CDS enzymes (CDS1 and 2 in mammals) convert phosphatidic acid (PA) to CDP-DG, an essential intermediate in the de novo synthesis of PI. Genetic deletion of CDS2 in primary mouse macrophages resulted in only modest changes in the steady-state levels of major phospholipid species, including PI, but substantial increases in several species of PA, CDP-DG, DG and TG. Stable isotope labelling experiments employing both 13C6- and 13C6D7-glucose revealed loss of CDS2 resulted in a minimal reduction in the rate of de novo PI synthesis but a substantial increase in the rate of de novo PA synthesis from G3P, derived from DHAP via glycolysis. This increased synthesis of PA provides a potential explanation for normal basal PI synthesis in the face of reduced CDS capacity (via increased provision of substrate to CDS1) and increased synthesis of DG and TG (via increased provision of substrate to LIPINs). However, under conditions of sustained GPCR-stimulation of PLC, CDS2-deficient macrophages were unable to maintain enhanced rates of PI synthesis via the 'PI cycle', leading to a substantial loss of PI. CDS2-deficient macrophages also exhibited significant defects in calcium homeostasis which were unrelated to the activation of PLC and thus probably an indirect effect of increased basal PA. These experiments reveal that an important homeostatic response in mammalian cells to a reduction in CDS capacity is increased de novo synthesis of PA, likely related to maintaining normal levels of PI, and provides a new interpretation of previous work describing pleiotropic effects of CDS2 deletion on lipid metabolism/signalling.

中文翻译：

---

CDS2 表达调节从头磷脂酸合成。


CDS 酶（哺乳动物中的 CDS1 和 CDS2）将磷脂酸 （PA） 转化为 CDP-DG，CDP-DG 是 PI 从头合成的必需中间体。原代小鼠巨噬细胞中 CDS2 的基因缺失仅导致包括 PI 在内的主要磷脂种类的稳态水平发生适度变化，但 PA、CDP-DG、DG 和 TG 的几种种类的稳态水平显著增加。采用 13C6 和 13C6D7-葡萄糖的稳定同位素标记实验显示，CDS2 的丢失导致 PI 从头合成速率的最小降低，但 G3P 从糖酵解衍生的 PA 从头合成的速率显着增加。PA 合成的增加为 CDS 容量降低（通过增加向 CDS1 提供底物）和 DG 和 TG 合成增加（通过增加向 LIPIN 提供底物）的情况下正常基础 PI 合成提供了潜在的解释。然而，在 PLC 持续 GPCR 刺激的条件下，CDS2 缺陷的巨噬细胞无法通过“PI 循环”维持增强的 PI 合成速率，导致 PI 的大量丢失。CDS2 缺陷型巨噬细胞也表现出钙稳态的显着缺陷，这与 PLC 的激活无关，因此可能是基础 PA 增加的间接影响。这些实验表明，哺乳动物细胞对 CDS 能力降低的重要稳态反应是 PA 的从头合成增加，可能与维持 PI 的正常水平有关，并为之前描述 CDS2 缺失对脂质代谢/信号传导的多效性影响的工作提供了新的解释。