Transcriptional analysis of antioxidant and immune defense genes in disk abalone (Haliotis discus discus) during thermal, low-salinity and hypoxic stress Mahanama De Zoysa a , Ilson Whang b , Youngdeuk Lee a , Sukkyoung Lee a , Jae-Seong Lee c , Jehee Lee a,d, ⁎ a Department of Marine Life Science, College of Ocean Science, Jeju National University, Jeju Special Self-Governing Province, 690-756, Republic of Korea b Department of Life Sciences, College of Natural Sciences, Jeju National University, Jeju Special Self-Governing Province, 690-756, Republic of Korea c Department of Chemistry, College of Natural Sciences, Hanyang University, Seoul, 133-791, Republic of Korea d Marine and Environmental Institute, Jeju National University, Jeju Special Self-Governing Province, 690-814, Republic of Korea abstract article info Article history: Received 31 May 2009 Received in revised form 10 August 2009 Accepted 11 August 2009 Available online 20 August 2009 Keywords: Haliotis discus discus Antioxidant enzymes Biomarker Immune response Oxidative stress This study describes the transcriptional analysis of antioxidant and immune defense genes in gills tissue of disk abalone exposed to thermal, salinity and hypoxia-related stress, using quantitative real-time PCR. Results showed that manganese superoxide dismutase (MnSOD), copper zinc superoxide dismutase (CuZnSOD), catalase (CAT), thioredoxin peroxidase (TPx), selenium dependant glutathione peroxidase (SeGPx), and thioredoxin-2 (TRx-2) transcripts were expressed differently in gills, and that they respond collectively as a classical enzymatic antioxidant defense system in abalone. Comparative analysis of expression profiles indicated that CAT, TPx and SeGPx transcripts were significantly up-regulated (p < 0.05) by all three physical stress conditions — thermal (28 °C), salinity (25‰) and hypoxia — relative to levels in respective controls. In contrast, CuZnSOD and TRx-2 transcription were down-regulated in response to thermal stress. Interestingly, all the antioxidant transcripts exhibited significant up-regulation in response to salinity-related stress. Meanwhile, hypoxia caused up-regulation of the MnSOD, CAT, TPx and SeGPx, but not the CuZnSOD and TRx-2 transcripts. One of the most significant outcomes was the more than 10-fold induction of SeGPx, suggesting that SeGPx is a potential biomarker gene among antioxidant enzymes, under conditions of physical stress. The effects of physical stress on the transcriptional responses of immune functional genes namely suppressor of cytokine signaling-2 (SOCS-2) and myxovirus resistance (Mx) were investigated. We observed that salinity and hypoxia increase both the SOCS-2 and Mx transcripts, while thermal stress at 28 °C exerts less of an effect, producing mixed transcriptional responses (both up and down regulation). Based upon these results, we postulate that abalones utilize antioxidant and immune defense mechanisms together to overcome physical stresses. © 2009 Elsevier Inc. All rights reserved. 1. Introduction Marine organisms are frequently exposed to natural sources that enhance the formation of reactive oxygen species (ROS), like superoxide anion (O 2 - ), hydrogen peroxide (H 2 O 2 ), alkyl peroxides, singlet oxygen ( 1 O 2 ), and hydroxyl radicals (OH . ). Some of these natural sources include environmental pollutants (heavy metals), microbial infections and primary physical stresses such as thermal, salinity-related, hypoxic and UV (Van der Oost et al., 2003; Abele and Puntarulo, 2004). The accumulation of excessive ROS in cells leads to oxidative stress that is a state of unbalanced tissue oxidation, followed by the peroxidation of lipids, proteins and nucleic acids (Di-Giulio et al., 1989). Cells possess a complex defense system to protect themselves from oxidative damage, using non-enzymatic scavengers and a range of antioxidant enzymes, including SOD, CAT, GPx, TPx and TRx, (Roch, 1999). SODs are metal-containing enzymes that catalyze the removal of O 2 - , producing H 2 O 2 and water as final by-products. CATs are heme-containing enzymes that catalyze the conversion of H 2 O 2 into water and molecular O 2 . TPx and peroxiredoxins (Prx) are recently discovered enzymes that are capable of reducing peroxides, such as H 2 O 2 and alkyl hydroperoxides. GPx removes the H 2 O 2 by coupling its reduction with the oxidation of glutathione (GSH) as a substrate. It also can reduce other peroxides, like fatty acids and other hydroperoxides. A thiol-specific TRx antioxidant system plays a vital role among antioxidant defense systems, along with other compo- nents like thioredoxin reductase (TRxR). TRx reduces the intracellular disulfides induced by ROS, and directly lowers ROS levels (Chae et al., 1999; Nordberg and Arner, 2001). Therefore, a defense system that has a diverse array of antioxidant enzymes must exist to reduce the oxidative stress caused by biological, physical and chemical stresses. Previous studies have shown that significant alterations exist in the ROS production and antioxidant enzyme expression or activities that exist in marine organisms in response to primary physical factors Comparative Biochemistry and Physiology, Part B 154 (2009) 387–395 ⁎ Corresponding author. Department of Marine Life Science, College of Ocean Science, Jeju National University, Jeju, 690-756, Republic of Korea. Tel.: +82 64 754 3472; fax: +82 64 756 3493. E-mail address: jehee@jejunu.ac.kr (J. Lee). 1096-4959/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.cbpb.2009.08.002 Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part B journal homepage: www.elsevier.com/locate/cbpb