Glycoconjugates of the human trabecular meshwork: a lectin histochemical study

Twelve specimens of resin-embedded human trabecular meshwork were probed with a panel of 21 biotinylated lectins, using an avidin-biotin peroxidase revealing system, in order to determine the normal pattern of saccharide expression in this tissue. High-mannose, intermediate and hybrid N-linked glycans, and complex N-linked bisected and non-bisected bi/tri-antennate glycans, as shown by the binding of Canavalia ensiformis (ConA), Pisum sativum (PSA), Lens culinaris (LCA) agglutinins and Phaseolus vulgaris erythroagglutinin (ePHA), were strongly expressed by the canal of Schlemm endothelium and juxtacanalicular tissue, but less so by the corneoscleal meshwork. Highly branced complex glycans were not found, as there was no binding by Phaseolus vulgaris leukoagglutinin (IPHA). Sialyl residues, especially those alpha 2,6-linked as demonstrated by strong Sambucus nigra (SNA) lectin staining, were also abundant in this area. N-acetyllactosamine sequences and some O-linked glycans were present in the trabecular meshwork, as shown by Solanum tuberosum (STA), Datura stramonium (DSA), and Jacalin (Jac) lectin binding, while fucose residues were not detected by Tetragonolobus purpureas (LTA) or Ulex europaeus-1 (UEA-1) agglutinins. These results indicate similarities with renal glomerular and vascular endothelium, although the lack of binding with UEA-1 agglutinin suggests differences which may relate to the specialized function of the trabecular meshwork. This study provides a baseline for comparative analysis of the glycans of human trabecular meshwork in pathological conditions such as primary open-angle glaucoma.