Differential expression of CCN-family members in primary human bone marrow-derived mesenchymal stem cells during osteogenic, chondrogenic and adipogenic differentiation

Rescue of murine hind limb ischemia via angiogenesis and lymphangiogenesis promoted by cellular communication network factor 2

Critical limb ischemia (CLI) is caused by severe arterial blockage with reduction of blood flow. The aim of this study was to determine whether therapeutic angiogenesis using cellular communication network factor 2 (CCN2) would be useful for treating CLI in an animal model. Recombinant CCN2 was administered intramuscularly to male C57BL/6J mice with hind limb ischemia. The therapeutic effect was evaluated by monitoring blood flow in the ischemic hind limb. In an in vivo assay, CCN2 restored blood flow in the ischemic hind limb by promoting both angiogenesis and lymphangiogenesis. VEGF-A and VEGF-C expression levels increased in the ischemic limb after treatment with CCN2. In an in vitro assay, CCN2 promoted proliferation of vascular and lymphatic endothelial cells, and it upregulated expression of Tgfb1 followed by expression of Vegfc and Vegfr3 in lymphatic endothelial cells under hypoxia. Suppression of Tgfb1 did not affect the activity of CCN2, activation of the TGF-β/SMAD signaling pathway, or expression of Vegfr3 in lymphatic endothelial cells. In summary, treatment using recombinant CCN2 could be a promising therapeutic strategy for CLI.

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.

Targeting the fatty acid binding proteins disrupts multiple myeloma cell cycle progression and MYC signaling

Multiple myeloma is an incurable plasma cell malignancy with only a 53% 5-year survival rate. There is a critical need to find new multiple myeloma vulnerabilities and therapeutic avenues. Herein, we identified and explored a novel multiple myeloma target: the fatty acid binding protein (FABP) family. In our work, myeloma cells were treated with FABP inhibitors (BMS3094013 and SBFI-26) and examined in vivo and in vitro for cell cycle state, proliferation, apoptosis, mitochondrial membrane potential, cellular metabolism (oxygen consumption rates and fatty acid oxidation), and DNA methylation properties. Myeloma cell responses to BMS309403, SBFI-26, or both, were also assessed with RNA sequencing (RNA-Seq) and proteomic analysis, and confirmed with western blotting and qRT-PCR. Myeloma cell dependency on FABPs was assessed using the Cancer Dependency Map (DepMap). Finally, MM patient datasets (CoMMpass and GEO) were mined for FABP expression correlations with clinical outcomes. We found that myeloma cells treated with FABPi or with FABP5 knockout (generated via CRISPR/Cas9 editing) exhibited diminished proliferation, increased apoptosis, and metabolic changes in vitro. FABPi had mixed results in vivo, in two pre-clinical MM mouse models, suggesting optimization of in vivo delivery, dosing, or type of FABP inhibitors will be needed before clinical applicability. FABPi negatively impacted mitochondrial respiration and reduced expression of MYC and other key signaling pathways in MM cells in vitro. Clinical data demonstrated worse overall and progression-free survival in patients with high FABP5 expression in tumor cells. Overall, this study establishes the FABP family as a potentially new target in multiple myeloma. In MM cells, FABPs have a multitude of actions and cellular roles that result in the support of myeloma progression. Further research into the FABP family in MM is warrented, especially into the effective translation of targeting these in vivo.

CCN6 influences transcription and controls mitochondrial mass and muscle organization

Mutations in Cellular Communication Network Factor 6 (CCN6) are linked to the debilitating musculoskeletal disease Progressive Pseudo Rheumatoid Dysplasia (PPRD), which disrupts mobility. Yet, much remains unknown about CCN6 function at the molecular level. In this study, we revealed a new function of CCN6 in transcriptional regulation. We demonstrated that CCN6 localizes to chromatin and associates with RNA Polymerase II in human chondrocyte lines. Using zebrafish as a model organism we validated the nuclear presence of CCN6 and its association with RNA Polymerase II in different developmental stages from 10 hpf embryo to adult fish muscle. In concurrence with these findings, we confirmed the requirement of CCN6 in the transcription of several genes encoding mitochondrial electron transport complex proteins in the zebrafish, both in the embryonic stages and in the adult muscle. Reduction in the expression of these genes upon morpholino-mediated knockdown of CCN6 protein expression led to reduced mitochondrial mass, which correlated with defective myotome organization during zebrafish muscle development. Overall, this study suggests that the developmental musculoskeletal abnormalities linked with PPRD could be contributed at least partly by impaired expression of genes encoding mitochondrial electron transport complexes due to defects in CCN6 associated transcriptional regulation.

Matricellular proteins in cutaneous wound healing

Cutaneous wound healing is a complex process that encompasses alterations in all aspects of the skin including the extracellular matrix (ECM). ECM consist of large structural proteins such as collagens and elastin as well as smaller proteins with mainly regulative properties called matricellular proteins. Matricellular proteins bind to structural proteins and their functions include but are not limited to interaction with cell surface receptors, cytokines, or protease and evoking a cellular response. The signaling initiated by matricellular proteins modulates differentiation and proliferation of cells having an impact on the tissue regeneration. In this review we give an overview of the matricellular proteins that have been found to be involved in cutaneous wound healing and summarize the information known to date about their functions in this process.

WISP-2 modulates the induction of inflammatory mediators and cartilage catabolism in chondrocytes

Wnt-1 inducible signaling pathway protein 2 (WISP-2/CCN5) is a recently identified adipokine that has been described as an important mediator of canonical Wnt activation in adipogenic precursor cells. In osteoarthritis (OA), the most common form of arthritis, chondrocytes exhibit aberrant and increased production of pro-inflammatory mediators and matrix degrading enzymes such as IL-1β and MMP-13. Although recent evidence suggests a role for Wnt signaling in OA physiopathology, little is known about the involvement of WISP-2 in cartilage degradation. In the present study, we determined the expression of WISP-2 in healthy and OA human chondrocytes. WISP-2 expression is modulated along chondrocyte differentiation and downregulated at the onset of hypertrophy by inflammatory mediators. We also investigated the effect of WISP-2 on cartilage catabolism and performed WISP-2 loss-of-function experiments using RNA interference technology in human T/C-28a2 immortalized chondrocytes. We demonstrated that recombinant human WISP-2 protein reduced IL-1β-mediated chondrocyte catabolism, that IL-1β and WNT/b-catenin signaling pathways are involved in rhWISP-2 protein and IL-1β effects in human chondrocytes, and that WISP-2 has a regulatory role in attenuating the catabolic effects of IL-1β in chondrocytes. Gene silencing of WISP-2 increased the induction of the catabolic markers MMP-13 and ADAMTS-5 and the inflammatory mediators IL-6 and IL-8 triggered by IL-1β in human primary OA chondrocytes in a Wnt/β-catenin dependent manner. In conclusion, here we have shown for the first time that WISP-2 may have relevant roles in modulating the turnover of extracellular matrix in the cartilage and that its downregulation may detrimentally alter the inflammatory environment in OA cartilage. We also proved the participation of Wnt/β-catenin signaling pathway in these processes. Thus, targeting WISP-2 might represent a potential therapeutical approach for degenerative and/or inflammatory diseases of musculoskeletal system, such as osteoarthritis.

