Dysregulation of macrophage PEPD in obesity determines adipose tissue fibro-inflammation and insulin resistance.

Resulting from impaired collagen turnover, fibrosis is a hallmark of adipose tissue (AT) dysfunction and obesity-associated insulin resistance (IR). Prolidase, also known as peptidase D (PEPD), plays a vital role in collagen turnover by degrading proline-containing dipeptides but its specific functional relevance in AT is unknown. Here we show that in human and mouse obesity, PEPD expression and activity decrease in AT, and PEPD is released into the systemic circulation, which promotes fibrosis and AT IR. Loss of the enzymatic function of PEPD by genetic ablation or pharmacological inhibition causes AT fibrosis in mice. In addition to its intracellular enzymatic role, secreted extracellular PEPD protein enhances macrophage and adipocyte fibro-inflammatory responses via EGFR signalling, thereby promoting AT fibrosis and IR. We further show that decreased prolidase activity is coupled with increased systemic levels of PEPD that act as a pathogenic trigger of AT fibrosis and IR. Thus, PEPD produced by macrophages might serve as a biomarker of AT fibro-inflammation and could represent a therapeutic target for AT fibrosis and obesity-associated IR and type 2 diabetes.

Human adipocyte function is impacted by mechanical cues.

Fibrosis is a hallmark of human white adipose tissue (WAT) during obesity-induced chronic inflammation. The functional impact of increased interstitial fibrosis (peri-adipocyte fibrosis) on adjacent adipocytes remains unknown. Here we developed a novel in vitro 3D culture system in which human adipocytes and decellularized material of adipose tissue (dMAT) from obese subjects are embedded in a peptide hydrogel. When cultured with dMAT, adipocytes showed decreased lipolysis and adipokine secretion and increased expression/production of cytokines (IL-6, G-CSF) and fibrotic mediators (LOXL2 and the matricellular proteins THSB2 and CTGF). Moreover, some alterations including lipolytic activity and fibro-inflammation also occurred when the adipocyte/hydrogel culture was mechanically compressed. Notably, CTGF expression levels correlated with the amount of peri-adipocyte fibrosis in WAT from obese individuals. Moreover, dMAT-dependent CTGF promoter activity, which depends on ß1-integrin/cytoskeleton pathways, was enhanced in the presence of YAP, a mechanosensitive co-activator of TEAD transcription factors. Mutation of TEAD binding sites abolished the dMAT-induced promoter activity. In conclusion, fibrosis may negatively affect human adipocyte function via mechanosensitive molecules, in part stimulated by cell deformation.

Using gene expression to predict the secretome of differentiating human preadipocytes.

OBJECTIVE: To characterize the secretome of differentiating human preadipocytes using global gene expression profiling. DESIGN: Gene expression was measured using microarrays at days 0, 1, 3, 5, 7 and 10 in primary preadipocytes undergoing adipogenesis (n=6 independent subjects). Predictive bioinformatic algorithms were employed to identify those differentially expressed genes that code for secreted proteins. MEASUREMENTS: Gene expression was assessed using microarrays and real-time reverse transcriptase PCR, bioinformatic predictive algorithms were used to identify the secretome of differentiating preadipocytes, and the secretion of the most significant candidates were confirmed at the protein level using western blots or ELISA tests. Gene expression was also assayed in the adipocyte and stroma vascular fraction (SVF) of obese subjects. RESULTS: Microarray analysis identified 33 genes whose expression significantly changed (false discovery rate of 1%) during adipogenesis and code for secreted proteins. Of these genes, 18 are novel candidate adipose tissue 'secretome' genes. Their relative gene expression in adipocyte and SVF of obese subjects revealed that most of these genes are more highly expressed in the SVF. A novel candidate, matrix gla protein (MGP), was upregulated (approximately 30-fold) during adipogenesis, second only to leptin (approximately 50-fold). MGP and another secretome candidate protein, inhibin beta B (INHBB), were detected in the secretion media of adipocytes isolated from adipose tissue explants. CONCLUSIONS: Gene expression coupled with predictive bioinformatic algorithms has proved a valid and alternative approach to further define the adipocyte secretome. Many of the novel candidate secretome genes are components of the coagulation and fibrinolytic systems. MGP and INHBB represent new adipokines whose function in adipose tissue remains to be unravelled.

