Osteopontin

Juvenile dermatomyositis calcifications selectively displayed markers of bone formation

OBJECTIVE

To determine the presence of small integrin-binding ligand N-linked glycoprotein (SIBLING) and bone components in juvenile dermatomyositis (DM) pathologic calcifications.

METHODS

Calcifications were removed from 4 girls with juvenile DM symptoms for mean +/- SD 36.9 +/- 48.3 months and were stained for SIBLING proteins: full-length osteopontin (OPN), bone sialoprotein (BSP), dentin matrix protein 1 (DMP1), dentin phosphoprotein (DPP), and matrix extracellular phosphoglycoprotein (MEPE); bone markers: osteocalcin (OC), core-binding factor alpha 1 (CBFalpha1), and alkaline phosphatase (AP) for osteoblasts; tartrate-resistant acid phosphatase (TRAP) for osteoclasts; and the mineral regulators osteonectin (ON) and matrix Gla protein (MGP). The deposit center, periphery, adjacent connective tissue, and vascular endothelial cells were examined.

RESULTS

Alizarin red stained calcified deposits that did not localize with collagen, like bone, under polarized light. Hematoxylin and eosin stain revealed a paucity of connective tissue and absence of bone-like structures. The deposits, connective tissue, and vascular endothelial cells were positive for BSP, DPP, DMP1, and AP; MEPE was not detected. OC, ON, and MGP were present in the deposits and vascular endothelial cells; OPN and CBFalpha1 were present in deposits and connective tissue. TRAP-positive osteoclasts were localized to the calcification periphery.

CONCLUSION

The disorganized juvenile DM calcifications differ in structure, composition, and protein content from bone, suggesting that they may not form through an osteogenic pathway. Osteoclasts at the deposit surface represent an attempt to initiate its resolution.

Polymeric osteopontin employs integrin alpha9beta1 as a receptor and attracts neutrophils by presenting a de novo binding site

Osteopontin (OPN) is a cytokine and ligand for multiple members of the integrin family. OPN undergoes the in vivo polymerization catalyzed by cross-linking enzyme transglutaminase 2, which consequently increases the bioactivity through enhanced interaction with integrins. The integrin alpha9beta1, highly expressed on neutrophils, binds to the sequence SVVYGLR only after intact OPN is cleaved by thrombin. The SVVYGLR sequence appears to be cryptic in intact OPN because alpha9beta1 does not recognize intact OPN. Because transglutaminase 2-catalyzed polymers change their physical and chemical properties, we hypothesized that the SVVYGLR site might also be exposed on polymeric OPN. As expected, alpha9beta1 turned into a receptor for polymeric OPN, a result obtained by cell adhesion and migration assays with alpha9-transfected cells and by detection of direct binding of recombinant soluble alpha9beta1 with colorimetry and surface plasmon resonance analysis. Because the N-terminal fragment of thrombin-cleaved OPN, a ligand for alpha9beta1, has been reported to attract neutrophils, we next examined migration of neutrophils to polymeric OPN using time-lapse microscopy. Polymeric OPN showed potent neutrophil chemotactic activity, which was clearly inhibited by anti-alpha9beta1 antibody. Unexpectedly, mutagenesis studies showed that alpha9beta1 bound to polymeric OPN independently of the SVVYGLR sequence, and further, SVVYGLR sequence of polymeric OPN was cryptic because SVVYGLR-specific antibody did not recognize polymeric OPN. These results demonstrate that polymerization of OPN generates a novel alpha9beta1-binding site and that the interaction of this site with the alpha9beta1 integrin is critical to the neutrophil chemotaxis induced by polymeric OPN.

A single-nucleotide polymorphism of the osteopontin gene may contribute to a susceptibility to Lewy body disease

In Lewy body disease, inflammation is discussed to be involved in the pathophysiological cascade. Osteopontin (OPN) is a multifunctional molecule, which is increased in inflammatory states. Here, we analyzed the allele frequency of two SNPs of the OPN gene, serum, and CSF OPN levels in Lewy body disease patients and controls. In accordance with our previous findings, we detected increased serum (P = 0.006) and CSF OPN levels (P = 0.0003) in the Lewy body disease cohort, compared to non-Lewy body disease subjects. The genotypic variation of SNP-66 was associated with the occurrence of Lewy body disease (odds ratio: 2.64, 95% CI 1.07-6.54, unadjusted P = 0.036). SNP+1239 was not related to Lewy body disease prevalence (odds ratio 1.61, 95% CI 0.66-3.91, P = 0.29). Genotype prevalence and OPN levels were not significantly related. These findings suggest that OPN is associated with the occurrence of Lewy body disease and SNP-66 may be a susceptibility factor.

