Identification of a domain in apolipoprotein B-100 that inhibits the procoagulant activity of tissue factor

Identification of Receptor Ligands in Apo B100 Reveals Potential Functional Domains

LDL, VLDL and other members of the low-density lipoparticles (LLPs) enter cells through a large family of receptors. The actual receptor ligand(s) in apolipoprotein B100, one of the main proteins of LLP, remain(s) unknown. The objective of this study was to identify true receptor ligand(s) in apo B100, a molecule of 4563 residues. Apo B100 contains 33 analogues of Cardin-Weintraub arginine/lysine-based receptor ligand motifs and shares key lysine motifs and sequence similarity with the LDL receptor-associated protein, MESD, and heat shock proteins. Eleven FITC-labeled synthetic peptides of 21-42 residues, with at least one ligand, were tested for binding and internalization using HeLa cells. All peptides bind but display different binding capacities and patterns. Peptides B0013, B0582, B2366, and B2932 mediate endocytosis and appear in distinct sites in the cytoplasm. B0708 and B3181 bind and remain on the cell surface as aggregates/clusters. Peptides B3119 (Site A) and B3347 (Site B), the putative ligands, showed low binding and no cell entry capacity. Apo B100 regions in this study share similarities with related proteins of known function including chaperone proteins and Apo BEC stimulating protein, and not directly related proteins, e.g., the DNA-binding domain of interferon regulatory factors, MSX2-interacting protein, and snake venom Zinc metalloproteinase-disintegrin-like proteins.

The Importance of Caveolin-1 as Key-Regulator of Three-Dimensional Growth in Thyroid Cancer Cells Cultured under Real and Simulated Microgravity Conditions

We recently demonstrated that the CAV1 gene was down-regulated, when poorly differentiated thyroid FTC-133 cancer cells formed spheroids under simulated microgravity conditions. Here, we present evidence that the caveolin-1 protein is involved in the inhibition of spheroid formation, when confluent monolayers are exposed to microgravity. The evidence is based on proteins detected in cells and their supernatants of the recent spaceflight experiment: "NanoRacks-CellBox-Thyroid Cancer". The culture supernatant had been collected in a special container adjacent to the flight hardware incubation chamber and stored at low temperature until it was analyzed by Multi-Analyte Profiling (MAP) technology, while the cells remaining in the incubation chamber were fixed by RNAlater and examined by mass spectrometry. The soluble proteins identified by MAP were investigated in regard to their mutual interactions and their influence on proteins, which were associated with the cells secreting the soluble proteins and had been identified in a preceding study. A Pathway Studio v.11 analysis of the soluble and cell-associated proteins together with protein kinase C alpha (PRKCA) suggests that caveolin-1 is involved, when plasminogen enriched in the extracellular space is not activated and the vascular cellular adhesion molecule (VCAM-1) mediated cell-cell adhesion is simultaneously strengthened and activated PRKCA is recruited in caveolae, while the thyroid cancer cells do not form spheroids.

Effect of resection of localized pancreaticobiliary adenocarcinoma on angiogenic markers and tissue factor related pro-thrombotic and pro-angiogenic activity

In this study, 52 patients were studied to elucidate the relative impact of resection of localized pancreaticobiliary adenocarcinoma (PBC) on circulating factors of tumour-associated angiogenesis e.g. tissue factor bearing microparticles (TFMP) and vascular endothelial growth factor (VEGF) and their clinicopathological significance to angiogenesis markers in cancer tissue from PBC patients. Angiogenesis array analysis on serum samples revealed that surgical resection of tumour lesion in PBC patients affects the levels of a panel of angiogenesis-related molecules, including VEGF that was verified by ELISA to significantly reduce (median & IQR: 1003(369-2000) vs. 457(159-834) pg/ml; p<0.05). Correspondingly, a significant decrease in the angiogenic activity (decreased capillary tube formation; p<0.05) of serum samples after the surgery was also found. Despite a decrease in number of circulating TFMP after surgery, this did not reach statistical significance; there was a significant reduction in pro-coagulant activity (prolonged prothrombin time, p<0.001) post-operatively. In addition, the activity of total microparticles (MP activity assay, p<0.05) was decreased significantly. Immunohistochemical staining of tumour tissue revealed a strong correlation between the microvessel density (MVD) and VEGF expression. Also, higher levels of circulating TFMP or TF related activity (prothrombin time) correlated significantly with TF expression and MVD on tumour tissues from PBC patients. These findings suggest that in pancreaticobiliary adenocarcinoma TF related angiogenesis drivers are equally significant to VEGF ones, raising the clinical question of whether the effectiveness of angiogenesis targeting studies could be improved through the 'dual' targeting of these pathways in PBC.

