Alzheimer's Disease (AD)-Like Pathology in Aged Monkeys after Infantile Exposure to Environmental Metal Lead (Pb): Evidence for a Developmental Origin and Environmental Link for AD

TLDR

Alzheimer’s disease’s sporadic nature suggests an environmental trigger, and rodent studies show that developmental lead exposure programs amyloid precursor protein and beta‑amyloid expression in later life. In 23‑year‑old monkeys exposed to lead as infants, AD‑related genes APP, BACE1, and Sp1 were up‑regulated, amyloid‑beta deposition was altered, DNA methyltransferase activity was reduced, and oxidative DNA damage increased, indicating that early lead exposure epigenetically primes the brain for Alzheimer‑like pathology.

Abstract

The sporadic nature of Alzheimer's disease (AD) argues for an environmental link that may drive AD pathogenesis; however, the triggering factors and the period of their action are unknown. Recent studies in rodents have shown that exposure to lead (Pb) during brain development predetermined the expression and regulation of the amyloid precursor protein (APP) and its amyloidogenic beta-amyloid (Abeta) product in old age. Here, we report that the expression of AD-related genes [APP, BACE1 (beta-site APP cleaving enzyme 1)] as well as their transcriptional regulator (Sp1) were elevated in aged (23-year-old) monkeys exposed to Pb as infants. Furthermore, developmental exposure to Pb altered the levels, characteristics, and intracellular distribution of Abeta staining and amyloid plaques in the frontal association cortex. These latent effects were accompanied by a decrease in DNA methyltransferase activity and higher levels of oxidative damage to DNA, indicating that epigenetic imprinting in early life influenced the expression of AD-related genes and promoted DNA damage and pathogenesis. These data suggest that AD pathogenesis is influenced by early life exposures and argue for both an environmental trigger and a developmental origin of AD.