Age- and gender-specific modulation of serum osteopontin and interferon-alpha by osteopontin genotype in systemic lupus erythematosus

Osteopontin (OPN) is a multifunctional cytokine involved in long bone remodeling and immune system signaling. Additionally, OPN is critical for interferon-alpha (IFN-alpha) production in murine plasmacytoid dendritic cells. We have previously shown that IFN-alpha is a heritable risk factor for systemic lupus erythematosus (SLE). Genetic variants of OPN have been associated with SLE susceptibility, and one study suggests that this association is particular to men. In this study, the 3' UTR SLE-risk variant of OPN (rs9138C) was associated with higher serum OPN and IFN-alpha in men (P=0.0062 and P=0.0087, respectively). In women, the association between rs9138 C and higher serum OPN and IFN-alpha was restricted to younger subjects, and risk allele carriers showed a strong age-related genetic effect of rs9138 genotype on both serum OPN and IFN-alpha (P<0.0001). In African-American subjects, the 5' region single nucleotide polymorphisms, rs11730582 and rs28357094, were associated with anti-RNP antibodies (odds ratio (OR)=2.9, P=0.0038 and OR=3.9, P=0.021, respectively). Thus, we demonstrate two distinct genetic influences of OPN on serum protein traits in SLE patients, which correspond to previously reported SLE-risk variants. This study provides a biologic relevance for OPN variants at the protein level, and suggests an influence of this gene on the IFN-alpha pathway in SLE.

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.

Neurochemical approaches in the laboratory diagnosis of Parkinson and Parkinson dementia syndromes: a review

The diagnosis of Parkinson disease (PD) is rendered on the basis of clinical parameters, whereby laboratory chemical tests or morphological imaging is only called upon to exclude other neurodegenerative diseases. The differentiation between PD and other diseases of the basal ganglia, especially the postsynaptic Parkinson syndromes multisystem atrophy (MSA) and progressive supranuclear palsy (PSP), is of decisive importance, on the one hand, for the response to an appropriate therapy, and on the other hand, for the respective prognosis of the disease. However, particularly at the onset of symptoms, it is difficult to precisely distinguish these diseases from each other, presenting with an akinetic-rigid syndrome. It is not yet possible to conduct a neurochemical differentiation of Parkinson syndromes. Therefore, a reliable biomarker is still to be found that might predict the development of Parkinson dementia. Since this situation is currently the subject of various different studies, the following synopsis is intended to provide a brief summary of the investigations addressing the field of the early neurochemical differential diagnosis of Parkinson syndromes and the early diagnosis of Parkinson dementia, from direct alpha-synuclein detection to proteomic approaches. In addition, an overview of the tested biomarkers will be given with regard to their possible introduction as a screening method.

Plasma osteopontin modulates chronic restraint stress-induced thymus atrophy by regulating stress hormones: inhibition by an anti-osteopontin monoclonal antibody

Osteopontin (OPN) is a cytokine implicated in mediating responses to certain stressors, including mechanical, oxidative, and cellular stress. However, the involvement of OPN in responding to other physical and psychological stress is largely unexplored. Our previous research revealed that OPN is critical for hind limb-unloading induced lymphoid organ atrophy through modulation of corticosteroid production. In this study, we demonstrate that OPN(-/-) mice are resistant to chronic restraint stress (CRS)-induced lymphoid (largely thymus) organ atrophy; additionally, the stress-induced up-regulation of corticosterone production is significantly reduced in OPN(-/-) mice. Underlying this observation is the fact that normal adrenocorticotropic hormone levels are substantially reduced in the OPN(-/-) mice. Our data demonstrate both that injection of OPN into OPN-deficient mice enhances the CRS-induced lymphoid organ atrophy and that injection of a specific anti-OPN mAb (2C5) into wild-type mice ameliorates the CRS-induced organ atrophy; changes in corticosterone levels were also partially reversed. These studies reveal that circulating OPN plays a significant role in the regulation of the hypothalamus-pituitary-adrenal axis hormones and that it augments CRS-induced organ atrophy.

