Runx1 regulates osteogenic differentiation of BMSCs by inhibiting adipogenesis through Wnt/β-catenin pathway

Runx1 alleviates osteoarthritis progression in aging mice

With rates growing quickly with age, osteoarthritis (OA) is the most common cause of chronic disability in aging persons. The discomfort and reduced motion associated with osteoarthritis have a significant impact on quality of life, and there is no known solution. Runt-related transcription factor 1(Runx1) has been shown to play a protective role in the development of osteoarthritis by promoting chondrogenesis. We had created models of ageing mice with osteoarthritis by anterior cruciate ligament transection (ACLT) and analyzed the effects of intra-articular injection of adeno-associated virus/Runx1 (AAV/Runx1) on the models. The results showed that the AAV/Runx1-group maintained better articular cartilage integrity and retained more proteoglycan than the OA group after injection of AAV-Runx1. The markers related to pathological changes in cartilage were downregulated, while the markers related to physiological changes in cartilage were upregulated. This suggests that Runx1 may impede OA progression on the knee joint of ageing mice, potentially playing a protective role in OA and becoming a probable treatment target for osteoarthritis among ageing patients in the future.

Human umbilical cord mesenchymal stem cells overexpressing RUNX1 promote tendon-bone healing by inhibiting osteolysis, enhancing osteogenesis and promoting angiogenesis

BACKGROUND

Rotator cuff injury (RCI) is a common shoulder injury, which is difficult to be completely repaired by surgery. Hence, new strategies are needed to promote the healing of tendon-bone.

OBJECTIVE

We aimed to investigate the effect of human umbilical cord mesenchymal stem cells (hUC-MSCs) overexpressing RUNX1 on the tendon-bone healing after RCI, and to further explore its mechanism.

METHODS

Lentiviral vector was used to mediate the overexpression of RUNX1. RUNX1-overexpressed UCB-MSCs (referred to as MSC-RUNX1) were co-cultured with osteoclasts, and TRAP staining was performed to observe the formation of osteoclasts. Then MSC-RUNX1 was cultured in osteogenic differentiation medium, Alizarin red staining was conducted to detect osteogenic differentiation. The expression of markers of osteogenesis and osteoclast was detected by RT-qPCR. EA. hy926 cells were co-cultured with MSC-RUNX1. Transwell assay was used to detect the migration, and the expression of angiogenesis related-genes VEGF and TGF-β was detected by RT-qPCR. The rat rotator cuff reconstruction model was established and MSCs were injected at the tendon-bone junction. Biomechanical test and micro-CT scanning were performed, and HE, Masson and Alcian Blue staining were used for histological evaluation of tendon-bone healing. TUNEL and PCNA immunofluorescence (IF) staining were performed to evaluate apoptosis and proliferation at the tendon-bone healing site. The levels of TNF-α, IL-6 and IL-8 in serum were detected by ELISA. The expression of CD31 and Endomucin that related to angiogenesis was detected by IF. Safranin O-fast and TRAP/CD40L immunohistochemical staining were used to assess the levels of osteoclasts and osteoblasts at the tendon-bone healing site.

RESULTS

hUC-MSCs overexpressing RUNX1 inhibited osteoclast formation and promoted osteogenic differentiation. MSC-RUNX1 could promote the migration and tube formation of EA. hy926 cells, and up-regulate the levels of VEGF and TGF-β. Model mice treated with MSC-RUNX1 partially restored the biomechanical indexes. Treatment of MSC-RUNX1 obviously increased the bone density, accompanied by the formation of new bone. In vivo experiments showed that MSC-RUNX1 treatment could promote tendon-bone healing and inhibit inflammatory response in rats. MSC-RUNX1 treatment also promoted angiogenesis at the tendon-bone healing site, while inhibiting osteoclast formation and promoting osteogenic differentiation.

CONCLUSION

hUC-MSCs overexpressing RUNX1 can inhibit the formation of osteoclasts and differentiation of osteoblasts, promote angiogenesis and inhibit inflammation, thereby promoting tendon-bone healing after RCI.

[Latest Findings on the Role of RUNX1 in Bone Development and Disorders]

Runt-related transcription factor (RUNX1) is a transcription factor closely involved in hematopoiesis. RUNX1 gene mutation plays an essential pathogenic role in the initiation and development of hematological tumors, especially in acute myeloid leukemia. Recent studies have shown that RUNX1 is also involved in the regulation of bone development and the pathological progression of bone-related diseases. RUNX1 promotes the differentiation of mesenchymal stem cells into chondrocytes and osteoblasts and modulates the maturation and extracellular matrix formation of chondrocytes. The expression of RUNX1 in mesenchymal stem cells, chondrocytes, and osteoblasts is of great significance for maintaining normal bone development and the mass and quality of bones. RUNX1 also inhibits the differentiation and bone resorptive activities of osteoclasts, which may be influenced by sexual dimorphism. In addition, RUNX1 deficiency contributes to the pathogenesis of osteoarthritis, delayed fracture healing, and osteoporosis, which was revealed by the RUNX1 conditional knockout modeling in mice. However, the roles of RUNX1 in regulating the hypertrophic differentiation of chondrocytes, the sexual dimorphism of activities of osteoclasts, as well as bone loss in diabetes mellitus, senescence, infection, chronic inflammation, etc, are still not fully understood. This review provides a systematic summary of the research progress concerning RUNX1 in the field of bone biology, offering new ideas for using RUNX1 as a potential target for bone related diseases, especially osteoarthritis, delayed fracture healing, and osteoporosis.

Acetylation and deacetylation of histone in adipocyte differentiation and the potential significance in cancer

Adipocytes are derived from pluripotent mesenchymal stem cells and can develop into several cell types including adipocytes, myocytes, chondrocytes, and osteocytes. Adipocyte differentiation is regulated by a variety of transcription factors and signaling pathways. Various epigenetic factors, particularly histone modifications, play key roles in adipocyte differentiation and have indispensable functions in altering chromatin conformation. Histone acetylases and deacetylases participate in the regulation of protein acetylation, mediate transcriptional and post-translational modifications, and directly acetylate or deacetylate various transcription factors and regulatory proteins. The adipocyte differentiation of stem cells plays a key role in various metabolic diseases. Cancer stem cells(CSCs) play an important function in cancer metastasis, recurrence, and drug resistance, and have the characteristics of stem cells. They are expressed in various cell lineages, including adipocytes. Recent studies have shown that cancer stem cells that undergo epithelial-mesenchymal transformation can undergo adipocytic differentiation, thereby reducing the degree of malignancy. This opens up new possibilities for cancer treatment. This review summarizes the regulation of acetylation during adipocyte differentiation, involving the functions of histone acetylating and deacetylating enzymes as well as non-histone acetylation modifications. Mechanistic studies on adipogenesis and acetylation during the differentiation of cancer cells into a benign cell phenotype may help identify new targets for cancer treatment.

