Wnt/beta-catenin signaling in mesenchymal progenitors controls osteoblast and chondrocyte differentiation during vertebrate skeletogenesis

MicroRNA-224 enhances the osteoblastic differentiation of hMSCs via Rac1

Osteogenesis is the differentiation of mesenchymal stem cells (MSCs) into osteoblasts. MicroRNAs (miRNAs) are short noncoding RNAs that target specific genes to mediate translational activities. In this study, we investigated how miR-224 regulates the osteoblastic differentiation of human MSCs (hMSCs) as well as the underlying mechanism. The results revealed the upregulation of miR-224 during hMSC differentiation. In vitro experiments showed that the downregulation of miR-224 suppressed the differentiation of hMSCs into osteoblasts. However, upregulation of miR-224 was concomitant with increased expression of relevant genes and augmented activity of alkaline phosphatase. Furthermore, the results indicated that Rac1 acted as the bona fide target of miR-224 and that Rac1 depletion promoted osteogenic differentiation in miR-224-silenced hMSCs. In addition, we found that both JAK/STAT3 and Wnt/β-catenin pathways were repressed by Rac1 depletion using quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blotting, and immunofluorescence. Our data indicate a novel molecular mechanism in relation to hMSCs differentiation into osteoblasts, which may facilitate bone anabolism via miR-224. SIGNIFICANCE OF THE STUDY: In this study, we mainly explored the effects of miR-224 on hMSCs differentiation into osteoblasts. We find that induced miR-224 expression in hMSCs is considered closely associated with specific osteogenesis-related genes, alkaline phosphatase activity, and matrix mineralization, indicating that miR-224 may serve as a promising biomarker for osteogenic differentiation. Our data indicate a novel molecular mechanism in relation to hMSCs differentiation into osteoblasts, which may facilitate bone anabolism via miR-224.

Micrornas at the Interface between Osteogenesis and Angiogenesis as Targets for Bone Regeneration

Bone formation and regeneration is a multistep complex process crucially determined by the formation of blood vessels in the growth plate region. This is preceded by the expression of growth factors, notably the vascular endothelial growth factor (VEGF), secreted by osteogenic cells, as well as the corresponding response of endothelial cells, although the exact mechanisms remain to be clarified. Thereby, coordinated coupling between osteogenesis and angiogenesis is initiated and sustained. The precise interplay of these two fundamental processes is crucial during times of rapid bone growth or fracture repair in adults. Deviations in this balance might lead to pathologic conditions such as osteoarthritis and ectopic bone formation. Besides VEGF, the recently discovered important regulatory and modifying functions of microRNAs also support this key mechanism. These comprise two principal categories of microRNAs that were identified with specific functions in bone formation (osteomiRs) and/or angiogenesis (angiomiRs). However, as hypoxia is a major driving force behind bone angiogenesis, a third group involved in this process is represented by hypoxia-inducible microRNAs (hypoxamiRs). This review was focused on the identification of microRNAs that were found to have an active role in osteogenesis as well as angiogenesis to date that were termed "CouplingmiRs (CPLGmiRs)". Outlined representatives therefore represent microRNAs that already have been associated with an active role in osteogenic-angiogenic coupling or are presumed to have its potential. Elucidation of the molecular mechanisms governing bone angiogenesis are of great relevance for improving therapeutic options in bone regeneration, tissue-engineering, and the treatment of bone-related diseases.

Osteoporosis therapies might lead to intervertebral disc degeneration via affecting cartilage endplate

Osteoporosis and intervertebral disc degeneration (IDD) are both age-related diseases of the musculoskeletal system. With the average life expectancy longer than ever, the morbidity caused by these two diseases is increasing. Nowadays, treatment strategies for osteoporosis are mainly aimed at increasing the mineral density of the bone. Some of these therapies, including vitamin D, calcium, bisphosphonates, Wnt signal activators and parathyroid hormone regulators, have been suggested to be capable of causing calcification of the cartilage endplate in the intervertebral disc. This alteration could block nutrient and oxygen transportation to the center part of the disc, thus lead to intervertebral disc degeneration. Consequently, we hypothesize that osteoporosis therapies might be a potential risk for IDD. This assumption indicates that we should take the alterations of the cartilage endplate into consideration in further osteoporosis treatment to avoid IDD in the patient.

Sclerostin/Receptor Related Protein 4 and Ginkgo Biloba Extract Alleviates β-Glycerophosphate-Induced Vascular Smooth Muscle Cell Calcification By Inhibiting Wnt/β-Catenin Pathway

BACKGROUND

Abnormal mineral metabolism in patients with chronic kidney disease (CKD) may lead to vascular calcification, which is markedly associated with adverse events, including ischemic cardiac diseases and all-cause cardiovascular mortality. Thus, preventing and treating vascular calcification play an important role in improving the prognosis of CKD patients.

OBJECTIVES

To investigate the potential functions of sclerostin and low-density lipoprotein receptor-related protein 4 (Lrp4) in alleviating the β-glycerophosphate (β-GP)-induced vascular smooth muscle cell (VSMC) calcification, and the protective effect of Ginkgo biloba extract (GBE).

METHODS

VSMC were extracted from Sprague-Dawley rat aorta and cultured in medium. The VSMCs were divided into 3 groups: (1) Negative control group, (2) β-GP group, in which the VSMCs were treated with β-GP, and (3) GBE and β-GP group, where the VSMCs were treated with both β-GP and GBE. The calcium nodules within the cells were examined by using Alizarin red S staining. The mRNA expression levels of β-catenin and bone gamma-carboxyglutamic-acid-containing proteins (BGP) were detected by real-time PCR. The protein levels of sclerostin and Lrp4 were determined by Western blot.

RESULTS

Alizarin red S staining showed that the VSMCs in β-GP group had a distinct orange-red precipitate when compared with VSMCs in the negative control group, while the orange-red precipitate of the GBE and β-GP group was significantly reduced compared to the β-GP group. Real-time PCR showed that the mRNA levels of β-catenin and BGP in VSMCs of β-GP group were significantly higher than those of the negative control group (p < 0.05); while they were significantly reduced in VSMCs of the GBE and β-GP group (p < 0.05). Western blot results showed that the expression of sclerostin in the β-GP group was significantly higher than that in the control group (p < 0.05), whereas Lrp4 was significantly lower than in control group (p < 0.05). Sclerostin in GBE and β-GP group was significantly reduced (p < 0.05), but Lrp4 was significantly elevated when compared with that of the β-GP group (p < 0.05).

CONCLUSION

β-GP induced VSMC calcification by activating the Wnt/β-catenin signaling pathway. Sclerostin and Lrp4 were involved in β-GP-induced VSMC calcification and play an important role. GBE could alleviate VSMC calcification induced by β-GP through inhibiting the Wnt/β-catenin signaling pathway.

Suppressing UPR-dependent overactivation of FGFR3 signaling ameliorates SLC26A2-deficient chondrodysplasias

Background

Mutations in the SLC26A2 gene cause a spectrum of currently incurable human chondrodysplasias. However, genotype-phenotype relationships of SLC26A2-deficient chondrodysplasias are still perplexing and thus stunt therapeutic development.

Methods

To investigate the causative role of SLC26A2 deficiency in chondrodysplasias and confirm its skeleton-specific pathology, we generated and analyzed slc26a2^−/− and Col2a1-Cre; slc26a2^fl/fl mice. The therapeutic effect of NVP-BGJ398, an FGFR inhibitor, was tested with both explant cultures and timed pregnant females.

