Impacts of an 8-week regimen of aged garlic extract and aerobic exercise on the levels of Fetuin-A and inflammatory markers in the liver and visceral fat tissue of obese male rats.

BACKGROUND & AIMS: Obesity-induced chronic low-grade systemic inflammation is linked to the development of numerous diseases. Fetuin-A is known to affect inflammation and insulin resistance in obesity conditions. Free fatty acid (FFA)-induced proinflammatory cytokine expression in adipocytes occurs only in the presence of both Fetuin-A and toll-like receptor 4 (TLR4) and removing either of them prevented FFA-induced insulin resistance. Aged garlic extract (AGE) and exercise training have anti-inflammatory effects; however, the impact of AGE on Fetuin-A is unknown. We examined the effects of AGE with or without aerobic training (AT) on Fetuin-A and inflammatory markers. METHODS: Forty healthy male Sprague Dawley rats were randomly assigned to normal diet (ND) (n = 8) or high-fat diet (HFD) groups (n = 32) and fed for 9 weeks. After 9 weeks ND group continued normal diet, and the HFD group was randomly assigned to the HFD, HFD + AGE (600 mg/kg, once daily), HFD + AT (5 days/week), and HFD + AGE + AT groups that were continued for 8 weeks (n = 8). The significance of differences among groups was assessed using one-way analysis of variance followed by the post-hoc Tukey test. Statistically significant differences were considered for p < 0.05. RESULTS: AGE, AT, and AGE + AT significantly decreased body weight, plasma Fetuin-A, HOMA-IR, mRNA and protein levels of Fetuin-A and NFƙB in the liver and mRNA and Protein levels of Fetuin-A, TLR4 and NFƙB in visceral adipose tissue (VAT) compared to HFD. However, only AGE + AT significantly decreased TLR4 protein levels in the liver. CONCLUSION: Although AT and AGE reduce Fetuin-A and inflammatory markers, a combination of the two may be more effective at lowering inflammation.

Microfat exerts an anti-fibrotic effect on human hypertrophic scar via fetuin-A/ETV4 axis.

BACKGROUND: Hypertrophic scar is a fibrotic disease following wound healing and is characterized by excessive extracellular matrix deposition. Autologous microfat grafting proves an effective strategy for the treatment thereof as it could improve the texture of scars and relieve relevant symptoms. This study aims to explore the potential mechanisms underlying the anti-fibrotic effect of microfat on hypertrophic scars. METHODS: In this study, we injected microfat into transplanted hypertrophic scars in mouse models and investigated the subsequent histological changes and differential expression of mRNAs therein. As for in vitro studies, we co-cultured microfat and hypertrophic scar fibroblasts (HSFs) and analyzed molecular profile changes in HSFs co-cultured with microfat by RNA sequencing. Moreover, to identify the key transcription factors (TFs) which might be responsible for the anti-fibrotic function of microfat, we screened the differentially expressed TFs and transfected HSFs with lentivirus to overexpress or knockdown certain differentially expressed TFs. Furthermore, comparative secretome analyses were conducted to investigate the proteins secreted by co-cultured microfat; changes in gene expression of HSFs were examined after the administration of the potential anti-fibrotic protein. Finally, the relationship between the key TF in HSFs and the microfat-secreted anti-fibrotic adipokine was analyzed. RESULTS: The anti-fibrotic effect of microfat was confirmed by in vivo transplanted hypertrophic scar models, as the number of α-SMA-positive myofibroblasts was decreased and the expression of fibrosis-related genes downregulated. Co-cultured microfat suppressed the extracellular matrix production of HSFs in in vitro experiment, and the transcription factor ETV4 was primarily differentially expressed in HSFs when compared with normal skin fibroblasts. Overexpression of ETV4 significantly decreased the expression of fibrosis-related genes in HSFs at both mRNA and protein levels. Fetuin-A secreted by microfat could also downregulate the expression of fibrosis-related genes in HSFs, partially through upregulating ETV4 expression. CONCLUSIONS: Our results demonstrated that transcription factor ETV4 is essential for the anti-fibrotic effect of microfat on hypertrophic scars, and that fetuin-A secreted by microfat could suppress the fibrotic characteristic of HSFs through upregulating ETV4 expression. Microfat wields an alleviative influence over hypertrophic scars via fetuin-A/ETV4 axis.

