Implication of adipocytes from subcutaneous adipose tissue and fatty acids in skin inflammation caused by λ-carrageenin in gilthead seabream (Sparusaurata)

Bioinformatic and gene expression analysis of the somatostatin/cortistatin gene family in the gilthead seabream (Sparus aurata)

Somatostatin (SST) and cortistatin (CST) are neuromodulators with distinct expression patterns and functions. While SST and CST have been extensively studied in mammalian central nervous system (CNS) and immune system, their roles in teleost fish remain poorly explored due to evolutionary emergence of multiple SST paralogous genes. This study aimed to identify SST isoforms in gilthead seabream (Sparus aurata) and assess their transcriptional levels. Phylogeny and synteny analyses reclassified the six SST genes and proteins as SST1, SST3, SST3-like, SST4, SST5, and SST6. The protein sequences showed high conservation, except for an additional region upstream of the SST3-like protein's leader region. Evolutionary differences were mainly due to specific amino acid residue changes in the mature peptide. Genetic analyses revealed constitutive expression of five genes (sst1, sst3, sst5, sst4 and sst6) in all studied organs, except for sst3 in the heart, liver, and blood. The highest expression of sst1, sst3, sst4 and sst6 genes occurred in the brain's forebrain, while sst5 was most expressed in the heart. However, sst4 exhibited very low basal expression across all analysed tissues. In vitro, λ-carrageenan and cantharidin upregulated sst6 transcription in head kidney leucocytes (HKLs), indicating a potential anti-inflammatory role similar to mammalian CST. Additionally, sst5 expression was downregulated during the innate cell-mediated cytotoxic response, suggesting a regulatory role. These findings provide insights into the SST/CST gene family in gilthead seabream, necessitating gene and protein reclassification, and underscore their significant neuroendocrine and immune system functions, relevant for teleost research.

Evaluating serum proteinogram methodologies for the diagnosis of inflammation in fish: Acute and chronic patterns in gilthead seabream (Sparus aurata) injected with λ-carrageenan

Proteinogram is a semiquantitative method specially used in clinic to separate the serum proteins from patients for use in the diagnosis of diseases. However, this methodology has only been applied very recently with this approach in farmed fish. Thus, the aim of this study was to explore the changes in the serum proteinogram of gilthead seabream (Sparus aurata), after triggering an acute or chronic sterile inflammation. For this, two experiments were carried out: i) Acute inflammation experiment: seabream specimens were injected intramuscularly with 50 μL of λ-carrageenan (0.5 mg fish-1) or buffer (control) and blood samples were collected at 3, 6 and 24 h post-injection; ii) Chronic inflammation experiment: specimens were injected at 0, 7 and 14 days with 500, 250 and 250 μL of λ-carrageenan, respectively (20 mg fish-1) or buffer, and blood samples were collected at 15 days post-injection. In both cases, serum was obtained and processed by electropherograms and HPLC-mass spectrometry. Results of electropherograms of control fish revealed four major proteins of 19.5, 76.3, 104.4, and 156.7 kDa in the serum. These four proteins were correlated with apolipoprotein A-II (II (the counterpart of mammalian albumin, Apo fraction), serotransferrin (β fraction), inter-α-trypsin inhibitor heavy chain H3-like (α1 fraction) and α-2-macroglobulin-like (α2 fraction) according to the results obtained with HPLC-mass spectrometry. In a statistical view (p < 0.05), no variations were detected in the four major serum protein bands between the control and the acutely inflamed groups. However, in chronically inflamed fish, the Apo fraction decreased statistically compared to the control group. In contrast, the α1 and α2 fractions were statistically increased in the serum of fish sampled 15 days after λ-carrageenan injection, compared to those found in the control fish. α1 and α2 protein fractions are recognized indicators of inflammation in mammals. Consequently, our study presents a novel method for assessing both acute and chronic λ-carrageenan-induced sterile inflammation in gilthead seabream, which could be applicable to other marine species for diagnostic purposes.

Review of Fish Neuropeptides: A Novel Perspective on Animal Welfare

Neuropeptides are highly variable but widely conserved molecules, the main functions of which are the regulation and coordination of physiological processes and behaviors. They are synthesized in the nervous system and generally act on other neuronal and non-neuronal tissues or organs. In recent years, diverse neuropeptide isoforms and their receptors have been identified in different fish species, regulating functions in the neuroendocrine (e.g., corticotropin-releasing hormone and arginine vasotocin), immune (e.g., vasoactive intestinal polypeptide and somatostatin), digestive (e.g., neuropeptide Y), and reproductive (e.g., isotocin) systems, as well as in the commensal microbiota. Interestingly, all these processes carried out by neuropeptides are integrated into the nervous system and are manifested externally in the behavior and affective states of fish, thus having an impact on the modulation of these actions. In this sense, the monitoring of neuropeptides may represent a new approach to assess animal welfare, targeting both physiological and affective aspects in fish. Therefore, although there are many studies investigating the action of neuropeptides in a wide range of paradigms, especially in mammals, their study within a fish welfare framework is scarce. To the best of our knowledge, this is the first review that gathers and integrates up-to-date information on neuropeptides from an animal welfare perspective. In this review, we summarize current findings on neuropeptides in fish and discuss their possible implication in the physiological and emotional state of fish, and therefore in their welfare.

