2.7 Lipidomics

All lipidomic analyses were performed at LipidALL Technologies (Changzhou, China) using an Agilent 1290 II UPLC coupled with a Sciex QTRAP 6500 PLUS (Lam et al., 2021). Individual lipid species were quantified by referencing spiked internal standards. d9-PC32:0 (16:0/16:0), d9-PC36:1p (18:0p/18:1), d7-LPC18:1, d7-PE33:1 (15:0/18:1), d9-PE36:1p (18:0p/18:1), d7-LPE18:1, d31-PS, C17-LPS, d7-PA33:1 (15:0/18:1), C17 LPA, d7-PG33:1 (15:0/18:1), C17:1-LPG, d7-PI33:1 (15:0/18:1), C17-LPI, d5-CL72:8 (18:2)4, C17-SL and C14-BMP were purchased from Avanti Polar Lipids (AL, United States). GM3-d18:1/18:0-d3 cells were obtained from Matreya LLC (PA, United States). A modified version of the reverse-phase HPLC/MRM was used for the quantification of glycerol lipids (DG and TG). A 2.6 µm Phenomenex Kinetex-C18 column (i.d. 4.6 × 100 mm) was applied for 17 min (flow rate: 170 µl) to separate the neutral lipids using an isocratic mobile phase (including chloroform:methanol:0.1 M ammonium acetate in the ratio of 100:100:4 [v/v/v]). Short, medium, and long-chain TGs were quantified using TG (14:0)3-d5, TG (16:0)3-d5, and TG (18:0)3-d5 (CDN isotopes). DGs were determined using the internal standards d5-DG17:0/17:0 and d5-DG18:1/18:1 (Avanti Polar Lipids). Free fatty acids were determined using the internal standards d31-16:0 (Sigma-Aldrich) and d8-20:4 (Cayman Chemicals).