Matrix-bound Cyr61/CCN1 is required to retain the properties of the bone marrow mesenchymal stem cell niche but is depleted with aging

Previously, we showed that extracellular matrices (ECMs), produced ex vivo by various types of stromal cells, direct bone marrow mesenchymal stem cells (BM-MSCs) in a tissue-specific manner and recapitulate physiologic changes characteristic of the aging microenvironment. In particular, BM-MSCs obtained from elderly donors and cultured on ECM produced by young BM stromal cells showed improved quantity, quality and osteogenic differentiation. In the present study, we searched for matrix components that are required for a functional BM-MSC niche by comparing ECMs produced by BM stromal cells from "young" (≤25 y/o) versus "elderly" (≥60 y/o) donors. With increasing donor age, ECM fibrillar organization and mechanical integrity deteriorated, along with the ability to promote BM-MSC proliferation and responsiveness to growth factors. Proteomic analyses revealed that the matricellular protein, Cyr61/CCN1, was present in young, but undetectable in elderly, BM-ECM. To assess the role of Cyr61 in the BM-MSC niche, we used genetic methods to down-regulate the incorporation of Cyr61 during production of young ECM and up-regulate its incorporation in elderly ECM. The results showed that Cyr61-depleted young ECM lost the ability to promote BM-MSC proliferation and growth factor responsiveness. However, up-regulating the incorporation of Cyr61 during synthesis of elderly ECM restored its ability to support BM-MSC responsiveness to osteogenic factors such as BMP-2 and IGF-1. We next examined aging bone and compared bone mineral density and Cyr61 content of L4-L5 vertebral bodies in "young" (9-11 m/o) and "elderly" (21-33 m/o) mice. Our analyses showed that low bone mineral density was associated with decreased amounts of Cyr61 in osseous tissue of elderly versus young mice. Our results strongly demonstrate a novel role for ECM-bound Cyr61 in the BM-MSC niche, where it is responsible for retention of BM-MSC proliferation and growth factor responsiveness, while depletion of Cyr61 from the BM niche contributes to an aging-related dysregulation of BM-MSCs. Our results also suggest new potential therapeutic targets for treating age-related bone loss by restoring specific ECM components to the stem cell niche.

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.

Ccn6 Is Required for Mitochondrial Integrity and Skeletal Muscle Function in Zebrafish

Mutations in the CCN6 (WISP3) gene are linked with a debilitating musculoskeletal disorder, termed progressive pseudorheumatoid dysplasia (PPRD). Yet, the functional significance of CCN6 in the musculoskeletal system remains unclear. Using zebrafish as a model organism, we demonstrated that zebrafish Ccn6 is present partly as a component of mitochondrial respiratory complexes in the skeletal muscle of zebrafish. Morpholino-mediated depletion of Ccn6 in the skeletal muscle leads to a significant reduction in mitochondrial respiratory complex assembly and activity, which correlates with loss of muscle mitochondrial abundance. These mitochondrial deficiencies are associated with notable architectural and functional anomalies in the zebrafish muscle. Taken together, our results indicate that Ccn6-mediated regulation of mitochondrial respiratory complex assembly/activity and mitochondrial integrity is important for the maintenance of skeletal muscle structure and function in zebrafish. Furthermore, this study suggests that defects related to mitochondrial respiratory complex assembly/activity and integrity could be an underlying cause of muscle weakness and a failed musculoskeletal system in PPRD.

CCN2 (Cellular Communication Network factor 2) in the bone marrow microenvironment, normal and malignant hematopoiesis

CCN2, formerly termed Connective Tissue Growth Factor, is a protein belonging to the Cellular Communication Network (CCN)-family of secreted extracellular matrix-associated proteins. As a matricellular protein it is mainly considered to be active as a modifier of signaling activity of several different signaling pathways and as an orchestrator of their cross-talk. Furthermore, CCN2 and its fragments have been implicated in the regulation of a multitude of biological processes, including cell proliferation, differentiation, adhesion, migration, cell survival, apoptosis and the production of extracellular matrix products, as well as in more complex processes such as embryonic development, angiogenesis, chondrogenesis, osteogenesis, fibrosis, mechanotransduction and inflammation. Its function is complex and context dependent, depending on cell type, state of differentiation and microenvironmental context. CCN2 plays a role in many diseases, especially those associated with fibrosis, but has also been implicated in many different forms of cancer. In the bone marrow (BM), CCN2 is highly expressed in mesenchymal stem/stromal cells (MSCs). CCN2 is important for MSC function, supporting its proliferation, migration and differentiation. In addition, stromal CCN2 supports the maintenance and longtime survival of hematopoietic stem cells, and in the presence of interleukin 7, stimulates the differentiation of pro-B lymphocytes into pre-B lymphocytes. Overexpression of CCN2 is seen in the majority of B-acute lymphoblastic leukemias, especially in certain cytogenetic subgroups associated with poor outcome. In acute myeloid leukemia, CCN2 expression is increased in MSCs, which has been associated with leukemic engraftment in vivo. In this review, the complex function of CCN2 in the BM microenvironment and in normal as well as malignant hematopoiesis is discussed. In addition, an overview is given of data on the remaining CCN family members regarding normal and malignant hematopoiesis, having many similarities and some differences in their function.

CCN6 regulates mitochondrial respiratory complex assembly and activity

Cellular communication network factor 6 (CCN6) mutations are linked with Progressive Pseudo Rheumatoid Dysplasia (PPRD) a debilitating musculoskeletal disorder. The function of CCN6 and the mechanism of PPRD pathogenesis remain unclear. Accordingly, we focused on the functional characterization of CCN6 and CCN6 mutants. Using size exclusion chromatography and native polyacrylamide gel electrophoresis we demonstrated that CCN6 is present as a component of the mitochondrial respiratory complex in human chondrocyte lines. By means of siRNA-mediated transfection and electron microscopy we showed that moderate reduction in CCN6 expression decreases the RER- mitochondria inter-membrane distance. Parallel native PAGE, immunoblotting and Complex I activity assays furthermore revealed increase in both mitochondrial distribution of CCN6 and mitochondrial respiratory complex assembly/activity in CCN6 depleted cells. CCN6 mutants resembling those linked with PPRD, which were generated by CRISPR-Cas9 technology displayed low level of expression of mutant CCN6 protein and inhibited respiratory complex assembly/activity. Electron microscopy and MTT assay of the mutants revealed abnormal mitochondria and poor cell viability. Taken together, our results indicate that CCN6 regulates mitochondrial respiratory complex assembly/activity as part of the mitochondrial respiratory complex by controlling the proximity of RER with the mitochondria, and CCN6 mutations disrupt mitochondrial respiratory complex assembly/activity resulting in mitochondrial defects and poor cell viability.

