Osteoclast-derived miR-23a-5p-containing exosomes inhibit osteogenic differentiation by regulating Runx2

BackgroundSome microRNAs (miRNAs) are involved in osteogenic differentiation. In recent years, increasing evidences have revealed that exosomes contain specific miRNAs. However, the effect and mechanism of miR-23a-5p-containing exosomes in osteoblast remain largely unclear.MethodsWe extracted exosomes from RANKL-induced RAW 264.7 cells, and identified exosomes via transmission electron microscopy, western blot and flow cytometry analysis. In addition, exosome secretion was inhibited by GW4869 and Rab27a siRNAs. miR-23a-5p expression was analyzed by qRT-PCR, and the related protein levels were examined by western blot assay. Furthermore, the number and distribution of osteoclasts were detected by TRAP staining, and early osteogenesis was evaluated by ALP staining. Combination of YAP1 and Runx2 was verified by Co-IP assay, and the regulation of miR-23a-5p and Runx2 was measured by dual luciferase reporter assay.ResultsWe successfully extracted exosomes from RANKL-induced RAW 264.7 cells, and successfully verified exosomes morphology. We also indicated that miR-23a-5p was highly expressed in exosomes from RANKL-induced RAW 264.7 cells, and osteoclast-derived miR-23a-5p-containing exosomes inhibited osteoblast activity, while its inhibition weakened osteoclasts. In mechanism, we demonstrated that Runx2 was a target gene of miR-23a-5p, YAP interacted with Runx2, and YAP or Runx2 inhibited MT1DP expression. In addition, we proved that knockdown of MT1DP facilitated osteogenic differentiation by regulating FoxA1 and Runx2.ConclusionsWe demonstrated that osteoclast-derived miR-23a-5p-containing exosomes could efficiently suppress osteogenic differentiation by inhibiting Runx2 and promoting YAP1-mediated MT1DP. Therefore, we suggested miR-23a-5p in exosomes might provide a novel mechanism for osteoblast function.     

Comparison of gingiva‐derived and bone marrow mesenchymal stem cells for osteogenesis

Presently, bone marrow is considered as a prime source of mesenchymal stem cells; however, there are some drawbacks and limitations. Compared with other mesenchymal stem cell (MSC) sources, gingiva‐derived mesenchymal stem cells (GMSCs) are abundant and easy to obtain through minimally invasive cell isolation techniques. In this study, MSCs derived from gingiva and bone marrow were isolated and cultured from mice. GMSCs were characterized by osteogenic, adipogenic and chondrogenic differentiation, and flow cytometry. Compared with bone marrow MSCs (BMSCs), the proliferation capacity was judged by CCK‐8 proliferation assay. Osteogenic differentiation was assessed by ALP staining, ALP assay and Alizarin red staining. RT‐qPCR was performed for ALP, OCN, OSX and Runx2. The results indicated that GMSCs showed higher proliferative capacity than BMSCs. GMSCs turned more positive for ALP and formed a more number of mineralized nodules than BMSCs after osteogenic induction. RT‐qPCR revealed that the expression of ALP, OCN, OSX and Runx2 was significantly increased in the GMSCs compared with that in BMSCs. Moreover, it was found that the number of CD90‐positive cells in GMSCs elevated more than that of BMSCs during osteogenic induction. Taking these results together, it was indicated that GMSCs might be a promising source in the future bone tissue engineering.     

MiR-26b-3p regulates osteoblast differentiation via targeting estrogen receptor α

BackgroundUnderstanding of the molecular mechanisms of miRNAs involved in osteoblast differentiation is important for the treatment of bone-related diseases.MethodsMC3T3-E1 cells were induced to osteogenic differentiation by culturing with bone morphogenetic protein 2 (BMP2). After transfected with miR-26b-3p mimics or inhibitors, the osteogenic differentiation of MC3T3-E1 cells was detected by ALP and ARS staining. Cell viability was analyzed by MTT. The expressions of miR-26b-3p and osteogenic related markers and signaling were examined by qPCR and western blot. Direct binding of miR-26b-3p and ER-α were determined by dual luciferase assay.ResultsmiR-26b-3p was significantly down-regulated during osteoblast differentiation. Overexpression of miR-26b-3p inhibited osteoblast differentiation, while inhibition of miR-26b-3p enhanced osteoblast differentiation. Further studies demonstrated miR-26b-3p inhibited the expression of estrogen receptor α (ER-α) by directly targeting to the CDS region of ER-α mRNA. Overexpression of ER-α rescued the suppression effects of miR-26b-3p on osteoblast differentiation, while knockdown of ER-α reversed the upregulation of osteoblast differentiation induced by knockdown of miR-26b-3p.ConclusionOur study demonstrates that miR-26b-3p suppresses osteoblast differentiation of MC3T3-E1 cells via directly targeting ER-α.     

