Fam20c regulates the calpain proteolysis system through phosphorylating Calpasatatin to maintain cell homeostasis

BACKGROUND

The family with sequence similarity 20-member C (FAM20C) kinase, a Golgi casein kinase, which is responsible for phosphorylating the majority of the extracellular phosphoproteins within S-x-E/pS motifs, and is fundamentally associated with multiple biological processes to maintain cell proliferation, biomineralization, migration, adhesion, and phosphate homeostasis. In dissecting how FAM20C regulates downstream molecules and potential mechanisms, however, there are multiple target molecules of FAM20C, particularly many phenomena remain elusive, such as changes in cell-autonomous behaviors, incompatibility in genotypes and phenotypes, and others.

METHODS

Here, assay for transposase-accessible chromatin using sequencing (ATAC-seq), RNA sequencing (RNA-seq), proteomics, and phosphoproteomics were performed in Fam20c-dificient osteoblasts and to facilitate an integrated analysis and determine the impact of chromatin accessibility, genomic expression, protein alterations, signaling pathway, and post translational modifcations.

RESULTS

By combining ATAC-seq and RNA-seq, we identified TCF4 and Wnt signaling pathway as the key regulators in Fam20c-dificient cells. Further, we showed Calpastatin/Calpain proteolysis system as a novel target axis for FAM20C to regulate cell migration and F-actin cytoskeleton by integrated analysis of proteomics and phosphoproteomics. Furthermore, Calpastatin/Calpain proteolysis system could negatively regulate the Wnt signaling pathway.

CONCLUSION

These observations implied that Fam20c knockout osteoblasts would cause cell homeostatic imbalance, involving changes in multiple signaling pathways in the conduction system.

Improving bone morphogenetic protein (BMP) production in CHO cells through understanding of BMP synthesis, signaling and endocytosis

Bone morphogenetic proteins (BMPs) are a group of growth factors with the clinical potential to regulate cartilage and bone formation. Functionally active mature recombinant human BMPs (rhBMPs), produced primarily in Chinese hamster ovary (CHO) cells for clinical applications, are considered difficult to express because they undergo maturation processes, signaling pathways, or endocytosis. Although BMPs are a family of proteins with similar mature domain sequence identities, their individual properties are diverse. Thus, understanding the properties of individual rhBMPs is essential to improve rhBMP production in CHO cells. In this review, we discuss various approaches to improve rhBMP production in CHO cells by understanding the overall maturation process, signaling pathways and endocytosis of individual rhBMPs.

An In Vitro and In Vivo Comparison of Osteogenic Differentiation of Human Mesenchymal Stromal/Stem Cells

The use of stem cells in regenerative medicine, including tissue engineering and transplantation, has generated a great deal of enthusiasm. Mesenchymal stromal/stem cells (MSCs) can be isolated from various tissues, most commonly, bone marrow but more recently adipose tissue, dental pulp, and Wharton's jelly, to name a few. MSCs display varying phenotypic profiles and osteogenic differentiating capacity depending and their site of origin. MSCs have been successfully differentiated into osteoblasts both in vitro an in vivo but discrepancies exist when the two are compared: what happens in vitro does not necessarily happen in vivo, and it is therefore important to understand why these differences occur. The osteogenic process is a complex network of transcription factors, stimulators, inhibitors, proteins, etc., and in vivo experiments are helpful in evaluating the various aspects of this osteogenic process without distractions and confounding variables. With that in mind, the results of in vitro experiments need to be carefully considered and interpreted with caution as they do not perfectly replicate the conditions found within living organisms. This is where in vivo experiments help us better understand interactions that might occur in the osteogenic process that cannot be replicated in vitro. Potentially, these differences could also be exploited to develop an optimal MSC cell therapeutic product that can be used for bone disorders. There are many bone disorders, most of which cause a great deal of discomfort. Clinically acceptable protocols could be developed in which MSCs are used to aid in bone regeneration providing relief for patients with chronic pain. The aim of this review is to examine the differences between studies conducted in vitro and in vivo with regard to the osteogenic process to better define the gaps in current osteogenic research. By better understanding osteogenic differentiation, we can better define treatment strategies for various bone disorders.

Pivotal role of Transient Receptor Potential Channels in oral physiology

BACKGROUND

Transient Receptor Potential (TRP) Channels constitute a large family of non-selective permeable ion channels involved in the perception of environmental stimuli with a central and continuously expanding role in oral tissue homeostasis. Recent studies indicate the regulatory role of TRPs in pulp physiology, oral mucosa sensation, dental pain nociception and salivary gland secretion. This review provides an update on the diverse functions of TRP channels in the physiology of oral cavity, with emphasis on their cellular location, the underlying molecular mechanisms and clinical significance.

