Differential roles of CCN family proteins during osteoblast differentiation: Involvement of Smad and MAPK signaling pathways

Inhibition of CCN5 Protects Against Apoptosis and Endoplasmic Reticulum Stress in Bisphenol A-Induced Sertoli Cells via p38/JNK MAPK Signaling Pathway

Bisphenol A (BPA) is the most common endocrine disruptor that has toxicity to the reproductive system and male infertility. However, the underlying mechanisms of BPA's toxicity to Sertoli cells remain poorly understood. Cellular communication network factor 5 (CCN5) is reported to regulate cell proliferation, apoptosis, and differentiation. Our study demonstrated a significant elevation of CCN5 expression in the testis of nonobstructive azoospermia patients and TM4 Sertoli cells exposed to BPA. Knockdown of CCN5 reduced apoptotic cells after BPA treatment, as determined by flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling assays. Cells exposed to BPA showed increased expressions of Bax and cleaved poly(ADP-ribose) polymerase, decreased expression of Bcl-2, as well as elevated activities of caspase-3 and caspase-9 in BPA-induced TM4 cells, which were reversed by CCN5 inhibition. Loss of CCN5 declined phosphorylation of protein kinase R-like endoplasmic reticulum kinase and eukaryotic translation initiation factor 2A and decreased activating transcription factor 4 and C/EBP-homologous protein in BPA-treated cells. Furthermore, silencing CCN5 blocked BPA-induced phosphorylation of p38 and c-Jun N-terminal kinase (JNK). Administration of anisomycin, a mitogen-activated protein kinase (MAPK) activator, reversed the effects of CCN5 knockdown on BPA-induced endoplasmic reticulum (ER) stress and apoptosis. Taken together, CCN5 promotes apoptosis and ER stress in Sertoli cells exposed to BPA by activating the p38/JNK MAPK signaling pathway.

Unlocking the therapeutic potential of WISP-1: A comprehensive exploration of its role in age-related musculoskeletal disorders

As the global population ages, the incidence of age-related musculoskeletal diseases continues to increase, driven by numerous complex and poorly understood factors. WNT-1 inducible secreted protein 1 (WISP-1), a secreted matrix protein, plays a critical role in the growth and development of the musculoskeletal system, including chondrogenesis, osteogenesis, and myogenesis. Numerous in vivo and in vitro studies have demonstrated that WISP-1 is significantly upregulated in age-related musculoskeletal conditions, such as osteoarthritis, osteoporosis, and sarcopenia, suggesting its involvement in the pathogenesis of these diseases. Regulating WISP-1 expression holds promise as a therapeutic strategy for improving musculoskeletal function, potentially offering new avenues for treating age-related musculoskeletal diseases in clinical practice. This review highlights the signaling pathways associated with WISP-1, its physiological roles within the musculoskeletal system, and its therapeutic potential in treating age-related musculoskeletal disorders.

Current status of Er:YAG laser in periodontal surgery

Lasers have numerous advantageous tissue interactions such as ablation or vaporization, hemostasis, bacterial killing, as well as biological effects, which induce various beneficial therapeutic effects and biological responses in the tissues. Thus, lasers are considered an effective and suitable device for treating a variety of inflammatory and infectious conditions of periodontal disease. Among various laser systems, the Er:YAG laser, which can be effectively and safely used in both soft and hard tissues with minimal thermal side effects, has been attracting much attention in periodontal therapy. This laser can effectively and precisely debride the diseased root surface including calculus removal, ablate diseased connective tissues within the bone defects, and stimulate the irradiated surrounding periodontal tissues during surgery, resulting in favorable wound healing as well as regeneration of periodontal tissues. The safe and effective performance of Er:YAG laser-assisted periodontal surgery has been reported with comparable and occasionally superior clinical outcomes compared to conventional surgery. This article explains the characteristics of the Er:YAG laser and introduces its applications in periodontal surgery including conventional flap surgery, regenerative surgery, and flapless surgery, based on scientific evidence from currently available basic and clinical studies as well as cases reports.

A monoallelic variant in CCN2 causes an autosomal dominant spondyloepimetaphyseal dysplasia with low bone mass

Cellular communication network factor 2 (CCN2) is a secreted extracellular matrix-associated protein, and its aberrantly increased expression has been implicated in a diversity of diseases involving pathological processes of fibrosis, chronic inflammation, or tissue injury, which has promoted the evaluation of CCN2 as therapeutic targets for multiple disorders. However, human phenotypes associated with CCN2 deficiency have remained enigmatic; variants in CCN2 have not yet been associated with a human phenotype. Here, we collected families diagnosed with spondyloepimetaphyseal dysplasia (SEMD), and screened candidate pathogenic genes for families without known genetic causes using next-generation sequencing. We identified a monoallelic variant in signal peptide of CCN2 (NM_001901.2: c.65 G > C [p.Arg22Pro]) as the cause of SEMD in 14 subjects presenting with different degree of short stature, premature osteoarthritis, and osteoporosis. Affected subjects showed decreased serum CCN2 levels. Cell lines harboring the variant displayed decreased amount of CCN2 proteins in culture medium and an increased intracellular retention, indicating impaired protein secretion. And the variant weakened the stimulation effect of CCN2 on osteogenesis of bone marrow mesenchymal stem cells. Zebrafish ccn2a knockout model and osteoblast lineage-specific Ccn2-deficient mice (Ccn2fl/fl;Prx1Cre) partially recapitulated the phenotypes including low bone mass observed in affected subjects. Pathological mechanism implicated in the skeletal abnormality in Ccn2fl/fl;Prx1Cre mice involved decreased bone formation, increased bone resorption, and abnormal growth plate formation. Collectively, our study indicate that monoallelic variants in CCN2 lead to a human inherited skeletal dysplasia, and highlight the critical role of CCN2 in osteogenesis in human.

CTGF regulates mineralization in human mature chondrocyte by controlling Pit-1 and modulating ANK via the BMP/Smad signalling

OBJECTIVE

Connective tissue growth factor (CTGF) exhibits potent proliferative, differentiated, and mineralizing effects, and is believed to be contribute to cartilage mineralization in Osteoarthritis (OA). However, the underlying mechanism of chondrocyte mineralization induced by CTGF remains obscure. As a key regulator of mineral responses, type III phosphate transporter 1 (Pit-1) has been associated with the pathogenesis of articular mineralization. Therefore, the primary objective of this study was to investigate whether CTGF influences the development of mature chondrocyte mineralization and the underlying mechanisms governing such mineralization.

METHODS

The effect of Connective tissue growth factor (CTGF) on human C-28/I2 chondrocytes were investigated. The chondrocytes were treated with CTGF or related inhibitors, and transfected with Overexpression and siRNA transfection of Type III Phosphate Transporter 1(Pit-1). Subsequently, the cells were subjected to Alizarin red S staining, PiPer Phosphate Assay Kit, Alkaline Phosphatase Diethanolamine Activity Kit, ELISA, RT-PCR or Western blot analysis.

RESULTS

Stimulation with Connective tissue growth factor (CTGF) significantly upregulated the expression of the Type III Phosphate Transporter 1(Pit-1) and mineralization levels in chondrocytes through activation of α5β1 integrin and BMP/Samd1/5/8 signaling pathways. Furthermore, treatment with overexpressed Pit-1 markedly increased the expression of Multipass Transmembrane Ankylosis (ANK) transporter in the cells. The inhibitory effect of CTGF receptor blockade using α5β1 Integrin blocking antibody was demonstrated by significantly suppressed the expression of Pit-1 and ANK transporter, as well as chondrocyte mineralization.

CONCLUSIONS

Our data indicate that Connective tissue growth factor (CTGF) plays a critical role inchondrocyte mineralization, which is dependent on the expression of the Type III Phosphate Transporter 1(Pit-1) and Multipass Transmembrane Ankylosis (ANK) transporter. Consequently, inhibition of CTGF activity may represent a novel therapeutic approach for the management of Osteoarthritis (OA).

