Azusa Maeda

CCN family 2/connective tissue growth factor modulates BMP signalling as a signal conductor, which action regulates the proliferation and differentiation of chondrocytes

Both CCN family 2/connective tissue growth factor (CCN2/CTGF) and bone morphogenetic protein (BMP)-2 play an important role in cartilage metabolism. We evaluated whether or not CCN2 would interact with BMP-2, and examined the combination effect of CCN2 with BMP-2 (CCN2-BMP-2) on the proliferation and differentiation of chondrocytes. Immunoprecipitation-western blotting analysis, solid-phase binding assay and surface plasmon resonance (SPR) spectroscopy showed that CCN2 directly interacted with BMP-2 with a dissociation constant of 0.77 nM as evaluated by SPR. An in vivo study revealed that CCN2 was co-localized with BMP-2 at the pre-hypertrophic region in the E18.5 mouse growth plate. Interestingly, CCN2-BMP-2 did not affect the BMP-2/CCN2-induced phosphorylation of p38 MAPK but caused less phosphorylation of ERK1/2 in cultured chondrocytes. Consistent with these results, cell proliferation assay showed that CCN2-BMP-2 stimulated cell growth to a lesser degree than by either CCN2 or BMP-2 alone, whereas the expression of chondrocyte marker genes and proteoglycan synthesis, representing the mature chondrocytic phenotype, was increased collaboratively by CCN2-BMP-2 treatment in cultured chondrocytes. These findings suggest that CCN2 may regulate the proliferating and differentiation of chondrocytes by forming a complex with BMP-2 as a novel modulator of BMP signalling.

CCN family 2/connective tissue growth factor (CCN2/CTGF) regulates the expression of Vegf through Hif-1α expression in a chondrocytic cell line, HCS-2/8, under hypoxic condition

Vascular endothelial growth factor (VEGF) is essential for establishing vascularization and regulating chondrocyte development and survival. We have demonstrated that VEGF regulates the expression of CCN2/connective tissue growth factor (CCN2/CTGF) an essential mediator of cartilage development and angiogenesis, suggesting that CCN2 functions in down-stream of VEGF, and that VEGF function is mediated in part by CCN2. On the other hand, the phenotype of Ccn2 mutant growth plates, which exhibit decreased expression of VEGF in the hypertrophic zone, indicates that Vegf expression is dependent on Ccn2 expression as well. Therefore, we investigated the molecular mechanisms underlying the induction of VEGF by CCN2 using a human chondrocytic cell line, HCS-2/8. Hypoxic stimulation (5% O(2)) of HCS-2/8 cells increased VEGF mRNA levels by approximately 8 fold within 6 h as compared with the cells cultured under normoxia. In addition, VEGF expression was further up-regulated under hypoxia in HCS-2/8 cells transfected with a Ccn2 expression plasmid. Hypoxia-inducible factor (HIF)-1alpha mRNA and protein levels were increased by stimulation with recombinant CCN2 (rCCN2). Furthermore, the activity of a VEGF promoter that contained a HIF-1 binding site was increased in HCS-2/8, when the cells were stimulated by rCCN2. These results suggest that CCN2 regulates the expression of VEGF at a transcriptional level by promoting HIF-1alpha activity. In fact, HIF-1alpha was detected in the nuclei of proliferative and pre-hypertrophic chondrocytes of wild-type mice, whereas it was not detected in Ccn2 mutant chondrocytes in vivo. This activation cascade from CCN2 to VEGF may therefore play a critical role in chondrocyte development and survival.

Biglycan modulates angiogenesis and bone formation during fracture healing.

Matrix proteoglycans such as biglycan (Bgn) dominate skeletal tissue and yet its exact role in regulating bone function is still unclear. In this paper we describe the potential role of (Bgn) in the fracture healing process. We hypothesized that Bgn could regulate fracture healing because of previous work showing that it can affect normal bone formation. To test this hypothesis, we created fractures in femurs of 6-week-old male wild type (WT or Bgn+/0) and Bgn-deficient (Bgn-KO or Bgn-/0) mice using a custom-made standardized fracture device, and analyzed the process of healing over time. The formation of a callus around the fracture site was observed at both 7 and 14 days post-fracture in WT and Bgn-deficient mice and immunohistochemistry revealed that Bgn was highly expressed in the fracture callus of WT mice, localizing within woven bone and cartilage. Micro-computed tomography (μCT) analysis of the region surrounding the fracture line showed that the Bgn-deficient mice had a smaller callus than WT mice. Histology of the same region also showed the presence of less cartilage and woven bone in the Bgn-deficient mice compared to WT mice. Picrosirius red staining of the callus visualized under polarized light showed that there was less fibrillar collagen in the Bgn-deficient mice, a finding confirmed by immunohistochemistry using antibodies to type I collagen. Interestingly, real time RT-PCR of the callus at 7 days post-fracture showed a significant decrease in relative vascular endothelial growth factor A (VEGF) gene expression by Bgn-deficient mice as compared to WT. Moreover, VEGF was shown to bind directly to Bgn through a solid-phase binding assay. The inability of Bgn to directly enhance VEGF-induced signaling suggests that Bgn has a unique role in regulating vessel formation, potentially related to VEGF storage or stabilization in the matrix. Taken together, these results suggest that Bgn has a regulatory role in the process of bone formation during fracture healing, and further, that reduced angiogenesis could be the molecular basis.

