Mitigation of ectopic calcification in osteopontin-deficient mice by exogenous osteopontin

Expression of osteogenic proteins in kidneys of cats with nephrocalcinosis

BACKGROUND

Nephrocalcinosis is a common pathological finding in cats with chronic kidney disease and nephrolithiasis. Understanding its pathogenesis may identify future therapeutic targets.

HYPOTHESIS

Nephrocalcinosis is associated with expression of an osteogenic phenotype.

ANIMALS

Kidneys with medullary mineralization were obtained from 18 cats (10 with and 8 without nephroliths) undergoing necropsy.

METHODS

Cross-sectional study. Microradiography and histopathology (modified von Kossa stain) were used to confirm parenchymal mineralization. Immunohistochemistry for 5 osteogenic markers was performed to determine their co-localization with nephrocalcinosis. The proportion of kidneys with stronger immunointensity in mineralized versus non-mineralized regions was analyzed using 1-tailed sign tests. The proportion of kidneys with co-localization of nephrocalcinosis and each marker was compared between kidneys with and without nephroliths using Fisher's exact tests.

RESULTS

Nephrocalcinosis co-localized with osteopontin immunoreactivity in all 18 cats (100%) and with osteocalcin in 12 cats (67%). Both osteogenic markers had stronger immunointensity in mineralized regions compared with non-mineralized regions. Limited co-localization was observed with other markers: bone morphogenic protein-2 in 2 kidneys (both with nephroliths) and tissue non-specific alkaline phosphatase in 1 kidney (without nephroliths); runt-related transcription factor-2 was undetected. No statistically significant differences were found in the co-localization of nephrocalcinosis with osteogenic proteins between kidneys with and without nephroliths.

CONCLUSIONS AND CLINICAL IMPORTANCE

Expression of osteogenic proteins in areas of nephrocalcinosis indicates that nephrocalcinosis is associated with the development of an osteogenic phenotype. Targeting these processes could offer a novel approach to prevent nephrolithiasis at its origin.

Role of osteokines in atherosclerosis

Despite their diverse physiologies and roles, the heart, skeletal muscles, and smooth muscles all derive from a common embryonic source as bones. Moreover, bone tissue, skeletal and smooth muscles, and the heart share conserved signaling pathways. The maintenance of skeletal health is precisely regulated by osteocytes, osteoblasts, and osteoclasts through coordinated secretion of bone-derived factors known as osteokines. Increasing evidence suggests the involvement of osteokines in regulating atherosclerotic vascular disease. Therefore, this review aims to examine the evidence for the role of osteokines in atherosclerosis development and progression comprehensively. Specifically discussed are extensively studied osteokines in atherosclerosis such as osteocalcin, osteopontin, osteoprotegerin, and fibroblast growth factor 23. Additionally, we highlighted the effects of exercise on modulating these key regulators derived from bone tissue metabolism. We believe that gaining an enhanced understanding of how osteocalcin contributes to the process of atherosclerosis will enable us to develop targeted and comprehensive therapeutic strategies against diseases associated with its progression.

Pharmacological and mechanistic aspects of quercetin in osteoporosis

Osteoporosis (OP) is a bone disease associated with increasing age. Currently, the most common medications used to treat OP are anabolic agents, anti-resorptive agents, and medications with other mechanisms of action. However, many of these medications have unfavorable adverse effects or are not intended for long-term use, potentially exerting a severe negative impact on a patient's life and career and placing a heavy burden on families and society. There is an urgent need to find new drugs that can replace these and have fewer adverse effects. Quercetin (Que) is a common flavonol in nature. Numerous studies have examined the therapeutic applications of Que. However, a comprehensive review of the anti-osteoporotic effects of Que has not yet been conducted. This review aimed to describe the recent studies on the anti-osteoporotic effects of Que, including its biological, pharmacological, pharmacokinetic, and toxicological properties. The outcomes demonstrated that Que could enhance OP by increasing osteoblast differentiation and activity and reducing osteoclast differentiation and activity via the pathways of Wnt/β-catenin, BMP/SMAD/RUNX2, OPG/RANKL/RANK, ERK/JNK, oxidative stress, apoptosis, and transcription factors. Thus, Que is a promising novel drug for the treatment of OP.

