Tumor Necrosis Factor-α Blunts the Osteogenic Effects of Muscle Cell-Derived Extracellular Vesicles by Affecting Muscle Cells.

Extracellular vesicles (EVs) play crucial roles in physiological and pathophysiological processes. Although studies have described muscle-bone interactions via humoral factors, we reported that EVs from C2C12 muscle cells (Myo-EVs) suppress osteoclast formation. Current clinical evidence suggests that inflammation induces both sarcopenia and osteoporosis. Although tumor necrosis factor-α (TNF-α) is a critical proinflammatory factor, the influences of TNF-α on muscle-bone interactions and Myo-EVs are still unclear. In the present study, we investigated the effects of TNF-α stimulation of C2C12 cells on osteoclast formation and osteoblastic differentiation modulated by Myo-EVs in mouse cells. TNF-α significantly decreased the protein amount in Myo-EVs, but did not affect the Myo-EV size distribution. TNF-α treatment of C2C12 myoblasts significantly decreased the suppression of osteoclast formation induced by Myo-EVs from C2C12 myoblasts in mouse bone marrow cells. Moreover, TNF-α treatment of C2C12 myoblasts in mouse preosteoclastic Raw 264.7 cells significantly limited the Myo-EV-induced suppression of osteoclast formation and decreased the Myo-EV-induced increase in mRNA levels of osteoclast formation-related genes. On the other hand, TNF-α treatment of C2C12 muscle cells significantly decreased the degree of Myo-EV-promoted mRNA levels of Osterix and osteocalcin, as well as ALP activity in mouse mesenchymal ST-2 cells. TNF-α also significantly decreased miR196-5p level in Myo-EVs from C2C12 myoblasts in quantitative real-time PCR. In conclusion, TNF-α stimulation of C2C12 muscle cells blunts both the osteoclast formation suppression and the osteoblastic differentiation promotion that occurs due to Myo-EVs in mouse cells. Thus, TNF-α may disrupt the muscle-bone interactions by direct Myo-EV modulation.

Extracellular vesicles secreted from mouse muscle cells improve delayed bone repair in diabetic mice.

Humoral factors that are secreted from skeletal muscles can regulate bone metabolism and contribute to muscle-bone relationships. Although extracellular vesicles (EVs) play important roles in physiological and pathophysiological processes, the roles of EVs that are secreted from skeletal muscles in bone repair have remained unclear. In the present study, we investigated the effects of the local administration of muscle cell-derived EVs on bone repair in control and streptozotocin-treated diabetic female mice. Muscle cell-derived EVs (Myo-EVs) were isolated from the conditioned medium from mouse muscle C2C12 cells by ultracentrifugation, after which Myo-EVs and gelatin hydrogel sheets were transplanted on femoral bone defect sites. The local administration of Myo-EVs significantly improved delayed bone repair that was induced by the diabetic state in mice 9 days after surgery. Moreover, this administration significantly enhanced the ratio of bone volume to tissue volume at the damaged sites 9 days after surgery in the control mice. Moreover, the local administration of Myo-EVs significantly blunted the number of Osterix-positive cells that were suppressed by the diabetic state at the damage sites after bone injury in mice. Additionally, Myo-EVs significantly blunted the mRNA levels of Osterix and alkaline phosphatase (ALP), and ALP activity was suppressed by advanced glycation end product 3 in ST2 cells that were treated with bone morphogenetic protein-2. In conclusion, we have shown for the first time that the local administration of Myo-EVs improves delayed bone repair that is induced by the diabetic state through an enhancement of osteoblastic differentiation in female mice.

Role of peripheral myelin protein 22 in chronic exercise-induced interactions of muscle and bone in mice.

