Lai Elida, Bikopoulos George, Wheeler Michael B, Rozakis-Adcock Maria, Volchuk Allen
Division of Cell and Molecular Biology, Toronto General Research Institute, University Health Network, 101 College Street, TMOT 10-707, Toronto, ON, Canada, M5G1L7.
Am J Physiol Endocrinol Metab. 2008 Mar;294(3):E540-50. doi: 10.1152/ajpendo.00478.2007. Epub 2008 Jan 15.
Chronic exposure to elevated saturated free fatty acid (FFA) levels has been shown to induce endoplasmic reticulum (ER) stress that may contribute to promoting pancreatic beta-cell apoptosis. Here, we compared the effects of FFAs on apoptosis and ER stress in human islets and two pancreatic beta-cell lines, rat INS-1 and mouse MIN6 cells. Isolated human islets cultured in vitro underwent apoptosis, and markers of ER stress pathways were elevated by chronic palmitate exposure. Palmitate also induced apoptosis in MIN6 and INS-1 cells, although the former were more resistant to both apoptosis and ER stress. MIN6 cells were found to express significantly higher levels of ER chaperone proteins than INS-1 cells, which likely accounts for the ER stress resistance. We attempted to determine the relative contribution that ER stress plays in palmitate-induced beta-cell apoptosis. Although overexpressing GRP78 in INS-1 cells partially reduced susceptibility to thapsigargin, this failed to reduce palmitate-induced ER stress or apoptosis. In INS-1 cells, palmitate induced apoptosis at concentrations that did not result in significant ER stress. Finally, MIN6 cells depleted of GRP78 were more susceptible to tunicamycin-induced apoptosis but not to palmitate-induced apoptosis compared with control cells. These results suggest that ER stress is likely not the main mechanism involved in palmitate-induced apoptosis in beta-cell lines. Human islets and MIN6 cells were found to express high levels of stearoyl-CoA desaturase-1 compared with INS-1 cells, which may account for the decreased susceptibility of these cells to the cytotoxic effects of palmitate.
长期暴露于升高的饱和游离脂肪酸（FFA）水平已被证明会诱导内质网（ER）应激，这可能有助于促进胰腺β细胞凋亡。在此，我们比较了FFA对人胰岛以及两种胰腺β细胞系（大鼠INS-1和小鼠MIN6细胞）凋亡和ER应激的影响。体外培养的分离人胰岛发生凋亡，慢性棕榈酸酯暴露会使ER应激途径的标志物升高。棕榈酸酯也会诱导MIN6和INS-1细胞凋亡，尽管前者对凋亡和ER应激的耐受性更强。发现MIN6细胞比INS-1细胞表达显著更高水平的ER伴侣蛋白，这可能是其ER应激抗性的原因。我们试图确定ER应激在棕榈酸酯诱导的β细胞凋亡中所起的相对作用。尽管在INS-1细胞中过表达GRP78可部分降低对毒胡萝卜素的敏感性，但这并未降低棕榈酸酯诱导的ER应激或凋亡。在INS-1细胞中，棕榈酸酯在未导致显著ER应激的浓度下诱导凋亡。最后，与对照细胞相比，GRP78缺失的MIN6细胞对衣霉素诱导的凋亡更敏感，但对棕榈酸酯诱导的凋亡不敏感。这些结果表明，ER应激可能不是β细胞系中棕榈酸酯诱导凋亡的主要机制。与INS-1细胞相比，发现人胰岛和MIN6细胞表达高水平的硬脂酰辅酶A去饱和酶-1，这可能是这些细胞对棕榈酸酯细胞毒性作用敏感性降低的原因。
