-23a-3p; hsa-miRNA-24-2-5p; hsa-miRNA-26a-5p; hsa-miRNA-29a-3p; hsa-miRNA-124-3p; hsa-miRNA-33a-5p; and hsa-miRNA-133a-3p. Within the cohort of HIV+ individuals, relative serum expression of miRNA-21-5p and miRNA-23a-3p was significantly lower (p < 0.001) while the expression of miRNA-24-2-5p was significantly higher (p = 0.030) in HIV+/OP+ compared to HIV+/OP-. Expression of miRNA-21-5p demonstrated a sensitivity of 84.6% and a specificity of 66.7 in distinguishing HIV+/OP+ individuals. Expression of circulating miRNAs related to bone metabolism; miRNA-23a-3p, miRNA-24-2-5p, and miRNA-21-5p is significantly altered in HIV+OP+ individuals, in line with data on other causes of osteoporosis, suggesting a common pattern of circulating miRNAs independent of the underlying cause.

The role of miR-150 regulates bone cell differentiation and function

BACKGROUND

mir-RNAs play a role in regulating bone homeostasis. In this study we assessed the functional role of mir-RNA 150 in bone homeostasis. We also assess the effects of miR-150 deficiency on osteoblast and osteoclast differentiation and function using in vivo and in vitro approaches.

METHODS

Wild type (WT) (C57BL/6J) and miR-150 KO mice were compared for a variety of parameters. Micro-CT imaging was conducted to quantify trabecular bone mass inferior to the distal growth plate of the femur. Von Kossa staining was performed for osteoblast culture mineralization. RT-qPCR, biochemical analysis and bone histomorphometry were utilized for quantification of relevant genes and serum protein measurements. Differentiation and function of osteoblasts and osteoclasts was performed using primarily cultures and assessed the cell autonomous response of mir-RNA-150 on cell differentiation and function.

RESULTS

Mir-150 exhibited expression in a variety of tissues and increases progressively with age. Through micro-CT imaging, we found that KO mice presented reduced bone mass at 4, 8, and 16 weeks of age compared to WT mice. Furthermore, histomorphometric analysis revealed increased trabecular separation, decreased bone thickness, and decreased osteoblast number in KO compared to WT mice. Mir-150 deficiency also correlated with higher bone resorption, accompanied with significant increases in CTX-1 serum levels, and a decrease in cell apoptotic rate ex vivo. Additionally, miR-150 KO mice showed increased osteoblast differentiation and decreased osteoclastogenesis ex vivo. Luciferase assay showed increased Osteoactivin/GPNMB expression in miR-150 KO osteoblasts compared to WT cells.

CONCLUSION

Our data suggests that miR-150 influences osteoblast and osteoclast functionality and differentiation; specifically, miR-150 serves as a negative regulator for osteoblasts and a positive regulator for osteoclasts by regulating, at least in part, Osteoactivin/GPNMB expression.

Isovaleric acid ameliorates ovariectomy-induced osteoporosis by inhibiting osteoclast differentiation

Osteoclasts (OCs) play important roles in bone remodelling and contribute to bone loss by increasing bone resorption activity. Excessively activated OCs cause diverse bone disorders including osteoporosis. Isovaleric acid (IVA), also known as 3-methylbutanoic acid is a 5-carbon branched-chain fatty acid (BCFA), which can be generated by bacterial fermentation of a leucine-rich diet. Here, we find that IVA suppresses differentiation of bone marrow-derived macrophages into OCs by RANKL. IVA inhibited the expression of OC-related genes. IVA-induced inhibitory effects on OC generation were attenuated by pertussis toxin but not by H89, suggesting a G_i -coupled receptor-dependent but protein kinase A-independent response. Moreover, IVA stimulates AMPK phosphorylation, and treatment with an AMPK inhibitor blocks IVA-induced inhibition of OC generation. In an ovariectomized mouse model, addition of IVA to the drinking water resulted in significant decrease of body weight gain and inhibited the expression of not only OC-related genes but also fusogenic genes in the bone tissue. IVA exposure also blocked bone destruction and OC generation in the bone tissue of ovariectomized mice. Collectively, the results demonstrate that IVA is a novel bioactive BCFA that inhibits OC differentiation, suggesting that IVA can be considered a useful material to control osteoclast-associated bone disorders, including osteoporosis.

