PRADER-WILLI SYNDROME IN MICE
Editor's Note: Gabi H. ('17) proposes a new project for her research involving the pancreas of Prader-Willi syndrome mouse models.
Islet size deficit and hormone production in the endocrine pancreas of a Prader-Willi Syndrome deletion mouse model
Proposal Summary:
Prader-WIlli syndrome is a complex genetic disorder caused by the lack of expression in genes in chromosome 15 that causes obesity, intellectual disability, and shortness in height in most of its patients. Prader-Willi syndrome is the most common known cause of life-threatening obesity in children. This research will aim at further understanding the pancreatic underdevelopment of a Prader-Willi Syndrome (PWS) mouse model, looking at both size of islets of Langerhans and hormone production in each of these islets. Deficits in pancreatic islet development and their role in the Prader-Willi syndrome phenotype will be investigated. This research will assess the size difference in the endocrine pancreas of PWS mice and littermates control groups and will quantify, through immunohistochemistry staining, the islet proportion of the 5 major pancreatic hormones: insulin, ghrelin, glucagon, somatostatin and pancreatic polypeptide. Immunohistochemistry staining will also be used to quantify the levels of developmentally important transcription factors. This research will help further understanding of the endocrine abnormalities of the PWS mouse model. It will identify if this PWS region of interest is responsible for deficits in developmentally important transcription factors in the pancreas resulting in dysregulation of the proportionality of endocrine cells in the pancreas.
Background:
Prader-Willi Syndrome (PWS) is a rare neurogenetic disorder caused by a lack of expression of paternally inherited genes in chromosome 15 by three main mechanisms: paternal deletion of the region, maternal uniparental disomy and imprinting defect (Angulo, Butler, & Cataletto, 2015). In paternal deletion, the paternal chromosome is not imprinted. In maternal uniparental disomy, both chromosome 15s are received from the mother. An imprinting defect is caused by microdeletions or epimutations. (Angulo, Butler, & Cataletto, 2015) These abnormalities disrupt the normal functioning of the hypothalamus, a portion of the brain that links the nervous system to the endocrine system and controls food intake (Sargis, 2016). Prader-Willi Syndrome is therefore characterized by endocrine, neurological, and behavioral abnormalities, and progresses through distinctive stages, beginning with hypotonia (poor feeding and failure to thrive), then by a childhood/adulthood period of hyperphagia (abnormally increased appetite), severe obesity, short stature and obsessive-compulsive behavior (Angulo, Butler, & Cataletto, 2015). Patients with Prader-Willi syndrome develop an insatiable appetite, which leads to chronic overeating, obesity, and possibly type 2 diabetes. In fact, Prader-Willi Syndrome is the most common known cause of life-threatening obesity in children (1 in 10,000-30,000 people worldwide) (NORD).
The pancreas is a glandular organ in the upper abdomen that serves as both a hormone-producing endocrine gland and a digestive exocrine gland. The endocrine cells are located in the islets of Langerhans, which are irregularly shaped patches of tissue that release hormones directly into the bloodstream (Islets of Langerhans). There are five known types of hormone-producing cells in the pancreas: alpha cells producing glucagon, beta cells producing insulin, delta cells producing somatostatin, PP cells producing pancreatic polypeptide, and epsilon cells producing ghrelin.. All of these hormones work together to maintain a balance in the body. Insulin’s main function is lowering glucose concentration in the bloodstream, and glucose works to raises sugar levels when they are too low. Somatostatin inhibits glucagon and insulin secretion, PP regulates pancreatic secretion activities and ghrelin regulates appetite, while also playing a role in regulating energy use. Endocrine features of PWS include low growth hormone (GH) response,which constitutes the low stature phenotype, low insulin-like growth factor (IGF)-I, and high ghrelin levels (Kuppens et al, 2015). However, not much research has been done on PWS and hormones specific to the pancreas. A previous study found that major pancreatic islet hormones like insulin and glucagon were decreased in the PWS mice model, similar to plasma levels (Stefan et al., 2011). It used immunohistochemical analysis of the pancreas to show disrupted morphology of PWS islets, with reduced α- and β-cell mass from an increase in programmed cell death . It also showed that the rate of insulin secretion was impaired in PWS β-cells . This project will explore in more depth the hypothesis that the pancreas of PWS deletion mice is significantly underdeveloped in size, hormone production, and significant transcription factors compared to control littermates.