Osteopontin: a fibrosis-related marker molecule in cardiac remodeling of enterovirus myocarditis in the susceptible host

The characteristics of dilated cardiomyopathy (DCM) resulting from chronic viral myocarditis are remodeling processes of the extracellular matrix. Based on our findings of enhanced osteopontin (OPN) expression in inflamed human hearts, we further investigated in the murine model of acute and chronic coxsackievirus (CV)B3-myocarditis the role of OPN regarding its involvement in resolution of cardiac virus infection and fibrosis. In hearts of A.BY/SnJ mice susceptible to chronic CVB3-myocarditis, a pronounced increase of OPN expression levels was detected by microarray analysis and quantitative RT-PCR during acute stages of myocarditis. Combined immunohistochemistry and in situ hybridization identified infiltrating macrophages as main OPN producers. In contrast to resistant C57BL/6 and OPN gene-deficient mice, transcription levels of matrix metalloproteinase-3, TIMP1 (tissue inhibitor of metalloproteinases-1), uPA (urokinase-type plasminogen activator), and transforming growth factor beta1 were elevated in susceptible mice, and as a consequence, procollagen-1alpha mRNA expression and fibrosis was considerably enhanced. Treatment of infected susceptible mice with the vitamin D analog ZK 191784 led to decreased myocardial expression levels of OPN, metalloproteinase-3, TIMP1, uPA, and procollagen-1alpha and subsequently to reduced fibrosis. Concurrently, the fibrosis-relevant signaling molecules pERK (phosphorylated extracellular signal-regulated kinase) and pAkt (phosphorylated Akt), increased in A.BY/SnJ mice, were diminished in ZK 191784-treated mice. Here, we show that high expression levels of OPN in acute myocarditis are associated with consecutive development of extensive fibrosis that can be reduced by treatment with a vitamin D analog. Thus, OPN may serve as a diagnostic tool as well as a potential therapeutic target to limit cardiac remodeling in chronic myocarditis.

Osteopontin is not crucial to protective immunity during murine tuberculosis

Upon infection with Mycobacterium (M.) tuberculosis, the development of a strong T helper 1 (Th1)-mediated adaptive immune response is considered as being most important for containment of the infection. Osteopontin (OPN) is a phosphorylated glycoprotein that is chemotactic for inflammatory cells and has been implicated in the induction of Th1 responses and granulomatous disease. We tested the hypothesis that OPN facilitates protective immunity during M. tuberculosis infection using wild-type (WT) and OPN knockout (KO) mice in a model of pulmonary tuberculosis. OPN expression was up-regulated in alveolar macrophages and lymphoid cells during M. tuberculosis infection. There were no significant differences in bacterial outgrowth, inflammation or recruitment of lymphocytes, macrophages and polymorphonuclear cells in the lungs after 2 and 5 weeks of infection. However, the numbers of CD4(+) and CD8(+) T cells were reduced in the absence of OPN 5 weeks after infection. Similar concentrations of cytokine were observed in lungs from both WT mice and OPN KO mice; however, there was a trend towards decreased levels of interferon-gamma (IFN-gamma) in OPN KO mice 5 weeks after infection. Despite an unaltered immune response in the early phase of tuberculosis, OPN KO mice had a modest survival advantage. Of note, both pulmonary bacterial loads and lung inflammation were reduced in these mice 31 weeks after infection. These data suggest that OPN is not crucial for protective immunity upon M. tuberculosis infection and during the late phase of tuberculosis may even be detrimental for the host.

The involvement of pro-inflammatory cytokines in nephrogenic systemic fibrosis - a mechanistic hypothesis based on preclinical results from a rat model treated with gadodiamide

The evidence for the potential involvement of gadolinium-based contrast agents (GBCAs) in the pathomechanism of nephrogenic systemic fibrosis (NSF), a rare but serious disease occurring in patients with severe or end-stage renal failure, has grown due to recent epidemiological and preclinical research. Nevertheless there is still uncertainty with regard to the prevailing patho-physiological processes that may lead to NSF. To examine the potential mechanism of the fibrotic skin changes we applied a recently published rat model of NSF for investigations into serum markers for inflammation. For this purpose male Wistar rats were treated either once, three, or eight times with a daily intravenous injection of 2.5 mmol/kg gadodiamide, the drug substance of the magnetic resonance imaging (MRI) agent Omniscan. Clinical observations, hematology, clinical pathology, histopathology including electron microscopy and gadolinium (Gd) determination in serum, skin, femur and liver tissue, and a multiplexed analysis of 70 protein serum markers were performed. Gd was detectable in the skin, femur, and liver of the gadodiamide-treated rats 6h after the first administration. Macroscopic skin changes, appearing as reddening and early scab formation, were observed in one animal after the third daily administration and affected all animals after 8 daily administrations. Microscopy revealed dermal infiltrations after three administrations, progressing towards inflammatory lesions, ulcerations and crusts. Among the investigated serum marker panel 13 cytokines were significantly (p<0.01) elevated 6 h after the first injection, and eight stayed elevated over all time points: the monocyte chemotactic proteins MCP-1 and MCP-3, the macrophage inflammatory proteins MIP-1beta and MIP-2, the tumor necrosis factor TNF-alpha, the extracellular matrix regulator tissue inhibitor of metalloproteinase type 1 (TIMP-1), the vascular epithelial growth factor (VEGF) and osteopontin. The latter cytokine is of particular interest, since this matrix cellular glycoprotein is involved in the regulation of dystrophic calcification but also plays a role as a chemoattractant for dendritic cells, macrophages and T-lymphocytes, which in turn activate inflammatory pathways. Reflecting the physiological role of osteopontin, we hypothesize that Gd release from the GBCA-complex leads to the formation of insoluble Gd-deposits subsequently eliciting a physiological response similar to that seen during dystrophic calcification, i.e. an up-regulation of osteopontin and chemoattractant cytokines. Concomitant increase in vascular permeability caused by MIP-1, TNF-alpha and VEGF may lead to extravasation of chelated Gd or Gd-deposits. The inherent persistence of the Gd-deposits may subsequently result in an overactivation of pro-inflammatory pathways progressing towards overt skin effects.

