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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2007;27:2302.)
© 2007 American Heart Association, Inc.

Brief Reviews

Osteopontin

A Multifunctional Molecule Regulating Chronic Inflammation and Vascular Disease

Marta Scatena; Lucy Liaw; Cecilia M. Giachelli

From the Department of Bioengineering (M.S., C.M.G.), University of Washington, Seattle; and the Maine Medical Center Research Institute (L.L.), Scarborough.

Correspondence to Marta Scatena, Department of Bioengineering, University of Washington, Box 355061, Seattle, WA 98195. E-mail mscatena{at}u.washington.edu

	Abstract

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
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.

Osteopontin OPN is expressed in chronic inflammatory diseases and regulates chemotaxis and cytokine production. Although OPN adhesive domains are characterized, signaling pathways mediating OPN effects on immune cells are not well established. OPN is cleaved by thrombin and matrix-metalloproteases to generate fragments with novel receptor binding sites and activity, suggesting that proteolysis is an important mechanism to regulate OPN function.

Key Words: osteopontin • osteopontin proteolytic processing • inflammation • atherosclerosis

	Introduction

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
OPN is an aspartic acid-rich, N-linked glycosylated protein that may be highly phosphorylated on serines and threonines depending on the cell type.^1,2 Functionally, OPN is a secreted protein with important roles in normal physiological as well pathological processes. During development it is expressed during gastrulation in the notochord and the embryonic /maternal interface,³ and later in regions of cartilage condensation and bone formation,^4,5 and a number of epithelial tissues.⁵ However, despite OPN expression during the embryonic phase, OPN^–/– mice develop normally and are fertile.⁶ In the adult, OPN protein is generally restricted to bones, kidneys and the epithelial linings.²

Clinically, OPN plasma levels are elevated in many diseases characterized by chronic inflammation, including Crohn disease,⁷ several types of cancer,^8–10 autoimmune diseases,^11,12 and obesity.¹³ Importantly, OPN plasma levels are significantly associated with the presence and the extent of cardiovascular disease independently of traditional risk factors.¹⁴ Plasma OPN levels are also higher in patients with restenosis, and it is an independent risk factor for restenosis.¹⁵ Furthermore, Ohmori et al determined that OPN levels were higher in patients presenting signs of vascular calcification than those without and correlated with the number of segments affected.¹⁴ Finally, very recently Golledge et al have shown that serum and tissue concentrations of OPN are associated with human abdominal aortic aneurysm.¹⁶ These results suggest that OPN plasma levels in patients affected with cardiovascular disease may reflect the extent of atherosclerosis and that OPN may play a role in plaque formation and vascular disease progression.

	OPN Role in Biomineralization

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
Several studies, including in OPN^–/– mice, demonstrate that one major physiological function of OPN is the control of biomineralization. OPN^–/– mice have impaired bone resorption leading to increased trabecular bone with age and in response to parathyroid hormone, ovariectomy or mechanical unloading.^17,18 OPN^–/– bones are hypermineralized and more fragile than those from wild-type mice,^19,20 indicating that OPN plays a role in regulating apatite crystal size and growth most likely by its ability to directly bind to specific apatite crystal faces.²¹ In addition, OPN appears to modulate osteoclast differentiation as well as bone resorption through the ligation of the _vβ₃ integrin.²²

OPN is also highly expressed in the kidney and is found at high levels in urine. Uropontin, the urinary form of OPN, suppresses growth and aggregation of calcium oxalate crystals, thus blocking the binding of the crystals to renal epithelial cells. As a consequence, OPN^–/– mice show increased susceptibility to oxalate-overload induced stone formation.^23,24 More recent studies also indicate that OPN plays a major role in the regulation of ectopic calcification and pathological mineralization of the vasculature, which will be described in greater detail below.^25–27

	OPN Role in Tissue Remodeling

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
OPN acts both as a matricellular protein, thereby facilitating adhesion and migration, as well as a soluble cytokine.²⁸ Several in vitro studies indicate that OPN induces adhesion, migration, and survival of several cell types, including smooth muscle cells, endothelial cells, renal epithelial cells, and inflammatory cells.^29–34 In vivo studies of OPN in disease and injury have suggested an important function for this molecule in inflammation and tissue remodeling.^1,2 In particular, OPN is de novo expressed in cells participating in renal and cardiovascular system of remodeling and repair processes.^25,35–39

In addition to being expressed in specific tissues, OPN is highly expressed in inflammatory cells associated with many diseases including cancer,⁴⁰ arterial restenosis,⁴¹ native and bioprosthetic valve stenosis,^42,43 renal tubulointerstitial fibrosis,³⁶ myocardial infarction,⁴⁴ stroke,⁴⁵ wound healing,^6,44 and in several chronic inflammatory diseases such as experimental autoimmune encephalitis,⁴⁶ rheumatoid arthritis,^47,48 and in a number of granulomatous diseases including sarcoidosis, foreign body granulomas, and tuberculosis.^49–51 Specific effects on inflammatory cells and the modulation of inflammation will be discussed in more detail below.

	OPN Structure and Proteolytic Processing

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
OPN contains several cell interacting domains as well as protease cleavage sites that may be important in regulating its activity (Figure 1). Cell interacting domains do not require phosphorylation (because recombinant bacterial proteins retain activity), and include (1) an arginine-glycine-aspartate (RGD)-containing domain that interacts with cell surface integrins _vβ₃, _vβ₁, _vβ₅,³⁰ and ₈β₁,⁵² (2) a serine-valine-valine-tyrosine-glutamate-leucine-arginine (SVVYGLR)-containing domain that interacts with ₉β₁,^53,54 ₄β₁,^55,56 and ₄β₇,⁵⁷ and (3) ELVTDFTDLPAT domain also reported to bind to ₄β₁.⁵⁵ We and others have shown that the SVVYGLR domain is cryptic in intact OPN and requires cleavage by thrombin to be functional.^54,56,58 Of these cell interacting domains the RGD sequence is 100% conserved between species, the SVVYGLR is structurally conserved between species (SLAYGLR for mouse and rat OPN), and the ELVTDFTDLPAT is the least conserved.

View larger version (30K): [in this window] [in a new window]   Figure 1. A, OPN structural features. The cell adhesive domains are indicated in color. The adhesive domain amino acids sequences as well as the known specific integrin receptors for each are also shown in color. The calcium binding domains are shown in gray, and other matrix binding domains are in black. Also shown are known phosphorylation sites. B, Amino acid sequence of human OPN. The adhesive sequences are shown in color. Arrows indicate known cleavage sites. Thrombin cleavage site in blue and MMP cleavage sites in orange.

