The impact of sphingosine-1-phosphate (S1P)-lyase deficiency on astrocyte physiology and on epigenetic regulation

鞘氨醇-1-磷酸（S1 P）是一种进化上保守的鞘脂代谢中间产物，调节脑中的多种生物学过程，包括神经发育、分化和存活。另一个有趣的发现是它在调节组蛋白乙酰化中的功能。S1 P特异性结合组蛋白脱乙酰酶HDAC 1和HDAC 2，从而抑制它们的酶活性并防止乙酰基从组蛋白尾部内的赖氨酸残基上去除。S1 P-裂解酶（SGPL 1）在鞘脂催化剂的最后一步不可逆地裂解S1 P，生成乙醇胺磷酸盐和长链醛。S1 P在大脑发育中的重要作用是毋庸置疑的。然而，关于S1 P参与神经退行性疾病病理学的报道是相当矛盾的。为了阐明S1 P在脑中的功能，我们建立了一种小鼠模型，其中SGPL 1在神经细胞中特异性失活（SGPL 1 fl/fl/内斯）。正如预期的那样，SGPL 1消融导致S1 P在脑中蓄积，引起神经元ER应激、细胞内钙增加、突触前结构和功能受损，并伴有小鼠的认知缺陷。此外，我们证明，SGPL 1缺乏阻断神经元自噬在其早期阶段，因为减少磷脂酰乙醇胺（PE）的生产。因此，S1 P的积累和同时下降的PE在SGPL 1缺陷的大脑造成相当大的神经元损伤。由于神经元损伤可能诱导炎症反应，我们研究了小胶质细胞的变化作为一个结果，S1 P在神经细胞中的积累。我们证实了SGPL 1 fl/fl/内斯小鼠脑中小胶质细胞活化的增加，如形态学和生化标志物所示。此外，在来自SGPL 1 fl/fl/内斯小鼠的FACS分选和培养的小胶质细胞中，注意到促炎细胞因子的分泌增加。由于编码SGPL 1的基因突变导致人类神经病理学的数量不断增加，我们决定扩展我们的研究，一方面分析SGPL 1 fl/fl/内斯小鼠中星形胶质细胞的命运，另一方面分析S1 P在SGPL 1耗尽的大脑中积累的表观遗传后果。因此，本项目旨在回答两个中心问题：I）SGPL 1的神经靶向消融如何诱导星形胶质细胞增生？II）S1 P依赖性调节组蛋白乙酰化的分子机制是什么？具体目标是：探讨星形胶质细胞增生的原因及其后果。IB.探讨原代培养星形胶质细胞的自噬作用。为了验证我们的假设，有关的分子机制，链接SGPL 1的活动，激活星形胶质细胞和自噬。研究SGPL 1缺陷脑中组蛋白乙酰化。IIb：研究钙对组蛋白乙酰化的影响。初步结果强烈鼓励实施该项目。

Sphingosine-1-phosphate (S1P), an evolutionarily conserved catabolic intermediate of sphingolipid metabolism regulates diverse biological processes in the brain including neural development, differentiation, and survival. Another interesting finding is its function in the regulation of histone acetylation. S1P specifically binds to histone deacetylases HDAC1 and HDAC2 thus inhibiting their enzymatic activity and preventing the removal of acetyl groups from lysine residues within histone tails. S1P-lyase (SGPL1) irreversibly cleaves S1P in the final step of sphingolipid catabolism generating ethanolamine phosphate and a long-chain aldehyde. There is no doubt on the essential role of S1P in brain development. Yet, reports on the involvement of S1P in the pathology of neurodegenerative diseases are rather conflicting. In an attempt to clarify the function of S1P in the brain, we generated a mouse model in which SGPL1 was inactivated specifically in neural cells (SGPL1fl/fl/Nes). As expected, SGPL1 ablation leads to S1P accumulation in the brain causing neuronal ER-stress, an increase in intracellular calcium, impairment of presynaptic architecture and function, accompanied by cognitive deficits in mice. In addition, we demonstrated that SGPL1 deficiency blocks neuronal autophagy at its early stages because of reduced phosphatidylethanolamine (PE) production. Thus accumulation of S1P and the simultaneous decline of PE in SGPL1 deficient brains cause considerable neuronal damage. As neuronal damage might induce inflammation, we investigated the microglial alterations as a result of S1P accumulation in neural cells. We evidenced increased microglial activation in the brains of SGPL1fl/fl/Nes mice as shown by morphological as well as biochemical markers. Also, an increased secretion of pro-inflammatory cytokines in FACS-sorted and cultured microglia from SGPL1fl/fl/Nes mice was noticed. Given the increasing number of human neuropathalogies as a result of mutations in the gene encoding SGPL1, we decided to extend our studies and analyse on the one hand the fate of astrocytes in SGPL1fl/fl/Nes mice and on the other hand the epigenetic consequences of S1P accumulation in SGPL1 depleted brains. The present project thus aims to answer two central questions:I) How does neural-targeted ablation of SGPL1 induce astrogliosis?II) Which molecular mechanism underlies S1P dependent regulation of histone acetylation?Specific goals are:Ia. To explore the causes of astrogliosis and of its consequences. Ib. To assess autophagy in primary cultured astrocytes.Ic. To verify our hypothesis regarding the molecular mechanism that links SGPL1 activity, activation of astrocytes and autophagy.IIa. To investigate histone acetylation in SGPL1 deficient brains.IIb: To study the involvement of calcium regarding histone acetylation.Preliminary results strongly encourage implementation of this project.