Development of a 3D bone marrow adipose tissue model

Over the past twenty years, evidence has accumulated that biochemically and spatially defined networks of extracellular matrix, cellular components, and interactions dictate cellular differentiation, proliferation, and function in a variety of tissue and diseases. Modeling in vivo systems in vitro has been undeniably necessary, but when simplified 2D conditions rather than 3D in vitro models are used, the reliability and usefulness of the data derived from these models decreases. Thus, there is a pressing need to develop and validate reliable in vitro models to reproduce specific tissue-like structures and mimic functions and responses of cells in a more realistic manner for both drug screening/disease modeling and tissue regeneration applications. In adipose biology and cancer research, these models serve as physiologically relevant 3D platforms to bridge the divide between 2D cultures and in vivo models, bringing about more reliable and translationally useful data to accelerate benchtop to bedside research. Currently, no model has been developed for bone marrow adipose tissue (BMAT), a novel adipose depot that has previously been overlooked as "filler tissue" but has more recently been recognized as endocrine-signaling and systemically relevant. Herein we describe the development of the first 3D, BMAT model derived from either human or mouse bone marrow (BM) mesenchymal stromal cells (MSCs). We found that BMAT models can be stably cultured for at least 3 months in vitro, and that myeloma cells (5TGM1, OPM2 and MM1S cells) can be cultured on these for at least 2 weeks. Upon tumor cell co-culture, delipidation occurred in BMAT adipocytes, suggesting a bidirectional relationship between these two important cell types in the malignant BM niche. Overall, our studies suggest that 3D BMAT represents a "healthier," more realistic tissue model that may be useful for elucidating the effects of MAT on tumor cells, and tumor cells on MAT, to identify novel therapeutic targets. In addition, proteomic characterization as well as microarray data (expression of >22,000 genes) coupled with KEGG pathway analysis and gene set expression analysis (GSEA) supported our development of less-inflammatory 3D BMAT compared to 2D culture. In sum, we developed the first 3D, tissue-engineered bone marrow adipose tissue model, which is a versatile, novel model that can be used to study numerous diseases and biological processes involved with the bone marrow.

Physical contact between mesenchymal stem cells and endothelial precursors induces distinct signatures with relevance to the very early phase of regeneration

Multipotent adult stem cells/precursor cells, especially of the mesenchymal and endothelial lineage, may have great potential for bone tissue engineering. Although their potential is highly recognized, not much is known about the underlying molecular mechanisms that initiate the regeneration process, connect osteogenesis, and angiogenesis and, finally, orchestrate renewal of bone tissue. Our study addressed these questions by generating two in vitro cell culture models to examine the changes in the global gene expression patterns of endothelial precursor cells and mesenchymal stem cells after 24 hours of either humoral (conditioned medium) or direct cell-cell interaction (co-culture). Endothelial precursor cells were isolated from human buffy coat and mesenchymal stem cells from the bone marrow of the femoral head. The comparison of the treated and control cells by microarray analyses revealed in total more than 1500 regulated genes, which were analyzed for their affiliation to angiogenesis and osteogenesis. Expression array analyses at the RNA and protein level revealed data with respect to regulated genes, pathways and targets that may represent a valid basis for further dissection of the systems biology of regeneration processes. It may also be helpful for the reconstitution of the natural composition of a regenerative microenvironment when targeting tissue regeneration both in vitro and in situ.

Wisp2 disruption represses Cxcr4 expression and inhibits BMSCs homing to injured liver

Liver regeneration/repair is a compensatory regrowth following acute liver failure, and bone marrow-derived mesenchyme stem cell (BMSC) transplantation is an effective therapy that promotes liver regeneration/repair. Wnt1 inducible signaling pathway protein 2 (Wisp2) is highly expressed in BMSCs, however, its function remains unclear. In this work, we used clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein -9 nuclease (CRISPR/Cas9) genome editing technology to knockdown Wisp2 in BMSCs, and these modified cells were then transplanted into rats which were induced by the 2-AAF/PH. By linking the expression of Cas9 to green fluorescent protein (GFP), we tracked BMSCs in the rats. Disruption of Wisp2 inhibited the homing of BMSCs to injured liver and aggravated liver damage as indicated by remarkably high levels of ALT and AST. Moreover, the key factor in BMSC transplantation, C-X-C chemokine receptor type 4 (Cxcr4), was down-regulated in the Wisp2 depleted BMSCs and had a lower expression in the livers of the corresponding rats. By tracing the GFP marker, more BMSCs were observed to differentiate into CD31 positive endothelial cells in the functional Wisp2 cells but less in the Wisp2 gene disrupted cells. In summary, Wisp2 promotes the homing of BMSCs through Cxcr4 related signaling during liver repair in rats.

The skeletal cell-derived molecule sclerostin drives bone marrow adipogenesis

The bone marrow niche is a dynamic and complex microenvironment that can both regulate, and be regulated by the bone matrix. Within the bone marrow (BM), mesenchymal stromal cell (MSC) precursors reside in a multi-potent state and retain the capacity to differentiate down osteoblastic, adipogenic, or chondrogenic lineages in response to numerous biochemical cues. These signals can be altered in various pathological states including, but not limited to, osteoporotic-induced fracture, systemic adiposity, and the presence of bone-homing cancers. Herein we provide evidence that signals from the bone matrix (osteocytes) determine marrow adiposity by regulating adipogenesis in the bone marrow. Specifically, we found that physiologically relevant levels of Sclerostin (SOST), which is a Wnt-inhibitory molecule secreted from bone matrix-embedded osteocytes, can induce adipogenesis in 3T3-L1 cells, mouse ear- and BM-derived MSCs, and human BM-derived MSCs. We demonstrate that the mechanism of SOST induction of adipogenesis is through inhibition of Wnt signaling in pre-adipocytes. We also demonstrate that a decrease of sclerostin in vivo, via both genetic and pharmaceutical methods, significantly decreases bone marrow adipose tissue (BMAT) formation. Overall, this work demonstrates a direct role for SOST in regulating fate determination of BM-adipocyte progenitors. This provides a novel mechanism for which BMAT is governed by the local bone microenvironment, which may prove relevant in the pathogenesis of certain diseases involving marrow adipose. Importantly, with anti-sclerostin therapy at the forefront of osteoporosis treatment and a greater recognition of the role of BMAT in disease, these data are likely to have important clinical implications.

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.

