Abstract
Even though the role of lipids in pandemic diseases such as obesity and diabetes is a focus of increasing research, the role of lipids during organogenesis, when diverse diseases may be triggered, is unexplored. Also, pig embryonic tissues represent an attractive option for organ transplantation. This study introduces a detailed morphological analysis of swine fetal tissues with matching location of lipids acquired by desorption electrospray ionization mass spectrometry (DESI-MS) imaging for the study of differential distribution of free fatty acids (FFA) and phospholipids (PL) in specific organs during fetal development. Samples from a pig fetuses around Day 50 of pregnancy were sectioned at a cryotome and mounted onto glass slides. Fixative agents were not used. DESI-MS images were run with a step size of 300 µm using a morphologically friendly (non-destructive) solvent combination, namely dimethylformamide/acetonitrile 1 : 1 (v/v). Data were acquired in the negative ion mode in the m/z range of 150 to 1000 from different sections representing the whole swine fetus body. Ion images were constructed using BioMAP software. After imaging, the whole-body tissue samples were stained with hematoxylin and eosin (H&E) and were overlaid to the DESI-MS lipid images. Differential distribution of FFA, phosphatidylcholines (PC), phosphatidylserines (PS), sulphatides (ST), and phosphatidylinositols (PI) was observed among organs, especially on nervous and circulatory systems, and digestive glands. Most lipids concentrated in the brain, spinal cord, and digestive glands such as the liver. For example, arachidonic acid was most abundant in neuronal tissue, whereas docosahexaenoic acid predominated in the liver and digestive glands. Distribution of PS (36 : 1) of m/z 788 was observed in all tissues except for the digestive system, but PS (40 : 6) of m/z 834.7 was exclusive of brain and spinal cord. Lipids related to brain and spinal cord were mostly polyunsaturated fatty acids as well as specific PS lipids. Arachidonic and eicosatrienoic acids are more concentrated in hindbrain and spinal cord, whereas PS was more abundant in the brain than in the spinal cord. There is no information on PS chemical composition during brain and spinal cord development, but PS concentration in the nervous tissue membranes varies with age, brain areas, cell type, and subcellular components. Several reports indicate that alteration in PS synthesis might participate in the mechanism of brain damage. Also, PS has been found to be altered in brain tumours. Oleic acid, fatty acid dimers, and the signalling lipid PI (38 : 3) were most significant for the digestive system and liver. Liver is one of the main organs involved in fatty acid metabolism (besides adipose tissue and muscle). By overlying morphological and molecular information, lipids seem to be a major player in the organogenesis process.
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