Determining the Neuronal Control of IOP

Summary

Glaucoma is a devastating neurodegenerative disease that causes blindness. Glaucoma results from increased pressure in the eye; however, the mechanistic basis of the pressure increase is largely undetermined. Neurons innervating the eye play a role in controlling pressure, but again the specific mechanisms are not clear. We will determine the mechanistic basis of neuronal control of eye pressure using mice and modern imaging and molecular methods.

Project Details

The objective of my proposal is to determine how neuronal control regulates aqueous humor (AQH) outflow and intraocular pressure (IOP). Glaucoma is a common blinding disease affecting over 70 million people. High IOP is a causal risk factor for glaucoma. Abnormally increased resistance to AQH drainage elevates IOP in glaucoma. The nervous system is important in controlling AQH drainage and hence IOP regulation. However, despite several previous studies, the precise mechanisms by which the nervous system controls IOP remain unclear. Historically, this was an intense field of study; however, contemporary research in this field has been few and far between. I will revisit how IOP is regulated by the nervous system using fluorescent transgenic mice, modern neurobiological techniques and unique and innovative tools we have developed to study the neuronal control of AQH drainage. This study will revitalize an understudied area of IOP and glaucoma research.

 In Specific Aim 1, we will determine the nature and patterning of limbal innervation. We will construct a detailed 3-dimensional (3D) map of the neuronal innervation of the AQH drainage structures by imaging either fluorescent protein-expressing neurons, or a subtype with specific neuronal immunolabeling, using high-resolution confocal microscopy and 3D reconstruction of whole-mounts of the anterior segment of mouse eyes. In Specific Aim 2, we will find out if experimental manipulation of IOP activates the neurons innervating the drainage structures. IOP activation of neurons will be determined in mice expressing neuronal activation reporters using high-resolution microscopy. Finally, in Specific Aim 3, we will test the functional contribution of the neurons in control of IOP and outflow using drugs that specifically inhibit various classes of neurons, combined with a novel physiological technique to measure outflow. These foundational studies will lay the groundwork for a more comprehensive study aimed at determining the precise mechanisms of IOP regulation by the nervous system.

The molecular basis for the primary risk factor for glaucoma, elevation of IOP, is largely undetermined. This is a critical field of study because the current drug therapies to lower IOP often are minimally effective and have unpleasant side effects. Surgery often becomes necessary to lower IOP as the disease progresses. Surgery carries risks for the patient, including possible vision loss, bleeding, low eye pressure, scarring, and cataracts; and often the IOP lowering effect of surgery is lost after only a few years. There is a pressing need for more effective therapies with lesser side effects; however, this means identifying the factors controlling IOP more precisely. Our foundational experiments funded by the BrightFocus grant will be used as a platform to study the neuronal control of IOP using modern techniques with the hope of developing novel glaucoma treatments.