Type 2 diabetes (T2D) is reaching epidemic proportions in Western societies. T2D occurs when the ?-cells of the pancreas do not secrete enough insulin to properly regulate peripheral blood glucose levels, usually in the face of obesity and associated peripheral insulin resistance. The mechanisms underlying insulin secretion are not properly understood. Using a forward genetics approach, we have discovered that a single nucleotide polymorphism (SNP) in the protein-coding region of the gene for tomosyn-2 is directly correlated with the hypoinsulinemic/hyperglycemic phenotype. Tomosyn-2 is a relatively uncharacterized protein and the mechanism by which it regulates insulin secretion is not known. The work proposed here in this Pathways to Independence Award application has two primary goals: 1) to elucidate the mechanism by which tomosyn-2 regulates insulin secretion in pancreatic ?-cells, and 2) to use my development of this novel area of T2D research to facilitate the development of my career from the mentored phase to an independent phase. During the mentored phase of the grant, I will receive training in mass spectrometry, in vitro liposome fusion assays, membrane biochemistry, and the generation of the tomosyn-2 knockout mouse. The research conducted in the mentored phase will examine the effect of identified phosphorylation sites on the ability of tomosyn-2 to regulate insulin secretion and to understand the mechanism by which tomosyn-2 is targeted for proteosomal degradation. During the independent phase of the grant, my research will examine the mechanism by which tomosyn-2 inhibits insulin secretion by regulating the activity of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins and characterize the role of novel tomosyn-2 binding proteins. These studies will provide novel clues to the mechanism by which tomosyn-2 inhibits insulin secretion and will further our understanding of the regulation of insulin secretio in T2D.
Genetic factors are estimated to contribute approximately 50% towards the risk of type 2 diabetes (T2D). Greater than 80% of people with T2D are obese. Yet, most people who are obese are not diabetic. We have reproduced this obesity-T2D dichotomy in mice by studying two mouse strains, C57BL/6 and BTBR T (+) tf, which differ in obesity-induced T2D. Using a mapping and breeding strategy, we identified a mutation in the gene that encodes tomosyn-2. A mutation in tomosyn-2 directly correlates with reduced insulin secretion, elevated plasma glucose, and reduced plasma insulin levels. We are the first to connect this relatively unknown protein with insulin homeostasis, and it is still unclear what role tomosyn-2 plays in insulin secretion. This proposal will investigate both the mechanism that regulates tomosyn-2 activity and its role in regulating insulin secretion. Together, this will provide insight into the novel mechanism regulating insulin secretion in T2D.
