Impairment of the immune system in GH-overexpressing transgenic zebrafish (Danio rerio)

Histomorphometric evaluation of melanomacrophage centers (MMCs) and CD3+ T cells of two morphs of brown trout (Salmo trutta) fed diets with immunostimulants

The brown trout (Salmo trutta) is a salmonid residing in riverine and coastal waters throughout the Northern Hemisphere, whose various populations evolved into distinct ecological morphs, differing in their migratory tendencies and preferred habitats. Unfortunately, due to progressing degradation of natural environment, the conservation of these populations is of growing importance and is undoubtedly a challenging task. Therefore, various means to refine the preparatory protocols for restocking using hatchery-reared fish are being pursued, some of which involve the administration of immunity-boosting substances. The current study assessed the effects of two dietary immunostimulants: Bioimmuno (4% inosine pranobex and 96% β-glucan) and Focus Plus (commercial preparation by Biomar, Denmark) on two morphs of the brown trout - the river trout (S. trutta morpha fario) and the sea trout (S. trutta morpha trutta). Tissue samples were obtained from ∼75 to 100g fish after 0, 2 and 4 weeks of experimental feeding. Multi-factorial analysis of conducted histological measurements of melanomacrophage centers (MMCs) revealed no changes of their parameters within spleens, but showed a decrease of the occupied tissue area and MMC counts in the livers, progressing with time regardless of the applied diet. Immunohistochemical analysis of CD3+ T cells showed their increased recruitment into mucosal folds of pyloric caeca in the 2-week sampling of trouts fed with the diet with 2% Bioimmuno addition, but this effect was not present in the 4-week sampling. When studying all groups jointly within each morph, there was a significant difference in terms of maintained CD3+ T cells levels, as sea trouts showed significantly higher tissue areas occupied by these cells than river trouts, both in the pyloric caeca and hepatic parenchyma. The study revealed that feeding with a diet enriched with Bioimmuno for 2 weeks may be a favorable enhancement of rearing protocols of brown trout stocks prior to their release, but more studies need to be conducted to test the possibility of an even shorter feeding period.

GH Overexpression Alters Spermatic Cells MicroRNAome Profile in Transgenic Zebrafish

Overexpression of growth hormone (GH) in gh-transgenic zebrafish of a highly studied lineage F0104 has earlier been reported to cause increased muscle growth. In addition to this, GH affects a broad range of cellular processes in transgenic fish, such as morphology, physiology, and behavior. Reports show changes such as decreased sperm quality and reduced reproductive performance in transgenic males. It is hypothesized that microRNAs are directly involved in the regulation of fertility potential during spermatogenesis. The primary aim of our study was to verify whether gh overexpression disturbs the sperm miRNA profile and influences the sperm quality in transgenic zebrafish. We report a significant increase in body weight of gh-transgenic males along with associated reduced sperm motility and other kinetic parameters in comparison to the non-transgenic group. MicroRNA transcriptome sequencing of gh-transgenic zebrafish sperms revealed expressions of 186 miRNAs, among which six miRNA were up-regulated (miR-146b, miR-200a-5p, miR-146a, miR-726, miR-184, and miR-738) and sixteen were down-regulated (miR-19d-3p, miR-126a-5p, miR-126b-5p, miR-22a-5p, miR-16c-5p, miR-20a-5p, miR-126b-3p, miR-107a-3p, miR-93, miR-2189, miR-202–5p, miR-221–3p, miR-125a, miR-125b-5p, miR-126a-3p, and miR-30c-5p) in comparison to non-transgenic zebrafish. Some of the dysregulated miRNAs were previously reported to be related to abnormalities in sperm quality and reduced reproduction ability in other species. In this study, an average of 134 differentially expressed miRNAs-targeted genes were predicted using the in silico approach. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis demonstrated that the genes of affected pathways were primarily related to spermatogenesis, sperm motility, and cell apoptosis. Our results suggested that excess GH caused a detrimental effect on sperm microRNAome, consequently reducing the sperm quality and reproductive potential of zebrafish males.

