Critical role of AKT protein in myeloma-induced osteoclast formation and osteolysis

Microarray analysis of signalling interactions between inflammation and angiogenesis in subchondral bone in temporomandibular joint osteoarthritis

Inflammation and angiogenesis, the major pathological changes of osteoarthritis (OA), are closely associated with joint pain; however, pertinent signalling interactions within subchondral bone of osteoarthritic joints and potential contribution to the peripheral origin of OA pain remain to be elucidated. Herein we developed a unilateral anterior crossbite mouse model with osteoarthritic changes in the temporomandibular joint. Microarray-based transcriptome analysis, besides quantitative real-time polymerase chain reaction, was performed to identify differentially expressed genes (DEGs). Overall, 182 DEGs (fold change ≥ 2, P < 0.05) were identified between the control and unilateral anterior crossbite groups: 168 were upregulated and 14 were downregulated. On subjecting significant DEGs to enrichment analyses, inflammation and angiogenesis were identified as the most affected. Inflammation-related DEGs were mainly enriched in T cell activation and differentiation and in the mammalian target of rapamycin/nuclear factor-κB/tumour necrosis factor signalling. Furthermore, angiogenesis-related DEGs were mainly enriched in the Gene Ontology terms angiogenesis regulation and vasculature development and in the KEGG pathways of phosphoinositide 3-kinase-protein kinase B/vascular endothelial growth factor/hypoxia-inducible factor 1 signalling. Protein-protein interaction analysis revealed a close interaction between inflammation- and angiogenesis-related DEGs, suggesting that phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit delta (Pi3kcd), cathelicidin antimicrobial peptide (Camp), C-X-C motif chemokine receptor 4 (Cxcr4), and MYB proto-oncogene transcription factor (Myb) play a central role in their interaction. To summarize, our findings reveal that in subchondral bone of osteoarthritic joints, signal interaction is interrelated between inflammation and angiogenesis and associated with the peripheral origin of OA pain; moreover, our data highlight potential targets for the inhibition of OA pain.

Epiberberine inhibits bone metastatic breast cancer-induced osteolysis

ETHNOPHARMACOLOGICAL RELEVANCE

The anti-tumor related diseases of Coptidis Rhizoma (Huanglian) were correlated with its traditional use of removing damp-heat, clearing internal fire, and counteracting toxicity. In the recent years, Coptidis Rhizoma and its components have drawn extensive attention toward their anti-tumor related diseases. Besides, Coptidis Rhizoma is traditionally used as an anti-inflammatory herb. Epiberberine (EPI) is a significant alkaloid isolated from Coptidis Rhizoma, and exhibits multiple pharmacological activities including anti-inflammatory. However, the effect of epiberberine on breast cancer and the inflammatory factors of metastatic breast cancer-induced osteolysis has not been demonstrated clearly.

AIM OF THE STUDY

Bone metastatic breast cancer can lead to osteolysis via inflammatory factors-induced osteoclast differentiation and function. In this study, we try to analyze the effect of epiberberine on breast cancer and the inflammatory factors of metastatic breast cancer-induced osteolysis.

METHODS

To evaluate whether epiberberine could suppress bone metastatic breast cancer-induced osteolytic damage, healthy female Balb/c mice were intratibially injected with murine triple-negative breast cancer 4T1 cells. Then, we examined the inhibitory effect and underlying mechanism of epiberberine on breast cancer-induced osteoclastogenesis in vitro. Xenograft assay was used to study the effect of epiberberine on breast cancer cells in vivo. Moreover, we also studied the inhibitory effects and underlying mechanisms of epiberberine on RANKL-induced osteoclast differentiation and function in vitro.

RESULTS

The results show that epiberberine displayed potential therapeutic effects on breast cancer-induced osteolytic damage. Besides, our results show that epiberberine inhibited breast cancer cells-induced osteoclast differentiation and function by inhibiting secreted inflammatory cytokines such as IL-8. Importantly, we found that epiberberine directly inhibited RANKL-induced differentiation and function of osteoclast without cytotoxicity. Mechanistically, epiberberine inhibited RANKL-induced osteoclastogensis via Akt/c-Fos signaling pathway. Furthermore, epiberberine combined with docetaxel effectively protected against bone loss induced by metastatic breast cancer cells.

CONCLUSIONS

Our findings suggested that epiberberine may be a promising natural compound for treating bone metastatic breast cancer-induced osteolytic damage by inhibiting IL-8 and is worthy of further exploration in preclinical and clinical trials.

Inhibition of receptor activator of nuclear factor kappa-B ligand-mediated osteoclast differentiation and bone resorption by Gryllus bimaculatus extract: An in vitro study

Excessive bone-resorbing osteoclast activity during bone remodeling is a major feature of bone diseases, such as osteoporosis. Therefore, the inhibition of osteoclast formation and bone resorption can be an effective therapeutic target for various bone diseases. Gryllus biomaculatus (GB) has recently been approved as an alternative food source because of its high nutritional value and environmental sustainability. Traditionally, GB has been known to have various pharmacological properties, including antipyretic and blood pressure-lowering activity, and it has recently been reported to have various biological activities, including protective effects against inflammation, oxidative stress, insulin resistance, and alcohol-induced liver injury. However, the effect of GB on osteoclast differentiation and bone metabolism has not yet been demonstrated. In this study, we confirmed the inhibitory effect of GB extract (GBE) on the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation. To determine the effect of GBE on RANKL-induced osteoclast differentiation and function, we performed TRAP and F-actin staining, as well as a bone-resorbing assay. The intracellular mechanisms of GBE responsible for the regulation of osteoclastogenesis were revealed by Western blot analysis and quantitative real-time polymerase chain reaction. We investigated the relationship between GBE and expression of osteoclast-specific molecules to further elucidate the underlying mechanisms. It was found that GBE significantly suppressed osteoclastogenesis by decreasing the phosphorylation of Akt, p38, JNK, and ERK, as well as Btk-PLCγ2 signaling, in pathways involved in early osteoclastogenesis as well as through the subsequent suppression of c-Fos, NFATc1, and osteoclastogenesis-specific marker genes. Additionally, GBE inhibited the formation of F-actin ring-positive osteoclasts and bone resorption activity of mature osteoclasts. Our findings suggest that GBE is a potential functional food and therapeutic candidate for bone diseases involving osteoclasts.

Advances in the roles of ATF4 in osteoporosis

Osteoporosis (OP) is characterized by reduced bone mass, decreased strength, and enhanced bone fragility fracture risk. Activating transcription factor 4 (ATF4) plays a role in cell differentiation, proliferation, apoptosis, redox balance, amino acid uptake, and glycolipid metabolism. ATF4 induces the differentiation of bone marrow mesenchymal stem cells (BM-MSCs) into osteoblasts, increases osteoblast activity, and inhibits osteoclast formation, promoting bone formation and remodeling. In addition, ATF4 mediates the energy metabolism in osteoblasts and promotes angiogenesis. ATF4 is also involved in the mediation of adipogenesis. ATF4 can selectively accumulate in osteoblasts. ATF4 can directly interact with RUNT-related transcription factor 2 (RUNX2) and up-regulate the expression of osteocalcin (OCN) and osterix (Osx). Several upstream factors, such as Wnt/β-catenin and BMP2/Smad signaling pathways, have been involved in ATF4-mediated osteoblast differentiation. ATF4 promotes osteoclastogenesis by mediating the receptor activator of nuclear factor κ-B (NF-κB) ligand (RANKL) signaling. Several agents, such as parathyroid (PTH), melatonin, and natural compounds, have been reported to regulate ATF4 expression and mediate bone metabolism. In this review, we comprehensively discuss the biological activities of ATF4 in maintaining bone homeostasis and inhibiting OP development. ATF4 has become a therapeutic target for OP treatment.

