Cartilage formation in growth plate and arteries: from physiology to pathology

Systemic factors associated with 10-year glaucoma progression in South Korean population: a single center study based on electronic medical records

Glaucoma is a multifactorial disease where various systemic features are involved in the progression of the disease. Based on initial systemic profiles in electronic medical records, this study aimed to develop a model predicting factors of long-term rapid retinal nerve fiber layer (RNFL) thinning over 5 years in 505 patients with primary open-angle glaucoma. Eyes with faster or slower RNFL thinning were stratified using a decision tree model, and systemic and ophthalmic data were incorporated into the models based on random forest and permutation methods, with the models interpreted by Shapley additive explanation plots (SHAP). According to the decision tree, a higher lymphocyte ratio (> 34.65%) was the most important systemic variable discriminating faster or slower RNFL thinning. Higher mean corpuscular hemoglobin (> 32.05 pg) and alkaline phosphatase (> 88.0 IU/L) concentrations were distinguishing factors in the eyes with lymphocyte ratios > 34.65% and < 34.65%, respectively. SHAP demonstrated larger baseline RNFL thickness, greater fluctuation of intraocular pressure (IOP), and higher maximum IOP as the strongest ophthalmic factors, while higher lymphocyte ratio and higher platelet count as the strongest systemic factors associated with faster RNFL thinning. Machine learning-based modeling identified several systemic factors as well as previously acknowledged ophthalmic risk factors associated with long-term rapid RNFL thinning.

Tricomposite gelatin-carboxymethylcellulose-alginate bioink for direct and indirect 3D printing of human knee meniscal scaffold

The development of technologies that could ease the production of customizable patient-specific tissue engineering constructs having required biomechanical properties and restoring function in damaged tissue is the need of the hour. In this study, we report the optimization of composite, bioactive and biocompatible tripolymeric hydrogel bioink, suitable for both direct and indirect printing of customizable scaffolds for cartilage tissue engineering applications. A customized hierarchical meniscal scaffold was designed using solid works software and developed using a negative mould made of polylactic acid (PLA) filament and by a direct 3D printing process. A composite tripolymeric bioink made of gelatin, carboxymethyl cellulose (CMC) and alginate was optimized and characterized for its printability, structural, bio-mechanical and bio-functional properties. The optimized composite hydrogel bioink was extruded into the negative mould with and without live cells, cross-linked and the replica of meniscus structure was retrieved aseptically. The cellular proliferation, apatite formation, and extracellular matrix secretion from negative printed meniscal scaffold were determined using MTT, live/dead and collagen estimation assays. A significant increase in collagen secretion, cellular proliferation and changes in biomechanical properties was observed in the 3D scaffolds with MG63-osteosarcoma cells indicating its suitability for cartilage tissue engineering.

TNAP as a therapeutic target for cardiovascular calcification: a discussion of its pleiotropic functions in the body

Cardiovascular calcification (CVC) is associated with increased morbidity and mortality. It develops in several diseases and locations, such as in the tunica intima in atherosclerosis plaques, in the tunica media in type 2 diabetes and chronic kidney disease, and in aortic valves. In spite of the wide occurrence of CVC and its detrimental effects on cardiovascular diseases (CVD), no treatment is yet available. Most of CVC involve mechanisms similar to those occurring during endochondral and/or intramembranous ossification. Logically, since tissue-nonspecific alkaline phosphatase (TNAP) is the key-enzyme responsible for skeletal/dental mineralization, it is a promising target to limit CVC. Tools have recently been developed to inhibit its activity and preclinical studies conducted in animal models of vascular calcification already provided promising results. Nevertheless, as its name indicates, TNAP is ubiquitous and recent data indicate that it dephosphorylates different substrates in vivo to participate in other important physiological functions besides mineralization. For instance, TNAP is involved in the metabolism of pyridoxal phosphate and the production of neurotransmitters. TNAP has also been described as an anti-inflammatory enzyme able to dephosphorylate adenosine nucleotides and lipopolysaccharide. A better understanding of the full spectrum of TNAP's functions is needed to better characterize the effects of TNAP inhibition in diseases associated with CVC. In this review, after a brief description of the different types of CVC, we describe the newly uncovered additional functions of TNAP and discuss the expected consequences of its systemic inhibition in vivo.

Estrogen inhibits vascular calcification in rats via hypoxia-induced factor-1α signaling

OBJECTIVE

Calcification serves as a surrogate for atherosclerosis-associated vascular diseases, and coronary artery calcification is mediated by multiple pathogenic factors. Estrogen is a known factor that protects the arterial wall against atherosclerosis, but its role in the coronary artery calcification development remains largely unclear. This study tested the hypothesis that estrogen inhibits coronary artery calcification via the hypoxia-induced factor-1α pathway.

METHODS

Eight-week-old healthy female Sprague-Dawley rats were castrated, and vitamin D3 was administered orally to establish. Hypoxia-induced factor-1 inhibitor was administered to test its effect on vascular calcification and expression of bone morphogenetic protein 2 and runt-related transcription factor-2. Vascular smooth muscle cell calcification was induced with CaCl2 in rat aortic smooth muscle cells in the presence or absence of E2(17β-estradiol) and bone morphogenetic protein 2 siRNA intervention.

RESULTS

The estrogen levels in ovariectomized rats were significantly decreased, as determined by ELISA. Expression of hypoxia-induced factor-1α mRNA and protein was significantly increased in vascular cells with calcification as compared to those without calcification (p < 0.01). E2 treatment decreased the calcium concentration in vascular cell calcification and cell calcium nodules in vitro (p < 0.05). E2 also lowered the levels of hypoxia-induced factor-1α mRNA and protein (p < 0.01). Oral administration of the hypoxia-induced factor-1α inhibitor dimethyloxetane in castrated rats alleviated vascular calcification and expression of osteogenesis-related transcription factors, bone morphogenetic protein 2 and RUNX2 (p < 0.01). Finally, bone morphogenetic protein 2 siRNA treatment decreased the levels of p-Smad1/5/8 in A7r5 calcification cells (p < 0.01).

CONCLUSION

Estrogen deficiency enhances vascular calcification. Treatment with estrogen reduces the expression of hypoxia-induced factor-1α as well as vascular calcification in rats. The estrogen effects occur in a fashion dependent on hypoxia-induced factor-1α regulation of bone morphogenetic protein-2 and downstream Smad1/5/8.

Calciprotein Particles and Serum Calcification Propensity: Hallmarks of Vascular Calcifications in Patients with Chronic Kidney Disease

Cardiovascular complications are one of the leading causes of mortality worldwide and are strongly associated with atherosclerosis and vascular calcification (VC). Patients with chronic kidney disease (CKD) have a higher prevalence of VC as renal function declines, which will result in increased mortality. Serum calciprotein particles (CPPs) are colloidal nanoparticles that have a prominent role in the initiation and progression of VC. The T₅₀ test is a novel test that measures the conversion of primary to secondary calciprotein particles indicating the tendency of serum to calcify. Therefore, we accomplished a comprehensive review as the first integrated approach to clarify fundamental aspects that influence serum CPP levels and T₅₀, and to explore the effects of CPP and calcification propensity on various chronic disease outcomes. In addition, new topics were raised regarding possible clinical uses of T₅₀ in the assessment of VC, particularly in patients with CKD, including possible opportunities in VC management. The relationships between serum calcification propensity and cardiovascular and all-cause mortality were also addressed. The review is the outcome of a comprehensive search on available literature and could open new directions to control VC.

