Vitamin K2 stimulates MC3T3‑E1 osteoblast differentiation and mineralization through autophagy induction

Knockdown of SMYD3 by RNA Interference Regulates the Expression of Autophagy-Related Proteins and Inhibits Bone Formation in Fluoride-Exposed Osteoblasts

This study aimed to explore the role of histone methyltransferase SET and MYND domain containing 3 (SMYD3) in bone metabolism of osteoblasts exposed to fluoride. The levels of urine fluoride, BALP, and OC and the mRNA expression of SMYD3 were determined in patients with skeletal fluorosis and non-fluoride-exposed people on informed consent. The expression of SMYD3 protein, OC contents, and BALP activities were detected in human osteoblast-like MG63 cells and rat primary osteoblasts treated with sodium fluoride (NaF) for 48 h. The autophagosomes were observed by transmission electron microscopy. Then, we knocked down SMYD3 to confirm whether it was involved in the regulation of bone formation and related to autophagy and Wnt/β-catenin pathway. We observed that OC and BALP levels in patients with skeletal fluorosis significantly increased, while the mRNA expression of SMYD3 significantly decreased in the skeletal fluorosis groups. In vitro, the OC contents, BALP activities, and expression of SMYD3 significantly increased, and many autophagosomes were observed in NaF treated osteoblasts. The downregulation of SMYD3 significantly inhibited OC contents, BALP activities, and expression of autophagy-related proteins, but with no significant changes in the Wnt/β-catenin pathway. Our results demonstrated that fluoride exposure with coal-burning pollution caused orthopedic injuries and abnormalities in the levels of OC and BALP and hindered normal bone metabolism. Silencing the SMYD3 gene could significantly reduce OC and BALP levels via inhibiting the increase in autophagy induced by fluoride.

The role of autophagy/lipophagy in the response of osteoblastic cells to hyperlipidemia (Review)

There has been interest in the connection between cardiovascular diseases and osteoporosis, both of which share hyperlipidemia as a common pathological basis. Osteoporosis is a progressive metabolic bone disease characterized by reduced bone mass, deteriorated bone microstructure, increased bone fragility and heightened risk of bone fractures. Dysfunction of osteoblastic cells, vital for bone formation, is induced by excessive internalization of lipids under hyperlipidemic conditions, forming the crux of hyperlipidemia-associated osteoporosis. Autophagy, a process fundamental to cell self-regulation, serves a critical role in osteoblastic cell function and bone formation. When activated by lipids, lipophagy inhibits osteoblastic cell differentiation in response to elevated lipid concentrations, resulting in reduced bone mass and osteoporosis. However, an in-depth understanding of the precise roles and mechanisms of lipophagy in the regulation of osteoblastic cell function is required. Study of the molecular mechanisms governing osteoblastic cell response to excessive lipids can result in a clearer understanding of osteoporosis; therefore, potential strategies for preventing hyperlipidemia-induced osteoporosis can be developed. The present review discusses recent progress in elucidating the molecular mechanisms of lipophagy in the regulation of osteoblastic cell function, offering insights into hyperlipidemia-induced osteoporosis.

Zinc Oxide Nanoparticles Trigger Autophagy in the Human Multiple Myeloma Cell Line RPMI8226: an In Vitro Study

Multiple myeloma (MM) is a malignant clonal proliferative plasma cell tumor. Zinc oxide nanoparticles (ZnO NPs) are used for antibacterial and antitumor applications in the biomedical field. This study investigated the autophagy-induced effects of ZnO NPs on the MM cell line RPMI8226 and the underlying mechanism. After RPMI8226 cells were exposed to various concentrations of ZnO NPs, the cell survival rate, morphological changes, lactate dehydrogenase (LDH) levels, cell cycle arrest, and autophagic vacuoles were monitored. Moreover, we investigated the expression of Beclin 1 (Becn1), autophagy-related gene 5 (Atg5), and Atg12 at the mRNA and protein levels, as well as the level of light chain 3 (LC3). The results showed that ZnO NPs could effectively inhibit the proliferation and promote the death of RPMI8226 cells in vitro in a dose- and time-dependent manner. ZnO NPs increased LDH levels, enhanced monodansylcadaverine (MDC) fluorescence intensity, and induced cell cycle arrest at the G2/M phases in RPMI8226 cells. Moreover, ZnO NPs significantly increased the expression of Becn1, Atg5, and Atg12 at the mRNA and protein levels and stimulated the production of LC3. We further validated the results using the autophagy inhibitor 3-methyladenine (3‑MA). Overall, we observed that ZnO NPs can trigger autophagy signaling in RPMI8226 cells, which may be a potential therapeutic approach for MM.

In Vitro and In Vivo Bone-Forming Effect of a Low-Molecular-Weight Collagen Peptide

This study reveals that low-molecular-weight collagen peptide (LMWCP) can stimulate the differentiation and the mineralization of MC3T3-E1 cells in vitro and attenuate the bone remodeling process in ovariectomized (OVX) Sprague-Dawley rats in vivo. Moreover, the assessed LMWCP increased the activity of alkaline phosphatase (ALP), synthesis of collagen, and mineralization in MC3T3-E1 cells. Additionally, mRNA levels of bone metabolism-related factors such as the collagen type I alpha 1 chain, osteocalcin (OCN), osterix, bone sialoprotein, and the Runt family-associated transcription factor 2 were increased in cells treated with 1,000 μg/ml of LMWCP. Furthermore, we demonstrated that critical bone morphometric parameters exhibited significant differences between the LMWCP (400 mg/kg)-receiving and vehicle-treated rat groups. Moreover, the expression of type I collagen and the activity of ALP were found to be higher in both the femur and lumbar vertebrae of OVX rats treated with LMWCP. Finally, the administration of LMWCP managed to alleviate osteogenic parameters such as the ALP activity and the levels of the bone alkaline phosphatase, the OCN, and the procollagen type 1 N-terminal propeptide in OVX rats. Thus, our findings suggest that LMWCP is a promising candidate for the development of food-based prevention strategies against osteoporosis.

Study of Active Phytochemicals and Mechanisms of Cnidii Fructus in Treating Osteoporosis Based on HPLC-Q-TOF-MS/MS and Network Pharmacology

INTRODUCTION

This study aimed to clarify the anti-osteoporosis mechanism of Cnidii Fructus (CF) via network pharmacology and experimental verification.

METHODS

HPLC fingerprints combined with HPLC-Q-TOF-MS/MS analysis confirmed common components (CCS) of CF. Then, network pharmacology was used to investigate the anti-OP mechanism of CF, including potential anti-OP phytochemicals, potential targets, and related signalling pathway. Molecular docking analysis was carried on investigating the protein-ligand interactions. Finally, in vitro experiments were performed to verify anti-OP mechanism of CF.

RESULTS

In this study, 17 compounds from CF were identified by HPLC-Q-TOF-MS/MS and HPLC fingerprints and then were further screened key compounds and potential targets by PPI analysis, ingredient-target network and hub network. The key compounds were SCZ10 (Diosmin), SCZ16 (Pabulenol), SCZ6 (Osthenol), SCZ8 (Bergaptol) and SCZ4 (Xanthotoxol). The potential targets were SRC, MAPK1, PIK3CA, AKT1 and HSP90AA1. Molecular docking further analysis indicated that the five key compounds have a good binding affinity with related proteins. CCK8 assays, TRAP staining experiments, and ALP activity assays concluded that osthenol and bergaptol inhibited osteoclast formation and promoted osteoblast bone formation to improve osteoporosis.

