G-quadruplex DNA in senescence of the neurovascular unit

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Project Summary The neurovascular unit (NVU) is a functional structure that consists of endothelial cells, surrounded by an extracellular matrix, neurons, astrocytes, and pericytes. The NVU enables regulation of regional cerebral blood flow and nutrient delivery to the brain tissue. With aging, a structural weakening of the NVU occurs, which is also associated with inflammatory signaling and transport deficiencies. Critically, it is not clear how neurons, astrocytes, pericytes, and endothelial cells undergo senescence in the NVU, and whether there are differences in senescence pathways between healthy NVU aging and NVU in Alzheimer's diseases (AD). The G-quadruplex (G4) is a non-canonical DNA secondary structure formed by four DNA strands containing multiple runs of guanines. G4s play important roles in DNA recombination, replication, and regulation of transcription. In our data, we demonstrated that brain samples from aged mice contain more G4s than that of young mice. We showed that mice treated with a small-molecule G4 stabilizer develop cognitive impairment and accelerated brain aging. Using a heterochronic parabiosis mouse model, we also showed that the levels of G4s are decreased in the brain of old parabiont, compared to the age-matched iso-parabiotic mice, implicating presence of rejuvenating factors that can reverse the elevation of G4s with aging. The effect of the old parabiont on the young partner is more pronounced (more G4s in the young), suggesting a strong negative influence of aging factors. Importantly, in a mouse model of AD, we demonstrated that G4s are stabilized in the brains, well before the deposition of amyloid occurs. We hypothesize that these converging lines of evidence point at а mechanism of senescence. Thus, the primary objective of the proposed studies is to investigate G4-associated cellular senescence in the NVU, in aging and AD. In Aim 1, we will compare G4s across cell types in the NVU. In Aim 2, we will determine whether G4s preferentially accumulate in the NVUs of brain regions most vulnerable to neurodegeneration. In Aim 3, we will investigate how a peripheral factor, CXCL10, contributes to NVU's G4 senescence. G4s might be a novel pathway that can be targeted to mitigate the detrimental effects of cellular senescence in the brain.