Glucose-Induced Changes in Gene Expression in Human Pancreatic Islets: Causes or Consequences of Chronic Hyperglycemia Emilia Ottosson-Laakso, 1 Ulrika Krus, 1 Petter Storm, 1 Rashmi B. Prasad, 1 Nikolay Oskolkov, 1 Emma Ahlqvist, 1 João Fadista, 2 Ola Hansson, 1 Leif Groop, 1,3 and Petter Vikman 1 Diabetes 2017;66:3013–3028 | https://doi.org/10.2337/db17-0311 Dysregulation of gene expression in islets from patients with type 2 diabetes (T2D) might be causally involved in the development of hyperglycemia, or it could develop as a consequence of hyperglycemia (i.e., glucotoxicity). To separate the genes that could be causally involved in pathogenesis from those likely to be secondary to hy- perglycemia, we exposed islets from human donors to normal or high glucose concentrations for 24 h and ana- lyzed gene expression. We compared these findings with gene expression in islets from donors with normal glucose tolerance and hyperglycemia (including T2D). The genes whose expression changed in the same direction after short-term glucose exposure, as in T2D, were considered most likely to be a consequence of hyperglycemia. Genes whose expression changed in hyperglycemia but not after short-term glucose exposure, particularly those that also correlated with insulin secretion, were consid- ered the strongest candidates for causal involvement in T2D. For example, ERO1LB, DOCK10, IGSF11, and PRR14L were downregulated in donors with hyperglyce- mia and correlated positively with insulin secretion, suggesting a protective role, whereas TMEM132C was upregulated in hyperglycemia and correlated negatively with insulin secretion, suggesting a potential pathogenic role. This study provides a catalog of gene expression changes in human pancreatic islets after exposure to glucose. The function of pancreatic islets is critical for maintaining glucose homeostasis, and dynamic changes of gene expres- sion is part of the islets’ response to blood glucose changes. In patients with type 2 diabetes (T2D), islet function de- clines progressively. Although the initial pathogenic trigger of impaired b-cell function is still unknown, elevated glu- cose levels are known to further aggravate b-cell function, a condition referred to as glucotoxicity, which can stimulate apoptosis and lead to reduced b-cell mass (1–5). Prolonged exposure to hyperglycemia also can induce endoplasmic re- ticulum (ER) stress and production of reactive oxygen spe- cies (6), which can further impair islet function and thereby the ability of islets to secrete the insulin needed to meet the increased demands imposed by insulin resistance and obe- sity (7). Although these changes are likely to contribute to deterioration of islet function in patients with manifest disease, they are less likely to explain the development of T2D in individuals with normoglycemia. In previous studies, we analyzed the gene expression profile in individuals with chronically elevated glucose as measured by elevated HbA 1c levels (8,9). However, these studies could not demonstrate whether the changes in gene expression are the cause or the consequence of hyperglyce- mia. One way to address this question is to compare gene expression in islets chronically exposed to hyperglycemia (prediabetes or diabetes) with gene expression changes after short-term exposure to hyperglycemia, with the assump- tion that gene expression changes seen in islets from pa- tients with T2D but not after short-term hyperglycemia are the cause rather than the consequence of hyperglycemia (i.e., contributing to the pathogenesis of T2D). Thus, we performed RNA sequencing of human islets incubated at physiological (5.5 mmol/L) and high (18.9 mmol/L) glucose concentrations and compared the glucose-regulated genes 1 Lund University Diabetes Centre, Department of Clinical Sciences, Lund Univer- sity, Malmö, Sweden 2 Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark 3 Finnish Institute of Molecular Medicine, University of Helsinki, Helsinki, Finland Corresponding author: Emilia Ottosson-Laakso, emilia.ottosson@scilifelab.se. Received 12 March 2017 and accepted 30 August 2017. This article contains Supplementary Data online at http://diabetes .diabetesjournals.org/lookup/suppl/doi:10.2337/db17-0311/-/DC1. © 2017 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. More information is available at http://www.diabetesjournals .org/content/license. Diabetes Volume 66, December 2017 3013 ISLET STUDIES