Objective
In order to alleviate the condition of beta cell loss in type 1 diabetics, we propose to investigate the use of GPR75, a receptor located on the cell membrane, to induce proliferation or enhanced survival of beta cells. This will be done by first analyzing mouse and human conditions with and without GPR75, to understand its importance in the insulin-producing cell. We will also administer GPR75 activators and to test how the receptor can be utilized to change beta cell function and survival. We will then analyze these cells for changes in protein and gene expression to elucidate the overall role of GPR75 and how it relates to other cell mechanisms. By performing this research, the capability of GPR75’s novel roles in beta cell replication and insulin secretion will be thoroughly tested. Since GPR75 is a member of the most successfully druggable class of receptors, our ultimate goal is to inform towards the use of pharmacologics targeting GPR75 to induce favorable changes to the beta cells in diabetic patients. By inducing beta cell proliferation or survival, it can alleviate or even prevent the beta cell loss which causes type 1 diabetes. By inducing greater insulin secretion, it can reduce the high blood sugar levels which cause diabetic complications.
Background Rationale
GPR75 is a recently discovered receptor that was found to be highly expressed in the beta cell in humans. In humans with a mutation which leaves them with less functional GPR75, the incidence of diabetes was lower than that of the normal population. When adding stimulators of GPR75 such as CCL5 or 20-HETE, beta cells were found to produce more insulin in response to glucose, and showed greatly increased replication. In a mouse model without GPR75, islets were smaller and less abundant, and displayed less proliferation. However, in a different mouse model with 20-HETE overexpression, islets were larger and more abundant, and showed more proliferation. These data taken together suggest GPR75 as having an important and overlooked role in beta cell health and replication. We plan to investigate and elucidate this role in experiments using healthy and diabetic conditions to prove the capability of GPR75 to increase functional beta cell mass in diabetics.
Description of Project
In patients suffering from type 1 diabetes, the underlying cause of disease is beta cell death. One prospect to cure diabetes is to cause beta cells to replicate, or to increase their survival rates. A recently discovered receptor in the beta cell, GPR75, has been shown to have positive effects on the beta cell when activated. It has been found that islets from diabetic donors express less GPR75 than healthy donors. When removing GPR75 from islets, the amount of insulin they produce in response to glucose is decreased. When administering one activator of the receptor, CCL5, it has been shown that beta cells have more insulin secretion in response to glucose, and increased proliferation. Another activator of the GPR75 receptor, the 20-HETE, has also been show to increase the beta cell self-duplication in mouse and human islets. In a mouse model with increased 20-HETE in the body, the size of the islets was far greater than normal. Removing the GPR75 receptor from the mice the islets had reduced beta cell replication, size, and quantity. With this information in mind, we hypothesize that GPR75 plays an important role in beta cell replication and/or survival, and can be utilized pharmacologically to help treat beta cell loss in diabetics.
Our proposal contains 3 major goals. Firstly, we will remove GPR75 from the beta cell in a mouse model to find what effects it has in a living system. We will measure those effects by measuring blood glucose levels, monitoring islet size and quantity, and checking rates of beta cell replication. We will further test the model by stressing the beta cells with conditions that frequently lead to diabetes, such as high-fat diet. These beta cells will be analyzed for any change in expression levels of other genes as well, to see how GPR75 interacts with the beta cell genome.
Secondly, we will translate these findings into human research. We will use human islets, human beta cell lines, and stem-cell derived beta-like cells in order to test findings from the mouse experiments. This will include administration of GPR75 activators to determine its effects on beta cell proliferation and insulin production. Islets from type 1 diabetic patients will be examined for any changes in GPR75 expression.
Finally, we will perform detailed analyses of human islets and human beta cell lines after removing GPR75 expression or administering GPR75 activators. This will be done by analyzing the differences in protein expression and RNA expression under these conditions, to find the mechanism by which beneficial changes in the beta cell are occurring. This information is vital in order to determine areas of future drug targets and to inform pharmacologic development.
Anticipated Outcome
Based on our preliminary data and previously published literature, we expect to find that GPR75 is a critical regulator of beta cell proliferation and survival. It has been shown that stimulation of GPR75 in islets, as well as in other cell types, leads to increased regeneration, and specifically in islets, increased insulin response. We anticipate seeing detrimental effects on the beta cell when blocking or removing GPR75 in both mouse and human islets. When stimulating islets with GPR75 activators, we expect increased survival, regeneration, and insulin production. This would be a crucial revelation, as stimulating GPR75 in beta cells of diabetic patients could alleviate the underlying cause of disease, beta cell death.
Relevance to T1D
Type 1 diabetes is caused by beta cell death resulting from autoimmune attack. When the beta cells die or otherwise can no longer produce enough insulin, blood sugar levels remain higher than normal, which causes the various complications of diabetes including neuropathy, nephropathy, cardiovascular disease, and ultimately can cause death. Administering insulin is currently the only treatment for type 1 diabetes, but the most sought-after solution is to treat the problem directly and prevent beta cell loss or restore beta cells before complications can even occur. For this reason, researching methods of increasing beta cell replication or survival is vital to curing type 1 diabetes. GPR75 is a receptor that has shown promising improvements to insulin secretion when stimulated in beta cells. In our preliminary studies, activating GPR75 has led to dramatically increased beta cell regeneration, in mouse and human pancreatic islets. Stimulating this receptor in beta cells of type 1 diabetic patients has the potential to lessen the burden of or even delay or prevent diabetes onset.