Project Summary/Abstract:
Alzheimer’s disease (AD) is a devastating neurodegenerative disease with no cure. It is characterized by ß-
amyloid (Aß)-containing senile plaques and tau-containing neurofibrillary tangles in the brain. Among many
mechanisms contributing to AD, excessive deposition of toxic Aß peptides is considered to play a key role.
Recent studies have demonstrated that Aß 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 Aß42
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 Aß
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 Aß deposition enhances astrocytic exocytosis of ATP, and chronic elevation of
astrocyte-derived ATP further induces neuroinflammation, impairs Aß 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 Aß 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 Aß deposition. The reduced Aß deposition could be due to decreased production
or increased clearance. To this end, the relative contents of APP products, including soluble APPa, Aß40, and
Aß42 will be quantified to assess the preference of Aß production. In addition, Aß-associated astrocytes and
microglia will be quantified as an indicator of glial-dependent Aß 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 Aß 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.