Recently, OPN was characterized as a substrate for several MMPs, including MMP2, MMP3, MMP7, MMP9,⁵⁹ and MMP12.⁶⁰ These exciting studies indicate that cleavage of OPN by MMPs can occur at several sites on the molecule, including within the SVVYGLR site, between the glycine and lysine residues, thereby potentially disrupting the integrin binding domain.⁵⁹ As a consequence, these new "matrix metalloproteinase (MMP)-activated" OPN forms may have differential ability to bind ₄/₉ integrins, thus regulating its activity and potentially altering cell responses. Indeed, previous studies by Green et al indicated the importance of the lysine residue within the SVVYGLR domain for proper interaction with ₄ integrins,⁵⁷ suggesting that partial truncation of this domain might abolish or greatly diminish binding. Furthermore, studies by Yokosaki at al indicate that the MMP N-terminal fragment lacking the lysine and arginine residues is also unable to interact with _9, and further that the ₉ binding is dependent on the tyrosine residue.^54,61 Are there pathophysiological functions for OPN fragments? Several in vitro studies have demonstrated that the N-terminal fragments generated both by thrombin cleavage and MMP cleavage induced enhanced adhesion when compared with the full length molecule. This appears to be attributable mostly to increased activity of the RGD site, perhaps an indication of conformational change resulting in higher affinity binding.^53,62 In addition, the thrombin cleaved fragment also increases hapoptaxis.⁶² The SVVYGLR cryptic domain exposed after thrombin cleavage is also able to induce adhesion and migration through the ₄ and ₉ integrins,⁵³ although at least the ₉-dependent functions appear to be lost in the N-terminal MMP generated fragment.^54,61 The C-terminal fragment of OPN generated by thrombin and MMP cleavage does not contain any integrin adhesive domains, it does not mediate adhesion when presented in immobilized form to cells, and it appears to suppress OPN mediated adhesion and migration in monocyte-derived cells.^53,63–64

OPN has also been reported to interact with the hyaluronic acid receptor, CD44. Although OPN does not bind to the standard CD44 isoform, CD44H,⁶⁵ it was reported to interact with CD44v3-v6 splice variants.⁶⁶ Though its binding site in OPN has not yet been defined, recent data suggest that this interaction might occur with the soluble C-terminal thrombin cleaved fragment in an RGD-independent fashion.⁶⁷ In addition, growing evidence suggests that OPN is a major regulator of CD44 surface expression, especially in osteoclasts.^22,68,69

The in vivo relevance of OPN fragments is unclear and largely unexplored. To date, only 3 studies have addressed the role of the cryptic SVVYGLR sequence in vivo. In a model of rheumatoid arthritis, an antibody specifically neutralizing only the SLAYGLR domain of mouse OPN (homologous to the SVVYGLR of human OPN) greatly reduced proliferation of synovial cells, leading to bone erosion and inflammatory cell infiltration in the arthritic joints. These findings correlated with increased expression of the integrin ₄ and ₉ in monocytes isolated from arthritic mice compared with monocytes isolated from normal mice.⁷⁰ The highly inflammatory environment of arthritic joints is likely rich in thrombin and MMPs, thus it is plausible that new bioactive OPN fragments could be generated. Another very recent study showed that the SVVYGLR sequence induces pro-MMP9 expression in isolated vascular smooth muscle cells and in diabetic mouse aortas.⁷¹ Finally, the SVVYGLR peptide has been shown to induce angiogenesis of in vitro and in vivo.^72,73 These data highlight the potential role of the OPN SVVYGLR sequence in signaling, and further understanding of the regulatory events initiated by the different OPN fragments might foster the development of strategies to reduce inflammatory diseases and preserve vascular structure and function.

OPN also interacts with structural components of the extracellular matrix. OPN contains 2 conserved N-terminal domains with heparin binding homology that are likely to regulate its binding to heparan sulfate proteoglycans. Furthermore, OPN binds directly to fibronectin⁷⁴ and collagen,^75,76 although the sequences responsible for these interactions are not yet established. Aspartic acid rich calcium binding domains as well as phosphorylated serine and threonine residues impart the mineral binding properties of OPN, which are independent of integrin binding domains. It is unknown whether proteolytic processing affects OPN interaction with matrix proteins.

	OPN Role in Inflammation

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
OPN is not expressed in circulating monocytes but it is one of the most abundant proteins expressed by macrophages and is a potent macrophage-chemotactic stimulus. Indeed, OPN appears to regulate macrophage infiltration during the inflammatory response.^77–79 Functional inhibition of OPN and genetic ablation of OPN in mice greatly impair macrophage recruitment in several models of inflammation. In a model of crescentic glomerulonephritis, neutralizing antibodies to OPN significantly reduced macrophage infiltration.⁸⁰ Correspondingly, acute macrophage infiltration was greatly diminished in obstructed kidneys of OPN-null mice compared with wild-type mice.⁸¹ Similarly, neutralizing antibodies to OPN were shown to block macrophage infiltration in response to the bacterial chemotactic peptide, formyl-methionine-leucine-phenylalanine.⁸²

Wound healing studies in mice also indicate that OPN is expressed during the acute inflammatory phase at very high levels in infiltrating leukocytes and other cell types. In contrast to wild-type mice, incisional wounds made in OPN-null mice showed more residual debris and less matrix organization, as well as an alteration in collagen fibrillogenesis.⁶ These results suggest that the matrix-binding capacity of OPN facilitates proper stromal and fibrillar collagen network organization, although an indirect mechanism is also possible. These data also suggest that OPN supports the activity of phagocytic cells. Other studies in bone wound healing and in the microglia associated with the developing brain support the hypothesis that OPN is a positive regulator of phagocytic activity.^83,84These studies found that OPN-coated calcified debris were internalized by macrophages,⁸⁴ and that OPN expressing microglia were active phagocytes.⁸³ Thus, OPN appears to modulate not only inflammatory cell accumulation but also the activation state.

Besides regulating the acute phase of the inflammatory reaction, OPN may alter chronic inflammatory responses as well. Chronic inflammation is characterized by the persistence of macrophages at sites of injury and disease. Deficits in macrophage accumulation have been noted in OPN^–/– mice when challenged with chronic inflammatory conditions, including atherosclerosis (see below), delayed-type hypersensitivity,^80,85 granulomatous disease,^51,85 anti-type II collagen antibody-induced arthritis,⁸⁶ and biomaterial implantation.^87,88These data suggest that OPN may be particularly important in promoting retention of macrophages at sites of chronic inflammation. Further analysis also suggests that OPN alters other macrophage responses. Indeed, we found that OPN blocks formation of macrophage-derived foreign body giant cells in vivo and in vitro, and regulates carbonic anhydrase expression and mineral resorption by macrophages responding to ectopic mineralization.^87,88 In addition, OPN control of macrophage activation state was suggested by the finding that OPN-producing tumors were able to inhibit macrophage activation (as measured by increased mannose receptor expression) when compared with tumors deficient in OPN.⁷⁷ In vitro studies have determined that OPN induces macrophage secretion of interleukin (IL)-12 and dampens the secretion of IL-10, potentially contributing to the development of type-1 immunity, a hallmark of chronic inflammatory diseases.^85,89 Many in vitro studies also emphasize the importance of an autocrine function for OPN in macrophages, suggesting that macrophages are both a source and target of OPN. Indeed, macrophages from OPN-null mice have several measurable deficiencies, including susceptibility to programmed cell death, which maybe responsible for the other phenotypes such as impaired macrophage accumulation⁸⁸ and migration in response to MCP-1.⁹⁰ OPN^–/– macrophages also show lower cytotoxicity against tumor cells.⁹¹ In addition, OPN silencing in RAW 264.7 macrophage-like cells impairs their migration, sensitizes them to serum withdrawal-induced cell death, and reduces their secretion of IL-12. These features may represent impairment of RAW 264.7 differentiation from monocytes to macrophages because they correspond to decreased expression of macrophage scavenger receptor A type 1.⁹²

Besides a clear role in macrophage biology, OPN also affects lymphocyte phenotype. OPN was cloned from activated CD4+ cells, where it is highly expressed.⁷⁹ Subsequently, OPN was found expressed by lymphocytes associated with sarcoidosis, and its expression correlated with granuloma maturity. Osteopontin induced T cell chemotaxis, supported T cell adhesion, and costimulated T cell proliferation.⁹³ OPN also induced CD40 ligand (CD40L) and IFN-gamma expression on human T cells, resulting in CD40L- and IFN-–dependent IL-12 production concomitantly with CD-3 stimulation. These findings suggest a functional role for osteopontin in early Th1 responses, namely regulation of T cell–dependent IL-12 production.^28,94 More recently, OPN has also been implicated in regulating the survival of CD4 and CD8 T cells in experimental autoimmune encephalomyelitis, a model of multiple sclerosis, suggesting that OPN contributes to the progression of this autoimmune disease.⁹⁵

Taken together, these data indicate that OPN modulates the inflammatory response at several levels, from immune cell accumulation to activation of Th1 cytokines and to cell survival, thus exacerbating the chronic inflammatory response. However, the forms of OPN, receptors, and signaling pathways involved in these processes are currently unknown.

