Objective
The overall objective of this research is to understand the roles of L-selectin and related molecules at different stages of type 1 diabetes, in those at risk of diabetes and whether these differ to those in people without diabetes. We will test the theories that: 1) L-selectin levels in the blood can identify those with T1D from controls and those who progress quickly from having islet autoantibodies to T1D developing clinical symptoms compared with those who progress slowly. 2) the expression of L-selectin in the immune cells of those with T1D is different in those without T1D. 3) The location of L-selectin and related molecules (e.g. ADAM10 and ADAM17) in the pancreas can differentiate between those with one type of diabetes (diagnosed 13 years). 4) That current therapies for T1D can indirectly affect the L-selectin pathway. We will test these theories by: Aim 1) Validate differences in L-selectin in the blood between patients with T1D (before and after diagnosis), those at risk of T1D and controls using a commercially available assay. Aim 2) Study L-selectin and related molecules in different types of immune cells. We will compare between those with T1D (before and after diagnosis) and controls. Aim 3) Locate L-selectin and related molecules in the pancreas and pancreatic lymph nodes in pancreatic samples from those with T1D and those without. Aim 4) Use techniques from Aims 1 and 2, to investigate whether therapies affect L-selectin in the blood and/or cells compared to placebo/control trial participants.
Background Rationale
L-selectin is a molecule that is involved in the trafficking or movement of immune cells to sites of inflammation, autoimmune attack, cancer and infections. Immune cells roll along specialized blood vessel walls through the binding of L-selectin on the immune cells to specific carbohydrate structures before movement through the vessel walls to the target area. As L-selectin is present on all immune cells, it needs to be tightly regulated. Once L-selectin has been activated, the fragment of L-selectin that is on the outside of the cell is cut off by molecules called ADAM10 or ADAM17, allowing for regulation of L-selectin. The fragment that is removed, is soluble in the blood and can be detected in blood samples. The role of L-selectin and related molecules (e.g. ADAM10 and ADAM17) and their pathways in immune-cell trafficking to the pancreas and related lymph nodes in T1D is not fully understood. The NOD mouse model has been used for many years in diabetes research. However, the relevance of the model has been challenged due to past failures in translating therapies from the mouse model to humans and the evidence that the infiltrating immune cells (also known as insulitis) is different between the mouse and human also. As L-selectin and related molecules could be key to understanding how and why immune cells infiltrate the pancreas, stronger evidence could be obtained through human studies. This research would be the first extensive study of L-selectin in humans with and without T1D and those at risk of T1D, allowing for more thorough and relevant research as we aim to target three areas of research concurrently: a) the pancreas (which is typically not generally accessible in living patients), b) soluble molecules in the blood and c) the immune cells.
Description of Project
Type 1 Diabetes (T1D) occurs when immune cells move into the pancreas and destroy the body’s own insulin producing cells. These immune cells move from the blood to the target area due to signalling molecules. One such molecule that has been identified is called L-selectin. L-selectin has been identified to be involved in other autoimmune diseases, various cancers and in response to infections. L-selectin can be found on white blood cells where it exerts its function. Once it has signalled cells to move from the blood stream, L-selectin is released from white blood cells by molecules called ADAM10 and ADAM17. Once it is released from cells, L-selectin is soluble and can be detected in the blood. These proteins, although crucial to how the autoimmune process happens have never been studied in detail in human T1D. We have generated some preliminary data from blood and pancreas samples from that indicates that the L-selectin pathway is affected in individuals with T1D. This research builds on this and aims to expand our knowledge of L-selectin and related molecules (e.g. ADAM17) in T1D and those at risk of T1D and whether levels and function differs compared to controls without diabetes. This research proposal brings together a combination of very experienced senior researchers and rarely career researchers from three universities that allows for this molecule to be explored in four different areas: 1) within the blood, 2) within different immune cells, 3) in pancreas samples and 4) patients with T1D that have received an immune system-targeted therapy. By understanding more about L-selectin, it’s related molecules and pathways, we hope to explain more about the differences in presentation of T1D, particularly in why some develop T1D very young while others do not. We will also explore use of L-selectin as a marker of risk of T1D which might help current screening efforts. Finally we will sim to identify possible targets for future T1D intervention therapies. There will be multiple outcomes from this project. Firstly we will know more about the L-selectin pathway in people with diabetes and those who will develop T1D in the future. As this pathway has been targeted for therapy in cancer, we will determine whether this pathway can also be targeted in future T1D clinical trials.
Anticipated Outcome
From Aim 1 of this study, exploring L-selectin in the blood, we hope to gather evidence of L-selectin levels across the course of type 1 diabetes. The cell work from Aim 2 will hopefully provide insights into the levels of L-selectin expressed on immune cells, how fast it is released from the cells and whether or not it is re-expressed. From this, we will be able to compare these characteristics between immune cell types, between patients with diabetes (before and after diagnosis) and controls and whether these are altered by the progression of disease in T1D. Outcomes of Aim 3 include confirming expression of L-selectin of immune cells between those diagnosed with diabetes very young (13 years) and those without diabetes. We should also be able to tell where in the pancreas immune cells with L-selectin are and potentially where they have entered the pancreas and related lymph nodes. Identification of where ADAM10 and ADAM17 are located in the pancreas could tell us where L-selectin could be released into the blood stream. Evidence could potentially arise from Aim 4 regarding any indirect effects of current T1D therapies have on L-selectin and it’s function of attracting cells to the pancreas.
Relevance to T1D
Type 1 Diabetes (T1D) results from the body’s own immune/white blood cells causing the destruction of the insulin producing cells within the pancreas. These immune cells have moved into the pancreas from the bloodstream because they have been signalled to do so. L-selectin, ADAM10 and ADAM17 are molecules that have been shown to be involved in this signalling process. Blocking of any of these molecules, or parts of the pathway they are involved in, could be vital in stopping the movement of these immune cells to the pancreas, therefore potentially preventing or slowing down their destruction of the insulin producing cells.
Some patients are diagnosed with T1D very young, for example under 7 years of age, whereas others are diagnosed in adolescence (>13 years) and some are diagnosed in adulthood. Those diagnosed younger, tend to have a more aggressive progression of disease, sudden onset of symptoms and being admitted to hospital with diabetic ketoacidosis (DKA). Lower amounts of L-selectin on immune cells and higher amounts of L-selectin in the blood stream have been seen in patients with T1D and DKA. Therefore, L-selectin levels may be a potential marker of risk of developing DKA.
There is also evidence to suggest that expression of the gene that produces L-selectin is increased in those with T1D compared to those without. This gene is also found at increased levels in the pancreas of those that rapidly progress to diabetes under 7 years, versus those that developed diabetes over the age of 13 years.