The activation of caspase-6 (Csp-6) is observed in Alzheimer’s Disease (AD) and mild cognitive impairment (MCI) (Guo et al., 2004, Am. J. Pathol., LeBlanc et al., SfN 2005). This activation is involved at an early stage of AD since immunoreactivity of active Csp-6 and Csp-6-cleaved tau is observed in MCI and in pretangles of AD brains. Active Csp-6 is found localized in the neurites or tangles but not in the nucleus of AD neurons, in contrast to its nuclear localization in ischemic brain apoptotic neurons. In other cell types, Csp-6 has been shown to cleave several intermediate filament proteins. These results suggest that active Csp-6 may lead to neuronal dysfunction before eventual cell death in MCI and AD by affecting the cytoskeleton of the neuron. This led us to study the substrates of Csp-6 in human primary neurons. Human primary neurons were fractionated to give protein fractions enriched in nuclear, membrane and cytosolic proteins. These proteins were in turn digested with recombinant active Csp-6 ...