Protein kinase C βII and δ/θ play critical roles in bone morphogenic protein-4-stimulated osteoblastic differentiation of MC3T3-E1 cells

DP2, a Carbohydrate Derivative, Enhances In Vitro Osteoblast Mineralisation

Bone fracture healing is a complex biological process involving four phases coordinated over time: hematoma formation, granulation tissue formation, bony callus formation, and bone remodelling. Bone fractures represent a significant health problem, particularly among the elderly population and patients with comorbidities. Therapeutic strategies proposed to treat such fractures include the use of autografts, allografts, and tissue engineering strategies. It has been shown that bone morphogenetic protein 2 (BMP-2) has a therapeutic potential to enhance fracture healing. Despite the clinical efficacy of BMP-2 in osteoinduction and bone repair, adverse side effects and complications have been reported. Therefore, in this in vitro study, we propose the use of a disaccharide compound (DP2) to improve the mineralisation process. We first evaluated the effect of DP2 on primary human osteoblasts (HOb), and then investigated the mechanisms involved. Our findings showed that (i) DP2 improved osteoblast differentiation by inducing alkaline phosphatase activity, osteopontin, and osteocalcin expression; (ii) DP2 induced earlier in vitro mineralisation in HOb cells compared to BMP-2 mainly by earlier activation of Runx2; and (iii) DP2 is internalized in HOb cells and activates the protein kinase C signalling pathway. Consequently, DP2 is a potential therapeutical candidate molecule for bone fracture repair.

Transcriptome dynamics of long noncoding RNAs and transcription factors demarcate human neonatal, adult, and human mesenchymal stem cell-derived engineered cartilage

The engineering of a native-like articular cartilage (AC) is a long-standing objective that could serve the clinical needs of millions of patients suffering from osteoarthritis and cartilage injury. An incomplete understanding of the developmental stages of AC has contributed to limited success in this endeavor. Using next generation RNA sequencing, we have transcriptionally characterized two critical stages of AC development in humans-that is, immature neonatal and mature adult, as well as tissue-engineered cartilage derived from culture expanded human mesenchymal stem cells. We identified key transcription factors (TFs) and long noncoding RNAs (lncRNAs) as candidate drivers of the distinct phenotypes of these tissues. AGTR2, SCGB3A1, TFCP2L1, RORC, and TBX4 stand out as key TFs, whose expression may be capable of reprogramming engineered cartilage into a more expandable and neonatal-like cartilage primed for maturation into biomechanically competent cartilage. We also identified that the transcriptional profiles of many annotated but poorly studied lncRNAs were dramatically different between these cartilages, indicating that lncRNAs may also be playing significant roles in cartilage biology. Key neonatal-specific lncRNAs identified include AC092818.1, AC099560.1, and KC877982. Collectively, our results suggest that tissue-engineered cartilage can be optimized for future clinical applications by the specific expression of TFs and lncRNAs.

Growth Factor Dose Tuning for Bone Progenitor Cell Proliferation and Differentiation on Resorbable Poly(propylene fumarate) Scaffolds

One approach to the development of an artificial graft material could rely on uniform coverage of a resorbable biomaterial with bone extracellular matrix (ECM). To achieve this on the surface of poly(propylene fumarate) (PPF) scaffolds, we selected a growth factor regime of basic fibroblast growth factor (FGF-2) (5 ng/mL), platelet-derived growth factor (PDGF-BB) (40 ng/mL), and epidermal growth factor (EGF) (20 ng/mL) to stimulate proliferation of bone marrow-derived human mesenchymal stem cells (BM-hMSCs). Bone morphogenetic protein (BMP) 4 (50 ng/mL), 6 (50 ng/mL), and 7 (27 ng/mL) in the presence of the following osteogenic substances: dexamethasone (10(-7) M), β-glycerophosphate (10 mM), and ascorbic acid (50 μg/mL) were chosen to induce differentiation of BM-hMSCs into ECM-secreting osteoblasts. These growth factors were also studied at 10× concentration to determine dose effect. Proliferation was analyzed by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, scanning electron microscopy (SEM), and toluidine blue staining, whereas differentiation was analyzed through alizarin red S staining and assay, alkaline phosphatase (ALP) staining and assay, and SEM. The proliferation study suggests that a combination of EGF, PDGF-BB, and FGF-2 growth factors at optimal concentration over a period of 1 week exhibits significantly (p = 0.001) higher number of cells (116,024 ± 5165) than these cytokines without EGF (91,706 ± 11,965). Increasing the dosage does not show any significant effect. The BM-hMSC differentiation study results show that ALP enzyme production and mineral deposition increase from day 14 to day 21 in all groups containing BMPs and osteogenic medium. However, mineralization is significantly higher in the BMP-7 group. Furthermore, the feasibility of translating the results from two dimensional thin films to three dimensional-printed PPF scaffolds was determined through uniform initial seeding and spreading of BM-hMSCs. Therefore, we have determined the optimum dose of growth factors for proliferation and differentiation of BM-hMSCs on the surface of PPF scaffolds, which can be used to produce ECM-coated implants for the treatment of bone defects.