Tissue factor-containing microparticles released from mesangial cells in response to high glucose and AGE induce tube formation in microvascular cells

Hyperglycaemia and the associated formation of advanced glycation end-products (AGE) have been implicated in the pathogenesis of diabetic vasculopathy. In addition to its role in coagulation, tissue factor (TF) is known to regulate vascular proliferation and angiogenesis. In this study, the influence of AGE and glucose on the expression of TF in human renal mesangial cells (HRMC) and the subsequent induction of capillary formation by human dermal microvascular endothelial cells (HDMEC) were measured. Furthermore, the activity of TF, incorporated into microparticles was investigated. Both AGE and elevated glucose were capable of upregulating the expression of TF expression in a concentration-dependent manner in HRMC but not in HDMEC. This TF antigen and activity in the conditioned media from HRMC was associated with microparticles. Moreover, the formation of capillaries was readily induced on supplementation of HDMEC with conditioned media, from AGE-treated or high glucose-treated HRMC but not on incubation of HDMEC with either AGE or hyperphysiological concentrations of glucose. Furthermore, the rate of capillary formation was suppressed on incubation of the conditioned media with a polyclonal antibody against TF but not against VEGF. This study indicates that TF-containing microparticles are an important pro-inflammatory mediator acting as a mediator between elevated glucose and the development of diabetic vasculopathy by altering the angiogenic properties of endothelial cells and offers one explanation for the correlation between diabetes and microvascular disease.

Effect of the factor VII R353Q missense mutation on plasma apolipoprotein B levels: impact of visceral obesity

An atherogenic dyslipidemia, characterized by increased plasma triglyceride and apolipoprotein (apo) B levels, low HDL-cholesterol concentrations and the development of small, dense LDL particles has been associated with the presence of abdominal-visceral obesity. Visceral obesity is also associated with a hypercoagulate state and elevated concentrations of procoagulant factors such as factor VII. Moreover, it is known that some genetic variants in the gene encoding factor VII alter its activity and concentration, and consequently these variants may have an impact on atherosclerosis development. The objective of this study was to verify whether the factor VII R353Q polymorphism contributes to predict the risk of an atherogenic dyslipidemia in absence and in the presence of visceral obesity. A sample of 299 French-Canadian men, selected in order to cover a wide range of body fatness values, participated in this study. We observed that the R353 allele was more commonly observed among men characterized by apo B levels below 1.09 g/l than among men with apo B levels greater or above this threshold value (allele frequency of 92.1 vs 85.4%, chi(2)=6.18, P=0.01). Multivariate analyses further showed that the genotype R353/R353 was associated with a lower risk to exhibit atherogenic concentrations of total-apo B (>/=1.09 g/l) and LDL apo B (>/=0.95 g/l) before (odds ratio:0.47, 95%CI=0.27-0.90, P=0.02; odds ratio:0.46, 95%CI=0.25-0.85, P=0.01, respectively) and after adjustments for age and visceral AT (odds ratio:0.49, 95%CI=0.24-0.91, P=0.02; odds ratio:0.44, 95%CI=0.23-0.85, P=0.01, respectively). When the two genotype groups were further divided on the basis of visceral adipose tissue (AT) accumulation using a cutoff point of 130 cm(2), we observed that R353/R353 homozygotes with low visceral AT were characterized by a more favorable lipoprotein-lipid profile, mainly lower total-cholesterol, total-apo B, and LDL-apo B levels compared with R353/R353 homozygotes with high levels of visceral AT. In contrast, irrespective of obesity, plasma lipid levels among carriers of the Q353 allele were similar to those of viscerally obese men homozygous for the R353 allele. In conclusion, results of the present study suggest that the factor VII R353 allele is associated with lower concentrations of plasma apo B levels. However, the presence of visceral obesity abolishes this effect. Further studies will be necessary to confirm this association and the mechanism involved.

