Regulation of collagen deposition and lysyl oxidase by tumor necrosis factor-alpha in osteoblasts

Myeloproliferative Disorders and its Effect on Bone Homeostasis: The Role of Megakaryocytes

Myeloproliferative Neoplasms (MPNs) are a heterogeneous group of chronic hematological diseases that arise from the clonal expansion of abnormal hematopoietic stem cells, of which Polycythemia Vera (PV), Essential Thrombocythemia (ET), and Primary Myelofibrosis (PMF) have been extensively reviewed in context of clonal expansion, fibrosis and other phenotypes. Here, we review current knowledge on the influence of different forms of MPN on bone health. Studies implicated various degrees of effect of different forms of MPN on bone density, and on osteoblast proliferation and differentiation, using murine models and human data. The majority of studies show that bone volume is generally increased in PMF patients, whereas it is slightly decreased or not altered in ET and PV patients, although possible differences between male and female phenotypes were not fully explored in most MPN forms. Osteosclerosis seen in PMF patients is a serious complication that can lead to bone marrow failure, and the loss of bone reported in some ET and PV patients can lead to osteoporotic fractures. Some MPN forms are associated with increased number of megakaryocytes (MKs), and several of the MK-associated factors in MPN are known to affect bone development. Here, we review known mechanisms involved in these processes, with focus on the role of MKs and secreted factors. Understanding MPN-associated changes in bone health could improve early intervention and treatment of this side effect of the pathology.

The effect of TNF-α on osteoblasts in metal wear-induced periprosthetic bone loss

Aims

This study aimed to examine the effects of tumour necrosis factor-alpha (TNF-α) on osteoblasts in metal wear-induced bone loss.

Methods

TNF-α immunoexpression was examined in periprosthetic tissues of patients with failed metal-on-metal hip arthroplasties and also in myeloid MM6 cells after treatment with cobalt ions. Viability and function of human osteoblast-like SaOs-2 cells treated with recombinant TNF-α were studied by immunofluorescence, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay, western blotting, and enzyme-linked immunosorbent assay (ELISA).

Results

Macrophages, lymphocytes, and endothelial cells displayed strong TNF-α immunoexpression in periprosthetic tissues containing metal wear debris. Colocalization of TNF-α with the macrophage marker CD68 and the pan-T cell marker CD3 confirmed TNF-α expression in these cells. Cobalt-treated MM6 cells secreted more TNF-α than control cells, reflecting the role of metal wear products in activating the TNF-α pathway in the myeloid cells. While TNF-α did not alter the immunoexpression of the TNF-receptor 1 (TNF-R1) in SaOs-2 cells, it increased the release of the soluble TNF-receptor 1 (sTNF-R1). There was also evidence for TNF-α-induced apoptosis. TNF-α further elicited the expression of the endoplasmic reticulum stress markers inositol-requiring enzyme (IRE)-1α, binding-immunoglobulin protein (BiP), and endoplasmic oxidoreductin1 (Ero1)-Lα. In addition, TNF-α decreased pro-collagen I α 1 secretion without diminishing its synthesis. TNF-α also induced an inflammatory response in SaOs-2 cells, as evidenced by the release of reactive oxygen and nitrogen species and the proinflammatory cytokine vascular endothelial growth factor.

Conclusion

The results suggest a novel osteoblastic mechanism, which could be mediated by TNF-α and may be involved in metal wear debris-induced periprosthetic bone loss.

Cite this article: Bone Joint Res 2020;9(11):827–839.

Lysyl oxidase inhibits TNF-α induced rat nucleus pulposus cell apoptosis via regulating Fas/FasL pathway and the p53 pathways

AIMS

Intervertebral disc degeneration (IVDD) has been regarded as the main cause of low back pain, which affects 80% of adults and still lack effective treatment. In IVDD, nucleus pulposus (NP) cell apoptosis has widely existed. Lysyl oxidase (LOX) has been demonstrated to protect chondrocyte against apoptosis in the TNF-α-treated human chondrocytes. Therefore, in this study, we investigated the anti-apoptosis effect of LOX on TNF-α-treated rat NP cells.

MAIN METHODS

Real-time quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and western blot analyses were used to detect the expression of LOX in TNF-α-treated rat NP cells. Then, the toxicity of exogenous LOX and its protective effect was evaluated by Cell Counting kit-8 (CCK-8). NP cell apoptosis was evaluated by flow cytometry analysis and TUNEL assay. The regulatory effects of LOX on the expression of extracellular matrix (ECM) molecules in TNF-α-treated rat NP cells were measured by RT-qPCR, western blot, and ELISA analyses. The molecular mechanism of LOX in regulating NP cell apoptosis was investigated by RT-qPCR and western blot analyses.

KEY FINDINGS

The expression of LOX in TNF-α-treated rat NP cells was significantly decreased. Exogenous LOX preserved the cell viability, reduced the rate of apoptosis and improved the ECM secretion in TNF-α-treated rat NP cells. Further molecular mechanism investigation showed that LOX inhibited the Fas/FasL and p53 pathways.

