# Dynamic changes in and time sequence of ultraviolet B-induced apoptosis in rat corneal epithelial cells

## TL;DR

This study examines how rat corneal epithelial cells undergo apoptosis after UVB exposure, showing rapid cell death linked to both extrinsic and intrinsic pathways.

## Contribution

The study provides a detailed time sequence of UVB-induced apoptosis in rat corneal epithelial cells, highlighting the involvement of both extrinsic and intrinsic pathways.

## Key findings

- UVB irradiation rapidly triggers apoptosis in rat corneal epithelial cells.
- Apoptosis involves both extrinsic (caspase-8, Bax) and intrinsic (mitochondrial membrane potential) pathways.
- Apoptotic rate peaks at 6 hours post-irradiation and declines afterward.

## Abstract

To systematically examine the dynamic changes and time sequence in corneal
epithelial cell apoptosis after excessive ultraviolet B irradiation.

Ultraviolet B (144 mJ/cm2) was used to irradiate rat corneal
epithelial cells for 2 h. Cell morphology was observed on differential
interference contrast microscopy, and the numbers of the different kinds of
apoptotic cells were counted using the ImageJ software. Cell viability was
measured with the 3-(4,5-dimethyl-2-thiazolyl)-2,5- diphenyl-2-H-tetrazolium
bromide method. Cell apoptotic rate and loss of mitochondrial membrane
potential were detected using flow cytometric analyses. The expression
levels of 3 apoptotic genes were measured with real-time quantitative
polymerase chain reaction at different time points within 0-24 h after
irradiation.

After 144-mJ/cm2 ultraviolet B irradiation for 2 h, the expression
levels of caspase-8 and Bax were highest at 0 h;
furthermore, the mitochondrial membrane potential decreased at 0 h and
remained constant for 6 h in a subsequent culture. At 6 h, caspase-3 was
activated. The decrease in cell viability and increase in apoptotic rate
peaked at 6 h. The caspase-3 expression level decreased within 12-24 h,
which led to a decline in apoptotic rate and change in apoptotic stage.

The corneal epithelial cells exhibited rapid apoptosis after ultraviolet B
irradiation, which was associated with both extrinsic and intrinsic
pathways.