GALNT3, a gene associated with hyperphosphatemic familial tumoral calcinosis, is transcriptionally regulated by extracellular phosphate and modulates matrix metalloproteinase activity

GALNT3 encodes UDP-N-acetyl-alpha-d-galactosamine: polypeptide N-acetylgalactosaminyl-transferarase 3 (ppGalNacT3), a glycosyltransferase which has been suggested to prevent proteolysis of FGF23, a potent phosphaturic protein. Accordingly, loss-of-function mutations in GALNT3 cause hyperphosphatemic familial tumoral calcinosis (HFTC), a rare autosomal recessive disorder manifesting with increased kidney reabsorption of phosphate, resulting in severe hyperphosphatemia and widespread ectopic calcifications. Although these findings definitely attribute a role to ppGalNacT3 in the regulation of phosphate homeostasis, little is currently known about the factors regulating GALNT3 expression. In addition, the effect of decreased GALNT3 expression in peripheral tissues has not been explored so far. In the present study, we demonstrate that GALNT3 expression is under the regulation of a number of factors known to be associated with phosphate homeostasis, including inorganic phosphate itself, calcium and 1,25-dihydroxyvitamin D(3). In addition, we show that decreased GALNT3 expression in human skin fibroblasts leads to increased expression of FGF7 and of matrix metalloproteinases, which have been previously implicated in the pathogenesis of ectopic calcification. Thus, the present data suggest that ppGalNacT3 may play a role in peripheral tissues of potential relevance to the pathogenesis of disorders of phosphate metabolism.

Hydrogen peroxide enhances osteopontin expression and matrix metalloproteinase activity in aortic vascular smooth muscle cells

1. Restenosis after percutaneous coronary intervention (PCI) is a major clinical complication. However, the underlying mechanisms remain poorly understood. The present aim of the present study was to test the hypothesis that reactive oxygen species (ROS) enhance osteopontin (OPN) expression and increase matrix metalloproteinase (MMP)-2 activity (two major factors that contribute to restenosis) in aortic vascular smooth muscle cells (VSMC), thus facilitating restenosis. 2. Primary cultured rat aortic VSMC were exposed to different concentrations (10, 50 and 100 micromol/L) of H(2)O(2). The expression of OPN mRNA and protein was determined by reverse transcription-polymerase chain reaction and Western blotting, respectively. The activity of MMP-2 was determined by gelatin zymography. 3. The expression of OPN mRNA and protein in VSMC was enhanced by H(2)O(2) in a dose-dependent manner. In addition, H(2)O(2) at all concentrations tested (which are comparable to those seen in diabetic vascular tissues) significantly increased MMP-2 activity in VSMC. 4. Because vascular ROS production is significantly increased in patients with ischaemic disease and OPN and MMP-2 have been shown to play critical role in restenosis, the results of the present study strongly suggest that a ROS-initiated and OPN- and MMP-2-mediated signalling pathway may play an important role in accelerated restenosis after PCI in patients with ischaemic disease. Therefore, the H(2)O(2)-OPN/MMP-2 system may be a new therapeutic target in reducing restenosis in patients undergoing PCI.

