Investigation of cellular stress response related heat shock proteinhsp70/Hsp70 and multixenobiotic transporterabcb1in Siberian freshwater amphipods upon cadmium exposure

Abstract

Stress gene responses in amphipods to cadmium 1 1 Title: Investigation of cellular stress response related heat shock protein hsp70/Hsp70 and 2 multixenobiotic transporter abcb1 in Siberian freshwater amphipods upon cadmium exposure 3 4 Authors: 13 14 15 16 17 18 19 20Stress gene responses in amphipods to cadmium 2 21 Abstract: Induction of stress response genes hsp70 and abcb1 and Hsp70 protein by 22 cadmium chloride (CdCl 2 ) was explored in amphipod species with different stress adaptation 23 strategies from the Lake Baikal area. Based on lethal concentrations (LC) the sensitivities to 24 CdCl 2 were ranked (24 hr LC50 -mg/L CdCl 2 ): Gammarus lacustris (1.7) < 25 Eulimnogammarus cyaneus (2.9) < E. verrucosus (8.3) < E. vittatus (18.2). Conjugated dienes 26 indicating lipid peroxidation were significantly increased by 5 mg/L CdCl 2 (24 hr exposure) 27 only in G. lacustris and E. cyaneus. Upon treatment with 0.54 -5.8 mg/L CdCl 2 hsp70 28 transcript levels were more increased in the toxicologically more sensitive species. Relating 29 the exposure concentrations to LCx values revealed that across the species the increases of 30 hsp70 transcript levels were comparatively low (up to 2.6-fold) up to LC50; at higher LCx 31 values hsp70 induction was more pronounced (up to a 9.1-fold by 5 mg/L CdCl 2 (≙LC70) in 32 E. cyaneus). In contrast, abcb1 inductions did not correspond with CdCl 2 LCx values across 33 species; abcb1 induction was highest (4.7-fold) in E. verrucosus by 5.0 mg/L CdCl 2 (≙LC45, 34 24 hr exposure). Induction of stress gene responses by lethal CdCl 2 concentrations indicates 35 that in the amphipods they are rather insensitive. 36 37 38 39 Key words: conjugated dienes, heavy metal, Lake Baikal, P-glycoprotein, stress protein 40 41 Stress gene responses in amphipods to cadmium 3 42 Introduction 43Cadmium is a non-essential heavy-metal that reaches the environment via various 44 anthropogenic and natural sources and at low concentrations causes poisoning in humans and 45 wildlife [1]. Toxic cadmium effects have often been attributed with increased levels of 46 reactive oxygen species (ROS) and reactive nitrogen species (RNS) causing damages of 47 biological macromolecules such as proteins [2]. Exposure to cadmium was found to lead to 48 the induction of cellular stress response genes hsp70 [3][4][5][6][7][8][9][10][11][12] and abcb1 [13, 14] in a range of 49 aquatic organisms. This induction of hsp70 and abcb1 by cadmium can be related to the 50 increased abundance of damaged cellular macromolecules such as cellular membrane 51 fragments or misfolded proteins [15, 16]. 52Lake Baikal in Eastern Siberia, the oldest, deepest and by volume largest lake in the 53 world, is a biodiversity hotspot with high degrees of endemicity of species [17, 18]. Baikal´s 54 water is generally highly pristine, however, the risk of water contamination by heavy metals 55 is increasing especially through the Selenga river, which is the largest tributary of Lake 56 Baikal and comprises almost half of the riverine inflow into...