SIGNIFICANCES

LOX played an anti-apoptotic role in TNF-α-treated rat NP cells which could be a promising reagent in IVDD treatment.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

Tocotrienol-rich fraction from annatto ameliorates expression of lysyl oxidase in human osteoblastic MG-63 cells

Lysyl oxidase (LOX) is required for the formation of bone collagen cross-links. Inactivation of the LOX gene in osteoblasts by DNA methylation and JAK signaling has been reported to cause loss of cross-links and an increased risk of fractures. Tocotrienols (T3s) have proven benefits on bone strength, but their potential effects on LOX remain largely unknown. Thus, the present study investigates the in vitro effects of T3s on LOX expression in human osteoblastic MG-63 cells. Results indicated that Tocotrienol-Rich Fraction (TRF), the δ-T3 rich oil extracted from Annatto was the most effective and significantly increased LOX expression. TRF treatment decreased de-novo methyltransferases (DNMTs), DNMT3A and DNMT3B levels. In addition, TRF significantly inhibited JAK2 activation and decreased expression of Fli1, a transcription factor of DNMTs. We conclude that TRF induced an increase in LOX expression via inhibition of de-novo methylation and reduction of Fli1 expression by the inactivation of JAK2.Abbreviations: CpG: cytosine-guanine dinucleotide; DNMT: DNA methyltransferase; Fli1: friend leukemia virus integration 1; JAK: janus kinase; LOX: lysyl oxidase; PCR: polymerase chain reaction; STAT: signal transducers and activators of transcription; T3s: tocotrienols; TPs: tocopherols; TRF: Tocotrienol-Rich Fraction.

Cartilage oligomeric matrix protein participates in the pathogenesis of liver fibrosis

BACKGROUND & AIMS

Liver fibrosis is characterized by significant accumulation of extracellular matrix (ECM) proteins, mainly fibrillar collagen-I, as a result of persistent liver injury. Cartilage oligomeric matrix protein (COMP) is largely found in the ECM of skeletal tissue. Increased COMP expression has been associated with fibrogenesis in systemic sclerosis, lung fibrosis, chronic pancreatitis, cirrhosis and hepatocellular carcinoma. We hypothesized that COMP could induce fibrillar collagen-I deposition and participate in matrix remodeling thus contributing to the pathophysiology of liver fibrosis.

METHODS

Thioacetamide (TAA) and carbon tetrachloride (CCl4) were used to induce liver fibrosis in wild-type (WT) and Comp-/- mice. In vitro experiments were performed with primary hepatic stellate cells (HSCs).

RESULTS

COMP expression was detected in livers from control WT mice and was upregulated in response to either TAA or CCl4-induced liver fibrosis. TAA-treated or CCl4-injected Comp-/- mice showed less liver injury, inflammation and fibrosis compared to their corresponding control WT mice. Challenge of HSCs with recombinant COMP (rCOMP) induced intra- plus extracellular collagen-I deposition and increased matrix metalloproteinases (MMPs) 2, 9 and 13, albeit similar expression of transforming growth factor beta (TGFβ) protein, in addition to Tgfβ, tumour necrosis factor alpha (Tnfα) and tissue inhibitor of metalloproteinases-1 (Timp1) mRNAs. We demonstrated that COMP binds collagen-I; yet, it does not prevent collagen-I cleavage by MMP1. Last, rCOMP induced collagen-I expression in HSCs via CD36 receptor signaling and activation of the MEK1/2-pERK1/2 pathway.

CONCLUSION

These results suggest that COMP contributes to liver fibrosis by regulating collagen-I deposition.

LAY SUMMARY

Cartilage oligomeric matrix protein (COMP) induces fibrillar collagen-I deposition via the CD36 receptor signaling and activation of the MEK1/2-pERK1/2 pathway, and participates in extracellular matrix remodeling contributing to the pathophysiology of liver fibrosis.

Revealing cytokine-induced changes in the extracellular matrix with secondary ion mass spectrometry

Cell-secreted matrices (CSMs), where extracellular matrix (ECM) deposited by monolayer cell cultures is decellularized, have been increasingly used to produce surfaces that may be reseeded with cells. Such surfaces are useful to help us understand cell-ECM interactions in a microenvironment closer to the in vivo situation than synthetic substrates with adsorbed proteins. We describe the production of CSMs from mouse primary osteoblasts (mPObs) exposed to cytokine challenge during matrix secretion, mimicking in vivo inflammatory environments. Time-of-flight secondary ion mass spectrometry data revealed that CSMs with cytokine challenge at day 7 or 12 of culture can be chemically distinguished from one another and from untreated CSM using multivariate analysis. Comparison of the differences with reference spectra from adsorbed protein mixtures points towards cytokine challenge resulting in a decrease in collagen content. This is supported by immunocytochemical and histological staining, demonstrating a 44% loss of collagen mass and a 32% loss in collagen I coverage. CSM surfaces demonstrate greater cell adhesion than adsorbed ECM proteins. When mPObs were reseeded onto cytokine-challenged CSMs they exhibited reduced adhesion and elongated morphology compared to untreated CSMs. Such changes may direct subsequent cell fate and function, and provide insights into pathological responses at sites of inflammation.

