Autophagy regulation in teleost fish: A double-edged sword

Comparative transcriptome, ultrastructure and histology analyses provide insights into the potential mechanism of growth arrest in south China carp (Cyprinus carpio rubrofuscus)

BACKGROUND

South China carp (Cyprinus carpio rubrofuscus), which is an economically important species, is traditionally cocultured with rice. Our previous study indicated that approximately 10-30% of these fish experienced growth arrest, severely impacting production. However, the molecular mechanism underlying growth inhibition in south China carp is currently unknown.

RESULTS

In this study, we compared the transcriptomes of the livers, muscles and intestines of carp in the fast-growing and slow-growing groups. We identified 2182, 2355 and 916 differentially expressed genes (DEGs), respectively. In the slow-growing group, the oxidative phosphorylation pathway was significantly upregulated in the liver. Transmission electron microscopy (TEM) confirmed mitochondrial damage in the liver, which was characterized by broken cristae and heterogeneous matrix. Additionally, analysis of antioxidant enzyme and transaminase activity also revealed that the livers in slow-growing individuals were unhealthy. In muscle tissue, the mitophagy and autophagy pathways were significantly dysregulated. Consequently, manifestations of mitochondrial damage and sparse myofilaments were clearly observed in slow-growing south China carp via TEM. Furthermore, pathways that regulate cell proliferation and migration, including the ECM receptor and focal adhesion, were significantly enriched in the intestine. Morphological examination revealed that the villus height and muscular layer height in the slow-growing group were significantly shorter than those in the fast-growing group, suggesting decreased intestinal cell motility. Overall, our study elucidated mitochondrial damage in the liver and muscle and detected morphological changes in intestinal villi.

CONCLUSIONS

In summary, our results help elucidate the genetic architecture related to growth arrest in south China carp and provide a basis for further research on the growth of teleosts.

Temperature and immune challenges modulate the transcription of genes of the ubiquitin and apoptosis pathways in two high-latitude Notothenioid fish across the Antarctic Polar Front

Thermal variations due to global climate change are expected to modify the distributions of marine ectotherms, with potential pathogen translocations. This is of particular concern at high latitudes where cold-adapted stenothermal fish such as the Notothenioids occur. However, little is known about the combined effects of thermal fluctuations and immune challenges on the balance between cell damage and repair processes in these fish. The aim of this study was to determine the effect of thermal variation on specific genes involved in the ubiquitination and apoptosis pathways in two congeneric Notothenioid species, subjected to simulated bacterial and viral infections. Adult fish of Harpagifer bispinis and Harpagifer antarcticus were collected from Punta Arenas (Chile) and King George Island (Antarctica), respectively, and distributed as follows: injected with PBS (control), LPS (2.5 mg/kg) or Poly I:C (2 mg/kg) and then submitted to 2, 5 and 8 °C. After 1 week, samples of gills, liver and spleen were taken to evaluate the expression by real-time PCR of specific genes involved in ubiquitination (E3-ligase enzyme) and apoptosis (BAX and SMAC/DIABLO). Gene expression was tissue-dependent and increased with increasing temperature in the gills and liver while showing an opposite pattern in the spleen. Studying a pair of sister species that occur across the Antarctic Polar Front can help us understand the particular pressures of intertidal lifestyles and the effect of temperature in combination with biological stressors on cell damage and repair capacity in a changing environment.

Pleiotropic attenuating effect of Ginkgo biloba against isoprenaline-induced myocardial infarction via improving Bcl-2/mTOR/ERK1/2/Na+, K+-ATPase activities

Objective

Myocardial infarction (MI) is linked to an imbalance in the supply and demand of blood oxygen in the heart muscles. Beta-blockers and calcium antagonists are just two of the common medications used to treat MI. However, these have reportedly been shown to be either ineffective or to have undesirable side effects. Extract of Ginkgo biloba leaves (GBE), a Chinese herbal product offers special compatibility benefits in therapeutic settings relating to inflammatory diseases and oxidative stress. In order to better understand how GBE affects MI in rats insulted by isoprenaline (ISO), the current study was designed.