Targeting Kindlin-2 in adipocytes increases bone mass through inhibiting FAS/PPARγ/FABP4 signaling in mice

Osteoporosis (OP) is a systemic skeletal disease that primarily affects the elderly population, which greatly increases the risk of fractures. Here we report that Kindlin-2 expression in adipose tissue increases during aging and high-fat diet fed and is accompanied by decreased bone mass. Kindlin-2 specific deletion (K2KO) controlled by Adipoq-Cre mice or adipose tissue-targeting AAV (AAV-Rec2-CasRx-sgK2) significantly increases bone mass. Mechanistically, Kindlin-2 promotes peroxisome proliferator-activated receptor gamma (PPARγ) activation and downstream fatty acid binding protein 4 (FABP4) expression through stabilizing fatty acid synthase (FAS), and increased FABP4 inhibits insulin expression and decreases bone mass. Kindlin-2 inhibition results in accelerated FAS degradation, decreased PPARγ activation and FABP4 expression, and therefore increased insulin expression and bone mass. Interestingly, we find that FABP4 is increased while insulin is decreased in serum of OP patients. Increased FABP4 expression through PPARγ activation by rosiglitazone reverses the high bone mass phenotype of K2KO mice. Inhibition of FAS by C75 phenocopies the high bone mass phenotype of K2KO mice. Collectively, our study establishes a novel Kindlin-2/FAS/PPARγ/FABP4/insulin axis in adipose tissue modulating bone mass and strongly indicates that FAS and Kindlin-2 are new potential targets and C75 or AAV-Rec2-CasRx-sgK2 treatment are potential strategies for OP treatment.

Conditional knockout of PDK1 in osteoclasts suppressed osteoclastogenesis and ameliorated prostate cancer-induced osteolysis in murine model

BACKGROUND

The development and maintenance of normal bone tissue is maintained by balanced communication between osteoblasts and osteoclasts. The invasion of cancer cells disrupts this balance, leading to osteolysis. As the only bone resorbing cells in vivo, osteoclasts play important roles in cancer-induced osteolysis. However, the role of 3-phosphoinositide-dependent protein kinase-1 (PDK1) in osteoclast resorption remains unclear.

METHODS

In our study, we used a receptor activator of nuclear factor-kappa B (RANK) promoter-driven Cre-LoxP system to conditionally delete the PDK1 gene in osteoclasts in mice. We observed the effect of osteoclast-specific knockout of PDK1 on prostate cancer-induced osteolysis. Bone marrow-derived macrophage cells (BMMs) were extracted and induced to differentiate osteoclasts in vitro to explore the role of PDK1 in osteoclasts.

RESULTS

In this study, we found that PDK1 conditional knockout (cKO) mice exhibited smaller body sizes when compared to the wild-type (WT) mice. Moreover, deletion of PDK1 in osteoclasts ameliorated osteolysis and rPDK1educed bone resorption markers in the murine model of prostate cancer-induced osteolysis. In vivo, we discovered that osteoclast-specific knockout of suppressed RANKL-induced osteoclastogenesis, bone resorption function, and osteoclast-specific gene expression (Ctsk, TRAP, MMP-9, NFATc1). Western blot analyses of RANKL-induced signaling pathways showed that conditional knockout of PDK1 in osteoclasts inhibited the early nuclear factor κB (NF-κB) activation, which consequently suppressed the downstream induction of NFATc1.

CONCLUSION

These findings demonstrated that PDK1 performs an important role in osteoclastogenesis and prostate cancer-induced osteolysis by modulating the PDK1/AKT/NF-κB signaling pathway.

A novel sprayable thermosensitive hydrogel coupled with zinc modified metformin promotes the healing of skin wound

A novel sprayable adhesive is established (ZnMet-PF127) by the combination of a thermosensitive hydrogel (Pluronic F127, PF127) and a coordination complex of zinc and metformin (ZnMet). Here we demonstrate that ZnMet-PF127 potently promotes the healing of traumatic skin defect and burn skin injury by promoting cell proliferation, angiogenesis, collagen formation. Furthermore, we find that ZnMet could inhibit reactive oxygen species (ROS) production through activation of autophagy, thereby protecting cell from oxidative stress induced damage and promoting healing of skin wound. ZnMet complex exerts better effects on promoting skin wound healing than ZnCl₂ or metformin alone. ZnMet complex also displays excellent antibacterial activity against Staphylococcus aureus or Escherichia coli, which could reduce the incidence of skin wound infections. Collectively, we demonstrate that sprayable PF127 could be used as a new drug delivery system for treatment of skin injury. The advantages of this sprayable system are obvious: (1) It is convenient to use; (2) The hydrogel can cover irregular skin defect sites evenly in a liquid state. In combination with this system, we establish a novel sprayable adhesive (ZnMet-PF127) and demonstrate that it is a potential clinical treatment for traumatic skin defect and burn skin injury.

The Molecular Mechanism of Traditional Chinese Medicine Prescription: Gu-tong Formula in Relieving Osteolytic Bone Destruction

Bone metastasis is a common complication in patients with advanced tumors, causing pain and bone destruction and affecting their quality of life. Typically, complementary and alternative medicine (CAM), with unique theoretical guidance, has played key roles in the treatment of tumor-related diseases. Gu-tong formula (GTF), as a representative prescription of traditional Chinese medicine, has been demonstrated to be an effective clinical medication for the relief of cancer pain. However, the molecular mechanism of GTF in the treatment of osteolytic metastasis is still unclear. Herein, we employ network pharmacology and molecular dynamics methods to uncover the potential treatment mechanism, indicating that GTF can reduce the levels of serum IL6 and TGFB1 and thus limit the scope of bone cortical damage. Among the active compounds, sesamin and deltoin can bind stably with IL6 and TGFB1, respectively, and have the potential to become anti-inflammatory and anticancer drugs. Although the reasons for the therapeutic effect of GTF are complex and comprehensive, this work provides biological plausibility in the treatment of osteolytic metastases, which has a guiding significance for the treatment of cancer pain with CAM.

Gallic acid inhibits osteoclastogenesis and prevents ovariectomy-induced bone loss

Osteoporosis is a common metabolic bone disease with a rapidly increasing prevalence, characterized by massive bone loss because of excessive osteoclast formation. Gallic acid (GA), a phenolic acid isolated from Cornus officinalis, has anti-inflammatory and anti-oxidant effects, but its effect on osteoclast formation has not been confirmed. In our study, we demonstrated that GA significantly inhibited RANKL-induced osteoclast formation and function of osteoclast in bone marrow monocytes (BMMs) and RAW264.7 cells in a dose-dependent manner without cytotoxicity. For molecular mechanisms, GA repressed osteoclastogenesis by blocking Akt, ERK, and JNK pathways, and suppressed osteoclastogenesis-related marker expression, including nuclear factor of the activated T-cell cytoplasmic 1 (NFATc1), c-Fos, and cathepsin K (CTSK). In addition, we further assessed the effect of GA in an ovariectomized mouse model, which indicated that GA has a notable effect on preventing bone loss. In conclusion, GA exerts notable effects in inhibiting osteoclastogenesis and preventing ovariectomy-induced bone loss, suggesting that GA is a potential agent in osteoporosis treatment.

Loss of phosphatidylinositol-4-phosphate 5-kinase type-1 gamma (Pip5k1c) in mesenchymal stem cells leads to osteopenia by impairing bone remodeling

Phosphatidylinositol-4-phosphate 5-kinase type-1 gamma (Pip5k1c) is a lipid kinase that plays a pivotal role in the regulation of receptor-mediated calcium signaling in multiple tissues; however, its role in the skeleton is not clear. Here, we show that while deleting Pip5k1c expression in the mesenchymal stem cells using Prx1-Cre transgenic mice does not impair the intramembranous and endochondral ossification during skeletal development, it does cause osteopenia in adult mice, but not rapidly growing young mice. We found Pip5k1c loss dramatically decreases osteoblast formation and osteoid and mineral deposition, leading to reduced bone formation. Furthermore, Pip5k1c loss inhibits osteoblastic, but promotes adipogenic, differentiation of bone marrow stromal cells. Pip5k1c deficiency also impairs cytoplasmic calcium influx and inactivates the calcium/calmodulin-dependent protein kinase, which regulates levels of transcription factor Runx2 by modulating its stability and subsequent osteoblast and bone formation. In addition, Pip5k1c loss reduces levels of the receptor activator of nuclear factor-κB ligand, but not that of osteoprotegerin, its decoy receptor, in osteoblasts in bone and in sera. Finally, we found Pip5k1c loss impairs the ability of bone marrow stromal cells to support osteoclast formation of bone marrow monocytes and reduces the osteoclast precursor population in bone marrow, resulting in reduced osteoclast formation and bone resorption. We conclude Pip5k1c deficiency causes a low-turnover osteopenia in mice, with impairment of bone formation being greater than that of bone resorption. Collectively, we uncover a novel function and mechanism of Pip5k1c in the control of bone mass and identify a potential therapeutic target for osteoporosis.

