Chronic Cold Stress Alters the Skin Mucus Interactome in a Temperate Fish Model

Dietary Debaryomyces hansenii promotes skin and skin mucus defensive capacities in a marine fish model

The present study explores the effects of two supplementation levels of Debaryomyces hansenii (1.1% and 2.2%) as a probiotic in a reference low fish meal-based diet on the skin mucosal tissue in Sparus aurata. This study includes the evaluation of fish performance coupled with a holistic study of the skin mucosa: i) a transcriptomic study of the skin tissue, and ii) the evaluation of its secreted mucus both in terms of skin mucosal-associated biomarkers and its defensive capacity by means of co-culture analysis with two pathogenic bacteria. Results showed that after 70 days of diet administration, fish fed the diet supplemented with D. hansenii at 1.1% presented increased somatic growth and a better feed conversion ratio, compared to fish fed the control diet. In contrast, fish fed the diet including 2.2% of the probiotic presented intermediate values. Regarding gene regulation, the probiotic administration at 1.1% resulted in 712 differentially expressed genes (DEGs), among which 53.4% and 46.6% were up- and down-regulated, respectively. In particular, D. hansenii modulated some skin biological processes related to immunity and metabolism. Specifically, D. hansenii administration induced a strong modulation of some immune biological-related processes (61 DEGs), mainly involved in B- and T-cell regulatory pathways. Furthermore, dietary D. hansenii promoted the skin barrier function by the upregulation of anchoring junction genes (23 DEGs), which reinforces the physical defense against potential skin damage. In contrast, the skin showed modulated genes related to extracellular exosome and membrane organization (50 DEGs). This modulated functioning is of great interest, particularly in relation to the increased skin mucus defensive capacity observed in the bacterial co-culture in vitro trials, which could be related to the increased modulation and exudation of the innate immune components from the skin cells into the mucus. In summary, the modulation of innate immune parameters coupled with increased skin barrier function and cell trafficking potentiates the skin's physical barrier and mucus defensive capacity, while maintaining the skin mucosa's homeostatic immune and metabolic status. These findings confirmed the advantages of D. hansenii supplementation in low fish meal-based diets, demonstrating the probiotic benefits on cultured marine species.

Fish Epidermal Mucus as a Source of Diverse Therapeutical Compounds

Microbes are helpful and destructive to human health and other living organisms. Microbes can be eliminated by using antibiotics against them, but their capability to resist regularly encountering antibiotics makes them more injurious. Microbes can adjust and adapt according to the chemicals used against them and become antibiotic resistant. Thus, the requirement for novel antimicrobial compounds increases with time to treat antibiotic-resistant microbes. Fish epidermal mucus encounters various pathogens present in their surrounding environment. It has become a rich source of novel antimicrobial compounds mainly antimicrobial peptides that can be used against various antibiotic-resistant pathogenic microbes. Compounds extracted from epidermal mucus can be used synergistically with other antibiotics or resistance modifying agents to inhibit the growth of resistant microbes. Fishes are consumed as a protein-rich food source worldwide and contribute to the world economy. Diseases in fish cause significant losses in the economic benefits exploited by fishermen and industries based on fisheries products. This paper will review compounds from fish epidermal mucus and their use to control the growth of antibiotic-resistant or non-resistant pathogenic microbes of humans and fishes. So, to increase fisheries' economic benefits and decrease infections involving resistant microbes.

Skin mucus metabolomics provides insights into the interplay between diet and wound in gilthead seabream (Sparus aurata)

The molecular processes underlying skin wound healing in several fish species have been elucidated in the last years, however, metabolomic insights are scarce. Here we report the skin mucus metabolome of wounded and non-wounded gilthead seabream (Sparus aurata) fed with silk fibroin microparticles, a functional additive considered to accelerate the wound healing process. The three experimental diets (commercial diet enriched with 0 mg (control), 50 mg or 100 mg of silk fibroin microparticles Kg^-1) were administered for 30 days and thereafter, a skin wound was inflicted. Skin mucus was collected on day 30 of feeding and 7 days post-wounding and subjected to metabolomic analysis by Ultra Performance Liquid Chromatography coupled with a high-resolution quadrupole-orbitrap mass spectrometry. The most enriched metabolite class was amino acids and derivatives, followed by nucleotides, nucleosides and analogues and carbohydrates and their derivatives. Metabolomic profiles revealed that the diet had a more profound effect than wounding in skin mucus. Metabolic pathway analysis of significantly affected metabolites revealed perturbations in the aminoacyl t-RNA biosynthesis in the skin. In particular, skin wound resulted in a decreased methionine level in mucus. Further, silk fibroin supplementation increased methionine level in skin mucus, which correlated with several wound morphometric parameters that characterized the epithelial healing capacity in seabream. The results provided new insight into the physiological consequences of skin wounds and how these processes could be influenced by dietary manipulation.

