Alzheimer?s disease (AD) is a devastating dementia, afflicting about 5.4 million individuals in the US alone. Its prevalence is rapidly rising due to increases in lifespan and the absence of even a single significant disease-modifying therapy. Genetic variants in the apolipoprotein E (ApoE) locus are associated with AD, as well as other chronic diseases and aging itself. In particular individuals with the ApoE2 allele are enriched among nonagenarians and centenarians in a range of genetic studies, whereas ApoE4 is associated with higher age-associated mortality. Similarly, the ApoE2 allele is protective for AD, whereas ApoE4 is the largest genetic risk factor. Of course, aging is the biggest risk for AD and it remains largely unknown how ApoE plays a role in connecting aging to AD. These findings alone warrant thorough analysis of how ApoE contributes to AD and/or aging, and specifically an analysis of the protective effects of ApoE2. By combining induced pluripotent stem cells (iPSC) and precise CRISPR/cas9 gene editing technology, it is now feasible to generate otherwise isogenic iPSC lines with ApoE alleles. We have made progress toward the generation of these lines and in this proposal will create iPSC lines with combinations of ApoE alleles, differentiate them into neurons and astrocytes, and assess cellular phenotypes associated with AD. We will compare and contrast the effects of ApoE2 and ApoE4, looking for specific mechanisms by which these alleles are protective or sensitizing to AD, respectively. In addition, we will seek to modify the severity of cellular phenotypes associated with neurodegeneration by modifying pathways linked to aging. Since we are working on human differentiated cells in culture, we have the capacity to interrogate several pathways linked to accelerated and delayed aging. This will be accomplished either (1) genetically, for example by expressing genes that accelerate or decelerate organismal aging such as progerin, a mutation in the LMNA gene associated with Hutchinson-Gilford progeria syndrome, or (2) pharmacologically, for example with rapamycin, a drug associated with longevity. The specific hypothesis is that by interrogating multiple aging-related pathways, we will define specific phenotypic interactions between individual pathways, ApoE2 or ApoE4 functions and AD phenotypes that can be assessed in differentiated cells. This unique approach offers the possibility of understanding how aging modifies AD risk at a mechanistic level, identifying potential prognostic and diagnostic markers, and developing and refining therapeutic targets for AD, as well as potentially other age- related cognitive disorders.
Genetic variants in the apolipoprotein E (ApoE) locus are associated with Alzheimer?s disease (AD) where ApoE4 is the largest risk factor with neurodegenerative effect while ApoE2 exhibits neuroprotection, however, how ApoE isoforms predispose to AD, or protect against it, is incompletely understood. By combining induced pluripotent stem cells (iPSC) and precise gene editing technology, it is now feasible to generate otherwise isogenic iPSC lines with ApoE alleles. In this proposal, we will assess cellular phenotypes associated with AD in neural cells derived from isogenic iPSC lines with combinations of ApoE alleles, and seek to modify the severity of cellular phenotypes associated with neurodegeneration by altering physiologic features of aging. Completion of this study will provide a comprehensive analysis of the effects of two known major risk factors for AD, aging and ApoE genotype. In turn, this will provide insight into a potential mechanisms underlying the protecting effects of ApoE2, as well as the underlying reasons why ApoE4 increases disease risk.
