Apolioprotein E Receptor Biology and Neurodegeneration

The foundation of this proposal rests,upon several primary facts. First, the actions of apoE4, the primary Alzheimers disease (AD) risk factor, are likely to be mediated and modulated by apoE receptors. Within the brain, the principal apoE receptors are LDLR, LRP, apoER2 and VLDLR. Second, single nucleotide polymorphisms (SNP)s that mOdulate exon splicing efficiency are rapidly emerging as a previously underappreciated class of functional genetic variants. These facts lead us to hypothesize thatapoE receptor SNPs, especially those that modulate splicing, represent excellent candidates for AD association. The third underpinning of this proposal is compelling preliminary data supporting this hypothesis at each stage of the proposed specific aims, which include Specific Aim 1: Evaluate the role of RNA splicing in the generation of variant apoE receptors. We will elucidate the role of splicing in the generation of variant-apoE receptors and evaluate the level of the proteins encoded by these mRNA variants relative to full-length receptor family members and their proteolytic fragments. As novel apoE receptors are identified at the mRNA level and validated by protein expression, stable cell lines expressing these clones will be sent to Core B for disbibution to Projects 1, 3, and 4. Specific Aim 2: Identify genetic polymorphisms that modulate apoE receptor splicing or expression. We will identify ESE-modifying SNPs in silico, evaluate the association between these SNPs and apoE receptor splicing efficiency in vivo in human brain and in vitro in minigene - transfected cell splicing assays. Additionally, we will identifySNPs that modulate apoE receptor.expressiol) by using an unequal allele expression screening approach. Specific Aim 3. Incorporate functional SNPs into a H~PMAPbased, association study of apoE receptors and AD odds. In collaboration with Steven Younkin, we will perform association studies for these four apoE receptors. By identifying haplotypes and linked SNPs with AD, this aim will also create new investigative avenues for other project leaders. In summary, these studies are significant and innovative because they have strong relevance to our understanding of the possible mechanistic etiology of AD, potentially facilitating therapy, and to AD genetics, facilitating early diagnosis and treatment.