MALDI mass spectrometry reveals that cumulus cells modulate the lipid profile of in vitro-matured bovine oocytes

The influence of cumulus cells (CC) on the lipid profile of bovine oocytes matured in two different lipid sources was investigated. Cumulus-oocyte complexes (COC) or denuded oocytes (DO) were matured in tissue culture medium (TCM) supplemented with fetal bovine serum (FBS) or serum substitute supplement (SSS). Lipid profiles of TCM, serum supplements, immature CC and oocyte (IO), and in vitro-matured oocytes from COC and DO were then analyzed by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) and submitted to partial least squares-discriminant analysis (PLS-DA). The developmental competence of such oocytes was also assessed. Differences in lipid composition were observed between two types of sera and distinctly influenced the lipid profile of CC. As revealed by PLS-DA, the abundance of specific ions corresponding to triacylglycerols (TAG) or phospholipids (PL) were higher in COC compared to DO both supplemented with FBS or SSS and to some extent affected the subsequent DO in vitro embryo development. DO exposed to SSS had however a marked diminished ability to develop to the blastocyst stage. These results indicate a modulation by CC of the oocyte TAG and PL profiles associated with a specific cell response to the serum supplement used for in vitro maturation.本研究探讨了卵丘细胞（cumulus cells, CC）对两种不同脂质来源条件下成熟牛卵母细胞脂质谱的影响。将卵丘-卵母细胞复合体（cumulus-oocyte complexes, COC）或裸卵母细胞（denuded oocytes, DO）置于添加胎牛血清（fetal bovine serum, FBS）或血清替代添加剂（serum substitute supplement, SSS）的组织培养液（tissue culture medium, TCM）中进行成熟培养。随后采用基质辅助激光解吸电离质谱（matrix assisted laser desorption ionization mass spectrometry, MALDI-MS）对培养液、血清添加剂、未成熟卵丘细胞与未成熟卵母细胞（immature CC and oocyte, IO），以及源自COC和DO的体外成熟卵母细胞的脂质谱进行分析，并通过偏最小二乘判别分析（partial least squares-discriminant analysis, PLS-DA）对数据进行统计分析。同时评估了上述卵母细胞的发育潜能。研究发现两种血清的脂质组成存在差异，且该差异显著影响卵丘细胞的脂质谱特征。偏最小二乘判别分析结果显示，在添加FBS或SSS的培养体系中，COC组内对应三酰甘油（triacylglycerols, TAG）或磷脂（phospholipids, PL）的特定离子丰度均高于DO组，且在一定程度上影响了后续DO的体外胚胎发育能力。然而，经SSS培养的DO组发育至囊胚期的能力显著降低。上述结果表明，卵丘细胞可对卵母细胞的三酰甘油与磷脂谱进行调控，该调控过程与卵母细胞对体外成熟所用血清添加剂的特异性细胞响应密切相关。