Fluoride regulates the expression of extracellular matrix HSPG and related signaling pathways FGFR3 and Ihh/PTHrP feedback loop during endochondral ossification

Skeletal fluorosis causes growth plate impairment and growth retardation during bone development. Longitudinal bone development is accomplished by endochondral ossification in growth plate. However, the mechanism of fluoride impairs growth plate is unclear. To explore the effect of fluoride on various glycosaminoglycans (GAGs) and related signaling pathways in growth plate during endochondral ossification, SD rats and ATDC5 cells were treated with fluoride and carried out a series of experiments. We found that the expression of heparan sulfate (HS), a kind of GAGs in extracellular matrix, was significantly increased in the growth plate of fluoride-treated rats compared with control rats. Furthermore, the expression of HS synthetic enzyme exostosin 1 (EXT1) and glypican 6 (GPC6), a core protein of HS proteoglycan (HSPG), were significantly increased in fluoride-treated ATDC5 cells compared with control cells (P < 0.05). The expression of related molecules including fibroblast growth factor receptor-3 (FGFR3), signal transducer and activator of transcription 1 (STAT1) and parathyroid hormone-related protein (PTHrP) were significantly increased in the fluoride-treated groups compared with control groups (P < 0.05), and there was significantly decreased in the expression of Indian hedgehog (Ihh) in fluoride-treated groups compared with control groups (P < 0.05). Our data suggested that fluoride increased the content of HSPG in extracellular matrix by promoting the expression of EXT1 and GPC6. Fluoride also activated FGFR3 signaling pathway, inhibited Ihh/PTHrP feedback loop and inhibited endochondral ossification. Nevertheless, the regulation of fluoride on HSPG and related pathways FGFR3 and Ihh/PTHrP feedback loop during endochondral ossification needs to be further studied.

Matrix vesicles from chondrocytes and osteoblasts: Their biogenesis, properties, functions and biomimetic models

BACKGROUND

Matrix vesicles (MVs) are released from hypertrophic chondrocytes and from mature osteoblasts, the cells responsible for endochondral and membranous ossification. Under pathological conditions, they can also be released from cells of non-skeletal tissues such as vascular smooth muscle cells. MVs are extracellular vesicles of approximately 100-300nm diameter harboring the biochemical machinery needed to induce mineralization.

SCOPE OF THE REVIEW

The review comprehensively delineates our current knowledge of MV biology and highlights open questions aiming to stimulate further research. The review is constructed as a series of questions addressing issues of MVs ranging from their biogenesis and functions, to biomimetic models. It critically evaluates experimental data including their isolation and characterization methods, like lipidomics, proteomics, transmission electron microscopy, atomic force microscopy and proteoliposome models mimicking MVs.

MAJOR CONCLUSIONS

MVs have a relatively well-defined function as initiators of mineralization. They bind to collagen and their composition reflects the composition of lipid rafts. We call attention to the as yet unclear mechanisms leading to the biogenesis of MVs, and how minerals form and when they are formed. We discuss the prospects of employing upcoming experimental models to deepen our understanding of MV-mediated mineralization and mineralization disorders such as the use of reconstituted lipid vesicles, proteoliposomes and, native sample preparations and high-resolution technologies.

GENERAL SIGNIFICANCE

MVs have been extensively investigated owing to their roles in skeletal and ectopic mineralization. MVs serve as a model system for lipid raft structures, and for the mechanisms of genesis and release of extracellular vesicles.

Functions of Rho family of small GTPases and Rho-associated coiled-coil kinases in bone cells during differentiation and mineralization

BACKGROUND

Members of Rho-associated coiled-coil kinases (ROCKs) are effectors of Rho family of small GTPases. ROCKs have multiple functions that include regulation of cellular contraction and polarity, adhesion, motility, proliferation, apoptosis, differentiation, maturation and remodeling of the extracellular matrix (ECM).

SCOPE OF THE REVIEW

Here, we focus on the action of RhoA and RhoA effectors, ROCK1 and ROCK2, in cells related to tissue mineralization: mesenchymal stem cells, chondrocytes, preosteoblasts, osteoblasts, osteocytes, lining cells and osteoclasts.

MAJOR CONCLUSIONS

The activation of the RhoA/ROCK pathway promotes stress fiber formation and reduces chondrocyte and osteogenic differentiations, in contrast to that in mesenchymal stem cells which stimulated the osteogenic and the chondrogenic differentiation. The effects of Rac1 and Cdc42 in promoting chondrocyte hypertrophy and of Rac1, Rac2 and Cdc42 in osteoclast are discussed. In addition, members of the Rho family of GTPases such Rac1, Rac2, Rac3 and Cdc42, acting upstream of ROCK and/or other protein effectors, may compensate the actions of RhoA, affecting directly or indirectly the actions of ROCKs as well as other protein effectors.

GENERAL SIGNIFICANCE

ROCK activity can trigger cartilage degradation and affect bone formation, therefore these kinases may represent a possible therapeutic target to treat osteoarthritis and osseous diseases. Inhibition of Rho/ROCK activity in chondrocytes prevents cartilage degradation, stimulate mineralization of osteoblasts and facilitate bone formation around implanted metals. Treatment with osteoprotegerin results in a significant decrease in the expression of Rho GTPases, ROCK1 and ROCK2, reducing bone resorption. Inhibition of ROCK signaling increases osteoblast differentiation in a topography-dependent manner.

Osteoblasts secrete Cxcl9 to regulate angiogenesis in bone

Communication between osteoblasts and endothelial cells (ECs) is essential for bone turnover, but the molecular mechanisms of such communication are not well defined. Here we identify Cxcl9 as an angiostatic factor secreted by osteoblasts in the bone marrow microenvironment. We show that Cxcl9 produced by osteoblasts interacts with vascular endothelial growth factor and prevents its binding to ECs and osteoblasts, thus abrogating angiogenesis and osteogenesis both in mouse bone and in vitro. The mechanistic target of rapamycin complex 1 activates Cxcl9 expression by transcriptional upregulation of STAT1 and increases binding of STAT1 to the Cxcl9 promoter in osteoblasts. These findings reveal the essential role of osteoblast-produced Cxcl9 in angiogenesis and osteogenesis in bone, and Cxcl9 can be targeted to elevate bone angiogenesis and prevent bone loss-related diseases.

Glucose stimulates chondrocyte differentiation of vascular smooth muscle cells and calcification: A possible role for IL-1β

Vascular calcification is a hallmark of type 2 diabetes. Glucose stimulates calcification in culture of vascular smooth muscle cells (VSMCs) but the underlying mechanisms remain obscure. We observed that high glucose levels stimulated mouse and human VSMC trans-differentiation into chondrocytes, with increased levels of Sox9, type II collagen, glycosaminoglycan and Runx2 expression, and increased alkaline phosphatase activity and mineralization. These effects were associated with increased expression of IL-1β, which stimulated alkaline phosphatase and calcification, suggesting that glucose induces chondrocyte differentiation of VSMCs, possibly through IL-1β activation.

Inflammation: a culprit for vascular calcification in atherosclerosis and diabetes

It is today acknowledged that aging is associated with a low-grade chronic inflammatory status, and that inflammation exacerbates age-related diseases such as osteoporosis, Alzheimer's disease, atherosclerosis and type 2 diabetes mellitus (T2DM). Vascular calcification is a complication that also occurs during aging, in particular in association with atherosclerosis and T2DM. Recent studies provided compelling evidence that vascular calcification is associated with inflammatory status and is enhanced by inflammatory cytokines. In the present review, we propose on one hand to highlight the most important and recent findings on the cellular and molecular mechanisms of vascular inflammation in atherosclerosis and T2DM. On the other hand, we will present the effects of inflammatory mediators on the trans-differentiation of vascular smooth muscle cell and on the deposition of crystals. Since vascular calcification significantly impacts morbidity and mortality in affected individuals, a better understanding of its induction and development will pave the way to develop new therapeutic strategies.