4-Hexylresorcinol inhibits osteoclastogenesis by suppressing the NF-κB signaling pathway and reverses bone loss in ovariectomized mice

4-Hexylresorcinol (4HR) is a small organic compound that is widely used as an antiseptic and antioxidant. In the present study, its role in osteoclastogenesis was investigated. Bone marrow-derived macrophages from mice were used to examine the role of 4HR in osteogenesis. An ovariectomy (OVX) mouse model was constructed to examine the effect of 4HR in vivo, followed by hematoxylin and eosin and tartrate resistant acid phosphatase staining. In the present study, 4HR effectively suppressed receptor activator of NF-κB ligand-induced osteoclastogenesis in a dose-dependent manner. 4HR was also found to significantly suppress the expression of osteoclast (OC)-specific markers, including tartrate-resistant acid phosphatase, cathepsin K, nuclear factor of activated T-cell cytoplasmic 1 and c-Fos in the presence of RANKL in BMMs. Furthermore, 4HR inhibited osteoclastogenesis by inhibiting the activation of the NF-κB signaling pathway in BMMs. Consistent with the in vitro results, 4HR effectively ameliorated OVX-induced bone loss and markedly reduced OC number in the proximal tibia in vivo. In conclusion, the present results suggested that 4HR inhibited osteoclastogenesis in vitro and rescued bone loss in vivo, suggesting that 4HR may serve as a novel therapeutic agent for osteoporosis treatment.

miRNAs in osteoclast biology

MicroRNAs (miRNAs) are a class of short RNA molecules that mediate the regulation of gene activity through interactions with target mRNAs and subsequent silencing of gene expression. It has become increasingly clear the miRNAs regulate many diverse aspects of bone biology, including bone formation and bone resorption processes. The role of miRNAs specifically in osteoclasts has been of recent investigation, due to clinical interest in discovering new paradigms to control excessive bone resorption, as is observed in multiple conditions including aging, estrogen deprivation, cancer metastases or glucocorticoid use. Therefore understanding the role that miRNAs play during osteoclastic differentiation is of critical importance. In this review, we highlight and discuss general aspects of miRNA function in osteoclasts, including exciting data demonstrating that miRNAs encapsulated in extracellular vesicles (EVs) either originating from osteoclasts, or signaling to osteoclast from divergent sites, have important roles in bone homeostasis.

Polyketal Nanoparticles Co-Loaded With miR-124 and Ketoprofen for Treatment of Rheumatoid Arthritis

Ketoprofen, a non-steroidal anti-inflammatory drug, can effectively relieve pain associated with arthritis, and microRNA-124 (miR-124) can inhibit the progression of the disease. In this study, poly (cyclohexane-1,4-diylacetone dimethylene ketal) (PCADK) nanoparticles (NPs) co-loaded with ketoprofen and miR-124 were successfully prepared using an emulsified solvent evaporation method. The co-loaded NPs exhibited a mean particle diameter of 160 nm. The acid sensitivity of the NPs was determined through in vitro release experiments. An adjuvant-induced arthritis rat model of arthritis was established for evaluating the pharmacodynamics of the NPs through clinical scoring and degree of swelling. The PCADK NPs exhibited more potent pharmacodynamic effects owing to the acid-sensitive properties of the carrier materials, compared with Poly (lactic-co-glycolic acid) (PLGA) NPs. Furthermore, PCADK co-loaded NPs exhibited superior anti-inflammatory effects compared to NPs loaded with either miR-124 or ketoprofen alone. In conclusion, co-delivery of ketoprofen and miR-124 through NPs is a promising strategy for the treatment of arthritis.

Expression of Circulating MicroRNAs Linked to Bone Metabolism in Chronic Kidney Disease-Mineral and Bone Disorder

The pathophysiology of chronic kidney disease-mineral and bone disorder (CKD-MBD) is complex and multifactorial. Recent studies have identified a link between microRNAs (miRNAs) and bone loss. In this study, we investigated the expression of miRNAs in CKD-MBD. In this case-control study, we included thirty patients with CKD-MBD (cases) and 30 age- and gender-matched healthy individuals (controls). Bone mineral density (BMD) and trabecular bone score (TBS) evaluation was performed with dual X-ray absorptiometry. The selected panel of miRNAs included: hsa-miRNA-21-5p; hsa-miRNA-23a-3p; hsa-miRNA-24-2-5p; hsa-miRNA-26a-5p; hsa-miRNA-29a-3; hsa-miRNA-124-3p; hsa-miRNA-2861. The majority of cases had low BMD values. The relative expression of miRNA-21-5p was 15 times lower [fold regulation (FR): -14.7 ± 8.1, p = 0.034), miRNA-124-3p, 6 times lower (FR: -5.9 ± 4, p = 0.005), and miRNA-23a-3p, 4 times lower (FR: -3.8 ± 2.0, p = 0.036) in cases compared to controls. MiRNA-23a-3p was significantly and inversely correlated with TBS, adjusted for calcium metabolism and BMD values (beta = -0.221, p = 0.003, 95% CI -0.360, -0,081) in cases. In a receiver operating characteristic (ROC) analysis, expression of miRNA-124-3p demonstrated 78% sensitivity and 83% specificity in identifying CKD patents with osteoporosis. Serum expression of miRNAs related to osteoblasts (miRNA-23a-3p) and osteoclasts (miRNA-21-5p, miRNA-124-3p) is significantly altered in patients with CKD-MBD.

