Induction and prevention of patterned neurodegeneration by amyloid precursor protein
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Alzheimer disease is characterized by the initial degeneration of a subset of cholinergic neurons. This pattern of degeneration can be triggered by overexpression of the amyloid precursor protein (APP) gene in humans. Interestingly, APP is widely expressed; it is therefore unclear why only certain cholinergic neurons are vulnerable to degeneration. We show that widespread expression of the human APP gene in the nematode Caenorhabditis elegans also induces age-dependent apoptotic degeneration of select cholinergic neurons. Identical results were obtained by overexpressing the orthologous worm gene apl-1. The pattern of neurodegeneration matched the cell-autonomous accumulation of APP protein in vulnerable neurons and could be activated cell-non-autonomously by distinct portions of APP. Vulnerability to APP accumulation and degeneration depended inversely on the level of ASK1/p38MAPK innate-immune signaling in cholinergic neurons. Lastly, we identify a compound P7C3 that blocks entrance to apoptosis caused by APP or immunodeficiency. Our results suggest that immunosenescence sculpts the cellular pattern of neurodegeneration by APP.