Early stage fetal neocortex exhibits a complex ganglioside profile as revealed by high resolution tandem mass spectrometry

In this study we report on the first mass spectrometric (MS) investigation of gangliosides and preliminary assessment of the expression and structure in normal fetal neocortex in early developmental stages: 14th (Neo14) and 16th (Neo16) gestational weeks. Ganglioside analysis was carried out using a hybrid quadrupole time-of-flight (QTOF) MS with direct sample infusion by nanoelectrospray ionization (nanoESI) in the negative ion mode. Under optimized conditions a large number of glycoforms i.e. 75 in Neo14 and 71 in Neo16 mixtures were identified. The ganglioside species were found characterized by a high diversity of the ceramide constitution, an elevated sialylation degree (up to pentasialylated gangliosides-GP1) and sugar cores modified by fucosylation (Fuc) and acetylation (O-Ac). Direct comparison between Neo14 and Neo16 revealed a prominent expression of monosialylated structures in the Neo16 as well as the presence of a larger number of polysialylated species in Neo14 which constitutes a clear marker of rapid development-dependant changes in the sialylation. Also the MS screening results highlighted that presumably O-acetylation process occurs faster than fucosylation. CID MS/MS under variable collision energy applied for the first time for structural analysis of a fucosylated pentasialylated species induced an efficient fragmentation with generation of ions supporting Fuc-GP1d isomer in early stage fetal brain neocortex.