Exercise is important for the prevention and treatment of sarcopenia and osteoporosis. Although the interactions between skeletal muscles and bone have recently been reported, the myokines linking muscle to bone during exercise remain unknown. We previously revealed that chronic exercise using treadmill running blunts ovariectomy-induced osteopenia in mice. We herein performed an RNA sequence analysis of the gastrocnemius and soleus muscles of male mice with or without chronic exercise to identify the myokines responsible for the effects of chronic exercise on the muscle/bone relationship. We extracted peripheral myelin protein 22 (PMP22) as a humoral factor that was putatively induced by chronic exercise in the soleus and gastrocnemius muscles of mice from the RNA sequence analysis. Chronic exercise significantly enhanced the expression of PMP22 in the gastrocnemius and soleus muscles of female mice. PMP22 suppressed macrophage-colony stimulating factor and receptor activator factor κB ligand-induced increases in the expression of osteoclast-related genes and osteoclast formation from mouse bone marrow cells. Moreover, PMP22 significantly inhibited osteoblast differentiation, alkaline phosphatase activity, and mineralization in mouse osteoblast cultures; however, the overexpression of PMP22 did not affect muscle phenotypes in mouse muscle C2C12 cells. A simple regression analysis revealed that PMP22 mRNA levels in the gastrocnemius and soleus muscles were positively related to cortical bone mineral density at the femurs of mice with or without chronic exercise. In conclusion, we identified PMP22 as a novel myokine induced by chronic exercise in mice. We first showed that PMP22 suppresses osteoclast formation and the osteoblast phenotype in vitro.

Irisin improves delayed bone repair in diabetic female mice.

INTRODUCTION: Irisin is a proteolytic product of fibronectin type II domain-containing 5, which is related to the improvement in glucose metabolism. Numerous studies have suggested that irisin is a crucial myokine linking muscle to bone in physiological and pathophysiological states. MATERIALS AND METHODS: We examined the effects of local irisin administration with gelatin hydrogel sheets and intraperitoneal injection of irisin on the delayed femoral bone repair caused by streptozotocin (STZ)-induced diabetes in female mice. We analyzed the femurs of mice using quantitative computed tomography and histological analyses and then measured the mRNA levels in the damaged mouse tissues. RESULTS: Local irisin administration significantly blunted the delayed bone repair induced by STZ 10 days after a femoral bone defect was generated. Local irisin administration significantly blunted the number of Osterix-positive cells that were suppressed by STZ at the damaged site 4 days after a femoral bone defect was generated, although it did not affect the mRNA levels of chondrogenic and adipogenic genes 4 days after bone injury in the presence or absence of diabetes. On the other hand, intraperitoneal injection of irisin did not affect delayed bone repair induced by STZ 10 days after bone injury. Irisin significantly blunted the decrease in Osterix mRNA levels induced by advanced glycation end products or high-glucose conditions in ST2 cells in the presence of bone morphogenetic protein-2. CONCLUSIONS: We first showed that local irisin administration with gelatin hydrogel sheets improves the delayed bone repair induced by diabetic state partially by enhancing osteoblastic differentiation.

Role of Macrophages and Plasminogen Activator Inhibitor-1 in Delayed Bone Repair Induced by Glucocorticoids in Mice.

Glucocorticoids delay fracture healing and induce osteoporosis. However, the mechanisms by which glucocorticoids delay bone repair have yet to be clarified. Plasminogen activator inhibitor-1 (PAI-1) is the principal inhibitor of plasminogen activators and an adipocytokine that regulates metabolism. We herein investigated the roles of macrophages in glucocorticoid-induced delays in bone repair after femoral bone injury using PAI-1-deficient female mice intraperitoneally administered with dexamethasone (Dex). Dex significantly decreased the number of F4/80-positive macrophages at the damaged site two days after femoral bone injury. It also attenuated bone injury-induced decreases in the number of hematopoietic stem cells in bone marrow in wild-type and PAI-1-deficient mice. PAI-1 deficiency significantly weakened Dex-induced decreases in macrophage number and macrophage colony-stimulating factor (M-CSF) mRNA levels at the damaged site two days after bone injury. It also significantly ameliorated the Dex-induced inhibition of macrophage phagocytosis at the damaged site. In conclusion, we herein demonstrated that Dex decreased the number of macrophages at the damaged site during early bone repair after femoral bone injury partly through PAI-1 and M-CSF in mice.

MicroRNA-196a-5p in Extracellular Vesicles Secreted from Myoblasts Suppresses Osteoclast-like Cell Formation in Mouse Cells.

