Isoform-dependent lysosomal degradation and internalization of Apolipoprotein E requires autophagy proteins

The human Apolipoprotein E4 isoform (APOE4) is the strongest genetic risk factor for late-onset Alzheimer's disease (AD), and lysosomal dysfunction has been implicated in AD pathogenesis. We found in cells stably expressing each APOE isoform that APOE4 increases lysosomal trafficking, accumulates in enlarged lysosomes and late endosomes, alters autophagic flux and the abundance of autophagy proteins and lipid droplets, and alters the proteomic contents of lysosomes following internalization. We investigated APOE-related lysosomal trafficking further in cell culture, and found that APOE from the post-golgi compartment is degraded by autophagy. We found that this autophagic process requires the lysosomal membrane protein LAMP2 in immortalized neuron-like and hepatic cells and in mouse brain tissue. Several macroautophagy-associated proteins were also required for autophagic degradation and internalization of APOE in hepatic cells. The dysregulated autophagic flux and lysosomal trafficking of APOE4 that we observed suggest a possible novel mechanism that may contribute to AD pathogenesis.

Cadmium exposure modulates the gut-liver axis in an Alzheimer’s disease mouse model

The human Apolipoprotein E4 (ApoE4) variant is the strongest known genetic risk factor for Alzheimer’s disease (AD). Cadmium (Cd) has been shown to impair learning and memory at a greater extent in humanized ApoE4 knock-in (ApoE4-KI) mice as compared to ApoE3 (common allele)-KI mice. Here, we determined how cadmium interacts with ApoE4 gene variants to modify the gut-liver axis. Large intestinal content bacterial 16S rDNA sequencing, serum lipid metabolomics, and hepatic transcriptomics were analyzed in ApoE3- and ApoE4-KI mice orally exposed to vehicle, a low dose, or a high dose of Cd in drinking water. ApoE4-KI males had the most prominent changes in their gut microbiota, as well as a predicted down-regulation of many essential microbial pathways involved in nutrient and energy homeostasis. In the host liver, cadmium-exposed ApoE4-KI males had the most differentially regulated pathways; specifically, there was enrichment in several pathways involved in platelet activation and drug metabolism. In conclusion, Cd exposure profoundly modified the gut-liver axis in the most susceptible mouse strain to neurological damage namely the ApoE4-KI males, evidenced by an increase in microbial AD biomarkers, reduction in energy supply-related pathways in gut and blood, and an increase in hepatic pathways involved in inflammation and xenobiotic biotransformation.

A human apolipoprotein L with detergent-like activity kills intracellular pathogens

Activation of cell-autonomous defense by the immune cytokine interferon-γ (IFN-γ) is critical to the control of life-threatening infections in humans. IFN-γ induces the expression of hundreds of host proteins in all nucleated cells and tissues, yet many of these proteins remain uncharacterized. We screened 19,050 human genes by CRISPR-Cas9 mutagenesis and identified IFN-γ–induced apolipoprotein L3 (APOL3) as a potent bactericidal agent protecting multiple non–immune barrier cell types against infection. Canonical apolipoproteins typically solubilize mammalian lipids for extracellular transport; APOL3 instead targeted cytosol-invasive bacteria to dissolve their anionic membranes into human-bacterial lipoprotein nanodiscs detected by native mass spectrometry and visualized by single-particle cryo–electron microscopy. Thus, humans have harnessed the detergent-like properties of extracellular apolipoproteins to fashion an intracellular lysin, thereby endowing resident nonimmune cells with a mechanism to achieve sterilizing immunity.