Bromodeoxyuridine DNA labelling reveals host and parasite proliferation in a fish-myxozoan model

Histone deacetylase 4 deletion results in abnormal chondrocyte hypertrophy and premature ossification from collagen type 2α1‑expressing cells

Histone deacetylase 4 (HDAC4) plays a vital role in chondrocyte hypertrophy and bone formation. To investigate the function of HDAC4 in postnatal skeletal development, the present study developed lineage‑specific HDAC4‑knockout mice [collagen type 2α1 (Col2α1)‑Cre, HDAC4d/d mice] by crossing transgenic mice expressing Cre recombinase. Thus, a specific ablation of HDAC4 was performed in Col2α1‑expressing mice cells. The knee joints of HDAC4fl/fl and Col2α1‑Cre, HDAC4d/d mice were analyzed at postnatal day (P)2‑P21 using an in vivo bromodeoxyuridine (BrdU) assay, and Safranin O, Von Kossa and whole‑body staining were used to evaluate the developmental growth plate, hypertrophic differentiation, mineralization and skeletal mineralization patterns. The trabecular bone was analyzed using microcomputed tomography. The expressions of BrdU, proliferating cell nuclear antigen (PCNA), matrix metalloproteinase (MMP)‑13, runt‑related transcription factor (Runx)‑2, osteoprotegerin (OPG), CD34, type X collagen (ColX), osteocalcin and Wnt5a were determined using immunohistochemistry, in situ hybridization (ISH) and reverse transcription‑quantitative (RT‑q)PCR. The results demonstrated that HDAC4‑null mice (HDAC4d/d mice) were severely runted; these mice had a shortened hypertrophic zone (histopathological evaluation), accelerated vascular invasion and articular mineralization (Von Kossa staining), elevated expressions of MMP‑13, Runx2, OPG and CD34 (RT‑qPCR and immunohistochemistry), downregulated expression of the proliferative marker BrdU and PCNA (immunohistochemistry), increased expression of ColX and decreased expression of Wnt5a (ISH). In conclusion, chondrocyte‑derived HDAC4 was responsible for regulating chondrocyte proliferation and differentiation as well as endochondral bone formation.

Challenge for macrophages and mast cells of Chelon ramada to counter an intestinal microparasite, Myxobolus mugchelo (Myxozoa)

Thinlip mullet Chelon ramada is the most abundant mullet species found in the Comacchio lagoons (northern Adriatic Sea, Italy). Histological and ultrastructural sections of the intestine of C. ramada showed that over 83% of 48 mullets were infected with the intestinal parasite Myxobolus mugchelo (Myxozoa). In histological sections, plasmodia of M. mugchelo containing mature spores were situated closer to mucosal folds and were surrounded by numerous mast cells (MCs). Mature spores, generally oval in shape, were observed in the paracellular space among the enterocytes or within them. Near the infected epithelial cells, several MCs, rodlet cells and few neutrophils occurred. In intestinal epithelium, large cells resembling macrophages, some with spores of M. mugchelo inside, were observed. These macrophage-like cells were foamy and possessed elongate striated granules. The number of MCs and macrophages in the intestinal epithelium was significantly higher in parasitized fish. In some parasitized intestines, portions of epithelium were displaced by spores, or the spores were observed inside the damaged enterocytes. Immunohistochemical analysis of C. ramada infected or uninfected intestinal tissue revealed the presence of histamine, serotonin (5-HT), leu-enkephalin and inducible-nitric oxide synthase in epithelial macrophages. Several epithelial cells positive to proliferating cell-nuclear antigen were also observed in the proximity of the macrophages. The current study is the first to record the occurrence of intraepithelial macrophages which engulf myxozoan spores. A hypothesis on migration of spores from pancreas via intestinal wall to gut lumen is presented.

Disruption of gut integrity and permeability contributes to enteritis in a fish-parasite model: a story told from serum metabolomics

Background

In the animal production sector, enteritis is responsible for serious economic losses, and intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and animal production efficiency. The effect of enteric parasites on the gut function of teleost fish, which represent the most ancient bony vertebrates, is far from being understood. The intestinal myxozoan parasite Enteromyxum leei dwells between gut epithelial cells and causes severe enteritis in gilthead sea bream (Sparus aurata), anorexia, cachexia, growth impairment, reduced marketability and increased mortality.