Muscle/bone interaction has been recently noted. Extracellular vesicles (EVs) play a vital role in physiological and pathophysiological processes by transferring microRNA (miRNA) to distant tissues. We previously reported that EVs secreted from C2C12 myoblasts (Myo-EVs) suppress osteoclast differentiation. In the present study, we identified 4 miRNAs in Myo-EVs that suppressed osteoclast-like cell formation in Raw264.7 cells using small RNA sequencing analysis. Among them, miR-196a-5p expression was higher in C2C12 cells compared to mouse osteoblasts and bone marrow cells. Transfection of miR-196a-5p mimic suppressed the mRNA levels of osteoclast-related genes and mitochondrial energy metabolism induced by receptor activator of nuclear factor-κB ligand in Raw264.7 cells. In contrast, miR-196a-5p mimic enhanced osteoblastic differentiation in ST-2 cells and MC3T3-E1 cells. In conclusion, we demonstrated that miR-196-5p suppresses osteoclast-like cell formation and mitochondrial energy metabolism in mouse cells, suggesting that it might be a crucial factor for muscle/bone interaction via EVs.

Role of irisin in effects of chronic exercise on muscle and bone in ovariectomized mice.

INTRODUCTION: Exercise is beneficial for the prevention and treatment of osteoporosis. Skeletal muscle affects other tissues via myokines, the release of which is regulated by acute exercise. However, the effects of chronic exercise on myokines linking muscle to bone have not been fully elucidated. Therefore, we investigated the effects of chronic exercise on bone and myokines using ovariectomized (OVX) mice. MATERIALS AND METHODS: Treadmill exercise with moderate intensity was performed for 8 weeks after OVX or sham surgery. We measured bone mineral density (BMD) at the femurs and tibias of mice by quantitative computed tomography and myokine mRNA levels in the gastrocnemius and soleus muscles. RESULTS: Treadmill exercise ameliorated decreases in trabecular and cortical BMD in the femurs of OVX mice. Irisin is a proteolytic product of fibronectin type III domain-containing 5 (Fndc5). Among the myokines examined, treadmill exercise increased irisin protein and Fndc5 mRNA levels in the gastrocnemius and soleus muscles of sham and OVX mice. Treadmill exercise increased peroxisome proliferator-activated receptor γ coactivator-1α mRNA levels in the gastrocnemius muscles of mice. Fndc5 mRNA levels in the gastrocnemius muscles positively correlated with trabecular BMD, but not with cortical BMD, at the femurs and tibias of mice in simple regression analyses. CONCLUSIONS: We demonstrated that chronic exercise elevated irisin expression in the gastrocnemius and soleus muscles of estrogen-deficient mice. Irisin might be related to increases in trabecular BMD in mice; however, further studies are needed to clarify the involvement of irisin in the effects of chronic exercise on muscle/bone interactions.

Role of plasminogen activator inhibitor-1 in muscle wasting induced by a diabetic state in female mice.

Muscle wasting is a complication in patients with diabetes and leads to a reduced quality of life. However, the detailed mechanisms of diabetes-induced muscle wasting remain unknown. Plasminogen activator inhibitor-1 (PAI-1), a serine protease inhibitor that suppresses plasminogen activator activity, is involved in the pathophysiology of various diseases, including diabetes. In the present study, we examined the role of endogenous PAI-1 in the decrease in muscle mass and the impaired grip strength induced by the diabetic state by employing streptozotocin (STZ)-treated PAI-1-deficient female mice. The analyses of skeletal muscles and grip strength were performed in PAI-1-deficient and wild-type mice 4 weeks after the induction of a diabetic state by STZ administration. PAI-1 deficiency did not affect muscle mass in the lower limbs measured by quantitative computed tomography or tissue weights of the tibialis anterior, gastrocnemius and soleus muscles of female mice with or without STZ treatment. On the other hand, PAI-1 deficiency significantly aggravated grip strength decreased by STZ in female mice. PAI-1 deficiency did not affect the mRNA levels of Pax7, MyoD, myogenin or myosin heavy chain in either the tibialis anterior or soleus muscles of female mice with or without STZ treatment. In conclusion, we revealed for the first time that PAI-1 deficiency aggravates grip strength impaired by the diabetic state in female mice, although it did not affect diabetes-decreased muscle mass.

Influence of Angptl1 on osteoclast formation and osteoblastic phenotype in mouse cells.

