The complete cDNA and amino acid sequence of bovine fetuin. Its homology with alpha 2HS glycoprotein and relation to other members of the cystatin superfamily

Serum fetuin-A and Ser312 phosphorylated fetuin-A responses and markers of insulin sensitivity after a single bout of moderate intensity exercise

Fetuin‐A (Fet‐A), secreted by the liver and adipose tissue, inhibits insulin receptor tyrosine kinase activity and modulates insulin action. Numerous studies have shown association of elevated serum Fet‐A concentrations with obesity, non‐alcoholic fatty liver disease, and type 2 diabetes. Both moderate body weight loss (5%–10%) and significant body weight loss have been shown to decrease serum Fet‐A and improve insulin sensitivity. Currently, there are no studies examining the effects of a single bout of exercise on serum Fet‐A or Ser312‐pFet‐A (pFet‐A) responses. We hypothesized that a single bout of moderate‐intensity exercise will lower serum Fet‐A and that these changes will be associated with an improvement in insulin sensitivity. Thirty‐one individuals with obesity and 11 individuals with normal body weight were recruited. Participants underwent a single bout of treadmill walking, expending 500 kcal at 60%–70% VO_2max. Oral glucose tolerance tests (OGTT) were administered before the single bout of exercise (Pre Ex) and 24 h after exercise (24h Post Ex). In individuals with obesity, we observed a transient elevation of serum Fet‐A concentrations, but not pFet‐A, immediately after exercise (Post Ex). Further, a single bout of exercise decreased glucose_AUC, insulin_AUC, and insulin resistance index in individuals with obesity. Consistent with this improvement in insulin sensitivity, we observed that Fet‐A_AUC, pFet‐A_AUC, 2 h pFet‐A, and 2 h pFet‐A/Fet‐A were significantly lower following a single bout of exercise. Further, reductions in serum Fet‐A_AUC 24h Post Ex were correlated with a reduction in insulin resistance index. Together, this suggests that alterations in serum Fet‐A following a single bout of moderate‐intensity endurance exercise may play a role in the improvement of insulin sensitivity.

Clinical Trial Registration

NCT03478046; https://clinicaltrials.gov/ct2/show/NCT03478046.

Glycoproteogenomics: A Frequent Gene Polymorphism Affects the Glycosylation Pattern of the Human Serum Fetuin/α-2-HS-Glycoprotein

Fetuin, also known as α-2-HS-glycoprotein (gene name: AHSG), is one of the more abundant glycoproteins secreted into the bloodstream. There are two frequently occurring alleles of human AHSG, resulting in three genotypes (AHSG*1, AHSG*2, and heterozygous AHSG1/2). The backbone amino acid sequences of fetuin coded by the AHSG*1 and AHSG*2 genes differ in two amino acids including one known O-glycosylation site (aa position 256). Although fetuin levels have been extensively studied, the originating genotype is often ignored in such analysis. As fetuin has been suggested repeatedly as a potential biomarker for several disorders, the question whether the gene polymorphism affects the fetuin profile is of great interest. In this work, we describe detailed proteoform profiles of fetuin, isolated from serum of 10 healthy and 10 septic patient individuals and investigate potential glycoproteogenomics correlations, e.g. how gene polymorphisms affect glycosylation. We established an efficient method for fetuin purification from individuals' serum using ion-exchange chromatography. Subsequently, we performed hybrid mass spectrometric approaches integrating data from native mass spectra and peptide-centric MS analysis. Our data reveal a crucial effect of the gene polymorphism on the glycosylation pattern of fetuin. Moreover, we clearly observed increased fucosylation in the samples derived from the septic patients. Our serum proteoform analysis, targeted at one protein obtained from 20 individuals, exposes the wide variability in proteoform profiles, which should be taken into consideration when using fetuin as biomarker. Importantly, focusing on a single or few proteins, the quantitative proteoform profiles can provide, as shown here, already ample data to classify individuals by genotype and disease state.

Protein-functionalized nanoparticles derived from end-functional polymers and polymer prodrugs for crossing the blood-brain barrier

Nanoparticles may provide a viable way for neuroprotective drugs to cross the blood-brain barrier (BBB), which limits the passage of most drugs from the peripheral circulation to the brain. Heterotelechelic polymer prodrugs comprising a neuroprotective model drug (adenosine) and a maleimide functionality were synthesized by the "drug-initiated" approach and subsequent nitroxide exchange reaction. Nanoparticles were obtained by nanoprecipitation and exhibited high colloidal stability with diameters in the 162-185 nm range and narrow size distributions. Nanoparticles were then covalently surface-conjugated to different proteins (albumin, α2-macroglobulin and fetuin A) to test their capability of enhancing BBB translocation. Their performances in terms of endothelial permeability and cellular uptake in an in vitro BBB model were compared to that of similar nanoparticles with surface-adsorbed proteins, functionalized or not with the drug. It was shown that bare NPs (i.e., NPs not surface-functionalized with proteins) without the drug exhibited significant permeability and cellular uptake, which were further enhanced by NP surface functionalization with α2-macroglobulin. However, the presence of the drug at the polymer chain-end prevented efficient passage of all types of NPs through the BBB model, likely due to adecrease in the hydrophobicity of the nanoparticle surface and alteration of the protein binding/coupling, respectively. These results established a new and facile synthetic approach for the surface-functionalization of polymer nanoparticles for brain delivery purposes.

