MicroRNA-194 reciprocally stimulates osteogenesis and inhibits adipogenesis via regulating COUP-TFII expression

MicroRNAs and their Modulatory Effect on the Hallmarks of Osteosarcopenia

PURPOSE OF THE REVIEW

Osteosarcopenia is a geriatric syndrome associated with disability and mortality. This review summarizes the key microRNAs that regulate the hallmarks of sarcopenia and osteoporosis. Our objective was to identify components similarly regulated in the pathology and have therapeutic potential by influencing crucial cellular processes in both bone and skeletal muscle.

RECENT FINDINGS

The simultaneous decline in bone and muscle in osteosarcopenia involves a complex crosstalk between these tissues. Recent studies have uncovered several key mechanisms underlying this condition, including the disruption of cellular signaling pathways that regulate bone remodeling and muscle function and regeneration. Accordingly, emerging evidence reveals that dysregulation of microRNAs plays a significant role in the development of each of these hallmarks of osteosarcopenia. Although the recent recognition of osteosarcopenia as a single diagnosis of bone and muscle deterioration has provided new insights into the mechanisms of these underlying age-related diseases, several knowledge gaps have emerged, and a deeper understanding of the role of common microRNAs is still required. In this study, we summarize current evidence on the roles of microRNAs in the pathogenesis of osteosarcopenia and identify potential microRNA targets for treating this condition. Among these, microRNAs-29b and -128 are upregulated in the disease and exert adverse effects by inhibiting IGF-1 and SIRT1, making them potential targets for developing inhibitors of their activity. MicroRNA-21 is closely associated with the occurrence of muscle and bone loss. Conversely, microRNA-199b is downregulated in the disease, and its reduced activity may be related to increased myostatin and GSK3β activity, presenting it as a target for developing analogues that restore its function. Finally, microRNA-672 stands out for its ability to protect skeletal muscle and bone when expressed in the disease, highlighting its potential as a possible therapy for osteosarcopenia.

NR2F2 Reactivation in Early-life Adipocyte Stem-like Cells Rescues Adipocyte Mitochondrial Oxidation

In humans, perinatal exposure to an elevated omega-6 (n6) relative to omega-3 (n3) Fatty Acid (FA) ratio is associated with the likelihood of childhood obesity. In mice, we show perinatal exposure to excessive n6-FA programs neonatal Adipocyte Stem-like cells (ASCs) to differentiate into adipocytes with lower mitochondrial nutrient oxidation and a propensity for nutrient storage. Omega-6 FA exposure reduced fatty acid oxidation (FAO) capacity, coinciding with impaired induction of beige adipocyte regulatory factors PPARγ, PGC1α, PRDM16, and UCP1. ASCs from n6-FA exposed pups formed adipocytes with increased lipogenic genes in vitro, consistent with an in vivo accelerated adipocyte hypertrophy, greater triacylglyceride accumulation, and increased % body fat. Conversely, n6-FA exposed pups had impaired whole animal 13 C-palmitate oxidation. The metabolic nuclear receptor, NR2F2, was suppressed in ASCs by excess n6-FA intake preceding adipogenesis. ASC deletion of NR2F2, prior to adipogenesis, mimicked the reduced FAO capacity observed in ASCs from n6-FA exposed pups, suggesting that NR2F2 is required in ASCs for robust beige regulator expression and downstream nutrient oxidation in adipocytes. Transiently re-activating NR2F2 with ligand prior to differentiation in ASCs from n6-FA exposed pups, restored their FAO capacity as adipocytes by increasing the PPARγ-PGC1α axis, mitochondrial FA transporter CPT1A, ATP5 family synthases, and NDUF family Complex I proteins. Our findings suggest that excessive n6-FA exposure early in life dampens an NR2F2-mediated induction of beige adipocyte regulators, resulting in metabolic programming that is shifted towards nutrient storage.

STUB1 increases adiponectin expression by inducing ubiquitination and degradation of NR2F2, thereby reducing hepatic stellate cell activation and alleviating non-alcoholic fatty liver disease

BACKGROUND

Adiponectin (APN) has exhibited ameliorating effects on non-alcoholic fatty liver disease (NAFLD). This study investigates the roles of APN and its regulatory molecules in hepatic stellate cell (HSC) activation and the progression of NAFLD.

METHODS

Mice were subjected to a high-fat diet (HFD) to establish NAFLD models. Liver tissue was examined for lipid metabolism, fibrosis, and inflammation. Mouse 3T3-L1 adipocytes were exposed to palmitic acid (PA) to mimic a high-fat environment. The conditioned medium (CM) from adipocytes was collected for the culture of isolated mouse HSCs. Gain- or loss-of-function studies of APN, nuclear receptor subfamily 2 group F member 2 (NR2F2), and STIP1 homology and U-box containing protein 1 (STUB1) were performed to analyze their roles in NAFLD and HSC activation in vivo and in vitro.

RESULTS

APN expression was poorly expressed in HFD-fed mice and PA-treated 3T3-L1 adipocytes, which was attributed to the transcription inhibition mediated by NR2F2. Silencing of NR2F2 restored the APN expression, ameliorating liver steatosis, fibrosis, and inflammatory cytokine infiltration in mouse livers and reducing HSC activation. Similarly, the NR2F2 silencing condition reduced HSC activation in vitro. However, these effects were counteracted by artificial APN silencing. STUB1 facilitated the ubiquitination and protein degradation of NR2F2, and its upregulation mitigated NAFLD-like symptoms in mice and HSC activation, effects reversed by the NR2F2 overexpression.

CONCLUSION

This study highlights the role of STUB1 in reducing HSC activation and alleviating NAFLD by attenuating NR2F2-mediated transcriptional repression of APN.

Deciphering adipose development: Function, differentiation and regulation

The overdevelopment of adipose tissues, accompanied by excess lipid accumulation and energy storage, leads to adipose deposition and obesity. With the increasing incidence of obesity in recent years, obesity is becoming a major risk factor for human health, causing various relevant diseases (including hypertension, diabetes, osteoarthritis and cancers). Therefore, it is of significance to antagonize obesity to reduce the risk of obesity-related diseases. Excess lipid accumulation in adipose tissues is mediated by adipocyte hypertrophy (expansion of pre-existing adipocytes) or hyperplasia (increase of newly-formed adipocytes). It is necessary to prevent excessive accumulation of adipose tissues by controlling adipose development. Adipogenesis is exquisitely regulated by many factors in vivo and in vitro, including hormones, cytokines, gender and dietary components. The present review has concluded a comprehensive understanding of adipose development including its origin, classification, distribution, function, differentiation and molecular mechanisms underlying adipogenesis, which may provide potential therapeutic strategies for harnessing obesity without impairing adipose tissue function.

Expression Analysis of circRNAs in Human Adipogenesis

Purpose

Adipogenesis is one of the major pathways for generating obesity or overweight that can cause a range of metabolic disorders. Circular RNAs (circRNAs), a specific type of RNAs, have a significant influence on metabolic disorders. This study aims to find differentially expressed circRNAs (DECs) during human subcutaneous adipose tissue (SATs) adipogenesis.

Patients and Methods

The human adipose tissue-derived stromal cells (hADSCs) were isolated from human SATs (n = 3), and then induced into adipocytes. Total RNAs were extracted from hADSCs and adipocytes, and he DECs were detected using circRNA microarray. The GO and KEGG pathways of DECs were analyzed by bioinformatic methods, and partial DECs were further validated by quantitative polymerase chain reaction (qPCR).

Results

Our study detected a total of 1987 DECs, among which, 1134 were found upregulated and 853 were downregulated. GO analysis showed that the upregulated DECs have catalytic activity in intracellular organelle and cytoplasms, whereas downregulated DECs are enriched in organelle lumen, and are involved in positive regulation of developmental process. In addition, pathway results demonstrated that upregulated DECs are involved in platinum drug resistance and cellular senescence, and downregulated DECs are enriched in proteoglycans in cancer and focal adhesion pathway. Two circRNAs, namely has_circ_0001600 and has_circ_0001947 were validated to be significantly upregulated in adipocytes compared to hADSCs.

Conclusion

Our study explored DECs between hADSCs derived from SATs and adipocytes, and report that two circRNAs named has_circ_0001600 and has_circ_0001947 might be important factors involved in human adipogenesis, however, the molecular mechanism should be further explored.

