Purpose: To determine a role for the water- and glycerol-transporting protein aquaporin-3 (AQP3) in mammalian corneal epithelium, where it is expressed but has no known function.
Methods: Corneal epithelial water and glycerol permeabilities were measured in living wild-type and AQP3-null mice using calcein fluorescence-quenching and 14C-glycerol-uptake assays, respectively. After removal of the corneal epithelium by scraping, re-epithelialization was followed by fluorescein staining. The contribution of AQP3-facilitated cell migration to corneal re-epithelialization was assessed using an organ culture model, in which initial resurfacing results from epithelial cell migration, as shown by BrdU analysis and 5-fluorouracil insensitivity, and by scratch wound assay using primary cultures of corneal epithelial cells from wild-type versus AQP3-null mice. Involvement of AQP3 in epithelial cell proliferation was investigated by morphometric and BrdU analysis of histologic sections, and by measurement of [3H]thymidine uptake in primary cultures of corneal epithelial cells.
Results: AQP3 deficiency did not alter corneal epithelial thickness, morphology, or glycerol content, though both water and glycerol permeabilities were reduced. Time to corneal re-epithelialization in vivo was significantly delayed in AQP3-null mice compared to wild-type mice. Delays were also found in organ and primary cultures, demonstrating a distinct defect in cell migration arising from AQP3 deletion. Delayed restoration of full-thickness epithelia of AQP3-null mice over days after scraping suggested a separate defect in epithelial cell proliferation, which was confirmed by reduction in proliferating BrdU-positive cells in AQP3-deficient mice during healing, and by reduced proliferation in primary cultures of corneal epithelial cells from AQP3-null mice.
Conclusions: The significant impairment in corneal re-epithelialization in AQP3-deficient mice results from distinct defects in corneal epithelial cell migration and proliferation. The results provide evidence for involvement of an aquaporin in cell proliferation and suggest AQP3 induction as a possible therapy to accelerate the resurfacing of corneal defects.