Anethole inhibits RANKL-induced osteoclastogenesis by downregulating ERK/AKT signaling and prevents ovariectomy-induced bone loss in vivo

Postmenopausal osteoporosis is a chronic population health hazard systemic metabolic disease caused by excessive bone resorption and reduced bone formation. The activity between osteoblast and osteoclast, with their mutual effects, influence the procedure of normal bone remodeling. Over-activated osteoclast differentiation and function play a crucial role in excessive bone resorption. Hence, therapy strategies targeting osteoclast activity may promote the bone mass preservation and delay the osteoporosis process. Natural compound (anethole) is emerging as potential therapeutics for various metabolic diseases. The purpose of this study is to investigate the potential effects of anethole on RANKL-induced osteoclast formation and function in vitro and in vivo. Here, in vitro TRAP staining assay was performed to investigate the inhibitory effect of anethole on osteoclast differentiation. Bone pits resorption assay revealed that osteoclast-mediated bone resorption was inhibited by anethole. At mRNA and protein levels, anethole significantly reduced the expression of osteoclast-specific genes expression in a concentration- or time-dependent manner, including NFATc1, MMP-9, DC-STAMP, c-F, TRAP, CTR, Cathepsin K, and V-ATPase d2. Furthermore, intracellular signaling transduction assay indicated that anethole inhibited osteoclast formation via blocking ERK and AKT signaling. GSK3β, the downstream signal of AKT, is simultaneously suppressed with anethole treatment. Based on ovariectomized (OVX) mice model, micro-CT and histological staining results suggested that anethole prevented estrogen deficiency-induced bone mass loss and increased osteoclast activity in vivo. In conclusion, our results show significant indications that anethole exhibits an osteoprotective effect and may be potential for the treatment of osteoporosis.

Glaucocalyxin A suppresses osteoclastogenesis induced by RANKL and osteoporosis induced by ovariectomy by inhibiting the NF-κB and Akt pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Glaucocalyxin A (GLA), the most abundant active component of the aboveground sections of Rabdosia japonica (Burm. f.) Hara var. glaucocalyx (Maxim.) Hara, possesses various pharmacological activities, such as antioxidant, antithrombosis, anticoagulation, antibacterial, antitumor, anti-inflammatory activities. According to previous studies, inflammation is closely associated with osteoclast differentiation and activity. Although GLA has demonstrated effective anti-inflammatory properties, its effects on osteoclast differentiation remain unclear.

AIM OF THE STUDY

To examine the possible inhibitory effects of GLA and its molecular mechanisms in osteogenesis induced by RANKL as well as ovariectomy (OVX)-induced osteoporosis (OP) in mice.

MATERIALS AND METHODS

Tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining, and a bone resorption pit assay were applied for identifying the effects of GLA on the differentiation of osteoclasts and the function of bone resorption. The mRNA expression of the genes related to osteoclast differentiation was measured by quantitative PCR. Protein expression of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), c-fos and phosphorylation of inhibitor of nuclear factor kappa B (IκBα), protein kinase B (AKT), c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38 in RANKL-induced osteoclasts was determined using western blotting. The effect of GLA on OP was studied using a mouse model of OVX.

RESULTS

At nontoxic concentrations ≤0.5 μM in vitro, GLA suppressed the formation of osteoclasts induced by RANKL with the decreased number and area size of TRAP-positive multinuclear osteoclasts, and the resorption of bone function by reducing F-actin ring number and bone resorption pit areas. It also reduced the expression of the genes specific for osteoclasts, which included genes encoding NFATc1, cathepsin K, c-fos, TRAP, vacuolar-type ATPase d2, and dendritic cell-specific transmembrane protein. Moreover, GLA repressed NF-κB and Akt pathway activation induced by RANKL. Micro-CT analysis of femur samples indicated decreased bone loss and greater trabecular bone density after GLA treatment, which showed that GLA played a protective role by inhibiting bone loss in OVX-induced OP mice in vivo.

CONCLUSIONS

Our study is the first to show that GLA has significant therapeutic potential in OP, which is the disease of osteoclast increase caused by estrogen deficiency.

Phospholipase Cγ Signaling in Bone Marrow Stem Cell and Relevant Natural Compounds Therapy

Excessive bone resorption has been recognized play a major role in the development of bone-related diseases such as osteoporosis, rheumatoid arthritis, Paget's disease of bone, and cancer. Phospholipase Cγ (PLCγ) family members PLCγ1 and PLCγ2 are critical regulators of signaling pathways downstream of growth factor receptors, integrins, and immune complexes and play a crucial role in osteoclast. Ca2+ signaling has been recognized as an essential pathway to the differentiation of osteoclasts. With growing attention and research about natural occurring compounds, the therapeutic use of natural active plant-derived products has been widely recognized in recent years. In this review, we summarized the recent research on PLCγ signaling in bone marrow stem cells and the use of several natural compounds that were proven to inhibit RANKL-mediated osteoclastogenesis via modulating PLCγ signaling pathways.

Sclerostin-Mediated Impaired Osteogenesis by Fibroblast-Like Synoviocytes in the Particle-Induced Osteolysis Model

Engineered biomaterials are envisioned to replace, augment, or interact with living tissues for improving the functional deformities associated with end-stage joint pathologies. Unfortunately, wear debris from implant interfaces is the major factor leading to periprosthetic osteolysis. Fibroblast-like synoviocytes (FLSs) populate the intimal lining of the synovium and are in direct contact with wear debris. This study aimed to elucidate the effect of Ti particles as wear debris on human FLSs and the mechanism by which they might participate in the bone remodeling process during periprosthetic osteolysis. FLSs were isolated from synovial tissue from patients, and the condition medium (CM) was collected after treating FLSs with sterilized Ti particles. The effect of CM was analyzed for the induction of osteoclastogenesis or any effect on osteogenesis and signaling pathways. The results demonstrated that Ti particles could induce activation of the NFκB signaling pathway and induction of COX-2 and inflammatory cytokines in FLSs. The amount of Rankl in the conditioned medium collected from Ti particle–stimulated FLSs (Ti CM) showed the ability to stimulate osteoclast formation. The Ti CM also suppressed the osteogenic initial and terminal differentiation markers for osteoprogenitors, such as alkaline phosphate activity, matrix mineralization, collagen synthesis, and expression levels of Osterix, Runx2, collagen 1α, and bone sialoprotein. Inhibition of the WNT and BMP signaling pathways was observed in osteoprogenitors after the treatment with the Ti CM. In the presence of the Ti CM, exogenous stimulation by WNT and BMP signaling pathways failed to stimulate osteogenic activity in osteoprogenitors. Induced expression of sclerostin (SOST: an antagonist of WNT and BMP signaling) in Ti particle–treated FLSs and secretion of SOST in the Ti CM were detected. Neutralization of SOST in the Ti CM partially restored the suppressed WNT and BMP signaling activity as well as the osteogenic activity in osteoprogenitors. Our results reveal that wear debris–stimulated FLSs might affect bone loss by not only stimulating osteoclastogenesis but also suppressing the bone-forming ability of osteoprogenitors. In the clinical setting, targeting FLSs for the secretion of antagonists like SOST might be a novel therapeutic approach for preventing bone loss during inflammatory osteolysis.

Combination of AZD3463 and DZNep Prevents Bone Metastasis of Breast Cancer by Suppressing Akt Signaling

Osteolysis resulting from osteoclast overactivation is one of the severe complications of breast cancer metastasis to the bone. Previous studies reported that the anti-cancer agent DZNep induces cancer cell apoptosis by activating Akt signaling. However, the effect of DZNep on breast cancer bone metastasis is unknown. We previously found that DZNep enhances osteoclast differentiation by activating Akt. Therefore, we explored the use of the anti-cancer agent AZD3463 (an Akt inhibitor) along with DZNep, as AZD3463 can act as an anti-cancer agent and can also potentially ameliorate bone erosion. We evaluated osteoclast and breast cancer cell phenotypes and Akt signaling in vitro by treating cells with DZNep and AZD3463. Furthermore, we developed a breast cancer bone metastasis animal model in mouse tibiae to further determine their combined effects in vivo. Treatment of osteoclast precursor cells with DZNep alone increased osteoclast differentiation, bone resorption, and expression of osteoclast-specific genes. These effects were ameliorated by AZD3463. The combination of DZNep and AZD3463 inhibited breast cancer cell proliferation, colony formation, migration, and invasion. Finally, intraperitoneal injection of DZNep and AZD3463 ameliorated tumor progression and protected against bone loss. In summary, DZNep combined with AZD3463 prevented skeletal complications and inhibited breast cancer progression by suppressing Akt signaling.