Ability of short-chain fatty acids to reduce inflammation and attract leucocytes to the inflamed skin of gilthead seabream (Sparus aurata L.)

The aim of the study was to investigate the potential preventive use of short-chain fatty acids (SCFAs) to modulate inflammatory responses in gilthead seabream (Sparus aurata) skin. Initially, in vitro experiments were conducted to evaluate the effects of various concentrations of butyric acid, acetic acid and propionic acid, as well as their combination, on the cytotoxicity and cell viability of three different cell lines. The results determined the safe concentration of SCFAs, which was then used for an in vivo study. Fish were allocated into six groups and administered different combinations of SCFAs via intramuscular injection, followed by an injection of carrageenan as an inflammatory agent. Skin samples were taken from the injection site three hours post-administration and used to analyse gene expression and immunohistochemistry. The results demonstrated that treatment with SCFAs resulted in increased expression of proinflammatory and anti-inflammatory genes and leucocyte markers in the inflamed skin of fish. The highest gene expression and recruitment of acidophilic granulocytes were observed in fish injected with propionic acid and carrageenan. It is concluded that acetic acid is the most effective anti-inflammatory SCFA tested in gilthead seabream exposed to acute inflammation induced by carrageenan injection. Acetic acid exhibited the most pronounced direct anti-inflammatory effect, although propionic acid appeared to play a significant role in several mechanisms contributing to the resolution of inflammation and recruitment of immune cells to the site of carrageenan-inflamed area in gilthead seabream skin.

Effects of dietary astaxanthin on immune status and lipid metabolism in gilthead seabream (Sparus aurata)

Astaxanthin (AX) is a carotenoid known to have one of the highest documented antioxidant capacities and has attracted considerable scientific and commercial interest. The incorporation of AX into aquaculture practices has been associated with improved pigmentation, modulation of the immune and endocrine systems, stress reduction, reproductive efficiency and general fish health. This study describes the effects of dietary AX (0, control, 20, 100 and 500 mg kg-1 AX per kg of diet) for 15 and 30 days on growth performance, immune and antioxidant status, histology and gene expression in gilthead seabream (Sparus aurata). Fish fed diets enriched with 500 mg kg-1 of AX for 15 days decreased in skin mucus peroxidase activity while at 30 days of trial, fish fed a diet supplemented with 20 mg kg-1 AX increased the peroxidase activity in serum. In addition, bactericidal activity against Vibrio harveyi increased in the skin mucus of fish fed any of the AX supplemented diets. Regarding antioxidant activities in the liver, catalase and glutathione reductase were decreased and increased, respectively, in fish fed a diet supplemented with 500 mg kg-1 of AX. Finally, although the expression of up to 21 inflammatory and lipid metabolism-related genes was analysed in visceral adipose tissue, only the expression of the interleukin 6 (il6) gene was up-regulated in fish fed a diet supplemented with 20 mg kg-1 of AX. The present results provide a detailed insight into the potent antioxidant properties of AX and its possible modulatory effects on the immune status and lipid metabolism of seabream, which may be of interest to the aquaculture sector.

In vitro immune-depression and anti-inflammatory activities of cantharidin on gilthead seabream (Sparus aurata) leucocytes activated by λ-carrageenan

Cantharidin is a natural compound with known therapeutic applications in humans. The aim of this study was to investigate the in vitro effects of cantharidin on gilthead seabream (Sparus aurata) head kidney leucocytes (HKL) stimulated with λ-carrageenan. HKLs were incubated for 24 h with cantharidin (0, 2.5 and 5 μg mL-1) and λ-carrageenan (0 and 1000 μg mL-1). The results showed that HKL viability only decreased by 15.2% after incubated with 5 μg mL-1 of cantharidin and λ-carrageenan. Cantharidin increased the peroxidase activity of HKLs only when incubated in combination with λ-carrageenan. Besides this, cantharidin inhibited the respiratory burst and phagocytic activities. Furthermore, cantharidin induced morphological changes in HKLs (apoptotic and vacuolization signs) that were enhanced when incubated with λ-carrageenan. Considering the analysis of the selected gene expression studied in HKLs [NF-κB subunits (rela, relb, crel, nfkb1, nfkb2), proinflammatory cytokines (il1b, tnfa), anti-inflammatory cytokines (il10, tgfb) and caspases (casp1, casp3, casp8, casp9)], although λ-carrageenan up-regulated the expression of the proinflammatory gene il1b, λ-carrageenan and cantharidin down-regulated its expression in HKLs. In addition, cantharidin up-regulated casp3 and casp9 expression. The casp3 and casp9 gene expression was down-regulated while casp1 gene expression was up-regulated in HKLs incubated with both cantharidin and λ-carrageenan. All the effects of cantharidin are related to its inhibitory effect on protein phosphatases, which induce apoptosis at long exposure times, and minimize the effects of λ-carrageenan. The present results provide detailed insight into the immune-depressive and anti-inflammatory properties of cantharidin on immune cells, which could be of interest to the aquaculture sector.