Plasma Circular-RNA 0005567 as a Potential Marker of Disease Activity in Rheumatoid Arthritis

Circular RNAs (circRNAs) are noncoding molecules and are generated through back splicing, during which the 5' and 3' ends are covalently joined. Consequently, the lack of free ends makes them stable and resistant to exonucleases, and they become more suitable biomarkers than other noncoding RNAs. The aim of the study was to find an association between selected circRNAs and disease activity in patients with RA. A total of 71 subjects, 45 patients with RA and 26 healthy controls (HCs), were enrolled. In the RA group, 24 patients had high disease activity (DAS-28-ESR > 5.1) and 21 individuals were in remission (DAS-28-ESR ≤ 2.6). The cell line SW982 was used to evaluate the biological function of circ_0005567. The concentration of circ_0005567 in RA patients was elevated compared to HCs (median, 177.5 [lower-upper quartile, 83.13-234.6] vs. 97.83 [42.03-145.4], p = 0.017). Patients with high disease activity had a higher concentration of circ_0005567 than the control group (185.4 [112.72-249.25] vs. 97.83 [42.03-145.4], p = 0.015). In the cell line model, we found an association between circ_0005567 and miR-194-5p concentration and increased expression of mRNAs that may be related to cell proliferation. The plasma concentration of circ_0005567 may be a new potential biomarker associated with disease activity in patients with RA.

miR-181b-1-3p affects the proliferation and differentiation of chondrocytes in TD broilers through the WIF1/Wnt/β-catenin pathway

Thiram is a plant fungicide, its excessive use has exceeded the required environmental standards. It causes tibial dyschondroplasia (TD) in broilers which is a common metabolic disease that affects the growth plate of tibia bone. It has been studied that many microRNAs (miRNAs) are involved in the differentiation of chondrocytes however, their specific roles and mechanisms have not been fully investigated. The selected features of tibial chondrocytes of broilers were studied in this experiment which included the expression of miR-181b-1-3p and the genes related to WIF1/Wnt/β-catenin pathway in chondrocytes through qRT-PCR, western blot and immunofluorescence. The correlation between miR-181b-1-3p and WIF1 was determined by dual luciferase reporter gene assay whereas, the role of miR-181b-1-3p and WIF1/Wnt/β-catenin in chondrocyte differentiation was determined by mimics and inhibitor transfection experiments. Results revealed that thiram exposure resulted in decreased expression of miR-181b-1-3p and increased expression of WIF1 in chondrocytes. A negative correlation was also observed between miR-181b-1-3p and WIF1. After overexpression of miR-181b-1-3p, the expression of ACAN, β-catenin and Col2a1 increased but the expression of GSK-3β decreased. It was observed that inhibition of WIF1 increased the expression of ALP, β-catenin, Col2a1 and ACAN but decreased the expression of GSK-3β. It is concluded that miR-181b-1-3p can reverse the inhibitory effect of thiram on cartilage proliferation and differentiation by inhibiting WIF1 expression and activating Wnt/β-catenin signaling pathway. This study provides a new molecular target for the early diagnosis and possible treatment of TD in broilers.

The Molecular Regulatory Mechanism in Multipotency and Differentiation of Wharton's Jelly Stem Cells

Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) are isolated from Wharton's jelly tissue of umbilical cords. They possess the ability to differentiate into lineage cells of three germ layers. WJ-MSCs have robust proliferative ability and strong immune modulation capacity. They can be easily collected and there are no ethical problems associated with their use. Therefore, WJ-MSCs have great tissue engineering value and clinical application prospects. The identity and functions of WJ-MSCs are regulated by multiple interrelated regulatory mechanisms, including transcriptional regulation and epigenetic modifications. In this article, we summarize the latest research progress on the genetic/epigenetic regulation mechanisms and essential signaling pathways that play crucial roles in pluripotency and differentiation of WJ-MSCs.

Exercise-regulated white adipocyte differentitation: An insight into its role and mechanism

White adipocytes play a key role in the regulation of fat mass amount and energy balance. An appropriate level of white adipocyte differentiation is important for maintaining metabolic homeostasis. Exercise, an important way to improve metabolic health, can regulate white adipocyte differentiation. In this review, the effect of exercise on the differentiation of white adipocytes is summarized. Exercise could regulate adipocyte differentiation in multiple ways, such as exerkines, metabolites, microRNAs, and so on. The potential mechanism underlying the role of exercise in adipocyte differentiation is also reviewed and discussed. In-depth investigation of the role and mechanism of exercise in white adipocyte differentiation would provide new insights into exercise-mediated improvement of metabolism and facilitate the application of exercise-based strategy against obesity.

Single-cell and spatial transcriptomics reveal changes in cell heterogeneity during progression of human tendinopathy

BACKGROUND

Musculoskeletal tissue degeneration impairs the life quality and motor function of many people, especially seniors and athletes. Tendinopathy is one of the most common diseases associated with musculoskeletal tissue degeneration, representing a major global healthcare burden that affects both athletes and the general population, with the clinical presentation of long-term recurring chronic pain and decreased tolerance to activity. The cellular and molecular mechanisms at the basis of the disease process remain elusive. Here, we use a single-cell and spatial RNA sequencing approach to provide a further understanding of cellular heterogeneity and molecular mechanisms underlying tendinopathy progression.

RESULTS

To explore the changes in tendon homeostasis during the tendinopathy process, we built a cell atlas of healthy and diseased human tendons using single-cell RNA sequencing of approximately 35,000 cells and explored the variations of cell subtypes' spatial distributions using spatial RNA sequencing. We identified and localized different tenocyte subpopulations in normal and lesioned tendons, found different differentiation trajectories of tendon stem/progenitor cells in normal/diseased tendons, and revealed the spatial location relationship between stromal cells and diseased tenocytes. We deciphered the progression of tendinopathy at a single-cell level, which is characterized by inflammatory infiltration, followed by chondrogenesis and finally endochondral ossification. We found diseased tissue-specific endothelial cell subsets and macrophages as potential therapeutic targets.

CONCLUSIONS

This cell atlas provides the molecular foundation for investigating how tendon cell identities, biochemical functions, and interactions contributed to the tendinopathy process. The discoveries revealed the pathogenesis of tendinopathy at single-cell and spatial levels, which is characterized by inflammatory infiltration, followed by chondrogenesis, and finally endochondral ossification. Our results provide new insights into the control of tendinopathy and potential clues to developing novel diagnostic and therapeutic strategies.

Transit Amplifying Cells (TACs): a still not fully understood cell population

Maintenance of tissue homeostasis and tissue regeneration after an insult are essential functions of adult stem cells (SCs). In adult tissues, SCs proliferate at a very slow rate within "stem cell niches", but, during tissue development and regeneration, before giving rise to differentiated cells, they give rise to multipotent and highly proliferative cells, known as transit-amplifying cells (TACs). Although differences exist in diverse tissues, TACs are not only a transitory phase from SCs to post-mitotic cells, but they also actively control proliferation and number of their ancestor SCs and proliferation and differentiation of their progeny toward tissue specific functional cells. Autocrine signals and negative and positive feedback and feedforward paracrine signals play a major role in these controls. In the present review we will consider the generation and the role played by TACs during development and regeneration of lining epithelia characterized by a high turnover including epidermis and hair follicles, ocular epithelial surfaces, and intestinal mucosa. A comparison between these different tissues will be made. There are some genes and molecular pathways whose expression and activation are common to most TACs regardless their tissue of origin. These include, among others, Wnt, Notch, Hedgehog and BMP pathways. However, the response to these molecular signals can vary in TACs of different tissues. Secondly, we will consider cultured cells derived from tissues of mesodermal origin and widely adopted for cell therapy treatments. These include mesenchymal stem cells and dedifferentiated chondrocytes. The possible correlation between cell dedifferentiation and reversion to a transit amplifying cell stage will be discussed.

Regulatory of miRNAs in tri-lineage differentiation of C3H10T1/2

MicroRNAs (miRNAs) are non-coding single-stranded RNA molecules encoded by endogenous genes, which play a vital role in cell generation, metabolism, apoptosis and stem cell differentiation. C3H10T1/2, a mesenchymal cell extracted from mouse embryos, is capable of osteogenic differentiation, adipogenic differentiation and chondrogenic differentiation. Extensive studies have shown that not only miRNAs can directly trigger targeted genes to regulate the tri-lineage differentiation of C3H10T1/2, but it also can indirectly regulate the differentiation by triggering different signaling pathways or various downstream molecules. This paper aims to clarify the regulatory roles of different miRNAs on C3H10T1/2 differentiation, and discussing their balance effect among osteogenic differentiation, adipogenic differentiation and chondrogenic differentiation of C3H10T1/2. We also review the biogenesis of miRNAs, Wnt signaling pathways, MAPK signaling pathways and BMP signaling pathways and provide some specific examples of how these signaling pathways act on C3H10T1/2 tri-lineage differentiation. On this basis, we hope that a deeper understanding of the differentiation and regulation mechanism of miRNAs in C3H10T1/2 can provide a promising therapeutic method for the clinical treatment of bone defects, osteoporosis, osteoarthritis and other diseases.

Integrative Analysis of lncRNA-miRNA-mRNA Regulatory Network Reveals the Key lncRNAs Implicated Potentially in the Differentiation of Adipocyte in Goats

Goats are popular in China because of their superior meat quality, delicate flesh, and unique flavor. Long noncoding RNAs (lncRNAs) play important roles in transcriptional and post-transcriptional regulation of gene expression. However, the effects of lncRNAs on adipocyte differentiation in goat has not been fully elucidated yet. In this investigation, we performed RNA-Seq analysis of intramuscular and subcutaneous adipocytes from Jianzhou Daer goat before and after differentiation, including both intramuscular preadipocytes (IMPA) vs. intramuscular adipocytes (IMA) and subcutaneous preadipocytes (SPA) vs. subcutaneous adipocytes (SA). A total of 289.49 G clean reads and 12,519 lncRNAs were obtained from 20 samples. In total, 3,733 differentially expressed RNAs (182 lncRNAs and 3,551 mRNAs) were identified by pairwise comparison. There were 135 differentially expressed lncRNAs (DELs) specific to intramuscular adipocytes, 39 DELs specific to subcutaneous adipocytes, and 8 DELs common to both adipocytes in these 182 DELs. Some well-known and novel pathways associated with preadipocyte differentiation were identified: fat acid metabolism, TGF-beta signaling pathway and PI3K-Akt signaling pathway. By integrating miRNA-seq data from another study, we also identified hub miRNAs in both types of fat cells. Our analysis revealed the unique and common lncRNA-miRNA-mRNA networks of two kinds of adipocytes. Several lncRNAs that regulate potentially goat preadipocyte differentiation were identified, such as XR_001918 647.1, XR_001917728.1, XR_001297263.2 and LNC_004191. Furthermore, our findings from the present study may contribute to a better understanding of the molecular mechanisms underlying in goat meat quality and provide a theoretical basis for further goat molecular breeding.

