Hagen Nadine, Van Veldhoven Paul P, Proia Richard L, Park Hyejung, Merrill Alfred H, van Echten-Deckert Gerhild
Kekulé-Institute, Life and Medical Sciences Membrane Biology and Lipid Biochemistry, University of Bonn, D-53121 Bonn, Germany.
J Biol Chem. 2009 Apr 24;284(17):11346-53. doi: 10.1074/jbc.M807336200. Epub 2009 Feb 27.
Cerebellar granule cells from sphingosine 1-phosphate (S1P) lyase-deficient mice were used to study the toxicity of this potent sphingolipid metabolite in terminally differentiated postmitotic neurons. Based on earlier findings with the lyase-stable, semi-synthetic, cis-4-methylsphingosine phosphate, we hypothesized that accumulation of S1P above a certain threshold induces neuronal apoptosis. The present studies confirmed this conclusion and further revealed that for S1P to induce apoptosis in lyase-deficient neurons it must also be produced by sphingosine-kinase2 (SK2). These conclusions are based on the finding that incubation of lyase-deficient neurons with either sphingosine or S1P results in a similar elevation in cellular S1P; however, only S1P addition to the culture medium induces apoptosis. This was not due to S1P acting on the S1P receptor but to hydrolysis of S1P to sphingosine that was phosphorylated by the cells, as described before for cis-4-methylsphingosine. Although the cells produced S1P from both exogenously added sphingosine as well as sphingosine derived from exogenous S1P, the S1P from these two sources were not equivalent, because the former was primarily produced by SK1, whereas the latter was mainly formed by SK2 (as also was cis-4-methylsphingosine phosphate), based on studies in neurons lacking SK1 or SK2 activity. Thus, these investigations show that, due to the existence of at least two functionally distinct intracellular origins for S1P, exogenous S1P can be neurotoxic. In this model, S1P accumulated due to a defective lyase, however, this cause of toxicity might also be important in other cases, as illustrated by the neurotoxicity of cis-4-methylsphingosine phosphate.
来自鞘氨醇-1-磷酸（S1P）裂解酶缺陷小鼠的小脑颗粒细胞被用于研究这种强效鞘脂代谢物在终末分化的有丝分裂后神经元中的毒性。基于早期对裂解酶稳定的半合成顺式-4-甲基鞘氨醇磷酸酯的研究结果，我们推测S1P积累超过一定阈值会诱导神经元凋亡。目前的研究证实了这一结论，并进一步揭示，S1P要在裂解酶缺陷的神经元中诱导凋亡，还必须由鞘氨醇激酶2（SK2）产生。这些结论基于以下发现：用鞘氨醇或S1P孵育裂解酶缺陷的神经元会导致细胞内S1P有类似程度的升高；然而，只有向培养基中添加S1P才会诱导凋亡。这不是由于S1P作用于S1P受体，而是由于S1P水解为鞘氨醇，然后被细胞磷酸化，正如之前对顺式-4-甲基鞘氨醇的描述。尽管细胞能从外源性添加的鞘氨醇以及外源性S1P衍生的鞘氨醇中产生S1P，但这两种来源的S1P并不等同，因为根据对缺乏SK1或SK2活性的神经元的研究，前者主要由SK1产生，而后者主要由SK2形成（顺式-4-甲基鞘氨醇磷酸酯也是如此）。因此，这些研究表明，由于S1P至少有两个功能不同的细胞内来源，外源性S1P可能具有神经毒性。在这个模型中，S1P因裂解酶缺陷而积累，然而，这种毒性原因在其他情况下可能也很重要，顺式-4-甲基鞘氨醇磷酸酯的神经毒性就说明了这一点。