Similar Albeit Not the Same: In-Depth Analysis of Proteoforms of Human Serum, Bovine Serum, and Recombinant Human Fetuin

Fetuin, also known as alpha-2-Heremans Schmid glycoprotein (AHSG), belongs to some of the most abundant glycoproteins secreted into the bloodstream. In blood, fetuins exhibit functions as carriers of metals and small molecules. Bovine fetuin, which harbors 3 N-glycosylation sites and a suggested half dozen O-glycosylation sites, has been used often as a model glycoprotein to test novel analytical workflows in glycoproteomics. Here we characterize and compare fetuin in depth, using protein from three different biological sources: human serum, bovine serum, and recombinant human fetuin expressed in HEK-293 cells, with the aim to elucidate similarities and differences between these proteins and the post-translational modifications they harbor. Combining data from high-resolution native mass spectrometry and glycopeptide centric LC-MS analysis, we qualitatively and quantitatively gather information on fetuin protein maturation, N-glycosylation, O-glycosylation, and phosphorylation. We provide direct experimental evidence that both the human serum and part of the recombinant proteins are processed into two chains (A and B) connected by a single interchain disulfide bridge, whereas bovine fetuin remains a single-chain protein. Although two N-glycosylation sites, one O-glycosylation site, and a phosphorylation site are conserved from bovine to human, the stoichiometry of the modifications and the specific glycoforms they harbor are quite distinct. Comparing serum and recombinant human fetuin, we observe that the serum protein harbors a much simpler proteoform profile, indicating that the recombinant protein is not ideally engineered to mimic human serum fetuin. Comparing the proteoform profile and post-translational modifications of human and bovine serum fetuin, we observe that, although the gene structures of these two proteins are alike, they represent quite distinct proteins when their glycoproteoform profile is also taken into consideration.

Protein-drug nanoconjugates: Finding the alternative proteins as drug carrier

Present study was conducted to establish the interaction of bovine fetuin-A to validate its binding modalities with doxorubicin (Dox). Fetuin-A was purified to highest purity and monodispersity. Green synthesis of fetuin-A conjugated gold nanoparticles (F-GNPs) has been performed giving typical UV-maxima with subtle variation in fourier transform infrared spectroscopy (FTIR). Atomic force microscopy (AFM) revealed spherical shaped, polydisperse F-GNPs of varying sizes, complementing the radius of hydration (19.5-62.4nm) by dynamic light scattering (DLS). Circular dichroism (CD) analysis of fetuin-A with respect to Dox interaction shows remarkable reduction in ellipticity with increasing concentrations of Dox (20-120μM). Fetuin-A:Dox and F-GNPs:Dox at variable concentrations revealed significantly enhanced absorption spectra, while a continuous decrease in florescence (560nm). This effect was more drastic when Dox interact with fetuin-A as compared to F-GNPs. Some known antimicrobial drugs were also investigated under similar conditions, giving strong quenching effect in a dose dependent manner suggesting the significant yet differential interactions. In cytotoxicity assay, fetuin-A:Dox conjugates revealed less toxicity as compared to F-GNPs:Dox and Dox alone. In-silico studies of the fetuin-A:Dox complex suggest that the drug binds in the major grove between beta-sheet and long loop region of D1 domain and stabilized by several hydrogen bonds.

Obesity and kidney disease: Beyond the hyperfiltration

In industrialized countries, overweight and obesity account for approximately 13.8% and 24.9% of the kidney disease observed in men and women, respectively. Moreover, obesity-associated glomerulopathy is now considered as "an emerging epidemic." Kidney function can be negatively impacted by obesity through several mechanisms, either direct or indirect. While it is well established that obesity represents the leading risk factor for type 2 diabetes and hypertension, awareness that obesity is associated with direct kidney damage independently of hypertension and diabetes is still not widespread. In this paper we will discuss the emerging role of adipose tissue, particularly in the visceral depot, in obesity-induced chronic kidney damage.

Maternal plasma fetuin-A concentration is lower in patients who subsequently developed preterm preeclampsia than in uncomplicated pregnancy: a longitudinal study

Objective: Fetuin-A is a negative acute phase protein reactant that acts as a mediator for lipotoxicity, leading to insulin resistance. Intravascular inflammation and insulin resistance have been implicated in the mechanisms of disease responsible for preeclampsia (PE). Maternal plasma concentrations of fetuin-A at the time of diagnosis of preterm PE are lower than in control patients with a normal pregnancy outcome. However, it is unknown if the changes in maternal plasma fetuin-A concentrations precede the clinical diagnosis of the disease. We conducted a longitudinal study to determine whether patients who subsequently developed PE had a different profile of maternal plasma concentrations of fetuin-A as a function of gestational age (GA) than those with uncomplicated pregnancies. Methods: A longitudinal case-control study was performed and included 200 singleton pregnancies in the following groups: (1) patients with uncomplicated pregnancies who delivered appropriate for gestational age (AGA) neonates (n = 160); and (2) patients who subsequently developed PE (n = 40). Longitudinal samples were collected at each prenatal visit and scheduled at 4-week intervals from the first or early second trimester until delivery. Plasma fetuin-A concentrations were determined by ELISA. Analysis was performed using mixed-effects models. Results: The profiles of maternal plasma concentrations of fetuin-A differ between PE and uncomplicated pregnancies. Forward analysis indicated that the rate of increase of plasma fetuin-A concentration in patients who subsequently developed PE was lower at the beginning of pregnancy (p = 0.001), yet increased faster mid-pregnancy (p = 0.0017) and reached the same concentration level as controls by 26 weeks. The rate of decrease was higher towards the end of pregnancy in patients with PE than in uncomplicated pregnancies (p = 0.002). The mean maternal plasma fetuin-A concentration was significantly lower in patients with preterm PE at the time of clinical diagnosis than in women with uncomplicated pregnancies (p < 0.05). In contrast, there were no significant differences in maternal plasma fetuin-A concentration in patients who developed PE at term. Conclusions: (1) The profile of maternal plasma concentrations of fetuin-A over time (GA) in patients who develop PE is different from that of normal pregnant women; (2) the rate of change of maternal plasma concentrations of fetuin-A is positive (increases over time) in the midtrimester of normal pregnancy, and negative (decreases over time) in patients who subsequently develop PE; (3) at the time of diagnosis, the maternal plasma fetuin-A concentration is lower in patients with preterm PE than in those with a normal pregnancy outcome; however, such differences were not demonstrable in patients with term PE.

Intraperitoneal administration of fetuin-A attenuates D-galactosamine/lipopolysaccharide-induced liver failure in mouse

BACKGROUND

Fulminant hepatic failure (FHF) is a devastating syndrome, which sometimes results in death or liver transplantation, in which inflammation would aggravate the development of fetuin-A which would act as an anti-inflammatory factor and may be an available approach to attenuate FHF.

AIMS

The purpose of this study was to investigate the effects of fetuin-A on D-galactosamine/lipopolysaccharide (D-GalN/LPS)-induced liver failure in mice.

