Mutations in the human phosphatase and tensin homolog (PTEN) gene cause PTEN hamartoma tumor syndrome (PHTS), which includes cataract development among its diverse clinical pathologies. Currently, it is not known whether cataract formation in PHTS patients is secondary to other systemic problems, or the result of the loss of a critical function of PTEN within the lens. We generated a mouse line with a lens-specific deletion of Pten (PTEN KO) and identified a regulatory function for PTEN in lens ion transport. Specific loss of PTEN in the lens resulted in cataract. PTEN KO lenses exhibited a progressive age-related increase in intracellular hydrostatic pressure, along with, increased intracellular sodium concentrations, and reduced Na+/K+-ATPase activity. Collectively, these defects lead to lens swelling, opacities and ultimately organ rupture. Activation of AKT was highly elevated in PTEN KO lenses compared to WT mice. Additionally, pharmacological inhibition of AKT restored normal Na+/K+-ATPase activity in primary cultured lens cells and reduced lens pressure in intact lenses from PTEN KO animals. These findings identify a direct role for PTEN in the regulation of lens ion transport through an AKT-dependent modulation of Na+/K+-ATPase activity, and provide a new animal model to investigate cataract development in PHTS patients.
Caterina Sellitto, Leping Li, Junyuan Gao, Michael L. Robinson, Richard Z. Lin, Richard T. Mathias, Thomas W. White
(A) Microelectrodes containing the sodium-sensitive dye SBFI were used to make a series of injections into lens fiber cells at different depths, and fluorescence emission was recorded using 360- and 380-nm excitation wavelengths. (B) 360/380 fluorescence emission ratios from lenses of 10-week-old WT and PTEN KO animals, plotted as a function of normalized radial distance from the lens center. (C) Emission ratios were converted to internal Na+ concentrations and plotted against radial distance. Fits of the data (dashed lines) showed a Na+ concentration gradient in WT lenses of 14.6 mM at the lens center to 4.4 mM at the lens surface. PTEN KO lenses had higher Na+ concentrations, with fitted values of 20.4 mM at the center and 7.9 mM at the surface. Pooled data were obtained from 6 animals per genotype.