Evaluating the Functional Properties of Spray-Dried Porcine Plasma in Gilthead Seabream (Sparus aurata) Fed Low Fish Meal Diets

Blood by-products are an untapped source of high-quality ingredients for aquafeeds, containing a broad variety of cytokines, hormones, growth factors, proteins, bioactive peptides, and amino acids. The effects of the spray-dried porcine plasma (SDPP), a type of processed animal protein on several immune parameters, were evaluated in sea bream using ex vivo and in vitro assays. In this study, fish were fed with two isoproteic, isolipidic, and isoenergetic diets: control diet (7% fish meal, FM) and SDPP diet (2% FM and 5% SDPP). At the end of the 92-days trial, those fed the SDPP diet were larger in body weight (p < 0.05) without differences in feed conversion ratio (p > 0.05). The ex vivo immune stimulation of splenocytes indicated that SDPP had a beneficial effect in promoting systemic immunity, since the surface cell marker (cd4), pro- (il-1β), and anti-inflammatory (tgf-β1) cytokines, and genes involved in humoral immunity (IgM) were up-regulated. The co-culture assays of skin mucus corroborated that SDPP enhanced the antibacterial capacity of mucus against V. anguillarum. In addition, main mucus biomarkers did not show significant differences, except for cortisol levels which were lower in the SDPP diet. The present study indicated that SDPP may be considered a functional ingredient in aquafeeds formulated with low FM levels.

Role of the melanocortin system in zebrafish skin physiology

The agouti-signaling protein (ASIP) acts as both a competitive antagonist and inverse agonist of melanocortin receptors which regulate dorsal-ventral pigmentation patterns in fish. However, the potential role of ASIP in the regulation of additional physiological pathways in the skin is unknown. The skin plays a crucial role in the immune function, acting as a physical limitation against infestation and also as a chemical barrier due to its ability to synthesize and secrete mucus and many immune effector proteins. In this study, the putative role of ASIP in regulating the immune system of skin has been explored using a transgenic zebrafish model overexpressing the asip1 gene (ASIPzf). Initially, the structural changes in skin induced by asip1 overexpression were studied, revealing that the ventral skin of ASIPzf was thinner than that of wild type (WT) animals. A moderate hypertrophy of mucous cells was also found in ASIPzf. Histochemical studies showed that transgenic animals appear to compensate for the lower number of cell layers by modifying the mucus composition and increasing lectin affinity and mucin content in order to maintain or improve protection against microorganism adhesion. ASIPzf also exhibit higher protein concentration under crowding conditions suggesting an increased mucus production under stressful conditions. Exposure to bacterial lipopolysaccharide (LPS) showed that ASIPzf exhibit a faster pro-inflammatory response and increased mucin expression yet severe skin injures and a slight increase in mortality was observed. Electrophysiological measurements show that the ASIP1 genotype exhibits reduced epithelial resistance, an indicator of reduced tissue integrity and barrier function. Overall, not only are ASIP1 animals more prone to infiltration and subsequent infections due to reduced skin epithelial integrity, but also display an increased inflammatory response that can lead to increased skin sensitivity to external infections.

Min pig skeletal muscle response to cold stress

The increased sensitivity of pigs to ambient temperature is due to today’s intensive farming. Frequent climate disasters increase the pressure on healthy pig farming. Min pigs are an indigenous pig breed in China with desirable cold resistance characteristics, and hence are ideal for obtaining cold-resistant pig breeds. Therefore, it is important to discover the molecular mechanisms that are activated in response to cold stress in the Min pig. Here, we conducted a transcriptomic analysis of the skeletal muscle of Min pigs under chronic low-temperature acclimation (group A) and acute short cold stress (group B). Cold exposure caused more genes to be upregulated. Totals of 125 and 96 differentially expressed genes (DEGs) were generated from groups A and B. Sixteen common upregulated DEGs were screened; these were concentrated in oxidative stress (SRXN1, MAFF), immune and inflammatory responses (ITPKC, AREG, MMP25, FOSL1), the nervous system (RETREG1, GADD45A, RCAN1), lipid metabolism (LRP11, LIPG, ITGA5, AMPD2), solute transport (SLC19A2, SLC28A1, SLCO4A1), and fertility (HBEGF). There were 102 and 73 genes that were specifically differentially expressed in groups A and B, respectively. The altered mRNAs were enriched in immune, endocrine, and cancer pathways. There were 186 and 91 differentially expressed lncRNAs generated from groups A and B. Analysis of the target genes suggested that they may be involved in regulating the MAPK signaling pathway for resistance to cold. The results of this study provide a comprehensive overview of cold exposure–induced transcriptional patterns in skeletal muscle of the Min pig. These results can guide future molecular studies of cold stress response in pigs for improving cold tolerance as a goal in breeding programs.

