iTRAQ analysis of gill proteins from the zebrafish (Danio rerio) infected with Aeromonas hydrophila

• Zebrafish gill play important roles in immune responses to Aeromonas hydrophila infection.
• The differential proteomes of the zebrafish gill were identified by iTRAQ.
• GO analysis showed that gill proteins were involved in stress and immune responses.
• Complement and phagosome pathways in gills were identified by KEGG analysis.

The gills are large mucosal surfaces and very important portals for pathogen entry in fish. The aim of this study was to determine the gill immune response at the protein levels, the differential proteomes of the zebrafish gill response to Aeromonas hydrophila infection were identified with isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 1338 proteins were identified and classified into the categories primarily related to cellular process (15.36%), metabolic process (11.95%) and biological regulation (8.29%). Of these, 82 differentially expressed proteins were reliably quantified by iTRAQ analysis, 57 proteins were upregulated and 25 proteins were downregulated upon bacterial infection. Gene ontology (GO) enrichment analysis showed that approximately 33 (8.8%) of the differential proteins in gills were involved in the stress and immune responses. Several upregulated proteins were observed such as complement component 5, serpin peptidase inhibitor clade A member 7, annexin A3a, histone H4, glyceraldehyde 3-phosphate dehydrogenase, creatine kinase, and peroxiredoxin. These protein expression changes were further validated at the transcript level using microarray analysis. Moreover, complement and coagulation cascades, pathogenic Escherichia coli infection and phagosome were the significant pathways identified by KEGG enrichment analysis. This is first report on proteome of fish gills against A. hydrophila infection, which contribute to understanding the defense mechanisms of the gills in fish.