Mechanisms of Traumatic Retinal Injury: Targeting the Arginase Pathway

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 DESCRIPTION (provided by applicant): The long term goal of this research is to delineate the molecular mechanisms that lead to trauma-induced retinal neuronal and vascular injury and identify novel strategies to prevent or reverse the damage and preserve vision. The lack of understanding of the detailed molecular mechanisms by which ocular trauma damages the retinal neurons and vascular cells represents a critical knowledge gap in developing effective therapies. Therefore, the goal of this research is to define these mechanisms and identify innovative approaches to prevent such damage, improve functional outcomes and reduce the risk of blindness to veterans returning from the battlefield. Preliminary data suggest that ischemia or trauma-induced activation of the mitochondrial, ureahydrolase enzyme arginase 2 causes microglia/macrophage activation, inflammation and neurovascular degeneration by increasing oxidative stress. Overactive arginase can increase oxidative stress by 1) decreasing the L-arginine supply needed by nitric oxide synthase (NOS) to produce NO, thereby causing NOS to become uncoupled and produce superoxide that reacts with NO to form the toxic oxidant peroxynitrite and/or 2) causing excessive activation of the ornithine-polyamine pathway, thereby leading to polyamine oxidation and production of toxic oxidants. The global hypothesis of this project is that excessive activation of arginase 2 causes microglia/macrophage activation and neurovascular damage by inducing NOS uncoupling and/or excessive activation of the polyamine metabolic pathway. The proposed experiments will test and develop this working model by studies in a mouse model of traumatic optic nerve injury. Two specific aims are proposed. Aim 1 is to test the hypothesis that traumatic retinal injury is mediated by arginase-induced uncoupling of NOS and/or altered polyamine metabolism. These studies will determine the effects of arginase knockdown on microglia/macrophage activation, neurovascular degeneration and vascular function following optic nerve injury. The protective effects of arginase deletion on microglia/macrophage activation, inflammation and neurovascular damage will be examined in relation to NOS function, polyamine metabolism and their activity in producing ROS. Vasorelaxation and permeability barrier function will be determined by in vivo imaging. Arginase 2 deletion should limit microglia/macrophage activation and mitigate the neurovascular damage/dysfunction by normalizing NOS function, reducing polyamine oxidation and limiting oxidative stress and inflammation. Aim 2 is to perform preclinical studies for prevention and treatment of traumatic neurovascular injury. These studies we will determine and compare the treatment efficacy and safety of inhibiting arginase signaling and/or polyamine metabolism in limiting or preventing microglia/macrophage activation, inflammation and retinal neurovascular injury in the model of traumatic injury as explained for Aim 1. The beneficial effects of the treatments in preserving retinal structure and neuronal function will also be assessed using in vivo imaging and electroretingraphic recording. The expected outcomes include validation of the arginase/polyamine pathway as a novel target for therapeutic intervention to attenuate oxidative stress, inflammation and neurovascular degeneration and promote healthy repair following traumatic retinal injury. The impact of this work will be to provide a new understanding of the complex interactions between arginase, NOS and polyamine metabolism-associated inflammation and injury that will serve as a basis for development of novel therapeutic agents to treat traumatic retinal injury. Successful completion of this project is highly relevant to the mission of VA and to the health and well-being of veterans.