SUMMARY/ABSTRACT Type 1 diabetes (T1D) is an autoimmune disease characterized by the destruction of the insulin producing ? cells. The diabetogenic response is complex influenced by genetic and environmental factors, which promote the breakdown of peripheral immunoregulation. Ill-defined properties intrinsic to ? cells are also believed to play a key role in T1D. ? cell reactivity to autoimmune and environmental insults, growth factors and nutrients for instance, influence loss of ? cell mass and/or function. Defining the pathways and mechanisms regulating these ? cell responses is important for the development of effective T1D immunotherapies and ? cell replacement approaches such as islet transplantation. This R21 application is based on our novel observation that NOD mice deficient in the AIM2 inflammasome molecule remain diabetes-free. AIM2 is a cytoplasmic immune sensor that is typically associated with host defense. Upon binding double stranded DNA from a microbial pathogen, AIM2 drives assembly of an inflammasome complex leading to production of proinflammatory IL-1? and IL-18 as well as pyroptosis- mediated cell death. Recent studies, however, have demonstrated that AIM2 can serve a regulatory function outside of host defense via a nonconical pathway that is independent of inflammasome activation. We find that the lack of diabetes in AIM2-deficient NOD mice is also independent of inflammasome activation. Furthermore, evidence suggests that AIM2 deficiency reduces ? cell sensitivity to autoimmune- mediated destruction while enhancing ? cell replication and function. We hypothesize that AIM2 functions as a ?thermostat? regulating the strength of responses to stress- and growth-inducing factors that impact ? cell survival, expansion and/or function. The overall goal of this proposal is 2-fold: 1) establish that AIM2 function is intrinsic to ? cells and affects T1D progression, and 2) begin to define the role of AIM2 in regulating ? cell reactivity to immunological insults and homeostasis. With this in mind, Specific Aim 1 will determine if AIM2 directly regulates ? cell sensitivity to cytokine and cell-contact-driven destruction, and in turn the development of overt diabetes in NOD mice. Experiments will include testing if an AIM2 variant expressed by NOD mice enhances ? cell destruction. Specific Aim 2 will define a role for AIM2 in ? cell homeostasis. Here we will determine if AIM2 regulates signaling events that stimulate ? cell replication. Together this work will establish a novel regulatory pathway in which AIM2 controls ? cell sensitivity to various immune stressors and factors that impact ? cell loss and function, and T1D progression. These findings will set the stage for future efforts to further define mechanisms by which AIM2 regulates ? cell reactivity, as well as exploit AIM2 for the purpose of T1D immunotherapy and ? cell replacement.