Findings

Two lethal forms of human SLC26A2-related chondrodysplasias, achondrogenesis type IB (ACG1B) and atelosteogenesis type II (AO2), are phenocopied by slc26a2^−/− mice. Unexpectedly, slc26a2^−/− chondrocytes are defective for collagen secretion, exhibiting intracellular retention and compromised extracellular deposition of ColII and ColIX. As a consequence, the ATF6 arm of the unfolded protein response (UPR) is preferentially triggered to overactivate FGFR3 signaling by inducing excessive FGFR3 in slc26a2^−/− chondrocytes. Consistently, suppressing FGFR3 signaling by blocking either FGFR3 or phosphorylation of the downstream effector favors the recovery of slc26a2^−/− cartilage cultures from impaired growth and unbalanced cell proliferation and apoptosis. Moreover, administration of an FGFR inhibitor to pregnant females shows therapeutic effects on pathological features in slc26a2^−/− newborns. Finally, we confirm the skeleton-specific lethality and pathology of global SLC26A2 deletion through analyzing the Col2a1-Cre; slc26a2^fl/fl mouse line.

Interpretation

Our study unveils a previously unrecognized pathogenic mechanism underlying ACG1B and AO2, and supports suppression of FGFR3 signaling as a promising therapeutic approach for SLC26A2-related chondrodysplasias.

Fund

This work was supported by National Natural Science Foundation of China (81871743, 81730065 and 81772377).

Cell number in mesenchymal stem cell aggregates dictates cell stiffness and chondrogenesis

Background

Although mesenchymal stem/stromal cell (MSC) chondrogenic differentiation has been thoroughly investigated, the rudiments for enhancing chondrogenesis have remained largely dependent on external cues. Focus to date has been on extrinsic variables such as soluble signals, culture conditions (bioreactors), and mechanical stimulation. However, the role of intrinsic mechanisms of MSC programming-based mechanobiology remains to be explored. Since aggregation of MSCs, a prerequisite for chondrogenesis, generates tension within the cell agglomerate, we inquired if the initial number of cells forming the aggregate (aggregate cell number (ACN)) can impact chondrogenesis.

Methods

Aggregates of varying ACN were formed using well-established centrifugation approach. Progression of chondrogenic differentiation in the aggregates was assessed over 3 weeks in presence and absence of transforming growth factor-beta 1 (TGF-β1). Mechanical properties of the cells were characterized using high-throughput real-time deformability cytometry (RT-DC), and gene expression was analyzed using Affymetrix gene array. Expression of molecular markers linked to chondrogenesis was assessed using western blot and immunofluorescence.

Results

Reducing ACN from 500 k to 70 k lead to activation and acceleration of the chondrogenic differentiation, independent of soluble chondro-inductive factors, which involves changes to β-catenin-dependent TCF/LEF transcriptional activity and expression of anti-apoptotic protein survivin. RT-DC analysis revealed that stiffness and size of cells within aggregates are modulated by ACN. A direct correlation between progression of chondrogenesis and emergence of stiffer cell phenotype was found. Affymetrix gene array analysis revealed a downregulation of genes associated with lipid synthesis and regulation, which could account for observed changes in cell stiffness. Immunofluorescence and western blot analysis revealed that increasing ACN upregulates the expression of lipid raft protein caveolin-1, a β-catenin binding partner, and downregulates the expression of N-cadherin. As a demonstration of the relevance of these findings in MSC-based strategies for skeletal repair, it is shown that implanting aggregates within collagenous matrix not only decreases the necessity for high cell numbers but also leads to marked improvement in the quality of the deposited tissue.

Conclusions

This study presents a simple and donor-independent strategy to enhance the efficiency of MSC chondrogenic differentiation and identifies changes in cell mechanics coincident with MSC chondrogenesis with potential translational applications.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1103-y) contains supplementary material, which is available to authorized users.

Glomerular mesangial cell and podocyte injuries in diabetic nephropathy

Diabetic nephropathy is one of the leading causes of end-stage renal disease and creates heavy healthcare burdens globally. Dysfunction of mesangial cells and podocytes contributes to diabetic nephropathy. Dysregulation of signaling involved in renal development and regeneration may cause diabetic kidney damages. Growing evidences suggest the importance of dysregulated dickkopf-1 (DKK1)/Wnt/ β-catenin signaling pathways in the pathogenesis of diabetic glomerular injuries. The inhibition of Wnt signaling in injured mesangial cells is likely attributed to the high glucose-induced Ras/Rac1 dependent superoxide formation. When DKK1, the cellular inhibitor of Wnt signaling, binds to the Kremen-2 receptor, depositions of extracellular matrix increase in the mesangium of diabetic kidneys. Additionally, reactivation of Notch-1 signaling has been implicated in podocytopathy during diabetic proteinuria development. Knocking down Notch-1 alleviates vascular endothelial growth factor (VEGF) expression, nephrin repression and proteinuria in diabetic kidneys. It is also found that epigenetic modulations by histone deacetylase 4 (HDAC4) and miR-29a could lead to diabetic nephropathy. High glucose increases the expression of HDAC4, which causes deacetylation with subsequent ubiquitination of nephrin. Overexpression of miR-29a in diabetic transgenic mice would decrease the expression of HDAC4 and stabilize nephrin. Surprisingly, reprogramming or reactivation of signaling involved in renal development or regeneration often brings about diabetic glomerular sclerosis in mesangial cells and podocytes. Better knowledge about modifications of embryonic stem cell signaling will have a chance to implement strategically focused pharmacological research programs aiming to the development of new drugs for diabetic kidney injuries.

Cellular biology of fracture healing

The biology of bone healing is a rapidly developing science. Advances in transgenic and gene-targeted mice have enabled tissue and cell-specific investigations of skeletal regeneration. As an example, only recently has it been recognized that chondrocytes convert to osteoblasts during healing bone, and only several years prior, seminal publications reported definitively that the primary tissues contributing bone forming cells during regeneration were the periosteum and endosteum. While genetically modified animals offer incredible insights into the temporal and spatial importance of various gene products, the complexity and rapidity of healing-coupled with the heterogeneity of animal models-renders studies of regenerative biology challenging. Herein, cells that play a key role in bone healing will be reviewed and extracellular mediators regulating their behavior discussed. We will focus on recent studies that explore novel roles of inflammation in bone healing, and the origins and fates of various cells in the fracture environment. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

A tale of two cities: The genetic mechanisms governing calvarial bone development

The skull bones must grow in a coordinated, three-dimensional manner to coalesce and form the head and face. Mammalian skull bones have a dual embryonic origin from cranial neural crest cells (CNCC) and paraxial mesoderm (PM) and ossify through intramembranous ossification. The calvarial bones, the bones of the cranium which cover the brain, are derived from the supraorbital arch (SOA) region mesenchyme. The SOA is the site of frontal and parietal bone morphogenesis and primary center of ossification. The objective of this review is to frame our current in vivo understanding of the morphogenesis of the calvarial bones and the gene networks regulating calvarial bone initiation in the SOA mesenchyme.

Regulatory mechanisms of sclerostin expression during bone remodeling

Osteocytes are embedded in bone matrices and are connected to each other to respond to mechanical loading on bone. Recent studies have demonstrated the roles of mechanical loading in bone accrual. Bone responds to mechanical loading by decreasing the expression of sclerostin, an inhibitor of Wnt/β-catenin signals, in osteocytes. This increases bone mass because the activation of Wnt/β-catenin signals in bone microenvironments promotes bone formation and suppresses bone resorption. Thus, in recent years, sclerostin have attracted increasing attention in bone metabolism. However, the regulatory mechanism of sclerostin expression during bone remodeling has not been fully elucidated. In this review, we summarized the regulation of bone formation and resorption by Wnt signals, a Wnt/β-catenin signal inhibitor sclerostin, and molecular mechanisms by which the expression of sclerostin is suppressed by mechanical loading and parathyroid hormone. We also discuss a possibility that osteoclasts suppress the expression of sclerostin during bone remodeling, which in turn, promote bone formation. The effectiveness of an anti-sclerostin antibody with anti-dickkopf-1 antibody for increasing bone mass was discussed.