METHODS

A mouse model of FHF induced by D-GalN/LPS was established and fetuin-A was injected intraperitoneally prior to D-GalN/LPS treatment. At different time points after D-GalN/LPS intervention, serum TNF-α and IL-6 levels were measured by ELISA. Fetuin-A mRNA and protein expression in liver tissues was assessed by RT-PCR, Western blotting and immunohistochemical staining. Besides, an observation of liver tissue injury, the apoptosis of hepatocytes, was analyzed by TUNEL assay.

RESULTS

Expression of fetuin-A mRNA and protein in liver tissue were significantly and gradually decreased after D-GalN/LPS administration. A pre-intervention of exogenous fetuin-A significantly improved the liver function, decreased TNF-α and IL-6 expression in peripheral blood, and liver tissue inhibited hepatocyte apoptosis responded to D-GalN/LPS induction so as to decrease the mortality rates of FHF mouse. Meanwhile, fetuin-A was negatively correlated with the hepatic pathological score and TNF-α protein staining in FHF mouse.

CONCLUSIONS

An intraperitoneal injection of fetuin-A attenuates D-GalN/LPS-induced FHF in mice. Fetuin-A might be a protective agent of liver damage partly through inhibiting liver inflammatory response and hepatocyte apoptosis.

Revision of the biodistribution of uranyl in serum: is fetuin-A the major protein target?

Uranium is a natural actinide present as uranyl U(VI) species in aqueous environments. Its toxicity is considered to be chemical rather than radiotoxicological. Whatever the route of entry, uranyl reaches the blood, is partly eliminated via the kidneys, and accumulated in the bones. In serum, its speciation mainly involves carbonate and proteins. Direct identification of labile uranyl-protein complexes is extremely difficult because of the complexity of this matrix. Thus, until now the biodistribution of the metal in serum has not been described, and therefore, little is known about the metal transport mechanisms leading to bone accumulation. A rapid screening method based on a surface plasmon resonance (SPR) technique was used to determine the apparent affinities for U(VI) of the major serum proteins. A first biodistribution of uranyl was obtained by ranking the proteins according to the criteria of both their serum concentrations and affinities for this metal. Despite its moderate concentration in serum, fetuin-A (FETUA) was shown to exhibit an apparent affinity within the 30 nM range and to carry more than 80% of the metal. This protein involved in bone mineralization aroused interest in characterizing the U(VI) and FETUA interaction. Using complementary chromatographic and spectroscopic approaches, we demonstrated that the protein can bind 3 U(VI) at different binding sites exhibiting Kd from ∼30 nM to 10 μM. Some structural modifications and functional properties of FETUA upon uranyl complexation were also controlled. To our knowledge, this article presents the first identification of a uranyl carrier involved in bone metabolism along with the characterization of its metal binding sites.

Biochemical characterization of trans-sialidase TS1 variants from Trypanosoma congolense

Background

Animal African trypanosomiasis, sleeping sickness in humans and Nagana in cattle, is a resurgent disease in Africa caused by Trypanosoma parasites. Trans-sialidases expressed by trypanosomes play an important role in the infection cycle of insects and mammals. Whereas trans-sialidases of other trypanosomes like the American T. cruzi are well investigated, relatively little research has been done on these enzymes of T. congolense.

Results

Based on a partial sequence and an open reading frame in the WTSI database, DNA sequences encoding for eleven T. congolense trans-sialidase 1 variants with 96.3% overall amino acid identity were amplified. Trans-sialidase 1 variants were expressed as recombinant proteins, isolated and assayed for trans-sialylation activity. The purified proteins produced α2,3-sialyllactose from lactose by desialylating fetuin, clearly demonstrating their trans-sialidase activity. Using an HPLC-based assay, substrate specificities and kinetic parameters of two variants were characterized in detail indicating differences in substrate specificities for lactose, fetuin and synthetic substrates. Both enzymes were able to sialylate asialofetuin to an extent, which was sufficient to reconstitute binding sites for Siglec-4. A mass spectrometric analysis of the sialylation pattern of glycopeptides from fetuin revealed clear but generally similar changes in the sialylation pattern of the N-glycans on fetuin catalyzed by the trans-sialidases investigated.

Conclusions

The identification and characterization of a trans-sialidase gene family of the African parasite T. congolense has opened new perspectives for investigating the biological role of these enzymes in Nagana and sleeping sickness. Based on this study it will be interesting to address the expression pattern of these genes and their activities in the different stages of the parasite in its infection cycle. Furthermore, these trans-sialidases have the biotechnological potential to be used for enzymatic modification of sialylated glycoconjugates.

The "thrifty" gene encoding Ahsg/Fetuin-A meets the insulin receptor: Insights into the mechanism of insulin resistance

Ahsg (fetuin-A) is a 55-59kDa phosphorylated glycoprotein synthesized in the adult predominantly by hepatocytes, from which it enters the circulation. When dysregulated, this glycoprotein operates to influence the clinical sequelae of insulin resistance-type 2 diabetes and cardiovascular disease. The pathological sequelae likely arise from two separable molecular "faces" of Ahsg-one acting at the level of the insulin receptor and a second face influencing ectopic biomineralization in the intima. A detailed understanding of these two functional faces of Ahsg is not yet clear for lack of structural studies. Ahsg has a physiological role in the biomineralization of bone, which when dysregulated can lead to ectopic calcification of soft tissues in the vasculature. Ahsg has a second physiological function in regulating how insulin signals through its receptor, a transmembrane tyrosine kinase. Dysregulation of this "face" of Ahsg results in morbid sequelae such as impaired glucose disposal and fatty liver. Ahsg binds to tandem fibronectin type 3 (Fn3) domains present in the 194 amino acid residue extracellular portion of the β-subunit of the insulin receptor, distant from the high-affinity pocket formed by two complementing α-subunits where insulin binds. Only two proteins are known to bind directly to the insulin receptor ectodomain - insulin and Ahsg - the former turns on the receptor's intrinsic tyrosine kinase (TK) activity, and the latter shuts it down. Recent X-ray crystallographic studies of the ectodomain of the insulin receptor now sharpen our understanding of the receptor's extracellular α-subunit and linked β-subunit. Ahsg genotype and its circulating level have been correlated with body morphometrics (obese versus lean and visceral adiposity) in epidemiological studies enrolling thousands of patients. Epidemiological studies from the clinic reveal high levels of circulating Ahsg in insulin resistance and diabetes. This review endeavors to explain how one protein can mediate diverse pathologies, but specifically addresses its metabolic "face" blunting insulin receptor activity, an action leading to insulin resistance.