CONCLUSION

Based on network pharmacology and in vitro experiments analysis, this study revealed that CF possessed an anti-OP effect, and its potential therapeutic effect may be involved with osthenol and bergaptol from CF.

Role of vitamins beyond vitamin D3 in bone health and osteoporosis (Review)

The objective of the present review was to summarize the molecular mechanisms associated with the effects of the vitamins A, C, E and K, and group B vitamins on bone and their potential roles in the development of osteoporosis. Epidemiological findings have demonstrated an association between vitamin deficiency and a higher risk of developing osteoporosis; vitamins are positively related to bone health upon their intake at the physiological range. Excessive vitamin intake can also adversely affect bone formation, as clearly demonstrated for vitamin A. Vitamins E (tocopherols and tocotrienols), K2 (menaquinones 4 and 7) and C have also been shown to promote osteoblast development through bone morphogenetic protein (BMP)/Smad and Wnt/β‑catenin signaling, as well as the TGFβ/Smad pathway (α‑tocopherol). Vitamin A metabolite (all‑trans retinoic acid) exerts both inhibitory and stimulatory effects on BMP‑ and Wnt/β‑catenin‑mediated osteogenesis at the nanomolar and micromolar range, respectively. Certain vitamins significantly reduce receptor activator of nuclear factor kappa‑B ligand (RANKL) production and RANKL/RANK signaling, while increasing the level of osteoprotegerin (OPG), thus reducing the RANKL/OPG ratio and exerting anti‑osteoclastogenic effects. Ascorbic acid can both promote and inhibit RANKL signaling, being essential for osteoclastogenesis. Vitamin K2 has also been shown to prevent vascular calcification by activating matrix Gla protein through its carboxylation. Therefore, the maintenance of a physiological intake of vitamins should be considered as a nutritional strategy for the prevention of osteoporosis.

Regulatory mechanisms of autophagy-related ncRNAs in bone metabolic diseases

Bone metabolic diseases have been tormented and are plaguing people worldwide due to the lack of effective and thorough medical interventions and the poor understanding of their pathogenesis. Non-coding RNAs (ncRNAs) are heterogeneous transcripts that cannot encode the proteins but can affect the expressions of other genes. Autophagy is a fundamental mechanism for keeping cell viability, recycling cellular contents through the lysosomal pathway, and maintaining the homeostasis of the intracellular environment. There is growing evidence that ncRNAs, autophagy, and crosstalk between ncRNAs and autophagy play complex roles in progression of metabolic bone disease. This review investigated the complex mechanisms by which ncRNAs, mainly micro RNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), regulate autophagic pathway to assist in treating bone metabolism disorders. It aimed at identifying the autophagy role in bone metabolism disorders and understanding the role, potential, and challenges of crosstalk between ncRNAs and autophagy for bone metabolism disorders treatment.

3D printed PLGA/MgO/PDA composite scaffold by low-temperature deposition manufacturing for bone tissue engineering applications

Introduction

Bones are easily damaged. Biomimetic scaffolds are involved in tissue engineering. This study explored polydopamine (PDA)-coated poly lactic-co-glycolic acid (PLGA)-magnesium oxide (MgO) scaffold properties and its effects on bone marrow mesenchymal stem cells (BMSCs) osteogenic differentiation.

Methods

PLGA/MgO scaffolds were prepared by low-temperature 3D printing technology and PDA coatings were prepared by immersion method. Scaffold structure was observed by scanning electron microscopy with an energy dispersive spectrometer (SEM-EDS), fourier transform infrared spectrometer (FTIR). Scaffold hydrophilicity, compressive/elastic modulus, and degradation rates were analyzed by water contact angle measurement, mechanical tests, and simulated-body fluid immersion. Rat BMSCs were cultured in scaffold extract. Cell activity on days 1, 3, and 7 was detected by MTT. Cells were induced by osteogenic differentiation, followed by evaluation of alkaline phosphatase (ALP) activity on days 3, 7, and 14 of induction and Osteocalcin, Osteocalcin, and Collagen I expressions.

Results

The prepared PLGA/MgO scaffolds had dense microparticles. With the increase of MgO contents, the hydrophilicity was enhanced, scaffold degradation rate was accelerated, magnesium ion release rate and scaffold extract pH value were increased, and cytotoxicity was less when magnesium mass ratio was less than 10%. Compared with other scaffolds, compressive and elastic modulus of PLGA/MgO (10%) scaffolds were increased; BMSCs incubated with PLGA/MgO (10%) scaffold extract had higher ALP activity and Osteocalcin, Osteopontin, and Collagen I expressions. PDA coating was prepared in PLGA/MgO (10%) scaffolds and the mechanical properties were not affected. PLGA/MgO (10%)/PDA scaffolds had better hydrophilicity and biocompatibility and promoted BMSC osteogenic differentiation.

Conclusion

Low-temperature 3D printing PLGA/MgO (10%)/PDA scaffolds had good hydrophilicity and biocompatibility, and were conducive to BMSC osteogenic differentiation.

ELP2-NLRP3-GSDMD/GSDME-mediated pyroptosis is induced by TNF-α in MC3T3-E1 cells during osteogenic differentiation

Tumour necrosis factor-α (TNF-α) is a cytokine involved in systemic inflammation. TNF-α slows down osteogenic differentiation, which may contribute to poor bone development in the inflammatory microenvironment. TNF-α inhibits osteogenic differentiation by activating the JAK-STAT3 pathway, of which Signal transducer and activator of transcription 3 (STAT3)-interacting protein 1 (StIP1, also known as elongator complex protein 2, ELP2) is a key protein in the JAK-STAT3 pathway. We investigated whether and how ELP2 activation mediates the TNF-α-induced pyroptosis during osteoblastic differentiation. Using in vitro cell cultures of preosteoblastic MC3T3-E1 cells, we found that TNF-α exposure causes cell pyroptosis in an inflammatory microenvironment during osteoblastic differentiation. Bioinformatics, protein docking model and co-immunoprecipitation analysis revealed an association between ELP2, STAT3 and NLRP3. Forced ELP2 expression promoted MC3T3-E1 cells pyroptosis, with an increase in the expression of STAT3, NLRP3 inflammasome, GSDMD/GSDME, osteoblast marker genes, and the activity of alkaline phosphatase. In contrast, ELP2 silencing ameliorated MC3T3-E1 cells pyroptosis, and osteogenic differentiation, especially after TNF-α stimulation. The TNF-α-induced cells pyroptosis during osteoblastic differentiation was therefore mediated by ELP2. These results suggest that ELP2 is upregulated at the pyroptosis of MC3T3-E1 cells and inhibits osteogenic differentiation in response to TNF-α through NLRP3-GSDMD/GSDME activation.

The Potential of Vitamin K as a Regulatory Factor of Bone Metabolism-A Review

Vitamin K (VK), a fat-soluble vitamin, is essential for the clotting of blood because of its role in the production of clotting factors in the liver. Moreover, researchers continue to explore the role of VK as an emerging novel bioactive molecule with the potential function of improving bone health. This review focuses on the effects of VK on bone health and related mechanisms, covering VK research history, homologous analogs, dietary sources, bioavailability, recommended intake, and deficiency. The information summarized here could contribute to the basic and clinical research on VK as a natural dietary additive and drug candidate for bone health. Future research is needed to extend the dietary VK database and explore the pharmacological safety of VK and factors affecting VK bioavailability to provide more support for the bone health benefits of VK through more clinical trials.