Hyperinsulinaemia triggered by dietary conjugated linoleic acid is associated with a decrease in leptin and adiponectin plasma levels and pancreatic beta cell hyperplasia in the mouse.

AIMS/HYPOTHESIS: Dietary supplementation with conjugated linoleic acids (CLA) has a fat-reducing effect in various species, but induces severe hyperinsulinaemia and hepatic steatosis in the mouse. This study aimed to determine the causes of the deleterious effects of CLA on insulin homeostasis. METHODS: The chronology of adipose and liver weight, hepatic triglyceride accumulation and selected blood parameters, including lipids, insulin, leptin and adiponectin, was determined in C57BL/6J female mice fed a 1% isomeric mixture of CLA for various periods of time ranging from 2 to 28 days. Insulin secretion was measured in 1-h static incubations of pancreatic islets, and pancreas morphometric parameters were determined in mice fed CLA for 28 days. RESULTS: Plasma levels of leptin and adiponectin sharply decreased after 2 days of CLA feeding, although adipose tissue mass only decreased after day 6. Hyperinsulinaemia developed at day 6 and consistently worsened up to day 28, in parallel with increases in hepatic lipid content. Islets from CLA-fed mice displayed three- to four-fold increased rates of glucose-stimulated insulin secretion, both in the absence and presence of isobutyl methylxanthine or carbachol. The increased insulin-releasing capacity of islets from CLA-fed mice was explained by an increase in beta cell mass and number. CONCLUSIONS/INTERPRETATION: The data suggest that CLA supplementation induces a profound reduction of leptinaemia and adiponectinaemia, followed by hyperinsulinaemia due to the increased secretory capacity of pancreatic islets, leading, in turn, to liver steatosis. These observations cast doubt on the safety of dietary supplements containing CLA.

PPAR-alpha-null mice are protected from high-fat diet-induced insulin resistance.

Peroxisome proliferator-activated receptor (PPAR)-alpha controls the expression of genes involved in lipid metabolism. PPAR-alpha furthermore participates to maintain blood glucose during acute metabolic stress, as shown in PPAR-alpha-null mice, which develop severe hypoglycemia when fasted. Here, we assessed a potential role for PPAR-alpha in glucose homeostasis in response to long-term high-fat feeding. When subjected to this nutritional challenge, PPAR-alpha-null mice remained normoglycemic and normoinsulinemic, whereas wild-type mice became hyperinsulinemic (190%; P < 0.05) and slightly hyperglycemic (120%; NS). Insulin tolerance tests (ITTs) and glucose tolerance tests (GTTs) were performed to evaluate insulin resistance (IR). Under standard diet, the response to both tests was similar in wild-type and PPAR-alpha-null mice. Under high-fat diet, however, the efficiency of insulin in ITT was reduced and the amount of hyperglycemia in GTT was increased only in wild-type and not in PPAR-alpha-null mice. The IR index, calculated as the product of the areas under glucose and insulin curves in GTT, increased fourfold in high-fat-fed wild-type mice, whereas it remained unchanged in PPAR-alpha-null mice. In contrast, PPAR-alpha deficiency allowed the twofold rise in adiposity and blood leptin levels elicited by the diet. Thus, the absence of PPAR-alpha dissociates IR from high-fat diet-induced increase in adiposity. The effects of PPAR-alpha deficiency on glucose homeostasis seem not to occur via the pancreas, because glucose-stimulated insulin secretion of islets was not influenced by the PPAR-alpha genotype. These data suggest that PPAR-alpha plays a role for the development of IR in response to a Western-type high-fat diet.

Inhibition of insulin gene expression by long-term exposure of pancreatic beta cells to palmitate is dependent on the presence of a stimulatory glucose concentration.