Comparison of osteogenic differentiation of embryonic stem cells and primary osteoblasts revealed by responses to IL-1β, TNF-α, and IFN-γ

There are well-established approaches for osteogenic differentiation of embryonic stem cells (ESCs), but few show direct comparison with primary osteoblasts or demonstrate differences in response to external factors. Here, we show comparative analysis of in vitro osteogenic differentiation of mouse ESC (osteo-mESC) and mouse primary osteoblasts. Both cell types formed mineralized bone nodules and produced osteogenic extracellular matrix, based on immunostaining for osteopontin and osteocalcin. However, there were marked differences in the morphology of osteo-mESCs and levels of mRNA expression for osteogenic genes. In response to the addition of proinflammatory cytokines interleukin-1β, tumor necrosis factor-α, and interferon-γ to the culture medium, primary osteoblasts showed increased production of nitric oxide (NO) and prostaglandin E2 (PGE2) at early time points and decreases in cell viability. In contrast, osteo-mESCs maintained viability and did not produce NO and PGE2 until day 21. The formation of bone nodules by primary osteoblasts was reduced markedly after cytokine stimulation but was unaffected in osteo-mESCs. Cell sorting of osteo-mESCs by cadherin-11 (cad-11) showed clear osteogenesis of cad-11(+) cells compared to unsorted osteo-mESCs and cad-11(-) cells. Moreover, the cad-11(+) cells showed a significant response to cytokines, similar to primary osteoblasts. Overall, these results show that while osteo-mESC cultures, without specific cell sorting, show characteristics of osteoblasts, there are also marked differences, notably in their responses to cytokine stimuli. These findings are relevant to understanding the differentiation of stem cells and especially developing in vitro models of disease, testing new drugs, and developing cell therapies.

TNF-α induced down-regulation of lysyl oxidase family in anterior cruciate ligament and medial collateral ligament fibroblasts

BACKGROUND

The lysyl oxidase (LOX) family has the capacity to catalyze the cross-linking of collagen and elastin, implicating its important fundamental role in injury healing. Tumor necrosis factor alpha (TNF-α) is considered to be an important chemical mediator in the acute inflammatory phase of the ligament injury. The role of the lysyl oxidase family induced by TNF-α in the knee ligaments' wound healing process is poorly understood. Our purpose was to determine the different expressions of the LOXs in poorly self-healing anterior cruciate ligament (ACL) and well functionally self-healing medial collateral ligament (MCL) induced by TNF-α.

METHODS

Semi-quantitative PCR, quantitative real-time PCR and western blot were performed for original research.

RESULTS

The results showed that all LOX family members were expressed at higher levels in MCL than those in ACL fibroblasts; the significant differences existed in the down-regulations of the LOXs induced by TNF-α; and the TNF-α-mediated down-regulations of the LOXs were more prominent in ACL than those in MCL fibroblasts. 1-20 ng/ml TNF-α down-regulated mRNA levels in ACL and MCL fibroblasts by up to 76% and 58% in LOX; 90% and 45% in LOXL-1; 97.5% and 90% in LOXL-2; 89% and 68% in LOXL-3; 52% and 25% in LOXL-4, respectively. Protein assay also showed LOXs had lower expressions in ACL than those in MCL.

CLINICAL RELEVANCE

Based on these results, the differential expressions of the LOXs might help to explain the intrinsic differences between the poorly self-healing ACL and well functionally self-healing MCL.

Effects of silicon on osteoblast activity and bone mineralization of MC3T3-E1 cells

Previous studies have reported that dietary silicon (Si) intake is positively associated with bone health including bone mineral density. Although the amount of Si intake is high among trace elements in humans, how dietary Si affects bone formation at the cellular level is not well addressed. The purpose of this study was to investigate the role of Si in osteoblast activity and bone mineralization. MC3T3-E1 was cultured as mature osteoblasts and treated with sodium metasilicate (0, 1, 5, 10, 25, 50, and 100 μM) as a source of Si. After 7 days of treatment, 5 and 10 μM of sodium metasilicate significantly increased intracellular alkaline phosphatase activity (p < 0.05) when compared to the control. Additionally, all doses of sodium metasilicate (1, 5, 10, 25, 50, and 100 μM) increased mineralized nodule formation at 14 days of differentiation as evidenced by increased Alizarin Red S staining. In the analysis of gene expression, 50 μM of sodium metasilicate upregulated type I collagen (COL-I) compared to the control group. However, the increase of COL-I gene expression as a result of treatment with 1, 10, 25, and 100 μM of sodium metasilicate did not reach statistical significance. mRNA expression of insulin-like growth factor-I and receptor activator of NF-κB ligand was not significantly changed at any dose of sodium metasilicate (0, 1, 5, 10, 25, 50, and 100 μM). In light of the results, we conclude that Si has a positive effect on bone metabolism by enhancing osteoblast mineralization activity.

