TGF-β inhibits osteogenesis by upregulating the expression of ubiquitin ligase SMURF1 via MAPK-ERK signaling

E3 ubiquitin ligases: key regulators of osteogenesis and potential therapeutic targets for bone disorders

Ubiquitination is a crucial post-translational modification of proteins that mediates the degradation or functional regulation of specific proteins. This process participates in various biological processes such as cell growth, development, and signal transduction. E3 ubiquitin ligases play both positive and negative regulatory roles in osteogenesis and differentiation by ubiquitination-mediated degradation or stabilization of transcription factors, signaling molecules, and cytoskeletal proteins. These activities affect the proliferation, differentiation, survival, and bone formation of osteoblasts (OBs). In recent years, advances in genomics, transcriptomics, and proteomics have led to a deeper understanding of the classification, function, and mechanisms of action of E3 ubiquitin ligases. This understanding provides new insights and approaches for revealing the molecular regulatory mechanisms of bone formation and identifying therapeutic targets for bone metabolic diseases. This review discusses the research progress and significance of the positive and negative regulatory roles and mechanisms of E3 ubiquitin ligases in the process of osteogenic differentiation. Additionally, the review highlights the role of E3 ubiquitin ligases in bone-related diseases. A thorough understanding of the role and mechanisms of E3 ubiquitin ligases in osteogenic differentiation could provide promising therapeutic targets for bone tissue engineering based on stem cells.

TGF-β signaling regulates differentiation of MSCs in bone metabolism: disputes among viewpoints

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into cells of different lineages to form mesenchymal tissues, which are promising in regard to treatment for bone diseases. Their osteogenic differentiation is under the tight regulation of intrinsic and extrinsic factors. Transforming growth factor β (TGF-β) is an essential growth factor in bone metabolism, which regulates the differentiation of MSCs. However, published studies differ in their views on whether TGF-β signaling regulates the osteogenic differentiation of MSCs positively or negatively. The controversial results have not been summarized systematically and the related explanations are required. Therefore, we reviewed the basics of TGF-β signaling and summarized how each of three isoforms regulates osteogenic differentiation. Three isoforms of TGF-β (TGF-β1/β2/β3) play distinct roles in regulating osteogenic differentiation of MSCs. Additionally, other possible sources of conflicts are summarized here. Further understanding of TGF-β signaling regulation in MSCs may lead to new applications to promote bone regeneration and improve therapies for bone diseases.

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

Transforming growth factor-βs (TGF-βs) and bone morphometric proteins (BMPs) belong to the TGF-β superfamily and perform essential functions during osteoblast and chondrocyte lineage commitment and differentiation, skeletal development, and homeostasis. TGF-βs and BMPs transduce signals through SMAD-dependent and -independent pathways; specifically, they recruit different receptor heterotetramers and R-Smad complexes, resulting in unique biological readouts. BMPs promote osteogenesis, osteoclastogenesis, and chondrogenesis at all differentiation stages, while TGF-βs play different roles in a stage-dependent manner. BMPs and TGF-β have opposite functions in articular cartilage homeostasis. Moreover, TGF-β has a specific role in maintaining the osteocyte network. The precise activation of BMP and TGF-β signaling requires regulatory machinery at multiple levels, including latency control in the matrix, extracellular antagonists, ubiquitination and phosphorylation in the cytoplasm, nucleus-cytoplasm transportation, and transcriptional co-regulation in the nuclei. This review weaves the background information with the latest advances in the signaling facilitated by TGF-βs and BMPs, and the advanced understanding of their diverse physiological functions and regulations. This review also summarizes the human diseases and mouse models associated with disordered TGF-β and BMP signaling. A more precise understanding of the BMP and TGF-β signaling could facilitate the development of bona fide clinical applications in treating bone and cartilage disorders.

Metformin ameliorates valve interstitial cell calcification by promoting autophagic flux

Calcific aortic valve disease (CAVD) is the most common heart disease of the developed world. It has previously been established that metformin administration reduces arterial calcification via autophagy; however, whether metformin directly regulates CAVD has yet to be elucidated. In the present study we investigated whether metformin alleviates valvular calcification through the autophagy-mediated recycling of Runx2. Calcification was reduced in rat valve interstitial cells (RVICs) by metformin treatment (0.5-1.5 mM) (P < 0.01), with a marked decrease in Runx2 protein expression compared to control cells (P < 0.05). Additionally, upregulated expression of Atg3 and Atg7 (key proteins required for autophagosome formation), was observed following metformin treatment (1 mM). Blocking autophagic flux using Bafilomycin-A1 revealed colocalisation of Runx2 with LC3 puncta in metformin treated RVICs (P < 0.001). Comparable Runx2 accumulation was seen in LC3 positive autolysosomes present within cells that had been treated with both metformin and hydroxychloroquine in combination (P < 0.001). Mechanistic studies employing three-way co-immunoprecipitation with Runx2, p62 and LC3 suggested that Runx2 binds to LC3-II upon metformin treatment in VICs. Together these studies suggest that the utilisation of metformin may represent a novel strategy for the treatment of CAVD.

The role of E3 ubiquitin ligases in bone homeostasis and related diseases

The ubiquitin-proteasome system (UPS) dedicates to degrade intracellular proteins to modulate demic homeostasis and functions of organisms. These enzymatic cascades mark and modifies target proteins diversly through covalently binding ubiquitin molecules. In the UPS, E3 ubiquitin ligases are the crucial constituents by the advantage of recognizing and presenting proteins to proteasomes for proteolysis. As the major regulators of protein homeostasis, E3 ligases are indispensable to proper cell manners in diverse systems, and they are well described in physiological bone growth and bone metabolism. Pathologically, classic bone-related diseases such as metabolic bone diseases, arthritis, bone neoplasms and bone metastasis of the tumor, etc., were also depicted in a UPS-dependent manner. Therefore, skeletal system is versatilely regulated by UPS and it is worthy to summarize the underlying mechanism. Furthermore, based on the current status of treatment, normal or pathological osteogenesis and tumorigenesis elaborated in this review highlight the clinical significance of UPS research. As a strategy possibly remedies the limitations of UPS treatment, emerging PROTAC was described comprehensively to illustrate its potential in clinical application. Altogether, the purpose of this review aims to provide more evidence for exploiting novel therapeutic strategies based on UPS for bone associated diseases.

Melatonin and bone-related diseases: an updated mechanistic overview of current evidence and future prospects

PURPOSE

Bone diseases account for an enormous cost burden on health systems. Bone disorders are considered as age-dependent diseases. The aging of world population has encouraged scientists to further explore the most effective preventive modalities and therapeutic strategies to overcome and reduce the high cost of bone disorders. Herein, we review the current evidence of melatonin's therapeutic effects on bone-related diseases.

