Periodic Reporting for period 4 - CESYDE (Ceramide Synthases in Diabetic Beta Cell Demise)
Reporting period: 2022-07-01 to 2022-12-31
The metabolic diseases obesity and diabetes are a major threat for global health. According to the World Health Organisation (WHO), more than 650 million and 400 million people are obese and have diabetes, respectively. Obesity is defined by increased body weight and fat deposition, whereas diabetes is characterized by chronically high blood glucose levels (hyperglycemia). The vast majority of diabetes cases belong to the subtype “type 2 diabetes” (T2D). No cure for T2D exists, and in most patients, existing drugs fail over time to keep blood glucose levels in a healthy range. Hence, new approaches for treating T2D are necessary, and thus we need to understand why T2D occurs on a molecular level.
In healthy people, the blood glucose level is kept in a normal range by several circulating hormones, with insulin, which is secreted by the beta cells in the pancreas, the most important one. After a meal, blood glucose concentration increases, which is sensed by the beta cells and stimulates insulin secretion into the blood stream. Afterwards, insulin acts on many different organs and tissues, such as liver, fat tissue, skeletal muscle, the brain and others to both increase glucose uptake into the tissues, and prevent glucose release into the circulation, thereby rapidly normalizing blood glucose levels. Obesity tends to increase the amount of insulin necessary to normalize blood glucose levels through a mechanism called “insulin resistance”. In most overweight and obese people, the beta cells can overcome insulin resistance by secreting more insulin, preventing hyperglycemia. In contrast, the insulin secretion in T2D patients is insufficient to keep blood glucose levels in the normal range, and hyperglycemia occurs. There is good evidence that in many T2D patients, beta cells are dysfunctional, meaning that they fail to respond to increasing glucose levels in the same manner as healthy beta cells. Moreover, during the development of T2D, beta cells may undergo a process termed programmed cell death (apoptosis) and die. It is still not completely understood, why and when exactly beta cells lose their functionality during development of T2D.
Several mechanisms have been proposed that might explain how beta cells become dysfunctional. One key finding was that exposing beta cells to high levels of saturated fatty acids will disturb their normal function, and induce cell death. Saturated fatty acids are often contained in energy dense food, and long-term consumption of a fatty acid rich diet could be a key component of obesity and insulin resistance, and similarly, might play a role in beta cell dysfunction. Several studies have indicated, that fatty acids are utilized in cells to generate complex, modified lipids, called sphingolipids. Sphingolipids are generated in cells by combining two fatty acids and one amino acid, and are components of cell membranes, but can also affect intracellular enzymatic processes. Several studies have shown that for example in liver cells, sphingolipids can play a critical role in the regulation of insulin resistance. The CESYDE project ultimately aims to understand how (and if) sphingolipids influence beta cell function and survival, and which enzyme involved in sphingolipid biosynthesis could be potentially targeted for a new therapeutic approach in T2D treatment. To this end, we use biochemical, genetic and molecular tools to analyze the function of several enzymes in the sphingolipid biosynthesis pathway, try to define how these are regulated, and which proteins interact with these enzymes in beta cells.
In healthy people, the blood glucose level is kept in a normal range by several circulating hormones, with insulin, which is secreted by the beta cells in the pancreas, the most important one. After a meal, blood glucose concentration increases, which is sensed by the beta cells and stimulates insulin secretion into the blood stream. Afterwards, insulin acts on many different organs and tissues, such as liver, fat tissue, skeletal muscle, the brain and others to both increase glucose uptake into the tissues, and prevent glucose release into the circulation, thereby rapidly normalizing blood glucose levels. Obesity tends to increase the amount of insulin necessary to normalize blood glucose levels through a mechanism called “insulin resistance”. In most overweight and obese people, the beta cells can overcome insulin resistance by secreting more insulin, preventing hyperglycemia. In contrast, the insulin secretion in T2D patients is insufficient to keep blood glucose levels in the normal range, and hyperglycemia occurs. There is good evidence that in many T2D patients, beta cells are dysfunctional, meaning that they fail to respond to increasing glucose levels in the same manner as healthy beta cells. Moreover, during the development of T2D, beta cells may undergo a process termed programmed cell death (apoptosis) and die. It is still not completely understood, why and when exactly beta cells lose their functionality during development of T2D.
Several mechanisms have been proposed that might explain how beta cells become dysfunctional. One key finding was that exposing beta cells to high levels of saturated fatty acids will disturb their normal function, and induce cell death. Saturated fatty acids are often contained in energy dense food, and long-term consumption of a fatty acid rich diet could be a key component of obesity and insulin resistance, and similarly, might play a role in beta cell dysfunction. Several studies have indicated, that fatty acids are utilized in cells to generate complex, modified lipids, called sphingolipids. Sphingolipids are generated in cells by combining two fatty acids and one amino acid, and are components of cell membranes, but can also affect intracellular enzymatic processes. Several studies have shown that for example in liver cells, sphingolipids can play a critical role in the regulation of insulin resistance. The CESYDE project ultimately aims to understand how (and if) sphingolipids influence beta cell function and survival, and which enzyme involved in sphingolipid biosynthesis could be potentially targeted for a new therapeutic approach in T2D treatment. To this end, we use biochemical, genetic and molecular tools to analyze the function of several enzymes in the sphingolipid biosynthesis pathway, try to define how these are regulated, and which proteins interact with these enzymes in beta cells.
We have demonstrated that the amount of specific types of sphingolipids in pancreatic islets is altered during development of beta cell dysfunction, both during obesity as well as without obesity, and that this is due to changes in the generation of new sphingolipids. We have generated beta cells with either reduced expression or total lack of several enzymes that are essential for generation of sphingolipids. Our experiments indicate that several of these enzymes do not affect growth and proliferation of these cells, but in contrast, either alone or in combination control processes such as insulin production and glucose stimulated insulin secretion. By quantifying protein expression in these cells, we have identified several proteins that are modulated by sphingolipids, which in turn may affect insulin secretion. In addition, we have identified several molecules that can potentially improve insulin secretion by changing cellular sphingolipid levels. Several of these major findings were reported in a publication in a scientific journal (Griess et al., Nature Cell Biology, 2023) as well as in national and international meetings.
We have identified specific sphingolipids that are altered during development of beta cell dysfunction and diabetes. Moreover, we identified enzymes in the sphingolipid synthesis pathway that are involved in key processes in beta cells including insulin synthesis and insulin secretion. Through complex biochemical and cell biological experiments, we could quantify which proteins interact with sphingolipids in living beta cells; these results helped us to find novel proteins that play important roles in insulin secretion, among other cellular functions. Overall, the research described here has helped to understand some of the events in beta cells that eventually lead to beta cell dysfunction and diabetes, which may eventually help to design better treatment options for this disease.