Prostaglandins (PG) play a major role in many endogenous processes including inflammation, labor, reproduction, and blood clotting. In the last two decades, these lipid signaling molecules have shown great potential as ocular hypotensive agents. Intraocular pressure (IOP) is a major risk factor in primary open-angled glaucoma (POAG), the second leading cause of blindness world-wide. Currently, prostaglandin F(2α) analogues are the most widely prescribed medications used to treat ocular hypertension. Studies have identified that almost all prostaglandin analogues exhibit anti-hypertensive effects in the eye, although they are not clinically available. Initial studies attributed the decrease in IOP observed to changes in hydraulic conductivity across the pressure-independent or uveoscleral pathway. More recent studies have shown that prostaglandin F(2α) analogues also lower IOP by affecting the pressure-dependent or trabecular pathway--the diseased tissue in POAG. Little is currently known about PG endogenous function, or the etiology of POAG. However, these studies suggest prostaglandin involvement in the maintenance of IOP in humans and identify the potential of PG analogues to treatment ocular hypertension. The research and findings presented in this dissertation address three specific aims designed to test the hypothesis that Endogenous prostaglandins, prostaglandin enzymes and prostaglandin receptors are involved in regulating conventional outflow facility. Specific aim 1 characterizes the distribution and activity of prostamide/prostaglandin F synthase (PM/PGFS) in the mouse and human eye using immunohistochemistry, western blot analysis and thin layer chromatography. Using techniques in biochemistry, molecular biology and physiology, specific aim 2, identifies the presence of the PG-EP₄ receptor within the outflow pathways, and the efficacy of a selective PG-EP₄ agonist, 3,7-dithiPGE₁, is also determined. Finally, specific aim 3 identifies PG-EP4 receptor coupling and downstream signaling using in vitro assays of transfected and primary cell lines to measure cAMP accumulation after treatment with a PG-EP₄ agonist. Collectively, these studies reveal the importance of PGE₂ synthesis and signaling to the conventional outflow pathway. They identify the PG-EP₄ receptor as a regulator of aqueous outflow and provide more specific therapeutic targets for the treatment of POAG.

<p>The trabecular meshwork (TM) is comparable to a bioactive filter that plays a major role in regulating outflow of aqueous humor of the eye and setting intraocular pressure (IOP). TM dysfunction may lead to ocular hypertension which is the major risk factor in glaucoma. Although the outflow properties of the TM have been assessed over the last sixty years, very little work has been done assessing its mechanical properties. Therefore, the major goals of these studies were two-fold: (1) to determine the relationship between mechanical properties of TM, specifically the bulk Young's modulus, and outflow function in normal and glaucomatous eyes, and (2) to establish a method and possible animal model for future testing of this relationship.</p><p>Outflow function was assessed by constant pressure perfusion in enucleated eyes at four pressure levels (10, 20, 30, and 40 mmHg) to determine outflow facilities and variability in outflow resistance with pressure elevation. A micro-strain analyzer (MSA) was used to determine the circumferential bulk Young's modulus of the TM post-perfusion. Based on their relative ease of availability, pigs and rats were explored as possible animal models. Due to the small size of rat eyes, atomic force microscopy (AFM) was used to assess the Young's modulus of TM rather than with a MSA.</p><p>We found that there was a relationship with better outflow function and a stiffer TM in normal eyes. Additionally, glaucomatous TM was found to be much softer and more variable than normal TM. Unfortunately, porcine TM did not serve as a good model for the bulk Young's modulus of human TM, presumably due to anatomical difference in its outflow pathway. Lastly, we were able to establish a new method for measuring the Young's modulus of rat TM for future work to determine potential mechanism for evaluating stiffness changes that may be associated with glaucoma.</p> / Dissertation

Glaucoma affects tens of millions of people and is the leading cause of irreversible blindness worldwide. Virtually all current glaucoma therapies target elevated intraocular pressure (IOP); however, the contribution of intracranial pressure (ICP) to glaucoma has recently garnered interest. Strain at the optic nerve head is now known to depend on the translaminar pressure difference (TLPD), which is the difference between IOP and ICP, rather than IOP alone. A better understanding of how IOP and ICP relate to glaucoma development and progression is essential for developing improved therapies and diagnostic tests. Glaucoma is commonly modeled in rats, yet aqueous humor dynamics are not well-documented in healthy nor diseased rat eyes. Moreover, because rats do not develop glaucoma spontaneously, it is essential to develop low-cost, reliable, and relevant models of glaucomatous pathology in the animal. The purpose of this dissertation work is to achieve the following goals: i) quantitatively assess aqueous humor dynamics in healthy, living rat eyes, ii) develop an ideal model of experimental glaucoma in rats, iii) quantitatively characterize aqueous humor dynamics throughout experimental glaucoma in living rats, and iv) investigate the effects of ICP manipulations on aqueous humor dynamics in living rats. Chapter 2 reports physiological parameters of aqueous humor dynamics for the first time in the eyes of living, healthy Brown-Norway rats, and presents a novel perfusion technique for efficiently and accurately estimating these parameters. Chapter 3 introduces the constant-pressure perfusion model of experimental glaucoma: a powerful new model which overcomes several limitations of existing techniques. The constant-pressure perfusion model induces IOP elevations which are prescribable and easily manipulated, does not directly target the trabecular meshwork or its vasculature, and offers continuous records of IOP rather than requiring regular animal handling and tonometry. Chapter 3 characterizes IOP-induced optic neuropathies in rats and demonstrates their resemblance to human glaucoma. Chapter 4 evaluates whether the constant-pressure perfusion model affects ocular physiology, specifically showing that resting IOP and conventional outflow facility are not permanently nor significantly altered in the model. Chapter 5 examines the effect of ICP manipulations on aqueous outflow physiology in living rats, and reports for the first time a graded effect of intracranial hypertension on conventional outflow facility. Evidence for a neural feedback mechanism that may serve to regulate the TLPD is also presented. Chapter 6 summarizes the results of this dissertation, provides recommendations for future work, and gives closing remarks. These collective projects provide insight into IOP regulation in both healthy and diseased rat eyes, advancing our understanding of glaucomatous development and damage in rats. A novel model of experimental glaucoma and several perfusion systems have been developed which are distinctly tailored for use in future glaucoma studies and will allow future investigators to study the disease with enhanced efficiency and exactitude. The results of this dissertation work suggest that detecting and correcting impairments of either IOP or ICP homeostatic capabilities may be of utmost importance for improving clinical outcomes in human glaucoma.