Glycan biomarkers for Alzheimer disease correlate with T-tau and P-tau in cerebrospinal fluid in subjective cognitive impairment

Alzheimer disease (AD) is a devastating disease and a global health problem, and current treatments are only symptomatic. A wealth of clinical studies support that the disease starts to develop decades before the first symptoms appear, emphasizing the importance of studying early changes for improving early diagnosis and guiding toward novel treatment strategies. Protein glycosylation is altered in AD but it remains to be clarified why these alterations occur and how they affect the disease development. Here, we used a glycomics approach to search for alterations in protein glycosylation in cerebrospinal fluid (CSF) in AD compared with nondemented controls. Using both matrix-assisted laser desorption ionization-time of flight and liquid chromatography–electrospray mass spectrometry, we observed an increase in N-glycans carrying bisecting N-acetylglucosamine in AD. Based on those findings, we designed an enzyme-linked multiwell plate assay to quantify N-glycans binding to the lectin Phaseolus vulgaris Erythroagglutinin (PHA-E), which is specific for N-glycans containing bisecting N-acetylglucosamine. Using this assay, we found a similar increase in CSF in AD compared with controls. Further analysis of CSF from 242 patients with subjective cognitive impairment (SCI), mild cognitive impairment (MCI), or AD dementia revealed significantly increased binding to PHA-E in MCI and AD compared to SCI. Interestingly, PHA-E binding correlated with CSF levels of phosphorylated tau and total tau and this correlation was most prominent in the SCI group (R = 0.53–0.54). This study supports a link between N-glycosylation, neurodegeneration, and tau pathology in AD and suggests that glycan biomarkers have potential to identify SCI cases at risk of developing AD

Potential Role of miRNAs in Developmental Haemostasis

MicroRNAs (miRNAs) are an abundant class of small non-coding RNAs that are negative regulators in a crescent number of physiological and pathological processes. However, their role in haemostasis, a complex physiological process involving multitude of effectors, is just beginning to be characterized. We evaluated the changes of expression of miRNAs in livers of neonates (day one after birth) and adult mice by microarray and qRT-PCR trying to identify miRNAs that potentially may also be involved in the control of the dramatic change of hepatic haemostatic protein levels associated with this transition. Twenty one out of 41 miRNAs overexpressed in neonate mice have hepatic haemostatic mRNA as potential targets. Six of them identified by two in silico algorithms potentially bind the 3′UTR regions of F7, F9, F12, FXIIIB, PLG and SERPINC1 mRNA. Interestingly, miR-18a and miR-19b, overexpressed 5.4 and 8.2-fold respectively in neonates, have antithrombin, a key anti-coagulant with strong anti-angiogenic and anti-inflammatory roles, as a potential target. The levels of these two miRNAs inversely correlated with antithrombin mRNA levels during development (miR-19b: R = 0.81; p = 0.03; miR-18a: R = 0.91; p<0.001). These data suggest that miRNAs could be potential modulators of the haemostatic system involved in developmental haemostasis

Colorectal Cancer Metastases Settle in the Hepatic Microenvironment Through \u3b15\u3b21 Integrin

Colorectal cancer (CRC) metastasis dissemination to secondary sites represents the critical point for the patient0s survival. The microenvironment is crucial to cancer progression, influencing tumour cell behaviour by modulating the expression and activation of molecules such as integrins, the cell-extracellular matrix interacting proteins participating in different steps of the tumour metastatic process. In this work, we investigated the role of a5b1 integrin and how the microenvironment influences this adhesion molecule, in a model of colon cancer progression to the liver. The culture medium conditioned by the IHH hepatic cell line, and the extracellular matrix (ECM) proteins, modulate the activation of a5b1 integrin in the colon cancer cell line HCT-116, and drives FAK phosphorylation during the process of cell adhesion to fibronectin, one of the main components of liver ECM. In these conditions, a5b1 modulates the expression/activity of another integrin, a2b1, involved in the cell adhesion to collagen I. These results suggest that a5b1 integrin holds a leading role in HCT-116 colorectal cancer cells adhesion to the ECM through the modulation of the intracellular focal adhesion kinase FAK and the a2b1 integrin activity. The driving role of the tumour microenvironment on CRC dissemination, here detected, and described, strengthens and adds new value to the concept that a5b1 integrin can be an appropriate and relevant therapeutic target for the control of CRC metastases

Tumor Biomarker Glycoproteins in the Seminal Plasma of Healthy Human Males Are Endogenous Ligands for DC-SIGN

Published online 2011 October 10. doi: 10.1074/mcp.M111.008730DC-SIGN is an immune C-type lectin that is expressed on both immature and mature dendritic cells associated with peripheral and lymphoid tissues in humans. It is a pattern recognition receptor that binds to several pathogens including HIV-1, Ebola virus, Mycobacterium tuberculosis, Candida albicans, Helicobacter pylori, and Schistosoma mansoni. Evidence is now mounting that DC-SIGN also recognizes endogenous glycoproteins, and that such interactions play a major role in maintaining immune homeostasis in humans and mice. Autoantigens (neoantigens) are produced for the first time in the human testes and other organs of the male urogenital tract under androgenic stimulus during puberty. Such antigens trigger autoimmune orchitis if the immune response is not tightly regulated within this system. Endogenous ligands for DC-SIGN could play a role in modulating such responses