High glucose induced differential expression of lysyl oxidase and its isoform in ARPE-19 cells

PURPOSE

Lysyl oxidase (LOX) stabilizes the extracellular matrix (ECM) by cross-linking collagen and elastin molecules. In proliferative diabetic retinopathy (PDR), there is ECM remodeling with neovascularization and basement membrane changes. While protease activities are well reported, the role of LOX in the pathogenesis of diabetic retinopathy is less studied. This study was done to see the effect of high glucose on the activity and expression of LOX and its isoforms in ARPE-19 cells.

MATERIALS AND METHODS

ARPE-19 cells were exposed to high glucose up to 48 h, and LOX activity was determined by N-acetyl-3,7-dihydroxyphenoxazine assay. The mRNA expression of LOX and its isoforms was done by real-time PCR and the protein expression by ELISA. Immunohistochemistry for LOX was done in epiretinal membrane from PDR.

RESULTS

With an increase in glucose concentration LOX activity and protein was reduced significantly at 30 mM glucose at 48 h. mRNA expression of LOX, LOXL1, and LOXL2 varied with time and concentration of glucose. Vascular endothelial growth factor (VEGF) increased the LOX activity as well as the mRNA expression. Pigment epithelium-derived factor (PEDF) downregulated the mRNA expression of LOX, LOXL1, and LOXL2. The matrix metalloprotease (MMP) activity increased significantly with the increase in glucose concentration. The diabetic neovascular membrane showed increased immunostaining of LOX.

CONCLUSIONS

This study suggests that although the LOX activity, which is composite of all the isoforms, was reduced under high glucose conditions, there was a differential mRNA expression with increased LOX and LOXL1 and decreased LOXL2 expression.

Pyrene exposure influences the craniofacial cartilage development of Sebastiscus marmoratus embryos

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants, which are known carcinogens and teratogens. However, the toxicity of PAHs during skeletal development and the mechanism involved are not completely clear. In the present study, rockfish (Sebastiscus marmoratus) embryos were exposed to pyrene (Pyr) for 7 days at 0.5, 5 and 50 nM which resulted in craniofacial skeleton deformities. Pyr exposure for 6 days reduced the expression of PCNA, Col2a1 and Sox9 in the craniofacial skeleton revealed using in situ hybridization. These results suggest that Pyr exposure impairs skeleton development via disrupting the proliferation of the chondrocytes. At the same time, Pyr exposure reduced the expression of lox1 and inhibited the activity of lysyl oxidase, which is the key enzyme controlling the collagen cross-linking, and which might therefore have been one of the reasons for the deformative Meckel's cartilage (lower jaw).

Adventitial fibroblast abormality in thoracic aortic aneurysms and aortic dissections

BACKGROUND

Development of thoracic aortic aneurysms and aortic dissections (TAAD) is attributed to unbearable wall tension superimposed on defective aortic wall integrity and impaired aortic repair mechanisms. Central to this repair mechanisms are well-balanced and adequately functional cellular components of the aortic wall, including endothelial cells, smooth muscle cells (SMCs), inflammatory cells, and adventitial fibroblasts. Adventitial fibroblasts naturally produce aortic extracellular matrix (ECM), and, when aortic wall is injured, they can be transformed into SMCs, which in turn are involved in aortic remodeling. We postulated the hypothesis that adventitial fibroblasts in patients with TAAD may have defects in ECM production and SMC transformation.

MATERIALS AND METHODS

Adventitial fibroblasts were procured from the adventitial layer of fresh aortic tissues of patients with TAAD (Group I) and of multi-organ donors (Group II), and 4-passage cell culture was performed prior to the experiment. To assess ECM production, cells were treated with TNF-α (50 pM) and the expression of MMP-2 / MMP-3 was analyzed using western blot technique. To assess SMC transformation capacity, cells were treated with TGF-β1 and expression of SM α-actin, SM-MHC, Ki-67 and SM calponin was evaluated using western blot technique. Fibroblasts were then treated with TGF-β1 (10 pM) for up to 10 days with TGF-β1 supplementation every 2 days, and the proportion of transformed SMC in the cell line was measured using immunofluorescence assay for fibroblast surface antigen every 2 days.

RESULTS

MMP-3 expression was significantly lower in group I than in group II. TGF-β1-stimulated adventitial fibroblasts in group I expressed less SM α-actin, SM-MHC, and Ki-67 than in group II. SM-calponin expression was not different between the two groups. Presence of fibroblast was observed on immunofluorescence assay after more than 6 days of TGF-β1 treatment in group I, while most fibroblasts were transformed to SMC within 4 days in group II.

CONCLUSION

ECM production and SMC transformation are compromised in adventitial fibroblasts from patients with TAAD. This result suggests that functional restoration of adventitial fibroblasts could well be a novel approach for the prevention and treatment of TAAD.