Defining osteoblast and adipocyte lineages in the bone marrow

Bone is a complex endocrine organ that facilitates structural support, protection to vital organs, sites for hematopoiesis, and calcium homeostasis. The bone marrow microenvironment is a heterogeneous niche consisting of multipotent musculoskeletal and hematopoietic progenitors and their derivative terminal cell types. Amongst these progenitors, bone marrow mesenchymal stem/stromal cells (BMSCs) may differentiate into osteogenic, adipogenic, myogenic, and chondrogenic lineages to support musculoskeletal development as well as tissue homeostasis, regeneration and repair during adulthood. With age, the commitment of BMSCs to osteogenesis slows, bone formation decreases, fracture risk rises, and marrow adiposity increases. An unresolved question is whether osteogenesis and adipogenesis are co-regulated in the bone marrow. Osteogenesis and adipogenesis are controlled by specific signaling mechanisms, circulating cytokines, and transcription factors such as Runx2 and Pparγ, respectively. One hypothesis is that adipogenesis is the default pathway if osteogenic stimuli are absent. However, recent work revealed that Runx2 and Osx1-expressing preosteoblasts form lipid droplets under pathological and aging conditions. Histone deacetylase 3 (Hdac3) and other epigenetic regulators suppress lipid storage in preosteoblasts and/or control marrow adiposity. Establishing a better understanding of fat storage in bone marrow cells, as well as the osteoblast-adipocyte relationship within the bone marrow niche is necessary to understand the mechanisms underlying disease- and aging-related marrow fat storage and may lead to the development of new therapeutic targets for "fatty bone" and osteoporosis.

Vitamin D, Inflammation and Osteoporosis in Rheumatoid Arthritis

Patients with Rheumatoid Arthritis (RA) commonly develop osteoporosis and fragility fractures. This fact cannot be explained only with the use of glucocorticoids, known to be detrimental for bone health. RA is characterized by a chronic inflammation caused by the continuous activation of innate and adaptive immunity with proinflammatory cytokines overproduction. This process is detrimental for several organs and physiological processes, including the impairment of bone remodeling. We will briefly review the pathogenesis of inflammation-related bone loss in RA, describing well-known and new molecular pathways and focusing on vitamin D and Parathyroid Hormone role.

[Bone mechanobiology, an emerging field: a review]

INTRODUCTION

Mechanobiology, at the interface between biology and biophysics, studies the impact of mechanical forces on tissues, cells and biomolecules. The application of orthodontic forces, followed by induced tooth displacement, is a striking example of its clinical application.

OBJECTIVE

The purpose of this article was to compile a review of the literature on the subject of mechanobiology; from its detection at bone level to the presentation of stimulated intracellular pathways.

MATERIALS AND METHODS

The literature search was conducted on the Pubmed database in April 2018, with associations of the terms "mechanobiology", "orthodontics", "cell culture", "physiopathology".

RESULTS

Three major areas of research were selected: highlighting of the phenomenon and its application in the field of bone biology; the cellular effectors of mechanobiology and its clinical applications. The use of mechanobiology in dentofacial orthopedics opens up a new field of reflection for clinicians regarding future advances in orthodontics.

Macrophage cells secrete factors including LRP1 that orchestrate the rejuvenation of bone repair in mice

The pace of repair declines with age and, while exposure to a young circulation can rejuvenate fracture repair, the cell types and factors responsible for rejuvenation are unknown. Here we report that young macrophage cells produce factors that promote osteoblast differentiation of old bone marrow stromal cells. Heterochronic parabiosis exploiting young mice in which macrophages can be depleted and fractionated bone marrow transplantation experiments show that young macrophages rejuvenate fracture repair, and old macrophage cells slow healing in young mice. Proteomic analysis of the secretomes identify differential proteins secreted between old and young macrophages, such as low-density lipoprotein receptor-related protein 1 (Lrp1). Lrp1 is produced by young cells, and depleting Lrp1 abrogates the ability to rejuvenate fracture repair, while treating old mice with recombinant Lrp1 improves fracture healing. Macrophages and proteins they secrete orchestrate the fracture repair process, and young cells produce proteins that rejuvenate fracture repair in mice.

The rate of repair declines with age; however, exposure to young circulations can rejuvenate fracture repair, but how this is accomplished is unknown. Here, the authors identify proteins, including low-density lipoprotein receptor-related protein 1 (Lrp1), as being secreted from young macrophages and rejuvenating fracture repair in mice.

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.

Gαs signaling controls intramembranous ossification during cranial bone development by regulating both Hedgehog and Wnt/β-catenin signaling

How osteoblast cells are induced is a central question for understanding skeletal formation. Abnormal osteoblast differentiation leads to a broad range of devastating craniofacial diseases. Here we have investigated intramembranous ossification during cranial bone development in mouse models of skeletal genetic diseases that exhibit craniofacial bone defects. The GNAS gene encodes Gα_s that transduces GPCR signaling. GNAS activation or loss-of-function mutations in humans cause fibrous dysplasia (FD) or progressive osseous heteroplasia (POH) that shows craniofacial hyperostosis or craniosynostosis, respectively. We find here that, while Hh ligand-dependent Hh signaling is essential for endochondral ossification, it is dispensable for intramembranous ossification, where Gα_s regulates Hh signaling in a ligand-independent manner. We further show that Gα_s controls intramembranous ossification by regulating both Hh and Wnt/β-catenin signaling. In addition, Gα_s activation in the developing cranial bone leads to reduced ossification but increased cartilage presence due to reduced cartilage dissolution, not cell fate switch. Small molecule inhibitors of Hh and Wnt signaling can effectively ameliorate cranial bone phenotypes in mice caused by loss or gain of Gnas function mutations, respectively. Our work shows that studies of genetic diseases provide invaluable insights in both pathological bone defects and normal bone development, understanding both leads to better diagnosis and therapeutic treatment of bone diseases.

Craniofacial abnormality with skeletal dysplasia in mice lacking chondroitin sulfate N-acetylgalactosaminyltransferase-1

Chondroitin sulfate (CS) proteoglycan is a major component of the extracellular matrix and plays an important part in organogenesis. To elucidate the roles of CS for craniofacial development, we analyzed the craniofacial morphology in CS N-acetylgalactosaminyltransferase-1 (T1) gene knockout (KO) mice. T1KO mice showed the impaired intramembranous ossification in the skull, and the final skull shape of adult mice included a shorter face, higher and broader calvaria. Some of T1KO mice exhibited severe facial developmental defect, such as eye defects and cleft lip and palate, causing embryonic lethality. At the postnatal stages, T1KO mice with severely reduced CS amounts showed malocclusion, general skeletal dysplasia and skin hyperextension, closely resembling Ehlers-Danlos syndrome-like connective tissue disorders. The production of collagen type 1 was significantly downregulated in T1KO mice, and the deposition of CS-binding molecules, Wnt3a, was decreased with CS in extracellular matrices. The collagen fibers were irregular and aggregated, and connective tissues were dysorganized in the skin and calvaria of T1KO mice. These results suggest that CS regulates the shape of the craniofacial skeleton by modulating connective tissue organization and that the remarkable reduction of CS induces hypoplasia of intramembranous ossification and cartilage anomaly, resulting in skeletal dysplasia.