METHODS

A structured search of bibliographic databases (PubMed and MEDLINE) was performed for peer reviewed studies on TRP channels function on oral cavity physiology the last ten years. A qualitative content analysis was performed in screened papers and a critical discussion of main findings is provided.

RESULTS

TRPs expression has been detected in major cell types of the oral cavity, including odontoblasts, periodontal ligament, oral epithelial, salivary gland cells, and chondrocytes of temporomandibular joints, where they mediate signal perception and transduction of mechanical, thermal, and osmotic stimuli. They contribute to pulp physiology through dentin formation, mineralization, and periodontal ligament formation along with alveolar bone remodeling in dental pulp and periodontal ligament cells. TRPs are also involved in oral mucosa sensation, dental pain nociception, saliva secretion, swallowing reflex and temporomandibular joints' development.

CONCLUSION

Various TRP channels regulate oral cavity homeostasis, playing an important role in the transduction of external stimuli to intracellular signals in a cell type-specific manner and presenting promising drug targets for the development of pharmacological strategies to manage oral diseases.

Combination of BMP2 and EZH2 Inhibition to Stimulate Osteogenesis in a 3D Bone Reconstruction Model

High concentrations of bone morphogenetic protein 2 (BMP2) in bone regeneration cause adverse events (e.g, heterotopic bone formation and acute inflammation). This study examines novel epigenetic strategies (i.e., EZH2 inhibition) for augmenting osteogenesis, thereby aiming to reduce the required BMP2 dose in vivo for bone regeneration and minimize these adverse effects. Human bone marrow-derived mesenchymal stem cells (BMSCs) were grown on three-dimensional (3D)-printed medical-grade polycaprolactone scaffolds and incubated in osteogenic media containing 50 ng/mL BMP2 and/or 5 μM GSK126 (EZH2 inhibitor) for 6 days (n = 3 per group and timepoint). Constructs were harvested for realtime quantitative polymerase chain reaction analysis at Day 10 and immunofluorescence (IF) microscopy at Day 21. After pretreating for 6 days and maintaining in osteogenic media for 4 days, BMSC-seeded scaffolds were also implanted in an immunocompromised subcutaneous murine model (n = 39; 3/group/donor and 3 control scaffolds) for histological analysis at 8 weeks. Pretreatment of BMSCs with BMP2 and BMP2/GSK126 costimulated expression of osteoblast-related genes (e.g., IBSP, SP7, RUNX2, and DLX5), as well as protein accumulation (e.g., collagen type 1/COL1A1 and osteocalcin/BGLAP) based on IF staining. While in vivo implantation for 8 weeks did not result in bone formation, increased angiogenesis was observed in BMP2 and BMP2/GSK126 groups. This study finds that BMP2 and GSK126 costimulate osteogenic differentiation of MSCs on 3D scaffolds in vitro and may contribute to enhanced vascularization when implanted in vivo to support bone formation. Thus, epigenetic priming with EZH2 inhibitors may have translational potential in bone healing by permitting a reduction of BMP2 dosing in vivo to mitigate its side effects. Impact statement While autografts are still the gold standard for bone reconstruction, tissue availability and donor morbidity are significant limitations. Previous attempts to use high concentrations of bone morphogenetic protein 2 (BMP2) have been shown to cause adverse events such as excessive bone formation and acute inflammation. Overall, the utilization of EZH2 inhibitors to modulate gene expression in favor of bone healing has been demonstrated in vitro in a tissue engineering strategy. Our study will pave the way to developing tissue engineering strategies involving GSK126 as an adjuvant to increase the effects of BMP2 for stimulating cells of interest on a three-dimensional scaffold for bone regeneration.

Local Wnt3a treatment restores bone regeneration in large osseous defects after surgical debridement of osteomyelitis