Involvement of circRNA_0007059 in the regulation of postmenopausal osteoporosis by promoting the microRNA-378/BMP-2 axis

Increasing evidence suggests that postmenopausal osteoporosis (PMO), a severe disturbance, imposes heavy physical, psychosocial, and financial burdens and dramatically influences the quality of life of postmenopausal women. Circular RNAs (circRNAs) and microRNAs (miRs) play important roles in the occurrence and development of PMO. However, the roles of circRNAs and miRs in osteoporosis regulation still need to be further investigated. circRNAs with different expression levels in patients with PMO were screened via RNA-seq and bioinformatics analysis. We found that circ_0007059 was upregulated in patients with PMO and during osteoclastogenesis of human bone marrow stromal cells (hBMSCs). Next, we investigated the effect of circ_0007059 overexpression during osteoclastogenesis of hBMSCs. circ_0007059 overexpression attenuated hBMSC differentiation into osteoclasts in vitro. This was demonstrated by downregulated bone morphogenetic protein 2 (BMP-2) expression, upregulated osteoclast-specific gene expression, and TRAP staining. circ_0007059 was demonstrated to directly target miR-378, which in turn targeted BMP-2 via bioinformatics analysis and the dual-luciferase reporter assay. Transfection of the miR-378 mimic reversed the effect of circ_0007059 on the osteoclastogenesis of hBMSCs. These results suggest that circ_0007059 plays an important role in osteoclastogenesis via the miR-378/BMP-2 signaling pathway. Targeting the circ_0007059/miR-378/BMP-2 axis is possibly a novel idea in osteoporosis treatment.

Sphingosylphosphorylcholine blocks ovariectomy-induced bone loss by suppressing Ca2+ /calmodulin-mediated osteoclast differentiation

Osteoporosis is a disease in which bone mineral density decreases due to abnormal activity of osteoclasts, and is commonly found in post‐menopausal women who have decreased levels of female hormones. Sphingosylphosphorylcholine (SPC) is an important biological lipid that can be converted to sphingosine‐1‐phosphate (S1P) by autotaxin. S1P is known to be involved in osteoclast activation by stimulating osteoblasts, but bone regulation by SPC is not well understood. In this study, we found that SPC strongly inhibits RANKL‐induced osteoclast differentiation. SPC‐induced inhibitory effects on osteoclast differentiation were not affected by several antagonists of S1P receptors or pertussis toxin, suggesting cell surface receptor independency. However, SPC inhibited RANKL‐induced calcineurin activation and subsequent NFATc1 activity, leading to decrease of the expression of Trap and Ctsk. Moreover, we found that bone loss in an experimental osteoporosis mouse model was recovered by SPC injection. SPC also blocked ovariectomy‐induced body weight increase and Nfatc1 gene expression in mice. We also found that SPC inhibits RANKL‐induced osteoclast differentiation in human macrophages. Since currently available treatments for osteoporosis, such as administration of female hormones or hormone receptor modulators, show serious side effects, SPC has potential as a new agent for osteoporosis treatment.

Role of MicroRNAs in Bone Pathology during Chikungunya Virus Infection

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

Exosomes as a Novel Approach to Reverse Osteoporosis: A Review of the Literature

Osteoporosis is a chronic disease requiring long-term, sometimes lifelong, management. With the aging population, the prevalence of osteoporosis is increasing, and with it so is the risk of hip fracture and subsequent poor quality of life and higher mortality. Current therapies for osteoporosis have various significant side effects limiting patient compliance and use. Recent evidence has demonstrated the significant role of exosomes in osteoporosis both in vivo and in vitro. In this review, we summarize the pathogenesis of senile osteoporosis, highlight the properties and advantages of exosomes, and explore the recent literature on the use of exosomes in osteogenesis regulation. This is a very helpful review as several exosomes-based therapeutics have recently entered clinical trials for non-skeletal applications, such as pancreatic cancer, renal transplantation, and therefore it is urgent for bone researchers to explore whether exosomes can become the next class of orthobiologics for the treatment of osteoporosis.