Participation of Hepcidins in the Inflammatory Response Triggered by λ-Carrageenin in Gilthead Seabream (Sparus aurata)

The role of hepcidins, antimicrobial peptides involved in iron metabolism, immunity, and inflammation, is studied. First, gilthead seabream (Sparus aurata L.) head-kidney leucocytes (HKLs) were incubated with λ-carrageenin to study the expression of hepcidin and iron metabolism-related genes. While the expression of most of the genes studied was upregulated, the expression of ferroportin gene (slc40a) was downregulated. In the second part of the study, seabream specimens were injected intramuscularly with λ-carrageenin or buffer (control). The expression of the same genes was evaluated in the head kidney, liver, and skin at different time points after injection. The expression of Hamp1m, ferritin b, and ferroportin genes (hamp1, fthb, and slc40a) was upregulated in the head kidney of fish from the λ-carrageenin-injected group, while the expression of Hamp2C and Hamp2E genes (hamp2.3 and hamp2.7) was downregulated. In the liver, the expression of hamp1, ferritin a (ftha), slc40a, Hamp2J, and Hamp2D (hamp2.5/6) genes was downregulated in the λ-carrageenin-injected group. In the skin, the expression of hamp1 and (Hamp2A Hamp2C) hamp2.1/3/4 genes was upregulated in the λ-carrageenin-injected group. A bioinformatic analysis was performed to predict the presence of transcription factor binding sites in the promoter region of hepcidins. The primary sequence of hepcidin was conserved among the different mature peptides, although changes in specific amino acid residues were identified. These changes affected the charge, hydrophobicity, and probability of hepcidins being antimicrobial peptides. This study sheds light on the poorly understood roles of hepcidins in fish. The results provide insight into the regulatory mechanisms of inflammation in fish and could contribute to the development of new strategies for treat inflammation in farm animals.

Conjugated Linoleic Acid Reduces Lipid Accumulation via Down-regulation Expression of Lipogenic Genes and Up-regulation of Apoptotic Genes in Grass Carp (Ctenopharyngodon idella) Adipocyte In Vitro

The relationship between conjugated linoleic acid (CLA) and lipogenesis has been extensively studied in mammals and some cell lines, but it is relatively rare in fish, and the potential mechanism of action of CLA reducing fat mass remains unclear. The established primary culture model for studying lipogenesis in grass carp (Ctenopharyngodon idella) preadipocytes was used in the present study, and the objective was to explore the effects of CLA on intracellular lipid and TG content, fatty acid composition, and mRNA levels of adipogenesis transcription factors, lipase, and apoptosis genes in grass carp adipocytes in vitro. The results showed that CLA reduced the size of adipocyte and lipid droplet and decreased the content of intracellular lipid and TG, which was accompanied by a significant down-regulation of mRNA abundance in transcriptional regulators including peroxisome proliferator-activated receptor (PPAR) γ, CCAAT/enhancer-binding protein (C/EBP) α, sterol regulatory element-binding protein (SREBP) 1c, lipase genes including fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), lipoprotein lipase (LPL). Meanwhile, it decreased the content of saturated fatty acids (SFAs) and n - 6 polyunsaturated fatty acid (n-6 PUFA) and increased the content of monounsaturated fatty acid (MUFA) and n - 3 polyunsaturated fatty acid (n-3 PUFA) in primary grass carp adipocyte. In addition, CLA induced adipocyte apoptosis through downregulated anti-apoptotic gene B-cell CLL/lymphoma 2 (Bcl-2) mRNA level and up-regulated pro-apoptotic genes tumor necrosis factor-α (TNF-α), Bcl-2-associated X protein (Bax), Caspase-3, and Caspase-9 mRNA level in a dose-dependent manner. These findings suggest that CLA can act on grass carp adipocytes through various pathways, including decreasing adipocyte size, altering fatty acid composition, inhibiting adipocyte differentiation, promoting adipocyte apoptosis, and ultimately decreasing lipid accumulation.