Ras-MAPK signaling in osteogenic differentiation: friend or foe?

A genetic mouse model mimicking MET related human osteofibrous dysplasia is characterized by delays in fracture repair and defective osteogenesis

Osteofibrous dysplasia (OFD) is a rare, benign, fibro-osseous lesion that occurs most commonly in the tibia of children. Tibial involvement leads to bowing and predisposes to the development of a fracture which exhibit significantly delayed healing processes, leading to prolonged morbidity. We previously identified gain-of-function mutations in the MET gene as a cause for OFD. In our present study, we test the hypothesis that gain-of-function MET mutations impair bone repair due to reduced osteoblast differentiation. A heterozygous Met exon 15 skipping (MetΔ15-HET) mouse was created to imitate the human OFD mutation. The mutation results in aberrant and dysregulation of MET-related signaling determined by RNA-seq in the murine osteoblasts extracted from the wide-type and genetic mice. Although no gross skeletal defects were identified in the mice, fracture repair was delayed in MetΔ15-HET mice, with decreased bone formation observed 2-week postfracture. Our data are consistent with a novel role for MET-mediated signaling regulating osteogenesis.

Dietary intervention rescues a bone porosity phenotype in a murine model of Neurofibromatosis Type 1 (NF1)

Neurofibromatosis type 1 (NF1) is a complex genetic disorder that affects a range of tissues including muscle and bone. Recent preclinical and clinical studies have shown that Nf1 deficiency in muscle causes metabolic changes resulting in intramyocellular lipid accumulation and muscle weakness. These can be subsequently rescued by dietary interventions aimed at modulating lipid availability and metabolism. It was speculated that the modified diet may rescue defects in cortical bone as NF1 deficiency has been reported to affect genes involved with lipid metabolism. Bone specimens were analyzed from wild type control mice as well as Nf1Prx1-/- (limb-targeted Nf1 knockout mice) fed standard chow versus a range of modified chows hypothesized to influence lipid metabolism. Mice were fed from 4 weeks to 12 weeks of age. MicroCT analysis was performed on the cortical bone to examine standard parameters (bone volume, tissue mineral density, cortical thickness) and specific porosity measures (closed pores corresponding to osteocyte lacunae, and larger open pores). Nf1Prx1-/- bones were found to have inferior bone properties to wild type bones, with a 4-fold increase in the porosity attributed to open pores. These measures were rescued by dietary interventions including a L-carnitine + medium-chain fatty acid supplemented chow previously shown to improve muscle histology function. Histological staining visualized these changes in bone porosity. These data support the concept that lipid metabolism may have a mechanistic impact on bone porosity and quality in NF1.

The IFITM5 mutation in osteogenesis imperfecta type V is associated with an ERK/SOX9-dependent osteoprogenitor differentiation defect

Osteogenesis imperfecta (OI) type V is the second most common form of OI, distinguished by hyperplastic callus formation and calcification of the interosseous membranes, in addition to the bone fragility. It is caused by a recurrent, dominant pathogenic variant (c.-14C>T) in interferon-induced transmembrane protein 5 (IFITM5). Here, we generated a conditional Rosa26-knockin mouse model to study the mechanistic consequences of the recurrent mutation. Expression of the mutant Ifitm5 in osteo-chondroprogenitor or chondrogenic cells resulted in low bone mass and growth retardation. Mutant limbs showed impaired endochondral ossification, cartilage overgrowth, and abnormal growth plate architecture. The cartilage phenotype correlates with the pathology reported in patients with OI type V. Surprisingly, expression of mutant Ifitm5 in mature osteoblasts caused no obvious skeletal abnormalities. In contrast, earlier expression in osteo-chondroprogenitors was associated with an increase in the skeletal progenitor cell population within the periosteum. Lineage tracing showed that chondrogenic cells expressing the mutant Ifitm5 had decreased differentiation into osteoblastic cells in diaphyseal bone. Moreover, mutant IFITM5 disrupted early skeletal homeostasis in part by activating ERK signaling and downstream SOX9 protein, and inhibition of these pathways partially rescued the phenotype in mutant animals. These data identify the contribution of a signaling defect altering osteo-chondroprogenitor differentiation as a driver in the pathogenesis of OI type V.

The unexplored role of alkali and alkaline earth elements (ALAEs) on the structure, processing, and biological effects of bioactive glasses

Bioactive glass has been employed in several medical applications since its inception in 1969. The compositions of these materials have been investigated extensively with emphasis on glass network formers, therapeutic transition metals, and glass network modifiers. Through these experiments, several commercial and experimental compositions have been developed with varying chemical durability, induced physiological responses, and hydroxyapatite forming abilities. In many of these studies, the concentrations of each alkali and alkaline earth element have been altered to monitor changes in structure and biological response. This review aims to discuss the impact of each alkali and alkaline earth element on the structure, processing, and biological effects of bioactive glass. We explore critical questions regarding these elements from both a glass science and biological perspective. Should elements with little biological impact be included? Are alkali free bioactive glasses more promising for greater biological responses? Does this mixed alkali effect show increased degradation rates and should it be employed for optimized dissolution? Each of these questions along with others are evaluated comprehensively and discussed in the final section where guidance for compositional design is provided.

Skeletal defects and bone metabolism in Noonan, Costello and cardio-facio-cutaneous syndromes

Noonan, Costello and Cardio-facio-cutaneous syndromes belong to a group of disorders named RASopathies due to their common pathogenetic origin that lies on the Ras/MAPK signaling pathway. Genetics has eased, at least in part, the distinction of these entities as they are presented with overlapping clinical features which, sometimes, become more pronounced with age. Distinctive face, cardiac and skeletal defects are among the primary abnormalities seen in these patients. Skeletal dysmorphisms range from mild to severe and may include anterior chest wall anomalies, scoliosis, kyphosis, short stature, hand anomalies, muscle weakness, osteopenia or/and osteoporosis. Patients usually have increased serum concentrations of bone resorption markers, while markers of bone formation are within normal range. The causative molecular defects encompass the members of the Ras/MAPK/ERK pathway and the adjacent cascades, important for the maintenance of normal bone homeostasis. It has been suggested that modulation of the expression of specific molecules involved in the processes of bone remodeling may affect the osteogenic fate decision, potentially, bringing out new pharmaceutical targets. Currently, the laboratory imprint of bone metabolism on the clinical picture of the affected individuals is not clear, maybe due to the rarity of these syndromes, the small number of the recruited patients and the methods used for the description of their clinical and biochemical profiles.

Ras family signaling pathway in immunopathogenesis of inflammatory rheumatic diseases

The Ras (rat sarcoma virus) is a GTP-binding protein that is considered one of the important members of the Ras-GTPase superfamily. The Ras involves several pathways in the cell that include proliferation, migration, survival, differentiation, and fibrosis. Abnormalities in the expression level and activation of the Ras family signaling pathway and its downstream kinases such as Raf/MEK/ERK1-2 contribute to the pathogenic mechanisms of rheumatic diseases including immune system dysregulation, inflammation, and fibrosis in systemic sclerosis (SSc); destruction and inflammation of synovial tissue in rheumatoid arthritis (RA); and autoantibody production and immune complexes formation in systemic lupus erythematosus (SLE); and enhance osteoblast differentiation and ossification during skeletal formation in ankylosing spondylitis (AS). In this review, the basic biology, signaling of Ras, and abnormalities in this pathway in rheumatic diseases including SSc, RA, AS, and SLE will be discussed.

From Stem to Sternum: The Role of Shp2 in the Skeleton

Src homology-2 domain-containing phosphatase 2 (SHP2) is a ubiquitously expressed phosphatase that is vital for skeletal development and maintenance of chondrocytes, osteoblasts, and osteoclasts. Study of SHP2 function in small animal models has led to insights in phenotypes observed in SHP2-mutant human disease, such as Noonan syndrome. In recent years, allosteric SHP2 inhibitors have been developed to specifically target the protein in neoplastic processes. These inhibitors are highly specific and have great potential for disease modulation in cancer and other pathologies, including bone disorders. In this review, we discuss the importance of SHP2 and related signaling pathways (e.g., Ras/MEK/ERK, JAK/STAT, PI3K/Akt) in skeletal development. We review rodent models of pathologic processes caused by germline mutations that activate SHP2 enzymatic activity, with a focus on the skeletal phenotype seen in these patients. Finally, we discuss SHP2 inhibitors in development and their potential for disease modulation in these genetic diseases, particularly as it relates to the skeleton.