Post-Transcriptional Regulation of Molecular Determinants during Cardiogenesis

Cardiovascular development is initiated soon after gastrulation as bilateral precardiac mesoderm is progressively symmetrically determined at both sides of the developing embryo. The precardiac mesoderm subsequently fused at the embryonic midline constituting an embryonic linear heart tube. As development progress, the embryonic heart displays the first sign of left-right asymmetric morphology by the invariably rightward looping of the initial heart tube and prospective embryonic ventricular and atrial chambers emerged. As cardiac development progresses, the atrial and ventricular chambers enlarged and distinct left and right compartments emerge as consequence of the formation of the interatrial and interventricular septa, respectively. The last steps of cardiac morphogenesis are represented by the completion of atrial and ventricular septation, resulting in the configuration of a double circuitry with distinct systemic and pulmonary chambers, each of them with distinct inlets and outlets connections. Over the last decade, our understanding of the contribution of multiple growth factor signaling cascades such as Tgf-beta, Bmp and Wnt signaling as well as of transcriptional regulators to cardiac morphogenesis have greatly enlarged. Recently, a novel layer of complexity has emerged with the discovery of non-coding RNAs, particularly microRNAs and lncRNAs. Herein, we provide a state-of-the-art review of the contribution of non-coding RNAs during cardiac development. microRNAs and lncRNAs have been reported to functional modulate all stages of cardiac morphogenesis, spanning from lateral plate mesoderm formation to outflow tract septation, by modulating major growth factor signaling pathways as well as those transcriptional regulators involved in cardiac development.

Mesenchymal stem cell extracellular vesicles-derived microRNA-194-5p delays the development of intervertebral disc degeneration by targeting TRAF6

Objective

Mesenchymal stem cells-derived extracellular vesicles (MSCs-EVs) can improve intervertebral disc degeneration (IDD). Considering that, their concrete mechanisms from microRNA-194-5p/tumor receptor-associated factor 6 (miR-194-5p/TRAF6) axis in IDD ask for disclosure in a scientific way.

Methods

Nucleus pulposus (NP) cells and MSCs were obtained. EVs were isolated from the obtained MSCs and identified. miR-194-5p expression in MSC-EVs was altered by sequence transfection. Subsequently, MSCs-EVs were co-cultured with NP cells intervened by tumor necrosis factor α (TNF-α). NP cell proliferation and apoptosis, along with their osteogenic differentiation ability were evaluated. miR-194-5p and TRAF6 expression and their interaction were determined.

Results

In TNF-α-intervened NP cells, miR-194-5p was down-regulated and TRAF6 was up-regulated. Restoring miR-194-5p effectively enhanced proliferation and osteogenic differentiation, and reduced apoptosis of TNF-α-intervened NP cells. miR-194-5p-enriched MSCs-EVs protected TNF-α-intervened NP cells. miR-194-5p targeted TRAF6, TRAF6 overexpression exerted negatively for the growth of TNF-α-intervened NP cells, and could reduce the protective effects of miR-194-5p on TNF-α-intervened NP cells.

Conclusion

It is elucidated that miR-194-5p derived from MSCs-EVs protects TNF-α-intervened NP cells through restricting TRAF6, replenishing a potential target for IDD treatment.

Update on the Effects of Energy Metabolism in Bone Marrow Mesenchymal Stem Cells Differentiation

Background

As common progenitor cells of osteoblasts and adipocytes, bone marrow mesenchymal (stromal) stem cells (BMSCs) play key roles in bone homeostasis, tissue regeneration, and global energy homeostasis; however, the intrinsic mechanism of BMSC differentiation is not well understood. Plasticity in energy metabolism allows BMSCs to match the divergent demands of osteo-adipogenic differentiation. Targeting BMSC metabolic pathways may provide a novel therapeutic perspective for BMSC differentiation unbalance related diseases.

Scope of review

This review covers the recent studies of glucose, fatty acids, and amino acids metabolism fuel the BMSC differentiation. We also discuss recent findings about energy metabolism in BMSC differentiation.

Major conclusions

Glucose, fatty acids, and amino acids metabolism provide energy to fuel BMSC differentiation. Moreover, some well-known regulators including environmental stress, hormone drugs, and biological and pathological factors may also influence BMSC differentiation by altering metabolism. This offers insight to the significance of metabolism on BMSC fate determination and provides the possibility of treating diseases related to BMSC differentiation, such as obesity and osteoporosis, from a metabolic perspective.

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.

Bone marrow adiposity during pathologic bone loss: molecular mechanisms underlying the cellular events

Bone marrow (BM) is a heterogeneous niche where bone marrow stromal cells (BMSCs), osteoblasts, osteoclasts, adipocytes, hematopoietic cells, and immune cells coexist. The cellular composition of BM changes with various pathophysiological states. A reduction in osteoblast number and a concomitant increase in adipocyte number in aging and pathological conditions put bone marrow adipose tissue (BMAT) into spotlight. Accumulating evidence strongly supports that an overwhelming production of BMAT is a major contributor to bone loss disorders. Therefore, BMAT-targeted therapy can be an efficient and feasible intervention for osteoporosis. However, compared to blocking bone-destroying molecules produced by BMAT, suppressing BMAT formation is theoretically a more effective and fundamental approach in treating osteoporotic bone diseases. Thus, a deep insight into the molecular basis underlying increased BM adiposity during pathologic bone loss is critical to formulate strategies for therapeutically manipulating BMAT. In this review, we comprehensively summarize the molecular mechanisms involved in adipocyte differentiation of BMSCs as well as the interaction between bone marrow adipocytes and osteoclasts. More importantly, we further discuss the potential clinical implications of therapeutically targeting the upstream of BMAT formation in bone loss diseases.

Construction of miRNA-mRNA network in the differentiation of chicken preadipocytes

1. MicroRNAs (miRNAs) play key roles in regulating lipid metabolism, adipogenesis and fat deposition in chicken. To date, there are only a few miRNAs that had been confirmed to be involved in chicken adipogenesis. The detailed mechanisms by which miRNAs regulate chicken adipogenesis remain largely unknown.

2. To identify candidate miRNAs involved in chicken preadipocyte differentiation and explore potential mechanisms behind their functions, the following study analysed and identified miRNA and mRNA expression levels in undifferentiated and differentiated preadipocytes. Hub miRNA-mRNA interactions were identified, and the degree of connectivity of DE miRNAs in the network was established.

3. A total of 145 DE miRNAs and 660 DE mRNAs were identified between undifferentiated and differentiated preadipocytes. An miRNA-mRNA network was constructed, including 29 DE miRNAs and 155 DE mRNAs, forming 470 miRNA-mRNA interactions. Functional enrichment analysis showed that DE mRNAs in the network were significantly enriched in 712 biological processes and 13 KEGG pathways. Based on the connectivity degree, five DE miRNAs with higher degrees miR-195-x, gga-miR-200a-3p, gga-miR-135a-5p, novel-m0067-5p and novel-m0270-5p were identified as hub miRNAs. Fifty-eight DE mRNAs interacted with these five hub miRNAs and formed 70 miRNA-mRNA interactions.

4. This study constructed a miRNA-mRNA network associated with chicken preadipocyte differentiation and identified five hub miRNAs in the network. The findings identified the number of chicken adipogenic miRNAs and laid the foundation for elucidating the miRNA-mediated regulatory mechanism in chicken adipogenesis.

Recent Developments in Delivery of MicroRNAs Utilizing Nanosystems for Metabolic Syndrome Therapy

Metabolic syndrome (MetS) is a set of complex, chronic inflammatory conditions that are characterized by central obesity and associated with an increased risk of cardiovascular diseases. In recent years, microRNAs (miRNAs) have become an important type of endocrine factors, which play crucial roles in maintaining energy balance and metabolic homeostasis. However, its unfavorable properties such as easy degradation in blood and off-target effect are still a barrier for clinical application. Nanosystem based delivery possess strong protection, high bioavailability and control release rate, which is beneficial for success of gene therapy. This review first describes the current progress and advances on miRNAs associated with MetS, then provides a summary of the therapeutic potential and targets of miRNAs in metabolic organs. Next, it discusses recent advances in the functionalized development of classic delivery systems (exosomes, liposomes and polymers), including their structures, properties, functions and applications. Furthermore, this work briefly discusses the intelligent strategies used in emerging novel delivery systems (selenium nanoparticles, DNA origami, microneedles and magnetosomes). Finally, challenges and future directions in this field are discussed provide a comprehensive overview of the future development of targeted miRNAs delivery for MetS treatment. With these contributions, it is expected to address and accelerate the development of effective NA delivery systems for the treatment of MetS.

