Mitochondrial Malfunction in T Cell Aging and Tissue Inflammation - PROJECT SUMMARY Advanced age renders humans susceptible to cancer, fatal infection, neurodegeneration and cardiovascular disease. Age-related immunodeficiency combines loss of protective immunity with gain in tissue inflammation, indicating the complex restructuring of the innate and adaptive immune system with age. An informative model system for immune aging is the autoimmune disease rheumatoid arthritis, in which T cells age prematurely by about 25 years and are key effector cells in tissue-destructive inflammation. In patients with rheumatoid arthritis, CD4+ T cells transition into pro-inflammatory effector cells due to defective mitochondria, resulting in poor ATP production, citric acid cycle reversal, and mitochondrial DNA seepage. In preliminary studies, we have discovered that mitochondrial malfunction is associated with the leakage of N-terminal formyl-methionine (f-Met) from the mitochondrial matrix, eliciting a strong innate immune response in surrounding macrophages and stromal cells. f-Met is the first amino acid in all bacterial and mitochondrial proteins and, as a bacterial motif, is a powerful danger-associated molecular pattern (DAMP) triggering innate immunity. CD4+ T cells from older individuals leak f-Met due to inappropriate opening of the mitochondrial permeability transition pore (mPTP), a high conductance channel that secures the containment of solutes in the mitochondrial matrix. We found that inappropriate pore opening and f-Met leakage have profound consequences for T cell differentiation and effector functions. Specifically, we have placed f-Met release across the inner mitochondrial membrane upstream of the T cell’s proteolytic machinery; with cytosolic f-Met minimizing lysosomal degradation and optimizing exosome formation. Essentially, leaky mitochondria turn f-Met-secreting older T cells into exosome superproducers. Here, we propose that the mitochondrial DAMP f-Met is a biomarker of T cell aging and a drugable target to mitigate immune aging in older populations. To pursue this hypothesis, we will map the molecular defects causing N-formyl-methionine leakage in CD4+ T cells of older individuals (Aim1), determine how cytosolic f-Met regulates lysosomal function and exosome generation (Aim2), and define the pro- inflammatory functions of f-Met-induced exosomes in T cell-macrophage and T cell-fibroblast interaction (Aim3). To leverage molecular understanding of mitochondrial abnormalities in aged T cells, we have assembled a series of targeted small molecule reagents that we will test for their ability to suppress and reverse pro- inflammatory T cell effector functions in vivo (Aim4). This proposal aims to define and manipulate biological processes underlying age-related mitochondrial failure with the goal to ameliorate or delay aging-induced tissue inflammation and develop molecular cues of mitochondrial aging into actionable biomarkers of immune aging.