Energy consumption and intestinal microbiome disorders of yellow catfish (Pelteobagrus fulvidraco) under cold stress

The yellow catfish (P. fulvidraco), as one of the economically-relevant freshwater fish found in China, cannot tolerate cold stress. Understanding the physiological and biochemical mechanisms under cold stress may provide insights for improving yellow catfish management in the cold. Therefore, we investigated the metabolic and intestinal microbiota changes in cold stress in response to induced cold stress. We found that cold stress in yellow catfish lead to a significant increase in the consumption of glucose and triglycerides, as well as increased use of cholesterol as an alternate energy source. Moreover, cold stress also activated several significant biological processes in the fish such as thermogenesis, oxidative phosphorylation, the spliceosome machinery, RNA transport, protein processing that occurs in the ER, and purine and pyrimidine metabolism pathways involved in energy production. On the other hand, many other mechanisms like insulin resistance, starch and sucrose metabolism, and the glyoxylate and dicarboxylate metabolic pathways that also served as energy production pathways were weakened. Furthermore, organic acids and their derivatives as well as the lipids and lipid-like molecules were mainly altered in cold stress; prenol lipids, steroids, and their derivatives were significantly upregulated, while fatty acyls and glycerophospholipids were significantly downregulated. Transcriptomic and metabolomic integrated analysis data revealed that carbohydrate metabolism, lipid metabolism, amino acid metabolism, and nucleotide metabolism were involved in cold stress resistance. In addition, the intestinal microbiota abundance was also reduce and the pathogenic bacteria of plesiomonas was rapidly appreciation, which suggesting that cold stress also impaired intestinal health. This research study could offer insights into winter management or the development of feed to promote cold resistance in yellow catfish.

Comparative genomics reveals putative evidence for high-elevation adaptation in the American pika (Ochotona princeps)

High-elevation environments have lower atmospheric oxygen content, reduced temperatures, and higher levels of UV radiation than found at lower elevations. As such, species living at high elevations must overcome these challenges to survive, grow, and reproduce. American pikas (Ochotona princeps) are alpine lagomorphs that are habitat specialists typically found at elevations >2,000 m. Previous research has shown putative evidence for high-elevation adaptation; however, investigations to date have been limited to a fraction of the genome. Here, we took a comparative genomics approach to identify putative regions under selection using a chromosomal reference genome assembly for the American pika relative to 8 other mammalian species targeted based on phylogenetic relatedness and (dis)similarity in ecology. We first identified orthologous gene groups across species and then extracted groups containing only American pika genes as well as unclustered pika genes to inform functional enrichment analyses; among these, we found 141 enriched terms with many related to hypoxia, metabolism, mitochondrial function/development, and DNA repair. We identified 15 significantly expanded gene families within the American pika across all orthologous gene groups that displayed functionally enriched terms associated with hypoxia adaptation. We further detected 196 positively selected genes, 41 of which have been associated with putative adaptation to hypoxia, cold tolerance, and response to UV following a literature review. In particular, OXNAD1, NRDC, and those genes critical in DNA repair represent important targets for future research to examine their functional implications in the American pika, especially as they may relate to adaptation to rapidly changing environments.