Contact of myeloma cells induces a characteristic transcriptome signature in skeletal precursor cells -Implications for myeloma bone disease

Physical interaction of skeletal precursors with multiple myeloma cells has been shown to suppress their osteogenic potential while favoring their tumor-promoting features. Although several transcriptome analyses of myeloma patient-derived mesenchymal stem cells have displayed differences compared to their healthy counterparts, these analyses insufficiently reflect the signatures mediated by tumor cell contact, vary due to different methodologies, and lack results in lineage-committed precursors. To determine tumor cell contact-mediated changes on skeletal precursors, we performed transcriptome analyses of mesenchymal stem cells and osteogenic precursor cells cultured in contact with the myeloma cell line INA-6. Comparative analyses confirmed dysregulation of genes which code for known disease-relevant factors and additionally revealed upregulation of genes that are associated with plasma cell homing, adhesion, osteoclastogenesis, and angiogenesis. Osteoclast-derived coupling factors, a dysregulated adipogenic potential, and an imbalance in favor of anti-anabolic factors may play a role in the hampered osteoblast differentiation potential of mesenchymal stem cells. Angiopoietin-Like 4 (ANGPTL4) was selected from a list of differentially expressed genes as a myeloma cell contact-dependent target in skeletal precursor cells which warranted further functional analyses. Adhesion assays with full-length ANGPTL4-coated plates revealed a potential role of this protein in INA-6 cell attachment. This study expands knowledge of the myeloma cell contact-induced signature in the stromal compartment of myelomatous bones and thus offers potential targets that may allow detection and treatment of myeloma bone disease at an early stage.

Regulation of the CCN genes by vitamin D: A possible adjuvant therapy in the treatment of cancer and fibrosis

The CCN family is composed of six cysteine-rich, modular, and conserved proteins whose functions span a variety of tissues and include cell proliferation, adhesion, angiogenesis, and wound healing. Roles for the CCN proteins throughout the entire body including the skin, kidney, brain, blood vessels, hematopoietic compartment and others, are continuously being elucidated. Likewise, an understanding of the regulation of this important gene family is constantly becoming clearer, through identification of transcription factors that directly activate, repress, or respond to upstream cell signaling pathways, as well as other forms of gene expression control. Vitamin D (1,25-dihydroxyvitamin D3 or calcitriol), a vitamin essential for numerous biological processes, acts as a potent gene expression modulator. The regulation of the CCN gene family members by calcitriol has been described in many contexts. Here, we provide a concise and thorough overview of what is known about calcitriol and its regulation of the CCN genes, and argue that its regulation is of physiological importance in a wide breadth of tissues in which CCN genes function. In addition, we highlight the effects of vitamin D on CCN gene expression in the setting of two common pathologic conditions, fibrosis and cancer, and propose that the therapeutic effects of vitamin D3 described in these disease states may in part be attributable to CCN gene modulation. As vitamin D is perfectly safe in a wide range of doses and already showing promise as an adjuvant therapeutic agent, a deeper understanding of its control of CCN gene expression may have profound implications in clinical management of disease.

The role of CCN family genes in haematological malignancies

Haematological malignancies, although a broad range of specific disease types, continue to show considerable overlap in classification, and patients are treated using similar chemotherapy regimes. In this review we look at the role of the CCN family of matricellular proteins and indicate their role in nine haematological malignancies including both myeloid and lymphoid neoplasms. The potential for further haematological neoplasms with CCN family associations is argued by summarising the demonstrated role of CCN family genes in the differentiation of haematopoietic stem cells (HSC) and mesenchymal stem cells. The expanding field of knowledge encompassing CCN family genes and cancers of the HSC-lineage highlights the importance of extracellular matrix-interactions in both normal physiology and tumorigenesis of the blood, bone marrow and lymph nodes.

Transcriptome analysis of cattle muscle identifies potential markers for skeletal muscle growth rate and major cell types

BACKGROUND

This study aimed to identify markers for muscle growth rate and the different cellular contributors to cattle muscle and to link the muscle growth rate markers to specific cell types.

RESULTS

The expression of two groups of genes in the longissimus muscle (LM) of 48 Brahman steers of similar age, significantly enriched for "cell cycle" and "ECM (extracellular matrix) organization" Gene Ontology (GO) terms was correlated with average daily gain/kg liveweight (ADG/kg) of the animals. However, expression of the same genes was only partly related to growth rate across a time course of postnatal LM development in two cattle genotypes, Piedmontese x Hereford (high muscling) and Wagyu x Hereford (high marbling). The deposition of intramuscular fat (IMF) altered the relationship between the expression of these genes and growth rate. K-means clustering across the development time course with a large set of genes (5,596) with similar expression profiles to the ECM genes was undertaken. The locations in the clusters of published markers of different cell types in muscle were identified and used to link clusters of genes to the cell type most likely to be expressing them. Overall correspondence between published cell type expression of markers and predicted major cell types of expression in cattle LM was high. However, some exceptions were identified: expression of SOX8 previously attributed to muscle satellite cells was correlated with angiogenesis. Analysis of the clusters and cell types suggested that the "cell cycle" and "ECM" signals were from the fibro/adipogenic lineage. Significant contributions to these signals from the muscle satellite cells, angiogenic cells and adipocytes themselves were not as strongly supported. Based on the clusters and cell type markers, sets of five genes predicted to be representative of fibro/adipogenic precursors (FAPs) and endothelial cells, and/or ECM remodelling and angiogenesis were identified.

CONCLUSIONS

Gene sets and gene markers for the analysis of many of the major processes/cell populations contributing to muscle composition and growth have been proposed, enabling a consistent interpretation of gene expression datasets from cattle LM. The same gene sets are likely to be applicable in other cattle muscles and in other species.

Connective Tissue Growth Factor reporter mice label a subpopulation of mesenchymal progenitor cells that reside in the trabecular bone region

Few gene markers selectively identify mesenchymal progenitor cells inside the bone marrow. We have investigated a cell population located in the mouse bone marrow labeled by Connective Tissue Growth Factor reporter expression (CTGF-EGFP). Bone marrow flushed from CTGF reporter mice yielded an EGFP+ stromal cell population. Interestingly, the percentage of stromal cells retaining CTGF reporter expression decreased with age in vivo and was half the frequency in females compared to males. In culture, CTGF reporter expression and endogenous CTGF expression marked the same cell types as those labeled using Twist2-Cre and Osterix-Cre fate mapping approaches, which previously had been shown to identify mesenchymal progenitors in vitro. Consistent with this past work, sorted CTGF+ cells displayed an ability to differentiate into osteoblasts, chondrocytes, and adipocytes in vitro and into osteoblast, adipocyte, and stromal cell lineages after transplantation into a parietal bone defect. In vivo examination of CTGF reporter expression in bone tissue sections revealed that it marked cells highly localized to the trabecular bone region and was not expressed in the perichondrium or periosteum. Mesenchymal cells retaining high CTGF reporter expression were adjacent to, but distinct from mature osteoblasts lining bone surfaces and endothelial cells forming the vascular sinuses. Comparison of CTGF and Osterix reporter expression in bone tissue sections indicated an inverse correlation between the strength of CTGF expression and osteoblast maturation. Down-regulation of CTGF reporter expression also occurred during in vitro osteogenic differentiation. Collectively, our studies indicate that CTGF reporter mice selectively identify a subpopulation of bone marrow mesenchymal progenitor cells that reside in the trabecular bone region.