Involvement of Noncoding RNAs in the Differentiation of Osteoclasts

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

NF-κB promotes osteoclast differentiation by overexpressing MITF via down regulating microRNA-1276 expression

BACKGROUND

Nuclear factor-kappa B (NF-κB) is an important nuclear transcription factor in cells, involving in a series of processes such as cell proliferation, apoptosis, and differentiation. In this study, we explored the specific mechanism of NF-κB on the differentiation of osteoclasts.

METHODS

MicroRNAs (miRNAs) expression microarray data GSE105027 related to osteoarthritis was obtained to screen out the differentially expressed miRNA. Phorbol-12-myristate-13-acetate (PMA) was used to induce THP-1 cells to differentiate into macrophages, followed by induction to osteoclasts using macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). ELISA and RT-qPCR were conducted to examine IL-6 and IL-1β expression. The binding of NF-κB to the miR-1276 promoter region was demonstrated by ChIP assay, and targeting relationship between miR-1276 and MITF was verified by dual luciferase reporter assay. KK, iKBα, NF-kB, p-IKK, p-iKBα, p-NF-kB expression was analyzed by western blot. NF-κB and miR-1276 expression in osteoclasts was examined later. After gain- and less-of-function study, the effects on osteoclast differentiation were detected by TRAP-positive osteoclasts, TRAP activity, TRAP-5b content, F-Actin expression, as well as osteoclast differentiation marker genes expression.

RESULTS

NF-κB was activated in osteoclasts, and down-regulation of NF-κB inhibited osteoclast differentiation. Next, miR-1276 was downregulated in osteoclasts after differentiation from monocytes. Meanwhile, NF-κB decreased the expression of miR-1276 by binding to the miR-1276 promoter, thereby elevating MITF expression, thereby promoting osteoclast differentiation.

CONCLUSION

In summary, NF-κB promoted osteoclast differentiation through downregulating miR-1276 to upregulate MITF.

Osteoclast Signal Transduction During Bone Metastasis Formation

Osteoclasts are myeloid lineage-derived bone-resorbing cells of hematopoietic origin. They differentiate from myeloid precursors through a complex regulation process where the differentiation of preosteoclasts is followed by intercellular fusion to generate large multinucleated cells. Under physiological conditions, osteoclastogenesis is primarily directed by interactions between CSF-1R and macrophage colony-stimulating factor (M-CSF, CSF-1), receptor activator of nuclear factor NF-κB (RANK) and RANK ligand (RANKL), as well as adhesion receptors (e.g., integrins) and their ligands. Osteoclasts play a central role in physiological and pathological bone resorption and are also required for excessive bone loss during osteoporosis, inflammatory bone and joint diseases (such as rheumatoid arthritis) and cancer cell-induced osteolysis. Due to the major role of osteoclasts in these diseases the better understanding of their intracellular signaling pathways can lead to the identification of potential novel therapeutic targets. Non-receptor tyrosine kinases and lipid kinases play major roles in osteoclasts and small-molecule kinase inhibitors are emerging new therapeutics in diseases with pathological bone loss. During the last few years, we and others have shown that certain lipid (such as phosphoinositide 3-kinases PI3Kβ and PI3Kδ) and tyrosine (Src−family and Syk) kinases play a critical role in osteoclast differentiation and function in humans and mice. Some of these signaling pathways shows similarity to immunoreceptor-like receptor signaling and involves important other enzymes (e.g., PLCγ2) and adapter proteins (such as the ITAM−bearing adapters DAP12 and the Fc-receptor γ-chain). Here, we review recently identified osteoclast signaling pathways and their role in osteoclast differentiation and function as well as pathological bone loss associated with osteolytic tumors of the bone. A better understanding of osteoclast signaling may facilitate the design of novel and more efficient therapies for pathological bone resorption and osteolytic skeletal metastasis formation.

