122 Proteome of extracellular vesicles from follicular fluid of bovine 3- to 6-mm follicles: Similarity and specificity compared with granulosa cells

Abstract

Extracellular vesicles (EVs) are released from cells and are present in most bodily fluids. Small EVs, 30-150 nm in diameter, known as exosomes, transport regulatory noncoding RNA, lipids, and proteins, and thus participate in cell-to-cell communications and signalling. Exosomes from bovine ovarian follicular fluid (FF) can stimulate proliferation of granulosa cells (GCs), cellular uptake, and cumulus expansion, and therefore might be useful in reproductive technologies. The aim of our study was to characterise the protein content of bovine FF exosomes and compare it with the GC proteome in order to better understand the origin of these EVs and their possible functions. We extracted EVs from FF of bovine 3- to 6-mm ovarian follicles (enclosed oocytes routinely used for in vitro embryo production (IVEP)) via a series of centrifugations at 2,000g to 100 000g. Transmission electron microscopy analysis revealed that 87.9% of extracted EVs had a larger size of exosomes, and 11.8% had smaller size (<30 nm); only 0.3% of EVs ranged from 150 to 250 nm. For proteome analysis, 80 µg of total proteins extracted from EVs and GCs originating from the same follicles were resolved on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). After trypsin proteolytic digestion, peptide mixtures were analysed via nanoflow liquid chromatography coupled to high-resolution tandem mass spectrometry (MS/MS) using LTQ Orbitrap Velos (Thermo Fisher Scientific). We used Mascot engine (Matrix Science) against the NCBIprot mammalian database to perform MS/MS ion searches; proteins identified with at least two peptides were clustered with Scaffold 4.0 software. We identified 542 protein isoforms that represented 221 and 299 clusters of unique proteins in EVs and GCs, respectively. Of these, 158 are common among EVs and GCs and demonstrate significant enrichment (P < 0.01) in Gene Ontology (GO) terms related to protein folding in endoplasmic reticulum, receptor-mediated endocytosis, cell-cell adhesion, translation processes, binding of proteins, RNA or cholesterol, and antioxidant activity. Of common proteins, 69.6% are mapped to the GO “extracellular exosome.” Of the 63 proteins over-represented in EVs, 37 are ribosomal proteins involved in translation, rRNA processing, and mRNA catabolic processes. Of the proteins over-represented in GCs, 141 are mainly involved in carbon, fatty acid, and tricarboxylic acid (TCA) metabolism, oxidation-reduction processes, NAD and poly(A) RNA binding, and cell cycle regulation. These proteins are enriched in GO terms related to membrane, mitochondrion, and extracellular exosomes. Our findings indicate that proliferating GCs of antral follicles actively synthesise and secrete exosomes, which contain significant quantity of different ribosomal proteins. These RNA-binding proteins may serve to compact the cargo of different types of RNAs-both regulatory and designated for degradation, which are transported by FF exosomes.

Funds were provided by INRA PHASE France and by the Russian Science Foundation (project 19-16-00115).