The Role of Osteopontin in Atherosclerosis and Its Clinical Manifestations (Atherosclerotic Cardiovascular Diseases)-A Narrative Review

Atherosclerotic cardiovascular diseases (ASCVDs) are the most common and severe public health problem nowadays. Osteopontin (OPN) is a multifunctional glycoprotein highly expressed at atherosclerotic plaque, which has emerged as a potential biomarker of ASCVDs. OPN may act as an inflammatory mediator and/or a vascular calcification (VC) mediator, contributing to atherosclerosis progression and eventual plaque destabilization. In this article, we discuss the complex role of OPN in ASCVD pathophysiology, since many in vitro and in vivo experimental data indicate that OPN contributes to macrophage activation and differentiation, monocyte infiltration, vascular smooth muscle cell (VSMC) migration and proliferation and lipid core formation within atherosclerotic plaques. Most but not all studies reported that OPN may inhibit atherosclerotic plaque calcification, making it "vulnerable". Regarding clinical evidence, serum OPN levels may become a biomarker of coronary artery disease (CAD) presence and severity. Significantly higher OPN levels have been found in patients with acute coronary syndromes than those with stable CAD. In limited studies of patients with peripheral artery disease, circulating OPN concentrations may be predictive of future major adverse cardiovascular events. Overall, the current literature search suggests the contribution of OPN to atherosclerosis development and progression, but more robust evidence is required.

Osteopontin - The stirring multifunctional regulatory factor in multisystem aging

Osteopontin (OPN) is a multifunctional noncollagenous matrix phosphoprotein that is expressed both intracellularly and extracellularly in various tissues. As a growth regulatory protein and proinflammatory immunochemokine, OPN is involved in the pathological processes of many diseases. Recent studies have found that OPN is widely involved in the aging processes of multiple organs and tissues, such as T-cell senescence, atherosclerosis, skeletal muscle regeneration, osteoporosis, neurodegenerative changes, hematopoietic stem cell reconstruction, and retinal aging. However, the regulatory roles and mechanisms of OPN in the aging process of different tissues are not uniform, and OPN even has diverse roles in different developmental stages of the same tissue, generating uncertainty for the future study and utilization of OPN. In this review, we will summarize the regulatory role and molecular mechanism of OPN in different tissues and cells, such as the musculoskeletal system, central nervous system, cardiovascular system, liver, and eye, during senescence. We believe that a better understanding of the mechanism of OPN in the aging process will help us develop targeted and comprehensive therapeutic strategies to fight the spread of age-related diseases.

Osteopontin in Cardiovascular Diseases

Unprecedented advances in secondary prevention have greatly improved the prognosis of cardiovascular diseases (CVDs); however, CVDs remain a leading cause of death globally. These findings suggest the need to reconsider cardiovascular risk and optimal medical therapy. Numerous studies have shown that inflammation, pro-thrombotic factors, and gene mutations are focused not only on cardiovascular residual risk but also as the next therapeutic target for CVDs. Furthermore, recent clinical trials, such as the Canakinumab Anti-inflammatory Thrombosis Outcomes Study trial, showed the possibility of anti-inflammatory therapy for patients with CVDs. Osteopontin (OPN) is a matricellular protein that mediates diverse biological functions and is involved in a number of pathological states in CVDs. OPN has a two-faced phenotype that is dependent on the pathological state. Acute increases in OPN have protective roles, including wound healing, neovascularization, and amelioration of vascular calcification. By contrast, chronic increases in OPN predict poor prognosis of a major adverse cardiovascular event independent of conventional cardiovascular risk factors. Thus, OPN can be a therapeutic target for CVDs but is not clinically available. In this review, we discuss the role of OPN in the development of CVDs and its potential as a therapeutic target.

GFOGER Peptide Modifies the Protein Content of Extracellular Vesicles and Inhibits Vascular Calcification

OBJECTIVE

Vascular calcification (VC) is an active process during which vascular smooth muscle cells (VSMCs) undergo an osteogenic switch and release extracellular vesicles (EVs). In turn, the EVs serve as calcification foci via interaction with type 1 collagen (COL1). We recently showed that a specific, six-amino-acid repeat (GFOGER) in the sequence of COL1 was involved in the latter's interaction with integrins expressed on EVs. Our main objective was to test the GFOGER ability to inhibit VC.

APPROACH

We synthesized the GFOGER peptide and tested its ability to inhibit the inorganic phosphate (Pi)-induced calcification of VSMCs and aortic rings. Using mass spectrometry, we studied GFOGER's effect on the protein composition of EVs released from Pi-treated VSMCs.

