The effect of glucolipotox treatment on DNA methylation, gene expression, and cellular function in human pancreatic islets

Abstract

Aims/hypothesis The aims of this project was to investigate the effect of glucolipotoxic treatment on DNA methylation and gene expression patterns in pancreatic islets and functionally test if and how these changes alter insulin secretion.
Methods Genome-wide mRNA expression and DNA methylation patterns were analyzed in human pancreatic islets after control or glucolipotoxic treatment. Alterations in insulin secretion and apoptosis was investigated. Functional experiments in a rat beta-cell line (INS-1 832/13) were performed on four genes found to have altered gene expression and DNA methylation patterns during glucolipotoxicity in human pancreatic islets. Individual gene knockdown was performed by siRNA transfection, and differences in insulin secretion, insulin content, mitochondrial function, cell numbers and apoptosis rate were investigated.
Results Glucolipotoxicity leads to islets being glucose-desensitized, as insulin secretion is not increased under high glucose conditions. A more than twofold increase in apoptosis was found in islets exposed to glucolipotoxicity. Gene expression was altered for 1 855 genes after glucolipotoxic treatment in comparison to control treated islets. Altered DNA methylation patterns was found in 1 469 of these. Functional follow-up studies showed that individual knockdown of the four genes impaired insulin secretion and mitochondrial function as well as altered apoptosis levels.
Conclusions/interpretation In total, our results suggest that glucolipotoxic treatment of human pancreatic islets induces methylation and expression changes that may contribute to impaired insulin secretion and T2D pathogenesis.

Popular Abstract

Is glucolipotoxicity involved in the development type 2 diabetes?

Insulin is a hormone important for keeping blood sugar levels stable throughout the day. Type 2 diabetes (T2D) is a disease that develops as a result of tissues, such as the muscle, becoming resistant to insulin and the cells responsible for producing insulin (beta-cells found in pancreatic islets) don’t produce enough insulin. This leads to high levels of blood sugar which is harmful for the body. In a typical T2D patient both high levels of sugars and fats are present in the blood, which is referred to as glucolipotoxicity. Family history of diabetes can only to some extent explain the onset of T2D, other factors such as epigenetic factors are believed to be involved. Epigenetics involves reversible changes to the genetic information stored in the DNA of the cells. Epigenetic changes such as DNA-methylation, affects gene expression without actually changing the genes of the DNA. The effect of glucolipotoxicity and its role in T2D is not well established, for this reason a study performed on human pancreatic islets treated to glucolipotoxicity was performed.

The gene expression and DNA methylation pattern of human pancreatic islets treated under glucolipotoxic and control conditions were studied. The amount of insulin secreted by the islets and cell death within the islets were measured to determine the effect of glucolipotoxicity.

Alterations in gene expression and DNA methylation patterns were observed after glucolipotox treatment which is proposed to be involved in the changes of insulin secretion and increased cell death found during our experiments.
Functional follow-up studies
Four of the genes, found to have altered gene expression and DNA methylation during glucolipotoxicity in human pancreatic islets were chosen for functional follow-up studies. The expression of these genes were lowered (by so called knockdown) individually in rat beta-cells. Insulin secretion and content were then analysed together with other cellular functions for studying the functionality of the cells.

Insulin secretion was affected after knockdown of either gene, and insulin content was decreased after knockdown of two of the genes. Cell functions were affected regardless of gene knockdown, for instance the level of cell death was altered in all cases. These results put together lends support to the hypothesis that glucolipotoxicity leads to epigenetic and gene expression changes, and could be involved in the development of T2D.

Master’s Degree Project in Molecular Biology 60 credits 2016-2017
Department of Biology, Lund University

Advisors: Karl Bacos and Charlotte Ling
Epigenetics and Diabetes, Lund University, CRC.

• author: Jönsson, Josefine
• supervisor: Karl Bacos; Charlotte Ling
• organization: Degree Projects in Molecular Biology
• course: MOBT01 20162
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8925254
• date added to LUP: 2017-09-11 11:30:04
• date last changed: 2017-09-11 11:30:04