E3 Ubiquitin Ligases: Potential Therapeutic Targets for Skeletal Pathology and Degeneration

The ubiquitination-proteasome system (UPS) is crucial in regulating a variety of cellular processes including proliferation, differentiation, and survival. Ubiquitin protein ligase E3 is the most critical molecule in the UPS system. Dysregulation of the UPS system is associated with many conditions. Over the past few decades, there have been an increasing number of studies focusing on the UPS system and how it affects bone metabolism. Multiple E3 ubiquitin ligases have been found to mediate osteogenesis or osteolysis through a variety of pathways. In this review, we describe the mechanisms of UPS, especially E3 ubiquitin ligases on bone metabolism. To date, many E3 ubiquitin ligases have been found to regulate osteogenesis or osteoclast differentiation. We review the classification of these E3 enzymes and the mechanisms that influence upstream and downstream molecules and transduction pathways. Finally, this paper reviews the discovery of the relevant UPS inhibitors, drug molecules, and noncoding RNAs so far and prospects the future research and treatment.

Identification of key sex-specific pathways and genes in the subcutaneous adipose tissue from pigs using WGCNA method

Background

Adipose tissues (ATs), including visceral ATs (VATs) and subcutaneous ATs (SATs), are crucial for maintaining energy and metabolic homeostasis. SATs have been found to be closely related to obesity and obesity-induced metabolic disease. Some studies have shown a significant association between subcutaneous fat metabolism and sexes. However, the molecular mechanisms for this association are still unclear. Here, using the pig as a model, we investigated the systematic association between the subcutaneous fat metabolism and sexes, and identified some key sex-specific pathways and genes in the SATs from pigs.

Results

The results revealed that 134 differentially expressed genes (DEGs) were identified in female and male pigs from the obese group. A total of 17 coexpression modules were detected, of which six modules were significantly correlated with the sexes (P < 0.01). Among the significant modules, the greenyellow module (cor = 0.68, P < 9e-06) and green module (cor = 0.49, P < 0.003) were most significantly positively correlated with the male and female, respectively. Functional analysis showed that one GO term and four KEGG pathways were significantly enriched in the greenyellow module while six GO terms and six KEGG pathways were significantly enriched in the green module. Furthermore, a total of five and two key sex-specific genes were identified in the two modules, respectively. Two key sex-specific pathways (Ras-MAPK signaling pathway and type I interferon response) play an important role in the SATs of males and females, respectively.

Conclusions

The present study identified some key sex-specific pathways and genes in the SATs from pigs, which provided some new insights into the molecular mechanism of being involved in fat formation and immunoregulation between pigs of different sexes. These findings may be beneficial to breeding in the pig industry and obesity treatment in medicine.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-022-01054-w.

Strontium- and peptide-modified silicate nanostructures for dual osteogenic and antimicrobial activity

Developing multifunctional nanostructures that promote bone repair while fighting infection is highly desirable in bone regenerative therapies. Previous efforts have focused on achieving one property or another by altering the chemical makeup of nanostructures or using growth factors or antibiotics. We present nanostructures with several simultaneous functional attributes including positive effects of strontium on bone formation and prevention of osteoclast differentiation along with incorporation of antimicrobial peptides (AMP) to prevent infection. To form these multifunctional nanostructures, mesoporous calcium silicate (CaMSN) was modified with high levels of strontium. For this, CaMSNs were either partially substituted (20 wt% Ca) or completely replaced with strontium (Sr) to form Sr-CaMSN or SrMSN. The mesoporous nature of these bioactive silicate nanostructures rendered a configuration for substantial AMP loading as well as their effective delivery. The physico-chemical and structural characterization of synthesized MSNs confirmed the mesoporous nature of the synthesized MSNs and their total surface area, pore size, pore volume and SBF-mediated bioactivity remained unaltered with the incorporation of Sr. However, biological evaluation confirmed that synthesized SrMSN upregulated osteogenic differentiation of mesenchymal stromal cells and significantly downregulated osteoclast differentiation. Also, the AMP-loaded MSNs prevented formation and growth of methicillin resistant Staphylococcus aureus (MRSA) biofilms. Thus, high Sr-containing AMP-loaded SrMSNs may combat MRSA-associated infection while promoting bone regeneration. The controlled availability of therapeutic Sr and AMP release as SrMSN degrade enables its potential application in bone tissue regeneration.

CD146 controls the quality of clinical grade mesenchymal stem cells from human dental pulp

Background

Human mesenchymal stem cells from dental pulp (hMSC-DP), including dental pulp stem cells from permanent teeth and exfoliated deciduous teeth, possess unique MSC characteristics such as expression of specific surface molecules and a high proliferation rate. Since hMSC-DP have been applied in numerous clinical studies, it is necessary to establish criteria to evaluate their potency for cell-based therapies.

Methods

We compared stem cell properties of hMSC-DP at passages 5, 10 and 20 under serum (SE) and serum-free (SF) culture conditions. Cell morphology, proliferation capacity, chromosomal stability, surface phenotypic profiles, differentiation and immunoregulation ability were evaluated. In addition, we assessed surface molecule that regulates hMSC-DP proliferation and immunomodulation.

Results

hMSC-DP exhibited a decrease in proliferation rate and differentiation potential, as well as a reduced expression of CD146 when cultured under continuous passage conditions. SF culture conditions failed to alter surface marker expression, chromosome stability or proliferation rate when compared to SE culture. SF-cultured hMSC-DP were able to differentiate into osteogenic, adipogenic and neural cells, and displayed the capacity to regulate immune responses. Notably, the expression level of CD146 showed a positive correlation with proliferation, differentiation, and immunomodulation, suggesting that CD146 can serve as a surface molecule to evaluate the potency of hMSC-DP. Mechanistically, we found that CD146 regulates proliferation and immunomodulation of hMSC-DP through the ERK/p-ERK pathway.

Conclusion

This study indicates that SF-cultured hMSC-DP are appropriate for producing clinical-grade cells. CD146 is a functional surface molecule to assess the potency of hMSC-DP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02559-4.

Multiple versus solitary giant cell lesions of the jaw: Similar or distinct entities?

The majority of giant cell lesions of the jaw present as a solitary focus of disease in bones of the maxillofacial skeleton. Less frequently they occur as multifocal lesions. This raises the clinical dilemma if these should be considered distinct entities and therefore each need a specific therapeutic approach. Solitary giant cell lesions of the jaw present with a great diversity of symptoms. Recent molecular analysis revealed that these are associated with somatic gain-of-function mutations in KRAS, FGFR1 or TRPV4 in a large component of the mononuclear stromal cells which all act on the RAS/MAPK pathway. For multifocal lesions, a small group of neoplastic multifocal giant cell lesions of the jaw remain after ruling out hyperparathyroidism. Strikingly, most of these patients are diagnosed with jaw lesions before the age of 20 years, thus before the completion of dental and jaw development. These multifocal lesions are often accompanied by a diagnosis or strong clinical suspicion of a syndrome. Many of the frequently reported syndromes belong to the so-called RASopathies, with germline or mosaic mutations leading to downstream upregulation of the RAS/MAPK pathway. The other frequently reported syndrome is cherubism, with gain-of-function mutations in the SH3BP2 gene leading through assumed and unknown signaling to an autoinflammatory bone disorder with hyperactive osteoclasts and defective osteoblastogenesis. Based on this extensive literature review, a RAS/MAPK pathway activation is hypothesized in all giant cell lesions of the jaw. The different interaction between and contribution of deregulated signaling in individual cell lineages and crosstalk with other pathways among the different germline- and non-germline-based alterations causing giant cell lesions of the jaw can be explanatory for the characteristic clinical features. As such, this might also aid in the understanding of the age-dependent symptomatology of syndrome associated giant cell lesions of the jaw; hopefully guiding ideal timing when installing treatment strategies in the future.