METHODS

This review summarized evidences from in vitro, in vivo, and clinical studies regarding the effects of melatonin on bone-related diseases, with a focus on the molecular mechanisms. Electronically, Scopus and MEDLINE®/PubMed databases were searched for articles published on melatonin and bone-related diseases from inception to June 2023.

RESULTS

The findings demonstrated that melatonin has beneficial effect in bone- and cartilage-related disorders such as osteoporosis, bone fracture healing, osteoarthritis, and rheumatoid arthritis, in addition to the control of sleep and circadian rhythms.

CONCLUSION

A number of animal and clinical studies have indicated that various biological effects of melatonin may suggest this molecule as an effective therapeutic agent for controlling, diminishing, or suppressing bone-related disorders. Therefore, further clinical studies are required to clarify whether melatonin can be effective in patients with bone-related diseases.

Research progress on the regulation of bone marrow stem cells by noncoding RNAs in adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a common spinal deformity in young women, but its pathogenesis remains unclear. The primary pathogenic factors contributing to its development include genetics, abnormal bone metabolism, and endocrine factors. Bone marrow stem cells (BMSCs) play a crucial role in the pathogenesis of AIS by regulating its occurrence and progression. Noncoding RNAs (ncRNAs) are also involved in the pathogenesis of AIS, and their role in regulating BMSCs in patients with AIS requires further evaluation. In this review, we discuss the relevant literature regarding the osteogenic, chondrogenic, and lipogenic differentiation of BMSCs. The corresponding mechanisms of ncRNA-mediated BMSC regulation in patients with AIS, recent advancements in AIS and ncRNA research, and the importance of ncRNA translation profiling and multiomics are highlighted.

Ubiquitin-specific proteases: Vital regulatory molecules in bone and bone-related diseases

Stabilization of bone structure and function involves multiple cell-to-cell and molecular interactions, in which the regulatory functions of post-translational modifications such as ubiquitination and deubiquitination shouldn't be underestimated. As the largest family of deubiquitinating enzymes, the ubiquitin-specific proteases (USPs) participate in the development of bone homeostasis and bone-related diseases through multiple classical osteogenic and osteolytic signaling pathways, such as BMP/TGF-β pathway, NF-κB/p65 pathway, EGFR-MAPK pathway and Wnt/β-catenin pathway. Meanwhile, USPs may also broadly regulate regulate hormone expression level, cell proliferation and differentiation, and may further influence bone homeostasis from gene fusion and nuclear translocation of transcription factors. The number of patients with bone-related diseases is currently enormous, making exploration of their pathogenesis and targeted therapy a hot topic. Pathological increases in the levels of inflammatory mediators such as IL-1β and TNF-α lead to inflammatory bone diseases such as osteoarthritis, rheumatoid arthritis and periodontitis. While impaired body metabolism greatly increases the probability of osteoporosis. Abnormal physiological activity of bone-associated cells results in a variety of bone tumors. The regulatory role of USPs in bone-related disease has received particular attention from academics in recent studies. In this review, we focuse on the roles and mechanisms of USPs in bone homeostasis and bone-related diseases, with the expectation of informing targeted therapies in the clinic.

Ubiquitin modification in osteogenic differentiation and bone formation: From mechanisms to clinical significance

The ubiquitin-proteasome system is an important pathway for mediating posttranslational modification and protein homeostasis and exerts a wide range of functions in diverse biological processes, including stem cell differentiation, DNA repair, and cell cycle regulation. Many studies have shown that ubiquitination modification plays a critical role in regulating the osteogenic differentiation of stem cells and bone formation through various mechanisms. This review summarizes current progress on the effects and mechanisms of ubiquitin modification on transcription factors and signaling pathways involved in osteogenic differentiation. Moreover, the review highlights the latest advances in the clinical application of drugs in bone tissue engineering. A thorough understanding of ubiquitin modifications may provide promising therapeutic targets for stem cell-based bone tissue engineering.

E3 Ubiquitin Ligases: Potential Therapeutic Targets for Skeletal Pathology and Degeneration

The ubiquitination-proteasome system (UPS) is crucial in regulating a variety of cellular processes including proliferation, differentiation, and survival. Ubiquitin protein ligase E3 is the most critical molecule in the UPS system. Dysregulation of the UPS system is associated with many conditions. Over the past few decades, there have been an increasing number of studies focusing on the UPS system and how it affects bone metabolism. Multiple E3 ubiquitin ligases have been found to mediate osteogenesis or osteolysis through a variety of pathways. In this review, we describe the mechanisms of UPS, especially E3 ubiquitin ligases on bone metabolism. To date, many E3 ubiquitin ligases have been found to regulate osteogenesis or osteoclast differentiation. We review the classification of these E3 enzymes and the mechanisms that influence upstream and downstream molecules and transduction pathways. Finally, this paper reviews the discovery of the relevant UPS inhibitors, drug molecules, and noncoding RNAs so far and prospects the future research and treatment.

Incorporation of NGR1 promotes bone regeneration of injectable HA/nHAp hydrogels by anti-inflammation regulation via a MAPK/ERK signaling pathway

Suitable bone grafts are commonly required to achieve successful bone regeneration, wherein much effort has been spent to optimize their osteogenesis. Increasing evidence has demonstrated that reducing the levels of TNF-α can enhance bone regeneration at the injury site. Notoginsenoside R1 (NGR1) has been extensively studied in the field of anti-inflammation and regenerative medicine. Nanosized hydroxyapatite (nHAp) possesses excellent biocompatibility and osteoconductivity. In this study, we fabricated a thermoresponsive, injectable hyaluronic acid/nHAp (HA/nHAp) composite hydrogel incorporated with NGR1 to promote bone regeneration. Furthermore, NGR1-HA/nHAp hydrogel could enhance bone regeneration than those of HA and HA/nHAp hydrogels, profited by the underlying osteoblastic mechanism that NGR1 could facilitate activation of the MAPK/ERK signaling pathway and down-regulate the expression of TNF-α, ultimately upregulated expression of osteogenic genes. In summary, the NGR1-HA/nHAp composite hydrogel with controlled inflammation, and excellent osteogenic effect, will have great potential for use in bone regeneration applications.