Methods

The heart weight index, serum lipid profile, cardiac marker enzymes, endogenous antioxidants [catalase (CAT), superoxide dismutase (SOD), glutathione (GSH), nitrites and malondialdehyde (MDA)], inflammatory mediators [tumour necrosis factor alpha (TNF-α) and interleukin-6 (IL-6)], immunohistochemical expressions of B-cell lymphoma factor-2 (Bcl-2), extracellular signal-regulated kinase (ERK1/2), and mammalian target of rapamycin (mTOR) and histopathological analysis were used to assess the cardioprotective properties of GBE.

Results

The findings showed that GBE effectively attenuated myocardial infarction by boosting the body's natural antioxidant defense system and reducing the release of inflammatory cytokines as well as heart injury marker enzymes. The expression of Bcl-2, ERK1/2 and mTOR was increased while the histomorphological alterations were reversed.

Conclusion

The cardioprotective effects of GBE may be due to a mechanism involving increased Bcl-2/mTOR/ERK1/2/Na+, K+-ATPase activity.

Uncoordinated 51-like kinase 1a/b and 2 in fish Megalobrama amblycephala: Molecular cloning, functional characterization, and their potential roles in glucose metabolism

Uncoordinated (Unc) 51-like kinase (ulk1) and ulk2 are closely involved in autophagy activation, but little is known about their roles in regulating glucose homeostasis. In this study, the genes of ulk1a, ulk1b and ulk2 were cloned and characterized in fish Megalobrama amblycephala. All the three genes shared the approximate N-terminal kinase domain and the C-terminal Atg1-like_tMIT domain structure, while the amino acid sequence identity of them are different between M. amblycephala and other vertebrates. Their transcripts were widely observed in various tissues (brain, muscle, gill, heart, spleen, eye, liver, intestine, abdominal adipose and kidney), but differed in tissue expression patterns. During the glucose tolerance test and the insulin tolerance test, the up-regulated transcriptions of ulk1a, ulk1b and ulk2 were all found despite some differences in the temporal patterns. At the same time, the activities of glycolytic enzymes like hexokinase and phosphofructokinase both showed parallel increases. Furthermore, the feeding of a high-carbohydrate diet decreased the transcriptions of ulk1a, ulk1b and ulk2. Collectively, this study demonstrated that ulk1a, ulk1b and ulk2 in M. amblycephala had similar molecular characterizations, but with different conservation and tissue expression patterns. In addition, ulk1/2 might play important roles in maintaining the glucose homeostasis in fish through regulating the glycolytic pathway.

Effects of dietary chloroquine on fish growth, hepatic intermediary metabolism, antioxidant and inflammatory responses in turbot

Autophagy is a conserved cellular self-digestion process and is essential for individual growth, cellular metabolism and inflammatory responses. It was responsive to starvation, pathogens infection and environmental stress. However, the information on the regulation of autophagy in fish hepatic intermediary metabolism, antioxidant system, and immune responses were limited. In the present study, turbot with inhibited autophagy flux was built by dietary chloroquine. The hepatic metabolic response, antioxidant enzymes and immune responses were explored. Results showed that dietary chloroquine induced the expression of Beclin 1, SQSTM and LC-3II, and effectively inhibited autophagy flux. Autophagy dysfunction depressed fish growth and feed utilization, while it induced clusters of liver lipid droplets. The genes involved in lipolysis and fatty acid β-oxidation, as well as the lipogenesis-related genes in chloroquine group were depressed. The phosphorylation of AMPK was activated in chloroquine group, and the genes involved in glycolysis were induced. The hepatic content of malonyldialdehyde and the activities of SOD and CAT were induced when autophagy was inhibited. The content of Complement 3, Complement 4 and Immunoglobulin M, as well as the activity of lysozyme in plasma were depressed in chloroquine group. Dietary chloroquine induced the expression of toll-like receptors and stimulated the expression of myd88 and nf-κb p65, as well as the pro-inflammatory cytokines, such as tnf-α and il-1β. The expression of anti-inflammatory cytokine tgf-β was depressed in the chloroquine group. Our results would extend the knowledge on the role of autophagy in teleost and assist in improving fishery production.

