Diabetes and Obesity Program, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010, Australia.
Biochem J. 2011 Apr 1;435(1):267-76. doi: 10.1042/BJ20101867.
Saturated fatty acids promote lipotoxic ER (endoplasmic reticulum) stress in pancreatic β-cells in association with Type 2 diabetes. To address the underlying mechanisms we employed MS in a comprehensive lipidomic screen of MIN6 β-cells treated for 48 h with palmitate. Both the overall mass and the degree of saturation of major neutral lipids and phospholipids were only modestly increased by palmitate. The mass of GlcCer (glucosylceramide) was augmented by 70% under these conditions, without any significant alteration in the amounts of either ceramide or sphingomyelin. However, flux into ceramide (measured by [3H]serine incorporation) was augmented by chronic palmitate, and inhibition of ceramide synthesis decreased both ER stress and apoptosis. ER-to-Golgi protein trafficking was also reduced by palmitate pre-treatment, but was overcome by overexpression of GlcCer synthase. This was accompanied by increased conversion of ceramide into GlcCer, and reduced ER stress and apoptosis, but no change in phospholipid desaturation. Sphingolipid alterations due to palmitate were not secondary to ER stress since they were neither reproduced by pharmacological ER stressors nor overcome using the chemical chaperone phenylbutyric acid. In conclusion, alterations in sphingolipid, rather than phospholipid, metabolism are more likely to be implicated in the defective protein trafficking and enhanced ER stress and apoptosis of lipotoxic β-cells.
饱和脂肪酸促进了与 2 型糖尿病相关的胰岛 β 细胞中脂肪毒性内质网（ER）应激。为了阐明潜在机制，我们采用 MS 对 MIN6 胰岛 β 细胞进行了全面的脂类组学筛选，这些细胞在棕榈酸作用下培养了 48 小时。棕榈酸处理仅使主要中性脂质和磷脂的总质量和饱和度适度增加。在这些条件下，GlcCer（葡萄糖神经酰胺）的质量增加了 70%，而神经酰胺或鞘磷脂的量没有任何明显变化。然而，慢性棕榈酸处理增加了鞘氨醇的通量（通过 [3H]丝氨酸掺入来测量），并且抑制鞘氨醇合成降低了 ER 应激和细胞凋亡。棕榈酸预处理还降低了 ER 到高尔基体的蛋白转运，但通过 GlcCer 合酶的过表达得到了克服。这伴随着鞘氨醇向 GlcCer 的转化率增加，以及 ER 应激和细胞凋亡减少，但磷脂去饱和没有变化。由于棕榈酸导致的神经鞘脂改变不是 ER 应激的次要原因，因为它们既不能被药理学 ER 应激源复制，也不能被化学伴侣苯丁酸克服。总之，神经鞘脂代谢的改变而不是磷脂代谢的改变更有可能与脂毒性β细胞中的蛋白转运缺陷、增强的 ER 应激和细胞凋亡有关。
