Abstract
Purpose :
The impact of phosphate homeostasis on lens growth, development, and transparency has been poorly studied. Our goal was to investigate the molecular mechanism behind how phosphate transporter Slc20a2 knockout (KO) mice develop microphthalmia and cataracts.
Methods :
Overall growth of the wild-type (WT), heterozygous (Het), and KO eye and lens were studied longitudinally in vivo in mice up to one year old by using a spectral domain optical coherence tomography (SD-OCT) system. Dissected lenses of WT and KO mice were examined for calcium deposits with alizarin red dye staining and for lens morphology with immunohistochemical staining of specific proteins imaged using confocal microscopy. Western blot analysis was performed to examine the expression of Slc20a2 and other lens proteins as well as the degradation of lens crystallin proteins.
Results :
OCT data revealed that compared to the WT and Het controls, KO mice had significantly smaller lens sizes from 2 to 26 weeks old and smaller eye sizes with shorter axial length for KO eyes. Alizarin red calcium staining showed calcium deposits in the inner region of KO lenses but not in WT or Het lenses. Immunohistochemical staining found drastically deformed fiber cells, with a loss of fiber cell organization. Western blot analysis showed increased levels of cleaved crystallins and reduced gap junction levels in KO lenses.
Conclusions :
Disruption of the Slc20a2 gene leads to recessive phenotypes in the eye and the lens. Slc20a2 transporter is essential for regulating the overall growth and transparency of the lens. The significant lens growth defect is probably related to alterations in cell proliferation, fiber cell elongation, and/or differentiation. Calcium deposits may result from an abnormal increase of calcium in the lens and important interactions between calcium and phosphate homeostasis. Cleaved crystallins and lower gap junction levels may be related to activation of calpains which cleave crystallins and promote cataract formation. It remains unclear how the calcium level is affected by disrupted phosphate hemostasis in this KO lens.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.