Long-term exposure of pancreatic beta cells to elevated levels of fatty acids (FAs) impairs glucose-induced insulin secretion. However, the effects of FAs on insulin gene expression are controversial. We hypothesized that FAs adversely affect insulin gene expression only in the presence of elevated glucose concentrations. To test this hypothesis, isolated rat islets were cultured for up to 1 week in the presence of 2.8 or 16.7 mmol/L glucose with or without 0.5 mmol/L palmitate. Insulin release, insulin content, and insulin mRNA levels were determined at the end of each culture period. Palmitate increased insulin release at each time point independently of the glucose concentration. In contrast, insulin content was unchanged in the presence of palmitate at 2.8 mmol/L glucose, but was markedly decreased in the presence of 0.5 mmol/L palmitate and 16.7 mmol/L glucose after 2, 3, and 7 days of culture. In the presence of a basal concentration of glucose, insulin mRNA levels were transiently increased by palmitate at 24 hours but were unchanged thereafter. In contrast, palmitate significantly inhibited the stimulatory effects of 16.7 mmol/L glucose on insulin mRNA levels after 2, 3, and 7 days. To determine whether the inhibitory effect of palmitate on glucose-stimulated insulin mRNA levels was associated with decreased insulin promoter activity, HIT-T15 cells were cultured for 24 hours in 11.1 mmol/L glucose in the presence or absence of palmitate, and insulin gene promoter activity was measured in transient transfection experiments using the insulin promoter-reporter construct INSLUC. INSLUC activity was decreased more than 2-fold after 24 hours of exposure to 0.5 mmol/L palmitate. We conclude that long-term exposure of pancreatic beta cells to palmitate decreases insulin gene expression only in the presence of elevated glucose concentrations, in part through inhibition of insulin gene promoter activity.

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats.

According to the glucose toxicity hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models of chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/L glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats.

According to the "glucose toxicity" hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models with chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/l glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.

Long-term exposure of isolated rat islets of Langerhans to supraphysiologic glucose concentrations decreases insulin mRNA levels.

Chronic hyperglycemia has been postulated to contribute to beta-cell dysfunction in type 2 diabetic patients. A deleterious effect of prolonged exposure to high glucose concentrations on insulin gene expression has been demonstrated in insulin-secreting cell lines. This study was designed to investigate in isolated rat islets the effects of long-term exposure to supraphysiologic glucose concentrations on insulin, GLUT2, and glucokinase gene expression. The acute effects of glucose on gene expression were investigated by culturing rat islets in 2.8 or 16.7 mmol/L glucose for 24 hours. Insulin, GLUT2, and glucokinase mRNA levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). As expected, glucose acutely increased relative insulin and GLUT2 mRNA levels by 2.8- +/- 0.5-fold (n = 5, P < .005) and 1.8- +/- 0.3-fold (n = 5, P < .05), respectively, but had no effect on glucokinase gene expression (1.1- +/- 0.1-fold increase, n = 4, NS). These results validate the use of semiquantitative RT-PCR to detect changes in gene expression in rat islets. Islets were then cultured in 5.6 or 16.7 mmol/L glucose for 2, 4, or 6 weeks. Relative insulin mRNA levels were higher in islets cultured in high glucose after 2 weeks (1.8+/-0.1 v 1.0+/-0.1, n = 4, P < .05), identical after 4 weeks (0.9+/-0.1 v 1.00+/-0.2, n = 4, NS), and significantly lower after 6 weeks (0.6+/-0.1 v 1.0+/-0.2, n = 6, P < .05). Relative GLUT2 mRNA levels were higher in islets cultured in high glucose after 2 weeks (1.7+/-0.2 v 1.0+/-0.2, n = 3, P < .05) and then identical in both groups after 4 weeks (1.0+/-0.1 v 1.0+/-0.1, n = 3, NS) and 6 weeks (1.0+/-0.2 v 1.0+/-0.1, n = 6, NS). Relative glucokinase mRNA levels were identical under both culture conditions at 2 (1.4+/-0.4 v 1.0+/-0.2, n = 3, NS), 4 (0.8+/-0.5 v 1.0+/-0.3, n = 3, NS), and 6 (0.9+/-0.2 v 1.0+/-0.1, n = 6, NS) weeks. These results indicate that a 6-week exposure of rat islets to supraphysiologic glucose concentrations decreases insulin mRNA levels without affecting GLUT2 and glucokinase gene expression. We conclude that the phenomenon of glucose toxicity decreasing insulin gene expression is not restricted to transformed cells, and might provide insight into the mechanisms by which chronic hyperglycemia adversely affects beta-cell function.

