Objective
The objectives of the proposed research are:
Aim 1: To determine the impact of glucose metabolism on the interferon response of beta-cells. Using a novel genetic model system for the anti-viral response of beta cells, we will determine how glucose, glucose metabolism, and downstream molecular signaling impact the response of beta-cells to a virus-mimicking signal. These experiments will provide a mechanistic, molecular understanding of metabolic modulation of the early anti-viral response in beta-cells.
Aim 2: To define the basis for selective beta-cell sensitivity to double stranded RNA mimicking viral infection. Our preliminary findings indicate that, consistent with the clinical features of type 1 diabetes, beta-cells are more sensitive than other islet cell types to damage inflicted by double stranded RNA. This includes both a stronger interferon response mounted by beta-cells, and a more severe damage to beta-cells by inflammatory cells that infiltrate islets. The differential sensitivity to inflammation appears to be independent of the presence of auto-antigens and autoreactive lymphocytes, suggesting an intrinsic difference in cellular wiring that makes beta-cells particularly prone to inflammatory damage. We will perform experiments using mouse models and human islets to determine the molecular basis for the differential sensitivity of beta-cells compared with non-beta islet cells. These experiments will test the provocative idea that selective destruction of beta-cells can result from an intrinsic sensitivity of beta-cells to double stranded RNA-triggered inflammatory damage, independently of individual genetic makeup associated with autoimmunity.
Aim 3: To model preventive strategies based on targeting metabolism. We will perform mouse experiments with drugs that modulate glycemic burden on beta-cells, such as insulin, metformin, GLP1 mimetics and SGLT2 inhibitors, and will test the impact on the interferon response of beta-cells. Our studies will be designed to specifically identify drugs that prevent the interferon response of beta-cells, potentially suggesting a novel entity for targeting to prevent T1D.
Background Rationale
In type 1 diabetes, T cell-mediated autoimmune destruction of beta-cells is preceded by, and dependent on, a strong anti-viral, type 1 interferon response in islets. It has been suggested that enteroviral infection is the initiating event for the anti-viral response, but a definitive demonstration of a causal virus is still lacking, despite decades of work. Regardless of the actual trigger of the islet interferon response, it is important to understand its dynamics and to identify means of modulating it.
Over the last several years we have established an experimental system which permits an in-depth investigation of the islet anti-viral response. The system is based on the introduction to islets of double stranded RNA, a type of molecule that is a strong trigger of an anti-viral response. Following the accumulation of double stranded RNA in beta cells, massive islet inflammation develops, followed by beta-cell destruction and diabetes, with features mimicking closely phenomena seen in human type 1 diabetes such as selective destruction of beta-cells and sparing of other cell types in islets.
Strikingly, we found that the development of an interferon response in beta-cells is strongly modulated by glucose, suggesting a surprising link between metabolism and pathologic islet inflammation. This raises the possibility of a vicious cycle whereby inflammation leads to beta-cell loss, resulting in hyperglycemia which further exacerbates inflammation. This model is consistent with past findings that reduced metabolic load on beta-cells is beneficial in type 1 diabetes. The benefit of manipulations such as the onset of insulin treatment upon diagnosis leading to the transient honeymoon period, are typically interpreted as reduction of beta-cell glucotoxicity. Our findings raise the possibility that lowering glucose may additionally directly interfere with the primary interferon response of beta-cells and consequently reduce inflammation and immune attack. This scenario, if supported by additional evidence as proposed here, can open up exciting translational possibilities.
Description of Project
Type 1 diabetes is thought to begin with, and depend on, a strong anti-viral response, involving activation of interferon and interferon-response genes. While the actual trigger of the anti-viral response of islets remains unknown, it is important to understand its dynamics and identify means of modulating it, as a potential avenue for intervening with early stage disease.
We have developed an experimental model system for the interferon response of beta-cells, based on a genetic modification in mice or human islets (disruption of RNA editing) which mimics the response to viral infection. The new model allows for studying the early anti-viral response of islets and how it leads to diabetes. In preliminary studies we found that beta-cells are particularly sensitive to damage triggered by the interferon response, while other cell types in the islets of Langerhans are spared – recapitulating a hallmark feature of type 1 diabetes, namely specific destruction of beta-cells. Strikingly, we found that the interferon response of beta-cells is modulated by glucose and glucose metabolism, suggesting a novel target for pharmacologic intervention in early stages of type 1 diabetes. Based on these findings, we hypothesize that 1) beta-cells are uniquely prone to elicit an anti-viral, interferon response, compared with other islet cell types; 2) the interferon response is strongly modulated by glucose metabolism, and is specifically detrimental to beta-cells; and 3) the interferon response of beta-cells can be modulated pharmacologically.
We propose experiments that will test these hypotheses, using mouse and human models.
In aim 1, we will determine the impact of glucose metabolism and beta-cell activity on the interferon response of beta-cells. These experiments will provide a mechanistic, molecular understanding of metabolic modulation of the early anti-viral response in beta-cells.
In aim 2, we will define the molecular basis for selective beta-cell sensitivity to the anti-viral response, compared with alpha-cells, using genetic manipulation in alpha and beta cells.
In aim 3 we will model preventive strategies based on targeting beta-cell glucose metabolism, using drugs that modulate glycemic burden on beta-cells such as insulin, metformin, GLP1 mimetics and SGLT2 inhibitors. These experiments will explore the feasibility of preventing the early interferon response of beta-cells, as a potential prevention approach for type 1 diabetes.
Overall, experiments in this SRA will study the interferon response of beta-cells, modeling an early and essential step in the development of type 1 diabetes, to understand fundamental aspects of the disease such as selective damage to beta-cells and to test the impact of drugs that target beta-cell glucose metabolism.
Anticipated Outcome
The expected outcome of this program is an understanding of the molecular mechanisms controlling the behavior of mouse and human beta-cells and alpha-cells in the presence of double stranded RNA and the resulting interferon response. Specifically, we will learn if, as suggested by our preliminary findings, glucose metabolism is an important modulator of the interferon response in beta-cells. In the longer run, a demonstration of metabolic drugs attenuating the interferon response of beta-cells may evolve into a novel approach for therapy in early stage type 1 diabetes.
Relevance to T1D
The anti-viral, interferon response of islets is an early hallmark of type 1 diabetes, with strong genetic evidence indicating that it is essential for the development of autoimmunity and beta-cell destruction. However, the molecular pathways that control this interferon response have not been elucidated and the process has not been targeted with drugs. The current program addresses head-on this phenomenon, and specifically the exciting possibility that the interferon response of beta-cells can be inhibited by existing drugs that target beta-cell glucose metabolism. The studies will provide fundamental information on an early, important, yet little understood stage in the development of type 1 diabetes. For example, they may lead to insights into why specifically beta-cells are destroyed in diabetes. In addition, the pharmacologic interventions to be tested here in mice, such as insulin, Metformin, GLP1 and SGLT2, are translatable to human patients.