Characteristics and expression profiles of circRNAs during abdominal adipose tissue development in Chinese Gushi chickens

Circular RNAs (circRNAs) play important roles in adipogenesis. However, studies on circRNA expression profiles associated with the development of abdominal adipose tissue are lacking in chickens. In this study, 12 cDNA libraries were constructed from the abdominal adipose tissue of Chinese domestic Gushi chickens at 6, 14, 22, and 30 weeks. A total of 1,766 circRNAs were identified by Illumina HiSeq 2500 sequencing. These circRNAs were primarily distributed on chr1 through chr10 and sex chromosomes, and 84.95% of the circRNAs were from gene exons. Bioinformatic analysis showed that each circRNA has 35 miRNA binding sites on average, and 62.71% have internal ribosome entry site (IRES) elements. Meanwhile, these circRNAs were primarily concentrated in TPM < 0.1 and TPM > 60, and their numbers accounted for 18.90% and 80.51%, respectively, exhibiting specific expression patterns in chicken abdominal adipose tissue. In addition, 275 differentially expressed (DE) circRNAs were identified by comparison analysis. Functional enrichment analysis showed that the parental genes of DE circRNAs were primarily involved in biological processes and pathways related to lipid metabolism, such as regulation of fat cell differentiation, fatty acid homeostasis, and triglyceride homeostasis, as well as fatty acid biosynthesis, fatty acid metabolism, and glycerolipid metabolism. Furthermore, ceRNA regulatory networks related to abdominal adipose development were constructed. The results of this study indicated that circRNAs can regulate lipid metabolism, adipocyte proliferation and differentiation, and cell junctions during abdominal adipose tissue development in chickens through complex ceRNA networks between circRNAs, miRNAs, genes, and pathways. The results of this study may help to expand the number of known circRNAs in abdominal adipose tissue and provide a valuable resource for further research on the function of circRNAs in chicken abdominal adipose tissue.

Macrophage-Stimulating Protein Enhances Osteoblastic Differentiation via the Recepteur d&apos;Origine Nantais Receptor and Extracellular Signal-Regulated Kinase Signaling Pathway

Background

Macrophage-stimulating protein (MSP; also known as macrophage stimulating 1 and hepatocyte growth factor-like protein) has been shown to play a crucial role in calcium homeostasis and skeletal mineralization in zebrafish. However, the precise role of MSP in osteoblasts has not been elucidated. In this study, we investigated the effect of MSP on osteoblast differentiation of pre-osteoblast cells.

Methods

Osteoblast differentiation upon MSP treatment was evaluated by analyzing the osteogenic gene expression, alkaline phosphatase (ALP) activity, and mineralized nodule formation. To assess changes in the MSP-RON signaling pathway, knockdown of Ron gene was performed using siRNA and pharmacological inhibitor treatment.

Results

Expression of the tyrosine kinase receptor RON, a receptor of MSP, was found to be significantly increased during osteoblast differentiation. MSP treatment significantly upregulated the expression of osteogenic marker genes and remarkably increased ALP activity and mineralized nodule formation. Conversely, knockdown of Ron significantly attenuated the expression of osteogenic marker genes and ALP activity that were induced upon MSP treatment. Mechanistically, MSP treatment significantly enhanced the phosphorylation of extracellular signal-regulated kinase (ERK); however, additional treatment with the selective ERK inhibitor PD98059 attenuated the effect of MSP on osteoblast differentiation.

Conclusions

Altogether, these results indicate that the MSP-RON axis is involved in promoting osteoblast differentiation via activation of the ERK signaling pathway.

Distinct Subsets of Noncoding RNAs Are Strongly Associated With BMD and Fracture, Studied in Weight-Bearing and Non-Weight-Bearing Human Bone

We investigated mechanisms resulting in low bone mineral density (BMD) and susceptibility to fracture by comparing noncoding RNAs (ncRNAs) in biopsies of non-weight-bearing (NWB) iliac (n = 84) and weight bearing (WB) femoral (n = 18) postmenopausal bone across BMDs varying from normal (T-score > -1.0) to osteoporotic (T-score ≤ -2.5). Global bone ncRNA concentrations were determined by PCR and microchip analyses. Association with BMD or fracture, adjusted by age and body mass index, were calculated using linear and logistic regression and least absolute shrinkage and selection operator (Lasso) analysis. At 10% false discovery rate (FDR), 75 iliac bone ncRNAs and 94 femoral bone ncRNAs were associated with total hip BMD. Eight of the ncRNAs were common for the two sites, but five of them (miR-484, miR-328-3p, miR-27a-5p, miR-28-3p, and miR-409-3p) correlated positively to BMD in femoral bone, but negatively in iliac bone. Of predicted pathways recognized in bone metabolism, ECM-receptor interaction and proteoglycans in cancer emerged at both sites, whereas fatty acid metabolism and focal adhesion were only identified in iliac bone. Lasso analysis and cross-validations identified sets of nine bone ncRNAs correlating strongly with adjusted total hip BMD in both femoral and iliac bone. Twenty-eight iliac ncRNAs were associated with risk of fracture (FDR < 0.1). The small nucleolar RNAs, RNU44 and RNU48, have a function in stabilization of ribosomal RNAs (rRNAs), and their association with fracture and BMD suggest that aberrant processing of rRNAs may be involved in development of osteoporosis. Cis-eQTL (expressed quantitative trait loci) analysis of the iliac bone biopsies identified two loci associated with microRNAs (miRNAs), one previously identified in a heel-BMD genomewide association study (GWAS). In this comprehensive investigation of the skeletal genetic background in postmenopausal women, we identified functional bone ncRNAs associated to fracture and BMD, representing distinct subsets in WB and NWB skeletal sites. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

CUEDC2 controls osteoblast differentiation and bone formation via SOCS3-STAT3 pathway

The CUE domain-containing 2 (CUEDC2) protein plays critical roles in many biological processes, such as the cell cycle, inflammation, and tumorigenesis. However, whether CUEDC2 is involved in osteoblast differentiation and plays a role in bone regeneration remains unknown. This study investigated the role of CUEDC2 in osteogenesis and its underlying molecular mechanisms. We found that CUEDC2 is expressed in bone tissues. The expression of CUEDC2 decreased during bone development and BMP2-induced osteoblast differentiation. The overexpression of CUEDC2 suppressed the osteogenic differentiation of precursor cells, while the knockdown of CUEDC2 showed the opposite effect. In vivo studies showed that the overexpression of CUEDC2 decreased bone parameters (bone volume, bone area, and bone mineral density) during ectopic bone formation, whereas its knockdown increased bone volume and the reconstruction percentage of critical-size calvarial defects. We found that CUEDC2 affects STAT3 activation by regulating SOCS3 protein stability. Treatment with a chemical inhibitor of STAT3 abolished the promoting effect of CUEDC2 silencing on osteoblast differentiation. Together, we suggest that CUEDC2 functions as a key regulator of osteoblast differentiation and bone formation by targeting the SOCS3–STAT3 pathway. CUEDC2 manipulation could serve as a therapeutic strategy for controlling bone disease and regeneration.

Recent progress on the role and molecular mechanism of chicken ovalbumin upstream promoter-transcription factor II in cancer

Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) is an orphan receptor that regulates the expression of genes involved in development and homeostasis. COUP-TFII is also dysregulated in cancer, where it plays important roles in oncogenesis and malignant progression. Recent studies have also investigated altered microRNA-mediated regulation of COUP-TFII in cancer. Although many investigators have studied the expression and clinical significance of COUP-TFII in several cancer types, there remain many controversies regarding its role in these diseases. In this review, we will describe the functions and underlying molecular mechanisms of COUP-TFII in several cancers, especially colorectal, gastric, breast, and prostate cancer; additionally, we will briefly summarize what is known about microRNA-mediated regulation of COUP-TFII.

The primary cilium directs osteopontin-induced migration of mesenchymal stem cells by regulating CD44 signaling and Cdc42 activation

The primary cilium acts as a sensory organelle with diverse receptors and ion channels to detect extracellular cues and regulate cellular functions, including cell migration. The migration of mesenchymal stem cells (MSCs) to bone remodeling sites is important for bone homeostasis. Recently, we have suggested that osteopontin (OPN) is a significant chemoattractant in MSC migration to bone remodeling sites. The objective of this study was to determine whether the primary cilium acts as a chemoattractant sensory unit to detect OPN cues and control MSC migration. We found that the loss of primary cilium induced by silencing of IFT88 reduced OPN-induced migration of MSCs. The effect of IFT88 silencing on cellular attachment, spreading, and proliferation was negligible. The loss of primary cilium did not affect the level of integrinβ1 or CD44, two known receptors for OPN. Interestingly, CD44 was localized to the primary cilium by OPN stimulus. Knockdown of IFT88 or CD44 dysregulated OPN-induced signaling activation and abolished OPN-induced Cdc42 activation. Our findings suggest that the primary cilium acts as a chemoattractant sensor for OPN to regulate MSC migration by controlling not only CD44-mediated OPN signaling, but also Cdc42-mediated actin cytoskeleton rearrangement.

