The testis is a complex and heterogeneous organ with endocrine and exocrine functions. The most abundant testicular lipids, seminolipids, (accounting for 3% of total lipids) are selective to maturing germ cells and crucial for male fertility1,2. Furthermore, phosphatidylcholines (PCs) play a major role on the structure and function of testes3. A comprehensive understanding of the overall lipid metabolites localisation is critical to understand testicular function and to this day, studies have been limited to specific lipid classes. With the technical improvement of ionization sources such as matrix-assisted laser/desorption ionization (MALDI) and desorption electrospray ionization (DESI-MSI), it is now possible to achieve pixel sizes that specifically distinguish the complex testicular anatomy.
Here we used a multi-modal mass spectrometry imaging (MSI) approach with MALDI-MSI and DESI-MSI as complementary approaches to improve the characterization of testicular lipid metabolites.
In both modes of ionisation using MALDI or DESI, distinct lipids profiles could be distinguished between Leydig/blood vessels, more mature germ cells and Sertoli cells/early germ cells.
In negative mode, the major lipid detected was a seminolipid, m/z 795.53 identified as C16:0-alkyl-C16:0-acyl and localised in the germ cells. Other seminolipids were also detected at lower intensities such as m/z 809.51 which was more intense depending on the maturity of the germ cells. The second most intense phospholipid detected was m/z 885.55 (PI (38:4, H-) that is highly localised in the Leydig and blood vessels.
In positive mode, mainly glycerophospholipids were detected. PC (36:1) and PC (38:5) have both been detected with a sodium and potassium cation, strongly localised in the Leydig/blood vessels cell types. PC (34:1) and PC (36:4) ( Na+ and K+) ions were mainly localised in the Sertoli cells/early germ cell type and PC (38:5) and PC 38:6) were localised in the more mature germ cells.