Beraprost ameliorates postmenopausal osteoporosis by regulating Nedd4-induced Runx2 ubiquitination

Inhibition of LPL suppresses the osteoclast differentiation of bone-marrow-derived macrophages by promoting the ACSL4 ubiquitination

BACKGROUND

The imbalance between osteoblast (OB) -led bone formation and osteoclast (OC) -induced bone resorption is a recognized reason of osteoporosis. However, further gene-related pathogenesis remains to be elucidated.

METHODS

The microarray profile GSE225974 was used to identify the differentially expressed genes (DEGs) between OC and peripheral blood mononuclear cells (PBMC). Bone-marrow-derived macrophages (BMMs) treated with 30 ng/ml macrophage-colony-stimulating factor (M-CSF) and 100 ng/ml receptor activator of NF-kappa B ligand (RANKL) was to induce osteoclastic differentiation in vitro. The expression of lipoprotein lipase (LPL) was measured by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting methods. Meanwhile, the regulatory role of LPL on osteoclastic differentiation was evaluated by monitoring cathepsin K levels and TRAP staining. Proteins related to LPL were obtained by STRING, and the interaction between proteins was verified by immunoprecipitation (IP) and ubiquitination analysis.

RESULTS

LPL was markedly up-expressed in OCs. Inhibition of LPL suppressed osteoclast differentiation of BMMs by inhibiting cathepsin K and number of TRAP-positive cells. Then the results of STRING demonstrated that proteins related to LPL including the lipid synthesis gene ACSL4. Erastin treatment prominently weakened the effects of si-LPL on cathepsin K levels and TRAP staining intensity by activating ferroptosis. Mechanically, inhibition of LPL suppressed osteoclast differentiation by promoting ubiquitination levels of ACSL4, and over-expression of USP14 reversed the effects of LPL knockdown on regulating ubiquitination of ACSL4.

CONCLUSION

Suppression of LPL inhibits the osteoclast differentiation of BMMs in vitro. The mechanism may be related to the LPL knockdown induced USP14 meidated the ACSL4 ubiquitination. Taken together, down-regulation of LPL may be a promising method to suppress osteoclast differentiation to treat osteoporosis.

Inhibition of NEURL3 Suppresses Osteoclast Differentiation via BMP7 Ubiquitination Modulation

Osteoporosis (OP) is a genetic disorder characterized by an imbalance between osteoblast-mediated bone formation and osteoclast-induced bone resorption. However, the underlying gene-related mechanisms of its pathogenesis remain to be fully elucidated. Aberrantly expressed neuralized E3 ubiquitin-protein ligase 3 (NEURL3), which is related to osteoclastic differentiation, was identified through the analysis of the microarray profile GSE176265. Bone marrow-derived macrophages (BMMs) were isolated from the femurs and tibias of C57BL/6 J mice and treated with 30 ng/mL macrophage-colony-stimulating factor (M-CSF) and 100 ng/mL receptor activator of nuclear factor-kappa B ligand (RANKL) to induce osteoclastic differentiation, thereby mimicking OP in vitro. To model OP in vivo, ovariectomy (OVX)-induced bone loss was performed in mice. High expression levels of NEURL3 were confirmed in clinical samples, OP model cells, and OP model mice using quantitative real-time polymerase chain reaction (qRT-PCR). The impact of NEURL3 on osteoclastic differentiation was assessed by evaluating cell viability and the expression levels of osteoclastogenesis-related marker genes. Additionally, bone loss in mice was quantified using micro-computed tomography before and after NEURL3 inhibition. Mechanistically, the effects of NEURL3 on osteogenic differentiation were investigated by determining the protein levels of osteogenic markers via Western blotting. NEURL3 was markedly overexpressed in serum samples collected from patients with OP, OVX-induced OP mouse models, and induced osteoclasts. Inhibition of NEURL3 leads to a 20% decrease in BMM survival rate and a reduction in the number of tartrate-resistant acid phosphatase (TRAP) positive cells, which is a characteristic of mature osteoclasts. Furthermore, the expression levels of osteoclastogenesis-related marker genes were reduced by 50%. In vivo studies revealed that suppressing NEURL3 resulted in a 38% improvement in trabecular bone volume (BV/TV) and a 28% increase in bone mineral density (BMD) in the OVX-induced OP mice. Mechanistically, NEURL3 promoted osteoclast differentiation by increasing the ubiquitination levels of BMP7. Inhibition of BMP7 reversed the effects of NEURL3 on osteoclast differentiation in BMMs. Suppression of NEURL3 inhibits osteoclast differentiation of BMMs in vitro and alleviates bone loss in vivo. The underlying mechanism may involve NEURL3-induced ubiquitination of BMP7. Collectively, the downregulation of NEURL3 represents a promising therapeutic strategy for suppressing osteoclast differentiation and treating OP.

