Cellular senescence and Associated Lysosomal Dysfunction in Immune Aging

PROJECT SUMMARY/ABSTRACT Cellular senescence is an age-related process, affecting cells that have either divided too much or suffered significant damage to their DNA, which involves both a halt to further proliferation and the elaboration of a secretory program that activates the immune system, presumably to flag these cells for immune clearance.

Although this is likely an important mechanism to prevent cancer, it is also a two-edged sword. Growing evidence indicates that the accumulation of uncleared senescent cells drives a steady, age-dependent increase in basal inflammation, termed “inflammaging”, that causes cumulative damage in many tissues,

contributing to their age-related degeneration. Importantly, senescent cells can induce new senescence in adjacent normal cells via their secreted factors, suggesting that the accumulation of senescent cells is a self- amplifying, exponential process. The role of the immune system in this vicious cycle is complex and particularly

important, as based on available evidence it both mediates the inflammation-related destruction and may contribute to the vicious cycle via senescence within the immune system itself. T cells in the human immune system can be very long-lived, and have the ability to infiltrate almost any tissue and cause destruction in various ways, but the role of senescence within the T cell repertoire is still

poorly understood. Several recently developed flow cytometry-based assays can readily measure in blood- derived immune cells the lysosomal dysfunction known to be strongly associated with cellular senescence in other cell types, but it is not yet clear if that means these cells are truly senescent. Nonetheless, such

lysosomal stress may still be indicative of potentially destructive cellular phenotypes, based on our own preliminary data and other published studies. This matters because the lysosomal dysfunction, if it is causative of these destructive properties, can be targeted by a variety of available interventions that may provide benefit

regardless of whether or not the pathogenic cells affected are canonically senescent. Conversely, if the cells in question are truly senescent, other classes of drugs (i.e. senolytics, senomorphics) may induce their clearance or reverse their pathogenicity. Understanding how these cellular phenotypes arise in the T cell repertoire, how

they can be detected in blood samples, and how they may be related to immune dysfunction in older individuals, is therefore an important undertaking for public health. This proposal seeks to advance these aims by bringing to bear a suite of state-of-the-art flow cytometry, proteomic, and gene expression profiling-based

techniques, combined with functional readouts, to definitively identify which lysosomally stressed T cells may have pathogenic potential, and to map their occurrence across a cohort of 120 young and old donors of both sexes. This work when completed will have generated a number of new diagnostic tools to detect specific

aging-related populations of T cells with potentially harmful properties, as well as having developed some early preclinical leads as to what classes of drugs may clear them or mitigate their pathogenicity.