Glycerophosphocholine (GPC) is an intracellular metabolite in phosphatidylcholine metabolism and has been studied for endogenous choline supply in cells. GPC, as a water-soluble supplement, has been expected to play a role in preventing brain disorders; however, recent studies have shown that intake of high levels of choline-containing compounds is related to trimethylamine N-oxide (TMAO) production in the liver, which is reportedly associated with the progression of atherosclerosis. In this study, we aimed to explore the mechanisms underlying the intestinal absorption and metabolism of GPC. Caco-2 cell monolayer experiments showed that exogenously added GPC was hydrolyzed to choline in the apical medium, and the resulting choline was transported into the Caco-2 cells and further to the basolateral medium. Subsequently, we focused on glycerophosphodiesterase 1 (Gpcpd1/GDE5), which hydrolyzes GPC to choline in vitro and is widely expressed in the gastrointestinal epithelium. Our results revealed that the Gpcpd1 protein was located not only in cells but also in the medium in which Caco-2 cells were cultured. Gpcpd1 siRNA decreased the GPC-hydrolyzing activity both inside Caco-2 cells and in conditioned medium, suggesting the involvement of Gpcpd1 in luminal GPC metabolism. Finally, we generated intestinal epithelial-specific Gpcpd1-deficient mice and found that Gpcpd1 deletion in intestinal epithelial cells affected GPC metabolism in intestinal tissues and partially abolished the increase in blood TMAO levels induced by GPC administration. These observations demonstrate that Gpcpd1 triggers choline production from GPC in the intestinal lumen and is a key endogenous enzyme that regulates TMAO levels following GPC supplementation.

中文翻译：

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Gpcpd1 在肠道 α-甘油磷酸胆碱代谢和三甲胺 N-氧化物产生中的作用。


甘油磷酸胆碱 （GPC） 是磷脂酰胆碱代谢中的一种细胞内代谢物，已被研究用于细胞中内源性胆碱的供应。GPC 作为一种水溶性补充剂，一直有望在预防脑部疾病方面发挥作用;然而，最近的研究表明，摄入高水平的含胆碱化合物与肝脏中氧化三甲胺 （TMAO） 有关，据报道这与动脉粥样硬化的进展有关。在这项研究中，我们旨在探讨 GPC 肠道吸收和代谢的潜在机制。Caco-2 细胞单层实验表明，外源添加的 GPC 在顶端培养基中水解为胆碱，所得胆碱被转运到 Caco-2 细胞中，并进一步转运到基底外侧培养基中。随后，我们专注于甘油磷酸二酯酶 1 （Gpcpd1/GDE5），它在体外将 GPC 水解为胆碱，并在胃肠道上皮中广泛表达。我们的结果显示，Gpcpd1 蛋白不仅位于细胞中，还位于培养 Caco-2 细胞的培养基中。Gpcpd1 siRNA 降低了 Caco-2 细胞内和条件培养基中的 GPC 水解活性，表明 Gpcpd1 参与管腔 GPC 代谢。最后，我们生成了肠上皮特异性 Gpcpd1 缺陷小鼠，发现肠上皮细胞中的 Gpcpd1 缺失影响了肠道组织中的 GPC 代谢，并部分消除了 GPC 给药诱导的血液 TMAO 水平升高。这些观察结果表明，Gpcpd1 触发肠腔中 GPC 产生胆碱，并且是补充 GPC 后调节 TMAO 水平的关键内源性酶。