Highly osteogenic PDL stem cell clones specifically express elevated levels of ICAM1, ITGB1 and TERT

Cells derived from the periodontal ligament (PDL) have previously been reported to have stem cell-like characteristics (PDL stem cells; PDLSCs) and play an important part in bone engineering, including that of alveolar bone. However, these populations have been heterogeneous, and thus far no specific marker has yet been established from adult human stem cells derived from PDL tissue. We have previously isolated highly purified single cell-derived PDLSC clones and delineated their phenotypic and functional characteristics. In this report, we further obtained three homogeneous and distinct PDLSC clones demonstrating low, moderate and high mineralized matrix forming ability-namely PC12, PC4 and PC3, respectively, and the expression of mesenchymal stem cell pathway-specific genes in these clones was investigated. PCR array revealed that the expression of intercellular adhesion molecule 1 (ICAM1), integrin beta 1 (ITGB1) and telomerase reverse transcriptase (TERT) was associated with highly osteogenic PDLSC clones, as determined by the expression of key osteoblastic markers and their ability to form alizarin red S positive mineralized matrix in vitro. The present results suggest that these three mesenchymal stem cell-associated markers could potentially be used to isolate PDLSCs with high osteogenic capability for engineering new bone.

Lysyl oxidase (lox) gene deficiency affects osteoblastic phenotype

Lysyl oxidase (LOX) catalyzes cross-linking of elastin and collagen, which is essential for the structural integrity and function of bone tissue. The present study examined the role of Lox gene deficiency for the osteoblast phenotype in primary calvarial osteoblasts from E18.5 Lox knockout (Lox ( -/- )) and wild type (wt) (C57BL/6) mice. Next to Lox gene depletion, mRNA expression of Lox isoforms, LOXL1-4, was significantly downregulated in Lox ( -/- ) bone tissue. A significant decrease of DNA synthesis of Lox ( -/- ) osteoblasts compared to wt was found. Early stages of osteoblastic apoptosis studied by annexin-V binding as well as later stages of DNA fragmentation were not affected. However, mineral nodule formation and osteoblastic differentiation were markedly decreased, as revealed by significant downregulation of osteoblastic markers, type I collagen, bone sialoprotein, and Runx2/Cbfa1.

MMPs/TIMPs and inflammatory signalling de-regulation in human incisional hernia tissues

Background: Incisional hernia is a common and important complication of laparotomies. Epidemiological studies allude to an underlying biological cause, at least in a subset of population. Interest has mainly focused on abnormal collagen metabolism. However, the role played by other determinants of extracellular matrix (ECM) composition is unknown. To date, there are few laboratory studies investigating the importance of biological factors contributing to incisional hernia development. We performed a descriptive tissue-based analysis to elucidate the possible relevance of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in association with local cytokine induction in human incisional hernia tissues. The expression profiles of MMPs, TIMPs and pro-inflammatory cytokine signalling were investigated in aponeurosis and skeletal muscle specimens taken intraoperatively from incisional hernia (n= 10) and control (n= 10) patients. Semiquantitative RT-PCR, zymography and immunoblotting analyses were done. Incisional hernia samples displayed alterations in the microstructure and loss of ECM, as assessed by histological analyses. Moreover, incisional hernia tissues showed increased MMP/TIMP ratios and de-regulated inflammatory signalling (tumor necrosis factor [TNFA] and interleukin [IL]-6 tended to increase, whereas aponeurosis TNFA receptors decreased). The changes were tissue-specific and were detectable at the mRNA and/or protein level. Statistical analyses showed several associations between individual MMPs, TIMPs, interstitial collagens and inflammatory markers. The increment of MMPs in the absence of a counterbalance by TIMPs, together with an ongoing de-regulated inflammatory signalling, may contribute in inducing a functional defect of the ECM network by post-translational mechanisms, which may trigger abdominal wall tissue loss and eventual rupture. The notable TIMP3 protein down-regulation in incisional hernia fascia may be of pathophysiological significance. We conclude that this study may help to pinpoint novel hypotheses of pathogenesis that can lead to a better understanding of the disease and ultimately to improvement in current therapeutic approaches.

Dried plum polyphenols attenuate the detrimental effects of TNF-alpha on osteoblast function coincident with up-regulation of Runx2, Osterix and IGF-I