Impaired bone homeostasis caused by osteomyelitis provokes serious variations in the bone remodeling process, thereby involving multiple inflammatory cytokines to activate bone healing. We have previously established a mouse model for post-traumatic osteomyelitis and studied bone regeneration after sufficient debridement. Moreover, we could further characterize the postinfectious inflammatory state of bony defects after debridement with elevated osteoclasts and decreased bone formation despite the absence of bacteria. In this study, we investigated the positive effects of Wnt-pathway modulation on bone regeneration in our previous established mouse model. This was achieved by local application of Wnt3a, a recombinant activator of the canonical Wnt-pathway. Application of Wnt3a could enhance new bone formation, which was verified by histological and μ-CT analysis. Moreover, histology and western blots revealed enhanced osteoblastogenesis and downregulated osteoclasts in a RANKL-dependent manner. Further analysis of Wnt-pathway showed downregulation after bone infections were reconstituted by application of Wnt3a. Interestingly, Wnt-inhibitory proteins Dickkopf 1 (DKK1), sclerostin, and secreted frizzled protein 1 (sFRP1) were upregulated simultaneously to Wnt-pathway activation, indicating a negative feedback for active form of Beta-catenin. In this study, we could demonstrate enhanced bone formation in defects caused by post-traumatic osteomyelitis after Wnt3a application. KEY MESSAGES: Osteomyelitis decreases bone regeneration Wnt3a restores bone healing after infection Canonical Wnt-pathway activation with negative feedback.

Inhibition of the epigenetic suppressor EZH2 primes osteogenic differentiation mediated by BMP2

Bone-stimulatory therapeutics include bone morphogenetic proteins (e.g. BMP2), parathyroid hormone, and antibody-based suppression of WNT antagonists. Inhibition of the epigenetic enzyme enhancer of zeste homolog 2 (EZH2) is both bone anabolic and osteoprotective. EZH2 inhibition stimulates key components of bone-stimulatory signaling pathways, including the BMP2 signaling cascade. Because of high costs and adverse effects associated with BMP2 use, here we investigated whether BMP2 dosing can be reduced by co-treatment with EZH2 inhibitors. Co-administration of BMP2 with the EZH2 inhibitor GSK126 enhanced differentiation of murine (MC3T3) osteoblasts, reflected by increased alkaline phosphatase activity, Alizarin Red staining, and expression of bone-related marker genes (e.g. Bglap and Phospho1). Strikingly, co-treatment with BMP2 (10 ng/ml) and GSK126 (5 μm) was synergistic and was as effective as 50 ng/ml BMP2 at inducing MC3T3 osteoblastogenesis. Similarly, the BMP2-GSK126 co-treatment stimulated osteogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells, reflected by induction of key osteogenic markers (e.g. Osterix/SP7 and IBSP). A combination of BMP2 (300 ng local) and GSK126 (5 μg local and 5 days of 50 mg/kg systemic) yielded more consistent bone healing than single treatments with either compound in a mouse calvarial critical-sized defect model according to results from μCT, histomorphometry, and surgical grading of qualitative X-rays. We conclude that EZH2 inhibition facilitates BMP2-mediated induction of osteogenic differentiation of progenitor cells and maturation of committed osteoblasts. We propose that epigenetic priming, coupled with bone anabolic agents, enhances osteogenesis and could be leveraged in therapeutic strategies to improve bone mass.

Extracellular Matrix in Secondary Palate Development

The secondary palate arises from outgrowths of epithelia-covered embryonic mesenchyme that grow from the maxillary prominence, remodel to meet over the tongue, and fuse at the midline. These events require the coordination of cell proliferation, migration, and gene expression, all of which take place in the context of the extracellular matrix (ECM). Palatal cells generate their ECM, and then stiffen, degrade, or otherwise modify its properties to achieve the required cell movement and organization during palatogenesis. The ECM, in turn, acts on the cells through their matrix receptors to change their gene expression and thus their phenotype. The number of ECM-related gene mutations that cause cleft palate in mice and humans is a testament to the crucial role the matrix plays in palate development and a reminder that understanding that role is vital to our progress in treating palate deformities. This article will review the known ECM constituents at each stage of palatogenesis, the mechanisms of tissue reorganization and cell migration through the palatal ECM, the reciprocal relationship between the ECM and gene expression, and human syndromes with cleft palate that arise from mutations of ECM proteins and their regulators. Anat Rec, 2019. © 2019 American Association for Anatomy.

Directed Differentiation of Human Pluripotent Stem Cells to Podocytes under Defined Conditions

A major cause of chronic kidney disease (CKD) is glomerular disease, which can be attributed to a spectrum of podocyte disorders. Podocytes are non-proliferative, terminally differentiated cells. Thus, the limited supply of primary podocytes impedes CKD research. Differentiation of human pluripotent stem cells (hPSCs) into podocytes has the potential to produce podocytes for disease modeling, drug screening, and cell therapies. In the podocyte differentiation process described here, hPSCs are first induced to primitive streak-like cells by activating canonical Wnt signaling. Next, these cells progress to mesoderm precursors, proliferative nephron progenitors, and eventually become mature podocytes by culturing in a serum-free medium. Podocytes generated via this protocol adopt podocyte morphology, express canonical podocyte markers, and exhibit podocyte phenotypes, including albumin uptake and TGF-β1 triggered cell death. This study provides a simple, defined strategy to generate podocytes for in vitro modeling of podocyte development and disease or for cell therapies.