BACKGROUND: Osteoblasts and osteoclasts play important roles during the bone remodeling in the physiological and pathophysiological states. Although angiopoietin family Angiopoietin like proteins (Angptls), including Angptl1, have been reported to be involved in inflammation, lipid metabolism and angiogenesis, the roles of Angptl1 in bone have not been reported so far. METHODS: We examined the effects of Angptl1 on the osteoblast and osteoclast phenotypes using mouse cells. RESULTS: Angptl1 significantly inhibited the osteoclast formation and mRNA levels of tartrate-resistant acid phosphatase and cathepsin K enhanced by receptor activator of nuclear factor κB ligand in RAW 264.7 and mouse bone marrow cells. Moreover, Angptl1 overexpression significantly enhanced Osterix mRNA levels, alkaline phosphatase activity and mineralization induced by bone morphogenetic protein-2 in ST2 cells, although it did not affect the expression of osteogenic genes in MC3T3-E1 and mouse osteoblasts. On the other hand, Angptl1 overexpression significantly reduced the mRNA levels of peroxisome proliferator-activated receptor γ and adipocyte protein-2 as well as the lipid droplet formation induced by adipogenic medium in 3T3-L1 cells. CONCLUSIONS: The present study first indicated that Angptl1 suppresses and enhances osteoclast formation and osteoblastic differentiation in mouse cells, respectively, although it inhibits adipogenic differentiation of 3T3-L1 cells. These data suggest the possibility that Angptl1 might be physiologically related to bone remodeling.

Roles of Olfactomedin 1 in Muscle and Bone Alterations Induced by Gravity Change in Mice.

Microgravity causes both muscle and bone loss. Although we previously revealed that gravity change influences muscle and bone through the vestibular system in mice, its detailed mechanism has not been elucidated. In this study, we investigated the roles of olfactomedin 1 (OLFM1), whose expression was upregulated during hypergravity in the soleus muscle, in mouse bone cells. Vestibular lesion significantly blunted OLFM1 expression in the soleus muscle and serum OLFM1 levels enhanced by hypergravity in mice. Moreover, a phosphatidylinositol 3-kinase inhibitor antagonized shear stress-enhanced OLFM1 expression in C2C12 myotubes. As for the effects of OLFM1 on bone cells, OLFM1 inhibited osteoclast formation from mouse bone marrow cells and mouse preosteoclastic RAW264.7 cells. Moreover, OLFM1 suppressed RANKL expression and nuclear factor-κB signaling in mouse osteoblasts. Serum OLFM1 levels were positively related to OLFM1 mRNA levels in the soleus muscle and trabecular bone mineral density of mice. In conclusion, we first showed that OLFM1 suppresses osteoclast formation and RANKL expression in mouse cells.

Plasminogen activator inhibitor-1 deficiency suppresses osteoblastic differentiation of mesenchymal stem cells in mice.

Plasminogen activator inhibitor-1 (PAI-1) is known as an inhibitor of fibrinolytic system. Previous studies suggest that PAI-1 is involved in the pathogenesis of osteoporosis induced by ovariectomy, diabetes, and glucocorticoid excess in mice. However, the roles of PAI-1 in early-stage osteogenic differentiation have remained unknown. In the current study, we investigated the roles of PAI-1 in osteoblastic differentiation of mesenchymal stem cells (MSCs) using wild-type (WT) and PAI-1-deficient (PAI-1 KO) mice. PAI-1 mRNA levels were increased with time during osteoblastic differentiation of MSCs or mesenchymal ST-2 cells. However, the increased PAI-1 levels declined at the mineralization phase in the experiment using MC3T3-E1 cells. PAI-1 deficiency significantly blunted the expression of osteogenic gene, such as osterix and alkaline phosphatase enhanced by bone morphogenetic protein (BMP)-2 in bone marrow-derived MSCs (BM-MSCs), adipose-tissue-derived MSCs (AD-MSCs), and bone marrow stromal cells of mice. Moreover, a reduction in endogenous PAI-1 levels by small interfering RNA significantly suppressed the expression of osteogenic gene in ST-2 cells. Plasmin did not affect osteoblastic differentiation of AD-MSCs induced by BMP-2 with or without PAI-1 deficiency. PAI-1 deficiency and a reduction in endogenous PAI-1 levels did not affect the phosphorylations of receptor-specific Smads by BMP-2 and transforming growth factor-ß in AD-MSCs and ST-2 cells, respectively. In conclusion, we first showed that PAI-1 is crucial for the differentiation of MSCs into osteoblasts in mice.

Factors influencing the surface modification of mesenchymal stem cells with fluorescein-pegylated lipids.

