In Vitro and In Vivo Biology of Telomere Stress Induced Senescence

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PROJECT SUMMARY Senescent cells have been implicated as drivers of aging and age-associated diseases. Senescent cells have sustained some form of stress that causes irreversible cell-cycle arrest, and these cells avoid apoptosis. These cells have a hyper-metabolic phenotype and secrete cytokines and chemokines resulting in the senescence associated secretory phenotype (SASP). The SASP contains multiple inflammatory components which promotes tissue dysfunction. These observations have been the impetus to develop senolytic drugs. These drugs are designed to cause the selective apoptosis of senescent cells and several senolytics have already entered clinical trials for potential use in idiopathic pulmonary fibrosis, osteoarthritis, chronic diabetes, etc. Many of these senolytic drugs have been developed via a candidate approach where drugs that were initially developed for the treatment of cancer are repurposed for the clearance of senescent cells. These drugs, unfortunately, have both on-target and off-target dose-limiting side effects such as thrombocytopenia and trabecular bone loss. Therefore, there is a need to develop senolytic drugs that target a specific underlying vulnerability of senescent cells without affecting healthy cells. In this project, we have performed an unbiased CRISPR-based, whole genome synthetic lethality screen to identify genes when knocked out, are lethal in the setting of a cell that has undergone telomere-induced senescence yet are well-tolerated when knockout in the context of a healthy, non-senescent cell. Through this screen, we identified that genetic alterations in ER stress pathways are specific vulnerabilities of senescent cells. Specifically, the targets ER-resident proteins, PARP16 and BIP, which were identified in the CRISPR screen, modulate ER stress pathways. Therefore, we hypothesize that due to their high secretory burden, senescent cells are particularly vulnerable to alterations in ER stress pathways. We propose to investigate the following: (1) Identify and characterize the set of genes which when knocked out in senescent cells cause the specific death of these cells without affecting the function of healthy cells; (2) Understand whether senescent cells that undergo telomere induced senescence have higher levels of ER stress and whether alterations in these pathways affect the viability of senescent cells and the production of SASP components; (3) Understand whether telomere-induced senescence affects the function of post- mitotic cells such as cardiomyocytes and in turn, whether cardiomyocyte senescence affect heart function. This proposal will therefore lead to a better understanding of the unique molecular vulnerabilities of senescent cells and clarify the molecular underpinnings of how cells maintain a state of senescence. Successful completion of this proposal will provide a foundation for the development of senolytics to treat a variety of aging-associated diseases. Finally, this proposal will provide me with an outstanding platform to build my basic science and clinical thinking skills so that I can pursue a career as a physician scientist.