Glycan profile of oviductal isthmus epithelium in normal and superovulated ewes

Glycans of oviductal isthmus are implicated in sperm-isthmus interaction, sperm storage, survival, and capacitation. Isthmus morphology and glycoprotein production are controlled by sex steroids, which could be responsible for alterations of some reproductive events in the superovulated ewes (SE). In this study, the oviductal isthmus epithelium was evaluated in normal and in SE using morphologic and lectin histochemical analysis. The epithelium of normal isthmi was significantly taller in folds than in crypts, whereas it significantly decreased in the folds of SE. Nonciliated cells (NCs) from normal, showed apical blebs revealing apocrine secretory activity, which was missing in SE. The quantitative analysis of lectin staining revealed higher Con A, DBA, and PNA reactivity but lower affinity to KOH-sialidase- (Ks)WGA, GSA II, LTA, UEA I, SBA, GSA I-B4, RCA120, KsPNA, MAL II, SNA in control isthmi compared with superovulated ones. The NCs apical blebs showed terminal fucose (Fuc), N-acetylgalactosamine (GalNAc), galactose (Gal), lactosamine, and O- and N-sialoglycans. In normal isthmi, the luminal surface of NCs and ciliated cells expressed Fuc, highly mannosilated N-glycans terminating with lactosamine as well as O-glycans ending with N-acetylglucosamine (GlcNAc) and GalNAc. Moreover, NCs microvilli contained Gal and α2-3-linked sialic acids. In SE, the luminal surface lacked Gal and GalNAcα1, 3(LFucα1,2)Galβ1,3/4GlcNAcβ1, whereas it was enriched with Fuc in the folds and with α2-3sialo-mucins both in crypts and in folds. The apical surface showed additional O- and N-linked sialoglycans in NCs and αGal in the cilia, which expressed α2-6-linked sialic acid only in the folds. The cytoplasm of control NCs showed highly mannosilated N-glycans throughout the epithelium and GlcNAc in the folds. After superovulation treatment, NCs expressed cytoplasmic terminal Fuc, βGalNAc, lactosamine, α2-3-, and α2-6-linked sialic acids in the folds. The cytoplasm of normal ciliated cells cells displayed a binding pattern similar to normal NCs except for the absence of higly mannosilated N-glycans in the folds, which appeared in superovulated samples. This study demonstrates glycan zone-specific distribution along the isthmus epithelium that is influenced by the superovulation treatment. Whether an alteration in the glycan distribution is implicated in the low-rate fertilization after natural mating of the superovulated sheep remains to be addressed.