Growth Hormone Overexpression Induces Hyperphagia and Intestinal Morphophysiological Adaptations to Improve Nutrient Uptake in Zebrafish

The excess of circulating growth hormone (GH) in most transgenic animals implies mandatory growth resulting in higher metabolic demand. Considering that the intestine is the main organ responsible for the digestion, absorption, and direction of dietary nutrients to other tissues, this study aimed to investigate the mechanisms by which gh overexpression modulates the intestine to support higher growth. For this purpose, we designed an 8-weeks feeding trial to evaluate growth parameters, feed intake, and intestinal morphometric indices in the adult gh-transgenic zebrafish (Danio rerio) model. To access the sensitivity of the intestine to the excess of circulating GH, the messenger RNA (mRNA) expression of intestine GH receptors (GHRs) (ghra and ghrb) was analyzed. In addition, the expression of insulin-like growth factor 1a (igf1a) and genes encoding for di and tripeptide transporters (pept1a and pept1b) were assessed. Gh-transgenic zebrafish had better growth performance and higher feed intake compared to non-transgenic sibling controls. Chronic excess of GH upregulates the expression of its cognate receptor (ghrb) and the main growth factor related to trophic effects in the intestine (igf1a). Moreover, transgenic zebrafish showed an increased intestinal absorptive area and higher expression of crucial genes related to the absorption of products from meal protein degradation. These results reinforce the ability of GH to modulate intestinal morphology and the mechanisms of assimilation of nutrients to sustain the energy demand for the continuous growth induced by the excess of circulating GH.

Evaluation of qPCR reference genes in GH-overexpressing transgenic zebrafish (Danio rerio)

Reference genes (RGs) must have a stable expression in tissues in all experimental conditions to normalize real-time quantitative reverse transcription PCR (qRT-PCR) data. F0104 is a highly studied lineage of zebrafish developed to overexpress the growth hormone (GH). It is assumed that the transgenic process may influence the expression levels of commonly used RGs. The objective of the present study was to make a comprehensive analysis of stability of canditade RGs actb1, actb2, b2m, eif2s2, eef1a1, gapdh, rplp2, rpl7, rpl13α, tuba1, and rps18, in gh-transgenic and non-transgenic zebrafish. Liver, brain, intestine and muscle samples from both groups had qRT-PCR results analyzed by dCt, geNorm, NormFinder, BestKeeper, and RefFinder softwares. Consensus analyses among software concluded that rpl13α, rpl7, and eef1a1 are the most stable genes for zebrafish, considering the studied groups and tissues. Gapdh, rps18, and tuba1 suffered variations in stability among different tissues of both groups, and so, they were listed as the genes with lowest stability. Results from an average pairwise variations test indicated that the use of two RGs would generate reliable results for gene expression analysis in the studied tissues. We conclude that genes that are commonly used in mammals for qRT-PCR assays have low stability in both non-transgenic and gh-transgenic zebrafish reinforcing the importance of using species-specific RGs.

Deletion of mstna and mstnb impairs the immune system and affects growth performance in zebrafish

Myostatin (Mstn) is a negative regulator of muscle development in vertebrates. Although its function in muscle growth has been well studied in mammals and fish, it remains unclear whether or how mstn functions in the immune system. In this study, mstna^-/- and mstnb^-/- homozygous zebrafish were firstly generated using CRISPR/Cas9 (Clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9). Deletion of mstnb but not mstna enhanced growth performance. Although survival rates under normal conditions were slightly decreased in both strains, mortality after dexamethasone-induced stress was increased by ∼30%. Furthermore, transcriptional levels of several critical immune-related genes were decreased, and the ability to withstand exposure to pathogenic E. tarda was decreased, compared with that of controls. In mstnb^-/- but not mstna^-/- zebrafish, expression of NF-κB subunits and several pro-inflammatory cytokines failed to respond to E. tarda exposure except nfkb1, c-rel and tnfα. Taken together, these results indicate that mstnb but not mstna plays a key role in zebrafish muscle growth. While each paralogue contributes to the response to bacterial insult, mstnb affects the immune system through activation of the NF-κB pathway, and mstna is likely to act upstream of NF-κB at some as yet unidentified target.

