Published online before print June 5, 2008

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Copyright © 2008 American Society for Investigative Pathology
American Journal of Pathology, doi:10.2353/ajpath.2008.071053

Accepted for publication March 25, 2008.

Article

Down Syndrome Fibroblast Model of Alzheimer-Related Endosome Pathology. Accelerated Endocytosis Promotes Late Endocytic Defects

Anne M. Cataldo^*@, Paul M. Mathews, Anne Boyer Boiteau^*, Linda C. Hassinger^*, Corrinne M. Peterhoff, Ying Jiang, Kerry Mullaney, Rachael L. Neve^¶, Jean Gruenberg^||, and Ralph A. Nixon

From the Laboratories of Molecular Neuropathology* and Molecular Neurogenetics,^¶ Mailman Research Center, McLean Hospital, Belmont, Massachusetts; the Departments of Psychiatry and Neuropathology, Harvard Medical School, Boston, Massachusetts; the Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York; the Departments of Psychiatry and Cell Biology, New York University School of Medicine, New York, New York; and the Department of Biochemistry,^|| University of Geneva, Geneva, Switzerland

^@ To whom correspondence should be addressed. E-mail: acataldo{at}mclean.harvard.edu.

	Abstract

Endocytic dysfunction is an early pathological change in Alzheimer's disease (AD) and Down's syndrome (DS). Using primary fibroblasts from DS individuals, we explored the interactions among endocytic compartments that are altered in AD and assessed their functional consequences in AD pathogenesis. We found that, like neurons in both AD and DS brains, DS fibroblasts exhibit increased endocytic uptake, fusion, and recycling, and trafficking of lysosomal hydrolases to rab5-positive early endosomes. Moreover, late endosomes identified using antibodies to rab7 and lysobisphosphatidic acid increased in number and appeared as enlarged, perinuclear vacuoles, resembling those in neurons of both AD and DS brains. In control fibroblasts, similar enlargement of rab5-, rab7-, and lysobisphosphatidic acid-positive endosomes was induced when endocytosis and endosomal fusion were increased by expression of either a rab5 or an active rab5 mutant, suggesting that persistent endocytic activation results in late endocytic dysfunction. Conversely, expression of a rab5 mutant that inhibits endocytic uptake reversed early and late endosomal abnormalities in DS fibroblasts. Our results indicate that DS fibroblasts recapitulate the neuronal endocytic dysfunction of AD and DS, suggesting that increased trafficking from early endosomes can account, in part, for downstream endocytic perturbations that occur in neurons in both AD and DS brains.

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