<i>TOMM40</i> suppression promotes neuronal cholesterol imbalance and molecular and behavioral phenotypes of Alzheimer's disease

Abstract INTRODUCTION While the apolipoprotein E ( APOE ) ε4 allele is a major risk factor for Alzheimer's disease (AD), the role of translocase of outer mitochondrial membrane 40 ( TOMM40 )—an adjacent gene involved in mitochondrial protein import—is not known. METHODS Human brain tissue, human induced pluripotent stem cell–derived neurons (iNeurons), and mice were used for study of gene expression, cholesterol metabolism, mitochondrial function, and animal cognition. RESULTS Human brain transcriptomics showed reduced TOMM40 expression that correlated with cholesterol regulatory gene expression, amyloid burden, and clinical AD diagnosis. In human iNeurons, TOMM40 knockdown (KD) disrupted mitochondria–endoplasmic reticulum contact sites (MERCs), causing mitochondrial dysfunction and promoting reactive oxygen species that led to activation of liver X receptor beta (NR1H2), upregulation of APOE and low‐density lipoprotein receptor ( LDLR ), and increased cellular cholesterol and amyloid beta (Aβ)42 independent of APOE ε4. Consistently, Tomm40 KD in mice induced increased brain cholesterol, Aβ42 content, and impaired memory. DISCUSSION TOMM40 is a novel mediator of AD pathology through dual effects on MERCs that regulate cholesterol homeostasis and mitochondrial function.