Histone methyltransferase SETDB1 promotes osteogenic differentiation in osteoporosis by activating OTX2-mediated BMP-Smad and Wnt/β-catenin pathways

Osteogenic differentiation plays important roles in the pathogenesis of osteoporosis. In this study, we explored the regulatory mechanism of histone methyltransferase SET domain bifurcated 1 (SETDB1) underlying the osteogenic differentiation in osteoporosis. The common osteoporosis-related genes were retrieved from the GeneCards, CTD, and Phenolyzer databases. The enrichment analysis was conducted on the candidate osteoporosis-related genes using the PANTHER software, and the binding site between transcription factors and target genes predicted by hTFtarget. The bioinformatics analyses suggested 6 osteoporosis-related chromatin/chromatin binding protein or regulatory proteins (HDAC4, SIRT1, SETDB1, MECP2, CHD7, and DKC1). Normal and osteoporosis tissues were collected from osteoporosis patients to examine the expression of SETDB1. It was found that SETDB1 was poorly expressed in osteoporotic femoral tissues, indicating that SETDB1 might be involved in the development of osteoporosis. We induced SETDB1 overexpression/knockdown, orthodenticle homeobox 2 (OTX2) overexpression, activation of Wnt/β-catenin or BMP-Smad pathways alone or in combination in osteoblasts or ovariectomized mice. The data indicated that SETDB1 methylation regulated H3K9me3 in the OTX2 promoter region and inhibited the expression of OTX2. Besides, the BMP-Smad and Wnt/β-catenin pathways were inhibited by OTX2, thereby resulting in inhibited osteogenic differentiation. Animal experiments showed that overexpressed SETDB1 could promote the increase of calcium level and differentiation of femoral tissues. In conclusion, upregulation of SETDB1 promotes osteogenic differentiation by inhibiting OTX2 and activating the BMP-Smad and Wnt/β-catenin pathways in osteoporosis.

A Novel Anti-Osteoporosis Mechanism of VK2: Interfering with Ferroptosis via AMPK/SIRT1 Pathway in Type 2 Diabetic Osteoporosis

Type 2 diabetic osteoporosis (T2DOP) is a chronic bone metabolic disease. Compared with traditional menopausal osteoporosis, the long-term high glucose (HG) microenvironment increases patients' risk of fracture and osteonecrosis. We were accumulating evidence that implicated ferroptosis as a pivotal mechanism of glucolipotoxicity-mediated death of osteocytes and osteoblast, a novel form of programmed cell death resulting from uncontrolled lipid peroxidation depending on iron. Vitamin K2 (VK2), a fat-soluble vitamin, is clinically applied to prevent osteoporosis and improve coagulation. This study aimed to clarify the role and mechanism of VK2 in HG-mediated ferroptosis. We established the mouse T2DOP model by intraperitoneal injection of streptozotocin solution and a high-fat and high-sugar diet. We also cultured bone marrow mesenchymal stem cells (BMSCs) in HG to simulate the diabetic environment in vitro. Based on our data, VK2 inhibited HG-mediated bone loss and ferroptosis, the latter manifested by decreased levels of mitochondrial reactive oxygen species, lipid peroxidation, and malondialdehyde and increased glutathione in vitro. In addition, VK2 treatment was capable of restoring bone mass and strengthening the expression of SIRT1, GPX4, and osteogenic markers in the distal femurs. As for further mechanism exploration, we found that VK2 could activate AMPK/SIRT1 signaling, and knockdown of SIRT1 by siRNA prevented the VK2-mediated positive effect in HG-cultured BMSCs. Summarily, VK2 could ameliorate T2DOP through the activation of the AMPK/SIRT1 signaling pathway to inhibit ferroptosis.

Role of Vitamin K in Bone and Muscle Metabolism

Vitamin K, a cofactor for the γ-glutamyl carboxylase enzyme, is required for the post-translational activation of osteocalcin and matrix Gla protein, which play a key role in bone and muscle homeostasis. In vivo and in vitro models for osteoporosis and sarcopenia suggest the vitamin K could exert a positive effect in both conditions. In bone, it increases osteoblastogenesis, whilst decreases osteoclast formation and function. In muscle, it is associated with increased satellite cell proliferation and migration and might play a role in energy metabolism. Observational trials suggest that high levels of vitamin K are associated with increased bone mineral density and reduced fracture risk. However, interventional studies for vitamin K supplementation yielded conflicting results. Clinical trials in sarcopenia suggest that vitamin K supplementation could improve muscle mass and function. One of the main limitations on the vitamin K studies are the technical challenges to measure its levels in serum. Thus, they are obtained from indirect sources like food questionnaires, or levels of undercarboxylated proteins, which can be affected by other environmental or biological processes. Although current research appoints to a beneficial effect of vitamin K in bone and muscle, further studies overcoming the current limitations are required in order to incorporate this supplementation in the clinical management of patients with osteosarcopenia.

Inhibition of Autophagy Maintains ESC Pluripotency and Inhibits Primordial Germ Cell Formation in Chickens

Autophagy plays an important role in the pluripotency and differentiation of stem cells. Transcriptome data showed that the autophagy genes MAP1LC3A and MAP1LC3B were significantly upregulated in primordial germ cells (PGCs). The Kyoto Encyclopedia of Genes and Genome (KEGG) results showed that the lysosome signaling pathway, which is related to autophagy, was significantly enriched in PGCs. Quantitative RT-PCR, western blotting, and transmission electron microscopy (TEM) results showed that autophagy was expressed in both embryonic stem cells (ESCs) and PGCs but was significantly activated in PGCs. To explore the role of autophagy in the differentiation of chicken ESCs into PGCs, autophagy was activated and inhibited using rapamycin and bafilomycin A1, respectively. Results of qRT-PCR, flow cytometry, and indirect immunofluorescence showed that the efficiency of PGC formation significantly decreased after autophagy inhibition. Our results showed, for the first time, that autophagy plays an indispensable role in the formation of chicken PGCs, which lays the foundation for studying the mechanism of autophagy in chicken PGCs and in bird gene editing and the rescue of endangered birds.

Odontogenesis-Associated Phosphoprotein (ODAPH) Overexpression in Ameloblasts Disrupts Enamel Formation via Inducing Abnormal Mineralization of Enamel in Secretory Stage

Odontogenesis-associated phosphoprotein (ODAPH) is a recently discovered enamel matrix protein. Our previous study demonstrated that knockouting out Odaph in mice resulted in enamel hypomineralization. To further investigate the effect of Odaph on enamel mineralization, we constructed an Odaph overexpression mouse model, controlled by an amelogenin promoter. Our histological analysis of OdaphTg mice revealed that the enamel layer was thinner than in WT mice. An uneven, thinner enamel layer was confirmed using micro-computed tomography (uCT). It was subsequently found that the Tomes' processes lost their normal morphology, resulting in the loss of the enamel prism structure. These results indicate that Odaph overexpression in ameloblasts led to enamel dysplasia. In conjunction with this, Odaph overexpression hindered Amelx secretion, and may result in endoplasmic reticulum stress. Interestingly, uCT revealed that enamel had higher mineral density at the secretory stage; due to this, we did the histological staining for the mineralization-related proteins Alkaline phosphatase (ALPL) and Runt-related transcription factor 2 (RUNX2). It was observed that these proteins were up-regulated in OdaphTg mice versus WT mice, indicating that Odaph overexpression led to abnormal enamel mineralization. To confirm this, we transfected ameloblast-like cell line (ALC) with Odaph overexpression lentivirus in vitro and identified that both Alpl and Runx2 were strikingly upregulated in OE-mus-Odaph versus OE-NC cells. We concluded that the ectopic overexpression of Odaph in ameloblasts led to abnormal enamel mineralization. In summary, Odaph profoundly influences amelogenesis by participating in enamel mineralization.