CCN1 secreted by tonsil-derived mesenchymal stem cells promotes endothelial cell angiogenesis via integrin αv β3 and AMPK

CCN1 is highly expressed in cancer cells and has been identified in the secretome of bone marrow-derived mesenchymal stem cells (BM-MSC). Although secreted CCN1 is known to promote angiogenesis, its underlying mechanism remains unclear. Here, we examined whether our recently-established tonsil-derived MSC (T-MSC) secrete CCN1 and, if any, how CCN1 promotes the angiogenesis of human umbilical vein endothelial cells (HUVEC). Compared with untreated control T-MSC, a higher level of CCN1 was secreted by T-MSC treated with activin A and sonic hedgehog, drugs known to induce endodermal differentiation. Expectedly, conditioned medium collected from differentiated T-MSC (DCM) significantly increased HUVEC migration and tube formation compared with that from control T-MSC (CCM), and these stimulatory effects were reversed by neutralization with anti-CCN1 antibody. Treatment with recombinant human CCN1 (rh-CCN1) alone also mimicked the stimulatory effects of DCM. Furthermore, treatment with either DCM or rh-CCN1 increased the phosphorylation of AMP kinase (AMPK), and ectopic expression of siRNA of the AMPK gene inhibited all observed effects of both DCM and rh-CCN1. However, no alteration of intracellular ATP levels or phosphorylation of LKB1, a well-known upstream factor of AMPK activation, was observed under our conditions. Finally, the neutralization of integrin α(v) β(3) with anti-integrin α(v) β(3) antibody almost completely reversed the effects of CCN1 on AMPK phosphorylation, and EC migration and tube formation. Taken together, we demonstrated that T-MSC increase the secretion of CCN1 in response to endodermal differentiation and that integrin α(v) β(3) and AMPK mediate CCN1-induced EC migration and tube formation independent of intracellular ATP levels alteration.

The expression of Wnt-1 inducible signaling pathway protein-2 in astrocytoma: Correlation between pathological grade and clinical outcome

Wnt-1 inducible signaling pathway protein-2 (WISP-2) is a member of the CCN family, which is critical for the control of cell morphology, motion, adhesion and other processes involved in tumorigenesis. The expression pattern and clinical significance of WISP-2 in astrocytomas remains unclear. In this study, reverse transcription-polymerase chain reaction was performed to systematically investigate the expression of WISP-2 in 47 astrocytoma tissues of different pathological grades and 10 normal brain tissues. The mRNA expression levels of WISP-2 in the astrocytoma tissues were observed to be significantly higher than those in the normal brain tissues. Furthermore, the upregulation of WISP-2 was found to be associated with astrocytomas of higher pathological grades. Subsequently, 154 astrocytoma and 15 normal brain tissues were analyzed using immunohistochemistry and similar results were obtained. Univariate and multivariate survival analyses were used to determine the correlations between WISP-2 expression and overall survival (OS) and progression-free survival (PFS). The results indicated that the expression of WISP-2 was found to negatively correlate with patient PFS and OS. These results demonstrated that the WISP-2 protein is involved in the pathogenesis and progression of human astrocytomas and may serve as a malignant biomarker of this disease.

WISP 1 is an important survival factor in human mesenchymal stromal cells

WNT-induced secreted protein 1 (WISP1/CCN4), a member of the CCN protein family, acts as a downstream factor of the canonical WNT signaling pathway. Its expression is known to affect proliferation and differentiation of human mesenchymal stromal cells (hMSCs), which are fundamental for the development and maintenance of the musculoskeletal system. Whereas a dysregulated, excessive expression of WISP1 often reflects its oncogenic potential via the inhibition of apoptosis, our study emphasizes the importance of WISP1 signaling for the survival of primary human cells. We have established the efficient and specific down-regulation of endogenous WISP1 transcripts by gene silencing in hMSCs and observed cell death as a consequence of WISP1 deficiency. This was confirmed by Annexin V staining for apoptotic cells. DNA microarray analyses of WISP1 down-regulated versus control samples revealed several clusters of differentially expressed genes important for apoptosis induction such as TNF-related apoptosis-inducing ligand 1 (TRAIL) and the corresponding apoptosis-inducing receptors TRAIL-R1 and -R2. An increased expression of TRAIL and its receptors TRAIL-R1 and -R2 in WISP1-deficient hMSCs was confirmed by immunocytofluorescence. Accordingly, WISP1 deficiency is likely to cause TRAIL-induced apoptosis. This is an important novel finding, which suggests that WISP1 is indispensable for the protection of healthy hMSCs against TRAIL-induced apoptosis.

Mesenchymal stem cell contact promotes CCN1 splicing and transcription in myeloma cells

CCN family member 1 (CCN1), also known as cysteine-rich angiogenic inducer 61 (CYR61), belongs to the extracellular matrix-associated CCN protein family. The diverse functions of these proteins include regulation of cell migration, adhesion, proliferation, differentiation and survival/apoptosis, induction of angiogenesis and cellular senescence. Their functions are partly overlapping, largely non-redundant, cell-type specific, and depend on the local microenvironment. To elucidate the role of CCN1 in the crosstalk between stromal cells and myeloma cells, we performed co-culture experiments with primary mesenchymal stem cells (MSC) and the interleukin-6 (IL-6)-dependent myeloma cell line INA-6. Here we show that INA-6 cells display increased transcription and induction of splicing of intron-retaining CCN1 pre-mRNA when cultured in contact with MSC. Protein analyses confirmed that INA-6 cells co-cultured with MSC show increased levels of CCN1 protein consistent with the existence of a pre-mature stop codon in intron 1 that abolishes translation of unspliced mRNA. Addition of recombinant CCN1-Fc protein to INA-6 cells was also found to induce splicing of CCN1 pre-mRNA in a concentration-dependent manner. Only full length CCN1-Fc was able to induce mRNA splicing of all introns, whereas truncated recombinant isoforms lacking domain 4 failed to induce intron splicing. Blocking RGD-dependent integrins on INA-6 cells resulted in an inhibition of these splicing events. These findings expand knowledge on splicing of the proangiogenic, matricellular factor CCN1 in the tumor microenvironment. We propose that contact with MSC-derived CCN1 leads to splicing and enhanced transcription of CCN1 which further contributes to the translation of angiogenic factor CCN1 in myeloma cells, supporting tumor viability and myeloma bone disease.