Dickkopf-1 reduces hypertrophic changes in human chondrocytes derived from bone marrow stem cells

The in vitro process of chondrogenic differentiation of mesenchymal stem cells (MSCs) induces a pre-apoptotic hypertrophic phenotype, guided by the active status of the WNT/β‑catenin pathway. To achieve a stable chondrocyte phenotype for cartilage tissue engineering, it is necessary to gain a better understanding of specific genes that regulate the cartilage tissue phenotype. RNA sequencing (RNA-seq) analysis of tissue samples from bone, cartilage, growth plate and muscle show that Dickkopf-1 (DKK1), a natural WNT canonical signaling inhibitor, is expressed in cartilage tissue. This observation reinforces the concept that inhibition of the WNT/β‑catenin pathway is critical for preventing avoid chondrocyte hypertrophy in vitro. We used two doses of DKK1 in a pellet cell culture system to inhibit the terminal differentiation of chondrocytes derived from bone marrow mesenchymal stem cells (MSCs). Bone marrow MSCs were cultured in chondrogenic induction medium with 50 and 200 ng/ml of DKK1 for 21 days. The highest doses of DKK1 reduce β‑catenin expression and nuclear localization at day 21, concomitant with reduced expression and activity of hypertrophy markers collagen type X (COL10A1) and alkaline phosphatase (ALPL), thus decreasing the pre-hypertrophic chondrocyte population. Furthermore, DKK1 stimulated expression of collagen type II (COL2A1) and glycosaminoglycans (GAGs), which represent healthy articular cartilage markers. We conclude that exogenous DKK1 impedes chondrocyte progression into a prehypertrophic stage and stimulates expression of healthy articular cartilage markers by blocking the WNT/β‑catenin pathway. Hence, DKK1 may promote a mature healthy articular cartilage phenotype and facilitate cartilage tissue engineering for joint repair.

Characterization of the Proliferating Layer Chondrocytes of Growth Plate for Cartilage Regeneration

IMPACT STATEMENT

In recent years, cell-based therapy is a promising strategy for repairing defect cartilage. However, in vitro expansion of articular chondrocytes (ACs) for collecting enough cell numbers eventually develops cell de-differentiation. In the present study, we choose the proliferative layer chondroctytes (PLCs) of growth plate as new candidate. The novel findings include (1) the higher proliferation potential of PLCs in comparison with the ACs, (2) PLCs produced more GAG than ACs, (3) the increased in GAG matrix production, (4) and lower senescence in PLCs. From these results, we found PLCs might be suitable as cell source for cartilage regeneration.

Diminished Canonical β-Catenin Signaling During Osteoblast Differentiation Contributes to Osteopenia in Progeria

Patients with Hutchinson-Gilford progeria syndrome (HGPS) have low bone mass and an atypical skeletal geometry that manifests in a high risk of fractures. Using both in vitro and in vivo models of HGPS, we demonstrate that defects in the canonical WNT/β-catenin pathway, seemingly at the level of the efficiency of nuclear import of β-catenin, impair osteoblast differentiation and that restoring β-catenin activity rescues osteoblast differentiation and significantly improves bone mass. Specifically, we show that HGPS patient-derived iPSCs display defects in osteoblast differentiation, characterized by a decreased alkaline phosphatase activity and mineralizing capacity. We demonstrate that the canonical WNT/β-catenin pathway, a major signaling cascade involved in skeletal homeostasis, is impaired by progerin, causing a reduction in the active β-catenin in the nucleus and thus decreased transcriptional activity, and its reciprocal cytoplasmic accumulation. Blocking farnesylation of progerin restores active β-catenin accumulation in the nucleus, increasing signaling, and ameliorates the defective osteogenesis. Moreover, in vivo analysis of the Zmpste24-/- HGPS mouse model demonstrates that treatment with a sclerostin-neutralizing antibody (SclAb), which targets an antagonist of canonical WNT/β-catenin signaling pathway, fully rescues the low bone mass phenotype to wild-type levels. Together, this study reveals that the β-catenin signaling cascade is a therapeutic target for restoring defective skeletal microarchitecture in HGPS. © 2018 American Society for Bone and Mineral Research.

Methacrylamide-modified collagen hydrogel with improved anti-actin-mediated matrix contraction behavior

For an ideal biomimetic microenvironment to realize reliable cartilage regeneration, the ability to induce mesenchymal stem cell (MSCs) differentiation along the chondrogenic lineage and prevent further dedifferentiation is expected. With native bioactivity, collagen has been proved to be preferential for inducing the chondrogenic differentiation of MSCs. However, the phenotypic maintenance of differentiated chondrocytes in a collagen matrix is still a challenge. Actin traction, which causes drastic contraction of the collagen matrix, is frequently observed and might be an important factor that affects cell fates including chondrogenic differentiation and phenotypic maintenance. In this study, photochemical modification was applied to acquire collagen hydrogels with improved mechanical strength and creep behavior. Accompanied by inherited bioactivity, the photo-crosslinked collagen hydrogel well supported the actin cytoskeleton functionalization while resisting the actin-mediated matrix contraction. Benefitting from this, the hydrogel system promoted MSCs proliferation and chondrogenic differentiation, and more importantly, prevented further dedifferentiation. By exploring the mesenchymal development-related signal transduction markers, it was revealed that the promoted chondrogenesis was achieved through inhibiting the over-expression of MAPK and Wnt/β-catenin signaling pathways that up-regulated dedifferentiated gene expression. The strategy of applying the hydrogel system to cartilage regeneration is foreseeable based on the positive heterotopic and orthotopic chondrogenic differentiation.

SLIT3 regulates endochondral ossification by β-catenin suppression in chondrocytes

Previously, we noted that SLIT3, slit guidance ligand 3, had an osteoprotective role with bone formation stimulation and bone resorption suppression. Additionally, we found that global Slit3 KO mice had smaller long bone. Skeletal staining showed short mineralized length in the newborn KO mice and wide hypertrophic chondrocyte area in the embryo KO mice, suggesting delayed chondrocyte maturation. The recombinant SLIT3 did not cause any change in proliferation of ATDC5 cells, but stimulated expressions of chondrocyte differentiation markers, such as COL2A1, SOX9, COL10A1, VEGF, and MMP13 in the cells. SLIT3 suppressed β-catenin activity in the cells, and activation of Wnt/β-catenin signaling by lithium chloride attenuated the SLIT3-stimulated differentiation markers. ATDC5 cells expressed only ROBO2 among their 4 isotypes, and the Robo2 knock-down with its siRNA reversed the SLIT3-stimulated differentiated markers in chondrocytes. Taken together, these indicate that SLIT3/ROBO2 promotes chondrocyte maturation via the inhibition of β-catenin signaling.

Runx1 regulates osteogenic differentiation of BMSCs by inhibiting adipogenesis through Wnt/β-catenin pathway

OBJECTIVE

Bone marrow stem cells (BMSCs) can commit to both adipocyte and osteoblast lineages. However, the mechanism underlying how transcription factors regulate this process remains elusive. Our aims were to determine the role of runt-related transcription factor 1 (Runx1) in BMSCs lineage determination and the underlying mechanisms.

STUDY DESIGN

BMSCs from mouse femur bone marrow were harvested and cultured in osteogenic medium. Runx1 was knocked down in BMSCs using lentivirus. Alkaline phosphatase (ALP), Von Kossa and Oil Red O staining were performed on the Runx1-transduced BMSCs and control cells to see the differences of osteogenic and adipogenic differentiation in these groups. Real-time quantitative PCR and Western blot were performed to analyse the expression levels of osteogenic and adipogenic factors regulated by Runx1 at gene and protein levels.

