Alzheimers disease pathology is characterized by depositions of -Amyloid (A) in senile plaques in the afflicted brain areas. Although A-toxicity is presumed to be a central component of disease pathology, the exact mechanism(s) of in vivo A toxicity is(are) still unclear. Morphological studies of postmortem Alzheimer's diseased brain consistently reveal abnormally increased autophagy in degenerating neurons. Recent work with an amyloid precursor protein (APP)-overexpressing mouse has demonstrated that APP, several APP-processing enzymes and the A40/42 peptides are enriched in autophagosomes. This suggests that autophagic vacuoles may be important subcellular sites of A production as well as possible targets of A toxicity. Research with huntingtin and -synuclein, other aggregate-prone proteins implicated in neurodegeneration, has demonstrated that autophagy may be a mechanism for the degradation of these proteins. Our lab has generated transgenic C. elegans lines that express A peptide in various tissues to examine the basic cellular mechanisms of A toxicity. In this model, increased autophagosomes are frequently associated with A-toxicity as assessed by electron microscopy. We have generated a transgenic C. elegans containing the GFP::LGG-1 translational fusion (from B. Levine) in the CL4176 (inducible muscle A) background. LGG-1 is a homologue of Atg8 (yeast) and LC3 (mammalian) proteins that are required for autophagy and localized to autophagosomes. When A is induced, both the expression of GFP::LGG-1 and its localization to autophagosomes is increased, confirming the induction of autophagy by A expression. In order to test the functional consequences of increased autophagy in this model, we examined the effects of RNAi-mediated knockdown of autophagy genes. Preliminary results suggest that RNAi against several autophagy genes, including
bec-1, delays paralysis induced by A toxicity. Furthermore, the induction of autophagy (as measured by the abundance of GFP::LGG-1 vesicles) is similarly suppressed by these RNAi treatments. Autophagy is fundamentally a membrane trafficking event responsible for delivering cytoplasmic cargo to the lysosome for degradation. Autophagy is not inherently a negative process, and in fact is implicated in survival during some stressful conditions. We are currently replicating our preliminary results, which suggest that autophagy contributes to cellular degeneration mediated by A toxicity. Future studies will be focused on determining the signaling events responsible for the induction of autophagy by A, as well as characterizing the components of autophagy that contribute to degeneration.