Runx1 Deficiency Promotes M2 Macrophage Polarization Through Enhancing STAT6 Phosphorylation

Our previous study had demonstrated that Runx1 promoted LPS-induced macrophage inflammatory response, however, the role of Runx1 in M2 macrophage polarization still remains largely unknown. This study was conducted to investigate the role of Runx1 in IL-4/IL-13-induced M2 macrophage polarization and its potential regulatory mechanism. We found that exposure of macrophages to IL-4/IL-13 induced a remarkable increasement in Runx1 expression level. Specifically, we established genetically modified mice lacking Runx1 in myeloid cells, including macrophages. RNA-Seq was performed to identify differentially expressed genes (DEGs) between Runx1 knockout and WT control bone marrow-derived macrophages (BMDMs). We identified 686 DEGs, including many genes which were highly expressed in M2 macrophage. In addition, bioinformatics analysis indicated that these DEGs were significantly enriched in extracellular matrix-related processes. Moreover, RT-qPCR analysis showed that there was an obvious upregulation in the relative expression levels of M2 marker genes, including Arg1, Ym1, Fizz1, CD71, Mmp9, and Tgm2, in Runx1 knockout macrophages, as compared to WT controls. Consistently, similar results were obtained in the protein and enzymatic activity levels of Arg1. Finally, we found that the STAT6 phosphorylation level was significantly enhanced in Runx1 knockout macrophages, and the STAT6 inhibitor AS1517499 partly reduced the upregulated effect of Runx1 deficiency on the M2 macrophage polarization. Taken together, Runx1 deficiency facilitates IL-4/IL-13-induced M2 macrophage polarization through enhancing STAT6 phosphorylation.

Genetic dissection of triplicated chromosome 21 orthologs yields varying skeletal traits in Down syndrome model mice

Down syndrome (DS) phenotypes result from triplicated genes, but the effects of three copy genes are not well known. A mouse mapping panel genetically dissecting human chromosome 21 (Hsa21) syntenic regions was used to investigate the contributions and interactions of triplicated Hsa21 orthologous genes on mouse chromosome 16 (Mmu16) on skeletal phenotypes. Skeletal structure and mechanical properties were assessed in femurs of male and female Dp9Tyb, Dp2Tyb, Dp3Tyb, Dp4Tyb, Dp5Tyb, Dp6Tyb, Ts1Rhr and Dp1Tyb;Dyrk1a+/+/- mice. Dp1Tyb mice, with the entire Hsa21 homologous region of Mmu16 triplicated, display bone deficits similar to those of humans with DS and served as a baseline for other strains in the panel. Bone phenotypes varied based on triplicated gene content, sex and bone compartment. Three copies of Dyrk1a played a sex-specific, essential role in trabecular deficits and may interact with other genes to influence cortical deficits related to DS. Triplicated genes in Dp9Tyb and Dp2Tyb mice improved some skeletal parameters. As triplicated genes can both improve and worsen bone deficits, it is important to understand the interaction between and molecular mechanisms of skeletal alterations affected by these genes.

MicroRNA-181a-5p Curbs Osteogenic Differentiation and Bone Formation Partially Through Impairing Runx1-Dependent Inhibition of AIF-1 Transcription

BACKGRUOUND

Evidence has revealed the involvement of microRNAs (miRNAs) in modulating osteogenic differentiation, implying the promise of miRNA-based therapies for treating osteoporosis. This study investigated whether miR-181a-5p influences osteogenic differentiation and bone formation and aimed to establish the mechanisms in depth.

METHODS

Clinical serum samples were obtained from osteoporosis patients, and MC3T3-E1 cells were treated with osteogenic induction medium (OIM) to induce osteogenic differentiation. miR-181a-5p-, Runt-related transcription factor 1 (Runx1)-, and/or allograft inflammatory factor-1 (AIF-1)-associated oligonucleotides or vectors were transfected into MC3T3-E1 cells to explore their function in relation to the number of calcified nodules, alkaline phosphatase (ALP) staining and activity, expression levels of osteogenesis-related proteins, and apoptosis. Luciferase activity, RNA immunoprecipitation, and chromatin immunoprecipitation assays were employed to validate the binding relationship between miR-181a-5p and Runx1, and the transcriptional regulatory relationship between Runx1 and AIF-1. Ovariectomy (OVX)-induced mice were injected with a miR-181a-5p antagonist for in vivo verification.

RESULTS

miR-181a-5p was highly expressed in the serum of osteoporosis patients. OIM treatment decreased miR-181a-5p and AIF-1 expression, but promoted Runx1 expression in MC3T-E1 cells. Meanwhile, upregulated miR-181a-5p suppressed OIM-induced increases in calcified nodules, ALP content, and osteogenesis-related protein expression. Mechanically, miR-181a-5p targeted Runx1, which acted as a transcription factor to negatively modulate AIF-1 expression. Downregulated Runx1 suppressed the miR-181a-5p inhibitor-mediated promotion of osteogenic differentiation, and downregulated AIF-1 reversed the miR-181a-5p mimic-induced inhibition of osteogenic differentiation. Tail vein injection of a miR-181a-5p antagonist induced bone formation in OVX-induced osteoporotic mice.

CONCLUSION

In conclusion, miR-181a-5p affects osteogenic differentiation and bone formation partially via the modulation of the Runx1/AIF-1 axis.

