Objective
The objective of this research project is to demonstrate that tTG2 plays a direct role in the etiology of T1D using a mouse model of diabetes and through complementary studies using human immune cells and islets. We will assess whether inhibition of tTG2 has the potential to prevent the loss of functional beta cells and investigate whether knockout of tTG2 improves the survival of transplanted iPSC-islets. These complementary lines of investigation validate tTG2 as a relevant biological axis in both the etiology and treatment of T1D, providing a means for eliminating key stress-related changes to impede the loss of insulin secretion and improving the survival and function of beta cell replacements.
Background Rationale
Type I diabetes is a disease in which the insulin-producing cells of the pancreas are recognized and destroyed by immune cells due to stress related changes to their behavior and inappropriate immune recognition due to changes in their characteristics. Recent studies demonstrate that cellular stress increases the activity of tTG2 and increases immune recognition of beta cells. The development of effective models to probe the importance of tTG2 in settings of spontaneous diabetes, newly developed in vitro co-culture methods using stem cell derived islets and human immune cells, advanced techniques to quantify autoantibodies and track autoreactive immune cells, and models to assess the survival of transplanted islets to model beta cell replacement therapy provide all of the neccesary tools to assess the therapeutic potential of blocking tTG2 activity to improve outcomes in T1D.
Description of Project
The Development of type 1 diabetes is caused by T cell mediated destruction of insulin producing beta cells. Stress in beta cells has been shown to activate enzymes that modify self-proteins and increase their immune recognition. One key enzyme, tissue transglutaminase (tTG2), has shown to be an important trigger of autoimmunity in Celiac disease and inflammatory bowel disease. For this reason, tTG2 inhibitors are under development to treat human autoimmune diseases. More recently, it has been shown that tTG2 activity is increased in stressed beta cells, generating modified proteins that can activate and expand autoreactive immune cells that release inflammatory cytokines and perpetuate beta cell destructions. Therefore, this project will evaluate tTG2 inhibition as a potential therapeutic target in T1D. We will first establish a role for tTG2 in T1D by comparing diabetes development and monitoring autoantibodies and autoreactive T cell responses in wild type versus tTG2 knockout mice. We will then test the effects of tTG2 inhibition in a mouse model of diabetes and through culture-based studies of human stem cell derived islets and immune cells. Finally, we will examine the effects of tTG2 inhibition and knockout in an islet transplant model. These findings would show that knocking out or inhibiting tTG2 delays immune mediated beta cell destruction and reduces T cell recognition of human islets. These key insights would provide motivation for engineering stem cell-derived beta cells with increased resilience under conditions of stress and for evaluating the efficacy of the commercially available tTG2 inhibitor for delaying diabetes progression and preserving residual insulin secretion in individuals with T1D.
Anticipated Outcome
We expect that loss of tTG2 activity – either through gene knockout or use of a small molecule inhibitor – will prevent stress related increases in immune recognition of beta cells, limit epitope spreading, and slow the progression of β cell damage and the incidence of diabetes. We further expect that loss of tTG2 activity will reduce in vitro immune recognition of step cell islets and will improve the survival and function of transplanted stem cell derived islets. The end result of this work will be new knowledge about the mechanisms that underlie the progression of type 1 diabetes and new methods for improving beta cell replacement strategies.
Relevance to T1D
Decreased beta cell function and elicitation of self-destructive immune responses through the activity of enzymes such as tTG2 are key contributors to the development and pathogenesis of Type 1 Diabetes. These changes accumulate over time, eventually destroying the insulin producing cells of the pancreas. In some subjects, the onset of diabetes can occur rapidly, necessitating a rapid and effective intervention. The proposed research would generate new knowledge about stress related changes that undermine beta cell function and increase immune destruction if pancreatic islets and validate potential therapeutic strategies that can be implemented to oppose these effects, thereby preventing loss of functional beta cells and improving the survival and function of replacement beta cells. The goal would be to translate these ideas into clinical practice, including strategies to halt disease progression in at risk individuals by inhibiting these pathways and to treat individuals with T1D by generating improved replacement stem cell islets to restore insulin secretion.