WISP1/CCN4: A Potential Target for Inhibiting Prostate Cancer Growth and Spread to Bone

Prostate cancer (PC) is a leading cause of death in men however the factors that regulate its progression and eventual metastasis to bone remain unclear. Here we show that WISP1/CCN4 expression in prostate cancer tissues was up-regulated in early stages of the disease and, further, that it correlated with increased circulating levels of WISP1 in the sera of patients at early stages of the disease. WISP1 was also elevated in the mouse prostate cancer model TRAMP in the hypoplastic diseased tissue that develops prior to advanced carcinoma formation. When the ability of anti-WISP1 antibodies to reduce the spread of PC3-Luc cells to distant sites was tested it showed that twice weekly injections of anti-WISP1 antibodies reduced the number and overall size of distant tumors developed after intracardiac (IC) injection of PC3-Luc cells in mice. The ability of antibodies against WISP1 to inhibit growth of PC3-Luc cancer cells in mice was also evaluated and showed that twice weekly injections of anti-WISP1 antibodies reduced local tumor growth when examined in xenografts. To better understand the mechanism of action, the migration of PC3-Luc cells through membranes with or without a Matrigel™ barrier showed the cells were attracted to WISP1, and that this attraction was inhibited by treatment with anti-WISP1 antibodies. We also show the expression of WISP1 at the bone-tumor interface and in the stroma of early grade cancers suggested WISP1 expression is well placed to play roles in both fostering growth of the cancer and its spread to bone. In summary, the up-regulation of WISP1 in the early stages of cancer development coupled with its ability to inhibit spread and growth of prostate cancer cells makes it both a potential target and an accessible diagnostic marker for prostate cancer.

Effect of CCN2 on FGF2-Induced Proliferation and MMP9 and MMP13 Productions by Chondrocytes

CCN2 (also known as connective tissue growth factor) interacts with several growth factors involved in endochondral ossification via its characteristic four modules and modifies the effect of such growth factors. Presently we investigated whether CCN2 interacts with fibroblast growth factor 2 (FGF2). Solid-phase binding assay, immunoprecipitation-Western blot analysis, and surface plasmon resonance (SPR) spectroscopy revealed that the C-terminal module of CCN2 (CT) directly bound to FGF2 with a dissociation constant of 5.5 nm. Next, we examined the combinational effects of CCN2 and FGF2 on the proliferation of and matrix metalloproteinase (MMP)-9 and -13 productions by cultured chondrocytes. FGF2 promoted not only the proliferation but also the production of MMP9 and -13, however, combined of FGF2 with CT module nullified the enhancement of both MMP productions and proliferation. To clarify the mechanism, we investigated the binding of CCN2 or its CT module to FGF receptor 1. As a result, we found that CCN2 bound to FGF receptor 1 with a dissociation constant of 362 nm, whereas the CT module did not. In addition, when we tested FGF signaling in chondrocytic HCS-2/8 cells stimulated by the combination of FGF2 with CT module, the level of ERK1/2, p38 MAPK, and c-Jun N-terminal kinase phosphorylation was decreased compared with that found with FGF2 alone. These findings suggest that CCN2 may regulate the proliferation and matrix degradation of chondrocytes by forming a complex with FGF2 as a novel modulator of FGF2 functions.

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

Background: WISP1 is expressed in bone, but its roles in osteogenesis are unclear. Results: WISP1 regulates bone mineral content, cortical and trabecular bone thickness, and bone strength during aging by modulating osteoblast and osteoclast function and Wnt signaling. Conclusion: WISP1 controls bone integrity by regulating bone turnover. Significance: WISP1 is a novel target for modulating bone turnover and improving bone strength. 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.

Role of mechanical-stress inducible protein Hcs24/CTGF/CCN2 in cartilage growth and regeneration: Mechanical stress induces expression of Hcs24/CTGF/CCN2 in a human chondrocytic cell line HCS-2/8, rabbit costal chondrocytes and meniscus tissue cells

Mechanical stress plays an important role in the cartilage metabolism. The aim of this study is to determine the influence of mechanical load magnitude and frequency on cartilage metabolism in terms of the expression of hypertrophic chondrocyte-specific gene product 24/connective tissue growth factor/CCN family 2 (Hcs24/CTGF/CCN2), as an essential mediator of extracellular matrix (ECM) production. When a human chondrocytic cell line, HCS-2/8 was exposed to uni-axial cyclic mechanical force (6% elongation, 10 times/min) only for 30 min, the expression level of Hcs24/CTGF/CCN2 (CCN2) increased, and c-Jun N-terminal protein kinase (JNK) was activated. These findings suggest that stretch-induced CCN2 may be mediated by the JNK pathway. When HCS-2/8 cells were subjected to cyclic tension force at 15 kPa, 30 cycles/min, which has been reported to be a degradation force for HCS-2/8 cells, the expressions of CCN2 and aggrecan were inhibited, and such expressions remained unchanged in rabbit hyaline costal cartilage cells. However, these expressions increased in rabbit meniscus tissue cells. These findings suggest that the sensitivity of mechanical stretch may be different depending on the type of cells. Furthermore, CCN2 was co-localized with aggrecan in this meniscus tissue region exposed to mechanical stress in vivo. These findings suggest that CCN2 induced by mechanical stress may therefore play some role in meniscus growth and regeneration.