Methods

This study aimed to outline the gut failure in this fish-parasite model using a multifaceted approach and to find and validate non-lethal serum markers of gut barrier dysfunction. Intestinal integrity was studied in parasitized and non-parasitized fish by immunohistochemistry with specific markers for cellular adhesion (E-cadherin) and tight junctions (Tjp1 and Cldn3) and by functional studies of permeability (oral administration of FITC-dextran) and electrophysiology (Ussing chambers). Serum samples from parasitized and non-parasitized fish were analyzed using non-targeted metabolomics and some significantly altered metabolites were selected to be validated using commercial kits.

Results

The immunodetection of Tjp1 and Cldn3 was significantly lower in the intestine of parasitized fish, while no strong differences were found in E-cadherin. Parasitized fish showed a significant increase in paracellular uptake measured by FITC-dextran detection in serum. Electrophysiology showed a decrease in transepithelial resistance in infected animals, which showed a diarrheic profile. Serum metabolomics revealed 3702 ions, from which the differential expression of 20 identified compounds significantly separated control from infected groups in multivariate analyses. Of these compounds, serum inosine (decreased) and creatine (increased) were identified as relevant and validated with commercial kits.

Conclusions

The results demonstrate the disruption of tight junctions and the loss of gut barrier function, a metabolomic profile of absorption dysfunction and anorexia, which further outline the pathophysiological effects of E. leei.

Dual RNA-seq reveals the effect of the flgM gene of Pseudomonas plecoglossicida on the immune response of Epinephelus coioides

Pseudomonas plecoglossicida is an important and highly pathogenic bacterium for aquaculture and causes serious losses. The expression level of flgM was found to be significantly upregulated post-infection compared with in vitro results, which was confirmed by quantitative real-time PCR. RNAi significantly reduced the expression level of flgM mRNA of P. plecoglossicida. Compared with infection with the wild-type strain, infection with the flgM-RNAi strain resulted in a delay in death and a 75% reduction in the mortality of Epinephelus coioides, followed by alleviation of the symptoms in E. coioides spleen. Moreover, compared with infection with the wild-type strain, infection with the flgM-RNAi strain of P. plecoglossicida resulted in a significant change in the transcriptome of the spleens of infected E. coioides and P. plecoglossicida. KEGG analysis for E. coioides showed that genes of 17 immune pathways were most affected by flgM-RNAi of P. plecoglossicida. Among them, the expression of mhc2, zap70, rhoh, tlr2, ca79a, hcst and cd32 in E. coioides spleen was predicted to be negatively related to flgM in P. plecoglossicida but positively related to genes involved in communication, metabolism and motility.

Hints on T cell responses in a fish-parasite model: Enteromyxum leei induces differential expression of T cell signature molecules depending on the organ and the infection status

BACKGROUD

Enteromyxum leei is a myxozoan parasite that produces a slow-progressing intestinal disease. This parasite invades the paracellular space of the intestinal epithelium and progresses from the posterior to the anterior intestine. The aim of the present study was to gain insights into fish T cell responses in the gilthead sea bream-E. leei infection model using a PCR-array with 30 signature molecules for different leukocyte responses in head kidney, spleen, anterior and posterior intestine.

RESULTS

The PCR-array results suggest that E. leei induced migration of T cells from head kidney to intestines where T_H1, CTL and T_H17 profiles were activated and kept in balance by the upregulation of regulatory cytokines. These results were partially validated by the use of cross-reacting antibodies and BrdU immunostaining to monitor proliferation. Zap70 immunostaining supported the increased number of T cells in the anterior intestine detected by gene expression, but double staining with BrdU did not show active proliferation of this cell type at a local level, supporting the migration from lymphohaematopoietic tissues to the site of infection. Global analyses of the expression profiles revealed a clear separation between infected and exposed, but non-infected fish, more evident in the target organ. Exposed, non-infected animals showed an intermediate phenotype closer to the control fish.

CONCLUSIONS

These results evidence a clear modulation of the T cell response of gilthead sea bream upon E. leei infection. The effects occurred both at local and systemic levels, but the response was stronger and more specific at the site of infection, the intestine. Altogether, this research poses a promising basis to understand the response against this important parasite and establish effective preventive or palliative measures.