Engineering a Pro-Osteogenic Secretome through the Transient Silencing of the Gene Encoding Secreted Frizzled Related Protein 1

The evidence sustaining the regenerative properties of mesenchymal stem cells' (MSCs) secretome has prompted a paradigm change, where MSCs have shifted from being considered direct contributors to tissue regeneration toward being seen as cell factories for producing biotech medicines. We have previously designed a method to prime MSCs towards osteogenic differentiation by silencing the Wnt/β-Catenin inhibitor Sfpr1. This approach produces a significant increase in bone formation in osteoporotic mice. In this current work, we set to investigate the contribution of the secretome from the MSCs where Sfrp1 has been silenced, to the positive effect seen on bone regeneration in vivo. The conditioned media (CM) of the murine MSCs line C3H10T1/2, where Sfrp1 has been transiently silenced (CM-Sfrp1), was found to induce, in vitro, an increase in the osteogenic differentiation of this same cell line, as well as a decrease of the expression of the Wnt inhibitor Dkk1 in murine osteocytes ex vivo. A reduction in the RANKL/OPG ratio was also detected ex vivo, suggesting a negative effect of CM-Sfrp1 on osteoclastogenesis. Moreover, this CM significantly increases the mineralization of human primary MSCs isolated from osteoportotic patients in vitro. Proteomic analysis identified enrichment of proteins involved in osteogenesis within the soluble and vesicular fractions of this secretome. Altogether, we demonstrate the pro-osteogenic potential of the secretome of MSCs primmed in this fashion, suggesting that this is a valid approach to enhance the osteo-regenerative properties of MSCs' secretome.

WISP2 downregulation inhibits the osteogenic differentiation of BMSCs in congenital scoliosis by regulating Wnt/β-catenin pathway

OBJECTIVES

Bone marrow mesenchymal stem cells (BMSCs) are instrumental in bone development, metabolism, and marrow microenvironment homeostasis. Despite this, the relevant effects and mechanisms of BMSCs on congenital scoliosis (CS) remain undefined. Herein, it becomes our focus to reveal the corresponding effects and mechanisms implicated.

METHODS

BMSCs from CS patients (hereafter referred as CS-BMSCs) and healthy donors (NC-BMSCs) were observed and identified. Differentially expressed genes in BMSCs were analyzed utilizing scRNA-seq and RNA-seq profiles. The multi-differentiation potential of BMSCs following the transfection or infection was evaluated. The expression levels of factors related to osteogenic differentiation and Wnt/β-catenin pathway were further determined as appropriate.

RESULTS

A decreased osteogenic differentiation ability was shown in CS-BMSCs. Both the proportion of LEPR⁺ BMSCs and the expression level of WNT1-inducible-signaling pathway protein 2 (WISP2) were decreased in CS-BMSCs. WISP2 knockdown suppressed the osteogenic differentiation of NC-BMSCs, while WISP2 overexpression facilitated the osteogenesis of CS-BMSCs via acting on the Wnt/β-catenin pathway.

CONCLUSIONS

Our study collectively indicates WISP2 knockdown blocks the osteogenic differentiation of BMSCs in CS by regulating Wnt/β-catenin signaling, thus providing new insights into the aetiology of CS.

The regulation and functions of the matricellular CCN proteins induced by shear stress

Shear stress is a frictional drag generated by the flow of fluid, such as blood or interstitial fluid, and plays a critical role in regulating cellular gene expression and functional phenotype. The matricellular CCN family proteins are dynamically regulated by shear stress of different flow patterns, and their expression significantly alters the microenvironment of cells. Secreted CCN proteins mainly bind to several cell surface integrin receptors to mediate their diverse functions in regulating cell survival, function, and behavior. Gene-knockout studies indicate major functions of CCN proteins in the cardiovascular and skeletal systems, the two primary systems in which CCN expressions are regulated by shear stress. In the cardiovascular system, the endothelium is directly exposed to vascular shear stress. Unidirectional laminar blood flow generates laminar shear stress, which promotes a mature endothelial phenotype and upregulates anti-inflammatory CCN3 expression. In contrast, disturbed flow generates oscillatory shear stress, which induces endothelial dysfunction through the induction of CCN1 and CCN2. Shear-induced CCN1 binds to integrin α6β1 and promotes superoxide production, NF-κB activation, and inflammatory gene expression in endothelial cells. Although the interaction between shear stress and CCN4-6 is not clear, CCN 4 exhibits a proinflammatory property and CCN5 inhibits vascular cell growth and migration. The crucial roles of CCN proteins in cardiovascular development, homeostasis, and disease are evident but not fully understood. In the skeletal system, mechanical loading on bone generates shear stress from interstitial fluid in the lacuna-canalicular system and promotes osteoblast differentiation and bone formation. CCN1 and CCN2 are induced and potentially mediate fluid shear stress mechanosensing in osteocytes. However, the exact roles of interstitial shear stress-induced CCN1 and CCN2 in bone are still not clear. In contrast to other CCN family proteins, CCN3 inhibits osteoblast differentiation, although its regulation by interstitial shear stress in osteocytes has not been reported. The induction of CCN proteins by shear stress in bone and their functions remain largely unknown and merit further investigation. This review discusses the expression and functions of CCN proteins regulated by shear stress in physiological conditions, diseases, and cell culture models. The roles between CCN family proteins can be compensatory or counteractive in tissue remodeling and homeostasis.

Myeloid CCN3 protects against aortic valve calcification

BACKGROUND

Cellular communication network factor 3 (CCN3) has been implicated in the regulation of osteoblast differentiation. However, it is not known if CCN3 can regulate valvular calcification. While macrophages have been shown to regulate valvular calcification, the molecular and cellular mechanisms of this process remain poorly understood. In the present study, we investigated the role of macrophage-derived CCN3 in the progression of calcific aortic valve disease.

METHODS

Myeloid-specific knockout of CCN3 (Mye-CCN3-KO) and control mice were subjected to a single tail intravenous injection of AAV encoding mutant mPCSK9 (rAAV8/D377Y-mPCSK9) to induce hyperlipidemia. AAV-injected mice were then fed a high fat diet for 40 weeks. At the conclusion of high fat diet feeding, tissues were harvested and subjected to histologic and pathologic analyses. In vitro, bone marrow-derived macrophages (BMDM) were obtained from Mye-CCN3-KO and control mice and the expression of bone morphogenic protein signaling related gene were verified via quantitative real-time PCR and Western blotting. The BMDM conditioned medium was cocultured with human valvular intersititial cells which was artificially induced calcification to test the effect of the conditioned medium via Western blotting and Alizarin red staining.

RESULTS

Echocardiography revealed that both male and female Mye-CCN3-KO mice displayed compromised aortic valvular function accompanied by exacerbated valve thickness and cardiac dysfunction. Histologically, Alizarin-Red staining revealed a marked increase in aortic valve calcification in Mye-CCN3-KO mice when compared to the controls. In vitro, CCN3 deficiency augmented BMP2 production and secretion from bone marrow-derived macrophages. In addition, human valvular interstitial cells cultured with conditioned media from CCN3-deficient BMDMs resulted in exaggerated pro-calcifying gene expression and the consequent calcification.

CONCLUSION

Our data uncovered a novel role of myeloid CCN3 in the regulation of aortic valve calcification. Modulation of BMP2 production and secretion in macrophages might serve as a key mechanism for macrophage-derived CCN3's anti-calcification function in the development of CAVD. Video Abstract.

Molecular and Genetic Interactions between CCN2 and CCN3 behind Their Yin-Yang Collaboration

Cellular communication network factor (CCN) 2 and 3 are the members of the CCN family that conduct the harmonized development of a variety of tissues and organs under interaction with multiple biomolecules in the microenvironment. Despite their striking structural similarities, these two members show contrastive molecular functions as well as temporospatial emergence in living tissues. Typically, CCN2 promotes cell growth, whereas CCN3 restrains it. Where CCN2 is produced, CCN3 disappears. Nevertheless, these two proteins collaborate together to execute their mission in a yin–yang fashion. The apparent functional counteractions of CCN2 and CCN3 can be ascribed to their direct molecular interaction and interference over the cofactors that are shared by the two. Recent studies have revealed the mutual negative regulation systems between CCN2 and CCN3. Moreover, the simultaneous and bidirectional regulatory system of CCN2 and CCN3 is also being clarified. It is of particular note that these regulations were found to be closely associated with glycolysis, a fundamental procedure of energy metabolism. Here, the molecular interplay and metabolic gene regulation that enable the yin–yang collaboration of CCN2 and CCN3 typically found in cartilage development/regeneration and fibrosis are described.