Previous studies have demonstrated that dried plums which contain high amounts of polyphenols can restore bone mass and structure, and significantly increase indices of bone formation. The purpose of this study was to determine how dried plum polyphenols influence osteoblast activity and mineralized nodule formation under normal and inflammatory conditions. MC3T3-E1 cells were plated and pretreated with dried plum polyphenols (0, 2.5, 5, 10 and 20 microg/ml) and 24 h later stimulated with TNF-alpha (0 or 1.0 ng/ml). The 5, 10 and 20 microg/ml doses of polyphenols significantly increased intracellular ALP activity under normal conditions at 7 and 14 days, and restored the TNF-alpha-induced suppression of intracellular ALP activity by 14 days (P<.001). Polyphenols also increased mineralized nodule formation under normal and inflammatory conditions. In the absence of TNF-alpha, 5 microg/ml of polyphenols significantly up-regulated the growth factor, IGF-I, compared to controls, and the 5 and 10 microg/ml doses increased the expression of lysyl oxidase involved in collagen crosslinking. TNF-alpha decreased the expression of Runx2, Osterix and IGF-I, and polyphenols restored their mRNA levels to that of the controls. Although TNF-alpha failed to alter lysyl oxidase at 18 h, the polyphenols up-regulated its expression (P<.05) in the presence of TNF-alpha. As expected, TNF-alpha up-regulated RANKL mRNA and polyphenols suppressed RANKL expression without altering OPG. Based on these findings, we conclude that dried plum polyphenols enhance osteoblast activity and function by up-regulating Runx2, Osterix and IGF-I and increasing lysyl oxidase expression, and at the same time attenuate osteoclastogenesis signaling.

Lysyl oxidase (LOX) down-regulation by TNFalpha: a new mechanism underlying TNFalpha-induced endothelial dysfunction

OBJECTIVE

TNFalpha is a pro-inflammatory cytokine that induces endothelial dysfunction and promotes atherosclerosis progression. Down-regulation of lysyl oxidase (LOX), a key enzyme in extracellular matrix maturation, by pro-atherogenic risk factors such as LDL and homocysteine, is associated with an impairment of endothelial barrier function. Our hypothesis is that the inflammatory cytokine TNFalpha could also modulate LOX expression/function in endothelial cells.

METHODS

The study was carried out in human umbilical vein endothelial cells (HUVEC), porcine aortic endothelial cells (PAEC) and bovine aortic endothelial cells (BAEC). LOX mRNA levels were analysed by real-time PCR and LOX activity was assessed by a high sensitive fluorescent assay. Promoter activity was determined by transient transfection using a luciferase reporter system.

RESULTS

TNFalpha decreases LOX mRNA levels in endothelial cells in a dose- and time-dependent manner. The effect of TNFalpha was observed at low concentrations (0.1-1 ng/mL) and was maximal at 2.5 ng/mL (after 21 h). In transfection assays, TNFalpha reduced LOX transcriptional activity to a similar extent than LOX mRNA. Furthermore, TNFalpha decreases endothelial LOX enzymatic activity. By using both TNF receptor (TNFR) agonist and blocking antibodies we determined the involvement of TNFR2 on LOX down-regulation. Moreover, while TNFR-associated factor-2 (TRAF-2) did not mediate signalling events leading to LOX inhibition, PKC inhibitors counteracted the TNFalpha-induced decrease of LOX mRNA levels. Finally, TNFalpha administration significantly reduced vascular LOX expression in rat aorta.

CONCLUSIONS

Endothelial dysfunction induced by TNFalpha is associated with a decrease of LOX expression/activity. Thus, LOX seems to be involved in the impairment of endothelial function triggered by different pathological conditions.

The protease domain of procollagen C-proteinase (BMP1) lacks substrate selectivity, which is conferred by non-proteolytic domains

Procollagen C-proteinase (PCP) removes the C-terminal pro-peptides of procollagens and also processes other matrix proteins. The major splice form of the PCP is termed BMP1 (bone morphogenetic protein 1). Active BMP1 is composed of an astacin-like protease domain, three CUB (complement, sea urchin Uegf, BMP1) domains and one EGF-like domain. Here we compare the recombinant human full-length BMP1 with its isolated proteolytic domain to further unravel the functional influence of the CUB and EGF domains. We show that the protease domain alone cleaves truncated procollagen VII within the short telopeptide region into fragments of similar size as the full-length enzyme does. However, unlike full-length BMP1, the protease domain does not stop at this point, but degrades its substrate completely. Moreover, the protease domain cleaves other matrix proteins such as fibronectin, collagen I and collagen IV, which are left intact by the full-length enzyme. In addition, we show for the first time that thrombospondin-1 is differently cleaved by both BMP1 and its catalytic domain. In summary, our data support the concept that the C-terminal domains of BMP1 are important for substrate recognition and for controlling and restricting its proteolytic activity via exosite binding.

Galanin treatment offsets the inhibition of bone formation and downregulates the increase in mouse calvarial expression of TNFalpha and GalR2 mRNA induced by chronic daily injections of an injurious vehicle