LIM domain proteins Pinch1/2 regulate chondrogenesis and bone mass in mice

The LIM domain-containing proteins Pinch1/2 regulate integrin activation and cell–extracellular matrix interaction and adhesion. Here, we report that deleting Pinch1 in limb mesenchymal stem cells (MSCs) and Pinch2 globally (double knockout; dKO) in mice causes severe chondrodysplasia, while single mutant mice do not display marked defects. Pinch deletion decreases chondrocyte proliferation, accelerates cell differentiation and disrupts column formation. Pinch loss drastically reduces Smad2/3 protein expression in proliferative zone (PZ) chondrocytes and increases Runx2 and Col10a1 expression in both PZ and hypertrophic zone (HZ) chondrocytes. Pinch loss increases sclerostin and Rankl expression in HZ chondrocytes, reduces bone formation, and increases bone resorption, leading to low bone mass. In vitro studies revealed that Pinch1 and Smad2/3 colocalize in the nuclei of chondrocytes. Through its C-terminal region, Pinch1 interacts with Smad2/3 proteins. Pinch loss increases Smad2/3 ubiquitination and degradation in primary bone marrow stromal cells (BMSCs). Pinch loss reduces TGF-β-induced Smad2/3 phosphorylation and nuclear localization in primary BMSCs. Interestingly, compared to those from single mutant mice, BMSCs from dKO mice express dramatically lower protein levels of β-catenin and Yap1/Taz and display reduced osteogenic but increased adipogenic differentiation capacity. Finally, ablating Pinch1 in chondrocytes and Pinch2 globally causes severe osteopenia with subtle limb shortening. Collectively, our findings demonstrate critical roles for Pinch1/2 and a functional redundancy of both factors in the control of chondrogenesis and bone mass through distinct mechanisms.

Fibroblast-Like-Synoviocytes Mediate Secretion of Pro-Inflammatory Cytokines via ERK and JNK MAPKs in Ti-Particle-Induced Osteolysis

Biomaterials are designed to replace and augment living tissues in order to provide functional support to skeletal deformities. However, wear debris produced from the interfaces of metal implants initiates inflammatory bone loss, causing periprosthetic osteolysis. Lately, fibroblast-like synoviocytes (FLS) have been shown to play a role in wear-debris-induced osteolysis. Thus, here we have tried to understand the underlying mechanism of FLS involvement in wear-debris-induced osteolysis. Our results demonstrate that the effects of Ti particle (1:100 cell-to-Ti particle ratio) on FLS can induce Cox-2 expression and activate NFkB signaling. Moreover, the mRNA expression of pro-inflammatory cytokines such as IL-6, IL-8, IL-11, IL-1β, and TNFα was found to be elevated. However, among these pro-inflammatory cytokines, the mRNA and protein levels of only IL-6, IL-1β, and TNFα were found to be significantly higher. Ti particles activated extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinases (MAPKs) as an early response in FLS. Co-inhibition of ERK and JNK signaling pathways by their specific inhibitors (PD9805 and SP600125, respectively) resulted in the suppression of mRNA and protein levels of IL-6, IL-1β, and TNFα in FLS. Taken together, targeting ERK and JNK MAPKs in FLS might provide a therapeutic option for reducing the secretion of bone-resorbing pro-inflammatory cytokines, thus preventing periprosthetic osteolysis.

A natural compound (LCA) isolated from Litsea cubeba inhibits RANKL-induced osteoclast differentiation by suppressing Akt and MAPK pathways in mouse bone marrow macrophages

ETHNOPHARMACOLOGICAL RELEVANCE

Litsea cubeba (Lour.) Pers. has been traditionally used as a folk prescription for treating rheumatic diseases in China.

AIM OF THE STUDY

This study aimed to investigate the effects and underlying mechanism of LCA, a new type of dibenzyl butane lignin compound extracted from L. cubeba, on macrophage colony stimulating factor (M-CSF) plus receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation in mouse-derived bone marrow macrophages (BMMs).

MATERIAL AND METHODS

TRAP staining, TRAP enzyme activity assay and actin ring staining were applied to identify the effects of LCA on osteoclast differentiation. Protein expression of NFATc1, c-Fos and MMP-9, and phosphorylation of p65, Akt, JNK, ERK and p38 in RANKL-induced osteoclasts was determined using western blotting to investigate the underlying mechanism.

RESULTS

LCA significantly suppressed RANKL-induced osteoclast differentiation by inhibiting TRAP activity, decreasing the number of TRAP⁺ multinuclear osteoclasts and reducing the formation of F-actin ring without obvious cytotoxicity in BMMs. Moreover, LCA treatment strongly reduced protein expression of NFATc1, c-Fos and MMP-9, and attenuated the phosphorylation of p65, Akt, JNK, ERK and p38 in RANKL-stimulated BMMs.

CONCLUSIONS

LCA ameliorated RANKL-induced osteoclast differentiation via inhibition of Akt and MAPK signalings in BMMs, and may serve as a potential pro-drug for bone destruction prevention.

Betulinic Acid Inhibits RANKL-Induced Osteoclastogenesis via Attenuating Akt, NF-κB, and PLCγ2-Ca2+ Signaling and Prevents Inflammatory Bone Loss

The increase of bone-resorbing osteoclast activity in bone remodeling is the major characteristic of various bone diseases. Thus, inhibiting osteoclastogenesis and bone-resorbing function may be an effective therapeutic target for bone diseases. Betulinic acid (BA), a natural plant-derived pentacyclic triterpenoid compound, is known to possess numerous pharmacological and biochemical properties including anti-inflammatory, anticancer, and antiadipogenic activity. However, the effect of BA on osteoclast differentiation and function in bone metabolism has not been demonstrated so far. In this study, we investigated whether BA could suppress RANKL-induced osteoclastogenesis and bone resorption. Interestingly, BA significantly suppressed osteoclastogenesis by decreasing the phosphorylation of Akt and IκB, as well as PLCγ2-Ca²⁺ signaling, in pathways involved in early osteoclastogenesis as well as through the subsequent suppression of c-Fos and NFATc1. The inhibition of these pathways by BA was once more confirmed by retrovirus infection of constitutively active (CA)-Akt and CA-Ikkβ retrovirus and measurement of Ca²⁺ influx. BA also significantly inhibited the expression of osteoclastogenesis-specific marker genes. Moreover, we found that BA administration restored the bone loss induced through acute lipopolysaccharide injection in mice by a micro-CT and histological analysis. Our findings suggest that BA is a potential therapeutic candidate for bone diseases involving osteoclasts.

Moderate Fluid Shear Stress Regulates Heme Oxygenase-1 Expression to Promote Autophagy and ECM Homeostasis in the Nucleus Pulposus Cells

In vertebrate, the nucleus pulposus (NP), which is an essential component of the intervertebral disk, is constantly impacted by fluid shear stress (FSS); however, molecular mechanism(s) through which FSS modulates the NP homeostasis is poorly understood. Here we show that FSS regulates the extracellular matrix (ECM) homeostasis in NP cells. A moderate dose of FSS (i.e., 12 dyne/cm²) increases the sulfated glycosaminoglycan (sGAG) content and protein levels of Col2a1 and Aggrecan and decreases those of matrix metalloproteinase 13 (MMP13) and a disintegrin and metalloproteinase with thrombospondin motif 5 (ADMATS5) in rat NP cells, while a higher dose of FSS (i.e., 24 dyne/cm²) displays opposite effects. Results from RNA sequencing analysis, quantitative real-time RT-PCR analysis and western blotting establish that the heme oxygenase-1 (HO-1) is a key downstream mediator of the FSS actions in NP cells. HO-1 knockdown abolishes FSS-induced alterations in ECM protein production and sGAG content in NP cells, which is reversed by HO-1 induction. Furthermore, FSS activates the autophagic pathway by increasing the LC3-II/LC3-I ratio, Beclin-1 protein level, and formation of autophagosome and autolysosome and thereby regulates ECM protein and sGAG production in a HO-1 dependent manner. Finally, we demonstrate that the intraflagellar transport (IFT) 88, a core trafficking protein of primary cilia, is critically involved in the HO-1-mediated autophagy activation and ECM protein and sGAG production in FSS-treated NP cells. Thus, we for the first time demonstrate that FSS plays an important role in maintaining ECM homeostasis through HO-1-dependent activation of autophagy in NP cells.