Acute Inflammatory Response in Osteoporotic Fracture Healing Augmented with Mechanical Stimulation is Regulated In Vivo through the p38-MAPK Pathway

Low-magnitude high-frequency vibration (LMHFV) has previously been reported to modulate the acute inflammatory response of ovariectomy-induced osteoporotic fracture healing. However, the underlying mechanisms are not clear. In the present study, we investigated the effect of LMHFV on the inflammatory response and the role of the p38 MAPK mechanical signaling pathway in macrophages during the healing process. A closed femoral fracture SD rat model was used. In vivo results showed that LMHFV enhanced activation of the p38 MAPK pathway at the fracture site. The acute inflammatory response, expression of inflammatory cytokines, and callus formation were suppressed in vivo by p38 MAPK inhibition. However, LMHFV did not show direct in vitro enhancement effects on the polarization of RAW264.7 macrophage from the M1 to M2 phenotype, but instead promoted macrophage enlargement and transformation to dendritic monocytes. The present study demonstrated that p38 MAPK modulated the enhancement effects of mechanical stimulation in vivo only. LMHFV may not have exerted its enhancement effects directly on macrophage, but the exact mechanism may have taken a different pathway that requires further investigation in the various subsets of immune cells.

CCN proteins in the musculoskeletal system: current understanding and challenges in physiology and pathology

The acronym for the CCN family was recently revised to represent “cellular communication network”. These six, small, cysteine-enriched and evolutionarily conserved proteins are secreted matricellular proteins, that convey and modulate intercellular communication by interacting with structural proteins, signalling factors and cell surface receptors. Their role in the development and physiology of musculoskeletal system, constituted by connective tissues where cells are interspersed in the cellular matrix, has been broadly studied. Previous research has highlighted a crucial balance of CCN proteins in mesenchymal stem cell commitment and a pivotal role for CCN1, CCN2 and their alter ego CCN3 in chondrogenesis and osteogenesis; CCN4 plays a minor role and the role of CCN5 and CCN6 is still unclear. CCN proteins also participate in osteoclastogenesis and myogenesis. In adult life, CCN proteins serve as mechanosensory proteins in the musculoskeletal system providing a steady response to environmental stimuli and participating in fracture healing. Substantial evidence also supports the involvement of CCN proteins in inflammatory pathologies, such as osteoarthritis and rheumatoid arthritis, as well as in cancers affecting the musculoskeletal system and bone metastasis. These matricellular proteins indeed show involvement in inflammation and cancer, thus representing intriguing therapeutic targets. This review discusses the current understanding of CCN proteins in the musculoskeletal system as well as the controversies and challenges associated with their multiple and complex roles, and it aims to link the dispersed knowledge in an effort to stimulate and guide readers to an area that the writers consider to have significant impact and relevant potentialities.

Omics Profiling of S2P Mutant Fibroblasts as a Mean to Unravel the Pathomechanism and Molecular Signatures of X-Linked MBTPS2 Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is an inherited skeletal dysplasia characterized by low bone density, bone fragility and recurrent fractures. The characterization of its heterogeneous genetic basis has allowed the identification of novel players in bone development. In 2016, we described the first X-linked recessive form of OI caused by hemizygous MBTPS2 missense variants resulting in moderate to severe phenotypes. MBTPS2 encodes site-2 protease (S2P), which activates transcription factors involved in bone (OASIS) and cartilage development (BBF2H7), ER stress response (ATF6) and lipid metabolism (SREBP) via regulated intramembrane proteolysis. In times of ER stress or sterol deficiency, the aforementioned transcription factors are sequentially cleaved by site-1 protease (S1P) and S2P. Their N-terminal fragments shuttle to the nucleus to activate gene transcription. Intriguingly, missense mutations at other positions of MBTPS2 cause the dermatological spectrum condition Ichthyosis Follicularis, Atrichia and Photophobia (IFAP) and Keratosis Follicularis Spinulosa Decalvans (KFSD) without clinical overlap with OI despite the proximity of some of the pathogenic variants. To understand how single amino acid substitutions in S2P can lead to non-overlapping phenotypes, we aimed to compare the molecular features of MBTPS2-OI and MBTPS2-IFAP/KFSD, with the ultimate goal to unravel the pathomechanisms underlying MBTPS2-OI. RNA-sequencing-based transcriptome profiling of primary skin fibroblasts from healthy controls (n = 4), MBTPS2-OI (n = 3), and MBTPS2-IFAP/KFSD (n = 2) patients was performed to identify genes that are differentially expressed in MBTPS2-OI and MBTPS2-IFAP/KFSD individuals compared to controls. We observed that SREBP-dependent genes are more downregulated in OI than in IFAP/KFSD. This is coupled to alterations in the relative abundance of fatty acids in MBTPS2-OI fibroblasts in vitro, while no consistent alterations in the sterol profile were observed. Few OASIS-dependent genes are suppressed in MBTPS2-OI, while BBF2H7- and ATF6-dependent genes are comparable between OI and IFAP/KFSD patients and control fibroblasts. Importantly, we identified genes involved in cartilage physiology that are differentially expressed in MBTPS2-OI but not in MBTPS2-IFAP/KFSD fibroblasts. In conclusion, our data provide clues to how pathogenic MBTPS2 mutations cause skeletal deformities via altered fatty acid metabolism or cartilage development that may affect bone development, mineralization and endochondral ossification.

The Emerging Roles of CCN3 Protein in Immune-Related Diseases

The CCN proteins are a family of extracellular matrix- (ECM-) associated proteins which currently consist of six secreted proteins (CCN1-6). CCN3 protein, also known as nephroblastoma overexpressed protein (NOV), is a member of the CCN family with multiple biological functions, implicated in major cellular processes such as cell growth, migration, and differentiation. Recently, CCN3 has emerged as a critical regulator in a variety of diseases, including immune-related diseases, including rheumatology arthritis, osteoarthritis, and systemic sclerosis. In this review, we will briefly introduce the structure and function of the CCN3 protein and summarize the roles of CCN3 in immune-related diseases, which is essential to understand the functions of the CCN3 in immune-related diseases.

Dynamic proteomic profiling of human periodontal ligament stem cells during osteogenic differentiation

Background

Human periodontal ligament stem cells (hPDLSCs) are ideal seed cells for periodontal regeneration. A greater understanding of the dynamic protein profiles during osteogenic differentiation contributed to the improvement of periodontal regeneration tissue engineering.

Methods

Tandem Mass Tag quantitative proteomics was utilized to reveal the temporal protein expression pattern during osteogenic differentiation of hPDLSCs on days 0, 3, 7 and 14. Differentially expressed proteins (DEPs) were clustered and functional annotated by Gene Ontology (GO) terms. Pathway enrichment analysis was performed based on the Kyoto Encyclopedia of Genes and Genomes database, followed by the predicted activation using Ingenuity Pathway Analysis software. Interaction networks of redox-sensitive signalling pathways and oxidative phosphorylation (OXPHOS) were conducted and the hub protein SOD2 was validated with western blotting.

Results

A total of 1024 DEPs were identified and clustered in 5 distinctive clusters representing dynamic tendencies. The GO enrichment results indicated that proteins with different tendencies show different functions. Pathway enrichment analysis found that OXPHOS was significantly involved, which further predicted continuous activation. Redox-sensitive signalling pathways with dynamic activation status showed associations with OXPHOS to various degrees, especially the sirtuin signalling pathway. SOD2, an important component of the sirtuin pathway, displays a persistent increase during osteogenesis. Data are available via ProteomeXchange with identifier PXD020908.

Conclusion

This is the first in-depth dynamic proteomic analysis of osteogenic differentiation of hPDLSCs. It demonstrated a dynamic regulatory mechanism of hPDLSC osteogenesis and might provide a new perspective for research on periodontal regeneration.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-020-02123-6.

