In vitro Exposure of Human Lens Epithelial Cells to X-rays at Varied Dose-Rates Initiates Protein Level Changes Relevant to Cataractogenesis.

BACKGROUND Accumulated body of evidence shows that ionizing radiation increases the risk of cataracts. The mechanisms are not clear and the International Commission on Radiological Protection (ICRP) indicates a need for research into understanding the process, particularly at low doses and low dose rates of exposure. Purpose: This study was designed to examine protein-level modifications in a human lens epithelial (HLE) cell-line following radiation exposures. Materials and methods: HLE cell-line was subjected to X-rays at varied doses (0-5 Gy) and dose-rates (1.62 cGy/min and 38.2 cGy/min). Cells were collected 20 h post-exposure, lysed and proteins were clarified following fractionation by a molecular weight cut-off filtration method. Fractionated cellular proteins were enzymatically digested and subjected to mass spectrometry analysis. Results Statistically significant radiation dose-related protein changes compared to the control group, were identified. Heatmap and hierarchical analysis showed distinct cluster of responses that were dose-rate dependant. Pathway analysis mapped the proteins to networks and biological functions related to mitochondrial dysfunction, reactive oxygen species generation, cell death, cancer, organismal injury and amyloidosis. Networks were shown to be centred on the Retinoblastoma 1 (RB1) protein with indirect interactions to TP53, a DNA damage response/repair protein. The directionalities of the dose-responses were shown to be a general downregulation of proteins at high dose rates and an upregulation at the low dose rate. In addition, consistent non-linear excursions were observed at doses <0.5 Gy that peaked at 0.25 Gy. Conclusion Findings from this work suggests that ionizing radiation exposure of the HLE cells initiates processes associated with protein misfolding, oxidative stress and cell death mechanisms and that these responses are dose-rate dependant and can be relevant to cataractogenesis.