	OPN Role in Vascular Disease

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
Remodeling and Biomineralization
OPN is reexpressed in proliferating and migratory vascular cells associated with neointima formation and in inflammatory cells. In human atherosclerotic lesions, OPN is expressed in smooth muscle cells in the lesion, in angiogenic endothelial cells, and in macrophages.^1,25 OPN is also re-expressed in SMC associated with human restenotic lesions.⁹⁶ Consistently animal models have confirmed the role of OPN in vascular remodeling. In a rat model of vascular stenosis, OPN was expressed in intimal smooth muscle cells undergoing proliferation and migration, and smooth muscle cells intimal accumulation was inhibited by anti-OPN antibodies.³⁸ Likewise, OPN was upregulated in regenerating endothelium following balloon denudation in rat carotid arteries.³⁰ More recently, Isoda et al showed that forced overexpression of OPN induced thickening of the medial layer and increased neointima formation following injury. These findings also correlated with increased SMC proliferation, migration and MMP production.⁹⁷ All these data indicate that during injury, OPN modulates the proliferation, migration, and accumulation of smooth muscle and endothelial cells involved in repair and remodeling processes of the vasculature.

OPN appears also to be an important regulator of vascular calcification and is associated with mineralized deposits in humans.²⁵ In mice, OPN levels are greatly elevated in the spontaneously mineralizing arteries of MGP^–/–, of mice and we have recently shown that OPN is major inducible inhibitor of vascular calcification.^26,87 Furthermore, studies by Harmey et al and Johnson et al also suggest that OPN is a component of inorganic pyrophosphate signaling and greatly synergize with it in inhibiting mineral deposition and aortic calcification.^98,99 These findings suggest that OPN may be an important regulator of arterial mineral deposition under conditions of injury and disease. Vascular calcification is now recognized as a marker of atherosclerotic plaque burden as well as a major contributor to loss of arterial compliance and increased pulse pressure seen with age, diabetes, and renal insufficiency. Thus, OPN, together with other biomineralization inhibitors, may control whether calcification occurs under these pathological conditions.

Mechanistically increasing evidence suggest that phosphorylated OPN directly associates with apatite deposits and blocks crystal growth in addition to inducing RGD-mediated mineral resorption in cardiovascular tissues.^87,100–103 Because of its beneficial anticalcific affects and ability to promote mineral resorption, OPN is currently being considered as a potential local therapeutic to limit or remove pathological mineralization in cardiovascular settings such as native valve repair and bioprosthetic valve material development.^104,105

Vascular Inflammation and Atherosclerosis
The atherosclerotic lesion is highly inflammatory and, like other chronic inflammatory diseases, is characterized by the persistence of macrophages and other immune cells. Macrophages and lipid-filled macrophages, often referred to as foam cells, are the first cells to comprise the lesion as determined in mouse animal models like the ApoE-null and the fat-fed LDLR-null mouse. More advanced lesions become complex; they are filled with smooth muscle cells and are characterized by the presence of extensive extracellular matrix and a large necrotic core filled with cholesterol clefts. In very advanced lesions, the matrix is often mineralized, and chondrocyte-like cells are associated with the mineral deposits.¹⁰⁶ Nevertheless, macrophages and foam cells are persistent even in very advanced lesions. They are especially localized in the shoulder region of the plaque, suggesting an unrelenting chronic inflammatory response.¹⁰⁷ We and others have shown that OPN is highly expressed in human as well as experimental animal atherosclerotic lesions, especially associated with macrophages and foam cells^1,41,108,109 (Figure 2). In recent years, in an attempt to define its role in atherosclerosis, 5 studies have examined the effect of OPN overexpression or deficiency in atherosclerotic lesion formation. Chiba et al¹¹⁰ examined OPN overexpression on atherosclerosis in fat-fed mice. Transgenic overexpression of OPN in lymphoid tissues via an IgG enhancer/SV40 promoter was associated with an increase in aortic lesion size. Consistently, Isoda et al showed that wide tissue overexpression of OPN in fat-fed mice resulted in fatty and mononuclear cell-rich lesion formation. In addition, these findings correlated with decreased expression of IL-10, a well-established atheroprotective cytokine, thus suggesting a possible mechanism behind OPN effects on lesion formation and progression.¹¹¹ In loss of function studies, Matsui et al observed significantly smaller atherosclerotic lesions in the aorta using oil red O staining in female ApoE^–/–OPN^–/– mice compared with female ApoE^–/–OPN^+/+ after 36 weeks of normal chow feeding.¹¹² We have independently confirmed these results in the innominate artery of 40-week-old female ApoE^–/–OPN^–/– mice (Scatena and Giachelli, 2005 unpublished). Matsui et al also determined that while male mice showed no significant difference in lesion size, plaques were more highly calcified in ApoE^–/–OPN^–/– compared with Apo^–/–OPN^+/+ mice, consistent with a beneficial anticalcific effect of OPN. Likewise, Strom et al found decreased atherosclerotic lesion size, increased proliferating and apoptotic cells in 34-week-old ApoE/LDL receptor/OPN triple null mice compared with ApoE/LDL receptor double null mice.¹¹³

View larger version (82K): [in this window] [in a new window]   Figure 2. Human carotid artery atheromas double stained for OPN and macrophages/foam cells (an anti-CD68 antibody was used). Purple stain shows OPN and brown staining shows macrophages/foam cells. Note that OPN in present in the extracellular space as well as associated with macrophages and foam cells (very dark, almost black staining indicating overlap of the two staining). Arrows indicate double stained macrophages and arrowheads double stained foam cells.

On the other hand, elegant studies by Bruemmer et al⁹⁰ examined OPN deficiency in an Angiotensin II (AII)-accelerated model of atherosclerosis and aneurysm formation in ApoE^–/– mice. Three-month-old male ApoE^–/– of OPN^–/– littermates were treated with AII by infusion for 4 weeks. Under these conditions, ApoE^–/–OPN^–/– mice had less atherosclerosis than ApoE^–/–OPN^+/+ mice. Leukocyte/lymphocyte-derived OPN appeared to be required for OPN function because bone marrow transplants from ApoE^–/–OPN^–/– mice into ApoE^–/– mice also led to decreased lesion size compared with mice receiving bone marrow from ApoE^–/–OPN^+/+ mice. Importantly, macrophage apoptosis within lesions was decreased in ApoE^–/–OPN^–/– compared with ApoE^–/–OPN^+/+ mice. The authors also confirmed the importance of OPN in leukocyte recruitment, because OPN^–/– mice had decreased leukocyte accumulation in response to intraperitoneal thioglycollate treatment. Finally, ApoE^–/–OPN^–/– mice had less AII-induced aortic aneurysm formation and decreased MMP-2 and MMP-9 activity than ApoE^–/–OPN^+/+ mice, suggesting a role for OPN in MMP regulation and vessel rupture. Together, these data support the notion that OPN is an important participant in atherosclerotic plaque formation, and implicate bone marrow cells as both source and target of the proatherosclerotic effects of OPN. However, the time course of OPN functions and mechanism by which OPN promotes macrophage accumulation and plaque rupture are still unclear. It is also unknown whether OPN fragments are generated during the onset of cardiovascular disease and whether they modulate leukocytes phenotype, thereby impacting the development and progression of the atherosclerotic plaque. However, many MMPs including MMP2, 3, 7, and 9 are present in the atherosclerotic lesion and often colocalized with lesion macrophages.¹¹⁴ It is thus likely that OPN becomes fragmented in the lesion environment. Future studies that specifically address the role of different OPN fragments in cardiovascular disease and other chronic inflammatory disease are greatly needed.