Trifloroside Induces Bioactive Effects on Differentiation, Adhesion, Migration, and Mineralization in Pre-Osteoblast MC3T3E-1 Cells

Gentianae Scabrae Radix is used in traditional medicine and is known to possess bioactive compounds, including secoiridoid glycosides, flavonoids, lignans, and triterpenes. Trifloroside (TriFs) is a secoiridoid glycoside known for its antioxidant activity; however, its other effects have not been studied. In the present study, we investigated the biological effects of TriFs isolated from the roots of Gentianae Scabrae Radix using pre-osteoblast MC3T3E-1 cells. No cellular toxicity was observed with 1 μM TriFs, whereas 5-100 μM TriFs showed a gradual increase in cell viability. Alkaline phosphatase staining and microscopic observations revealed that 1-10 μM TriFs stimulated osteogenic activity during early osteoblast differentiation. Trifloroside also increased mineral apposition during osteoblast maturation. Biochemical analyses revealed that TriFs promoted nuclear RUNX2 expression and localization by stimulating the major osteogenic BMP2-Smad1/5/8-RUNX2 pathway. Trifloroside also increased p-GSK3β, β-catenin, p-JNK, and p-p38, but not Wnt3a, p-AKT, and p-ERK. Moreover, TriFs increased the MMP13 levels and promoted cell migration and adhesion. In contrast, TriFs-induced osteoblast differentiation and maturation had negligible effects on autophagy and necrosis. Our findings suggest that TriFs induces osteogenic effects through differentiation, adhesion, migration, and mineral apposition. Therefore, TriFs is suggested as a potential drug target in osteoblast-mediated bone diseases.

Alzheimer's disease-associated inflammatory pathways might contribute to osteoporosis through the interaction between PROK2 and CSF3

This study aimed to explore the potential molecular pathways and targets of Alzheimer's disease leading to osteoporosis using bioinformatics tools. The Alzheimer's and osteoporosis microarray gene expression data were retrieved from the Gene Expression Omnibus, and differentially expressed genes in the blood microenvironment related to Alzheimer's disease and osteoporosis were identified. The intersection of the three datasets (GSE97760, GSE168813, and GSE62402) was used to obtain 21 co-expressed targets in the peripheral blood samples in patients with Alzheimer's disease and osteoporosis. Based on the degree algorithm, the top 10 potential core target genes related to these diseases were identified, which included CLEC4D, PROK2, SIGLEC7, PDGFB, PTCRA, ECH1, etc. Two differentially expressed mRNAs, Prokineticin 2 (PROK2) and three colony-stimulating factor 3 (CSF3), were screened in the GSE62402 dataset associated with osteoporosis. Protein–protein rigid docking with ZDOCK revealed that PROK2 and CSF3 could form a stable protein docking model. The interaction of PROK2 and CSF3, core genes related to osteoporosis inflammation, plays an important role in the mechanism of osteoporosis in patients with Alzheimer's. Therefore, abnormalities or alterations in the inflammatory pathways in the peripheral blood samples of Alzheimer's patients may affect the course of osteoporosis.

Effects of Triterpene Soyasapogenol B from Arachis hypogaea (Peanut) on Differentiation, Mineralization, Autophagy, and Necroptosis in Pre-Osteoblasts

Triterpenes are a diverse group of natural compounds found in plants. Soyasapogenol B (SoyB) from Arachis hypogaea (peanut) has various pharmacological properties. This study aimed to elucidate the pharmacological properties and mechanisms of SoyB in bone-forming cells. In the present study, 1–20 μM of SoyB showed no cell proliferation effects, whereas 30–100 μM of SoyB increased cell proliferation in MC3T3-E1 cells. Next, osteoblast differentiation was analyzed, and it was found that SoyB enhanced ALP staining and activity and bone mineralization. SoyB also induced RUNX2 expression in the nucleus with the increased phosphorylation of Smad1/5/8 and JNK2 during osteoblast differentiation. In addition, SoyB-mediated osteoblast differentiation was not associated with autophagy and necroptosis. Furthermore, SoyB increased the rate of cell migration and adhesion with the upregulation of MMP13 levels during osteoblast differentiation. The findings of this study provide new evidence that SoyB possesses biological effects in bone-forming cells and suggest a potentially beneficial role for peanut-based foods.

Vitamin K2 Improves Osteogenic Differentiation by Inhibiting STAT1 via the Bcl-6 and IL-6/JAK in C3H10 T1/2 Clone 8 Cells

Osteogenic activity of vitamin K2 (VK2), a small molecular nutrient, has been suggested. However, the underlying mechanisms have not been fully elucidated. Therefore, this study aimed to explore the mechanisms by which VK2 promotes osteogenic differentiation. The effects of VK2 on osteogenic differentiation indicators were determined in C3H10 T1/2 clone 8 cells. The RNA-seq analysis was used to explore the hypothesis that VK2 promotes osteogenic differentiation. Small interfering RNA (siRNA) assay and plasmid transfection assay were used to determine the potential role of VK2 in the modulation of Bcl-6/STAT axis and IL-6/JAK/STAT signaling pathway. VK2 significantly increased alkaline phosphatase (ALP) activity, ALP, osteocalcin (OCN), and RUNX2 abundance, and RUNX2 protein expression. RNA-seq analysis showed that there were 314 differentially expressed genes (DEGs) upregulated and 1348 DEGs downregulated by VK2. PPI analysis determined the top 10 hub genes upregulated or downregulated by VK2. Overexpression of Bcl-6 increased osteogenic differentiation and decreased expression of STAT1. Administration with VK2 restored the inhibition by siBcl-6 in osteogenic differentiation. Knockdown of IL-6 decreased the mRNA levels of genes associated with the JAK/STAT signaling pathway, and increased markers of osteoblast differentiation. Furthermore, treatment with VK2 improved inhibition in osteogenic differentiation and decreased enhancement of JAK/STAT signaling pathway related genes by overexpression of IL-6. Our study suggests that VK2 could improve osteogenic differentiation via the Bcl-6/STAT axis and IL-6/JAK/STAT signaling pathway.

Effects of Scoparone on differentiation, adhesion, migration, autophagy and mineralization through the osteogenic signalling pathways

Scoparone (SCOP), an active and efficient coumarin compound derived from Artemisia capillaris Thunb, has been used as a traditional Chinese herbal medicine. Herein, we investigated the effects of SCOP on the osteogenic processes using MC3T3‐E1 pre‐osteoblasts in in vitro cell systems. SCOP (C₁₁H₁₀O₄, > 99.17%) was purified and identified from A. capillaries. SCOP (0.1 to 100 μM concentrations) did not have cytotoxic effects in pre‐osteoblasts; however, it promoted alkaline phosphatase (ALP) staining and activity, and mineralized nodule formation under early and late osteogenic induction. SCOP elevated osteogenic signals through the bone morphogenetic protein 2 (BMP2)‐Smad1/5/8 pathway, leading to the increased expression of runt‐related transcription factor 2 (RUNX2) with its target protein, matrix metallopeptidase 13 (MMP13). SCOP also induced the non‐canonical BMP2‐MAPKs pathway, but not the Wnt3a‐β‐catenin pathway. Moreover, SCOP promoted autophagy, migration and adhesion under the osteogenic induction. Overall, the findings of this study demonstrated that SCOP has osteogenic effects associated with cell differentiation, adhesion, migration, autophagy and mineralization.

