AD Brain Neuronal Types Accumulating PIB-Binding Abeta

Alzheimer’s disease (AD) is a uniquely human disorder. The PET imaging ligand Pittsburgh Compound B (PIB; 11C-6-OH-BTA1), used by clinicians to detect Abeta amyloid pathology in living patients early in the disease before cognitive deficits are measureable, binds in strikingly higher amounts to human AD brain Abeta than to the Abeta in natural or genetic animal models of AD pathology. The cellular and molecular basis for this difference is completely unknown. We hypothesize that these differences between humans and animal models are critical for disease manifestation. Current animal models of AD, including primates, inadequately recapitulate the full extent of the human disease, in particular lacking the later stages in which significant neuronal death and dementia occur. Defining the specific differences between humans and animal models such as this exceptional difference in PIB binding has the potential to drive the improvement of current animal models which will expedite understanding of disease mechanisms. Testing of therapeutic strategies in better representative animal models will also be more likely to successfully translate to humans. We find that the native AD brain PIB binding site copurifies with a subpopulation of synaptosomes, and is separable and distinct from the bulk of Abeta pathology in the AD brain. In the proposed work we will use the high affinity fluorescent PIB analog, CN-PIB, to specifically label the synaptosome subpopulation of interest in human autopsy brain and in the APP-PS1 knock in mouse model of Abeta pathology. This fluorescent marker in combination with antibodies to other key components will enable us to use flow cytometry to quantitatively analyze on a particle-by particle basis the presence and co-localization of markers of neuronal type and the amounts of those components from human autopsy brain and mouse model brain. Flow sorting cytometry will then be used to isolate specific synaptosomes and/or components with desired markers for verification by other techniques. By identifying the proteins in the flow sorted CN-PIB-binding synaptosomes using highly sensitive mass spectroscopic techniques and proteomic analysis we will determine the type of neuron that those synaptosomes were derived from in humans and in mouse models of AD. This information will allow us to trace the PIB-binding sites back to their origin in specific synaptosome populations to identify the neuronal population(s) involved in early disease/pathology stages and ultimately to determine the molecular nature of the disruption of the human synaptic biology and how it differs from the mouse model.