The Secondary Metabolites of Bacillus subtilis Strain Z15 Induce Apoptosis in Hepatocellular Carcinoma Cells

The lipopeptides produced by Bacillus subtilis have anti-cancer potential. We had previously identified a secondary metabolite of B. subtilis strain Z15 (BS-Z15), which has an operon that regulates lipopeptide synthesis, and also demonstrated that the fermentation products of this strain exerted antioxidant and pro-immune effects. The purpose of this study was to investigate in vitro and in vivo the anticancer effects of BS-Z15 secondary metabolites (BS-Z15 SMs) on hepatocellular carcinoma (HCC) cells. BS-Z15 SMs significantly inhibited H22 cell-derived murine xenograft tumor growth without any systemic toxicity. In addition, BS-Z15 SMs decreased the viability of H22 cells and BEL-7404 cells in vitro with respective IC50 values of 33.83 and 27.26 µg/mL. Consistent with this, BS-Z15 SMs induced apoptosis and G0/G1 phase arrest in the BEL-7404 cells, and the mitochondrial membrane potential was also significantly reduced in a dose-dependent manner. Mechanistically, BS-Z15 SMs upregulated the pro-apoptotic p53, Bax, cytochrome C, and cleaved-caspase-3/9 proteins and downregulated the anti-apoptotic Bcl-2. These findings suggest that the induction of apoptosis in HCC cells by BS-Z15 SMs may be related to the mitochondrial pathway. Thus, the secondary metabolites of B. subtilis strain Z15 are promising to become new anti-cancer drugs for the clinical treatment of liver cancer.

Posttranslational Modification in Bone Homeostasis and Osteoporosis

Bone is responsible for providing mechanical protection, attachment sites for muscles, hematopoiesis micssroenvironment, and maintaining balance between calcium and phosphorate. As a highly active and dynamically regulated organ, the balance between formation and resorption of bone is crucial in bone development, damaged bone repair, and mineral homeostasis, while dysregulation in bone remodeling impairs bone structure and strength, leading to deficiency in bone function and skeletal disorder, such as osteoporosis. Osteoporosis refers to compromised bone mass and higher susceptibility of fracture, resulting from several risk factors deteriorating the balanced system between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. This balanced system is strictly regulated by translational modification, such as phosphorylation, methylation, acetylation, ubiquitination, sumoylation, glycosylation, ADP-ribosylation, S-palmitoylation, citrullination, and so on. This review specifically describes the updating researches concerning bone formation and bone resorption mediated by posttranslational modification. We highlight dysregulated posttranslational modification in osteoblast and osteoclast differentiation. We also emphasize involvement of posttranslational modification in osteoporosis development, so as to elucidate the underlying molecular basis of osteoporosis. Then, we point out translational potential of PTMs as therapeutic targets. This review will deepen our understanding between posttranslational modification and osteoporosis, and identify novel targets for clinical treatment and identify future directions.

MiR-147b-3p promotes osteogenesis by targeting NDUFA4 and PI3K/AKT pathway

BACKGROUND

Osteoporosis (OP) is a progressive metabolic bone disease characterized by impaired bone microarchitecture, decreased bone strength, and dysregulated bone remodeling, leading to an increased risk of fractures. Among osteoporotic fractures, osteoporotic vertebral compression fractures (OVCF) are the most common and can significantly impact patients' quality of life. Growing evidence suggests that microRNAs (miRNAs) play a crucial role in bone homeostasis by regulating osteoblast differentiation, bone metabolism, and remodeling processes. Notably, miR-147b-3p has been found to be downregulated in OVCF; however, its specific role in osteogenic regulation remains largely unknown. Therefore, further investigation is warranted to elucidate the function and underlying mechanism of miR-147b-3p in osteogenic differentiation.