NEDD4 E3 Ligases: Functions and Mechanisms in Bone and Tooth

Protein ubiquitination is a precisely controlled enzymatic cascade reaction belonging to the post-translational modification of proteins. In this process, E3 ligases catalyze the binding of ubiquitin (Ub) to protein substrates and define specificity. The neuronally expressed developmentally down-regulated 4 (NEDD4) subfamily, belonging to the homology to E6APC terminus (HECT) class of E3 ligases, has recently emerged as an essential determinant of multiple cellular processes in different tissues, including bone and tooth. Here, we place special emphasis on the regulatory role of the NEDD4 subfamily in the molecular and cell biology of osteogenesis. We elucidate in detail the specific roles, downstream substrates, and upstream regulatory mechanisms of the NEDD4 subfamily. Further, we provide an overview of the involvement of E3 ligases and deubiquitinases in the development, repair, and regeneration of another mineralized tissue—tooth.

Bu-Gu-Sheng-Sui decoction promotes osteogenesis via activating the ERK/Smad signaling pathways

Osteoporosis is a systemic metabolic skeletal disease, which becomes a common public health problem that seriously endangers people’s health. Bu-Gu-Sheng-Sui decoction (BGSSD) is a safe and effective Chinese medicine formulation for the treatment of osteoporosis. Numerous studies have indicated that it played a significant role in bone anabolism. However, the underlying mechanism remains unclear. Herein, we selected senescence-accelerated mice prone 6 (SAMP6) and MC3T3-E1 cells to study the effects of BGSSD on osteogenesis and then investigated the potential mechanism of BGSSD. Our research found that BGSSD protected the bone mass in SAMP6, increased the expression of osteogenic specific factor Runx2, and improved bone trabecular structure. In vitro, BGSSD accelerated the proliferation and differentiation of MC3T3-E1 cells, which was characterized by stimulating the activity of Alkaline phosphatase (ALP) and raising the expression of Runx2. Moreover, BGSSD could effectively boost the expression levels of ERK and Smad in SAMP6 and MC3T3-E1. Therefore, we speculate that BGSSD may promote bone formation through ERK/Smad pathways. Collectively, our results highlight the importance of BGSSD as a compound in promoting osteogenic differentiation and osteogenesis, demonstrating that BGSSD may become a latent drug to prevent and treat osteoporosis.

The Effect of the NFκB-USP9X-Cx43 Axis on the Dynamic Balance of Bone Formation/Degradation during Ossification of the Posterior Longitudinal Ligament of the Cervical Spine

Connexin 43- (Cx43-) mediated nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) signaling has been found involved in the ossification of the posterior longitudinal ligament (OPLL). However, the underlying mechanism how OPLL is regulated has not been elucidated. In the present study, primary ligament fibroblast were isolated; immunoprecipitation (IP) and liquid chromatography-mass spectrometry (LC-MS) assays were applied to identify potential binding proteins of Cx43. Protein interaction was then confirmed by co-IP assay. Alkaline phosphatase (ALP) activity and alizarin red staining were used to evaluate ossification. Luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay were employed to assess the binding between NF-κB p65 and target gene. Lipoxygenase inhibitor (5,8,11-eicosatriynoic acid, EPA) was applied to induce endoplasmic reticulum (ER) stress, and 4-phenylbutyrate (4-PBA) was used as an ER-stress inhibitor. Expression of USP9X, Cx43, and nuclei p65 in ligaments from patients and controls was detected by Western blotting. The results showed that ubiquitin-specific protease 9 X-chromosome (USP9X), a deubiquitylating enzyme, was a candidate of Cx43 binding proteins, and USP9X inhibited Cx43 ubiquitination. In vitro experiments showed that USP9X promoted ossification of primary ligament fibroblasts and nuclear translocation of NF-κB p65 by regulating Cx43 expression. Moreover, NF-κB can bind to the USP9X promoter to promote its transcription. When ER stress was inhibited by 4-PBA, USP9X levels, NF-κB nuclei translocation, and ALP activity were decreased. Reverse results were obtained when ER stress was induced by EPA. PDTC, an NF-κB inhibitor, could abolish the effects of EPA. Furthermore, USP9X, Cx43, and nuclei p65 were significantly upregulated in ligaments from OPLL patients than non-OPLL controls. USP9X was positively correlated with CX43 and nuclei p65 in OPLL samples. Overall, the findings suggest that the ER stress–NFκB-USP9X-Cx43 signaling pathway plays an important role in OPLL progression.

The mechanosensitive lncRNA Neat1 promotes osteoblast function through paraspeckle-dependent Smurf1 mRNA retention

Mechanical stimulation plays an important role in bone remodeling. Exercise-induced mechanical loading enhances bone strength, whereas mechanical unloading leads to bone loss. Increasing evidence has demonstrated that long noncoding RNAs (lncRNAs) play key roles in diverse biological, physiological and pathological contexts. However, the roles of lncRNAs in mechanotransduction and their relationships with bone formation remain unknown. In this study, we screened mechanosensing lncRNAs in osteoblasts and identified Neat1, the most clearly decreased lncRNA under simulated microgravity. Of note, not only Neat1 expression but also the specific paraspeckle structure formed by Neat1 was sensitive to different mechanical stimulations, which were closely associated with osteoblast function. Paraspeckles exhibited small punctate aggregates under simulated microgravity and elongated prolate or larger irregular structures under mechanical loading. Neat1 knockout mice displayed disrupted bone formation, impaired bone structure and strength, and reduced bone mass. Neat1 deficiency in osteoblasts reduced the response of osteoblasts to mechanical stimulation. In vivo, Neat1 knockout in mice weakened the bone phenotypes in response to mechanical loading and hindlimb unloading stimulation. Mechanistically, paraspeckles promoted nuclear retention of E3 ubiquitin ligase Smurf1 mRNA and downregulation of their translation, thus inhibiting ubiquitination-mediated degradation of the osteoblast master transcription factor Runx2, a Smurf1 target. Our study revealed that Neat1 plays an essential role in osteoblast function under mechanical stimulation, which provides a paradigm for the function of the lncRNA-assembled structure in response to mechanical stimulation and offers a therapeutic strategy for long-term spaceflight- or bedrest-induced bone loss and age-related osteoporosis.

