The overall objectives of this proposal are to better understand the regulation of insulin secretion by free calcium ions (Ca2+) and the role of abnormal Ca2+ signaling in the pathophysiology of Type 2 diabetes mellitus (T2DM). Glucose stimulation evokes changes in intracellular Ca2+ ([Ca2+]c) in islets and insulin- secreting cell lines that temporally correlate with insulin secretion. Although much is known about the contribution of Ca2+ influx through voltage-gated Ca2+ channels to B-cell insulin secretion, our knowledge of the contribution of endoplasmic reticulum (ER) Ca2+ stores is limited. This is in part due to few reports of direct measurements of secretagogue effects on [Ca2+]ER and incomplete understanding of the mechanisms that regulate ER Ca2+ stores in B-cells. The proposed experiments will focus on defining these mechanisms. Preliminary studies suggest that sarcoendoplasmic reticulum Ca2+-ATPase (SERCA), a key regulator of ER Ca2+ homeostasis, is impaired in islets from the db/db mouse model of T2DM. This raises the intriguing possibility that loss of B-cell function in T2DM is related to defects in ER Ca2+ signaling. We will employ a combination of biosensor technology, RNA silencing, novel transgenic and imaging approaches to identify and characterize underlying regulatory mechanisms. The proposed experiments will [1] identify spatial and temporal interplay between cytoplasmic and ER Ca2+ signaling in single cells;[2] determine kinetics of signals that affect ER Ca2+ mobilization;[3] define novel mechanisms that regulate ER Ca2+ store refilling;[4] define the role of mitochondria in regulation of ER Ca2+ homeostasis;[5] determine whether stromal interaction molecule (STIM) couples ER Ca2+ levels with store-operated Ca2+ entry (SOCE);and [6] define the role of ER Ca2+ signaling defects in B-cell dysfunction associated with diabetes. The following hypotheses will be tested: [1] glucose stimulates ER Ca2+ signaling;[2] glucose-induced [Ca2+]c and [Ca2+]ER oscillations are temporally and causally interrelated;[3] STIM1 is expressed in B-cells and essential for SOCE;[4] mitochondria and plasma membrane-related Ca2+-ATPase-1 (Pmr-1) regulate ER Ca2+ homeostasis;[5] B-cell dysfunction in T2DM is due to defects in ER Ca2+ homeostasis consequent to decreased expression of SERCA and STIM. We will test these hypotheses in MIN6 B-cells, islets and primary B-cells from transgenic biosensor mice and db/db mice. Identification and characterization of the signaling pathways that control ER Ca2+ is a necessary step in advancing our knowledge of the molecular mechanisms regulating B-cell Ca2+ signal transduction and function. The experiments will contribute new information essential to improve understanding of the pathogenesis of T2DM, and facilitate development of novel strategies used in the preservation and maintenance of B-cell function in patients with diabetes.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK074966-05
Application #
7930510
Study Section
Cellular Aspects of Diabetes and Obesity Study Section (CADO)
Program Officer
Appel, Michael C
Project Start
2006-05-10
Project End
2012-04-30
Budget Start
2010-05-01
Budget End
2012-04-30
Support Year
5
Fiscal Year
2010
Total Cost
$281,017
Indirect Cost
Name
Upstate Medical University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
058889106
City
Syracuse
State
NY
Country
United States
Zip Code
13210
Kono, Tatsuyoshi; Tong, Xin; Taleb, Solaema et al. (2018) Impaired Store-Operated Calcium Entry and STIM1 Loss Lead to Reduced Insulin Secretion and Increased Endoplasmic Reticulum Stress in the Diabetic ?-Cell. Diabetes 67:2293-2304
Leech, Colin A; Kopp, Richard F; Nelson, Heather A et al. (2017) Stromal Interaction Molecule 1 (STIM1) Regulates ATP-sensitive Potassium (KATP) and Store-operated Ca2+ Channels in MIN6 ?-Cells. J Biol Chem 292:2266-2277
Kopp, Richard F; Leech, Colin A; Roe, Michael W (2014) Resveratrol Interferes with Fura-2 Intracellular Calcium Measurements. J Fluoresc 24:279-84
Brickley, Deanna R; Agyeman, Abena S; Kopp, Richard F et al. (2013) Serum- and glucocorticoid-induced protein kinase 1 (SGK1) is regulated by store-operated Ca2+ entry and mediates cytoprotection against necrotic cell death. J Biol Chem 288:32708-19
Kaihara, Kelly A; Dickson, Lorna M; Jacobson, David A et al. (2013) ?-Cell-specific protein kinase A activation enhances the efficiency of glucose control by increasing acute-phase insulin secretion. Diabetes 62:1527-36
Xu, Qin; Kopp, Richard F; Chen, Yanyi et al. (2012) Gating of connexin 43 gap junctions by a cytoplasmic loop calmodulin binding domain. Am J Physiol Cell Physiol 302:C1548-56
Dzhura, Igor; Chepurny, Oleg G; Leech, Colin A et al. (2011) Phospholipase C-? links Epac2 activation to the potentiation of glucose-stimulated insulin secretion from mouse islets of Langerhans. Islets 3:121-8
Wicksteed, Barton; Brissova, Marcela; Yan, Wenbo et al. (2010) Conditional gene targeting in mouse pancreatic ß-Cells: analysis of ectopic Cre transgene expression in the brain. Diabetes 59:3090-8
Chepurny, Oleg G; Kelley, Grant G; Dzhura, Igor et al. (2010) PKA-dependent potentiation of glucose-stimulated insulin secretion by Epac activator 8-pCPT-2'-O-Me-cAMP-AM in human islets of Langerhans. Am J Physiol Endocrinol Metab 298:E622-33
Dzhura, Igor; Chepurny, Oleg G; Kelley, Grant G et al. (2010) Epac2-dependent mobilization of intracellular Ca²+ by glucagon-like peptide-1 receptor agonist exendin-4 is disrupted in ?-cells of phospholipase C-? knockout mice. J Physiol 588:4871-89

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