Mechanisms in endocrinology: micro-RNAs: targets for enhancing osteoblast differentiation and bone formation

Identifying Biomarkers for Osteogenic Potency Assay Development

There has been extensive exploration of how cells may serve as advanced therapy medicinal products to treat skeletal pathologies. Osteoblast progenitors responsible for production of extracellular matrix that is subsequently mineralized during bone formation have been characterised as a rare bone marrow subpopulation of cell culture plastic adherent cells. Conveniently, they proliferate to form single-cell derived colonies of fibroblastoid cells, termed colony forming unit fibroblasts that can subsequently differentiate to aggregates resembling small areas of cartilage or bone. However, donor heterogeneity and loss of osteogenic differentiation capacity during extended cell culture have made the discovery of reliable potency assay biomarkers difficult. Nonetheless, functional osteoblast models derived from telomerised human bone marrow stromal cells have allowed extensive comparative analysis of gene expression, microRNA, morphological phenotypes and secreted proteins. This chapter highlights numerous insights into the molecular mechanisms underpinning osteogenic differentiation of multipotent stromal cells and bone formation, discussing aspects involved in the choice of useful biomarkers for functional attributes that can be quantitively measured in osteogenic potency assays.

Antagonizing microRNA-19a/b augments PTH anabolic action and restores bone mass in osteoporosis in mice

Postmenopausal bone loss often leads to osteoporosis and fragility fractures. Bone mass can be increased by the first 34 amino acids of human parathyroid hormone (PTH), parathyroid hormone‐related protein (PTHrP), or by a monoclonal antibody against sclerostin (Scl‐Ab). Here, we show that PTH and Scl‐Ab reduce the expression of microRNA‐19a and microRNA‐19b (miR‐19a/b) in bone. In bones from patients with lower bone mass and from osteoporotic mice, miR‐19a/b expression is elevated, suggesting an inhibitory function in bone remodeling. Indeed, antagonizing miR‐19a/b in vivo increased bone mass without overt cytotoxic effects. We identified TG‐interacting factor 1 (Tgif1) as the target of miR‐19a/b in osteoblasts and essential for the increase in bone mass following miR‐19a/b inhibition. Furthermore, antagonizing miR‐19a/b augments the gain in bone mass by PTH and restores bone loss in mouse models of osteoporosis in a dual mode of action by supporting bone formation and decreasing receptor activator of NF‐κB ligand (RANKL)‐dependent bone resorption. Thus, this study identifies novel mechanisms regulating bone remodeling, which opens opportunities for new therapeutic concepts to treat bone fragility.

MicroRNA-101a enhances trabecular bone accrual in male mice

High-throughput microRNA sequencing was performed during differentiation of MC3T3-E1 osteoblasts to develop working hypotheses for specific microRNAs that control osteogenesis. The expression data show that miR-101a, which targets the mRNAs for the epigenetic enzyme Ezh2 and many other proteins, is highly upregulated during osteoblast differentiation and robustly expressed in mouse calvaria. Transient elevation of miR-101a suppresses Ezh2 levels, reduces tri-methylation of lysine 27 in histone 3 (H3K27me3; a heterochromatic mark catalyzed by Ezh2), and accelerates mineralization of MC3T3-E1 osteoblasts. We also examined skeletal phenotypes of an inducible miR-101a transgene under direct control of doxycycline administration. Experimental controls and mir-101a over-expressing mice were exposed to doxycycline in utero and postnatally (up to 8 weeks of age) to maximize penetrance of skeletal phenotypes. Male mice that over-express miR-101a have increased total body weight and longer femora. MicroCT analysis indicate that these mice have increased trabecular bone volume fraction, trabecular number and trabecular thickness with reduced trabecular spacing as compared to controls. Histomorphometric analysis demonstrates a significant reduction in osteoid volume to bone volume and osteoid surface to bone surface. Remarkably, while female mice also exhibit a significant increase in bone length, no significant changes were noted by microCT (trabecular bone parameters) and histomorphometry (osteoid parameters). Hence, miR-101a upregulation during osteoblast maturation and the concomitant reduction in Ezh2 mediated H3K27me3 levels may contribute to the enhanced trabecular bone parameters in male mice. However, the sex-specific effect of miR-101a indicates that more intricate epigenetic mechanisms mediate physiological control of bone formation and homeostasis.

Exosomes: A Tool for Bone Tissue Engineering

Mesenchymal stem cells (MSCs) have been repeatedly shown to be a valuable source for cell-based therapy in regenerative medicine, including bony tissue repair. However, engraftment at the injury site is poor. Recently, it has been suggested that MSCs and other cells act through a paracrine signaling mechanism. Exosomes are nanostructures that have been implicated in this process. They carry DNA, RNA, proteins, and lipids and play an important role in cell-to-cell communication directly modulating their target cell at a transcriptional level. In a bone microenvironment, they have been shown to increase osteogenesis and osteogenic differentiation in vivo and in vitro. In the following review, we will discuss the most advanced and significant knowledge of biological functions of exosomes in bone regeneration and their clinical applications in osseous diseases. Impact statement Mesenchymal stem cells have been shown to be a promising tool in bone tissue engineering. Recently, it has been suggested that they secrete exosomes containing messenger RNA, proteins, and lipids, thus acting through paracrine signaling mechanisms. Considering that exosomes are nonteratogenic and have low immunogenic potential, they could potentially replace stem-cell based therapy and thus eradicate the risk of neoplastic transformation associated with cell transplantations in bone regeneration.

Menopausal Transition: Prospective Study of Estrogen Status, Circulating MicroRNAs, and Biomarkers of Bone Metabolism

OBJECTIVE

Osteoporosis is associated with an impaired balance between bone resorption and formation, which in turn leads to bone loss and fractures. Many recent studies have underlined the regulatory role of microRNAs (miRNAs) in bone remodeling processes and their potential as biomarkers of osteoporosis. The purpose of this study was to prospectively examine the association of circulating miRNAs and bone biomarkers with estrogen status in women before and after oophorectomy, as well as in oophorectomized women on estrogen therapy.

METHODS

In this prospective study, we included 11 women before oophorectomy and hysterectomy and at 201 ± 24 days after the surgery. Another 11 women were evaluated 508 ± 127 days after oophorectomy and hysterectomy and after an additional 203 ± 71 days of estradiol treatment. Serum miRNAs were profiled by sequencing. Estrogen status and biomarkers of bone metabolism were quantified. Bone mineral density was assessed in the lumbar spine.

RESULTS

Our analysis revealed 17 miRNAs associated with estrogen levels. Of those miRNAs that were upregulated with estrogen deficiency and downregulated after estrogen therapy, miR-422a correlated with serum beta-carboxy-terminal type I collagen crosslinks (β-CTX) and procollagen 1 N-terminal propeptide (P1NP); and miR-1278 correlated with serum β-CTX, P1NP, osteocalcin, sclerostin, and Dickkopf-1(Dkk1). In contrast, we found an inverse association of miR-24-1-5p with estrogen status and a negative correlation with serum β-CTX, P1NP, osteoprotegerin, and sclerostin levels.

