No abstract

A fundamental question about the early pathogenesis of Alzheimer's disease (AD) concerns how toxic aggregates of amyloid ␤ protein (A␤) are formed from its nontoxic soluble form. We hypothesized previously that GM1 ganglioside-bound A␤ (GA␤) is involved in the process. We now examined this possibility using a novel monoclonal antibody raised against GA␤ purified from an AD brain. Here, we report that GA␤ has a conformation distinct from that of soluble A␤ and initiates A␤ aggregation by acting as a seed. Furthermore, GA␤ generation in the brain was validated by both immunohistochemical and immunoprecipitation studies. These results imply a mechanism underlying the onset of AD and suggest that an endogenous seed can be a target of therapeutic strategy.

a b s t r a c tElevated amyloid-b peptide (Ab) in brain contributes to Alzheimer's disease (AD) pathogenesis. We demonstrated the presence of exosome-associated Ab in the cerebrospinal fluid (CSF) of cynomolgus monkeys and APP transgenic mice. The levels of exosome-associated Ab notably decreased in the CSF of aging animals. We also determined that neuronal exosomes, but not glial exosomes, had abundant glycosphingolipids and could capture Ab. Infusion of neuronal exosomes into brains of APP transgenic mice decreased Ab and amyloid depositions, similarly to what reported previously on neuroblastoma-derived exosomes. These findings highlight the role of neuronal exosomes in Ab clearance, and suggest that their downregulation might relate to Ab accumulation and, ultimately, the development of AD pathology.

Cancer cells undergo distinct metabolic changes to cope with their hypoxic environment. These changes are achieved at least partly by the action of transcriptional factors called hypoxia-inducible factors (HIFs). We investigated gene expression in cultured human colon cancer cells induced by hypoxic conditions with special reference to cell-adhesion molecules and carbohydrate determinants having cell-adhesive activity by using DNA-microarray and RT-PCR techniques. Hypoxic culture of colon cancer cells induced a marked increase in expression of selectin ligands, the sialyl Lewis x and sialyl Lewis a determinants at the cell surface, which led to a definite increase in cancer cell adhesion to endothelial E-selectin. The transcription of genes for fucosyltransferase VII (FUT7), sialyltransferase ST3Gal-I (ST3O), and UDP-galactose transporter-1 (UGT1), which are all known to be involved in the synthesis of the carbohydrate ligands for E-selectin, was significantly induced in cancer cells by hypoxic culture. In addition, a remarkable induction was detected in the genes for syndecan-4 (SDC4) and α5-integrin (ITGA5), the cell-adhesion molecules involved in the enhanced adhesion of cancer cells to fibronectin. The transcriptional induction by hypoxia was reproduced in the luciferase-reporter assays for these genes, which were significantly suppressed by the co-transfection of a dominant-negative form of HIF. These results indicate that the metabolic shifts of cancer cells partly mediated by HIFs significantly enhance their adhesion to vascular endothelial cells, through both selectin- and integrin-mediated pathways, and suggest that this enhancement further facilitates hematogenous metastasis of cancers and tumor angiogenesis