The role of the Smad2/3/4 signaling pathway in osteogenic differentiation regulation by ClC-3 chloride channels in MC3T3-E1 cells

Background

ClC-3 chloride channels promote osteogenic differentiation. Transforming growth factor-β1 (TGF-β1) and its receptors are closely related to ClC-3 chloride channels, and canonical TGF-β1 signaling is largely mediated by Smad proteins. The current study aimed to explore the role of the Smad2/3/4 signaling pathway in the mechanism by which ClC-3 chloride channels regulate osteogenic differentiation in osteoblasts.

Methods

First, real-time PCR and western blotting were used to detect the expression of Smad and mitogen-activated protein kinase (MAPK) proteins in response to ClC-3 chloride channels. Second, immunocytochemistry, coimmunoprecipitation (Co-IP) and immunofluorescence analyses were conducted to assess formation of the Smad2/3/4 complex and its translocation to the nucleus. Finally, markers of osteogenic differentiation were determined by real-time PCR, western blotting, ALP assays and Alizarin Red S staining.

Results

ClC-3 chloride channels knockdown led to increased expression of Smad2/3 but no significant change in p38 or Erk1/2. Furthermore, ClC-3 chloride channels knockdown resulted in increases in the formation of the Smad2/3/4 complex and its translocation to the nucleus. In contrast, the inhibition of TGF-β1 receptors decreased the expression of Smad2, Smad3, p38, and Erk1/2 and the formation of the Smad2/3/4 complex. Finally, the expression of osteogenesis-related markers were decreased upon ClC-3 and Smad2/3/4 knockdown, but the degree to which these parameters were altered was decreased upon the knockdown of ClC-3 and Smad2/3/4 together compared to independent knockdown of ClC-3 or Smad2/3/4.

Conclusions

The Smad2/3 proteins respond to changes in ClC-3 chloride channels. The Smad2/3/4 signaling pathway inhibits osteogenic differentiation regulation by ClC-3 chloride channels in MC3T3-E1 cells.

Alkaline Phosphatase: An Old Friend as Treatment Target for Cardiovascular and Mineral Bone Disorders in Chronic Kidney Disease

Alkaline phosphatase (ALP) is an evolutionary conserved enzyme and widely used biomarker in clinical practice. Tissue-nonspecific alkaline phosphatase (TNALP) is one of four human isozymes that are expressed as distinct TNALP isoforms after posttranslational modifications, mainly in bone, liver, and kidney tissues. Beyond the well-known effects on bone mineralization, the bone ALP (BALP) isoforms (B/I, B1, B1x, and B2) are also involved in the pathogenesis of ectopic calcification. This narrative review summarizes the recent clinical investigations and mechanisms that link ALP and BALP to inflammation, metabolic syndrome, vascular calcification, endothelial dysfunction, fibrosis, cardiovascular disease, and mortality. The association between ALP, vitamin K, bone metabolism, and fracture risk in patients with chronic kidney disease (CKD) is also discussed. Recent advances in different pharmacological strategies are highlighted, with the potential to modulate the expression of ALP directly and indirectly in CKD–mineral and bone disorder (CKD-MBD), e.g., epigenetic modulation, phosphate binders, calcimimetics, vitamin D, and other anti-fracture treatments. We conclude that the significant evidence for ALP as a pathogenic factor and risk marker in CKD-MBD supports the inclusion of concrete treatment targets for ALP in clinical guidelines. While a target value below 120 U/L is associated with improved survival, further experimental and clinical research should explore interventional strategies with optimal risk–benefit profiles. The future holds great promise for novel drug therapies modulating ALP.

Ferutinin induces osteoblast differentiation of DPSCs via induction of KLF2 and autophagy/mitophagy

Osteoblast differentiation is critically reduced in various bone-related pathogenesis, including arthritis and osteoporosis. For future development of effective regenerative therapeutics, herein, we reveal the involved molecular mechanisms of a phytoestrogen, ferutinin-induced initiation of osteoblast differentiation from dental pulp-derived stem cell (DPSC). We demonstrate the significantly increased expression level of a transcription factor, Kruppel-like factor 2 (KLF2) along with autophagy-related molecules in DPSCs after induction with ferutinin. The loss-of-function and the gain-of-function approaches of KLF2 confirmed that the ferutinin-induced KLF2 modulated autophagic and OB differentiation-related molecules. Further, knockdown of the autophagic molecule (ATG7 or BECN1) from DPSC resulted not only in a decreased level of KLF2 but also in the reduced levels of OB differentiation-related molecules. Moreover, mitochondrial membrane potential-related molecules were increased and induction of mitophagy was observed in DPSCs after the addition of ferutinin. The reduction of mitochondrial as well as total ROS generations; and induction of intracellular Ca²⁺ production were also observed in ferutinin-treated DPSCs. To test the mitochondrial respiration in DPSCs, we found that the cells treated with ferutinin showed a reduced extracellular acidification rate (ECAR) than that of their vehicle-treated counterparts. Furthermore, mechanistically, chromatin immunoprecipitation (ChIP) analysis revealed that the addition of ferutinin in DPSCs not only induced the level of KLF2, but also induced the transcriptionally active epigenetic marks (H3K27Ac and H3K4me3) on the promoter region of the autophagic molecule ATG7. These results provide strong evidence that ferutinin stimulates OB differentiation via induction of KLF2-mediated autophagy/mitophagy.

Folate ameliorates homocysteine-induced osteoblast dysfunction by reducing endoplasmic reticulum stress-activated PERK/ATF-4/CHOP pathway in MC3T3-E1 cells

INTRODUCTION

Homocysteine (Hcy) is considered a newly identified risk factor for osteoporosis. Nevertheless, the underlying mechanism of folate (FA), a key factor in the metabolism of Hcy, in protection against osteoblast dysfunction remains unclear. The purpose of this study was to investigate the mechanism by which FA attenuates Hcy-induced osteoblast damage.

MATERIALS AND METHODS

The Hcy-induced MC3T3-E1 cells were treated with different concentrations of FA. Cell morphology, cell density, cell proliferation ability, alkaline phosphatase (ALP) activity and mineralization capacity were observed and determined; the gene expression of B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX) and ERS-associated factors, including glucose-regulated protein 78 (GRP-78), activating transcription factor 4 (ATF-4) and growth arrest and DNA damage inducible gene 153 (CHOP/GADD153), were assessed by RT-PCR; and protein levels of GRP-78 and ATF-4 were analyzed by western blotting.

RESULTS

Hcy suppressed the proliferation, differentiation and mineralization ability of MC3T3-E1 cells in a concentration-dependent manner and activated the ERS signaling pathway. After intervention with different concentrations of FA, the cell viability and density, ALP activity, number of mineralized nodules, calcium content and Bcl-2 gene expression were all significantly increased, whereas the gene expression of GRP-78, CHOP/GADD153, ATF-4 and Bax was markedly downregulated, and protein levels of GRP-78 and ATF-4 were also markedly decreased.

CONCLUSION

The adverse effects of Hcy on osteoblast differentiation are dose dependent. FA not only protects against osteoblasts apoptosis but also has a direct osteogenic effect on Hcy-induced osteoblasts, which could be partially mediated by inhibition of the PERK-activated ERS pathway.

