Choline-dependent metabolism in PNS myelination

摘要 细胞合成胆碱的能力有限，因此细胞依赖于 进口胆碱的蛋白质转运体。胆碱被用来合成 磷脂酰胆碱，髓鞘的结构脂成分是从磷脂酰胆碱 合成的。磷脂酰胆碱也会被代谢生成 磷脂酰肌醇，其磷酸化衍生物是重要的 调节髓鞘形成的信号脂质。胆碱参与合成 组蛋白的通用甲基供体S-腺苷甲硫氨酸 和DNA甲基化，从而调节基因表达。考虑到 胆碱在磷脂生物合成的十字路口的位置 和表观遗传调控，我们对 胆碱输入和胆碱依赖代谢的调节 髓鞘胶质细胞。雪旺细胞的胆碱转运蛋白尚未被 已确认身份。 我们发现类胆碱转运蛋白1(CTL1)是一种重要的 雪旺细胞髓鞘形成的调节因子。雪旺细胞中CTL1的缺失 (CTL1sc-KO)导致PNS中局灶性高髓鞘形成的早期发生。 生化分析显示胆碱类化合物的含量总体上有所下降。 髓鞘中的磷脂。此外，CTL1缺失会损害髓鞘 雪旺细胞中的基因表达和DNA修饰发生改变。从这些观察来看，我们 假设CTL1是雪旺细胞胆碱转运蛋白。我们还假设胆碱依赖 新陈代谢进入磷脂信号和表观遗传修饰，这对 髓鞘形成。为此，我们将研究雪旺细胞髓鞘形成过程中胆碱代谢的三个方面。 目的1将验证CTL1是雪旺细胞胆碱转运体的假设。MALDI-TOF和Tandem 将进行质谱分析，以直接测量胆碱输入CTL1sc-KO雪旺细胞。 CTL1缺失对磷脂酰胆碱合成的影响也将被分析。在目标2中，我们将测试 CTL1sc-KO小鼠髓鞘缺陷是PI(3，5)P2和PI(3，4，5)P3失衡所致的假说 综合。这是基于观察到CTL1sc-KO神经的磷脂酰肌醇含量发生了变化。 这些髓鞘缺陷与PI(3，5)P2和PI(3，4，5)P3失调的小鼠相似 综合。目的3将验证CTL1缺失通过调控雪旺细胞基因表达改变基因表达的假说 组蛋白和DNA甲基化。 脂类代谢紊乱，包括胆碱，是许多遗传性疾病的潜在机制。 与PNS髓鞘缺陷有关。此外，磷脂的膳食补充剂已经 被认为是治疗PNS神经病的潜在治疗选择。因此，这项研究的结果 将为理解胆碱代谢在发育过程中的意义提供重要的见解 治疗PNS神经病的治疗策略。

ABSTRACT Cells have a limited capacity to synthesize choline, thus cells depend on protein transporters to import choline. Choline is used to synthesize phosphatidylcholine, from which structural lipid components of myelin are synthesized. Phosphatidylcholine is also metabolized to generate phosphotidylinositols, whose phosphorylated derivatives are important signaling lipids that regulate myelination. Choline is involved in synthesis of the universal methyl donor, S-adenosylmethionine (SAM) for histone and DNA methylation, thus regulating gene expression. Considering the position of choline at the crossroad for the biosynthesis of phospholipids and epigenetic regulation, we have very little to no understanding of the regulation of choline import and choline-dependent metabolism in myelinating glial cells. Choline transporter for Schwann cells has not been identified. We have identified choline-like-transporter 1 (CTL1) as an important regulator of Schwann cell myelination. CTL1 deletion in Schwann cells (CTL1sc-KO) results in early onset of focal hyper-myelination in the PNS. Biochemical analysis revealed an overall decrease in choline-derived   phospholipids in the myelin. Furthermore, CTL1 loss impaired myelin gene expression and exhibited altered DNA modifications in Schwann cells. From these observations, we hypothesize that CTL1 is a Schwann cell choline transporter. We also hypothesize that choline-dependent metabolism feeds into the phospholipid signaling and epigenetic modifications that are important for myelination. To this end, we will investigate three aspects of choline metabolism in Schwann cell myelination. Aim 1 will test the hypothesis that CTL1 is a Schwann cell choline transporter. MALDI-TOF and tandem mass spectrometry will be performed to directly measure choline import into CTL1sc-KO Schwann cells. Impact of CTL1 loss on phosphatidylcholine synthesis will also be analyzed. In Aim 2, we will test the hypothesis that myelin defects in CTL1sc-KO mice results from imbalance in PI(3,5)P2 and PI(3,4,5)P3 synthesis. This is based on the observation that phosphatidylinositol contents are altered in CTL1sc-KO nerve and the myelination defects resemble those seen in mice with dysregulated PI(3,5)P2 and PI(3,4,5)P3 synthesis. Aim 3 will test the hypothesis that CTL1 loss alters gene expression in Schwann cells by modulating histone and DNA methylation. Perturbed lipid metabolism, including choline, is an underlying mechanism in many hereditary diseases associated with PNS myelination defects. Furthermore, dietary supplement of phospholipids has been considered as a potential therapeutic option for treating PNS neuropathies. Therefore, results from this study will provide important insights into understanding the implication of choline metabolism in developing therapeutic strategies to treat PNS neuropathies.