RESULTS

In BMSCs with Runx1 knockdown, the expression levels of osteogenic-related genes decreased significantly while the adipogenic genes C/EBPα, PPARγ and Fabp4 increased by 12-fold, 10-fold, and 30-fold, respectively, compared with the control cells. ALP activity and Von kossa staining were greatly decreased in Runx1-transfected cells while the Oil Red O staining was comparable to that in the control groups. Canonical Wnt signaling was investigated in the Runx1-deficient BMSCs, and a 50% decrease in the expression of active β-catenin in these cells was found. Lef1 and Tcf1, which are regulated by β-catenin were also decreased in Runx1-deficient cells compared with the levels in controls. Moreover, although there was no difference in the expression of Wnt3a among the three groups of cells, the expression of Wnt10b decreased by 80% in Runx1-deficient BMSCs compared with the levels in the other two groups.

CONCLUSIONS

Our results show Runx1 promotes the capacity of osteogenesis in BMSCs while inhibits their adipogenesis through canonical Wnt/β-catenin pathway, which provides new insights into osteoblast development.

The Role of Wnt Pathway in the Pathogenesis of OA and Its Potential Therapeutic Implications in the Field of Regenerative Medicine

Introduction

Osteoarthritis (OA) is a degenerative joint disease characterized by articular cartilage degradation, subchondral damage, and bone remodelling, affecting most commonly weight-bearing joints, such as the knee and hip. The loss of cartilage leads to joint space narrowing, pain, and loss of function which could ultimately require total joint replacement. The Wnt/β catenin pathway is involved in the pathophysiology of OA and has been proposed as a therapeutic target. Endogenous and pharmacological inhibitors of this pathway were recently investigated within innovative therapies including the use of platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs).

Methods

A review of the literature was performed on the PubMed database based on the following inclusion criteria: article written in English language in the last 20 years and dealing with (1) the role of Wnt-β catenin pathway in the pathogenesis of osteoarthritis and (2) pharmacologic or biologic strategies modulating the Wnt-β catenin pathway in the OA setting.

Results

Evidences support that Wnt signalling pathway is likely linked to OA progression and severity. Its inhibition through natural antagonists and new synthetic or biological drugs shares the potential to improve the clinical condition of the patients by affecting the pathological activity of Wnt/β-catenin signalling.

Conclusions

While further research is needed to better understand the mechanisms regulating the molecular interaction between OA regenerative therapies and Wnt, it seems that biologic therapies for OA exert modulation on Wnt/β catenin pathway that might be relevant in achieving the beneficial clinical effect of those therapeutic strategies.

Maximal strength training improves musculoskeletal health in amphetamine users in clinical treatment

Amphetamine use leads to impaired skeletal health and elevated risk of osteoporosis. In the current study, we document that maximal strength training (MST), as a part of clinical treatment, works as a countermeasure, improving muscle force generating capacity, body composition, and skeletal health at sites particularly prone to osteoporotic fractures.

INTRODUCTION

Amphetamine users have attenuated musculoskeletal health. MST with heavy loads, few repetitions, and emphasis on maximal mobilization in the concentric phase may increase muscle force generating capacity and skeletal health. This study investigated if MST-induced improvements in force generating capacity improved bone mineral density (BMD), trabecular bone score, and body composition in amphetamine users participating in 3-months clinical treatment.

METHODS

Of 40 randomized patients, 23 completed the study: 11 in the supervised training group (TG; 8 men, 3 women, 34 ± 10 years) and 12 in the control group (CG; 9 men, 3 women, 32 ± 8 years). The TG performed hack-squat MST three times a week for 12 weeks with an intensity of ~90% of one repetition maximum (1RM). Both groups attended conventional clinical treatment. Pre-training and post-training, we assessed hack-squat 1RM and rate of force development (RFD), BMD, body composition and trabecular bone score by dual X-ray absorptiometry, and serum bone metabolism markers.

RESULTS

MST induced increases in 1RM (70%) and RFD (86%), and resulted in BMD improvements at lumbar spine (3.6%) and total hip (2.4%); all improvements were different from CG (p < 0.05). Both the 1RM and RFD increases were associated with BMD improvements (lumbar spine: r = 0.73 (1RM), r = 0.60 (RFD); total hip: r = 0.61 (1RM); all p < 0.05). No differences were observed in trabecular bone score or bone metabolism markers.

CONCLUSIONS

MST improved force generating capacity and skeletal health at sites prone to bone loss in amphetamine users, and advocate that MST should be implemented as a clinical strategy to restore the patients' musculoskeletal health.

Enhanced osteogenic differentiation and bone regeneration of poly(lactic-co-glycolic acid) by graphene via activation of PI3K/Akt/GSK-3β/β-catenin signal circuit

The reconstruction of bone defects by guiding autologous bone tissue regeneration with artificial biomaterials is a potential strategy in the area of bone tissue engineering. The development of new polymers with good biocompatibility, favorable mechanical properties, and osteoinductivity is of vital importance. Graphene and its derivatives have attracted extensive interests due to the exceptional physiochemical and biological properties of graphene. In this study, poly(lactic-co-glycolic acid) (PLGA) films incorporated by graphene nanoplates were fabricated. The results indicated that the incorporation of proper graphene nanoplates into poly(lactic-co-glycolic acid) film could enhance the adhesion and proliferation of rat bone marrow-derived mesenchymal stem cells (rBMSCs). The augmentation of alkaline phosphatase activity, calcium mineral deposition, and the expression level of osteogenic-related genes of rBMSCs on the composite films were observed. Moreover, the incorporation of graphene might activate the PI3K/Akt/GSK-3β/β-catenin signaling pathway, which appeared to be the mechanism behind the osteoinductive properties of graphene. Moreover, the in vivo furcation defect implantation results revealed better guiding bone regeneration properties in the graphene-incorporated group. Thus, we highlight this graphene-incorporated film as a promising platform for the growth and osteogenic differentiation of BMSCs that can achieve application in bone regeneration.

Berberine derivative, Q8, stimulates osteogenic differentiation

Berberine has been implicated to be involved in maintaining bone health due to its anti-oxidative and osteogenic properties. However, low potency and low bioavailability limit the clinical development of the drug. To overcome these obstacles, we previously synthesized a compound, Q8, which is a structural homolog of berberine. The present study examined the pharmacological functions of Q8 to evaluate its potential use in bone regeneration with respect to osteoblast differentiation. Here, we report that Q8 enhanced BMP4-induced alkaline phosphatase (ALP) activity and transcription from the ALP promoter. In addition, Q8 suppressed the expression and activity of PPARγ (a known negative regulator of osteogenesis due to its stimulatory effects on adipogenesis and its role as an adipogenic transcription factor), which in turn increases β-catenin expression in the nucleus, and ultimately promotes osteoblast differentiation. Meanwhile, Q8 reversed the inhibitory effects of the PPARγ agonist, rosiglitazone, on osteoblast differentiation. This study demonstrated that Q8 promotes osteoblast differentiation via inhibition of PPARγ and the enhancement of osteoblast function by Q8 may contribute to the prevention for osteoporosis.

Postnatal Skeletal Deletion of Dickkopf-1 Increases Bone Formation and Bone Volume in Male and Female Mice, Despite Increased Sclerostin Expression

The Wnt antagonist Dickkopf-1 (Dkk1) is a negative regulator of osteoblast function and bone mass. However, because of the lack of appropriate models, many aspects of its role in the regulation of postnatal bone turnover and its cellular source have remained unknown. In this study, we deleted Dkk1 postnatally and in different cell types using various Cre-drivers (Rosa26-ERT2-Cre, Osx-cre, Dmp1-Cre) and assessed to which extent cells of the osteoblastic lineage contribute to the effects of Dkk1 on bone turnover and homeostasis. Female and male mice were examined at 12 weeks of age. Mice with a global or cell type-specific deletion of Dkk1 showed a two- to threefold higher bone volume compared with their Cre-negative littermates. The mineral apposition rate and the bone formation rate were increased two- to fourfold in all three mouse lines, despite a significant increase in systemic and skeletal levels of sclerostin. Dkk1 deletion further reduced the number of osteoclasts about twofold, which was accompanied by a strong decrease in the receptor activator of nuclear factor-κB ligand/osteoprotegerin mRNA ratio in femoral bone. Despite similar increases in bone mass, the deletion of Dkk1 in osterix-expressing cells reduced circulating Dkk1 significantly (males, -79%; females, -77%), whereas they were not changed in Dkk1^fl/fl ;Dmp1-Cre mice. However, both lines showed significantly reduced Dkk1 mRNA levels in bone. In summary, we show that lack of Dkk1 in cells of the osteoblastic lineage leads to high bone mass with increased bone formation, despite increased levels of sclerostin. Moreover, the majority of systemic Dkk1 appears to originate from osteoprogenitors but not from mature osteoblasts or osteocytes. Nevertheless, the amount of Dkk1 produced locally by more mature osteogenic cells is sufficient to modulate bone mass. Thus, this study highlights the importance of local Wnt signaling on postnatal bone homeostasis. © 2018 American Society for Bone and Mineral Research.

