Expression patterns of peroxiredoxin genes in bronchial epithelial cells exposed to diesel exhaust particles

Highlights

• Diesel exhaust particles alter expression patterns of peroxiredoxins genes in bronchial epithelial airways cells.

• Gene expression levels of PRDX 2, 5 and 6 decreased in BEAS-2B cells exposed to DEPs for a short period of time.

• Decrease in PRDX levels affecting cellular functions.

Abstract

Several mechanisms have been suggested to explain the adverse effects of air pollutants on airway cells. One such explanation is the presence of high concentrations of oxidants and pro-oxidants in environmental pollutants. All animal and plant cells have developed several mechanisms to prevent damage by oxidative molecules. Among these, the peroxiredoxins (PRDXs) are of interest due to a high reactivity with reactive oxygen species (ROS) through the functioning of the thioredoxin/thioredoxin reductase system. This study aimed to verify the gene expression patterns of the PRDX family in bronchial epithelial airway cells (BEAS-2B) cells exposed to diesel exhaust particles (DEPs) at a concentration of 15 μg/mL for 1 or 2 h because this it is a major component of particulate matter in the atmosphere. There was a significant decrease in mRNA fold changes of PRDX2 (0.43 ± 0.34; *p = 0.0220), PRDX5 (0.43 ± 0.34; *p = 0.0220), and PRDX6 (0.33 ± 0.25; *p = 0.0069) after 1 h of exposure to DEPs. The reduction in mRNA levels may consequently lead to a decrease in the levels of PRDX proteins, increasing oxidative stress in bronchial epithelial cells BEAS-2B and thus, negatively affecting cellular functions.

Introduction

The epithelial cells of the airways are an important link between the environment and internal structures of the human body. Consequently, the air quality influences a number of physiological functions causing increased morbidity and mortality (Schraufnagel et al., 2019). The deterioration in air quality is mainly caused by rapid industrialization, urbanization, population growth, low quality of fuel, and usage of old motors in developing countries. Among all existing internal combustion engines, the diesel engine is a major concern in relation to the environment and public health, as it is the most popular engine and responsible for a large part of urban particulate matter. (Yang et al., 2015; Steiner et al., 2016; Sunil et al., 2017).

Diesel engines constitute a major source of particulate matter released into the air in urban environments as they produce diesel exhaust particles (DEP), which are considered the major components of particulate matter in the atmosphere. It is known that toxic compounds can adsorb on particle surfaces and, when activated, they can participate in redox reactions, leading to reactive oxygen species (ROS) formation. The small size of DEPs makes their reaching of deep regions in the respiratory tract and then the blood circulatory system easier leading to acute irritation, asthma-like symptoms, allergic responses, as well as higher risk for lung cancer (Steiner et al., 2016).

Several mechanisms have been suggested to explain the adverse effects of air pollutants on airways. The most consistent and widely accepted explanation of these is that atmospheric pollutants produce elevated levels of oxidants and pro-oxidants once in contact with the respiratory epithelium (Øvrevik, 2019).

Human cells have evolved several mechanisms to prevent oxidative damage caused by these oxidant molecules. Among them, superoxide dismutase (SOD) and catalase (CAT) are primary defense mechanism against HO• formation. Catalase, glutathione peroxidase (GPX) and PRDX act together to protect cells from the toxic effects of hydrogen peroxide.

Peroxirredoxins (PRDX) are important hydroperoxide detoxification enzymes. These belong to a family of cysteine-dependent peroxidases and exhibit high reactivity with hydrogen peroxide, organic hydroperoxides of DEP's and peroxynitrite. PRDX have several biological functions, ranging from regulation of cell proliferation and metabolism to pathways of cell death and aging. They facilitate the regulation of ROS by coupling with the thioredoxin/thioredoxin reductase system, playing major roles not only in peroxide defense, but also in regulating peroxide-mediated cell signaling. (Poole et al., 2011; Radyuk and Orr, 2018).

Six isoforms of PRDX have been identified in humans. PRDX1, 2 and 6 have a cytoplasmic localization. PRDX1 and 2 have been also detected in the nucleus. PRDX 3 has a mitochondrial localization. PRDX4 is transported through the endoplasmic reticulum and golgi for secretion. PRDX 5 is found either in the lysosomes or in peroxisomes (Rhee and Kil, 2017). PRDX1 and PRDX2 when exposed to high concentrations of peroxide may have the peroxidatic cysteine (CysP) hyperoxidized to cysteine sulfinic acid (CysP-SO2H), resulting in the loss of the peroxidase function of these enzymes since thioredoxin (the biological reductant) are able to reduce disulfides but not the hyperoxidized intermediates (Barranco-Medina et al., 2009, Rhee and Woo, 2011; Veal et al., 2018). While disulfide oxidized enzymes are dimers the hyperoxidized species are decamers or higher molecular weight (HMW) oligomers that presents molecular chaperone activity and are able to protect other important proteins from inactivation by oxidative unfolding (Ni and Lee, 2007).

On the other hand, since that the PRDX1 and PRDX2 are very abundant proteins its hyperoxidation also allow the availability of reduced thioredoxin to participate of another protective signaling pathways related to cell survival or apoptosis (Rhee and Woo, 2011; Veal et al., 2018). Is important to mention, that CysP-SO2H can be specifically reduced by sulfiredoxin (Srx) an enzyme that are able to reduce specifically CysP-SO2H restoring the peroxidase activity and favoring the dissociation of HMW complexes (Veal et al., 2018). Nevertheless, the CP-SO2H reduction rates by Srx is very slow when compared to the disulfide reduction by Trx (Mishra et al., 2015) suggesting an important physiological role of Prx hyperoxidized species.

In fact, under very harsh oxidative conditions the 2-Cys Prx can be hyperoxidized to cysteine sulfonic acid (CysP-SO3H) a species that is not reduced by sulfuredoxin and are removed of the cell by proteolysis (Lim et al., 2008).Although several studies have demonstrated that exposure to DEPs could alter the expression of genes involved in the activation of a range of intracellular transduction pathways linked to apoptosis or oxidative stress, the role played by PRDX in this process remains unknown. Therefore, this study was undertaken to evaluate the expression patterns of PDRX 1, 2, 3, 4, 5 and 6 antioxidant enzymes in BEAS-2B cells when exposed to 15 μg/mL of DEPs for either one or two hours.