Laser capture proteomics reveals new candidates for sperm-interacting proteins in the bovine oviduct epithelium.

IN BRIEF: The molecular interactions between spermatozoa and the oviduct epithelium that are involved in capacitation and sperm availability during fertilization still remain largely unknown in many species. This study provides comprehensive proteomes of the apical and basal part of the bovine oviduct epithelium (isthmus and ampulla, pre- and post-ovulatory) and presents new protein candidates for sperm binding in the bovine functional sperm reservoir. ABSTRACT: The proximal region of the oviduct (isthmus) serves as a sperm reservoir in many mammalian species. This reservoir is composed of epithelial cells that bind sperm primarily to their apical cilia and ensure the survival of high-quality sperm until ovulation. The species-specific molecular interactions between spermatozoa and the oviduct epithelium, however, are still poorly understood. The aim of this study is to identify new candidates for sperm-interacting proteins in the bovine reservoir using laser capture proteomics. Ipsilateral oviducts were collected from cyclic cows at pre- and post-ovulatory stages. Isthmus and ampulla tissue samples were fixed, paraffin-embedded, sectioned and subjected to laser microdissection to establish pools of microsamples separating the apical part of the epithelium, containing potential sperm-interacting proteins, from the basal part, containing proteins not currently located or secreted on the cell surface. Proteins were analyzed by nanoLC-MS/MS, and differentially abundant proteins (DAPs) were identified using t-tests. A total of 505 and 512 proteins could be identified in apical and basal microsamples, respectively. Only 8/141 regional and 1/79 cycle stage-related DAPs were shared between both epithelium parts, indicating a selective regulation of protein expression. Of the apical proteins, 19 were predicted to be candidates for sperm interactions, including annexins (ANXA) 1, 2, 5 and 8; oviduct glycoprotein 1 (OVGP1); voltage-dependent anion-selective channel proteins (VDAC) 1 and 2; apolipoprotein A1 (APOA1). This work provides the first proteomic characterization of microdissected cellular compartments of the bovine oviduct epithelium and presents new candidates for improving sperm quality in assisted reproductive technologies.