The roles of Runx1 in skeletal development and osteoarthritis: A concise review

Runt-related transcription factor-1 (Runx1) is well known for its functions in hematopoiesis and leukemia but recent research has focused on its role in skeletal development and osteoarthritis (OA). Deficiency of the Runx1 gene is fatal in early embryonic development, and specific knockout of Runx1 in cell lineages of cartilage and bone leads to delayed cartilage formation and impaired bone calcification. Runx1 can regulate genes including collagen type II (Col2a1) and X (Col10a1), SRY-box transcription factor 9 (Sox9), aggrecan (Acan) and matrix metalloproteinase 13 (MMP-13), and the up-regulation of Runx1 improves the homeostasis of the whole joint, even in the pathological state. Moreover, Runx1 is activated as a response to mechanical compression, but impaired in the joint with the pathological progress associated with osteoarthritis. Therefore, interpretation about the role of Runx1 could enlarge our understanding of key marker genes in the skeletal development and an increased understanding of Runx1 could be helpful to identify treatments for osteoarthritis. This review provides the most up-to-date advances in the roles and bio-mechanisms of Runx1 in healthy joints and osteoarthritis from all currently published articles and gives novel insights in therapeutic approaches to OA based on Runx1.

Runx1 is a key regulator of articular cartilage homeostasis by orchestrating YAP, TGFβ, and Wnt signaling in articular cartilage formation and osteoarthritis

Runt-related transcription factor 1 (Runx1) plays a key role in cartilage formation, but its function in articular cartilage formation is unclear. We generated non-inducible and inducible Runx1-deficient mice (Runx1f/fCol2α1-Cre and Runx1f/fCol2α1-CreER mice) and found that chondrocyte-specific Runx1-deficient mice developed a spontaneous osteoarthritis (OA)-like phenotype and showed exacerbated articular cartilage destruction under OA, characterized by articular cartilage degradation and cartilage ossification, with decreased Col2α1 expression and increased Mmp13 and Adamts5 expression. RNA-sequencing analysis of hip articular cartilage from the Runx1f/fCol2α1-Cre mice compared to that from wild-type mice and subsequent validation analyses demonstrated that Runx1 is a central regulator in multiple signaling pathways, converging signals of the Hippo/Yap, TGFβ/Smad, and Wnt/β-catenin pathways into a complex network to regulate the expression of downstream genes, thereby controlling a series of osteoarthritic pathological processes. RNA-sequencing analysis of mutant knee joints showed that Runx1's role in signaling pathways in articular cartilage is different from that in whole knee joints, indicating that Runx1 regulation is tissue-specific. Histopathologic analysis confirmed that Runx1 deficiency decreased the levels of YAP and p-Smad2/3 and increased the levels of active β-catenin. Overexpression of Runx1 dramatically increased YAP expression in chondrocytes. Adeno-associated virus-mediated Runx1 overexpression in the knee joints of osteoarthritic mice showed the protective effect of Runx1 on articular cartilage damaged in OA. Our results notably showed that Runx1 is a central regulator of articular cartilage homeostasis by orchestrating the YAP, TGFβ, and Wnt signaling pathways in the formation of articular cartilage and OA, and targeting Runx1 and its downstream genes may facilitate the design of novel therapeutic approaches for OA.

Knockdown of FOXA1 enhances the osteogenic differentiation of human bone marrow mesenchymal stem cells partly via activation of the ERK1/2 signalling pathway

Background

The available therapeutic options for large bone defects remain extremely limited, requiring new strategies to accelerate bone healing. Genetically modified bone mesenchymal stem cells (BMSCs) with enhanced osteogenic capacity are recognised as one of the most promising treatments for bone defects.

Methods

We performed differential expression analysis of miRNAs between human BMSCs (hBMSCs) and human dental pulp stem cells (hDPSCs) to identify osteogenic differentiation-related microRNAs (miRNAs). Furthermore, we identified shared osteogenic differentiation-related miRNAs and constructed an miRNA-transcription network. The Forkhead box protein A1 (FOXA1) knockdown strategy with a lentiviral vector was used to explore the role of FOXA1 in the osteogenic differentiation of MSCs. Cell Counting Kit-8 was used to determine the effect of the knockdown of FOXA1 on hBMSC proliferation; real-time quantitative reverse transcription PCR (qRT-PCR) and western blotting were used to investigate target genes and proteins; and alkaline phosphatase (ALP) staining and Alizarin Red staining (ARS) were used to assess ALP activity and mineral deposition, respectively. Finally, a mouse model of femoral defects was established in vivo, and histological evaluation and radiographic analysis were performed to verify the therapeutic effects of FOXA1 knockdown on bone healing.

Results

We identified 22 shared and differentially expressed miRNAs between hDPSC and hBMSC, 19 of which were downregulated in osteogenically induced samples. The miRNA-transcription factor interaction network showed that FOXA1 is the most significant and novel osteogenic differentiation biomarker among more than 300 transcription factors that is directly targeted by 12 miRNAs. FOXA1 knockdown significantly promoted hBMSC osteo-specific genes and increased mineral deposits in vitro. In addition, p-ERK1/2 levels were upregulated by FOXA1 silencing. Moreover, the increased osteogenic differentiation of FOXA1 knockdown hBMSCs was partially rescued by the addition of ERK1/2 signalling inhibitors. In a mouse model of femoral defects, a sheet of FOXA1-silencing BMSCs improved bone healing, as detected by microcomputed tomography and histological evaluation.

Conclusion

These findings collectively demonstrate that FOXA1 silencing promotes the osteogenic differentiation of BMSCs via the ERK1/2 signalling pathway, and silencing FOXA1 in vivo effectively promotes bone healing, suggesting that FOXA1 may be a novel target for bone healing.

Upregulation of Runt related transcription factor 1 (RUNX1) contributes to tendon-bone healing after anterior cruciate ligament reconstruction using bone mesenchymal stem cells

Background

Anterior cruciate ligament (ACL) injury could lead to functional impairment along with disabilities. ACL reconstruction often fails owing to the regeneration failure of tendon–bone interface. Herein, we aimed to investigate the effects of Runt related transcription factor 1 (RUNX1) on tendon–bone healing after ACL reconstruction using bone mesenchymal stem cells (BMSCs).

Methods

BMSCs were isolated from the marrow cavity of rat femur, followed by the modification of RUNX1 with lentiviral system. Then, an ACL reconstruction model of rats was established with autografts.

Results

Results of flow cytometry exhibited positive-antigen CD44 and CD90, as well as negative-antigen CD34 and CD45 of the BMSCs. Then, we found that RUNX1-upregulated BMSCs elevated the decreased biomechanical strength of the tendon grafts after ACL reconstruction. Moreover, based on the histological observation, upregulation of RUNX1 was linked with better recovery around the bone tunnel, a tighter tendon–bone interface, and more collagen fibers compared to the group of BMSCs infected with LV-NC. Next, RUNX1-upregulated BMSCs promoted osteogenesis after ACL reconstruction, as evidenced by the mitigation of severe loss and erosion of the cartilage and bone in the tibial and femur area, as well as the increased number of osteoblasts identified by the upregulation of alkaline phosphatase, osteocalcin, and osteopontin in the tendon–bone interface.

