Periodic Reporting for period 1 - INSULYSOSOME (The role of CD63 in lysosomal degradation of insulin granules in pancreatic beta cells in T2D diabetes)
Periodo di rendicontazione: 2018-11-01 al 2020-10-31
Concerns about the global diabetes epidemic continue to grow. In 2019, it has been established that 463 million people live with Diabetes. According to the last predictions made by the international Diabetes Federation in 2030 this number should reach 578 million. This developments are very alarming as the number of actual cases surpasses above estimations. Sedentary life style and overnutrition, hallmarks of our modern society, account for this epidemic disease propagation.
To maintain blood glucose at a normal level, the pancreatic β cell harbors an exemplary nutrient sensing machinery that is coupled to secretion of insulin. The pancreatic β cell mainly senses increasing glucose levels and secretes insulin that acts to promote the energy storage in different organs. Inversely, the β cell decreases insulin secretion to make available stored energy upon low glucose levels during fasting. Overnutrition conditions in combination with physical inactivity may trigger obesity and insulin resistance. To meet high insulin demands encountered in obese people, the pancreatic β cell will enhance its insulin secretory capacity. However, these compensatory mechanisms will eventually be overwhelmed culminating in β cell failure and full-blown type 2 diabetes (T2D).
While huge research efforts have been intended to unravel and target molecular mechanisms behind T2D, the picture is still far from being complete. While mechanisms linking glucose sensing to release of insulin have been widely investigated, little is known about how nutrients impact on insulin granule generation and their destination in the cell. Hence, novel research insights leading to therapeutic approaches are highly demanded to prevent enormous health costs and negative consequences of our modern lifestyle.
We have recently discovered a novel concept in which the newly-made insulin granules can be routed either for secretion in presence or for degradation in absence of nutrients. Moreover, we have discovered that routing insulin granules for degradation could be a hallmark of diabetic ß cells that may contribute to secretory dysfunction in T2D. Based on these findings, we have explored more fundamentally the role insulin granule degradation in ß cell function. It is essential to understand the molecular mechanisms behind the degradation of insulin in pancreatic ß cells and to address how this deregulation can promote progression of T2D.
To maintain blood glucose at a normal level, the pancreatic β cell harbors an exemplary nutrient sensing machinery that is coupled to secretion of insulin. The pancreatic β cell mainly senses increasing glucose levels and secretes insulin that acts to promote the energy storage in different organs. Inversely, the β cell decreases insulin secretion to make available stored energy upon low glucose levels during fasting. Overnutrition conditions in combination with physical inactivity may trigger obesity and insulin resistance. To meet high insulin demands encountered in obese people, the pancreatic β cell will enhance its insulin secretory capacity. However, these compensatory mechanisms will eventually be overwhelmed culminating in β cell failure and full-blown type 2 diabetes (T2D).
While huge research efforts have been intended to unravel and target molecular mechanisms behind T2D, the picture is still far from being complete. While mechanisms linking glucose sensing to release of insulin have been widely investigated, little is known about how nutrients impact on insulin granule generation and their destination in the cell. Hence, novel research insights leading to therapeutic approaches are highly demanded to prevent enormous health costs and negative consequences of our modern lifestyle.
We have recently discovered a novel concept in which the newly-made insulin granules can be routed either for secretion in presence or for degradation in absence of nutrients. Moreover, we have discovered that routing insulin granules for degradation could be a hallmark of diabetic ß cells that may contribute to secretory dysfunction in T2D. Based on these findings, we have explored more fundamentally the role insulin granule degradation in ß cell function. It is essential to understand the molecular mechanisms behind the degradation of insulin in pancreatic ß cells and to address how this deregulation can promote progression of T2D.
To tackle our first objective, we have engineered unique cellular imaging tools allowing us to trace these processes in space and time and to identify underlying molecular mechanisms. With these tools, we investigated insulin granule degradation in pancreatic β cell under overnutrition conditions. We observed that chronic exposure to elevated glucose and saturated fatty acids promoted insulin granule degradation. Indeed, using microscopy to track fluorescent markers of insulin granules and lysosomes, we highlighted an increased co-localization between insulin granules and lysosomes. These data were confirmed by electronic microscopy allowing us to evidence the accumulation of insulin granules in the degradation compartment.
Enhanced degradation of cellular components can counteract energy depletion caused by shortage of environmental nutrients through a process called autophagy. Interestingly, our laboratory has recently discovered that β cells employ a very distinct and so far unknown mechanism to adapt to nutrient depletion. Indeed, β cells induce insulin granule degradation independent of autophagy upon nutrient withdrawal. We thus next asked whether nutrient stress imposed by overnutrition treatment evoked similar effects. Our data indicated that degradation of insulin granules was likely to contribute to suppression of autophagy in overnutrition conditions for β cells. Hence, we propose that enhancement of insulin granule degradation leads to compromised autophagy accelerating β cell failure and T2D.