Age-related increase of kynurenine enhances miR29b-1-5p to decrease both CXCL12 signaling and the epigenetic enzyme Hdac3 in bone marrow stromal cells

Mechanisms leading to age-related reductions in bone formation and subsequent osteoporosis are still incompletely understood. We recently demonstrated that kynurenine (KYN), a tryptophan metabolite, accumulates in serum of aged mice and induces bone loss. Here, we report on novel mechanisms underlying KYN's detrimental effect on bone aging. We show that KYN is increased with aging in murine bone marrow mesenchymal stem cells (BMSCs). KYN reduces bone formation via modulating levels of CXCL12 and its receptors as well as histone deacetylase 3 (Hdac3). BMSCs responded to KYN by significantly decreasing mRNA expression levels of CXCL12 and its cognate receptors, CXCR4 and ACKR3, as well as downregulating osteogenic gene RUNX2 expression, resulting in a significant inhibition in BMSCs osteogenic differentiation. KYN's effects on these targets occur by increasing regulatory miRNAs that target osteogenesis, specifically miR29b-1-5p. Thus, KYN significantly upregulated the anti-osteogenic miRNA miR29b-1-5p in BMSCs, mimicking the up-regulation of miR-29b-1-5p in human and murine BMSCs with age. Direct inhibition of miR29b-1-5p by antagomirs rescued CXCL12 protein levels downregulated by KYN, while a miR29b-1-5p mimic further decreased CXCL12 levels. KYN also significantly downregulated mRNA levels of Hdac3, a target of miR-29b-1-5p, as well as its cofactor NCoR1. KYN is a ligand for the aryl hydrocarbon receptor (AhR). We hypothesized that AhR mediates KYN's effects in BMSCs. Indeed, AhR inhibitors (CH-223191 and 3',4'-dimethoxyflavone [DMF]) partially rescued secreted CXCL12 protein levels in BMSCs treated with KYN. Importantly, we found that treatment with CXCL12, or transfection with an miR29b-1-5p antagomir, downregulated the AhR mRNA level, while transfection with miR29b-1-5p mimic significantly upregulated its level. Further, CXCL12 treatment downregulated IDO, an enzyme responsible for generating KYN. Our findings reveal novel molecular pathways involved in KYN's age-associated effects in the bone microenvironment that may be useful translational targets for treating osteoporosis.

LncRNA Nron regulates osteoclastogenesis during orthodontic bone resorption

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

Early-onset preeclampsia, plasma microRNAs, and endothelial cell function

BACKGROUND

Preeclampsia is a hypertensive pregnancy disorder in which generalized systemic inflammation and maternal endothelial dysfunction are involved in the pathophysiology. MiRNAs are small noncoding RNAs responsible for post-transcriptional regulation of gene expression and involved in many physiological processes. They mainly downregulate translation of their target genes.

OBJECTIVE

We aimed to compare the plasma miRNA concentrations in preeclampsia, healthy pregnant women, and nonpregnant women. Furthermore, we aimed to evaluate the effect of 3 highly increased plasma miRNAs in preeclampsia on endothelial cell function in vitro.

STUDY DESIGN

We compared 3391 (precursor) miRNA concentrations in plasma samples from early-onset preeclamptic women, gestational age-matched healthy pregnant women, and nonpregnant women using miRNA 3.1. arrays (Affymetrix) and validated our findings by real-time quantitative polymerase chain reaction. Subsequently, endothelial cells (human umbilical vein endothelial cells) were transfected with microRNA mimics (we choose the 3 miRNAs with the greatest fold change and lowest false-discovery rate in preeclampsia vs healthy pregnancy). After transfection, functional assays were performed to evaluate whether overexpression of the microRNAs in endothelial cells affected endothelial cell function in vitro. Functional assays were the wound-healing assay (which measures cell migration and proliferation), the proliferation assay, and the tube-formation assay (which assesses formation of endothelial cell tubes during the angiogenic process). To determine whether the miRNAs are able to decrease gene expression of certain genes, RNA was isolated from transfected endothelial cells and gene expression (by measuring RNA expression) was evaluated by gene expression microarray (Genechip Human Gene 2.1 ST arrays; Life Technologies). For the microarray, we used pooled samples, but the differently expressed genes in the microarray were validated by real-time quantitative polymerase chain reaction in individual samples.

RESULTS

No significant differences (fold change <-1.2 or >1.2 with a false-discovery rate <0.05) were found in miRNA plasma concentrations between healthy pregnant and nonpregnant women. The plasma concentrations of 26 (precursor) miRNAs were different between preeclampsia and healthy pregnancy. The 3 miRNAs that were increased with the greatest fold change and lowest false-discovery rate in preeclampsia vs healthy pregnancy were miR-574-5p, miR-1972, and miR-4793-3p. Transfection of endothelial cells with these miRNAs in showed that miR-574-5p decreased (P<.05) the wound-healing capacity (ie, decreased endothelial cell migration and/or proliferation) and tended (P<.1) to decrease proliferation, miR-1972 decreased tube formation (P<.05), and also tended (P<.1) to decrease proliferation, and miR-4793-3p tended (P<.1) to decrease both the wound-healing capacity and tube formation in vitro. Gene expression analysis of transfected endothelial cells revealed that miR-574-5p tended (P<.1) to decrease the expression of the proliferation marker MKI67.

