Cross-sectional functional magnetic resonance imaging studies using a memory task in patients with mild cognitive impairment have produced discordant results, with some studies reporting increased hippocampal activity--consistent with findings in genetic at-risk populations--and other studies reporting decreased hippocampal activity, relative to normal controls. However, previous studies in mild cognitive impairment have not included markers of amyloid-β, which may be particularly important in prediction of progression along the Alzheimer's disease continuum. Here, we examine the contribution of amyloid-β deposition to cross-sectional and longitudinal measures of hippocampal functional magnetic resonance imaging activity, hippocampal volume, global cognition and clinical progression over 36 months in 33 patients with mild cognitive impairment. Amyloid-β status was examined with positron emission tomography imaging using Pittsburg compound-B, hippocampal functional magnetic resonance imaging activity was assessed using an associative face-name memory encoding task, and hippocampal volume was quantified with structural magnetic resonance imaging. Finally global cognition was assessed using the Mini-Mental State Examination and clinical progression was assessed using the Clinical Dementia Rating (Sum of Boxes). At baseline, amyloid-β positive patients with mild cognitive impairment showed increased hippocampal activation, smaller hippocampal volumes, and a trend towards lower Mini-Mental State Examination scores and higher Clinical Dementia Ratings compared to amyloid-β negative patients with mild cognitive impairment. Longitudinally, amyloid-β positive patients with mild cognitive impairment continued to show high levels of hippocampal activity, despite increasing rates of hippocampal atrophy, decline on the Mini-Mental State Examination and faster progression on the Clinical Dementia Ratings. When entered simultaneously into the same linear mixed model, amyloid-β status, hippocampal activation, and hippocampal volume independently predicted clinical progression. These results indicate that amyloid-β positive patients with mild cognitive impairment are more likely on a path towards Alzheimer's disease dementia than amyloid-β negative patients. Increased hippocampal activity is discussed in relation to neuronal compensation and/or amyloid-β induced excitoxicity.
Measles virus is a paramyxovirus which, like other members of the family such as respiratory syncytial virus, is a major cause of morbidity and mortality worldwide. The cell surface receptor for measles virus in humans is CD46, a complement cofactor. We report here the crystal structure at 3.1 Å resolution of the measles virus-binding fragment of CD46. The structure reveals the architecture and spatial arrangement of two glycosylated short consensus repeats with a pronounced interdomain bend and some flexibility at the domain interface. Amino acids involved in measles virus binding define a large, glycan-free surface that extends from the top of the first to the bottom of the second repeat. The extended virus-binding surface of CD46 differs strikingly from those reported for the human virus receptor proteins CD4 and intercellular cell adhesion molecule-1 (ICAM-1), suggesting that the CD46 structure utilizes a novel mode of virus recognition. A highly hydrophobic and protruding loop at the base of the first repeat bears a critical virus-binding residue, thereby defining an important recognition epitope. Molecules that mimic the conformation of this loop potentially could be effective anti-viral agents by preventing binding of measles virus to CD46.
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