Actin structure in the outflow tract of normal and glaucomatous eyes

Abstract

Purpose. To characterize the in situ distribution of actin in Schlemm's canal endothelium (SCE) and juxtacanalicular tissue (JCT) cells in glaucomatous human eyes, and compare to the distribution in normal eyes. Methods. Fresh human eye bank eyes were perfused and fixed at pressure ( n=27 normal eyes and 22 confirmed glaucomatous eyes). Schlemm's canal was opened by microdissection and outflow tissues were labelled for confocal microscopy to visualize F-actin, nuclei, laminin and/or CD31. Images were acquired in Z-series from the inner wall of Schlemm's canal, juxtacanalicular tissue and outer corneoscleral meshwork. Results. In normal eyes, inner wall Schlemm's canal endothelial (SCE) cells showed a dense peripheral F-actin band, as previously described. JCT cells showed a more random and amorphous F-actin distribution. In glaucoma eyes, peripheral F-actin bands were less common in inner wall SCE cells; instead, F-actin was more centrally located within the cell and appeared ‘tangled’. These actin tangles were also prominent in JCT cells of glaucoma eyes. Glaucoma eyes also demonstrated structures with features of cross-linked actin networks (CLANs), and more frequent occurrence of punctuate actin concentrations. There was a significant degree of heterogeneity, with some regions from glaucomatous eyes appearing normal and vice versa. Conclusion. F-actin architecture in human outflow pathway cells in situ differs between normal and glaucoma eyes, with glaucomatous tissue showing a more ‘disordered’ actin architecture overall. Some of these changes are likely due to effects secondary to administration of anti-glaucoma medications. Most of the changes that we observed could potentially affect the biomechanical properties of the outflow pathway tissues in glaucoma, but their role in the pathogenesis of ocular hypertension remains unclear.