The mechanical behavior of vascular grafts: a review

The development of intimal hyperplasia (IH) near the anastomosis of a vascular graft to artery is directly related to changes in the wall shear rate distribution. Mismatch in compliance and diameter at the end-to-end anastomosis of a compliant artery and rigid graft cause shear rate disturbances that may induce intimal hyperplasia and ultimately graft failure. The principal strategy being developed to prevent IH is based on the design and fabrication of compliant synthetic or innovative tissue-engineered grafts with viscoelastic properties that mirror those of the human artery. The goal of this review is to discuss how mechanical properties including compliance mismatch, diameter mismatch, Young's modulus and impedance phase angle affect graft failure due to intimal hyperplasia.

The role of the C-terminal domain in the inhibitory functions of tissue factor pathway inhibitor

Tissue factor pathway inhibitor (TFPI) inhibits the activity of coagulation factors VIIa and Xa through Kunitz domains, thereby inhibiting the activity of tissue factor. However, it has been shown that the C-terminal of this inhibitor is essential for the maximal anticoagulant activity of TFPI. We have investigated the endogenous ability of the C-terminal of TFPI to influence coagulation. A synthetic peptide corresponding to residues 254-265 within the C-terminal of TFPI was prepared and shown to be capable of inhibiting tissue factor pathway by preventing the activation of factor VII. Mutational analysis of the peptide revealed the identity of the key lysine residues.

Monocyte tissue factor response is decreased in patients with hyperlipidemia

Monocytes are potent regulators of blood coagulation through the expression of tissue factor (TF) on stimulation and of tissue factor pathway inhibitor (TFPI), a selective inhibitor of TF pathway. As hyperlipidemia can modify some monocyte functions, we compared the TF and TFPI expression by circulating monocytes and the plasma TFPI levels between 65 healthy normolipemic controls and 38 nontreated hyperlipemic patients. TF and TFPI relationships with plasma lipoproteins are also examined. TF and TFPI expression were evaluated in peripheral mononuclear cells after isolation from blood by density gradient centrifugation and after short culture with or without lipopolysaccharide (LPS). TF and TFPI activity and antigen were measured in mononuclear cell lysates using amidolytic assay and enzyme-linked immunosorbent assay, respectively. TFPI activity and antigen were measured in plasma using the same methods. Plasma factor VII (FVII) activity and antigen were also determined. LPS-stimulated monocyte TF activity and antigen were lower in hyperlipidemic patients than in controls (0.0001<p<0.03). This decrease of monocyte TF expression in hyperlipidemic patients was not related to an increase of monocyte TFPI. Monocyte TF activity was negatively correlated to atherogenic fractions and positively correlated to protective fractions, specially after ex vivo LPS stimulation. Increased TFPI and FVII plasma levels were found in hyperlipidemic patients compared to controls. These results indicate an impairment of TF production by circulating monocytes from hyperlipidemic subjects, which is linked to the increase of atherogenic lipoprotein fractions. Further studies are required to elucidate the mechanism of this inhibition.

Comparison of the inhibitory effects of ApoB100 and tissue factor pathway inhibitor on tissue factor and the influence of lipoprotein oxidation

The procoagulant activity of tissue factor is regulated by circulating inhibitors such as tissue factor pathway inhibitor (TFPI) and LDL. These 2 inhibitors also readily associate making the distinction between their activities difficult. We have examined the relative contributions of intact and C-terminal truncated TFPI and ApoB100. By following the inhibitory potential of the preparations, over a period of 120 minutes, it was demonstrated that TFPI and LDL-resembling particles inhibited tissue factor at different rates. TFPI was found to be a short, fast-acting inhibitor, whereas the action of LDL-resembling particles was more prolonged but slower. The oxidation of LDL has been closely associated with the development of cardiovascular disease, including atherosclerosis and thrombosis. Positively charged amino acids, particularly lysine residues, are prone to alterations via the formation of adducts by lipid peroxidation products. These residues are important in the inhibition of tissue factor activity by ApoB100. They also play an important role in the inhibitory Kunitz domains of TFPI. We have shown that the decline in the ability of LDL to inhibit tissue factor was as a result of modifications in LDL arising from oxidation. By examining the effects of oxidation on full-length and C-terminal truncated TFPI bound to LDL-resembling particles, we found that TFPI is only affected when in close association with ApoB100. C-terminal truncated TFPI was not affected significantly by oxidation. Finally, chemical modification of lysine and arginine residues reduced the overall inhibition of tissue factor by TFPI. We propose that TFPI and LDL act separately to inhibit tissue factor in vivo. However, the oxidation of LDL can alter both the endogenous activity of ApoB100 and reduce that of closely associated TFPI, compromising normal hemostasis.