Seasonal variations in the skin epidermal structure and mucosal immune parameters of rainbow trout skin (Oncorhynchus mykiss) at different stages of farming

The aim of this study was to investigate the seasonal changes in the epidermal structure and the innate immunity parameters of skin mucus in rainbow trout. The skin epidermis and mucus samples were collected over three consecutive seasons including winter, spring and late summer from three different weight groups i.e., 2-20 g (W1), 100-200 g (W2) and 400-600 g (W3) fish. The skin mucosal immunity analysis of rainbow trout showed that the haemagglutination activity increased significantly with increasing fish size from W1 to W3 in all three seasons, while no significant seasonal changes occurred in haemagglutination activity. Moreover, the bactericidal activity against fish pathogens increased significantly with increasing water bacterial load in late summer. The SDS-PAGE analysis of mucus showed a high amount of low molecular weight proteins (<35 kDa) in the late summer that was correlated with the increase in bactericidal activity. Histological analysis of the epidermis structure of rainbow trout skin showed that the density and size of goblet cells and consequently the mucus secretion significantly increased in W3 group in all seasons. In all three weight groups of fish, the density of goblet cells significantly increased from winter to spring and late summer along with increasing water temperature. Moreover, the goblet cell density showed a significant positive relationship with the soluble protein concentration and haemagglutination activity (p < 0.01). The results of this study demonstrated the more active immune role of the skin epidermal cells and mucus in rainbow trout during summer to protect fish against the pathogenic microorganisms. Given its potent bactericidal properties and the lack of haemolytic activity, the rainbow trout mucus might be used as a safe and inexpensive source for developing antimicrobial agents to prevent and treat some bacterial diseases in human and fish.

Specific immunity proteomic profile of the skin mucus of Antarctic fish Chionodraco hamatus and Notothenia coriiceps

The white-blooded Antarctic icefish is the only known vertebrate lacking oxygen-transporting haemoglobins. Fish skin mucus, as the first line of defence against pathogens, can reflect fish welfare. In this study, we analysed the skin mucus proteome profiles of the two Antarctic fish species, the white-blooded Antarctic icefish, Chionodraco hamatus, and the red-blooded Antarctic fish, Notothenia coriiceps, unfolding the different proteins by liquid chromatography coupled with tandem mass spectrometry isobaric tags for relative and absolute quantitation (iTRAQ) technology. Of the 4444 totally identified proteins, 227 differentially expressed proteins (DEPs) were found in the comparison between C. hamatus and N. coriiceps, of which 121 were upregulated and 106 were downregulated in the icefish. In the Kyoto Encyclopedia of Genes and Genomes pathway annotation, we found two pathways "Legionellosis" and "Complement and coagulation cascades" were significantly enriched, among of which innate immune candidate proteins such as C3, CASP1, ASC, F3 and C9 were significantly upregulated, suggesting their important roles in C. hamatus immune system. Additionally, the DEP protein-protein interaction network analysis and "Response to stress" GO category provided candidate biomarkers for deep understanding of the distinct immune response of the two Antarctic fish underlying the cold adaptation.

Post-translational protein deimination signatures in sea lamprey (Petromyzon marinus) plasma and plasma-extracellular vesicles

Lampreys are a jawless vertebrate species belonging to an ancient vertebrate lineage that diverged from a common ancestor with humans ~500 million years ago. The sea lamprey (Petromyzon marinus) has a filter feeding ammocoete larval stage that metamorphoses into a parasitic adult, feeding both on teleost and elasmobranch fish. Lampreys are a valuable comparative model species for vertebrate immunity and physiology due to their unique phylogenetic position, unusual adaptive immune system, and physiological adaptions such as tolerance to salinity changes and urea. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family which catalyses post-translational deimination/citrullination in target proteins, enabling proteins to gain new functions (moonlighting). The identification of deiminated protein targets in species across phylogeny may provide novel insights into post-translational regulation of physiological and pathophysiological processes. Extracellular vesicles (EVs) are membrane vesicles released from cells that carry cargos of small molecules and proteins for cellular communication, involved in both normal and pathological processes. The current study identified deimination signatures in proteins of both total plasma and plasma-EVs in sea lamprey and furthermore reports the first characterisation of plasma-EVs in lamprey. EVs were poly-dispersed in the size range of 40-500 nm, similar to what is observed in other taxa, positive for CD63 and Flotillin-1. Plasma-EV morphology was confirmed by transmission electron microscopy. Assessment of deimination/citrullination signatures in lamprey plasma and plasma-EVs, revealed 72 deimination target proteins involved in immunity, metabolism and gene regulation in whole plasma, and 37 target proteins in EVs, whereof 24 were shared targets. Furthermore, the presence of deiminated histone H3, indicative of gene-regulatory mechanisms and also a marker of neutrophil extracellular trap formation (NETosis), was confirmed in lamprey plasma. Functional protein network analysis revealed some differences in KEGG and GO pathways of deiminated proteins in whole plasma compared with plasma-EVs. For example, while common STRING network clusters in plasma and plasma-EVs included Peptide chain elongation, Viral mRNA translation, Glycolysis and gluconeogenesis, STRING network clusters specific for EVs only included: Cellular response to heat stress, Muscle protein and striated muscle thin filament, Nucleosome, Protein processing in endoplasmic reticulum, Nucleosome and histone deacetylase complex. STRING network clusters specific for plasma were: Adipokinetic hormone receptor activity, Fibrinogen alpha/beta chain family, peptidase S1A, Glutathione synthesis and recycling-arginine, Fructose 1,6-bisphosphate metabolic process, Carbon metabolism and lactate dehydrogenase activity, Post-translational protein phosphorylation, Regulation of insulin-like growth factor transport and clotting cascade. Overall, for the EV citrullinome, five STRING network clusters, 10 KEGG pathways, 15 molecular GO pathways and 29 Reactome pathways were identified, compared with nine STRING network clusters, six KEGG pathways, two Molecular GO pathways and one Reactome pathway specific for whole plasma; while further pathways were shared. The reported findings indicate that major pathways relevant for immunity and metabolism are targets of deimination in lamprey plasma and plasma-EVs, with some differences, and may help elucidating roles for the conserved PAD enzyme family in regulation of immune and metabolic function throughout phylogeny.