	Conclusions

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
OPN is emerging as a key regulator of immune cell biology. Most of the evidence indicates that persistence of OPN expression by immune type cells exacerbates chronic inflammatory diseases, including vascular disease. Furthermore, several in vitro and few in vivo studies show that both the thrombin and MMP proteolytically cleaved OPN fragments in general possess higher activity than the full-length form. In addition, at least the thrombin cleaved fragment also gains a new cell interacting domain (SVVYGLR). Therefore, we would like to propose that especially when associated with inflammatory processes, the secreted lower activity full-length OPN is rapidly cleaved and, thus, activated.

Much evidence also suggests that physiologically, OPN is a regulator of bone homeostasis and a natural inhibitor of soft tissue mineralization. Because of the multi-domain structure of OPN and the existence of active OPN cleaved products, it is possible that different functions might be modulated by discrete OPN domains as well as different fragments. Thus, understanding differences in the mechanisms and structure/function relationships governing anticalcific versus proinflammatory properties of OPN could help create specific therapeutics aimed at targeting these functions selectively.

	Acknowledgments

 
Sources of Funding

These studies were funded by NIH grants HL62329, HL081785, and HL18645 (to C.G.) and by American Heart Association grant 025250N (to L.L.).

Disclosures

None.

	Footnotes

 
Original received March 28, 2007; final version accepted August 15, 2007.

	References

Top Abstract Introduction OPN Role in Biomineralization OPN Role in Tissue... OPN Structure and Proteolytic... OPN Role in Inflammation OPN Role in Vascular... Conclusions References

 
1. Giachelli CM, Liaw L, Murry CE, Schwartz SM, Almeida M. Osteopontin expression in cardiovascular diseases. Ann N Y Acad Sci. 1995; 760: 109–126.[Medline] [Order article via Infotrieve]

2. Giachelli CM, Steitz S. Osteopontin: a versatile regulator of inflammation and biomineralization. Matrix Biol. 2000; 19: 615–622.[CrossRef][Medline] [Order article via Infotrieve]

3. Thayer JM, Giachelli CM, Mirkes PE, Schwartz SM. Expression of osteopontin in the head process late in gastrulation in the rat. J Exp Zool. 1995; 272: 240–244.[CrossRef][Medline] [Order article via Infotrieve]

4. Nakase T, Takaoka K, Hirakawa K, Hirota S, Takemura T, Onoue H, Takebayashi K, Kitamura Y, Nomura S. Alterations in the expression of osteonectin, osteopontin and osteocalcin mRNAs during the development of skeletal tissues in vivo. Bone Miner. 1994; 26: 109–122.[Medline] [Order article via Infotrieve]

5. Nomura S, Wills AJ, Edwards DR, Heath JK, Hogan BL. Expression of genes for non-collagenous proteins during embryonic bone formation. Connect Tissue Res. 21: 31–35, 1989; discussion 36–39.

6. Liaw L, Birk DE, Ballas CB, Whitsitt JS, Davidson JM, Hogan BL. Altered wound healing in mice lacking a functional osteopontin gene (spp1). J Clin Invest. 1998; 101: 1468–1478.[Medline] [Order article via Infotrieve]

7. Agnholt J, Kelsen J, Schack L, Hvas CL, Dahlerup JF, Sorensen ES. Osteopontin, a protein with cytokine-like properties, is associated with inflammation in Crohn’s disease. Scand J Immunol. 2007; 65: 453–460.[CrossRef][Medline] [Order article via Infotrieve]

8. Standal T, Borset M, Sundan A. Role of osteopontin in adhesion, migration, cell survival and bone remodeling. Exp Oncol. 2004; 26: 179–184.[Medline] [Order article via Infotrieve]

9. Fedarko NS, Jain A, Karadag A, Van Eman MR, Fisher LW. Elevated serum bone sialoprotein and osteopontin in colon, breast, prostate, and lung cancer. Clin Cancer Res. 2001; 7: 4060–4066.[Abstract/Free Full Text]

10. Singhal H, Bautista DS, Tonkin KS, O’Malley FP, Tuck AB, Chambers AF, Harris JF. Elevated plasma osteopontin in metastatic breast cancer associated with increased tumor burden and decreased survival. Clin Cancer Res. 1997; 3: 605–611.[Abstract]

11. Comabella M, Pericot I, Goertsches R, Nos C, Castillo M, Blas Navarro J, Rio J, Montalban X. Plasma osteopontin levels in multiple sclerosis. J Neuroimmunol. 2005; 158: 231–239.[CrossRef][Medline] [Order article via Infotrieve]

12. Wong CK, Lit LC, Tam LS, Li EK, Lam CW. Elevation of plasma osteopontin concentration is correlated with disease activity in patients with systemic lupus erythematosus. Rheumatology (Oxford). 2005; 44: 602–606.[CrossRef][Medline] [Order article via Infotrieve]

13. Gomez-Ambrosi J, Catalan V, Ramirez B, Rodriguez A, Colina I, Silva C, Rotellar F, Mugueta C, Gil MJ, Cienfuegos JA, Salvador J, Fruhbeck G. Plasma osteopontin levels and expression in adipose tissue are increased in obesity. J Clin Endocrinol Metab. 2007.

14. Ohmori R, Momiyama Y, Taniguchi H, Takahashi R, Kusuhara M, Nakamura H, Ohsuzu F. Plasma osteopontin levels are associated with the presence and extent of coronary artery disease. Atherosclerosis. 2003; 170: 333–337.[CrossRef][Medline] [Order article via Infotrieve]

15. Kato R, Momiyama Y, Ohmori R, Tanaka N, Taniguchi H, Arakawa K, Kusuhara M, Nakamura H, Ohsuzu F. High plasma levels of osteopontin in patients with restenosis after percutaneous coronary intervention. Arterioscler Thromb Vasc Biol. 2006; 26: e1–e2.[Free Full Text]

16. Golledge J, Muller J, Shephard N, Clancy P, Smallwood L, Moran C, Dear AE, Palmer LJ, Norman PE. Association between osteopontin and human abdominal aortic aneurysm. Arterioscler Thromb Vasc Biol. 2007; 27: 655–660.[Abstract/Free Full Text]

17. Ishijima M, Tsuji K, Rittling SR, Yamashita T, Kurosawa H, Denhardt DT, Nifuji A, Noda M. Resistance to unloading-induced three-dimensional bone loss in osteopontin-deficient mice. J Bone Miner Res. 2002; 17: 661–667.[CrossRef][Medline] [Order article via Infotrieve]

18. Kitahara K, Ishijima M, Rittling SR, Tsuji K, Kurosawa H, Nifuji A, Denhardt DT, Noda M. Osteopontin deficiency induces parathyroid hormone enhancement of cortical bone formation. Endocrinology. 2003; 144: 2132–2140.[Abstract/Free Full Text]

19. Boskey AL, Spevak L, Paschalis E, Doty SB, McKee MD. Osteopontin deficiency increases mineral content and mineral crystallinity in mouse bone. Calcif Tissue Int. 2002; 71: 145–154.[CrossRef][Medline] [Order article via Infotrieve]

20. Hruska KA, Rifas L, Cheng SL, Gupta A, Halstead L, Avioli L. X-linked hypophosphatemic rickets and the murine Hyp homologue. Am J Physiol. 1995; 268: F357–F362.[Medline] [Order article via Infotrieve]

