Altered mechanobiology of Schlemm’s canal endothelial cells in glaucoma

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 38; pp. 13876 - 13881
• Main Authors: Overby, Darryl R., Zhou, Enhua H., Vargas-Pinto, Rocio, Pedrigi, Ryan M., Fuchshofer, Rudolf, Braakman, Sietse T., Gupta, Ritika, Perkumas, Kristin M., Sherwood, Joseph M., Vahabikashi, Amir, Dang, Quynh, Kim, Jae Hun, Ethier, C. Ross, Stamer, W. Daniel, Fredberg, Jeffrey J., Johnson, Mark
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 23.09.2014; National Acad Sciences
• Subjects: Biological Sciences; Biomechanics; Canals; Cell culture; Cells; Cells, Cultured; Cytoskeleton - metabolism; Cytoskeleton - pathology; Delta cells; Density; Endothelial cells; Endothelial Cells - metabolism; Endothelial Cells - pathology; Endothelium; Eye - metabolism; Eye - pathology; Eyes; Gels; Gene expression; Glaucoma; Glaucoma - metabolism; Glaucoma - pathology; Humans; Microscopy, Atomic Force; Stiffness; Trabecular meshwork; primary open-angle glaucoma; cytoskeleton; cell mechanics; modulus
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1410602111

Increased flow resistance is responsible for the elevated intraocular pressure characteristic of glaucoma, but the cause of this resistance increase is not known. We tested the hypothesis that altered biomechanical behavior of Schlemm’s canal (SC) cells contributes to this dysfunction. We used atomic force microscopy, optical magnetic twisting cytometry, and a unique cell perfusion apparatus to examine cultured endothelial cells isolated from the inner wall of SC of healthy and glaucomatous human eyes. Here we establish the existence of a reduced tendency for pore formation in the glaucomatous SC cell—likely accounting for increased outflow resistance—that positively correlates with elevated subcortical cell stiffness, along with an enhanced sensitivity to the mechanical microenvironment including altered expression of several key genes, particularly connective tissue growth factor. Rather than being seen as a simple mechanical barrier to filtration, the endothelium of SC is seen instead as a dynamic material whose response to mechanical strain leads to pore formation and thereby modulates the resistance to aqueous humor outflow. In the glaucomatous eye, this process becomes impaired. Together, these observations support the idea of SC cell stiffness—and its biomechanical effects on pore formation—as a therapeutic target in glaucoma. Significance Glaucoma is a leading cause of blindness. The elevated intraocular pressure characteristic of many cases of glaucoma is attributable to increased resistance to aqueous humor outflow. However, the cause of this increased flow resistance has eluded investigators for over 140 y. Here we demonstrate that cells from the canal of Schlemm of glaucomatous eyes have altered gene expression and increased cytoskeletal stiffness that leads to reduced pore formation in these cells, likely accounting for increased outflow resistance associated with glaucoma. These findings thus establish that dysfunctional cytoskeletal mechanics may lie at the heart of this disease process and thereby motivate development of glaucoma therapeutics that target cell stiffness.