Investigating the role of alternative splicing in islets of Langerhans in the development of type 2 diabetes

• Applicants: Dr. Meriem Ouni; Thilo Speckmann, Ph.D.
• Subject Area: Nutritional Sciences
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525802829

Comprehensive transcriptome analyses of islets of Langerhans revealed significant expression differences between diabetes-prone New Zealand Obese (NZO) and diabetes-resistant C57BL/6-ob/ob (ob/ob) mice, as well as diabetes genes playing roles in β-cell function and viability. Here, we hypothesize that differential gene expression is not the sole cause of the stark differences in diabetes susceptibility, but that there are contributions from alternative splicing events driving protein isoform diversity. The ultimate goal of this project is to explore the role of alternative splicing in the development of type 2 diabetes. Preliminary work using RNA-seq data of islets from male mice found a change in a neuronal splicing pattern in NZO mice, as well as SNPs that could alter splicing. These results will be further explored in four work packages. 1. Initially, we will characterize alternative splicing events which potentially contribute to islet cell dysfunction. Translation to humans will be assessed using publicly available datasets of human islet cells. The extent to which alternative isoforms contribute to an altered translation rate will be examined via ribosome profiling. Furthermore, we will examine whether splicing alters expression of functional domains or intracellular protein localization of candidates harboring splicing quantitative trait loci in human islet cells, and whether this has an impact on insulin secretion. 2. Moreover, we aim to identify gene variants (SNPs) which can influence alternative splicing. When comparing NZO and ob/ob mouse strains, numerous SNPs which potentially affect splicing patterns were identified. Therefore, a detailed analysis on the localization of these SNPs will be performed, including whether and how they impinge on regulatory sequences. As a translational approach, SNPs that prove to be relevant for splicing will be compared with diabetes-associated SNPs in humans. 3. A third focus will be on clarifying how loss of a neuronal splicing signature in islets of Langerhans is associated with diabetes. For example, β-cells express the neuron-enriched splicing factors Srrm3 and Srrm4 (serine/arginine repetitive matrix 3/4). However, NZO islets express significantly less Srrm4, and known SRRM4-regulated exons consequently show an increased rate of exclusion. The extent to which this alters β-cell function and survival will be investigated. 4. Finally, we will explore the influence of epigenetics on alternative splicing. Differentially expressed microRNAs as well as DNA methylation patterns in islet cells will be analyzed and the effects of these epigenetic changes on splice events will be investigated, particularly in the comparison of NZO and ob/ob mice. The goal is to identify differentially methylated splice sites that can explain a particular splicing event.

• DFG Programme: Research Grants