Focal adhesion protein Kindlin-2 regulates bone homeostasis in mice

Our recent studies demonstrate that the focal adhesion protein Kindlin-2 is critical for chondrogenesis and early skeletal development. Here, we show that deleting Kindlin-2 from osteoblasts using the 2.3-kb mouse Col1a1-Cre transgene minimally impacts bone mass in mice, but deleting Kindlin-2 using the 10-kb mouse Dmp1-Cre transgene, which targets osteocytes and mature osteoblasts, results in striking osteopenia in mice. Kindlin-2 loss reduces the osteoblastic population but increases the osteoclastic and adipocytic populations in the bone microenvironment. Kindlin-2 loss upregulates sclerostin in osteocytes, downregulates β-catenin in osteoblasts, and inhibits osteoblast formation and differentiation in vitro and in vivo. Upregulation of β-catenin in the mutant cells reverses the osteopenia induced by Kindlin-2 deficiency. Kindlin-2 loss additionally increases the expression of RANKL in osteocytes and increases osteoclast formation and bone resorption. Kindlin-2 deletion in osteocytes promotes osteoclast formation in osteocyte/bone marrow monocyte cocultures, which is significantly blocked by an anti-RANKL-neutralizing antibody. Finally, Kindlin-2 loss increases osteocyte apoptosis and impairs osteocyte spreading and dendrite formation. Thus, we demonstrate an important role of Kindlin-2 in the regulation of bone homeostasis and provide a potential target for the treatment of metabolic bone diseases.

Umbelliferone Prevents Lipopolysaccharide-Induced Bone Loss and Suppresses RANKL-Induced Osteoclastogenesis by Attenuating Akt-c-Fos-NFATc1 Signaling

Excessive bone resorption plays a central role in the development of inflammatory bone diseases, including osteoporosis and rheumatoid arthritis. Thus, identification of agents that can effectively suppress excessive osteoclast formation and function is crucial for the prevention and treatment of inflammatory bone loss. Umbelliferone (Umb), a derivative of coumarin, is a natural bioactive compound with anti-inflammatory and antioxidant properties. However, the effect of Umb on metabolic bone diseases is unknown. In this study, we found that Umb exhibited a strong inhibitory effect on lipopolysaccharide (LPS)-induced inflammatory bone loss in vivo. Histological analysis confirmed that Umb prevented trabecular bone matrix degradation and osteoclast formation in bone tissue. In addition, Umb suppressed RANKL-induced osteoclast differentiation and abrogated bone resorption. We found that the anti-osteoclastic and anti-resorptive activities of Umb are mediated via suppression of the RANKL-induced Akt-c-Fos-NFATc1 signaling pathway and the attenuation of osteoclast-specific genes, such as TRAP, OSCAR, ATP6v0d2, and CtsK. In particular, Umb downregulated the stability of c-Fos and NFATc1 proteins, but did not suppress the expression of their mRNAs. These results indicate that Umb may be a potential therapeutic agent for inflammatory bone diseases associated with abnormal osteoclast formation and function.

NRF2 Is One of the Players Involved in Bone Marrow Mediated Drug Resistance in Multiple Myeloma

Multiple myeloma with clonal plasma expansion in bone marrow is the second most common hematologic malignancy in the world. Though the improvement of outcomes from the achievement of novel agents in recent decades, the disease progresses and leads to death eventually due to the elusive nature of myeloma cells and resistance mechanisms to therapeutic agents. In addition to the molecular and genetic basis of resistance pathomechanisms, the bone marrow microenvironment also contributes to disease progression and confers drug resistance in myeloma cells. In this review, we focus on the current state of the literature in terms of critical bone marrow microenvironment components, including soluble factors, cell adhesion mechanisms, and other cellular components. Transcriptional factor nuclear factor erythroid-derived-2-like 2 (NRF2), a central regulator for anti-oxidative stresses and detoxification, is implicated in chemoresistance in several cancers. The functional roles of NRF2 in myeloid-derived suppressor cells and multiple myeloma cells, and the potential of targeting NRF2 for overcoming microenvironment-mediated drug resistance in multiple myeloma are also discussed.

PI3K/Akt inhibitor LY294002 potentiates homoharringtonine antimyeloma activity in myeloma cells adhered to stromal cells and in SCID mouse xenograft

Homoharringtonine (HHT) is a known anti-leukemia drug that inhibits multiple myeloma (MM) cells both in vitro and in vivo. Our prior study demonstrated that the potency of HHT in MM cells was compromised significantly when myeloma cells were co-cultured with BM stromal cells. This study aimed to investigate whether PI3K/Akt inhibitor LY294002 could potentiate the antimyeloma activity of HHT against MM cells adhered to BM stromal cells and in vivo xenograft models. A co-culture system composed of MM cells and human stromal cells was employed to mimic MM cells in bone marrow niche. The inhibitory and pro-apoptotic effect of HHT and LY294002 was determined by CCK-8 assay or flow cytometry. Expression of PI3K/Akt signaling molecules and anti-apoptotic protein myeloid cell leukemia-1 (Mcl-1) was assessed by western blot analysis and/or reverse transcription real-time quantitative PCR (RT-qPCR). MM xenografts were used to evaluate antitumor effect of combined therapy with HHT and LY294002. Adhesion to BM stromal cells rendered MM cells resistant to HHT whereas silencing Mcl-1 partly reversed the resistance. LY294002 induced apoptosis in MM cells and potentiated the antimyeloma effects of HHT by inhibiting the PI3K/Akt signal pathway which was abnormally activated during adhesion. LY294002 also enhanced the antimyeloma effect of HHT in in vivo xenograft models. These findings suggest that activation of PI3K/Akt signal pathway was responsible for the resistance to HHT in MM cells adhered to stromal cells. LY294002 can potentiate the antimyeloma activity of HHT both in vitro and in vivo, which may represent a new clinical treatment in MM.

eIF2α signaling regulates ischemic osteonecrosis through endoplasmic reticulum stress

Osteonecrosis of the femoral head (ONFH) primarily results from ischemia/hypoxia to the femoral head, and one of the cellular manifestations is the endoplasmic reticulum (ER) stress. To understand possible linkage of ischemic osteonecrosis to the ER stress, a surgery-induced animal model was employed and salubrinal was administered to evaluate the role of ER stress. Salubrinal is a synthetic chemical that inhibits de-phosphorylation of eIF2α, and it can suppress cell death from the ER stress at a proper dose. The results indicated that the ER stress was associated with ONFH and salubrinal significantly improved ONFH-induced symptoms such as osteonecrosis, bone loss, reduction in vessel perfusion, and excessive osteoclastogenesis in the femoral head. Salubrinal also protected osteoblast development by upregulating the levels of ATF4, ALP and RUNX2, and it stimulated angiogenesis of endothelial cells through elevating ATF4 and VEGF. Collectively, the results support the notion that the ER stress is an important pathological outcome in the surgery-induced ONFH model, and salubrinal improves ONFH symptoms by enhancing angiogenesis and bone healing via suppressing the ER stress.

Molecular mechanisms, current management and next generation therapy in myeloma bone disease

Multiple myeloma (MM) bone disease is a major cause of morbidity and mortality in MM patients and persists even in patients in remission. This bone disease is caused by an uncoupling of bone remodeling, with increased osteoclast and decreased osteoblast activity and formation, culminating in lytic bone destruction. Bisphosphonates are the current standard of care but new therapies are needed. As the molecular mechanisms controlling MM bone disease are increasingly well understood, new therapeutic targets are extensively explored in the preclinical setting and initial clinical trials with novel compounds now show promising results. In this review, we will provide a comprehensive overview of the biology of MM bone disease, summarize its current clinical management and discuss preclinical and clinical data on next generation therapies.