Genome-Wide CRISPR/Cas9-Based Screening for Deubiquitinase Subfamily Identifies Ubiquitin-Specific Protease 11 as a Novel Regulator of Osteogenic Differentiation

The osteoblast differentiation capacity of mesenchymal stem cells must be tightly regulated, as inadequate bone mineralization can lead to osteoporosis, and excess bone formation can cause the heterotopic ossification of soft tissues. The balanced protein level of Msh homeobox 1 (MSX1) is critical during normal osteogenesis. To understand the factors that prevent MSX1 protein degradation, the identification of deubiquitinating enzymes (DUBs) for MSX1 is essential. In this study, we performed loss-of-function-based screening for DUBs regulating MSX1 protein levels using the CRISPR/Cas9 system. We identified ubiquitin-specific protease 11 (USP11) as a protein regulator of MSX1 and further demonstrated that USP11 interacts and prevents MSX1 protein degradation by its deubiquitinating activity. Overexpression of USP11 enhanced the expression of several osteogenic transcriptional factors in human mesenchymal stem cells (hMSCs). Additionally, differentiation studies revealed reduced calcification and alkaline phosphatase activity in USP11-depleted cells, while overexpression of USP11 enhanced the differentiation potential of hMSCs. These results indicate the novel role of USP11 during osteogenic differentiation and suggest USP11 as a potential target for bone regeneration.

Mir24-2-5p suppresses the osteogenic differentiation with Gnai3 inhibition presenting a direct target via inactivating JNK-p38 MAPK signaling axis

Background: Congenital anomalies are increasingly becoming a global pediatric health concern, which requires immediate attention to its early diagnosis, preventive strategies, and efficient treatments. Guanine nucleotide binding protein, alpha inhibiting activity polypeptide 3 (Gnai3) gene mutation has been demonstrated to cause congenital small jaw deformity, but the functions of Gnai3 in the disease-specific microRNA (miRNA) upregulations and their downstream signaling pathways during osteogenesis have not yet been reported. Our previous studies found that the expression of Mir24-2-5p was significantly downregulated in the serum of young people with overgrowing mandibular, and bioinformatics analysis suggested possible binding sites of Mir24-2-5p in the Gnai3 3'UTR region. Therefore, this study was designed to investigate the mechanism of Mir24-2-5p-mediated regulation of Gnai3 gene expression and explore the possibility of potential treatment strategies for bone defects.

Methods: Synthetic miRNA mimics and inhibitors were transduced into osteoblast precursor cells to regulate Mir24-2-5p expression. Dual-luciferase reporter assay was utilized to identify the direct binding of Gnai3 and its regulator Mir24-2-5p. Gnai3 levels in osteoblast precursor cells were downregulated by shRNA (shGnai3). Agomir, Morpholino Oligo (MO), and mRNA were microinjected into zebrafish embryos to control mir24-2-5p and gnai3 expression. Relevant expression levels were determined by the qRT-PCR and Western blotting. CCK-8 assay, flow cytometry, and transwell migration assays were performed to assess cell proliferation, apoptosis, and migration. ALP, ARS and Von Kossa staining were performed to observe osteogenic differentiation. Alcian blue staining and calcein immersions were performed to evaluate the embryonic development and calcification of zebrafish.

Results: The expression of Mir24-2-5p was reduced throughout the mineralization process of osteoblast precursor cells. miRNA inhibitors and mimics were transfected into osteoblast precursor cells. Cell proliferation, migration, osteogenic differentiation, and mineralization processes were measured, which showed a reverse correlation with the expression of Mir24-2-5p. Dual-luciferase reporter gene detection assay confirmed the direct interaction between Mir24-2-5p and Gnai3 mRNA. Moreover, in osteoblast precursor cells treated with Mir24-2-5p inhibitor, the expression of Gnai3 gene was increased, suggesting that Mir24-2-5p negatively targeted Gnai3. Silencing of Gnai3 inhibited osteoblast precursor cells proliferation, migration, osteogenic differentiation, and mineralization. Promoting effects of osteoblast precursor cells proliferation, migration, osteogenic differentiation, and mineralization by low expression of Mir24-2-5p was partially rescued upon silencing of Gnai3. In vivo, mir24-2-5p Agomir microinjection into zebrafish embryo resulted in shorter body length, smaller and retruded mandible, decreased cartilage development, and vertebral calcification, which was partially rescued by microinjecting gnai3 mRNA. Notably, quite similar phenotypic outcomes were observed in gnai3 MO embryos, which were also partially rescued by mir24-2-5p MO. Besides, the expression of phospho-JNK (p-JNK) and p-p38 were increased upon Mir24-2-5p inhibitor treatment and decreased upon shGnai3-mediated Gnai3 downregulation in osteoblast precursor cells. Osteogenic differentiation and mineralization abilities of shGnai3-treated osteoblast precursor cells were promoted by p-JNK and p-p38 pathway activators, suggesting that Gnai3 might regulate the differentiation and mineralization processes in osteoblast precursor cells through the MAPK signaling pathway.

Conclusions: In this study, we investigated the regulatory mechanism of Mir24-2-5p on Gnai3 expression regulation in osteoblast precursor cells and provided a new idea of improving the prevention and treatment strategies for congenital mandibular defects and mandibular protrusion.

Spatial-Temporal Patterns and Inflammatory Factors of Bone Matrix Remodeling

The bone extracellular matrix (ECM) contains organic and mineral constituents. The establishment and degradation processes of ECM connect with spatial and temporal patterns, especially circadian rhythms in ECM. These patterns are responsible for the physical and biological characteristics of bone. The disturbances of the patterns disrupt bone matrix remodeling and cause diverse bone diseases, such as osteogenesis imperfecta (OI) and bone fracture. In addition, the main regulatory factors and inflammatory factors also follow circadian rhythms. Studies show that the circadian oscillations of these factors in bone ECM potentially influence the interactions between immune responses and bone formation. More importantly, mesenchymal stem cells (MSCs) within the specific microenvironments provide the regenerative potential for tissue remodeling. In this review, we summarize the advanced ECM spatial characteristics and the periodic patterns of bone ECM. Importantly, we focus on the intrinsic connections between the immunoinflammatory system and bone formation according to circadian rhythms of regulatory factors in bone ECM. And our research group emphasizes the multipotency of MSCs with their microenvironments. The advanced understandings of bone ECM formation patterns and MSCs contribute to providing optimal prevention and treatment strategies.

