Project Summary Aging is characterized by a general decline in overall health and a gradual deterioration across multiple organ systems. However, our understanding of the aging process and whether we can improve health span remains a topic of active research. One of the hallmarks of aging is cellular senescence, a stress response that limits the propagation of damaged cells by causing irreversible cell cycle arrest. The DNA damage response is one of the key events leading to senescence. Cells in early senescence show increased satellite transcription and centromere instability and dysmorphism, known as the senescence-associated distension of satellites (SADS). Cyclic GMP-AMP synthase (cGAS) is a cytosolic innate immune sensor that recognizes and responds to microbial and self-DNA. Cytoplasmic cGAS is essential for the establishment of senescence and the secretion of inflammatory mediators characteristic of senescence. However, little is known of cGAS deposition and function in the nucleus. Nuclear cGAS has been reported to inhibit the DNA Damage Response (DDR) via homologous recombination (HR) in the nucleus and to be enriched at repetitive sequences such as centromeres and long interspersed nuclear element (LINE) DNA repeats. Despite these recent findings, the question remains whether cGAS contributes to senescence entry by modulating HR repair and whether cGAS concentration at centromeres and LINEs plays a role in the formation of SADS in early senescence. To answer these questions, I propose the following two aims: Aim 1 will determine whether cGAS inhibition of the DDR contributes to cell entry into senescence. Aim 2 will determine whether cGAS plays a role in SADS formation in senescence. The findings of this project will provide mechanistic insight on the effect of nuclear cGAS in the DDR and centromere stability, and its role in the establishment of senescence. Advancing our knowledge of nuclear cGAS can further current efforts to develop inhibitors of cGAS as potential anti-inflammatory or anti-aging therapy as strategies that extend healthy lifespan. This proposal will be the first to examine the relationship between nuclear cGAS and senescence using cutting edge technology in imaging and unique expertise in its influence at repetitive elements. One of this fellowship's training goals is to develop the repertoire of skills and body of knowledge for a successful career in the biology of aging research. The second goal is to gain experience in effectively communicating research in a variety of settings. To achieve these goals, completion of the proposed research, attending the Gordon Research Conference, presenting at national and international conferences, and my sponsor's mentoring will ensure the success of this training plan. Furthermore, this proposal will take place in the excellent environment of the interdisciplinary and supportive Molecular Biology, Cell Biology, and Biochemistry program at Brown University. Completion of this r...