Conclusion

Elevated expression of RUNX1 contributed to tendon–bone healing after ACL reconstruction using BMSCs.

Enamel matrix derivative expedites osteogenic differentiation of BMSCs via Wnt/β-catenin pathway in high glucose microenvironment

INTRODUCTION

The influence of enamel matrix derivative (EMD) on proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was explored in high glucose (HG) microenvironment with interaction of Wnt/β-catenin pathway.

MATERIALS AND METHODS

Extraction of BMSCs from Sprague-Dawley rats, culture, and identification were manifested. The cells were treated with different concentration of EMD in HG to figure out the most available concentration for proliferation and osteogenic differentiation. Then, observation of cell growth curve and cell cycle changes, and detection of Osterix, runt-related transcription factor 2 (Runx2), COL-I, early osteogenic indexes, Calcium salt deposition, and β-catenin protein in Wnt/β-catenin pathway were assured. After adding Wnt/β-catenin pathway inhibitor (XAV-939) in the cells with osteogenesis induction, detection of binding of β-catenin to Osterix was clarified.

RESULTS

Via identification BMSCs cultured in vitro was qualified. Different concentrations of EMD could accelerate cell proliferation in HG and osteogenesis induction, and 75 μg/mL EMD had the best effect. The HG augmented BMSCs proliferation and the propidium iodide index of flow cytometry cycle was elevated in HG, which were strengthened via the EMD. After BMSCs' osteogenesis induction, Osterix, Runx2, CoL-1, early osteogenic indexes, and calcium salt deposition were reduced, but elevated via EMD. β-Catenin was the lowest in the HG, but elevated after EMD. After addition of XAV-939, reduction of β-catenin and the downstream (Osterix and Runx2) were manifested. Detection of binding protein bands was in β-catenin and Osterix of the HG after EMD treatment.

CONCLUSION

EMD may facilitate the osteogenic differentiation of BMSCs via activating the Wnt/β-catenin pathway in HG.

Suppression of bone remodeling associated with long-term bisphosphonate treatment is mediated by microRNA-30a-5p

Oral bisphosphonates (BPs) are a first-line treatment for osteoporosis. It is becoming a hot topic to identify new indicators for the early prediction of therapeutic effects and adverse reactions during the long-term use of BPs. To determine whether microRNA (miRNA) expression is modulated by long-term BPs treatment, we performed miRNA expression profiling analysis in patients receiving long-term BP treatment for postmenopausal OP. To assess the effect of BPs on miRNA expression, we used an Affymetrix Genechip miRNA array to analyze serum samples obtained from postmenopausal OP patients on long-term BP treatment and healthy controls. MiRNAs affected by BPs and their predicted targets were examined. We also investigated the effects of miRNA on osteoblast differentiation in vitro and on ovariectomy-induced bone loss in vivo. We observed that the level of miR-30a-5p was significantly increased in patients receiving long-term BP treatment for postmenopausal OP. Furthermore, miR-30a-5p was negatively correlated with bone formation. Consistent with this, in vitro osteoblast activity and matrix mineralization were increased by an antagomir of miR-30a-5p and decreased by an agomir of miR-30a-5p. We also found that miR-30a-5p directly targeted RUNX1 to inhibit osteoblastic differentiation. Consistent with the in vitro results, miR-30a-5p antagomir administration promoted bone formation in ovariectomized mice. Our findings identified miR-30a-5p as a novel mediator of long-term BP treatment that regulates bone formation in postmenopausal OP patients.

Therapeutic Treatments for Osteoporosis-Which Combination of Pills Is the Best among the Bad?

Osteoporosis is a chronical, systemic skeletal disorder characterized by an increase in bone resorption, which leads to reduced bone density. The reduction in bone mineral density and therefore low bone mass results in an increased risk of fractures. Osteoporosis is caused by an imbalance in the normally strictly regulated bone homeostasis. This imbalance is caused by overactive bone-resorbing osteoclasts, while bone-synthesizing osteoblasts do not compensate for this. In this review, the mechanism is presented, underlined by in vitro and animal models to investigate this imbalance as well as the current status of clinical trials. Furthermore, new therapeutic strategies for osteoporosis are presented, such as anabolic treatments and catabolic treatments and treatments using biomaterials and biomolecules. Another focus is on new combination therapies with multiple drugs which are currently considered more beneficial for the treatment of osteoporosis than monotherapies. Taken together, this review starts with an overview and ends with the newest approaches for osteoporosis therapies and a future perspective not presented so far.

circ-Iqsec1 induces bone marrow-derived mesenchymal stem cell (BMSC) osteogenic differentiation through the miR-187-3p/Satb2 signaling pathway

BACKGROUND

Bone marrow-derived mesenchymal stem cells (BMSCs) are general progenitor cells of osteoblasts and adipocytes and they are characterized as a fundamental mediator for bone formation. The current research studied the molecular mechanisms underlying circRNA-regulated BMSC osteogenic differentiation.

METHODS

Next-generation sequencing (NGS) was employed to study abnormal circRNA and mRNA expression in BMSCs before and after osteogenic differentiation induction. Bioinformatics analysis and luciferase reporting analysis were employed to confirm correlations among miRNA, circRNA, and mRNA. RT-qPCR, ALP staining, and alizarin red staining illustrated the osteogenic differentiation ability of BMSCs.

RESULTS

Data showed that circ-Iqsec1 expression increased during BMSC osteogenic differentiation. circ-Iqsec1 downregulation reduced BMSC osteogenic differentiation ability. The present investigation discovered that Satb2 played a role during BMSC osteogenic differentiation. Satb2 downregulation decreased BMSC osteogenic differentiation ability. Bioinformatics and luciferase data showed that miR-187-3p linked circ-Iqsec1 and Satb2. miR-187-3p downregulation or Satb2 overexpression restored the osteogenic differentiation capability of BMSCs post silencing circ-Iqsec1 in in vivo and in vitro experiments. Satb2 upregulation restored osteogenic differentiation capability of BMSCs post miR-187-3p overexpression.