CONCLUSION

The reported miRNAs associated with estrogen status and bone metabolism could be potential biomarkers of bone pathophysiology and would facilitate studies on the prevention of postmenopausal osteoporosis. Our findings require validation in an extended cohort.

miRNA-148b and its role in various cancers

miRNA-148b belongs to the family miR-148/-152, with significant differences in nonseed sequences, which can target diverse mRNA molecules. Reportedly, it may undergo deregulation in lung and ovarian cancers and downregulation in gastric, pancreatic and colon cancers. However, there is a need for further studies to better characterize its mechanism of action and in different types of cancer. In this review, we focus on the aberrant expression of miR-148b in different cancer types and highlight its main target genes and signaling pathways, as well as its pathophysiologic role and relevance to tumorigenesis in several types of cancer.

Kaempferol Ameliorates the Inhibitory Activity of Dexamethasone in the Osteogenesis of MC3T3-E1 Cells by JNK and p38-MAPK Pathways

Kaempferol has been reported to exhibit beneficial effect on the osteogenic differentiation in mesenchymal stem cells (MSC) and osteoblasts. In our previous study, dexamethasone (DEX) demonstrated inhibitory effect on MC3T3-E1 cells differentiation. In this study, we mainly explored the protective effect of kaempferol on the inhibitory activity of DEX in the osteogenesis of MC3T3-E1 cells. We found that kaempferol ameliorated the proliferation inhibition, cell cycle arrest, and cell apoptosis and increased the activity of alkaline phosphatase (ALP) and the mineralization in DEX-treated MC3T3-E1 cells. Kaempferol also significantly enhanced the expression of osterix (Osx) and runt-related transcription factor 2 (Runx2) in MC3T3-E1 cells treated with DEX. In addition, kaempferol attenuated DEX-induced reduction of cyclin D1 and Bcl-2 expression and elevation of p53 and Bax expression. Kaempferol also activated JNK and p38-MAPK pathways in DEX-treated MC3T3-E1 cells. Furthermore, kaempferol improved bone mineralization in DEX-induced bone damage in a zebrafish larvae model. These data suggested that kaempferol ameliorated the inhibitory activity of DEX in the osteogenesis of MC3T3-E1 cells by activating JNK and p38-MAPK signaling pathways. Kaempferol exhibited great potentials in developing new drugs for treating glucocorticoid-induced osteoporosis.

Mesenchymal Stem Cell-Derived Extracellular Vesicles Inhibit Osteoporosis via MicroRNA-27a-Induced Inhibition of DKK2-Mediated Wnt/β-Catenin Pathway

Osteoporosis (OP) is a systemic skeletal disease that promotes bone fragility and the risk of fractures. Recent studies have shown the relevance of microRNAs (miRNAs) in the development of OP. This study aimed to evaluate the possible mechanisms of action underlying miR-27a loaded by mesenchymal stem cell (MSC)-derived extracellular vesicles (MSC-EVs) in OP. Serum samples from OP patients and normal controls were collected for miRNA microarray analysis. The expression of filtered miRNA was upregulated in osteoblasts (OB) and osteoclasts (OCs) for biological activity assessment. After developing OP mice using ovariectomy (OVX) and confirming OP, the miR-27a expression level was upregulated in mice by MSC-EV application. Dual-luciferase assays were conducted to validate the relationship between miR-27a and DKK2 expression. The poor expression of miR-27a was observed in patients with OP. miR-27a increased the expression of OB markers, the number of ALP-positive cells, and the number of calcium nodules in OCs. In OVX mice, miR-27a increased bone density, improved bone structure damage recovery, decreased the levels of bone resorption markers, and decreased OC number. miR-27a transmitted by MSC-EVs interacted with DKK2. MSC-EVs exerted the same protective effects as miR-27a on OP, whereas miR-27a inhibitor abolished the attenuating effects of MSC-EVs. In contrast, DKK2 depletion reversed the stimulatory effects of the miR-27a inhibitor on OP. The Wnt/β-catenin pathway was activated upon MSC-EV application and DKK2 silencing and was impaired upon the downregulation of the expression of miR-27a. MSC-EVs are effective in preventing mouse OP. This mechanism is mediated by the miR-27a/DKK2/Wnt/β-catenin signaling pathway.

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

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

Designing biomaterials for the delivery of RNA therapeutics to stimulate bone healing

Ribonucleic acids (small interfering RNA, microRNA, and messenger RNA) have been emerging as a promising new class of therapeutics for bone regeneration. So far, however, research has mostly focused on stability and complexation of these oligonucleotides for systemic delivery. By comparison, delivery of RNA nanocomplexes from biomaterial carriers can facilitate a spatiotemporally controlled local delivery of osteogenic oligonucleotides. This review provides an overview of the state-of-the-art in the design of biomaterials which allow for temporal and spatial control over RNA delivery. We correlate this concept of spatiotemporally controlled RNA delivery to the most relevant events that govern bone regeneration to evaluate to which extent tuning of release kinetics is required. In addition, inspired by the physiological principles of bone regeneration, potential new RNA targets are presented. Finally, considerations for clinical translation and upscaled production are summarized to stimulate the design of clinically relevant RNA-releasing biomaterials.

The miRNA-15b/USP7/KDM6B axis engages in the initiation of osteoporosis by modulating osteoblast differentiation and autophagy

Osteoporosis is a metabolic disease that results from oxidative stress or inflammation in renal disorders. microRNAs (miRNAs) are recently implicated to participate in osteoporosis, but the mechanism remains largely unexplored. Herein, we aimed to explore the potential role of miR-15b in osteoblast differentiation and autophagy in osteoporosis. We established osteoporosis models through ovariectomy and determined that miR-15b was highly expressed whereas USP7 and KDM6B were poorly expressed in tissue of osteoporosis mice. Treatment of silenced miR-15b resulted in the elevation of decreased bone mineral density (BMD), the maximum elastic stress and the maximum load of osteoporosis mice. In osteoblasts, miR-15 overexpression decreased proliferation but suppressed the cell differentiation and autophagy, accompanied with decreased expression of USP7. Mechanistically, miR-15 bound and inhibited USP7 expression, while overexpression of USP7 promoted autophagy of osteoblasts. USP7, importantly, strengthened the stability of KDM6B and promoted KDM6B expression. MG132 protease inhibitor increased KDM6B and USP7 expression in osteoblasts. Silencing of KDM6B reversed the promoting effect on autophagy and proliferation induced by overexpression of USP7. Taken altogether, miR-15b inhibits osteoblast differentiation and autophagy to aggravate osteoporosis by targeting USP7 to regulate KDM6B expression.