MiRNA-1271-5p regulates osteogenic differentiation of human bone marrow-derived mesenchymal stem cells by targeting forkhead box O1 (FOXO1)

Forkhead box O1 (FOXO1) is a key regulator of osteogenesis. The aim of this study was to identify the mechanisms of microRNAs (miRNAs) targeting FOXO1 in osteogenic differentiation of human bone marrow mesenchymal stem cells (hMSCs). Three miRNA target prediction programs were used to search for potential miRNAs that target FOXO1. Quantitative real-time polymerase chain reaction was conducted to detect the expression of miR-1271-5p and FOXO1 during osteogenic differentiation. Target gene prediction and screening, luciferase reporter assay was used to verify the downstream target gene of miR-1271-5p. The expression levels of FOXO1 and Runx2 were detected by RT-qPCR and Western blot analysis. Alkaline phosphatase (ALP) activity and matrix mineralization were detected by biochemical methods. The expression levels of Runx2, ALP, and osteocalcin were detected by RT-qPCR. Our results showed that miR-1271-5p was downregulated during osteogenic induction. And the expression levels of miR-1271-5p were higher in osteoporotic tissues than that in adjacent nonosteoporotic tissues. The expression levels of FOXO1 were lower in osteoporotic tissues than that in adjacent nonosteoporotic tissues. And a negative correlation was found between miR-1271-5p and FOXO1 in osteoporotic tissues. Overexpression of miR-1271-5p downregulated FOXO1 and inhibited osteogenic differentiation in hMSCs. Overexpression of miR-1271-5p downregulated the expression of osteogenic markers and reduced ALP activity. In addition, ectopic expression of FOXO1 reversed the effect of miR-1271-5p on osteogenic differentiation. In conclusion, miR-1271-5p functioned as a therapeutic target of osteogenic differentiation in hMSCs by inhibiting FOXO1, which provides valuable insights into the use of miR-1271-5p as a target in the treatment of osteoporosis and other bone metabolic diseases.     

Collagen-derived dipeptide prolyl-hydroxyproline promotes osteogenic differentiation through Foxg1

Prolyl-hydroxyproline (Pro-Hyp) is one of the major constituents of collagen-derived dipeptides. We previously reported that Pro-Hyp promotes the differentiation of osteoblasts by increasing Runx2, osterix and Col1α1 mRNA expression levels. Here, to elucidate the mechanism of Pro-Hyp promotion of osteoblast differentiation, we focus on the involvement of Foxo1 in osteoblast differentiation via Runx2 regulation and the role of Foxg1 in Foxo1 regulation. The addition of Pro-Hyp had no effect on MC3T3-E1 cell proliferation in Foxo1- or Foxg1-knockdown cells. In Foxo1-knockdown cells, the addition of Pro-Hyp increased ALP activity, but in Foxg1-knockdown cells, it had no effect on ALP activity. An enhancing effect of Pro-Hyp on the Runx2 and osterix expression levels was observed in Foxo1-knockdown cells. However, no enhancing effect of Pro-Hyp on osteoblastic gene expression was observed when Foxg1 was knocked down. These results demonstrate that Pro-Hyp promotes osteoblastic MC3T3-E1 cell differentiation and upregulation of osteogenic genes via Foxg1 expression.     

GNAS knockdown suppresses osteogenic differentiation of mesenchymal stem cells via activation of Hippo signaling pathway

Bone marrow-derived mesenchymal stem cells (BMSCs) are a suitable option for cell-based tissue engineering therapies due to their ability to renew and differentiate into multiple different tissue types, such as bone. Over the last decade, the effect of GNAS on the regulation of osteoblast differentiation has attracted great attention. Herein, this study aimed to explore the role of GNAS in osteogenic differentiation of MSCs. A total of 85 GNAS^f/f male mice were selected for animal experiments and 10 GNAS^f/f male mice for BMSC isolation to conduct cell experiments. The mice and BMSCs were treated with Verteporfin (a Hippo signaling pathway inhibitor) to inhibit the Hippo signaling pathway or recombinant adenovirus-expressing Cre to knockout the GNAS expression. Next, computed tomography scan, Von Kossa staining, and alizarin red staining were performed to detect osteogenic differentiation ability. Moreover, immunohistochemistry and alkaline phosphatase (ALP) staining were used to assess the expression of Oc and Osx in femur tissues and ALP activity. At last, the expression of GNAS, osteogenic markers, and factors related to the Hippo signaling pathway was evaluated. Initially, the results displayed successful knockout of the GNAS gene from mice and BMSCs. Moreover, the data indicated that GNAS knockout inhibits expression of Oc, Osx, ALP, BMP-2, and Runx2, and ALP activity. Additionally, GNAS knockout promotes activation of the Hippo signaling pathway, so as to repress osteogenic differentiation. Collectively, depleted GNAS exerts an inhibitory role in osteogenic differentiation of MSCs by activating Hippo signaling pathway, providing a candidate mediator for osteoporosis.     