CCN2 enhances resistance to cisplatin-mediating cell apoptosis in human osteosarcoma

Osteosarcoma (OS) is the most common form of malignant bone tumor and is an aggressive malignant neoplasm exhibiting osteoblastic differentiation. Cisplatin is one of the most efficacious antitumor drugs for osteosarcoma patients. However, treatment failures are common due to the development of chemoresistance. CCN2 (also known as CTGF), is a secreted protein that binds to integrins, modulates the invasive behavior of certain human cancer cells. However, the effect of CCN2 in cisplatin-mediated chemotherapy is still unknown. Here, we found that CCN2 was upregulated in human osteosarcoma cells after treatment with cisplatin. Moreover, overexpression of CCN2 increased the resistance to cisplatin-mediated cell apoptosis. In contrast, reduction of CCN2 by CCN2 shRNA promoted the chemotherapeutic effect of cisplatin. We also found that CCN2 provided resistance to cisplatin-induced apoptosis through upregulation of Bcl-xL and survivin. Knockdown of Bcl-xL or survivin removed the CCN2-mediated resistance to apoptosis induced by cisplatin. On the other hand, CCN2 also promoted FAK, MEK, and ERK survival signaling pathways to enhance tumor survival during cisplatin treatment. In a mouse xenograft model, overexpression of CCN2 promoted resistance to cisplatin. However, knockdown of CCN2 increased the therapeutic effect of cisplatin. Therefore, our data suggest that CCN2 might be a critical oncogene of human osteosarcoma for cisplatin-resistance and supported osteosarcoma cell growth in vivo and in vitro.

The CCN family proteins: modulators of bone development and novel targets in bone-associated tumors

The CCN family of proteins is composed of six extracellular matrix-associated proteins that play crucial roles in skeletal development, wound healing, fibrosis, and cancer. Members of the CCN family share four conserved cysteine-rich modular domains that trigger signal transduction in cell adhesion, migration, proliferation, differentiation, and survival through direct binding to specific integrin receptors and heparan sulfate proteoglycans. In the present review, we discuss the roles of the CCN family proteins in regulating resident cells of the bone microenvironment. In vertebrate development, the CCN family plays a critical role in osteo/chondrogenesis and vasculo/angiogenesis. These effects are regulated through signaling via integrins, bone morphogenetic protein, vascular endothelial growth factor, Wnt, and Notch via direct binding to CCN family proteins. Due to the important roles of CCN family proteins in skeletal development, abnormal expression of CCN proteins is related to the tumorigenesis of primary bone tumors such as osteosarcoma, Ewing sarcoma, and chondrosarcoma. Additionally, emerging studies have suggested that CCN proteins may affect progression of secondary metastatic bone tumors by moderating the bone microenvironment. CCN proteins could therefore serve as potential therapeutic targets for drug development against primary and metastatic bone tumors.

CCN4 regulates vascular smooth muscle cell migration and proliferation

The migration and proliferation of vascular smooth muscle cells (VSMCs) are essential elements during the development of atherosclerosis and restenosis. An increasing number of studies have reported that extracellular matrix (ECM) proteins, including the CCN protein family, play a significant role in VSMC migration and proliferation. CCN4 is a member of the CCN protein family, which controls cell development and survival in multiple systems of the body. Here, we sought to determine whether CCN4 is involved in VSMC migration and proliferation. We examined the effect of CCN4 using rat cultured VSMCs. In cultured VSMCs, CCN4 stimulated the adhesion and migration of VSMCs in a dose-dependent manner, and this effect was blocked by an antibody for integrin α5β1. CCN4 expression was enhanced by the pro-inflammatory cytokine tumor necrosis factor α (TNF-α). Furthermore, knockdown of CCN4 by siRNA significantly inhibited the VSMC proliferation. CCN4 also could up-regulate the expression level of marker proteins of the VSMCs phenotype. Taken together, these results suggest that CCN4 is involved in the migration and proliferation of VSMCs. Inhibition of CCN4 may provide a promising strategy for the prevention of restenosis after vascular interventions.

One-step bone marrow-derived cell transplantation in talarosteochondral lesions: mid-term results

PURPOSE

to verify the capability of scaffold-supported bone marrow-derived cells to be used in the repair of osteochondral lesions of the talus.

METHODS

using a device to concentrate bone marrow-derived cells, a scaffold (collagen powder or hyaluronic acid membrane) for cell support and platelet gel, a one-step arthroscopic technique was developed for cartilage repair. In a prospective clinical study, we investigated the ability of this technique to repair talar osteochondral lesions in 64 patients. The mean follow-up was 53 months. Clinical results were evaluated using the American Orthopaedic Foot and Ankle Society (AOFAS) scale score. We also considered the influence of scaffold type, lesion area, previous surgery, and lesion depth.

RESULTS

the mean preoperative AOFAS scale score was 65.2 ± 13.9. The clinical results peaked at 24 months, before declining gradually to settle at a score of around 80 at the maximum follow-up of 72 months.

CONCLUSIONS

the use of bone marrow-derived cells supported by scaffolds to repair osteochondral lesions of the talus resulted in significant clinical improvement, which was maintained over time.

LEVEL OF EVIDENCE

level IV, therapeutic case series.

WISP3-IGF1 interaction regulates chondrocyte hypertrophy

WISP3 (Wnt induced secreted protein 3) is a multi-domain protein of mesenchymal origin. Mutations in several domains of WISP3 cause PPRD (progressive pseudo rheumatoid dysplasia), which is associated with cartilage loss and restricted skeletal development. Despite several studies focusing on the functional characterization of WISP3, the molecular details underlying the course of PPRD remain unresolved. We are interested in analyzing the function of WISP3 in the context of cartilage integrity. The current study demonstrates that WISP3 binds to insulin-like growth factor 1 (IGF1) and inhibits IGF1 secretion. Additionally, WISP3 curbs IGF1-mediated collagen X expression, accumulation of reactive oxygen species (ROS) and alkaline phosphatase activity, all of which are associated with the induction of chondrocyte hypertrophy. Interestingly, both IGF1 and ROS in turn trigger an increase in WISP3 expression. Together, our results are indicative of an operational WISP3-IGF1 regulatory loop whereby WISP3 preserves cartilage integrity by restricting IGF1-mediated hypertrophic changes in chondrocytes, at least partly, upon interaction with IGF1.

Diverse effects of cyclic AMP variants on osteogenic and adipogenic differentiation of human mesenchymal stromal cells

Osteogenic differentiation of human mesenchymal stromal cells (hMSCs) may potentially be used in cell-based bone tissue-engineering applications to enhance the bone-forming potential of these cells. Osteogenic differentiation and adipogenic differentiation are thought to be mutually exclusive, and although several signaling pathways and cues that induce osteogenic or adipogenic differentiation, respectively, have been identified, there is no general consensus on how to optimally differentiate hMSCs into the osteogenic lineage. Some pathways have also been reported to be involved in both adipogenic and osteogenic differentiation, as for example, the protein kinase A (PKA) pathway, and the aim of this study was to investigate the role of cAMP/PKA signaling in differentiation of hMSCs in more detail. We show that activation of this pathway with dibutyryl-cAMP results in enhanced alkaline phosphatase expression, whereas another cAMP analog induces adipogenesis in long-term mineralization cultures. Adipogenic differentiation, induced by 8-bromo-cAMP, was accompanied by stronger PKA activity and higher expression of cAMP-responsive genes, suggesting that stronger activation correlates with adipogenic differentiation. In addition, a whole-genome expression analysis showed an increase in expression of adipogenic genes in 8-br-cAMP-treated cells. Furthermore, by means of quantitative polymerase chain reaction, we show differences in peroxisome proliferator-activated receptor-γ activation, either alone or in combination with dexamethasone, thus demonstrating differential effects of the PKA pathway, most likely depending on its mode of activation.