CONCLUSION

We conclude that in the early-onset preeclampsia group in our study different concentrations of plasma miRNAs are present as compared with healthy pregnancy. Our results suggest that miR-574-5p and miR-1972 decrease the proliferation (probably via decreasing MKI67) and/or migration as well as the tube-formation capacity of endothelial cells. Therefore, these miRNAs may be antiangiogenic factors affecting endothelial cells in preeclampsia.

High-Throughput Fluorescence-Based Screen Identifies the Neuronal MicroRNA miR-124 as a Positive Regulator of Alphavirus Infection

MicroRNAs (miRNAs) are small regulatory RNAs which act by modulating the expression of target genes. In addition to their role in maintaining essential physiological functions in the cell, miRNAs can also regulate viral infections. They can do so directly by targeting RNAs of viral origin or indirectly by targeting host mRNAs, and this can result in a positive or negative outcome for the virus. Here, we performed a fluorescence-based miRNA genome-wide screen in order to identify cellular miRNAs involved in the regulation of arbovirus infection in human cells. We identified 16 miRNAs showing a positive effect on Sindbis virus (SINV) expressing green fluorescent protein (GFP), among which were a number of neuron-specific ones such as miR-124. We confirmed that overexpression of miR-124 increases both SINV structural protein translation and viral production and that this effect is mediated by its seed sequence. We further demonstrated that the SINV genome possesses a binding site for miR-124. Both inhibition of miR-124 and silent mutations to disrupt this binding site in the viral RNA abolished positive regulation. We also proved that miR-124 inhibition reduces SINV infection in human differentiated neuronal cells. Finally, we showed that the proviral effect of miR-124 is conserved in other alphaviruses, as its inhibition reduces chikungunya virus (CHIKV) production in human cells. Altogether, our work expands the panel of positive regulation of the viral cycle by direct binding of host miRNAs to the viral RNA and provides new insights into the role of cellular miRNAs as regulators of alphavirus infection.IMPORTANCE Arthropod-borne (arbo) viruses are part of a class of pathogens that are transmitted to their final hosts by insects. Because of climate change, the habitat of some of these insects, such as mosquitoes, is shifting, thereby facilitating the emergence of viral epidemics. Among the pathologies associated with arbovirus infection, neurological diseases such as meningitis and encephalitis represent a significant health burden. Using a genome-wide miRNA screen, we identified neuronal miR-124 as a positive regulator of the Sindbis and chikungunya alphaviruses. We also showed that this effect was in part direct, thereby opening novel avenues to treat alphavirus infections.

Denosumab inhibits MCF-7 cell line-induced spontaneous osteoclastogenesis via the RANKL/MALAT1/miR-124 axis

Background

Denosumab is an inhibitor of receptor activator of NF-κB ligand (RANKL), which inhibits bone metastasis (BM) in breast cancer (BC), but does not completely control cancer cell BM in some BC patients. This study was designed to study whether denosumab inhibits human BC cells (MCF-7) cell line-induced spontaneous osteoclastogenesis via RANKL/metastasis-associated lung adenocarcinoma transcript 1 (MALAT1)/miR-124 axis.

Methods

We established a co-culture system of MCF-7-induced spontaneous osteoclastogenesis in RAW 264.7 cells, and denosumab is added into the co-culture system to inhibit RAW 264.7 cell differentiation into osteoclasts. Real-time PCR (RT-PCR), immunofluorescence and western blotting analysis were used to detect gene expression, while tartrate-resistant acid phosphatase (TRAP) staining was used to assess osteoclast formation.

Results

Denosumab inhibits MCF-7 cell line-induced spontaneous osteoclastogenesis, and the inhibition of denosumab was found to be more pronounced after MALAT1 downregulation and miR-124 overexpression. However, MALAT1 knockdown or miR-124 overexpression did not alter RANKL protein expression. Moreover, the dual luciferase gene reporter system showed that miR-124 targeted the inhibition of MALAT1, while si-MALAT1 upregulated miR-124 expression. miR-124-mimics were able to decrease the expression of Rab27a, IL-11, activated T-cell nuclear factor 1 (NFATc1) and TARP protein.

