Animal models of corneal endothelial dysfunction to facilitate development of novel therapies

Abstract

Progressive corneal endothelial disease eventually leads to corneal edema and vision loss due to the limited regenerative capacity of the corneal endothelium in vivo and is a major indication for corneal transplantation. Despite the relatively high success rate of corneal transplantation, there remains a pressing global clinical need to identify improved therapeutic strategies to address this debilitating condition. To evaluate the safety and efficacy of novel therapeutics, there is a growing demand for pre-clinical animal models of corneal endothelial dysfunction. In this review, experimentally induced, spontaneously occurring and genetically modified animal models of corneal endothelial dysfunction are described to assist researchers in making informed decisions regarding the selection of the most appropriate animal models to meet their research goals.

Keywords: Corneal endothelium; corneal endothelial disease; corneal endothelial injury; fuchs endothelial corneal dystrophy; pre-clinical animal models.

Figure 1

Corneal endothelial regenerative capacity varies by species. Following corneal endothelial injury, rabbits demonstrate rapid and robust mitosis consistent with their high regenerative capacity. The corneal endothelial cells of rodents also demonstrate some mitotic capacity although it is slower than in rabbits. By contrast, cats and non-human primates demonstrate little mitotic ability consistent with that of humans.

Figure 2

Transcorneal cryoinjury in rabbits. (A) An 8-mm diameter cryoprobe cooled to an approximate temperature of −196 °C was applied to the cornea for 15 seconds and the cornea was allowed to thaw spontaneously. Following cryoinjury, multimodal advanced ocular imaging including slit lamp biomicroscopy, FD-OCT and IVCM were utilized to monitor clinical progression as well as endothelial wound healing. These imaging modalities demonstrated maximal edema and thickening of the central cornea on PID 3 with return to normal corneal thickness and transparency on PID 14. After euthanasia at the completion of the study, alizarin red staining was performed in corneal wholemounts to evaluate endothelial cell morphology and density. (B) Cryoinjury was performed in two different age groups of rabbits and CCT was evaluated for 14 days post-injury. CCT gradually decreased and returned to normal on PID 11 in 0.67-year-old rabbits, but CCT still remained elevated at >500 µm on PID 14 in 3-year-old rabbits. *P values represent comparison of CCT before and after cryoinjury in 0.67-year-old rabbits; ^†, P values represent comparison of CCT before and after cryoinjury in 3-year-old rabbits; paired t-test. CCT, central corneal thickness; FD-OCT, Fourier-domain optical coherence tomography; IVCM, in vivo confocal microscopy; PID, post-injury day.

Figure 3

Corneal endothelial wounds and healing vary depending on the inciting cause. (A) A 2-mm diameter cryoprobe of approximately −196 °C was applied to the cornea for 3 seconds in 6-month old mice. Immediately after cryoinjury, CECs were destroyed and inflammatory debris were observed on PID 1. On PID 3, regenerating CECs were observed migrating into the wound area. (B) A 302 nm UV-B with irradiance of 5,900 mW/cm2 was exposed to the cornea of 6-month-old mice. In contrast to cryoinjury, UV irradiation resulted in mild cellular changes on PID 1 and a bare Descemet’s membrane with little cellular debris on PID 3. CEC, corneal endothelial cell; PID, post-injury day.

Figure 4

Anterior segment photography, FD-OCT and IVCM imaging of a 9-year-old male neutered Boston Terrier. (A) Right eye. The right cornea had a normal thickness and clarity for 3 months after the initial visit. However, IVCM showed progressive CEC damage of the central cornea including disrupted cell borders, pleomorphism, and polymegathism. (B) Left eye. Focal corneal edema was observed in the temporal paraxial cornea at the initial visit. With IVCM, mild pleomorphism and polymegathism was observed in the nasal cornea while marked pleomorphism and polymegathism with multinucleated giant cells and a guttae-like structure were found in the central and temporal cornea. CEC, corneal endothelial cell; FD-OCT, Fourier-domain optical coherence tomography; IVCM, in vivo confocal microscopy.