Short-term effects of calcium ions on the apoptosis and onset of mineralization of human dental pulp cells in vitro and in vivo

Calcium ions (Ca2+) are a major constituent of most pulp-capping materials and have an important role in the mineralization of human dental pulp cells (hDPCs). A previous study by our group has shown that increased levels of Ca2+ can promote hDPC-mediated mineralization in long-term cultures (21 days). However, the initiation of mineralization occurs in the early stage of osteogenic inductive culture, and the effects of Ca2+ on the mineralization of hDPCs in short-term cultures (five days) have not been studied in detail. Furthermore, the underlying mechanism by which Ca2+ stimulates the mineralization of hDPCs has remained controversial. A strong correlation between mineralization and cell apoptosis and/or death has been identified. Thus, the present study hypothesized that Ca2+ may promote the onset of hDPC-mediated mineralization through inducing their apoptosis and/or death. To verify this hypothesis, Ca2+ was added to the growth culture medium and osteogenic culture medium at various concentrations. Alizarin Red S staining and reverse transcription-polymerase chain reaction analysis were used to evaluate the onset of mineralization. Furthermore, the cell counting kit-8 and fluorescein isothiocyanate-Annexin V/propidium iodide double-staining method were adopted to detect the proliferation and apoptosis of hDPCs in the growth culture medium. An animal experiment and scanning electron microscopic observation of ceramic graft implants were applied to measure the mineralization in vivo. The results showed that 5.4 and 9.0 mM Ca2+ accelerated the onset of mineralized matrix nodule formation, promoted osteopontin mRNA expression and induced marked cell apoptosis and necrosis, but had no obvious effect on cell proliferation. These findings indicated a positive association between cell apoptosis and/or death and the timing of formation as well as the quantity of extracellular mineralization induced by Ca2+ in short-term cultured hDPCs.

Vascular smooth muscle cell in atherosclerosis

Vascular smooth muscle cells (VSMCs) exhibit phenotypic and functional plasticity in order to respond to vascular injury. In case of the vessel damage, VSMCs are able to switch from the quiescent 'contractile' phenotype to the 'proinflammatory' phenotype. This change is accompanied by decrease in expression of smooth muscle (SM)-specific markers responsible for SM contraction and production of proinflammatory mediators that modulate induction of proliferation and chemotaxis. Indeed, activated VSMCs could efficiently proliferate and migrate contributing to the vascular wall repair. However, in chronic inflammation that occurs in atherosclerosis, arterial VSMCs become aberrantly regulated and this leads to increased VSMC dedifferentiation and extracellular matrix formation in plaque areas. Proatherosclerotic switch in VSMC phenotype is a complex and multistep mechanism that may be induced by a variety of proinflammatory stimuli and hemodynamic alterations. Disturbances in hemodynamic forces could initiate the proinflammatory switch in VSMC phenotype even in pre-clinical stages of atherosclerosis. Proinflammatory signals play a crucial role in further dedifferentiation of VSMCs in affected vessels and propagation of pathological vascular remodelling.

Vascularization of primary and secondary ossification centres in the human growth plate

Background

The switch from cartilage template to bone during endochondral ossification of the growth plate requires a dynamic and close interaction between cartilage and the developing vasculature. Vascular invasion of the primarily avascular hypertrophic chondrocyte zone brings chondroclasts, osteoblast- and endothelial precursor cells into future centres of ossification.

Vascularization of human growth plates of polydactylic digits was studied by immunohistochemistry, confocal-laser-scanning-microscopy and RT-qPCR using markers specific for endothelial cells CD34 and CD31, smooth muscle cells α-SMA, endothelial progenitor cells CD133, CXCR4, VEGFR-2 and mesenchymal progenitor cells CD90 and CD105. In addition, morphometric analysis was performed to quantify RUNX2⁺ and DLX5⁺ hypertrophic chondrocytes, RANK⁺ chondro- and osteoclasts, and CD133⁺ progenitors in different zones of the growth plate.

Results

New vessels in ossification centres were formed by sprouting of CD34⁺ endothelial cells that did not co-express the mature endothelial cell marker CD31. These immature vessels in the growth plate showed no abluminal coverage with α-SMA⁺ smooth muscle cells, but in their close proximity single CD133⁺ precursor cells were found that did not express VEGFR-2, a marker for endothelial lineage commitment. In periosteum and in the perichondrial groove of Ranvier that harboured CD90⁺/CD105⁺ chondro-progenitors, in contrast, mature vessels were found stabilized by α-SMA⁺ smooth muscle cells.

Conclusion

Vascularization of ossification centres of the growth plate was mediated by sprouting of capillaries coming from the bone collar or by intussusception rather than by de-novo vessel formation involving endothelial progenitor cells. Vascular invasion of the joint anlage was temporally delayed compared to the surrounding joint tissue.

Mesenchymal Stem Cells for Treating Articular Cartilage Defects and Osteoarthritis

Articular cartilage damage and osteoarthritis are the most common joint diseases. Joints are prone to damage caused by sports injuries or aging, and such damage regularly progresses to more serious joint disorders, including osteoarthritis, which is a degenerative disease characterized by the thinning and eventual wearing out of articular cartilage, ultimately leading to joint destruction. Osteoarthritis affects millions of people worldwide. Current approaches to repair of articular cartilage damage include mosaicplasty, microfracture, and injection of autologous chondrocytes. These treatments relieve pain and improve joint function, but the long-term results are unsatisfactory. The long-term success of cartilage repair depends on development of regenerative methodologies that restore articular cartilage to a near-native state. Two promising approaches are (i) implantation of engineered constructs of mesenchymal stem cell (MSC)-seeded scaffolds, and (ii) delivery of an appropriate population of MSCs by direct intra-articular injection. MSCs may be used as trophic producers of bioactive factors initiating regenerative activities in a defective joint. Current challenges in MSC therapy are the need to overcome current limitations in cartilage cell purity and to in vitro engineer tissue structures exhibiting the required biomechanical properties. This review outlines the current status of MSCs used in cartilage tissue engineering and in cell therapy seeking to repair articular cartilage defects and related problems. MSC-based technologies show promise when used to repair cartilage defects in joints.

Evaluation of a porcine model of early aortic valve sclerosis

BACKGROUND

Calcific aortic valve disease (CAVD) is associated with significant cardiovascular morbidity. While late-stage CAVD is well-described, early pathobiological processes are poorly understood due to the lack of animal models that faithfully replicate early human disease. Here we evaluated a hypercholesterolemic porcine model of early diet-induced aortic valve sclerosis.

METHODS

Yorkshire swine were fed either a standard or high-fat/high-cholesterol diet for 2 or 5 months. Right coronary aortic valve leaflets were excised and analyzed (immuno)histochemically.

