Integrative analyses of gene expression and alternative splicing to gain insights into the effects of copper on hepatic lipid metabolism in swamp eel (Monopterus albus)

Copper (Cu) is a common contaminant in water and can potentially cause hepatic tissue damage and toxicity in aquatic organisms. Herein we performed transcriptome analysis to investigate the effects of 100 mu g/L and 400 mu g/L Cu2+ (96-h exposure) on hepatic lipid metabolism in swamp eel (Monopterus albus). We identified 1004 and 2766 differentially expressed genes (DEGs) in the 100 and 400 mu g/L Cu2+ groups, respectively. 4 upregulated DEGs (e.g. DGAT2 and SRD5A1) and 25 down-regulated DEGs related with lipid metabolism (e.g. FABP7A, CYP51, FADS2 and ACAA2) were found in 100 mu g/L Cu2+ group. In 400 mu g/L Cu2+ group, 52 upregulated lipid metabolism genes (e.g. PPAR alpha, RXR alpha, ACSL4A, CPT-1, CPT-2, ACOX3, HADHA and ACADL) were identified, and 22 genes related with lipd metabolism including FABP7A, CYP51, CYP27B1, etc. were significantly down-regulated (p < 0.05). Gene ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed that low concentrations of Cu (100 mu g/L Cu2+) affected only few pathways, however, high concentrations of Cu (400 mu g/L Cu2+) significantly affected more pathways, and peroxisome proliferator-activated receptor signaling and fatty acid degradation pathways were simultaneously in both two groups. Furthermore, upon alternative splicing analysis, we identified 55 and 81 differentially alternatively spliced (DAS) genes in the low and high concentration groups, respectively. Among these DAS genes, ACACA, DEGS2 and ST3GAL3 were associated with lipid metabolic process and fatty acid biosynthesis. The expression levels of 11 DEGs related to fatty acid degradation were validated by quantitative real-time PCR with significant up-regulation in 400 mu g/L Cu2+ group, and the DAS gene of skipping exon 29 in ACACA which involved in fatty acid biosynthesis was validated by semiquantitative PCR. These results suggest that high Cu concentration (400 mu g/L Cu2+) might reduce fatty acid deposition in swamp eel livers. To summarize, the genes and pathways identified herein should further our understanding of the mechanisms underlying Cu-induced lipid metabolism disorder. Furthermore, the present study highlights the importance of alternative splicing analysis, in tandem with gene expression surveys, to characterize molecular pathways in environmental studies.

Automated summary

Copper contamination can have adverse effects on lipid metabolism in swamp eel livers, leading to significant changes in gene expression and alternative splicing, particularly with more pronounced impacts on lipid metabolism pathways under high copper concentrations.