Fetuin-A exerts a protective effect against experimentally induced intestinal ischemia/reperfusion by suppressing autophagic cell death.

Intestinal tissue is highly susceptible to ischemia/reperfusion injury in many hazardous health conditions. The anti-inflammatory and antioxidant glycoprotein fetuin-A showed efficacy in cerebral ischemic injury; however, its protective role against intestinal ischemia/reperfusion remains elusive. Therefore, this study investigated the protective role of fetuin-A supplementation against intestinal structural changes and dysfunction in a rat model of intestinal ischemia/reperfusion. We equally divided 72 male rats into control, sham, ischemia/reperfusion, and fetuin-A-pretreated ischemia/reperfusion (100 mg/kg/day fetuin-A intraperitoneally for three days prior to surgery and a third dose 1 h prior to the experiment) groups. After 2 h of reperfusion, the jejunum was dissected and examined for spontaneous contractility. A jejunal homogenate was used to assess inflammatory and oxidative stress enzymes. Staining of histological sections was carried out with hematoxylin, eosin and Masson's trichrome stain for evaluation. Immunohistochemistry was performed to detect autophagy proteins beclin-1, LC3, and p62. This study found that fetuin-A significantly improved ischemia/reperfusion-induced mucosal injury by reducing the percentage of areas of collagen deposition, increasing the amplitude of spontaneous contraction, decreasing inflammation and oxidative stress, and upregulating p62 expression, which was accompanied by beclin-1 and LC3 downregulation. Our findings suggest that fetuin-A treatment can prevent ischemia/reperfusion-induced jejunal structural and functional changes by increasing antioxidant activity and regulating autophagy disturbances observed in the ischemia/reperfusion rat model. Furthermore, fetuin-A may provide a protective influence against intestinal ischemia/reperfusion complications.

The hepatokine fetuin-A disrupts functional maturation of pancreatic beta cells.

AIMS/HYPOTHESIS: Neonatal beta cells carry out a programme of postnatal functional maturation to achieve full glucose responsiveness. A partial loss of the mature phenotype of adult beta cells may contribute to a reduction of functional beta cell mass and accelerate the onset of type 2 diabetes. We previously found that fetuin-A, a hepatokine increasingly secreted by the fatty liver and a determinant of type 2 diabetes, inhibits glucose-stimulated insulin secretion (GSIS) of human islets. Since fetuin-A is a ubiquitous fetal glycoprotein that declines peripartum, we examined here whether fetuin-A interferes with the functional maturity of beta cells. METHODS: The effects of fetuin-A were assessed during in vitro maturation of porcine neonatal islet cell clusters (NICCs) and in adult human islets. Expression alterations were examined via microarray, RNA sequencing and reverse transcription quantitative real-time PCR (qRT-PCR), proteins were analysed by western blotting and immunostaining, and insulin secretion was quantified in static incubations. RESULTS: NICC maturation was accompanied by the gain of glucose-responsive insulin secretion (twofold stimulation), backed up by mRNA upregulation of genes governing beta cell identity and function, such as NEUROD1, UCN3, ABCC8 and CASR (Log2 fold change [Log2FC] > 1.6). An active TGFß receptor (TGFBR)-SMAD2/3 pathway facilitates NICC maturation, since the TGFBR inhibitor SB431542 counteracted the upregulation of aforementioned genes and de-repressed ALDOB, a gene disallowed in mature beta cells. In fetuin-A-treated NICCs, upregulation of beta cell markers and the onset of glucose responsiveness were suppressed. Concomitantly, SMAD2/3 phosphorylation was inhibited. Transcriptome analysis confirmed inhibitory effects of fetuin-A and SB431542 on TGFß-1- and SMAD2/3-regulated transcription. However, contrary to SB431542 and regardless of cMYC upregulation, fetuin-A inhibited beta cell proliferation (0.27 ± 0.08% vs 1.0 ± 0.1% Ki67-positive cells in control NICCs). This effect was sustained by reduced expression (Log2FC ≤ -2.4) of FOXM1, CENPA, CDK1 or TOP2A. In agreement, the number of insulin-positive cells was lower in fetuin-A-treated NICCs than in control NICCs (14.4 ± 1.2% and 22.3 ± 1.1%, respectively). In adult human islets fetuin-A abolished glucose responsiveness, i.e. 1.7- and 1.1-fold change over 2.8 mmol/l glucose in control- and fetuin-A-cultured islets, respectively. In addition, fetuin-A reduced SMAD2/3 phosphorylation and suppressed expression of proliferative genes. Of note, in non-diabetic humans, plasma fetuin-A was negatively correlated (p = 0.013) with islet beta cell area. CONCLUSIONS/INTERPRETATION: Our results suggest that the perinatal decline of fetuin-A relieves TGFBR signalling in islets, a process that facilitates functional maturation of neonatal beta cells. Functional maturity remains revocable in later life, and the occurrence of a metabolically unhealthy milieu, such as liver steatosis and elevated plasma fetuin-A, can impair both function and adaptive proliferation of beta cells. DATA AVAILABILITY: The RNAseq datasets and computer code produced in this study are available in the Gene Expression Omnibus (GEO): GSE144950; https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE144950.

