. Glaucoma is a common blinding disease that affects over 66 million people worldwide and is frequently associated with elevated intraocular pressure (IOP). However, a homeostatic mechanism to adjust elevated IOP must exist since less than 10% of people develop glaucoma. Elevated IOP is caused by increased resistance to aqueous humor outflow through the trabecular meshwork (TM). When TM cells are subjected to sustained elevated IOP, they initiate remodeling of the extracellular matrix (ECM) by releasing specific proteinases including matrix metalloproteinases (MMPs). ECM turnover produces a new, reduced resistance to allow greater aqueous humor outflow through the TM and decrease IOP. Examination of the molecules involved in remodeling, their proteolytic targets and modes and sites of action is critical in order for us to understand how IOP is adjusted. Our long-term goal is to determine the molecular mechanisms by which elevated IOP is homeostatically adjusted in normal eyes. The goal of this current proposal is to further elucidate the function of two ECM components, ADAMTS4 and hyaluronan, and their roles in IOP homeostasis. ADAMTS4 (A Disintegrin and Metalloproteinase with Thrombospondin motifs) is a proteolytic enzyme that degrades ECM components in the TM. ADAMTS4 increases outflow facility in anterior segment perfusion culture suggesting a role for ADAMTS4 in normal homeostatic responses to elevated IOP. Here, we propose a working model whereby ADAMTS4 is activated at specialized cellular structures, then cleaves its target molecules and is internalized into the cell in endosomes. These endosomes may be recycled to the cell surface to release active ADAMTS4 back into the ECM. We will investigate how ADAMTS4 is proteolytically activated and its cellular fate following activation in TM cells. Hyaluronan concentrations in TM decrease during aging and in POAG, which may be due to decreased synthesis, increased degradation or increased cellular hyaluronan uptake. Recently, three genes involved in hyaluronan synthesis and six genes responsible for hyaluronan degradation have been identified and we will investigate their mRNA levels in response to pressure. We will also determine how decreased hyaluronan concentration affects outflow facility in anterior segment perfusion culture. Finally, the effects of hyaluronan concentration on ADAMTS4/MMP expression, localization and/or activation in TM cells will be determined. Investigation into the molecular mechanisms by which ADAMTS4 and hyaluronan are regulated in the TM will provide new information on the complex series of events that leads to homeostatic adjustment of IOP. Studying the molecular details of normal IOP homeostasis should facilitate development of novel therapies targeted at reducing IOP in glaucoma patients.

Public Health Relevance

Glaucoma is a leading cause of vision loss, affecting approximately 67 million people worldwide, but the underlying cause(s) of this disease is poorly understood. Current treatments for glaucoma are directed toward treating the symptoms but not the cause of the disease. This study focuses on understanding how glaucoma develops at the molecular level and thus may facilitate development of new therapies targeted at reducing elevated intraocular pressure.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY019643-03
Application #
8288856
Study Section
Anterior Eye Disease Study Section (AED)
Program Officer
Chin, Hemin R
Project Start
2010-08-01
Project End
2015-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
3
Fiscal Year
2012
Total Cost
$221,760
Indirect Cost
$77,760
Name
Oregon Health and Science University
Department
Ophthalmology
Type
Schools of Medicine
DUNS #
096997515
City
Portland
State
OR
Country
United States
Zip Code
97239
Aga, Mini; Bradley, John M; Wanchu, Rohan et al. (2014) Differential effects of caveolin-1 and -2 knockdown on aqueous outflow and altered extracellular matrix turnover in caveolin-silenced trabecular meshwork cells. Invest Ophthalmol Vis Sci 55:5497-509
Keller, Kate E; Yang, Yong-Feng; Sun, Ying Ying et al. (2014) Interleukin-20 receptor expression in the trabecular meshwork and its implication in glaucoma. J Ocul Pharmacol Ther 30:267-76
Acott, Ted S; Kelley, Mary J; Keller, Kate E et al. (2014) Intraocular pressure homeostasis: maintaining balance in a high-pressure environment. J Ocul Pharmacol Ther 30:94-101
Keller, Kate E; Vranka, Janice A; Haddadin, Ramez I et al. (2013) The effects of tenascin C knockdown on trabecular meshwork outflow resistance. Invest Ophthalmol Vis Sci 54:5613-23
Keller, Kate E; Acott, Ted S (2013) The Juxtacanalicular Region of Ocular Trabecular Meshwork: A Tissue with a Unique Extracellular Matrix and Specialized Function. J Ocul Biol 1:3
Pasutto, Francesca; Keller, Kate E; Weisschuh, Nicole et al. (2012) Variants in ASB10 are associated with open-angle glaucoma. Hum Mol Genet 21:1336-49