RESULTS

Calcification of mouse VSMCs (MOVAS-1 cells), primary human VSMCs, and rat aortic rings was lower in the presence of GFOGER than with Pi alone (with relative decreases of 66, 58, and 91%, respectively; p < 0.001 for all) (no effect was observed with the scramble peptide GOERFG). A comparative proteomic analysis of EVs released from MOVAS-1 cells in the presence or absence of Pi highlighted significant differences in EVs' protein content. Interestingly, the expression of some of the EVs' proteins involved in the calcification process (such as osteogenic markers, TANK-binding kinase 1, and casein kinase II) was diminished in the presence of GFOGER peptide (data are available via ProteomeXchange with identifier PXD018169∗). The decrease of osteogenic marker expression observed in the presence of GFOGER was confirmed by q-RT-PCR analysis.

CONCLUSION

GFOGER peptide reduces vascular calcification by modifying the protein content of the subsequently released EVs, in particular by decreasing osteogenicswitching in VSMCs.

Quantitative determination of osteopontin in bovine, buffalo, yak, sheep and goat milk by Ultra-high performance liquid chromatography-tandem mass spectrometry and stable isotope dimethyl labeling

Osteopontin (OPN) is a multifunctional protein present in different tissues, body fluids and milk. Different milk has different level of OPN content. To determine the amount of osteopontin in bovine, buffalo, yak, sheep and goat milk, we developed an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method to detect an osteopontin signature peptide. The signature peptides selected by searching Uniprot database for trypsin digested osteopontin. The sample preparation procedure includes trypsin digestion, dimethyl labeling of tryptic peptides, purification and concentration of labeled tryptic peptide with solid phase extraction. The limit of detection and limit of quantification are 0.5 mg L^-1 and 2.0 mg L^-1, respectively. The method has satisfactory analytical performance with a linearity of R² ≥ 0.998, recoveries of 103.7-111.0%, and precision of 1.8-6.2%. It is also validated and successfully applied to quantifying osteopontin content in bovine, buffalo, yak, sheep and goat milk.

Osteopontin in Vascular Disease

Inflammatory cytokines are necessary for an acute response to injury and the progressive healing process. However, when this acute response does not resolve and becomes chronic, the same proteins that once promoted healing then contribute to chronic inflammatory pathologies, such as atherosclerosis. OPN (Osteopontin) is a secreted matricellular cytokine that signals through integrin and CD44 receptors, is highly upregulated in acute and chronic inflammatory settings, and has been implicated in physiological and pathophysiologic processes. Evidence from the literature suggests that OPN may fit within the Goldilocks paradigm with respect to cardiovascular disease, where acute increases are protective, attenuate vascular calcification, and promote postischemic neovascularization. In contrast, chronic increases in OPN are clinically associated with an increased risk for a major adverse cardiovascular event, and OPN expression is a strong predictor of cardiovascular disease independent of traditional risk factors. With the recent finding that humans express multiple OPN isoforms as the result of alternative splicing and that these isoforms have distinct biologic functions, future studies are required to determine what OPN isoform(s) are expressed in the setting of vascular disease and what role each of these isoforms plays in vascular disease progression. This review aims to discuss our current understanding of the role(s) of OPN in vascular disease pathologies using evidence from in vitro, animal, and clinical studies. Where possible, we discuss what is known about OPN isoform expression and our understanding of OPN isoform contributions to cardiovascular disease pathologies.

Osteopontin protects against high phosphate-induced nephrocalcinosis and vascular calcification

Pathologic calcification is a significant cause of increased morbidity and mortality in patients with chronic kidney disease. The precise mechanisms of ectopic calcification are not fully elucidated, but it is known to be caused by an imbalance of procalcific and anticalcific factors. In the chronic kidney disease population, an elevated phosphate burden is both highly prevalent and a known risk factor for ectopic calcification. Here we tested whether osteopontin, an inhibitor of calcification, protects against high phosphate load-induced nephrocalcinosis and vascular calcification. Osteopontin knockout mice were placed on a high phosphate diet for 11 weeks. Osteopontin deficiency together with phosphate overload caused uremia, nephrocalcinosis characterized by substantial renal tubular and interstitial calcium deposition, and marked vascular calcification when compared with control mice. Although the osteopontin-deficient mice did not exhibit hypercalcemia or hyperphosphatemia, they did show abnormalities in the mineral metabolism hormone fibroblast growth factor-23. Thus, endogenous osteopontin plays a critical role in the prevention of phosphate-induced nephrocalcinosis and vascular calcification in response to high phosphate load. A better understanding of osteopontin's role in phosphate-induced calcification will hopefully lead to better biomarkers and therapies for this disease, especially in patients with chronic kidney disease and other at-risk populations.