Intermittent Administration of Parathyroid Hormone 1-34 Enhances Osteogenesis of Human Mesenchymal Stem Cells by Regulating Protein Kinase Cδ

Human mesenchymal stem cells (hMSCs) can differentiate into osteoblasts and are regulated by chemical cues. The recombinant N-terminal (1–34 amino acids) fragment of the parathyroid hormone (PTH (1–34)) is identified to promote osteogenesis. The osteoanabolic effects of intermittent PTH (1–34) treatment are linked to a complex consisting of signaling pathways; additionally, protein kinase C (PKC) act as mediators of multifunctional signaling transduction pathways, but the role of PKC δ (PKCδ), a downstream target in regulating osteoblast differentiation during intermittent administration of PTH (1–34) is less studied and still remains elusive. The purpose of this study is to examine the role of PKCδ during intermittent and continuous PTH (1–34) administration using osteoblast-lineage-committed hMSCs. Relative gene expression of osteoblast-specific genes demonstrated significant upregulation of RUNX2, type I Collagen, ALP, and Osterix and increased alkaline phosphatase activity in the presence of PTH (1–34). Intermittent PTH (1–34) administration increased PKC activity at day 7 of osteogenic differentiation, whereas inhibition of PKC activity attenuated these effects. In addition, the specific isoform PKCδ was activated upon treatment. These findings demonstrate that intermittent PTH (1–34) treatment enhances the osteogenesis of hMSCs by upregulating osteoblast-specific genes via PKCδ activation.

Orthodontic Forces Induce the Cytoprotective Enzyme Heme Oxygenase-1 in Rats

Orthodontic forces disturb the microenvironment of the periodontal ligament (PDL), and induce craniofacial bone remodeling which is necessary for tooth movement. Unfortunately, orthodontic tooth movement is often hampered by ischemic injury and cell death within the PDL (hyalinization) and root resorption. Large inter-individual differences in hyalinization and root resorption have been observed, and may be explained by differential protection against hyalinization. Heme oxygenase-1 (HO-1) forms an important protective mechanism by breaking down heme into the strong anti-oxidants biliverdin/bilirubin and the signaling molecule carbon monoxide. These versatile HO-1 products protect against ischemic and inflammatory injury. We postulate that orthodontic forces induce HO-1 expression in the PDL during experimental tooth movement. Twenty-five 6-week-old male Wistar rats were used in this study. The upper three molars at one side were moved mesially using a Nickel-Titanium coil spring, providing a continuous orthodontic force of 10 cN. The contralateral side served as control. After 6, 12, 72, 96, and 120 h groups of rats were killed. On parasagittal sections immunohistochemical staining was performed for analysis of HO-1 expression and quantification of osteoclasts. Orthodontic force induced a significant time-dependent HO-1 expression in mononuclear cells within the PDL at both the apposition- and resorption side. Shortly after placement of the orthodontic appliance HO-1 expression was highly induced in PDL cells but dropped to control levels within 72 h. Some osteoclasts were also HO-1 positive but this induction was shown to be independent of time- and mechanical stress. It is tempting to speculate that differential induction of tissue protecting- and osteoclast activating genes in the PDL determine the level of bone resorption and hyalinization and, subsequently, “fast” and “slow” tooth movers during orthodontic treatment.