Connective tissue growth factor promotes chemotaxis of preosteoblasts through integrin α5 and Ras during tensile force-induced intramembranous osteogenesis

In vertebrates, new bone formation via intramembranous osteogenesis is a critical biological event for development, remodeling, and fracture healing of bones. Chemotaxis of osteoblast lineage cells is an essential cellular process in new bone formation. Connective tissue growth factor (CTGF) is known to exert chemotactic properties on various cells; however, details of CTGF function in the chemotaxis of osteoblast lineage cells and underlying molecular biological mechanisms have not been clarified. The aim of the present study was to evaluate the chemotactic properties of CTGF and its underlying mechanisms during active bone formation through intramembranous osteogenesis. In our mouse tensile force-induced bone formation model, preosteoblasts were aggregated at the osteogenic front of calvarial bones. CTGF was expressed at the osteogenic front, and functional inhibition of CTGF using a neutralizing antibody suppressed the aggregation of preosteoblasts. In vitro experiments using μ-slide chemotaxis chambers showed that a gradient of CTGF induced chemotaxis of preosteoblastic MC3T3-E1 cells, while a neutralizing integrin α5 antibody and a Ras inhibitor inhibited the CTGF-induced chemotaxis of MC3T3-E1 cells. These findings suggest that the CTGF-integrin α5-Ras axis is an essential molecular mechanism to promote chemotaxis of preosteoblasts during new bone formation through intramembranous osteogenesis.

In Vitro Cytological Responses against Laser Photobiomodulation for Periodontal Regeneration

Periodontal disease is a chronic inflammatory disease caused by periodontal bacteria. Recently, periodontal phototherapy, treatment using various types of lasers, has attracted attention. Photobiomodulation, the biological effect of low-power laser irradiation, has been widely studied. Although many types of lasers are applied in periodontal phototherapy, molecular biological effects of laser irradiation on cells in periodontal tissues are unclear. Here, we have summarized the molecular biological effects of diode, Nd:YAG, Er:YAG, Er,Cr:YSGG, and CO₂ lasers irradiation on cells in periodontal tissues. Photobiomodulation by laser irradiation enhanced cell proliferation and calcification in osteoblasts with altering gene expression. Positive effects were observed in fibroblasts on the proliferation, migration, and secretion of chemokines/cytokines. Laser irradiation suppressed gene expression related to inflammation in osteoblasts, fibroblasts, human periodontal ligament cells (hPDLCs), and endothelial cells. Furthermore, recent studies have revealed that laser irradiation affects cell differentiation in hPDLCs and stem cells. Additionally, some studies have also investigated the effects of laser irradiation on endothelial cells, cementoblasts, epithelial cells, osteoclasts, and osteocytes. The appropriate irradiation power was different for each laser apparatus and targeted cells. Thus, through this review, we tried to shed light on basic research that would ultimately lead to clinical application of periodontal phototherapy in the future.

VNUT/SLC17A9, a vesicular nucleotide transporter, regulates osteoblast differentiation

Osteoblasts release adenosine triphosphate (ATP) out of the cell following mechanical stress. Although it is well established that extracellular ATP affects bone metabolism via P2 receptors [such as purinergic receptor P2X7 (P2X7R) and purinergic receptor P2Y2 (P2Y2R)], the mechanism of ATP release from osteoblasts remains unknown. Recently, a vesicular nucleotide transporter [VNUT, solute carrier family 17 member 9 (SLC17A9)] that preserves ATP in vesicles has been identified. The purpose of this study was to elucidate the role of VNUT in osteoblast bone metabolism. mRNA and protein expression of VNUT were confirmed in mouse bone and in osteoblasts by quantitative real-time PCR (qPCR) and immunohistochemistry. Next, when compressive force was applied to MC3T3-E1 cells by centrifugation, the expression of Slc17a9, P2x7r, and P2y2r was increased concomitant with an increase in extracellular ATP levels. Furthermore, compressive force decreased the osteoblast differentiation capacity of MC3T3-E1 cells. shRNA knockdown of Slc17a9 in MC3T3-E1 cells reduced levels of extracellular ATP and also led to increased osteoblast differentiation after the application of compressive force as assessed by qPCR analysis of osteoblast markers such as Runx2, Osterix, and alkaline phosphatase (ALP) as well as ALP activity. Consistent with these observations, knockdown of P2x7r or P2y2r by siRNA partially rescued the downregulation of osteoblast differentiation markers, caused by mechanical loading. In conclusion, our results demonstrate that VNUT is expressed in osteoblasts and that VNUT inhibits osteoblast differentiation in response to compressive force by mechanisms related to ATP release and P2X7R and/or P2Y2R activity.

Effects of Low-Level Er:YAG Laser Irradiation on Proliferation and Calcification of Primary Osteoblast-Like Cells Isolated From Rat Calvaria

Several reports have shown that the photo-bio-modulation of cells by various lasers has favorable biological effects. However, the effects of low-level Er:YAG laser irradiation on osteoblasts remain unclear. The purpose of this study was to evaluate the effects of low-level Er:YAG laser irradiation on proliferation and osteogenic differentiation of primary osteoblast-like cells isolated from the calvariae of 3-5-day-old Wistar rats. Cells were irradiated by Er:YAG laser at energy fluences of 2.2, 3.3, and 4.3 J/cm2, respectively. After irradiation, cell surface temperatures were measured and cell proliferation was evaluated by flow cytometry and CCK-8. Calcification was evaluated by measuring areas of Alizarin red S staining after 7, 14, and 21 days culture in osteoinductive medium. Gene expression in non-irradiated and laser-irradiated cells was evaluated by qPCR at 3, 6, and 12 h, as well as 1, 3, 7, and 14 days after irradiation. Microarray analysis was performed to comprehensively evaluate the gene expression of non-irradiated and irradiated cells at 3.3 J/cm2 at 6 h after irradiation. No pronounced increase of cell surface temperature was induced by irradiation. Irradiation did not affect osteoblast-like cell proliferation. Osteoblast-like cell calcification was significantly increased 7 days after Er:YAG laser irradiation at 3.3 J/cm2. Bglap expression was significantly increased in cells irradiated at 3.3 J/cm2 6 h post-irradiation. Microarray analysis showed that irradiation at 3.3 J/cm2 caused an upregulation of inflammation-related genes and downregulation of Wisp2. Gene set enrichment analysis also clarified enrichment of inflammation-related and Notch signaling gene sets. In conclusion, low-level Er:YAG laser irradiation at 3.3 J/cm2 enhanced calcification of primary osteoblast-like cells via enhanced Bglap expression and enriched Notch signaling.

The thrombospondin module 1 domain of the matricellular protein CCN3 shows an atypical disulfide pattern and incomplete CWR layers

The members of the CCN (Cyr61/CTGF/Nov) family are a group of matricellular regulatory proteins that are essential to a wide range of functional pathways in cell signalling. Through interacting with extracellular matrix components and growth factors via one of their four domains, the CCN proteins are involved in critical biological processes such as angiogenesis, cell proliferation, bone development, fibrogenesis and tumorigenesis. Here, the crystal structure of the thrombospondin module 1 (TSP1) domain of CCN3 (previously known as Nov) is presented, which shares a similar three-stranded fold with the thrombospondin type 1 repeats of thrombospondin-1 and spondin-1, but with variations in the disulfide connectivity. Moreover, the CCN3 TSP1 domain lacks the typical π-stacked ladder of charged and aromatic residues on one side of the domain that is seen in other TSP1 domains. Using conservation analysis among orthologous domains, it is shown that a charged cluster in the centre of the domain is the most conserved site and this cluster is predicted to be a potential functional epitope for heparan sulfate binding. This variant TSP1 domain has also been used to revise the sequence determinants of TSP1 domains and to derive improved Pfam sequence profiles for the identification of novel TSP1 domains in more than 10 000 proteins across diverse phyla.