Dysregulated ECM remodeling proteins lead to aberrant osteogenesis of Costello syndrome iPSCs

Costello syndrome (CS) is an autosomal dominant disorder caused by mutations in HRAS. Although CS patients have skeletal abnormalities, the role of mutated HRAS in bone development remains unclear. Here, we use CS induced pluripotent stem cells (iPSCs) undergoing osteogenic differentiation to investigate how dysregulation of extracellular matrix (ECM) remodeling proteins contributes to impaired osteogenesis. Although CS patient-derived iPSCs develop normally to produce mesenchymal stem cells (MSCs), the resulting CS MSCs show defective osteogenesis with reduced alkaline phosphatase activity and lower levels of bone mineralization. We found that hyperactivation of SMAD3 signaling during the osteogenic differentiation of CS MSCs leads to aberrant expression of ECM remodeling proteins such as MMP13, TIMP1, and TIMP2. CS MSCs undergoing osteogenic differentiation also show reduced β-catenin signaling. Knockdown of TIMPs permits normal differentiation of CS MSCs into osteoblasts and enhances β-catenin signaling in a RUNX2-independent manner. Thus, this study demonstrates that enhanced TIMP expression induced by hyperactivated SMAD3 signaling impairs the osteogenic development of CS MSCs via an inactivation of β-catenin signaling.

Activin-A Induces Early Differential Gene Expression Exclusively in Periodontal Ligament Fibroblasts from Fibrodysplasia Ossificans Progressiva Patients

Fibrodysplasia Ossificans Progressiva (FOP) is a rare genetic disease characterized by heterotopic ossification (HO). It is caused by mutations in the Activin receptor type 1 (ACVR1) gene, resulting in enhanced responsiveness to ligands, specifically to Activin-A. Though it has been shown that capturing Activin-A protects against heterotopic ossification in animal models, the exact underlying mechanisms at the gene expression level causing ACVR1 R206H-mediated ossifications and progression are thus far unknown. We investigated the early transcriptomic changes induced by Activin-A of healthy control and patient-derived periodontal ligament fibroblasts (PLF) isolated from extracted teeth by RNA sequencing analysis. To study early differences in response to Activin-A, periodontal ligament fibroblasts from six control teeth and from six FOP patient teeth were cultured for 24 h without and with 50 ng/mL Activin-A and analyzed with RNA sequencing. Pathway analysis on genes upregulated by Activin-A in FOP cells showed an association with pathways involved in, among others, Activin, TGFβ, and BMP signaling. Differential gene expression induced by Activin-A was exclusively seen in the FOP cells. Median centered supervised gene expression analysis showed distinct clusters of up- and downregulated genes in the FOP cultures after stimulation with Activin-A. The upregulated genes with high fold changes like SHOC2, TTC1, PAPSS2, DOCK7, and LOX are all associated with bone metabolism. Our open-ended approach to investigating the early effect of Activin-A on gene expression in control and FOP PLF shows that the molecule exclusively induces differential gene expression in FOP cells and not in control cells.

Genome-Wide Integrated Analysis Revealed Functions of lncRNA-miRNA-mRNA Interaction in Growth of Intermuscular Bones in Megalobrama amblycephala

Intermuscular bone (IB) occurs in the myosepta of teleosts. Its existence has an adverse influence on the edible and economic value of fish, especially for aquaculture species belonging to Cypriniformes. The growth mechanism of IBs is quite lacking. In this study, we firstly used single molecular real-time sequencing (SMRT) technology to improve the draft genome annotation and full characterization of the transcriptome for one typical aquaculture species, blunt snout bream (Megalobrama amblycephala). The long non-coding RNA (lncRNA), microRNA (miRNA), and messenger RNA (mRNA) expression profiles in two IB growth stages (1 and 3 years old) were compared through transcriptome and degradome analyses. A total of 126 miRNAs, 403 mRNAs, and 353 lncRNAs were found to be differentially expressed between the two stages. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the significantly upregulated map2k6 and cytc in the MAPK/p53 signaling pathway and the significantly downregulated lama3 and thbs4b in the extracellular matrix (ECM)–receptor pathway may play a key regulatory role in IB growth. Bioinformatics analysis subsequently revealed 14 competing endogenous RNA (ceRNA) pairs related to the growth of IBs, consisting of 10 lncRNAs, 7 miRNAs, and 10 mRNAs. Of these, dre-miR-24b-3p and dre-miR-193b-3p are core regulatory factors interacting with four lncRNAs and three mRNAs, the interaction mechanism of which was also revealed by subsequent experiments at the cellular level. In conclusion, our data showed that IBs had higher activity of cell apoptosis and lower mineralization activity in IB_III compared to IB_I via interaction of MAPK/p53 and ECM–receptor signaling pathways. The downregulated zip1 interacted with miR-24a-3p and lnc017705, decreased osteoblast differentiation and Ca²⁺ deposition in the IB_III stage. Our identified functional mRNAs, lncRNAs, and miRNAs provide a data basis for in-depth elucidation of the growth mechanism of teleost IB.

Membrane-type 1 Matrix Metalloproteinase Modulates Tissue Homeostasis by a Non-proteolytic Mechanism

Membrane-type 1 matrix metalloproteinase (MT1-MMP, MMP-14), a transmembrane proteinase with a short cytoplasmic tail, is a major effector of extracellular matrix remodeling. Genetic silencing of MT1-MMP in mouse (Mmp14 ^-/- ) and man causes dwarfism, osteopenia, arthritis, and lipodystrophy, abnormalities ascribed to defective collagen turnover. We have previously shown non-proteolytic functions of MT1-MMP mediated by its cytoplasmic tail, where the unique tyrosine (Y573) controls intracellular signaling. The Y573D mutation blocks TIMP-2/MT1-MMP-induced Erk1/2 and Akt signaling without affecting proteolytic activity. Here, we report that a mouse with the MT1-MMP Y573D mutation (Mmp14 ^Y573D/Y573D ) shows abnormalities similar to but also different from those of Mmp14 ^-/- mice. Skeletal stem cells (SSC) of Mmp14 ^Y573D/Y573D mice show defective differentiation consistent with the mouse phenotype, which is rescued by wild-type SSC transplant. These results provide the first in vivo demonstration that MT1-MMP modulates bone, cartilage, and fat homeostasis by controlling SSC differentiation through a mechanism independent of proteolysis.

From the Performance to the Essence: The Biological Mechanisms of How Tantalum Contributes to Osteogenesis

Despite the brilliant bioactive performance of tantalum as an orthopedic biomaterial verified through laboratory researches and clinical practice in the past decades, scarce evidences about the essential mechanisms of how tantalum contributes to osteogenesis were systematically discussed. Up to now, a few studies have uncovered preliminarily the biological mechanism of tantalum in osteogenic differentiation and osteogenesis; it is of great necessity to map out the panorama through which tantalum contributes to new bone formation. This minireview summarized current advances to demonstrate the probable signaling pathways and underlying molecular cascades through which tantalum orchestrates osteogenesis, which mainly contain Wnt/β-catenin signaling pathway, BMP signaling pathway, TGF-β signaling pathway, and integrin signaling pathway. Limits of subsistent studies and further work are also discussed, providing a novel vision for the study and application of tantalum.

Network and pathway-based analyses of genes associated with osteoporosis

Osteoporosis (OP) is a disease characterized by bone mass loss, bone microstructure damage, increased bone fragility, and easy fracture. The molecular mechanism underlying OP remains unclear.In this study, we identified 217 genes associated with OP, and formed a gene set [OP-related genes gene set (OPgset)].The highly enriched GOs and pathways showed OPgset genes were significantly involved in multiple biological processes (skeletal system development, ossification, and osteoblast differentiation), and several OP-related pathways (Wnt signaling pathway, osteoclast differentiation, steroid hormone biosynthesis, and adipocytokine signaling pathway). Besides, pathway crosstalk analysis indicated three major modules, with first module consisted of pathways mainly involved in bone development-related signaling pathways, second module in Wnt-related signaling pathway and third module in metabolic pathways. Further, we calculated degree centrality of a node and selected ten key genes/proteins, including TGFB1, IL6, WNT3A, TNF, PTH, TP53, WNT1, IGF1, IL10, and SERPINE1. We analyze the K-core and construct three k-core sub-networks of OPgset genes.In summary, we for the first time explored the molecular mechanism underlying OP via network- and pathway-based methods, results from our study will improve our understanding of the pathogenesis of OP. In addition, these methods performed in this study can be used to explore pathogenesis and genes related to a specific disease.

