PI15, a novel secreted WNT-signaling antagonist, regulates chondrocyte differentiation.

PURPOSE/AIM OF STUDY: During the development of the vertebrate skeleton, the progressive differentiation and maturation of chondrocytes from mesenchymal progenitors is precisely coordinated by multiple secreted factors and signaling pathways. The WNT signaling pathway has been demonstrated to play a major role in chondrogenesis. However, the identification of secreted factors that fine-tune WNT activity has remained elusive. Here, in this study, we have identified PI15 (peptidase inhibitor 15, protease Inhibitor 15, SugarCrisp), a member of the CAP (cysteine rich secretory proteins, antigen 5, and pathogenesis related 1 proteins) protein superfamily, as a novel secreted WNT antagonist dynamically upregulated during chondrocyte differentiation. MATERIALS AND METHODS: ATDC5 cells, C3H10T1/2 micromass cultures and primary chondrocyte cells were used as in vitro models of chondrogenesis. PI15 levels were stably depleted or overexpressed by viral shRNA or expression vectors. Chondrogenesis was evaluated by qPCR gene expression analysis and Alcian blue staining. Protein interactions were determined by coimmunoprecipitation assays. RESULTS AND CONCLUSIONS: shRNA-mediated knockdown of PI15 in ATDC5 cells, C3H10T1/2 cells or primary chondrocytes inhibits chondrogenesis, whereas the overexpression of PI15 strongly enhances chondrogenic potential. Mechanistically, PI15 binds to the LRP6 WNT co-receptor and blocks WNT-induced LRP6 phosphorylation, thus repressing WNT-induced transcriptional activity and alleviating the inhibitory effect of WNT signaling on chondrogenesis. Altogether, our findings suggest that PI15 acts as a key regulator of chondrogenesis and unveils a mechanism through which chondrocyte-derived molecules can modulate WNT activity as differentiation proceeds, thereby creating a positive feedback loop that further drives differentiation.

Royal Jelly Enhances the Ability of Myoblast C2C12 Cells to Differentiate into Multilineage Cells.

Royal jelly (RJ) is recognized as beneficial to mammalian health. Multilineage differentiation potential is an important property of mesenchymal stem cells (MSCs). C2C12 cells have an innate ability to differentiate into myogenic cells. Like MSCs, C2C12 cells can also differentiate into osteoblast- and adipocyte-lineage cells. We recently reported that RJ enhances the myogenic differentiation of C2C12 cells. However, the effect of RJ on osteoblast or adipocyte differentiation is still unknown. Here in this study, we have examined the effect of RJ on the osteoblast and adipocyte differentiation of C2C12 cells. Protease-treated RJ was used to reduce the adverse effects caused by RJ supplementation. To induce osteoblast or adipocyte differentiation, cells were treated with bone morphogenetic proteins (BMP) or peroxisome proliferator-activated receptor γ (PPARγ) agonist, respectively. RNA-seq was used to analyze the effect of RJ on gene expression. We found that RJ stimulates osteoblast and adipocyte differentiation. RJ regulated 279 genes. RJ treatment upregulated glutathione-related genes. Glutathione, the most abundant antioxidative factor in cells, has been shown to promote osteoblast differentiation in MSC and MSC-like cells. Therefore, RJ may promote osteogenesis, at least in part, through the antioxidant effects of glutathione. RJ enhances the differentiation ability of C2C12 cells into multiple lineages, including myoblasts, osteoblasts, and adipocytes.

Inhibition of TET-mediated DNA demethylation suppresses osteoblast differentiation.

DNA methylation is an epigenetic modification critical for the regulation of chromatin structure and gene expression during development and disease. The ten-eleven translocation (TET) enzyme family catalyzes the hydroxymethylation and subsequent demethylation of DNA by oxidizing 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). Little is known about TET protein function due to a lack of pharmacological tools to manipulate DNA hydroxymethylation levels. In this study, we examined the role of TET-mediated DNA hydroxymethylation during BMP-induced C2C12 osteoblast differentiation using a novel cytosine-based selective TET enzyme inhibitor, Bobcat339 (BC339). Treatment of C2C12 cells with BC339 increased global 5mC and decreased global 5hmC without adversely affecting cell viability, proliferation, or apoptosis. Furthermore, BC339 treatment inhibited osteoblast marker gene expression and decreased alkaline phosphatase activity during differentiation. Methylated DNA immunoprecipitation and bisulfite sequencing showed that inhibition of TET with BC339 led to increased 5mC at specific CpG-rich regions at the promoter of Sp7, a key osteoblast transcription factor. Consistent with promoter 5mC marks being associated with transcriptional repression, luciferase activity of an Sp7-promoter-reporter construct was repressed by in vitro DNA methylation or BC339. Chromatin immunoprecipitation analysis confirmed that TET2 does indeed occupy the promoter region of Sp7. Accordingly, forced overexpression of SP7 rescued the inhibition of osteogenic differentiation by BC339. In conclusion, our data suggest that TET-mediated DNA demethylation of genomic regions, including the Sp7 promoter, plays a role in the initiation of osteoblast differentiation. Furthermore, BC339 is a novel pharmacological tool for the modulation of DNA methylation dynamics for research and therapeutic applications.