N-glycans of Human Protein C Inhibitor: Tissue-Specific Expression and Function

Protein C inhibitor (PCI) is a serpin type of serine protease inhibitor that is found in many tissues and fluids in human, including blood plasma, seminal plasma and urine. This inhibitor displays an unusually broad protease specificity compared with other serpins. Previous studies have shown that the N-glycan(s) and the NH2-terminus affect some blood-related functions of PCI. In this study, we have for the first time determined the N-glycan profile of seminal plasma PCI, by mass spectrometry. The N-glycan structures differed markedly compared with those of both blood-derived and urinary PCI, providing evidence that the N-glycans of PCI are expressed in a tissue-specific manner. The most abundant structure (m/z 2592.9) had a composition of Fuc3Hex5HexNAc4, consistent with a core fucosylated bi-antennary glycan with terminal Lewisx. A major serine protease in semen, prostate specific antigen (PSA), was used to evaluate the effects of N-glycans and the NH2-terminus on a PCI function related to the reproductive tract. Second-order rate constants for PSA inhibition by PCI were 4.3±0.2 and 4.1±0.5 M−1s−1 for the natural full-length PCI and a form lacking six amino acids at the NH2-terminus, respectively, whereas these constants were 4.8±0.1 and 29±7 M−1s−1 for the corresponding PNGase F-treated forms. The 7–8-fold higher rate constants obtained when both the N-glycans and the NH2-terminus had been removed suggest that these structures jointly affect the rate of PSA inhibition, presumably by together hindering conformational changes of PCI required to bind to the catalytic pocket of PSA

Zinc ions bind to and inhibit activated protein C

Zn2+ ions were found to efficiently inhibit activated protein C (APC), suggesting a potential regulatory function for such inhibition. APC activity assays employing a chromogenic peptide substrate demonstrated that the inhibition was reversible and the apparent K I was 13 +/- 2 muM. k cat was seven fold decreased whereas K M was unaffected in the presence of 10 muM Zn2+. The inhibitory effect of Zn2+ on APC activity was also observed when factor Va was used as a substrate in an assay coupled to a prothrombinase assay. The interaction of Zn2+ with APC was accompanied by a reversible ~40% decrease in tryptophan fluorescence, consistent with the ion inducing a conformational change in the protein. The apparent K D was 7.4 +/- 1.5 muM and thus correlated well with the apparent K I. In the presence of physiological Ca2+ concentration the K I and K D values were three to four fold enhanced, presumably due to the Ca2+-induced conformational change affecting the conformation of the Zn2+-binding site. The inhibition mechanism was non-competitive both in the absence and presence of Ca2+. Comparisons of sequences and structures suggested several possible sites for zinc binding. The magnitude of the apparent KI in relation to the blood and platelet concentrations of Zn2+ supports a physiological role for this ion in the regulation of anticoagulant activity of APC. These findings broaden the understanding of this versatile serine protease and enable the future development of potentially more efficient anticoagulant APC variants for treatments of thrombotic diseases

Kinetic evidence that allosteric activation of antithrombin by heparin is mediated by two sequential conformational changes

The serpin, antithrombin, requires allosteric activation by a sequencespecific pentasaccharide unit of heparin or heparan sulfate glycosaminoglycans to function as an anticoagulant regulator of blood clotting proteases. Surprisingly, X-ray structures have shown that the pentasaccharide produces similar inducedfit changes in the heparin binding site of native and latent antithrombin despite large differences in the heparin affinity and global conformation of these two forms. Here we present kinetic evidence for similar induced-fit mechanisms of pentasaccharide binding to native and latent antithrombins and kinetic simulations which together support a three-step mechanism of allosteric activation of native antithrombin involving two successive conformational changes. Equilibrium binding studies of pentasaccharide interactions with native and latent antithrombins and the salt dependence of these interactions suggest that each conformational change is associated with distinct spectroscopic changes and is driven by a progressively better fit of the pentasaccharide in the binding site. The observation that variant antithrombins that cannot undergo the second conformational change bind the pentasaccharide like latent antithrombin and are partially activated suggests that both conformational changes contribute to allosteric activation, in agreement with a recently proposed model of allosteric activation

Live Cell FRET Imaging Reveals Amyloid β-Peptide Oligomerization in Hippocampal Neurons

Amyloid β-peptide (Aβ) oligomerization is believed to contribute to the neuronal dysfunction in Alzheimer disease (AD). Despite decades of research, many details of Aβ oligomerization in neurons still need to be revealed. Förster resonance energy transfer (FRET) is a simple but effective way to study molecular interactions. Here, we used a confocal microscope with a sensitive Airyscan detector for FRET detection. By live cell FRET imaging, we detected Aβ42 oligomerization in primary neurons. The neurons were incubated with fluorescently labeled Aβ42 in the cell culture medium for 24 h. Aβ42 were internalized and oligomerized in the lysosomes/late endosomes in a concentration-dependent manner. Both the cellular uptake and intracellular oligomerization of Aβ42 were significantly higher than for Aβ40. These findings provide a better understanding of Aβ42 oligomerization in neurons