Project Description:
In the first step of the research, the number of nuclei per islet in the pancreata of both the PWS group and the control (wild type) group at three distinct ages: 15 days, 1 month and 6 months will be quantified. Collecting data for multiple different ages will ensure that whatever pattern is seen is due primarily to a difference in the phenotype and not due to aging.
In the second step, immunohistochemistry staining of the pancreatic sections will be performed and the relative proportions of alpha, beta, delta, epsilon, and pp cells in the pancreata of PWS and unaffected control mice will be analyzed. This data will allow a comparison between the percentage of cells producing each hormone in the PWS mice and the control mice group. This will also be performed in three distinct ages: 6 months, 1 month and 15 days.
In the third step, the circulating levels of blood glucose, insulin, and glucagon in these animals will be measured using ELISA staining technique. Depending on what this data looks like, the levels of developmentally important transcription factors from the pancreata of these mice will be quantified in order to identify if loss of the PWS region gene of interest may cause dysregulation of developmentally important transcription factors. If this is the case, it will support the hypothesis that the deletion of this PWS region is linked to dysregulation of the proportionality of endocrine cells in the pancreas when compared to wild type (control) littermates.
The data collected in this research will help to understand the endocrine profile of PWS patients and potentially explain some of the symptoms associated with the disease, including life-threatening obesity. This study is part of a larger project that attempts to narrow down the number of genes known to be responsible for PWS, potentially finding one gene that is the source of all the PWS phenotypes. This information could help with future research and potential treatments for PWS patients.
Research Strategy:
In order to compare islet development between the two groups of mice, images of the HOECHST stained islets of 6 month old mice, both control and PWS, will be printed and the nuclei in each islet will be counted using a counter. Using an excel spreadsheet, the number of nuclei per islets will be graphed and comapred between PWS and control. If the results are as hypothesized, the same process will be used with islets from 1 month old mice and 15 days old mice. This will confirm if the underdevelopment is in fact a phenotype of our PWS model and not simply a detriment that happens with age.
Once these numbers have been recorded, I will look into hormone production of the pancreas. I will perform immunohistochemistry (IHC) of the pancreatic sections following the protocol used by the lab. I will use rabbit anti-insulin antibody paired with an antibody directed toward a second pancreatic hormone (ghrelin, somatostatin, pancreatic polypeptide). Each stain has to be performed with insulin in order for the nuclei to be clearly marked and visible under the microscope. I will use IHC staining instead of other staining techniques because it will provide me with quantitative data of the percentage of nuclei producing each hormone, which will be sufficient in supporting my hypothesis. In order to measure the circulating levels of blood glucose, insulin, and glucagon in these animals I will use the ELISA staining technique using Thermo Fisher ELISA kit, and quantify these levels in comparison to the control group.
References:
Angulo, M. A., Butler, M. G., & Cataletto, M. E. (2015). Prader-Willi syndrome: A review of clinical,
genetic, and endocrine findings. Journal of Endocrinological Investigation J Endocrinol Invest, 38(12), 1249-1263.
Kuppens, R., Diène, G., Bakker, N., Molinas, C., Faye, S., Nicolino, M., . . . Hokken-Koelega, A.
(2015). Elevated ratio of acylated to unacylated ghrelin in children and young adults with
Prader–Willi syndrome.Endocrine, 633-642.
Prader Willi Syndrome - NORD (National Organization for Rare Disorders). (n.d.). Retrieved February
28, 2016, from http://rarediseases.org/rare-diseases/prader-willi-syndrome/
Sargis, R. M. (n.d.). An Overview of the Hypothalamus. Retrieved February 28, 2016, from
http://www.endocrineweb.com/endocrinology/overview-hypothalamus
Stefan, M., Simmons, R., Bertera, S., Trucco, M., Esni, F., Drain, P., & Nicholls, R. (2011). Global
deficits in development, function, and gene expression in the endocrine pancreas in a deletion mouse model of Prader-Willi syndrome. AJP: Endocrinology and Metabolism, 909-922. doi:10.1152/ajpendo.00185.2010.