Does leptin regulate insulin secretion?

The hormone leptin secreted by adipocytes plays a major role in body weight homeostasis. Its main target is the hypothalamus, but it also affects several peripheral tissues directly. The direct effect of leptin on insulin secretion by pancreatic beta cells has been investigated in several studies, though with controversial results. Interpretation of these data must take into account the animal model and the leptin concentrations used. Experiments carried out on islets from ob/ob mice harbouring a mutation in the leptin gene are not representative of the leptin effect in normal animals because ob/ob islets are very sensitive to the hormone and show altered regulation of insulin secretion. In normal rodent islets, physiological concentrations of leptin seem to inhibit insulin secretion only when the islets are maximally stimulated with high concentrations of glucose associated with secretion potentiators. Several isoforms of the leptin receptor are expressed in pancreatic beta cells. Indirect experimental evidence suggests that leptin signalling in islets requires the long isoform of the receptor. The molecular mechanisms underlying the effect of leptin on insulin secretion are unknown. Our hypothesis is that physiological concentrations of leptin in normal rodents do not affect the direct pathway (coupling a rise in glucose concentration to insulin secretion) but modulate a potentiation of glucose-induced insulin secretion involving cyclic AMP or phospholipase C/protein kinase C activation.

Glucose-insulin kinetics of a bioartificial pancreas made of an AN69 hydrogel hollow fiber containing porcine islets and implanted in diabetic mice.

The goal of this study was to determine whether porcine islets encapsulated in hollow fibers made of AN69 copolymer can correct hyperglycemia in diabetic mice and provide normal tolerance to a glucose challenge. In vitro perifusion of hollow fibers demonstrated the rapid kinetics of insulin release in response to glucose. Two fibers containing islets were transplanted into the peritoneal cavity of each of 17 streptozotocin induced diabetic mice. In 11 mice, diabetes was reversed within 3 days with plasma glucose levels decreasing from 19.7 +/- 0.9 (mean +/- SEM) before implantation to 10.9 +/- 0.8 mmol/L. Intraperitoneal glucose tolerance tests were performed in transplanted (n = 7), nondiabetic (n = 15), and diabetic mice (n = 6). A normal glucose pattern was observed in the transplanted diabetic mice. This was achieved in the presence of plasma insulin levels lower than those observed in control nondiabetic mice, suggesting the presence of a state of hypersensitivity to insulin, which was demonstrated in this model by exogenous insulin tolerance tests. In conclusion, encapsulation of islets suspended in ultraculture medium in biocompatible membranes of AN69 can provide xenograft survival, and complete normalization of glucose tolerance can be achieved.

Inhibition of insulin secretion by leptin in normal rodent islets of Langerhans.

The recently discovered adipose cell-specific hormone called leptin decreases food intake and increases energy expenditure in rodents through a pathway involving hypothalamic leptin receptors, OB-R. In addition, leptin decreases insulin circulating levels independent of the reduction in food intake. Whether or not the hormone has a direct effect on pancreatic beta-cells is not clear, because previous in vitro studies have led to controversial results depending on the animal model used. The present study was designed to investigate the effects of leptin in islets of Langerhans isolated from normal rodents. Three isoforms of the leptin receptor, OB-Ra, b, and f, were detected by RT-PCR analysis of total RNA from rat islets. In static incubations, leptin (10 ng/ml) did not alter basal insulin secretion nor insulin secretion stimulated by glucose alone, potassium chloride, or ketoisocaproic acid. In contrast, insulin secretion stimulated by glucose + 3-isobutyl 1-methylxanthine (IBMX) was inhibited by 34 +/- 15% (n = 4, P < 0.05). This was further substantiated in perifusion experiments, in which leptin decreased by 31 +/- 3% (n = 5, P < 0.01) glucose + IBMX-stimulated insulin release. Similarly, in mouse islets a significant inhibitory effect of leptin (-31 +/- 4%, n = 6, P < 0.05) was observed only on glucose + IBMX-stimulated insulin secretion, with no effect of the hormone on basal nor glucose-stimulated secretion. Finally, leptin was totally inefficient in islets isolated from obese fa/fa rats, which bear a mutation in OB-R. These results suggest that, in normal rodent islets, leptin specifically inhibits IBMX-potentiated glucose-induced insulin secretion, through a direct effect involving at least one of the three isoforms of OB-R expressed in islets.