CMTM3 suppresses bone formation and osteogenic differentiation of mesenchymal stem cells through inhibiting Erk1/2 and RUNX2 pathways

Osteoporosis, fracture, large-scale craniofacial defects and osteonecrosis are hot topics and are still underdiagnosed and undertreated in the clinic. It is urgent to understand the molecular mechanisms corresponding to the regulation of bone formation. CMTM3 (CKLF-like MARVEL transmembrane domain containing 3) connects the classic chemokine to the transmembrane 4 superfamily and plays an important role in intracellular vesicles transport, EGF receptor function maintenance and cancer development. However, its expression and function in bone remain unclear. In this paper, we found that the bone volume/total volume, trabecular number, trabecular thickness and bone surface area/bone volume of Cmtm3 KO mice increased significantly, and trabecular separation and trabecular pattern factor decreased in Cmtm3 KO mice compared with WT mice by microcomputed tomography. Moreover, the bone mineral content, bone mineral density, ultimate force and stiffness were also increased in Cmtm3 KO mice. Using in vitro analysis, we showed that CMTM3 expression decreases during the differentiation of hBMSCs to osteoblasts. Knockdown of CMTM3 promoted ALP and mineralization of hBMSCs and facilitated osteoblastic differentiation with increasing RUNX2 expression. However, overexpression of CMTM3 got the opposite results. These results proved that CMTM3 was essential for osteogenic differentiation. In addition, knockdown of CMTM3 enhanced p-Erk1/2, but had no significant effect on p-Akt or p-STAT3 in hBMSCs and MC3T3-E1 cells. Taken together, our results indicated that Erk1/2 and RUNX2 pathways mediated by CMTM3 were involved in the process of osteogenic differentiation, and CMTM3 might be a new potential target in the treatment of bone formation-related disease.

E3 Ubiquitin Ligase-Mediated Regulation of Osteoblast Differentiation and Bone Formation

The ubiquitin–proteasome system (UPS) is an essential pathway that regulates the homeostasis and function of intracellular proteins and is a crucial protein-degradation system in osteoblast differentiation and bone formation. Abnormal regulation of ubiquitination leads to osteoblast differentiation disorders, interfering with bone formation and ultimately leading to osteoporosis. E3 ubiquitin ligases (E3) promote addition of a ubiquitin moiety to substrate proteins, specifically recognizing the substrate and modulating tyrosine kinase receptors, signaling proteins, and transcription factors involved in the regulation of osteoblast proliferation, differentiation, survival, and bone formation. In this review, we summarize current progress in the understanding of the function and regulatory effects of E3 ligases on the transcription factors and signaling pathways that regulate osteoblast differentiation and bone formation. A deep understanding of E3 ligase-mediated regulation of osteoblast differentiation provides a scientific rationale for the discovery and development of novel E3-targeting therapeutic strategies for osteoporosis.

MiR-27a-3p promotes the osteogenic differentiation by activating CRY2/ERK1/2 axis

Background

Osteoporosis seriously disturbs the life of people. Meanwhile, inhibition or weakening of osteogenic differentiation is one of the important factors in the pathogenesis of osteoporosis. It was reported that miR-27a-3p reduced the symptoms of osteoporosis. However, the mechanism by which miR-27a-3p in osteogenic differentiation remains largely unknown.

Methods

To induce the osteogenic differentiation in MC3T3-E1 cells, cells were treated with osteogenic induction medium (OIM). RT-qPCR was used to evaluate the mRNA expression of miR-27a-3p and CRY2 in cells. The protein levels of CRY2, Runt-related transcription factor 2 (Runx2), osteopontin (OPN), osteocalcin (OCN) and the phosphorylation level of extracellular regulated protein kinases (ERK) 1/2 in MC3T3-E1 cells were evaluated by western blotting. Meanwhile, calcium nodules and ALP activity were tested by alizarin red staining and ALP kit, respectively. Luciferase reporter gene assay was used to analyze the correlation between CRY2 and miR-27a-3p.

Results

The expression of miR-27a-3p and the phosphorylation level of ERK1/2 were increased by OIM in MC3T3-E1 cells, while CRY2 expression was decreased. In addition, OIM-induced increase of calcified nodules, ALP content and osteogenesis-related protein expression was significantly reversed by downregulation of miR-27a-3p and overexpression of CRY2. In addition, miR-27a-3p directly targeted CRY2 and negatively regulated CRY2. Meanwhile, the inhibitory effect of miR-27a-3p inhibitor on osteogenic differentiation was reversed by knockdown of CRY2 or using honokiol (ERK1/2 signal activator). Furthermore, miR-27a-3p significantly inhibited the apoptosis of MC3T3-E1 cells treated by OIM. Taken together, miR-27a-3p/CRY2/ERK axis plays an important role in osteoblast differentiation.

Conclusions

MiR-27a-3p promoted osteoblast differentiation via mediation of CRY2/ERK1/2 axis. Thereby, miR-27a-3p might serve as a new target for the treatment of osteoporosis.

Inhibition of Bone Morphogenetic Protein 2 Suppresses the Stemness Maintenance of Cancer Stem Cells in Hepatocellular Carcinoma via the MAPK/ERK Pathway

Background

Hepatocellular carcinoma (HCC) remains a life-threatening malignant tumor. Cancer stem cells (CSCs) harbor tumor-initiating capacity and can be used as a therapeutic target for human malignancies. Bone morphogenetic proteins (BMPs) play a regulatory role in CSCs. This study investigated the role and mechanism of BMP2 in CSCs in HCC.

Methods

BMP2 expression in HCC tissues and cells, and CSCs from HepG2 cells and SMMC7721 cells (HepG2-CSCs and SMMC7721-CSCs) was measured. The association between BMP2 expression and prognosis of HCC patients was analyzed. CSCs were interfered with BMP2 to evaluate the abilities of colony and tumor sphere formation, levels of stemness-related markers, epithelial-mesenchymal transition (EMT), and invasion and migration. Levels of MAPK/ERK pathway-related proteins in HepG2-CSCs were detected after BMP2 knockdown. The effect of the activated MAPK/ERK pathway on HepG2-CSCs was assessed. Finally, the effect of BMP2 inhibition on CSCs in HCC was verified in vivo.

Results

BMP2 showed obvious upregulation in HCC tissues and cells and was further upregulated in CSCs in HCC, with its higher expression indicative of worse prognosis. Silencing BMP2 inhibited colony and tumor sphere formation, levels of stemness-related markers, as well as EMT, invasion and migration of HepG2-CSCs and SMMC7721-CSCs. The MAPK/ERK pathway was suppressed after BMP2 knockdown, and its activation reversed the inhibitory effect of shBMP2 on hepatic CSCs. BMP2 accelerated tumor growth and EMT of CSCs in HCC in vivo.

Conclusion

We concluded that BMP2 knockdown inhibited the EMT, proliferation and invasion of CSCs in HCC, thereby hindering the stemness maintenance via suppressing the MAPK/ERK pathway.