Artificial introduction of functional molecules on the cell surface may be a promising way to improve the therapeutic effects of cell therapy. Pegylated lipids are conventionally used in drug carriers. The lipid part of pegylated lipids noncovalently interacts with the cell surface. However, little information is available regarding conditions for cell-surface modification by using pegylated lipids. In this study, we synthesized fluorescein-labeled pegylated lipids and evaluated the factors that affect modification efficiency by using human mesenchymal stem cells (hMSCs). As the concentration of the pegylated lipid as well as the exposure time increased, the modification efficiency increased. The modification efficiency at 37°C was 20- and 3-fold higher than that at 4°C and 25°C, respectively. In addition, with an increase in the molecular weight of polyethylene glycol (PEG), more pegylated lipids were extracellularly distributed than those intracellularly distributed. At the optimal condition, pegylated lipids were observed mainly on the cell membrane by confocal microscopy. In contrast, the cell condition (adherent or nonadherent) had little or no effect on the cell-surface modification efficiency. The results of this study will be useful for constructing an optimal modification method for introducing functional molecules on the cell surface.

Effects of Growth Hormone on Muscle and Bone in Female Mice: Role of Follistatin.

The interactions between muscle and bone are noted in the clinical relationships between sarcopenia and osteoporosis. Myokines secreted from the skeletal muscles play roles in muscle-bone interactions related to various physiological and pathophysiological states. Although numerous evidence suggests that growth hormone (GH) influences both muscle and bone, the effects of GH on the muscle-bone interactions have remained unknown. We, therefore, investigated the influences of GH administration for 8 weeks on muscle and bone, including myokine expression, in mice with or without ovariectomy (OVX). GH administration significantly increased muscle mass in the whole body and lower limbs, as well as tissue weights of the extensor digitorum longus (EDL) and soleus muscles in mice with or without OVX. Moreover, it markedly increased grip strength in both mice. As for femurs, GH administration significantly increased cortical thickness and area in mice with or without OVX. Moreover, GH significantly blunted the decrease in the ratio of bone volume to tissue volume at the trabecular bone in mice with OVX. GH administration significantly decreased follistatin mRNA levels in the EDL, but not the soleus, muscles in mice with or without OVX, although it did not affect the other myokines examined. However, GH administration significantly elevated serum follistatin levels in mice. In conclusion, this study indicates that GH administration increases skeletal muscle mass and grip strength and cortical and trabecular bone-related parameters obtained by micro-computed tomography analyses in mice. However, myokine regulation might not be critical for the effects of GH on muscle and bone.

Matrix vesicles promote bone repair after a femoral bone defect in mice.

Matrix vesicles (MtVs) are one of the extracellular vesicles (EVs) secreted by osteoblasts. Although MtVs have a classically-defined function as an initiator of ossification and recent findings suggest a role for MtVs in the regulation of bone cell biology, the effects of MtVs on bone repair remain unclear. In the present study, we employed collagenase-released EVs (CREVs) containing abundant MtVs from mouse osteoblasts. CREVs were administered locally in gelatin hydrogels to damaged sites after a femoral bone defect in mice. CREVs exhibited the characteristics of MtVs with a diameter <200 nm. The local administration of CREVs significantly promoted the formation of new bone with increases in the number of alkaline phosphatase (ALP)-positive cells and cartilage formation at the damaged site after the femoral bone defect. However, the addition of CREVs to the medium did not promote the osteogenic differentiation of ST2 cells or the ALP activity or mineralization of mouse osteoblasts in vitro. In conclusion, we herein showed for the first time that MtVs enhanced bone repair after a femoral bone defect partly through osteogenesis and chondrogenesis in mice. Therefore, MtVs have potential as a tool for bone regeneration.

Renal failure suppresses muscle irisin expression, and irisin blunts cortical bone loss in mice.