21. Boskey AL, Maresca M, Ullrich W, Doty SB, Butler WT, Prince CW. Osteopontin-hydroxyapatite interactions in vitro: inhibition of hydroxyapatite formation and growth in a gelatin–gel. Bone Miner. 1993; 22: 147–159.[Medline] [Order article via Infotrieve]

22. Chellaiah MA, Hruska KA. The integrin alpha(v)beta(3) and CD44 regulate the actions of osteopontin on osteoclast motility. Calcif Tissue Int. 2003; 72: 197–205.[CrossRef][Medline] [Order article via Infotrieve]

23. Wesson JA, Johnson RJ, Mazzali M, Beshensky AM, Stietz S, Giachelli C, Liaw L, Alpers CE, Couser WG, Kleinman JG, Hughes J. Osteopontin is a critical inhibitor of calcium oxalate crystal formation and retention in renal tubules. J Am Soc Nephrol. 2003; 14: 139–147.[Abstract/Free Full Text]

24. Wesson JA, Worcester EM, Wiessner JH, Mandel NS, Kleinman JG. Control of calcium oxalate crystal structure and cell adherence by urinary macromolecules. Kidney Int. 1998; 53: 952–957.[CrossRef][Medline] [Order article via Infotrieve]

25. Giachelli CM, Bae N, Almeida M, Denhardt DT, Alpers CE, Schwartz SM. Osteopontin is elevated during neointima formation in rat arteries and is a novel component of human atherosclerotic plaques. J Clin Invest. 1993; 92: 1686–1696.[Medline] [Order article via Infotrieve]

26. Speer MY, McKee MD, Guldberg RE, Liaw L, Yang HY, Tung E, Karsenty G, Giachelli CM. Inactivation of the osteopontin gene enhances vascular calcification of matrix Gla protein-deficient mice: evidence for osteopontin as an inducible inhibitor of vascular calcification in vivo. J Exp Med. 2002; 196: 1047–1055.[Abstract/Free Full Text]

27. Steitz SA, Speer MY, Curinga G, Yang HY, Haynes P, Aebersold R, Schinke T, Karsenty G, Giachelli CM. Smooth muscle cell phenotypic transition associated with calcification: upregulation of Cbfa1 and downregulation of smooth muscle lineage markers. Circ Res. 2001; 89: 1147–1154.[Abstract/Free Full Text]

28. O’Regan AW, Nau GJ, Chupp GL, Berman JS. Osteopontin (Eta-1) in cell-mediated immunity: teaching an old dog new tricks. Immunol Today. 2000; 21: 475–478.[CrossRef][Medline] [Order article via Infotrieve]

29. Liaw L, Almeida M, Hart CE, Schwartz SM, Giachelli CM. Osteopontin promotes vascular cell adhesion and spreading and is chemotactic for smooth muscle cells in vitro. Circ Res. 1994; 74: 214–224.[Abstract/Free Full Text]

30. Liaw L, Lindner V, Schwartz SM, Chambers AF, Giachelli CM. Osteopontin and beta 3 integrin are coordinately expressed in regenerating endothelium in vivo and stimulate Arg-Gly-Asp-dependent endothelial migration in vitro. Circ Res. 1995; 77: 665–672.[Abstract/Free Full Text]

31. Liaw L, Skinner MP, Raines EW, Ross R, Cheresh DA, Schwartz SM, Giachelli CM. The adhesive and migratory effects of osteopontin are mediated via distinct cell surface integrins. Role of alpha v beta 3 in smooth muscle cell migration to osteopontin in vitro. J Clin Invest. 1995; 95: 713–724.[Medline] [Order article via Infotrieve]

32. Scatena M, Almeida M, Chaisson ML, Fausto N, Nicosia RF, Giachelli CM. NF-kappaB mediates alphavbeta3 integrin-induced endothelial cell survival. J Cell Biol. 1998; 141: 1083–1093.[Abstract/Free Full Text]

33. Weintraub AS, Giachelli CM, Krauss RS, Almeida M, Taubman MB. Autocrine secretion of osteopontin by vascular smooth muscle cells regulates their adhesion to collagen gels. Am J Pathol. 1996; 149: 259–272.[Abstract]

34. Yoo KH, Thornhill BA, Forbes MS, Coleman CM, Marcinko ES, Liaw L, Chevalier RL. Osteopontin regulates renal apoptosis and interstitial fibrosis in neonatal chronic unilateral ureteral obstruction. Kidney Int. 2006; 70: 1735–1741.[CrossRef][Medline] [Order article via Infotrieve]

35. Fischer JW, Tschope C, Reinecke A, Giachelli CM, Unger T. Upregulation of osteopontin expression in renal cortex of streptozotocin-induced diabetic rats is mediated by bradykinin. Diabetes. 1998; 47: 1512–1518.[Abstract/Free Full Text]

36. Giachelli CM, Pichler R, Lombardi D, Denhardt DT, Alpers CE, Schwartz SM, Johnson RJ. Osteopontin expression in angiotensin II-induced tubulointerstitial nephritis. Kidney Int. 1994; 45: 515–524.[Medline] [Order article via Infotrieve]

37. Graf K, Do YS, Ashizawa N, Meehan WP, Giachelli CM, Marboe CC, Fleck E, Hsueh WA. Myocardial osteopontin expression is associated with left ventricular hypertrophy. Circulation. 1997; 96: 3063–3071.[Abstract/Free Full Text]

38. Liaw L, Lombardi DM, Almeida MM, Schwartz SM, deBlois D, Giachelli CM. Neutralizing antibodies directed against osteopontin inhibit rat carotid neointimal thickening after endothelial denudation. Arterioscler Thromb Vasc Biol. 1997; 17: 188–193.[Abstract/Free Full Text]

39. Thomas SE, Lombardi D, Giachelli C, Bohle A, Johnson RJ. Osteopontin expression, tubulointerstitial disease, and essential hypertension.

40. Tuck AB, O’Malley FP, Singhal H, Tonkin KS, Harris JF, Bautista D, Chambers AF. Osteopontin and p53 expression are associated with tumor progression in a case of synchronous, bilateral, invasive mammary carcinomas. Arch Pathol Lab Med. 1997; 121: 578–584.[Medline] [Order article via Infotrieve]

41. O’Brien ER, Garvin MR, Stewart DK, Hinohara T, Simpson JB, Schwartz SM, Giachelli CM. Osteopontin is synthesized by macrophage, smooth muscle, and endothelial cells in primary and restenotic human coronary atherosclerotic plaques. Arterioscler Thromb. 1994; 14: 1648–1656.[Abstract/Free Full Text]

42. Schoen FJ, Levy RJ, Piehler HR. Pathological considerations in replacement cardiac valves. Cardiovascular Pathology. 1992; 1: 29–52.[CrossRef]

43. O’Brien KD, Kuusisto J, Reichenbach DD, Ferguson M, Giachelli C, Alpers CE, Otto CM. Osteopontin is expressed in human aortic valvular lesions [see comments]. Circulation. 1995; 92: 2163–2168.[Abstract/Free Full Text]

44. Murry CE, Giachelli CM, Schwartz SM, Vracko R. Macrophages express osteopontin during repair of myocardial necrosis. Am J Pathol. 1994; 145: 1450–1462.[Abstract]

45. Ellison JA, Velier JJ, Spera P, Jonak ZL, Wang X, Barone FC, Feuerstein GZ. Osteopontin and its integrin receptor alpha(v) beta3 are upregulated during formation of the glial scar after focal stroke. Stroke. 1998; 29: 1698–1706;discussion 1707.