DNA methylation is critical for tooth agenesis: implications for sporadic non-syndromic anodontia and hypodontia

Hypodontia is caused by interactions among genetic, epigenetic, and environmental factors during tooth development, but the actual mechanism is unknown. DNA methylation now appears to play a significant role in abnormal developments, flawed phenotypes, and acquired diseases. Methylated DNA immunoprecipitation (MeDIP) has been developed as a new method of scanning large-scale DNA-methylation profiles within particular regions or in the entire genome. Here, we performed a genome-wide scan of paired DNA samples obtained from 4 patients lacking two mandibular incisors and 4 healthy controls with normal dentition. We scanned another female with non-syndromic anodontia and her younger brother with the same gene mutations of the PAX9,MSX1,AXIN2 and EDA, but without developmental abnormalities in the dentition. Results showed significant differences in the methylation level of the whole genome between the hypodontia and the normal groups. Nine genes were spotted, some of which have not been associated with dental development; these genes were related mainly to the development of cartilage, bone, teeth, and neural transduction, which implied a potential gene cascade network in hypodontia at the methylation level. This pilot study reveals the critical role of DNA methylation in hypodontia and might provide insights into developmental biology and the pathobiology of acquired diseases.

The osteogenic or adipogenic lineage commitment of human mesenchymal stem cells is determined by protein kinase C delta

BACKGROUND

Mesenchymal stem cells (MSCs) have the potential to differentiate into specialized cell lineages such as osteoblasts and adipocytes in vitro. There exists a reciprocal relationship between osteogenic and adipogenic differentiation of MSCs that an osteogenic phenotype occurs at the expense of an adipogenic phenotype and vice versa, which in turn influence one another's phenotype through negative feedback loops. Thus, it is important to understand what signaling molecules modulate the lineage commitment of MSCs. Protein kinase C (PKC) plays a central role in cellular signal transduction for mediating diverse biological functions, and dysregulation of PKC activity is involved in various metabolic diseases including cancer, diabetes, and heart disease. Although the role of individual PKC isoforms has been investigated in various fields, the potential role of PKC in bone metabolism is not completely understood. In this study, we investigated the potential role of PKCδ in osteogenic lineage commitment of human bone marrow-derived mesenchymal stem cells (hBMSCs).

RESULTS

We observed that expression and phosphorylation of PKCδ were increased during osteogenic differentiation of hBMSCs. Pharmacological inhibition and genetic ablation of PKCδ in hBMSCs resulted in a significant attenuation of osteogenic differentiation as evidenced by reduced ALP activity and ECM mineralization, as well as down-regulation of the expression of osteoblast-specific genes. These effects were also accompanied by induction of adipogenic differentiation and up-regulation of the expression of adipocyte-specific genes involved in lipid synthesis in osteogenic induction of hBMSCs. Additionally, the activation of AMPK, which is a key cellular energy sensor, induced osteogenesis of hBMSCs. However, the inhibition of AMPK activity by compound C did not affect the activation of PKCδ at all, indicating that there is no direct correlation between AMPK and PKCδ in osteogenesis of hBMSCs.

CONCLUSIONS

These results suggest that PKCδ is a critical regulator for the balance between osteogenesis and adipogenesis of hBMSCs and thus has a potential novel therapeutic target for the treatment of metabolic bone diseases.

Molars and incisors: show your microarray IDs

Background

One of the key questions in developmental biology is how, from a relatively small number of conserved signaling pathways, is it possible to generate organs displaying a wide range of shapes, tissue organization, and function. The dentition and its distinct specific tooth types represent a valuable system to address the issues of differential molecular signatures. To identify such signatures, we performed a comparative transcriptomic analysis of developing murine lower incisors, mandibular molars and maxillary molars at the developmental cap stage (E14.5).