MicroRNA-409-3p promotes osteoblastic differentiation via activation of Wnt/β-catenin signaling pathway by targeting SCAI

Osteogenic differentiation is an important process of new bone formation, microRNA-409-3p (miR-409-3p) has been reported to be up-regulated in the osteogenic differentiation of human bone marrow mesenchymal stem cells (MSCs). The present study aimed to investigate the regulatory effect of miR-409-3p on osteogenic differentiation of MSCs and its molecular mechanism. The expression of miR-409-3p in osteoblast (human skull osteoblast, HCO) and bone marrow-derived MSCs (MSC-A, MSC-B, MSC-U) were detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The binding of miR-409-3p to suppressor of cancer cell invasion (SCAI) in MSC-B was investigated by performing a dual-luciferase reporter gene assay. MSC-B was selected to transfect with miR-409-3p analog/complementary sequence (cs), miR-409-3p analog + SCAI and miR-409-3p cs + small interfering (si)-SCAI, as well as control, respectively. The alkaline phosphatase (ALP) activity, Alizarin Red staining, and the expression of osteogenic markers (ALP, osteocalcin (OCN), osteopontin (OPN), runt-related transcription factor 2 (RUNX2)) in MSC-B during osteoblastic differentiation were tested by RT-qPCR and Western blotting, respectively. Additionally, the Wnt/β-catenin pathway was inhibited by dickkopf-related protein 1 (DKK-1) to get the roles of miR-409-3p during the osteoblastic differentiation of MSC-B when transfected with miR-409-3p analog. The expression of miR-409-3p in HCO was higher than that in these three MSCs and showed an increasing time-dependent trend on the 0 and 21st day of osteoblastic differentiation. MiR-409-3p directly regulated SCAI by targeting SCAI 3′UTR. Further, miR-409-3p suppressed SCAI expression, but SCAI up-regulation suppressed the osteoblastic differentiation, as well as reduced the relative mRNA/protein expression of Wnt/β-catenin signaling pathway-related genes (Axis inhibition protein 1 (AXIN1), β-catenin, Lymphoid Enhancer Binding Factor 1, Cellular-myelocytomatosis (c-myc) and cyclin D1). Importantly, disruption of Wnt signaling also blocked miR-409-3p induced osteoblastic differentiation of MSCs. Therefore, miR-409-3p promotes osteoblastic differentiation through the activation of the Wnt/β-catenin pathway by down-regulating SCAI expression.

Osteoblast-n-Osteoclast: Making Headway to Osteoporosis Treatment

Background:

Bone is a dynamic tissue that continuously undergoes the modeling and remodeling process to maintain its strength and firmness. Bone remodeling is determined by the functioning of osteoblast and osteoclast cells. The imbalance between the functioning of osteoclast and osteoblast cells leads to osteoporosis. Osteoporosis is divided into primary and secondary osteoporosis. Generally, osteoporosis is diagnosed by measuring bone mineral density (BMD) and various osteoblast and osteoclast cell markers.

Methods:

Relevant literature reports have been studied and data has been collected using various search engines like google scholar, scihub, sciencedirect, pubmed, etc. A thorough understanding of the mechanism of bone targeting strategies has been discussed and related literature has been studied and compiled.

Results:

Bone remodeling process has been described in detail including various approaches for targeting bone. Several bone targeting moieties have been stated in detail along with their mechanisms. Targeting of osteoclasts and osteoblasts using various nanocarriers has been discussed in separate sections. The toxicity issues or Biosafety related to the use of nanomaterials have been covered.

Conclusion:

The treatment of osteoporosis targets the inhibition of bone resorption and the use of agents that promote bone mineralization to slow disease progression. Current osteoporosis therapy involves the use of targeting moieties such as bisphosphonates and tetracyclines for targeting various drugs. Nanotechnology has been used for targeting various drug molecules such as RANKLinhibitors, parathyroid hormone analogues, estrogen agonists and antagonists, Wnt signaling enhancer and calcitonin specifically to bone tissue (osteoclast and osteoblasts). So, a multicomponent treatment strategy targeting both the bone cells will be more effective rather than targeting only osteoclasts and it will be a potential area of research in bone targeting used to treat osteoporosis. The first section of the review article covers various aspects of bone targeting. Another section comprises details of various targeting moieties such as bisphosphonates, tetracyclines; and various nanocarriers developed to target osteoclast and osteoblast cells and summarized data on in vivo models has been used for assessment of bone targeting, drawbacks of current strategies and future perspectives.

Application of Biomarkers for the Prediction and Diagnosis of Bone Metastasis in Breast Cancer

The most common metastatic site of breast cancer is the bone. Metastatic bone disease can alter the integrity of the bone and cause serious complications, thereby greatly reducing health-related quality of life and leading to high medical costs. Although diagnostic methods and treatments for bone metastases (BM) are improving, some patients with early breast cancer who are at high risk of BM are not diagnosed early enough, leading to delayed intervention. Moreover, whole-body scintigraphy cannot easily distinguish BM from non-malignant bone diseases. To circumvent these issues, specific gene and protein biomarkers are being investigated for their potential to predict, diagnose, and evaluate breast cancer prognosis. In this review, we summarized the current biomarkers associated with BM in breast cancer and their role in clinical applications to assist in the diagnosis and treatment of BM in the future.

The crosstalk between bone metabolism, lncRNAs, microRNAs and mRNAs in coronary artery calcification

The association between Coronary Artery Calcification (CAC) and osteoporosis has been reported but not fully understood. Therefore, using an original bioinformatic framework we analyzed transcriptomic profiles of 20 elderly women with high CAC score and 31 age- and sex-matching controls from São Paulo Ageing & Health study (SPAH). We integrated differentially expressed microRNA (miRNA) and long-noncoding RNA (lncRNA) interactions with coding genes associated with CAC, in the context of bone-metabolism genes mined from literature. Top non-coding regulators of bone metabolism in CAC included miRNA 497-5p/195 and 106a-5p, and lncRNA FAM197Y7. Top non-coding RNAs revealed significant interplay between genes regulating bone metabolism, vascularization-related processes, chromatin organization, prostaglandin and calcium co-signaling. Prostaglandin E2 receptor 3 (PTGER3), Fibroblasts Growth Factor Receptor 1 (FGFR1), and One Cut Homeobox 2 (ONECUT2) were identified as the most susceptible to regulation by the top non-coding RNAs. This study provides a flexible transcriptomic framework including non-coding regulation for biomarker-related studies.

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

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

Osteocytic miR21 deficiency improves bone strength independent of sex despite having sex divergent effects on osteocyte viability and bone turnover

Osteocytes play a critical role in mediating cell-cell communication and regulating bone homeostasis, and osteocyte apoptosis is associated with increased bone resorption. miR21, an oncogenic microRNA, regulates bone metabolism by acting directly on osteoblasts and osteoclasts, but its role in osteocytes is not clear. Here, we show that osteocytic miR21 deletion has sex-divergent effects in bone. In females, miR21 deletion reduces osteocyte viability, but suppresses bone turnover. Conversely, in males, miR21 deletion increases osteocyte viability, but stimulates bone turnover and enhances bone structure. Further, miR21 deletion differentially alters osteocyte cytokine production in the two sexes. Interestingly, despite these changes, miR21 deletion increases bone mechanical properties in both sexes, albeit to a greater extent in males. Collectively, our findings suggest that miR21 exerts both sex-divergent and sex-equivalent roles in osteocytes, regulating osteocyte viability and altering bone metabolism through paracrine actions on osteoblasts and osteoclasts differentially in males vs females, whereas, influencing bone mechanical properties independent of sex.

