Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, 65 Tsuruma-cho, Showa-ku, Nagoya 466-8550, Japan.
Neuroscience. 2011 Mar 10;176:188-98. doi: 10.1016/j.neuroscience.2010.11.035. Epub 2010 Dec 9.
Peripheral neuropathy has been reported to prevail in obese or pre-diabetic individuals, yet its etiology remains unknown. Palmitate, a saturated fatty acid increased in obesity and diabetes, is known to induce apoptosis in multiple types of cells and this effect may be mediated by ceramide, a member of the sphingolipid family. To clarify whether de novo ceramide synthesis from palmitate contributes to apoptosis of Schwann cells, we cultured immortalized mouse Schwann cells (IMS) and rat primary Schwann cells with palmitate, a ceramide analogue C2-ceramide as well as inhibitors of the de novo ceramide synthesis (myriocin and fumonisin B1). Apoptosis of IMS detected by nuclear staining and cell membrane inversion was significantly increased by incubation with palmitate for 48 h in a dose-dependent fashion. This enhanced apoptosis was partially but significantly suppressed by myriocin and fumonisin B1. Western blot analysis and immunostaining revealed that palmitate clearly activated caspase-3 in IMS. Unexpectedly, the ceramide synthesis inhibitors failed to suppress the palmitate-induced caspase-3 activation in spite of complete restoration in ceramide accumulation. The results seemed relevant to the observations that C2-ceramide did not activate caspase-3 while provoking apoptosis with a clear dose-dependency. In agreement, the pro-apoptotic action of C2-ceramide was not attenuated by caspase inhibitors that partially suppressed palmitate-induced apoptosis. These results in IMS were well reproducible in rat primary Schwann cells, indicating that the observed phenomena are not specific to the cell line. Collectively, we have reached a conclusion that palmitate induces apoptosis in Schwann cells via both a ceramide-mediated, caspase-3-independent pathway and ceramide-independent, caspase-3-dependent pathways. Given the fact that palmitate and ceramide are increased in obese or pre-diabetic subjects, these lipids may be implicated in the pathogenesis of peripheral neuropathy observed in these disorders.
周围神经病变在肥胖或糖尿病前期个体中较为常见，但病因仍不清楚。棕榈酸是肥胖和糖尿病中增加的一种饱和脂肪酸，已知可诱导多种类型细胞凋亡，这种效应可能是通过神经酰胺介导的，神经酰胺是鞘脂类家族的一员。为了阐明棕榈酸从头合成神经酰胺是否有助于施万细胞凋亡，我们培养了永生化的小鼠施万细胞（IMS）和大鼠原代施万细胞，并用棕榈酸、神经酰胺类似物 C2-神经酰胺以及从头合成神经酰胺的抑制剂（美拉霉素和伏马菌素 B1）处理这些细胞。用棕榈酸孵育 48 小时后，通过核染色和细胞膜反转检测到 IMS 的凋亡明显增加，且呈剂量依赖性。美拉霉素和伏马菌素 B1 部分但显著抑制了这种增强的凋亡。Western blot 分析和免疫染色显示，棕榈酸明显激活了 IMS 中的半胱天冬酶-3。出乎意料的是，尽管神经酰胺积累完全恢复，但神经酰胺合成抑制剂未能抑制棕榈酸诱导的半胱天冬酶-3 活化。这些结果与以下观察结果有关，即 C2-神经酰胺虽然在具有明显剂量依赖性的情况下引发凋亡，但不能激活半胱天冬酶-3。同样，C2-神经酰胺的促凋亡作用不受部分抑制棕榈酸诱导凋亡的半胱天冬酶抑制剂的削弱。这些在 IMS 中的结果在大鼠原代施万细胞中得到很好的重现，表明所观察到的现象不是细胞系特有的。总之，我们得出的结论是，棕榈酸通过神经酰胺介导的、半胱天冬酶-3 非依赖性途径和神经酰胺非依赖性、半胱天冬酶-3 依赖性途径诱导施万细胞凋亡。鉴于肥胖或糖尿病前期个体中棕榈酸和神经酰胺增加的事实，这些脂质可能与这些疾病中观察到的周围神经病变的发病机制有关。
