Schulthess Fabienne T, Katz Sophie, Ardestani Amin, Kawahira Hiroshi, Georgia Senta, Bosco Domenico, Bhushan Anil, Maedler Kathrin
Centre for Biomolecular Interactions, University of Bremen, Bremen, Germany.
PLoS One. 2009;4(2):e4394. doi: 10.1371/journal.pone.0004394. Epub 2009 Feb 6.
Apoptosis is a hallmark of beta-cell death in both type 1 and type 2 diabetes mellitus. Understanding how apoptosis contributes to beta-cell turnover may lead to strategies to prevent progression of diabetes. A key mediator of apoptosis, mitochondrial function, and cell survival is apoptosis inducing factor (AIF). In the present study, we investigated the role of AIF on beta-cell mass and survival using the Harlequin (Hq) mutant mice, which are hypomorphic for AIF.
METHODOLOGY/PRINCIPAL FINDINGS: Immunohistochemical evaluation of pancreata from Hq mutant mice displayed much smaller islets compared to wild-type mice (WT). Analysis of beta-cell mass in these mice revealed a greater than 4-fold reduction in beta-cell mass together with an 8-fold increase in beta-cell apoptosis. Analysis of cell cycle dynamics, using BrdU pulse as a marker for cells in S-phase, did not detect significant differences in the frequency of beta-cells in S-phase. In contrast, double staining for phosphorylated Histone H3 and insulin showed a 3-fold increase in beta-cells in the G2 phase in Hq mutant mice, but no differences in M-phase compared to WT mice. This suggests that the beta-cells from Hq mutant mice are arrested in the G2 phase and are unlikely to complete the cell cycle. beta-cells from Hq mutant mice display increased sensitivity to hydrogen peroxide-induced apoptosis, which was confirmed in human islets in which AIF was depleted by siRNA. AIF deficiency had no effect on glucose stimulated insulin secretion, but the impaired effect of hydrogen peroxide on beta-cell function was potentiated.
CONCLUSIONS/SIGNIFICANCE: Our results indicate that AIF is essential for maintaining beta-cell mass and for oxidative stress response. A decrease in the oxidative phosphorylation capacity may counteract the development of diabetes, despite its deleterious effects on beta-cell survival.
细胞凋亡是1型和2型糖尿病中β细胞死亡的标志。了解细胞凋亡如何影响β细胞更新可能会带来预防糖尿病进展的策略。凋亡诱导因子（AIF）是细胞凋亡、线粒体功能和细胞存活的关键介质。在本研究中，我们使用AIF基因低表达的丑角（Hq）突变小鼠，研究了AIF对β细胞数量和存活的作用。
方法/主要发现：与野生型小鼠（WT）相比，Hq突变小鼠胰腺的免疫组织化学评估显示胰岛小得多。对这些小鼠β细胞数量的分析表明，β细胞数量减少了4倍以上，同时β细胞凋亡增加了8倍。以BrdU脉冲作为S期细胞的标志物分析细胞周期动力学，未检测到S期β细胞频率的显著差异。相比之下，磷酸化组蛋白H3和胰岛素的双重染色显示，Hq突变小鼠G2期的β细胞增加了3倍，但与WT小鼠相比，M期没有差异。这表明Hq突变小鼠的β细胞停滞在G2期，不太可能完成细胞周期。Hq突变小鼠的β细胞对过氧化氢诱导的细胞凋亡敏感性增加，这在通过siRNA耗尽AIF的人胰岛中得到证实。AIF缺乏对葡萄糖刺激的胰岛素分泌没有影响，但过氧化氢对β细胞功能的损害作用增强。
结论/意义：我们的结果表明，AIF对于维持β细胞数量和氧化应激反应至关重要。氧化磷酸化能力的降低可能会抵消糖尿病的发展，尽管其对β细胞存活有有害影响。
