Optogenetic Modulation of Intraocular Pressure in a Glucocorticoid-Induced Ocular Hypertension Mouse Model

Abstract

Steroid-induced glaucoma is a common form of secondary open angle glaucoma characterized by ocular hypertension (elevated intraocular pressure [IOP]) in response to prolonged glucocorticoid exposure. Elevated IOP occurs with increased outflow resistance and altered trabecular meshwork (TM) function. Recently, we used an optogenetic approach in TM to regulate the 5-phosphatase, OCRL, which contributes to regulating PI(4,5)P2 levels. Here, we applied this system with the aim of reversing compromised outflow function in a steroid-induced ocular hypertension mouse model. Methods: Elevated IOP was induced by chronic subconjunctival dexamethasone injections in wild-type C57Bl/6j mice. AAV2 viruses containing optogenetic modules of cryptochrome 2 (Cry2)-OCRL-5ptase and CIBN-GFP were injected into the anterior chamber. Four weeks after viral expression and dexamethasone exposure, IOP was measured by tonometer and outflow facility was measured by perfusion apparatus. Human TM cells were treated with dexamethasone, stimulated by light and treated with rhodamine-phalloidin to analyze actin structure.Results: Dexamethasone treatment elevated IOP and decreased outflow facility in wildtype mice. Optogenetic constructs were expressed in the TM of mouse eyes. Light stimulation caused CRY2-OCRL-5ptase to translocate to plasma membrane (CIBN-CAAX-GFP) and cilia (CIBN-SSTR3-GFP) in TM cells, which rescued the IOP and outflow facility. In addition, aberrant actin structures formed by dexamethasone treatment were reduced by optogenetic stimulation in human TM cells in culture.Conclusions: Subcellular targeting of inositol phosphatases to remove PIP2 represents a promising strategy to reverse defective TM function in steroid-induced ocular hypertension.

Advances in Ophthalmic Optogenetics: Approaches and Applications

“…The recent advances in optogenetics have also been applied to the field of glaucoma [ 5 , 6 , 63 ]. Glaucoma comprises a group of progressive optic neuropathies characterized by an abnormal increase in intraocular pressure (IOP), which damages the optic nerve over time and consequently results in injury and eventual loss of RGCs and retinal nerve fiber layers [ 64 ].…”

“…Optogenetic approaches are used in animal models of glaucoma to understand the mechanisms that ultimately lead to the loss of RGCs. These studies use the optogenetic CRY2-CIBN system to study the role of a specific enzyme, inositol polyphosphate 5-phosphatase (OCRL), in modulating IOP prior to RGC loss [ 5 , 6 ]. Evidence of the role of this enzyme in glaucoma pathogenesis derives from patients with mutations in OCRL who develop Lowe syndrome, a multisystem disease causing abnormalities in the brain, kidneys, and eyes.…”

“…Interestingly, OCRL is localized in the primary cilia and plasma membrane of trabecular meshwork (TM) cells, a spongy tissue located around the base of the cornea involved in draining the aqueous humor via the anterior chamber of the eye. Targeted optogenetic modulation of OCRL to the primary cilia and plasma membrane was shown to cause contraction of the TM and an increase in outflow facility, which are correlated with a decrease in IOP [ 6 ]. These findings support the idea that defects in the regulation of aqueous humor outflow may be critical for the subsequent development of glaucoma.…”

“…Over the past decade, optogenetics has been intensively applied in both groundbreaking experimental laboratory settings for the discovery of novel biological mechanisms and in the explorations of novel technological techniques to convert optogenetics into innovative therapeutic methods [ 5 , 6 , 7 , 8 ]. Especially from a therapeutic standpoint, the feasibility of this technique was proven on multiple occasions [ 9 , 10 ].…”

“…Such strategies are attractive because they have the potential to salvage vision irrespective of the genetic etiology. Hence, optogenetic approaches to treat diseases that affect the inner retina, such as glaucoma, are also being explored [ 5 , 6 ]. As optogenetic strategies are being intensely investigated, it appears crucial to consider the opportunities and challenges such therapies may offer.…”