Quantification of Retinal Vasculature in LDL Receptor Knockout Mice

Abstract

Purpose: : The LDL receptor (LDLR) knockout mouse is known to develop hyperglycemia and hyperinsulinemia when fed a high-fat diet and is considered a model for type II diabetes mellitus. The purpose of this study was to evaluate the ophthalmic findings in this model of diabetes and to quantitatively compare the retinal vasculature in LDL receptor knockout mice fed either a standard or a high fat diet.

Methods: : LDLR knockout mice were fed either a chow diet from birth until age 13 months or a chow diet from birth until 12 months, and then a high-fat diet from 12 months to 15 months. At age 13 or 15 months (respectively), the mouse retinal vasculature was imaged using fluorescein angiography. The images were then processed with ImageJ, to calculate the fractal dimension of the retinal blood vessels, a quantitative measure of pattern and complexity. The mice were then sacrificed and enucleated. The eyes were formalin fixed, paraffin embedded, sectioned and stained with H&E. Immunohistochemistry was performed using antibodies to CD31 and alpha smooth muscle actin (SMA), to stain mature endothelial cells and pericytes, respectively. For each eye, three 40X high power fields were analyzed, one of the central retina and two of the peripheral retina. A blinded rater then counted the number of stained vessels in each section.

Results: : Utilizing both automated and manual image processing, the mean fractal dimension in the mice fed a high-fat diet was higher than in mice fed a chow diet (p=0.041 and p=0.039, respectively). The mean number of blood vessels staining for CD31 (endothelial cells) in the retinas of mice fed a high fat diet was significantly higher than in the mice fed a chow diet (p=0.0048). There was no significant difference between the number of vessels staining for SMA (pericytes) in the two groups (p=0.545).

Conclusions: : The retinal vessels of LDLR knockout mice fed a high fat diet had greater vascularity than in mice fed a chow diet. Loss of pericytes, a common finding in early non-proliferative diabetic retinopathy, may account for the similarity in the number of pericytes. These results are the first to characterize the retinal vasculature of LDLR knockout mice and support the hypothesis that LDLR knockout mice fed a high fat diet may be an appropriate ophthalmic model for studies of metabolic syndrome and type II diabetes mellitus.

Keywords: diabetic retinopathy • transgenics/knock-outs • imaging/image analysis: clinical