RAF2 promotes the autophagic degradation of the Amyloid-β peptide.

RAF2 promotes the autophagic degradation of the Amyloid- peptide. Yan Zhang¹, Diego Rincon-Limas¹, Pedro Fernandez-Funez^1,2. 1) Neurology, University of Florida, Gainesville, FL; 2) Neuroscience, University of Florida, Gainesville, FL.

Alzheimers disease (AD) is an incurable neurodegenerative disorder clinically characterized by progressive cognitive impairment. Both the Amyloid- (A) peptide and Tau are key pathological hallmarks of AD, but A42 seems to have a leading role in AD pathogenesis. To gain insight into the cellular mechanisms regulating A42 neurotoxicity, we performed a genetic screen using our fly model expressing human A42. The screen identified RING-associated factor 2 (RAF2) as a potent suppressors of A42 neurotoxicity in the eye. We also found that RAF2 suppresses A42 neurotoxicity in the mushroom bodies, suggesting that RAF2 protective activity is conserved in brain neurons. RAF2 also rescued the eye phenotype of APP; BACE, a more physiological model of AD, indicating that RAF2 targets mature, secreted A42. Interestingly, RAF2 co-expression reduces the levels of A42, suggesting the RAF2 promotes A42 degradation. RAF2 is a new protein with a zinc rfinger in its C-terminus, but its biological function is unknown at this time. To determine the molecular mechanisms mediating RAF2 neuroprotection, we cloned the full-length cDNA of RAF2 and three deletions constructs. Co-expression of these constructs demonstrated that SRS is the only critical domain for A42 neuroprotection. We also learned that both RAF2 and RAF2-SRS inhibit Notch signaling, suggesting that RAF2 interferes with vesicle trafficking. To support this, we found that RAF2 co-localizes with endo-lysosomal vesicles in S2 cells. Finally, overexpression of RAF2 in flies induced the accumulation of autophagosomes. These results led us to hypothesize that RAF2 exerts its protective activity by promoting the degradation of A42 contained in endocytic vesicles. In conclusion, we have identified a new protective mechanism against A42 that implicates the interaction of endocytic trafficking and autophagy. Since these pathways are highly conserved in humans, we propose that promoting RAF2 activity may results in neuroprotection in AD patients.