COUP-TFII in Health and Disease

The nuclear receptors (NRs) belong to a vast family of evolutionary conserved proteins acting as ligand-activated transcription factors. Functionally, NRs are essential in embryogenesis and organogenesis and in adulthood they are involved in almost every physiological and pathological process. Our knowledge of NRs action has greatly improved in recent years, demonstrating that both their expression and activity are tightly regulated by a network of signaling pathways, miRNA and reciprocal interactions. The Chicken Ovalbumin Upstream Promoter Transcription Factor II (COUP-TFII, NR2F2) is a NR classified as an orphan due to the lack of a known natural ligand. Although its expression peaks during development, and then decreases considerably, in adult tissues, COUP-TFII is an important regulator of differentiation and it is variably implicated in tissues homeostasis. As such, alterations of its expression or its transcriptional activity have been studied and linked to a spectrum of diseases in organs and tissues of different origins. Indeed, an altered COUP-TFII expression and activity may cause infertility, abnormality in the vascular system and metabolic diseases like diabetes. Moreover, COUP-TFII is actively investigated in cancer research but its role in tumor progression is yet to be fully understood. In this review, we summarize the current understanding of COUP-TFII in healthy and pathological conditions, proposing an updated and critical view of the many functions of this NR.

Increased COUP-TFII Expression Mediates the Differentiation Imbalance of Bone Marrow-Derived Mesenchymal Stem Cells in Femoral Head Osteonecrosis

Objective

Bone marrow-derived mesenchymal stem cells (BMSCs) have multilineage differentiation potential, which allows them to progress to osteogenesis, adipogenesis, and chondrogenesis. An imbalance of differentiation between osteogenesis and adipogenesis will result in pathologic conditions inside the bone. This type of imbalance is also one of the pathological findings in osteonecrosis of the femoral head (ONFH). Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) was previously reported to mediate the differentiation of mesenchymal stem cells. This study investigated the expression of the osteogenesis regulator Runx2, osteocalcin, the adipogenesis regulator PPARγ, and COUP-TFII in the femoral head tissue harvested from ONFH patients, and characterized the effect of COUP-TFII on the differentiation of primary BMSCs.

Methods

Thirty patients with ONFH were recruited and separated into 3 groups: the trauma-, steroid- and alcohol-induced ONFH groups (10 patients each). Bone specimens were harvested from patients who underwent hip arthroplasty, and another 10 specimens were harvested from femoral neck fracture patients as the control group. Expression of the osteogenesis regulator Runx2, osteocalcin, the adipogenesis regulator PPARγ, C/EBP-α, and COUP-TFII was analyzed by Western blotting. Primary bone marrow mesenchymal cells were harvested from ONFH cells treated with COUP-TFII RNA interference to evaluate the effect of COUP-TFII on MSCs.

Results

ONFH patients had significantly increased expression of the adipogenesis regulator PPARγ and C/EBP-α and decreased expression of the osteogenesis regulator osteocalcin. ONFH bone tissue also revealed higher COUP-TFII expression. Immunohistochemical staining displayed strong COUP-TFII immunoreactivity adjacent to osteonecrotic trabecular bone. Increased COUP-TFII expression in the bone tissue correlated with increased PPARγ and decreased osteocalcin expression. Knockdown of COUP-TFII with siRNA in BMSCs reduced adipogenesis and increased osteogenesis in mesenchymal cells.

Conclusion

Increased COUP-TFII expression mediates the imbalance of BMSC differentiation and progression to ONFH in patients. This study might reveal a new target in the treatment of ONFH.

Androgen-Regulated microRNAs (AndroMiRs) as Novel Players in Adipogenesis

The development, homeostasis, or increase of the adipose tissue is driven by the induction of the adipogenic differentiation (adipogenesis) of undifferentiated mesenchymal stem cells (MSCs). Adipogenesis can be inhibited by androgen stimulation of these MSCs resulting in the transcription initiation or repression of androgen receptor (AR) regulated genes. AR not only regulates the transcription of protein-coding genes but also the transcription of several non-coding microRNAs involved in the posttranscriptional gene regulation (herein designated as AndroMiRs). As microRNAs are largely involved in differentiation processes such as adipogenesis, the involvement of AndroMiRs in the androgen-mediated inhibition of adipogenesis is likely, however, not yet intensively studied. In this review, existing knowledge about adipogenesis-related microRNAs and AndroMiRs is summarized, and putative cross-links are drawn, which are still prone to experimental validation.

Perspectives on miRNAs as Epigenetic Markers in Osteoporosis and Bone Fracture Risk: A Step Forward in Personalized Diagnosis

Aging is associated with an increased incidence of age-related bone diseases. Current diagnostics (e.g., conventional radiology, biochemical markers), because limited in specificity and sensitivity, can distinguish between healthy or osteoporotic subjects but they are unable to discriminate among different underlying causes that lead to the same bone pathological condition (e.g., bone fracture risk). Among recent, more sensitive biomarkers, miRNAs — the non-coding RNAs involved in the epigenetic regulation of gene expression, have emerged as fundamental post-transcriptional modulators of bone development and homeostasis. Each identified miRNA carries out a specific role in osteoblast and osteoclast differentiation and functional pathways (osteomiRs). miRNAs bound to proteins or encapsulated in exosomes and/or microvesicles are released into the bloodstream and biological fluids where they can be detected and measured by highly sensitive and specific methods (e.g., quantitative PCR, next-generation sequencing). As such, miRNAs provide a prompt and easily accessible tool to determine the subject-specific epigenetic environment of a specific condition. Their use as biomarkers opens new frontiers in personalized medicine. While miRNAs circulating levels are lower than those found in the tissue/cell source, their quantification in biological fluids may be strategic in the diagnosis of diseases that affect tissues, such as bone, in which biopsy may be especially challenging. For a biomarker to be valuable in clinical practice and support medical decisions, it must be (easily) measurable, validated by independent studies, and strongly and significantly associated with a disease outcome. Currently, miRNAs analysis does not completely satisfy these criteria, however. Starting from in vitro and in vivo observations describing their biological role in bone cell development and metabolism, this review describes the potential use of bone-associated circulating miRNAs as biomarkers for determining predisposition, onset, and development of osteoporosis and bone fracture risk. Moreover, the review focuses on their clinical relevance and discusses the pre-analytical, analytical, and post-analytical issues in their measurement, which still limits their routine application. Taken together, research and clinical findings may be helpful for creating miRNA-based diagnostic tools in the diagnosis and treatment of bone diseases.

MicroRNAs and their regulatory networks in Chinese Gushi chicken abdominal adipose tissue during postnatal late development

Background

Abdominal fat is the major adipose tissue in chickens. The growth status of abdominal fat during postnatal late development ultimately affects meat yield and quality in chickens. MicroRNAs (miRNAs) are endogenous small noncoding RNAs that regulate gene expression at the post-transcriptional level. Studies have shown that miRNAs play an important role in the biological processes involved in adipose tissue development. However, few studies have investigated miRNA expression profiles and their interaction networks associated with the postnatal late development of abdominal adipose tissue in chickens.

Results

We constructed four small RNA libraries from abdominal adipose tissue obtained from Chinese domestic Gushi chickens at 6, 14, 22, and 30 weeks. A total of 507 known miRNAs and 53 novel miRNAs were identified based on the four small RNA libraries. Fifty-one significant differentially expressed (SDE) miRNAs were identified from six combinations by comparative analysis, and the expression patterns of these SDE miRNAs were divided into six subclusters by cluster analysis. Gene ontology enrichment analysis showed that the SDE miRNAs were primarily involved in the regulation of fat cell differentiation, regulation of lipid metabolism, regulation of fatty acid metabolism, and unsaturated fatty acid metabolism in the lipid metabolism- or deposition-related biological process categories. In addition, we constructed differentially expressed miRNA–mRNA interaction networks related to abdominal adipose development. The results showed that miRNA families, such as mir-30, mir-34, mir-199, mir-8, and mir-146, may have key roles in lipid metabolism, adipocyte proliferation and differentiation, and cell junctions during abdominal adipose tissue development in chickens.

Conclusions

This study determined the dynamic miRNA transcriptome and characterized the miRNA–mRNA interaction networks in Gushi chicken abdominal adipose tissue for the first time. The results expanded the number of known miRNAs in abdominal adipose tissue and provide novel insights and a valuable resource to elucidate post-transcriptional regulation mechanisms during postnatal late development of abdominal adipose tissue in chicken.

Whole Blood Transcriptome Analysis for Lifelong Monitoring in Elite Sniffer Dogs Produced by Somatic Cell Nuclear Transfer

Reproductive cloning by somatic cell nuclear transfer (SCNT) is a valuable method to propagate service dogs with desirable traits because of higher selection rates in cloned dogs. However, incomplete reprogramming is a major barrier to SCNT, and the assessment of reprogramming is limited to preimplantation embryos and tissues from dead and/or adult tissue. Thus, lifelong monitoring in SCNT dogs can be useful to evaluate the SCNT service dogs for propagation. We applied microarray and qRT-PCR to profile of mRNA and miRNA in whole blood samples collected from four cloned dogs (S), three age-matched control dogs (A), and a donor dog (D). In the analysis of differentially expressed genes in S-A, A-D, and S-D pairs, most genomes were completely reprogrammed and rejuvenated in the cloned offspring. However, several RNAs were differentially expressed. Interestingly, the altered genes are associated with aging and senescence. Furthermore, we identified potential biomarkers such as mirR-223 (NFIB; CLIC4), miRN-494 (ARHGEF12), miR-106b (PPP1R3B; CC2D1A), miR-20a (CC2D1A; PPP1R3B), miR-30e (IGJ; HIRA), and miR-19a (TNRC6A) by miRNA-target mRNA pairing for monitoring rejuvenation, aging/senescence, and reprogramming in cloned dogs. The novel comparative transcriptomic information about SCNT and age-matched dogs can be used to assess the lifelong health of cloned dogs and to facilitate the selection of training animals with minimal invasive procedures.