Results

231 genes were identified as being differentially expressed between mandibular incisors and molars, with a fold change higher than 2 and a false discovery rate lower than 0.1, whereas only 96 genes were discovered as being differentially expressed between mandibular and maxillary molars. Numerous genes belonging to specific signaling pathways (the Hedgehog, Notch, Wnt, FGF, TGFβ/BMP, and retinoic acid pathways), and/or to the homeobox gene superfamily, were also uncovered when a less stringent fold change threshold was used. Differential expressions for 10 out of 12 (mandibular incisors versus molars) and 9 out of 10 selected genes were confirmed by quantitative reverse transcription-PCR (qRT-PCR). A bioinformatics tool (Ingenuity Pathway Analysis) used to analyze biological functions and pathways on the group of incisor versus molar differentially expressed genes revealed that 143 genes belonged to 9 networks with intermolecular connections. Networks with the highest significance scores were centered on the TNF/NFκB complex and the ERK1/2 kinases. Two networks ERK1/2 kinases and tretinoin were involved in differential molar morphogenesis.

Conclusion

These data allowed us to build several regulatory networks that may distinguish incisor versus molar identity, and may be useful for further investigations of these tooth-specific ontogenetic programs. These programs may be dysregulated in transgenic animal models and related human diseases leading to dental anomalies.

Diabetes-induced increased oxidative stress in cardiomyocytes is sustained by a positive feedback loop involving Rho kinase and PKCβ2

We previously reported that acute inhibition of the RhoA/Rho kinase (ROCK) pathway normalized contractile function of diabetic rat hearts, but the underlying mechanism is unclear. Protein kinase C (PKC) β(2) has been proposed to play a major role in diabetic cardiomyopathy at least in part by increasing oxidative stress. Further evidence suggests that PKC positively regulates RhoA expression through induction of inducible nitric oxide synthase (iNOS) in diabetes. However, in preliminary studies, we found that inhibition of ROCK itself reduced RhoA expression in diabetic hearts. We hypothesized that there is an interaction between RhoA/ROCK and PKCβ(2) in the form of a positive feedback loop that sustains their activation and the production of reactive oxygen species (ROS). This was investigated in cardiomyocytes isolated from diabetic and control rat hearts, incubated with or without cytochalasin D or inhibitors of ROCK, RhoA, PKCβ(2), or iNOS. Inhibition of RhoA and ROCK markedly attenuated the diabetes-induced increases in PKCβ(2) activity and iNOS and RhoA expression in diabetic cardiomyocytes, while having no effect in control cells. Inhibition of PKCβ(2) and iNOS also normalized RhoA expression and ROCK overactivation, whereas iNOS inhibition reversed the increase in PKCβ(2) activity. Each of these treatments also normalized the diabetes-induced increase in production of ROS. Actin cytoskeleton disruption attenuated the increased expression and/or activity of all of these targets in diabetic cardiomyocytes. These data suggest that, in the diabetic heart, the RhoA/ROCK pathway contributes to contractile dysfunction at least in part by sustaining PKCβ(2) activation and ROS production via a positive feedback loop that requires an intact cytoskeleton.

PKC signaling inhibits osteogenic differentiation through the regulation of Msx2 function

Protein kinase C (PKC) signaling regulates osteoblast differentiation, but little is known about its downstream effectors. We examined the effect of modulating PKC activity on osteogenic transcription factors and found that the protein level of Msx2 is affected. Msx2 is induced by osteogenic signals such as BMPs and it plays critical roles in bone formation and osteoblast differentiation. Here, we examined the role of PKC signaling in regulating the function of Msx2. We found that the inhibition of PKC signaling enhances osteogenic differentiation in BMP2-stimulated C2C12 cells. Treatment with inhibitors of PKC activity or overexpression of kinase-defective (KD), dominant-negative mutant PKC isoforms strongly reduced the level of Msx2 protein. Several PKC isoforms (α, β, δ, and ζ) interacted with Msx2, and PKCβ phosphorylated Msx2 at Thr135 and Thr141. Msx2 repressed the transcriptional activity of the osteogenic transcription factor Runx2, and this repression was relieved by inhibition of PKC activity or overexpression of the KD mutant PKC isoforms. In addition, PKC prolonged the half-life of Msx2 protein. These results suggest that PKC signaling modulates osteoblast differentiation, at least in part, through the regulation of Msx2.

