title: Targets of caspase-6 activity in human neurons and Alzheimer disease.
abstract: Caspase-6 activation occurs early in Alzheimer disease and sometimes precedes the clinical manifestation of the disease in aged individuals. The active Caspase-6 is localized in neuritic plaques, in neuropil threads, and in neurofibrillary tangles containing neurons that are not morphologically apoptotic in nature. To investigate the potential consequences of the activation of Caspase-6 in neurons, we conducted a proteomics analysis of Caspase-6-mediated cleavage of human neuronal proteins. Proteins from the cytosolic and membrane subcellular compartments were treated with recombinant active Caspase-6 and compared with undigested proteins by two-dimensional gel electrophoresis. LC/MS/MS analyses of the proteins that were cleaved identified 24 different potential protein substrates. Of these, 40% were cytoskeleton or cytoskeleton-associated proteins. We focused on the cytoskeleton proteins because these are critical for neuronal structure and function. Caspase-6 cleavage of alpha-Tubulin, alpha-Actinin-4, Spinophilin, and Drebrin was confirmed. At least one Caspase-6 cleavage site was identified for Drebrin, Spinophilin, and alpha-Tubulin. A neoepitope antiserum to alpha-Tubulin cleaved by Caspase-6 immunostained neurons, neurofibrillary tangles, neuropil threads, and neuritic plaques in Alzheimer disease and co-localized with active Caspase-6. These results imply that the early and neuritic activation of Caspase-6 in Alzheimer disease could disrupt the cytoskeleton network of neurons, resulting in impaired neuronal structure and function in the absence of cell death. This study provides novel insights into the pathophysiology of Alzheimer disease.
authors.affiliation: The Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Ch. Cote Ste-Catherine, Montreal, Quebec H3T 1E2, Canada.
authors.forename: Guy
authors.initials: G
authors.lastname: Klaiman
authors.forename: Tracy L
authors.initials: TL
authors.lastname: Petzke
authors.forename: Jennifer
authors.initials: J
authors.lastname: Hammond
authors.forename: Andréa C
authors.initials: AC
authors.lastname: Leblanc
mesh_terms: D000544:Alzheimer Disease / Q000201:enzymology / Q000378:metabolism*; D053178:Caspase 6 / Q000378:metabolism*; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000032:analysis*; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D009474:Neurons / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D003598:Cytoskeletal Proteins; D011994:Recombinant Proteins; D053178:Caspase 6