The cause of the elevated aqueous humor outflow resistance associated with primary open angle glaucoma (POAG) is unknown. Studies aimed at determining the locus of this resistance in both normal and POAG eyes indicate that the bulk of outflow resistance occurs in the immediate vicinity of the inner wall endothelium of Schlemm's canal (SC). Pores found in the inner wall endothelial cells (SC cells) appear important in fluid transport across this endothelium. Our group and others have found that there is a significant reduction of inner wall pore density in POAG eyes. It is likely that these pores are formed in response to cell deformation resulting from the transcellular pressure drop across the inner wall endothelium. If SC cells were to become stiffer, then fewer pores might be expected to form, presumably leading to elevated outflow resistance. Accordingly, we hypothesize that the ocular hypertension characteristic of POAG results from an intro, including magnetic twisting cytometry (MTC), atomic force microscopy (AFM), and a unique embodiment of traction force microscopy called cell mapping rheometry. These studies will allow us to evaluate the stiffness of these cells and the traction forces they can generate. Second, we will investigate the behavior of SC cells on a stretchable gel substrate, and in a microporous filter perfusion system that allows us to grow these cells on a filter and perfuse them in a basal to apical direction (the physiological direction). These studies will examine how SC cells respond to mechanical distension. Third, our studies will focus on the biomechanics of pore formation in these cells and how this process is modulated by SC cell stiffness in enucleated human eyes and in an organ culture system. Fourth, to test the hypothesis that mediators of outflow resistance exert their effects through mechanical events involving changes in SC cell deformation and pore formation, we will use a finite riments, we will compare the biomechanical behavior of normal C cells to those of glaucomatous SC cells. Together, these aims will allow us to definitively determine whether increased stiffness of SC cells leads to a decreased inner wall porosity and consequently the increased outflow resistance characteristic of most cases of POAG.

Public Health Relevance

Most treatments for glaucoma focus on altering the rate of aqueous humor formation or altering the path of aqueous humor outflow, but do not target the diseased tissue responsible for the elevated intraocular pressure characteristic of most cases of glaucoma. These treatments often slow the progression of the disease at the optic nerve, but frequently do not stop it. If we can determine the cause of the elevated pressure, then we may be able to develop a more effective pressure-lowering treatment or cure for this debilitating disease.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Anterior Eye Disease Study Section (AED)
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Chin, Hemin R
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Northwestern University at Chicago
Biomedical Engineering
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United States
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Vargas-Pinto, Rocio; Lai, Julia; Gong, Haiyan et al. (2015) Finite element analysis of the pressure-induced deformation of Schlemm's canal endothelial cells. Biomech Model Mechanobiol 14:851-63
Stamer, W Daniel; Braakman, Sietse T; Zhou, Enhua H et al. (2015) Biomechanics of Schlemm's canal endothelium and intraocular pressure reduction. Prog Retin Eye Res 44:86-98
Braakman, Sietse T; Pedrigi, Ryan M; Read, A Thomas et al. (2014) Biomechanical strain as a trigger for pore formation in Schlemm's canal endothelial cells. Exp Eye Res 127:224-35
Vargas-Pinto, R; Gong, H; Vahabikashi, A et al. (2013) The effect of the endothelial cell cortex on atomic force microscopy measurements. Biophys J 105:300-9
Zhou, Enhua H; Martinez, Fernando D; Fredberg, Jeffrey J (2013) Cell rheology: mush rather than machine. Nat Mater 12:184-5
Wang, Jenny W; Woodward, David F; Stamer, W Daniel (2013) Differential effects of prostaglandin E2-sensitive receptors on contractility of human ocular cells that regulate conventional outflow. Invest Ophthalmol Vis Sci 54:4782-90
Coughlin, Mark F; Bielenberg, Diane R; Lenormand, Guillaume et al. (2013) Cytoskeletal stiffness, friction, and fluidity of cancer cell lines with different metastatic potential. Clin Exp Metastasis 30:237-50
Stamer, W Daniel; Acott, Ted S (2012) Current understanding of conventional outflow dysfunction in glaucoma. Curr Opin Ophthalmol 23:135-43
Zhou, E H; Krishnan, R; Stamer, W D et al. (2012) Mechanical responsiveness of the endothelial cell of Schlemm's canal: scope, variability and its potential role in controlling aqueous humour outflow. J R Soc Interface 9:1144-55
Perkumas, K M; Stamer, W D (2012) Protein markers and differentiation in culture for Schlemm's canal endothelial cells. Exp Eye Res 96:82-7

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