Role of TTYH1 in mobilizing lipids and ApoE in glia: Implications for brain aging and neurodegeneration

PROJECT SUMMARY Lipids occupy over half of the dry weight of human brain. Brain cells rely on lipid metabolism to meet energy needs, perform signaling functions, and regulate membrane integrity and dynamics. Alterations in lipidomic profiles have been observed in aging brains and in neurodegenerative diseases such as Alzheimer’s disease (AD) and related dementia (ADRD), suggesting that reprogramed lipid metabolic pathways may be involved in disease pathogenesis. Notably, APOE and other lipid metabolism related genes have been associated with late-onset AD. Despite these observations, how aberrant metabolism of certain lipid classes mechanistically contribute to brain cell malfunction remains largely undefined. We sought to identify molecular pathways pertinent to brain lipid metabolism by utilizing approaches that combine molecular genetics and omics. Our transcriptomic analysis identified Tweety Homolog 1 (TTYH1) whose expression in human brain highly correlates with APOE. Such correlation between TTYH1 and APOE is lost in astrocytes of AD patients. Using human primary astrocyte and Drosophila model, we found that TTYH1 and its fly ortholog are required for ApoE secretion. Cell biology experiments further suggest that TTYH1 and its ortholog are required for autophagy and lipid droplet (LD) breakdown in glia. Lipidomic analyses of drosophila brains and human astrocytes deficient in TTYH1 orthologs revealed altered phospholipid abundances indicative of elevated cytosolic phospholipase A2 (cPLA2) activity. These preliminary findings inform our overarching hypothesis that TTYH1 is essential for a novel pathway connecting glial LD breakdown to lipoprotein secretion. In aim 1, we will test if cPLA2-activating ceramide metabolites regulates LD breakdown in glia, and define the function of TTYH1 in this process. Aim 2 will elucidate the mechanism of how TTYH1 regulates lipoprotein secretion in astrocytes. The significance of TTYH1-mediated lipid mobilization in brain aging and ADRD will be evaluated in Aim 3. We will assess the functional outcomes of perturbing TTYH1 ortholog in drosophila models of aging and ADRD. We will also examine the role of glial TTYH1 on neuronal homeostasis using coculture of brain cells derived from Ttyh1 conditional knockout mice. In summary, the project will integrate molecular genetics and lipidomics to illuminate a novel lipid metabolic pathway that hinges on TTYH1 in brain aging and ADRD. Findings from this project will aid in defining whether TTYH1 and its associated molecular players can serve as therapeutic targets for treating neurodegeneration.