Abstract

Reactive oxygen species (ROS) can cause severe damage to cells and organs but they are also important mediators of inflammatory responses and cellular signalling. Due to the significant role of ROS, the cells have evolved a broad antioxidative system to regulate the concentration of these species. Peroxiredoxins (Prxs) are enzymes that participate in the regulation of the cellular redox-homeostasis by detoxifying hydrogen peroxide. Prxs are not classified as conventional antioxidant enzymes and their physiological role, whether protective or regulatory, is still unclear.

The aim of this project was to study the localization and regulation of Prxs in normal human lung and also their role in selected lung disorders (pulmonary sarcoidosis, pleural mesothelioma, lung carcinomas and chronic obstructive disorder, COPD). Additionally the expression of thioredoxin (Trx) and thioredoxin reductase (TrxR) was analysed in the lung of smokers and COPD patients. These enzymes are important reductants in cell and Prxs are one of their targets. Lung is an important organ in the field of ROS and antioxidant research since it is especially vulnerable to exogenous oxidative stress caused by pollutants, cigarette smoke and also by high oxygen pressure.

The results showed that all six human Prxs were expressed in healthy human lung but in a cell-specific manner. The most prominent expression was detected in the epithelium and in macrophages, the cells most prone to oxidative stress. There were also differences in subcellular locations of Prxs.

The expression of Prxs in non-malignant lung diseases (pulmonary sarcoidosis and COPD) and in smoker's lung was very similar with that in normal lung. Higher expression of Prx V and VI was detected in a subpopulation of macrophages sampled from COPD patients' lung. In contrast, Trx expression was induced in the bronchial epithelium of smoker's lung.

Differences in the expression compared to normal lung were seen in lung malignancies (pleural mesothelioma and lung carcinomas). Interestingly, different Prxs were highly expressed in different types of carcinomas. In pleural mesothelioma, all Prxs except Prx IV were highly expressed when compared to normal pleura, in adenocarcinoma Prxs I, II, VI and especially IV, and in squamous cell carcinoma Prxs I, II and IV were upregulated.

Tests performed on cultured cells in vitro revealed only a minor increase in the Prx expression after severe oxidant stress in malignant lung cell line originating from alveolar type II pneumocytes (A549) or non-malignant cell line derived from bronchial epithelium. None of the tested growth factors or cytokines affected Prx expression or oxidation state, but severe oxidant stress influenced remarkably the oxidation state of the Prxs.