BACKGROUND: Chronic renal failure induces bone mineral disorders and sarcopenia. Skeletal muscle affects other tissues, including bone, by releasing myokines. However, the effects of chronic renal failure on the interactions between muscle and bone remain unclear. METHODS: We investigated the effects of renal failure on bone, muscle, and myokines linking muscle to bone using a mouse 5/6 nephrectomy (Nx) model. Muscle mass and bone mineral density (BMD) were analysed by quantitative computed tomography 8 weeks after Nx. RESULTS: Nephrectomy significantly reduced muscle mass in the whole body (12.1% reduction, P < 0.05), grip strength (10.1% reduction, P < 0.05), and cortical BMD at the femurs of mice (9.5% reduction, P < 0.01) 8 weeks after surgery, but did not affect trabecular BMD at the femurs. Among the myokines linking muscle to bone, Nx reduced the expression of irisin, a proteolytic product of fibronectin type III domain-containing 5 (Fndc5), in the gastrocnemius muscles of mice (38% reduction, P < 0.01). Nx increased myostatin mRNA levels in the gastrocnemius muscles of mice (54% increase, P < 0.01). In simple regression analyses, cortical BMD, but not trabecular BMD, at the femurs was positively related to Fndc5 mRNA levels in the gastrocnemius muscles of mice (r = 0.651, P < 0.05). The weekly administration of recombinant irisin to mice ameliorated the decrease in cortical BMD, but not muscle mass or grip strength, induced by Nx (6.2% reduction in mice with Nx vs. 3.3% reduction in mice with Nx and irisin treatment, P < 0.05). CONCLUSIONS: The present results demonstrated that renal failure decreases the expression of irisin in the gastrocnemius muscles of mice. Irisin may contribute to cortical bone loss induced by renal failure in mice as a myokine linking muscle to bone.

[Controlling Cell Dynamics by Cell-surface Modification].

Although the concept of a drug delivery system (DDS) is usually applied to conventional drug therapy, it is also important for cell-based therapy. The surface manipulation of living cells represents a powerful tool for controlling cell behaviors in the body, such as enhancement of cell-cell interactions, targeted delivery of cells, and protection from immunological rejection. Functional groups, including amines, thiols, and carbonyls, offer excellent opportunities for chemical modification through the formation of covalent bonds with exogenous molecules. Non-natural reactive groups introduced by metabolic labeling were recently utilized for targeted chemical modification. On the other hand, noncovalent strategies are also available; two major examples are electrostatic interaction with a negative charge on the cell surface and hydrophobic insertion or interaction with the cell membrane. In this study, we analyzed factors affecting cell surface modifications using PEG-lipid and succeeded in enhancing the efficacy of modification by cyclodextrin. Then, mesenchymal stem cells (MSCs), whose therapeutic effect has been demonstrated at the clinical stage and which have been clinically used as a drug, were decorated with PEG-lipid conjugates having a targeted ligand such as peptide or scFv, which are recognized by ICAM1. The peptide or scFv decoration enhanced the cell adhesion of MSCs on cytokine treated-endothelial cells. This technique will prompt the targeted delivery of MSCs to intended therapy sites, and underscores the promise of cell surface engineering as a tool for improving cell-based therapy.

Serpinb1a suppresses osteoclast formation.

Serpinb1a, a serine protease inhibitor family protein, has been implicated in immunoregulation and several metabolic disorders, such as diabetes and obesity; however, its roles in bone remain unknown. Therefore, we herein investigated the physiological functions of Serpinb1a in osteoclastic and osteoblastic differentiation using mouse cell lines. Serpinb1a overexpression markedly reduced the number of tartrate-resistant acid phosphatase (TRAP)- and calcitonin receptor-positive multinucleated cells increased by receptor activator nuclear factor κB ligand (RANKL) in mouse preosteoclastic RAW 264.7 cells. Moreover, it significantly decreased the mRNA levels of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), TRAP and cathepsin K in these cells. Regarding osteoblasts, Serpinb1a overexpression significantly reduced the mRNA levels of alkaline phosphatase (ALP) and osteocalcin as well as ALP activity induced by bone morphogenetic protein-2 (BMP-2) in mouse mesenchymal ST2 cells, although it did not alter osteoblast differentiation in mouse osteoblastic MC3T3-E1 cells. Concerning the pathophysiological relevance of Serpinb1a, Serpinb1a mRNA levels were decreased in the soleus and gastrocnemius muscles of mice 4 weeks after bilateral sciatic nerve resection. In conclusion, we herein revealed for the first time that Serpinb1a inhibited osteoclast formation induced by RANKL in RAW 264.7 cells and suppressed BMP-2-induced ALP activity in ST2 cells.

Effects of fluid flow shear stress to mouse muscle cells on the bone actions of muscle cell-derived extracellular vesicless.