Neuroendocrine-immune interaction: Evolutionarily conserved mechanisms that maintain allostasis in an ever-changing environment

It has now become accepted that the immune system and neuroendocrine system form an integrated part of our physiology. Immunological defense mechanisms act in concert with physiological processes like growth and reproduction, energy intake and metabolism, as well as neuronal development. Not only are psychological and environmental stressors communicated to the immune system, but also, vice versa, the immune response and adaptation to a current pathogen challenge are communicated to the entire body, including the brain, to evoke adaptive responses (e.g., fever, sickness behavior) that ensure allocation of energy to fight the pathogen. This phenomenon is evolutionarily conserved. Hence it is both interesting and important to consider the evolutionary history of this bi-directional neuroendocrine-immune communication to reveal phylogenetically ancient or relatively recently acquired mechanisms. Indeed, such considerations have already disclosed an extensive "common vocabulary" of information pathways as well as molecules and their receptors used by both the neuroendocrine and immune systems. This review focuses on the principal mechanisms of bi-directional communication and the evidence for evolutionary conservation of the important physiological pathways involved.

Ontogenic development of kidney, thymus and spleen and phenotypic expression of CD3 and CD4 receptors on the lymphocytes of cobia (Rachycentroncanadum)

In the present study was evaluated the ontogenic of immunocompetent organs of cobia up to 53 days after hatching (dah) through histology and immunohistochemistry techniques. The kidney was the first lymphohematopoietic organ to appear, at 1 dah, followed by the spleen at 5 dah and the thymus at 7 dah. The first CD3 receptors on the lymphocytes were observed in 27% of the thymic tissue at 7 dah and in 99% at 53 dah. The phenotypic expression of CD3 receptors was registered in 10% of the kidney at 8 dah and in 32% at 53 dah. CD4 receptors were observed in 5% and 63% of the thymic area at 7 and 53 dah, respectively. In the kidney, T4 lymphocytes were first observed at 13 dah in 9% of the organ and in 28% at 53 dah, defining the functional development of the specific system associated with immunological memory capacity.

Effects of somatotrophic axis (GH/GHR) double transgenesis on structural and molecular aspects of the zebrafish immune system

The development of growth hormone (GH) transgenic fish has been shown to be a promising method to improve growth rates. However, the role of GH is not restricted only to processes involved in growth. Several others physiological processes, including immune function, are impaired due to GH imbalances. Given the importance of generating GH transgenic organisms for aquaculture purposes, it is necessary to develop strategies to reduce or compensate for the collateral effects of GH. We hypothesized that the generation of double transgenic fish that overexpress GH and growth hormone receptor (GHR) in the skeletal muscle could be a possible alternative to compensate for the deleterious effects of GH on the immune system. Specifically, we hypothesized that increased GHR amounts in the skeletal muscle would be able to reduce the level of circulating GH, attenuating the GH signaling on the immune cells while still increasing the growth rate. To test this hypothesis, we evaluated the size of the immune organs, T cell content in the thymus and head kidney, and expression of immune-related genes in double-transgenic fish. Contrary to our expectations, we found that the overexpression of GHR does not decrease the deleterious effect of GH excess on the size of the thymus and head kidney, and in the content of CD3(+) and CD4(+) cells in the thymus and head kidney. Unexpectedly, the control GHR transgenic group showed similar impairments in immune system parameters. These results indicate that GHR overexpression does not reverse the impairments caused by GH and, in addition, could reinforce the damage to the immune functions in GH transgenic zebrafish.