Activity profile of innate immune-related enzymes and bactericidal of freshwater fish epidermal mucus extract at different pH

The epidermal mucus of fish performs diverse functions from prevention of mechanical abrasion to limit pathogen invasions. The current experiment was designed to extract skin mucus proteins of three freshwater fish, i.e. common carp (Cyprinus carpio), mrigal (Cirrhinus mrigala) and rohu (Labeo rohita) with organic solvent (methanol) and dissolve in different pH of Tris-HCl buffers to examine the significance of pH in the solubilisation of skin mucus proteins. The protein profiles of different pH solubilised methanol fish skin mucus extracts were determined by SDS-PAGE. The non-specific immune enzymes, alkaline phosphatase, lysozyme and protease of fish skin mucus were compared and this present study demonstrated that these enzymes differed in their activity depending on pH buffers. The higher lysozyme and protease activity were observed at the pH of 8.0 and higher alkaline phosphatase activity in the pH 9.0 of C. mrigala fish skin mucus methanol extract. In addition, the bactericidal activity was evaluated against the pathogens Proteus vulgaris and Pseudomonas aeruginosa. The pH 8.0 of C. mrigala skin mucus extract revealed better bactericidal activity than other fish species mucus pH buffers against both P. vulgaris and P. aeruginosa. In the case of protein profile from SDS-PAGE, based on pH buffers and the solubilisation of proteins, differences in the resolution of bands were observed. The higher alkaline pH of 9.0 showed smeared gel bands in all the three fish skin mucus methanol extract. The present study suggests that methanol extracted C. mrigala fish skin mucus at pH 8.0 showed better innate immune enzymes and bactericidal activity. The additional examinations of C. mrigala skin mucus methanol extract in this pH aids in identifying novel bioactive molecules. This is the study of proteome of three fish species skin mucus in the effect of pH. Further analyses are required to evaluate proteins present in fish skin mucus extracted with methanol and the influence of pH on protein solubility. These findings could be helpful in exploring natural alternatives to antibiotics in aquaculture industry against infectious pathogens.

Environmental Salinity Modifies Mucus Exudation and Energy Use in European Sea Bass Juveniles

The European sea bass (Dicentrarchus labrax) is a euryhaline marine teleost that can often be found in brackish and freshwater or even in hypersaline environments. Here, we exposed sea bass juveniles to sustained salinity challenges for 15 days, simulating one hypoosmotic (3‰), one isosmotic (12‰) and one hyperosmotic (50‰) environment, in addition to control (35‰). We analyzed parameters of skin mucus exudation and mucus biomarkers, as a minimally invasive tool, and plasma biomarkers. Additionally, Na⁺/K⁺-ATPase activity was measured, as well as the gill mucous cell distribution, type and shape. The volume of exuded mucus increased significantly under all the salinity challenges, increasing by 130% at 50‰ condition. Significantly greater amounts of soluble protein (3.9 ± 0.6 mg at 50‰ vs. 1.1 ± 0.2 mg at 35‰, p < 0.05) and lactate (4.0 ± 1.0 µg at 50‰ vs. 1.2 ± 0.3 µg at 35‰, p < 0.05) were released, with clear energy expenditure. Gill ATPase activity was significantly higher at the extreme salinities, and the gill mucous cell distribution was rearranged, with more acid and neutral mucin mucous cells at 50‰. Skin mucus osmolality suggested an osmoregulatory function as an ion-trap layer in hypoosmotic conditions, retaining osmosis-related ions. Overall, when sea bass cope with different salinities, the hyperosmotic condition (50‰) demanded more energy than the extreme hypoosmotic condition.