Preliminary biochemical characterization of the novel, non-AT1, non-AT2 angiotensin binding site from the rat brain

A novel binding site for angiotensins II and III was recently discovered in brain membranes in the presence of the sulfhydryl reactive angiotensinase inhibitor parachloromercuribenzoate. This binding site is distinctly different from the other known receptors for angiotensins: AT₁, AT₂, AT₄, and mas oncogene protein (Ang 1-7 receptor). Preliminary biochemical characterization studies have been done on this protein by crosslinking it with (125)I-labeled photoaffinity probes and solubilizing the radiolabeled binding site. Polyacrylamide gel electrophoresis studies and isoelectric focusing indicate that this membrane bound binding site is a protein with a molecular weight of 70-85 kDa and an isoelectric point of ~7. Cyanogen bromide hydrolysis of the protein yielded two radiolabeled fragments of 12.5 and 25 kDa. The protein does not appear to be N-glycosylated based upon the failure of PNGaseF to alter its migration rate on a 7.5% polyacrylamide gel. The binding of angiotensin II to this protein is not affected by GTPγS or Gpp(NH)p, suggesting that it is not a G protein-coupled receptor. Further characterization studies are directed to identify this protein either as a novel angiotensin receptor, an angiotensin scavenger (clearance receptor) or an angiotensinase.

Facile synthesis of 4-mercaptophenylboronic acid functionalized gold nanoparticles for selective enrichment of glycopeptides

In the work, 4-mercaptophenylboronic acid (4-MPBA)-functionalized gold nanoparticles were synthesized via a facile approach. At first, gold nanoparticles (about 50 nm) were prepared by a simple and convenient hydrothermal method based on a polyol process. Then, gold nanoparticles were modified with 4-MPBA by the well-known reaction of Au with the thiol groups. The MPBA-functionalized gold nanoparticles were characterized by Fourier transform infrared spectra and UV/Vis adsorption spectra. Due to the fact that the boronic acid group on the surface of 4-MPBA-modified gold particles can form tight yet reversible covalent bonds with glycopeptides containing cis-1,2-diols groups, the MPBA-modified gold nanoparticles were successfully applied to selective enrichment of glycopeptides. Isolation and enrichment of glycopeptides in a standard protein (asialofetuin and horseradish peroxidase) digestion and a complex sample were performed using MPBA-modified gold nanoparticles, followed by matrix-assisted laser desorption/ionization quadruple ion trap time-of-flight (MALDI-QIT-TOF) mass spectrometric analysis. The experimental results demonstrated that MPBA-modified gold nanoparticles synthesized by the facile approach have the powerful potential for selective enrichment of glycopeptides, and can be an alternative tool in glycoproteomics.

Multivalent binding of carbohydrates by the human alpha-defensin, HD5

Four of the six human alpha-defensins (human neutrophil peptides 1-3 and human alpha-defensin 5; HD5) have a lectin-like ability to bind glycosylated proteins. Using HD5 as a model, we applied surface plasmon resonance techniques to gain insights into this property. HD5 bound natural glycoproteins > neoglycoproteins based on BSA > nonglycosylated BSA >> free sugars. The affinity of HD5 for simple sugars covalently bound to BSA was orders of magnitude greater than its affinity for the same sugars in solution. The affinity of HD5 for protein-bound carbohydrates resulted from multivalent interactions which may also involve noncarbohydrate residues of the proteins. HD5 showed concentration-dependent self-association that began at submicromolar concentrations and proceeded to dimer and tetramer formation at concentrations below 5 microM. The (R9A, R28A) and (R13A, R32A) analogs of HD5 showed greatly reduced self-association as well as minimal binding to BSA and to BSA-affixed sugars. From this and other evidence, we conclude that the extensive binding of HD5 to (neo)glycoproteins results from multivalent nonspecific interactions of individual HD5 molecules with carbohydrate and noncarbohydrate moieties of the target molecule and that the primary binding events are magnified and enhanced by subsequent in situ assembly and oligomerization of HD5. Self-association and multivalent binding may play integral roles in the ability of HD5 to protect against infections caused by viruses and other infectious agents.

Improved protein sequence coverage by on resin deglycosylation and cysteine modification for biomarker discovery

Membrane proteins and secreted factors (soluble proteins or extracellular matrix components) are the targets of most monoclonal antibodies, which are currently in clinical development. These proteins are frequently post-translationally modified, e.g. by the formation of disulfide bonds or by glycosylation, which complicates their identification using proteomics technologies. Here, we describe a novel methodology for the on resin deglycosylation and cysteine modification of proteins after in vitro, in vivo or ex vivo biotinylation. Biotinylated proteins are captured on streptavidin resin and all subsequent modifications, as well as the proteolytic digestion, which yields peptides for MS analysis, are performed on resin. Using biotinylated bovine fetuin-A as a test protein, an improvement in sequence coverage from 7.9 to 58.7% could be shown, including the identification of all three glycosylation sites. Furthermore, a complex mixture derived from the ex vivo biotinylation of vascular structures in human kidney with cancer obtained by perfusion after surgical resection revealed almost a doubling of sequence coverage for all checked proteins when analyzed by LC-MALDI TOF/TOF.

Fetuin-A induces cytokine expression and suppresses adiponectin production

BACKGROUND

The secreted liver protein fetuin-A (AHSG) is up-regulated in hepatic steatosis and the metabolic syndrome. These states are strongly associated with low-grade inflammation and hypoadiponectinemia. We, therefore, hypothesized that fetuin-A may play a role in the regulation of cytokine expression, the modulation of adipose tissue expression and plasma concentration of the insulin-sensitizing and atheroprotective adipokine adiponectin.

