Temporal Proteomics Links the APP London Mutation to Early Cholesterol Remodeling Cell Programs in Human Neurons

A recent study unveils how familial Alzheimer's disease (AD) mutations in amyloid precursor protein (APP) impact early neuronal protein and lipid homeostasis. Isogenic KOLF2.1J iPSC-derived neurons were engineered with a heterozygous or homozygous APP-London mutation (V717I) for a comprehensive proteomic analysis. The results showed that maturation primarily drove proteomic variation, while genotype-dependent effects were more pronounced in homozygous APP-London neurons.

At four weeks, homozygous APP-London neurons displayed higher APP levels and increased alpha-CTF signal via immunoblot analysis. However, the ratio of alpha-CTF to FL-APP did not differ significantly from control neurons, suggesting an accumulation of APP-derived species. The proteomic remodeling in APP-London mutants primarily affected synaptic, endosomal, and calcium signaling pathways.

Remarkably, homozygous APP-London neurons exhibited a distinct buildup of cholesterol-biosynthetic enzymes and altered cholesterol transporter abundance. These neurons also showed increased free/total cellular cholesterol levels without significant changes in bulk cellular cholesterol or induction of SREBP2 target transcripts. Pharmacological intervention in cholesterol metabolism affected A beta 40 and Abeta 42 secretion in a compound-specific manner, but had minimal impact on overall cellular cholesterol levels.

The study identified SYT4 as a potential gamma-secretase target or associated factor, warranting further investigation. The findings highlight cholesterol dyshomeostasis as an early metabolic phenotype in neurons carrying the APP-London mutation, expanding the molecular phenotype beyond altered A beta secretion.