We have previously shown that after bone fracture, galanin (GAL) and GAL receptor expression is increased in osteoblast-like cells of callus; however, the role of elevated GAL/GAL receptors in this instance of bone injury is not known. We hypothesize that in injury, GAL may facilitate bone formation by suppressing the production of cytokines such as TNFalpha and IL-1alpha, thereby affecting bone collagen formation and collagenolysis by key matrix metalloproteinases (MMPs). In studies to explore this hypothesis, we used a mouse calvarial injection model to (1) investigate whether mild injury caused by a daily subcutaneous injection of a glycerol-containing vehicle onto calvaria affected osteoblast/bone formation-associated histomorphometric parameters and gene expression (mRNA encoding GAL, GAL receptors, TNFalpha, IL-1beta, collagen type I, MMP-2 and -13) compared to non-injected, control mice and (2) determine the effect of GAL+vehicle treatment on these entities. Five groups of 4-week-old mice were used: a non-injected control group; a vehicle (50/50 solution of 10 mM PBS+0.025% BSA/5.4 M glycerol)-treated group; and 3 GAL-treated groups (0.2, 2 and 20 ng doses). Solutions were injected subcutaneously onto calvaria in a 10 mul volume, every day for 2 weeks. Vehicle injection reduced calvarial periosteal osteoblast cell height (P<0.001), osteoblast number (P<0.001) and osteoid thickness (P<0.01), relative to values in non-injected animals at 2 weeks. Vehicle injection also inhibited BFR in this periosteal bone relative to values in non-injected animals at both 1 and 2 weeks (P<0.05 and P<0.001, respectively). Increasing concentrations of GAL reversed the above-listed inhibitory effects caused by vehicle. This reversal was demonstrated by a dose-dependent effect of GAL on osteoblast cell height (Pearson's r=0.330; P<0.05), osteoblast number (Pearson's r=0.715; P=0.000), osteoid thickness (Pearson's r=0.516; P=0.000) and BFR (Pearson's r=0.525; P<0.05) after 2 weeks of GAL+vehicle treatment; with the 20 ng/day GAL+vehicle injection schedule returning these measured parameters toward non-injected control values. All GAL+vehicle treatments had no effect on calvarial expression of GAL, GALR1, GALR3, collagen type 1 and MMP-2 mRNAs compared to levels in vehicle-injected controls. GAL treatment did, however, produce dose-dependent effects on calvarial expression of GALR2 (Pearson's r=0.763; P=0.000), MMP-13 (Pearson's r=0.806; P=0.000), IL-1beta (Pearson's r=0.807; P=0.000) and TNFalpha (Pearson's r=0.542; P=0.000) mRNAs with 20 ng/day of GAL+vehicle producing the strongest reversal of vehicle-associated changes. Thus, the 20 ng/day GAL+vehicle regimen offset the inhibition of osteoblastic activity, and therefore bone formation caused by daily glycerol-containing vehicle injection. This effect on bone formation may be due in part to the peptide suppressing the formation and associated activity of TNFalpha, IL-1beta and MMP-13, as TNFalpha and IL-1beta are known inhibitors of bone formation and MMP-13 is involved in collagenolysis. Furthermore, these effects may be due to the action of GAL via GALR2, as it was the only GAL receptor affected by this GAL treatment regimen. These results indicate that GAL can facilitate bone formation associated with injury and reveal potential efficacy for GAL in treating osseous conditions where bone formation may be inhibited due to excess TNFalpha and IL-1beta production.

TNF-alpha neutralization ameliorates obstruction-induced renal fibrosis and dysfunction

Upper urinary tract obstruction results in tubulointerstitial fibrosis and a progressive decline in renal function. Although several inflammatory mediators have been implicated in the pathophysiology of renal obstruction, the contribution of TNF-alpha to obstruction-induced fibrosis and renal dysfunction has not been thoroughly evaluated. To study this, male Sprague-Dawley rats were subjected to left unilateral ureteral obstruction vs. sham operation. Rats received either vehicle or a pegylated form of soluble TNF receptor type 1 (PEG-sTNFR1) every 84 h. The kidneys were harvested 1, 3, or 7 days postoperatively, and tissue samples were analyzed for TNF-alpha expression (ELISA), macrophage infiltration (ED-1 staining), transforming growth factor-beta(1) expression (ELISA, RT-PCR), collagen I and IV activity (Western Blot, immunohistochemistry), alpha-smooth muscle actin accumulation (immunohistochemistry, Western blot analysis), and angiotensinogen expression (Western blot). In a separate arm, the glomerular filtration rate (inulin clearance) of rats subjected to unilateral ureteral obstruction in the presence of either vehicle or PEG-sTNFR1 was determined. Renal obstruction induced increased tissue TNF-alpha and transforming growth factor-beta(1) levels, collagen I and IV activity, interstitial volume, alpha-smooth muscle actin accumulation, angiotensinogen expression, and renal dysfunction, whereas treatment with PEG-sTNFR1 significantly reduced each of these markers of renal fibrosis. These results demonstrate that TNF-alpha mediates obstruction-induced renal fibrosis and identify TNF-alpha neutralization as a potential therapeutic option for the amelioration of obstruction-induced renal injury.