METHODS

The GSE93883 and GSE74209 datasets were retrieved from the Gene Expression Omnibus (GEO) database to investigate specific microRNAs involved in the regulation of osteogenesis. Differential expression of miR-147b-3p and NDUFA4 was assessed between healthy controls and patients with osteoporotic vertebral compression fractures (OVCF) using real-time quantitative PCR.To modulate the expression levels of miR-147b-3p in MC3T3-E1 cells, both the miR-147b-3p mimic and inhibitor were utilized. Cell viability was evaluated via the CCK-8 assay to assess the impact of miR-147b-3p on MC3T3-E1 cell proliferation. Real-time PCR and Western blot analysis were conducted to quantify the expression levels of osteogenic markers across different experimental groups. Alizarin red staining (ARS) was employed to examine the effect of miR-147b-3p on the mineralization capacity of MC3T3-E1 cells. In vivo experiments were performed to evaluate the functional role of miR-147b-3p. Bioinformatics databases were used to predict the potential target gene of miR-147b-3p (NDUFA4), and the predictions were validated by a dual luciferase reporter gene assay.To investigate the regulatory role of the miR-147b-3p/NDUFA4 axis in osteogenic differentiation, MC3T3-E1 cells were transfected with the NDUFA4 overexpression plasmid and miR-147b-3p mimic. Western blot analysis was performed to assess the phosphorylation levels of PI3K and AKT, in order to explore whether the miR-147b-3p/NDUFA4 axis regulates osteogenic differentiation through the PI3K/AKT signaling pathway.

RESULTS

Our results indicated a significant downregulation of miR-147b-3p and a concurrent upregulation of NDUFA4 in patients with osteoporotic vertebral compression fractures (OVCF). A luciferase reporter assay confirmed that NDUFA4 is a direct target gene of miR-147b-3p.To examine the functional role of miR-147b-3p, both in vitro and in vivo experiments were conducted.The experimental findings revealed that the miR-147b-3p mimic significantly enhanced cell viability, increased protein expressions of Alkaline Phosphatase (ALP) and Runt-related Transcription Factor 2 (RUNX2), and promoted mineralization as evidenced by Alizarin Red S staining. Conversely, treatment with the miR-147b-3p inhibitor or overexpression plasmid for NDUFA4 (pNDUFA4) produced opposite effects.Furthermore, the miR-147b-3p/NDUFA4 axis was found to regulate the PI3K/AKT signaling pathway.The miR-147b-3p mimic significantly increased the phosphorylation levels of PI3K (p-PI3K) and AKT (p-AKT), whereas pNDUFA4 led to their reduction.

CONCLUSIONS

This study demonstrated that miR-147b-3p plays a crucial role in promoting osteogenic differentiation in osteoporotic vertebral compression fractures (OVCF) by targeting NDUFA4 and modulating the PI3K/AKT signaling pathway. These findings provide new insights into the molecular mechanisms underlying the progression of osteoporotic vertebral fractures.

Hypoxia Promotes Osteoclast Differentiation by Weakening USP18-Mediated Suppression on the NF-κB Signaling Pathway

Osteoporosis, a prevalent metabolic bone disorder, is characterized by reduced bone density and increased fracture risk. The pathogenesis of osteoporosis is closely associated with an imbalance in bone remodeling, in which the resorption function of osteoclasts exceeds the formation function of osteoblasts. Hypoxia has been implicated in the promotion of osteoclast differentiation and the subsequent development of osteoporosis. The ubiquitin-proteasome system (UPS) and its regulatory enzymes, deubiquitinating enzymes (DUBs), play a significant role in bone homeostasis. In this study, we investigated the contribution and mechanism of Ubiquitin-specific protease 18 (USP18), a DUB, in osteoclast differentiation under hypoxic conditions. BMDMs and RAW264.7 cells were treated with RANKL to induce osteoclastogenesis and were subjected to overexpression or knockdown of USP18 under normoxic or hypoxia conditions. Osteoclast formation was assessed using TRAP staining, and the expression of osteoclast marker genes was determined using qRT-PCR. The activation of the NF-κB signaling pathway was evaluated using immunoblotting. We found that hypoxia significantly enhanced the differentiation of BMDMs and RAW264.7 cells into osteoclasts, accompanied by a notable downregulation of USP18 expression. The overexpression of USP18 inhibited RANKL-induced osteoclast differentiation, while the knockdown of USP18 promoted that process, unveiling the inhibitory effect of USP18 in osteoclastogenesis. Furthermore, the overexpression of USP18 rescued the hypoxia-induced increase in osteoclast differentiation. Mechanistic insights revealed that USP18 inhibits osteoclastogenesis by suppressing the NF-κB signaling pathway, with a potential target on TAK1 or its upstream molecules. This study indicates that hypoxia promotes osteoclast differentiation through the downregulation of USP18, which, in turn, relieves the suppression of the activation of the NF-κB signaling pathway. The USP18 emerges as a potential therapeutic target for osteoporosis treatment, highlighting the importance of the hypoxia-DUB axis in the pathogenesis of the disease.