RESULTS

Early human-like proteoglycan-rich onlays formed between the endothelial layer and elastic lamina in the fibrosa layer of valve leaflets, with accelerated formation associated with hypercholesterolemia (P<.05). Lipid deposition was more abundant in hypercholesterolemic swine (P<.001), but was present in a minority (28%) of onlays. No myofibroblasts, MAC387-positive macrophages, or fascin-positive dendritic cells were detected in 2-month onlays, with only scarce myofibroblasts present at 5 months. Cells that expressed osteochondral markers Sox9 and Msx2 were preferentially found in dense proteoglycan-rich onlays (P<.05) and with hypercholesterolemia (P<.05). Features of more advanced human CAVD, including calcification, were not observed in this necessarily short study.

CONCLUSIONS

Early aortic valve sclerosis in hypercholesterolemic swine is characterized by the formation of proteoglycan-rich onlays in the fibrosa, which can occur prior to significant lipid accumulation, inflammatory cell infiltration, or myofibroblast activation. These characteristics mimic those of early human aortic valve disease, and thus the porcine model has utility for the study of early valve sclerosis.

The relationship between serum hypoxia-inducible factor 1α and coronary artery calcification in asymptomatic type 2 diabetic patients

Background

Hypoxia-inducible factor 1 (HIF-1), a master regulator of oxygen homeostasis, is a heterodimer consisting of HIF-1α and HIF-1β subunits, and is implicated in calcification of cartilage and vasculature. The goal of this study was to determine the relationship between serum HIF-1α with coronary artery calcification (CAC) in patients with type 2 diabetes.

Methods

The subjects were 405 (262 males, 143 females, age 51.3 ± 6.4 years) asymptomatic patients with type 2 diabetes mellitus. Serum HIF-1α and interleukin-6 (IL-6) levels were measured by ELISA. CAC scores were assessed by a 320-slice CT scanner. The subjects were divided into 4 quartiles depending on serum HIF-1α levels.

Results

Average serum HIF-1α was 184.4 ± 66.7 pg/ml. Among patients with higher CAC scores, HIF-1α levels were also significantly increased (p <0.001). HIF-1α levels positively correlated with CRP, IL-6, UKPDS risk score, HbA1c, FBG, and CACS, but did not correlate with diabetes duration, age, and LDL. According to the multivariate analysis, HIF-1α levels significantly and independently predict the presence of CAC. ROC curve analysis showed that the serum HIF-1α level can predict the extent of CAC, but the specificity was lower than the traditional risk factors UKPDS and HbA1c.

Conclusion

As a marker of hypoxia, serum HIF-1α level may be an independent risk factor for the presence of CAC. These findings indicate that elevated serum HIF-1α may be involved in vascular calcification in patients with type 2 diabetes mellitus.

Development of a model of elevated intraocular pressure in rats by gene transfer of bone morphogenetic protein 2

PURPOSE

To determine whether inducing calcification in the trabecular meshwork results in elevated IOP in living rats. To use this property to create an elevated IOP animal model by gene transfer of bone morphogenetic protein 2 (BMP2).

METHODS

Calcification was assessed by alizarin red staining in primary human trabecular meshwork (HTM) cells and alkaline phosphatase (ALP) activity in the angle tissue. Brown Norway (BN) and Wistar rats were intracamerally injected with Ad5BMP2 (OS) and control Ad5.CMV-Null (OD). IOPs were taken twice a week and expressed as mean integral pressures. Morphology was assessed on fixed, paraffin-embedded anterior segments. Retinal ganglion cells (RGCs) were quantified on retrograde and Brn-3a-labeled flat mounts using MetaMorph software.

RESULTS

BMP2-treated cells displayed marked increase in calcification. Trabecular meshwork tissue showed moderate ALP activity at 13 days postinjection. Fifty-four of 55 BN and 15 of 19 Wistar rats displayed significantly elevated IOP. In a representative 29-day experiment, the integral IOP difference between treated and control eyes was 367.7 ± 83 mm Hg-days (P = 0.007). Morphological evaluation revealed a well-organized trabecular meshwork tissue, exhibiting denser matrix in the treated eyes. The Ad5BMP2-treated eye showed 34.4% ± 4.8% (P = 0.00002) loss of peripheral RGC over controls.

CONCLUSIONS

Gene transfer of the calcification inducer BMP2 gene to the trabecular meshwork induces elevated IOP in living rats without altering the basic structure of the tissue. This strategy generates an elevated IOP model in rats that would be useful for evaluation of glaucoma drugs targeting the outflow pathway.

Preparation of collagen scaffolds with controlled pore structures and improved mechanical property for cartilage tissue engineering

Appropriate pore structures and mechanical properties are required for scaffolds that are used for tissue engineering and regenerative medicine. In this study, pre-prepared ice particulates were used as a porogen material to prepare collagen porous scaffolds with well-controlled pore structures and improved mechanical properties. Porogen ice particulates initiated the formation of interconnected large spherical pores surrounded by small pores. The large spherical pores were well compacted and increased the elastic modulus of the scaffolds. The unique pore structures facilitated cell penetration, resulting in a homogeneous cell distribution throughout the scaffolds. The excellent mechanical properties protected the scaffolds from deformation during cell culturing and implantation. The collagen porous scaffolds facilitated cartilage regeneration when bovine articular chondrocytes were cultured in these scaffolds. The use of pre-prepared ice particulates as a porogen material proved to be a useful method to control the pore structure and improve the mechanical properties of collagen-based porous scaffolds.

Cartilage tissue engineering with controllable shape using a poly(lactic-co-glycolic acid)/collagen hybrid scaffold

It is of critical importance to prepare three-dimensional biodegradable porous scaffolds for cartilage tissue engineering. We developed a poly(lactic- co-glycolic acid)/collagen hybrid scaffold, which combined the advantages of natural type I collagen and synthetic polymer polylactin 910 knitted mesh (90:10 copolymer of glycolic acid and lactic acid), and a method using this poly(lactic- co-glycolic acid)/collagen scaffold to regenerate cartilage with controllable shape. The mechanically strong poly(lactic- co-glycolic acid) mesh served as a mechanical skeleton supporting the scaffold, and the collagen benefited cell seeding, distribution, and tissue formation. Bovine chondrocytes were cultured in the hybrid scaffold and transplanted into the subcutaneous sites of nude mice for 4 weeks. All the samples showed spatially uniform cell distribution, natural chondrocyte morphology, and deposition of abundant cartilaginous extracellular matrices such as type II collagen and aggrecan. Production of glycosaminoglycans per DNA reached 74.63% of the natural articular cartilage. The mechanical strength was 62.76% and 71.43% in Young’s modulus and stiffness, respectively, compared to the native articular cartilage. All the samples successfully maintained the original shapes. Our method provides a new strategy for regeneration of cartilage tissue with designed shapes.

Phospholipases of mineralization competent cells and matrix vesicles: roles in physiological and pathological mineralizations

The present review aims to systematically and critically analyze the current knowledge on phospholipases and their role in physiological and pathological mineralization undertaken by mineralization competent cells. Cellular lipid metabolism plays an important role in biological mineralization. The physiological mechanisms of mineralization are likely to take place in tissues other than in bones and teeth under specific pathological conditions. For instance, vascular calcification in arteries of patients with renal failure, diabetes mellitus or atherosclerosis recapitulates the mechanisms of bone formation. Osteoporosis—a bone resorbing disease—and rheumatoid arthritis originating from the inflammation in the synovium are also affected by cellular lipid metabolism. The focus is on the lipid metabolism due to the effects of dietary lipids on bone health. These and other phenomena indicate that phospholipases may participate in bone remodelling as evidenced by their expression in smooth muscle cells, in bone forming osteoblasts, chondrocytes and in bone resorbing osteoclasts. Among various enzymes involved, phospholipases A₁ or A₂, phospholipase C, phospholipase D, autotaxin and sphingomyelinase are engaged in membrane lipid remodelling during early stages of mineralization and cell maturation in mineralization-competent cells. Numerous experimental evidences suggested that phospholipases exert their action at various stages of mineralization by affecting intracellular signaling and cell differentiation. The lipid metabolites—such as arachidonic acid, lysophospholipids, and sphingosine-1-phosphate are involved in cell signaling and inflammation reactions. Phospholipases are also important members of the cellular machinery engaged in matrix vesicle (MV) biogenesis and exocytosis. They may favour mineral formation inside MVs, may catalyse MV membrane breakdown necessary for the release of mineral deposits into extracellular matrix (ECM), or participate in hydrolysis of ECM. The biological functions of phospholipases are discussed from the perspective of animal and cellular knockout models, as well as disease implications, development of potent inhibitors and therapeutic interventions.