Wound-Induced Changes in Antioxidant Enzyme Activities in Skin Mucus and in Gene Expression in the Skin of Gilthead Seabream (Sparus aurata L.)

This study investigated the antioxidant enzyme activities in the skin mucus of gilthead seabream (Sparus aurata L.) at 3 and 7 days post-wounding (dpw). The expression levels of the genes that encode stress proteins (grp170, grp94, grp75, sod and hsp70) and skin regeneration-related proteins (tf, igf1, tgfb1, der1, apo1 and erdj3) in the skin also were determined. Mucus and skin samples were obtained from the left and right flanks of non-wounded and wounded fish. In both flanks of the wounded fish, catalase and glutathione reductase activities in the skin mucus increased (p < 0.05) at 3 and 7 dpw (100 ± 31% and 111 ± 25%, respectively), whereas superoxide dismutase activity increased (p < 0.05) only at 7 dpw (135 ± 15%). The expression levels of stress proteins in the skin of the wounded flank of the wounded fish mainly increased at 7 dpw (grp170 increased to 288 ± 85%, grp94 to 502 ± 143%, grp75 to 274 ± 69%, sod to 569 ± 99%, and hsp70 increased to 537 ± 14%) (p < 0.05). However, the expression levels of the tissue regeneration-related genes varied depending on the flank investigated, on the experimental time, and on the gene studied. To the best of our knowledge, this is the first work to determine the effect of a wound in different skin parts of the same fish.

Carvacrol, Thymol, and Garlic Essential Oil Promote Skin Innate Immunity in Gilthead Seabream (Sparus aurata) Through the Multifactorial Modulation of the Secretory Pathway and Enhancement of Mucus Protective Capacity

One of the main targets for the use of phytogenics in aquafeeds is the mucosal tissues as they constitute a physical and biochemical shield against environmental and pathogenic threats, comprising elements from both the innate and acquired immunity. In the present study, the modulation of the skin transcriptional immune response, the bacterial growth capacity in skin mucus, and the overall health condition of gilthead seabream (Sparus aurata) juveniles fed a dietary supplementation of garlic essential oil, carvacrol, and thymol were assessed. The enrichment analysis of the skin transcriptional profile of fish fed the phytogenic-supplemented diet revealed the regulation of genes associated to cellular components involved in the secretory pathway, suggesting the stimulation, and recruitment of phagocytic cells. Genes recognized by their involvement in non-specific immune response were also identified in the analysis. The promotion of the secretion of non-specific immune molecules into the skin mucus was proposed to be involved in the in vitro decreased growth capacity of pathogenic bacteria in the mucus of fish fed the phytogenic-supplemented diet. Although the mucus antioxidant capacity was not affected by the phytogenics supplementation, the regulation of genes coding for oxidative stress enzymes suggested the reduction of the skin oxidative stress. Additionally, the decreased levels of cortisol in mucus indicated a reduction in the fish allostatic load due to the properties of the tested additive. Altogether, the dietary garlic, carvacrol, and thymol appear to promote the gilthead seabream skin innate immunity and the mucus protective capacity, decreasing its susceptibility to be colonized by pathogenic bacteria.

Evaluating mucus exudation dynamics through isotopic enrichment and turnover of skin mucus fractions in a marine fish model

Fish skin mucus is composed of insoluble components, which form the physical barrier, and soluble components, which are key for interrelationship functions. Mucus is continuously secreted, but rates of production and exudation are still unknown, as are the underlying mechanisms. Using stable isotope analysis, here, we evaluate skin mucus turnover and renewal in gilthead sea bream, separating raw mucus and its soluble and insoluble fractions. Isotopic abundance analysis reveals no differences between mucus and white muscle, thus confirming mucus samples as reliable non-invasive biomarkers. Mucus production was evaluated using a single labelled meal packaged in a gelatine capsule, with both ¹³C and ¹⁵N, via a time-course trial. ¹³C was gradually allocated to skin mucus fractions over the first 12 h and was significantly (4-fold) higher in the soluble fraction, indicating a higher turnover of soluble mucus components that are continuously produced and supplied. ¹⁵N was also gradually allocated to mucus, indicating incorporation of new proteins containing the labelled dietary amino acids, but with no differences between fractions. When existent mucus was removed, dietary stable isotopes revealed stimulated mucus neoformation dependent on the components. All this is novel knowledge concerning skin mucus dynamics and turnover in fish and could offer interesting non-invasive approaches to the use of skin mucus production in ecological or applied biological studies such as climate change effects, human impact, alterations in trophic networks or habitat degradation, especially of wild-captured species or protected species.

