The Lysosomal Membrane Damage in Abeta Mediated Neurotoxicity

The most prevalent form of senile dementia, Alzheimer’s disease (AD) is chacterized by proteinacious deposits in the cerebrovascular (CVA) and in the paraenchyma as senile plaques (SP). The major component of SP and CV A is the 4.5 kDa Aß that is derived from the transmembrane amyloid precursor (APP) protein. Biochemical analysis of the amyloid pepetides from AD brain indicated that both Aß1-42 is the principal species associated with SP amyloid, while bot hAßl-42 is the Aß1-40 are abundant in CVA deposits. Recent evidence has indicated that the longer Aß1-42(43) forms may be more closely related to pathogenesis that the shorter ASl-40 isoform. Mutation associated with inherited, familiar AD have been shown that generate the amyloid peptide and favor the production of the longer Aß1-42 isoform. Therefore, The overall goal of this research project is to elucidate some of the mechanisms for the accumulation of ß-amyloid deposits in Alzheimer’s disease (AD) and the potential role of these deposits in neuronal degeneration. Earlier studies in our laboratory have indicated that Aß1-42 but not Aß1- 40 is internalized and forms protease-resistant aggregates inside the organelle, named lysosomes of several cultured cell lines. Although the pathological consequence of this intracellular Aß remains to be established, we and other have recently demonstrated that intracellular Aß1-42 aggregates alter the normal catabolic processing of the APP to cause the accumulation of insoluble APP amyloidogenic fragments. A similar series of APP amyloidogenic fragments has been related to dysfunction of lysosomes in both cultured cells and AD brain. To further understand the biochemical properties of Aß peptide, we have chemically synthesized several different isoforms of Aß and our data indicates that Aß is able to self-assemble in a fiber-like structure and display a number of properties associated with surfactant. These observations, along with the findings that the neuronal toxicity of Aß in cultured neurons is dependent on the aggregation state of the peptide suggest the hypothesis that Aß may act as a lysosomotropic detergent, a class of cytotoxic, self-assembling amphipathic molecules that accumulate in lysosomes and ultimately result in the dysfunction of lysosomes and cell death. Therefore, we have proposed to test the hypothesis that the toxic mechanism of Aß in cultured neurons may be similar to that of lysosomotropic detergents during the previous award period. Our preliminary data indicates that treatment of cultured neurons with Aß1-42 aggregates causes the increase in lysosomal hydrolase synthesis, production of oxygen radicals and eventually lead to the instability of lysosomal membrane and cell death. Furthermore, the loss of lysosomal membrane integrity is only specific for Aß1-42 aggregates since the addition of high concentration of non-accumulating Aß1-28 and freshly dissolved Aß1-40 do not cause the release of lysosomal contents. The specific aims of this proposal are designed to more completely characterize the intracellular Aß accumulation and its role in oxygen radical mediated lysosomal membrane damage in AD. We will determine whether the Aß induced lysosomal membrane leakage is dependent on their intracellular Aß aggregates in endosomes/lysosomes. In addition, we will determined whether the determined whether a primary target of the reactive oxygen species (ROS) produced by cells in response to Aß1-42 internalization is the lysosomal lipids. We will also determine the role of lysosomal iron in the generation of ROS and lysosomal membrane injury.