46. Jansson M, Panoutsakopoulou V, Baker J, Klein L, Cantor H. Cutting edge: Attenuated experimental autoimmune encephalomyelitis in eta-1/osteopontin-deficient mice. J Immunol. 2002; 168: 2096–2099.[Abstract/Free Full Text]

47. Ohshima S, Kobayashi H, Yamaguchi N, Nishioka K, Umeshita-Sasai M, Mima T, Nomura S, Kon S, Inobe M, Uede T, Saeki Y. Expression of osteopontin at sites of bone erosion in a murine experimental arthritis model of collagen-induced arthritis: possible involvement of osteopontin in bone destruction in arthritis. Arthritis Rheum. 2002; 46: 1094–1101.[CrossRef][Medline] [Order article via Infotrieve]

48. Sakata N, Noma A, Yamamoto Y, Okamoto K, Meng J, Takebayashi S, Nagai R, Horiuchi S. Modification of elastin by pentosidine is associated with the calcification of aortic media in patients with end-stage renal disease. Nephrol Dial Transplant. 2003; 18: 1601–1609.[Abstract/Free Full Text]

49. Carlson I, Tognazzi K, Manseau EJ, Dvorak HF, Brown LF. Osteopontin is strongly expressed by histiocytes in granulomas of diverse etiology. Lab Invest. 1997; 77: 103–108.[Medline] [Order article via Infotrieve]

50. Nau GJ, Chupp GL, Emile JF, Jouanguy E, Berman JS, Casanova JL, Young RA. Osteopontin expression correlates with clinical outcome in patients with mycobacterial infection. Am J Pathol. 2000; 157: 37–42.[Abstract/Free Full Text]

51. Nau GJ, Liaw L, Chupp GL, Berman JS, Hogan BL, Young RA. Attenuated host resistance against Mycobacterium bovis BCG infection in mice lacking osteopontin. Infect Immun. 1999; 67: 4223–4230.[Abstract/Free Full Text]

52. Schnapp LM, Hatch N, Ramos DM, Klimanskaya IV, Sheppard D, Pytela R. The human integrin alpha 8 beta 1 functions as a receptor for tenascin, fibronectin, and vitronectin. J Biol Chem. 1995; 270: 23196–23202.[Abstract/Free Full Text]

53. Smith LL, Cheung HK, Ling LE, Chen J, Sheppard D, Pytela R, Giachelli CM. Osteopontin N-terminal domain contains a cryptic adhesive sequence recognized by alpha9beta1 integrin. J Biol Chem. 1996; 271: 28485–28491.[Abstract/Free Full Text]

54. Yokosaki Y, Matsuura N, Sasaki T, Murakami I, Schneider H, Higashiyama S, Saitoh Y, Yamakido M, Taooka Y, Sheppard D. The integrin alpha(9)beta(1) binds to a novel recognition sequence (SVVYGLR) in the thrombin-cleaved amino-terminal fragment of osteopontin. J Biol Chem. 1999; 274: 36328–36334.[Abstract/Free Full Text]

55. Bayless KJ, Davis GE. Identification of dual alpha 4beta1 integrin binding sites within a 38 amino acid domain in the N-terminal thrombin fragment of human osteopontin. J Biol Chem. 2001; 276: 13483–13489.[Abstract/Free Full Text]

56. Bayless KJ, Meininger GA, Scholtz JM, Davis GE. Osteopontin is a ligand for the alpha4beta1 integrin. J Cell Sci. 1998; 111: 1165–1174.[Abstract]

57. Green PM, Ludbrook SB, Miller DD, Horgan CM, Barry ST. Structural elements of the osteopontin SVVYGLR motif important for the interaction with alpha(4) integrins. FEBS Lett. 2001; 503: 75–79.[CrossRef][Medline] [Order article via Infotrieve]

58. Smith LL, Giachelli CM. Structural requirements for alpha 9 beta 1-mediated adhesion and migration to thrombin-cleaved osteopontin. Exp Cell Res. 1998; 242: 351–360.[CrossRef][Medline] [Order article via Infotrieve]

59. Agnihotri R, Crawford HC, Haro H, Matrisian LM, Havrda MC, Liaw L. Osteopontin, a novel substrate for matrix metalloproteinase-3 (stromelysin-1) and matrix metalloproteinase-7 (matrilysin). J Biol Chem. 2001; 276: 28261–28267.[Abstract/Free Full Text]

60. Hou P, Troen T, Ovejero MC, Kirkegaard T, Andersen TL, Byrjalsen I, Ferreras M, Sato T, Shapiro SD, Foged NT, Delaisse JM. Matrix metalloproteinase-12 (MMP-12) in osteoclasts: new lesson on the involvement of MMPs in bone resorption. Bone. 2004; 34: 37–47.[Medline] [Order article via Infotrieve]

61. Yokosaki Y, Tanaka K, Higashikawa F, Yamashita K, Eboshida A. Distinct structural requirements for binding of the integrins alphavbeta6, alphavbeta3, alphavbeta5, alpha5beta1 and alpha9beta1 to osteopontin. Matrix Biol. 2005; 24: 418–427.[CrossRef][Medline] [Order article via Infotrieve]

62. Senger DR, Perruzzi CA, Papadopoulos Sergiou A, Van de Water L. Adhesive properties of osteopontin: regulation by a naturally occurring thrombin-cleavage in close proximity to the GRGDS cell-binding domain. Mol Biol Cell. 1994; 5: 565–574.[Abstract]

63. Gao YA, Agnihotri R, Vary CP, Liaw L. Expression and characterization of recombinant osteopontin peptides representing matrix metalloproteinase proteolytic fragments. Matrix Biol. 2004; 23: 457–466.[CrossRef][Medline] [Order article via Infotrieve]

64. Maeda K, Takahashi K, Takahashi F, Tamura N, Maeda M, Kon S, Uede T, Fukuchi Y. Distinct roles of osteopontin fragments in the development of the pulmonary involvement in sarcoidosis. Lung. 2001; 179: 279–291.[CrossRef][Medline] [Order article via Infotrieve]

65. Smith LL, Greenfield BW, Aruffo A, Giachelli CM. CD44 is not an adhesive receptor for osteopontin. J Cell Biochem. 1999; 73: 20–30.[CrossRef][Medline] [Order article via Infotrieve]

66. Weber GF, Ashkar S, Glimcher MJ, Cantor H. Receptor-ligand interaction between CD44 and osteopontin (Eta-1). Science. 1996; 271: 509–512.[Abstract]

67. Weber GF, Ashkar S, Cantor H. Interaction between CD44 and osteopontin as a potential basis for metastasis formation. Proc Assoc Am Physicians. 1997; 109: 1–9.[Medline] [Order article via Infotrieve]

68. Chellaiah MA, Biswas RS, Rittling SR, Denhardt DT, Hruska KA. Rho-dependent Rho kinase activation increases CD44 surface expression and bone resorption in osteoclasts. J Biol Chem. 2003; 278: 29086–29097.[Abstract/Free Full Text]

69. Chellaiah MA, Kizer N, Biswas R, Alvarez U, Strauss-Schoenberger J, Rifas L, Rittling SR, Denhardt DT, Hruska KA. Osteopontin deficiency produces osteoclast dysfunction due to reduced CD44 surface expression. Mol Biol Cell. 2003; 14: 173–189.[Abstract/Free Full Text]

70. Yamamoto N, Sakai F, Kon S, Morimoto J, Kimura C, Yamazaki H, Okazaki I, Seki N, Fujii T, Uede T. Essential role of the cryptic epitope SLAYGLR within osteopontin in a murine model of rheumatoid arthritis. J Clin Invest. 2003; 112: 181–188.[CrossRef][Medline] [Order article via Infotrieve]

71. Lai CF, Seshadri V, Huang K, Shao JS, Cai J, Vattikuti R, Schumacher A, Loewy AP, Denhardt DT, Rittling SR, Towler DA. An osteopontin-NADPH oxidase signaling cascade promotes pro-matrix metalloproteinase 9 activation in aortic mesenchymal cells. Circ Res. 2006; 98: 1479–1489.[Abstract/Free Full Text]

