Spatial segmentation and metabolite annotation involved in sperm maturation in the rat epididymis by MALDI imaging mass spectrometry

Abstract

Spermatozoa acquire their fertilizing capacity during a complex maturation process that occurs in the epididymis. This process involves a substantial molecular remodeling at the surface of the gamete. Epididymis is divided into three regions (the caput, corpus, and cauda) or into 19 intraregional segments based on histology. Most studies carried out on epididymal maturation have been performed on sperm samples or tissue extracts. Here, we used MALDI imaging mass spectrometry in the positive and negative ion modes combined with spatial segmentation and automated metabolite annotation to study the precise localization of metabolites directly in the rat epididymis. The spatial segmentation revealed that the rat epididymis could be divided into several molecular clusters different from the 19 intraregional segments. The discriminative m/z values that contributed the most to each molecular cluster were then annotated and corresponded mainly to phosphatidylcholines, sphingolipids, glycerophosphates, triacylglycerols, plasmalogens, phosphatidylethanolamines, and lysophosphatidylcholines. A substantial remodeling of lipid composition during epididymal maturation was observed. It was characterized in particular by an increase in the number of sphingolipids and plasmalogens and a decrease in the proportion of triacylglycerols annotated from caput to cauda. Ion images reveal that molecules belonging to the same family can have very different localizations along the epididymis. For some of them, annotation was confirmed by on-tissue MS/MS experiments. A 3D model of the epididymis head was reconstructed from 61 sections analyzed with a lateral resolution of 50 μm and can be used to obtain information on the localization of a given analyte in the whole volume of the tissue.

Edible Bird’s Nest Supplementation Improves Male Reproductive Parameters of Sprague Dawley Rat

“…On the other hand, 250 mg/kg BW/d EBN demonstrated a slight decrease in the percentage of viability without a statistically significant difference compared to 50 mg/kg BW/d EBN. A discrepancy in the result of sperm viability may probably due to the different membrane sensitivity of the epididymal sperm ( Hall et al, 1991 ; Lagarrigue et al, 2020 ). The process of harvesting sperm from the cauda epididymis might be mixed up with the adjacent caput epididymis.…”

Space and Time Coherent Mapping for Subcellular Resolution of Imaging Mass Spectrometry

“…We tentatively assigned three possible neurotransmitters to these ionized molecules. There are reports by others regarding the MS imaging for neurotransmitters (Sugiyama et al, 2019; with MALDI [ 17 ]), MS imaging in the epididymis (Lagarrigue et al, 2020; with MALDI [ 18 ]), and MS imaging in the leech (Meriaux et al, 2011; with MALDI and SIMS [ 19 ]). However, we did not find any MSI data that reported neurotransmitters in the epididymis of the leech.…”

Study of the Distribution of Acetaminophen and Its Metabolites in Rats, from the Whole-Body to Isolated Organ Levels, by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging after On-Tissue Chemical Derivatization

“…Segmentation is an unsupervised clustering of the dataset on the basis of molecular and spatial features without the use of prior histological knowledge. 45 Despite the use of consecutive sections, the histological images obtained from the two sets of testis sections were relatively different due to the particularly complex anatomical structures of the testis. However, the spatial segmentation maps obtained with and without OTCD corresponded to the same anatomical structures of the testis: the interstitial tissue, the seminiferous epithelium, and the lumen (Supporting Information: Figure S8B,C).…”

“…For an objective assessment of the possible delocalization of all the detected compounds, we compared spatial segmentation maps obtained from testis sections with and without OTCD. Segmentation is an unsupervised clustering of the dataset on the basis of molecular and spatial features without the use of prior histological knowledge . Despite the use of consecutive sections, the histological images obtained from the two sets of testis sections were relatively different due to the particularly complex anatomical structures of the testis.…”