Utilization of transgenic models in the evaluation of osteogenic differentiation of embryonic stem cells

Previous studies reported that embryonic stem cells (ESCs) can be induced to differentiate into cells showing a mature osteoblastic phenotype by culturing them under osteo-inductive conditions. It is probable that osteogenic differentiation requires that ESCs undergo differentiation through an intermediary step involving a mesenchymal lineage precursor. Based on our previous studies indicating that adult mesenchymal progenitor cells express α-smooth muscle actin (αSMA), we have generated ESCs from transgenic mice in which an αSMA promoter directs the expression of red fluorescent protein (RFP) to mesenchymal progenitor cells. To track the transition of ESC-derived MSCs into mature osteoblasts, we have utilized a bone-specific fragment of rat type I collagen promoter driving green fluorescent protein (Col2.3GFP). Following osteogenic induction in ESCs, we have observed expression of alkaline phosphatase (ALP) and subsequent mineralization as detected by von Kossa staining. After 1 week of osteogenic induction, ESCs begin to express αSMARFP. This expression was localized to the peripheral area encircling a typical ESC colony. Nevertheless, these αSMARFP positive cells did not show activation of the Col2.3GFP promoter, even after 7 weeks of osteogenic differentiation in vitro. In contrast, Col2.3GFP expression was detected in vivo, in mineralized areas following teratoma formation. Our results indicate that detection of ALP activity and mineralization of ESCs cultured under osteogenic conditions is not sufficient to demonstrate osteogenic maturation. Our study indicates the utility of the promoter-visual transgene approach to assess the commitment and differentiation of ESCs into the osteoblast lineage.

Cell-specific effects of TNF-α and IL-1β on alkaline phosphatase: implication for syndesmophyte formation and vascular calcification

Tumor necrosis factor (TNF)-α and interleukin (IL)-1β stimulate tissue non-specific alkaline phosphatase (TNAP) activity and mineralization in cultures of vascular smooth muscle cells (VSMCs). They are, therefore, considered as stimulators of vascular calcification in the context of atherosclerosis and diabetes type 2. In contrast, although ankylosing spondylitis (AS) leads to the formation of syndesmophytes, which are ectopic ossifications from entheses (where ligaments, tendons and capsules are attached to bone), anti-TNF-α therapies fail to block bone formation in this disease. In this context, our aims were to compare the effects of TNF-α and IL-1β on TNAP activity and mineralization in entheseal cells and VSMCs. Organotypic cultures of mouse ankle entheses were treated or not with TNF-α and IL-1β for 5 days. Micro-computed tomography was performed to determine trabecular bone parameters, and histology to assess TNAP activity and mineralization. Human mesenchymal stem cells cultured in pellets in chondrogenic conditions and human VSMCs were also used to determine the effects of cytokines on TNAP activity and expression, measured by quantitative PCR. In organotypic cultures, TNF-α and IL-1β significantly reduced the tibia BV/TV ratio. They also inhibited TNAP activity in entheseal chondrocytes in situ, and in mouse and human chondrocytes in vitro. In contrast, TNF-α stimulated TNAP expression and activity in human VSMCs. These differences were likely due to cell-specific effects of peroxisome proliferator-activated receptor γ (PPARγ), which is inhibited by TNF-α. Indeed, in human chondrocytes and VSMCs, the PPARγ inhibitor GW-9662 displayed the same opposite effects as TNF-α on TNAP expression. In conclusion, whereas TNF-α and IL-1β stimulate TNAP activity in VSMCs, they inhibit it in entheseal cells in situ and on chondrocytes in vitro. The identification of PPARγ as a likely mediator of cytokine effects deserves consideration for future research on the mechanisms of ectopic ossification.

Bone Gla protein increases HIF-1alpha-dependent glucose metabolism and induces cartilage and vascular calcification

OBJECTIVE

Bone Gla Protein (BGP, osteocalcin) is commonly present in the calcified vasculature and was recently shown as energy metabolism-regulating hormone. This study investigates the role of BGP in cartilage and vasculature mineralization.

METHODS AND RESULTS

We established an in vitro BGP-overexpression model in chondrocytes (ATDC5) and vascular smooth muscle cells (MOVAS). BGP overexpression upregulated markers of chondrogenic differentiation and intensified staining for minerals. BGP overexpression enhanced glucose uptake and increased expression of glucose transporters and glycolysis enzymes while decreasing gluconeogenesis enzymes. Treatment with purified BGP activated insulin signaling pathway and upregulated genes of glucose transport and utilization. Both BGP overexpression and treatment with purified BGP resulted in stabilization of hypoxia-inducible factor 1α (HIF-1α) in chondrocytes and vascular smooth muscle cells, shown essential in mediating the direct metabolic effect of BGP. The in vivo model of 1,25(OH)(2)D(3)-induced vascular calcification in rats revealed a correlation between calcification, elevated BGP levels, and increased HIF-1α expression in aortas and bone growth plates. The in vivo introduction of BGP siRNA, coadministered with 1,25(OH)(2)D(3), prevented 1,25(OH)(2)D(3)-induced HIF-1α stabilization, and diminished osteochondrogenic differentiation and mineralization of aortas.

CONCLUSIONS

This study demonstrates novel mechanism by which BGP locally shifts cells toward glycolytic breakdown of glucose, in a HIF-1α-dependent manner, and stimulates calcification of cartilage and vasculature.

The emergence of phosphate as a specific signaling molecule in bone and other cell types in mammals

Although considerable advances in our understanding of the mechanisms of phosphate homeostasis and skeleton mineralization have recently been made, little is known about the initial events involving the detection of changes in the phosphate serum concentrations and the subsequent downstream regulation cascade. Recent data has strengthened a long-established hypothesis that a phosphate-sensing mechanism may be present in various organs. Such a phosphate sensor would detect changes in serum or local phosphate concentration and would inform the body, the local environment, or the individual cell. This suggests that phosphate in itself could represent a signal regulating multiple factors necessary for diverse biological processes such as bone or vascular calcification. This review summarizes findings supporting the possibility that phosphate represents a signaling molecule, particularly in bone and cartilage, but also in other tissues. The involvement of various signaling pathways (ERK1/2), transcription factors (Fra-1, Runx2) and phosphate transporters (PiT1, PiT2) is discussed.

Do cytokines induce vascular calcification by the mere stimulation of TNAP activity?