Long-term culture of free or encapsulated islets isolated from specific pathogen-free (SPF) pigs.

As the risk of recipient contamination is a limiting factor for xenotransplantation, the use of specific pathogen-free (SPF) pigs is mandatory. This study investigated the long-term culture of SPF pig islets and evaluated their insulin production when encapsulated in AN69 hollow fibres. Insulin secretion was studied after 3 weeks (n = 10), 2 months (n = 8) and 3 months (n = 3) by 45-min incubation in the presence of 2.8, 5.5, 11 and 16.5mM glucose. Although a decrease in the amount of secreted insulin occurred (1385 +/- 421 and 4323 +/- 1068 microns U/ml at 3 weeks for 2.8 and 16.5 mM glucose respectively; 702 +/- 261 and 2397 +/- 1047 microU/ml at 2 months; 59 +/- 23 and 154 +/- 34 microU/ml at 3 months), glucose-dependent insulin secretion was observed in all cases, i.e. stimulation indices of 8.1 +/- 3.1 (p < 0.05 vs the presence of 5.5 mM glucose) at 3 weeks, 3.3 +/- 1.1 at 2 months and 3.0 +/- 0.7 at 3 months. The insulin secretion of encapsulated SPF pig islets, cultured for 1 or 3 weeks, was evaluated under perifusion conditions using a stimulus of 10mM glucose plus 5.5 mM theophylline. Glucose stimulation resulted in a significant two-fold increase in insulin secretion (p < 0.05), which was maintained over culture time. These results indicate that SPF-isolated islets remained functional when cultured for several weeks either as free or encapsulated islets, although the magnitude of insulin secretion decreased dramatically after three months of culture.

Characterization of recombinant von Willebrand factors mutated on cysteine 509 or 695.

The interacting domain of vWF with platelet GPIb has been shown to overlap the large A1 loop formed by the intra-chain disulfide bond linking Cys 509 to Cys 695. In order to further investigate the role of the conformation of this region, we have expressed in COS-7 cells three mutated full-length recombinant vWFs (rvWFs) in which the substitutions Cys509Gly, Cys509Arg or Cys695Gly have been introduced by site-directed mutagenesis. SDS-agarose gel electrophoresis demonstrated an impaired multimerization of the mutants with undetectable high molecular weight multimers and a decrease of the relative amounts of the intermediate sized multimers. Binding analysis showed that rvWFC509G and rvWFC509R did not interact with botrocetin but spontaneously interacted with GPIb; the latter binding remained unchanged in the presence of ristocetin. This indicates that the substitution of Cys509 by Gly or Arg creates a conformation of vWF that increases its binding to GPIb. In contrast, rvWFC695G which did not react with botrocetin was also unable to interact with GPIb even in the presence of ristocetin, indicating that sequences interacting with GPIb are masked and/or disrupted. In conclusion, the substitution of each of the Cys509 and 695 results in mutant proteins which may be "locked" into active or inactive conformations in regard to the binding to platelet GPIb receptor.

A monoclonal antibody (B724) to von Willebrand factor recognizing an epitope within the A1 disulphide loop (Cys509-Cys695) discriminates between type 2A and type 2B von Willebrand disease.

Monoclonal antibody (MoAb) B724 to von Willebrand factor (vWF) completely inhibits its interaction with heparin, sulphatides and botrocetin and consequently botrocetin-induced binding of vWF to platelets. MoAb B724 has no effect on the binding of vWF to collagen or to ristocetin-treated platelets nor on vWF-dependent platelet aggregation induced with ristocetin and asialo-vWF-mediated platelet aggregation. MoAb B724 preferentially recognizes a conformation of native vWF, in solution, or immobilized through a coated antibody. It exhibits a markedly lower affinity for vWF immobilized onto collagen or plastic surfaces. Using proteolytic fragments of vWF, B724 epitope was localized within the 512-673 sequence of the A1 disulphide loop of vWF, MoAb B724 was used as second antibody in a two-site ELISA to test a series of patients with type 1, 2A, 2B and 2N vWD or haemophilia A and recombinant wild type or mutated vWFs. Results were compared with those obtained by control ELISAs performed using polyclonal antibodies. Using MoAb B724, strikingly lower levels of vWFAg were observed in plasma from most patients with type 2B vWD, and in seven out of the eight rvWF mutated close to or within the A1 disulphide loop. Therefore MoAb B724, which interferes with this loop involved in the function of vWF, appears to be a useful tool for rapid screening of conformational changes in this region.