Methotrexate chemotherapy reduces osteogenesis but increases adipogenic potential in the bone marrow

Intensive use of cancer chemotherapy is increasingly linked with long-term skeletal side effects such as osteopenia, osteoporosis and fractures. However, cellular mechanisms by which chemotherapy affects bone integrity remain unclear. Methotrexate (MTX), used commonly as an anti-metabolite, is known to cause bone defects. To study the pathophysiology of MTX-induced bone loss, we examined effects on bone and marrow fat volume, population size and differentiation potential of bone marrow stromal cells (BMSC) in adult rats following chemotherapy for a short-term (five once-daily doses at 0.75 mg/kg) or a 6-week term (5 doses at 0.65 mg/kg + 9 days rest + 1.3 mg/kg twice weekly for 4 weeks). Histological analyses revealed that both acute and chronic MTX treatments caused a significant decrease in metaphyseal trabecular bone volume and an increase in marrow adipose mass. In the acute model, proliferation of BMSCs significantly decreased on days 3-9, and consistently the stromal progenitor cell population as assessed by CFU-F formation was significantly reduced on day 9. Ex vivo differentiation assays showed that while the osteogenic potential of isolated BMSCs was significantly reduced, their adipogenic capacity was markedly increased on day 9. Consistently, RT-PCR gene expression analyses showed osteogenic transcription factors Runx2 and Osterix (Osx) to be decreased but adipogenic genes PPARγ and FABP4 up-regulated on days 6 and 9 in the stromal population. These findings indicate that MTX chemotherapy reduces the bone marrow stromal progenitor cell population and induces a switch in differentiation potential towards adipogenesis at the expense of osteogenesis, resulting in osteopenia and marrow adiposity.

CCN5/WISP-2: A micromanager of breast cancer progression

The gain of plasticity by a subset of cancer cells is a unique but common sequence of cancer progression from epithelial phenotype to mesenchymal phenotype (EMT) that is followed by migration, invasion and metastasis to a distant organ, and drug resistance. Despite multiple studies, it is still unclear how cancer cells regulate plasticity. Recent studies from our laboratory and others' proposed that CCN5/WISP-2, which is found intracellularly (in the nucleus and cytoplasm) and extracellularly, plays a negative regulator of plasticity. It prevents the EMT process in breast cancer cells as well as pancreatic cancer cells. Multiple genetic insults, including the gain of p53 mutations that accumulate over the time, may perturb CCN5 expression in non-invasive breast cancer cells, which ultimately helps cells to gain invasive phenotypes. Moreover, emerging evidence indicates that several oncogenic lesions such as miR-10b upregulation and activation of TGF-β-signaling can accumulate during CCN5 crisis in breast cancer cells. Collectively, these studies indicate that loss of CCN5 activity may promote breast cancer progression; application of CCN5 protein may represent a novel therapeutic intervention in breast cancer and possibly pancreatic cancer.

CCN3 modulates bone turnover and is a novel regulator of skeletal metastasis

The CCN family of proteins is composed of six secreted proteins (CCN1-6), which are grouped together based on their structural similarity. These matricellular proteins are involved in a large spectrum of biological processes, ranging from development to disease. In this review, we focus on CCN3, a founding member of this family, and its role in regulating cells within the bone microenvironment. CCN3 impairs normal osteoblast differentiation through multiple mechanisms, which include the neutralization of pro-osteoblastogenic stimuli such as BMP and Wnt family signals or the activation of pathways that suppress osteoblastogenesis, such as Notch. In contrast, CCN3 is known to promote chondrocyte differentiation. Given these functions, it is not surprising that CCN3 has been implicated in the progression of primary bone cancers such as osteosarcoma, Ewing’s sarcoma and chondrosarcoma. More recently, emerging evidence suggests that CCN3 may also influence the ability of metastatic cancers to colonize and grow in bone.

1,25-dihydroxyvitamin D3 treatment delays cellular aging in human mesenchymal stem cells while maintaining their multipotent capacity

1,25-dihydroxyvitamin D3 (1,25D3) was reported to induce premature organismal aging in fibroblast growth factor-23 (Fgf23) and klotho deficient mice, which is of main interest as 1,25D3 supplementation of its precursor cholecalciferol is used in basic osteoporosis treatment. We wanted to know if 1,25D3 is able to modulate aging processes on a cellular level in human mesenchymal stem cells (hMSC). Effects of 100 nM 1,25D3 on hMSC were analyzed by cell proliferation and apoptosis assay, β-galactosidase staining, VDR and surface marker immunocytochemistry, RT-PCR of 1,25D3-responsive, quiescence- and replicative senescence-associated genes. 1,25D3 treatment significantly inhibited hMSC proliferation and apoptosis after 72 h and delayed the development of replicative senescence in long-term cultures according to β-galactosidase staining and P16 expression. Cell morphology changed from a fibroblast like appearance to broad and rounded shapes. Long term treatment did not induce lineage commitment in terms of osteogenic pathways but maintained their clonogenic capacity, their surface marker characteristics (expression of CD73, CD90, CD105) and their multipotency to develop towards the chondrogenic, adipogenic and osteogenic pathways. In conclusion, 1,25D3 delays replicative senescence in primary hMSC while the pro-aging effects seen in mouse models might mainly be due to elevated systemic phosphate levels, which propagate organismal aging.

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

CCN family proteins play diverse roles in many aspects of cellular processes such as proliferation, differentiation, adhesion, migration, angiogenesis and survival. In the bone tissue of vertebrate species, the expression of most CCN family members has been observed in osteoblasts. However, their spatial and temporal distributions, as well as their functions, are still only partially understood. In this study, we evaluated the localization of CCN family members in skeletal tissue in vivo and comparatively analyzed the gene expression patterns and functions of the members in murine osteoblasts in primary culture. Immunofluorescent analyses revealed that the CCN family members were differentially produced in osteoblasts and osteocytes. The presence of all Ccn transcripts was confirmed in those osteoblasts. Among the members, CCN1, CCN2, CCN4 and CCN5 were found in osteocytes. CCN4 and CCN5 were distributed in osteocytes located inside of bone matrix as well. Next, we investigated the expression pattern of Ccn family members during osteoblast differentiation. Along with differentiation, most of the members followed proper gene expression patterns; whereas, Ccn4 and Ccn5 showed quite similar patterns. Furthermore, we evaluated the effects of CCN family members on the osteoblastic activities by using recombinant CCN proteins and RNA interference method. Five members of this family displayed positive effects on osteoblast proliferation or differentiation. Of note, CCN3 drastically inhibited the osteoblast activities. Each Ccn specific siRNA could modulate osteoblast activities in a manner expected by the observed effect of respective recombinant CCN protein. In addition, we found that extracellular signal-regulated kinase1/2 and p38 mitogen-activated protein kinase pathways were critically involved in the CCN family member-mediated modification of osteoblast activities. Collectively, all Ccn family members were found to be differentially expressed along with differentiation and therefore could participate in progression of the osteoblast lineage.