Tumor necrosis factor alpha regulates myogenesis to inhibit differentiation and promote proliferation in satellite cells.

TNF-α and NF-κB signaling is involved in the wasting of skeletal muscle in various conditions, in addition to cancer cachexia. TNF-α and NF-κB signaling promotes the expression level of muscle RING finger protein 1, a ubiquitin ligase, causing muscle degradation. Several studies have indicated that of TNF-α and NF-κB signaling suppresses muscle differentiation by reducing the levels of MyoD protein. On the other hand, TNF-α and NF-κB is required for myoblast proliferation. Thus, the role of TNF-α and NF-κB signaling in the process of myogenesis and regeneration of skeletal muscle is not completely elucidated. Here, we reported that TNF-α reduced the width of single fibers of skeletal muscle in an organ culture model. TNF-α and p65 repressed the transactivation of MyoD and suppressed myoblast differentiation. In addition, TNF-α increased the number of satellite cells, and NF-κB signaling was promoted at the proliferation stage during skeletal muscle regeneration in vivo. TNF-α and NF-κB signaling regulate myogenesis to inhibit differentiation and promote proliferation in satellite cells.

KIF22 regulates mitosis and proliferation of chondrocyte cells.

Point mutations in KIF22 have been linked to spondyloepimetaphyseal dysplasia with joint laxity, type 2 (SEMDJL2). Skeletal features of SEMDJL2 include short stature and joint laxity. Mechanisms underlying these limb abnormalities are unknown. Here in this manuscript, we have investigated the function of KIF22 in chondrocytes. Quantitative PCR and immunostaining revealed that Kif22 was highly expressed in proliferating-zone growth-plate chondrocytes. Kif22 knockdown resulted in defective mitotic spindle formation and reduced cell proliferation. Forced expression of SEMDJL-associated mutant Kif22 constructs likewise induced abnormal mitotic spindle morphology and reduced proliferation. Mice expressing a KIF22 truncation mutant had shorter growth plates and shorter tibial bones compared to wild-type mice. These results suggest that KIF22 regulates mitotic spindle formation in proliferating chondrocytes thereby linking the stunted longitudinal bone growth observed in SEMDJL2 to failures of chondrocyte division.

Nobiletin, a NF-κB signaling antagonist, promotes BMP-induced bone formation.

The NF-κB family of transcription factors plays an important role in skeletal development and bone homeostasis. In osteoblast cells, NF-κB signaling has been shown to suppress survival, proliferation, and differentiation. Furthermore, pharmacological suppression of NF-κB enhances osteoblast differentiation and bone formation. Thus, NF-κB antagonists are promising candidates as anabolic agents for enhancing bone mass. In this study, we describe the mechanism by which nobiletin, an inhibitor of NF-κB activity, regulates osteoblast differentiation and mineralization. We found that in MC3T3-E1 osteoblast cells, nobiletin inhibited a TNF-α responsive NF-κB luciferase reporter and also decreased the induction of classical NF-κB target genes by TNF-α. Consistent with this, nobiletin prevented TNF-α -mediated suppression of osteogenesis and potently enhanced the differentiation and mineralization of MC3T3-E1 cells. Likewise, in an in vivo BMP2-induced ectopic bone formation assay, nobiletin markedly enhanced ossicle bone volume. Western blotting and SMAD-responsive luciferase assays also demonstrated that NF-κB suppression of BMP signaling could be inhibited by nobiletin. Thus, our data suggest that mechanistically, nobiletin prevents the endogenous repression of BMP signaling by TNF-α, thereby enhancing osteoblast activity. In conclusion, nobiletin is a novel NF-κB antagonist that may be a useful anabolic agent for bone formation.

Physicochemical Properties, Cytocompatibility, and Biocompatibility of a Bioactive Glass Based Retrograde Filling Material.

