Role of Endogenous Galectin-3 on Cell Biology of Immortalized Retinal Pigment Epithelial Cells In Vitro

Galectin-3 is a multifunctional protein that is associated with diseases of the chorioretinal interface, in which the retinal pigment epithelium (RPE) plays a central role in disease development and progression. Since galectin-3 can function extracellularly as well as intracellularly via different mechanisms, we developed an immortalized human RPE cell line (ARPE-19) with a knockdown for galectin-3 expression (ARPE-19/LGALS3^+/-) using a sgRNA/Cas9 all-in-one expression vector. By Western blot analysis, a reduced galectin-3 expression of approximately 48 to 60% in heterozygous ARPE-19/LGALS3^+/- cells was observed when compared to native controls. Furthermore, ARPE-19/LGALS3^+/- cells displayed a flattened, elongated phenotype with decreased E-cadherin as well as enhanced N-cadherin and α-smooth muscle actin mRNA expression, indicating an epithelial-mesenchymal transition of the cells. Compared to wildtype controls, ARPE-19/LGALS3^+/- cells had significantly reduced metabolic activity to 86% and a substantially decreased proliferation to 73%. Furthermore, an enhanced cell adhesion and a diminished migration of immortalized galectin-3 knockdown RPE cells was observed compared to native ARPE-19 cells. Finally, by Western blot analysis, reduced pAKT, pERK1/2, and β-catenin signaling were detected in ARPE-19/LGALS3^+/- cells when compared to wildtype controls. In summary, in RPE cells, endogenous galectin-3 appears to be essential for maintaining the epithelial phenotype as well as cell biological functions such as metabolism, proliferation, or migration, effects that might be mediated via a decreased activity of the AKT, ERK1/2, and β-catenin signaling pathways.