Role of nutritional vitamin D in osteoporosis treatment

Osteoporosis is a systemic skeletal disorder characterized by a decrease in bone mass and microarchitectural deterioration of bone tissue. The World Health Organization has defined osteoporosis as a decrease in bone mass (50%) and bony quality (50%). Vitamin D, a steroid hormone, is crucial for skeletal health and in mineral metabolism. Its direct action on osteoblasts and osteoclasts and interaction with nonskeletal tissues help in maintaining a balance between bone turnover and bone growth. Vitamin D affects the activity of osteoblasts, osteoclasts, and osteocytes, suggesting that it affects bone formation, bone resorption, and bone quality. At physiological concentrations, active vitamin D maintains a normal rate of bone resorption and formation through the RANKL/OPG signal. However, active vitamin D at pharmacological concentration inhibits bone resorption at a higher rate than that of bone formation, which influences the bone quality and quantity. Nutritional vitamin D rather than active vitamin D activates osteoblasts and maintains serum 25(OH)D3 concentration. Despite many unanswered questions, much data support nutritional vitamin D use in osteoporosis patients. This article emphasizes the role of nutritional vitamin D replacement in different turnover status (high or low bone turnover disorders) of osteoporosis together with either anti-resorptive (Bisphosphonate, Denosumab et.) or anabolic (Teriparatide) agents when osteoporosis persists.

Postnatal deletion of β-catenin in osterix-expressing cells is necessary for bone growth and intermittent PTH-induced bone gain

wnt/β-catenin signaling has been shown to influence bone homeostasis and is important for parathyroid hormone (PTH)-induced bone gain. To further understand the role of β-catenin in the early stages of osteoblastic lineage cells for postnatal bone homeostasis and the anabolic actions of PTH on bone, we examined mice with postnatal disruption of β-catenin in osterix-expressing cells (β-catenin KO mice) by mating floxed β-catenin mice with transgenic mice expressing cre under the control of the osterix promoter suppressible by doxycycline. After withdrawal of doxycycline, β-catenin KO mice developed progressive bone loss, ectopic cartilage formation, accumulation of mesenchymal stromal cells, and bone marrow adiposity. The β-catenin-defective osteoblasts sorted by flow cytometry from β-catenin KO mice exhibited decreased EdU incorporation, increased annexin V activity, and profound alterations in gene expression including wnt target genes, osteoclast regulators, and osteoblast markers. A dramatic increase in osteoclasts was observed in both neonatal and postnatal β-catenin KO mice. Intermittent administration of PTH for 4 weeks significantly increased bone mass in control mice; however, this anabolic effect of PTH was substantially blunted in β-catenin KO mice. Our data indicate that β-catenin in osterix-expressing cells is required for postnatal osteoblast differentiation, osteoblast proliferation, and bone resorption, and is essential for the anabolic actions of PTH in bone.

Regulation of Osteoblast Metabolism by Wnt Signaling

Wnt/β-catenin signaling plays a critical role in the achievement of peak bone mass, affecting the commitment of mesenchymal progenitors to the osteoblast lineage and the anabolic capacity of osteoblasts depositing bone matrix. Recent studies suggest that this evolutionarily-conserved, developmental pathway exerts its anabolic effects in part by coordinating osteoblast activity with intermediary metabolism. These findings are compatible with the cloning of the gene encoding the low-density lipoprotein related receptor-5 (LRP5) Wnt co-receptor from a diabetes-susceptibility locus and the now well-established linkage between Wnt signaling and metabolism. In this article, we provide an overview of the role of Wnt signaling in whole-body metabolism and review the literature regarding the impact of Wnt signaling on the osteoblast's utilization of three different energy sources: fatty acids, glucose, and glutamine. Special attention is devoted to the net effect of nutrient utilization and the mode of regulation by Wnt signaling. Mechanistic studies indicate that the utilization of each substrate is governed by a unique mechanism of control with β-catenin-dependent signaling regulating fatty acid β-oxidation, while glucose and glutamine utilization are β-catenin-independent and downstream of mammalian target of rapamycin complex 2 (mTORC2) and mammalian target of rapamycin complex 1 (mTORC1) activation, respectively. The emergence of these data has provided a new context for the mechanisms by which Wnt signaling influences bone development.

Active mitochondria support osteogenic differentiation by stimulating β-catenin acetylation

Bone marrow stromal (a.k.a. mesenchymal stem) cells (BMSCs) can differentiate into osteoblasts (OBs), adipocytes, or chondrocytes. As BMSCs undergo OB differentiation, they up-regulate mitochondrial oxidative phosphorylation (OxPhos). Here, we investigated the mechanism(s) connecting mitochondrial OxPhos to OB differentiation. First, we found that treating BMSC-like C3H10T1/2 cells with an OxPhos inhibitor reduces their osteogenic potential. Interestingly, ATP levels were not reduced, as glycolysis compensated for the decreased OxPhos. Thus, mitochondria support OB differentiation not only by supplying ATP, but also by other mechanisms. To uncover these mechanisms, we stimulated OxPhos in C3H10T1/2 cells by replacing media glucose with galactose and observed that this substitution increases both OxPhos and osteogenesis even in the absence of osteoinducers. β-Catenin, an important signaling pathway in osteogenesis, was found to be responsive to OxPhos stimulation. β-Catenin activity is maintained by acetylation, and mitochondria generate the acetyl donor acetyl-CoA, which upon entering the Krebs cycle is converted to citrate capable of exiting mitochondria. Cytosolic citrate is converted back to acetyl-CoA by ATP citrate lyase (ACLY). We found that inhibiting ACLY with SB204990 (SB) reverses the galactose-induced β-catenin activity and OB differentiation. This suggested that acetylation is involved in β-catenin activation after forced OxPhos stimulation, and using immunoprecipitation, we indeed detected SB-sensitive β-catenin acetylation. Both β-catenin acetylation and activity increased during osteoinduction coincident with OxPhos activation. These findings suggest that active mitochondria support OB differentiation by promoting β-catenin acetylation and thus activity.