YAP and TAZ Mediate Osteocyte Perilacunar/Canalicular Remodeling

Bone fragility fractures are caused by low bone mass or impaired bone quality. Osteoblast/osteoclast coordination determines bone mass, but the factors that control bone quality are poorly understood. Osteocytes regulate osteoblast and osteoclast activity on bone surfaces but can also directly reorganize the bone matrix to improve bone quality through perilacunar/canalicular remodeling; however, the molecular mechanisms remain unclear. We previously found that deleting the transcriptional regulators Yes-associated protein (YAP) and transcriptional co-activator with PDZ-motif (TAZ) from osteoblast-lineage cells caused lethality in mice due to skeletal fragility. Here, we tested the hypothesis that YAP and TAZ regulate osteocyte-mediated bone remodeling by conditional ablation of both YAP and TAZ from mouse osteocytes using 8 kb-DMP1-Cre. Osteocyte-conditional YAP/TAZ deletion reduced bone mass and dysregulated matrix collagen content and organization, which together decreased bone mechanical properties. Further, YAP/TAZ deletion impaired osteocyte perilacunar/canalicular remodeling by reducing canalicular network density, length, and branching, as well as perilacunar flourochrome-labeled mineral deposition. Consistent with recent studies identifying TGF-β as a key inducer of osteocyte expression of matrix-remodeling enzymes, YAP/TAZ deletion in vivo decreased osteocyte expression of matrix proteases MMP13, MMP14, and CTSK. In vitro, pharmacologic inhibition of YAP/TAZ transcriptional activity in osteocyte-like cells abrogated TGF-β-induced matrix protease gene expression. Together, these data show that YAP and TAZ control bone matrix accrual, organization, and mechanical properties by regulating osteocyte-mediated bone remodeling. Elucidating the signaling pathways that control perilacunar/canalicular remodeling may enable future therapeutic targeting of bone quality to reverse skeletal fragility. © 2019 American Society for Bone and Mineral Research.

CCN1 stimulated the osteoblasts via PTEN/AKT/GSK3β/cyclinD1 signal pathway in Myeloma Bone Disease

BACKGROUNDS

Myeloma-related bone disease (MBD) is a common complication of multiple myeloma (MM), which can both decrease life quality and influence the prognosis of the patients. We have found that CCN1 stimulated proliferation and differentiation of osteoblasts in MM in vitro and in vivo, while its mechanism still remains unknown.

METHOD

Bone marrow mononuclear cells were collected from MM patients and differentiated into the osteoblasts. After co-culture with CCN1 in vitro, the intracellular signaling antibody array and western blot were performed to explore the signaling pathway. Furthermore, GSK3β inhibitor TWS119 was used to check the pathway of CCN1 might have on osteoblasts in vitro.

RESULTS

For the protein array kit, the expressions of GSK3β, 4E-BP1, and PTEN are decreased in CCN1 group. For western blots, the CCN1 group also has lower expression comparing to the control group in PTEN (P = .031). Meanwhile p-AKT and cyclinD1 levels have increased in the CCN1 group (P = .002, P = .039). After adding TWS119 as another group, western blot was performed again to verify the pathway. For upstream proteins PTEN and p-AKT, TWS119 group has higher expression level compared to that in CCN1 group (P = .003, P = .001). And for downstream protein cyclinD1, TWS119 group also presented higher level than the control group (P = .02). CCN1 could have almost the same effect on GSK3β as the specific inhibitor TWS119 had.

CONCLUSIONS

CCN1 can stimulate osteoblasts through PTEN/AKT/GSK3β/cyclinD1 pathway in MBD, which has the potential to be a novel therapy of MBD.

Roles of matricellular CCN2 deposited by osteocytes in osteoclastogenesis and osteoblast differentiation

In this study, we investigated the effect of CCN2 (cellular communication network factor 2), previously termed connective tissue growth factor, deposited in bone matrix on osteoclastogenesis and osteoblast differentiation. To mimic the bone matrix environment, osteocytic MLO-Y4 cells had been embedded in collagen-gel with recombinant CCN2 (rCCN2), and mouse macrophage-like RAW264.7 cells were inoculated on the gel and treated with receptor activator of NF-κB ligand (RANKL). NFATc1 and cathepsin K (CTSK) productions were more increased in the combination of RAW264.7 and MLO-Y4 cells treated with rCCN2 than the combination without rCCN2. Next, we isolated an osteocyte-enriched population of cells and osteoclast progenitor cells from wild type and tamoxifen-inducible Ccn2-deficient (KO) mice and performed similar analysis. NFATc1 and CTSK productions were decreased in the KO osteocyte-enriched population at 6 months after the tamoxifen injection, regardless of the origin of the osteoclast progenitor cells. Interestingly, CTSK production was rather increased in KO osteocytes at 1 year after the injection. Finally, the combination of osteoblastic MC3T3-E1 and MLO-Y4 cells in rCCN2-containing bone matrix revealed the up-regulation of osteoblastic marker genes. These findings suggest that CCN2 supplied by osteocytes regulates both osteoclastogenesis and osteoblast differentiation.

The official unified nomenclature adopted by the HGNC calls for the use of the acronyms, CCN1-6, and discontinuation in the use of CYR61, CTGF, NOV and WISP 1-3 respectively

An examination of the confusion generated around the use of different acronyms for CCN proteins has been performed by the editors of the HUGO Gene Nomenclature Committee upon the request of the International CCN Society Scientific Committee. After careful consideration of the various arguments, and after polling the community of researchers who have published in the field over the past ten years, the HGNC have decided to adopt and approve the CCN nomenclature for all 6 genes. Effective October 2018, the genes referred to as CYR61, CTGF, NOV and WISP1-3 will be respectively designated by the gene symbols CCN1-6 with corresponding gene names « cellular communication Q2 network factor 1-6 ». We believe that this decision will be a step towards better communication between researchers working in the field, and will set the stage for fruitful collaborative projects. Accordingly, the Journal of Cell Communication and Signaling, the official journal of the International CCN Society, available both in print and online, constitutes a unique window into the CCN field. This official nomenclature will benefit the international scientific community that is supported by the established and renowned professionalism of the Springer-Nature publishing group.

CYR61/CCN1 Regulates Sclerostin Levels and Bone Maintenance

CYR61/CCN1 is a matricellular protein that resides in the extracellular matrix, but serves regulatory rather than structural roles. CYR61/CCN1 is found in mineralized tissues and has been shown to influence bone healing in vivo and osteogenic differentiation in vitro. In this study we generated Cyr61 bone-specific knockout mice to examine the physiological role of CYR61/CCN1 in bone development and maintenance in vivo. Extensive analysis of Cyr61 conditional knockout mice showed a significant decrease in both trabecular and cortical bone mass as compared to WT littermates. Our data suggest that CYR61/CCN1 exerts its effects on mature osteoblast/osteocyte function to modulate bone mass. Specifically, changes were observed in osteocyte/osteoblast expression of RankL, VegfA, and Sost. The increase in RankL expression was correlated with a significant increase in osteoclast number; decreased VegfA expression was correlated with a significant decrease in bone vasculature; increased Sost expression was associated with decreased Wnt signaling, as revealed by decreased Axin2 expression and increased adiposity in the bone marrow. Although the decreased number of vascular elements in bone likely contributes to the low bone mass phenotype in Cyr61 conditional knockout mice, this cannot explain the observed increase in osteoclasts and the decrease in Wnt signaling. We conducted in vitro assays using UMR-106 osteosarcoma cells to explore the role CYR61/CCN1 plays in modulating Sost mRNA and protein expression in osteocytes and osteoblasts. Overexpression of CYR61/CCN1 can suppress Sost expression in both control and Cyr61 knockout cells, and blocking Sost with siRNA can rescue Wnt responsiveness in Cyr61 knockout cells in vitro. Overall, our data suggest that CYR61/CCN1 modulates mature osteoblast and osteocyte function to regulate bone mass through angiogenic effects as well as by modulating Wnt signaling, at least in part through the Wnt antagonist Sost. © 2018 American Society for Bone and Mineral Research.