The miR-193a-3p-MAP3k3 Signaling Axis Regulates Substrate Topography-Induced Osteogenesis of Bone Marrow Stem Cells

Substrate topographical features induce osteogenic differentiation of bone marrow stem cells (BMSCs), but the underlying mechanisms are unclear. As microRNAs (miRNAs) play key roles in osteogenesis and bone regeneration, it would be meaningful to elucidate the roles of miRNAs in the intracellular signaling cascade of topographical cue-induced osteogenic differentiation. In this study, the miRNA expression profile of the topographical feature-induced osteogenic differentiation group is different from that of the chemical-factors-induced osteogenic differentiation group. miR-193a-3p is sensitive to substrate topographical features and its downregulation enhances osteogenic differentiation only in the absence of osteogenesis-inducing medium. Also, substrate topographical features specifically activate a nonclassical osteogenetic pathway-the mitogen-activated protein kinase (MAPK) pathway. Loss- and gain-of-function experiments demonstrate that miR-193a-3p regulates the MAPK pathway by targeting the MAP3k3 gene. In conclusion, this data indicates that different osteogenic-lineage-related intracellular signaling cascades are triggered in BMSCs subjected to biophysical or chemical stimulation. Moreover, the miR-193a-3p-MAP3k3 signaling axis plays a pivotal role in the transduction of biophysical cues from the substrate to regulate the osteogenic lineage specification of BMSCs, and hence may be a promising molecular target for bone regenerative therapies.

Soluble yerba mate (Ilex Paraguariensis) extract enhances in vitro osteoblastic differentiation of bone marrow-derived mesenchymal stromal cells

ETHNOPHARMACOLOGICAL RELEVANCE

Yerba mate (Ilex paraguariensis) consumption has been associated with beneficial effects on bone health.

AIM OF THE STUDY

The purpose of this study was to evaluate the mechanism by which soluble yerba mate (SYM) stimulates osteoblast differentiation of bone marrow-derived mesenchymal stromal cells (BM-MSCs).

MATERIALS AND METHODS

BM-MSCs from male Wistar rats were induced towards osteoblastic differentiation with different concentrations of SYM (10, 20, and 50 μg/mL). Osteoblastic differentiation was evaluated by measuring proliferation rates, alkaline phosphatase activity, MMP-2 activity, mineralization, and gene expression of Runx2, Osterix, β-catenin (Catnb), collagen type I (Col1a1), osteopontin (Opn), osteocalcin (Ocn), bone sialoprotein (Bsp), bone morphogenetic protein-2 (Bmp2), osteoprotegerin (Opg), and Rankl. We also analyzed cytokine production and MAP kinase pathways.

RESULTS

SYM (10 μg/mL) did not show a cytotoxic effect and induced a slight increase in ALP activity; however, a great increase in mineralization was observed. SYM was also able to reduce TNF-α and IL-10 production; increase the expression of transcription factors Runx2, Osterix, and Catnb; and increase matrix proteins Opn, Bsp, Ocn, and Bmp2. We also observed a decrease in intracellular signaling of ERK, JNK, and p38 MAPK, which seemed to be related to the SYM response.

CONCLUSIONS

Together, these results help to explain the promoting effect on osteoblast differentiation produced by a low SYM concentration. However, a higher SYM concentration presented deleterious effects, including cytotoxicity, decreased ALP activity, increased cytokine production, decreased bone marker gene expression, increased MAPK signaling, and significant mineralization reduction. In conclusion, our results suggest a concentration-specific direct stimulatory effect of SYM on osteoblastic differentiation in vitro.

A genetic-phenotypic classification for syndromic micrognathia

Micrognathia is a common craniofacial deformity which represents hypoplastic development of the mandible, accompanied by retrognathia and consequent airway problems. Usually, micrognathia is accompanied by multiple systematic defects, known as syndromic micrognathia, and is in close association with genetic factors. Now, large quantities of pathogenic genes of syndromic micrognathia have been revealed. However, how these different pathogenic genes could lead to similar phenotypes, and whether there are some common characteristics among these pathogenic genes are still unknown. In this study, we proposed a genetic-phenotypic classification of syndromic micrognathia based on pathogenic genes information obtained from Phenolyzer, DAVID, OMIM, and PubMed database. Pathogenic genes of syndromic micrognathia could be divided into four groups based on gene function, including cellular processes and structures, cell metabolism, cartilage and bone development, and neuromuscular function. In addition, these four groups exhibited various clinical characteristics, and the affected systems, such as central nervous system, skeletal system, cardiovascular system, oral and dental system, respiratory system and muscle, were different in these four groups. This classification could provide meaningful insights into the pathogenesis of syndromic micrognathia, and offer some clues for understanding the molecular mechanism, as well as guiding precise clinical diagnosis and treatment for syndromic micrognathia.

Parathyroid hormone enhances the osteo/odontogenic differentiation of dental pulp stem cells via ERK and P38 MAPK pathways

OBJECTIVE

Parathyroid hormone (PTH) is a main systemic mediator of calcium and phosphate homeostasis in the bone. Dental pulp stem cells (DPSCs) have been extensively studied in the regeneration of bone and tooth tissues. This paper aims to uncover the influences of PTH on the proliferative ability and osteo/odontogenic differentiation of DPSCs, as well as the underlying mechanisms.

MATERIALS AND METHODS

The optimal concentration of PTH on DPSCs was determined by alkaline phosphatase (ALP) activity assay, ALP staining and western blot analysis. Proliferative ability and cell cycle distribution of DPSCs were analyzed by Cell counting kit-8, 5-ethynyl-20-deoxyuridine assay, and flow cytometry. Osteo/odontogenic capacity of DPSCs was evaluated and finally, the involvement of mitogen-activated protein kinase (MAPK) pathway was assessed.

RESULTS

Purified DPSCs were obtained by enzymatic digestion, which presented a typical fibroblast-like morphology. 10^-9  mol/L PTH was concerned as the optimal concentration for DPSCs induction. 10^-9  mol/L PTH treatment did not change the proliferative rate of DPSCs (p > .05). Relative expressions of DSPP/DSPP, RUNX2/RUNX2, OSX/OSX, and ALP/ALP were upregulated in PTH-treated DPSCs relative to control group. Particularly, their mRNA/protein levels at Day 7 were markedly higher relative to those at Day 3 (p < .05 or p < .01). Mineralized nodules were formed after PTH induction, and calcium content increased by cetylpyridinium chloride quantitative analysis. Mechanistically, the protein levels of p-ERK and p-P38 significantly increased after PTH treatment, and the inhibitors targeting MAPK were identified that weakened the effects of PTH on the committed differentiation of DPSCs.

CONCLUSIONS

PTH enhances the osteo/odontogenic differentiation capacity of DPSCs via ERK and P38 signaling pathways.

Multiple and Promising Applications of Strontium (Sr)-Containing Bioactive Glasses in Bone Tissue Engineering

Improving and accelerating bone repair still are partially unmet needs in bone regenerative therapies. In this regard, strontium (Sr)-containing bioactive glasses (BGs) are highly-promising materials to tackle this challenge. The positive impacts of Sr on the osteogenesis makes it routinely used in the form of strontium ranelate (SR) in the clinical setting, especially for patients suffering from osteoporosis. Therefore, a large number of silicate-, borate-, and phosphate-based BGs doped with Sr and produced in different shapes have been developed and characterized, in order to be used in the most advanced therapeutic strategies designed for the management of bone defects and injuries. Although the influence of Sr incorporation in the glass is debated regarding the obtained physicochemical and mechanical properties, the biological improvements have been found to be substantial both in vitro and in vivo. In the present study, we provide a comprehensive overview of Sr-containing glasses along with the current state of their clinical use. For this purpose, different types of Sr-doped BG systems are described, including composites, coatings and porous scaffolds, and their applications are discussed in the light of existing experimental data along with the significant challenges ahead.

Osseointegration effect of biomimetic intrafibrillarly mineralized collagen applied simultaneously with titanium implant: A pilot in vivo study

OBJECTIVES

To investigate the promoting effects of biomimetic intrafibrillarly mineralized collagen (IMC) bone scaffold material on the osseointegration of a titanium implant simultaneously grafted into a critical-sized bone defect as well as the underlying mechanisms involved.

