Metabolic syndrome affects mouse corneal epithelium and nerve morphology

Abstract

Purpose: Diet-induced obesity is accompanied by a metabolic syndrome that causes systemic inflammatory changes. The metabolic syndrome is a cluster of disorders that include abdominal obesity, dyslipidemia, hypertension, elevated fasting glucose levels, and insulin resistance progressing to type 2 diabetes. Corneal nerve damage is an early event in the progression of diabetic keratopathy, a condition affecting approximately 70% of diabetics. This study uses metabolic syndrome as a model to investigate early changes in corneal anatomy that precede the development of type 2 diabetes.

Methods: Five week old C57BL/6 mice were fed a high fat milk diet (HFD, 42% kcal) for 10 weeks and were subsequently analyzed for systemic inflammatory and metabolic changes. Mice on a normal chow diet served as controls. Excised corneas were labeled with nerve-specific anti-tubulin β III antibody and nuclei were stained with DAPI. Two central and four paracentral regions per cornea were imaged by immunofluorescence microscopy. The effect of the HFD on corneal nerve morphology and epithelial basal cell density was evaluated using ImageJ and a custom MATLAB program. Data analysis was performed using an unpaired two-tailed t-test. A p-value of ≤ 0.05 was considered significant.

Results: Mice on a HFD had a 35% decrease in central epithelial vertical branch density (p=0.019) and a 42% decrease in epithelial and basal nerve density (p=0.006 and p=0.026, respectively), compared to control mice. Paracentral nerve density was not different between the two groups. After 10wk on a HFD, mice had a significant increase in central epithelial basal cell density, but not paracentral basal cell density, compared to mice on a chow diet (p=0.0006).

Conclusions: Diet-induced metabolic syndrome is accompanied by early anatomical changes in corneal nerves and in the corneal epithelium. These prediabetic changes occur in the central cornea prior to the development of hyperglycemia and insulin resistance, raising the possibility that these changes are linked to the systemic inflammation caused by the metabolic syndrome.