The differential amino acid requirement within osteopontin in alpha4 and alpha9 integrin-mediated cell binding and migration

Osteopontin (OPN) contains at least two major integrin recognition domains, Arg159-Gly-Asp161 (RGD) and Ser162-Val-Val-Tyr-Gly-Leu-Arg168 (SVVYGLR), recognized by alphavbeta3 and alpha5beta1 and alpha4 and alpha9 integrins, respectively. OPN is specifically cleaved by thrombin and matrix metalloproteinase (MMP)-3 or MMP-7 at a position of Arg168/Ser169 (R/S) and Gly166/Leu167 (G/L), respectively. We in this study examined the requirement of residues within SVVYGLR for the alpha4 and alpha9 integrin recognition and how MMP-cleavage influences the integrin recognition. The residues, Val164, Tyr165, and Leu167 are critical for alpha4 and alpha9 integrin recognition in both cell adhesion and cell migration. The residue Arg168 is additionally required for alpha9 integrin recognition in cell adhesion and this explains why alpha9 integrin binds to only thrombin cleaved form of OPN. alpha4 integrin is able to bind to SVVYG (MMP-cleaved form of RAA OPN-N half), while alpha9 integrin is not, supporting the above notion that Arg168 is additionally required for alpha9 integrin-mediated cell adhesion. The residue Val163 is important for alpha4, but not for alpha9 integrin recognition in cell migration. Importantly, we found that the replacement of Arg168 by Ala (R168A mutant) induces the augmentation of cell migration via alpha4 and alpha9 integrins.

Relationship between plasma osteopontin and oxidative stress in patients with coronary artery disease

BACKGROUND

It is known that oxidative stress plays an important role in the pathogenesis of atherosclerosis and that an association exists between osteopontin (OPN) and atherosclerosis.

OBJECTIVES

It was proposed that malondialdehyde (MDA), a biomarker of lipid peroxidation and oxidative stress, would be related to plasma OPN levels in patients with coronary artery disease (CAD).

METHODS/RESULTS

Plasma OPN and MDA levels were measured in 71 patients (60 males and 11 females; mean age 61.7 +/- 10 years). Fifty-eight patients had significant CAD (group I) and 13 patients were free of CAD as defined angiographically (group II). Plasma OPN was measured by enzyme-linked immunosorbent assay (ELISA), while MDA was determined spectrophotometrically. Multivariate regression analysis revealed that ln-transformed OPN levels were independently associated with MDA after adjustment for age, hypertension and diabetes mellitus (R(2) = 0.278, p = 0.0004 and beta regression coefficient = 0.252 [standard error = 0.0958], p = 0.011). OPN and MDA levels were higher in patients with diabetes (73.6 +/- 36.2 ng/ml versus 56.1 +/- 30.9 ng/ml, p = 0.02 and 2.5 +/- 0.5 microM versus 2.0 +/- 0.5 microM, p = 0.002, respectively).

CONCLUSIONS

The association between OPN and MDA levels in patients with CAD suggests an interaction between OPN and oxidative stress. This interaction may play a role in the pathogenesis of atherosclerosis.

Age-related medial elastocalcinosis in arteries: mechanisms, animal models, and physiological consequences

With age, the calcium content of the arterial wall increases. Calcification occurs at two main levels: intimal plaques and the medial elastic fiber network. The latter has been referred to as medial elastocalcinosis and is the subject of this review. The mechanisms involved in elastocalcinosis are complex and involve polar, apolar, and active processes. Vascular calcification may be species specific to humans. As laboratory animals, such as the rat, grow old, they suffer from only very mild arterial calcification. Different animal models of induction of massive arterial calcification by pharmacological and other means exist. Although extrapolation from such models to the clinical situation in terms of etiology is difficult, such models could be useful in the nonclinical study of the pathophysiological consequences of vascular calcification. Vascular calcification modifies arterial wall stiffness, and this could have clinically significant consequences on cardiac function and downstream circulatory control.

Potential relationship between hepatobiliary osteopontin and peroxisome proliferator-activated receptor alpha expression following ethanol-associated hepatic injury in vivo and in vitro