MATERIALS AND METHODS

A critical-sized bone defect was created in the rat femur, and a titanium (Ti) implant surrounded by IMC or extrafibrillarly mineralized collagen (EMC) bone scaffold material was placed in the defect. A blank group and a natural bone group were included as controls. Osseointegration was assessed by micro-computed tomographic, histological, and biochemical evaluations at 12 weeks postoperatively. Microarray technology was applied for transcriptional profile analysis at days 7 and 14 postoperatively.

RESULTS

Significant bone regeneration and osseointegration were observed in the IMC and EMC groups according to μ-CT and histological analyses. The bone volume (BV)/total volume (TV) fraction, bone-to-implant contact percentage, and bone area percentage as well as ultimate shear strength and maximal pull-out force were all significantly higher in the IMC group than in the EMC group (all p < 0.05). Transcriptional analysis revealed overexpression of genes mainly associated with cell proliferation, immuno-inflammatory response, skeletogenesis, angiogenesis, neurogenesis, and skeletogenesis-related pathways during the early process of osseointegration in the IMC group.

CONCLUSION

Our data suggest that IMC placed simultaneously with a Ti implant may be a promising strategy in jawbone defect reconstruction. Several candidate genes that were found to be differentially expressed in the IMC group may be responsible for the superior osseointegration effects in this model.

The effects of dynamic compressive loading on human mesenchymal stem cell osteogenesis in the stiff layer of a bilayer hydrogel

Bilayer hydrogels with a soft cartilage-like layer and a stiff bone-like layer embedded with human mesenchymal stem cells (hMSCs) are promising for osteochondral tissue engineering. The goals of this work were to evaluate the effects of dynamic compressive loading (2.5% applied strain, 1 Hz) on osteogenesis in the stiff layer and spatially map local mechanical responses (strain, stress, hydrostatic pressure, and fluid velocity). A bilayer hydrogel was fabricated from soft (24 kPa) and stiff (124 kPa) poly (ethylene glycol) hydrogels. With hMSCs embedded in the stiff layer, osteogenesis was delayed under loading evident by lower OSX and OPN expressions, alkaline phosphatase activity, and collagen content. At Day 28, mineral deposits were present throughout the stiff layer without loading but localized centrally and near the interface under loading. Local strains mapped by particle tracking showed substantial equivalent strain (~1.5%) transferring to the stiff layer. When hMSCs were cultured in stiff single-layer hydrogels subjected to similar strains, mineralization was inhibited. Finite element analysis revealed that hydrostatic pressures ≥~600 Pa correlated to regions lacking mineralization in both hydrogels. Fluid velocities were low (~1-10 nm/s) in the hydrogels with no apparent correlation to mineralization. Mineralization was recovered by inhibiting ERK1/2, indicating cell-mediated inhibition. These findings suggest that high strains (~1.5%) combined with higher hydrostatic pressures negatively impact osteogenesis, but in a manner that depends on the magnitude of each mechanical response. This work highlights the importance of local mechanical responses in mediating osteogenesis of hMSCs in bilayer hydrogels being studied for osteochondral tissue engineering.

Interplay between microRNAs and Wnt, transforming growth factor-β, and bone morphogenic protein signaling pathways promote osteoblastic differentiation of mesenchymal stem cells

Osteoblasts are terminally differentiated cells with mesenchymal origins, known to possess pivotal roles in sustaining bone microstructure and homeostasis. These cells are implicated in the pathophysiology of various bone disorders, especially osteoporosis. Over the last few decades, strategies to impede bone resorption, principally by bisphosphonates, have been mainstay of treatment of osteoporosis; however, in recent years more attention has been drawn on bone-forming approaches for managing osteoporosis. MicroRNAs (miRNAs) are a broad category of noncoding short sequence RNA fragments that posttranscriptionally regulate the expression of diverse functional and structural genes in a negative manner. An accumulating body of evidence signifies that miRNAs direct mesenchymal stem cells toward osteoblast differentiation and bone formation through bone morphogenic protein, transforming growth factor-β, and Wnt signaling pathways. MiRNAs are regarded as excellent future therapeutic candidates because of their small size and ease of delivery into the cells. Considering their novel therapeutic significance, this review discusses the main miRNAs contributing to the anabolic aspects of bone formation and illustrates their interactions with corresponding signaling pathways involved in osteoblastic differentiation.

Crosstalk between neuropeptides SP and CGRP in regulation of BMP2-induced bone differentiation

AIM OF THE STUDY

The peripheral nervous system is involved in regulation of bone metabolism via sensory and sympathetic innervation. Substance P (SP) and calcitonin gene-related peptide (CGRP) are two sensory neuropeptides that have been associated with regulation of osteogenic differentiation. However, the interaction between SP and CGRP both with each other and the bone morphogenetic protein 2 (BMP2) in regulation of osteogenic differentiation has not been studied. Therefore, the aim of this study was to investigate the interaction between SP and CGRP on BMP2-induced bone differentiation using model progenitor cells.

MATERIALS AND METHODS

C2C12 myoblasts and MC3T3 pre-osteoblasts were treated with SP and CGRP, both individually and in combination, in the presence of BMP2. The effects of the neuropeptides on BMP2-induced osteogenic differentiation were assessed by measuring alkaline phosphatase (ALP) activity, mineralization, and expression of osteogenic markers.

RESULTS

Both SP and CGRP enhanced BMP2 signaling, Runx2 mRNA expression, as well as mineralization in vitro. Co-stimulation with SP and CGRP resulted in down-regulation of BMP2-induced bone differentiation, suggesting potential crosstalk between the two neuropeptides in regulation of BMP2 signaling.

CONCLUSIONS

Based on the results shown here, CGRP can mitigate augmenting effects of SP on BMP2 signaling and the three pathways potentially converge on Runx2 to regulate BMP2-induced bone differentiation.

Biomimetic intrafibrillar mineralized collagen promotes bone regeneration via activation of the Wnt signaling pathway

Purpose

The purpose of this study was to assess the effects of biomimetic intrafibrillar mineralized collagen (IMC) bone scaffold materials on bone regeneration and the underlying biological mechanisms.

Materials and methods

A critical-sized bone defect in the rat femur was created; then IMC, extrafibrillar mineralized collagen, and nano-hydroxyapatite bone scaffold materials were grafted into the defect. Ten weeks after implantation, micro-computed tomography and histology were applied to evaluate the bone regeneration. Furthermore, microarray technology was applied for transcriptional profile analysis at two postoperative time points (7 and 14 days). Subsequently, the critical genes involved in bone regeneration identified by transcriptional analysis were verified both in vivo through immunohistochemical analysis and in vitro by quantitative real-time transcription polymerase chain reaction evaluation.

Results

Significantly increased new bone formation was found in the IMC group based on micro-computed tomography and histological evaluation (P<0.05). Transcriptional analysis revealed that the early process of IMC-guided bone regeneration involves the overexpression of genes mainly associated with inflammation, immune response, skeletal development, angiogenesis, neurogenesis, and the Wnt signaling pathway. The roles of the Wnt signaling pathway-related factors Wnt5a, β-catenin, and Axin2 were further confirmed both in vivo and in vitro.

Conclusion

The IMC bone scaffold materials significantly enhanced bone regeneration via activation of the Wnt signaling pathway.

