Nguyen Tuyet Thi, Quan Xianglan, Hwang Kyu-Hee, Xu Shanhua, Das Ranjan, Choi Seong-Kyung, Wiederkehr Andreas, Wollheim Claes B, Cha Seung-Kuy, Park Kyu-Sang
Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Republic of Korea;
Nestlé Institute of Health Sciences, Lausanne, Switzerland, and.
Am J Physiol Endocrinol Metab. 2015 Jun 1;308(11):E933-41. doi: 10.1152/ajpendo.00009.2015. Epub 2015 Apr 7.
Inorganic phosphate (Pi) plays an important role in cell signaling and energy metabolism. In insulin-releasing cells, Pi transport into mitochondria is essential for the generation of ATP, a signaling factor in metabolism-secretion coupling. Elevated Pi concentrations, however, can have toxic effects in various cell types. The underlying molecular mechanisms are poorly understood. Here, we have investigated the effect of Pi on secretory function and apoptosis in INS-1E clonal β-cells and rat pancreatic islets. Elevated extracellular Pi (1~5 mM) increased the mitochondrial membrane potential (ΔΨm), superoxide generation, caspase activation, and cell death. Depolarization of the ΔΨm abolished Pi-induced superoxide generation. Butylmalonate, a nonselective blocker of mitochondrial phosphate transporters, prevented ΔΨm hyperpolarization, superoxide generation, and cytotoxicity caused by Pi. High Pi also promoted the opening of the mitochondrial permeability transition (PT) pore, leading to apoptosis, which was also prevented by butylmalonate. The mitochondrial antioxidants mitoTEMPO or MnTBAP prevented Pi-triggered PT pore opening and cytotoxicity. Elevated extracellular Pi diminished ATP synthesis, cytosolic Ca(2+) oscillations, and insulin content and secretion in INS-1E cells as well as in dispersed islet cells. These parameters were restored following preincubation with mitochondrial antioxidants. This treatment also prevented high-Pi-induced phosphorylation of ER stress proteins. We propose that elevated extracellular Pi causes mitochondrial oxidative stress linked to mitochondrial hyperpolarization. Such stress results in reduced insulin content and defective insulin secretion and cytotoxicity. Our data explain the decreased insulin content and secretion observed under hyperphosphatemic states.
无机磷酸盐（Pi）在细胞信号传导和能量代谢中发挥着重要作用。在胰岛素释放细胞中，Pi转运进入线粒体对于ATP的生成至关重要，ATP是代谢-分泌偶联中的一种信号因子。然而，升高的Pi浓度在各种细胞类型中可能具有毒性作用。其潜在的分子机制尚不清楚。在此，我们研究了Pi对INS-1E克隆β细胞和大鼠胰岛分泌功能及细胞凋亡的影响。细胞外Pi升高（1~5 mM）会增加线粒体膜电位（ΔΨm）、超氧化物生成、半胱天冬酶激活和细胞死亡。ΔΨm的去极化消除了Pi诱导的超氧化物生成。线粒体磷酸盐转运体的非选择性阻滞剂丁基丙二酸可防止ΔΨm超极化、超氧化物生成以及Pi引起的细胞毒性。高Pi还促进了线粒体通透性转换（PT）孔的开放，导致细胞凋亡，丁基丙二酸也可防止这种情况。线粒体抗氧化剂线粒体靶向性抗氧化剂（mitoTEMPO）或锰（III）四（4 - 苯甲酸）卟啉（MnTBAP）可防止Pi触发的PT孔开放和细胞毒性。细胞外Pi升高会减少INS-1E细胞以及分散的胰岛细胞中的ATP合成、细胞质Ca(2+)振荡、胰岛素含量和分泌。用线粒体抗氧化剂预孵育后，这些参数得以恢复。这种处理还可防止高Pi诱导的内质网应激蛋白磷酸化。我们提出，细胞外Pi升高会导致与线粒体超极化相关联的线粒体氧化应激。这种应激会导致胰岛素含量降低、胰岛素分泌缺陷和细胞毒性。我们的数据解释了在高磷血症状态下观察到的胰岛素含量和分泌减少的现象。
