Identification of senescent cell types

Senescent cells (SnCs) increase in tissues with age and are established to play a causal role in aging and age- related conditions/syndromes. SnCs confer their adverse effects, at least in part, through their senescence- associated secretory phenotype (SASP), which is pro-inflammatory. A particularly debilitating, deadly, and costly condition that plagues the elderly is susceptibility to severe morbidity and mortality upon infection. The recent SARS-CoV-2 pandemic illuminated this problem dramatically. Why are older COVID-19 patients at higher risk (>350X) of cytokine storm, multi-organ failure and death upon infection with SARS-CoV-2 compared to younger individuals? Similarly, why are the elderly more susceptible to progression to sepsis and acute respiratory distress syndrome upon infection? We hypothesize it is because of the increased SnC burden in the elderly with their inflammatory SASP that drives chronic sterile inflammation and dysregulates the innate and adaptive immune responses of older individuals with infection. We developed a novel experimental paradigm in which to test this hypothesis called normal microbial experience (NME). Specified pathogen-free (SPF) mice are exposed to pet store as a model of "community acquired infections." The pet store mice carry mouse hepatitis virus (MHV), a ß-coronavirus closely related to SARS-CoV-2. Young SPF survive NME, but old mice experience 100% mortality within two weeks. This is due to an increased inflammatory response in old mice compared to young upon NME exposure. Pharmacologic or genetic approaches to clear SnCs after NME reduced mortality of old mice by 50% and improved adaptive immunity against MHV. We found that in vitro and in vivo, SnCs hyper- respond to challenge with pathogen-associated molecular patterns compared to healthy cells, leading to increased expression of inflammatory cytokines/chemokines. Additionally, we found that senescent immune cells are particularly deleterious and able to drive secondary senescence and tissue damage through both gain-of function and loss-of function mechanisms. While provocative, there remains large gaps in knowledge, which if addressed offer completely novel approaches to improving immune function and preventing severe infections in the elderly. Here, we propose to identify the senescent immune and other SnC type(s) that impede resilience to pathogens in old mice and the mechanism(s) involved. To prove cause and effect and move towards translation, we propose in this Project to identify the key SnCs as possible therapeutic targets and optimize senotherapeutic drugs to improve the immune response in aged mice. To address the role of SnCs in driving immune dysfunction, the Specific Aims of Project 1 are: 1) To identify the SnCs that drive adverse outcomes and immune dysfunction upon exposure of aged mice to environmental microbes, viral infection, or LPS; 2) To determine if removal of SnCs is sufficient to prevent mortality and improve immune function upon exposure of mice to environmental pathogens, viral infection, or LPS; and 3) To optimize senotherapeutic strategies to improve the immune response of aged mice.