LL-37 inhibits LPS-induced inflammation and stimulates the osteogenic differentiation of BMSCs via P2X7 receptor and MAPK signaling pathway

Oral diseases, such as periapical periodontitis and periodontitis, are characterized by inflammation-induced bone loss. LL-37, a human antimicrobial peptide (AMP), has multiple biological functions and the potential to promote osteogenesis. Therefore, this study aimed to investigate the regulatory effects of LL-37 within normal and inflammatory microenvironments. The roles of P2X7 receptor (P2X7R) and mitogen-activated protein kinase (MAPK) signaling pathway were also demonstrated. The results showed that LL-37 promoted bone marrow stromal cell (BMSC) proliferation, migration and osteogenic differentiation. LL-37 inhibited the expression of the inflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and receptor activator of nuclear factor kappa-B ligand (RANKL) at both protein and gene levels, and attenuated the lipopolysaccharide (LPS)-induced inhibition of osteogenesis. Immunofluorescence (IF) confirmed P2X7R expression in BMSCs. BBG, a P2X7R antagonist, significantly attenuated LL-37-promoted osteogenesis. The phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun NH2-terminal kinase (JNK) increased after LL-37 stimulation, which did not affect p38 phosphorylation. The effects of LL-37 on osteogenesis-related gene expression were markedly attenuated by selective inhibitors of ERK1/2 and JNK. Furthermore, a mouse model of LPS-stimulated calvarial osteolysis was established, and results showed that LL-37 markedly inhibited osteoclastic bone resorption. In conclusion, we speculate that LL-37 inhibits inflammation and promotes BMSC osteogenesis via P2X7R and MAPK signaling pathway.

Oestrogen receptor α regulates the odonto/osteogenic differentiation of stem cells from apical papilla via ERK and JNK MAPK pathways

OBJECTIVES

Oestrogen receptor (ER) is a common nucleus receptor that is essential for the regulation of cell growth, proliferation and differentiation. This study was to examine whether ERα can affect the proliferation and odonto/osteogenic differentiation of stem cells from apical papilla (SCAPs).

MATERIALS AND METHODS

Stem cells from apical papillas were isolated, purified and then transfected with ERα lentiviruses. The proliferation capacity was investigated by cell counting kit-8 (CCK-8) assay and flow cytometry. The odonto/osteogenic differentiation ability was analysed by alkaline phosphatase (ALP) activity, alizarin red staining, western blot assay (WB) and real-time RT-PCR. MAPK pathway and its downstream transcriptional factors were explored by WB assay.

RESULTS

As indicated by CCK-8 assay and flow cytometry, ERα had no significant effect on the proliferation of SCAPs. When ERα was overexpressed, the ALP activity and the formation of calcified nodules were significantly enhanced in SCAPs. Moreover, the odonto/osteogenic markers (DMP1/DMP1, DSPP/DSP, RUNX2/RUNX2, OCN/OCN) in SCAPs were significantly up-regulated at both mRNA and protein levels. On the contrary, the odonto/osteogenic differentiation ability of SCAPs was remarkably inhibited after suppression of ERα. Mechanistically, the protein levels of phosphorylated ERK and JNK significantly increased after ERα overexpression. Moreover, some downstream transcriptional factors of MAPK pathway were simultaneously activated by ERα overexpression.

CONCLUSIONS

Together, the data accumulated here indicated that ERα can enhance the odonto/osteogenic differentiation of SCAPs via ERK and JNK MAPK pathways.

WAIF1 Is a Cell-Surface CTHRC1 Binding Protein Coupling Bone Resorption and Formation

The osteoclast-derived collagen triple helix repeat containing 1 (CTHRC1) protein stimulates osteoblast differentiation, but the underlying mechanism remains unclear. Here, we identified Wnt-activated inhibitory factor 1 (WAIF1)/5T4 as a cell-surface protein binding CTHRC1. The WAIF1-encoding Trophoblast glycoprotein (Tpbg) gene, which is abundantly expressed in the brain and bone but not in other tissues, showed the same expression pattern as Cthrc1. Tpbg downregulation in marrow stromal cells reduced CTHRC1 binding and CTHRC1-stimulated alkaline phosphatase activity through PKCδ activation of MEK/ERK, suggesting a novel WAIF1/PKCδ/ERK pathway triggered by CTHRC1. Unexpectedly, osteoblast lineage-specific deletion of Tpbg downregulated Rankl expression in mouse bones and reduced both bone formation and resorption; importantly, it impaired bone mass recovery following RANKL-induced resorption, reproducing the phenotype of osteoclast-specific Cthrc1 deficiency. Thus, the binding of osteoclast-derived CTHRC1 to WAIF1 in stromal cells activates PKCδ-ERK osteoblastogenic signaling and serves as a key molecular link between bone resorption and formation during bone remodeling. © 2018 American Society for Bone and Mineral Research.

The MEK5/ERK5 mitogen-activated protein kinase cascade is an effector pathway of bone-sustaining bisphosphonates that regulates osteogenic differentiation and mineralization

Bisphosphonates play an important role in the treatment of metabolic bone diseases such as osteoporosis. In addition to their anti-resorptive activity by triggering osteoclast apoptosis, nitrogen-containing bisphosphonates (N-BP) may also influence osteogenic differentiation, which might rely on their capacity to inhibit the mevalonate pathway. In vascular endothelial cells inhibition of this pathway by cholesterol-lowering statins activates the MEK5/ERK5 mitogen-activated protein kinase cascade, which plays an important role in cellular differentiation, apoptosis or inflammatory processes. Here we evaluated whether N-BP may also target the MEK5/ERK5 pathway and analysed the consequences of ERK5 activation on osteogenic differentiation. We show that N-BP dose-dependently activate ERK5 in primary human endothelial cells and osteoblasts. The mechanism likely involves farnesyl pyrophosphate synthase inhibition and subsequent functional inhibition of the small GTPase Cdc42 since siRNA-mediated knockdown of both genes could reproduce N-BP-induced ERK5 activation. ERK5 activation resulted in regulation of several bone-relevant genes and was required for calcification and osteogenic differentiation of bone marrow-derived mesenchymal stems cells as evident by the lack of alkaline phosphatase induction and alizarin-red S staining observed upon ERK5 knockdown or upon differentiation initiation in presence of a pharmacological ERK5 inhibitor. Our data provide evidence that N-BP activate the MEK5/ERK5 cascade and reveal an essential role of ERK5 in osteogenic differentiation and mineralization of skeletal precursors.

MAPK signaling has stage-dependent osteogenic effects on human adipose-derived stem cells in vitro

OVERVIEW

The use of pro-osteogenic growth factors, such as BMP2, in human adipose-derived stem cell (ASC) osteogenesis is well described. Because these growth factors work via signal transduction pathways, such as the mitogen-activated protein kinase (MAPK) cascade, a study of the relationship between MAPK signaling and ASC osteogenesis was conducted.

MATERIALS AND METHODS

ERK, JNK, and p38MAPK activation were measured in ASCs osteo-induced using either dexamethasone or vitamin D3 and correlated with mineralization. Activation and mineralization were also measured without dexamethasone or using the glucocorticoid, cortisone. The expression of the MAPK phosphatase, MKP1, and its relationship to mineralization was also assessed. The effect of decreasing MAPK activation on mineralization through the use of exogenous inhibitors was examined along with siRNA-knockdown and adenoviral overexpression of ERK1/2. Finally, the effect of ERK1/2 overexpression on ASCs induced on PLGA scaffolds was assessed.

RESULTS

ASC mineralization in dexamethasone or vitamin D3-induced ASCs correlated with both increased ERK1/2 and JNK1/2 activation. ASCs induced without dexamethasone also mineralized, with JNK1/2 signaling possibly mediating this event. No link between cortisone induction and MAPK signaling could be ascertained. ASCs treated with ERK, JNK, or p38MAPK inhibitors showed decreased osteogenic gene expression and diminished mineralization. Mineralization levels were also affected by viruses designed to inhibit or augment ERK1/2 expression and activity. Finally, ASC mineralization appeared to be a balance between the MAPK kinase activity and MKP1.

CONCLUSIONS

It is likely that MAPK signaling plays a significant role in ASC osteogenesis, affecting differentiation in kinase- and stage-specific manners.

PD-1 is required to maintain stem cell properties in human dental pulp stem cells

Programmed cell death-1 (PD-1) belongs to an inhibitory signaling pathway capable of maintaining central and peripheral immune tolerance. Blockage of PD-1 has been identified as a promising immunotherapeutic approach for cancer and chronic infectious diseases. However, it is unknown whether PD-1 pathway regulates stem cell function. It is generally believed that mesenchymal stem cells (MSCs) produce PD-1 ligand, but fail to express PD-1. In this study, we show that neural crest-derived MSCs from dental pulp (MSC-DP), but not MSCs from bone marrow, expressed PD-1. Knocking down PD-1 expression in MSC-DP results in a significantly reduced capacity for cell proliferation and accelerated multipotential differentiation. Mechanistically, we show that PD-1 regulates a SHP2/ERK/Notch cascade to maintain proliferation and a SHP2/ERK/β-catenin cascade to inhibit osteo-/odontogenic differentiation. This study indicates that PD-1 is a key surface molecule controlling cell proliferation and multipotential differentiation of MSC-DP. Through regulating PD-1/SHP2/ERK signaling, we can significantly improve the quality and quantity of culture-expanded MSC-DP for potential clinical therapies.