Engineering biomaterials to integrate and heal: the biocompatibility paradigm shifts

This article focuses on one of the major failure routes of implanted medical devices, the foreign body reaction (FBR)--that is, the phagocytic attack and encapsulation by the body of the so-called "biocompatible" biomaterials comprising the devices. We then review strategies currently under development that might lead to biomaterial constructs that will harmoniously heal and integrate into the body. We discuss in detail emerging strategies to inhibit the FBR by engineering biomaterials that elicit more biologically pertinent responses.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Sox9 transcriptionally represses Spp1 to prevent matrix mineralization in maturing heart valves and chondrocytes

Sox9 is an SRY-related transcription factor required for expression of cartilaginous genes in the developing skeletal system and heart valve structures. In contrast to positively regulating cartilaginous matrix, Sox9 also negatively regulates matrix mineralization associated with bone formation. While the transcriptional activation of Sox9 target genes during chondrogenesis has been characterized, the mechanisms by which Sox9 represses osteogenic processes are not so clear. Using ChIP-on-chip and luciferase assays we show that Sox9 binds and represses transactivation of the osteogenic glycoprotein Spp1. In addition, Sox9 knockdown in post natal mouse heart valve explants and rib chondrocyte cultures promotes Spp1 expression and matrix mineralization, while attenuating expression of cartilage genes Type II Collagen and Cartilage Link Protein. Further, we show that Spp1 is required for matrix mineralization induced by Sox9 knockdown. These studies provide insights into the molecular mechanisms by which Sox9 prevents pathologic matrix mineralization in tissues that must remain cartilaginous.

Recent progress in the treatment of vascular calcification

Vascular calcification is common in patients with advanced chronic kidney disease and is associated with poorer outcomes. Although the pathophysiology is not completely understood, it is clear that it is a multifactorial process involving altered mineral metabolism, as well as changes in systemic and local factors that can promote or inhibit vascular calcification, and all of these are potential therapeutic targets. Current therapy is closely linked to strategies for preventing disordered bone and mineral metabolism in advanced kidney disease and involves lowering the circulating levels of both phosphate and calcium. The efficacy of compounds that specifically target calcification, such as bisphosphonates and thiosulfate, has been shown in animals but only in small numbers of humans, and safety remains an issue. Additional therapies, such as pyrophosphate, vitamin K, and lowering of pH, are supported by animal studies, but are yet to be investigated clinically. As the mineral composition of vascular calcifications is the same as in bone, potential effects on bone must be addressed with any therapy for vascular calcification.

Local low-dose lovastatin delivery improves the bone-healing defect caused by Nf1 loss of function in osteoblasts

Postfracture tibial nonunion (pseudoarthrosis) leads to lifelong disability in patients with neurofibromatosis type I (NF1), a disorder caused by mutations in the NF1 gene. To determine the contribution of NF1 in bone healing, we assessed bone healing in the Nf1(ob) (-/-) conditional mouse model lacking Nf1 specifically in osteoblasts. A closed distal tibia fracture protocol and a longitudinal study design were used. During the 21- to 28-day postfracture period, callus volume, as expected, decreased in wild-type but not in Nf1(ob) (-/-) mice, suggesting delayed healing. At these two time points, bone volume (BV/TV) and volumetric bone mineral density (vBMD) measured by 3D micro-computed tomography were decreased in Nf1(ob) (-/-) callus-bridging cortices and trabecular compartments compared with wild-type controls. Histomorphometric analyses revealed the presence of cartilaginous remnants, a high amount of osteoid, and increased osteoclast surfaces in Nf1(ob) (-/-) calluses 21 days after fracture, which was accompanied by increased expression of osteopontin, Rankl, and Tgfbeta. Callus strength measured by three-point bending 28 days after fracture was reduced in Nf1(ob) (-/-) versus wild-type calluses. Importantly, from a clinical point of view, this defect of callus maturation and strength could be ameliorated by local delivery of low-dose lovastatin microparticles, which successfully decreased osteoid volume and cartilaginous remnant number and increased callus BV/TV and strength in mutant mice. These results thus indicate that the dysfunctions caused by loss of Nf1 in osteoblasts impair callus maturation and weaken callus mechanical properties and suggest that local delivery of low-dose lovastatin may improve bone healing in NF1 patients.