Vascular calcification occurs during aging in the general population and is increased in the intima by atherosclerosis and in the media by diabetes type 2. In both intima and media, calcification may lead to the formation of a tissue very similar if not identical to bone, with bone cells and bone marrow. Since vascular calcification is associated with cardiovascular complications, a better understanding of the inducing mechanisms could lead to the development of new therapeutic strategies. Many studies have provided evidence for a role of inflammation and inflammatory cytokines such as tumour necrosis factor (TNF)-α and interleukin (IL)-1β in the vascular calcification process. TNF-α and IL-1β have indeed been shown to stimulate in vitro the expression by vascular smooth muscle cells (VSMCs) of tissue-non specific alkaline phosphatase (TNAP), a key enzyme in the mineralization process, and to trigger the trans-differentiation of VSMCs into osteoblast-like cells, expressing the master transcription factor RUNX2. These data are however somewhat contradictory with the known inhibitory effects of inflammatory cytokines on bone formation. TNF-α for instance dramatically decreases RUNX2 RNA expression, protein stability and activity, and as a consequence, is a potent inhibitor of osteoblast differentiation and bone formation. In the present article, we propose a new hypothesis to explain this calcification paradox. We propose that cytokines block bone formation by decreasing RUNX2-mediated type I collagen production in osteoblasts, whereas they induce vascular ossification by the mere stimulation of TNAP by VSMCs, independently of RUNX2. We propose that this stimulation of TNAP in VSMCs in vitro and in vivo may be sufficient to induce the calcification of collagen fibrils, and that the absence of crystal clearance, in turn, induces the differentiation of VSMCs and/or mesenchymal stem cells into bone-forming cells, eventually leading to formation of a bone-like tissue. In case future experimental studies support this hypothesis, the early stimulatory and late inhibitory effects of inflammation on vascular calcification will have to be taken into consideration in the development of new therapeutic strategies.

Specific binding and mineralization of calcified surfaces by small peptides

Several small (<25aa) peptides have been designed based on the sequence of the dentin phosphoprotein, one of the major noncollagenous proteins thought to be involved in the mineralization of the dentin extracellular matrix during tooth development. These peptides, consisting of multiple repeats of the tripeptide aspartate-serine-serine (DSS), bind with high affinity to calcium phosphate compounds and, when immobilized, can recruit calcium phosphate to peptide-derivatized polystyrene beads or to demineralized human dentin surfaces. The affinity of binding to hydroxyapatite surfaces increases with the number of (DSS)(n) repeats, and though similar repeated sequences-(NTT)(n), (DTT)(n), (ETT)(n), (NSS)(n), (ESS)(n), (DAA)(n), (ASS)(n), and (NAA)(n)-also showed HA binding activity, it was generally not at the same level as the natural sequence. Binding of the (DSS)(n) peptides to sectioned human teeth was shown to be tissue-specific, with high levels of binding to the mantle dentin, lower levels of binding to the circumpulpal dentin, and little or no binding to healthy enamel. Phosphorylation of the serines of these peptides was found to affect the avidity, but not the affinity, of binding. The potential utility of these peptides in the detection of carious lesions, the delivery of therapeutic compounds to mineralized tissues, and the modulation of remineralization is discussed.

Differential effects of hypoxia on osteochondrogenic potential of human adipose-derived stem cells

Human adipose tissue-derived stem cells (hATSC) have been contemplated as reparative cells for cartilage engineering. Chondrogenic differentiation of hATSC can be induced by an enriched culture medium and a three-dimensional environment. Given that bone is vascularized and cartilage is not, oxygen tension has been suggested as a regulatory factor for osteochondrogenic differentiation. Our work aimed at determining whether hypoxia affects the osteochondrogenic potential of hATSC. hATSC were cultured in chondrogenic or osteogenic medium for 28 days, in pellets or monolayers, and under 5% or 20% oxygen tension. Cell differentiation was monitored by real-time PCR (COL2A1, aggrecan, Runx2, and osteocalcin). The chondrogenic differentiation was further evaluated by Alcian blue and immunohistological staining for glycosaminoglycans (GAGs) and type II collagen, respectively. Osteogenic differentiation was also assessed by the staining of mineralized matrix (Alizarin Red) and measurement of alkaline phosphatase (ALP) activity. The expression of chondrogenic markers was upregulated when hATSC were exposed to hypoxia in chondrogenic medium. Conversely, osteocalcin expression, mineralization, and ALP activity were severely reduced under hypoxic conditions even in the presence of osteogenic medium. Our data strongly suggest that hypoxia favors the chondrogenic differentiation of hATSC as evidenced by the expression of the chondrogenic markers, whereas it could alter their osteogenic potential. Our results highlight the differential regulatory role of hypoxia on the chondrogenic and osteogenic differentiation processes of hATSC. These data could help us exploit the potential of tissue engineering and stem cells to replace or restore the function of osteoarticular tissues.

Identification of phenotypic discriminating markers for intervertebral disc cells and articular chondrocytes

OBJECTIVE

The present study was conducted to improve our knowledge of intervertebral disc (IVD) cell biology by comparing the phenotype of nucleus pulposus (NP) and annulus fibrosus (AF) cells with that of articular chondrocytes (ACs).

METHODS

Rabbit cells from NP and AF were isolated and their phenotype was compared with that of AC by real-time PCR analysis of type I (COL1A1), II (COL2A1) and V (COL5A1) collagens, aggrecan transcript (AGC1), matrix Gla protein (MGP) and Htra serine peptidase 1 (Htra1).

RESULTS

Transcript analysis indicated that despite certain similarities, IVD cells exhibit distinct COL2A1/COL1A1 and COL2A1/AGC1 ratios as compared with AC. The expression pattern of COL5A1, MGP and Htra1 makes it possible to define a phenotypic signature for NP and AF cells.

CONCLUSIONS

Our study shows that NP and AF cells exhibit a clearly distinguishable phenotype from that of AC. Type V collagen, MGP and HtrA1 could greatly help to discriminate among NP, AF and AC cells.

TNF-alpha and IL-1beta inhibit RUNX2 and collagen expression but increase alkaline phosphatase activity and mineralization in human mesenchymal stem cells

AIMS

Joint inflammation leads to bone erosion in rheumatoid arthritis (RA), whereas it induces new bone formation in spondyloarthropathies (SpAs). Our aims were to clarify the effects of tumour necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta) on osteoblast differentiation and mineralization in human mesenchymal stem cells (MSCs).

MAIN METHODS

In MSCs, expression of osteoblast markers was assessed by real-time PCR and ELISA. Activity of tissue-nonspecific alkaline phosphatase (TNAP) and mineralization were determined by the method of Lowry and alizarin red staining respectively. Involvement of RUNX2 in cytokine effects was investigated in osteoblast-like cells transfected with a dominant negative construct.

KEY FINDINGS

TNF-alpha (from 0.1 to 10 ng/ml) and IL-1beta (from 0.1 to 1 ng/ml) stimulated TNAP activity and mineralization in MSCs. Addition of 50 ng/ml of IL-1 receptor antagonist in TNF-alpha-treated cultures did not reverse TNF-alpha effects, indicating that IL-1 was not involved in TNF-alpha-stimulated TNAP activity. Both TNF-alpha and IL-1beta decreased RUNX2 expression and osteocalcin secretion, suggesting that RUNX2 was not involved in mineralization. This hypothesis was confirmed in osteoblast-like cells expressing a dominant negative RUNX2, in which TNAP expression and activity were not reduced. Finally, since mineralization may merely rely on increased TNAP activity in a collagen-rich tissue, we investigated cytokine effects on collagen expression, and observed that cytokines decreased collagen expression in osteoblasts from MSC cultures.

SIGNIFICANCE

The different effects of cytokines on TNAP activity and collagen expression may therefore help explain why inflammation decreases bone formation in RA whereas it induces ectopic ossification from collagen-rich entheses during SpAs.