The Effect and Osteoblast Signaling Response of Trace Silicon Doping Hydroxyapatite

It is commonly accepted that silicon-doped hydroxyapatite (HAp) can achieve good repair effects for both spinal fusion and bone defect filling. However, the underlying mechanism by which silicon aids such beneficial effects is still not fully understood. Herein, we report on silicon-doped hydroxyapatites with excellent biocompatibility to osteoblast cells and suggest the signaling pathway involved. Non-doped HAp and trace Si-doped HAp (Si/HAp) with Si concentration close to and higher than natural bones were synthesized (i.e., 32, 260, and 2000 ppm Si). The composition, crystal lattice vibration pattern, and morphology of these samples are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and SEM, respectively. Positive biological activities of these Si-doped HAp materials were demonstrated through a cytotoxicity study and with the MTT and alkaline phosphatase (ALP) activity assays. The Si-doped samples were not toxic to MC3T3-E1 cells. Indeed, osteoblast proliferation measurement illustrated that 2000 ppm Si-doped HAp increased osteoblast proliferation by about 1.6 times compared to non-doped HAp. The ALP assay also proves that the trace Si doping has the function to enhance cell proliferation and differentiation. The ALP assay showed that Si doping also enhanced cell differentiation. QRT-PCR results revealed that Si-doped HAp enhanced osteogenic differentiation of osteoblast cells by upregulating genes such as MAPK3, Fzd1, Wnt1, Lrp6, and BMP2. In conclusion, Si-doped HAp promotes osteoblast proliferation and differentiation by activating the Wnt/β-catenin and MAPK signaling pathways. This work could provide useful information of the beneficial effects of silicon in human bones and provide clues as to the molecular mechanism of the promotive effect of Si-doped HAp biomaterials.

Alginate-aker injectable composite hydrogels promoted irregular bone regeneration through stem cell recruitment and osteogenic differentiation

With SAG usage, the hBMSC migration ability was stimulated through CXCR4 elevation while osteogenic differentiation was promotedviathe ERK signaling pathway.

Sex dimorphic regulation of osteoprogenitor progesterone in bone stromal cells

Increasing peak bone mass is a promising strategy to prevent osteoporosis. A mouse model of global progesterone receptor (PR) ablation showed increased bone mass through a sex-dependent mechanism. Cre-Lox recombination was used to generate a mouse model of osteoprogenitor-specific PR inactivation, which recapitulated the high bone mass phenotype seen in the PR global knockout mouse mode. In this work, we employed RNA sequencing analysis to evaluate sex-independent and sex-dependent differences in gene transcription of osteoprogenitors of wild-type and PR conditional knockout mice. PR deletion caused marked sex hormone-dependent changes in gene transcription in male mice as compared to wild-type controls. These transcriptional differences revealed dysregulation in pathways involving immunomodulation, osteoclasts, bone anabolism, extracellular matrix interaction and matrix interaction. These results identified many potential mechanisms that may explain our observed high bone mass phenotype with sex differences when PR was selectively deleted in the MSCs.

Microarray gene expression of periosteum in spontaneous bone regeneration of mandibular segmental defects

Spontaneous bone regeneration could occur to reestablish mandibular bony continuity in patients who underwent partial or total mandibulectomy for tumors with periosteum-preserving. However, scarce data is available related to the precise role of periosteum in this bone regeneration. Therefore we aimed to investigate the gene expression of periosteum that were involved in the mandibular bone regeneration. Mandibular segmental defects were created in six mini-pigs with periosteum preserved. The periosteum of defects and control site were harvested at 1 and 2 weeks. Gene ontology (GO) analysis showed that the mechanisms concerning immature wound healing were clearly up-regulated at week 1. In contrast, by week-2, the GO categories of skeletal development, ossification and bone mineralization were significantly over-represented at week-2 with several genes encoding cell differentiation, extracellular matrix formation, and anatomical structure development. Furthermore, Tgfβ/Bmp, Wnt and Notch signaling were all related to the osteogenic process in this study. Besides osteogenesis, genes related to angiogenesis and neurogenesis were also prominent at week-2. These findings revealed that the gene expression profile of the periosteum’s cells participating in bone regeneration varied in different time points, and numbers of candidate genes that differentially expressed during early healing stages of intramembranous bone regeneration were suggested.

TGF-β inhibits osteogenesis by upregulating the expression of ubiquitin ligase SMURF1 via MAPK-ERK signaling

High incidence of osteoporotic fractures emphasizes the necessity of developing effective measures to promote osteogenesis. In our study, we investigated a possible role of MAPK-ERK signaling in the TGF-β-mediated osteoblastic differentiation. Our results indicated that TGF-β activated the MAPK-ERK pathway and inhibited osteogenesis in mesenchymal pluripotent cell line, C3H10T1/2, and preosteoblastic cell line, MC3T3 cells. And the downregulation of MAPK-ERK signaling using pharmacological inhibitor U0126 and RNA interference rescued osteoblast differentiation suppressed by TGF-β, which was confirmed by Alkaline phosphatase (ALP) staining and alizarrn red staining, and the enhanced expression of osteogenesic markers. Western blotting analysis indicated that TGF-β induced protein expression of E3 ubiquitin-protein ligase SMURF1, which contributed to the degradation of RUNX2 and SMAD1 as evidenced by SMURF1 inhibition using RNA interference and proteasome inhibitor MG132. Moreover, we observed that the expression of SMURF1 was decreased, while that of SMAD1 and RUNX2 increased by MAPK-ERK inhibitor U0126 in TGF-β-treated differentiating preosteoblasts, suggesting that MAPK-ERK regulated the transcription of osteogenesis-related genes. Furthermore, a synergistic effect between U0126 and bone morphogenic protein (BMP)-2 on osteoblast differentiation and bone formation was observed both in cell cultures and experimental animals. In conclusion, our results revealed that TGF-β inhibited osteoblastic differentiation by inducing the MAPK-ERK pathway which upregulated the expression of ubiquitin ligase SMURF1 and resulted in reduced presence of osteogenic proteins. In addition, the potentiation of BMP-2 on osteogenic activity by ERK1/2 inhibitor U0126 suggests that it may have potential clinical utility for promoting osteogenesis in bone fracture repair.

Hypoxia Promotes Osteogenesis of Human Placental-Derived Mesenchymal Stem Cells

Placental-derived mesenchymal stem cells (pMSCs) are promising candidates for regenerative medicine because they possess high proliferative capacity and multi-differentiation potential. Human pMSCs are residing in an environment with low oxygen tension in the body. Heme oxygenase-1 (HO-1) is known to participate in the regulation of MSC differentiation. The present study aimed to investigate the impact of hypoxia on the osteogenic differentiation of human pMSCs, and to elucidate the role of HO-1 in the osteogenic differentiation of hypoxic pMSCs. Human pMSCs were cultured under normoxia (21% O2) or hypoxia (5% O2) for 3 days. We found that hypoxia maintained the morphology and immunophenotype of human pMSCs. The expression of stemness markers Oct4, Nanog, and Sox2 was increased under hypoxia. After a 5-day hypoxic culture, the proliferation ability of pMSCs was increased, which might be correlated with the increased expression of stem cell factor. During osteogenic induction, hypoxia increased the expression of osteogenic genes including osteopontin, osteocalcin, and alkaline phosphatase (ALP). Moreover, hypoxia increased the mineralization and ALP levels of human pMSCs as evidenced by Alizarin Red staining and ALP staining. Upregulation of HO-1 by cobalt-protoporphyrin treatment increased the osteogenic differentiation of pMSCs under hypoxia, while inhibition of HO-1 by Zn-protoporphyrin reduced the osteogenic differentiation of hypoxic pMSCs. Taken together, our data suggest that hypoxia can promote the osteogenic differentiation of human pMSCs. Upregulation of HO-1 can further increase the osteogenesis of human pMSCs under hypoxia. Our findings will highlight the therapeutic potential of MSCs in the tissue engineering of bones.