Phosphorylation status of fetuin-A is critical for inhibition of insulin action and is correlated with obesity and insulin resistance.

Fetuin-A (Fet-A), a hepatokine associated with insulin resistance, obesity, and incident type 2 diabetes, is shown to exist in both phosphorylated and dephosphorylated forms in circulation. However, studies on fetuin-A phosphorylation status in insulin-resistant conditions and its functional significance are limited. We demonstrate that serum phosphofetuin-A (Ser312) levels were significantly elevated in high-fat diet-induced obese mice, insulin-resistant Zucker diabetic fatty rats, and in individuals with obesity who are insulin resistant. Unlike serum total fetuin-A, serum phosphofetuin-A was associated with body weight, insulin, and markers of insulin resistance. To characterize potential mechanisms, fetuin-A was purified from Hep3B human hepatoma cells. Hep3B Fet-A was phosphorylated (Ser312) and inhibited insulin-stimulated glucose uptake and glycogen synthesis in L6GLUT4 myoblasts. Furthermore, single (Ser312Ala) and double (Ser312Ala + Ser120Ala) phosphorylation-defective Fet-A mutants were without effect on glucose uptake and glycogen synthesis in L6GLUT4 myoblasts. Together, our studies demonstrate that phosphorylation status of Fet-A (Ser312) is associated with obesity and insulin resistance and raise the possibility that Fet-A phosphorylation may play a role in regulation of insulin action.

A single intraperitoneal injection of bovine fetuin-A attenuates bone resorption in a murine calvarial model of particle-induced osteolysis.

Particle-induced osteolysis, which by definition is an aseptic inflammatory reaction to implant-derived wear debris eventually leading to local bone destruction, remains the major reason for long-term failure of orthopedic endoprostheses. Fetuin-A, a 66kDa glycoprotein with diverse functions, is found to be enriched in bone. Besides being an important inhibitor of ectopic calcification, it has been described to influence the production of mediators of inflammation. Furthermore, a regulatory role in bone metabolism has been assigned. In the present study, the influence of a single dose of bovine fetuin-A, intraperitoneally injected in mice subjected to particle-induced osteolysis of the calvaria, was analyzed. Twenty-eight male C57BL/6 mice, twelve weeks of age, were randomly divided into four groups. Groups 2 and 4 were subjected to ultra-high molecular weight polyethylene (UHMWPE) particles placed on their calvariae while groups 1 and 3 were sham-operated. Furthermore, groups 3 and 4 received a single intraperitoneal injection of 20mg bovine fetuin-A while groups 1 and 2 were treated with physiologic saline. After 14days calvarial bone was qualitatively and quantitatively assessed using microcomputed tomography (µCT) and histomorphometrical approaches. Application of fetuin-A led to a reduction of particle-induced osteolysis in terms of visible osteolytic lesions and eroded bone surface. The reduction of bone thickness and bone volume, as elicited by UHMWPE, was alleviated by fetuin-A. In conclusion, fetuin-A was found to exert an anti-resorptive effect on particle-induced osteolysis in-vivo. Thus, fetuin-A could play a potentially osteoprotective role in the treatment of bone metabolic disorders.

Effect of Exogenous Fetuin-A on TGF-ß/Smad Signaling in Hepatic Stellate Cells.