RNA-based scaffolds for bone regeneration: application and mechanisms of mRNA, miRNA and siRNA

Globally, more than 1.5 million patients undergo bone graft surgeries annually, and the development of biomaterial scaffolds that mimic natural bone for bone grafting remains a tremendous challenge. In recent decades, due to the improved understanding of the mechanisms of bone remodeling and the rapid development of gene therapy, RNA (including messenger RNA (mRNA), microRNA (miRNA), and short interfering RNA (siRNA)) has attracted increased attention as a new tool for bone tissue engineering due to its unique nature and great potential to cure bone defects. Different types of RNA play roles via a variety of mechanisms in bone-related cells in vivo as well as after synthesis in vitro. In addition, RNAs are delivered to injured sites by loading into scaffolds or systemic administration after combination with vectors for bone tissue engineering. However, the challenge of effectively and stably delivering RNA into local tissue remains to be solved. This review describes the mechanisms of the three types of RNAs and the application of the relevant types of RNA delivery vectors and scaffolds in bone regeneration. The improvements in their development are also discussed.

Single-cell high-content imaging parameters predict functional phenotype of cultured human bone marrow stromal stem cells

Cultured human bone marrow stromal (mesenchymal) stem cells (hBM-MSCs) are heterogenous cell populations exhibiting variable biological properties. Quantitative high-content imaging technology allows identification of morphological markers at a single cell resolution that are determinant for cellular functions. We determined the morphological characteristics of cultured primary hBM-MSCs and examined their predictive value for hBM-MSC functionality. BM-MSCs were isolated from 56 donors and characterized for their proliferative and differentiation potential. We correlated these data with cellular and nuclear morphological features determined by Operetta; a high-content imaging system. Cell area, cell geometry, and nucleus geometry of cultured hBM-MSCs exhibited significant correlation with expression of hBM-MSC membrane markers: ALP, CD146, and CD271. Proliferation capacity correlated negatively with cell and nucleus area and positively with cytoskeleton texture features. In addition, in vitro differentiation to osteoblasts as well as in vivo heterotopic bone formation was associated with decreased ratio of nucleus width to length. Multivariable analysis applying a stability selection procedure identified nuclear geometry and texture as predictors for hBM-MSCs differentiation potential to osteoblasts or adipocytes. Our data demonstrate that by employing a limited number of cell morphological characteristics, it is possible to predict the functional phenotype of cultured hBM-MSCs and thus can be used as a screening test for "quality" of hBM-MSCs prior their use in clinical protocols.

Biomimetic open porous structured core-shell microtissue with enhanced mechanical properties for bottom-up bone tissue engineering

Background: Microtissues constructed with hydrogels promote cell expansion and specific differentiation by mimicking the microarchitecture of native tissues. However, the suboptimal mechanical property and osteogenic activity of microtissues fabricated by natural polymers need further improvement for bone reconstruction application. Core-shell designed structures are composed of an inner core part and an outer part shell, combining the characteristics of different materials, which improve the mechanical property of microtissues. Methods: A micro-stencil array chip was used to fabricate an open porous core-shell micro-scaffold consisting of gelatin as shell and demineralized bone matrix particles modified with bone morphogenetic protein-2 (BMP-2) as core. Single gelatin micro-scaffold was fabricated as a control. Rat bone marrow mesenchymal stem cells (BMSCs) were seeded on the micro-scaffolds, after which they were dynamic cultured and osteo-induced in mini-capsule bioreactors to fabricate microtissues. The physical characteristics, biocompatibility, osteo-inducing and controlled release ability of the core-shell microtissue were evaluated in vitro respectively. Then microtissues were tested in vivo via ectopic implantation and orthotopic bone implantation in rat model. Results: The Young's modulus of core-shell micro-scaffold was nearly triple that of gelatin micro-scaffold, which means the core-shell micro-scaffolds have better mechanical property. BMSCs rapidly proliferated and retained the highest viability on core-shell microtissues. The improved osteogenic potential of core-shell microtissues was evidenced by the increased calcification based on von kossa staining and osteo-relative gene expression. At 3months after transplantation, core-shell microtissue group formed the highest number of mineralized tissues in rat ectopic subcutaneous model, and displayed the largest amount of new bony tissue deposition in rat orthotopic cranial defect. Conclusion: The novel core-shell microtissue construction strategy developed may become a promising cell delivery platform for bone regeneration.

CircRNA_28313/miR-195a/CSF1 axis modulates osteoclast differentiation to affect OVX-induced bone absorption in mice

Osteoblastic bone formation and osteoclastic bone resorption dynamically maintain the bone homeostasis; in the present study, we attempt to investigate the mechanism of the excessive activation of osteoclasts inducing the deregulation of bone homeostasis from the perspective of non-coding RNA regulation. Differentially expressed patterns of circRNAs were examined in non-treated and RANKL + CSF1-treated bone marrow monocyte/macrophage (BMM) cells and differentially-expressed miRNAs during osteoclast differentiation were analyzed and identified. We found that circRNA_28313 was significantly induced by RANKL + CSF1 treatment. circRNA_28313 knockdown significantly inhibited RANKL + CSF1-induced differentiation of osteoclasts within BMM cells in vitro, while suppressed ovariectomized (OVX)-induced bone resorption in mice in vivo. Via bioinformatics analyses, it has been demonstrated that miR-195a might bind to circRNA_28313 and CSF1 and together form a circRNA-miRNA-mRNA network. circRNA_28313 relieves miR-195a-mediated suppression on CSF1 via acting as a ceRNA, therefore modulating the osteoclast differentiation in BMM cells. In conclusion, circRNA_28313, miR-195a, and CSF1 form a ceRNA network to function in RANKL + CSF1-induced osteoclast differentiation, thus affecting OVX-induced bone absorption in mice.

microRNA-96 promotes osteoblast differentiation and bone formation in ankylosing spondylitis mice through activating the Wnt signaling pathway by binding to SOST

Ankylosing spondylitis (AS) refers to a type of arthritis manifested with chronic inflammation of spine joints. microRNAs (MiRNAs) have been identified as new therapeutic targets for inflammatory diseases. In this study, we evaluated the influence of microRNA-96 (miR-96) on osteoblast differentiation together with bone formation in a murine model of AS. The speculated relationship that miR-96 could bind to sclerostin (SOST) was verified by dual luciferase reporter assay. After successful model establishment, the mice with AS and osteoblasts isolated from mice with AS were treated with mimics or inhibitors of miR-96, or DKK-1 (a Wnt signaling inhibitor). The effects of gain- or loss-of-function of miR-96 on the inflammatory cytokine release (IL-6, IL-10, and TNF-α), alkaline phosphatase (ALP) activity, calcium nodule formation, along with the viability of osteoblasts were determined. It was observed that miR-96 might target and regulate SOST. Besides, miR-96 was expressed at a high level in AS mice while SOST expressed at a low level. TOP/FOP-Flash luciferase reporter assay confirmed that miR-96 activated the Wnt signaling pathway. Moreover, AS mice overexpressing miR-96 exhibited increased contents of IL-6, IL-10 and TNF-α, ALP activity, calcium nodule numbers, and viability of osteoblasts. In contrast, inhibition of miR-96 resulted in suppression of the osteoblast differentiation and bone formation. In conclusion, the study implicates that overexpressing miR-96 could improve osteoblast differentiation and bone formation in AS mice via Wnt signaling pathway activation, highlighting a potential new target for AS treatment.

