Effects of ApoE-enhancing Compounds on Alzheimers Disease Phenotypes In Vivo

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PROJECT SUMMARY Apolipoprotein E (apoE), a cholesterol-transporting apolipoprotein, is critically involved in the pathophysiology of a number of human disorders, including cardiovascular diseases, ischemia and neurodegenerative diseases. Most notably, among the common allele variants of the APOE gene (APOE2, APOE3 and APOE4), the APOE4 allele (encoding apoE4 isoform) underlies the single strongest risk factor for late-onset Alzheimer’s disease (AD). ApoE regulates the clearance, aggregation, and deposition of amyloid-β (Aβ) in an isoform-dependent manner and also regulates other AD-relevant brain functions such as neuroinflammation and synaptic plasticity. ApoE is mainly produced and secreted from astrocytes in the brain. It has been postulated that an increase in the levels of apoE (especially the apoE3 isoform present in the majority of the human population) leads to decreased amyloid levels. Therefore, it is conceivable that an increase of apoE may furnish therapeutic benefits for AD. The idea of pharmacological enhancement of apoE has been tested using several nuclear receptor agonists, such as bexarotene and T0901317(retinoid X receptor (RXR) and liver X receptor (LXR) agonist, respectively). Since these compounds induce a number of genes other than apoE (such as ABCA1) which have widespread physiological effects, it is difficult to pin-point the exact contribution of apoE elevation in AD-associated phenotypic changes in the brain. To this end, we have conducted high throughput screening (HTS) in order to identify novel small molecules that can enhance apoE production in human primary astrocytes. We have identified a number of small molecule hits that can increase apoE levels via previously unknown mechanisms, including ones promoting apoE secretion without co-inducing ABCA1. Using these compounds as chemical tools, we will first confirm pharmacological activities of the identified apoE modulators in vivo and further test to discover compound(s) that can affect AD-like phenotypes in mouse models of AD. Thus, by using physiologically relevant brain cells for HTS, our proposed studies will help not only to establish translational significance of pharmacological modulation of apoE levels in the brain, but also to understand regulatory mechanisms of brain apoE levels which will provide broad translational significance on other apoE-linked human disease pathophysiology. Successful completion of our proposed studies will also lead to the identification of new tool compounds that modulate apoE secretion through previously unknown mechanisms of action in vivo, or that are ideal for further drug discovery efforts.