Association of Anabolic Effect of Calcitriol with Osteoclast-Derived Wnt 10b Secretion

Canonical Wnt (Wingless/Integrated) signaling is crucial in bone development and the Wnt ligand can promote osteoblast differentiation from mesenchymal progenitor cells. Calcitriol, an active vitamin D3, is used clinically for treatment of secondary hyperparathyroidism (SHPT) in chronic kidney disease (CKD) patients. The bone effects of calcitriol in SHPT remains uncertain. We hypothesized that calcitriol improves bone mass by suppressing osteoclast activity, and simultaneously promoting Wnt ligand secretion. We designed a cross-sectional study in maintenance hemodialysis patients to explore the effects of calcitriol on different bone turnover markers and specifically emphasized the Wnt 10b levels. Then, we explored the source of Wnt 10b secretion by using osteoclasts and osteoblasts treated with calcitriol in cell culture studies. Finally, we explored the effects of calcitriol on bone microarchitectures in CKD mice, using the 5/6 nephrectomy CKD animal model with analysis using micro-computed tomography. Calcitriol promoted the growth of both trabecular and cortical bones in the CKD mice. Wnt 10b and Procollagen 1 N-terminal Propeptide (P1NP) significantly increased, but Tartrate-resistant acid phosphatase 5b (Trap 5b) significantly decreased in the calcitriol-treated maintenance hemodialysis patients. Calcitriol enhanced Wnt 10b secretion from osteoclasts in a dose-dependent manner. Treatment of SHPT with calcitriol improved the bone anabolism by inhibiting osteoclasts and promoting osteoblasts that might be achieved by increasing the Wnt 10b level.

The "mechanostat" principle in cell differentiation. The osteochondroprogenitor paradigm

The "mechanostat" principle may be depicted as an oscillating signal of a signaling molecule, in which the amplitude, frequency, cumulative level, delay, and duration of the curve encode the information for concrete cellular responses and biological activities. When the oscillating signal is kept sustained (present delay), cell exit may be performed, whereas when the oscillating signal remains robust, cell proliferation may take place. B-catenin-Wnt signaling pathway has a key role in the differentiation of osteochondroprogenitor cells. Sustained downregulation of the β-catenin-Wnt pathway forces osteochondroprogenitors to a chondrogenic fate instead of an osteoblastic one. Other signaling, for example, bone morphogenetic protein and Notch signaling pathways interact with the Wnt pathway. The crosstalk between biochemical and mechanical stimuli produces the final information that leads to the final cell fate decisions, through the "mechanostat" principle.

Frontal Bone Healing Is Sensitive to Wnt Signaling Inhibition via Lentiviral-Encoded Beta-Catenin Short Hairpin RNA

The Wnt/β-catenin signaling pathway plays an integral role in skeletal biology, spanning from embryonic skeletal patterning through bone maintenance and bone repair. Most experimental methods to antagonize Wnt signaling in vivo are either systemic or transient, including genetic approaches, use of small-molecule inhibitors, or neutralizing antibodies. We sought to develop a novel, localized model of prolonged Wnt/β-catenin signaling blockade by the application and validation of a lentivirus encoding β-catenin short hairpin RNA (shRNA). Efficacy of lentiviral-encoded β-catenin shRNA was first confirmed in vitro using bone marrow mesenchymal stromal cells, and in vivo using an intramedullary long bone injection model in NOD SCID mice. Next, the effects of β-catenin knockdown were assessed in a calvarial bone defect model, in which the frontal bone demonstrates enhanced bone healing associated with heightened Wnt/β-catenin signaling. Lentivirus encoding either β-catenin shRNA or random sequence shRNA with enhanced green fluorescent protein (control) was injected overlying the calvaria of NOD SCID mice and bone defects were created in either the frontal or parietal bones. Among mice treated with lentivirus encoding β-catenin shRNA, frontal bone defect healing was significantly reduced by all radiographic and histologic metrics. In contrast, parietal bone healing was minimally impacted by β-catenin shRNA. In aggregate, our data document the application and validation of a lentivirus encoding β-catenin shRNA model that represents an easily replicable tool for examining the importance of locoregional Wnt/β-catenin signaling in bone biology and regeneration.

Aberrantly expressed messenger RNAs and long noncoding RNAs in degenerative nucleus pulposus cells co-cultured with adipose-derived mesenchymal stem cells

Background

Stem cell therapy is considered as a promising alternative to treat intervertebral disc degeneration (IDD). Extensive work had been done on identifying and comparing different types of candidate stem cells, both in vivo and in vitro. However, few studies have shed light on degenerative nucleus pulposus cells (NPCs), especially their biological behavior under the influence of exogenous stem cells, specifically the gene expression and regulation pattern. In the present study, we aimed to determine messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs), which are differentially expressed during the co-culturing process with adipose-derived mesenchymal stem cells (ASCs) and to explore the involved signaling pathways and the regulatory networks.

Methods

We compared degenerative NPCs co-cultured with ASCs with those cultured solely using lncRNA-mRNA microarray analysis. Based on these data, we investigated the significantly regulated signaling pathways based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database. Moreover, 23 micro RNAs (miRNAs), which were demonstrated to be involved in IDD were chosen; we investigated their theoretic regulatory importance associated with our microarray data.

Results

We found 632 lncRNAs and 1682 mRNAs were differentially expressed out of a total of 40,716 probes. We then confirmed the microarray data by real-time PCR. Furthermore, we demonstrated 197 upregulated, and 373 downregulated Gene Ontology terms and 176 significantly enriched pathways, such as the mitogen-activated protein kinase (MAPK) pathway. Also, a signal-net was constructed to reveal the interplay among differentially expressed genes. Meanwhile, a mRNA-lncRNA co-expression network was constructed for the significantly changed mRNAs and lncRNAs. Also, the competing endogenous RNA (ceRNA) network was built.

Conclusion

Our results present the first comprehensive identification of differentially expressed lncRNAs and mRNAs of degenerative NPCs, altered by co-culturing with ASCs, and outline the gene expression regulation pattern. These may provide valuable information for better understanding of stem cell therapy and potential candidate biomarkers for IDD treatment.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1677-x) contains supplementary material, which is available to authorized users.

Effect of exercise on bone in poorly controlled type 1 diabetes mediated by the ActRIIB/Smad signaling pathway

Myostatin (MSTN) is not only a key negative regulator of skeletal muscle secretion, however is also an endocrine factor that is transmitted to bone. To investigate the effect and possible mechanism of weight-bearing treadmill running on bone with poorly controlled Type 1 diabetes, rats were randomly divided into three groups: Normal control (NC), diabetic mellitus (DM) and diabetic exercise training groups (DM-WTR). The DM-WTR rats were trained with weight-bearing running. The results demonstrated that the levels of serum insulin, body weight, bone mass, muscle mass, grip strength, and serum calcium in the DM-WTR rats were significantly increased, whereas the levels of blood glucose, alkaline phosphatase, and tartrate-resistant acid phosphatase were markedly reduced in the DM-WTR rats compared with the DM rats. Weight-bearing running inhibited streptozocin (STZ)-induced MSTN mRNA and protein expression in the diabetic rats. The mRNA and protein expression levels of activin type IIB receptor and mothers against decapentaplegic homolog 2/3 and its phosphorylation in femur DM-WTR rats were reduced compared with DM rats. In addition, weight-bearing running enhanced the STZ-induced Wnt and β-catenin expression levels and reduced the STZ-induced glycogen synthase kinase (GSK)-3β expression in diabetic rats' femora. In conclusion, the results suggested that weight-bearing running could partially ameliorate STZ-induced femur atrophy via MSTN downregulation, and this may be associated with the inactivation of Activin A Receptor Type 2B/Smad2/3 signaling pathways and the activation of the Wnt/GSK3β/β-catenin signaling pathway. Further studies are needed to verify these conclusions.

Plants and Their Bioactive Constituents in Mesenchymal Stem Cell-Based Periodontal Regeneration: A Novel Prospective

Periodontitis is a common chronic inflammatory disease, which causes the destruction of both the soft and mineralized tissues. However, current treatments such as bone graft materials, barrier membranes, and protein products all have difficulties in regenerating the complete periodontal tissue structure. Stem cell-based tissue engineering has now emerged as one of the most effective treatments for the patients suffering from periodontal diseases. Plants not only can be substrates for life processes, but also contain hormones or functional molecules. Numbers of preclinical studies have revealed that products from plant can be successfully applied in modulating proliferation and differentiation of human mesenchymal stem cells. Plant-derived substances can induce stem cells osteogenic differentiation, and they also possess angiogenic potency. Furthermore, in the field of tissue engineering, plant-derived compounds or plant extracts can be incorporated with biomaterials or utilized as biomaterials for cell transplantation. So it is speculated that botanical products may become a new perspective in stem cell-based periodontal regeneration. However, the lack of achieving predict clinical efficacy and quality control has been the major impediment to its extensive application. This review gives an overview of the prospect of applying different plant-derived substances in various human mesenchymal stem cells-based periodontal regeneration.

