Project Summary Vascular aging impacts all perfused tissues and organs. Senescent vascular smooth muscle cells (VSMC) accumulate in aging vessels, where the release of senescence-associated cytokines promotes chronic inflammation, atherosclerosis, and the generation of more senescent cells. Given their significant contributions to vascular pathology, senescent VSMC are now being viewed as a therapeutic target. However, treatments to eliminate, reverse, or prevent VSMC senescence cannot be developed without knowing the factors that drive senescence. New data from our laboratory suggests that one key factor in this process is nuclear interleukin 2 receptor a. Our preliminary data show that IL-2Ra localizes to the nucleus of quiescent VSMC but leaves the nucleus when VSMC are stimulated to proliferate. Senescent VSMC, which do not divide when stimulated, continue to express IL-2Ra in the nucleus when cultured under proliferative conditions. Nuclear localization of IL-2Ra may occur through the cytoplasmic tail, which contains a cluster of basic amino acids consistent with DNA binding and nuclear localization. This C terminal tail also contains two known phosphorylation sites. Treatment of VSMC with two different phosphatase inhibitors significantly increased nuclear localization of IL-2Ra. Based on these findings, we hypothesize that localization of IL-2Ra to the nucleus inhibits proliferation, and that irreversible localization of IL-2Ra to the nucleus promotes senescence. This hypothesis will be addressed by the following aims: Aim I: Define how IL-2Ra impacts VSMC proliferation and senescence. Aim II: Determine how the C terminus, and its phosphorylation, impacts intracellular localization of IL-2Ra and VSMC senescence. Aim III: Determine how IL-2Ra is retained in the nucleus of senescent VSMC. Results from this project will establish that nuclear IL-2Ra directly impacts senescence in VSMC. These findings will provide a strong rationale for future studies determining the mechanism by which nuclear IL-2Ra impacts cell division and senescence, how transport of IL-2Ra is regulated, and how the absence of IL-2Ra affects VSMC biology and pathology in vivo. In total, these future studies will define a new pathway for regulating cell division and senescence in VSMC and potentially other cells expressing IL-2Ra.