The ideal retrograde filling material that is easy to handle, has good physicochemical properties, and is biocompatible has not yet been developed. The current study reports the development of a novel bioactive glass based powder for use as a retrograde filling material that is capable of altering the consistency and hardening rate of mixtures when mixed with existing bioactive glass based cement. Furthermore, its physicochemical properties, in vitro effects on human cementoblast-like cells, and in vivo effects on inflammatory responses were evaluated. The surface of the hardened cement showed the formation of hydroxyapatite-like precipitates and calcium and silicate ions were eluted from the cement when the pH level was stabilized at 10.5. Additionally, the cement was found to be insoluble and exhibited favorable handling properties. No adverse effects on viability, proliferation, and expression of differentiated markers were observed in the in vitro experiment, and the cement was capable of inducing calcium deposition in the cells. Moreover, the cement demonstrated a lower number of infiltrated inflammatory cells compared to the other materials used in the in vivo mouse subcutaneous implantation experiment. These findings suggest that the retrograde filling material composed of bioactive glass and the novel bioactive glass based powder exhibits favorable physicochemical properties, cytocompatibility, and biocompatibility.

Vignacyanidin Polyphenols Isolated from Vigna Angularis Bean Promote Osteoblast Differentiation.

BACKGROUND/AIM: An effective bone regenerative method needs to be established for the dental field. To identify a novel osteogenic factor for bone regeneration, we examined the effect of vignacyanidin (VIG) on osteoblastogenesis. MATERIALS AND METHODS: W20-17 cells, MC3T3-E1 cells, and primary cultured murine calvarial osteoblasts were used. Osteoblast differentiation was stimulated by ß-glycerophosphate, ascorbic acid, or bone morphogenetic protein (BMP)-4. Adipogenesis was induced using dexamethasone, 3-isobutyl-1-methylxanthine, insulin, and rosiglitazone. Differentiation or proliferation markers were determined using western blotting and/or the quantitative reverse transcription polymerase chain reaction. Adipogenic cells were visualized by Oil Red O staining. RESULTS: VIG treatment increased the expression of osteoblastic markers and alkaline phosphatase activity of osteoblast-lineage cells in a concentration-dependent manner. However, adipogenesis and cell proliferation were not affected by VIG. CONCLUSION: VIG treatment promoted osteoblast differentiation in osteoblast-lineage cells.

Daily Oral Administration of Protease-Treated Royal Jelly Protects Against Denervation-Induced Skeletal Muscle Atrophy.

Honeybees produce royal jelly (RJ) from their cephalic glands. Royal jelly is a source of nutrition for the queen honey bee throughout its lifespan and is also involved in fertility and longevity. Royal jelly has long been considered beneficial to human health. We recently observed that RJ delayed impairment of motor function during aging, affecting muscle fiber size. However, how RJ affects skeletal muscle metabolism and the functional component of RJ is as of yet unidentified. We demonstrate that feeding mice with RJ daily prevents a decrease in myofiber size following denervation without affecting total muscle weight. RJ did not affect atrophy-related genes but stimulated the expression of myogenesis-related genes, including IGF-1 and IGF receptor. Trans-10-hydroxy-2-decenoic acid (10H2DA) and 10-hydroxydecanoic acid (10HDAA), two major fatty acids contained in RJ. After ingestion, 10H2DA and 10HDAA are metabolized into 2-decenedioic acid (2DA) and sebacic acid (SA) respectively. We found that 10H2DA, 10HDAA, 2DA, and SA all regulated myogenesis of C2C12 cells, murine myoblast cells. These novel findings may be useful for potential preventative and therapeutic applications for muscle atrophy disease included in Sarcopenia, an age-related decline in skeletal muscle mass and strength.

Oral Administration of Geranylgeraniol Rescues Denervation-induced Muscle Atrophy via Suppression of Atrogin-1.

BACKGROUND/AIM: Geranylgeraniol (GGOH), a C20 isoprenoid naturally occurs in several foods. We previously reported that GGOH treatment reduced the expression levels of Atrogin-1 which is involved in skeletal muscle degradation and stimulates the myogenic differentiation of C2C12 myoblasts. However, the effect of GGOH supplementation on skeletal muscle metabolism in vivo is unknown. MATERIALS AND METHODS: Skeletal muscle atrophy was induced by denervation. The expression levels of Atrogin-1 were assessed by western blotting or real time PCR. RESULTS: Intraoral administration of GGOH reduced the decrease in the cross-sectional area of muscle fibers and also suppressed the expression levels of Atrogin-1 in denervation induced muscle atrophy. Also, GGOH treatment suppressed the expression of Atrogin-1 and the decrease in skeletal muscle fiber size by glucocorticoid in vitro. CONCLUSION: Intraoral administration of GGOH rescues denervation-induced muscle atrophy via suppression of Atrogin-1.