TGFβ1 Suppressed Matrix Mineralization of Osteoblasts Differentiation by Regulating SMURF1-C/EBPβ-DKK1 Axis

Transforming growth factor β1 (TGFβ1) is a major mediator in the modulation of osteoblast differentiation. However, the underlying molecular mechanism is still not fully understood. Here, we show that TGFβ1 has a dual stage-dependent role in osteoblast differentiation; TGFβ1 induced matrix maturation but inhibited matrix mineralization. We discovered the underlying mechanism of the TGFβ1 inhibitory role in mineralization using human osteoprogenitors. In particular, the matrix mineralization-related genes of osteoblasts such as osteocalcin (OCN), Dickkopf 1 (DKK1), and CCAAT/enhancer-binding protein beta (C/EBPβ) were dramatically suppressed by TGFβ1 treatment. The suppressive effects of TGFβ1 were reversed with anti-TGFβ1 treatment. Mechanically, TGFβ1 decreased protein levels of C/EBPβ without changing mRNA levels and reduced both mRNA and protein levels of DKK1. The degradation of the C/EBPβ protein by TGFβ1 was dependent on the ubiquitin–proteasome pathway. TGFβ1 degraded the C/EBPβ protein by inducing the expression of the E3 ubiquitin ligase Smad ubiquitin regulatory factor 1 (SMURF1) at the transcript level, thereby reducing the C/EBPβ-DKK1 regulatory mechanism. Collectively, our findings suggest that TGFβ1 suppressed the matrix mineralization of osteoblast differentiation by regulating the SMURF1-C/EBPβ-DKK1 axis.

MMP-1 promotes osteogenic differentiation of human bone marrow mesenchymal stem cells via the JNK and ERK pathway

Enhancing the functions of mesenchymal stem cells (MSCs) is considered a potential approach for promoting tissue regeneration. In this study, we investigated the effects of Matrix Metalloproteinase-1 (MMP-1) on bone marrow mesenchymal stem cells (BMSCs) and its mechanism. Our results showed that knockdown of MMP-1 impeded scratch closure, attenuated proliferation, inhibited ALP activity, ALP denser staining and mineralization in vitro, and decreased expression of RUNX2, OSX, OPN and OCN in BMSCs, while 20 ng/mL recombinant human MMP-1 protein (rhMMP-1) significantly accelerated scratch closure, enhanced proliferation, ALP activity, ALP denser staining and mineralization in vitro, and increased expression of RUNX2, OSX, OPN and OCN. In addition, knockdown of MMP-1 inhibited the expression of phosphorylated c-Jun N-terminal kinase (p-JNK) and phosphorylated extracellular regulated protein kinases (p-ERK), while 20 ng/mL rhMMP-1 increased the expression of p-JNK and p-ERK in BMSCs. Furthermore, inhibition of c-Jun N-terminal kinase (JNK) and extracellular regulated protein kinases (ERK) by their inhibitor SP600125 and PD98059 dramatically blocked MMP-1-enhanced ALP activity and mineralization in BMSCs. Our results revealed that MMP-1 could accelerate the osteogenic differentiation potentials of BMSCs via the JNK and ERK pathway, providing the mechanism underlying MSC biology and identifying a potential target for improving bone tissue regeneration.

Mechanism of traumatic heterotopic ossification: In search of injury-induced osteogenic factors

Heterotopic ossification (HO) is a pathological condition of abnormal bone formation in soft tissue. Three factors have been proposed as required to induce HO: (a) osteogenic precursor cells, (b) osteoinductive agents and (c) an osteoconductive environment. Since Urist's landmark discovery of bone induction in skeletal muscle tissue by demineralized bone matrix, it is generally believed that skeletal muscle itself is a conductive environment for osteogenesis and that resident progenitor cells in skeletal muscle are capable of differentiating into osteoblast to form bone. However, little is known about the naturally occurring osteoinductive agents that triggered this osteogenic response in the first place. This article provides a review of the emerging findings regarding distinct types of HO to summarize the current understanding of HO mechanisms, with special attention to the osteogenic factors that are induced following injury. Specifically, we hypothesize that muscle injury‐induced up‐regulation of local bone morphogenetic protein‐7 (BMP‐7) level, combined with glucocorticoid excess‐induced down‐regulation of circulating transforming growth factor‐β1 (TGF‐β1) level, could be an important causative mechanism of traumatic HO formation.

Mechanism of TGF-β1 inhibiting Kupffer cell immune responses in cholestatic cirrhosis

Effect of exogenous transforming growth factor-β1 (TGF-β1) on cholestatic mice by inhibiting Kupffer cell immune responses in liver was investigated. To induce cholestasis, BALB/c mice received a sham operation (Mock group), or underwent a bile duct ligation (BDL group) and then were subcutaneously injected with TGF-β1 at multiple sites (TGF group). Liver functions were evaluated according to the levels of alanine aminotransferase (ALT), aspartate aminotransferase AST and γ-glutamyltranspeptidase (γ-GT) in serum samples. Expression of nuclear factor-κB (NF-κB), interleukin-6 (IL-6), IL-1β and tumor necrosis factor-α (TNF-α) was detected. Expression of inducible nitric oxide synthase (iNOS) and arginase-1 (Arg-1) in Kupffer cells (KCs) of the liver was detected. The isolated KCs were divided into control group, LPS group, TGF group and Galunisertib group and western blot analysis was used to detect the expression of NF-κB, IL-6, IL-1β, TNF-α, iNOS and Arg-1. The percentage of CD40, CD86, CD204 and CD206 as macrophage cell surface antigens were measured by flow cytometry. The indexes of liver function and liver fibrosis of the mice in the TGF group were significantly lower than those in the BDL group (P<0.05). The levels of IL-1β, IL-6 and TNF-α in the liver were lower than those in the BDL group, while the level of IL-10 was significantly increased (P<0.05). M2-type transformation occurred in liver Kupffer cells of mice in the TGF group. In cell experiments, TGF treatment downregulated the expression of IL-1β, IL-6, TNF-α and NF-κB, increased the expression of IL-10, and induced M2-type transformation in macrophages (P<0.05). In conclusion, TGF-ß1 diminished the progression of cholestasis in mice by inhibiting the inflammatory response of KCs and regulating KC polarization.

TGF-β1 plays a protective role in glucocorticoid-induced dystrophic calcification

Dystrophic calcification (DC) is the deposition of calcium in degenerated tissue which occurs as a reaction to tissue damage. Sometimes if tissue repair fails, it can progress into heterotopic ossification (HO), a pathological condition of abnormal bone formation. HO happens frequently in severe trauma patients such as in blast injury, central nervous system injury and burn injury, in which excessive endogenous glucocorticoid production has always been found. Glucocorticoids have a big impact on bone and muscle. However, few studies have investigated the impact of glucocorticoids on DC/HO formation in muscle. This study aimed to determine the role of glucocorticoids in DC/HO pathogenesis following muscular injury and the possible underlying mechanism. In this study, we administered a high dose of a synthetic glucocorticoid, dexamethasone (DEX), to animals with muscle injury induced by cardiotoxin (CTX) injection to mimic a glucocorticoid excess state following severe muscle trauma. The findings reported here showed that DEX treatment together with CTX-induced muscle injury led to a significant amount of DC in muscle. This effect was likely related to protein level alterations in the fibrinolytic system and resultant decreased circulating transforming growth factor-beta 1 (TGF-β1), given that supplementation of recombinant TGF-β1 markedly rescued this phenomenon. In summary, our results suggest that glucocorticoid excess impairs muscle regeneration and promotes DC/HO, and that TGF-β1 could be a key factor in modulating this process.