miR-877-3p promotes TGF-β1-induced osteoblast differentiation of MC3T3-E1 cells by targeting Smad7

MicroRNAs (miRNAs) are emerging as important regulators of various physiological and pathological processes and may serve key roles in the maintenance of bone homeostasis via effects on osteoblast differentiation. The aim of the present study was to define the role of miR-877-3p in osteoblast differentiation using MC3T3-E1 cells, an osteoblast precursor cell line. It was demonstrated using RT-qPCR analysis that miR-877-3p was gradually increased in MC3T3-E1 cells during the osteoblastic differentiation induced by transforming growth factor (TGF)-β1. Gain-of-function and loss-of-function experiments revealed that the overexpression of miR-877-3p promoted the osteoblastic differentiation of MC3T3-E1 cells, whereas depletion of miR-877-3p inhibited this process in vitro and in vivo. Bioinformatics analysis and validation experiments demonstrated that Smad7, which acts as a negative regulator of osteogenesis, was a target of miR-877-3p. Furthermore, the overexpression of Smad7 partially reversed the osteoblastic differentiation of MC3T3-E1 cells induced by miR-877-3p. In conclusion, the results of the present study suggest that the miR-877-3p/Smad7 axis is associated with the osteoblastic differentiation of MC3T3-E1 cells and may indicate a potential therapeutic approach for osteogenesis disorders.

Enhanced Transfection of Human Mesenchymal Stem Cells Using a Hyaluronic Acid/Calcium Phosphate Hybrid Gene Delivery System

Human mesenchymal stem cells (hMSCs) show enormous potential in regenerative medicine and tissue engineering. However, current use of hMSCs in clinics is still limited because there is no appropriate way to control their behavior in vivo, such as differentiation to a desired cell type. Genetic modification may provide an opportunity to control the cells in an active manner. One of the major hurdles for genetic manipulation of hMSCs is the lack of an efficient and safe gene delivery system. Herein, biocompatible calcium phosphate (CaP)-based nanoparticles stabilized with a catechol-derivatized hyaluronic acid (dopa-HA) conjugate were used as a carrier for gene transfection to hMSCs for improved differentiation. Owing to the specific interactions between HA and CD44 of bone marrow-derived hMSCs, dopa-HA/CaP showed significantly higher transfection in hMSCs than branched polyethylenimine (bPEI, MW 25 kDa) with no cytotoxicity. The co-delivery of a plasmid DNA encoding bone morphogenetic protein 2 (BMP-2 pDNA) and micro RNA 148b (miRNA-148b) by dopa-HA/CaP achieved significantly improved osteogenic differentiation of hMSCs.

MicroRNA-92a-1-5p influences osteogenic differentiation of MC3T3-E1 cells by regulating β-catenin

Osteoblastic differentiation is a complex process that is critical for proper bone formation. An increasing number of studies have suggested that microRNAs (miRNAs) are pivotal regulators in various physiological and pathological processes, including osteogenesis. Here, we discuss the influence of miRNA-92a-1-5p on osteogenic differentiation. We found that miR-92a-1-5p was obviously downregulated during osteogenic differentiation of MC3T3-E1 cells. Gain-of-function and loss-of-function experiments revealed that miR-92a-1-5p was a negative regulator of osteogenic differentiation. Experimental validation demonstrated that β-catenin, which acts as a positive regulator of osteogenic differentiation, was negatively regulated by miR-92a1-5p. The findings of this study provide new insights into the possibility of miR-92a1-5p being a potential therapeutic target in the management of bone regeneration-related diseases.

MiR-148a regulates bone marrow mesenchymal stem cells-mediated fracture healing by targeting insulin-like growth factor 1

The purpose of this study was to investigate the underlying molecular mechanisms of fracture healing mediated by bone marrow mesenchymal stem cells. Differentially expressed microRNAs in acutely injured subjects and healthy volunteers were screened by microarray analysis. The dual luciferase reporter system was used to verify whether insulin-like growth factor 1 (IGF1) was the direct target gene regulated by miR-148a. The expression level of miR-148a and IGF1 after osteogenic differentiation was detected by quantitative real-time polymerase chain reaction. Western blot was used to determine the protein expression of bone markers, including IGF1, runt-related transcription factor 2 (Runx2), osteocalcin, and osteopontin in rat bone marrow-derived mesenchymal stem cells. Alkaline phosphatase and alizarin red staining was used to detect alkaline phosphatase activity and calcium deposition. An animal fracture model was used for in vivo experiments. MiR-148a was highly expressed in acutely injured subjects compared with healthy volunteers, and IGF1 was a target of miR-148a. Moreover, compared with the negative control group, IGF1 messenger RNA expression was significantly increased in the miR-148a antagomir group. During osteogenic differentiation, the expression of IGF1, Runx2, osteocalcin, and osteopontin was higher in the miR-148a antagomir group than other groups. In vivo experiments further confirmed that upregulation of IGF1 enhanced fracture healing efficiently by decreasing callus width and area and improving bone mineral density, maximum load, stiffness, and energy absorption. It was proved that IGF1 was the direct target gene of miR-148a, and the use of rat bone marrow-derived mesenchymal stem cells with low expression of miR-148a could improve fracture healing by upregulating IGF1.

Role of microRNA-141-3p in the progression and metastasis of hepatocellular carcinoma cell

Hepatocellular carcinoma (HCC) is a leading cause of cancer related death worldwide. However, the mechanisms underlying HCC progression and metastasis are still in obscure. Here, we used bioinformatic analysis to identify miRNAs that regulate GP73, a specific marker for HCC diagnosis and prognosis. The correlations between miR-141-3p and clinic-pathological factors were analyzed in HCC patient samples; proliferation, migration, invasion, and colony formation were studied using established HCC cell lines. Expression levels of target genes (miR-141-3p, GP73, E-cadherin, N-cadherin, occludin, vimentin, and cytokeratin 18) were detected by either Western blot or qRT-PCR analysis. Xenograft models were established to evaluate tumor growth and metastasis. MiR-141-3p was significantly reduced in HCC tumors and cell lines, highly correlated with tumor progression. In contrast, GP73 was negatively correlated with miR-141-3p in HCC tumors. MiR-141-3p overexpression significantly decreased HCC cell proliferation, migration, and invasion by inhibiting epithelial-mesenchymal transition (EMT). GP73 overexpression partially restored the inhibitory effects of miR-141-3p, while miR-141-3p overexpression markedly inhibited tumor growth and pulmonary metastasis, which were partially reversed by GP73 overexpression. Our findings suggest that miR-141-3p targets GP73 to reverse EMT, subsequently inhibiting HCC progression and metastasis. Thus, overexpression of miR-141-3p could serve as a therapeutic strategy to arrest HCC.