Osteopontin (OPN) up-regulation is known to mediate hepatic inflammation in a rodent model of alcoholic liver disease (ALD) and alcohol ingestion is reported to inhibit hepatic peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activity leading to hepatic steatosis and inflammation. Therefore, the objective of this study was to investigate the potential relationship between the anti-inflammatory PPAR-alpha and proinflammatory OPN in rats and mice livers, and cell cultures of hepatocytes and biliary epithelium. Experiments were designed to evaluate the influence of ethanol (EtOH), lipopolysaccharide (LPS), and acetaldehyde (ACA) on OPN and PPAR-alpha expression levels in vivo (rats and mice) and in vitro (hepatocytes and biliary epithelium). Adult Sprague-Dawley rats and C57BL6 mice were fed EtOH-containing Lieber-DeCarli liquid diet for 6 weeks and injected with a single dose of LPS. A combination of EtOH and LPS treated rats and mice showed significant induction of hepatic OPN expression compared with the controls. Similarly, cells exposed to physiological doses of EtOH, LPS, a combination of EtOH and LPS, and ACA resulted in increased OPN protein and mRNA expression. Rats and mice in ALD model and cells treated with EtOH and ACA showed downregulation of PPAR-alpha mRNA. Also, DNA binding activity of PPAR-alpha to PPAR response element was significantly reduced following treatment. Overexpression of PPAR-alpha rescued the reduced PPAR-alpha activity and PPAR-alpha agonist, bezafibrate, elevated PPAR-alpha activity after treatment of EtOH, LPS, and ACA when cells were exposed by bezafibrate. To further delineate the potential relationship between OPN and PPAR-alpha, OPN(-/-) mice showed no change of PPAR-alpha mRNA level although wild-type mice showed downregulation of PPAR-alpha mRNA after EtOH treatment. In conclusion, the current study suggests that OPN is induced by EtOH and its metabolite ACA and opposite relationship likely exist between PPAR-alpha and OPN expression within the liver during ALD.

Differential coupling of Arg- and Gly389 polymorphic forms of the beta1-adrenergic receptor leads to pathogenic cardiac gene regulatory programs

The beta(1)-adrenergic receptor (beta(1)AR; ADRB1) polymorphism Arg389Gly is located in an intracellular loop and is associated with distinct human and mouse cardiovascular phenotypes. To test the hypothesis that beta(1)-Arg389 and beta(1)-Gly389 alleles could differentially couple to pathways beyond that of classic G(s)-adenylyl cyclase (AC)/cAMP signaling, we performed comparative gene expression profile analyses on hearts from wild-type and transgenic mice that expressed either human beta(1)-Arg389 or beta(1)-Gly389 receptors, or AC5, sampling at an early age prior to the onset of pathological features. All three models upregulated the expression of genes associated with RNA metabolism and translation and downregulated genes associated with mitochondria and energy metabolism, consistent with shared cAMP-driven increase in cardiac contractility, protein synthesis, and compensatory downregulation of mitochondrial energy production. Both beta(1)AR alleles activated additional genes associated with other pathways. Uniquely, beta(1)-Arg389 hearts exhibited upregulated expression of genes associated with inflammation, programmed cell death, and extracellular matrix. These observations expand the scope of 7-transmembrane domain receptor signaling propagation beyond known cognate G protein couplings. Moreover, they implicate alterations of a repertoire of processes evoked by a single amino acid variation in the cardiac beta(1)AR that might be exploited for genotype-specific heart failure diagnostics and therapeutics.

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.

The bone-adipose axis in obesity and weight loss

Body fat and lean mass are correlated with bone mineral density, with obesity apparently exerting protection against osteoporosis. The pathophysiological relevance of adipose tissue in bone integrity resides in the participation of adipokines in bone remodeling through effects on deposition and resorption. On the other hand, the skeleton has recently emerged as an endocrine organ with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The cross-talk between adipose tissue and the skeleton constitutes a homeostatic feedback system with adipokines and molecules secreted by osteoblasts and osteoclasts representing the links of an active bone-adipose axis. Given the impact of bariatric surgery on absorption and the adipokine secretory pattern, to focus on the changes taking place following surgical-induced weight loss on this dynamic system merits detailed consideration.

Characterization of osteopontin expression and function after status epilepticus

PURPOSE

Osteopontin is a cytokine found in many tissues and plays a role in tissue injury and repair. This study had two goals: to characterize osteopontin expression after status epilepticus (SE), and to test the hypotheses that osteopontin affects the susceptibility to seizures or alters cell death and inflammation after SE.

METHODS

Pilocarpine was used to induce SE in OPN(-/-) and OPN(+/+) mice to compare seizure susceptibility, neuropathological markers including real time PCR for inflammatory genes, and osteopontin immunohistochemistry. The effect of added osteopontin on excitotoxicity by N-methyl-d-aspartate in neuronal cultures of ONP(-/-) mice was determined.

RESULTS

Neurons undergoing degeneration showed osteopontin immunoreactivity 2-3 days after SE. After 10 to 31 days degenerating axons in the thalamus were osteopontin-positive. The susceptibility to seizures of OPN(-/-) and OPN(+/+) mice in the pilocarpine, fluorothyl, and maximal electroshock models was similar. There were no significant differences in the extent of neuronal damage after pilocarpine-induced SE, the expression of several neuropathological markers or the RNA levels of selected inflammatory genes. Recombinant and natural bovine osteopontin did not affect the extent of NMDA-induced cell death in OPN(-/-) mouse neuronal cultures.