Evaluation of an Acute Osmotic Stress in European Sea Bass via Skin Mucus Biomarkers

Simple Summary

Skin mucus biomarkers have become relevant indicators for studying fish physiological status and welfare. Here, we evaluated them in terms of the acute osmotic response of the sea bass. Change of mucus volume exuded and main stress-related metabolites explain the putative energy loss implied in a hyper/hypo-osmotic response. We demonstrated that skin mucus is a valuable tool, comparable to classical blood markers, for evaluating sea bass response to acute salinity challenges as well as some other potentially stressful situations. This technique will allow ecologists, physiologists, and aquafarmers to monitor fish welfare and to analyse endangered migrating species without affecting their vulnerable populations.

Abstract

European sea bass is a marine teleost which can inhabit a broad range of environmental salinities. So far, no research has studied the physiological response of this fish to salinity challenges using modifications in skin mucus as a potential biological matrix. Here, we used a skin mucus sampling technique to evaluate the response of sea bass to several acute osmotic challenges (for 3 h) from seawater (35‰) to two hypoosmotic environments, diluted brackish water (3‰) and estuarine waters (12‰), and to one hyperosmotic condition (50‰). For this, we recorded the volume of mucus exuded and compared the main stress-related biomarkers and osmosis-related parameters in skin mucus and plasma. Sea bass exuded the greatest volume of skin mucus with the highest total contents of cortisol, glucose, and protein under hypersalinity. This indicates an exacerbated acute stress response with possible energy losses if the condition is sustained over time. Under hyposalinity, the response depended on the magnitude of the osmotic change: shifting to 3‰ was an extreme salinity change, which affected fish aerobic metabolism by acutely modifying lactate exudation. All these data enhance the current scarce knowledge of skin mucus as a target through which to study environmental changes and fish status.

Biochemical and biological characterization of the Hypanus americanus mucus: A perspective on stingray immunity and toxins

Stingrays skin secretions are largely studied due to the human envenoming medical relevance of the sting puncture that evolves to inflammatory events, including necrosis. Such toxic effects can be correlated to the biochemical composition of the sting mucus, according to the literature. Fish skin plays important biological roles, such as the control of the osmotic pressure gradient, protection against mechanical forces and microorganism infections. The mucus, on the other hand, is a rich and complex fluid, acting on swimming, nutrition and the innate immune system. The elasmobranch's epidermis is a tissue composed mainly by mucus secretory cells, and marine stingrays have already been described to present secretory glands spread throughout the body. Little is known about the biochemical composition of the stingray mucus, but recent studies have corroborated the importance of mucus in the envenomation process. Aiming to assess the mucus composition, a new non-invasive mucus collection method was developed that focused on peptides and proteins, and biological assays were performed to analyze the toxic and immune activities of the Hypanus americanus mucus. Pathophysiological characterization showed the presence of peptidases on the mucus, as well as the induction of edema and leukocyte recruitment in mice. The fractionated mucus improved phagocytosis on macrophages and showed antimicrobial activity against T. rubrumç. neoformans and C. albicans in vitro. The proteomic analyses showed the presence of immune-related proteins like actin, histones, hemoglobin, and ribosomal proteins. This protein pattern is similar to those reported for other fish mucus and stingray venoms. This is the first report depicting the Hypanus stingray mucus composition, highlighting its biochemical composition and importance for the stingray immune system and the possible role on the envenomation process.

Differential Expression of Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF) in Different Regions of Normal and Preeclampsia Placentae

Background: Our recent study indicates differential protein levels of neurotrophins and angiogenic factors in various regions of the normotensive and preeclampsia (PE) placenta. These changes may be in a response to differential mRNA expression of neurotrophins.Methods: This study examines the mRNA levels of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in different regions of the placenta in normotensive control (NC) women and women with PE. Thirty NC women and forty one women with PE (18 delivered at term [T-PE] and 23 delivered preterm [PT-PE]) were included in the study. Placental samples were taken from four regions: central basal (CM), central chorionic (CF), peripheral basal (PM), and peripheral chorionic (PF). The mRNA levels of neurotrophins were measured by quantitative real-time PCR.Results: The BDNF mRNA levels were higher in peripheral fetal region as compared to peripheral basal region in NC (p < 0.05) group, PE group (p < 0.05) and term PE group (p < 0.01). The BDNF mRNA levels were lower in the central basal region of preterm PE group (p < 0.05) as compared to the NC group.Conclusion: The present study indicates that NGF and BDNF are expressed differentially across various regions of the placenta. This has implications for selection of the sampling site in the placenta while carrying out placental studies.