Objective. To explore the effects of low concentration of exogenous fetuin-A intervention on TGF-ß1 induced LX2 cells through detection of the expression of mRNA and protein of Smad2, Smad3, and Smad7. Methods. MTT assay was used to detect the LX2 cells proliferation and the regression equation calculating software was applied to determine IC50 of fetuin-A. RT-PCR was used to determine the relative content of Smad2, Smad3, and Smad7 mRNA in LX2 cells. Western blot was used to detect the LX2 cells relative content of Smad2, Smad3, Smad7 protein expression, respectively. Results. The analysis from RT-PCR and western blot showed that when compared with the other groups TGF-ß1 + fetuin-A group increased the expression of Smad2 and Smad3 while decreased the expression of Smad7 (P < 0.05). Conclusion. Fetuin-A may improve the excessive activation of hepatic stellate cells which is caused by an enhanced positive regulation of Smad2 and Smad3 protein and the deficiency in negative regulation of Smad7 protein. This is through inhibiting the expression of Smad2 and Smad3 gene and promoting the expression of Smad7 gene. As a result, the development of liver fibrosis will be reduced.

Facilitatory effects of fetuin-A on atherosclerosis.

OBJECTIVE: Fetuin-A is a circulating glycoprotein that is produced by liver and adipose tissue. Fetuin-A is known to induce insulin resistance and suppress vascular calcification. There are conflicting reports that show increased or decreased serum fetuin-A levels in patients with coronary artery disease (CAD). Since the role of fetuin-A in atherosclerosis remains still controversial, we aimed to clarify it in this study. METHODS: We investigated the expression of fetuin-A in atheromatous plaques in CAD patients and restenosis lesions in balloon-injured rat carotid arteries in vivo. We also assessed in vitro effects of fetuin-A on inflammatory molecules in human umbilical vein endothelial cells (HUVECs), oxidized low-density lipoprotein-induced foam cell formation in human monocyte-derived macrophages, and the migration, proliferation, and extracellular matrix expression in human aortic smooth muscle cells (HASMCs) in a serum-free culture system. RESULTS: Fetuin-A was abundantly expressed in cultured human monocytes, macrophages, fibroblasts, HASMCs, and human coronary artery SMCs, atheromatous plaques in human coronary arteries, and restenosis lesions in rat carotid arteries. In vitro experiments showed that fetuin-A stimulated interleukin-6, monocyte chemotactic protein-1, intercellular adhesion molecule-1, and E-selectin expression in HUVECs. Fetuin-A enhanced macrophage foam cell formation associated with scavenger receptors (CD36 and SR-A) and acyl-CoA:cholesterol acyltransferase-1 up-regulation and ATP-binding cassette transporter A1 down-regulation, and increased cell proliferation and collagen-1 and -3 expression via PI3K/AKT/c-Src/NF-κB/ERK1/2 pathways in HASMCs. CONCLUSION: Our results indicate that fetuin-A exerts the stimulatory effects on inflammatory responses in HUVECs, macrophage foam cell formation, and proliferation and collagen production in HASMCs, leading to the development of atherosclerosis.

Free Fatty Acids Activate Renin-Angiotensin System in 3T3-L1 Adipocytes through Nuclear Factor-kappa B Pathway.

The activity of a local renin-angiotensin system (RAS) in the adipose tissue is closely associated with obesity-related diseases. However, the mechanism of RAS activation in adipose tissue is still unknown. In the current study, we found that palmitic acid (PA), one kind of free fatty acid, induced the activity of RAS in 3T3-L1 adipocytes. In the presence of fetuin A (Fet A), PA upregulated the expression of angiotensinogen (AGT) and angiotensin type 1 receptor (AT1R) and stimulated the secretion of angiotensin II (ANG II) in 3T3-L1 adipocytes. Moreover, the activation of RAS in 3T3-L1 adipocytes was blocked when we blocked Toll-like receptor 4 (TLR4) signaling pathway using TAK242 or NF-κB signaling pathway using BAY117082. Together, our results have identified critical molecular mechanisms linking PA/TLR4/NF-κB signaling pathway to the activity of the local renin-angiotensin system in adipose tissue.

Fetuin-A decrease induced by a low-protein diet enhances vascular calcification in uremic rats with hyperphosphatemia.

