Background: Ocular injury is the fourth most common injury in combat. For both combatants and civilians, blast-related injuries, which are the most common cause of ocular damage, frequently result in retinal detachment (RD). RD is a separation of the neural retina from the retinal pigmented epithelium, which can ultimately lead to blindness. Even if repaired by surgical reattachment, a majority of patients do not achieve restoration of normal vision. A high percentage of traumatic brain injury (TBI) is also associated with visual dysfunction. The retinal pathology in TBI is similar to what occurs with RD.We are proposing to reduce the effects of injury by using Rho Kinase (ROCK) inhibition. We discovered that RD, which uncouples photoreceptors from their synaptic partners and therefore blocks vision, increases RhoA activity. RhoA activation in turn stimulates several kinases, which results in cytoskeletal disruption. Rod terminals pull away from their bipolar partners, and cone pedicles round up and eliminate synaptic invaginations. However, by inhibiting ROCK activity we can dramatically reduce presynaptic retraction and synaptic disjunction. We use adult pigs with surgically induced RDs as preclinical animal models. In the porcine retina, we are able to assess quantitatively the level of synaptic pathology, cell death, and retinal activity with electroretinograms (ERGs). Preliminary ERG results indicate preventing synaptic structural damage results in improved retinal function.Thus, we want to transform trauma care for combatants and civilians with vision-threatening injuries by applying a new pharmacological treatment to retina injured by blast or blunt trauma.Objective/Hypothesis: From in vitro and in vivo models we have learned that retinal injury activates ROCK and Lim kinase (LIMK) resulting in actomyosin contraction and actin depolymerization. These cytoskeletal changes cause disruption of the first synapse in the visual pathway. We propose to use inhibitors of RhoA signaling, specifically ROCK and LIMK inhibitors, to reduce synaptic damage and cell death after retinal injury and improve visual recovery.Specific Aims/Study Design: In Aim 1, we will test the ability of the new ROCK inhibitor netarsudil-M1, AR-13503, to stabilize photoreceptor synapses via single injection and/or a sustained release delivery system over several days. We create RDs by subretinal injection of BSS. One eye is treated with drug, the fellow eye with vehicle. Thus, the fellow eye of each animal serves as its own control. Analysis of results is by the paired t-test. Although our data indicate that AR-13503 effectively reduces retinal damage over the short term, longer-duration protection would be optimal in the combat theater. We will test a fiber with AR-13503 that can elute drug into the vitreous cavity consistently for weeks. We assess morphological synaptic damage of rods and cones by image analysis of immunolabeled and confocal scanned retinal sections. We test for retinal function in the outer retina with ERGs and correlate these data with our structural analysis. Because the pig eye is similar to the human eye, these data have translational value. In Aim 2, we will determine how long after an RD injury drug can be applied and still reduce synaptic disruption. In clinical applications, it is likely that treatment will occur only sometime after the injury. To mimic this situation, we will create RDs, delay the intravitreal injection of drug for specified times, and then assess synaptic preservation anatomically and functionally as above. In Aim 3, we will determine if additional drug (either a ROCK or LIMK inhibitor) at the time of retinal reattachment surgery helps promote recovery. Once the retina is stabilized by ROCK inhibition, it must be reattached. Because reattachment may constitute another injury event, more ROCK inhibition may be necessary. ROCK and LIMK inhibitors will be applied shortly before surgery. LIMK inhibition, in particular, may mitigate neuritic sprouting by rod cells that is seen in human RDs. One eye will be treated; the fellow eye is the control. After reattachment, the retina will be monitored by ERG and ocular imaging (fundus and OCT) before structural assessment.Impact/Military Benefit: Visual disability from ocular trauma is a major problem in military operations. Blast-related injuries often result in RD. RD is one of the top three risk factors for blindness. We are proposing a procedure to first stabilize the detached and adjacent retina and prevent further damage by blocking RhoA activity. Drug would be applied by intravitreal injection in combat support hospitals. Surgical repair then would follow and may be improved with adjunctive treatment (additional application of kinase inhibitors). There has not been a pharmacological advance in retinal repair in more than a decade, yet the incidence of retinal damage in combat as well civilian settings, because of terrorist activities, has increased. Our procedures may also be applicable to TBI-induced retinal damage, which shows similar synaptic damage, and eventually may be useful to damaged brain tissue after TBI.
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