Prader-WIlli syndrome is a complex genetic disorder caused by the lack of expression in genes in chromosome 15 that causes obesity, intellectual disability, and shortness in height in most of its patients. Prader-Willi syndrome is the most common known cause of life-threatening obesity in children. This research will aim at further understanding the pancreatic underdevelopment of a Prader-Willi Syndrome (PWS) mouse model, looking at both size of islets of Langerhans and hormone production in each of these islets. Deficits in pancreatic islet development and their role in the Prader-Willi syndrome phenotype will be investigated. This research will assess the size difference in the endocrine pancreas of PWS mice and littermates control groups and will quantify, through immunohistochemistry staining, the islet proportion of the 5 major pancreatic hormones: insulin, ghrelin, glucagon, somatostatin and pancreatic polypeptide. Immunohistochemistry staining will also be used to quantify the levels of developmentally important transcription factors. This research will help further understanding of the endocrine abnormalities of the PWS mouse model. It will identify if this PWS region of interest is responsible for deficits in developmentally important transcription factors in the pancreas resulting in dysregulation of the proportionality of endocrine cells in the pancreas.
Background:
Prader-Willi Syndrome (PWS) is a rare neurogenetic disorder caused by a lack of expression of paternally inherited genes in chromosome 15 by three main mechanisms: paternal deletion of the region, maternal uniparental disomy and imprinting defect (Angulo, Butler, & Cataletto, 2015). In paternal deletion, the paternal chromosome is not imprinted. In maternal uniparental disomy, both chromosome 15s are received from the mother. An imprinting defect is caused by microdeletions or epimutations. (Angulo, Butler, & Cataletto, 2015) These abnormalities disrupt the normal functioning of the hypothalamus, a portion of the brain that links the nervous system to the endocrine system and controls food intake (Sargis, 2016). Prader-Willi Syndrome is therefore characterized by endocrine, neurological, and behavioral abnormalities, and progresses through distinctive stages, beginning with hypotonia (poor feeding and failure to thrive), then by a childhood/adulthood period of hyperphagia (abnormally increased appetite), severe obesity, short stature and obsessive-compulsive behavior (Angulo, Butler, & Cataletto, 2015). Patients with Prader-Willi syndrome develop an insatiable appetite, which leads to chronic overeating, obesity, and possibly type 2 diabetes. In fact, Prader-Willi Syndrome is the most common known cause of life-threatening obesity in children (1 in 10,000-30,000 people worldwide) (NORD).
The pancreas is a glandular organ in the upper abdomen that serves as both a hormone-producing endocrine gland and a digestive exocrine gland. The endocrine cells are located in the islets of Langerhans, which are irregularly shaped patches of tissue that release hormones directly into the bloodstream (Islets of Langerhans). There are five known types of hormone-producing cells in the pancreas: alpha cells producing glucagon, beta cells producing insulin, delta cells producing somatostatin, PP cells producing pancreatic polypeptide, and epsilon cells producing ghrelin.. All of these hormones work together to maintain a balance in the body. Insulin’s main function is lowering glucose concentration in the bloodstream, and glucose works to raises sugar levels when they are too low. Somatostatin inhibits glucagon and insulin secretion, PP regulates pancreatic secretion activities and ghrelin regulates appetite, while also playing a role in regulating energy use. Endocrine features of PWS include low growth hormone (GH) response,which constitutes the low stature phenotype, low insulin-like growth factor (IGF)-I, and high ghrelin levels (Kuppens et al, 2015). However, not much research has been done on PWS and hormones specific to the pancreas. A previous study found that major pancreatic islet hormones like insulin and glucagon were decreased in the PWS mice model, similar to plasma levels (Stefan et al., 2011). It used immunohistochemical analysis of the pancreas to show disrupted morphology of PWS islets, with reduced α- and β-cell mass from an increase in programmed cell death . It also showed that the rate of insulin secretion was impaired in PWS β-cells . This project will explore in more depth the hypothesis that the pancreas of PWS deletion mice is significantly underdeveloped in size, hormone production, and significant transcription factors compared to control littermates.