CONCLUSION

Taken together, our study found that circ-Iqsec1 induced BMSC osteogenic differentiation through the miR-187-3p/Satb2 signaling pathway.

Runx1 protects against the pathological progression of osteoarthritis

Runt-related transcription factor-1 (Runx1) is required for chondrocyte-to-osteoblast lineage commitment by enhancing both chondrogenesis and osteogenesis during vertebrate development. However, the potential role of Runx1 in joint diseases is not well known. In the current study, we aimed to explore the role of Runx1 in osteoarthritis induced by anterior cruciate ligament transaction (ACLT) surgery. We showed that chondrocyte-specific Runx1 knockout (Runx1f/fCol2a1-Cre) aggravated cartilage destruction by accelerating the loss of proteoglycan and collagen II in early osteoarthritis. Moreover, we observed thinning and ossification of the growth plate, a decrease in chondrocyte proliferative capacity and the loss of bone matrix around the growth plate in late osteoarthritis. We overexpressed Runx1 by adeno-associated virus (AAV) in articular cartilage and identified its protective effect by slowing the destruction of osteoarthritis in cartilage in early osteoarthritis and alleviating the pathological progression of growth plate cartilage in late osteoarthritis. ChIP-seq analysis identified new targets that interacted with Runx1 in cartilage pathology, and we confirmed the direct interactions of these factors with Runx1 by ChIP-qPCR. This study helps us to understand the function of Runx1 in osteoarthritis and provides new clues for targeted osteoarthritis therapy.

Circ_FBLN1 promotes the proliferation and osteogenic differentiation of human bone marrow-derived mesenchymal stem cells by regulating let-7i-5p/FZD4 axis and Wnt/β-catenin pathway

BACKGROUND

Recently, more and more circular RNAs (circRNAs) have been identified in osteogenesis. In this study, we aimed to explore the effect of circ_FBLN1 on the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs).

METHODS

The protein levels of osteogenesis-related genes, let-7i-5p, frizzled class receptor 4 (FZD4), Ki67, Wnt6 and β-catenin were measured by western blot assay. The levels of circ_FBLN1, FBLN1 mRNA and FZD4 mRNA were determined by quantitative real-time polymerase chain reaction (qRT-PCR) assay. The feature of circ_FBLN1 was investigated by RNase R and Actinomycin D assays. Cell proliferation ability was evaluated by colony formation assay and 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay. The targeting relationship between let-7i-5p and circ_FBLN1 or FZD4 was verified by dual-luciferase reporter assay.

RESULTS

Circ_FBLN1 level was enhanced during the osteogenic differentiation of hBMSCs. Silencing of circ_FBLN1 repressed cell proliferation and osteogenic differentiation in hBMSCs. For mechanism analysis, circ_FBLN1 was found to act as a sponge for let-7i-5p and FZD4 served as a direct target gene of let-7i-5p. Let-7i-5p was downregulated during the osteogenic differentiation of hBMSCs and let-7i-5p inhibition restored the effects of circ_FBLN1 knockdown on the proliferation and osteogenesis of hBMSCs. Moreover, let-7i-5p overexpression suppressed cell proliferation and osteogenesis in hBMSCs through targeting FZD4. In addition, circ_FBLN1 knockdown reduced the levels of Wnt6 and β-catenin in hBMSCs, indicating the inactivation of Wnt/β-catenin pathway.

CONCLUSION

Knockdown of circ_FBLN1 inhibited the proliferation and osteogenesis of hBMSCs by regulating let-7i-5p/FZD4 axis and repressing Wnt/β-catenin pathway.

Uncarboxylated osteocalcin promotes osteogenesis and inhibits adipogenesis of mouse bone marrow-derived mesenchymal stem cells via the PKA-AMPK-SIRT1 axis

Osteoporosis is a bone disease characterized by reduced bone density, thin cortical bone and large gaps in the bone's honeycomb structure, which increases the risk of bone fragility. Uncarboxylated osteocalcin (unOC), a vitamin K-dependent bone protein, is known to regulate carbohydrate and energy metabolism. A previous study demonstrated that unOC promotes the differentiation of mouse bone marrow-derived mesenchymal stem cells (BMSCs) into osteoblasts, but inhibits their differentiation into adipocytes. However, the underlying mechanism remains unknown. The present study showed that unOC regulated the differentiation potential of BMSCs via protein kinase A (PKA)/AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1) signaling. SIRT1, a member of the sirtuin family with deacetylation functions, was upregulated by unOC in BMSCs. Transfection analyses with SIRT1 small interfering RNA indicated that the unOC-induced differentiation shift in BMSCs required SIRT1. Examination of SIRT1 downstream targets revealed that unOC regulated the acetylation levels of runt-related transcription factor (RUNX) 2 and peroxisome proliferator-activated receptor γ (PPARγ). Therefore, unOC inhibited adipogenic differentiation by PPARγ acetylation and promoted osteogenic differentiation by RUNX2 deacetylation. Moreover, phosphorylated PKA and AMPK protein levels increased after unOC treatment, which led to the upregulation of SIRT1. Western blot analysis with PKA and AMPK inhibitors indicated that the PKA-AMPK signaling pathway functioned upstream of SIRT1 and positively regulated SIRT1 expression. These findings led us to propose a model in which unOC regulated BMSC osteogenic differentiation through the PKA-AMPK-SIRT1 axis, giving evidence towards the therapeutic potential of unOC in osteoporosis treatment.

LLLI promotes BMSC proliferation through circRNA_0001052/miR-124-3p

Osteoporosis (OP) is a multifactorial bone disease that occurs worldwide. The treatment of OP is still unsatisfactory. Bone mesenchymal stem cell (BMSC) differentiation is a key process in OP pathogenesis. Low-level laser irradiation (LLLI) has been reported to regulate BMSC proliferation, but the role of circRNAs in the LLLI-based promotion of BMSC proliferation remains unclear. CircRNAs are essential molecular regulators that participate in numerous biological processes and have therapeutic potential. miR-124-3p is an essential microRNA (miRNA), and its expression changes are related to BMSC proliferation ability. In the present study, gain-loss function of experiments demonstrated that circRNA_0001052 could regulate the proliferation of BMSCs by acting as a miR-124-3p sponge through the Wnt4/β-catenin pathway. The results of this study strongly suggest that circRNA_0001052 plays an essential role in BMSC proliferation in response to LLLI treatment, which is a potential therapeutic manipulation with clinical applications.