A FKBP5 mutation is associated with Paget's disease of bone and enhances osteoclastogenesis

Paget's disease of bone (PDB) is a common metabolic bone disease that is characterized by aberrant focal bone remodeling, which is caused by excessive osteoclastic bone resorption followed by disorganized osteoblastic bone formation. Genetic factors are a critical determinant of PDB pathogenesis, and several susceptibility genes and loci have been reported, including SQSTM1, TNFSF11A, TNFRSF11B, VCP, OPTN, CSF1 and DCSTAMP. Herein, we report a case of Chinese familial PDB without mutations in known genes and identify a novel c.163G>C (p.Val55Leu) mutation in FKBP5 (encodes FK506-binding protein 51, FKBP51) associated with PDB using whole-exome sequencing. Mutant FKBP51 enhanced the Akt phosphorylation and kinase activity in cells. A study of osteoclast function using FKBP51^V55L KI transgenic mice proved that osteoclast precursors from FKBP51^V55L mice were hyperresponsive to RANKL, and osteoclasts derived from FKBP51^V55L mice displayed more intensive bone resorbing activity than did FKBP51^WT controls. The osteoclast-specific molecules tartrate-resistant acid phosphatase, osteoclast-associated receptor and transcription factor NFATC1 were increased in bone marrow-derived monocyte/macrophage cells (BMMs) from FKBP51^V55L mice during osteoclast differentiation. However, c-fos expression showed no significant difference in the wild-type and mutant groups. Akt phosphorylation in FKBP51^V55L BMMs was elevated in response to RANKL. In contrast, IκB degradation, ERK phosphorylation and LC3II expression showed no difference in wild-type and mutant BMMs. Micro-CT analysis revealed an intensive trabecular bone resorption pattern in FKBP51^V55L mice, and suspicious osteolytic bone lesions were noted in three-dimensional reconstruction of distal femurs from mutant mice. These results demonstrate that the mutant FKBP51^V55L promotes osteoclastogenesis and function, which could subsequently participate in PDB development.

uPA-derived peptide, Å6 is involved in the suppression of lipopolysaccaride-promoted inflammatory osteoclastogenesis and the resultant bone loss

Introduction

Chronic inflammatory diseases such as rheumatoid arthritis and periodontitis frequently cause bone destruction. Inflammation‐induced bone loss results from the increase of bone‐resorbing osteoclasts. Recently, we demonstrated that urokinase type plasminogen activator (uPA) suppressed lipopolysaccaride (LPS)‐inflammatory osteoclastogenesis through the adenosine monophosphate‐activated protein kinase (AMPK) pathway, whereas its receptor (uPAR) promoted that through the Akt pathway.

Methods

We investigated the effects of uPA‐derived peptide (Å6) in the LPS‐induced inflammatory osteoclastogenesis and bone destruction.

Results

We found that Å6 attenuated inflammatory osteoclastogenesis and bone loss induced by LPS in mice. We also showed that Å6 attenuated the LPS‐promoted inflammatory osteoclastogenesis by inactivation of NF‐κB in RAW264.7 mouse monocyte/macrophage lineage cells. Furthermore, we showed that Å6 attenuated the Akt phosphorylation, and promoted the AMPK phosphorylation.

Conclusion

Å6 is involved in the suppression of LPS‐promoted inflammatory osteoclastgensis and bone destruction by regulating the AMPK and Akt pathways. These findings provide a basis for clinical strategies to improve the bone loss caused by inflammatory diseases.

MK2206 enhances the cytocidal effects of bufalin in multiple myeloma by inhibiting the AKT/mTOR pathway

Despite the development of promising cancer therapeutic drugs, multiple myeloma (MM) remains an incurable disease. Bufalin is a bufanolide steroid compound of the traditional Chinese medicine Chan Su that was previously shown to exert growth suppression effects on myeloma cell lines. Previous studies conducted by our group demonstrated that bufalin activated the AKT/mTOR pathway in myeloma cells, which is considered an essential pathway to disease progression and is related to drug resistance in MM. In view of the significant role of AKT in MM, the allosteric AKT inhibitor MK2206 was selected in order to enhance the antitumor effects of bufalin in different MM cell lines (NCI-H929, U266, LP-1 and RPMI8226). The data indicated that MK2206 enhanced the cytotoxicity of bufalin in MM cells, via the suppression of cellular proliferation and the induction of apoptosis, as demonstrated by cleavage of apoptosis-related proteins. This effect was further noted in the presence of exogenous interleukin-6 and/or following the co-culture of MM cells with bone marrow stromal cells (BMSC). This process was associated with the inhibition of the AKT/mTOR pathway. The combination of bufalin with MK2206 reduced the secretion of IL-6 in U266 cells. The combined treatment exhibited similar anti-MM effects in bortezomib-resistant cell lines (NCI-H929R, U266R). In addition to the in vitro cell line models, the synergistic effect was noted in primary MM cells and in MM xenografts of BALB-c and NOD-SCID mice. In conclusion, the data suggested that MK2206 significantly enhanced the cytocidal effects of bufalin in MM cells, regardless of the sensitivity to bortezomib, via the inhibition of the AKT/mTOR pathway. The study provided the basis of a promising treatment approach for MM.

Methyl Gallate Inhibits Osteoclast Formation and Function by Suppressing Akt and Btk-PLCγ2-Ca2+ Signaling and Prevents Lipopolysaccharide-Induced Bone Loss

In the field of bone research, various natural derivatives have emerged as candidates for osteoporosis treatment by targeting abnormally elevated osteoclastic activity. Methyl gallate, a plant-derived phenolic compound, is known to have numerous pharmacological effects against inflammation, oxidation, and cancer. Our purpose was to explore the relation between methyl gallate and bone metabolism. Herein, we performed screening using methyl gallate by tartrate resistant acid phosphatase (TRAP) staining and revealed intracellular mechanisms responsible for methyl gallate-mediated regulation of osteoclastogenesis by Western blotting and quantitative reverse transcription polymerase chain reaction (RT-PCR). Furthermore, we assessed the effects of methyl gallate on the characteristics of mature osteoclasts. We found that methyl gallate significantly suppressed osteoclast formation through Akt and Btk-PLCγ2-Ca²⁺ signaling. The blockade of these pathways was confirmed through transduction of cells with a CA-Akt retrovirus and evaluation of Ca²⁺ influx intensity (staining with Fluo-3/AM). Indeed, methyl gallate downregulated the formation of actin ring-positive osteoclasts and resorption pit areas. In agreement with in vitro results, we found that administration of methyl gallate restored osteoporotic phenotype stimulated by acute systemic injection of lipopolysaccharide in vivo according to micro-computed tomography and histological analysis. Our data strongly indicate that methyl gallate may be useful for the development of a plant-based antiosteoporotic agent.

TCRP1 expression is associated with platinum sensitivity in human lung and ovarian cancer cells

Platinum-based drugs, including cisplatin (DDP) and oxaliplatin (L-OHP), are among the most potent chemotherapy drugs, and are widely utilized for the treatment of human lung and ovarian cancer. However, certain patients do not respond to platinum-based agents, and even those who initially benefit from the treatment will eventually exhibit resistance to these drugs. Although certain factors have been investigated for their potential to predict platinum resistance, more effective predictors for the improved management of patients with lung and ovarian cancer are required. Tongue cancer resistance-associated protein 1 (TCRP1) is a newly identified gene, which was cloned from a multi-drug resistant cell line of tongue cancer. Previous data has shown that TCRP1 is able to mediate DDP resistance in human oral squamous cell carcinoma cells. However, the contribution of TCRP1 to the resistance of platinum agents in human lung and ovarian cancer cells remains to be elucidated. Our previous study showed that TCRP1 expression levels in samples of lung and ovarian cancer were significantly increased compared with normal controls. In the present study, it was demonstrated that TCRP1 contributed to the resistance to DDP and L-OHP in human lung and ovarian cancer cells. Knockdown of TCRP1 resensitized the cells to the platinum-based agents. The present study identified a positive correlation between TCRP1 expression and primary resistance to DDP and L-OHP in lung cancer cells. In addition, it was observed that cells treated with nuclear factor (NF)-κB inhibitor BAY 11-7082 displayed increased sensitivity to DDP and L-OHP. The results of the present study suggested that TCRP1 may be associated with resistance to DDP and L-OHP in lung and ovarian cancer cells, and the Akt/NF-κB signaling pathway may be involved in the functioning of TCRP1. These findings identify TCRP1 as a potential predictor of platinum resistance in the treatment of lung and ovarian cancer.