Potential of RNA-binding protein human antigen R as a driver of osteogenic differentiation in osteoporosis

Background

Emerging evidence has correlated the human antigen R (HuR) with the low-density lipoprotein receptor-related protein 6 (LRP6) gene, an important therapeutic target for osteoporosis. Herein, we sought to probe the regulatory role of HuR in the LRP6 gene and their interaction in the progression of osteoporosis.

Methods

HuR and downstream potential target genes were predicted by bioinformatics analysis to identify their potential functions in bone metabolism following osteoporosis. The effect of HuR on the osteoblastic differentiation and viability and apoptosis of mouse embryo osteoblast precursor cells (MC3T3-E1) was evaluated after artificial modulation of HuR expression.

Results

Bone phenotypes were observed in ovariectomized mice in response to adenovirus-mediated HuR overexpression. Poor expression of HuR was identified in the bone tissues of ovariectomized mice. Silencing of HuR inhibited the osteoblastic differentiation of MC3T3-E1 cells, as evidenced by decreased expression of Runx2 and Osterix along with reduced ALP activity. Mechanistically, HuR stabilized LRP6 mRNA and promoted its translation by binding to the 3'UTR of LRP6 mRNA, leading to activation of the downstream Wnt pathway. By this mechanism, osteoblastic differentiation of MC3T3-E1 cells was induced. In ovariectomized mice, overexpression of HuR alleviated osteoporosis-related phenotypes.

Conclusion

Overall, these data together support the promoting role of HuR in the osteoblastic differentiation, highlighting a potential novel strategy for osteoporosis treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-03073-w.

New Therapeutics Targeting Arterial Media Calcification: Friend or Foe for Bone Mineralization?

The presence of arterial media calcification, a highly complex and multifactorial disease, puts patients at high risk for developing serious cardiovascular consequences and mortality. Despite the numerous insights into the mechanisms underlying this pathological mineralization process, there is still a lack of effective treatment therapies interfering with the calcification process in the vessel wall. Current anti-calcifying therapeutics may induce detrimental side effects at the level of the bone, as arterial media calcification is regulated in a molecular and cellular similar way as physiological bone mineralization. This especially is a complication in patients with chronic kidney disease and diabetes, who are the prime targets of this pathology, as they already suffer from a disturbed mineral and bone metabolism. This review outlines recent treatment strategies tackling arterial calcification, underlining their potential to influence the bone mineralization process, including targeting vascular cell transdifferentiation, calcification inhibitors and stimulators, vascular smooth muscle cell (VSMC) death and oxidative stress: are they a friend or foe? Furthermore, this review highlights nutritional additives and a targeted, local approach as alternative strategies to combat arterial media calcification. Paving a way for the development of effective and more precise therapeutic approaches without inducing osseous side effects is crucial for this highly prevalent and mortal disease.

Ataxia-televangelist mutated (ATM)/ ATR serine/threonine kinase (ATR)-mediated RAD51 recombinase (RAD51) promotes osteogenic differentiation and inhibits osteoclastogenesis in osteoporosis

Osteoporosis is a metabolic bone disease that significantly affects the quality of life and can even lead to death. In this study, we aimed to investigate the role of RAD51 recombinase (RAD51) in osteoblast and osteoclast differentiation. We analyzed differentially expressed genes using microarray analysis. The osteogenic differentiation capability was analyzed by alkaline phosphatase (ALP) staining and alizarin red staining assays. Osteogenesis and osteoclast related genes expression was detected using quantitative real-time PCR (qPCR) and Western blotting. The phosphorylation of Ataxia-telangiectasia mutated (ATM) and ATR serine/threonine kinase (ATR) was tested using Western blotting. The effect of RAD51 on osteoporosis was also explored in vivo. The results showed that RAD51 was downregulated in osteoporosis, but upregulated in differentiated osteoblasts. Overexpression of RAD51 enhanced the differentiation of osteoblasts and suppressed the formation of osteoclasts. Furthermore, p-ATM and p-ATR levels were upregulated in osteoblasts and downregulated in osteoclasts. RAD51 expression was reduced by the ATM/ATR pathway inhibitor AZ20. AZ20 treatment inhibited osteoblastogenesis and promoted osteoclastogenesis, whereas RAD51 reversed the effects induced by AZ20. Moreover, RAD51 improved bone microarchitecture in vivo. Taken together, ATM/ATR signaling-mediated RAD51 promoted osteogenic differentiation and suppressed osteoclastogenesis. These findings reveal a critical role for RAD51 in osteoporosis.

lncRNA Kcnq1ot1 promotes bone formation by inhibiting miR‑98‑5p/Tbx5 axis in MC3T3‑E1 cells

Long non-coding (lnc)RNA KCNQ1 opposite strand/antisense transcript 1 (Kcnq1ot1) has been shown to regulate multiple biological processes. However, the functional role of Kcnq1ot1 in osteoporosis and the underlying mechanism are still unclear. The present study aimed to investigate the function of lncRNA Kcnq1ot1 in osteogenic differentiation. Alkaline phosphatase (ALP) activity was measured using an ALP assay kit. Western blotting was performed to assess the expression levels of osteogenic differentiation-associated proteins. Reverse transcription-quantitative PCR was performed to detect Kcnq1ot1, microRNA (miR)-98-5p and T-box transcription factor 5 (Tbx5) expression levels. The binding of Kcnq1ot1 with miR-98-5p and that of miR-98-5p with Tbx5 were predicted by starBase and TargetScan databases, respectively, and verified using dual luciferase reporter assays. The mineralization of MC3T3-E1 cells was observed using an Alizarin red S staining assay. The results revealed that expression of Kcnq1ot1 was increased and that of miR-98-5p was decreased during osteogenic differentiation. Additionally, Kcnq1ot1 was shown to target miR-98-5p and inhibit its expression. Inhibiting miR-98-5p reversed the inhibitory effect of Kcnq1ot1 knockdown on osteogenic differentiation and mineralization of MC3T3-E1 cells. Furthermore, Kcnq1ot1 regulated Tbx5 expression via miR-98-5p. Overexpressing miR-98-5p or downregulating Tbx5 expression reversed the promotive effect of Kcnq1ot1 overexpression on osteogenic differentiation and mineralization of MC3T3-E1 cells. In conclusion, these findings suggested that Kcnq1ot1 may promote bone formation by inhibiting miR-98-5p and upregulating Tbx5. Kcnq1ot1, miR-98-5p and Tbx5 may therefore serve as promising targets for the treatment of osteoporosis.

The effects of Omarigliptin on promoting osteoblastic differentiation

Osteoporosis significantly impacts the normal life of the elderly and is reported to be closely related to dysfunction of osteoblastic differentiation. Runt-related transcription factor-2 (Runx2) is a critical transcriptional factor involved in the regulation of osteoblast differentiation. Omarigliptin is a novel dipeptidyl peptidase-4 (DDP-4) inhibitor and this study proposes to probe into its possible therapeutic function against Osteoporosis by investigating its impacts on osteoblastic differentiation. Osteogenic medium was used to induce osteoblastic differentiation in MC3T3‑E1 cells, and was verified by the increased alkaline phosphatase (ALP) activity, enhanced mineralization, and promoted expression level of osteoblastic differentiation-related factors, including bone morphogenetic protein-2 (BMP-2), ALP, osteocalcin (Ocn), collagen type I alpha 1 (Col1a1), Collagen Type I alpha 2 (Col1a2), Runx2, osterix (Sp7), fibroblast growth factor receptor 2 (Fgfr2), and fibroblast growth factor receptor 3 (Fgfr3), accompanied by the activation of the p38 and Akt pathways. After treatment with Omarigliptin, the ALP activity and mineralization were further promoted, accompanied by the further upregulation of osteoblastic differentiation-related factors, and activation of the p38 and Akt pathways. Lastly, Omarigliptin-induced osteoblastic differentiation, promoted ALP activity, and increased expression levels of Sp7, Fgfr2, Fgfr3, BMP-2, Ocn, ALP, Col1a1, and Col1a2, in the osteogenic medium- cultured MC3T3‑E1 cells were dramatically abolished by the knockdown of Runx2. Taken together, our data reveal that Omarigliptin promoted osteoblastic differentiation by regulating Runx2.