Role of ubiquitination in the occurrence and development of osteoporosis (Review)

The ubiquitin (Ub)‑proteasome system (UPS) plays a pivotal role in maintaining protein homeostasis and function to modulate various cellular processes including skeletal cell differentiation and bone homeostasis. The Ub ligase E3 promotes the transfer of Ub to the target protein, especially transcription factors, to regulate the proliferation, differentiation and survival of bone cells, as well as bone formation. In turn, the deubiquitinating enzyme removes Ub from modified substrate proteins to orchestrate bone remodeling. As a result of abnormal regulation of ubiquitination, bone cell differentiation exhibits disorder and then bone homeostasis is affected, consequently leading to osteoporosis. The present review discussed the role and mechanism of UPS in bone remodeling. However, the specific mechanism of UPS in the process of bone remodeling is still not fully understood and further research is required. The study of the mechanism of action of UPS can provide new ideas and methods for the prevention and treatment of osteoporosis. In addition, the most commonly used osteoporosis drugs that target ubiquitination processes in the clinic are discussed in the current review.

A p38 MAP kinase inhibitor suppresses osteoclastogenesis and alleviates ovariectomy-induced bone loss through the inhibition of bone turnover

Inhibition of excessive osteoclastic activity is an efficient therapeutic strategy for many bone diseases induced by increased bone resorption, such as osteoporosis. BMS-582949, a clinical p38α inhibitor, is a promising drug in Phase II studies for treating rheumatoid arthritis. However, its function on bone resorption is largely unknown. In this study, we find that BMS-582949 represses RANKL-induced osteoclast differentiation in a dose-dependent manner. Moreover, BMS-582949 inhibits osteoclastic F-actin ring formation and osteoclast-specific gene expression. Mechanically, BMS-582949 treatment attenuates RANKL-mediated osteoclastogenesis through mitogen-activated protein kinases (MAPKs) and protein kinase B (AKT) signaling pathways without disturbing nuclear factor-κB (NF-κB) signaling. Interestingly, BMS-582949 impairs osteoclastic mitochondrial biogenesis and functions, such as oxidative phosphorylation (OXPHOS). Furthermore, BMS-582949 administration prevents bone loss in ovariectomized mouse mode by inhibiting both bone resorption and bone formation in vivo. Taken together, these findings indicate that BMS-582949 may be a potential and effective drug for the therapy of osteolytic diseases.

Osteoporotic osseointegration: therapeutic hallmarks and engineering strategies

Osteoporosis is a systemic skeletal disease caused by an imbalance between bone resorption and formation. Current treatments primarily involve systemic medication and hormone therapy. However, these systemic treatments lack directionality and are often ineffective for locally severe osteoporosis, with the potential for complex adverse reactions. Consequently, treatment strategies using bioactive materials or external interventions have emerged as the most promising approaches. This review proposes twelve microenvironmental treatment targets for osteoporosis-related pathological changes, including local accumulation of inflammatory factors and reactive oxygen species (ROS), imbalance of mitochondrial dynamics, insulin resistance, disruption of bone cell autophagy, imbalance of bone cell apoptosis, changes in neural secretions, aging of bone cells, increased local bone tissue vascular destruction, and decreased regeneration. Additionally, this review examines the current research status of effective or potential biophysical and biochemical stimuli based on these microenvironmental treatment targets and summarizes the advantages and optimal parameters of different bioengineering stimuli to support preclinical and clinical research on osteoporosis treatment and bone regeneration. Finally, the review addresses ongoing challenges and future research prospects.

