Inoue Yuko, Moriyasu Yuji
Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka, Japan.
Autophagy. 2006 Jul-Sep;2(3):244-6. doi: 10.4161/auto.2745. Epub 2006 Jul 29.
It has been generally accepted that autophagy contributes to the degradation of cellular components under nutrient starvation conditions. In a previous study, however, we showed that the degradation of membrane phospholipids occurs mainly by mechanisms distinct from autophagy in suspension-cultured tobacco (Nicotiana tabacum) BY-2 cells. In response to deprivation of sucrose, the amounts of total phospholipids and a major phospholipid, phosphatidylcholine (PC), decreased. 3-Methyladenine, which inhibits autophagy, did not affect the degradation of total phospholipids or PC. On the other hand, glycerol inhibited PC degradation although it did not block autophagy. In the present study, we labeled intracellular phospholipids by loading cells with a fluorochrome-labeled fatty acid and observed cellular morphology by fluorescence microscopy. Most cellular membrane structures were stained at the start of starvation; but 12 h after starvation treatment, concomitant with PC degradation, fluorescence on membranes disappeared and instead the central vacuole became fluorescent. 3-Methyladenine did not inhibit this process, whereas glycerol did. These results suggest that the degradation of membrane phospholipids can be traced by light microscopy and support the notion that autophagy is not a main contributor to the degradation of membrane phospholipids in tobacco cells cultured in sucrose-free medium.
人们普遍认为，自噬有助于在营养饥饿条件下细胞成分的降解。然而，在之前的一项研究中，我们发现悬浮培养的烟草（Nicotiana tabacum）BY-2细胞中膜磷脂的降解主要通过不同于自噬的机制发生。在蔗糖缺乏的情况下，总磷脂和一种主要磷脂磷脂酰胆碱（PC）的量减少。抑制自噬的3-甲基腺嘌呤不影响总磷脂或PC的降解。另一方面，甘油抑制PC降解，尽管它不阻断自噬。在本研究中，我们通过用荧光染料标记的脂肪酸加载细胞来标记细胞内磷脂，并通过荧光显微镜观察细胞形态。在饥饿开始时，大多数细胞膜结构被染色；但饥饿处理12小时后，伴随着PC降解，膜上的荧光消失，取而代之的是中央液泡变得有荧光。3-甲基腺嘌呤不抑制这一过程，而甘油则抑制。这些结果表明，膜磷脂的降解可以通过光学显微镜追踪，并支持这样一种观点，即在无蔗糖培养基中培养的烟草细胞中，自噬不是膜磷脂降解的主要因素。
