ApoE, lipid and immune mechanisms of human neurons and glia

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Abstract There is a significant knowledge gap for how apolipoprotein E (APOE) function can modulate cellular responses to lipid perturbations and inflammatory mechanisms in the neuron and glia dependent pathophysiology seen in Lewy body dementia (LBD), Parkinson’s disease (PD), and Alzheimer’s disease (AD). This project will reveal how APOE can mediate neuronal-glia interactions in their combined responses to lipid and inflammatory processes. Appropriate lipid transfer between neurons and glia via lipid transporters such as apolipoproteins, is essential for maintaining metabolic and structural integrity of neurons, with dysfunction leading to synaptic and cellular damage. APOE facilitates lipid transport between cells and is also involved in cellular responses to inflammation. We hypothesize that APOE is a primary point of convergence for mediating neuronal and glial responses to lipid accumulation and inflammation in the brain in aging and neurodegenerative diseases, and that alterations in APOE function will modulate downstream pathophysiological mechanisms leading to degeneration. Using our advanced and refined in vitro platform of human induced pluripotent stem cell (iPSC) derived neurons, astrocytes and microglia, this proposal addresses new questions of how APOE modulates neuron-glia mechanisms induced by elevated glycolipids, cholesterol and inflammatory processes, and how such mechanisms are key determinants in the pathophysiology that leads to LBD, PD and late-onset AD. To test this hypothesis, we have 2 Specific Aims: Specific Aim 1 uses APOE3/3, APOE4/4, APOE2/2 and APOEKO human neurons, astrocytes, microglia and neuron-glia co-cultures, under conditions of elevated glycolipids and cholesterol, achieved through pharmacological inhibition of glucocerebrosidase and NPC1 pathways. APOE isoform specific function is also examined using recombinant APOE isoforms. Experiments will measure adaptive and pathophysiological cellular responses of lipid regulation and transport, structural damage to synapses and neurons, and readouts of cellular function. Specific Aim 2 uses the APOE iPSC neuron-glia platform to determine how APOE modulates neuron-glia pathophysiological responses to inflammatory stimuli, and interactions of APOE with the classical complement cascade. Experiments will determine APOE-dependent neuron, microglia and astrocyte responses to viral- and bacterial-like inflammation induced by Poly(I:C) and LPS, on inflammatory pathway activation, APOE- complement pathway interactions, lipid transport, pre-degenerative changes, and cellular dysfunction. Clinical data shows that lipid dyshomeostasis and inflammation can significantly contribute to the etiology and onset of age-related neurodegenerative disorders. The proposed experiments will provide critical neuronal and glial mechanistic data on how APOE can regulate such lipid and inflammatory disturbances.