PPAR Gamma-Regulated MicroRNA 199a-5p Underlies Bone Marrow Adiposity in Aplastic Anemia

Increased propensity of bone marrow-derived mesenchymal stem cells (BM-MSCs) toward adipogenic differentiation has been implicated in the fatty bone marrow and defective hematopoiesis of aplastic anemia (AA). However, the underlying molecular mechanism remains to be investigated. In this study, we found that microRNA 199a-5p (miR-199a-5p) exhibits significantly higher expression in AA BM-MSCs compared with the normal control and is demonstrated to facilitate adipogenic differentiation of BM-MSCs through lentivirus-mediated miR-199a overexpression. Mechanistic investigation reveals that miR-199a-5p could be regulated by PPAR gamma (PPARγ) in a transcription-independent manner and regulates adipogenic differentiation by targeting the expression of transforming growth factor beta induced (TGFBI), which is subsequently validated as a negative regulator of adipogenesis. Besides, the positive correlation between PPARγ and miR-199a-5p expression as well as the inverse relationship between miR-199a-5p and TGFBI expression in normal and AA BM-MSCs was observed. Altogether, our work demonstrates that PPARγ-regulated miR-199a-5p promotes adipogenesis of BM-MSCs by inhibiting TGFBI expression, which might be a novel mechanism underlying the bone marrow adiposity in AA, and provides promising therapeutic targets for AA treatment.

Identification of differentially expressed MiRNAs profile in a thiram-induced tibial dyschondroplasia

Tetramethyl thiuram disulfide (thiram) is a dithiocarbamate, which is widely used on seeds and storing food grains. The incorporation of thiram into the food chain could be a risk for both human beings and animals. Thiram-contaminated feed has been considered a common cause of tibial dyschondrolplasia (TD) in many avian species. The molecular mechanism of action of thiram on TD involving microRNA (miRNA) is not fully understood. For this purpose, the morbidity and pathologic changes were evaluated to understand the TD, and high-throughput RNA sequencing (RNA-Seq) was performed to explore the differentially expressed miRNAs (DEGs). RT-qPCR was used to confirm the validity as compared with sequencing data. The results showed that the marked alterations in the growth plate of the TD chickens were noticeable, with shrinking cells and irregular chondrocyte columns as compared with control group. In this study, we identified total 375 (p < 0.1), 340 (p < 0.05) and 266 (p < 0.01) significant DEGs between the TD and control groups. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of DEGs showed that the target miRNAs were significantly enriched in different treatment groups, such as apoptosis, mRNA surveillance pathway, mitophagy-animal, etc. This study provides theoretical basis for in-depth understanding the pathogenesis of thiram-induced TD and explore the new insights towards the proposed molecular mechanism of specific miRNA as biomarkers for effective gene diagnosis and treatment of TD in broilers.

miR-149-3p Regulates the Switch between Adipogenic and Osteogenic Differentiation of BMSCs by Targeting FTO

Bone marrow-derived mesenchymal stem cells (BMSCs) have been suggested to possess the capacity to differentiate into different cell lineages. Maintaining a balanced stem cell differentiation program is crucial to the bone microenvironment and bone development. MicroRNAs (miRNAs) have played a critical role in regulating the differentiation of BMSCs into particular lineage. However, the role of miR-149-3p in the adipogenic and osteogenic differentiation of BMSCs has not been extensively discovered. In this study, we aimed to detect the expression levels of miR-149-3p during the differentiation of BMSCs and investigate whether miR-149-3p participated in the lineage choice of BMSCs or not. Compared with mimic-negative control (NC), miR-149-3p mimic decreased the adipogenic differentiation potential of BMSCs and increased the osteogenic differentiation potential. Further analysis revealed that overexpression of miR-149-3p repressed the expression of fat mass and obesity-associated (FTO) gene through binding to the 3ʹ UTR of the FTO mRNA. Also, the role of miR-149-3p mimic in inhibiting adipogenic lineage differentiation and potentiating osteogenic lineage differentiation was mainly through targeting FTO, which also played an important role in regulating body weight and fat mass. In addition, BMSCs treated with miR-149-3p anti-miRNA oligonucleotide (AMO) exhibited higher potential to differentiate into adipocytes and lower tendency to differentiate into osteoblasts compared with BMSCs transfected with NC. In summary, our results detected the effects of miR-149-3p in cell fate specification of BMSCs and revealed that miR-149-3p inhibited the adipogenic differentiation of BMSCs via a miR-149-3p/FTO regulatory axis. This study provided cellular and molecular insights into the observation that miR-149-3p was a prospective candidate gene for BMSC-based bone tissue engineering in treating osteoporosis.

Transcriptome Analysis Reveals the Effect of Long Intergenic Noncoding RNAs on Pig Muscle Growth and Fat Deposition

Muscle growth and fat deposition are the two important biological processes in the development of pigs which are closely related to the pig production performance. Long intergenic noncoding RNAs (lincRNAs), with lack of coding potential and the length of at least 200nt, have been extensively studied to play important roles in many biological processes. However, the importance and molecular regulation mechanism of lincRNAs in the process of muscle growth and fat deposition in pigs are still to be further studied comprehensively. In our study, we used the data, including liver, abdominal fat, and longissimus dorsi muscle of 240 days' age of two F2 full-sib female individuals from the white Duroc and Erhualian crossbreed, to identify 581 putative lincRNAs associated with pig muscle growth and fat deposition. The 581 putative lincRNAs shared many common features with other mammalian lincRNAs, such as fewer exons, lower expression levels, and shorter transcript lengths. Cross-tissue comparisons showed that many transcripts were tissue-specific and were involved in the important biological processes in their corresponding tissues. Gene ontology and pathway analysis revealed that many potential target genes (PTGs) of putative lincRNAs were involved in pig muscle growth and fat deposition-related processes, including muscle cell proliferation, lipid metabolism, and fatty acid degradation. In Quantitative Trait Locus (QTLs) analysis, some PTGs were screened from putative lincRNAs, MRPL12 is associated with muscle growth, GCGR and SLC25A10 were associated with fat deposition, and PPP3CA, DPYD, and FGGY were related not only to muscle growth but also to fat deposition. Therefore, it implied that these lincRNAs might participate in the biological processes related to muscle growth or fat deposition through homeostatic regulation of PTGs, but the detailed molecular regulatory mechanisms still needed to be further explored. This study lays the molecular foundation for the in-depth study of the role of lincRNAs in the pig muscle growth and fat deposition and further provides the new molecular markers for understanding the complex biological mechanisms of pig muscle growth and fat deposition.

MiRNA-19a-3p alleviates the progression of osteoporosis by targeting HDAC4 to promote the osteogenic differentiation of hMSCs

To clarify the function of microRNA-19a-3p (miRNA-19a-3p) in the osteogenic differentiation of human-derived mesenchymal stem cells (hMSCs) and the potential mechanism. Serum levels of miRNA-19a-3p, RUNX2 and OCN in osteoporosis patients and controls were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Alkaline phosphatase (ALP) content and calcification ability during the process of osteogenic differentiation were examined by ALP staining and alizarin red staining, respectively. After altering miRNA-19a-3p level by transfection of miRNA-19a-3p mimic or inhibitor, we detected relative levels of miRNA-19a-3p, RUNX2 and OCN in hMSCs by qRT-PCR. The binding relationship between miRNA-19a-3p and HDAC4 was predicted by TargetScan and further verified by dual-luciferase reporter gene assay. Relative expression of HDAC4 was detected by Western blot and qRT-PCR in hMSCs transfected with miRNA-19a-3p mimic or inhibitor. Regulatory effects of miRNA-19a-3p/HDAC4 axis on osteogenic differentiation of hMSCs were evaluated. MiRNA-19a-3p was downregulated in osteoporosis patients. Its level gradually increased in hMSCs with the prolongation of osteogenic differentiation. Overexpression of miRNA-19a-3p upregulated levels of RUNX2 and OCN, and enhanced ALP activity. Knockdown of miRNA-19a-3p obtained the opposite trends. Dual-luciferase reporter gene assay verified that miRNA-19a-3p could target to 3'UTR of HDAC4. Protein level of HDAC4 was negatively regulated by miRNA-19a-3p in hMSCs. More importantly, co-overexpression of miRNA-19a-3p and HDAC4 could reverse the regulatory effects of miRNA-19a-3p on enhancing ALP activity and upregulating RUNX2 and OCN. MiRNA-19a-3p promotes the osteogenic differentiation of hMSCs by inhibiting HDAC4 expression, thus alleviating the progression of osteoporosis.

