Astrocytic exocytosis of ATP in amyloid pathology and Alzheimer's disease

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Project Summary/Abstract: Alzheimer’s disease (AD) is a devastating neurodegenerative disease with no cure. It is characterized by β- amyloid (Aβ)-containing senile plaques and tau-containing neurofibrillary tangles in the brain. Among many mechanisms contributing to AD, excessive deposition of toxic Aβ peptides is considered to play a key role. Recent studies have demonstrated that Aβ deposition in the brain triggers robust morphological and transcriptomic changes in astrocytes. How these alterations of astrocyte functions may contribute to the development of AD remains unclear. The preliminary studies of the PI’s research group show that Aβ42 induces ATP release in cultured astrocytes. Further, loss of vesicular nucleotide transporter (Vnut), which is responsible of loading cytosolic ATP into the excretory lysosomes, in astrocytes dramatically reduces Aβ plaques by ~50% and improved cognitive function in 6-month-old female 5xFAD mice. These data strongly suggest that elimination of ATP exocytosis in astrocytes blocks the accumulation of amyloid plaques and alleviates the cognitive decline. With the strong support of these exciting preliminary data, the proposed research hypothesize that Aβ deposition enhances astrocytic exocytosis of ATP, and chronic elevation of astrocyte-derived ATP further induces neuroinflammation, impairs Aβ production and clearance, and exacerbates cognitive decline. The proposed research will address this central hypothesis in specific aims: Aim 1: To examine the dynamic interaction between astrocytic exocytosis of ATP and Aβ deposition. Briefly, microdialysis will be used to assess how extracellular ATP levels in the brain are altered when Vnut is deleted in astrocytes in response to Aβ deposition. The reduced Aβ deposition could be due to decreased production or increased clearance. To this end, the relative contents of APP products, including soluble APPα, Aβ40, and Aβ42 will be quantified to assess the preference of Aβ production. In addition, Aβ-associated astrocytes and microglia will be quantified as an indicator of glial-dependent Aβ clearance. Aim 2: To assess the contributions of the astrocytic exocytosis of ATP on neuroinflammation in mouse models of AD. Neuroinflammation in 5xFAD mice without astrocytic Vnut will be examined using immunoblotting, immunofluorescence, qPCR and ELISA, and compared to appropriate control mice. In addition, to explore additional contributing mechanisms, the transcriptomes of astrocytes of these mice will be analyzed using RNA Seq and bioinformatics. Throughout the project, all the data on neuroinflammation, the extracellular ATP levels, and Aβ deposition will be correlated with the learning and memory of the same mice at 6 and 12 months of age. With a novel genetic mouse model, the proposed research will provide valuable insight into the roles of astrocytes and purinergic signaling in AD. This will help generate key preliminary data to support a more in-depth investigation in a future R01 grant. In the long term, this line of research may reveal new therapeutic approaches to treat AD and possibly other neurodegenerative diseases, by targeting purinergic signaling.