Diversity of glycoconjugate pattern in the bladder epithelium of horse and donkey revealed by lectin histochemistry

The glycoconjugates expressed on the mucosal surface of urinary bladder act as a barrier against invasion by pathogenic microorganisms and injury from toxic substances in the urine. Also, they serve as a major source for soluble urinary glycoproteins, which can actively modify the urine composition. Glycoconjugate pattern characterizes distinct cellular populations, cell differentiation and maturation, as well as cell morpho-functional changes in both normal and pathological conditions. The informations on the bladder glycoconjugates suggest that glycosaminoglycans are only a minor component at urothelial level compared with glycoproteins. In this research we characterized the glycoconjugate pattern in the bladder epithelium by lectin histochemistry, comparatively in the horse and donkey. Tissue fragments were fixed in 4% (w/v) neutral formalin and then embedded in paraffin wax. Sections were stained with a panel of twelve lectins, in combination with KOH saponification and sialidase digestion. The entire urothelium reacted with SNA, KOH-sialidase (s)-PNA, s-SBA, Con A, GSA II in horse bladder, and showed additional binding sites for MAL II and GSA I-B4 in the donkey one. The urothelium luminal surface bound MAL II, DBA, LTA in the horse and DBA and LTA I in the donkey. In addition, the urothelium of the horse bladder stained with PNA, SBA and GSA I-B4 in the basal and luminal regions and with UEA I in the adluminal zone. These results demonstrate remarkable inter-specific difference of the glycoprotein pattern expressed in the urothelium of two Equine species, despite the very close taxonomic vicinity. It is noteworthy that glycans terminating with Galβ1,3GalNAc (PNA reactivity) and Fucα1,2Galβ1,4GlcNAcβ (UEA I affinity) lack in the epithelium lining the donkey urinary bladder.