RSPO3-LGR4 Regulates Osteogenic Differentiation Of Human Adipose-Derived Stem Cells Via ERK/FGF Signalling

The four R-spondins (RSPOs) and their three related receptors, LGR4, 5 and 6, have emerged as a major ligand-receptor system with critical roles in development and stem cell survival. However, the exact roles of the RSPO-LGR system in osteogenesis remain largely unknown. In the present study, we showed that RSPO3-shRNA increased the osteogenic potential of human adipose-derived stem cells (hASCs) significantly. Mechanistically, we demonstrated that RSPO3 is a negative regulator of ERK/FGF signalling. We confirmed that inhibition of the ERK1/2 signalling pathway blocked osteogenic differentiation in hASCs, and the increased osteogenic capacity observed after RSPO3 knockdown in hASCs was reversed by inhibition of ERK signalling. Further, silencing of LGR4 inhibited the activity of ERK signalling and osteogenic differentiation of hASCs. Most importantly, we found that loss of LGR4 abrogated RSPO3-regulated osteogenesis and RSPO3-induced ERK1/2 signalling inhibition. Collectively, our data show that ERK signalling works downstream of LGR4 and RSPO3 regulates osteoblastic differentiation of hASCs possibly via the LGR4-ERK signalling.

Temporal sequence of hard and soft tissue healing around titanium dental implants

The objective of the present review was to summarize the evidence available on the temporal sequence of hard and soft tissue healing around titanium dental implants in animal models and in humans. A search was undertaken to find animal and human studies reporting on the temporal dynamics of hard and soft tissue integration of titanium dental implants. Moreover, the influence of implant surface roughness and chemistry on the molecular mechanisms associated with osseointegration was also investigated. The findings indicated that the integration of titanium dental implants into hard and soft tissue represents the result of a complex cascade of biological events initiated by the surgical intervention. Implant placement into alveolar bone induces a cascade of healing events starting with clot formation and continuing with the maturation of bone in contact with the implant surface. From a genetic point of view, osseointegration is associated with a decrease in inflammation and an increase in osteogenesis-, angiogenesis- and neurogenesis-associated gene expression during the early stages of wound healing. The attachment and maturation of the soft tissue complex (i.e. epithelium and connective tissue) to implants becomes established 6-8 weeks following surgery. Based on the findings of the present review it can be concluded that improved understanding of the mechanisms associated with osseointegration will provide leads and targets for strategies aimed at enhancing the clinical performance of titanium dental implants.

Histone deacetylase 3 suppresses Erk phosphorylation and matrix metalloproteinase (Mmp)-13 activity in chondrocytes

Histone deacetylase (Hdac3) inhibitors are emerging therapies for many diseases including cancers and neurological disorders; however, these drugs are teratogens to the developing skeleton. Hdac3 is essential for proper endochondral ossification as its deletion in chondrocytes increases cytokine signaling and the expression of matrix remodeling enzymes. Here we explored the mechanism by which Hdac3 controls matrix metalloproteinase (Mmp)-13 expression in chondrocytes. In Hdac3-depleted chondrocytes, extracellular signal-regulated kinase (Erk)1/2 as well as its downstream substrate, Runx2, were hyperphosphorylated as a result of decreased expression and activity of the Erk1/2 specific phosphatase, Dusp6. Erk1/2 kinase inhibitors and Dusp6 adenoviruses reduced Mmp13 expression and partially rescued matrix production in Hdac3-deficient chondrocytes. Postnatal chondrocyte-specific deletion of Hdac3 with an inducible Col2a1-Cre caused premature production of pErk1/2 and Mmp13 in the growth plate. Thus, Hdac3 controls the temporal and spatial expression of tissue-remodeling genes in chondrocytes to ensure proper endochondral ossification during development.

Human Amnion-Derived Mesenchymal Stem Cells Protect Human Bone Marrow Mesenchymal Stem Cells against Oxidative Stress-Mediated Dysfunction via ERK1/2 MAPK Signaling

Epidemiological evidence suggests that bone is especially sensitive to oxidative stress, causing bone loss in the elderly. Previous studies indicated that human amnion-derived mesenchymal stem cells (HAMSCs), obtained from human amniotic membranes, exerted osteoprotective effects in vivo. However, the potential of HAMSCs as seed cells against oxidative stress-mediated dysfunction is unknown. In this study, we systemically investigated their antioxidative and osteogenic effects in vitro. Here, we demonstrated that HAMSCs signicantly promoted the proliferation and osteoblastic differentiation of H2O2-induced human bone marrow mesenchymal stem cells (HBMSCs), and down-regulated the reactive oxygen species (ROS) level. Further, our results suggest that activation of the ERK1/2 MAPK signal transduction pathway is essential for both HAMSCs-mediated osteogenic and protective effects against oxidative stress-induced dysfunction in HBMSCs. U0126, a highly selective inhibitor of extracellular ERK1/2 MAPK signaling, significantly suppressed the antioxidative and osteogenic effects in HAMSCs. In conclusion, by modulating HBMSCs, HAMSCs show a strong potential in treating oxidative stress- mediated bone deficiency.

Activation of the Extracellular Signal-Regulated Kinase Signaling Is Critical for Human Umbilical Cord Mesenchymal Stem Cell Osteogenic Differentiation

Human umbilical cord mesenchymal stem cells (hUCMSCs) are recognized as candidate progenitor cells for bone regeneration. However, the mechanism of hUCMSC osteogenesis remains unclear. In this study, we revealed that mitogen-activated protein kinases (MAPKs) signaling is involved in hUCMSC osteogenic differentiation in vitro. Particularly, the activation of c-Jun N-terminal kinases (JNK) and p38 signaling pathways maintained a consistent level in hUCMSCs through the entire 21-day osteogenic differentiation period. At the same time, the activation of extracellular signal-regulated kinases (ERK) signaling significantly increased from day 5, peaked at day 9, and declined thereafter. Moreover, gene profiling of osteogenic markers, alkaline phosphatase (ALP) activity measurement, and alizarin red staining demonstrated that the application of U0126, a specific inhibitor for ERK activation, completely prohibited hUCMSC osteogenic differentiation. However, when U0126 was removed from the culture at day 9, ERK activation and osteogenic differentiation of hUCMSCs were partially recovered. Together, these findings demonstrate that the activation of ERK signaling is essential for hUCMSC osteogenic differentiation, which points out the significance of ERK signaling pathway to regulate the osteogenic differentiation of hUCMSCs as an alternative cell source for bone tissue engineering.

MiR-221-inhibited adipose tissue-derived mesenchymal stem cells bioengineered in a nano-hydroxy apatite scaffold

The repair of skeletal defects is the main goal of bone tissue engineering. Recent literature highlighted various regulatory roles of microRNAs in stem cell fate determination. In addition, the role of porous hydroxyapatite/polycaprolacton (nHA/PCL) as a bioactive scaffold which enhances adipose tissue-derived mesenchymal stem cells (AT-MSCs) growth and osteogenic differentiation has been proved. The aim of the present study was to investigate the synergistic potential of both down-regulating miR-221 and nHA/PCL scaffold seeding in osteogenic potential of AT-MSCs. After isolation and characterization of AT-MSCs, the transfection of anti-miR-221 was performed into the cells using lipofectamine 2000 and the transfected cells were seeded into a synthesized nHA/PCL scaffold. The DAPI staining confirmed the presence of AT-MSCs on nHA/PCL scaffold. Quantitative expression of osteoblast marker genes, Runx2, and osteocalcin of the transfected cells in the scaffold were evaluated. Interestingly, significant upregulation of transcribed Runx2 and osteocalcin genes (P < 0.01) were observed in miR-221-inhibited nHA/PCL seeded cells. Also, alkaline phosphatase activity (ALP) was significantly higher (P < 0.01) in miR-221-inhibited AT-MSCs seeded on nHA/PCL than those seeded on nHA/PCL or transfected with anti-miR-221, individually. The results of this combination suggest a valuable method for enhancing osteogenesis in AT-MSCs. This method could be applicable for gene-cell therapy of bone defects.