Comparison of several non-specific skin mucus immune defences in three piscine species of aquaculture interest

Fish skin mucus is a viscous and semipermeable barrier made mainly of water, glycoproteins and soluble proteins. It represents an important defence against the environment and previous studies have reported the presence of different substances involved in immune defence responses in it. The aim of the present work was to characterize skin mucus protease activity by zymography and esterase activity of the subfamily of carboxylesterases in three species of interest for aquaculture: gilthead sea bream, sea bass and meagre. Mucus antioxidant power was also determined by adapting ferric reducing antioxidant power (FRAP) analysis. As a result of these non-specific immune defence parameters, we compared the antibacterial capacity of skin mucus in these species via in vitro dual bacteria strains-skin mucus co-culture growths. We used Pseudomonas anguilliseptica and Vibrio anguillarum as marine pathogenic bacteria and Escherichia coli as non-pathogenic. For each fish species, in the respective zymograms, we determined a pattern of proteolytic digestion bands. A high-molecular-weight band (around 200 kDa; H-band) was evident in sea bream and sea bass, and showed chymotrypsin activity. One or two intermediate-molecular-weight bands (around 75 kDa; I-bands) with non-trypsin and non-chymotrypsin activity, and putatively with metalloprotease activity, were evident in all species. Finally, low-molecular-weight bands (between 14 and 30 kDa; L-bands) showed distinct patterns for each species and matched trypsin activity. Despite the conservative pattern of digestion bands, the levels of total proteolytic activity (TPA) were 5 and 10 times higher in meagre than in sea bass and sea bream, respectively. In parallel, three carboxylesterase activities were detected in the mucus of the three fish species, using myristate (pNPM-CE activity), butyrate (pNPB-CE activity) and acetate (pNPA-CE activity) as substrates. Both pNPB-CE and pNPA-CE were the most abundant in fish mucus, and meagre was again the species with the highest levels. In contrast, the antioxidant power of meagre skin mucus was the lowest. We established the capacity of skin mucus to block or limit bacterial growth (lytic activity) using 24 h growth curves. The log-growth phase of V. anguillarum was strongly blocked by sea bream and meagre mucus for a few hours; but not by sea bass mucus. However, if mucus was not renewed, log-growth was at the end of 24 h studied period. For its part, P. anguilliseptica growth curve was delayed by the three mucus types during the entire growth period. Only meagre achieved lytic activity against E. coli growth. All parameters studied here will be of a great interest as non-invasive bioindicators of non-specific immune defences in fish skin mucus.

Liver proteomics of gilthead sea bream (Sparus aurata) exposed to cold stress

The gilthead sea bream (Sparus aurata, L.) is very sensitive to low temperatures, which induce fasting and reduced growth performances. There is a strong interest in understanding the impact of cold on fish metabolism to foster the development and optimization of specific aquaculture practices for the winter period. In this study, an 8 week feeding trial was carried out on gilthead sea bream juveniles reared in a Recirculated Aquaculture System (RAS) by applying a temperature ramp in two phases of four weeks each: a cooling phase from 18 °C to 11 °C and a cold maintenance phase at 11 °C. Liver protein profiles were evaluated with a shotgun proteomics workflow based on filter-aided sample preparation (FASP) and liquid chromatography-mass spectrometry (LC-ESI-Q-TOF MS/MS) followed by label-free differential analysis. Along the whole trial, sea breams underwent several changes in liver protein abundance. These occurred mostly during the cooling phase when catabolic processes were mainly observed, including protein and lipid degradation, together with a reduction in protein synthesis and amino acid metabolism. A decrease in protein mediators of oxidative stress protection was also seen. Liver protein profiles changed less during cold maintenance, but pathways such as the methionine cycle and sugar metabolism were significantly affected. These results provide novel insights on the dynamics and extent of the metabolic shift occurring in sea bream liver with decreasing water temperature, supporting future studies on temperature-adapted feed formulations. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD011059.