Three-Dimensional Co-Culture System of Human Osteoblasts and Osteoclast Precursors from Osteoporotic Patients as an Innovative Model to Study the Role of Nutrients: Focus on Vitamin K2

Several natural compounds, such as vitamin K2, have been highlighted for their positive effects on bone metabolism. It has been proposed that skeletal disorders, such as osteoporosis, may benefit from vitamin K2-based therapies or its regular intake. However, further studies are needed to better clarify the effects of vitamin K2 in bone disorders. To this aim, we developed in vitro a three-dimensional (3D) cell culture system one step closer to the bone microenvironment based on co-culturing osteoblasts and osteoclasts precursors obtained from bone specimens and peripheral blood of the same osteoporotic patient, respectively. Such a 3-D co-culture system was more informative than the traditional 2-D cell cultures when responsiveness to vitamin K2 was analyzed, paving the way for data interpretation on single patients. Following this approach, the anabolic effects of vitamin K2 on the osteoblast counterpart were found to be correlated with bone turnover markers measured in osteoporotic patients’ sera. Overall, our data suggest that co-cultured osteoblasts and osteoclast precursors from the same osteoporotic patient may be suitable to generate an in vitro 3-D experimental model that potentially reflects the individual’s bone metabolism and may be useful to predict personal responsiveness to nutraceutical or drug molecules designed to positively affect bone health.

Multiple functions of autophagy in vascular calcification

Background

Vascular calcification is a closely linked to cardiovascular diseases, such as atherosclerosis, chronic kidney disease, diabetes, hypertension and aging. The extent of vascular calcification is closely correlate with adverse clinical events and cardiovascular all-cause mortality. The role of autophagy in vascular calcification is complex with many mechanistic unknowns.

Methods

In this review, we analyze the current known mechanisms of autophagy in vascular calcification and discuss the theoretical advantages of targeting autophagy as an intervention against vascular calcification.

Results

Here we summarize the functional link between vascular calcification and autophagy in both animal models of and human cardiovascular disease. Firstly, autophagy can reduce calcification by inhibiting the osteogenic differentiation of VSMCs related to ANCR, ERα, β-catenin, HIF-1a/PDK4, p62, miR-30b, BECN1, mTOR, SOX9, GHSR/ERK, and AMPK signaling. Conversely, autophagy can induce osteoblast differentiation and calcification as mediated by CREB, degradation of elastin, and lncRNA H19 and DUSP5 mediated ERK signaling. Secondly, autophagy also links apoptosis and vascular calcification through AMPK/mTOR/ULK1, Wnt/β-catenin and GAS6/AXL synthesis, as apoptotic cells become the nidus for calcium-phosphate crystal deposition. The failure of mitophagy can activate Drp1, BNIP3, and NR4A1/DNA‑PKcs/p53 mediated intrinsic apoptotic pathways, which have been closely linked to the formation of vascular calcification. Additionally, autophagy also plays a role in osteogenesis by regulating vascular calcification, which in turn regulates expression of proteins related to bone development, such as osteocalcin, osteonectin, etc. and regulated by mTOR, EphrinB2 and RhoA. Furthermore, autophagy also promotes vitamin K2-induced MC3T3 E1 osteoblast differentiation and FGFR4/FGF18- and JNK/complex VPS34–beclin-1-related bone mineralization via vascular calcification.

Conclusion

The interaction between autophagy and vascular calcification are complicated, with their interaction affected by the disease process, anatomical location, and the surrounding microenvironment. Autophagy activation in existent cellular damage is considered protective, while defective autophagy in normal cells result in apoptotic activation. Identifying and maintaining cells at the delicate line between these two states may hold the key to reducing vascular calcification, in which autophagy associated clinical strategy could be developed.

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.

Vitamin K and D Supplementation and Bone Health in Chronic Kidney Disease-Apart or Together?

Vitamin K (VK) and vitamin D (VD) deficiency/insufficiency is a common feature of chronic kidney disease (CKD), leading to impaired bone quality and a higher risk of fractures. CKD patients, with disturbances in VK and VD metabolism, do not have sufficient levels of these vitamins for maintaining normal bone formation and mineralization. So far, there has been no consensus on what serum VK and VD levels can be considered sufficient in this particular population. Moreover, there are no clear guidelines how supplementation of these vitamins should be carried out in the course of CKD. Based on the existing results of preclinical studies and clinical evidence, this review intends to discuss the effect of VK and VD on bone remodeling in CKD. Although the mechanisms of action and the effects of these vitamins on bone are distinct, we try to find evidence for synergy between them in relation to bone metabolism, to answer the question of whether combined supplementation of VK and VD will be more beneficial for bone health in the CKD population than administering each of these vitamins separately.

Protection of Icariin Against Hydrogen Peroxide-Induced MC3T3-E1 Cell Oxidative Damage

Objective

The aim of the present study was to evaluate the potential protective mechanism of icariin against oxidative damage caused by hydrogen peroxide in MC3T3‐E1 cells.

Methods

MC3T3‐E1 cells were treated with different concentrations of icariin to explore the optimal dose of icariin. MC3T3‐E1 cells were divided into groups treated with various concentrations of hydrogen peroxide (H₂O₂; 0, 0.1, 0.2, 0.5, 1, and 2 mM) for 24 h to induce oxidative damage and cell viability was assessed by Cell Counting Kit‐8 (CCK‐8) assay. Then, cells were divided into five groups: control, H₂O₂ (0.2 mM), icariin (0.1 μM) and H₂O₂ (0.2 mM), + icariin (0.1 μM). Cell viability was detected by CCK‐8 assay. In addition, the content of glutathione and superoxide dismutase and the activity level of malondialdehyde in these treatment groups were determined. Alkaline phosphatase (ALP) and alizarin red S (ARS) staining were also performed to measure the early and late osteogenesis, respectively. Protein expression of β‐catenin and cyclin D1 was measured by western blot assay. Then, we used an antagonist of Wnt/β‐catenin signaling pathway (DKK‐1) and western blot analysis to further explore potential mechanism.

Results

After 24 h of exposure to 0.2 mM H₂O₂, the viability of MC3T3‐E1 cells was significantly decreased compared to that of the control cells. We first found that icariin can promote cell proliferation of MC3T3‐E1 cells in a dose‐dependent manner, with the dosage 0.1 μM showing the best pro‐proliferative effect. Furthermore, icariin could promote the protein expression of OSX and RUNX2. The results showed that icariin can reverse the inhibitory osteogenic effects of MC3T3‐E1 caused by H₂O₂. In addition, icariin could increase the Wnt‐signaling related proteins. The results showed that MC3T3‐E1 cells in the H₂O₂ (0.2 mM) + icariin (0.1 μM) + Wnt‐signaling antagonist (DKK‐1) group had weaker ALP and ARS staining compared with that observed in the control and H₂O₂ (0.2 mM) + icariin (0.1 μM) groups. The ALP activity and calcium content were decreased in the 0.2 mM H₂O₂ + 0.1 μM icariin + DKK‐1 group compared to that observed in the 0.2 mM H₂O₂ + 0.1 μM icariin group.