CCN2, connective tissue growth factor, stimulates collagen deposition by gingival fibroblasts via module 3 and alpha6- and beta1 integrins

CCN2, (connective tissue growth factor, CTGF) is a matricellular factor associated with fibrosis that plays an important role in the production and maintenance of fibrotic lesions. Increased collagen deposition and accumulation is a common feature of fibrotic tissues. The mechanisms by which CCN2/CTGF contributes to fibrosis are not well understood. Previous studies suggest that CTGF exerts some of its biological effects at least in part by integrin binding, though this mechanism has not been previously shown to contribute to fibrosis. Utilizing full length CCN2/CTGF, CCN2/CTGF fragments, and integrin neutralizing antibodies, we provide evidence that the effects of CCN2/CTGF to stimulate extracellular matrix deposition by gingival fibroblasts are mediated by the C-terminal half of CCN2/CTGF, and by alpha6 and beta1 integrins. In addition, a synthetic peptide corresponding to a region of CCN2/CTGF domain 3 that binds alpha6beta1 inhibits the collagen-deposition assay. These studies employed a new and relatively rapid assay for CCN2/CTGF-stimulated collagen deposition based on Sirius Red staining of cell layers. Data obtained support a pathway in which CCN2/CTGF could bind to alpha6beta1 integrin and stimulate collagen deposition. These findings provide new experimental methodologies applicable to uncovering the mechanism and signal transduction pathways of CCN2/CTGF-mediated collagen deposition, and may provide insights into potential therapeutic strategies to treat gingival fibrosis and other fibrotic conditions.

Diverse biological functions of extracellular collagen processing enzymes

Collagens are abundant proteins in higher organisms, and are formed by a complex biosynthetic pathway involving intracellular and extracellular post-translational modifications. Starting from simple soluble precursors, this interesting pathway produces insoluble functional fibrillar and non-fibrillar elements of the extracellular matrix. The present review highlights recent progress and new insights into biological regulation of extracellular procollagen processing, and some novel functions of byproducts of these extracellular enzymatic transformations. These findings underscore the notion that released propeptides and other proteolytic products of extracellular matrix proteins have important biological functions, and that structural proteins are multifunctional. An emerging concept is that a dynamic interplay exists between extracellular products and byproducts with cells that helps to maintain normal cellular phenotypes and tissue integrity.

L-carnitine and isovaleryl L-carnitine fumarate positively affect human osteoblast proliferation and differentiation in vitro

Age-related bone loss is characterized by decreased osteoblast activity, possibly related to the reduction of energy production. Carnitine promotes energy availability and its concentration declines with age; Therefore, two Carnitine derivatives, L-carnitine fumarate (LC) and isovaleryl L-carnitine fumarate (Iso-V-LC), have been tested on several parameters of human osteoblasts in vitro. Both compounds significantly increased osteoblast activity, but the new compound Iso-V-LC was more efficient than LC at lower concentrations. They both significantly enhanced cell proliferation, [3H]-proline incorporation and the expression of collagen type I (COLLI), and the bone sialoproteins (BSPs) and osteopontin (OPN). The percentage of alkaline phosphatase (ALP)-positive cells and the secretion of osteocalcin were not modified by LC and Iso-V-LC. Both molecules increased the formation of mineralized nodules, but Iso-V-LC reached the maximum effect at a concentration 10-fold lower than that of LC. Furthermore, we showed that insulin-like growth factor (IGF)-I and IGF-II mRNA levels were not modified by the treatment. However, the two compounds induced an increase of insulin-like growth factor binding protein (IGFBP)-3 and a decrease of IGFBP-5 in both osteoblast lysates and the extracellular matrix (ECM). In conclusion these data suggest that carnitine and, in particular, its new derivative, Iso-V-LC supplementation in the elderly may stimulate osteoblast activity and decrease age-related bone loss.

Inhibition of lysyl oxidase activity can delay phenotypic modulation of chondrocytes in two-dimensional culture

OBJECTIVE

Chondrocytes frequently de-differentiate in two-dimensional (2D) culture, especially in the presence of serum. To examine the role of lysyl oxidase (LOX) induced cross-linking in this phenomenon, the effect of the specific LOX inhibitor beta-aminopropionitrile (BAPN) was studied in 2D chondrocyte culture.

DESIGN

Chick embryo sternal chondrocytes (both proliferative and hypertrophic, from caudal and cranial zones, respectively) were cultured in the presence and absence of BAPN. The production and activities of LOX and LOX-like (LOXL) were assessed by enzyme assay and the use of specific antibodies. Seventeen batches of serum of different origin were compared. Chondrocyte phenotype was assessed both morphologically and biochemically, the latter by quantitative analysis of production of radiolabeled cartilage collagens II, IX, X and XI, and the de-differentiation marker collagen I, for up to 4 weeks in culture.

RESULTS

LOX and LOXL were identified, by Western blotting and immunofluorescence, and LO activity was measured in the medium, with both proliferative and hypertrophic chondrocytes. Inhibition of LO activity prevented or delayed chondrocyte de-differentiation, as characterized by changes in cell shape and synthesis of the five different collagen types, from the first days of culture for up to 4 weeks, depending on the origin of the serum added to the culture medium.

CONCLUSION

LO activity may be involved in the control of chondrocyte phenotype, in addition to serum factors. Inhibition of LO activity by BAPN may be useful for the maintenance of the chondrocyte phenotype in 2D culture. Specific variations in the relative proportions of collagens II, IX and XI could be involved in the mechanism underlying these observations.