Enhancing postmenopausal osteoporosis: a study of KLF2 transcription factor secretion and PI3K-Akt signaling pathway activation by PIK3CA in bone marrow mesenchymal stem cells

Introduction

Mesenchymal stem cells can develop into osteoblasts, making them a promising cell-based osteoporosis treatment. Despite their therapeutic potential, their molecular processes are little known. Bioinformatics and experimental analysis were used to determine the molecular processes of bone marrow mesenchymal stem cell (BMSC) therapy for postmenopausal osteoporosis (PMO).

Material and methods

We used weighted gene co-expression network analysis (WGCNA) to isolate core gene sets from two GEO microarray datasets (GSE7158 and GSE56815). GeneCards found PMO-related genes. GO, KEGG, Lasso regression, and ROC curve analysis refined our candidate genes. Using the GSE105145 dataset, we evaluated KLF2 expression in BMSCs and examined the link between KLF2 and PIK3CA using Pearson correlation analysis. We created a protein-protein interaction network of essential genes involved in osteoblast differentiation and validated the functional roles of KLF2 and PIK3CA in BMSC osteoblast differentiation in vitro.

Results

We created 6 co-expression modules from 10 419 differentially expressed genes (DEGs). PIK3CA, the key gene in the PI3K-Akt pathway, was among 197 PMO-associated DEGs. KLF2 also induced PIK3CA transcription in PMO. BMSCs also expressed elevated KLF2. BMSC osteoblast differentiation involved the PI3K-Akt pathway. In vitro, KLF2 increased PIK3CA transcription and activated the PI3K-Akt pathway to differentiate BMSCs into osteoblasts.

Conclusions

BMSCs release KLF2, which stimulates the PIK3CA-dependent PI3K-Akt pathway to treat PMO. Our findings illuminates the involvement of KLF2 and the PI3K-Akt pathway in BMSC osteoblast development, which may lead to better PMO treatments.

Liuwei Dihuang Pills Enhance Osteogenic Differentiation in MC3T3-E1 Cells through the Activation of the Wnt/β-Catenin Signaling Pathway

OBJECTIVE

The therapeutic efficacy and molecular mechanisms of traditional Chinese medicines (TCMs), such as Liuwei Dihuang pills (LWDH pills), in treating osteoporosis (OP) remain an area of active research and interest in modern medicine. This study investigated the mechanistic underpinnings of LWDH pills in the treatment of OP based on network pharmacology, bioinformatics, and in vitro experiments.

METHODS

The active ingredients and targets of LWDH pills were retrieved through the TCMSP database. OP-related targets were identified using the CTD, GeneCards, and DisGeNET databases. The STRING platform was employed to construct a protein-protein interaction (PPI) network, and core targets for LWDH pills in treating OP were identified. The GO functional and KEGG pathway enrichment analyses for potential targets were performed using the R package "clusterProfiler". A "drug-target" network diagram was created using Cytoscape 3.7.1 software. The viability of MC3T3-E1 cells was evaluated using the CCK-8 method after treatment with various concentrations (1.25%, 2.5%, 5%, and 10%) of LWDH pill-medicated serum for 24, 48, and 72 h. Following a 48 h treatment of MC3T3-E1 cells with LWDH pill-medicated serum, the protein levels of collagen Ⅰ, RUNX2, Wnt3, and β-catenin were quantified using the Western blot analysis, and the activity of alkaline phosphatase (ALP) was measured.

RESULTS

A total of 197 putative targets for LWDH pills for OP treatment were pinpointed, from which 20 core targets were singled out, including TP53, JUN, TNF, CTNNB1 (β-catenin), and GSK3B. The putative targets were predominantly involved in signaling pathways such as the Wnt signaling pathway, the MAPK signaling pathway, and the PI3K-Akt signaling pathway. The intervention with LWDH pill-medicated serum for 24, 48, and 72 h did not result in any notable alterations in the cell viability of MC3T3-E1 cells relative to the control group (all p > 0.05). Significant upregulation in protein levels of collagen Ⅰ, RUNX2, Wnt3, and β-catenin in MC3T3-E1 cells was observed in response to the treatment with 2.5%, 5%, and 10% of LWDH pill-medicated serum in comparison to that with the 10% rabbit serum group (all p < 0.05). Furthermore, the intervention with LWDH pill-medicated serum resulted in the formation of red calcified nodules in MC3T3-E1 cells, as indicated by ARS staining.