Evidence for a calcification process in the trabecular meshwork

The human trabecular meshwork (TM) expresses many genes that have been associated with physiological (bone, cartilage, teeth) and pathological (vascular systems, kidney) calcification. In particular, the TM highly expresses the inhibitor of calcification Matrix Gla (MGP) gene, which encodes a vitamin K-dependent protein that requires post-translational activation to inhibit the formation of calcium precipitates. TM cells have high activity of the activating gamma-carboxylase enzyme and produce active MGP. Silencing MGP increases the activity of alkaline phosphatase (ALP), an enzyme of the matrix vesicles and marker of calcification. Overexpressing MGP reduces the ALP activity induced by bone morphogenetic 2 (BMP2), a potent inducer of calcification. In this review we gathered evidence for the existence of a mineralization process in the TM. We selected twenty regulatory calcification genes, reviewed their functions in their original tissues and looked at their relative abundance in the TM by heat maps derived from existing microarrays. Although results are not yet fully conclusive and more experiments are needed, examining TM expression in the light of the calcification literature brings up many similarities. One such parallel is the role of mechanical forces in bone induction and the high levels of mineralization inhibitors found in the constantly mechanically stressed TM. During the next few years, examination of other calcification-related regulatory genes and pathways, as well as morphological examination of knockout animals, would help to elucidate the relevance of a calcification process to TM's overall function.

Matrix vesicles in the fibrous cap of atherosclerotic plaque: possible contribution to plaque rupture

Plaque rupture is the most common type of plaque complication and leads to acute ischaemic events such as myocardial infarction and stroke. Calcification has been suggested as a possible indicator of plaque instability. Although the role of matrix vesicles in the initial stages of arterial calcification has been recognized, no studies have yet been carried out to examine a possible role of matrix vesicles in plaque destabilization. Tissue specimens selected for the present study represented carotid specimens obtained from patients undergoing carotid endarterectomy. Serial frozen cross-sections of the tissue specimens were cut and mounted on glass slides. The thickness of the fibrous cap (FCT) in each advanced atherosclerotic lesion, containing a well developed lipid/necrotic core, was measured at its narrowest sites in sets of serial sections. According to established criteria, atherosclerotic plaque specimens were histologically subdivided into two groups: vulnerable plaques with thin fibrous caps (FCT <100 μm) and presumably stable plaques, in which fibrous caps were thicker than 100 μm. Twenty-four carotid plaques (12 vulnerable and 12 presumably stable plaques) were collected for the present analysis of matrix vesicles in fibrous caps. In order to provide a sufficient number of representative areas from each plaque, laser capture microdissection (LCM) was carried out. The quantification of matrix vesicles in ultrathin sections of vulnerable and stable plaques revealed that the numbers of matrix vesicles were significantly higher in fibrous caps of vulnerable plaques than those in stable plaques (8.908±0.544 versus 6.208±0.467 matrix vesicles per 1.92 μm² standard area; P= 0.0002). Electron microscopy combined with X-ray elemental microanalysis showed that some matrix vesicles in atherosclerotic plaques were undergoing calcification and were characterized by a high content of calcium and phosphorus. The percentage of calcified matrix vesicles/microcalcifications was significantly higher in fibrous caps in vulnerable plaques compared with that in stable plaques (6.705±0.436 versus 5.322±0A94; P= 0.0474). The findings reinforce a view that the texture of the extracellular matrix in the thinning fibrous cap of atherosclerotic plaque is altered and this might contribute to plaque destabilization.

Expression of cartilage-specific markers in calcified and non-calcified atherosclerotic lesions

Recently, molecular mechanisms resembling endochondral ossification were suggested to be important for atherosclerotic vessel calcification. The aim of this study was to investigate in a series of human atherosclerotic (non-diabetic) lesions of the crural arteries the distribution and expression of classical marker genes of the endochondral ossification pathway. Immunostaining for marker proteins S-100 protein and collagen types II and X were performed on atherosclerotic lesions of different grades (according to Stary). Quantitative real-time PCR for human COL1A1, COL2A1, COL10A1, SOX9, and BMP-2 was applied on RNA isolated from atherosclerotic arteries. In most samples, no expression of collagen type II and S-100 protein was found. Exceptionally, S-100 protein and type II collagen expression was observed very focally within advanced atherosclerotic plaques. Type X collagen was not detected in any of the lesions investigated. Overall, in our study we found no evidence that chondrogenic differentiation pathways are generally active in atherosclerotic plaque formation. In particular type X collagen, one important molecule in cartilage calcification, was not expressed in any of the investigated specimens. Occasionally, however, chondrocytic differentiation markers occur within atherosclerotic lesions. This most likely represents a metaplastic event associated, but not causative for atherosclerotic vessel degeneration and calcification.

Skeletal dysplasias and the growth plate

Skeletal dysplasias are disorders in which there is derangement in the growth or shape of the skeleton. Long bone grows from cartilage that persists near the ends until skeletal maturity as the growth plate. Developmental biology work has identified the major regulatory proteins in growth plate chondroyte function. There are hundreds of skeletal dysplasias, and the molecular genetic etiology of many was defined in the past decade and a half. Now that the causative genes for these disorders have been identified, they can be broadly classified by the function of the protein that these genes encode for into disorders caused by extracellular structural proteins, proteins that regulate normal growth plate chondrocyte differentiation and patterning, and enzymes that process these proteins. There are clinical similarities within each group, and the phenotype can be predicted based on the role of the mutated protein in normal growth plate function. As such, this framework to classify the skeletal dysplasias has practical clinical implications.

Presence of an established calcification marker in trabecular meshwork tissue of glaucoma donors

PURPOSE

To determine the presence of calcification markers in the trabecular meshwork tissue from glaucoma donors and in trabecular meshwork cells insulted by dexamethasone (DEX) and transforming growth factor beta2 (TGFbeta2), factors associated with glaucoma. To investigate as well the effect of silencing the inhibitor of calcification matrix Gla (MGP) in the trabecular meshwork cells.

METHODS

Trabecular meshwork tissue was obtained from perfused postmortem anterior segments of glaucomatous and normal eyes. Primary trabecular meshwork cells were obtained from residual corneal rims after surgical corneal transplantation. Calcification marker alkaline phosphatase (ALP) enzyme activity was assayed by fluorescence produced after substrate cleavage. DNA quantification was evaluated by fluorescence produced after binding to the Hoechst dye. Transfection of siRNA to primary cells was accomplished by nucleofector electroporation with trabecular meshwork-optimized conditions. cDNA quantification was performed with the use of TaqMan real-time PCR.

RESULTS

Human trabecular meshworks from glaucoma donors exhibited significantly higher levels of ALP activity than their matched counterparts with normal eyes. The normalized ALP of the control specimens was 7.3 +/- 1.6 ng ALP/microg DNA (n = 4), whereas that of the glaucomatous tissue was 37.0 +/- 10.7 ng ALP/microg genomic DNA (n = 5; P

CONCLUSIONS

The increased activity of the calcification marker, ALP, in glaucomatous trabecular meshworks might be indicative of an undergoing mineralization process during development of the disease. Inhibition of the calcification mechanism represented by the presence of active MGP appears to be compromised in glaucomatous tissue.