Role of microRNAs in osteogenesis of stem cells

Osteogenic differentiation is a controlled developmental process in which external and internal factors including cytokines, growth factors, transcription factors (TFs), signaling pathways and microRNAs (miRNAs) play important roles. Various stimulatory and inhibitory TFs contribute to osteogenic differentiation and are responsible for bone development. In addition, cross-talk between several complex signaling pathways regulates the osteogenic differentiation of some stem cells. Although much is known about regulatory genes and signaling pathways in osteogenesis, the role of miRNAs in osteogenic differentiation still needs to be explored. miRNAs are small, approximately 22 nucleotides, single-stranded nonprotein coding RNAs which are abundant in many mammalian cell types. They paly significant regulated roles in various biological processes and serve as promising biomarkers for disease states. Recently, emerging evidence have shown that miRNAs are the key regulators of osteogenesis of stem cells. They may endogenously regulate osteogenic differentiation of stem cells through direct targeting of positive or negative directors of osteogenesis and depending on the target result in the promotion or inhibition of osteogenic differentiation. This review aims to provide a general overview of miRNAs participating in osteogenic differentiation of stem cells and explain their regulatory effect based on the genes targeted with these miRNAs.

miR‑124 regulates the osteogenic differentiation of bone marrow‑derived mesenchymal stem cells by targeting Sp7

MicroRNAs (miRNAs) are novel key regulators of cellular differentiation. miR‑124 has been reported to regulate osteogenic differentiation of bone marrow‑derived mesenchymal stem cells (BMSCs). However, the specific mechanisms involved have not yet been fully elucidated. The present study aimed to investigate the effect of miR‑124 on osteogenic differentiation of BMSCs and its underlying mechanisms. In the present study, it was found that alkaline phosphatase (ALP) activity, osteocalcin (OC) secretion, and the protein levels of osterix (Sp7) and runt‑related transcription factor 2 (Runx2) were significantly increased, whereas the expression of miR‑124 was decreased in a time‑dependent manner during osteogenic differentiation of BMSCs. Following overexpression of miR‑124 via transfection of miR‑124 mimics in BMSCs, Runx2 protein expression and ALP activity were significantly decreased. By contrast, inhibition of miR‑124 expression led to an increase in ALP activity and Runx2 expression. Sp7 expression was suppressed in BMSCs transfected with miR‑124 mimics while increased when miR‑124 expression was inhibited, indicating that miR‑124 regulates the expression of Sp7. Moreover, a luciferase reporter assay further verified that Sp7 is the direct target of miR‑124. Finally, the effect of miR‑124 inhibitor on promoting the differentiation of BMSCs was abolished following treatment with a small interfering RNA targeting Sp7. Taken together, the present study demonstrates that miR‑124 inhibits the osteogenic differentiation of BMSCs by targeting Sp7.

MicroRNA-194 overexpression protects against hypoxia/reperfusion-induced HK-2 cell injury through direct targeting Rheb

Renal ischemia-reperfusion injury, a major cause of renal failure, always leads to acute kidney injury and kidney fibrosis. MicroRNAs (miRs) have been reported to be associated with renal ischemia-reperfusion injury. miR-194 was downregulated following renal ischemia-reperfusion injury; however, the function and mechanism of miR-194 in renal ischemia-reperfusion injury have not yet been fully understood. In the present study, we constructed renal ischemia-reperfusion injury model in vitro through treatment of human kidney proximal tubular epithelial cells HK-2 by hypoxia/reperfusion (H/R). We observed that miR-194 was decreased in H/R-induced HK-2 cells. miR-194 mimic increased H/R-induced HK-2 cell survival, whereas miR-194 inhibitor further strengthened H/R- inhibited HK-2 cell survival. Also, we observed that miR-194 overexpression suppressed oxidative stress markers, including malondialdehyde, glutathione, and secretion of pro-inflammatory cytokines, including IL-6, IL-1β, and TNF-α; however, miR-194 inhibitor showed the reverse effects. Results from dual-luciferase analysis confirmed that Ras homology enriched in brain (Rheb) was a direct target of miR-194. Finally, we corroborated that miR-194 affected cell growth, oxidative stress, and inflammation through targeting Rheb in H/R-induced HK-2 cells. In conclusion, our results suggested that miR-194 protect against H/R-induced injury in HK-2 cells through direct targeting Rheb.

Prognostic Role of Chicken Ovalbumin Upstream Promoter Transcription Factor II in Isocitrate Dehydrogenase-Mutant Glioma with 1p19q Co-Deletion

BACKGROUND

Chicken ovalbumin upstream promoter transcription factor II is known to play a crucial role in the tumor microenvironment. However, the role of NR2F2 in gliomas is unknown.

METHODS

The genomic and clinical data of 530 cases of lower grade gliomas (LGGs) patients and 167 cases of glioblastoma (GBM) patients in The Cancer Genome Atlas (TCGA) were extracted for analysis. R2 and UCSC Xena browser were used for Kaplan-Meier survival in the GSE16011 dataset and TCGA dataset, respectively. GraphPad Prism 7 was used to compare the differences in NR2F2 expression between various groups and subtypes.

RESULTS

LGG patients with low NR2F2 expression had a significantly favorable outcome compared with those with high NR2F2 expression (p < 0.05). By matching histological subtypes and gene expression profiles of LGG patients, grade II glioma group showed lowest levels of NR2F2 expression compared with grade III gliomas and GBM. Patients diagnosed with astrocytoma have highest expression of NR2F2 but lowest OS (p < 0.05). In LGGs, NR2F2 expression was significantly downregulated in patient group with IDH mutation and 1p19q co-deletion (p < 0.05).

CONCLUSION

Our study suggests that NR2F2 can be used as a prognostic marker in LGG patients with IDH mutation and 1p19 co-deletion.

MiRNA-10b Reciprocally Stimulates Osteogenesis and Inhibits Adipogenesis Partly through the TGF-β/SMAD2 Signaling Pathway

As the population ages, the medical and socioeconomic impact of age-related bone disorders will further increase. An imbalance between osteogenesis and adipogenesis of mesenchymal stem cells (MSCs) can lead to various bone and metabolic diseases such as osteoporosis. Thus, understanding the molecular mechanisms underlying MSC osteogenic and adipogenic differentiation is important for the discovery of novel therapeutic paradigms for these diseases. miR-10b has been widely reported in tumorigenesis, cancer invasion and metastasis. However, the effects and potential mechanisms of miR-10b in the regulation of MSC adipogenic and osteogenic differentiation have not been explored. In this study, we found that the expression of miR-10b was positively correlated with bone formation marker genes ALP, RUNX2 and OPN, and negatively correlated with adipogenic markers CEBPα, PPARγ and AP2 in clinical osteoporosis samples. Overexpression of miR-10b enhanced osteogenic differentiation and inhibited adipogenic differentiation of human adipose-derived mesenchymal stem cells (hADSCs) in vitro, whereas downregulation of miR-10b reversed these effects. Furthermore, miR-10b promoted ectopic bone formation in vivo. Target prediction and dual luciferase reporter assays identified SMAD2 as a potential target of miR-10b. Silencing endogenous SMAD2 expression in hADSCs enhanced osteogenesis but repressed adipogenesis. Pathway analysis indicated that miR-10b promotes osteogenic differentiation and bone formation via the TGF-β signaling pathway, while suppressing adipogenic differentiation may be primarily mediated by other pathways. Taken together, our findings imply that miR-10b acts as a critical regulator for balancing osteogenic and adipogenic differentiation of hADSCs by repressing SMAD2 and partly through the TGF-β pathway. Our study suggests that miR-10b is a novel target for controlling bone and metabolic diseases.

Elevated extracellular calcium ions promote proliferation and migration of mesenchymal stem cells via increasing osteopontin expression

Supplementation of mesenchymal stem cells (MSCs) at sites of bone resorption is required for bone homeostasis because of the non-proliferation and short lifespan properties of the osteoblasts. Calcium ions (Ca2+) are released from the bone surfaces during osteoclast-mediated bone resorption. However, how elevated extracellular Ca2+ concentrations would alter MSCs behavior in the proximal sites of bone resorption is largely unknown. In this study, we investigated the effect of extracellular Ca2+ on MSCs phenotype depending on Ca2+ concentrations. We found that the elevated extracellular Ca2+ promoted cell proliferation and matrix mineralization of MSCs. In addition, MSCs induced the expression and secretion of osteopontin (OPN), which enhanced MSCs migration under the elevated extracellular Ca2+ conditions. We developed in vitro osteoclast-mediated bone resorption conditions using mouse calvaria bone slices and demonstrated Ca2+ is released from bone resorption surfaces. We also showed that the MSCs phenotype, including cell proliferation and migration, changed when the cells were treated with a bone resorption-conditioned medium. These findings suggest that the dynamic changes in Ca2+ concentrations in the microenvironments of bone remodeling surfaces modulate MSCs phenotype and thereby contribute to bone regeneration.

Involvement of microRNA-23b in TNF-α-reduced BMSC osteogenic differentiation via targeting runx2

Elucidation of the molecular mechanism governing bone marrow mesenchymal stem cell (BMSC) osteogenic differentiation is of great importance for improving the treatment of osteoporosis. TNF-α is a well-known inhibitory factor during osteogenic differentiation of BMSCs. In our experiment, we consistently observed that TNF-α significantly inhibited BMSC osteogenic differentiation, which was partially rescued by BAY 11-7082 (NF-κB inhibitor). In this study, we examined the potential roles of microRNAs (miRNAs) involved in TNF-α-mediated reduction of BMSC osteogenesis. We found that microRNA-23b (miR-23b) was dramatically induced under the stimulation of TNF-α, which was abolished by BAY 11-7082. Similar to the effect of TNF-α, miR-23b agonist (agomir-23b) obviously impaired BMSC osteogenic differentiation in vitro and in vivo. However, agomir-23b had no effect on osteoclast activity. Overexpression of miR-23b significantly reduced runx2, the master transcription factor during osteogenesis, suggesting that miR-23b acts as an endogenous attenuator of runx2 in BMSCs. Mutation of the putative miR-23b binding site in runx2 mRNA blocked miR-23b-mediated repression of the runx2 3' untranslated region (3'UTR) luciferase reporter activity, suggesting that miR-23b directly binds to runx2 3'UTR. Furthermore, infection with Ad-runx2 (adenovirus carrying the entire CDS sequence of runx2) effectively rescued the inhibition of BMSC osteogenic differentiation in miR-23b-overexpressing cells, indicating that the inhibiting effect of miR-23b on osteogenesis is mediated by suppression of runx2. Moreover, caudal vein injection of agomir-23b notably caused severe osteoporosis in mice, and forced expression of runx2 by combined injecting Ad-runx2 attenuated the bone loss induced by miR-23b. Collectively, these data indicated that miR-23b was involved in TNF-α-mediated reduction of BMSC osteogenesis by targeting runx2. These findings may provide new insights into understanding the regulatory role of miR-23b in the process of BMSC osteogenic differentiation in inflammatory conditions and a novel therapeutic target for osteoporosis.