CONCLUSION

We demonstrated that osteopontin is up-regulated in response to SE in distinct temporal sequences in the hippocampus, specifically in degenerating neurons and axons. However, osteopontin did not appear to regulate neurodegeneration or inflammation within the first 3 days after SE.

Plasma osteopontin increases after bariatric surgery and correlates with markers of bone turnover but not with insulin resistance

CONTEXT

Osteopontin (OPN) is a multifunctional protein involved in bone metabolism, cardiovascular disease, diabetes, and obesity. OPN levels are elevated in the plasma and adipose tissue of obese subjects, and are decreased with diet-induced weight loss.

OBJECTIVE

We investigated the effect of bariatric surgery on plasma OPN concentrations in morbidly obese patients.

SETTING

The study was performed at a university hospital.

SUBJECTS

We investigated 40 obese patients aged 43.1 +/- 1.8 yr, scheduled to undergo bariatric surgery. Roux-en-Y gastric bypass (RYGB) was performed in 30 subjects (27 females, three males), and laparoscopic adjustable gastric banding (LAGB) in 10 subjects (eight females, two males).

STUDY DESIGN

All patients were studied before and 1 yr (10.3-14.8 months) after the intervention.

MAIN OUTCOME MEASURES

OPN, leptin, C-reactive protein, insulin, the homeostatic model assessment insulin resistance index, calcium, 25-hydroxyvitamin D, C telopeptide, and osteocalcin were determined.

RESULTS

Both bariatric procedures significantly reduced body weight, body mass index, insulin, leptin, and C-reactive protein 1 yr after surgery. Plasma OPN increased from 31.4 +/- 3.8 to 52.8 +/- 3.7 ng/ml after RYGB (P < 0.001) and from 29.8 +/- 6.9 to 46.4 +/- 10.6 ng/ml after LAGB (P = 0.042). Preoperative OPN correlated with age, insulin, the homeostatic model assessment insulin resistance index, and postoperative OPN. Postoperative OPN correlated with C telopeptide and osteocalcin.

CONCLUSIONS

One year after RYGB and LAGB, plasma OPN levels significantly increased and correlated with biomarkers of bone turnover. Unlike other proinflammatory cytokines, OPN does not normalize but increases further after bariatric surgery.

Osteopontin as a new player in mast cell biology

The secreted glycoprotein osteopontin (OPN) sets into motion an astounding variety of activities that range from bone remodeling via immunomodulation to the inhibition of apoptosis. In the current issue of the European Journal of Immunology, OPN now also enters mast cell biology and the regulation of IgE-dependent immune responses since it is reported that connective tissue-type mast cells from fetal murine skin constitutively secrete biologically active OPN. Moreover, it is shown that, in vitro, OPN augments IgE-mediated mast cell degranulation and migration via ligand binding to cognate OPN receptors on the mast cell surface (CD44, alpha v integrin) and that the magnitude of an IgE-mediated passive cutaneous anaphylaxis reaction is augmented by OPN in vivo. Here, we discuss why this newly discovered property of OPN fits well into the emerging concept that OPN may serve as a multi-purpose environmental damage-response protein.

Osteopontin expression in human and murine obesity: extensive local up-regulation in adipose tissue but minimal systemic alterations

Obesity is associated with a chronic low-grade inflammation characterized by macrophage infiltration of adipose tissue (AT) that may underlie the development of insulin resistance and type 2 diabetes. Osteopontin (OPN) is a multifunctional protein involved in various inflammatory processes, cell migration, and tissue remodeling. Because these processes occur in the AT of obese patients, we studied in detail the regulation of OPN expression in human and murine obesity. The study included 20 morbidly obese patients and 20 age- and sex-matched control subjects, as well as two models (diet-induced and genetic) of murine obesity. In high-fat diet-induced and genetically obese mice, OPN expression was drastically up-regulated in AT (40 and 80-fold, respectively) but remained largely unaltered in liver (<2-fold). Moreover, OPN plasma concentrations remained unchanged in both murine models of obesity, suggesting a particular local but not systemic importance for OPN. OPN expression was strongly elevated also in the AT of obese patients compared with lean subjects in both omental and sc AT. In addition, we detected three OPN isoforms to be expressed in human AT and, strikingly, an obesity induced alteration of the OPN isoform expression pattern. Analysis of AT cellular fractions revealed that OPN is exceptionally highly expressed in AT macrophages in humans and mice. Moreover, OPN expression in AT macrophages was strongly up-regulated by obesity. In conclusion, our data point toward a specific local role of OPN in obese AT. Therefore, OPN could be a critical regulator in obesity induced AT inflammation and insulin resistance.