Although dietary phosphate restriction is important for treating hyperphosphatemia in patients with chronic kidney disease, it remains unclear whether a low-protein diet (LPD), which contains low phosphate, has beneficial effects on malnutrition, inflammation, and vascular calcification. The effects of LPD on inflammation, malnutrition, and vascular calcification were therefore assessed in rats. Rats were fed a normal diet or diets containing 0.3% adenine and low/normal protein and low/high phosphate. After 6 wk, serum and urinary biochemical parameters, systemic inflammation, and vascular calcification were examined. The protective effect of fetuin-A and albumin were assessed in cultured vascular smooth muscle cells. Rats fed the diet containing 0.3% adenine developed severe azotemia. LPD in rats fed high phosphate induced malnutrition (decreases in body weight, food intake, serum albumin and fetuin-A levels, and urinary creatinine excretion) and systemic inflammation (increases in serum tumor necrosis factor-α and urinary oxidative stress marker). LPD decreased the serum fetuin-A level and fetuin-A synthesis in the liver and increased serum calcium-phosphate precipitates. A high-phosphate diet increased aortic calcium content, which was enhanced by LPD. Reduced fetal calf serum in the medium of cultured vascular smooth muscle cells enhanced phosphate-induced formation of calcium-phosphate precipitates in the media and calcification of vascular smooth muscle cells, both of which were prevented by fetuin-A administration. Our results suggest that phosphate restriction by restricting dietary protein promotes vascular calcification by lowering the systemic fetuin-A level and increasing serum calcium-phosphate precipitates and induces inflammation and malnutrition in uremic rats fed a high-phosphate diet.

Effect of serum components on biofilm formation by Aspergillus fumigatus and other Aspergillus species.

Biofilm production by microorganisms is critical for their pathogenicity. Serum promotes biofilm production by Aspergillus fumigatus; however, its effects on other Aspergillus spp. have not been reported. We analyzed biofilm formation by five Aspergillus spp., i.e., A. fumigatus, A. flavus, A. nidulans, A. niger, and A. terreus, and examined the effects of serum/serum proteins such as fetal bovine serum (FBS), fetuin A, and bovine serum albumin (BSA) on hyphal growth, hyphal branching, and extracellular matrix (ECM) formation. The antifungal susceptibility of A. fumigatus isolates that formed biofilms was also examined. All serum/serum proteins promoted the growth of all these fungal species; growth promotion was most evident with FBS, followed by fetuin A and BSA. This effect was most evident in case of A. fumigatus and least evident in case of A. terreus. Electron microscopy showed thick ECM layers surrounding fungal cell walls after culture with FBS, particularly in A. fumigatus. An increase in hyphal branching caused by fetuin A was the highest in case of A. fumigatus and A. nidulans. Biofilm-forming A. fumigatus showed resistance to most antifungal agents, although a synergism of micafungin and amphotericin B was suggested. Our results indicate that serum promotes biofilm formation, including thick ECM, by many Aspergillus spp., particularly A. fumigatus, and that this may be closely related to its virulence.

Fetuin-A and albumin alter cytotoxic effects of calcium phosphate nanoparticles on human vascular smooth muscle cells.

Calcification is a detrimental process in vascular ageing and in diseases such as atherosclerosis and arthritis. In particular, small calcium phosphate (CaP) crystal deposits are associated with inflammation and atherosclerotic plaque de-stabilisation. We previously reported that CaP particles caused human vascular smooth muscle cell (VSMC) death and that serum reduced the toxic effects of the particles. Here, we found that the serum proteins fetuin-A and albumin (≥ 1 µM) reduced intracellular Ca2+ elevations and cell death in VSMCs in response to CaP particles. In addition, CaP particles functionalised with fetuin-A, but not albumin, were less toxic than naked CaP particles. Electron microscopic studies revealed that CaP particles were internalised in different ways; via macropinocytosis, membrane invagination or plasma membrane damage, which occurred within 10 minutes of exposure to particles. However, cell death did not occur until approximately 30 minutes, suggesting that plasma membrane repair and survival mechanisms were activated. In the presence of fetuin-A, CaP particle-induced damage was inhibited and CaP/plasma membrane interactions and particle uptake were delayed. Fetuin-A also reduced dissolution of CaP particles under acidic conditions, which may contribute to its cytoprotective effects after CaP particle exposure to VSMCs. These studies are particularly relevant to the calcification observed in blood vessels in patients with kidney disease, where circulating levels of fetuin-A and albumin are low, and in pathological situations where CaP crystal formation outweighs calcification-inhibitory mechanisms.

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.