Special AT-rich sequence-binding protein 2 and its related genes play key roles in the differentiation of MC3T3-E1 osteoblast like cells

Special AT-rich sequence-binding protein (SATB) plays a critical role in bone generation and osteoblast differentiation. In the present study, the differentially expressed genes by SATB2 overexpression were analyzed in MC3T3-E1 osteoblast-like cells using Alizarin red S staining, wound healing assay and Agilent's Human Oligo Microarray. Calcium mineralization and motility were significantly enhanced in SATB2-overexpressed cells compared with untreated control. In addition, using the GeneSpringGX 7.3 program to compare the identified genes expressed in SATB2-overexpresed cells with untreated control, we found several unique genes closely associated with osteoblast differentiation, including SOX2, MBP2, WNT11 and MEN1 (up-regulated genes), and ILK, FGF23, FGFR2, and SNAI1 (down-regulated genes). Consistent with microarray data, real-time RT-PCR confirmed the significant up- and down-regulation of these genes at mRNA level in SATB2-overexpressed MC3T3-E1 cells. Overall, our findings suggest that the molecular regulation of SATB2 can be an attractive approach to develop a novel therapeutic strategy for bone-related diseases.

Melatonin promotes osteoblastic differentiation through the BMP/ERK/Wnt signaling pathways

Although melatonin has a variety of biological actions such as antitumor, antiangiogenic, and antioxidant activities, the osteogenic mechanism of melatonin still remains unclear. Thus, in the present study, the molecular mechanism of melatonin was elucidated in the differentiation of mouse osteoblastic MC3T3-E1 cells. Melatonin enhanced osteoblastic differentiation and mineralization compared to untreated controls in preosteoblastic MC3T3-E1 cells. Also, melatonin increased wound healing and dose-dependently activated osteogenesis markers such as runt-related transcription factor 2 (Runx2), osteocalcin (OCN), bone morphogenic protein (BMP)-2 and -4 in MC3T3-E1 cells. Of note, melatonin activated Wnt 5 α/β, β-catenin and the phosphorylation of c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) in a time-dependent manner while it attenuated phosphorylation of glycogen synthase kinase 3 beta (GSK-3β) in MC3T3-E1 cells. Consistently, confocal microscope observation revealed that BMP inhibitor Noggin blocked melatonin-induced nuclear localization of β-catenin. Furthermore, Western blotting showed that Noggin reversed activation of β-catenin and Wnt5 α/β and suppression of GSK-3β induced by melatonin in MC3T3-E1 cells, which was similarly induced by ERK inhibitor PD98059. Overall, these findings demonstrate that melatonin promotes osteoblastic differentiation and mineralization in MC3T3-E1 cells via the BMP/ERK/Wnt pathways.

An oligodeoxynucleotide with promising modulation activity for the proliferation and activation of osteoblast

The paper explored the regulatory role of oligodeoxynucleotides (ODNs) with specific sequences in the proliferation and activation of osteoblast, using human osteoblast-like cell line MG 63 as the model. Through the administration of ODNs to MG 63 cells at a concentration of 1.0 μg/mL, ODN MT01 with positive effects on proliferation and activation of osteoblast was selected from 11 different ODNs by methyl thiazolyl tetrazolium (MTT) assay and alkaline phosphatase (ALP) activity measurement. To get a deeper insight into the molecular mechanism, effects of ODN MT01 treatment on the expression level of Sp7, runx-2, collagen-I, osteoprotegerin (OPG) and RANK ligand (RANKL) were determined using quantitative real time PCR and Western blotting. Remarkably, the mRNA and protein expression levels of Sp7, runx-2, collagen-I and OPG were improved after ODN MT01 treatment. Meanwhile, the protein expression level of RANKL was dramatically decreased. These results suggested that ODN MT01 had a significant impact in facilitating osteogenic proliferation and activation, and provided a direct evidence for the notion that single strand ODN could regulate the balance of bone formation and resorption, and thus was of great potential in the rebuilding of alveolar bone.