Wedelolactone Enhances Osteoblastogenesis through ERK- and JNK-mediated BMP2 Expression and Smad/1/5/8 Phosphorylation

Our previous study showed that wedelolactone, a compound isolated from Ecliptae herba, has the potential to enhance osteoblastogenesis. However, the molecular mechanisms by which wedelolactone promoted osteoblastogenesis from bone marrow mesenchymal stem cells (BMSCs) remain largely unknown. In this study, treatment with wedelolactone (2 μg/mL) for 3, 6, and 9 days resulted in an increase in phosphorylation of extracellular signal-regulated kinases (ERKs), c-Jun N-terminal protein kinase (JNK), and p38. Phosphorylation of mitogen-activated protein kinases (MAPKs), ERK and JNK started to increase on day 3 of treatment, and p38 phosphorylation was increased by day 6 of treatment. Expression of bone morphogenetic protein (BMP2) mRNA and phosphorylation of Smad1/5/8 was enhanced after treatment of cells with wedelolactone for 6 and 9 days. The addition of the JNK inhibitor SP600125, ERK inhibitor PD98059, and p38 inhibitor SB203580 suppressed wedelolactone-induced alkaline-phosphatase activity, bone mineralization, and osteoblastogenesis-related marker genes including Runx2, Bglap, and Sp7. Increased expression of BMP2 mRNA and Smad1/5/8 phosphorylation was blocked by SP600125 and PD98059, but not by SB203580. These results suggested that wedelolactone enhanced osteoblastogenesis through induction of JNK- and ERK-mediated BMP2 expression and Smad1/5/8 phosphorylation.

Characterization of bone morphology in CCN5/WISP5 knockout mice

CCN5/WISP2 is part of the CCN family of matricellular proteins, but is distinct in that it lacks the C-terminal (CT) domain. Although CCN5 has been shown to impact cell proliferation and differentiation in vitro, its role in vivo is unclear. We therefore generated mice using ES cells developed by the Knockout Mouse Project (KOMP) in which exons 2-5, which encode the all of the conserved protein coding regions, are replaced by a lacZ cassette. Ccn5 ^LacZ/LacZ mice were viable and apparently normal. Based on previous studies showing that CCN5 impacts osteoblast proliferation and differentiation, we performed an analysis of adult bone phenotype. LacZ expression was examined in adult bone, and was found to be strong within the periosteum, but not in trabecular bone or bone marrow. Micro-CT analysis revealed no apparent changes in bone mineral density (BMD) or bone tissue volume (BV/TV) in Ccn5 ^LacZ/LacZ mice. These studies indicate that CCN5 is not required for normal bone formation, but they do not rule out a role in mechanotransduction or repair processes. The availability of Ccn5 ^LacZ mice enables studies of CCN5 expression and function in multiple tissues.

Western Blotting Analysis of CCN Proteins in Calcified Tissues

Western blotting is widely used for protein analysis. We routinely perform such analysis for evaluating the production levels of CCN family proteins in a variety of cells under various conditions. In this chapter, we describe our Western blotting protocol to estimate protein production profiles of CCN family members after having assessed the specificity of the antibodies against each CCN member protein to ensure no cross-reaction with other CCN member proteins.

WISP1/CCN4 aggravates cartilage degeneration in experimental osteoarthritis

OBJECTIVE

Increased Wisp1 expression was previously reported in experimental and human osteoarthritis (OA). Moreover, adenoviral overexpression of Wisp1 in naïve mouse knee joints resulted in early OA-like cartilage lesions. Here, we determined how the matricellular protein WISP1 is involved in the pathology that occurs in the complex osteoarthritic environment with aging and experimental OA in wild type (WT) and Wisp1^-/- mice.

METHODS

WT and Wisp1^-/- mice were aged or experimental OA was induced with intraarticular collagenase injection, destabilization of the medial meniscus (DMM) or anterior cruciate ligament transection (ACLT). Joint pathology was assessed using histology and microCT. Protease expression was evaluated with qRT-PCR and activity was determined by immunohistochemical staining of the aggrecan neoepitope NITEGE. Protease expression in human end-stage OA synovial tissue was determined with qRT-PCR after stimulation with WISP1.

RESULTS

With aging, spontaneous cartilage degeneration in Wisp1^-/- was not decreased compared to their WT controls. However, we observed significantly decreased cartilage degeneration in Wisp1^-/- mice after induction of three independent experimental OA models. While the degree of osteophyte formation was comparable between WT and Wisp1^-/- mice, increased cortical thickness and reduced trabecular spacing was observed in Wisp1^-/- mice. In addition, we observed decreased MMP3/9 and ADAMTS4/5 expression in Wisp1^-/- mice, which was accompanied by decreased levels of NITEGE. In line with this, stimulation of human OA synovium with WISP1 increased the expression of various proteases.

CONCLUSIONS

WISP1 plays an aggravating role in the development of post-traumatic experimental OA.

Structural analyses of von Willebrand factor C domains of collagen 2A and CCN3 reveal an alternative mode of binding to bone morphogenetic protein-2

Bone morphogenetic proteins (BMPs) are secreted growth factors that promote differentiation processes in embryogenesis and tissue development. Regulation of BMP signaling involves binding to a variety of extracellular proteins, among which are many von Willebrand factor C (vWC) domain-containing proteins. Although the crystal structure of the complex of crossveinless-2 (CV-2) vWC1 and BMP-2 previously revealed one mode of the vWC/BMP-binding mechanism, other vWC domains may bind to BMP differently. Here, using X-ray crystallography, we present for the first time structures of the vWC domains of two proteins thought to interact with BMP-2: collagen IIA and matricellular protein CCN3. We found that these two vWC domains share a similar N-terminal fold that differs greatly from that in CV-2 vWC, which comprises its BMP-2-binding site. We analyzed the ability of these vWC domains to directly bind to BMP-2 and detected an interaction only between the collagen IIa vWC and BMP-2. Guided by the collagen IIa vWC domain crystal structure and conservation of surface residues among orthologous domains, we mapped the BMP-binding epitope on the subdomain 1 of the vWC domain. This binding site is different from that previously observed in the complex between CV-2 vWC and BMP-2, revealing an alternative mode of interaction between vWC domains and BMPs.

Transforming growth factor β1 regulates the expression of CCN2 in human keratinocytes via Smad-ERK signalling

Connective tissue growth factor (CCN2/CTGF) and transforming growth factor β1 (TGF-β1) are important regulators of skin wound healing, but controversy remains regarding their expression in epithelial cell lineages. Here, we investigate the expression of CCN2 in keratinocytes during reepithelialisation and its regulation by TGF-β1. CCN2 was detected in the epidermis of healing full-thickness porcine wounds. Human keratinocytes were incubated with or without 10 ng/ml TGF-β1, and signalling pathways were blocked with 10-μM SIS3 or 20-μM PD98059. Semi-quantitative real-time PCR was used to study CCN2 mRNA expression, and western blot was used to measure CCN2, phosphorylated-ERK1/2, ERK1/2, phosphorylated-Smad3 and Smad2/3 proteins. CCN2 was transiently expressed in neoepidermis at the leading edge of the wound in vivo. In vitro, CCN2 expression was induced by TGF-β1 at 2 hours (7·5 ± 1·9-fold mRNA increase and 3·0 ± 0·6-fold protein increase) and 12 hours (5·4 ± 1·9-fold mRNA increase and 3·3 ± 0·6-fold protein increase). Compared with inhibiting the SMAD pathway, inhibiting the mitogen-activated protein kinase (MAPK) pathway was more effective in reducing TGF-β1-induced CCN2 mRNA and protein expression. Inhibition of the MAPK pathway had minimal impact on the activity of the SMAD pathway. CCN2 is expressed in keratinocytes in response to tissue injury or TGF-β1. In addition, TGF-β1 induces CCN2 expression in keratinocytes through the ras/MEK/ERK pathway. A complete understanding of CCN2 expression in keratinocytes is critical to developing novel therapies for wound healing and cutaneous malignancy.