Circ-ITCH sponges miR-214 to promote the osteogenic differentiation in osteoporosis via upregulating YAP1

Osteoporosis is the most prevailing primary bone disease and a growing health care burden. The aim of this study was to clarify the functional roles and mechanisms of the circ-ITCH regulating osteogenic differentiation of osteoporosis. Circ-ITCH and yes-associated protein 1 (YAP1) levels were downregulated, but the miR‐214 level was upregulated in osteoporotic mice and patients. Knockdown of circ-ITCH inhibited the alkaline phosphatase (ALP) activity, mineralized nodule formation, and expression of runt-related transcription factor 2 (RUNX2), osteopontin (OPN), and osteocalcin (OCN) during osteogenic induction. Furthermore, miR-214 was a target of circ-ITCH, knockdown of miR-214 could impede the regulatory effects of sh-circ-ITCH on osteogenic differentiation. Moreover, miR-214 suppressed hBMSCs osteogenic differentiation by downregulating YAP1. Finally, in vivo experiments indicated that overexpression of circ-ITCH could improve osteogenesis in ovariectomized mice. In conclusion, circ-ITCH upregulated YAP1 expression to promote osteogenic differentiation in osteoporosis via sponging miR-214. Circ-ITCH could act as a novel therapeutic target for osteoporosis.

Shared Genetic and Epigenetic Mechanisms between the Osteogenic Differentiation of Dental Pulp Stem Cells and Bone Marrow Stem Cells

OBJECTIVE

To identify the shared genetic and epigenetic mechanisms between the osteogenic differentiation of dental pulp stem cells (DPSC) and bone marrow stem cells (BMSC).

MATERIALS AND METHODS

The profiling datasets of miRNA expression in the osteogenic differentiation of mesenchymal stem cells from the dental pulp (DPSC) and bone marrow (BMSC) were searched in the Gene Expression Omnibus (GEO) database. The differential expression analysis was performed to identify differentially expressed miRNAs (DEmiRNAs) dysregulated in DPSC and BMSC osteodifferentiation. The target genes of the DEmiRNAs that were dysregulated in DPSC and BMSC osteodifferentiation were identified, followed by the identification of the signaling pathways and biological processes (BPs) of these target genes. Accordingly, the DEmiRNA-transcription factor (TFs) network and the DEmiRNAs-small molecular drug network involved in the DPSC and BMSC osteodifferentiation were constructed.

RESULTS

16 dysregulated DEmiRNAs were found to be overlapped in the DPSC and BMSC osteodifferentiation, including 8 DEmiRNAs with a common expression pattern (8 upregulated DEmiRNAs (miR-101-3p, miR-143-3p, miR-145-3p/5p, miR-19a-3p, miR-34c-5p, miR-3607-3p, miR-378e, miR-671-3p, and miR-671-5p) and 1 downregulated DEmiRNA (miR-671-3p/5p)), as well as 8 DEmiRNAs with a different expression pattern (i.e., miR-1273g-3p, miR-146a-5p, miR-146b-5p, miR-337-3p, miR-382-3p, miR-4508, miR-4516, and miR-6087). Several signaling pathways (TNF, mTOR, Hippo, neutrophin, and pathways regulating pluripotency of stem cells), transcription factors (RUNX1, FOXA1, HIF1A, and MYC), and small molecule drugs (curcumin, docosahexaenoic acid (DHA), vitamin D3, arsenic trioxide, 5-fluorouracil (5-FU), and naringin) were identified as common regulators of both the DPSC and BMSC osteodifferentiation.

CONCLUSION

Common genetic and epigenetic mechanisms are involved in the osteodifferentiation of DPSCs and BMSCs.

SIRT1, a promising regulator of bone homeostasis

Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent deacetylase, epigenetically regulates various cell metabolisms, including inflammation, tumorigenesis, and bone metabolism. Many clinical studies have found the potential of SIRT1 in predicting and treating bone-related disorders, such as osteoporosis and osteonecrosis, suggesting that SIRT1 might be a regulator of bone homeostasis. In order to identify the mechanisms that underlie the pivotal role of SIRT1 in bone homeostasis, many studies revealed that SIRT1 could maintain the balance between bone formation and absorption via regulating the ratio of osteoblasts to osteoclasts. SIRT1 controls the differentiation of mesenchymal stem cells (MSCs) and bone marrow-derived macrophages, increasing osteogenesis and reducing osteoclastogenesis. Besides, SIRT1 can enhance bone-forming cells' viability, including MSCs and osteoblasts under adverse conditions by resisting senescence, suppressing apoptosis, and promoting autophagy in favor of osteogenesis. Furthermore, the effect on bone vasculature homeostasis enables SIRT1 to become a valuable strategy for ischemic osteonecrosis and senile osteoporosis. The review systemically discusses SIRT1 pathways and the critical role in bone homeostasis and assesses whether SIRT1 is a potential target for manipulation and therapy, to lay a solid foundation for further researches in the future.

Mechanisms of miR‑128‑3p in inhibiting osteoblast differentiation from bone marrow‑derived mesenchymal stromal cells

The authors' previous study demonstrated that miR-128 may exert an inhibitory effect on the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs), but its downstream mechanisms remain to be elucidated. The aim of the present study was to investigate the microRNA (miRNA/miR) and mRNA profiles of differentiated and undifferentiated BM-MSCs and explore new downstream targets for miR-128. The sequencing datasets of GSE107279 (miRNA) and GSE112318 (mRNA) were downloaded from the Gene Expression Omnibus database. The differentially expressed miRNAs (DEMs) and genes (DEGs) were identified using the DESeq2 method. The target genes of DEMs were predicted by the miRwalk 2.0 database. The hub target genes of miR-128 were screened by constructing the protein-protein interaction (PPI) network and module analysis. The expression levels of miR-128 and crucial target genes were validated by reverse transcription-quantitative (RT-q) PCR before or after transfection of miR-128 mimics to BM-MSCs. The miRNA expression profile analysis identified miR-128 as one of the significantly downregulated DEMs (total 338) in differentiated BM-MSCs compared with the undifferentiated control. A total of 103 predicted target genes of miR-128-3p were overlapped with upregulated DEGs. By calculating the topological properties of each protein in the PPI network, 6 upregulated genes (KIT, NTRK2, YWHAB, GAB1, AXIN1 and RUNX1; fold change was the highest for NTRK2) were considered to be hub genes. Of these, 4 were enriched in module 4 (RUNX1, KIT, GAB1 and AXIN1; RUNX1 was particularly crucial as it can interact with the others), while one was enriched in module 7 (YWHAB). The expression levels of miR-128 and these 6 target genes during the osteogenic differentiation were experimentally confirmed by RT-qPCR. In addition, the expression levels of these 6 genes were significantly reversed after transfection of miR-128-3p mimics into rat BM-MSCs compared with the miR-control group. These findings indicated that miR-128-3p may inhibit the osteoblast differentiation of BM-MSCs by downregulation of these 6 genes, particularly RUNX1, YWHAB and NTRK2.

