Regulation of PWS Genes in the Endocrine Pancreas

Funding Summary

Pancreatic beta cells produce and secrete two hormones, insulin and amylin, that are important regulators of food intake. These beta cells also express several PWS-region genes, but their function in the pancreas isn’t known. This project will shed light on the role of PWS genes in pancreatic beta cells by studying how PWS genes are regulated in response to cellular signals such as glucose and free fatty acids. The research team will also study the regulation of PWS genes in mouse models that are at risk of developing diabetes.

Dr. Theresa Strong, Director of Research Programs, shares details on this project in this short video clip. 

Lay Abstract

Individuals with the Prader-Willi Syndrome (PWS) suffer from a complex disease with multi-hormonal abnormalities that includes increased appetite and food intake which usually leads to severe childhood obesity. Prolonged exposure to obesity can lead to life-threatening secondary diseases, such as Diabetes, increased blood pressure and heart failure. It is currently not known how loss of PWS genes lead to these pathologies. Most PWS research was focused on the brain and other organ systems in the periphery are less studied. The pancreatic beta cells produce and secrete two hormones, insulin and islet amyloid polypeptide (Iapp, also called amylin), which are important regulators of early development and also regulate food intake by inducing satiety in the brain. Beta cells express several PWS genes but their local beta-cell function is unknown. Further, insulin and islet amyloid polypeptide are activated by the protease PC1/3 which was shown to be strongly reduced in research models of PWS. We thus aim to shed light on the role of PWS genes in pancreatic beta cells. We are going to excise pancreata from mice and purify various endocrine cells to study how PWS genes are regulated in response to common modulators of the beta cell (glucose, free fatty acids, cytokines). Similarly, we are going to study the regulation of PWS genes specifically in beta cells in mouse models that are at risk of developing diabetes (high-fat diet feeding, aging, reduced PC1/3). A special focus will be put on the interaction of PC1/3 and PWS genes. For this, we are going to delete PC1/3 or the PWS gene Snord116 specifically in beta cells and explore the molecular and functional consequence of this. Further, we are going to study whether these manipulations alter the activation of the satiety hormones insulin and islet amyloid polypeptide. We expect to shed light on the role of PWS genes in the beta cell of the endocrine pancreas. Further down the road, given that our hypothesis holds true, the idea of a “PWS gene --> PC1/3 --> insulin/Iapp --> satiety --> food intake --> obesity” axis could be evaluated in living mice with beta cell-specific deletion of PWS genes.

Research Outcomes: Public Summary

Individuals with PWS suffer from various endocrine pathologies. The dogma is that genetic changes in the brain influence peripheral tissues, such as the insulin-producing pancreatic beta cell. We alternatively hypothesized that altered expression of PWS genes in the beta cells themselves might induce some of these changes. We confirmed previously published data showing several PWS genes highly expressed in mouse beta cells but also identified some discrepancies. These data will guide further experiments exploring the role of PWS in insulin-producing cells, e.g. will tell us which PWS gene to focus on. We next isolated insulin-producing cells from mice and treated them with typical stimuli that these cells normally are exposed to in the course of development of type 2 diabetes, namely increased levels of glucose, proinflammatory cytokines and free fatty acids. We found that the PWS gene Snord116 is initially (mildly) downregulated and then after a few days returns to baseline. We then checked how the PWS gene Snord116 is regulated in insulin-producing cells in a mouse model that has an increased risk to develop type 2 diabetes or develops frank diabetes. Aging, feeding a fat-rich diet, becoming hyperglyemic (increased blood glucose) or frank diabetes were all associated with reduced levels of Snord116, although in some of these mouse models expression levels of Snord116 normalized with time. These data suggest that PWS genes are differentially regulated in beta cells in situations of metabolic stress, meaning that the amount of RNA is changed upon exposure to a diabetic milieu. However, whether these changes are a direct consequence of the diabetic milieu or are induced by other mediators remains to be investigated. Finally, we also attempted to use genetic tricks to produce living mice that lack the PWS gene Snord116 in the pancreas or in insulin-producing cells. These models should have helped us to see whether Snord116 RNA in insulin-producing beta cells (and not only the brain) induce metabolic features of PWS. However, we unexpectedly failed to achieve biologically meaningful deletion of Snord116 due to what we think technical (genetic) reasons.