Nutrient signaling and stem cell maintenance in aging epithelia

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DESCRIPTION (provided by applicant): The age-related decline in regenerative capacity of many tissues constitutes a poorly understood problem that limits human healthspan. As studies in vertebrate systems point to both stem cell (SC) autonomous and non- autonomous causes for this age-related decline, analyzing SC function in an in vivo context is required, preferentially i short-lived, genetically accessible model systems. In recent years, Dr. Jasper's lab has established the fly intestine as a model to explore somatic SC aging, and to identify interventions that modulate SCs to preserve tissue homeostasis and extend lifespan. The Drosophila posterior midgut epithelium is regenerated by intestinal SCs (ISCs), is experimentally accessible, and of sufficient complexity to model the regenerative activity of similar tissues in vertebrates. Studies in the fly midgut have not only discovered mechanisms that promote the age-related regenerative decline in this tissue, but have also established that improving ISC proliferative homeostasis extends lifespan. Dr. Kennedy's lab, in turn, has performed groundbreaking work on aging and progeroid diseases for many years, with a specific recent focus on nutrient-responsive signaling pathways in the control of aging in mice. Here, Dr. Jasper and Dr. Kennedy propose to combine the strength of the fly system with genetic studies in mice to uncover evolutionarily conserved mechanisms of SC aging. Specifically, it will be tested whether the control of SC maintenance by nutrient-responsive signaling, which the applicants have characterized in the ISC lineage, is conserved in the mouse tracheal epithelial SC (Basal Cell, BC) lineage. The BC lineage has significant similarity with the fly ISC lineage, and serves as an accessible model for insight into epithelial regeneration in vertebrates that is likely to impact a major disease of aging: chronic obstructive pulmonary disease (COPD). The proposed work will address the role of TSC/Tor signaling, a conserved regulator of lifespan, on SC maintenance in flies and mice. Based on preliminary results, the applicants propose a conserved role for the negative regulator of Tor, TSC1/2, in shielding somatic SCs from dietary fluctuations, thus preserving SC identity and regenerative capacity in aging tissues. This model will be tested using genetic and pharmacological approaches to perturb the Tor pathway and to assess SC maintenance and regenerative capacity in aging animals. The study, which includes genetic work in mice and flies, as well as pharmacological interventions with new TorC1-specific inhibitors, will be performed in close collaboration between the Kennedy and Jasper labs, making the multi-PI mechanism optimal. The TSC/Tor pathway has emerged as an evolutionarily conserved nutrient sensor that influences life- and healthspan. Characterizing the biological consequences of long-term Tor repression is critical to develop specific intervention protocols that can promote tissue homeostasis and maintain regenerative capacity. The proposed studies will seek to achieve this important goal.