Trans-differentiation via Epigenetics: A New Paradigm in the Bone Regeneration

In regenerative medicine, growing cells or tissues in the laboratory is necessary when damaged cells can not heal by themselves. Acquisition of the required cells from the patient's own cells or tissues is an ideal option without additive side effects. In this context, cell reprogramming methods, including the use of induced pluripotent stem cells (iPSCs) and trans-differentiation, have been widely studied in regenerative research. Both approaches have advantages and disadvantages, and the possibility of de-differentiation because of the epigenetic memory of iPSCs has strengthened the need for controlling the epigenetic background for successful cell reprogramming. Therefore, interest in epigenetics has increased in the field of regenerative medicine. Herein, we outline in detail the cell trans-differentiation method using epigenetic modification for bone regeneration in comparison to the use of iPSCs.

Distinct DNA methylation profiles in bone and blood of osteoporotic and healthy postmenopausal women

DNA methylation affects expression of associated genes and may contribute to the missing genetic effects from genome-wide association studies of osteoporosis. To improve insight into the mechanisms of postmenopausal osteoporosis, we combined transcript profiling with DNA methylation analyses in bone. RNA and DNA were isolated from 84 bone biopsies of postmenopausal donors varying markedly in bone mineral density (BMD). In all, 2529 CpGs in the top 100 genes most significantly associated with BMD were analyzed. The methylation levels at 63 CpGs differed significantly between healthy and osteoporotic women at 10% false discovery rate (FDR). Five of these CpGs at 5% FDR could explain 14% of BMD variation. To test whether blood DNA methylation reflect the situation in bone (as shown for other tissues), an independent cohort was selected and BMD association was demonstrated in blood for 13 of the 63 CpGs. Four transcripts representing inhibitors of bone metabolism-MEPE, SOST, WIF1, and DKK1-showed correlation to a high number of methylated CpGs, at 5% FDR. Our results link DNA methylation to the genetic influence modifying the skeleton, and the data suggest a complex interaction between CpG methylation and gene regulation. This is the first study in the hitherto largest number of postmenopausal women to demonstrate a strong association among bone CpG methylation, transcript levels, and BMD/fracture. This new insight may have implications for evaluation of osteoporosis stage and susceptibility.

An HDAC Inhibitor, Entinostat/MS-275, Partially Prevents Delayed Cranial Suture Closure in Heterozygous Runx2 Null Mice

Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal disorder caused by mutations in RUNX2, coding a key transcription factor of early osteogenesis. CCD patients suffer from developmental defects in cranial bones. Despite numerous investigations and clinical approaches, no therapeutic strategy has been suggested to prevent CCD. Here, we show that fetal administration of Entinostat/MS-275, a class I histone deacetylase (HDAC)-specific inhibitor, partially prevents delayed closure of cranial sutures in Runx2^+/- mice strain of C57BL/6J by two mechanisms: 1) posttranslational acetylation of Runx2 protein, which stabilized the protein and activated its transcriptional activity; and 2) epigenetic regulation of Runx2 and other bone marker genes. Moreover, we show that MS-275 stimulates osteoblast proliferation effectively both in vivo and in vitro, suggesting that delayed skeletal development in CCD is closely related to the decreased number of progenitor cells as well as the delayed osteogenic differentiation. These findings provide the potential benefits of the therapeutic strategy using MS-275 to prevent CCD. © 2017 American Society for Bone and Mineral Research.

Pin1, the Master Orchestrator of Bone Cell Differentiation

Pin1 is an enzyme that specifically recognizes the peptide bond between phosphorylated serine or threonine (pS/pT-P) and proline. This recognition causes a conformational change of its substrate, which further regulates downstream signaling. Pin1^-/- mice show developmental bone defects and reduced mineralization. Pin1 targets RUNX2 (Runt-Related Transcription Factor 2), SMAD1/5, and β-catenin in the FGF, BMP, and WNT pathways, respectively. Pin1 has multiple roles in the crosstalk between different anabolic bone signaling pathways. For example, it controls different aspects of osteoblastogenesis and increases the transcriptional activity of Runx2, both directly and indirectly. Pin1 also influences osteoclastogenesis at different stages by targeting PU.1 (Purine-rich nucleic acid binding protein 1), C-FOS, and DC-STAMP. The phenotype of Pin1^-/- mice has led to the recent identification of multiple roles of Pin1 in different molecular pathways in bone cells. These roles suggest that Pin1 can be utilized as an efficient drug target in congenital and acquired bone diseases. J. Cell. Physiol. 232: 2339-2347, 2017. © 2016 Wiley Periodicals, Inc.