METHODOLOGY AND PRINCIPAL FINDINGS

Human monocytic THP1 cells and human in vitro differenttiated adipocytes as well as C57BL/6 mice were treated with fetuin-A. mRNA expression of the genes encoding inflammatory cytokines and the adipokine adiponectin (ADIPOQ) was assessed by real-time RT-PCR. In 122 subjects, plasma levels of fetuin-A, adiponectin and, in a subgroup, the multimeric forms of adiponectin were determined. Fetuin-A treatment induced TNF and IL1B mRNA expression in THP1 cells (p<0.05). Treatment of mice with fetuin-A, analogously, resulted in a marked increase in adipose tissue Tnf mRNA as well as Il6 expression (27- and 174-fold, respectively). These effects were accompanied by a decrease in adipose tissue Adipoq mRNA expression and lower circulating adiponectin levels (p<0.05, both). Furthermore, fetuin-A repressed ADIPOQ mRNA expression of human in vitro differentiated adipocytes (p<0.02) and induced inflammatory cytokine expression. In humans in plasma, fetuin-A correlated positively with high-sensitivity C-reactive protein, a marker of subclinical inflammation (r = 0.26, p = 0.01), and negatively with total- (r = -0.28, p = 0.02) and, particularly, high molecular weight adiponectin (r = -0.36, p = 0.01).

CONCLUSIONS AND SIGNIFICANCE

We provide novel evidence that the secreted liver protein fetuin-A induces low-grade inflammation and represses adiponectin production in animals and in humans. These data suggest an important role of fatty liver in the pathophysiology of insulin resistance and atherosclerosis.

Is the anti-inflammatory effect of regular exercise responsible for reduced cardiovascular disease?

Engaging in regular physical activity reduces the risk of developing CVD (cardiovascular disease), but it is not certain to what degree this may be due to the anti-inflammatory effects of exercise. Following acute exercise, there is a transient increase in circulating levels of anti-inflammatory cytokines, whereas chronic exercise reduces basal levels of pro-inflammatory cytokines. Exercise training also induces the expression of antioxidant and anti-inflammatory mediators in the vascular wall that may directly inhibit the development of atherosclerosis. Limited studies in humans and more comprehensive assessments in animal models have confirmed that exercise is atheroprotective and helped identify a number of the mechanisms to explain these effects. This review explores the relationship between systemic and vascular wall inflammation and the role that the anti-inflammatory effects of exercise have on the development and progression of CVD.

Ion-pair chromatographic separation of glycoprotein derived oligosaccharides as their 8-aminopyrene-1,3,6-trisulfonic acid derivatives

A reversed-phase ion-pair gradient liquid chromatographic method has been developed for separation of 8-aminopyrene-1,3,6-trisulfonic acid (APTS) labeled oligosaccharides derived from some glycoproteins. This separation mode has high capability for structural recognition of oligosaccharide isomers, which are usually difficult to separate using commonly used partition chromatography. In addition, some glycoprotein-derived complex-type oligosaccharides that have linkage isomers in one lactosamine arm and neuraminic acids existing in fetuin, as well as differences in the numbers of lactosamine branches, are separable using this mode. The ion-pair mode is promising for simple analyses of glycoprotein-derived oligosaccharides that are labeled with APTS.

Alpha2-Heremans-Schmid glycoprotein/fetuin-A is associated with insulin resistance and fat accumulation in the liver in humans

OBJECTIVE

The alpha(2)-Heremans-Schmid glycoprotein (AHSG; fetuin-A in animals) impairs insulin signaling in vitro and in rodents. Whether AHSG is associated with insulin resistance in humans is under investigation. In an animal model of diet-induced obesity that is commonly associated with hepatic steatosis, an increase in Ahsg mRNA expression was observed in the liver. Therefore, we hypothesized that the AHSG plasma protein, which is exclusively secreted by the liver in humans, may not only be associated with insulin resistance but also with fat accumulation in the liver.

RESEARCH DESIGN AND METHODS

Data from 106 healthy Caucasians without type 2 diabetes were included in cross-sectional analyses. A subgroup of 47 individuals had data from a longitudinal study. Insulin sensitivity was measured by a euglycemic-hyperinsulinemic clamp, and liver fat was determined by (1)H magnetic resonance spectroscopy.

RESULTS

AHSG plasma levels, adjusted for age, sex, and percentage of body fat, were higher in subjects with impaired glucose tolerance compared with subjects with normal glucose tolerance (P = 0.006). AHSG plasma levels were negatively associated with insulin sensitivity (r = -0.22, P = 0.03) in cross-sectional analyses. Moreover, they were positively associated with liver fat (r = 0.27, P = 0.01). In longitudinal analyses, under weight loss, a decrease in liver fat was accompanied by a decrease in AHSG plasma concentrations. Furthermore, high AHSG levels at baseline predicted less increase in insulin sensitivity (P = 0.02).

CONCLUSIONS

We found that high AHSG plasma levels are associated with insulin resistance in humans. Moreover, AHSG plasma levels are elevated in subjects with fat accumulation in the liver. This is consistent with a potential role of AHSG as a link between fatty liver and insulin resistance.

A novel approach for identification and characterization of glycoproteins using a hybrid linear ion trap/FT-ICR mass spectrometer

Combining source collision-induced dissociation (CID) and tandem mass spectral acquisition in a pseudo-MS(3) experiment using a linear ion trap results in a highly selective and sensitive approach to identifying glycopeptide elution from a protein digest. The increased sensitivity is partially attributed to the nonselective nature of source CID, which allows simultaneous activation of all charge states and coeluting glycoforms generating greater ion abundance for the mass-to-charge (m/z) 204 and/or 366 oxonium ions. Unlike source CID alone, a pseudo-MS(3) approach adds selectivity while improving sensitivity by eliminating chemical noise during the tandem mass spectral acquisition of the oxonium ions in the linear ion trap. Performing the experiments in the hybrid linear ion trap/Fourier transform-ion cyclotron resonance (FT-ICR) enables subsequent high-resolution/high-mass accuracy full-scan mass spectra (MS) and parallel acquisition of MS/MS in the linear ion trap to be completed in 2 s directly following the pseudo-MS(3) scan to collate identification and characterization of glycopeptides in one experimental scan cycle. Analysis of bovine fetuin digest using the combined pseudo-MS(3), high-resolution MS, and data-dependent MS/MS events resulted in identification of four N-linked and two O-linked glycopeptides without enzymatic cleavage of the sugar moiety or release of the sialic acids before analysis. In addition, over 95% of the total protein sequence was identified in one analytical run.