Considerable variation in the concentration of osteopontin in human milk, bovine milk, and infant formulas

Osteopontin (OPN) is a multifunctional bioactive protein that is implicated in numerous biological processes such as bone remodeling, inhibition of ectopic calcification, and cellular adhesion and migration, as well as several immune functions. Osteopontin has cytokine-like properties and is a key factor in the initiation of T helper 1 immune responses. Osteopontin is present in most tissues and body fluids, with the highest concentrations being found in milk. In the present study, ELISA for human and bovine milk OPN were developed and OPN concentration in human breast milk, bovine milk, and infant formulas was measured and compared. The OPN concentration in human milk was measured to approximately 138 mg/L, which corresponds to 2.1% (wt/wt) of the total protein in human breast milk. This is considerably higher than the corresponding OPN concentrations in bovine milk (approximately 18 mg/L) and infant formulas (approximately 9 mg/L). Moreover, bovine milk OPN is shown to induce the expression of the T helper 1 cytokine IL-12 in cultured human lamina propria mononuclear cells isolated from intestinal biopsies. Finally, the OPN concentration in plasma samples from umbilical cords, 3-mo-old infants, and pregnant and nonpregnant adults was measured. The OPN level in plasma from 3-mo-old infants and umbilical cords was found to be 7 to 10 times higher than in adults. Thus, the high levels of OPN in milk and infant plasma suggest that OPN is important to infants and that ingested milk OPN is likely to induce cytokine production in neonate intestinal immune cells.

The role of osteopontin in inflammatory processes

Osteopontin (OPN) is a matricellular protein that mediates diverse biological functions. OPN is involved in normal physiological processes and is implicated in the pathogenesis of a variety of disease states, including atherosclerosis, glomerulonephritis, cancer, and several chronic inflammatory diseases. Through interactions with several integrins, OPN mediates cell migration, adhesion, and survival in many cell types. OPN also functions as a Th1 cytokine, promotes cell-mediated immune responses, and plays a role in chronic inflammatory and autoimmune diseases. Besides its function in inflammation, OPN is also a regulator of biomineralization and a potent inhibitor of vascular calcification.

Evidence of enhanced expression of osteopontin in spinal hyperostosis of the twy mouse

STUDY DESIGN

Gene expression and protein localization of osteopontin (OPN) in spinal hyperostosis of the twy mouse by means of in situ hybridization, immunohistochemistry, and Northern blot analysis.

OBJECTIVE

To verify the involvement of OPN in spinal hyperostosis in the twy mouse and elucidate its ossification pattern at molecular levels.

SUMMARY OF BACKGROUND DATA

OPN is a molecule that consistently colocalizes with ectopic calcification in human pathologic conditions. The twy mouse, which shows ectopic calcification of the spinal ligament resulting in hind limb paralysis, is considered to be a model for human ossification of the posterior longitudinal ligament of the spine.

METHODS

Twenty-eight each of age-matched twy, heterozygote, and wild-type mice were killed at 2, 4, 8, 12, and 16 weeks old and subject to histologic and/or molecular analyses. Sections were hybridized with RNA probes for OPN and also stained with anti-OPN antibodies. Total cellular RNA was extracted from the cervicothoracic spine of each genotype at 2- and 16-week-old, and gene expression for OPN and COL10A1 was quantified by Northern blot analysis.

RESULTS

Enhanced expression of OPN mRNA was observed in spinal hyperostotic lesions of the twy mouse, specifically in cells of the spinal ligament and chondrogenic cells in the outer layer of the anulus fibrosus. These trends were also confirmed by immunohistochemical analyses. Northern blot analysis showed that a considerable amount of OPN transcripts was detected in all genotypes at 2 weeks old, but the robust expression of OPN mRNA was maintained only in twy mice at 16 weeks old. COL10A1 transcripts were hardly detected regardless of the genotype at 16 weeks old.

CONCLUSION

OPN was overexpressed in the hyperostotic spinal lesions of twy mice, and the hyperostosis was induced mainly by ectopic ossification of the spinal ligament. Because OPN is considered to be an inhibitor of calcification, further studies will be necessary to verify whether OPN overexpressed in the twy mouse is functional.