Conclusions

Denosumab inhibits MALAT1 expression by inhibiting RANKL, thereby upregulating miR-124 expression, which ultimately inhibits MCF-7 cell line-induced pseudo osteoclastogenesis.

MicroRNA Alterations for Diagnosis, Prognosis, and Treatment of Osteoporosis: A Comprehensive Review and Computational Functional Survey

Osteoporosis (OP) is a systemic bone disease with a series of clinical symptoms. The use of screening biomarkers in OP management is therefore of clinical significance, especially in the era of precision medicine and intelligent healthcare. MicroRNAs (miRNAs) are small, non-coding RNAs with the potential to regulate gene expression at the post-transcriptional level. Accumulating evidence indicates that miRNAs may serve as biomarkers for OP prediction and prevention. However, few studies have emphasized the role of miRNAs in systems-level pathogenesis during OP development. In this article, literature-reported OP miRNAs were manually collected and analyzed based on a systems biology paradigm. Functional enrichment studies were performed to decode the underlying mechanisms of miRNAs in OP etiology and therapeutics in three-dimensional space, i.e., integrated miRNA–gene–pathway analysis. In particular, interactions between miRNAs and three well-known OP pathways, i.e., estrogen–endocrine, WNT/β-catenin signaling, and RANKL/RANK/OPG, were systematically investigated, and the effects of non-genetic factors on personalized OP prevention and therapy were discussed. This article is a comprehensive review of OP miRNAs, and bridges the gap between an understanding of OP pathogenesis and clinical translation.

Osteoclastogenesis in periodontal diseases: Possible mediators and mechanisms

BACKGROUND

Periodontitis is the inflammation of the tooth-supporting structures and is one of the most common diseases of the oral cavity. The outcome of periodontal infections is tooth loss due to a lack of alveolar bone support. Osteoclasts are giant, multi-nucleated, and bone-resorbing cells that are central for many osteolytic diseases, including periodontitis. Receptor activator of nuclear factor-kB ligand (RANKL) is the principal factor involved in osteoclast differentiation, activation, and survival. However, under pathological conditions, a variety of pro-inflammatory cytokines secreted by activated immune cells also contribute to osteoclast differentiation and activity. Lipopolysaccharide (LPS) is a vital component of the outer membrane of the Gram-negative bacteria. It binds to the Toll-like receptors (TLRs) expressed in many cells and elicits an immune response.

HIGHLIGHTS

The presence of bacterial LPS in the periodontal area stimulates the secretion of RANKL as well as other inflammatory mediators, activating the process of osteoclastogenesis. RANKL, either independently or synergistically with LPS, can regulate osteoclastogenesis, while LPS alone cannot. MicroRNA, IL-22, M1/M2 macrophages, and memory B cells have recently been shown to modulate osteoclastogenesis in periodontal diseases.

CONCLUSION

In this review, we summarize the mechanism of osteoclastogenesis accompanying periodontal diseases at the cellular level. We discuss a) the effects of LPS/TLR signaling and other cytokines on RANKL-dependent and -independent mechanisms involved in osteoclastogenesis; b) the recently identified role of several endogenous factors such as miRNA, IL-22, M1/M2 macrophages, and memory B cells in regulating osteoclastogenesis during periodontal pathogenesis.

IL-17 promotes osteoblast differentiation, bone regeneration, and remodeling in mice

Bone homeostasis is maintained by concerted actions of bone-forming osteoblasts and bone-resorbing osteoclasts. A wide range of evidence indicates that a proinflammatory cytokine IL-17 promotes osteoclastogenesis. However, the role of IL-17 in osteoblasts is less well-understood. In the current study, the effect of IL-17 on osteogenic differentiation was investigated in mouse calvarial cells. IL-17 stimulated osteoblast differentiation, mineralization, proliferation, motility, and osteoblast-dependent osteoclastogenesis in vitro. The pro-osteogenic role of IL-17 was dependent on Act1 and the generation of reactive oxygen species. In a critical size calvarial defect model, IL-17 significantly augmented bone regeneration. Importantly, IL-17 also remarkably increased bone remodeling and restored osteoclastogenesis in zoledronate-treated mice. Furthermore, IL-17 conspicuously stimulated the formation of lamellar bones. These data not only provide a clue to understand the role of IL-17 in bone metabolism but also suggest possible applications in bone augmentation therapies.