Epitope mapping of inhibitory monoclonal antibodies to human von Willebrand factor by using recombinant cDNA libraries.

Two recombinant expression libraries containing small (300-600 base pairs) cDNA fragments of von Willebrand Factor (vWF) were screened in order to map the epitope of monoclonal antibodies (MAbs) to vWF. Among eleven MAbs tested, seven were effectively mapped. The epitopes of MAbs 418 and 522, which inhibit the binding of vWF to Factor VIII (FVIII), were localized between Leu 2 and Arg 53 and between Glu 35 and Ile 81 of the vWF subunit respectively, within the N-terminal trypsin fragment called SpIII-T4 [amino acids (aa) 1-272] which contains a binding domain for FVIII. The epitope of MAb 710, which inhibits the binding of vWF to glycoprotein Ib (GPIb), was identified between Ser 593 and Ser 678 on the tryptic 52/48 kDa fragment (aa 449-728) which contains binding domains for GPIb, collagen, heparin, sulfatides and subendothelium extracellular matrices. The epitope of MAb 723, which does not interfere with any known function of vWF, was localized between Ser 523 and Gly 588. The epitopes of MAb 505 and MAb 400, which inhibit the binding of vWF to collagen, were identified between Leu 927 and Arg 1114 within the SPI fragment (aa 911-1365) corresponding to the central part of the vWF subunit. The epitope of MAb 9, which inhibits the binding of vWF to GPIIb/IIIa, was identified in the C-terminal part of the vWF subunit between Gln 1704 and Asp 1746, the latter being the third aa of the RGD sequence common to adhesive proteins and serving as a recognition site for integrin receptors.

Influence of mutations and size of multimers in type II von Willebrand disease upon the function of von Willebrand factor.

We compared the properties of plasma von Willebrand factor (vWF) from normal individuals and from two patients with type IIA (Glu875Lys) and type IIB (duplication of Met 540) von Willebrand disease (vWD) with the corresponding fully multimerized recombinant proteins. We included cryosupernatant from normal human plasma and type IIA plasma (Cys509Arg). Functions of vWF were analyzed by binding assays to platelets in the presence of ristocetin or botrocetin. Parameters of binding (number of binding sites per vWF subunit, and dissociation constant Kd) were quantitatively estimated from the binding isotherms of 125I-botrocetin or glycocalicin to vWF, independently of the size of the multimers. We found that ristocetin- or botrocetin-induced binding to platelets was correlated in all cases with the size of vWF multimers. In the absence of inducer, only type IIB rvWF Met-Met540 spontaneously bound to platelets. No significant difference of binding of purified botrocetin to vWF was found between normal and patients' plasma, or between wild-type rvWF (rvWF-WT) and rvWF-Lys875. In contrast, affinity of botrocetin for type IIB rvWF Met-Met540 was decreased. Botrocetin-induced binding of glycocalicin to vWF from all plasma and cryosupernatant was similar. Compared with rvWF-WT, binding of glycocalicin to rvWF-Lys875 was normal. In contrast, the affinity for type IIB rvWF Met-Met540 was 10-fold greater. Thus, our data suggest that, in the patients tested, the abnormal IIA phenotype results from the lack of large-sized multimers and is independent of the point mutations. In contrast, the type IIB mutation is directly involved by providing a conformation to the vWF subunits that allows the high molecular weight multimers to spontaneously interact with platelet glycoprotein Ib.

Interaction of von Willebrand factor with platelets activated by thrombin or a synthetic 7-amino acid peptide derived from the cleaved thrombin receptor.

