Caspase-3 in lens epithelium

Abstract: Purpose: To model the time evolution of active caspase-3 protein expression in a healthy lens, and in a lens exposed to UVR-300 nm (UVR-B). To develop an automated method to classify the fluorescent signal of biomarkers in the lens epithelial cells.Methods: Six-week old Sprague-Dawley rats were used. Firstly, expression of active caspase-3 was studied in the lens epithelium of healthy rats. Secondly, rats were unilaterally exposed in vivo to 1 kJ/m2 UVR-B for 15 minutes. At 0.5, 8, 16, and 24 hours after the UVR-B exposure, the exposed and the contralateral non-exposed lenses were removed. Immunohistochemistry was done on three mid-sagittal sections from each lens. The florescent labelling for active caspase-3 in each lens section was counted three times. The time evolution of active caspase-3 expression in response to UVR-B exposure was modelled as a function of cell position in the lens epithelium. An automated objective method was developed to quantify the lens epithelial cells and to classify the fluorescent signal of active caspase-3. Active caspase-3 was selected as a model signal.Results: Active caspase-3 was abundant in the anterior pole of the normal lenses. Spatial distribution of active caspase-3 labelling in the lens epithelium was fitted to a logistic model. The probability of active caspase-3 expression was higher in the UVR-B exposed lenses (95% CI = 0.12 ± 0.01). There was no difference in the expression of active caspase-3 between the 0.5 and the 24 hours groups or between the 8 and the 16 hours groups. A difference was noted, when comparing the 0.5 and 24 hours groups with the 8 and 16 hours groups (Test statistic 7.01, F1;36;0.95= 4.11). Exposure to UVR-B has an impact on the average probability of labelling for active caspase-3 as a function of cell position. The probability of labelling as a function of cell number also varied as a function of time after UVR-B exposure. The automated method counted the lens epithelial cells and estimated the proportion of active caspase-3 labelling in the lens epithelium.Conclusions: Active caspase-3 is present in the healthy lens epithelial cells. Active caspase-3 exhibits higher expression at the anterior pole of the lens and the expression decreases towards the periphery. After UVR-B exposure, the expression of active caspase-3 in the lens epithelium increases with a peak of expression occurring around 16 hours after exposure. The average probability of labelling in the lens epithelium is dependent on both the UVR-B exposure and the time period elapsed after the exposure. The automated method enables objective and fast quantification of lens epithelial cells and the expression of fluorescent signal in the lens cells.