Systemic investigation of bone and muscle abnormalities in dystrophin/utrophin double knockout mice during postnatal development and the mechanisms

The dystrophin-/-/utrophin-/-/ double knockout (dKO-Hom) mouse is a murine model of human Duchenne muscular dystrophy. This study investigated the bone and muscle abnormalities of dKO-Hom mouse and mechanisms. We collected bone and skeletal muscle samples from control mice and three muscular dystrophic mouse models at different ages and performed micro-computer tomography and histological analyses of both bone and skeletal muscle tissues. Serum receptor activator of nuclear factor kappa-Β ligand (RANKL) and sclerostin (SOST) levels, osteoclastogenesis and serum proteomics were also analyzed. Our results indicated that dKO-Hom mice developed skeletal muscle histopathologies by 5 days of age, whereas bone abnormalities developed at 4 weeks of age. Furthermore, our results indicated that the numbers of osteoblasts and osteoclasts were decreased in the proximal tibia and spine trabecular bone of dKO-Hom mice compared to wild-type (WT) mice, which correlated with a significant reduction in serum RANKL levels. The number of tibia cortical osteocytes also decreased, whereas serum SOST levels increased significantly in dKO-Hom mice than WT mice. Osteoblastic number was significantly lower, but osteoclast number increased, in the spine L6 of dKO-Hom mice than WT mice at 6 weeks of age, resulting in a decrease in bone formation and an increase in bone resorption. Serum proteomics results revealed abnormal proteome profiles in dKO-Hom mice compared to control mice. In conclusion, our study elucidated the timing of development of bone and muscle abnormalities. The bone abnormalities in dKO-Hom mice are correlated with lower serum RANKL and higher SOST levels that resulted in dysregulation of osteogenesis and osteoclastogenesis and bone loss.

Cationic Polymer Nanoparticles-Mediated Delivery of miR-124 Impairs Tumorigenicity of Prostate Cancer Cells

MicroRNAs (miRNAs) play a pivotal role in regulating the expression of genes involved in tumor development, invasion, and metastasis. In particular, microRNA-124 (miR-124) modulates the expression of carnitine palmitoyltransferase 1A (CPT1A) at the post-transcriptional level, impairing the ability of androgen-independent prostate cancer (PC3) cells to completely metabolize lipid substrates. However, the clinical translation of miRNAs requires the development of effective and safe delivery systems able to protect nucleic acids from degradation. Herein, biodegradable polyethyleneimine-functionalized polyhydroxybutyrate nanoparticles (PHB-PEI NPs) were prepared by aminolysis and used as cationic non-viral vectors to complex and deliver miR-124 in PC3 cells. Notably, the PHB-PEI NPs/miRNA complex effectively protected miR-124 from RNAse degradation, resulting in a 30% increase in delivery efficiency in PC3 cells compared to a commercial transfection agent (Lipofectamine RNAiMAX). Furthermore, the NPs-delivered miR-124 successfully impaired hallmarks of tumorigenicity, such as cell proliferation, motility, and colony formation, through CPT1A modulation. These results demonstrate that the use of PHB-PEI NPs represents a suitable and convenient strategy to develop novel nanomaterials with excellent biocompatibility and high transfection efficiency for cancer therapy.

High bone microarchitecture, strength, and resistance to bone loss in MRL/MpJ mice correlates with activation of different signaling pathways and systemic factors

The MRL/MpJ mice have demonstrated an enhanced tissue regeneration capacity for various tissues. In the present study, we systematically characterized bone microarchitecture and found that MRL/MpJ mice exhibit higher bone microarchitecture and strength compared to both C57BL/10J and C57BL/6J WT mice at 2, 4, and 10 months of age. The higher bone mass in MRL/MpJ mice was correlated to increased osteoblasts, decreased osteoclasts, higher cell proliferation, and bone formation, and enhanced pSMAD5 signaling earlier during postnatal development (2-month old) in the spine trabecular bone, and lower bone resorption rate at later age. Furthermore, these mice exhibit accelerated fracture healing via enhanced pSMAD5, pAKT and p-P38MAPK pathways compared to control groups. Moreover, MRL/MpJ mice demonstrated resistance to ovariectomy-induced bone loss as evidenced by maintaining higher bone volume/tissue volume (BV/TV) and lower percentage of bone loss later after ovariectomy. The consistently higher serum IGF1 level and lower RANKL level in MRL/MpJ mice may contribute to the maintenance of high bone mass in uninjured and injured bone. In conclusion, our results indicate that enhanced pSMAD5, pAKT, and p-P38MAPK signaling, higher serum IGF-1, and lower RANKL level contribute to the higher bone microarchitecture and strength, accelerated healing, and resistance to osteoporosis in MRL/MpJ mice.