Antagonizing miR-218-5p attenuates Wnt signaling and reduces metastatic bone disease of triple negative breast cancer cells

Wnt signaling is implicated in bone formation and activated in breast cancer cells promoting primary and metastatic tumor growth. A compelling question is whether osteogenic miRNAs that increase Wnt activity for bone formation are aberrantly expressed in breast tumor cells to support metastatic bone disease. Here we report that miR-218-5p is highly expressed in bone metastases from breast cancer patients, but is not detected in normal mammary epithelial cells. Furthermore, inhibition of miR-218-5p impaired the growth of bone metastatic MDA-MB-231 cells in the bone microenvironment in vivo. These findings indicate a positive role for miR-218-5p in bone metastasis. Bioinformatic and biochemical analyses revealed a positive correlation between aberrant miR-218-5p expression and activation of Wnt signaling in breast cancer cells. Mechanistically, miR-218-5p targets the Wnt inhibitors Sclerostin (SOST) and sFRP-2, which highly enhances Wnt signaling. In contrast, delivery of antimiR-218-5p decreased Wnt activity and the expression of metastasis-related genes, including bone sialoprotein (BSP/IBSP), osteopontin (OPN/SPP1) and CXCR-4, implicating a Wnt/miR-218-5p regulatory network in bone metastatic breast cancer. Furthermore, miR-218-5p also mediates the Wnt-dependent up-regulation of PTHrP, a key cytokine promoting cancer-induced osteolysis. Antagonizing miR-218-5p reduced the expression of PTHrP and Rankl, inhibited osteoclast differentiation in vitro and in vivo, and prevented the development of osteolytic lesions in a preclinical metastasis model. We conclude that pathological elevation of miR-218-5p in breast cancer cells activates Wnt signaling to enhance metastatic properties of breast cancer cells and cancer-induced osteolytic disease, suggesting that miR-218-5p could be an attractive therapeutic target for preventing disease progression.

Circular RNAs and hereditary bone diseases

Circular RNA (circRNA) is a non-linear form of RNA derived from exonic, intronic, and exon-intron gene regions. circRNAs are characterized by covalent closed loops, highly stable nuclease resistance, and specific expression in species and developmental stages. CircRNA molecules have been identified as playing roles in the regulation of cell transcription, transcriptional expression after translation, interactions with microRNAs, and protein coding. A high stability and tissue- and disease-specific expression allow circRNAs to serve as potential biomarkers both for diseases and prognosis. CircRNAs function in bone remodeling by directly participating in bone-related signaling pathways and by forming the circRNA-miRNA-mRNA axis. Studies have seldom reported on the low incidence of circRNAs in genetic bone disorders. The current study reviews the characteristics of circRNAs and recent research on their role in rare hereditary bone diseases.

Regulation of Bone Metabolism by microRNAs

PURPOSE OF REVIEW

The small non-coding microRNAs (miRNAs) have emerged as important post-transcriptional regulators of various physiological and pathological processes. The purpose of this article is to review the important recent advances on the role of miRNAs in bone remodeling and metabolic bone disorders.

RECENT FINDINGS

In a physiological context, miRNAs regulate bone formation and bone resorption, thereby contributing to the maintenance of bone homeostasis. Under pathological conditions, an aberrant miRNA signaling contributes to the onset and progression of skeletal disorders, such as osteoporosis. Furthermore, miRNAs can be secreted to circulation and have clinical potential as non-invasive biomarkers. In a therapeutic setting, miRNA delivery or antagonism has been reported to affect several diseases under pre-clinical conditions thereby emerging as novel pharmacological tools. miRNAs are key regulators of bone remodeling in health and disease. The future perspectives in the field include the role of secreted miRNAs in cell-cell communication in the bone environment. Furthermore, the clinical potential of using miRNAs as diagnostic tools and therapeutic targets to treat metabolic bone diseases provides an attractive future direction.

Regulatory effect of microRNA-34a on osteogenesis and angiogenesis in glucocorticoid-induced osteonecrosis of the femoral head

Glucocorticoid-induced osteonecrosis of the femoral head (GIOFH) is a common and devastating orthopedic disease, and its underlying mechanism remains unclear. The aim of this study was to determine the role of microRNA-34a (mir-34a) in GIOFH. C57 mouse mesenchymal stem cells (mMSCs) and human umbilical vein endothelial cells (HUVECs) were cultured with dexamethasone (Dex). A total of 48 adult rats were treated with glucocorticoids, and after the onset of GIOFH, each femoral head was removed. Mir-34a mimics, an inhibitor and over-expressing lentivirus were used in vitro and in vivo, respectively. Real-time PCR, immunohistochemistry, ELISA, cell proliferation assays, osteoblastic differentiation, and endothelial activity assays were employed to evaluate the effect of mir-34a on mMSCs, osteoblasts, and vascular endothelial cells in glucocorticoid-treated mice. We found that Dex inhibited mMSC proliferation and osteoblastic differentiation, as well as the viability and activity of endothelial cells. Dex also caused osteonecrosis and decreased new vessel formation in vivo. Mir-34a alleviated the inhibitory effects of Dex on mMSCs and osteoblasts, while facilitating its inhibitory effects on endothelial cells. Mir-34a is an important regulator in osteogenesis and angiogenesis, and it might be useful as a therapeutic target for GIOFH. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:417-424, 2018.

Targeting the Metastatic Bone Microenvironment by MicroRNAs

Bone metastases are a common and devastating feature of late-stage breast cancer. Metastatic bone disease is a consequence of disturbed bone remodeling due to pathological interactions between cancer cells and the bone microenvironment (BME). In the BME, breast cancer cells severely alter the balanced bone formation and bone resorption driven by osteoblasts and osteoclasts. The complex cellular cross talk in the BME is governed by secreted molecules, signaling pathways and epigenetic cues including non-coding RNAs. MicroRNAs (miRNAs) are small non-coding RNAs that reduce protein abundance and regulate several biological processes, including bone remodeling. Under pathological conditions, abnormal miRNA signaling contributes to the progression of diseases, such as bone metastasis. Recently miRNAs have been demonstrated to regulate several key drivers of bone metastasis. Furthermore, miRNAs are implicated as important regulators of cellular interactions within the metastatic BME. As a consequence, targeting the BME by miRNA delivery or antagonism has been reported to limit disease progression in experimental and preclinical conditions positioning miRNAs as emerging novel therapeutic tools in metastatic bone disease. This review will summarize our current understanding on the composition and function of the metastatic BME and discuss the recent advances how miRNAs can modulate pathological interactions in the bone environment.

