Proliferative vitreo retinopathy (PVR) is associated with extracellular matrix 
membrane (ECM) formation on the neural retina and disruption of the multilayered 
retinal architecture leading to distorted vision and blindness. During disease 
progression in PVR, retinal pigmented epithelial cells (RPE) lose cell-cell 
adhesion, undergo epithelial-to-mesenchymal transition (EMT), and deposit ECM 
leading to tissue fibrosis. The EMT process is mediated via exposure to vitreous 
cytokines and growth factors such as TGF-β2. Previous studies have shown that 
Na,K-ATPase is required for maintaining a normal polarized epithelial phenotype 
and that decreased Na,K-ATPase function and subunit levels are associated with 
TGF-β1-mediated EMT in kidney cells. In contrast to the basolateral localization 
of Na,K-ATPase in most epithelia, including kidney, Na,K-ATPase is found on the 
apical membrane in RPE cells. We now show that EMT is also associated with 
altered Na,K-ATPase expression in RPE cells. TGF-β2 treatment of ARPE-19 cells 
resulted in a time-dependent decrease in Na,K-ATPase β1 mRNA and protein levels 
while Na,K-ATPase α1 levels, Na,K-ATPase activity, and intracellular sodium 
levels remained largely unchanged. In TGF-β2-treated cells reduced Na,K-ATPase 
β1 mRNA inversely correlated with HIF-1α levels and analysis of the Na,K-ATPase 
β1 promoter revealed a putative hypoxia response element (HRE). HIF-1α bound to 
the Na,K-ATPase β1 promoter and inhibiting the activity of HIF-1α blocked the 
TGF-β2 mediated Na,K-ATPase β1 decrease suggesting that HIF-1α plays a potential 
role in Na,K-ATPase β1 regulation during EMT in RPE cells. Furthermore, 
knockdown of Na,K-ATPase β1 in ARPE-19 cells was associated with a change in 
cell morphology from epithelial to mesenchymal and induction of EMT markers such 
as α-smooth muscle actin and fibronectin, suggesting that loss of Na,K-ATPase β1 
is a potential contributor to TGF-β2-mediated EMT in RPE cells.