RUNX1 regulates TGF-β induced migration and EMT in colorectal cancer

Colorectal cancer (CRC) was one of the most malignant tumors worldwide due to its metastasis. Epithelial-to-mesenchymal transition (EMT) plays an important role in CRC migration, and transforming growth factor-β (TGF-β) works as a dominating cytokine in CRC EMT process. Here, we originally identified RUNX1 as an important factor among TGF-β induced EMT in CRC. We found that RUNX1 was overexpressed with the treatment of TGF-β, accompanied with enhanced cancer cell migration and EMT which was characterized by up-graded N-Cadherin levels. Vice versa, knockdown of RUNX1 attenuated the migration ability of TGF-β induced CRC cells. In addition, decreased expression of N-Cadherin suggested that EMT was also attenuated after knocking down RUNX1. Similar decrease was observed in EMT regulator snail family transcriptional repressor 1 (SNAI1). And the knockdown effect of RUNX1 cannot be reversed by the addition of TGF-β. Moreover, we observed that RUNX1 expression was higher in CRC tumor tissues than in normal epithelial tissues. The enhanced expression was detected in cancer cell nucleus. These results revealed RUNX1 could regulate colorectal cancer migration via TGF-β signaling pathway, and RUNX1 might serve as a potential target for preventing CRC metastasis.

miR-205 regulates bone turnover in elderly female patients with type 2 diabetes mellitus through targeted inhibition of Runx2

The present study aimed to explore the expression of microribonucleic acid (microRNA) (miR)-205 in bone tissues and serum of elderly female patients with type 2 diabetes mellitus (T2DM) complicated with osteoporosis (OP), and to investigate the effect of miR-205 on osteogenesis/adipogenesis of bone marrow mesenchymal stem cells (BMSCs) and its mechanism in elderly female mice with T2DM + OP. The bone tissues and serum of 24 female patients with T2DM + OP at the Third Affiliated Hospital of Qiqihar Medical University were collected as the research group, while those of 24 healthy people were collected as the control group. The expression level of miR-205 was detected in both groups via reverse transcription-polymerase chain reaction (RT-PCR). Then the elderly female mouse model of T2DM + OP was established as a model group, while normal mice of the same age were used as the control group. The mice in the model and control groups were transfected with miR-205 mimic, negative control (NC)-mimic, miR-205-inhibitor and NC-inhibitor. Alizarin red S (ARS) staining and RT-PCR were conducted after osteogenic induction for 21 days, and oil red O (ORO) staining and RT-PCR were performed after adipogenic induction for 24 days. The overexpression of miR-205 inhibited osteogenic differentiation and promoted adipogenic differentiation of BMSCs in elderly female mice with T2DM + OP, while knockdown of miR-205 promoted osteogenic differentiation and inhibited adipogenic differentiation of BMSCs in elderly female mice with T2DM + OP. In addition, miR-205 was able to directly suppress the expression of its target gene RUNX family transcription factor 2 (Runx2). The expression level of miR-205 was obviously increased in female patients with T2DM + OP and the elderly female mouse model of T2DM + OP. In addition, miR-205 was able to regulate the osteogenic/adipogenic differentiation of BMSCs, and miR-205/Runx2 may be a new method and target for the treatment of female patients with T2DM + OP.

MiR-596 inhibits osteoblastic differentiation and cell proliferation by targeting Smad3 in steroid-induced osteonecrosis of femoral head

Background

It is reported that miR-596 has a potential diagnostic value for non-traumatic osteonecrosis of the femoral head (NOFH), but its underlying mechanisms in NOFH is unclear.

Methods

The expression of miR-596 and Smad3 was detected by western blot and quantitative real-time PCR. The relationship between the two molecules was explored using Dual-Luciferase Reporter Assay. Glucocorticoid (GC)—dexamethasone, was used to induce bone marrow mesenchymal stem cell (BMSC) osteogenic differentiation, and the effects of miR-596 on BMSC osteogenic differentiation and proliferation were determined.

Results

MiR-596 expression was upregulated, while Smad3 expression was inhibited in the bone marrow samples of patients with steroid-induced osteonecrosis of femoral head (SANFH). Overexpression of miR-596 inhibited the proliferation and osteogenic differentiation of BMSCs induced by GC. Meanwhile, the opposite results were observed in the miR-596 inhibitor group. In addition, Smad3 was a target gene of miR-596, and negatively regulated by miR-596. The promotion effect of the miR-596 inhibitor on BMSC proliferation and osteogenic differentiation was reversed by si-Smad3.

Conclusion

MiR-596 can suppress GC-BMSC osteoblastic differentiation and proliferation by regulating Smad3 expression.

Complex Interplay between the RUNX Transcription Factors and Wnt/β-Catenin Pathway in Cancer: A Tango in the Night

Cells are designed to be sensitive to a myriad of external cues so they can fulfil their individual destiny as part of the greater whole. A number of well-characterised signalling pathways dictate the cell's response to the external environment and incoming messages. In healthy, well-ordered homeostatic systems these signals are tightly controlled and kept in balance. However, given their powerful control over cell fate, these pathways, and the transcriptional machinery they orchestrate, are frequently hijacked during the development of neoplastic disease. A prime example is the Wnt signalling pathway that can be modulated by a variety of ligands and inhibitors, ultimately exerting its effects through the β-catenin transcription factor and its downstream target genes. Here we focus on the interplay between the three-member family of RUNX transcription factors with the Wnt pathway and how together they can influence cell behaviour and contribute to cancer development. In a recurring theme with other signalling systems, the RUNX genes and the Wnt pathway appear to operate within a series of feedback loops. RUNX genes are capable of directly and indirectly regulating different elements of the Wnt pathway to either strengthen or inhibit the signal. Equally, β-catenin and its transcriptional co-factors can control RUNX gene expression and together they can collaborate to regulate a large number of third party co-target genes.