Phosphate feeding induces arterial medial calcification in uremic mice: role of serum phosphorus, fibroblast growth factor-23, and osteopontin

Arterial medial calcification is a major complication in patients with chronic kidney disease and is a strong predictor of cardiovascular and all-cause mortality. We sought to determine the role of dietary phosphorus and the severity of uremia on vascular calcification in calcification-prone DBA/2 mice. Severe and moderate uremia was induced by renal ablation of varying magnitudes. Extensive arterial-medial calcification developed only when the uremic mice were placed on a high-phosphate diet. Arterial calcification in the severely uremic mice fed a high-phosphate diet was significantly associated with hyperphosphatemia. Moderately uremic mice on this diet were not hyperphosphatemic but had a significant rise in their serum levels of fibroblast growth factor 23 (FGF-23) and osteopontin that significantly correlated with arterial medial calcification. Although there was widespread arterial medial calcification, there was no histological evidence of atherosclerosis. At early stages of calcification, the osteochondrogenic markers Runx2 and osteopontin were upregulated, but the smooth muscle cell marker SM22alpha decreased in medial cells, as did the number of smooth muscle cells in extensively calcified regions. These findings suggest that phosphate loading and the severity of uremia play critical roles in controlling arterial medial calcification in mice. Further, FGF-23 and osteopontin may be markers and/or inducers of this process.

Reduced foreign body reaction to implanted biomaterials by surface treatment with oriented osteopontin

The foreign body reaction (FBR), which leads to the encapsulation of implanted biomaterials, has been implicated in the failure of many medical devices. The protein layer that is nonspecifically adsorbed onto the implant surface immediately after implantation is thought to dictate this reaction. It is hypothesized that biomaterial surfaces having specific proteins with precisely controlled orientations will decrease the FBR. Previously, we have reported that osteopontin (OPN) adsorbed on positively charged surfaces has a preferable orientation for in vitro cell adhesion and spreading as compared to negatively charged surfaces. It is expected that coating a layer of OPN in its preferred orientation on an implant surface will decrease the FBR. In this work, in vivo studies were performed to test this hypothesis. A positively charged polymer (p(HEMA-co-AEMA)) and a negatively charged polymer (p(HEMA-co-CEA)) coated with OPN were implanted subcutaneously in wild-type mice for 7 or 28 days. Uncoated polymers were used as control. For the 7-day implants, cells on OPN-coated p(HEMA-co-AEMA) spread more than cells on the other three materials. Following 28 days of implantation the implants were explanted and the capsule thickness and vascularity around the implants were characterized. Additionally, the macrophage and foreign body giant cells (FBGCs) around the implants were quantified. It was found in this study that the modification of the positively charged polymer surface with OPN in a controlled orientation led to a reduction in the foreign body reaction as determined by capsule thickness. Our finding provides valuable information for designing better biocompatible biomaterials with improved in vivo performance.

Noncollagenous bone matrix proteins as a part of calcific aortic valve disease regulation

Clinically, calcific aortic valve disease is a progressive continuum from obstructive fibro(sclero)tic valve thickening to aortic stenosis. Recent evidence suggests that, in addition to nonbone miscellaneous mineralization, calcified valves present distinct signs of active bone remodeling; and in this context, noncollagenous bone-associated proteins are assumed to have a critical role. The expression of 5 bone matrix proteins-bone morphogenetic protein-2 and -4, bone sialoprotein II, osteopontin, and osteoprotegerin-was examined by reverse transcriptase polymerase chain reaction (n = 31) and immunolabeling (n = 83) in the clinical continuum from healthy pliable valves to heavily calcified ones. As a known structural pathologic sign, the extent of neovascularization was also examined. We observed progressive increase in the gene expression of osteopontin (7.4-fold elevation, P < .001) and bone sialoprotein II (5.8-fold elevation, P < .05), and also 1.7-fold elevation (P < .05) in osteoprotegerin gene expression during the disease course. These findings were congruent with that of immunohistochemical analysis. Surprisingly, bone morphogenetic protein-2 and -4 showed a comparable significant decrease in messenger RNA levels in calcified valves (P < .01 and P < .05, respectively). Our results support the view that aortic valve calcification is an actively regulated process. Furthermore, the results suggest that the expression of pro- and anticalcific noncollagenous bone-associated matrix proteins is altered during the disease continuum and that this imbalance may contribute to the pathology of calcific aortic valve disease.

Simple obesity is associated with reduced breast arterial calcification and increased plasma osteopontin level

BACKGROUND

We undertook this study to evaluate whether simple obesity is associated with breast arterial calcifications.

