This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Brief Background of the problem and hypothesis: Tau is a microtubule-associated protein that stabilizes the neuronal cytoskeleton and functions in vesicular transport and axonal polarity. Pathological alterations in tau are thought to play a causative role in several neurodegenerative disorders, including Alzheimer's disease (AD). In AD, beta-amyloid (A?) deposition is accompanied by the gradual replacement of the neuronal cytoskeleton with insoluble NFTs that develop following modifications of tau that include hyperphosphorylation and proteolytic cleavage. However, to date the relationship between A? deposition and NFTs remains unknown. One possible link between A? and NFTs is the aberrant activation of caspases, proteolytic enzymes responsible for the proper execution of programmed cell death or apoptosis. Recent studies have determined that caspase activation may interconnect these two hallmark pathologies. Thus, in the human AD brain our laboratory as well as others have demonstrated the presence of caspase-cleavage products (CCPs) of tau that are associated with markers of NFT formation. Furthermore, caspase-cleaved tau co-localizes with intracellular A?1-42 in the AD brain and is induced by A?1-42, in vitro. Collectively, these results indicate that tangles and amyloid are interconnected through a common pathway, namely caspase-mediated proteolysis. To test this hypothesis directly, we propose in the present application to examine the effects of crossing a novel Tg mouse model of AD (3xTg-AD mice) with mice overexpressing the antiapoptotic protein, Bcl-2 (Bcl-2 OE Tg mice). Our overall hypothesis is that progeny of such a cross will show attenuation in caspase activation and prevention in the pathology and behavioral problems associated with 3xTg-AD mice.
The specific Aims of the proposal are:
Aim 1 : To establish a novel transgenic mouse model of AD that overexpresses the antiapoptotic protein, Bcl-2. Preliminary data suggest that caspase cleavage of tau occurs in an age-dependent manner in 3xTg-AD mice. Bcl-2 is powerful anti-apoptotic protein that rescues many types of neurons from apoptosis caused by injury or disease and can enhance neuronal survival during development. In this aim, we test the hypothesis that progeny resulting from crossing these two Tg mice models are viable and properly overexpress A?, tau and Bcl-2 in an age-dependent manner. Because all subsequent specific aims can only be carried out following the success of this specific aim, we will provide preliminary data to demonstrate the successful crossbreeding and survival of such progeny for at least 24 months.
Aim 2 : Assess whether overexpression of Bcl-2 will prevent caspase activation, the cleavage of tau and APP and lead to fewer tangle alterations in AD mice. Recent in vitro and in vivo data suggest that caspase activation and subsequent cleavage of tau may be a key event linking A? with NFTs in AD. In this aim, we plan to test this hypothesis directly, by determining whether overexpression of an antiapoptotic protein, Bcl-2, prevents caspase activation and NFT formation in an animal model of AD.
Aim 3 : Determine whether caspases play a role in the turnover of the amyloid precursor protein and tau following the overexpression of Bcl-2 in 3xTg-AD mice. Evidence suggests that both the amyloid precursor protein (APP) and tau are substrates for caspase-mediated cleavage. The overexpression of Bcl-2 and attenuation of caspase activation may lead to alterations in the levels of APP, A? and tau in 3xTg-AD mice. We hypothesize that we will observe higher levels of both APP and tau following overexpression of Bcl-2.
Aim 4 : To determine whether overexpression of Bcl-2 in 3xTg-AD mice improves cognition. An important determinant for this proposal will be to assess not only the pathology but also cognition following overexpression of Bcl-2. Standard Morris or radial arm mazes will be employed in addition to using a novel memory paradigm involving place recognition. Taken together, we believe the design and rationale for this project should allow us to answer whether caspases play an active role in the pathogenesis associated with AD. We believe this to be both an important and timely study that could identify new targets for the treatment of this disease. Results from this proposal may provide impetus to test pharmacological blockade of caspases as a therapeutic intervention in treating AD.
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