72. Hamada Y, Nokihara K, Okazaki M, Fujitani W, Matsumoto T, Matsuo M, Umakoshi Y, Takahashi J, Matsuura N. Angiogenic activity of osteopontin-derived peptide SVVYGLR. Biochem Biophys Res Commun. 2003; 310: 153–157.[CrossRef][Medline] [Order article via Infotrieve]

73. Hamada Y, Yuki K, Okazaki M, Fujitani W, Matsumoto T, Hashida MK, Harutsugu K, Nokihara K, Daito M, Matsuura N, Takahashi J. Osteopontin-derived peptide SVVYGLR induces angiogenesis in vivo. Dent Mater J. 2004; 23: 650–655.[Medline] [Order article via Infotrieve]

74. Mukherjee BB, Nemir M, Beninati S, Cordella Miele E, Singh K, Chackalaparampil I, Shanmugam V, DeVouge MW, Mukherjee AB. Interaction of osteopontin with fibronectin and other extracellular matrix molecules. Ann N Y Acad Sci. 1995; 760: 201–212.[Medline] [Order article via Infotrieve]

75. Kaartinen MT, Pirhonen A, Linnala Kankkunen A, Maenpaa PH. Transglutaminase-catalyzed cross-linking of osteopontin is inhibited by osteocalcin. J Biol Chem. 1997; 272: 22736–22741.[Abstract/Free Full Text]

76. Martin SM, Schwartz JL, Giachelli CM, Ratner BD. Enhancing the biological activity of immobilized osteopontin using a type-1 collagen affinity coating. J Biomed Mater Res A. 2004; 70: 10–19.[Medline] [Order article via Infotrieve]

77. Crawford HC, Matrisian LM, Liaw L. Distinct roles of osteopontin in host defense activity and tumor survival during squamous cell carcinoma progression in vivo. Cancer Res. 1998; 58: 5206–5215.[Abstract/Free Full Text]

78. Wang X, Louden C, Ohlstein EH, Stadel JM, Gu JL, Yue TL. Osteopontin expression in platelet-derived growth factor-stimulated vascular smooth muscle cells and carotid artery after balloon angioplasty. Arterioscler Thromb Vasc Biol. 1996; 16: 1365–1372.[Abstract/Free Full Text]

79. Weber GF, Cantor H. The immunology of Eta-1/osteopontin. Cytokine Growth Factor Rev. 1996; 7: 241–248[CrossRef][Medline] [Order article via Infotrieve]

80. Yu XQ, Nikolic-Paterson DJ, Mu W, Giachelli CM, Atkins RC, Johnson RJ, Lan HY. A functional role for osteopontin in experimental crescentic glomerulonephritis in the rat. Proc Assoc Am Physicians. 1998; 110: 50–64.[Medline] [Order article via Infotrieve]

81. Ophascharoensuk V, Giachelli CM, Gordon K, Hughes J, Pichler R, Brown P, Liaw L, Schmidt R, Shankland SJ, Alpers CE, Couser WG, Johnson RJ. Obstructive uropathy in the mouse: role of osteopontin in interstitial fibrosis and apoptosis. Kidney Int. 1999; 56: 571–580.[CrossRef][Medline] [Order article via Infotrieve]

82. Giachelli CM, Lombardi D, Johnson RJ, Murry CE, Almeida M. Evidence for a role of osteopontin in macrophage infiltration in response to pathological stimuli in vivo. Am J Pathol. 1998; 152: 353–358.[Abstract]

83. Choi JS, Cha JH, Park HJ, Chung JW, Chun MH, Lee MY. Transient expression of osteopontin mRNA and protein in amoeboid microglia in developing rat brain. Exp Brain Res. 2004; 154: 275–280.[CrossRef][Medline] [Order article via Infotrieve]

84. McKee MD, Nanci A. Osteopontin at mineralized tissue interfaces in bone, teeth, and osseointegrated implants: ultrastructural distribution and implications for mineralized tissue formation, turnover, and repair. Microsc Res Tech. 1996; 33: 141–164.[CrossRef][Medline] [Order article via Infotrieve]

85. Ashkar S, Weber GF, Panoutsakopoulou V, Sanchirico ME, Jansson M, Zawaideh S, Rittling SR, Denhardt DT, Glimcher MJ, Cantor H. Eta-1 (osteopontin): an early component of type-1 (cell-mediated) immunity. Science. 2000; 287: 860–864.[Abstract/Free Full Text]

86. Yumoto K, Ishijima M, Rittling SR, Tsuji K, Tsuchiya Y, Kon S, Nifuji A, Uede T, Denhardt DT, Noda M. Osteopontin deficiency protects joints against destruction in anti-type II collagen antibody-induced arthritis in mice. Proc Natl Acad Sci U S A. 2002; 99: 4556–4561.[Abstract/Free Full Text]

87. Steitz SA, Speer MY, McKee MD, Liaw L, Almeida M, Yang H, Giachelli CM. Osteopontin inhibits mineral deposition and promotes regression of ectopic calcification. Am J Pathol. 2002; 161: 2035–2046.[Abstract/Free Full Text]

88. Tsai AT, Rice J, Scatena M, Liaw L, Ratner BD, Giachelli CM. The role of osteopontin in foreign body giant cell formation. Biomaterials. 2005; 26: 5835–5843.[CrossRef][Medline] [Order article via Infotrieve]

89. Weber GF, Zawaideh S, Hikita S, Kumar VA, Cantor H, Ashkar S. Phosphorylation-dependent interaction of osteopontin with its receptors regulates macrophage migration and activation. J Leukoc Biol. 2002; 72: 752–761.[Abstract/Free Full Text]

90. Bruemmer D, Collins AR, Noh G, Wang W, Territo M, Arias-Magallona S, Fishbein MC, Blaschke F, Kintscher U, Graf K, Law RE, Hsueh WA. Angiotensin II-accelerated atherosclerosis and aneurysm formation is attenuated in osteopontin-deficient mice. J Clin Invest. 2003; 112: 1318–1331.[CrossRef][Medline] [Order article via Infotrieve]

91. Bourassa B, Monaghan S, Rittling SR. Impaired anti-tumor cytotoxicity of macrophages from osteopontin-deficient mice. Cell Immunol. 2004; 227: 1–11.[CrossRef][Medline] [Order article via Infotrieve]

92. Nystrom T, Duner P, Hultgardh-Nilsson A. A constitutive endogenous osteopontin production is important for macrophage function and differentiation. Exp Cell Res. 2007.

93. O’Regan AW, Chupp GL, Lowry JA, Goetschkes M, Mulligan N, Berman JS. Osteopontin is associated with T cells in sarcoid granulomas and has T cell adhesive and cytokine-like properties in vitro. J Immunol. 1999; 162: 1024–1031.[Abstract/Free Full Text]

94. O’Regan AW, Hayden JM, Berman JS. Osteopontin augments CD3-mediated interferon-gamma and CD40 ligand expression by T cells, which results in IL-12 production from peripheral blood mononuclear cells. J Leukoc Biol. 2000; 68: 495–502.[Abstract/Free Full Text]

95. Hur EM, Youssef S, Haws ME, Zhang SY, Sobel RA, Steinman L. Osteopontin-induced relapse and progression of autoimmune brain disease through enhanced survival of activated T cells. Nat Immunol. 2007; 8: 74–83.[CrossRef][Medline] [Order article via Infotrieve]

96. Panda D, Kundu GC, Lee BI, Peri A, Fohl D, Chackalaparampil I, Mukherjee BB, Li XD, Mukherjee DC, Seides S, Rosenberg J, Stark K, Mukherjee AB. Potential roles of osteopontin and alphaVbeta3 integrin in the development of coronary artery restenosis after angioplasty. Proc Natl Acad Sci U S A. 1997; 94: 9308–9313.[Abstract/Free Full Text]