METHODS

Mammograms and patient records of 1309 women who underwent screening or diagnostic mammography were reviewed retrospectively. Patients were divided into two groups according to body mass index. Mammograms were evaluated for the presence of arterial calcification and results were coded. Plasma osteopontin levels were measured.

RESULTS

The prevalence of breast arterial calcification of patients classified with simple obesity was lower than the non-obese group. Obese group exhibited significantly increased circulating osteopontin concentrations as compared with non-obese group. Plasma osteopontin level is an independent protective factor for the presence of breast arterial calcification.

CONCLUSIONS

Simple obesity is associated with reduced breast arterial calcification. Our study indicates the use of breast artery calcification as an indicator of cardiovascular disease or arterial status should be reconsidered.

Identification of osteopontin phosphorylation sites involved in bone remodeling and inhibition of pathological calcification

Osteopontin is a noncollagenous, phosphorylated extracellular glycoprotein, expressed in mineralized and nonmineralized tissues, organs and body fluids. The protein contains an RGD tripeptide cell-binding motif, and is subjected to a variety of posttranslational modifications that play important roles in its multiple biological functions, such as bone remodeling and inhibition of pathological calcification. In this study, we have expressed bovine osteopontin in a prokaryotic system and identified the seven amino acid residues phosphorylated in vitro by CKII.

Role of carbonic anhydrase II in ectopic calcification

INTRODUCTION

Osteopontin (OPN) is a potent inhibitor of ectopic calcification. Previous studies suggested that, in addition to blocking apatite crystal growth, OPN promoted regression of ectopic calcification by inducing the expression of acid-generating carbonic anhydrase II (CAR2) in monocyte-derived cells.

METHODS

To test this hypothesis, OPN and CAR2 expression and calcification of subcutaneously implanted glutaraldehyde-fixed bovine pericardium (GFBP) were studied in CAR2 mutant mice.

RESULTS

Consistent with previous studies in Black Swiss mice, GFBP calcified to a greater extent in OPN-deficient mice compared to wild types on the C57Bl/6 background. GFBP implanted in CAR2-deficient mice (CAR2(-/-)) were significantly more calcified than those implanted into wild-type mice (CAR2(+/+)) [37+/-5 vs. 20+/-6.5 microg Ca/mg tissue, respectively, at 30 days (P<.001), and 42+/-5 versus 20+/-4 microg Ca/mg tissue at 60 days, respectively (P<.001)]. On the other hand, OPN levels within and surrounding the implants were similar in CAR2(+/+) and CAR2(-/-) mice, suggesting that OPN expression in the absence of CAR2 was not sufficient to mitigate ectopic calcification.

CONCLUSIONS

These results indicate that CAR2 expression is an important regulator of ectopic calcification, potentially by facilitating OPN mediated mineral regression.

Control of osteopontin signaling and function by post-translational phosphorylation and protein folding

Osteopontin (OPN) plays roles in a variety of cellular processes from bone resorption and extracellular matrix (ECM) remodeling to immune cell activation and inhibition of apoptosis. Because it binds receptors (integrins, CD44 variants) typically engaged by ECM molecules, OPN acts as a "soluble" ECM molecule. A persistent theme throughout the characterization of how OPN functions has been the importance of phosphorylation. The source of the OPN used in specific experiments and the location of modified sites is an increasingly important consideration for OPN research. We review briefly some of the ways OPN impacts on the biology of mammalian systems with an emphasis on the importance of serine phosphorylation in modulating its signaling ability. We describe experiments that support the hypothesis that differences in the post-translational phosphorylation of OPN expressed by different cell types regulate how it impacts on target cells. Analyses of OPN's potential secondary structure reveal a possible beta-sheet conformation that offers an interpretation of certain experimental observations, specifically the effect of thrombin cleavage; it is consistent with an interaction between the C-terminal region of the protein and the central integrin-binding RGD sequence.