CONCLUSIONS

LWDH pills may upregulate the Wnt/β-catenin signaling pathway to elevate the expression of osteogenic differentiation proteins, including collagen Ⅰ and RUNX2, and to increase the ALP activity in MC3T3-E1 cells for the treatment of OP.

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.

Mechanism of miRNA-31 Regulating Wnt/β-catenin Signaling Pathway by Targeting Satb2 in the Osteogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells

OBJECTIVE

To explore the expression of miR-31 and Satb2 gene in the serum of postmenopausal women with osteoporosis (OP).

METHODS

97 postmenopausal women with OP and 100 healthy women were selected as research subjects. MSCs were purchased from Shanghai Zhong Qiao Xin Zhou Biotechnology Co., Ltd. Bone marrow-derived mesenchymal stem cells (BMSCs) were isolated, identified and transfected, and then quantified by alkaline phosphatase (ALP) levels. The expression levels of miR-31 and Satb2 gene mRNA were determined by qRT-PCR. The proteins of RUNX2, OCN and BMP and Wnt/β-catenin pathway-related proteins (GSK-3, Frizzled 1, Lrp5, Lrp6 and β-catenin) were tested by Western blotting.

RESULTS

In the OP group, the relative expression of miR-31 was 3.61±0.54, significantly higher than that (1.75±0.27) in the healthy control group (t=9.422, P<0.001). The relative expression of mRNA of Satb2 gene was 0.86±0.12, significantly lower than that (1.35±0.21) in the healthy control group (t=5.897, P<0.001).

CONCLUSIONS

The increase in miR-31 expression can down-regulate the Wnt/β-catenin pathway by targeting the expression of Satb2 gene, thereby inhibiting the osteogenic differentiation of BMSCs. This provides an important reference for further understanding the mechanism of OP and identifying targets for early diagnosis and treatment.

GATA4-activated lncRNA MALAT1 promotes osteogenic differentiation through inhibiting NEDD4-mediated RUNX1 degradation

Postmenopausal osteoporosis (PMOP) brings a lot of inconvenience to patients and serious economic burden to society. The osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) plays vital role in the process of PMOP treatment. However, the functional mechanism remains unclear. In this study, GATA4, MALAT1 and KHSRP were downregulated in bone tissues of PMOP patients, while NEDD4 was overexpressed. Through functional experiments, GATA4 overexpression strikingly accelerated osteogenic differentiation of BMSCs and promoted bone formation in vitro and in vivo, while these effects were dramatically reversed after MALAT1 silence. Intermolecular interaction experiments confirmed that GATA4 activated the transcription of MALAT1, which could form a 'RNA-protein' complex with KHSRP to decay NEDD4 mRNA. NEDD4 promoted the degradation of Runx1 by ubiquitination. Moreover, NEDD4 silencing blocked the inhibitory effects of MALAT1 knockdown on BMSCs osteogenic differentiation. In sum up, GATA4-activated MALAT1 promoted BMSCs osteogenic differentiation via regulating KHSPR/NEDD4 axis-regulated RUNX1 degradation, ultimately improving PMOP.

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.

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.

Engineering Multifunctional Hydrogel-Integrated 3D Printed Bioactive Prosthetic Interfaces for Osteoporotic Osseointegration