Ethanolic extract of Schizonepeta tenuifolia attenuates osteoclast formation and activation in vitro and protects against lipopolysaccharide-induced bone loss in vivo

Background

Excessive osteoclast activity is a major cause of metabolic bone disorders, such as osteopenia, rheumatoid arthritis, and osteoporosis. Thus, discovery of agents targeting osteoclast differentiation and bone resorption is important for development of novel treatments for bone diseases. It has been demonstrated that ethanolic extract of schizonepeta tenuifolia (EEST) has potent anti-oxidant and anti-inflammatory activities. However, the beneficial effects of EEST on bone metabolism have not been studied. Therefore, we intend to investigate the effects of EEST on osteoclast differentiation.

Methods

We examined the effects and mechanisms of action of the EEST on osteoclastogenesis in vitro in bone marrow macrophages (BMMs) stimulated with receptor activator of nuclear factor kappa-B ligand (RANKL) and in vivo using a mouse model of lipopolysaccharide (LPS)-induced bone destruction.

Results

We found that EEST inhibited phosphorylation of Akt and IkB at early stages of RANKL-induced osteoclastogenesis. Furthermore, EEST negatively controlled the transcription and translation levels of nuclear factor of activated T cells c1 (NFATc1) and the translation level of c-Fos at the final stage of osteoclast differentiation. Reflecting these effects, EEST blocked both filamentous actin (F-actin) ring formation and bone resorbing activity of mature osteoclasts in vitro. The inhibitory effects of EEST on osteoclast formation and activity were observed in an LPS-mediated bone erosion mouse model using micro-CT and histological analysis.

Conclusions

EEST is a potential agent that is able to treat osteoclast-related bone diseases, such as osteoporosis.

The blocking of uPAR suppresses lipopolysaccharide-induced inflammatory osteoclastogenesis and the resultant bone loss through attenuation of integrin β3/Akt pathway

Introduction

Chronic inflammatory diseases, such as rheumatoid arthritis and periodontitis, cause the bone destruction by promotion of the differentiation of monocyte/macrophage lineage cells into mature osteoclasts (OCs) with active bone‐resorbing character. However, the detailed mechanisms underlying this disorder remain unclear. We herein investigated the role of urokinase plasminogen activator receptor (uPAR) in the bone destruction caused by chronic inflammation.

Methods

We investigated that the effect of uPAR on inflammatory OC formation induced by lipopolysaccharide (LPS) in inflammatory diseases.

Results

We found that the LPS more weakly induced OC formation and the resultant bone loss in uPAR‐deficient mice than in wild‐type mice. Additionally, we demonstrated that uPAR significantly potentiated LPS‐induced OC formation of RAW264.7 mouse monocyte/macrophage linage cells in integrin β3/Akt‐dependent manner. Moreover, we showed that the blocking of uPAR function by the administration of anti‐uPAR neutralizing antibody significantly attenuated the LPS‐induced OC formation and the resultant bone loss in mice.

Conclusions

These results strongly suggest that uPAR negatively regulates the LPS‐induced inflammatory OC formation and the resultant bone loss mediated through the integrin β3/Akt pathway. Our findings partly clarify the molecular mechanisms underlying bone destruction caused by chronic inflammatory diseases, and would benefit research on identifying antibody therapy for the treatment of these diseases.

Identification of candidate genes for myeloma-induced osteocyte death based on microarray data

Background

The study was aimed to investigate the molecular mechanisms of osteocyte death in multiple myeloma (MM) patients.

Methods

GSE27372 was downloaded from Gene Expression Omnibus, including three HOB-01 (osteocyte cell line) control samples and three HOB-01 samples co-cultured with JJN3 (human MM cell line). After the differentially expressed genes (DEGs) were identified by Student’s t test method, enrichment analyses were performed for them using DAVID software. Using TRANSFAC, TSGene, and tumor-associated gene (TAG) databases, functional annotation was conducted for the DEGs. Additionally, protein-protein interaction (PPI) network and sub-network analyses were performed using STRING database and Cytoscape software.

Results

Total 393 DEGs were identified, including 22 transcription factors (e.g., KLF4 and IRF8) and 37 TAGs. Enrichment analysis suggested that EGF, S1PR1, and NPY1R were enriched in the function of circulatory system development. EGF (degree = 31) and EGR1 (degree = 19) had high degrees and interactions in the PPI network. In the sub-network, S1PR1, C3AR1, and NPY1R could interact with each other.

Conclusions

These DEGs might participate in the osteocyte apoptosis induced by myeloma cells. These findings might provide a theoretical basis for a better understanding of the osteolysis in MM patients.

Targeting leiomyomas with all-trans-retinoic acid at phosphoinositide 3-kinase pathway suppression: Effective roles of β-catenin and of signaling interactions

AIM

Leiomyomas, monoclonal tumors developed by the transformation of myometrium somatic stem cells, are a major health concern that can severely impair quality of life. Pathological alterations of signaling pathways have been recognized as a key feature in a variety of human diseases. Our objective was to analyze treatment with all-trans-retinoic acid (ATRA) by suppression of the phosphoinositide 3-kinase (PI3K) pathway on growth, signaling pattern and interactions among PI3K/B-cell lymphoma 2 (Bcl2)/retinol leiomyoma proteins.

METHODS

Cultures of paired myometrium and leiomyoma cells from premenopausal women undergoing hysterectomy were collected. Western blot and analysis of variance were used for analysis.

RESULTS

Significant differences were detected between treatment with ATRA alone or with LY294002 (a PI3K growth suppressor) in response to treatment and among cell samples and cell numbers. Leiomyoma cells were less affected. Immunochemical analysis of signaling patterns demonstrated that treatments affected most of the examined protein levels differently. Significant differences between the cell type responses to treatment in pyruvate phosphate dikinase 1 (pPDK1), Bad and pβ-catenin levels were identified. The pβ-catenin level showed highly significant interaction between response to treatment and cell type.

CONCLUSIONS

ATRA treatment on PI3K pathway suppression significantly affected growth, signaling pattern and interactions among PI3K/Bcl2/retinol proteins involved in the growth, survival and apoptosis of leiomyomas. Interpretation of our results suggests that increasing knowledge of the role of signaling interplay in the pathogenesis of leiomyomas may present an opportunity to use specific signal transduction inhibitors for treating and preventing this disorder.

Dihydroartemisinin prevents breast cancer-induced osteolysis via inhibiting both breast caner cells and osteoclasts

Bone is the most common site of distant relapse in breast cancer, leading to severe complications which dramatically affect the patients’ quality of life. It is believed that the crosstalk between metastatic breast cancer cells and osteoclasts is critical for breast cancer-induced osteolysis. In this study, the effects of dihydroartemisinin (DHA) on osteoclast formation, bone resorption, osteoblast differentiation and mineralization were initially assessed in vitro, followed by further investigation in a titanium-particle-induced osteolysis model in vivo. Based on the proved inhibitory effect of DHA on osteolysis, DHA was further applied to MDA-MB-231 breast cancer-induced mouse osteolysis model, with the underlying molecular mechanisms further investigated. Here, we verified for the first time that DHA suppressed osteoclast differentiation, F-actin ring formation and bone resorption through suppressing AKT/SRC pathways, leading to the preventive effect of DHA on titanium-particle-induced osteolysis without affecting osteoblast function. More importantly, we demonstrated that DHA inhibited breast tumor-induced osteolysis through inhibiting the proliferation, migration and invasion of MDA-MB-231 cells via modulating AKT signaling pathway. In conclusion, DHA effectively inhibited osteoclastogenesis and prevented breast cancer-induced osteolysis.

