Lipid transport is integral to lipid metabolism and stress response in the central nervous system. Lipoproteins are the major intercellular lipid carrier between neurons and glia. The lipid composition, trafficking, and metabolic fate of lipoproteins are largely dependent on the associated apolipoproteins. Disrupted function of apolipoproteins result in neurodegenerative phenotypes in animal models of neurodegeneration. Furthermore, allelic variation of the Apolipoprotein E (APOE) gene is the major risk factor of Alzheimer's Disease (AD). Glial cells such as astrocytes and microglia are the major cell types that process and secret ApoE in the nervous system. Glia also serve a protective role by mitigating neuronal oxidative stress, a common hallmark of AD and other neurodegenerative diseases. While it is well established that apolipoproteins play critical roles in lipid metabolism, our understanding of apolipoprotein transport in the nervous system is still limited. In addition, whether glial cells couple oxidative stress response with apolipoprotein trafficking remains to be tested. Since intracellular vesicular compartments are required for the trafficking of apolipoproteins, we hypothesize that endolysosomal proteins functionally interact with ApoE in brain. By examining the expression profile of putative endolysosomal genes, we identify Tweety Homolog 1 (TTYH1) that co-expresses with APOE in human brain. Preliminary studies performed in mammalian cells and Drosophila mutant of tty, homolog of TTYH1, suggest that tty and TTYH1 are required for the secretion of apolipoproteins, such as ApoD and ApoE, from glia and regulating oxidative stress in the nervous system. tty mutant flies show shortened lifespan and locomotor phenotypes. Our central hypothesis is that tty and TTYH1 regulate apolipoprotein trafficking to mitigate oxidative stress in glial cells. In this proposal, we aim to address the roles of tty and TTYH1 in: 1) the secretion of apolipoprotein from glia to circulation; and 2) mitigating glial oxidative stress via apolipoprotein secretion. Our long-term goal is to delineate specific pathway that regulate ApoE/D processing and secretion in glial cells and reveal new therapeutic targets for AD and related dementias.
APOE genotype is the major genetic risk factor for Alzheimer's disease. Our understanding of ApoE trafficking in the central nervous system remains limited. This project aims to define the role of TTYH1, a gene highly co- expressed with APOE in human brain, and its homolog in regulating the secretion of ApoE in glial cells.