Rapamycin inhibits osteoblast proliferation and differentiation in MC3T3-E1 cells and primary mouse bone marrow stromal cells

While the roles of the mammalian target of rapamycin (mTOR) signaling in regulation of cell growth, proliferation, and survival have been well documented in various cell types, its actions in osteoblasts are poorly understood. In this study, we determined the effects of rapamycin, a specific inhibitor of mTOR, on osteoblast proliferation and differentiation using MC3T3-E1 preosteoblastic cells (MC-4) and primary mouse bone marrow stromal cells (BMSCs). Rapamycin significantly inhibited proliferation in both MC-4 cells and BMSCs at a concentration as low as 0.1 nM. Western blot analysis shows that rapamycin treatment markedly reduced levels of cyclin A and D1 protein in both cell types. In differentiating osteoblasts, rapamycin dramatically reduced osteoblast-specific osteocalcin (Ocn), bone sialoprotein (Bsp), and osterix (Osx) mRNA expression, ALP activity, and mineralization capacity. However, the drug treatment had no effect on osteoblast differentiation parameters when the cells were completely differentiated. Importantly, rapamycin markedly reduced levels of Runx2 protein in both proliferating and differentiating but not differentiated osteoblasts. Finally, overexpression of S6K in COS-7 cells significantly increased levels of Runx2 protein and Runx2 activity. Taken together, our studies demonstrate that mTOR signaling affects osteoblast functions by targeting osteoblast proliferation and the early stage of osteoblast differentiation.     

Role of diabetes- and obesity-related protein in the regulation of osteoblast differentiation

Although thyroid hormone (TH) is known to exert important effects on the skeleton, the nuclear factors constituting the TH receptor coactivator complex and the molecular pathways by which TH mediates its effects on target gene expression in osteoblasts remain poorly understood. A recent study demonstrated that the actions of TH on myoblast differentiation are dependent on diabetes- and obesity-related protein (DOR). However, the role of DOR in osteoblast differentiation is unknown. We found DOR expression increased during in vitro differentiation of bone marrow stromal cells into osteoblasts and also in MC3T3-E1 cells treated with TH. However, DOR expression decreased during cellular proliferation. To determine whether DOR acts as a modulator of TH action during osteoblast differentiation, we examined whether overexpression or knockdown of DOR in MC3T3-E1 cells affects the ability of TH to induce osteoblast differentiation by evaluating alkaline phosphatase (ALP) activity. ALP activity was markedly increased in DOR-overexpressing cells treated with TH. In contrast, loss of DOR dramatically reduced TH stimulation of ALP activity in MC3T3-E1 cells and primary calvaria osteoblasts transduced with lentiviral DOR shRNA. Consistent with reduced ALP activity, mRNA levels of osteocalcin, ALP, and Runx2 were decreased significantly in DOR shRNA cells. In addition, a common single nucleotide polymorphism (SNP), DOR1 found on the promoter of human DOR gene, was associated with circulating osteocalcin levels in nondiabetic subjects. Based on these data, we conclude that DOR plays an important role in TH-mediated osteoblast differentiation, and a DOR SNP associates with plasma osteocalcin in men.     

Morphological and proteomic analysis of early stage of osteoblast differentiation in osteoblastic progenitor cells

Bone remodeling relies on a dynamic balance between bone formation and resorption, mediated by osteoblasts and osteoclasts, respectively. Under certain stimuli, osteoprogenitor cells may differentiate into premature osteoblasts and further into mature osteoblasts. This process is marked by increased alkaline phosphatase (ALP) activity and mineralized nodule formation. In this study, we induced osteoblast differentiation in mouse osteoprogenitor MC3T3-E1 cells and divided the process into three stages. In the first stage (day 3), the MC3T3-E1 cell under osteoblast differentiation did not express ALP or deposit a mineralized nodule. In the second stage, the MC3T3-E1 cell expressed ALP but did not form a mineralized nodule. In the third stage, the MC3T3-E1 cell had ALP activity and formed mineralized nodules. In the present study, we focused on morphological and proteomic changes of MC3T3-E1 cells in the early stage of osteoblast differentiation — a period when premature osteoblasts transform into mature osteoblasts. We found that mean cell area and mean stress fiber density were increased in this stage due to enhanced cell spreading and decreased cell proliferation. We further analyzed the proteins in the signaling pathway of regulation of the cytoskeleton using a proteomic approach and found upregulation of IQGAP1, gelsolin, moesin, radixin, and Cfl1. After analyzing the focal adhesion signaling pathway, we found the upregulation of FLNA, LAMA1, LAMA5, COL1A1, COL3A1, COL4A6, and COL5A2 as well as the downregulation of COL4A1, COL4A2, and COL4A4. In conclusion, the signaling pathway of regulation of the cytoskeleton and focal adhesion play critical roles in regulating cell spreading and actin skeleton formation in the early stage of osteoblast differentiation.