The Nrf2 activator RTA-408 attenuates osteoclastogenesis by inhibiting STING dependent NF-κb signaling

The dysregulation of ROS production and osteoclastogenesis is involved in the progress of osteoporosis. To identify novel and effective targets to treat this disease, it is important to explore the underlying mechanisms. In our study, we firstly tested the effect of the Nrf2 activator RTA-408, a novel synthetic triterpenoid under clinical investigation for many diseases, on osteoclastogenesis. We found that it could inhibit osteoclast differentiation and bone resorption in a time- and dose-dependent manner. Further, RTA-408 enhanced the expression and activity of Nrf2 and significantly suppressed RANKL-induced reactive oxygen species (ROS) production. Nrf2 regulates the STING expression and STING induces the production of IFN-β. Here, we found that RTA-408 could suppress STING expression, but that it does not affect Ifnb1 expression. RANKL-induced degradation of IκBα and the nuclear translocation of P65 was suppressed by RTA-408. Although this compound was not found to influence STING-IFN-β signaling, it suppressed the RANKL-induced K63-ubiquitination of STING via inhibiting the interaction between STING and the E3 ubiquitin ligase TRAF6. Further, adenovirus-mediated STING overexpression rescued the suppressive effect of RTA-408 on NF-κB signaling and osteoclastogenesis. In vivo experiments showed that this compound could effectively attenuate ovariectomy (OVX)-induced bone loss in C57BL/6 mice by inhibiting osteoclastogenesis. Collectively, we show that RTA-408 inhibits NF-κB signaling by suppressing the recruitment of TRAF6 to STING, in addition to attenuating osteoclastogenesis and OVX-induced bone loss in vivo, suggesting that it could be a promising candidate for treating osteoporosis in the future.

METTL3 Regulates Osteoblast Differentiation and Inflammatory Response via Smad Signaling and MAPK Signaling

Osteoblasts are crucial bone-building cells that maintain bone homeostasis, whereas inflammatory stimuli can inhibit osteogenesis and activate inflammatory response. N6-methyladenosine (m⁶A) is the most abundant mRNA modification in eukaryotes and plays important roles in multiple biological processes. However, whether m⁶A modification affects osteoblast differentiation and inflammatory response remains unknown. To address this issue, we investigated the expression of the N6-adenosine methyltransferase METTL3 and found that it was upregulated during osteoblast differentiation and downregulated after LPS stimulation. We then knocked down METTL3 and observed decreased levels of osteogenic markers, ALP activity, and mineralized nodules, as well as Smad1/5/9 phosphorylation, in LPS-induced inflammation. METTL3 knockdown promoted the mRNA expression and stability of negative regulators of Smad signaling, Smad7 and Smurf1, the same regulatory pattern identified when the m⁶A-binding protein YTHDF2 was silenced. Moreover, METTL3 depletion enhanced proinflammatory cytokine expression and increased the phosphorylation of ERK, p38, JNK, and p65 in MAPK and NF-κB signaling pathways. The increase in cytokine expression was inhibited after MAPK signaling inhibitor treatment. All data suggest that METTL3 knockdown inhibits osteoblast differentiation and Smad-dependent signaling by stabilizing Smad7 and Smurf1 mRNA transcripts via YTHDF2 involvement and activates the inflammatory response by regulating MAPK signaling in LPS-induced inflammation.

Experimental study of the synergistic effect and network regulation mechanisms of an applied combination of BMP-2, VEGF, and TGF-β1 on osteogenic differentiation

The study aimed to explore the osteogenic effect induced by the combined use of bone morphogenetic protein-2 (BMP-2), vascular endothelial growth factor (VEGF), and transforming growth factor-β1 (TGF-β1), attain the best combination for osteogenic quality and efficiency, and explore the network regulation mechanisms of induced osteogenesis. MC3T3-E1 cells were cultured in vitro, and BMP-2, VEGF, and TGF β1 were added to osteogenic induction mediums in different combinations to conduct experiments. At 7 and 14 days, the alkaline phosphatase (ALP) and Alizarin Red S (ARS) staining of the applied BMP-2 and VEGF combination were deeper and the quantitative analysis were higher than those of the other groups. After optimizing the time-effect relationship of the combined application, with BMP-2, VEGF, and TGF-β1 adding in the early stage and BMP-2 and VEGF adding in the late, the ALP and ARS staining of these groups were deeper and the quantitative analyses were meaningfully higher than the BMP-2 and VEGF combination group at 7 and 14 days. The expression of the RUNX2 gene and the Smad1 signaling pathway in the optimized combination group was also significantly higher. The results demonstrate that the combination of BMP-2, VEGF, and TGF-β1 applied according to the time-effect relationship can significantly promote osteogenic differentiation mainly through the classical BMP-receptor-Smad signal pathway.

Distinctive requirement of PKCε in the control of Rho GTPases in epithelial and mesenchymally transformed lung cancer cells

Diacylglycerol (DAG)/phorbol ester-regulated protein kinase C (PKC) isozymes have been widely linked to tumor promotion and the development of a metastatic phenotype. PKCε, an oncogenic member of the PKC family, is abnormally overexpressed in lung cancer and other cancer types. This kinase plays significant roles in proliferation, survival and migration; however its role in epithelial-to-mesenchymal transition (EMT) has been scarcely studied. Silencing experiments in non-small lung cancer (NSCLC) cells revealed that PKCε or other DAG-regulated PKCs (PKCα and PKCδ) were dispensable for the acquisition of a mesenchymal phenotype induced by transforming growth factor beta (TGF-β). Unexpectedly, we found a nearly complete down-regulation of PKCε expression in TGF-β-mesenchymally transformed NSCLC cells. PMA and AJH-836 (a DAG-mimetic that preferentially activates PKCε) promote ruffle formation in NSCLC cells via Rac1, however they fail to induce these morphological changes in TGF-β-mesenchymally transformed cells despite their elevated Rac1 activity. Several Rac Guanine nucleotide Exchange-Factors (Rac-GEFs) were also up-regulated in TGF-β-treated NSCLC cells, including Trio and Tiam2, which were required for cell motility. Lastly, we found that silencing or inhibiting PKCε enhances RhoA activity and stress fiber formation, a phenotype also observed in TGF-β-transformed cells. Our studies established a distinctive involvement of PKCε in epithelial and mesenchymal NSCLC cells, and identified a complex interplay between PKCε and small GTPases that contributes to regulation of NSCLC cell morphology and motile activity.