Project Description:
In the first step of the research, the number of nuclei per islet in the pancreata of both the PWS group and the control (wild type) group at three distinct ages: 15 days, 1 month and 6 months will be quantified. Collecting data for multiple different ages will ensure that whatever pattern is seen is due primarily to a difference in the phenotype and not due to aging.
In the second step, immunohistochemistry staining of the pancreatic sections will be performed and the relative proportions of alpha, beta, delta, epsilon, and pp cells in the pancreata of PWS and unaffected control mice will be analyzed. This data will allow a comparison between the percentage of cells producing each hormone in the PWS mice and the control mice group. This will also be performed in three distinct ages: 6 months, 1 month and 15 days.
In the third step, the circulating levels of blood glucose, insulin, and glucagon in these animals will be measured using ELISA staining technique. Depending on what this data looks like, the levels of developmentally important transcription factors from the pancreata of these mice will be quantified in order to identify if loss of the PWS region gene of interest may cause dysregulation of developmentally important transcription factors. If this is the case, it will support the hypothesis that the deletion of this PWS region is linked to dysregulation of the proportionality of endocrine cells in the pancreas when compared to wild type (control) littermates.
The data collected in this research will help to understand the endocrine profile of PWS patients and potentially explain some of the symptoms associated with the disease, including life-threatening obesity. This study is part of a larger project that attempts to narrow down the number of genes known to be responsible for PWS, potentially finding one gene that is the source of all the PWS phenotypes. This information could help with future research and potential treatments for PWS patients.
Research Strategy:
In order to compare islet development between the two groups of mice, images of the HOECHST stained islets of 6 month old mice, both control and PWS, will be printed and the nuclei in each islet will be counted using a counter. Using an excel spreadsheet, the number of nuclei per islets will be graphed and comapred between PWS and control. If the results are as hypothesized, the same process will be used with islets from 1 month old mice and 15 days old mice. This will confirm if the underdevelopment is in fact a phenotype of our PWS model and not simply a detriment that happens with age.
Once these numbers have been recorded, I will look into hormone production of the pancreas. I will perform immunohistochemistry (IHC) of the pancreatic sections following the protocol used by the lab. I will use rabbit anti-insulin antibody paired with an antibody directed toward a second pancreatic hormone (ghrelin, somatostatin, pancreatic polypeptide). Each stain has to be performed with insulin in order for the nuclei to be clearly marked and visible under the microscope. I will use IHC staining instead of other staining techniques because it will provide me with quantitative data of the percentage of nuclei producing each hormone, which will be sufficient in supporting my hypothesis. In order to measure the circulating levels of blood glucose, insulin, and glucagon in these animals I will use the ELISA staining technique using Thermo Fisher ELISA kit, and quantify these levels in comparison to the control group.
References:
Angulo, M. A., Butler, M. G., & Cataletto, M. E. (2015). Prader-Willi syndrome: A review of clinical,
genetic, and endocrine findings. Journal of Endocrinological Investigation J Endocrinol Invest, 38(12), 1249-1263.
Kuppens, R., Diène, G., Bakker, N., Molinas, C., Faye, S., Nicolino, M., . . . Hokken-Koelega, A.
(2015). Elevated ratio of acylated to unacylated ghrelin in children and young adults with
Prader–Willi syndrome.Endocrine, 633-642.
Prader Willi Syndrome - NORD (National Organization for Rare Disorders). (n.d.). Retrieved February
28, 2016, from http://rarediseases.org/rare-diseases/prader-willi-syndrome/
Sargis, R. M. (n.d.). An Overview of the Hypothalamus. Retrieved February 28, 2016, from
http://www.endocrineweb.com/endocrinology/overview-hypothalamus
Stefan, M., Simmons, R., Bertera, S., Trucco, M., Esni, F., Drain, P., & Nicholls, R. (2011). Global
deficits in development, function, and gene expression in the endocrine pancreas in a deletion mouse model of Prader-Willi syndrome. AJP: Endocrinology and Metabolism, 909-922. doi:10.1152/ajpendo.00185.2010.