Suppressive effect of alpha2 Heremans-Schmid glycoprotein on in vitro calcification of osteogenesis

BACKGROUND

alpha(2) Heremans-Schmid glycoprotein (alpha(2)HS glycoprotein) is predominantly found in bone. To date, we have investigated plasma alpha(2)HS levels in immature babies and neonates as well as the histological distribution in various neonatal tissues in order to clarify its physiological significance. In an effort to understand the physiological function of alpha(2)HS glycoprotein in bones, we studied the effects of alpha(2)HS glycoprotein in cultured osteogenesis model using rat marrow cells.

METHODS

We added different concentrations of alpha(2)HS glycoprotein to cultured marrow cells, including osteoblasts in the presence of dexamethasone, in an attempt to elucidate the effects of alpha(2)HS glycoprotein on osteoblast growth and bone calcification in vitro.

RESULTS

The results showed that total DNA content was significantly increased with 0.2-20 nM (f.c.) alpha(2)HS glycoprotein, but was neither suppressed nor increased with 200 nM (f.c.) alpha(2)HS glycoprotein. Although ALP activity increased with 0.2 or 2 nM (f.c.) alpha(2)HS glycoprotein, it decreased with 20 or 200 nM (f.c.) alpha(2)HS glycoprotein. While 0.2 nM (f.c.) alpha(2)HS glycoprotein had no effect on calcium or osteocalcin content, 2 nM (f.c.) alpha(2)HS glycoprotein decreased both calcium content and osteocalcin content by about half, and no calcium or osteocalcin was observed with 20 or 200 nM (f.c.). Calcium staining of cultured marrow cells revealed that the number of stained cell tubercles decreased in a concentration-dependent manner.

CONCLUSION

These findings suggest that alpha(2)HS glycoprotein regulates the growth of osteoblasts and acts as an inhibitory factor in the regulation of bone calcification.

Differential detergent fractionation for non-electrophoretic bovine peripheral blood monocyte proteomics reveals proteins involved in professional antigen presentation

Professional antigen presenting cells (APC), dendritic cells (DC) and their myeloid progenitors, monocytes/macrophages are critical controllers of innate and adaptive immunity. Here we show that differential detergent fractionation (DDF) analysis of bovine monocytes reveals proteins related to antigen pattern recognition, uptake and presentation to immunocompetent lymphocytes. We identify 53 bovine proteins involved in immune function of professional APC. In particular, 13 adhesion molecules, three toll-like receptors (TLR1, 6 and 8), three antigen uptake-related proteins (including mannose receptor [MR] precursor), and eight actin-like proteins involved in active endocytosis were identified. In addition, MHC class I and II-related proteins, cytokines, active substances and growth factors have been identified. We conclude that the DDF approach can provide interpretable and meaningful functional information concerning protein expression profiles associated with monocyte activation, transformation into macrophages and/or immature DC, and maturation of monocyte-derived DC in the presence of multiple bovine pathogens.

Adsorption of serum fetuin to hydroxylapatite does not contribute to osteoblast phenotype modifications

Osteoblasts exhibit enhanced differentiation and altered gene profiles when cultured on hydroxyapatite (HA) compared to plastic surfaces. To begin determining mechanisms for this response, we used proteomics to identify proteins predominantly found in osteoblasts on HA but not plastic surfaces. Two-dimensional gel electrophoresis and Western analyses indicate that fetuin is abundant in extracts from HA, but not plastic surfaces. Incubation of HA and plastic surfaces with cell culture medium (containing 10% serum) under cell-free conditions shows that fetuin is predominantly derived from the culture medium serum and readily adsorbs to the HA surface. However, we did detect low levels of fetuin B mRNA in osteoblasts. Serum albumin, actin-beta, apolipoprotein-AI, and vimentin also adsorbed to HA. To determine the role of fetuin in the HA-induced osteoblast phenotype changes, osteoblasts were seeded onto fetuin-coated or uncoated HA under serum-free conditions. Osteoblast morphology was similar on both HA surfaces, suggesting that HA alone (without adsorbed serum proteins) is sufficient for cell attachment and spreading. Similarly, genes previously reported to be modulated by HA (glvr-1, DMP-1, osteoglycin, and proliferin 3) were modulated even in the absence of fetuin or other serum proteins. These data show that HA surface can be enriched selectively with fetuin from serum; however, neither fetuin or other serum proteins are required to mediate HA-induced osteoblast attachment, spreading, or changes in expression of genes examined. This finding suggests that factors intrinsic to HA are required for the response.

The Serum Glycoprotein Fetuin-A Promotes Lewis Lung Carcinoma Tumorigenesis via Adhesive-Dependent and Adhesive-Independent Mechanisms

Fetuin-A is a serum glycoprotein in the cystatin family associated with the regulation of soft tissue calcification. We tested the role of systemic fetuin in tumor cell growth and metastasis by injecting Lewis lung carcinoma (LLC) cells into fetuin-A null and their wild-type (WT) littermate control C57BL/6 mice via the tail vein, s.c., and intrasplenic routes. In the experimental metastasis assay, the lungs of the WT mice were filled with metastatic nodules, whereas the lungs of the fetuin-A null mutant mice were virtually free of colonies at the end of 2 weeks. Lung colonization responded to the levels of serum fetuin-A in a dose-dependent manner, as observed by the formation of half as many colonies in mice heterozygous for the fetuin-A locus compared with homozygous WT mice and restoration of lung colonization by the administration of purified fetuin-A to fetuin-A-null mice. Serum fetuin-A also influenced the growth of LLC cells injected s.c.: fetuin-A-null mice developed small s.c. tumors only after a substantial delay. Similarly, intrasplenic injection of LLC cells resulted in rapid colonization of the liver with metastasis to the lungs within 2 weeks in the WT but not fetuin-A null mice. To examine the mechanism by which fetuin-A influences LLC colonization and growth, we showed that LLC tumor cells adhere to fetuin-A in a Ca2+-dependent fashion, resulting in growth of the tumor cells. These studies support the role of fetuin-A as a major growth promoter in serum that can influence tumor establishment and growth.