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Key Words Collapse

MESH Headings

• Adult
• Aged
• Aged, 80 and over
• Alkaline Phosphatase/metabolism
• Biomarkers/metabolism
• Calcinosis/enzymology
• Calcium-Binding Proteins/genetics
• Cells, Cultured
• Dexamethasone/pharmacology
• Electroporation/methods
• Extracellular Matrix Proteins/genetics
• Female
• Gene Silencing
• Glaucoma/enzymology
• Humans
• Male
• Middle Aged
• Polymerase Chain Reaction
• RNA, Small Interfering/pharmacology
• Tissue Donors
• Trabecular Meshwork/drug effects
• Trabecular Meshwork/enzymology
• Transfection
• Transforming Growth Factor beta2/pharmacology
• Up-Regulation
• Matrix Gla Protein

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Grants

• R01 EY013126 NEI NIH HHS
• R01 EY013126-08 NEI NIH HHS
• R01 EY011906 NEI NIH HHS
• R01 EY011906-10 NEI NIH HHS
• EY13126 NEI NIH HHS
• EY11906 NEI NIH HHS

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Affiliation(s)

Wei Xue Department of Ophthalmology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7041, USA
Núria Comes
Teresa Borrás

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Phosphate stimulates matrix Gla protein expression in chondrocytes through the extracellular signal regulated kinase signaling pathway

Whereas increasing evidence suggests that inorganic phosphate (Pi) may act as a signaling molecule in mineralization-competent cells, its mechanisms of action remain largely unknown. The aims of the present work were to determine whether Pi regulates expression of matrix Gla protein (MGP), a mineralization inhibitor, in growth plate chondrocytes and to identify the involved signaling pathways. Chondrogenic ATDC5 cells and primary growth plate chondrocytes were used. Messenger RNA and protein analyses were performed by quantitative PCR and Western blotting, respectively. The activation and role of MAPKs were, respectively, determined by Western blotting and the use of specific inhibitors. Immunohistological detection of ERK1/2 was performed in rib organ cultures from newborn mice. The results indicate that Pi markedly stimulates expression of MGP in ATDC5 cells and primary growth plate chondrocytes. Investigation of the involved intracellular signaling pathways reveals that Pi activates ERK1/2 in a cell-specific manner, because the stimulation was observed in ATDC5 and primary chondrocytes, MC3T3-E1 osteoblasts, and ST2 stromal cells, but not in L929 fibroblasts or C2C12 myogenic cells. Accordingly, immunohistological detection of ERK1/2 phosphorylation in rib growth plates revealed a marked signal in chondrocytes. Finally, a specific ERK1/2 inhibitor, UO126, blocks Pi-stimulated MGP expression in ATDC5 cells, indicating that ERK1/2 mediates, mainly, the effects of Pi. These data demonstrate, for the first time, that Pi regulates MGP expression in growth plate chondrocytes, thereby suggesting a key role for Pi and ERK1/2 in the regulation of bone formation.

Bone morphogenetic protein-induced MSX1 and MSX2 inhibit myocardin-dependent smooth muscle gene transcription

During the onset and progression of atherosclerosis, the vascular smooth muscle cell (VSMC) phenotype changes from differentiated to dedifferentiated, and in some cases, this change is accompanied by osteogenic transition, resulting in vascular calcification. One characteristic of dedifferentiated VSMCs is the down-regulation of smooth muscle cell (SMC) marker gene expression. Bone morphogenetic proteins (BMPs), which are involved in the induction of osteogenic gene expression, are detected in calcified vasculature. In this study, we found that the BMP2-, BMP4-, and BMP6-induced expression of Msx transcription factors (Msx1 and Msx2) preceded the down-regulation of SMC marker expression in cultured differentiated VSMCs. Either Msx1 or Msx2 markedly reduced the myocardin-dependent promoter activities of SMC marker genes (SM22alpha and caldesmon). We further investigated interactions between Msx1 and myocardin/serum response factor (SRF)/CArG-box motif (cis element for SRF) using coimmunoprecipitation, gel-shift, and chromatin immunoprecipitation assays. Our results showed that Msx1 or Msx2 formed a ternary complex with SRF and myocardin and inhibited the binding of SRF or SRF/myocardin to the CArG-box motif, resulting in inhibition of their transcription.

Matrix GLA protein function in human trabecular meshwork cells: inhibition of BMP2-induced calcification process

PURPOSE

The matrix GLA (MGP) gene has been found to be among the 10 most highly expressed genes in the human trabecular meshwork (TM), and its expression is affected by conditions associated with glaucoma. Because MGP protein has been shown to play a key role in inhibiting calcification in cartilage and arterial vessels, MGP's function in human TM was investigated.

METHODS

Perfused TM tissue and primary human TM (HTM) cells originated from donors of nonglaucomatous eyes. MGP mRNA was assayed by relative quantitative and real-time PCR. AdhMGP recombinant adenovirus was generated by bacterial transposition. Western blot analyses were cross-reacted with MGP N-terminal- and conformational-specific antibodies. MGP/BMP2 colocalization was analyzed by confocal microscopy. gamma-Carboxylation activity was measured by incorporation of 14CO2 into FLEEL synthetic peptide. Alkaline phosphatase (ALP) activity was used as a marker of osteogenic differentiation and a calcification precursor. Calcification was assessed by measuring direct calcium (o-cresolphthalein). Normalization was conducted with a telomerase probe (genomic DNA).

RESULTS

HTM cells contained high levels of gamma-carboxylase activity and were able to convert MGP to its active conformation. Overexpression of MGP in HTM cells reduced ALP activity in a model of BMP2-induced osteogenesis. MGP colocalized intracellularly with BMP2. HTM cells aged in culture exhibited increased calcium content, increased ALP, decreased normalized MGP expression and lower gamma-carboxylase activity.

CONCLUSIONS

MGP protein is active and functions as an inhibitor of BMP2-induced ALP activity in the HTM cells. The human TM may undergo a calcification process with age. Inhibition of the calcification mechanism mediated by MGP could be used to regulate resistance and elevated IOP.

The nitric oxide donor sodium nitroprusside inhibits mineralization in ATDC5 cells

The aim of this study was to test whether the nitric oxide (NO) donor sodium nitroprusside (SNP) has an effect on mineralization in ATDC5 cells. Mineralization in ATDC5 cell culture was induced by addition of beta-glycerophosphate or inorganic phosphate, visualized by staining precipitated calcium with an alizarin red stain, and quantified using atomic absorption spectrometry. SNP was shown to inhibit the mineralization of ADTC5 cells. This inhibition was not affected by inhibitors of guanylyl cyclase nor mimicked by a cyclic guanosine monophosphate (cGMP) analog. Furthermore, SNP did not inhibit phosphate uptake or inhibit apoptosis in ATDC5 cells. These findings indicate that SNP can specifically inhibit matrix mineralization via a cGMP-independent pathway and that the effect is not mediated by inhibition of phosphate transport or apoptosis. These results suggest a preventive role of NO in premature or pathological mineralization.

Mesenchymal stem cell therapy to rebuild cartilage

Disorders affecting cartilage touch almost the whole population and are one of the leading causes of invalidity in adults. To repair cartilage, therapeutic approaches initially focused on the implantation of autologous chondrocytes, but this technique proved unsatisfactory because of the limited number of chondrocytes obtained at harvest. The discovery that several adult human tissues contain mesenchymal stem cells (MSCs) capable of differentiating into chondrocytes raised the possibility of injecting MSCs to repair cartilages. The important data published recently on the factors controlling chondrocyte commitment must be thoroughly considered to make further progress towards this therapeutic approach. The potential application of MSC therapy provides new hope for the development of innovative treatments for the repair of cartilage disorders.