Comparison of normal aging with Alzheimer's Disease: cellular, synaptic, and vascular indices affecting brain plasticity and neurogenesis

Adult hippocampal neurogenesis (AHN) and angiogenesis occur together in the neurogenic niche of the hippocampus dentate gyrus (DG) and support cognitive functions and behavioral responses to stress in rodents. Connectivity between newborn and existing granule neurons is fundamental for these functions. We found that normally aging (NA) subjects into their eighth decade of life have a stable number of progenitor cells (NPCs) and immature neurons, but angiogenesis and neuroplasticity are decreased with aging and directly correlated with each other, suggesting that, even if AHN occurs in older adults, the vascular support and connectivity of newborn neurons might be reduced. Moreover, we do not know if more NPCs differentiate into glia in older individuals, as it happens in aging rodents. AHN is lower in Alzheimer’s Disease (AD), and if NPCs preferentially differentiate into glia or do not, divide, differentiate and mature efficiently, remains unknown. We investigated expression of Kruppel Like Factor 9 (Klf9), a transcription factor necessary for neurogenesis-dependent synaptic plasticity, and we found an age-associated decline in Klf9 expression. We further tested if the observed age-associated angiogenesis decline could be due to reduced expression of vascular endothelial growth factor receptor 2 (VEGFR2), which regulates both angiogenesis and AHN. Our pilot data show that number of intra- and extra- vascular cells expressing VEGFR2 are fewer with aging. Altered vascular and dendrite/spine plasticity could contribute to NA and AD, and isolating key molecular regulators could lead to designing new treatments for AD. Here we propose to assess hypothesis-generated molecular targets, and in a parallel project (1R01AG076949), we have proposed to perform, in the same 140 subjects and brain region, proteomics, single nucleus and spatial multiomics (RNA and ATAC) sequencing, using data driven approaches which could reveal unanticipated molecular underpinnings of brain aging and AD. The approach proposed here allows combined visualization of selected molecular targets at the single cell level, and detailed anatomical mapping of cell, capillary, dendrite and spine structure and connectivity. Our rigorous methods assure detailed clinical assessment, brain tissue quality, uniform tissue processing, use of toxicology and neuropathology, and strict inclusion/exclusion criteria. We will study hippocampi from NIMH, Columbia University Taub Institute Brain Bank (see letter), and the Columbia/NYSPI brain collection. We will assess aging effects in NA subjects (N=100, age 14-90 years, 57 males and 43 females), and will assess how NA differs from AD comparing NA subjects aged 60 and older with age- and sex-matched AD subjects (N=40, Braak stages 1 through 4). Aims are to quantify: (1) Neuronal and glial differentiation of NPCs. (2) Dendrites, spines and synapses, and their molecular regulators: 2a. Golgi- stained dendrites and spines; 2b. Neurofilament-immunoreactive dendrites; 2c. Spine and synaptic proteins spinophilin, SYN1 and PSD95; 2d. Klf9 mRNA. (3) Angiogenesis and VEGFR2. (4) Relationships between cellular and morphological data from Aims 1-3, and AD Braak stages, stress exposure, education level and sex.