Association between human α 2-Heremans Schmidt glycoprotein (AHSG) polymorphism and endometriosis in Korean women

OBJECTIVE

To evaluate the relationship between the alpha 2-Heremans Schmidt glycoprotein (AHSG) gene polymorphism and endometriosis.

DESIGN

Case-control study.

SETTING

Department of Obstetrics and Gynecology, Seoul National University Hospital, Korea.

PATIENT(S)

Seventy-nine women with endometriosis and 105 women without endometriosis.

INTERVENTION(S)

Determination of AHSG gene polymorphism.

MAIN OUTCOME MEASURE(S)

Prevalence of AHSG genotypes or alleles.

RESULT(S)

The allele frequencies of AHSG 1 and AHSG 2 were found to be 0.69 and 0.31, respectively. The proportion of noncarriers of the AHSG 2 allele was significantly higher in women with endometriosis than in women without (55.7% vs. 39.0%). Women not carrying the AHSG 2 allele were found to have twice the risk of endometriosis than those carrying at least one copy of this allele. No significant difference was noted in the distribution of the AHSG alleles or AHSG genotypes between early stage endometriosis and late stage endometriosis.

CONCLUSION(S)

Endometriosis is associated with the AHSG gene polymorphism in Korean women.

The comparative analysis of serum proteomes for the discovery of biomarkers for acute myeloid leukemia

OBJECTIVE

Acute myeloid leukemia (AML) develops as the consequence of a series of genetic changes in a hematopoietic precursor cell. However, the definitive diagnostic protein biomarkers for AML are still unclear. In our study to identify the biomarkers for an initial diagnosis, detection of relapse, and monitoring the minimal residual disease in AML by a less invasive method, serum proteins reflecting alterations in their proteomes were analyzed.

MATERIALS AND METHODS

We compared the two-dimensional electrophoresis patterns of human sera of 12 patients with AML with those of 12 normal subjects. The differentially expressed spots were identified by matrix-assisted laser desorption/ionization time-of-flight and electrospray ionization quadupole time-of-flight mass spectrometries.

RESULTS

Eight proteins that expressed differentially in the AML group were found. The expression levels of alpha-2-HS-glycoprotein, complement-associated protein SP-40, 40, RBP4 gene product, lipoprotein C-III, and an unknown protein were downregulated in serum of AML patients, whereas the other three proteins, including immunoglobulin heavy-chain variant, proteosome 26S ATPase subunit 1, and haptoglobin-1 were upregulated.

CONCLUSION

These results suggest that these proteins can be used as less invasive diagnostic and monitoring biomarkers of AML if further studies are done.

Kidney-bone, bone-kidney, and cell-cell communications in renal osteodystrophy

The relationship between bone and the kidney in renal osteodystrophy is a complex interplay of kidney to bone connections, bone to kidney connections, and cell to cell connections. In addition, such interactions have a profound effect on the vasculature. In this review, we discuss the role of the bone morphogenetic proteins (BMPs) in the skeleton, kidney, and vasculature. In addition, we propose that deficiencies of these BMPs seen in chronic kidney disease (CKD) result in decreased bone remodeling and a compensatory secondary hyperparathyroidism (high turnover state). Treatment of the hyperparathyroidism blocks this compensatory arm and thus decreased bone remodeling occurs (low turnover). We review animal models of CKD in which treatment with BMP-7 resulted in normalization of both high and low turnover states. Finally, we discuss vascular calcification as it relates to bone metabolism. We discuss the roles of BMP-7 and 2 other bone regulatory proteins, osteoprotegerin (OPG) and alpha2-HS glycoprotein (AHSG, human fetuin), in the human vasculature and their implications for vascular calcification.

Members of the cystatin superfamily interact with MMP-9 and protect it from autolytic degradation without affecting its gelatinolytic activities

Matrix metalloproteinases (MMPs), like other proteinases, can undergo autolytic degradation once activated in vivo. Whereas the activities of these enzymes are tightly regulated by tissue inhibitors of matrix metalloproteinases (TIMPs), it is not clear mechanistically how these enzymes are protected from autolysis in their active state. We previously reported that MMPs particularly MMP-9 and MMP-2 interact with the serum glycoprotein fetuin-A [Arch. Biochem. Biophys. (1995) 322, 250], a member of the cystatin superfamily. In the present analyses, we demonstrate that this interaction protects MMP-9 from autolytic degradation without interfering with its enzymatic activity, allowing it to efficiently digest gelatin. Our data demonstrate that MMP-9 binds to members of the cystatin family with K(diss) ranging from 25 to 58 nM for fetuin-A and 1.5-1.9 microM for cystatin C. The ability of fetuin-A to protect MMP-9 from autolysis requires a molar ratio of at least 8:1 (fetuin-A/MMP-9). More interestingly, our data show that the other members of the cystatin also have the ability to protect MMP-9 from autolysis, provided they are in molar excess relative to MMP-9. Taken together, our data suggest that cystatins, particularly fetuin-A, in any cellular compartment including the circulatory system, efficiently protect MMP-9 and possibly other MMPs from autolysis. This mechanism ensures the digestion of the preferred substrate for MMP-9 without sacrificing the enzyme in the process.

Biochemical aspects and functional role of the copper-containing amine oxidases

The copper-containing amine oxidases of the class EC 1.4.3.6 share many biochemical similarities. They contain cupric copper and catalyse the same general reaction. In mammals, diamine oxidase has a role in the metabolism of histamine, some other diamines and spermine oxidase, involved in the metabolism of polyamines. However, the functional role of benzylamine oxidase (BAO) and the tissue semicarbazide-sensitive amine oxidases (SSAO) is still under investigation. Circulating BAO is derived from the tissue SSAO. It has a high affinity for benzylamine and its role in the extra-cellular matrix includes the maturation of pro-elastin and control of the inflammatory process.

Alpha2-HS glycoprotein: a protein in search of a function

In this issue (pp. 305-310) Jun Ren and Amy J. Davidoff author an article entitled 'Alpha2-HS glycoprotein, a putative inhibitor of tyrosine kinase, prevents glucose toxicity associated with cardiomyocyte dysfunction'. The protein responsible for this biological activity has recently come to the forefront of research on the biological activity of plasma proteins.