Effect of inhibition of CBP-coactivated β-catenin-mediated Wnt signalling in uremic rats with vascular calcifications

Uremic vascular calcification is a regulated cell-mediated process wherein cells in the arterial wall transdifferentiate to actively calcifying cells resulting in a process resembling bone formation. Wnt signalling is established as a major driver for vessel formation and maturation and for embryonic bone formation, and disturbed Wnt signalling might play a role in vascular calcification. ICG-001 is a small molecule Wnt inhibitor that specifically targets the coactivator CREB binding protein (CBP)/β-catenin-mediated signalling. In the present investigation we examined the effect of ICG-001 on vascular calcification in uremic rats. Uremic vascular calcification was induced in adult male rats by 5/6-nephrectomy, high phosphate diet and alfacalcidol. The presence of uremic vascular calcification in the aorta was associated with induction of gene expression of the Wnt target gene and marker of proliferation, cyclinD1; the mediator of canonical Wnt signalling, β-catenin and the matricellular proteins, fibronectin and periostin. Furthermore, genes from fibrosis-related pathways, TGF-β and activin A, as well as factors related to epithelial-mesenchymal transition, snail1 and vimentin were induced. ICG-001 treatment had significant effects on gene expression in kidney and aorta from healthy rats. These effects were however limited in uremic rats, and treatment with ICG-001 did not reduce the Ca-content of the uremic vasculature.

Sclerostin is upregulated in the early stage of chondrogenic differentiation, but not required in endochondral ossification in vitro

Sclerostin is a potent inhibitor of the canonical Wnt signaling pathway. Wnt signaling pathways have multiple roles in the regulation of cartilage development, growth, and maintenance. This study focused on the role of sclerostin in the process of chondrogenic differentiation. We hypothesized that sclerostin is essential to induce chondrogenic differentiation and regulate endochondral ossification. ATDC5 cells were used to investigate chondrogenic differentiation and terminal calcification. During chondrogenic differentiation, intrinsic sclerostin was upregulated in the early stage, but downregulated in the late stage. Addition of sclerostin elevated expressions of Sox9 and Col2a1 (P<0.05) and reduced expressions of Runx2, Col10a1, MMP-3, MMP-13, and ADAMTS5 (P<0.05) through inhibition of the Wnt-β-catenin signaling pathway (P<0.05). Terminal calcification was significantly inhibited by sclerostin (P<0.05). In contrast, deletion of sclerostin decreased expressions of Sox9 and Col2a1 (P<0.05), increased expressions of Runx2, Col10a1, MMP-3, and MMP-13 (P<0.05), and promoted terminal calcification (P<0.05). This study provides insights into the possible role of sclerostin in the regulation of chondrogenic differentiation. Sclerostin is upregulated in the early stage of chondrogenic differentiation, but is not required in endochondral ossification. Sclerostin is a candidate modulator for chondrogenic differentiation.

Transcriptome analyses reveal molecular mechanisms that regulate endochondral ossification in amphibian Bufo gargarizans during metamorphosis

BACKGROUND

A developmental transition from aquatic to terrestrial existence is one of the most important events in the evolution of terrestrial vertebrates. Amphibian metamorphosis is a classic model to study this transition. The development of the vertebrate skeleton can reflect its evolutionary history. Endochondral ossification serves a vital role in skeletal development. Thus, we sought to unravel molecular mechanisms that regulate endochondral ossification during Bufo gargarizans metamorphosis.

METHODS

The alizarin red-alcian blue double staining method was used to visualize the skeletal development of B. gargarizans during metamorphosis. RNA sequencing (RNA-seq) was used to explore the transcriptome of B. gargarizans in four key developmental stages during metamorphosis. Real-time quantitative PCR (RT-qPCR) was used to validate the expression patterns of endochondral ossification related genes.

RESULTS

Endochondral ossification increased gradually in skeletal system of B. gargarizans during metamorphosis. A total of 137,264 unigenes were assembled and 44,035 unigenes were annotated. 10,352 differentially expressed genes (DEGs) were further extracted among four key developmental stages. In addition, 28 endochondral ossification related genes were found by searching for DEG libraries in B. gargarizans. Of the 28 genes, 10 genes were validated using RT-qPCR.

CONCLUSIONS

The exquisite coordination of the 28 genes is essential for regulation of endochondral ossification during B. gargarizans metamorphosis.

GENERAL SIGNIFICANCE

The present study will not only provide an invaluable genomic resource and background for further research of endochondral ossification in amphibians but will also aid in enhancing our understanding of the evolution of terrestrial vertebrates.

Origin of Reparative Stem Cells in Fracture Healing

PURPOSE OF REVIEW

The identity and functional roles of stem cell population(s) that contribute to fracture repair remains unclear. This review provides a brief history of mesenchymal stem cell (MSCs) and provides an updated view of the many stem/progenitor cell populations contributing to fracture repair.

RECENT FINDINGS

Functional studies show MSCs are not the multipotential stem cell population that form cartilage and bone during fracture repair. Rather, multiple studies have confirmed the periosteum is the primary source of stem/progenitor cells for fracture repair. Newer work is also identifying other stem/progenitor cells that may also contribute to healing. Although the heterogenous periosteal cells migrate to the fracture site and contribute directly to callus formation, other cell populations are involved. Pericytes and bone marrow stromal cells are now thought of as key secretory centers that mostly coordinate the repair process. Other populations of stem/progenitor cells from the muscle and transdifferentiated chondroctyes may also contribute to repair, and their functional role is an area of active research.

In-Vivo Nucleus Pulposus-Specific Regulation of Adult Murine Intervertebral Disc Degeneration via Wnt/Beta-Catenin Signaling

B-Catenin, transcription factor of Wnt signaling, is promoted in patients with intervertebral disc (IVD) degeneration, but Wnt signaling decreases with aging. We hypothesize that IVD degeneration is associated with decreased Wnt signaling despite more b-Catenin. Chronic compression of tail IVDs of young-adult and aged Wnt-reporter (TOPGAL) animals initiated an age-related cascade of degenerative-like changes, which included reduced Wnt ligand expression and Wnt signaling in nucleus pulposus cells, despite elevation of b-Catenin protein and gene expression. To determine the effect of upregulated and downregulated Wnt signaling in adult discs, b-Catenin in the nucleus pulposus was stabilized (Shh-CreEr^T2/b-Catenin^{fl(Ex3)/fl(Ex3)}, cACT) or knocked out (Shh-CreEr^T2/b-Catenin^fl/fl, cKO). cACT discs had promoted expression of Wnt-targets and -ligands, brachyury, extracellular matrix production and 34% greater compressive stiffness than WT (b-Catenin^{fl(Ex3)/fl(Ex3)}) discs, but 50% less tensile stiffness. By contrast, knockout reversed the cACT phenotype: less protein expression of b-catenin in the nucleus pulposus, less expression of brachyury, heightened expression of extracellular matrix breakdown and 46% less compressive stiffness than wild-type (b-Catenin^fl/fl,WT) discs. These data suggest that intervertebral disc degeneration is associated with loss of Wnt signaling and that the concomitant increase in b-catenin is a regenerative response, potentially offering a therapeutic approach to degeneration.