Small integrin-binding ligand N-linked glycoproteins (SIBLINGs): multifunctional proteins in cancer

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets.

Thrombin

Thrombin is a Na+-activated, allosteric serine protease that plays opposing functional roles in blood coagulation. Binding of Na+ is the major driving force behind the procoagulant, prothrombotic and signaling functions of the enzyme, but is dispensable for cleavage of the anticoagulant protein C. The anticoagulant function of thrombin is under the allosteric control of the cofactor thrombomodulin. Much has been learned on the mechanism of Na+ binding and recognition of natural substrates by thrombin. Recent structural advances have shed light on the remarkable molecular plasticity of this enzyme and the molecular underpinnings of thrombin allostery mediated by binding to exosite I and the Na+ site. This review summarizes our current understanding of the molecular basis of thrombin function and allosteric regulation. The basic information emerging from recent structural, mutagenesis and kinetic investigation of this important enzyme is that thrombin exists in three forms, E*, E and E:Na+, that interconvert under the influence of ligand binding to distinct domains. The transition between the Na+ -free slow from E and the Na+ -bound fast form E:Na+ involves the structure of the enzyme as a whole, and so does the interconversion between the two Na+ -free forms E* and E. E* is most likely an inactive form of thrombin, unable to interact with Na + and substrate. The complexity of thrombin function and regulation has gained this enzyme pre-eminence as the prototypic allosteric serine protease. Thrombin is now looked upon as a model system for the quantitative analysis of biologically important enzymes.

Interplay between oxidative stress and immunity in the progression of alcohol-mediated liver injury

Inflammation is recognized increasingly as having an important role in the pathogenesis of alcoholic liver disease (ALD). Nonetheless, the mechanisms by which alcohol maintains hepatic inflammation are still characterized incompletely. Several studies have demonstrated that ethanol-induced oxidative stress promotes immune responses in ALD by stimulating both humoral and cellular reactions against liver proteins adducted to hydroxyethyl free radicals and several lipid peroxidation products. Moreover, ALD patients have autoantibodies targeting cytochrome P4502E1 and oxidized phospholipids. In both chronic alcohol-fed rats and heavy drinkers, the elevation of IgG against lipid peroxidation-derived antigens is associated with tumor necrosis factor-alpha production and the severity of liver inflammation. On this basis, we propose that allo- and autoimmune reactions associated with oxidative stress might contribute to fueling hepatic inflammation in ALD.

NMDA receptor subunit NR2b: effects on LH release and GnRH gene expression in young and middle-aged female rats, with modulation by estradiol

BACKGROUND/AIMS

The loss of reproductive capacity during aging involves changes in the neural regulation of the hypothalamic gonadotropin-releasing hormone (GnRH) neurons controlling reproduction. This neuronal circuitry includes glutamate receptors on GnRH neurons. Previously, we reported an increase in the expression of the NR2b subunit protein of the NMDA receptor on GnRH neurons in middle-aged compared to young female rats. Here, we examined the functional implications of the NR2b subunit on the onset of reproductive aging, using an NR2b-specific antagonist ifenprodil.

METHODS

Young (3-5 months) and middle-aged (10-13 months) female rats were ovariectomized (OVX), 17beta-estradiol (E2) or vehicle (cholesterol) treated, and implanted with a jugular catheter. Serial blood sampling was undertaken every 10 min for 4 h, with ifenprodil (10 mg/kg) or vehicle injected (i.p.) after 1 h of baseline sampling. The pulsatile release of pituitary LH and levels of GnRH mRNA in hypothalamus were quantified as indices of the reproductive axis.

RESULTS

Our results showed effects of ifenprodil on both endpoints. In OVX rats given cholesterol, neither age nor ifenprodil had any effects on LH release. In E2-treated rats, aging was associated with significant decreases in pulsatile LH release. Additionally, ifenprodil stimulated parameters of pulsatile LH release in both young and middle-aged animals. Ifenprodil had few effects on GnRH mRNA; the only significant effect of ifenprodil was found in the middle-aged, cholesterol group.

CONCLUSION

Together, these findings support a role for the NR2b subunit of the NMDAR in GnRH/LH regulation. Because most of these effects were exhibited on pituitary LH release in the absence of a concomitant change in GnRH gene expression, it is likely that NMDA receptors containing the NR2b subunit play a role in GnRH-induced LH release, independent of de novo GnRH gene expression.