Oei, J. H. | bioRxiv Science

bioRxiv2025

TOMM40 suppression promotes neuronal cholesterol imbalance and molecular and behavioral phenotypes of Alzheimer's disease

INTRODUCTIONWhile the APOE4 allele is a major risk factor for Alzheimers disease (AD), the role of TOMM40--an adjacent gene involved in mitochondrial protein import--is not known. METHODSMice, human iPSC-derived neurons (iNeurons), and human brain tissue were used for study of animal cognition, cholesterol metabolism, mitochondrial function, and gene expression. RESULTSTOMM40 knockdown (KD) impaired memory in mice and increased cholesterol and A{beta} 42 in mouse brains and human iNeurons. KD disrupted mitochondria-endoplasmic reticulum contact sites (MERCs), causing mitochondrial dysfunction and promoting reactive oxygen species that led to activation of LXRB (NR1H2), upregulation of APOE and LDLR. and increased cellular cholesterol and A{beta} 42 independent of APOE4. Human brain transcriptomics showed reduced TOMM40 expression that correlated with cholesterol regulatory gene expression, amyloid burden, and clinical AD diagnosis. DISCUSSIONTOMM40 is a novel mediator of AD pathology through dual effects on MERCs that regulate cholesterol homeostasis and mitochondrial function. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=163 SRC="FIGDIR/small/685963v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@e3e3e2org.highwire.dtl.DTLVardef@1861f67org.highwire.dtl.DTLVardef@77a813org.highwire.dtl.DTLVardef@1bb9a83_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2024

TOMM40 regulates hepatocellular and plasma lipid metabolism via an LXR-dependent pathway

The gene encoding TOMM40 (Transporter of Outer Mitochondrial Membrane 40) is adjacent to that encoding APOE, which has a central role in lipid and lipoprotein metabolism. Human genetic variants near APOE and TOMM40 are strongly associated with plasma lipid levels, but a specific role for TOMM40 in lipid metabolism has not been established. Investigating this, we show that suppression of TOMM40 in human hepatoma cells upregulates expression of APOE and LDLR in part via activation of LXRB (NR1H2) by oxysterols, with consequent increased uptake of VLDL and LDL. This is in part due to disruption of mitochondria-endoplasmic reticulum contact sites, with resulting accrual of reactive oxygen species and non-enzymatically derived oxysterols. With TOMM40 knockdown, cellular triglyceride and lipid droplet content are increased, effects attributable in part to receptor-mediated VLDL uptake, since lipid staining is significantly reduced by concomitant suppression of either LDLR or APOE. In contrast, cellular cholesterol content is reduced due to LXRB-mediated upregulation of the ABCA1 transporter as well as increased production and secretion of oxysterol-derived cholic acid. Consistent with the findings in hepatoma cells, in vivo knockdown of TOMM40 in mice results in significant reductions of plasma triglyceride and cholesterol concentrations, reduced hepatic cholesterol and increased triglyceride content, and accumulation of lipid droplets leading to development of steatosis. These findings demonstrate a role for TOMM40 in regulating hepatic lipid and plasma lipoprotein levels and identify mechanisms linking mitochondrial function with lipid metabolism. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=132 SRC="FIGDIR/small/600910v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@17b0c8forg.highwire.dtl.DTLVardef@17599aaorg.highwire.dtl.DTLVardef@1bb6ab2org.highwire.dtl.DTLVardef@15a035f_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