Fetuin-A-containing calciprotein particles reduce mineral stress in the macrophage.

The formation of fetuin-A-containing calciprotein particles (CPP) may facilitate the clearance of calcium phosphate nanocrystals from the extracellular fluid. These crystals may otherwise seed extra-osseous mineralization. Fetuin-A is a partially phosphorylated glycoprotein that plays a critical role in stabilizing these particles, inhibiting crystal growth and aggregation. CPP removal is thought to be predominantly mediated by cells of the reticuloendothelial system via type I and type II class A scavenger receptor (SR-AI/II). Naked calcium phosphate crystals are known to stimulate macrophages and other cell types in vitro, but little is known of the effect of CPP on these cells. We report here, for the first time, that CPP induce expression and secretion of tumour necrosis factor (TNF)-α, interleukin (IL)-1ß in murine RAW 264.7 macrophages. Importantly, however, CPP induced significantly lower cytokine secretion than hydroxyapatite (HAP) crystals of equivalent size and calcium content. Furthermore, CPP only had a modest effect on macrophage viability and apoptosis, even at very high levels, compared to HAP crystals, which were strongly pro-apoptotic at much lower levels. Fetuin-A phosphorylation was found to modulate the effect of CPP on cytokine secretion and apoptosis, but not uptake via SR-AI/II. Prolonged exposure of macrophages to CPP was found to result in up-regulated expression of SR-AI/II. CPP formation may help protect against some of the pro-inflammatory and harmful effects of calcium phosphate nanocrystals, perhaps representing a natural defense system for calcium mineral stress. However, in pathological states where production exceeds clearance capacity, these particles may still stimulate pro-inflammatory and pro-apoptotic cascades in macrophages, which may be important in the pathogenesis of vascular calcification.

Ahsg-fetuin blocks the metabolic arm of insulin action through its interaction with the 95-kD ß-subunit of the insulin receptor.

We previously have shown that Ahsg, a liver glycoprotein, inhibits insulin receptor (InsR) tyrosine kinase (TK) activity and the ERK1/2 mitogenic signaling arm of insulin signaling. Here we show that Ahsg blocks insulin-stimulated GLUT4 translocation and Akt activation in intact cells (mouse myoblasts). Furthermore, Ahsg inhibits InsR autophosphorylation of highly-purified insulin holoreceptors in a cell-free, ATP-dependent system, with an IC50 within the range of single-chain Ahsg concentrations in human serum. Binding of (125)I-insulin to living cells overexpressing the InsR shows a dissociation constant (KD) of 250pM, unaltered in the presence of 300 nM Ahsg. A mutant InsR cDNA encoding the signal peptide, the ß-subunit and the furin processing site, but deleting the α-subunit, was stably expressed in HEK293 cells. Treatment with peroxovanadate, but not insulin, dramatically increased the 95 kD ß-subunit tyrosine phosphoryation. The level of tyrosine phosphorylation of the 95-kD ß-subunit can be driven down sharply by treatment of living HEK293 transfectant cells with physiological doses of Ahsg. Treatment of myogenic cells with Ahsg blunts insulin-stimulated InsR autophosphorylation and AKT phosphorylation. Taken together, we show that Ahsg antagonizes the metabolic functions initiated by InsR activation without interference in insulin binding. The experiments suggest a direct interaction of Ahsg with the InsR ectodomain ß-subunit in a mode that does not significantly alter the high-affinity binding of insulin to the holoreceptor's two complementing α-subunits.

Effects of increased fetuin-A in human trophoblast cells and associated pregnancy outcomes.

OBJECTIVE: The purpose of this study was to determine whether fetuin-A affects trophoblast viability and invasion, whether growth factors that bind receptors that activate tyrosine kinase are impaired by fetuin-A, and whether elevated maternal serum fetuin-A levels are associated with adverse pregnancy outcomes. STUDY DESIGN: We studied viability and invasion in first-trimester extravillous trophoblast cells that were exposed to fetuin-A, insulin-like growth factor, and placental growth factor. Insulin receptor substrates expression was assessed. We compared serum fetuin-A levels in 111 preeclampsia cases and 95 controls. RESULTS: Fetuin-A reduced extravillous trophoblast cell viability and invasion in the presence or absence of growth factors. Fetuin-A reduced insulin receptor substrate-1 and tyrosine phosphorylated insulin receptor substrate-1 expression in extravillous trophoblast cells that had been treated with insulin-like growth factor. Elevated serum fetuin-A levels were more prevalent in preeclampsia cases than control subjects, even after we controlled for diabetes mellitus, hypertension, and obesity. CONCLUSION: Fetuin-A may decrease trophoblast viability and invasion caused by the inhibition of receptor tyrosine kinase activity. Elevated serum levels of fetuin-A may be associated with preeclampsia.