Dissecting the multiple myeloma-bone microenvironment reveals new therapeutic opportunities

Multiple myeloma is a plasma cell skeletal malignancy. While therapeutic agents such as bortezomib and lenalidomide have significantly improved overall survival, the disease is currently incurable with the emergence of drug resistance limiting the efficacy of chemotherapeutic strategies. Failure to cure the disease is in part due to the underlying genetic heterogeneity of the cancer. Myeloma progression is critically dependent on the surrounding microenvironment. Defining the interactions between myeloma cells and the more genetically stable hematopoietic and mesenchymal components of the bone microenvironment is critical for the development of new therapeutic targets. In this review, we discuss recent advances in our understanding of how microenvironmental elements contribute to myeloma progression and, therapeutically, how those elements can or are currently being targeted in a bid to eradicate the disease.

Novel therapeutic strategies for multiple myeloma

Multiple myeloma (MM) is a plasma-cell malignancy which remains incurable despite the recent emergence of multiple novel agents. Importantly, recent genetic and molecular analyses have revealed the complexity and heterogeneity of this disease, highlighting the need for therapeutic strategies to eliminate all clones. Moreover, the bone marrow microenvironment, including stromal cells and immune cells, plays a central role in MM pathogenesis, promoting tumor cell growth, survival, and drug resistance. New classes of agents including proteasome inhibitors, immunomodulatory drugs, monoclonal antibodies, and histone deacetylase inhibitors have shown remarkable efficacy; however, novel therapeutic approaches are still urgently needed to further improve patient outcomes. In this review, we discuss the recent advances and future strategies to ultimately develop MM therapies with curative potential.

Syringetin suppresses osteoclastogenesis mediated by osteoblasts in human lung adenocarcinoma

Bone metastasis in lung cancer results in an unfavorable outcome for patients by not only impairing the quality of life, yet also increasing the cancer-related death rates. In the present study, we discuss a novel treatment strategy that may benefit these patients. Human CD14+ monocytes treated with macrophage-colony stimulating factor (M-CSF)/receptor activator of nuclear factor κB ligand (RANKL) differentiated into osteoclasts, whereas syringetin (SGN), a flavonoid derivative found in both grapes and wine, suppressed the osteoclastogenesis in vitro in a dose-dependent manner. In addition, SGN inhibited osteoclast formation induced by human lung adenocarcinoma A549 and CL1-5 cells. The associated signaling transduction pathway in osteoclastogenesis and SGN inhibition was found to be via the AKT/mammalian target of rapamycin (mTOR) signaling pathway. Blocking AKT and mTOR by respective inhibitors significantly decreased lung adenocarcinoma-mediated osteoclastogenesis. Moreover, SGN regulated the lung adenocarcinoma-mediated interaction between osteoblasts and osteoclasts by suppressing the stimulatory effect of lung adenocarcinoma on M-CSF and RANKL production in osteoblasts, and reversing the inhibitory effect of the lung adenocarcinoma on OPG production in osteoblasts. The present study has two novel findings. It is the first to illustrate lung adenocarcinoma-mediated interaction between osteoblasts and osteoclasts, leading to osteolytic bone metastasis. It also reveals that SGN, a flavonoid derivative, directly inhibits osteoclastogenesis and reverses lung adenocarcinoma-mediated osteoclastogenesis. In conclusion, the present study suggests that SGN, a natural compound, prevents and treats bone metastasis in patients with lung cancer.

Impaired bone homeostasis in amyotrophic lateral sclerosis mice with muscle atrophy

There is an intimate relationship between muscle and bone throughout life. However, how alterations in muscle functions in disease impact bone homeostasis is poorly understood. Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by progressive muscle atrophy. In this study we analyzed the effects of ALS on bone using the well established G93A transgenic mouse model, which harbors an ALS-causing mutation in the gene encoding superoxide dismutase 1. We found that 4-month-old G93A mice with severe muscle atrophy had dramatically reduced trabecular and cortical bone mass compared with their sex-matched wild type (WT) control littermates. Mechanically, we found that multiple osteoblast properties, such as the formation of osteoprogenitors, activation of Akt and Erk1/2 pathways, and osteoblast differentiation capacity, were severely impaired in primary cultures and bones from G93A relative to WT mice; this could contribute to reduced bone formation in the mutant mice. Conversely, osteoclast formation and bone resorption were strikingly enhanced in primary bone marrow cultures and bones of G93A mice compared with WT mice. Furthermore, sclerostin and RANKL expression in osteocytes embedded in the bone matrix were greatly up-regulated, and β-catenin was down-regulated in osteoblasts from G93A mice when compared with those of WT mice. Interestingly, calvarial bone that does not load and long bones from 2-month-old G93A mice without muscle atrophy displayed no detectable changes in parameters for osteoblast and osteoclast functions. Thus, for the first time to our knowledge, we have demonstrated that ALS causes abnormal bone remodeling and defined the underlying molecular and cellular mechanisms.

Myelomatous plasma cells display an aberrant gene expression pattern similar to that observed in normal memory B cells

Memory B cells (MBCs) remain in a quiescent state for years, expressing pro-survival and anti-apoptotic factors while repressing cell proliferation and activation genes. During their differentiation into plasma cells (PCs), their expression pattern is reversed, with a higher expression of genes related to cell proliferation and activation, and a lower expression of pro-survival genes. To determine whether myelomatous PCs (mPCs) share characteristics with normal PCs and MBCs and to identify genes involved in the pathophysiology of multiple myeloma (MM), we compared gene expression patterns in these three cell sub-types. We observed that mPCs had features intermediate between those of MBCs and normal PCs, and identified 3455 genes differentially expressed in mPCs relative to normal PCs but with a similar expression pattern to that in MBCs. Most of these genes are involved in cell death and survival, cell growth and proliferation and protein synthesis. According to our findings, mPCs have a gene expression pattern closer to a MBC than a PC with a high expression of genes involved in cell survival. These genes should be physiologically inactivated in the transit from MBC to PC, but remain overexpressed in mPCs and thus may play a role in the pathophysiology of the disease.

Wedelolactone inhibits breast cancer-induced osteoclastogenesis by decreasing Akt/mTOR signaling

The bone is the most common metastatic site of breast cancer. Bone metastasis causes pain, pathologic fractures, and severely reduces the quality of life. Breast cancer causes osteolytic bone metastasis, which is dependent on osteoclast-mediated bone resorption. While current treatments rely on palliative anti-resorptive agents, there is a need to develop a drug based on potential alternative therapies. This study is the first to determine that wedelolactone (WDL), a natural coumarin isolated from plants, can inhibit breast cancer-mediated osteoclastogenesis. Osteoclasts were generated from human CD14(+) monocytes cultured with M-CSF/RANKL and WDL suppressed human osteoclast differentiation and activity in vitro in a dose-dependent manner. Moreover, WDL inhibited the upregulation of osteoclasts stimulated by MDA‑MB‑231 breast cancer cells. The activity of WDL on osteoclasts and breast cancer-mediated osteoclastogenesis was associated with the inhibition of Akt/mammalian target of the rapamycin signaling pathway (mTOR). Blocking Akt and mTOR by specific inhibitors significantly decreased osteoclast differentiation and bone resorption. Furthermore, WDL regulated breast cancer-enhanced interaction of osteoblasts and osteoclasts by decreasing M-CSF expression in MDA‑MB‑231-stimulated osteoblasts. Thus, this study suggests that WDL may be a potential natural agent for preventing and treating bone destruction in patients with bone metastasis due to breast cancer.

AKT as a therapeutic target in multiple myeloma

INTRODUCTION

Multiple myeloma remains an incurable malignancy with poor survival. Novel therapeutic approaches capable of improving outcomes in patients with multiple myeloma are urgently required. AKT is a central node in the phosphatidylinositol-3-kinase/AKT/mammalian target of rapamycin signaling pathway with high expression in advanced and resistant multiple myeloma. AKT contributes to multiple oncogenic functions in multiple myeloma which may be exploited therapeutically. Promising preclinical data has lent support for pursuing further development of AKT inhibitors in multiple myeloma. Lead drugs are now entering the clinic.

AREAS COVERED

The rationale for AKT inhibition in multiple myeloma, pharmacological subtypes of AKT inhibitors in development, available results of clinical studies of AKT inhibitors and suitable drug partners for further development in combination with AKT inhibition in multiple myeloma are discussed.

EXPERT OPINION

AKT inhibitors are a welcome addition to the armamentarium against multiple myeloma and promising clinical activity is being reported from ongoing trials in combination with established and/or novel treatment approaches. AKT inhibitors may be set to improve patient outcomes when used in combination with synergistic drug partners.