Conclusion

The results showed that icariin can increase the viability of MC3T3‐E1 cells, reverse the oxidative stress induced by H₂O₂ and protect MC3T3‐E1 cells against H₂O₂‐induced inhibition of osteogenic differentiation, which may occur through the Wnt/β‐catenin signaling pathway.

Maqui berry extract prevents cigarette smoke induced oxidative stress in human osteoblasts in vitro

Oxidative stress which can be induced by cigarette smoke (CS) is associated with an altered osteoblast differentiation, and an inhibition of the mineralization process. Therefore, treatments focusing on reducing oxidative stress in osteoblasts could be a potential therapy supporting bone formation. Maqui berry extract (MBE) is the richest natural source of delphinidins with high antioxidant activity. In the present study, we pre-/ co-/ post-incubated MBE in cigarette smoke extract (CSE)-affected human osteoblasts (hOBs), to investigate the effects of MBE as an antioxidant on hOBs. Our results clearly showed that high concentrations of MBE are toxic for hOBs, while physiological concentrations of MBE have no negative effects in vitro. Physiological concentrations of MBE can reduce oxidative stress caused by CSE in hOBs by activating the antioxidative regulator Nrf2 and its regulated antioxidative enzymes. Moreover, the physiological concentration of MBE prevents the detrimental effects of CSE-induced oxidative damage on hOBs by increasing cell viability, differentiation capability and matrix mineralization. Pre-incubation with MBE showed a positive effect on the activation of the cellular antioxidant system in hOBs. Thus, we conclude that MBE at physiological concentrations can effectively protect osteoblasts from oxidative stress-induced damage by activating the cells' antioxidative defense system.

Osteogenic Properties of Novel Methylsulfonylmethane-Coated Hydroxyapatite Scaffold

Despite numerous advantages of using porous hydroxyapatite (HAp) scaffolds in bone regeneration, the material is limited in terms of osteoinduction. In this study, the porous scaffold made from nanosized HAp was coated with different concentrations of osteoinductive aqueous methylsulfonylmethane (MSM) solution (2.5, 5, 10, and 20%) and the corresponding MH scaffolds were referred to as MH2.5, MH5, MH10, and MH20, respectively. The results showed that all MH scaffolds resulted in burst release of MSM for up to 7 d. Cellular experiments were conducted using MC3T3-E1 preosteoblast cells, which showed no significant difference between the MH2.5 scaffold and the control with respect to the rate of cell proliferation (p > 0.05). There was no significant difference between each group at day 4 for alkaline phosphatase (ALP) activity, though the MH2.5 group showed higher level of activity than other groups at day 10. Calcium deposition, using alizarin red staining, showed that cell mineralization was significantly higher in the MH2.5 scaffold than that in the HAp scaffold (p < 0.0001). This study indicated that the MH2.5 scaffold has potential for both osteoinduction and osteoconduction in bone regeneration.

Vitamin K2 Can Rescue the Dexamethasone-Induced Downregulation of Osteoblast Autophagy and Mitophagy Thereby Restoring Osteoblast Function In Vitro and In Vivo

Chronic long-term glucocorticoids (GC) use is associated with glucocorticoid-induced osteoporosis (GIOP) by inhibiting the survival and impairing the functions of osteoblasts. Autophagy and mitophagy play key roles in osteoblast differentiation, mineralization and survival, and mounting evidence have implicated osteoblast autophagy and mitophagy as a novel mechanism in the pathogenesis of GIOP. Vitamin K2 (VK2) is an essential nutrient supplement that have been shown to exert protective effects against osteoporotic bone loss including GIOP. In this study, we showed that the glucocorticoid dexamethasone (Dex) deregulated osteoblast autophagy and mitophagy by downregulating the expression of autophagic and mitophagic markers LC3-II, PINK1, Parkin. This consequently led to inhibition of osteoblast differentiation and mineralization function in vitro. Interestingly, co-treatment with VK2 significantly attenuated the Dex-induced downregulation of LC3-II, PINK1, Parkin, thereby restoring autophagic and mitophagic processes and normal osteoblastic activity. In addition, using an established rat model of GIOP, we showed that VK2 administration can protect rats against the deleterious effects of Dex on bone by reinstating autophagic and mitophagic activities in bone tissues. Collectively, our results provide new insights into the role of osteoblast autophagy and mitophagy in GIOP. Additionally, the use of VK2 supplementation to augment osteoblast autophagy/mitophagy may significantly improve clinical outcomes of GIOP patients.

Glucocorticoids Enhanced Osteoclast Autophagy Through the PI3K/Akt/mTOR Signaling Pathway

Autophagy is an evolutionarily conserved dynamic process and present in variety of cells at basal levels to maintain homeostasis and to promote cell survival in response to stresses. The early bone loss with excessive glucocorticoids (GCs) was reported to be related with the extension of the life span of osteoclasts. However, the connection between GCs induced bone loss and osteoclast autophagy remains to be elucidated. Autophagy was detected in a Dexamethasone (Dex) induced osteoporotic mice model and primary osteoclast cultures by autophagosome detection kit, and autophagy-related proteins were assayed by Western blotting and Immunostaining. The bone morphology was examined by micro-CT and TRAP staining. The trabecular bone micro-architecture was deteriorated, and the osteoclast number and spread area were increased in the Dex-treated mice compared with the control group (P < 0.01). Meanwhile, autophagy in pre-osteoclasts was increased in mice under Dex administration evidenced by the increased number of autophagosome and up-regulation of autophagy-related protein levels. Further, the enhanced autophagy under Dex treatment was verified in primary cultured osteoclasts, as shown by the increased levels of Beclin 1 and LC3-II/LC3-I and the autophagy complex formation members including Atg1, Atg13, and Atg7. However, the expressions of PI3K, p-Akt and p-mTOR in primary cultured osteoclasts were inhibited under Dex induced autophagy. Using the selective PTEN inhibitor SF1670 to activate the PI3K/Akt/mTOR pathway reversed this osteoclast autophagy under Dex treatment. Our study suggests that osteoclast autophagy was enhanced in glucocorticoids induced bone loss, and the PI3K/Akt/mTOR signaling pathway mediated the increased autophagy in primary cultured osteoclasts under glucocorticoids treatment.

Biological Factors, Metals, and Biomaterials Regulating Osteogenesis through Autophagy

Bone loss raises great concern in numerous situations, such as ageing and many diseases and in both orthopedic and dentistry fields of application, with an extensive impact on health care. Therefore, it is crucial to understand the mechanisms and the determinants that can regulate osteogenesis and ensure bone balance. Autophagy is a well conserved lysosomal degradation pathway, which is known to be highly active during differentiation and development. This review provides a revision of the literature on all the exogen factors that can modulate osteogenesis through autophagy regulation. Metal ion exposition, mechanical stimuli, and biological factors, including hormones, nutrients, and metabolic conditions, were taken into consideration for their ability to tune osteogenic differentiation through autophagy. In addition, an exhaustive overview of biomaterials, both for orthopedic and dentistry applications, enhancing osteogenesis by modulation of the autophagic process is provided as well. Already investigated conditions regulating bone regeneration via autophagy need to be better understood for finely tailoring innovative therapeutic treatments and designing novel biomaterials.