The interactions between skeletal muscle and bone have been recently noted, and muscle-derived humoral factors related to bone metabolism play crucial roles in the muscle/bone relationships. We previously reported that extracellular vesicles from mouse muscle C2C12 cells (Myo-EVs) suppress osteoclast formation in mice. Although mechanical stress is included in extrinsic factors which are important for both muscle and bone, the detailed roles of mechanical stress in the muscle/bone interactions have still remained unknown. In present study, we examined the effects of fluid flow shear stress (FFSS) to C2C12 cells on the physiological actions of muscle cell-derived EV. Applying FFSS to C2C12 cells significantly enhanced muscle cell-derived EV-suppressed osteoclast formation and several osteoclast-related gene levels in mouse bone marrow cells in the presence of receptor activator nuclear factor κB ligand (RANKL). Moreover, FFSS to C2C12 cells significantly enhanced muscle cell-derived EV-suppressed mitochondria biogenesis genes during osteoclast formation with RANKL treatment. In addition, FFSS to C2C12 cells significantly enhanced muscle cell-derived EV-suppressed osteoclast formation and several osteoclast-related gene levels in Raw264.7 cells in the presence of RANKL. Small RNA-seq-analysis showed that FFSS elevated the expression of miR196a-5p and miR155-5p with the suppressive actions of osteoclast formation and low expression in mouse bone cells. On the other hand, muscle cell-derived EVs with or without FFSS to C2C12 cells did not affect the expression of osteogenic genes, alkaline phosphatase activity and mineralization in mouse osteoblasts. In conclusion, we first showed that FFSS to C2C12 cells enhances the suppressive effects of muscle cell-derived EVs on osteoclast formation in mouse cells. Muscle cell-derived EVs might be partly involved in the effects of mechanical stress on the muscle/bone relationships.

Role of tissue factor in delayed bone repair induced by diabetic state in mice.

BACKGROUND: Tissue factor (TF) is the primary activator of the extrinsic coagulation protease cascade. Although TF plays roles in various pathological states, such as thrombosis, inflammatory diseases, cancer, and atherosclerosis, its involvement in bone metabolism remains unknown. MATERIALS AND METHODS: The present study examined the roles of TF in delayed bone repair induced by a diabetic state in mice using wild-type (WT) and low TF-expressing (LTF) male mice. A diabetic state was induced by intraperitoneal injections of streptozotocin (STZ). RESULTS: A prolonged diabetic state significantly reduced total and trabecular bone mineral densities (BMD) as well as cortical bone thickness in WT and LTF mice; these BMD parameters were similar between WT and LTF mice treated with or without STZ. The diabetic state induced in WT mice delayed the repair of the femur following injury. The diabetic state induced in LTF mice was associated with further delays in bone repair. In in vitro experiments, TF significantly decreased receptor activator of nuclear factor-κB ligand-induced osteoclast formation and osteoclastogenic gene expression in RAW264.7 cells. However, it did not affect the gene expression levels of runt-related transcription factor 2 and osterix as well as alkaline phosphatase activity in mouse primary osteoblasts. CONCLUSION: Low TF state was associated with enhanced bone repair delay induced by diabetic state in mice. The TF-induced suppression of bone remodeling may be a contributing factor to the protective effects of TF against delayed bone repair in a diabetic state.

Myonectin inhibits the differentiation of osteoblasts and osteoclasts in mouse cells.

Myonectin is a myokine, which is involved in the pathophysiology of diabetes and obesity, and various myokines are involved in the interactions between skeletal muscle and bone. However, roles of myonectin in bone have still remained unknown. We therefore examined the effects of myonectin on mouse osteoblast and osteoclast differentiation in vitro. Myonectin significantly suppressed the mRNA levels of osteogenic genes and alkaline phosphatase (ALP) activity in mouse osteoblasts. As for osteoclasts, myonectin significantly suppressed osteoclast formation as well as the mRNA levels of osteoclast-related genes enhanced by receptor activator nuclear factor κB ligand (RANKL) from mouse monocytic RAW264.7 cells. Moreover, myonectin significantly suppressed osteoclast formation from mouse bone marrow cells in the presence of macrophage-colony stimulating factor and RANKL. On the other hand, myonectin significantly suppressed RANKL-induced oxygen consumption rate and peroxisome proliferator-activated receptor γ coactivator-1ß mRNA levels in RAW264.7 cells, although myonectin did not affect these mitochondrial biogenesis parameters in mouse osteoblasts. In conclusion, the present study demonstrated that myonectin suppresses the differentiation and ALP activity in mouse osteoblasts. Moreover, myonectin suppressed osteoclast differentiation from mouse bone marrow and RAW264.7 cells partly through an inhibition of mitochondrial biogenesis.