Thrombin and the 7-mer agonist peptide from its receptor (SFLLRNP) were compared for their ability to promote the binding of vWF to platelets. Identical Ca(2+)-dependence and kinetics of activation were observed. Studies of inhibition of the binding by a series of monoclonal antibodies to GPIb, GPIIb/IIIa and vWF and experiments performed using platelets from patients with Glanzmann thrombasthenia or Bernard-Soulier syndrome enabled to identify GPIIb/IIIa as the receptor of vWF. Binding isotherms of vWF in the presence of an excess of either agonist yielded a similar number of binding sites but an apparent dissociation constant slightly but consistently higher with the 7-mer peptide than with thrombin. The latter point was confirmed by studying the binding of limiting amounts of vWF to platelets as a function of the agonist concentration. The lower affinity in the presence of 7-mer peptide was not corrected by adding increasing amounts of FPR-thrombin, a derivative with irreversibly blocked active site but retaining the binding properties of the active enzyme. Conversely, the higher affinity observed with thrombin was decreased when platelets were treated with Serratia protease which selectively cleaved GPIb but did not affect the function of the thrombin receptor and GPIIb/IIa. Our data thus suggest that both the 7-mer peptide and thrombin are able to induce the assembly of functional GPIIb/IIIa.(ABSTRACT TRUNCATED AT 250 WORDS)

Aurin tricarboxylic acid inhibits platelet adhesion to collagen by binding to the 509-695 disulphide loop of von Willebrand factor and competing with glycoprotein Ib.

Aurin tricarboxylic acid (ATA) is known to inhibit ristocetin-induced platelet agglutination but not arachidonic acid-, epinephrine- or ADP-induced aggregation. Its capacity to abolish human von Willebrand factor (vWF)-platelet interactions was further investigated by measurement of platelet adhesion to collagen, platelet agglutination tests and binding studies. In flowing blood using parallel-plate perfusion chambers and human collagen, ATA inhibited platelet adhesion to completion in a dose-dependent manner only at the highest shear rate tested (2,600 s-1). It was without effect at 100 and 650 s-1. ATA completely abolished vWF-dependent platelet agglutination induced by ristocetin, botrocetin and asialo-vWF, respectively. 125I-vWF binding to ristocetin- and botrocetin-treated platelets, to heparin and to sulfatides as well as 125I-botrocetin binding to vWF was competitively inhibited by ATA. By contrast, binding of 125I-vWF to collagen was not affected. To further localize the domain of vWF interacting with ATA, experiments of inhibition of binding of selected 125I-monoclonal antibodies (MoAbs) to immobilized vWF by ATA were performed. Our data led to the conclusion that: 1) the interaction of ATA with vWF involves sequences of the A1 disulphide loop of vWF (residues 509-695) and close epitopes which interact with GPIb and 2) the inhibition of platelet adhesion by ATA occurs only at a high shear rate where vWF is known to play a key role. Thus ATA, which blocks the vWF/GPIb pathway by interfering with vWF and not with platelets, is a potential tool in preventing the early stages of thrombosis.

HTLV-I-associated myelopathy associated with blood transfusion in the United States: epidemiologic and molecular evidence linking donor and recipient.

Six months after receiving 58 units of blood components, a 65-year-old white man from New York City, with no other risk factors for human T-lymphotropic virus type I (HTLV-I) infection, developed HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Investigation of blood donors identified a 25-year-old white Hispanic woman from Florida whose platelets had been given to the patient and who was seropositive for the virus on a serum specimen obtained 2 years after the donation. She was born in Cuba and had had 2 sexual relationships with men who either had been born in or had resided in the Caribbean. Polymerase chain reaction (PCR) studies of peripheral blood mononuclear cells indicated that both donor and recipient were infected with HTLV-I. Molecular studies of a 595-nucleotide sequence in the 5' envelope region of HTLV-I indicated that the viruses from donor and recipient were identical in each of 32 positions in which published HTLV-I sequences demonstrate molecular heterogeneity; the donor and recipient viruses were also identical in 2 additional positions in which they differed from all published sequences. Transfusion-associated HAM/TSP has occurred in the United States, but additional cases should be prevented by screening blood donations for HTLV-I. Molecular studies of HTLV-I may prove useful in defining the genetic heterogeneity of HTLV-I isolates in the United States and in studying transmission of this virus.