Non-targeted proteomic analysis of Asian elephant (Elephas maximus) seminal plasma using an in-solution digestion technique and liquid chromatography tandem-mass spectrometry

Abstract

Seminal plasma proteins have recently been reported to play a significant role as valuable materials for understanding male reproductive biology, identifying causes of fertility problems, and developing reproductive biomarkers. Proteomic analysis of seminal plasma holds promise in advancing the understanding of male Asian elephant reproductive biology. This study aims to explore seminal plasma proteins of Asian elephants and their probable functions to provide fundamental information about male reproduction in this species. The protein solution from pooled seminal plasma from 10 bulls (a total of 33 ejaculates) was digested into peptides and identified using LC-MS/MS. Out of 986 proteins, 597 were mapped and matched with 58 species in UniProt databases, including Elephas maximus. These mapped proteins were mostly involved in binding function, catalytic activity, cellular process, and metabolic process. Only 29 mapped proteins were recognized to be related in reproductive process, mainly associated in spermatogenesis and sperm capacitation. Additionally, several seminal plasma proteins related to fertility or semen quality in other mammals were also found in Asian elephant semen, such as keratin type I, aldose reductase, thrombospondon-1, fibronectin 1, platelet-activating factor acetyl hydrolase, mannosidase, and semenogelin-2. This discovery clearly reveals the beneficial protein profile in seminal plasma of the Asian elephant and serves as a crucial step in investigating infertility and poor semen quality in this valuable species.

Keywords: Asian elephant; male reproduction; protein; proteomic analysis; seminal plasma.

Figure 1

The bar graph illustrating the quantity of mapped Asian elephant SP proteins obtained from Uniprot database of seminal plasma samples from a cohort of 10 male elephants: E2, E3, E4, E5, E6, E8, E9, E10, E11, and E13. The solid bar represents the SP proteins that are common to both individual samples and the pooled sample from all bulls, whereas the striped bar indicates the total number of SP proteins found in the individual samples.

Figure 2

Classification of seminal plasma proteins from Asian elephant semen in terms of (A) molecular function, (B) biological process, and (C) cellular component using PANTHER as a gene ontology analysis. The quantities of proteins in each class are presented as percentages in pie charts.

Figure 3

The protein–protein interaction (PPI) network of mapped Asian elephant SP proteins, constructed using data from the STRING database, was recognized in Homo sapiens (human). Sixty-one SP proteins displayed interactions among them at different levels. The different types of associations are presented in different colors of the linkage lines between proteins: light blue for curated database interactions, pink for experimental interactions, green for gene neighborhoods, red for gene fusions, blue for gene co-occurrence, light green for text-mining, black for co-expression, and purple for protein homology.

Figure 4

Pie chart showing percentage of seminal plasma proteins from Asian elephant semen divided into several functions that are involved in the reproductive process using UniProt as a gene ontology analysis.