Pattern of expression of CCN family members Cyr61, CTGF and NOV in human acute and chronic wounds

The CCN family is a group of extremely cysteine-rich proteins that are found within the extracellular matrix and are comprised of cysteine-rich 61 (Cyr61/CCN1), connective tissue growth factor (CTGF/CCN 2) and nephroblastoma over-expressed (NOV/CCN3). Collectively, these proteins stimulate mitosis, adhesion, apoptosis, extracellular matrix production, growth arrest and migration, and regulate angiogenesis, tumour growth, placentation, implantation, embryogenesis and endochondral ossification. Despite such diverse activity, CCN protein function has not been explored in human wounds and healing. In the present study, we investigated the expression of these proteins in samples of normal, acute and chronic wounds using immunohistochemical staining and real-time quantitative RT-PCR. Statistical analysis was performed using the Fisher's exact test. Our results showed that, although all CCN proteins were present in normal, acute and chronic wounds, their expression levels differed, particularly in the case of connective tissue growth factor (CTGF), for which significantly reduced levels were found in chronic wounds compared to acute wounds (p<0.002). Thus, the lack of CTGF in wound tissues may contribute to the abnormal healing of clinical wounds. This suggests that CCN proteins may play an important role in human tissue wound healing. This further suggests that human wound healing may be promoted by manipulating the levels of this protein.

CCN2/CTGF silencing blocks cell aggregation in embryonal carcinoma P19 cell

Connective tissue growth factor (CCN2/CTGF) is a matricellular-secreted protein involved in extracellular matrix remodeling. The P19 cell line is an embryonic carcinoma line widely used as a cellular model for differentiation and migration studies. In the present study, we employed an exogenous source of CCN2 and small interference RNA to address the role of CCN2 in the P19 cell aggregation phenomenon. Our data showed that increasing CCN2 protein concentrations from 0.1 to 20 nM decreased the number of cell clusters and dramatically increased cluster size without changing proliferation or cell survival, suggesting that CCN2 induced aggregation. In addition, CCN2 specific silencing inhibited typical P19 cell aggregation, which could be partially rescued by 20 nM CCN2. The present study demonstrates that CCN2 is a key molecule for cell aggregation of embryonic P19 cells.

CCN5: biology and pathophysiology

CCN5 is one of six proteins in the CCN family. This family of proteins has been shown to play important roles in many processes, including proliferation, migration, adhesion, extracellular matrix regulation, angiogenesis, tumorigenesis, fibrosis, and implantation. In this review, we focus on the biological and putative pathophysiological roles of CCN5. This intriguing protein is structurally unique among the CCN family members, and has a unique biological activity profile as well.

CCN5: biology and pathophysiology

CCN5 is one of six proteins in the CCN family. This family of proteins has been shown to play important roles in many processes, including proliferation, migration, adhesion, extracellular matrix regulation, angiogenesis, tumorigenesis, fibrosis, and implantation. In this review, we focus on the biological and putative pathophysiological roles of CCN5. This intriguing protein is structurally unique among the CCN family members, and has a unique biological activity profile as well.

Housekeeping gene stability influences the quantification of osteogenic markers during stem cell differentiation to the osteogenic lineage

Real-time reverse transcription PCR (RT-qPCR) relies on a housekeeping or normalizer gene whose expression remains constant throughout the experiment. RT-qPCR is commonly used for characterization of human bone marrow mesenchymal stem cells (hBMSCs). However, to the best of our knowledge, there are no studies validating the expression stability of the genes used as normalizers during hBMSCs differentiation. This work aimed to study the stability of the housekeeping genes beta-actin, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and ribosomal protein L13A (RPL13A) during the osteogenic differentiation of hBMSCs. Their stability was evaluated via RT-qPCR in 14 and 20 day differentiation assays to the osteogenic lineage. Different normalization strategies were evaluated to quantify the osteogenic markers collagen type I, bone sialoprotein and osteonectin. Cell differentiation was confirmed via alizarin red staining. The results demonstrated up-regulation of beta-actin with maximum fold changes (MFC) of 4.38. GAPDH and RPL13A were not regulated by osteogenic media after 14 days and presented average fold changes lower than 2 in 20 day cultures. RPL13A (MFC < 2) had a greater stability when normalizing as a function of culture time compared with GAPDH (MFC </= 2.2), which resulted in expression patterns of the osteogenic markers more consistent with the observed differentiation process. The results suggest that beta-actin regulation could be associated with the morphological changes characteristic of hBMSCs osteogenic differentiation, and provide evidence for the superior performance of RPL13A as a normalizer gene in osteogenic differentiation studies of hBMSCs. This work highlights the importance of validating the normalizer genes used for stem cells characterization via RT-qPCR.

Multipotential differentiation of human anulus fibrosus cells: an in vitro study

BACKGROUND

The existence of fibrocartilage, bone-like tissues, nerves, and blood vessels in the anulus fibrosus during intervertebral disc degeneration has been well documented. Migration of differentiated cells from outside the intervertebral disc has been hypothesized as a possible mechanism for the formation of these tissues. We hypothesized that the normal anulus fibrosus tissue contains multipotent progenitor cells, which are able to differentiate into cartilage and/or fibrocartilage cells, osteoblasts, neurons, and blood vessel cells.

METHODS

We isolated anulus fibrosus cells from the nondegenerative intervertebral discs of adolescent (thirteen to sixteen-year-old) patients with idiopathic scoliosis and cultured the cells in vitro in induction media containing different stimuli. Immunophenotypic analysis of cell surface markers was performed by flow cytometry. Expression of markers of adipogenesis, osteogenesis, chondrogenesis, neurogenesis, and differentiation into endothelial lineages was determined with use of immunostaining, cytohistological staining, and reverse transcription-polymerase chain reaction.

RESULTS

Anulus fibrosus cells expressed several of the cell surface antigens that are sometimes associated with mesenchymal stem cells, including CD29, CD49e, CD51, CD73, CD90, CD105, CD166, CD184, and Stro-1, and two neuronal stem cell markers, nestin and neuron-specific enolase. Furthermore, varying the stimulants added to the induction media determined whether anulus fibrosus cells differentiated into adipocytes, osteoblasts, chondrocytes, neurons, or endothelial cells.

CONCLUSIONS

Anulus fibrosus cells isolated from nondegenerative intervertebral discs can differentiate into adipocytes, osteoblasts, chondrocytes, neurons, and endothelial cells in vitro.