Effect of PET graft coated with silk fibroin via EDC/NHS crosslink on graft-bone healing in ACL reconstruction

SF coating via EDC/NHS crosslink improved the osseointegration of PET ligaments within the bone tunnel.

PPARG Post-translational Modifications Regulate Bone Formation and Bone Resorption

The peroxisome proliferator-activated receptor gamma (PPARγ) regulates osteoblast and osteoclast differentiation, and is the molecular target of thiazolidinediones (TZDs), insulin sensitizers that enhance glucose utilization and adipocyte differentiation. However, clinical use of TZDs has been limited by side effects including a higher risk of fractures and bone loss. Here we demonstrate that the same post-translational modifications at S112 and S273, which influence PPARγ pro-adipocytic and insulin sensitizing activities, also determine PPARγ osteoblastic (pS112) and osteoclastic (pS273) activities. Treatment of either hyperglycemic or normoglycemic animals with SR10171, an inverse agonist that blocks pS273 but not pS112, increased trabecular and cortical bone while normalizing metabolic parameters. Additionally, SR10171 treatment modulated osteocyte, osteoblast, and osteoclast activities, and decreased marrow adiposity. These data demonstrate that regulation of bone mass and energy metabolism shares similar mechanisms suggesting that one pharmacologic agent could be developed to treat both diabetes and metabolic bone disease.

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PPARγ S273 regulates osteoclast differentiation and insulin sensitivity

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PPARγ S112 regulates osteoblast and adipocyte differentiation

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PPARγ and PPARα regulate osteocyte activities of bone formation and turnover

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SR10171, a PPARγ inverse agonist and PPARα weak agonist, is anabolic for bone

Diabetes is a condition with compromised energy balance and is associated with bone fractures. Some treatment options for diabetes sensitize the patient to insulin via targeting the transcription factor PPARγ. PPARγ is also key regulator of bone formation and bone resorption. Anti-diabetic drugs TZDs target PPARγ protein and this leads to bone loss and increase in fractures in postmenopausal women. Bone mass and energy metabolism share similar regulating pathways, and here we demonstrate a new class of insulin sensitizers that is a selective modulator of PPARγ activity; resulting in a pharmacologic agent that can be beneficial for both diabetes and metabolic bone disease.

Turning Bone Morphogenetic Protein 2 (BMP2) on and off in Mesenchymal Cells

The concentration, location, and timing of bone morphogenetic protein 2 (BMP2, HGNC:1069, GeneID: 650) gene expression must be precisely regulated. Abnormal BMP2 levels cause congenital anomalies and diseases involving the mesenchymal cells that differentiate into muscle, fat, cartilage, and bone. The molecules and conditions that influence BMP2 synthesis are diverse. Understandably, complex mechanisms control Bmp2 gene expression. This review includes a compilation of agents and conditions that can induce Bmp2. The currently known trans-regulatory factors and cis-regulatory elements that modulate Bmp2 expression are summarized and discussed. Bone morphogenetic protein 2 (BMP2, HGNC:1069, GeneID: 650) is a classical morphogen; a molecule that acts at a distance and whose concentration influences cell behavior. In mesenchymal cells, the concentration of BMP2 influences myogenesis, adipogenesis, chondrogenesis, and osteogenesis. Because the amount, timing, and location of BMP2 synthesis influence the allocation of cells to muscle, fat, cartilage, and bone, the mechanisms that regulate the Bmp2 gene are crucial. Key early mesodermal events that require precise Bmp2 regulation include heart specification and morphogenesis. Originally named for its osteoinductive properties, healing fractures requires BMP2. The human Bmp2 gene also has been linked to osteoporosis and osteoarthritis. In addition, all forms of pathological calcification in the vasculature and in cardiac valves involve the pro-osteogenic BMP2. The diverse tissues, mechanisms, and diseases influenced by BMP2 are too numerous to list here (see OMIM: 112261). However, in all BMP2-influenced pathologies, changes in the behavior and differentiation of pluripotent mesenchymal cells are a recurring theme. Consequently, much effort has been devoted to identifying the molecules and conditions that influence BMP2 synthesis and the complex mechanisms that control Bmp2 gene expression. This review begins with an overview of the Bmp2 gene's chromosomal neighborhood and then summarizes and evaluates known regulatory mechanisms and inducers.

