ER stress generates immunogenicity in human pancreatic β cells

Abstract

Abstract Type 1 diabetes (T1D) is an autoimmune disease in which autoreactive T cells target and destroy pancreatic islet β cells. The key events that break peripheral tolerance in patients genetically predisposed to autoimmunity remain poorly understood. Many physiological and environmental triggers associated with T1D cause endoplasmic reticulum (ER) stress, which may increase abnormal protein post-translational modification (PTM). We hypothesized that β cell ER stress generates neo-antigens that can activate autoreactive T cells in T1D. Chemical (Thapsigargin) induction of ER stress in human islets or insulinomas increased their recognition (135–360 fold) by human T cells known to preferentially recognize deamidated GAD65, as measured by IFNγ secretion. This increased immunogenicity was accompanied by increased activation of the PTM enzyme tissue transglutaminase 2 (Tgase2; 2 fold). We will confirm the role of this enzyme in ER stress-induced human β cell immunogenicity with shRNA. We are also working to validate this pathway as a therapeutic target as follows: First, we are measuring calcium dynamics to determine if cytosolic calcium is crucial to ER stress-dependent immunogenicity. Second, we are assessing whether other triggers of ER stress, such as cytokines and glucose, also generate GAD65 PTM in human β cells. β cell ER stress generated through a variety of sources may be an opportunity for therapeutic intervention to prevent the destruction of β cells. Our on-going work will define the ER stress-induced pathways and PTM that contribute to recognition of GAD65. These findings will also have implications for the recognition of other autoantigens and for the development of T1D.