Browsing by Author "Yamamoto, Wataru"

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    Endoplasmic reticulum calcium dynamics and insulin secretion in pancreatic β cells
    (2017-08-15) Yamamoto, Wataru; Evans-Molina, Carmella; Day, Richard; Sturek, Michael; Obukhov, Alexander; Wek, Ronald
    Under normal conditions, ER Ca2+ levels are estimated to be at least three orders of magnitude higher than intracellular Ca2+. This steep Ca2+ concentration gradient is maintained by the balance of Ca2+ uptake into the ER via the sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) pump and ER Ca2+ release through Ryanodine receptors (RyR) and Inositol 1,4,5-triphosphate (IP3) receptors (IP3R). Emerging data suggest that alterations in β cell ER Ca2+ levels lead to diminished insulin secretion and reduced β cell survival in both type 1 and type 2 diabetes. However, the mechanisms leading to β cell ER Ca2+ loss remain incompletely understood, and a specific role for either RyR or IP3R dysfunction in diabetes has been largely untested. To this end, we applied intracellular and ER-Ca2+ imaging techniques in INS-1 β cells and isolated mouse and human islets to define whether RyR or IP3R activity were altered under diabetogenic conditions. Results revealed preferential alterations in RyR function in response to ER stress, while pro-inflammatory cytokine stress primarily impacted IP3R activity. Consistent with this, pharmacological inhibition of RyR and IP3Rs prevented ER Ca2+ loss under ER and pro-inflammatory stress, respectively. However, RyR inhibition was unique in its ability to prevent β cell death, delayed initiation of the unfolded protein response (UPR), and dysfunctional glucose-induced Ca2+ oscillations in tunicamycin treated INS-1 β cells and islets from Akita mice. Monitoring at the single cell level revealed that ER stress acutely increased intracellular Ca2+ transients and this was dependent on both ER Ca2+ leak from the RyR and plasma membrane depolarization, suggesting ER Ca2+ dynamics regulate cellular excitability. Collectively, our findings suggest that ER-stress induced RyR dysfunction regulates β cell ER Ca2+ dynamics, propagation of the UPR, insulin secretion, and cell survival. These data indicate that RyR-mediated loss of ER Ca2+ and β cell hyperexcitability may be early pathogenic events in diabetes.
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    Human adipose derived stromal/stem cells (hASCs) protect against STZ-induced hyperglycemia; analysis of hASC-derived paracrine effectors
    (Wiley, 2014-07) Kono, Tatsuyoshi M.; Sims, Emily K.; Moss, Dan R.; Yamamoto, Wataru; Ahn, Geonyoung; Diamond, Julie; Tong, Xin; Day, Kathleen H.; Territo, Paul R.; Hanenberg, Helmut; Traktuev, Dmitry O.; March, Keith L.; Evans-Molina, Carmella; Department of Medicine, IU School of Medicine
    Adipose-derived stromal/stem cells (ASCs) ameliorate hyperglycemia in rodent models of islet transplantation and autoimmune diabetes, yet the precise human ASC (hASC)-derived factors responsible for these effects remain largely unexplored. Here, we show that systemic administration of hASCs improved glucose tolerance, preserved β cell mass, and increased β cell proliferation in streptozotocin-treated nonobese diabetic/severe combined immunodeficient mice. Coculture experiments combining mouse or human islets with hASCs demonstrated that islet viability and function were improved by hASCs following prolonged culture or treatment with proinflammatory cytokines. Analysis of hASC-derived factors revealed vascular endothelial growth factor and tissue inhibitor of metalloproteinase 1 (TIMP-1) to be highly abundant factors secreted by hASCs. Notably, TIMP-1 secretion increased in the presence of islet stress from cytokine treatment, while TIMP-1 blockade was able to abrogate in vitro prosurvival effects of hASCs. Following systemic administration by tail vein injection, hASCs were detected in the pancreas and human TIMP-1 was increased in the serum of injected mice, while recombinant TIMP-1 increased viability in INS-1 cells treated with interleukin-1beta, interferon-gamma, and tumor necrosis factor alpha. In aggregate, our data support a model whereby factors secreted by hASCs, such as TIMP-1, are able to mitigate against β cell death in rodent and in vitro models of type 1 diabetes through a combination of local paracrine as well as systemic effects.
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    SERCA2 Deficiency Impairs Pancreatic β-Cell Function in Response to Diet-Induced Obesity
    (American Diabetes Association, 2016-10) Tong, Xin; Kono, Tatsuyoshi; Anderson-Baucum, Emily K.; Yamamoto, Wataru; Gilon, Patrick; Lebeche, Djamel; Day, Richard N.; Shull, Gary E.; Evans-Molina, Carmella; Cellular and Integrative Physiology, School of Medicine
    The sarcoendoplasmic reticulum (ER) Ca2+ ATPase 2 (SERCA2) pump is a P-type ATPase tasked with the maintenance of ER Ca2+ stores. Whereas β-cell SERCA2 expression is reduced in diabetes, the role of SERCA2 in the regulation of whole-body glucose homeostasis has remained uncharacterized. To this end, SERCA2 heterozygous mice (S2HET) were challenged with a high-fat diet (HFD) containing 45% of kilocalories from fat. After 16 weeks of the HFD, S2HET mice were hyperglycemic and glucose intolerant, but adiposity and insulin sensitivity were not different between HFD-fed S2HET mice and HFD-fed wild-type controls. Consistent with a defect in β-cell function, insulin secretion, glucose-induced cytosolic Ca2+ mobilization, and the onset of steady-state glucose-induced Ca2+ oscillations were impaired in HFD-fed S2HET islets. Moreover, HFD-fed S2HET mice exhibited reduced β-cell mass and proliferation, altered insulin production and proinsulin processing, and increased islet ER stress and death. In contrast, SERCA2 activation with a small molecule allosteric activator increased ER Ca2+ storage and rescued tunicamycin-induced β-cell death. In aggregate, these data suggest a critical role for SERCA2 and the regulation of ER Ca2+ homeostasis in the β-cell compensatory response to diet-induced obesity.