WNT Agonist Decreases Tissue Damage and Improves Renal Function After Ischemia-Reperfusion

Renal ischemia-reperfusion (IR) injury (IRI) after shock states or transplantation causes tissue damage and delayed graft function, respectively. The Wnt/β-catenin signaling pathway plays a critical role in nephrogenesis. We therefore hypothesized that pharmacological activation of the Wnt/β-catenin signaling by the Wnt agonist, a synthetic pyrimidine, could protect kidneys from IRI. Adult male rats were subjected to bilateral clamping of the renal pedicles with microvascular clips for 60 min, followed by reperfusion. The Wnt agonist (5 mg/kg body weight) or vehicle (20% dimethyl sulfoxide in saline) was administered intravenously 1 h before ischemia. Blood and renal tissues were collected 24 h after IR for evaluation. Renal IR caused a significant reduction of β-catenin and its downstream target gene cyclin D1 by 65% and 39%, respectively, compared with the sham, whereas the Wnt agonist restored them to sham levels. The number and intensity of cells staining with the proliferation marker Ki67 in ischematized kidneys were enhanced by the Wnt agonist. The integrity of the renal histological architecture in the Wnt agonist group was better preserved than the vehicle group. The Wnt agonist significantly lowered serum levels of creatinine, aspartate aminotransferase, and lactate dehydrogenase and inhibited the production of interleukin 6 and interleukin 1β and myeloperoxidase activities. Lastly, the Wnt agonist reduced inducible nitric oxide synthase, nitrotyrosine proteins, and 4-hydroxynonenal in the kidneys by 60%, 47%, and 21%, respectively, compared with the vehicle. These results indicate that the Wnt agonist improves renal regeneration and function while attenuating inflammation and oxidative stress in the kidneys after IR. Thus, pharmacologic stimulation of the Wnt/β-catenin signaling provides a beneficial effect on the prevention of renal IRI.

Epigenetic Priming Confers Direct Cell Trans-Differentiation From Adipocyte to Osteoblast in a Transgene-Free State

The bone marrow of healthy individuals is primarily composed of osteoblasts and hematopoietic cells, while that of osteoporosis patients has a larger portion of adipocytes. There is evidence that the epigenetic landscape can strongly influence cell differentiation. We have shown that it is possible to direct the trans-differentiation of adipocytes to osteoblasts by modifying the epigenetic landscape with a DNA methyltransferase inhibitor (DNMTi), 5'-aza-dC, followed by Wnt3a treatment to signal osteogenesis. Treating 3T3-L1 adipocytes with 5'-aza-dC induced demethylation in the hypermethylated CpG regions of bone marker genes; subsequent Wnt3a treatment drove the cells to osteogenic differentiation. When old mice with predominantly adipose marrow were treated with both 5'-aza-dC and Wnt3a, decreased fatty tissue and increased bone volume were observed. Together, our results indicate that epigenetic modification permits direct programming of adipocytes into osteoblasts in a mouse model of osteoporosis, suggesting that this approach could be useful in bone tissue-engineering applications.

Cyclooxygenase-2 suppresses the anabolic response to PTH infusion in mice

We previously reported that the ability of continuously elevated PTH to stimulate osteoblastic differentiation in bone marrow stromal cell cultures was abrogated by an osteoclastic factor secreted in response to cyclooxygenase-2 (Cox2)-produced prostaglandin E₂. We now examine the impact of Cox2 (Ptgs2) knockout (KO) on the anabolic response to continuously elevated PTH in vivo. PTH (40 μg/kg/d) or vehicle was infused for 12 or 21 days in 3-mo-old male wild type (WT) and KO mice in the outbred CD-1 background. Changes in bone phenotype were assessed by bone mineral density (BMD), μCT and histomorphometry. PTH infusion for both 12 and 21 days increased femoral BMD in Cox2 KO mice and decreased BMD in WT mice. Femoral and vertebral trabecular bone volume fractions were increased in KO mice, but not in WT mice, by PTH infusion. In the femoral diaphysis, PTH infusion increased cortical area in Cox2 KO, but not WT, femurs. PTH infusion markedly increased trabecular bone formation rate in the femur, serum markers of bone formation, and expression of bone formation-related genes, growth factors, and Wnt target genes in KO mice relative to WT mice, and decreased gene expression of Wnt antagonists only in KO mice. In contrast to the differential effects of PTH on anabolic factors in WT and KO mice, PTH infusion increased serum markers of resorption, expression of resorption-related genes, and the percent bone surface covered by osteoclasts similarly in both WT and KO mice. We conclude that Cox2 inhibits the anabolic, but not the catabolic, effects of continuous PTH. These data suggest that the bone loss with continuously infused PTH in mice is due largely to suppression of bone formation and that this suppression is mediated by Cox2.

