Hyaluronan in the human trabecular meshwork.

PURPOSE Hyaluronan (HA) is a high-molecular weight glycosaminoglycan that can affect water and solute fluxes in the extracellular matrix. The distribution of HA in the human trabecular meshwork of nonglaucomatous eyes was examined to help understand the potential role of HA in the regulation of aqueous outflow resistance. METHODS Histolocalization of HA was established in situ in the trabecular meshwork of human eyes with no known diseases of the anterior segment. A specific biotinylated HA-binding peptide was used as a probe for this study, with enhanced sensitivity of HA detection achieved by modifications of the fixation and staining procedures. RESULTS Evaluation of HA staining in the aqueous outflow pathway in comparison to that in other ocular structures (e.g., the vitreous) showed pronounced staining in the trabecular meshwork. The staining intensity was similar between various layers of the meshwork. Both the filtering and the anterior nonfiltering portions of the trabecular meshwork showed pronounced HA staining. The staining was localized primarily to the trabecular meshwork endothelial cells. CONCLUSIONS Pronounced HA staining observed in the various layers of the trabecular meshwork suggests that substantial amount of HA is present in the nonglaucomatous outflow pathway. The staining pattern suggests that HA is associated with the endothelial cells lining the trabecular beams. This finding supports potential roles for this glycosaminoglycan in the regulation of the physiological aqueous outflow resistance or in the maintenance of the outflow channels or both. Histochemical localization of HA in the various layers of the non-glaucomatous meshwork provides a useful basis for future comparative studies of HA distribution and relative amounts in the trabecular meshworks of eyes affected by various types of glaucoma.