Blázquez C, Galve-Roperh I, Guzmán M
Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, 28040 Madrid, Spain.
FASEB J. 2000 Nov;14(14):2315-22. doi: 10.1096/fj.00-0122com.
Recent observations support the importance of ceramide synthesis de novo in the induction of apoptosis. However, the downstream targets of de novo-synthesized ceramide are unknown. Here we show that palmitate incorporated into ceramide and induced apoptotic DNA fragmentation in astrocytes. These effects of palmitate were exacerbated when fatty acid breakdown was uncoupled and were not evident in neurons, which show a very low capacity to take up and metabolize palmitate. Palmitate-induced apoptosis of astrocytes was prevented by L-cycloserine and fumonisin B1, two inhibitors of ceramide synthesis de novo, and by PD098059, an inhibitor of the extracellular signal-regulated kinase (ERK) cascade. Accordingly, palmitate activated ERK by a process that was dependent on ceramide synthesis de novo and Raf-1, but independent of kinase suppressor of Ras. Other potential targets of ceramide in the control of cell fate, namely, c-Jun amino-terminal kinase, p38 mitogen-activated protein kinase, and protein kinase B, were not significantly affected in astrocytes exposed to palmitate. Results show that the Raf-1/ERK cascade is the selective downstream target of de novo-synthesized ceramide in the induction of apoptosis in astrocytes and also highlight the importance of ceramide synthesis de novo in apoptosis of astrocytes, which might have pathophysiological relevance.
近期的观察结果支持从头合成神经酰胺在诱导细胞凋亡中的重要性。然而，从头合成的神经酰胺的下游靶点尚不清楚。在此我们表明，棕榈酸酯掺入神经酰胺并在星形胶质细胞中诱导凋亡性DNA片段化。当脂肪酸分解解偶联时，棕榈酸酯的这些作用会加剧，而在神经元中则不明显，因为神经元摄取和代谢棕榈酸酯的能力非常低。棕榈酸酯诱导的星形胶质细胞凋亡可被L-环丝氨酸和伏马菌素B1（两种从头合成神经酰胺的抑制剂）以及细胞外信号调节激酶（ERK）级联反应的抑制剂PD098059所阻止。因此，棕榈酸酯通过一个依赖于从头合成神经酰胺和Raf-1，但独立于Ras激酶抑制因子的过程激活ERK。在暴露于棕榈酸酯的星形胶质细胞中，神经酰胺在控制细胞命运方面的其他潜在靶点，即c-Jun氨基末端激酶、p38丝裂原活化蛋白激酶和蛋白激酶B，并未受到显著影响。结果表明，Raf-1/ERK级联反应是从头合成的神经酰胺在诱导星形胶质细胞凋亡中的选择性下游靶点，也突出了从头合成神经酰胺在星形胶质细胞凋亡中的重要性，这可能具有病理生理学意义。