A Zfp609 circular RNA regulates myoblast differentiation by sponging miR-194-5p

Skeletal muscle development and growth regulatory mechanism is the focus of both animal genetics and medicine. The recent studies indicate that covalently closed circular RNAs (circRNAs) also play important role on muscle development through sequestering specific miRNAs. The present study was conducted to determine the functional roles of circZfp609, a recently identified circRNA, in the regulation of myogenesis in mouse myoblast cell line (C2C12). circZfp609 is predicted to has binding sites of miR-194-5p. circZfp609 knockdown increased the expression of Myf5 and MyoG, which indicated that circZfp609 suppressed myogenic differentiation. Via a luciferase screening assay, circZfp609 is observed to sponge to miR-194-5p with four potential binding sites. Specifically, we show that circZfp609 can sponge miR-194-5p to sequester its inhibition on BCLAF1 so as to repress the myogenic differentiation. Modulation of circZfp609 expression in muscle tissue may emerge as a potential target in breeding strategies attempting to control muscle development.

Analysis of miRNA expression in patients with rheumatoid arthritis during remission and relapse after a 5-year trial of tofacitinib treatment

The physiopathology of rheumatoid arthritis (RA) is mediated by proinflammatory cytokines, some of which are regulated by the JAK/STAT pathway. Tofacitinib is a JAK inhibitor, but its role in the regulation of microRNAs (miRNAs) is unknown. There is also no information regarding the role of miRNAs in the clinical relapse/remission of RA. The present project aims to identify a signature profile of miRNA expression in a subgroup of RA patients who had to discontinue tofacitinib treatment (because of the ending of a 5-year open-label clinical trial) and to describe the expression of miRNAs during RA remission or flare-up. The relative expression of 61 miRNAs was determined in serum samples with the Firefly™ BioWorks assay. Statistical analysis was performed by means of Student's t-test and heatmap analysis was performed with Firefly™ Analysis Workbench software and in the software GraphPad® Prism v5.0. Target prediction and Gene Ontology analysis were carried out using bioinformatic tools. We found a distinctive signature of miRNA expression associated with relapse, featuring upregulated expression of hsa‑miR‑432‑5p (p < 0.05). We also found upregulation of hsa‑miR‑194‑5p (p < 0.05) in samples of patients with RA flare-up. Gene Ontology analysis of the target genes for hsa‑miR‑432‑5p was performed to identify relevant pathways associated with relapse; the implications of these pathways in the physiopathology of RA are discussed. Tofacitinib treatment does not have a direct effect on the expression of measured miRNAs. The changes in hsa‑miR‑432‑5p and hsa‑miR‑194‑5p are associated with the regulation of proinflammatory pathways and RA flare-up.

miR-145-5p Increases Osteoclast Numbers In Vitro and Aggravates Bone Erosion in Collagen-Induced Arthritis by Targeting Osteoprotegerin

BACKGROUND Osteoprotegerin (OPG) inhibits bone resorption and binds with strong affinity to receptor activator of NF κB ligand (RANKL), thereby preventing RANKL from binding to its receptor RANK. Osteoclasts have documented effects on bone erosion of rheumatoid arthritis (RA). The aim of this study was to examine the role of miR-145-5p in the regulation of RA osteoclast differentiation and bone erosion. MATERIAL AND METHODS Expression of microRNA-145-5p in human peripheral blood mononuclear cells (PBMC) and synovial tissue was assayed by real-time polymerase chain reaction (RT-PCR). OPG, RANK, and RANKL expression in RAW-264.7 cells was examined by RT-PCR and Western blot analysis. Osteoclast formation was detected by tartrate-resistant acid phosphatase (TRAP) staining. The effect of miR-145-5p on predicted target mRNAs was examined by luciferase reporter assays. Collagen-induced arthritis (CIA) was induced by injecting DBA/1 mice with bovine type II collagen (CII), and miR-145-5p agomir was administered by intravenous injection. Morphological changes in the CIA joint were assessed by micro-computed tomography (CT) and histopathology. RESULTS miR-145-5p levels significantly increased in RA PBMC and synovial tissue compared with normal PBMC and osteoarthritis (OA) tissue. After transfection of RAW-264.7 cells with miR-145-5p, RANK and RANKL expression increased significantly, while OPG expression decreased significantly. TRAP staining results showed osteoclast numbers increased. Micro-CT analysis of the arthritic joints showed that the miR-145-5p agomir caused bone erosion in mice, and histopathological analysis revealed that miR-145-5p agomir aggravates cartilage erosion. CONCLUSIONS Our findings indicate that administration of miR-145-5p aggravates joint erosion in CIA mice. This suggests that miR-145-5p is a potential target for the treatment of RA.

Downregulation of COUP-TFII inhibits glioblastoma growth via targeting MPC1

Chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is a steroid receptor that is broadly expressed in many tissues throughout embryonic development. Previous studies indicated that COUP-TFII is dysregulated in multiple types of cancer and serves crucial roles in cancer development. The mitochondrial pyruvate carrier 1 (MPC1) is involved in transporting pyruvate for entry into the citric acid cycle, an important event in cancer progression. However, the roles of COUP-TFII and MPC1 in glioma remain unknown. In the present study, it was demonstrated that MPC1 is downregulated in glioblastoma. Furthermore, the inhibition of COUP-TFII was able to increase MPC1 expression and inhibit the growth of glioblastoma cells in vitro and in vivo. The findings from the present study demonstrated that downregulation of COUP-TFII inhibits glioblastoma growth via targeting MPC1. Therefore, COUP-TFII is a potential therapeutic target for glioma.

MicroRNA-194 Regulates the Development and Differentiation of Sensory Patches and Statoacoustic Ganglion of Inner Ear by Fgf4

Background

MicroRNA 194 is involved in the differentiation of various types of cells, such as adipose derived stem cells, human embryonic stem cells, and bone marrow mesenchymal stem cells. Previously, we found that miR-194 was highly expressed in the inner ear sensory patch and neurons in mice embryos. However, the role of miR-194 in the development of the inner ear and its underlying mechanism have not been elucidated yet.

Material/Methods

The expression level of miR-194 has been altered by using antisense morpholino oligonucleotides (MO) and synthesized miRNAs in zebrafish.

Results

We found that miR-194 was vastly expressed in the inner ear and central nervous system (CNS) in zebrafish. Loss of function of miR-194 could strongly affected the development of zebrafish embryos, including delayed embryonic development, edema of the pericardium, small head, axial deviation, delayed development of inner ear, closer location of two otoliths, delayed fusion of the semicircular canals, and abnormal otolith number in some cases. In addition, the behavior of zebrafish was also adversely affected with impaired balance and biased swimming route. Misexpression of miR-194 could strongly affected the development and differentiation of spiral ganglion neuron (SGN) in inner ear through Fgf4 in vitro. Similar results have also been observed that the overexpression and knockdown of miR-194 strongly disturbed the development and differentiation of the sensory patches and Statoacoustic ganglion (SAG) through Fgf4 in zebrafish in vivo. Our results indicated that miR-194 may regulate the development and differentiation of sensory patches and SAG through Fgf4.

Conclusions

Our data revealed a vital role of miR-194 in regulating the development and differentiation of the inner ear.

The Potential Role of miRNAs as New Biomarkers for Osteoporosis

Osteoporosis is the most common metabolic bone disorder affecting up to 40% of postmenopausal women, characterized by a reduction in bone mass and strength leading to bone fragility and fractures. Despite the available tools for diagnosis and stratification of a fracture risk, bone loss occurs insidiously and osteoporosis is often diagnosed after the first fracture has occurred, with important health-related outcomes. Therefore, the need of markers that could efficiently diagnose bone fragility and osteoporosis is still necessary. Over the past few years, novel studies have focused on miRNAs, small noncoding RNAs that are differentially expressed in many pathological conditions, making them attractive biomarkers. To date, the role of miRNAs in bone disorders remains in great part unclear. In particular, limited and partly conflicting information is available concerning their use as potential biomarkers for osteoporosis, due to differences in patient selection, type of samples, and analytical methods. Despite these limits, concordant information about some specific miRNAs is now arising, making likely their use as additional tools to stratify the risk of osteoporosis and possibly fractures. In this review, we summarize the most relevant studies concerning circulating miRNAs differentially expressed in osteoporotic patients along with their function in bone cells and bone turnover.