Pin1 plays a critical role as a molecular switch in canonical BMP signaling

Pin1 is a peptidyl prolyl cis-trans isomerase that specifically binds to the phosphoserine-proline or phosphothreonine-proline motifs of numerous proteins. Previously, we reported that Pin1 deficiency resulted in defects in osteoblast differentiation during early bone development. In this study, we found that adult Pin1-deficient mice developed osteoporotic phenotypes compared to age-matched controls. Since BMP2 stored in the bone matrix plays a critical role in adult bone maintenance, we suspected that BMP R-Smads (Smad1 and Smad5) could be critical targets for Pin1 action. Pin1 specifically binds to the phosphorylated linker region of Smad1, which leads to structural modification and stabilization of the Smad1 protein. In this process, Pin1-mediated conformational modification of Smad1 directly suppresses the Smurf1 interaction with Smad1, thereby promoting sustained activation of the Smad1 molecule. Our data demonstrate that post-phosphorylational prolyl isomerization of Smad1 is a converging signal to stabilize the Smad1 molecule against the ubiquitination process mediated by Smurf1. Therefore, Pin1 is a critical molecular switch in the determination of Smad1 fate, opposing the death signal transmitted to the Smad1 linker region by phosphorylation cascades after its nuclear localization and transcriptional activation. Thus, Pin1 could be developed as a major therapeutic target in many skeletal diseases.

Down-regulated non-coding RNA (lncRNA-ANCR) promotes osteogenic differentiation of periodontal ligament stem cells

OBJECTIVE

Our studies aimed to figure out how anti-differentiation noncoding RNA (ANCR) regulates the proliferation and osteogenic differentiation of periodontal ligament stem cells (PDLSCs).

DESIGN

In this study, we used lentivirus infection to down-regulate the expression of ANCR in PDLSCs. Then we compared the proliferation of control cells and PDLSC/ANCR-RNAi cells by Cell Counting Kit-8. And the osteogenic differentiation of control cells and PDLSC/ANCR-RNAi cells were evaluated by Alkaline phosphatase (ALP) activity quantification and Alizarin red staining. WNT inhibitor was used to analyze the relationship between ANCR and canonical WNT signalling pathway. The expression of osteogenic differentiation marker mRNAs, DKK1, GSK3-β and β-catenin were evaluated by qRT-PCR.

RESULTS

The results showed that down-regulated ANCR promoted proliferation of PDLSCs. Down-regulated ANCR also promoted osteogenic differentiation of PDLSCs by up-regulating osteogenic differentiation marker genes. After the inhibition of canonical WNT signalling pathway, the osteogenic differentiation of PDLSC/ANCR-RNAi cells was inhibited too. qRT-PCR results also demonstrated that canonical WNT signalling pathway was activated for ANCR-RNAi on PDLSCs during the procedure of proliferation and osteogenic induction.

CONCLUSIONS

These results indicated that ANCR was a key regulator of the proliferation and osteogenic differentiation of PDLSCs, and its regulating effects was associated with the canonical WNT signalling pathway, thus offering a new target for oral stem cell differentiation studies that could also facilitate oral tissue engineering.

Epigenetic modifications and canonical wingless/int-1 class (WNT) signaling enable trans-differentiation of nonosteogenic cells into osteoblasts

Mesenchymal cells alter and retain their phenotype during skeletal development through activation or suppression of signaling pathways. For example, we have shown that Wnt3a only stimulates osteoblast differentiation in cells with intrinsic osteogenic potential (e.g. MC3T3-E1 pre-osteoblasts) and not in fat cell precursors or fibroblasts (3T3-L1 pre-adipocytes or NIH3T3 fibroblasts, respectively). Wnt3a promotes osteogenesis in part by stimulating autocrine production of the osteoinductive ligand Bmp2. Here, we show that the promoter regions of the genes for Bmp2 and the osteoblast marker Alp are epigenetically locked to prevent their expression in nonosteogenic cells. Both genes have conserved CpG islands that exhibit increased CpG methylation, as well as decreased acetylation and increased methylation of histone H3 lysine 9 (H3-K9) specifically in nonosteogenic cells. Treatment of pre-adipocytes or fibroblasts with the CpG-demethylating agent 5'-aza-2'-deoxycytidine or the histone deacetylase inhibitor trichostatin-A renders Bmp2 and Alp responsive to Wnt3a. Hence, drug-induced epigenetic activation of Bmp2 gene expression contributes to Wnt3a-mediated direct trans-differentiation of pre-adipocytes or fibroblasts into osteoblasts. We propose that direct conversion of nonosteogenic cells into osteoblastic cell types without inducing pluripotency may improve prospects for novel epigenetic therapies to treat skeletal afflictions.