Autophagy regulation of virus infection in aquatic animals

Autophagy is a conserved intracellular degradation process that is required to maintain host homeostasis and cope with invading pathogens. Over the past few decades, studies on mammals have greatly increased our understanding of the relationship between autophagy and virus infection. Autophagy may convey the invader to lysosomes to degrade or activate the host immune response against virus replication. However, many viruses have developed some strategies that evade the degradative nature of autophagy or hijack this pathway for their gain. It follows that autophagy during viral infection is a double‐edged sword. In contrast to mammals, the review on autophagy modulated by the aquatic animal virus is limited. Here, after a brief description of the main information about autophagy, we highlight current progress on the interplays between autophagy and virus infection in aquatic animals, including the phenomenon of autophagy upon virus infection, the effect of modulating autophagy on virus replication, and the crosstalk between autophagy and immune response during virus infection. This review will help us better understand the pathogenic mechanism of aquatic animal viruses and develop proper antiviral countermeasures aimed at modulating autophagy.

GATA-3 in Atlantic salmon (Salmo salar): Tissue distribution and its regulation of IL-4/13a promoter

GATA3 is a transcription factor that plays an important role in T cell lineage differentiation and T-helper 2 (Th2) type immune responses. In this study, we developed two rat antibodies against Atlantic salmon GATA-3 (anti-rSsGATA-3a and anti-rSsGATA-3b, respectively). The western blotting and immunofluorescence results showed that anti-rSsGATA-3b antibodies recognized endogenous SsGATA-3 proteins, while the anti-rSsGATA-3a antibodies did not bind SsGATA-3. Immunohistochemical analysis revealed that SsGATA-3 positive cells were detected in all tissues tested, with relatively high number of immune reactive cells in the gills and spleen. Furthermore, the immunohistochemical study revealed that SsGATA-3 was expressed in pillar cells, epithelial cells, chondrocytes, perichondrium cells, and some undifferentiated basal cells. In addition, we determined 577 bp of the upstream promoter sequence of SsIL-4/13a and found four motifs that matched SsGATA-3 binding sites. The promoter regions of SsIL-4/13a were assessed by transfecting four deletion reporter constructs and SsGATA-3 overexpression plasmids. The result showed that SsGATA-3 enhanced the activity of SsIL-4/13a promoters within the region ranging from -317 to -302 bp upstream of the transcriptional start site. Antibodies against Th2 markers such as GATA-3 are valuable in addressing the diversity of T cell responses in fish.

The Early Peritoneal Cavity Immune Response to Vibrio Anguillarum Infection and to Inactivated Bacterium in Olive Flounder (Paralichthys olivaceus)

The peritoneal cavity plays an important role in the immune response, and intraperitoneal administration is an ideal vaccination route in fish. However, immune responses in the peritoneal cavity of teleost fish are still not completely characterized. This study characterized the morphology of peritoneal cavity cells (PerC cells) and their composition in flounder (Paralichthys olivaceus). Flow cytometric analysis of the resident PerC cells revealed two populations varying in granularity and size. One population, approximately 15.43% ± 1.8%, was smaller with a lower granularity, designated as lymphocytes. The other population of the cells, about 78.17% ± 3.52%, was larger with higher granularity and was designated as myeloid cells. The results of cytochemical staining and transmission electron microscopy indicated that peritoneal cavity in flounder normally contains a resident population of leukocytes dominated by granulocytes, macrophages, dendritic cells, and lymphocytes. The percentages of IgM+, CD4+, G-CSFR+, MHCII+, and CD83+ leukocytes among PerC cells determined by flow cytometry were 3.13% ± 0.4%, 2.83% ± 0.53%, 21.12% ± 1.44%, 27.11% ± 3.30%, and 19.64% ± 0.31%, respectively. Further, the changes in IgM+, CD4+, G-CSFR+, MHCII+, and CD83+ leukocytes in flounder after Vibrio anguillarum infection and immunization were compared. The composition changed rapidly after the infection or vaccination treatment and included two stages, a non-specific stage dominated by phagocytes and a specific immune stage dominated by lymphocytes. Due to the virulence effectors of bacteria, the infected group exhibited a more intense and complicated PerC cells immune response than that of the immunization group. Following our previous study, this is the first report on the morphology and composition of PerC cells and the early activation of PerC cells in flounder response to V. anguillarum infection and vaccination.