Endocannabinoid system as a therapeutic target for PVR

ABSTRACT Two ocular cell types, retinal pigment epithelium (RPE) and Müller glia (MG) have been implicated to play important roles in the development and final outcome of proliferative vitreoretinopathy (PVR) by undergoing Trans differentiation to myofibroblasts. The endocannabinoid system, including endocannabinoid ligands and their receptors, including CB1, CB2, and non-CB1/CB2 cannabinoid receptors, play essential roles in health and disease, and are promising therapeutic targets. Previously, it has been shown that blockade of CB1 and activation of CB2 inhibit fibrosis. Our preliminary results demonstrate that myofibroblast trans differentiation of both RPE and MG cells can be inhibited by N-oleoyl dopamine (OLDA), an endogenous inverse agonist for GPR6, a non-CB1/CB2 cannabinoid receptor. In addition, CB1 selective inverse agonist/antagonist SR141716A inhibited myofibroblast trans differentiation of MG cells. Based on the literature and our preliminary data, we hypothesize that CB1 and GPR6 inverse agonists/antagonists and CB2 agonists inhibit myofibroblastic changes by working via CB1, GPR6, CB2 receptors respectively and modifying downstream signaling pathways crucial for myofibroblast trans differentiation. To test our hypothesis, CB1, CB2 and GPR6 will either be activated by selective agonists or inhibited by inverse agonists or shRNA knockdown to examine their role on myofibroblast trans differentiation, assessed by mesenchymal and myofibroblast marker protein expression and matrix contraction, a key function of myofibroblasts. In addition, effects of CB1, CB2 and GPR6 ligands on signaling pathways activated by profibrotic cytokine TGF2 will be examined by assessing activation status of key signaling molecules, as well as nuclear localization of fibrotic transcription factors. Finally, the expression of CB1, CB2 and GPR6 receptors will be investigated in human retinal scar tissues from PVR patients. The main goal of this project is to test the potential of CB1, CB2 and GPR6 ligands as preventative treatments of PVR. Furthermore, this project will identify fibrotic signaling pathways targeted by the endocannabinoid system and should contribute to the development of specific and effective therapeutic agents for PVR.