Sal B targets TAZ to facilitate osteogenesis and reduce adipogenesis through MEK-ERK pathway

Salvianolic acid B (Sal B), a major bioactive component of Chinese herb, was identified as a mediator for bone metabolism recently. The aim of this study is to investigate the underlying mechanisms by which Sal B regulates osteogenesis and adipogenesis. We used MC3T3-E1 and 3T3-L1 as the study model to explore the changes of cell differentiation induced by Sal B. The results indicated that Sal B at different concentrations had no obvious toxicity effects on cell proliferation during differentiation. Furthermore, Sal B facilitated osteogenesis but inhibited adipogenesis by increasing the expression of transcriptional co-activator with PDZ-binding motif (TAZ). Accordingly, TAZ knock-down offset the effects of Sal B on cell differentiation into osteoblasts or adipocytes. Notably, the Sal B induced up-expression of TAZ was blocked by U0126 (the MEK-ERK inhibitor), rather than LY294002 (the PI3K-Akt inhibitor). Moreover, Sal B increased the p-ERK/ERK ratio to regulate the TAZ expression as well as the cell differentiation. In summary, this study suggests for the first time that Sal B targets TAZ to facilitate osteogenesis and reduce adipogenesis by activating MEK-ERK signalling pathway, which provides evidence for Sal B to be used as a potential therapeutic agent for the management of bone diseases.

Opposing roles and potential antagonistic mechanism between TGF-β and BMP pathways: Implications for cancer progression

The transforming growth factor β (TGF-β) superfamily participates in tumour proliferation, apoptosis, differentiation, migration, invasion, immune evasion and extracellular matrix remodelling. Genetic deficiency in distinct components of TGF-β and BMP-induced signalling pathways or their excessive activation has been reported to regulate the development and progression of some cancers. As more in-depth studies about this superfamily have been conducted, more evidence suggests that the TGF-β and BMP pathways play an opposing role. The cross-talk of these 2 pathways has been widely studied in kidney disease and bone formation, and the opposing effects have also been observed in some cancers. However, the antagonistic mechanisms are still insufficiently investigated in cancer. In this review, we aim to display more evidences and possible mechanisms accounting for the antagonism between these 2 pathways, which might provide some clues for further study in cancer.

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Describe the basics of TGF-β and BMP signalling

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Summarize the potential mechanisms accounting for the antagonism between TGF-β and BMP pathways

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Provide some evidence about the antagonistic effects between pathways observed in some cancers

Inhibition of transforming growth factor-β signaling pathway enhances the osteogenic differentiation of unrestricted somatic stem cells

In recent years, extensive studies have been performed to enhance stem cell-based therapies for bone and cartilage repair. Among various sources of stem cells, cord blood-derived unrestricted somatic stem cells (USSCs) seem to be the most appropriate option for an autologous transplantation. Among different signaling pathways, the transforming growth factor-β (TGF-β) pathway is shown as an important regulator of proliferation and osteogenic differentiation in osteoblast progenitors as well as mesenchymal stem cells. Due to its contradictory and temporally variable effects on different cell types, we sought to investigate whether and how the TGF-β signaling pathway regulates the osteogenic differentiation of the USSCs. Therefore, in the current study, we treated USSCs with the recombinant protein TGF-β1 (1 ng/mL) and showed that the expression of matrix metalloproteinase 9, a well-known effector in this pathway, was significantly induced, indicating that the TGF-β signaling pathway is active in USSCs. Then we applied a TGF-β receptor antagonist (SB431542; 10 μM) to the osteogenic media cultured USSCs for single periods of 3.5 days within the 21-day differentiation period starting at day 0, 3.5, 7, 10.5, 14, and 17.5. The expression analysis results of the of the osteogenic marker runt-related transcription factor 2 as well as the production of bone matrix showed that SB431542 induced the osteogenic differentiation of USSCs more significantly during the early stage of differentiation, suggesting that the TGF-β pathway temporally regulates the osteogenic differentiation of USSCs.

Deubiquitinating Enzymes and Bone Remodeling

Bone remodeling, which is essential for bone homeostasis, is controlled by multiple factors and mechanisms. In the past few years, studies have emphasized the role of the ubiquitin-dependent proteolysis system in regulating bone remodeling. Deubiquitinases, which are grouped into five families, remove ubiquitin from target proteins and are involved in several cell functions. Importantly, a number of deubiquitinases mediate bone remodeling through regulating differentiation and/or function of osteoblast and osteoclasts. In this review, we review the functions and mechanisms of deubiquitinases in mediating bone remodeling.

LncRNA KCNQ1OT1 promotes osteogenic differentiation to relieve osteolysis via Wnt/β-catenin activation

Background

Resveratrol (RSV) has been reported to stimulate osteoblast differentiation in which Wnt/β-catenin signaling pathway played a crucial role. However, whether and how RSV activated Wnt/β-catenin pathway in osteogenic differentiation still remained elusive.

Methods

In vivo polymethylmethacrylate (PMMA) particle-induced osteolysis (PIO) mouse model and in vitro PMMA particle-stimulated mouse mesenchymal stem cells (mMSCs) experiments were established. Relative expression levels of lncRNA KCNQ1OT1, β-catenin, Runx2, Osterix and osteocalcin were determined using quantitative Real-Time PCR. Western blotting was used to measure β-catenin protein expression. In addition, the alkaline phosphatase activity and mineral deposition level using alizarin red S staining were performed to examine osteogenic differentiation status. The interaction between KCNQ1OT1 and β-catenin was confirmed by RNA pull down assay.

Results

RSV significantly attenuated PIO in vivo and PMMA-particle inhibition of osteogenic differentiation of mMSCs. Moreover, KCNQ1OT1 exerted the similar function in mMSCs by regulating β-catenin. Further study demonstrated that RSV exerted its effect on osteoblastic differentiation by regulating KCNQ1OT1. Consequently, RSV alleviated PMMA-particle inhibition of osteoblastic differentiation via Wnt/β-catenin pathway activation in vivo and in vitro.

Conclusion

RSV accelerated osteoblast differentiation by regulating lncRNA KCNQ1OT1 via Wnt/β-catenin pathway activation, indicating the functional role of RSV in modulating osteogenesis.