Trypsin inhibitory activity of bovine fetuin de-O-glycosylated by endo-alpha-N-acetylgalactosaminidase

The effects of bovine fetuin O-glycans on its trypsin inhibitory activity were examined. De-sialylated (asialo-) and de-O-glycosylated fetuin were prepared from native fetuin using Arthrobacter neuraminidase and the mixture of it and Bacillus endo-alpha-N-acetylgalactosaminidase, respectively. De-sialylation and de-O-glycosylation from fetuin were confirmed with SDS-PAGE followed by western blotting using anti-human Thomsen-Friedenreich antigen (T antigen) antibody which recognizes O-linked galactosyl beta1,3 N-acetylgalactosamine (Gal beta1-->3GalNAc). Native fetuin completely inhibited the trypsin activity at about a 1:1 molar ratio. In contrast, the trypsin inhibitory activity of asialo- and de-O-glycosylated fetuin decreased about a half and one-third of that of native fetuin, respectively.

Analysis of nonderivatized neutral and sialylated oligosaccharides by electrospray mass spectrometry

An HPLC/MS method has been developed that allows rapid, direct analysis of underivatized sialylated as well as neutral oligosaccharides. The method involves the separation of oligosaccharides from salts and proteins using RP-HPLC with a formic acid/acetonitrile/water mobile phase system and on-line electrospray mass spectrometry analysis in the positive ion mode. Under the solution conditions employed, both neutral and acidic (sialylated) oligosaccharides are protonated and therefore detected. In contrast to MALDI-TOF MS, no loss of sialic acid is observed when operating in the positive ion mode. Furthermore, the capability of this method to provide quantitative estimates of the relative abundance of each oligosaccharide mass has been demonstrated using fetuin as a model compound.

Atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry

A novel ionization source for biological mass spectrometry is described that combines atmospheric pressure (AP) ionization and matrix-assisted laser desorption/ionization (MALDI). The transfer of the ions from the atmospheric pressure ionization region to the high vacuum is pneumatically assisted (PA) by a stream of nitrogen, hence the acronym PA-AP MALDI. PA-AP MALDI is readily interchangeable with electrospray ionization on an orthogonal acceleration time-of-flight (oaTOF) mass spectrometer. Sample preparation is identical to that for conventional vacuum MALDI and uses the same matrix compounds, such as alpha-cyano-4-hydroxycinnamic acid. The performance of this ion source on the oaTOF mass spectrometer is compared with that of conventional vacuum MALDI-TOF for the analysis of peptides. PA-AP MALDI can detect low femtomole amounts of peptides in mixtures with good signal-to-noise ratio and with less discrimination for the detection of individual peptides in a protein digest. Peptide ions produced by this method generally exhibit no metastable fragmentation, whereas an oligosaccharide ionized by PA-AP MALDI shows several structurally diagnostic fragment ions. Total sample consumption is higher for PA-AP MALDI than for vacuum MALDI, as the transfer of ions into the vacuum system is relatively inefficient. This ionization method is able to produce protonated molecular ions for small proteins such as insulin, but these tend to form clusters with the matrix material. Limitations of the oaTOF mass spectrometer for singly charged high-mass ions make it difficult to evaluate the ionization of larger proteins.

Positive and negative elements modulate the promoter of the human liver-specific alpha2-HS-glycoprotein gene

The human alpha2-HS-glycoprotein (AHSG) and the 63-kDa rat phosphoprotein (pp63) are homologous plasma proteins that belong to the fetuin family. AHSG and pp63 are involved in important functions such as inhibition of insulin receptor tyrosine kinase activity, inhibition of protease activities, and regulation of calcium metabolism and osteogenesis. Studies of the AHSG proximal promoter performed in vitro in rat and human cells indicate that several NF-1 and C/EBP binding sites exert a positive effect on its transcriptional activity. However, until now, no distal elements have been examined in this gene, in either species. We report that the human AHSG gene promoter acts in a liver-specific manner and is further controlled by three distal, 5'-flanking elements. The negative elements III and I are, respectively, located 5' and 3' of the positive element II. All three elements require the natural context of the human AHSG gene to fully exert their negative or positive effect. Element I harbours a single binding site for NF-1. This nuclear factor thus appears to be able to up- or downregulate the AHSG gene depending on the site it binds to. Elements I, II and possibly III are absent in the rodent Ahsg gene encoding pp63.

Gastrin-induced gene expression in oxyntic mucosa and ECL cells of rat stomach

The histamine-producing ECL cells are numerous in the acid-producing (oxyntic) mucosa. They respond to gastrin by secretion of histamine that acts on parietal cells to produce acid. In addition, gastrin has a trophic effect on the oxyntic mucosa which is exerted on stem cells and ECL cells. To elucidate the molecular actions of gastrin on the stomach we attempted to identify genes that are regulated by gastrin in oxyntic mucosa and in isolated ECL cells. Differential display polymerase chain reaction was used to identify mRNAs that are differentially expressed in rats that are hypergastrinemic after treatment with the proton pump inhibitor omeprazole for 48 h compared with rats that are hypogastrinemic after 24 h fasting. Differences in mRNA levels were confirmed by Northern blot analysis (comparing mRNA from fasted rats, omeprazole-treated rats and rats treated with omeprazole + the CCK2 (cholecystokinin) receptor antagonist YF476). The cDNAs were identified by sequencing followed by data base search. Hypergastrinemia induced by omeprazole treatment resulted in overexpression of mRNA for histidine decarboxylase, fetuin, pepsinogen and cytochrome P450 in the oxyntic mucosa. This was prevented by CCK2 receptor blockade. In isolated ECL cells gastrin upregulated mRNAs for histidine decarboxylase and synaptotagmin V as well as one mRNA transcript without known homology.

cDNA sequencing of guinea pig alpha 2-HS glycoprotein, its expression in various tissues and acute phase expression

cDNA encoding alpha 2-HS glycoprotein was amplified from guinea pig liver mRNA by reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends, cloned and sequenced. By RT-PCR and nested PCR, alpha 2-HS glycoprotein mRNA was detected not only in liver tissue but also in pancreas, stomach, small intestine, colon, spleen, kidney, testis, skeletal muscle, brain, heart and leukocytes, but not in the lung. The alpha 2-HS glycoprotein mRNA levels in the liver were reduced to half at 48 h after subcutaneous injection of turpentine oil.