Global MicroRNA Profiling in Human Bone Marrow Skeletal-Stromal or Mesenchymal-Stem Cells Identified Candidates for Bone Regeneration

Bone remodeling and regeneration are highly regulated multistep processes involving posttranscriptional regulation by microRNAs (miRNAs). Here, we performed a global profiling of differentially expressed miRNAs in bone-marrow-derived skeletal cells (BMSCs; also known as stromal or mesenchymal stem cells) during in vitro osteoblast differentiation. We functionally validated the regulatory effects of several miRNAs on osteoblast differentiation and identified 15 miRNAs, most significantly miR-222 and miR-423, as regulators of osteoblastogenesis. In addition, we tested the possible targeting of miRNAs for enhancing bone tissue regeneration. Scaffolds functionalized with miRNA nano-carriers enhanced osteoblastogenesis in 3D culture and retained this ability at least 2 weeks after storage. Additionally, anti-miR-222 enhanced in vivo ectopic bone formation through targeting the cell-cycle inhibitor CDKN1B (cyclin-dependent kinase inhibitor 1B). A number of additional miRNAs exerted additive osteoinductive effects on BMSC differentiation, suggesting that pools of miRNAs delivered locally from an implanted scaffold can provide a promising approach for enhanced bone regeneration.

Icariin ameliorates dexamethasone‑induced bone deterioration in an experimental mouse model via activation of microRNA‑186 inhibition of cathepsin K

The present study aimed to investigate bone deterioration in glucocorticoid‑induced osteoporosis (GIOP) mice, and the anti‑osteoporosis effect and underlying molecular mechanism of icariin. Dexamethasone (DSM) treatment was demonstrated to facilitate the induction of hypercalciuria in GIOP mice. Icariin treatment reversed the dexamethasone (DXM)‑induced disequilibrium of calcium homeostasis and bone resorption, and increased serum alkaline phosphatase, tartrate resistant acid phosphatase, osteocalcin and deoxypyridinoline. Haematoxylin and eosin staining revealed an increase in disconnections and separation in the trabecular bone network of the tibial proximal metaphysis, in the GIOP group. Icariin treatment reversed the DXM‑induced trabecular deleterious effects, and stimulated bone remodeling in GIOP mice. Furthermore, the results demonstrated that the mRNA and protein expression of cathepsin K were significantly increased in GIOP mice, compared with the control group. Icariin treatment may suppress the expression of cathepsin K in the tibia of GIOP mice. The levels of microRNA (miR)‑186 were markedly reduced in the tibia of GIOP mice compared with control group; however, this was inhibited by icariin treatment. Bioinformatics analysis demonstrated that miR‑186 regulates cathepsin K via binding to the upstream 3'‑untranslated region. Furthermore, transfection with miR‑186 mimics resulted in inhibition of cathepsin K expression, whereas miR‑186 inhibitors facilitated cathepsin K expression in osteoclasts. In conclusion, the present study demonstrated the protective effects of icariin against bone deteriorations in the experimental GIOP mice, and the underlying mechanism was mediated, at least partially, via activation of miR‑186‑mediated suppression of cathepsin K. These results provide evidence to support the use of icariin as a therapeutic approach in the management of glucocorticoid‑induced bone loss, and the disequilibrium of calcium homeostasis.

MicroRNA‑206 contributes to the progression of steroid‑induced avascular necrosis of the femoral head by inducing osteoblast apoptosis by suppressing programmed cell death 4

The expression of microRNA-206 (miR-206) is aberrantly induced in steroid-induced avascular necrosis of femoral head (SANFH). Therefore, investigating the function of miR-206 in SANFH and uncovering the functional mechanism associated with the condition will promote the understanding and treatment of the disease. The purpose of the present study was to investigate the pro-osteoclasteogenic effect of miR-206 that occurs through regulation of programmed cell death 4 (PDCD4). The expression of miR-206 and PDCD4 was analyzed in the clinical SANFH specimens. The level of miR-206 and PDCD4 was regulated in human osteoblast lineage hFOB1.19 and the effect of different treatments on cell viability, proliferation, apoptosis and differentiation potential of osteoblasts were analyzed with a Cell Counting kit-8, 5-ethynyl-2′-deoxyuridine staining, flow cytometry and Hoechst staining. The expression of miR-206 was upregulated while PDCD4 was downregulated in the SANFH specimens. Induced expression of miR-206 decreased cell viability and proliferation, while apoptosis was induced. At the molecular level, overexpression of miR-206 inhibited the expression of PDCD4, alkaline phosphatase (ALP) and B-cell lymphoma 2 (Bcl-2), and increased the expression of apoptosis regulator Bcl2-X-associated protein (Bax). Inhibiting the expression of miR-206 increased cell viability and proliferation but had no effect on cell apoptosis, as detected by flow cytometry and Hoechst staining. However, at the molecular level, inhibiting the expression of miR-206 induced expression of PDCD4, ALP and Bcl-2, while it decreased the expression of Bax. Additionally, knockdown of PDCD4 blocked the effect of miR-206 inhibition on hFOB1.19 cells, representing a PDCD4-dependent manner of miR-206 in inducing apoptosis of osteoblasts. Therefore, miR-206 promoted the onset of SANFH by inducing apoptosis and suppressed the proliferation of osteoblasts, which was dependent on the inhibition of PDCD4.

MiR-5100 promotes osteogenic differentiation by targeting Tob2

MicroRNAs have emerged as pivotal regulators in various physiological and pathological processes, including osteogenesis. Here we discuss the contribution of miR-5100 to osteoblast differentiation and mineralization. We found that miR-5100 was upregulated during osteoblast differentiation in ST2 and MC3T3-E1 cells. Next, we verified that miR-5100 can promote osteogenic differentiation with gain-of-function and loss-of-function experiments. Target prediction analysis and experimental validation demonstrated that Tob2, which acts as a negative regulator of osteogenesis, was negatively regulated by miR-5100. Furthermore, we confirmed that the important bone-related transcription factor osterix, which can be degraded by binding to Tob2, was influenced by miR-5100 during osteoblast differentiation. Collectively, our results revealed a new molecular mechanism that fine-tunes osteoblast differentiation through miR-5100/Tob2/osterix networks.

Hypoxia-inducible factor 1Α may regulate the commitment of mesenchymal stromal cells toward angio-osteogenesis by mirna-675-5P

BACKGROUND AIMS

During bone formation, angiogenesis and osteogenesis are regulated by hypoxia, which is able to induce blood vessel formation, as well as recruit and differentiate human mesenchymal stromal cells (hMSCs). The molecular mechanisms involved in HIF-1α response and hMSC differentiation during bone formation are still unclear. This study aimed to investigate the synergistic role of hypoxia and hypoxia-mimetic microRNA miR-675-5p in angiogenesis response and osteo-chondroblast commitment of hMSCs.

METHODS

By using a suitable in vitro cell model of hMSCs (maintained in hypoxia or normoxia), the role of HIF-1α and miR-675-5p in angiogenesis and osteogenesis coupling was investigated, using fluorescence-activated cell sorting (FACS), gene expression and protein analysis.