Tensile stress stimulates the expression of osteogenic cytokines/growth factors and matricellular proteins in the mouse cranial suture at the site of osteoblast differentiation

Mechanical stress promotes osteoblast proliferation and differentiation from mesenchymal stem cells (MSCs). Although numerous growth factors and cytokines are known to regulate this process, information regarding the differentiation of mechanically stimulated osteoblasts from MSCs in in vivo microenvironment is limited. To determine the significant factors involved in this process, we performed a global analysis of differentially expressed genes, in response to tensile stress, in the mouse cranial suture wherein osteoblasts differentiate from MSCs. We found that the gene expression levels of several components involved in bone morphogenetic protein, Wnt, and epithelial growth factor signalings were elevated with tensile stress. Moreover gene expression of some extracellular matrices (ECMs), such as cysteine rich protein 61 (Cyr61)/CCN1 and galectin-9, were upregulated. These ECMs have the ability to modulate the activities of cytokines and are known as matricellular proteins. Cyr61/CCN1 expression was prominently increased in the fibroblastic cells and preosteoblasts in the suture. Thus, for the first time we demonstrated the mechanical stimulation of Cyr61/CCN1 expression in osteogenic cells in an ex vivo system. These results suggest the importance of matricellular proteins along with the cytokine-mediated signaling for the mechanical regulation of MSC proliferation and differentiation into osteoblastic cell lineage in vivo.

Gene Expression Analysis of CCN Protein in Bone Under Mechanical Stress

To investigate mechanical-dependent bone remodeling, we had previously applied various types of mechanical loading onto the teeth of rats and mice. In vitro cultured bone cells were then used to elucidate the mechanisms underlying the specific phenomenon revealed by in vivo experiments. This review describes the techniques used to upregulate CCN2 expression in bone cells produced by different types of mechanical stress, such as fluid shear stress and substrate strain in vitro, and compression or tension force in vivo.

Immunohistochemical Analysis of CCN Proteins in Calcified Tissues

Immunohistochemistry is a major technique to determine the distribution and localization of differentially produced proteins in the context of an intact tissue. It exploits one of the properties of antibodies, specific binding to an antigen, i.e., to the epitope of its target protein, in combination with a color-developing enzymatic reaction or tagged fluorophore. We have clarified the spatial and temporal expression patterns of CCN family proteins in several different types of animal tissues by using this immunohistochemical technique to support our corresponding data obtained in vitro. In this chapter, we provide our protocol for immunohistochemistry optimized for paraffin-embedded sections after having determined the optimal conditions for the use of antibodies against each member of the CCN family.

Role of Osteogenic Growth Peptide (OGP) and OGP(10-14) in Bone Regeneration: A Review

Bone regeneration is a process that involves several molecular mediators, such as growth factors, which directly affect the proliferation, migration and differentiation of bone-related cells. The osteogenic growth peptide (OGP) and its C-terminal pentapeptide OGP(10–14) have been shown to stimulate the proliferation, differentiation, alkaline phosphatase activity and matrix mineralization of osteoblastic lineage cells. However, the exact molecular mechanisms that promote osteoblastic proliferation and differentiation are not completely understood. This review presents the main chemical characteristics of OGP and/or OGP(10–14), and also discusses the potential molecular pathways induced by these growth factors to promote proliferation and differentiation of osteoblasts. Furthermore, since these peptides have been extensively investigated for bone tissue engineering, the clinical applications of these peptides for bone regeneration are discussed.

Analysis of Expression of CCN Family Genes in Skeletal Tissue-Derived Cells

The quantitative reverse transcription polymerase chain reaction or real-time PCR has become a routine technique for the detection and comparison of amounts of specific mRNA transcripts, done by measuring amplified levels of specific cDNAs. In this chapter, we provide our real-time RT-PCR experimental procedure using SYBR Green I for the quantitative analysis of CCN family gene expression. Especially, we describe the extraction and purification steps for RNA derived from mesenchymal cells, such as chondrocytes and osteoblasts that produce a large amount of extracellular matrix in detail.

Analysis of Signaling Pathways Activated by CCN Proteins

CCN family proteins activate multiple intracellular phosphorylated kinase cascades to yield the multiple physiological functions of a variety of target cells. In this chapter, we describe our protocol examining the effects of these proteins on signal transduction pathways, especially mitogen-activated protein kinase cascades, activated by CCN member proteins, which examinations have been carried out mainly by using Western blotting methodologies.

The role of the CCN family of proteins in blood cancers

Haematopoiesis is the term used to describe the production of blood cells. This is a tightly regulated hierarchical system in which mature circulating blood cells develop from a small population of haematopoietic stem (HSC) and progenitor cells within the microenvironment of the bone marrow. Molecular and genetic abnormalities arising in these stem cells lead to a block in the normal programme of proliferation and differentiation and result in the development of the blood cancers known as the leukaemias and lymphomas. Recently the regulatory role of the bone marrow microenvironment or niche has also become increasingly recognised. The interface between the bone and bone marrow (endosteum) and the region surrounding the blood vessels (perivascular) provide distinct niches harbouring quiescent HSC or proliferative HSC respectively. Current chemotherapeutic regimes can often successfully target the proliferative HSC but disease relapse occurs due to residual quiescent HSC. Understanding these developmental and regulatory processes and the associated cell communication mechanisms are thus crucial to the development of new treatment strategies. The CCN family of proteins have been recognised to play a key role in all aspects of haematopoiesis.

p38 MAPK Signaling in Osteoblast Differentiation

The skeleton is a highly dynamic tissue whose structure relies on the balance between bone deposition and resorption. This equilibrium, which depends on osteoblast and osteoclast functions, is controlled by multiple factors that can be modulated post-translationally. Some of the modulators are Mitogen-activated kinases (MAPKs), whose role has been studied in vivo and in vitro. p38-MAPK modifies the transactivation ability of some key transcription factors in chondrocytes, osteoblasts and osteoclasts, which affects their differentiation and function. Several commercially available inhibitors have helped to determine p38 action on these processes. Although it is frequently mentioned in the literature, this chemical approach is not always as accurate as it should be. Conditional knockouts are a useful genetic tool that could unravel the role of p38 in shaping the skeleton. In this review, we will summarize the state of the art on p38 activity during osteoblast differentiation and function, and emphasize the triggers of this MAPK.

Involvement of multiple CCN family members in platelets that support regeneration of joint tissues

OBJECTIVES

Platelet-rich plasma (PRP) has been widely used to enhance the regeneration of damaged joint tissues, such as osteoarthritic and rheumatoid arthritic cartilage. The aim of this study is to clarify the involvement of all of the CCN family proteins that are crucially associated with joint tissue regeneration.

METHODS

Cyr61-CTGF-NOV (CCN) family proteins in human platelets and megakaryocytic cells were comprehensively analyzed by Western blotting analysis. Production of CCN family proteins in megakaryocytes in vivo was confirmed by immunofluorescence analysis of mouse bone marrow cells. Effects of CCN family proteins found in platelets on chondrocytes were evaluated by using human chondrocytic HCS-2/8 cells.

RESULTS

Inclusion of CCN2, a mesenchymal tissue regenerator, was confirmed. Of note, CCN3, which counteracts CCN2, was newly found to be encapsulated in platelets. Interestingly, these two family members were not detectable in megakaryocytic cells, but their external origins were suggested. Furthermore, we found for the first time CCN5 and CCN1 that inhibits ADAMTS4 in both platelets and megakaryocytes. Finally, application of a CCN family cocktail mimicking platelets onto HCS-2/8 cells enhanced their chondrocytic phenotype.

CONCLUSIONS

Multiple inclusion of CCN1, 2 and 3 in platelets was clarified, which supports the harmonized regenerative potential of PRP in joint therapeutics.

Osteoblast-derived WNT-induced secreted protein 1 increases VCAM-1 expression and enhances prostate cancer metastasis by down-regulating miR-126

Bone metastases of prostate cancer (PCa) may cause intractable pain. Wnt-induced secreted protein-1 (WISP-1) belongs to the CCN family (CTGF/CYR61/NOV) that plays a key role in bone formation. We found that osteoblast-conditioned medium (OBCM) stimulates migration and vascular cell adhesion molecule-1 (VCAM-1) expression in human PCa (PC3 and DU145) cells. Osteoblast transfection with WISP-1 shRNA reduced OBCM-mediated PCa migration and VCAM-1 expression. Stimulation of PCa with OBCM or WISP-1 elevated focal adhesion kinase (FAK) and p38 phosphorylation. Either FAK and p38 inhibitors or siRNA abolished osteoblast-derived WISP-1-induced migration and VCAM-1 expression. Osteoblast-derived WISP-1 inhibited miR-126 expression. Moreover, miR-216 mimic reversed the WISP-1-enhanced migration and VCAM-1 expression. This study suggests that osteoblast-derived WISP-1 promotes migration and VCAM-1 expression in human PCa cells by down-regulating miR-126 expression via αvβ1 integrin, FAK, and p38 signaling pathways. Thus, WISP-1 may be a new molecular therapeutic target in PCa bone metastasis.

