Type 2 diabetes (T2D) is caused by a failure of beta cells to produce sufficient insulin to maintain euglycemia. As a consequence of genetic/environmental factors, insulin resistance develops that pressures beta cells to increase insulin production. Although beta cells have some capacity to compensate for the demand, by approximately one-third of ~600 million individuals with obesity in the world develop go on to develop diabetes. The factors that lead to beta cell failure are unknown. Due to the polygenic nature of the disease, it is likely many genes modify beta cell function, and polymorphisms in any single gene would not be detected because they present minor contributions. Our underlying hypothesis is that multiple genes impact the efficiency of proinsulin folding in the endoplasmic reticulum (ER) and modify the progression of T2D. Significantly, our preliminary studies show that a high fat diet is sufficient to cause proinsulin misfolding well before diabetes development in C57BL/6 mice. In addition, we have identified genetic modifiers that exacerbate proinsulin misfolding and beta cell failure. We hypothesize that the fundamental cause of beta cell failure in T2D is a breakdown at the level of the ER with failure to efficiently fold excessive amounts of proinsulin and resulting consequences on downstream processing and secretion. To test our hypothesis, we have established a team of outstanding investigators to work together to identify critical proteins that modify proinsulin folding using state-of-the-art proteomics, biochemistry, cell biology, murine genetics and bioinformatics. In preliminary studies we developed methods to differentiate between specific disulfide bond defects and other misfolded conformations of proinsulin, generated all of the necessary murine strains and validated the proteomic mass spectrometry approach for proinsulin interactions using human islets. We have also demonstrated the potential of small molecules to improve proinsulin production in challenged islets. We expect our novel approach will identify distinct defects in the proinsulin folding pathway that represent the earliest changes leading to beta cell demise in both murine models and humans. The three aims of our R24 grant focus on defining how proinsulin folding patterns change when islets are challenged, and to identify how protein interactions with proinsulin may predict the efficiency of proinsulin trafficking through the secretory pathway, impacting islet health.
Aim 1 will quantify the folded and unfolded state of proinsulin by measuring intermediates in the folding process in normal and diseased islets from well-characterized murine models.
Aim 2 will define how the proteins that interact with proinsulin change during progression from normal, obese non-diabetic to T2D islets from human donors.
Aim 3 will elucidate what interventions and chaperone functions may preserve productive proinsulin folding and restore an efficient proinsulin ?proteostasis? network. Collectively, our proposed studies may identify novel biomarkers and avenues for therapeutic intervention in T2D, and therefore are of paramount importance to the mission of NIDDK.

Public Health Relevance

About ~9.3% of US population have Type 2 Diabetes where almost 80 million adults (>20 years of age) are prediabetic of which ~1/3 progress to beta cell failure and require insulin. Recent insight indicates that many genes contribute to beta cell failure to increase proinsulin folding and secretion. To identify genetic modifiers that predispose to beta cell failure, we have assembled an excellent team of investigators with complimentary expertise in genetic models of ER stress/beta cell failure, proinsulin/insulin biochemistry and human islet/beta cell biology and proteomics that should revolutionize the development of novel diagnostics and therapies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Resource-Related Research Projects (R24)
Project #
5R24DK110973-02
Application #
9351508
Study Section
Special Emphasis Panel (ZDK1)
Program Officer
Wang, Xujing
Project Start
2016-09-12
Project End
2020-06-30
Budget Start
2017-07-01
Budget End
2018-06-30
Support Year
2
Fiscal Year
2017
Total Cost
Indirect Cost
Name
Sanford Burnham Prebys Medical Discovery Institute
Department
Type
DUNS #
020520466
City
La Jolla
State
CA
Country
United States
Zip Code
92037
Zhang, Shuping; Macias-Garcia, Alejandra; Velazquez, Jason et al. (2018) HRI coordinates translation by eIF2?P and mTORC1 to mitigate ineffective erythropoiesis in mice during iron deficiency. Blood 131:450-461
Chandrahas, Vishwanatha K; Han, Jaeseok; Kaufman, Randal J (2018) Coordinating Organismal Metabolism During Protein Misfolding in the ER Through the Unfolded Protein Response. Curr Top Microbiol Immunol 414:103-130
Poothong, Juthakorn; Tirasophon, Witoon; Kaufman, Randal J (2017) Functional analysis of the mammalian RNA ligase for IRE1 in the unfolded protein response. Biosci Rep 37:
Yao, Ting; Deng, Zhuo; Gao, Yong et al. (2017) Ire1? in Pomc Neurons Is Required for Thermogenesis and Glycemia. Diabetes 66:663-673
Choi, Woo-Gyun; Han, Jaeseok; Kim, Ji-Hyeon et al. (2017) eIF2? phosphorylation is required to prevent hepatocyte death and liver fibrosis in mice challenged with a high fructose diet. Nutr Metab (Lond) 14:48
DeZwaan-McCabe, Diane; Sheldon, Ryan D; Gorecki, Michelle C et al. (2017) ER Stress Inhibits Liver Fatty Acid Oxidation while Unmitigated Stress Leads to Anorexia-Induced Lipolysis and Both Liver and Kidney Steatosis. Cell Rep 19:1794-1806
Han, Jaeseok; Kaufman, Randal J (2017) Physiological/pathological ramifications of transcription factors in the unfolded protein response. Genes Dev 31:1417-1438
Poothong, Juthakorn; Sopha, Pattarawut; Kaufman, Randal J et al. (2017) IRE1? nucleotide sequence cleavage specificity in the unfolded protein response. FEBS Lett 591:406-414
Jin, Jung-Kang; Blackwood, Erik A; Azizi, Khalid et al. (2017) ATF6 Decreases Myocardial Ischemia/Reperfusion Damage and Links ER Stress and Oxidative Stress Signaling Pathways in the Heart. Circ Res 120:862-875