3D printed porous titanium alloy implants is an advanced orthopedic material for joint replacement. However, the high risk of aseptic loosening and periprosthetic infection is difficult to avoid, and the declined autophagy of osteoporosis-derived bone marrow mesenchymal stem cells (OP-BMSCs) further severely impairs the osseointegration under the osteoporotic circumstance. It is thus becoming urgently significant to develop orthopedic materials with autophagy regulation and antibacterial bioactivity. In this regard, a novel class of multifunctional hydrogel-integrated 3D printed bioactive prosthetic interfaces is engineered for in situ osseointegration in osteoporosis. The hydrogel is fabricated from the dynamic crosslinking of synthetic polymers, natural polymers, and silver nanowires to deliver autophagy-regulated rapamycin. Therefore, the resultant soft material exhibits antibacterial ability, biocompatibility, degradability, conductive, self-healing, and stimuli-responsive abilities. In vitro experiments demonstrate that the hydrogel-integrated 3D printed bioactive prosthetic interfaces can restore the declined cellular activities of OP-BMSCs by upregulating the autophagy level and show excellent antibacterial activity against S. aureus and MRSA. More remarkably, the multifunctional 3D printed bioactive prosthetic interfaces significantly improve osseointegration and inhibit infection in osteoporotic environment in vivo. This study provides an efficient strategy to develop novel prosthetic interfaces to reduce complications after arthroplasty for patients with osteoporosis.

Increased Expression of Prolyl Endopeptidase Induced by Oxidative Stress in Nucleus Pulposus Cells Aggravates Intervertebral Disc Degeneration

A healthy microenvironment of the intervertebral disc tissue is characterized by hypoxia owing to its sparse vascular distribution. Oxidative stress plays a pivotal role in the pathological development of intervertebral disc degeneration (IVDD). We found that the expression of prolyl endopeptidase (PREP) increased in degenerative nucleus pulposus (NP) tissues. The purpose of this study was to determine whether PREP is involved in oxidative-stress-induced IVDD. Tertbutyl hydroperoxide can inhibit the expression of PREP by activating the PI3K/AKT signaling pathway at low concentrations in NP cells. Knockdown of PREP protected NP cells from apoptosis induced by oxidative stress, whereas overexpression of PREP exacerbated the apoptosis of NP cells. We also investigated the connection between the PI3K/AKT signaling pathway and PREP and found that the activation of the PI3K/AKT signaling pathway downregulated the expression of PREP by inhibiting p53. As a crucial transcription factor, p53 binds to the PREP promoter region and promotes its transcription. Overexpression of PREP also impairs protein secretion in the extracellular matrix of NP cells. Furthermore, the in vivo knockout of PREP could attenuate puncture-induced IVDD. These findings suggested that the downregulation of PREP might maintain the viability of NP cells and attenuate IVDD under oxidative stress.

Urolithin A suppresses RANKL-induced osteoclastogenesis and postmenopausal osteoporosis by, suppresses inflammation and downstream NF-κB activated pyroptosis pathways

Osteoporosis (OP) is characterized by decreased trabecular bone volume and microarchitectural deterioration in the medullary cavity. Urolithin A (UA) is a biologically active metabolite generated by the gut microbiota. UA is the measurable product considered the most relevant urolithin as the final metabolic product of polyphenolic compounds. Considering that catabolic effects mediated by the intestinal microbiota are highly involved in pathological bone disorders, exploring the biological influence and molecular mechanisms by which UA alleviates OP is crucial. Our study aimed to investigate the effect of UA administration on OP progression in the context of estrogen deficiency-induced bone loss. The in vivo results indicated that UA effectively reduced ovariectomy-induced systemic bone loss. In vitro, UA suppressed Receptor Activator for Nuclear Factor-κB Ligand (RANKL)-triggered osteoclastogenesis in a concentration-dependent manner. Signal transduction studies and sequencing analysis showed that UA significantly decreased the expression of inflammatory cytokines (e.g., IL-6 and TNF-α) in osteoclasts. Additionally, attenuation of inflammatory signaling cascades inhibited the NF-κB-activated NOD-like receptor signaling pathway, which eventually led to decreased cytoplasmic secretion of IL-1β and IL-18 and reduced expression of pyroptosis markers (NLRP3, GSDMD, and caspase-1). Consistent with this finding, an NLRP3 inflammasome inhibitor (MCC950) was employed to treat OP, and modulation of pyroptosis was found to ameliorate osteoclastogenesis and bone loss in ovariectomized (OVX) mice, suggesting that UA suppressed osteoclast formation by regulating the inflammatory signal-dependent pyroptosis pathway. Conceivably, UA administration may be a safe and promising therapeutic strategy for osteoclast-related bone diseases such as OP.