REGULATION AND PROCESSING OF AMYLOID PRECURSOR PROTEIN GENES AND GENE PRODUCTS

Aging

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Abstract

Summary of Work: A major focus of this project is to discover the role of the Amyloid Precursor Protein (APP) in the etiology and pathology of Alzheimer's Disease (AD). The normal physiological role of this protein is also under investigation. APP is important to study since the processing of APP and the effect of Presenilin (PS) mutations on APP processing bear directly on the increased production and extracellular deposition of A-beta peptides in AD. The processing of APP also generates two secreted forms of the protein, which may have neurotrophic or neurotoxic properties. Brains of AD patients exhibit decreased synaptic connectivity and selective and massive neuronal loss. We are interested in examining the mechanisms involved in this cell death. Previously, we showed that over-expression of FAD mutant forms of APP in stably transfected PC12 cells led to increased apoptotic cell death over several days and that over-expression of these same APPs by adenovirus-mediated gene transfer led to cell death of primary cortical neurons. More recently, we have been studying the effects of several A-beta peptides on human neuroblastoma and astrocytoma cells. Low concentrations of A-beta 1-42 kill SH-SY5Y cells by apoptosis as measured by an ELISA method while higher concentrations kill by necrosis. A-beta 1-40 is much less potent. A-beta 17-42, derived from APP by alpha- and gamma-secretase cutting of APP, dose-dependently kills these cells apoptotically. Early changes in gene expression after A-beta peptide treatment of these cells as monitored by cDNA array techniques include increases in apoptosis-related and oxidative stress-related genes and decreases in neurotrophic factor and growth-related proto-oncogenes. Treatment of astrocytoma cells with A-beta peptides leads to their activation and induction of MCP-1 gene transcription and protein synthesis. Initial studies suggest that A-beta 1-42 and 1-40 are activating these cells by different signal transduction pathways. These results provide a rationale for targeting particular elements of apoptotic and inflammatory pathways as well as APP processing for therapeutic intervention in AD.