Biglycan potentially regulates angiogenesis during fracture repair by altering expression and function of endostatin

The small proteoglycan biglycan (Bgn) is highly expressed in the organic matrix of bone and plays a role in bone formation. Previous work implicated Bgn in vessel growth during bone healing [1]. By infusing barium sulfate (BaSO4) into WT and Bgn-deficient mice we discovered the positive effect of Bgn in modulating angiogenesis during fracture healing. Using micro-computed tomography angiography we found significant differences in the vessel size and volume among other parameters. To further understand the mechanistic basis for this, we explored the relationship between Bgn and the anti-angiogenic protein endostatin. Immunohistochemistry (IHC) showed co-localization of Bgn and endostatin in regions of bone formation, with increased endostatin staining in Bgn-KO compared to WT at 14days post-fracture. To further elucidate the relationship between Bgn and endostatin, an endothelial cell tube formation assay was used. This study showed that endothelial cells treated with endostatin had significantly decreased vessel length and vessel branches compared to untreated cells, while cells treated with endostatin and Bgn at a 1:1M ratio had vessel length and vessel branches comparable to untreated cells. This indicated that Bgn was able to mitigate the inhibitory effect of endostatin on endothelial cell growth. In summary, these results suggest that Bgn is needed for proper blood vessel formation during fracture healing, and one mechanism by which Bgn impacts angiogenesis is through inhibition of endostatin.

CCN4/WISP-1 positively regulates chondrogenesis by controlling TGF-β3 function

The CCN family of proteins plays important roles in development and homeostasis of bone and cartilage. To understand the role of CCN4 in chondrogenesis, human bone marrow stromal cells (hBMSCs) were transduced with CCN4 adenovirus (adCCN4) or siRNA to CCN4 (siCCN4) in the presence or absence of transforming growth factor-β3 (TGF-β3). Overexpression of CCN4 enhanced TGF-β3-induced SMAD2/3 phosphorylation and chondrogenesis of hBMSCs in an in vitro assay using a micromass culture model. On the other hand, knockdown of CCN4 inhibited the TGF-β3-induced SMAD2/3 phosphorylation and synthesis of cartilage matrix in micromass cultures of hBMSCs. Immunoprecipitation-western blot analysis revealed that CCN4 bound to TGF-β3 and regulated the ability of TGF-β3 to bind to hBMSCs. In vivo analysis confirmed there was a significant decrease in the gene expression levels of chondrocyte markers in cartilage samples from Ccn4-knock out (KO) mice, compared to those from wild type (WT) control. In order to investigate the regenerative properties of the articular cartilage in Ccn4-KO mice, articular cartilage defects were surgically performed in the knee joints of young mice, and the results showed that the cartilage was partially repaired in WT mice, but not in Ccn4-KO mice. In conclusion, these results show, for the first time, that CCN4 has a positive influence on chondrogenic differentiation by modulating the effects of TGF-β3.

CCN4/WISP1 controls cutaneous wound healing by modulating proliferation, migration and ECM expression in dermal fibroblasts via α5β1 and TNFα

Understanding the mechanisms that control cutaneous wound healing is crucial to successfully manage repair of damaged skin. The goal of the current study was to uncover novel extracellular matrix (ECM) components that control the wound healing process. Full thickness skin defects were created in mice and used to show CCN4 up-regulation during wound-healing as early as 1u202fday after surgery, suggesting a role in inflammation and subsequent dermal migration and proliferation. To determine how CCN4 could regulate wound healing we used Ccn4-KO mice and showed they had delayed wound closure accompanied by reduced expression of Col1a1 and Fn mRNA. Boyden chamber assays using Ccn4-deficient dermal fibroblasts showed they have reduced migration and proliferation compared to WT counterparts. To confirm CCN4 has a role in proliferation and migration of dermal cells, siRNA knockdown and transduction of CCN4 adenoviral transduction were used and resulted in reduced or enhanced migration of human adult dermal fibroblast (hADF) cells respectively. The induced migration of the dermal fibroblasts by CCN4 appears to work via α5β1 integrin receptors that further stimulates down-stream ERK/JNK signaling. The regulation of CCN4 by TNF-α prompted us look further at their potential relationship. Treatment of hADFs with CCN4 and TNF-α alone or together showed CCN4 counteracted the inhibition of TNF-α on COL1A1 and FN mRNA expression and the stimulation of TNF-α on MMP-1 and MMP3 mRNA expression. CCN4 appeared to counterbalance the effects of TNF-α by inhibiting downstream NF-κB/p-65 signaling. Taken together we show CCN4 stimulates dermal fibroblast cell migration, proliferation and inhibits TNF-α stimulation, all of which could regulate wound healing.