Abstract
Purpose :
Diabetic keratopathy occurs in approximately 70% of all diabetics. Our recent studies demonstrated that vitamin D receptor (VDR) knockout (KO) mice have significantly slower healing rates than wild type (WT) mice, and that a supplemental diet rich in calcium, phosphate, and lactose could normalize the healing rate (REF). We have also shown that diabetic VDR KO mice have slower epithelial healing rates than diabetic WT mice. This study was designed to determine if the supplemental diet or a vitamin D-deficient diet will affect the corneal epithelial healing rate of VDR KO or WT diabetic mice (respectively). We also measured nerve density in these mice.
Methods :
Streptozotocin injection was used to induce diabetes. For corneal epithelium wound healing, mice were anesthetized and 2 mm central wounds were made in one eye using an Alger brush. Corneal wounds were photographed over time with a slit lamp. Unwounded corneas were stained with a b3-tubulin antibody and photographed with a confocal microscope. Corneal sub-basal nerve density and nerve terminal numbers were assessed by computer-assisted analysis. Wound healing was assessed after curve fitting using the parallelism test.
Results :
VDR KO diabetic mice on both the normal and supplemental diets had significantly slower wound healing than WT diabetic mice. The vitamin D-deficient diet (10 weeks) did not affect wound healing. There was no difference in nerve density between 8-week WT and VDR KO mice. However, six weeks after streptozotocin injection, VDR KO diabetic mice showed significantly decreased nerve density which was not rescued by the supplemental diet. Nerve terminal numbers in the superficial epithelium were also significantly decreased in diabetic VDR KO mice vs. WT diabetics. The vitamin D deficient diet (10 weeks) resulted in a significantly decreased nerve density in diabetic mice.
Conclusions :
VDR KO significantly reduces both corneal epithelial wound healing and nerve density in diabetic mice. The supplemental diet did not fully rescue wound healing or nerve density, thus the diabetic VDR KO affect is likely not related to hypocalcemia. A vitamin D-deficient diet for 10 weeks reduced nerve density but not wound healing. This works supports the hypothesis that very low vitamin D levels can exacerbate pre-existing conditions such as diabetes.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.