RESULTS

Hypoxia induced miR-675-5p expression and a hypoxia-angiogenic response, as demonstrated by increase in vascular endothelial growth factor messenger RNA and protein release. MiR-675-5p overexpression in normoxia promoted the down-regulation of MSC markers and the up-regulation of osteoblast and chondroblast markers, as demonstrated by FACS and protein analysis. Moreover, miR-675-5p depletion in a low-oxygen condition partially abolished the hypoxic response, including angiogenesis, and in particular restored the MSC phenotype, demonstrated by cytofluorimetric analysis. In addition, current preliminary data suggest that the expression of miR-675-5p during hypoxia plays an additive role in sustaining Wnt/β-catenin pathways and the related commitment of hMSCs during bone ossification.

DISCUSSION

MiR-675-5p may trigger complex molecular mechanisms that promote hMSC osteoblastic differentiation through a dual strategy: increasing HIF-1α response and activating Wnt/β-catenin signaling.

MicroRNAs and Fracture Healing

MicroRNAs (miRNAs) are small molecules found to have major regulatory roles in many biological processes. This review aims to provide an overview of the recent advances in knowledge of the role of miRNAs in fracture healing and bone repair. A search of the published literature was performed (using the PubMed database) to include all relevant studies published in English. These studies were then reviewed and the results condensed into this review paper. MiRNAs have now been shown to have significant alterations in expression levels in bone tissue in the presence of fractures. This is thought to be related to the process of fracture healing through effects on osteoblasts and bone growth factors. These small molecules are also detectable in the circulation where their expression appears to be altered by the presence of fractures. Although further research is required in this area, miRNAs may present an opportunity for future clinical applications in fracture management.

The Roles of Long Non-Protein-Coding RNAs in Osteo-Adipogenic Lineage Commitment

Osteoblasts and adipocytes share a common mesenchymal progenitor in the bone marrow. This implies that a reciprocal relationship exists between osteogenic and adipogenic differentiation. Further, cells of osteoblast lineage transdifferentiate into adipocytes under some circumstances. Dysregulation of osteo-adipogenic fate-determination leads to bone diseases such as osteoporosis, accompanied by an increase in bone marrow adipose tissue. Thus, the fine-tuning of osteo-adipogenesis is necessary for bone homeostasis. Osteo-adipogenic progression is governed by a complex crosstalk of extrinsic signals, transcription factors, and epigenetic factors. Long non-protein-coding RNAs (lncRNAs) act in part as epigenetic regulators in a broad range of biological activities, such as chromatin organization, transcriptional regulation, post-translational modifications, and histone modification. In this review, we highlight the roles of epigenetic regulators, particularly lncRNAs, in the osteo-adipogenic lineage commitment of bone marrow mesenchymal stem cells and the adipogenic transdifferentiation of osteoblasts.

MicroRNAs in bone diseases

MicroRNAs are small, noncoding single-stranded RNAs that have emerged as important posttranscriptional regulators of gene expression, with an essential role in vertebrate development and different biological processes. This review highlights the recent advances in the function of miRNAs and their roles in bone remodeling and bone diseases. MicroRNAs (miRNAs) are a class of small (∼22 nt), noncoding single-stranded RNAs that have emerged as important posttranscriptional regulators of gene expression. They are essential for vertebrate development and play critical roles in different biological processes related to cell differentiation, activity, metabolism, and apoptosis. A rising number of experimental reports now indicate that miRNAs contribute to every step of osteogenesis and bone homeostasis, from embryonic skeletal development to maintenance of adult bone tissue, by regulating the growth, differentiation, and activity of different cell systems inside and outside the skeleton. Importantly, emerging information from animal studies suggests that targeting miRNAs might become an attractive and new therapeutic approach for osteoporosis or other skeletal diseases, even though there are still major concerns related to potential off target effects and the need of efficient delivery methods in vivo. Moreover, besides their recognized effects at the cellular level, evidence is also gathering that miRNAs are excreted and can circulate in the blood or other body fluids with potential paracrine or endocrine functions. Thus, they could represent suitable candidates for becoming sensitive disease biomarkers in different pathologic conditions, including skeletal disorders. Despite these promising perspectives more work remains to be done until miRNAs can serve as robust therapeutic targets or established diagnostic tools for precision medicine in skeletal disorders.

miR-940 upregulation contributes to human cervical cancer progression through p27 and PTEN inhibition

Cervical cancer is considered as a gynecological malignancy accompanied with high rates of mortality across the world. Effective diagnostic, prognostic markers as well as therapeutic targets are necessary to be explored. The p27 and PTEN are known to modulate tumor cell growth and proliferation. However, the molecular mechanisms modulating these genes have not completely been elucidated. In our study, real-time (RT) quantitative PCR indicated that miR‑940 levels were upregulated in human cervical cancer tissue samples and cell lines. Overexpression of miR‑940 could reduce overall survival in patients. Ectopic miR‑940 accelerated cervical cancer cell growth, proliferation and cell cycle arrest in vitro as well as tumor formation in vivo. p27 and PTEN were evidenced as direct targets for miR‑940 and inhibition of p27 and PTEN recovered the suppressive function of miR‑940-silenced cell towards to proliferation and tumorigenicity in cervical cancer cells. In addition, miR‑940 expression was inversely associated with p27 and PTEN expression levels and actively with cyclin D1 in cervical cancer specimens. The results from our study demonstrated that miR‑940 regulated p27 and PTEN post-transcriptionally and might play a significant role in cervical cancer development and progression. Thus, miR‑940 might provide a potential value as therapeutic target for cervical cancer treatment in future.

miR-203 and miR-320 Regulate Bone Morphogenetic Protein-2-Induced Osteoblast Differentiation by Targeting Distal-Less Homeobox 5 (Dlx5)

MicroRNAs (miRNAs) are a family of small, non-coding RNAs (17–24 nucleotides), which regulate gene expression either by the degradation of the target mRNAs or inhibiting the translation of genes. Recent studies have indicated that miRNA plays an important role in regulating osteoblast differentiation. In this study, we identified miR-203 and miR-320b as important miRNAs modulating osteoblast differentiation. We identified Dlx5 as potential common target by prediction algorithms and confirmed this by knock-down and over expression of the miRNAs and assessing Dlx5 at mRNA and protein levels and specificity was verified by luciferase reporter assays. We examined the effect of miR-203 and miR-320b on osteoblast differentiation by transfecting with pre- and anti-miRs. Over-expression of miR-203 and miR-320b inhibited osteoblast differentiation, whereas inhibition of miR-203 and miR-320b stimulated alkaline phosphatase activity and matrix mineralization. We show that miR-203 and miR-320b negatively regulate BMP-2-induced osteoblast differentiation by suppressing Dlx5, which in turn suppresses the downstream osteogenic master transcription factor Runx2 and Osx and together they suppress osteoblast differentiation. Taken together, we propose a role for miR-203 and miR-320b in modulating bone metabolism.