Clearance of fetuin-A--containing calciprotein particles is mediated by scavenger receptor-A.

RATIONALE: Fetuin-A is a liver-derived plasma protein involved in the regulation of calcified matrix metabolism. Biochemical studies showed that fetuin-A is essential for the formation of protein-mineral complexes, called calciprotein particles (CPPs). CPPs must be cleared from circulation to prevent local deposition and pathological calcification. OBJECTIVE: We studied CPP clearance in mice and in cell culture to identify the tissues, cells, and receptors involved in the clearance. METHODS AND RESULTS: In mice, fetuin-A-containing CPPs were rapidly cleared by the reticuloendothelial system, namely Kupffer cells of the liver and marginal zone macrophages of the spleen. Macrophages from scavenger receptor-AI/II (SR-A)-deficient mice cleared CPPs less efficiently than macrophages from wild-type mice, suggesting that SR-AI/II is involved in CPP binding and endocytosis. Accordingly, we found reduced clearance of CPPs in SR-A/MARCO-deficient mice. CONCLUSIONS: We could demonstrate that fetuin-A-containing CPPs facilitate the clearance of mineral debris by macrophages via SR-A. Since the same receptor also contributes to the uptake of modified low-density lipoprotein particles in atherosclerosis, defective endocytosis of both types of particle may impinge on lipid as well as mineral debris clearance in calcifying atherosclerosis.

Fetuin A, a serum component, promotes growth and biofilm formation by Aspergillus fumigatus.

Aspergillus fumigatus is an all-important pathogenic fungus and is known for its angiotropism. When it invades human organs, A. fumigatus makes direct contact with blood and its components by causing inflammation and invading vascular structures. To learn the effect of its contact with blood on the development of infection, we examined the effect of serum on A. fumigatus growth. In Dulbecco's modified Eagle's medium containing 10% fetal bovine serum, hyphal tip growth was accelerated, forming a thickened and well-networked biofilm associated with extracellular matrix, and fetuin A was identified as the active component in the serum that accelerates fungal growth leading to formation of a community. These results suggest that fetuin A is a novel accelerator of the growth of A. fumigatus and that it participates in the formation of thick biofilm.

A hepatic protein, fetuin-A, occupies a protective role in lethal systemic inflammation.

BACKGROUND: A liver-derived protein, fetuin-A, was first purified from calf fetal serum in 1944, but its potential role in lethal systemic inflammation was previously unknown. This study aims to delineate the molecular mechanisms underlying the regulation of hepatic fetuin-A expression during lethal systemic inflammation (LSI), and investigated whether alterations of fetuin-A levels affect animal survival, and influence systemic accumulation of a late mediator, HMGB1. METHODS AND FINDINGS: LSI was induced by endotoxemia or cecal ligation and puncture (CLP) in fetuin-A knock-out or wild-type mice, and animal survival rates were compared. Murine peritoneal macrophages were challenged with exogenous (endotoxin) or endogenous (IFN-γ) stimuli in the absence or presence of fetuin-A, and HMGB1 expression and release was assessed. Circulating fetuin-A levels were decreased in a time-dependent manner, starting between 26 h, reaching a nadir around 24-48 h, and returning towards base-line approximately 72 h post onset of endotoxemia or sepsis. These dynamic changes were mirrored by an early cytokine IFN-γ-mediated inhibition (up to 50-70%) of hepatic fetuin-A expression. Disruption of fetuin-A expression rendered animals more susceptible to LSI, whereas supplementation of fetuin-A (20-100 mg/kg) dose-dependently increased animal survival rates. The protection was associated with a significant reduction in systemic HMGB1 accumulation in vivo, and parallel inhibition of IFN-γ- or LPS-induced HMGB1 release in vitro. CONCLUSIONS: These experimental data suggest that fetuin-A is protective against lethal systemic inflammation partly by inhibiting active HMGB1 release.