Osteopontin

Osteopontin (OPN) is a multifunctional molecule highly expressed in chronic inflammatory and autoimmune diseases, and it is specifically localized in and around inflammatory cells. OPN is a secreted adhesive molecule, and it is thought to aid in the recruitment of monocytes-macrophages and to regulate cytokine production in macrophages, dendritic cells, and T-cells. OPN has been classified as T-helper 1 cytokine and thus believed to exacerbate inflammation in several chronic inflammatory diseases, including atherosclerosis. Besides proinflammatory functions, physiologically OPN is a potent inhibitor of mineralization, it prevents ectopic calcium deposits and is a potent inducible inhibitor of vascular calcification. Clinically, OPN plasma levels have been found associated with various inflammatory diseases, including cardiovascular burden. It is thus imperative to dissect the OPN proinflammatory and anticalcific functions. OPN recruitment functions of inflammatory cells are thought to be mediated through its adhesive domains, especially the arginine-glycine-aspartate (RGD) sequence that interacts with several integrin heterodimers. However, the integrin receptors and intracellular pathways mediating OPN effects on immune cells are not well established. Furthermore, several studies show that OPN is cleaved by at least 2 classes of proteases: thrombin and matrix-metalloproteases (MMPs). Most importantly, at least in vitro , fragments generated by cleavage not only maintain OPN adhesive functions but also expose new active domains that may impart new activities. The role for OPN proteolytic fragments in vivo is almost completely unexplored. We believe that further knowledge of the effects of OPN fragments on cell responses might help in designing therapeutics targeting inflammatory and cardiovascular diseases.

Arterial calcification and stiffness in chronic kidney disease

1. Patients with chronic kidney disease (CKD) demonstrate a high burden of vascular disease. This vascular disease is unusual by way of a preponderance of medial calcification. Further, traditional cardiovascular risk factors fail to fully explain the high cardiovascular event rate in this population. 2. The present review examines the problem of medial calcification and arterial stiffness evident in patients with CKD and explores evidence for its existence and the potential pathological process involved. Many factors are emerging as potential culprits in this disease entity, although the specific roles of components such as fetuin-A, matrix Gla protein, osteopontin and fibroblast growth factor-23 have yet to be determined. Calcium and phosphate balance remains integral to the pathological process. 3. Pulse wave velocity has proven to be a useful tool to assess and follow arterial stiffness in CKD patients and is discussed. 4. Finally, techniques aimed at reducing or reversing arterial calcification and stiffness are discussed, with as yet no definitive answers available.

Mechanisms of vascular calcification

Vascular calcification is highly prevalent and correlated with high rates of cardiovascular mortality in chronic kidney disease patients. Recent evidence suggests that mineral, hormonal, and metabolic imbalances that promote phenotype change in vascular cells as well as deficiencies in specific mineralization inhibitory pathways may be important contributory factors for vascular calcification in these patients. This article reviews current mechanisms proposed for the regulation of vascular calcification and data supporting their potential contribution to this process in chronic kidney disease.

Osteopontin: role in cell signaling and cancer progression

Cell migration and degradation of the extracellular matrix (ECM) are crucial steps in tumor progression. Several matrix-degrading proteases, including matrix metalloproteases, are highly regulated by growth factors, cytokines and ECM proteins. Osteopontin (OPN), a chemokine-like, calcified ECM-associated protein, plays a crucial role in determining the metastatic potential of various cancers. Since its first identification in bone, the multifaceted roles of OPN have been an area of intense investigation. Extensive research has elucidated the pivotal role of OPN in regulating the cell signaling that controls tumor progression and metastasis. This review focuses on recent advances in understanding the functional role of the OPN-induced signaling pathway in the regulation of cell migration and tumor progression and the implications for identifying novel targets for cancer therapy.

Arteriosclerosis, calcium phosphate deposition and cardiovascular disease in uremia: current concepts at the bench

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease. A growing body of data points to nontraditional risk factors, including disturbances in mineral metabolism, as important determinants of the extremely high cardiovascular morbidity and mortality rates in these patients. Disturbances in mineral metabolism, especially elevated calcium and phosphate levels, have been linked to vascular and valvular calcification, both of which are associated with poor prognosis in chronic kidney disease patients. This review highlights important recent findings regarding the etiology of vascular calcification, with special emphasis on pathways that may be particularly relevant in chronic kidney disease patients.

RECENT FINDINGS

New studies indicate that not only vascular intimal calcification (associated with atherosclerosis) but also vascular medial calcification are correlated with decreased survival in chronic kidney disease patients. With the relatively recent recognition of vascular calcification as an actively regulated process, a growing list of inducers (calcium, phosphate, inflammatory cytokines) and inhibitors (matrix Gla protein, fetuin, pyrophosphate, osteopontin) have been discovered. Interesting recent evidence suggests that they may contribute to the prevalence of this pathology in chronic kidney disease patients.

SUMMARY

Vascular calcification is associated with decreased survival in chronic kidney disease patients. Understanding the causes and regulatory factors controlling vascular calcification will help refine therapeutic modalities currently in use, as well as develop novel therapeutics to abate and potentially reverse this deleterious process.