R-spondin1 regulates cell proliferation of corneal endothelial cells via the Wnt3a/β-catenin pathway.

To evaluate the effect of Roof plate-specific spondin 1 (R-spondin1) on the proliferation of corneal endothelial cells (CECs) and to determine whether the Wnt/β-catenin pathway is involved in the activities of R-spondin1. The proliferation of rabbit CECs (RCECs) and human CECs (HCECs) was measured by 5-bromo-2'-deoxyuridine (BrdU) incorporation into DNA. The effect of R-spondin1 on CEC density was evaluated in ex vivo organ-cultured rabbit and human corneal tissues. The cell density of HCECs cultured with R-spondin1 was also evaluated in vitro. The subcellular localization of function-associated markers of CECs (zona occludens 1 [ZO-1] and Na+/K+-ATPase) was determined by immunohistocytochemistry. The expression of cell cycle proteins and localization of β-catenin were determined by immunoblotting. The in vitro proliferation of RCECs and HCECs increased by 1.2- to 1.3-fold in response to R-spondin1. The CEC densities of rabbit and human corneal tissues were increased significantly by R-spondin1 treatment. Na+/K+-ATPase and ZO-1 were well preserved on the plasma membranes. When HCECs were maintained in the presence of R-spondin1 for up to 90 days, the maximum cell density was observed at approximately 50 days, and the cell density was maintained for up to 90 days. R-spondin1 facilitated the nuclear import of β-catenin in RCECs within 30 minutes, which subsequently upregulated cyclin D and downregulated p27, leading to G1/S progression by hyperphosphorylation of the retinoblastoma protein. The unique effects of R-spondin1 on the proliferation of CECs, regardless of species, indicate that R-spondin1 may play a key role in maintaining corneal endothelium homeostasis through the Wnt/β-catenin pathway.