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Articles by H. Y Gaisano
Total Records ( 6 ) for H. Y Gaisano
  E Masson , S Koren , F Razik , H Goldberg , E. P Kwan , L Sheu , H. Y Gaisano and I. G. Fantus

Thioredoxin-interacting protein (TxNIP) is an endogenous inhibitor of thioredoxin, a ubiquitous thiol oxidoreductase, that regulates cellular redox status. Diabetic mice exhibit increased expression of TxNIP in pancreatic islets, and recent studies suggest that TxNIP is a proapoptotic factor in β-cells that may contribute to the development of diabetes. Here, we examined the role of TxNIP deficiency in vivo in the development of insulin-deficient diabetes and whether it impacted on pancreatic β-cell mass and/or insulin secretion. TxNIP-deficient (Hcb-19/TxNIP–/–) mice had lower baseline glycemia, higher circulating insulin concentrations, and higher total pancreatic insulin content and β-cell mass than control mice (C3H). Hcb-19/TxNIP–/– did not develop hyperglycemia when injected with standard multiple low doses of streptozotocin (STZ), in contrast to C3H controls. Surprisingly, although β-cell mass remained higher in Hcb-19/TxNIP–/– mice compared with C3H after STZ exposure, the relative decrease induced by STZ was as great or even greater in the TxNIP-deficient animals. Consistently, cultured pancreatic INS-1 cells transfected with small-interfering RNA against TxNIP were more sensitive to cell death induced by direct exposure to STZ or to the combination of inflammatory cytokines interleukin-1β, interferon-, and tumor necrosis factor-. Furthermore, when corrected for insulin content, isolated pancreatic islets from TxNIP–/– mice exhibited reduced glucose-induced insulin secretion. These data indicate that TxNIP functions as a regulator of β-cell mass and influences insulin secretion. In conclusion, the relative resistance of TxNIP-deficient mice to STZ-induced diabetes appears to be because of an increase in β-cell mass. However, TxNIP deficiency is associated with sensitization to STZ- and cytokine-induced β-cell death, indicating complex regulatory roles of TxNIP under different physiological and pathological conditions.

  J Vikman , H Svensson , Y. C Huang , Y Kang , S. A Andersson , H. Y Gaisano and L. Eliasson

Synaptosomal protein of 25 kDa (SNAP-25) is important for Ca2+-dependent fusion of large dense core vesicles (LDCVs) in insulin-secreting cells. Exocytosis is further enhanced by cAMP-increasing agents such as glucagon-like peptide-1 (GLP-1), and this augmentation includes interaction with both PKA and cAMP-GEFII. To investigate the coupling between SNAP-25- and cAMP-dependent stimulation of insulin exocytosis, we have used capacitance measurements, protein-binding assays, and Western blot analysis. In insulin-secreting INS-1 cells overexpressing wild-type SNAP-25 (SNAP-25WT), rapid exocytosis was stimulated more than threefold by cAMP, similar to the situation in nontransfected cells. However, cAMP failed to potentiate rapid exocytosis in INS-1 cells overexpressing a truncated form of SNAP-25 (SNAP-251-197) or Botulinum neurotoxin A (BoNT/A). Close dissection of the exocytotic response revealed that the inability of cAMP to stimulate exocytosis in the presence of a truncated SNAP-25 was confined to the release of primed LDCVs within the readily releasable pool, especially from the immediately releasable pool, whereas cAMP enhanced mobilization of granules from the reserve pool in both SNAP-251-197 (P < 0.01) and SNAP-25WT (P < 0.05) cells. This was supported by hormone release measurements. Augmentation of the immediately releasable pool by cAMP has been suggested to act through the cAMP-GEFII-dependent, PKA-independent pathway. Indeed, we were able to verify an interaction between SNAP-25 with both cAMP-GEFII and RIM2, two proteins involved in the PKA-independent pathway. Thus we hypothesize that SNAP-25 is a necessary partner in the complex mediating cAMP-enhanced rapid exocytosis in insulin-secreting cells.

  D Choi , A Radziszewska , S. A Schroer , N Liadis , Y Liu , Y Zhang , P. P. L Lam , L Sheu , Z Hao , H. Y Gaisano and M. Woo

Fas/Fas ligand belongs to the tumor necrosis factor superfamily of receptors/ligands and is best known for its role in apoptosis. However, recent evidence supports its role in other cellular responses, including proliferation and survival. Although Fas has been implicated as an essential mediator of β-cell death in the pathogenesis of type 1 diabetes, the essential role of Fas specifically in pancreatic β-cells has been found to be controversial. Moreover, the role of Fas on β-cell homeostasis and function is not clear. The objective of this study is to determine the role of Fas specifically in β-cells under both physiological and diabetes models. Mice with Fas deletion specifically in the β-cells were generated using the Cre-loxP system. Cre-mediated Fas deletion was under the control of the rat insulin promoter. Absence of Fas in β-cells leads to complete protection against FasL-induced cell death. However, Fas is not essential in determining β-cell mass or susceptibility to streptozotocin- or HFD-induced diabetes. Importantly, Fas deletion in β-cells leads to increased p65 expression, enhanced glucose tolerance, and glucose-stimulated insulin secretion, with increased exocytosis as manifested by increased changes in membrane capacitance and increased expression of Syntaxin1A, VAMP2, and munc18a. Together, our study shows that Fas in the β-cells indeed plays an essential role in the canonical death receptor-mediated apoptosis but is not essential in regulating β-cell mass or diabetes development. However, β-cell Fas is critical in the regulation of glucose homeostasis through regulation of the exocytosis machinery.

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