Effects of DDT on Amyloid Precursor Protein Levels and Amyloid Beta Pathology: Mechanistic Links to Alzheimer's Disease Risk

BACKGROUND: The interaction of aging -related, genetic, and environmental factors is thought to contribute to the etiology of late -onset, sporadic Alzheimer's disease (AD). We previously reported that serum levels of p,p'-dichlorodiphenyldichloroethylene (DDE), a long-lasting metabolite of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT), were significantly elevated in patients with Al) and associated with the risk of AD diagnosis. However, the mechanism by which DDT may contribute to AD pathogenesis is unknown. OBJECTIVES: This study sought to assess effects of DDT exposure on the amyloid pathway in multiple in vitro and in viva models. METHODS: Cultured cells (SH-SY5Y and primary neurons), transgenic flies overexpressing amyloid beta (A11), and C57BL/6J and 3xTG-AD mice were treated with DDT to assess impacts on the amyloid pathway. Real time quantitative polymerase chain reaction, multiplex assay, western immunoblotting and immunohistochemical methods were used to assess the effects of DDT on amyloid precursor protein (APP) and other contributors to amyloid processing and deposition. RESULTS: Exposure to DDT revealed significantly higher APP mRNA and protein levels in immortalized and primary neurons, as well as in wild type and AD -models. This was accompanied by higher levels of secreted A beta in SH-SY5Y cells, an effect abolished by the sodium channel antagonist tetrodotoxin. Transgenic flies and 3xTG-AD mice had more Ali pathology following DDT exposure. Furthermore, loss of the synaptic markers synaptophysin and PSD95 were observed in the cortex of the brains of 3xTG-AD mice. DISCUSSION: Sporadic Alzheimer's disease risk involves contributions from genetic and environmental factors. Here, we used multiple model systems, including primary neurons, transgenic flies, and mice to demonstrate the effects of DDT on APP and its pathological product Ap. These data, combined with our previous epidemiological findings, provide a mechanistic framework by which DDT exposure may contribute to increased risk of AD by impacting the amyloid pathway.