Enhancer AAV-based genetic access and manipulation of specific brain cell types implicated in aging and Alzheimer's Disease - Project Summary / Abstract Alzheimer disease (AD) is the most prevalent type of age-progressive dementia, significantly affecting many individuals aged 65 and older. Recent studies have uncovered disease relevant cell types and neural circuits in the AD brains including humans and animal models and have identified molecular and functional alterations in specific neuronal and non-neuronal cell types in aging and AD. New investigations that target and manipulate specific brain cell types that are selectively affected by aging and AD progression could lead to major breakthroughs in understanding the cellular and neural mechanisms underlying aging and AD/ADRD. Genetically engineered viral vectors, including adeno-associated viruses (AAVs), are increasingly important neurobiological tools for cell-type-specific neural circuit mapping and genetic payload delivery. AAV vectors that incorporate gene regulatory elements in the viral genomes (enhancer AAVs) have been developed recently to target specific types of neurons and other brain cell types for neural circuit analysis in the mouse and non-human primate models. Of note, almost all of this work has been done in young adult animals, thus their performance and feasibility needs to be established before they can be properly used in aging and AD neuroscience research. In response to RFA-AG-25-024, we propose to leverage our recent technological advances to optimize and develop cell-type-selective enhancer AAVs for genetic access to diverse cell types and their related neural circuit analysis in multiple AD mouse models. Our guiding hypothesis is that brain cell-type-specific enhancers can be further optimized and developed to study disease relevant cell types and neural circuits in the brain environments of aging and AD animals. We will test our hypothesis that both vulnerable neuronal cell types and non-neuronal cell types including oligodendrocytes and vascular cells are critically implicated in AD pathogenesis and progression. In the R61 phase, we propose to screen newly developed enhancer AAV tools initially characterized in healthy young adults and determine their effectiveness in targeting AD-relevant specific brain cell types in vivo in older and degenerating brains. We will test and examine selected enhancer AAVs using different delivery methods and different titers, and we will establish an optimized standard operating protocol for enhancer AAV applications. In the R33 phase, we will use the optimized AAV-enhancer tools to monitor and manipulate brain cell types to understand how they contribute to the aging and disease processes and address their mechanistic implications, including an explicit test that Aβ triggers tauopathy in hippocampal cell types. The enhancer AAVs will express genetic payloads including fluorescent reporters, optogenetic and chemogenetic tools, calcium indicators designed to map and manipulate brain cell subtypes including neuronal and non-neuronal cell types. We will conduct neural circuit manipulation and mapping experiments including cell-type-specific viral tracing, in vivo structural and functional imaging and behavioral experiments to validate our proposed hypothesis.