Long Noncoding RNA FAM83H-AS1 Modulates SpA-Inhibited Osteogenic Differentiation in Human Bone Mesenchymal Stem Cells

Osteomyelitis, an infection of the bone and bone marrow, imposes a heavy burden on public health care systems owing to its progressive bone destruction and sequestration. Human bone mesenchymal stem cells (hBMSCs) play a key role in the process of bone formation, and mounting evidence has confirmed that long noncoding RNAs (lncRNAs) are involved in hBMSC osteogenic differentiation. Nevertheless, the exact function and molecular mechanism of lncRNAs in osteogenic differentiation during osteomyelitis development remain to be explored. In this study, hBMSCs were treated with staphylococcal protein A (SpA) during osteogenic differentiation induction to mimic osteomyelitis in vitro The results of lncRNA microarray analysis revealed that FAM83H-AS1 presented the lowest expression among the significantly downregulated lncRNAs. Functionally, ectopic expression of FAM83H-AS1 contributed to osteogenic differentiation of SpA-induced hBMSCs. Additionally, our findings revealed that FAM83H-AS1 negatively regulated microRNA 541-3p (miR-541-3p), and WNT3A was validated as a target gene of miR-541-3p. Mechanically, FAM83H-AS1 elevated WNT3A expression by competitively binding with miR-541-3p. Lastly, it was demonstrated that FAM83H-AS1/miR-541-3p/WNT3A ameliorated SpA-mediated inhibition of the osteogenic differentiation of hBMSCs, which provided a novel therapeutic strategy for patients with osteomyelitis.

Single-cell impedance analysis of osteogenic differentiation by droplet-based microfluidics

Single-cell analysis is critical to understanding its heterogeneity and biological processes, such as stem cell differentiation, and elucidating the underlying mechanisms of cellular metabolism. New tools to promote intercellular variability studies help elucidate cellular regulation mechanisms. Here an impedance measurement and analysis system was built to monitor the osteogenic differentiation of single bone marrow mesenchymal stem cells (BM-MSCs) in droplets. The biochip including a microelectrode array was designed based on droplet microfluidics and fabricated. A novel theoretical electrical model was proposed to simulate the electrical properties of cells in the droplets. Impedance measurements showed that single cells are substantially heterogeneous during osteoblast differentiation at different stages (days 0, 7, 14 and 21) and different cell passages (passages 6, 7 and 11). This result was consistent with the appearance of two biomarkers (alkaline phosphatase and calcium nodules), which are the gold standard biomarkers of osteoblastogenesis and differentiation. The device enabled highly efficient single-cell trapping, accurate positioning, and sensitive, label-free and noninvasive impedance measurements of individual cells with multiple channels. This system provides a strategy for exploring the processes of osteoblastogenesis and differentiation at the single-cell level and has substantial potential for applications in the biomedical field.

RUNX1 promotes tumour metastasis by activating the Wnt/β-catenin signalling pathway and EMT in colorectal cancer

Background

Runt-related transcription factor 1 (RUNX1) plays the roles of an oncogene and an anti-oncogene in epithelial tumours, and abnormally elevated RUNX1 has been suggested to contribute to the carcinogenesis of colorectal cancer (CRC). However, the mechanism remains unclear.

Methods

The expression of RUNX1 in CRC and normal tissues was detected by real-time quantitative PCR and Western blotting. The effect of RUNX1 on CRC migration and invasion was conducted by functional experiments in vitro and in vivo. Chromatin Immunoprecipitation assay verified the direct regulation of RUNX1 on the promoter of the KIT, which leads to the activation of Wnt/β-catenin signaling.

Results

RUNX1 expression is upregulated in CRC tissues. Upregulated RUNX1 promotes cell metastasis and epithelial to mesenchymal transition (EMT) of CRC both in vitro and in vivo. Furthermore, RUNX1 can activate Wnt/β-catenin signalling in CRC cells by directly interacting with β-catenin and targeting the promoter and enhancer regions of KIT to promote KIT transcription. These observations demonstrate that RUNX1 upregulation is a common event in CRC specimens and is closely correlated with cancer metastasis and that RUNX1 promotes EMT of CRC cells by activating Wnt/β-catenin signalling. Moreover, RUNX1 is regulated by Wnt/β-catenin.

Conclusion

Our findings first demonstrate that RUNX1 promotes CRC metastasis by activating the Wnt/β-catenin signalling pathway and EMT.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1330-9) contains supplementary material, which is available to authorized users.

Correlational study on altered epicardial adipose tissue as a stratification risk factor for valve disease progression through IL-13 signaling

AIMS

Genetic and environmental factors all interact in the risk of progression of valvular dysfunctions. Previous studies reported a relation between valve diseases and epicardial adipose tissue (EAT) thickness. The aim of this study was to verify the possible relationship between the molecular pattern of EAT related to IL-13 fibrogenic cytokine expression and valve dysfunction.

METHODS AND RESULTS

A valvular heart disease (VHD) population was stratified according to their median EAT thickness (7 mm). The molecular expression of IL-13 in EAT is directly related to the molecular expression of genes associated with extracellular matrix (ECM) turnover, macrophage infiltration and promotion of the formation of ectopic calcific nodules involved in aorta coarctation and calcification.

CONCLUSION

IL-13 gene expression in altered EAT is directly related to the expression of genes involved in ECM turnover and the formation of ectopic calcific nodules, suggesting measurements of EAT as a stratification risk factor for valve instability in the VHD patients.

Anabolic Therapies in Osteoporosis and Bone Regeneration

Osteoporosis represents the most common bone disease worldwide and results in a significantly increased fracture risk. Extrinsic and intrinsic factors implicated in the development of osteoporosis are also associated with delayed fracture healing and impaired bone regeneration. Based on a steadily increasing life expectancy in modern societies, the global implications of osteoporosis and impaired bone healing are substantial. Research in the last decades has revealed several molecular pathways that stimulate bone formation and could be targeted to treat both osteoporosis and impaired fracture healing. The identification and development of therapeutic approaches modulating bone formation, rather than bone resorption, fulfils an essential clinical need, as treatment options for reversing bone loss and promoting bone regeneration are limited. This review focuses on currently available and future approaches that may have the potential to achieve these aims.