Comparative immunoendocrine responses to stressors in rainbow trout (oncorhynchus mykiss) and gilthead sea bream (sparus aurata)
- Autores: Ali Reza Khansari
- Directores de la Tesis: Lluís Tort Bardolet (dir. tes.), Felipe Reyes Lopez (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Joaquim Gutiérrez Fruitós (presid.), Joan Carles Balasch (secret.), Juan Miguel Mancera (voc.)
- Programa de doctorado: Programa Oficial de Doctorado en Acuicultura
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
All animals may be exposed to stressors along their life. Fish under aquaculture conditions inhabit a potentially stressful medium that may impose extra challenges to the animal. In fish, the stress response and their consequences on immune system have been widely described. It involves the activation of the Hypothalamic-Pituitary-Interrenal (HPI) and Brain-Sympathetic-Chromaffin (BSC) axis as the neuroendocrine crosstalk that promotes the secretion of stress hormones. In this ambit, the fish head kidney is equivalent to the mammalian bone marrow and adrenal gland. Therefore, the stress response not only will activate the HPI axis to secrete hormones but also will modulate the fish immune response affecting the expression of cytokines and the whole immune reaction. Until recently, it was assumed that the effect of hormones involved in the physiological stress response (such as cortisol, ACTH, adrenaline) is species-independent and constant but, to our knowledge no study systematically compared the effect of hormones or identical stress conditions in several species at the same time. Thus, our aim was to unveil the interaction between the neuroendocrine and the immune system in two different fish species (rainbow trout and gilthead sea bream) in response to stress hormones through evaluating the gene expression.
At first, it was intended to investigate the cytokine modulation of pro- (IL-1β, IL-6, TNF-α) and anti-inflammatory cytokines (IL-10, TGF-β) by stress hormones (cortisol, ACTH, adrenaline) and also utilizing antagonist receptors in rainbow trout (Oncorhynchus mykiss) and gilthead sea bream (Sparus aurata) head kidney primary cell culture (HKPCC). Our data showed that cortisol and ACTH decreased the expression of immune-related genes in sea bream but not in rainbow trout. On the other hand, while adrenaline was found to be suppressor of the pro-inflammatory cytokines (IL-1β, IL-6) in rainbow trout, the opposite effect was observed in sea bream increasing expression of (IL-1β, IL-6). Based on the results obtained, we also aimed to investigate the interaction between endocrine and immune system particularly the cellular immunity in the presence of an immune stimulator (Vibrio anguillarum bacterin). Our results show an increase of pro- (IL-1β, IL-6, TNF-α) and anti-inflammatory cytokines (IL-10, TGFβ1) after V. anguillarum treatment in both species excluding sea bream TGFβ1. The stress hormones (cortisol, ACTH and adrenaline) did not modulate the expression of stimulated cytokines in rainbow trout, whereas in sea bream cortisol was able to reduce stimulated gene expression in all cytokines. Overall, the findings confirm the close regional interaction between endocrine and cytokine messengers in the head kidney even in the presence of V. anguillarum bacterin, and also a clear difference between the two fish species in both the sensitivity to bacterin and to hormonal stimuli. Altogether, in contrary to classical view of stress hormone as an immune suppressor, we demonstrated distinct effect of hormones in different species.
Considering the modulatory effect of stress hormones at regional level, we evaluated the effect of anoxia and V. anguillarum immersion (formalin killed bacteria) on the gene expression of rainbow trout and sea bream at physiological level, evaluating the expression pattern both at systemic and mucosal level. The response of fish to external stressors after 1, 6 and 24 hours post-stress was studied at first in systemic level. Therefore, the effect of stress on HPI axis activation and gene expression (cytokines and stress genes) was evaluated in liver and spleen of rainbow trout and sea bream. In this particular part of the work, we included the expression analysis in zebrafish as another fish model organism.
Importantly, at plasmatic level cortisol increased at 1 hours post anoxia (hpa) and then decreased at 6 hpa in trout and zebrafish but not in sea bream whose cortisol levels remained high compared to control, suggesting a greater degree of responsiveness to stress in gilthead sea bream. Moreover, when fish were exposed to anoxia plus vaccination the cortisol level was also augmented at 1 and 6 h in rainbow trout and sea bream and restored to the basal level at 24 h, whereas in zebrafish the response was higher indicating a longer response of HPI axis to the combination of both stressors. The gene expression pattern in liver and spleen was found to be differential and time dependent among species. Altogether, these results indicate that similar cortisol secretion kinetics takes place in the studied species. However, the modulation of genes appears to be decreased.
With regard to the importance of mucosal tissue (skin, gills and intestine) of fish, which are in intimate contact with the immediate environment, we also evaluated the effect of external stimuli that may produce local alterations in mucosal tissues when these potential threats are perceived by specific tissue receptors located at these regions. Our results showed a differential gene expression pattern between rainbow trout and gilthead sea bream, confirming that the enhancing response to a stressor at local level is tissue-dependent and species-specific rather than suppressive at systemic level. Thereby we have found gilthead sea bream more stressful than rainbow trout.
By taking into consideration the higher degree of stress in sea bream, the expression response in hypothalamus and pituitary genes after anoxia and vaccination was studied in the gilthead sea bream. The results show that stress by anoxia is primarily stimulating both hypothalamic CRH and pituitary POMCB at short time whereas vaccine stimulates hypothalamic (CRH and TRH) and pituitary peptides (PRL, GH) at longer time points (while POMCa and POMCb at short term), as a possible result of feedback since GR expression in hypothalamus is also stimulated. Thus, the results confirm that at central nervous system different stressors show different stimulatory abilities as anoxia is perceived immediately and vaccine is not, which could be directly associated to the particular dynamics of the central stress response.
In summary, the present work supports the view that different species show a differential immune-related gene expression profile when subjected to several stressors. These differences may reside in the distinct sensitivity to the bacterin stimuli and to hormonal stimuli, and also to the dynamics of the central response to those stressors. We also conclude that it should be further assessed if fish from seawater may be more stressed than fresh water fish as for the results obtained in cortisol and gene expression regulation.