Modulation of Wnt/β-catenin Signaling Attenuates Periapical Bone Lesions

Wnt/β-catenin signaling plays an important role in bone biology. The present study investigated the involvement of Wnt/β-catenin signaling in rat periapical bone destruction and whether lithium chloride (LiCl), a glycogen synthase kinase-3β (GSK-3β) inhibitor, promotes bone restoration. Rat bone marrow mesenchymal cells (BMMSCs) treated with Porphyromonas gingivalis lipopolysaccharide ( Pg LPS) showed decreased osteogenic potential through inhibited Wnt/β-catenin signaling as quantified by Western blot, immunofluorescence, and luciferase reporter assay. Transient Wnt3a treatment in vitro partially restored mineralization and Runx2/Osx and osteocalcin expression in cultures with Pg LPS-induced osteogenic arrest. Prolonged Wnt3a treatment impaired osteogenic commitment. X-ray microtomography showed dramatically enhanced periapical bone formation in rats gavage-fed with LiCl for 2 wks, while continuous LiCl treatment for 4 wks impaired periapical bone healing. LiCl treatment also increased GSK-3β phosphorylation and osteocalcin expression in periapical tissue. Collectively, these results indicate that Wnt/β-catenin has dichotomous functions in bone homeostasis. Modulation of this signaling pathway by LiCl may be a potential therapeutic option for bone destruction in endodontic disease.

Growth differentiation factor 5 is a key physiological regulator of dendrite growth during development

Dendrite size and morphology are key determinants of the functional properties of neurons. Here, we show that growth differentiation factor 5 (GDF5), a member of the bone morphogenetic protein (BMP) subclass of the transforming growth factor β superfamily with a well-characterised role in limb morphogenesis, is a key regulator of the growth and elaboration of pyramidal cell dendrites in the developing hippocampus. Pyramidal cells co-express GDF5 and its preferred receptors, BMP receptor 1B and BMP receptor 2, during development. In culture, GDF5 substantially increased dendrite, but not axon, elongation from these neurons by a mechanism that depends on activation of SMADs 1/5/8 and upregulation of the transcription factor HES5. In vivo, the apical and basal dendritic arbours of pyramidal cells throughout the hippocampus were markedly stunted in both homozygous and heterozygous Gdf5 null mutants, indicating that dendrite size and complexity are exquisitely sensitive to the level of endogenous GDF5 synthesis.

Transient receptor potential melastatin 4 channel controls calcium signals and dental follicle stem cell differentiation

Elevations in the intracellular Ca(2+) concentration are a phenomena commonly observed during stem cell differentiation but cease after the process is complete. The transient receptor potential melastatin 4 (TRPM4) is an ion channel that controls Ca(2+) signals in excitable and nonexcitable cells. However, its role in stem cells remains unknown. The aim of this study was to characterize TRPM4 in rat dental follicle stem cells (DFSCs) and to determine its impact on Ca(2+) signaling and the differentiation process. We identified TRPM4 gene expression in DFSCs, but not TRPM5, a closely related channel with similar function. Perfusion of cells with increasing buffered Ca(2+) resulted in a concentration-dependent activation of currents typical for TRPM4, which were also voltage-dependent and had Na(+) conductivity. Molecular suppression with shRNA decreased channel activity and cell proliferation during osteogenesis but not adipogenesis. As a result, enhanced mineralization and phosphatase enzyme activity were observed during osteoblast formation, although DFSCs failed to differentiate into adipocytes. Furthermore, the normal agonist-induced first and secondary phases of Ca(2+) signals were transformed into a gradual and sustained increase which confirmed the channels' ability to control Ca(2+) signaling. Using whole genome microarray analysis, we identified several genes impacted by TRPM4 during DFSC differentiation. These findings suggest an inhibitory role for TRPM4 on osteogenesis while it appears to be required for adipogenesis. The data also provide a potential link between the Ca(2+) signaling pattern and gene expression during stem cell differentiation.