Identification of Human Aqueous Humor Leucine-rich G protein-coupled receptor-5 as a Novel Biomarker of Proliferative Diabetic Retinopathy

Abstract

Purpose: Proliferative diabetic retinopathy (PDR) is characterized by retinal pathologic neovascularization, which lead to visual loss. Leucine-rich G protein-coupled receptor-5 (LGR5) is known to be a stem cell marker in many organs. LGR5 may have important roles in PDR because LGR5 potentiate the Wnt/β-catenin pathway, which plays crucial roles in pathologic neovascularization in the retina and pathogenesis of PDR. The association between LGR5 and retinal pathologic neovascularization has not yet been reported. We investigated whether LGR5 can be detected in human aqueous humor, and compared aqueous humor LGR5 level in normal control and patients with PDR to confirm the relationship between LGR5 and PDR. Methods: Aqueous humor was collected from 7 naïve PDR patients and 3 control subjects before intravitreal injection and cataract surgery, respectively. LGR5 was assessed by western blotting. Additionally, key members of Wnt/β-catenin pathway were assessed by western blotting and compared in aqueous humor mixture of PDR (n=5) and control group (n=5), respectively. The correlation of aqueous humor LGR5 level with clinical parameters (nonperfusion area, neovascularization area) was also investigated using ultra-wide fundus angiography (Optos PLC, Dunfermline, Scotland) image. Results: In the present study, it was confirmed that LGR5 is detected in aqueous humor. The aqueous humor LGR5 level increased in PDR patients (P = 0.017), and key members of Wnt/β-catenin pathway all increased in PDR compared to control (P < 0.01). There was no significant correlation between clinical parameters (nonperfusion index, neovascularization index) and aqueous humor LGR5 (r = 0.734, P = 0.060; r = 0.346, P = 0.448, respectively). Conclusion: This finding might support the hypothesis that LGR5 has important roles in PDR especially considering the roles of the Wnt/β-catenin pathway, which is activated by LGR5, contributing to retinal pathologic neovascularization.