Synergic stress in striped catfish (Pangasianodon hypophthalmus, S.) exposed to chronic salinity and bacterial infection: Effects on kidney protein expression profile

• Kidney proteome of catfish exposed to chronic salinity and infection was investigated.
• Both stressors activate similar pathways involved in the general stress response.
• Chronic saline stress decreases several immune responses during bacterial infection.
• Chronic sterile inflammation increases susceptibility to microbial infection.

Hyperosmotic stress has often been investigated from osmoregulation perspectives while the effects of such stress on the immune capacity remain largely unexplored. In this study, striped catfish were submitted to a gradual hyperosmotic stress (up to 20 ppt), followed by an infection with a virulent strain of an intracellular bacteria, Edwardsiella ictaluri. Physiological parameters (plasma osmolarity, gill NaK ATPase) have been investigated. Moreover, a label free quantitative proteomics workflow was used to study how salinity affects the proteome of kidney of no infected and infected fish. The flow consisted in initial global profiling of relative peptide abundances (by LC/MS, peak area quantification based on extracted ion currents) followed by identification (by MS/MS). Differentially expressed proteins were analysed in DAVID interface to isolate functional pathways involved in the response to bacterial infection and which are influenced by environmental salinity changes. In response to hyperosmotic stress, plasma osmolarity increased while gill Na+ K+ ATPase slightly increased. In kidney proteome, 2024 proteins were identified, among which 496 proteins were differentially expressed. Hierarchical clustering analysis leads to isolation of 4 main clusters. Several pathways and functional categories, mostly related to cell metabolism, response to stress, cell structure, immunity and ion homeostasis were highlighted and discussed.SignificanceThe striped catfish is a highly worldwide commercialized species and is mainly produced in the Mekong Delta (Vietnam), which is currently subjected to sea level rise and increasing salt intrusions in these aquacultures resources. Moreover, salt is commonly used as antiseptic in aquacultures to treat microbial diseases. To date, the effect of prolonged exposure to hyperosmotic condition have been mainly looking at changes regarding the growth and the osmoregulation while the effect of such stress on the immune capacity and susceptibility to pathogen have been poorly investigated. This study aims to highlight molecular changes in kidney occurring during acclimation to hyperosmotic conditions, particularly those involved in fish immune defences.

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