Effects of Vitamin D receptor knockout and Vitamin D deficiency on corneal epithelial wound healing and nerve density in diabetic mice

Diabetic keratopathy occurs in ∼70% of all people with diabetes. This study was designed to examine the effects of vitamin D receptor knockout (VDR^‒/^‒) and vitamin D deficiency (VDD) on corneal epithelial wound healing and nerve density in diabetic mice. Diabetes was induced using the low-dose streptozotocin method. Corneal epithelial wounds were created using an Algerbrush, and wound healing was monitored over time. Corneal nerve density was measured in unwounded mice. VDR^‒/^‒ and VDD diabetic mice (diabetic for 8 and 20 weeks, respectively) had slower healing ratios than wild-type diabetic mice. VDR^‒/^‒ and VDD diabetic mice also showed significantly decreased nerve density. Reduced wound healing ratios and nerve densities were not fully rescued by a supplemental diet rich in calcium, lactose, and phosphate. We conclude that VDR^‒/^‒ and VDD significantly reduce both corneal epithelial wound healing and nerve density in diabetic mice. Because the supplemental diet did not rescue wound healing or nerve density, these effects are likely not specifically related to hypocalcemia. This work supports the hypothesis that low vitamin D levels can exacerbate preexisting ophthalmic conditions, such as diabetes.