Objective
The overall objective of this proposal is to validate the intracellular mannosylation pathway as a therapeutic target for the induction of insulin expression in alpha cells. If successful, the research conducted within this proposal will have identified a novel molecular mechanism that prevents non-beta cells from producing insulin. Our objective is to find novel approaches to overcome this repression and develop small molecules induce insulin expression in alpha cells.
Background Rationale
In preliminary data, we have surprisingly identified a role of the mannosylation pathway in preventing alpha cells from producing insulin. Mannose is a sugar closely related to glucose, that plays important roles in ensuring that proteins are correctly localized inside of cells and at their membranes. Here, we aim to molecularly understand how mannosylation affects insulin expression. We will then develop first compounds to inhibit the pathway, which may become the starting point for future drug development.
Description of Project
In type 1 diabetes, the insulin-producing beta cells in the islets of Langerhans are being destroyed by an autoimmune reaction. Inducing insulin expression in other non-beta cells is a key objective of regenerative medicine approaches aiming at developing a cure of type 1 diabetes. Pancreatic alpha cells, that also reside in the islets of Langerhans, have long been proposed as an endogenous cell source for the regeneration of beta cell mass. However clinical translation of currently available approaches has not been achieved so far.
In order to identify factors that are involved in preventing alpha cells from expressing insulin, we have conducted an unbiased genetic screen and knocked-out every gene in an alpha cell line. Surprisingly, we found that loss of any of four closely related proteins causes the same result, the induction of insulin in alpha cells. These proteins are all involved in an enzymatic reaction that results in the transfer of mannose to proteins. Mannose, a sugar closely related to glucose, has been linked to diabetes in several previous publications but alpha cell specific effects have never been studied.
Here, we propose to investigate in detail how these enzymes we identified cause the induction of insulin in alpha cells. We will test whether intracellular mannose levels or the function of mannosylated proteins underly the insulin induction. We will then identify additional genes that synergize and antagonize with the loss of the mannosylation enzymes, aiming to uncover the molecular mechanism of the effect. We will further study whether the inhibition for mannosylation also is conserved in primary pancreatic islets, where we will determine effects on the different cell types present. Finally, we will conduct chemical screens to find first small molecule inhibitors of the pathway.
Following successful completion of this project, we aim to have validated a novel therapeutic target and discovered novel chemical inhibitors to induce insulin expression in alpha cells.
Anticipated Outcome
At the end of the 2 year project period, we aim to understand how mannosylation enzymes prevent alpha cells from producing insulin and how this mechanism can be exploited for synergies for even stronger insulin induction. Furthermore, we will have developed potent small molecule inhibitors of the mannosylation enzymes that can form the basis of drug development.
Relevance to T1D
In type 1 diabetes, the insulin-producing beta cells in the islets of Langerhans are being destroyed by an autoimmune reaction. Inducing insulin expression in other non-beta cells is a key aim of regenerative medicine towards a cure of type 1 diabetes. Pancreatic alpha cells, that also reside in the islets of Langerhans, have long been proposed as an endogenous cell source for the regeneration of beta cell mass. However clinical translation of currently available approaches has not been achieved so far. Additional therapeutic targets like the ones we are studying in this proposal, may prove valuable in enabling other cell types unaffected by the autoimmune attack to start producing insulin. Engaging multiple such therapeutic targets synergistically may be required for clinical efficacy, highlighting the importance of validating novel pathways as proposed here.