97. Isoda K, Nishikawa K, Kamezawa Y, Yoshida M, Kusuhara M, Moroi M, Tada N, Ohsuzu F. Osteopontin plays an important role in the development of medial thickening and neointimal formation. Circ Res. 2002; 91: 77–82.[Abstract/Free Full Text]

98. Harmey D, Hessle L, Narisawa S, Johnson KA, Terkeltaub R, Millan JL. Concerted regulation of inorganic pyrophosphate and osteopontin by akp2, enpp1, and ank: an integrated model of the pathogenesis of mineralization disorders. Am J Pathol. 2004; 164: 1199–1209.[Abstract/Free Full Text]

99. Johnson K, Goding J, Van Etten D, Sali A, Hu SI, Farley D, Krug H, Hessle L, Millan JL, Terkeltaub R. Linked deficiencies in extracellular PP(i) and osteopontin mediate pathologic calcification associated with defective PC-1 and ANK expression. J Bone Miner Res. 2003; 18: 994–1004.[CrossRef][Medline] [Order article via Infotrieve]

100. Jono S, McKee MD, Murry CE, Shioi A, Nishizawa Y, Mori K, Morii H, Giachelli CM. Phosphate regulation of vascular smooth muscle cell calcification. Circ Res. 2000; 87: E10–E17.[Medline] [Order article via Infotrieve]

101. Jono S, Peinado C, Giachelli CM. Phosphorylation of osteopontin is required for inhibition of vascular smooth muscle cell calcification. J Biol Chem. 2000; 275: 20197–20203.[Abstract/Free Full Text]

102. Ohri R, Tung E, Rajachar R, Giachelli CM. Mitigation of ectopic calcification in osteopontin-deficient mice by exogenous osteopontin. Calcif Tissue Int. 2005; 76: 307–315.[CrossRef][Medline] [Order article via Infotrieve]

103. Wada T, McKee MD, Stietz S, Giachelli CM. Calcification of vascular smooth muscle cell cultures: inhibition by osteopontin. Circ Res. 1999; 84: 1–6.[Abstract/Free Full Text]

104. Giachelli CM. Ectopic calcification: new concepts in cellular regulation. Z Kardiol. 2001; 90 Suppl 3: 31–37.

105. Levy RJ, Qu X, Underwood T, Trachy J, Schoen FJ. Calcification of valved aortic allografts in rats: effects of age, crosslinking,and inhibitors. J Biomed Mater Res. 1995; 29: 217–226.[CrossRef][Medline] [Order article via Infotrieve]

106. Rattazzi M, Bennett BJ, Bea F, Kirk EA, Ricks JL, Speer M, Schwartz SM, Giachelli CM, Rosenfeld ME. Calcification of advanced atherosclerotic lesions in the innominate arteries of ApoE-deficient mice: potential role of chondrocyte-like cells. Arterioscler Thromb Vasc Biol. 2005; 25: 1420–1425.[Abstract/Free Full Text]

107. Gough PJ, Raines EW. Gene therapy of apolipoprotein E-deficient mice using a novel macrophage-specific retroviral vector. Blood. 2003; 101: 485–491.[Abstract/Free Full Text]

108. Kwon HM, Hong BK, Kang TS, Kwon K, Kim HK, Jang Y, Choi D, Park HY, Kang SM, Cho SY, Kim HS. Expression of osteopontin in calcified coronary atherosclerotic plaques. J Korean Med Sci. 2000; 15: 485–493.[Medline] [Order article via Infotrieve]

109. Parrish AR, Ramos KS. Osteopontin mRNA expression in a chemically-induced model of atherogenesis. Ann N Y Acad Sci. 1995; 760: 354–356.[CrossRef][Medline] [Order article via Infotrieve]

110. Chiba S, Okamoto H, Kon S, Kimura C, Murakami M, Inobe M, Matsui Y, Sugawara T, Shimizu T, Uede T, Kitabatake A. Development of atherosclerosis in osteopontin transgenic mice. Heart Vessels. 2002; 16: 111–117.[CrossRef][Medline] [Order article via Infotrieve]

111. Isoda K, Kamezawa Y, Ayaori M, Kusuhara M, Tada N, Ohsuzu F. Osteopontin transgenic mice fed a high-cholesterol diet develop early fatty-streak lesions. Circulation. 2003; 107: 679–681.[Abstract/Free Full Text]

112. Matsui Y, Rittling SR, Okamoto H, Inobe M, Jia N, Shimizu T, Akino M, Sugawara T, Morimoto J, Kimura C, Kon S, Denhardt D, Kitabatake A, Uede T. Osteopontin deficiency attenuates atherosclerosis in female apolipoprotein e-deficient mice. Arterioscler Thromb Vasc Biol. 2003; 23: 1029–1034.[Abstract/Free Full Text]

113. Strom A, Ahlqvist E, Franzen A, Heinegard D, Hultgardh-Nilsson A. Extracellular matrix components in atherosclerotic arteries of Apo E/LDL receptor deficient mice: an immunohistochemical study. Histol Histopathol. 2004; 19: 337–347.[Medline] [Order article via Infotrieve]

114. Dollery CM, Libby P. Atherosclerosis and proteinase activation. Cardiovasc Res. 2006; 69: 625–635.[Abstract/Free Full Text]

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				S. M. Swift, B. R. Gaume, K. M. Small, B. J. Aronow, and S. B. Liggett Differential coupling of Arg- and Gly389 polymorphic forms of the {beta}1-adrenergic receptor leads to pathogenic cardiac gene regulatory programs Physiol Genomics, September 17, 2008; 35(1): 123 - 131. [Abstract] [Full Text] [PDF]

				D. A. Towler Oxidation, Inflammation, and Aortic Valve Calcification: Peroxide Paves an Osteogenic Path J. Am. Coll. Cardiol., September 2, 2008; 52(10): 851 - 854. [Full Text] [PDF]

				L. L. Demer and Y. Tintut Vascular Calcification: Pathobiology of a Multifaceted Disease Circulation, June 3, 2008; 117(22): 2938 - 2948. [Full Text] [PDF]

				M. Riedl, G. Vila, C. Maier, A. Handisurya, S. Shakeri-Manesch, G. Prager, O. Wagner, A. Kautzky-Willer, B. Ludvik, M. Clodi, et al. Plasma Osteopontin Increases After Bariatric Surgery and Correlates with Markers of Bone Turnover But Not with Insulin Resistance J. Clin. Endocrinol. Metab., June 1, 2008; 93(6): 2307 - 2312. [Abstract] [Full Text] [PDF]

				F. W. Kiefer, M. Zeyda, J. Todoric, J. Huber, R. Geyeregger, T. Weichhart, O. Aszmann, B. Ludvik, G. R. Silberhumer, G. Prager, et al. Osteopontin Expression in Human and Murine Obesity: Extensive Local Up-Regulation in Adipose Tissue but Minimal Systemic Alterations Endocrinology, March 1, 2008; 149(3): 1350 - 1357. [Abstract] [Full Text] [PDF]

				P. Zahradka Novel Role for Osteopontin in Cardiac Fibrosis Circ. Res., February 15, 2008; 102(3): 270 - 272. [Full Text] [PDF]

				D. A. Towler Vascular Calcification: A Perspective On An Imminent Disease Epidemic IBMS BoneKEy, February 1, 2008; 5(2): 41 - 58. [Abstract] [Full Text] [PDF]

				N. J. Brown Aldosterone and Vascular Inflammation Hypertension, February 1, 2008; 51(2): 161 - 167. [Full Text] [PDF]

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