WNT1-induced Secreted Protein-1 (WISP1), a Novel Regulator of Bone Turnover and Wnt Signaling

WISP1/CCN4 (hereafter referred to as WISP1), a member of the CCN family, is found in mineralized tissues and is produced by osteoblasts and their precursors. In this study, Wisp1-deficient (Wisp1(-/-)) mice were generated. Using dual-energy x-ray absorptiometry, we showed that by 3 months, the total bone mineral density of Wisp1(-/-) mice was significantly lower than that of WT mice. Further investigation by micro-computed tomography showed that female Wisp1(-/-) mice had decreased trabecular bone volume/total volume and that both male and female Wisp1(-/-) mice had decreased cortical bone thickness accompanied by diminished biomechanical strength. The molecular basis for decreased bone mass in Wisp1(-/-) mice arises from reduced bone formation likely caused by osteogenic progenitors that differentiate poorly compared with WT cells. Osteoclast precursors from Wisp1(-/-) mice developed more tartrate-resistant acid phosphatase-positive cells in vitro and in transplants, suggesting that WISP1 is also a negative regulator of osteoclast differentiation. When bone turnover (formation and resorption) was induced by ovariectomy, Wisp1(-/-) mice had lower bone mineral density compared WT mice, confirming the potential for multiple roles for WISP1 in controlling bone homeostasis. Wisp1(-/-) bone marrow stromal cells had reduced expression of β-catenin and its target genes, potentially caused by WISP1 inhibition of SOST binding to LRP6. Taken together, our data suggest that the decreased bone mass found in Wisp1(-/-) mice could potentially be caused by an insufficiency in the osteodifferentiation capacity of bone marrow stromal cells arising from diminished Wnt signaling, ultimately leading to altered bone turnover and weaker biomechanically compromised bones.

Gene expression differences between ruptured anterior cruciate ligaments in young male and female subjects

BACKGROUND

The incidence of anterior cruciate ligament (ACL) injuries is two to eightfold greater in female compared with male athletes. Anatomic, hormonal, and neuromuscular factors have been associated with this disparity. This study compared gene expression and structural features in ruptured but otherwise normal ACL tissue from young female and male athletes.

METHODS

A biopsy sample of ruptured ACL tissue (which would normally have been discarded) was obtained intraoperatively from seven female and seven male athletes (12.7 to 22.6 years old). Each sample was divided into portions for histological and gene expression analyses. Specimens for gene analysis were frozen and ground, and RNA was extracted and purified. Microarray analysis was performed on RNA isolated from four female and three male study participants (13.9 to 18.5 years old) who had a noncontact injury. Genes with an expression level that differed significantly between these female and male athletes were grouped into functionally associated networks with use of IPA software (Qiagen). Three genes of interest were chosen for further validation by RT-qPCR (reverse transcription-quantitative polymerase chain reaction) analysis of the samples from all fourteen patients. Several statistical methods were used to examine sex-related differences.

RESULTS

Microarray analysis of the RNA isolated from the ruptured ACL tissue from the female and male athletes identified thirty-two genes with significant differential expression. Fourteen of these genes were not linked to the X or Y chromosome. IPA analysis grouped these genes into pathways involving development and function of skeletal muscle and growth, maintenance, and proliferation of cells. RT-qPCR confirmed significant differences in expression of three selected genes: ACAN (aggrecan) and FMOD (fibromodulin) were upregulated in female compared with male study participants, and WISP2 (WNT1 inducible signaling pathway protein 2) was downregulated. No morphological differences among the ruptured tissue from the various participants were apparent on histological examination.

CONCLUSIONS

The genes identified in this study as differing distinctly according to sex produce major molecules in the ACL extracellular matrix. Significant upregulation of ACAN and FMOD (which regulate the matrix) and downregulation of WISP2 (which is involved in collagen turnover and production) may account for the weaker ACLs in female compared with male individuals.

Cellular and molecular actions of CCN2/CTGF and its role under physiological and pathological conditions

CCN family protein 2 (CCN2), also widely known as connective tissue growth factor (CTGF), is one of the founding members of the CCN family of matricellular proteins. Extensive investigation on CCN2 over decades has revealed the novel molecular action and functional properties of this unique signalling modulator. By its interaction with multiple molecular counterparts, CCN2 yields highly diverse and context-dependent biological outcomes in a variety of microenvironments. Nowadays, CCN2 is recognized to conduct the harmonized development of relevant tissues, such as cartilage and bone, in the skeletal system, by manipulating extracellular signalling molecules involved therein by acting as a hub through a web. However, on the other hand, CCN2 occasionally plays profound roles in major human biological disorders, including fibrosis and malignancies in major organs and tissues, by modulating the actions of key molecules involved in these clinical entities. In this review, the physiological and pathological roles of this unique protein are comprehensively summarized from a molecular network-based viewpoint of CCN2 functionalities.

Connective tissue growth factor (CTGF/CCN2) negatively regulates BMP-2 induced osteoblast differentiation and signaling

Connective tissue growth factor (CTGF/CCN2) and bone morphogenetic protein (BMP)-2 are both produced and secreted by osteoblasts. Both proteins have been shown to have independent effects in regulating osteoblast proliferation, maturation and mineralization. However, how these two proteins interact during osteoblast differentiation remains unknown. In this study, we utilized two cell culture model systems, osteoblasts derived from CTGF knockout (KO) mice and osteoblasts infected with an adenovirus which over-expresses CTGF (Ad-CTGF), to investigate the effects of CTGF and BMP-2 on osteoblast development and function in vitro. Contrary to a previously published report, osteoblast maturation and mineralization were similar in osteogenic cultures derived from KO and WT calvaria in the absence of BMP-2 stimulation. Interestingly, in KO and WT osteoblast cultures stimulated with BMP-2, the KO osteoblasts exhibited enhanced osteoblast differentiation. This increase in osteoblast differentiation was accompanied by increased protein levels of phosphorylated Smad 1/5/8 and mRNA expression levels of bone morphogenetic protein receptor Ib. We also examined osteoblast differentiation in cultures that were infected with an adenoviral-CTGF vector (Ad-CTGF) and in controls. Continuous over-expression of CTGF resulted in decreased osteoblast maturation and mineralization in both unstimulated and BMP-2 stimulated cultures. Impaired osteoblast differentiation in cultures over-expressing CTGF was accompanied by decreased protein levels of phosphorylated Smad 1/5/8. Collectively, the data from these studies demonstrate that CTGF acts to negatively regulate BMP-2 induced signaling and osteoblast differentiation, and warrant additional studies to determine the precise mechanism(s) responsible for this effect. J. Cell. Physiol. 229: 672-681, 2014. © 2013 Wiley Periodicals, Inc.

Compressive force-produced CCN2 induces osteocyte apoptosis through ERK1/2 pathway

Osteocytes produce various factors that mediate the onset of bone formation and resorption and play roles in maintaining bone homeostasis and remodeling in response to mechanical stimuli. One such factor, CCN2, is thought to play a significant role in osteocyte responses to mechanical stimuli, but its function in osteocytes is not well understood. Here, we showed that CCN2 induces apoptosis in osteocytes under compressive force loading. Compressive force increased CCN2 gene expression and production, and induced apoptosis in osteocytes. Application of exogenous CCN2 protein induced apoptosis, and a neutralizing CCN2 antibody blocked loading-induced apoptosis. We further examined how CCN2 induces loaded osteocyte apoptosis. In loaded osteocytes, extracellular signal-regulated kinase 1/2 (ERK1/2) was activated, and an ERK1/2 inhibitor blocked loading-induced apoptosis. Furthermore, application of exogenous CCN2 protein caused ERK1/2 activation, and the neutralizing CCN2 antibody inhibited loading-induced ERK1/2 activation. Therefore, this study demonstrated for the first time to our knowledge that enhanced production of CCN2 in osteocytes under compressive force loading induces apoptosis through activation of ERK1/2 pathway.