To confirm our findings in vivo, we decided to study insulin granule degradation in mice subjected to a metabolic stress by feeding animals a high-fat diet (HFD) or in a genetic model of T2D mouse. Interestingly, we observed the same increase of insulin granule degradation and the same inhibition of autophagy in mouse and human pancreatic β cells.
Our findings provide strong evidence for increased insulin granule degradation in diabetic β cells. Through a collaboration with an industrial partner, we have generated a compound with the potential to prevent degradation of insulin granules. We confirmed that the compound enhanced insulin content and autophagy in the β cells. Strikingly, a two-week treatment of obese mice prior β cell failure retarded diabetic progression.
Taken together, our data demonstrate that the nutrient sensing machinery in β cells controls targeting of insulin granules towards secretion or degradation. Nutrient stress-imposed deregulation favours triggering of insulin granule degradation and suppression of autophagy. This mechanism may contribute to insulin loss, reduced secretory capacity and to decreased autophagy, hallmarks of β cell dysfunction in T2D.
The work has been presented at numerous meetings including for example at the EMBO workshop “Lysosome and Metabolism” in 2018 in Naples or at the EASD meeting in Berlin in 2018 and was finally published in Nature Communications in 2019.
Enhanced degradation of cellular components can counteract energy depletion caused by shortage of environmental nutrients through a process called autophagy. Interestingly, our laboratory has recently discovered that β cells employ a very distinct and so far unknown mechanism to adapt to nutrient depletion. Indeed, β cells induce insulin granule degradation independent of autophagy upon nutrient withdrawal. We thus next asked whether nutrient stress imposed by overnutrition treatment evoked similar effects. Our data indicated that degradation of insulin granules was likely to contribute to suppression of autophagy in overnutrition conditions for β cells. Hence, we propose that enhancement of insulin granule degradation leads to compromised autophagy accelerating β cell failure and T2D.
To confirm our findings in vivo, we decided to study insulin granule degradation in mice subjected to a metabolic stress by feeding animals a high-fat diet (HFD) or in a genetic model of T2D mouse. Interestingly, we observed the same increase of insulin granule degradation and the same inhibition of autophagy in mouse and human pancreatic β cells.
Our findings provide strong evidence for increased insulin granule degradation in diabetic β cells. Through a collaboration with an industrial partner, we have generated a compound with the potential to prevent degradation of insulin granules. We confirmed that the compound enhanced insulin content and autophagy in the β cells. Strikingly, a two-week treatment of obese mice prior β cell failure retarded diabetic progression.
Taken together, our data demonstrate that the nutrient sensing machinery in β cells controls targeting of insulin granules towards secretion or degradation. Nutrient stress-imposed deregulation favours triggering of insulin granule degradation and suppression of autophagy. This mechanism may contribute to insulin loss, reduced secretory capacity and to decreased autophagy, hallmarks of β cell dysfunction in T2D.
The work has been presented at numerous meetings including for example at the EMBO workshop “Lysosome and Metabolism” in 2018 in Naples or at the EASD meeting in Berlin in 2018 and was finally published in Nature Communications in 2019.
The discovery made by our laboratory related to degradation of insulin granules in pancreatic β cells in the context of nutrient deprivation is the cornerstone of my project. New results that have been generated with the help of the Marie Skłodowska-Curie actions clearly go beyond the knowledge we had generated before I received this award. (1) We provide the first evidence for aberrant degradation of insulin granules to contribute to β cell failure in T2D. (2) We described also how mechanistically degradation of insulin granules occurs. (3) Finally, our study strengthened that targeting of enhanced insulin degradation in T2D may be a valuable treatment option for patients. We thus fully met the main objectives of the project as foreseen. Our concept is new and innovative in the field and it may thus stimulate research in several other laboratories. Having developed a fundamentally new concept based on our own data, we now have a strong basis for future work in our laboratory.
Existing treatments do not succeed in restoring a normal blood glucose in the long term, since β-cell function declines over time. Moreover, there is presently no single drug able to reverse all aspects of the disease. In addition, most of these medications have been shown to lose effectiveness with long-term use. We are convinced that the novelty of these results that have been obtained and the therapeutic potential could help to prevent the enormous health costs and negative consequences of modern lifestyle.
Existing treatments do not succeed in restoring a normal blood glucose in the long term, since β-cell function declines over time. Moreover, there is presently no single drug able to reverse all aspects of the disease. In addition, most of these medications have been shown to lose effectiveness with long-term use. We are convinced that the novelty of these results that have been obtained and the therapeutic potential could help to prevent the enormous health costs and negative consequences of modern lifestyle.