Proteomic profiling of gills during carp edema virus infection provides insights into immune responses and cellular stress associated with koi sleepy disease

Carp edema virus (CEV) causes koi sleepy disease (KSD), a severe disease targeting the gills of common carp, which is associated with gills dysfunction and mortality. In this study, we employed a combination of proteomics and clinical, histopathological, physiological, and transcriptional analyses to characterise the alterations induced by the virus in the gills proteome of experimentally infected koi. Gills collected at the peak of the disease showed high viral loads and marked epithelial hyperplasia with interlamellar occlusion, leading to severe hyponatraemia and hyperammonaemia. Two-dimensional differential in-gel electrophoresis (2D-DIGE) revealed 91 differentially abundant protein spots, 85 of which were identified by mass spectrometry. Interferon-stimulated and innate effector proteins, including Mx, Mx2, Gig1, Trim21, lysozyme C and apolipoprotein A1, were strongly upregulated, together with heat shock proteins and chaperonins, which are indicative of cellular stress and enhanced protein folding. Furthermore, the upregulation of Mmp13 and Tgm1 may be linked to abnormal cell proliferation within the gills lamellae and contribute to the characteristic tissue occlusion. In contrast, antioxidant enzymes, cytoskeletal regulators and metabolic enzymes involved in energy and xenobiotic metabolism were suppressed. Ingenuity Pathway Analysis revealed networks associated with protein quality control, inflammation, nucleic acid metabolism, and impaired chemotaxis. These molecular changes are consistent with gills hyperplasia and interlamellar space occlusion, providing a mechanistic link between viral infection and tissue dysfunction. Overall, our results define a CEV-specific gills response that explains the characteristic pathology and functional impairment of the gills observed in KSD.