Transcriptional responses to environmental metal exposure in wild yellow perch (Perca flavescens) collected in lakes with differing environmental metal concentrations (Cd, Cu, Ni)

Abstract

To investigate the mechanisms involved in metal stress in wild fish, yellow perch (Perca flavescens) were collected in eight lakes of the Rouyn-Noranda and Sudbury regions (Canada). Due to mining and smelting activities, these two regions indeed present a broad contamination gradient in metal concentrations (Cd, Cu, Zn and Ni; water, sediment and prey) and offer a unique research opportunity to investigate relationships between metal bioaccumulation and resulting deleterious effects in indigenous biota chronically exposed to metal mixtures. The expression level of genes encoding for proteins involved in metal detoxification (metallothioneins, mts), protein protection (heat shock protein-70, hsp-70), growth (insulin-like growth factor-1, igf-1), aerobic energy metabolism (cytochrome c oxydase, cco-1) and protection against oxidative stress (Cu/Zn superoxide dismutase, sod-1) were assessed in fish liver and muscle in association with protein and enzymatic assays for cytochrome c oxidase (CCO). Bioaccumulation of both Cd and Cu increased in response to higher ambient metal concentrations, but the two metals clearly have different modes of action. For Cd, changes in gene expression levels were more marked in the liver than in the dorsal muscle, whereas for Cu the opposite trend was observed. Hepatic Cd accumulation was linked to decreased cco-1 and sod-1 gene expression, whereas Cu accumulation was associated with a decrease in CCO enzymatic activity and an increase in total protein concentration and in cco-1, mts and hsp-70 gene expression levels. For Ni, no significant correlations were observed at the transcriptional level, but increasing hepatic Ni concentrations were significantly and positively correlated with protein concentrations and CCO activity. By coupling gene expression to biochemical and physiological endpoints, this work provides new insights into the mechanisms involved in metal stress and the adaptive response of fish chronically exposed to metal mixtures.

Energy metabolism and pesticides: biochemical and molecular responses to copper in roach Rutilus rutilus

“…This may be due to a decrease of oxygen availability in gills and then of ETS activity producing ATP, or could be due to a direct impact of Cu. Finally, results of the present study are in agreement with Pierron et al 12 They observed an increase in gene expression of CCOX subunit 1 and a decrease of CCOX enzymatic activity in wild yellow perch (Perca flavescens) in response to Cu exposure in lakes. Moreover a decrease of citrate synthase enzymatic activity has been shown in wild yellow perch muscle.…”

Effects of chronic metal exposure on wild fish populations revealed by high-throughput cDNA sequencing

“…For example, for ATP synthase, genes encoding for membrane subunits (c and f) were up-regulated while genes encoding for subunits located in the matrix (b and c) were down-regulated (Table 1, Tables S2, S3). As previously described in yellow perch liver (Pierron et al 2009), such an increase in the transcription levels of genes encoding for membrane subunits could reflect a compensatory mechanism to counteract the toxic effects of Cd and Cu on the mitochondrial inner membrane (Garceau et al 2010;Pierron et al 2009). Furthermore, the mitochondrial inner Fig.…”

“…For example, this could explain why increasing Cd concentrations were associated with a decrease in the transcription level of the gene encoding for acetyl-coenzyme A synthetase, a gene that is known to be up-regulated in response to PPAR activation by dietary fatty acids (Schoonjans et al 1995). In addition, previous studies have reported that in situ metal exposure impairs aerobic capacities of metal-contaminated yellow perch (Couture and Kumar 2003;Garceau et al 2010;Pierron et al 2009). Since lipids are the main fuel of aerobic ATP production, a Cd-induced impairment in lipid metabolism may be involved in the lower aerobic capacities reported in contaminated wild fish.…”

“…Hepatic metal concentrations were determined using inductively coupled plasma mass spectrometry (ICP-MS, Thermo Elemental, Model X-7) according to a method described previously (Pierron et al 2009). In parallel, certified reference materials from the National Research Council of Canada (TORT2), as well as blanks, were submitted to the same treatment in order to monitor analytical accuracy and recovery.…”

“…The reaction specificity was determined for each reaction from the dissociation curve of the PCR product and electrophoresis. The relative quantification of each gene expression level was normalized according to the b-actin gene expression as previously described (Pierron et al 2009). Total RNAs were quantified and 500 ng used for reversetranscription.…”