Zn Stimulates the Phospholipids Biosynthesis via the Pathways of Oxidative and Endoplasmic Reticulum Stress in the Intestine of Freshwater Teleost Yellow Catfish

Endoplasmic Reticulum Stress-Mediated Autophagy and Apoptosis Alleviate Dietary Fat-Induced Triglyceride Accumulation in the Intestine and in Isolated Intestinal Epithelial Cells of Yellow Catfish

BACKGROUND

The intestine is the main organ for absorbing dietary fat. High dietary lipid intake leads to fat deposition in the intestine and adversely influences fat absorption and health, but the underlying mechanism is unknown.

OBJECTIVES

We used yellow catfish and their isolated intestinal epithelial cells to test the hypothesis that endoplasmic reticulum (ER) stress, autophagy, and apoptosis mediate fat-induced changes in lipid metabolism.

METHODS

Male and female yellow catfish (weight: 3.79 ± 0.16 g; age: 3 mo) were fed diets containing lipid at 6.98% (low-fat diet; LFD), 11.3% (middle-fat diet; MFD), or 15.4% (high-fat diet; HFD) (by weight) for 8 wk. Each dietary group had 3 replicates, 30 fish per replicate. Their intestinal epithelial cells were isolated and incubated for 24 h in control solution or various concentrations of fatty acids (FAs) with or without 2-h pretreatment with an inhibitor [3-methyladenine (3-MA), 4-phenyl butyric acid (4-PBA), or Ac-DVED-CHO (AC)]. Triglyceride (TG) contents, genes, and enzymes involved in lipid metabolism, ER stress, autophagy, and apoptosis were determined in intestinal tissue and cells; immunoblotting, BODIPY 493/503 staining, ultrastructural observation, and the detection of autophagic and apoptotic vesicles were performed on intestinal cells.

RESULTS

Compared with the LFD and MFD, the HFD increased intestinal TG content by 120-226%, activities of lipogenic enzymes by 19.0-245%, expression of genes related to lipogenesis (0.77-8.4-fold), lipolysis (0.36-6.0-fold), FA transport proteins (0.79-1.7-fold), ER stress (0.55-7.5-fold), autophagy (0.56-4.2-fold), and apoptosis (0.80-5.2-fold). Using isolated intestinal epithelial cells and inhibitors (4-PBA, 3-MA, and AC), we found that ER stress mediated FA-induced activation of autophagy (11.0-50.1%) and apoptosis (10.4-32.0%), and lipophagy and apoptosis mediated FA-induced lipolysis (3.40-41.6%).

CONCLUSIONS

An HFD upregulated lipogenesis, lipolysis, and FA transport, induced ER stress, and activated autophagy and apoptosis. ER stress, autophagy, and apoptosis play important regulatory roles in fat-induced changes in lipid metabolism in the intestine and intestinal epithelial cells of yellow catfish.

Comparative transcriptome analyses reveal changes of gene expression in fresh and cryopreserved yellow catfish (Pelteobagrus fulvidraco) sperm and the effects of Cryoprotectant Me2SO

This study, for the first time in fish, compared the transcriptome of fresh and frozen-thawed sperm, and would help to better understand the effect of cryopreservation on fish sperm and then better preserve the aquatic germplasm resources. Here, we employed high-throughput sequencing technology to obtain the transcriptome of yellow catfish from fresh sperm, cryopreserved sperm with and without cryoprotectant. When cryoprotectant (Me₂SO) was excluded, down-regulated genes were significantly enriched into calcium ion binding, cytoskeletal protein binding, microfilament motor activity, calmodulin binding and carnitine O-acyltransferase activity, which affected Ca²⁺ regulation, cellular morphology, motility and metabolism. Moreover, heat shock proteins and genes associated with regulation of cholesterol, HCO₃^- and protein tyrosine phosphorylation (PTP) were down-regulated, and thus would impair ability against stress, membrane rigidity, pH regulation and signal transduction of cryopreserved sperm. After Me₂SO was added, the amounts of DEGs decreased significantly and down-regulation of genes were found mainly in cytoskeleton and heat shock proteins, thereby suggesting that Me₂SO effectively reduced the impact caused by low temperature on gene expression. Whether adding Me₂SO or not, the up-regulated genes were mainly found in ribosomal proteins genes. However, when Me₂SO was added, over-expression of some genes might contribute to maintain normal function of cryopreserved sperm.

Molecular characterization of nine suppressors of cytokine signaling (SOCS) genes from yellow catfish Pelteobagrus fulvidraco and their changes in mRNA expression to dietary carbohydrate levels

Suppressors of cytokine signaling (SOCS) are important molecules that mediates the regulation of glucose homeostasis. Here, we cloned and characterized the full-length cDNA sequences of nine genes of the SOCS family (SOCS1, 2, 3, 3b, 5, 5b, 6, 7 and CISH) from yellow catfish P. fulvidraco, explored their mRNA abundance across the tissues and their mRNA changes to dietary carbohydrate levels. Structural analysis indicated that the nine members shared conserved functional domains to the orthologues of the mammalian SOCS members, such as SRC homology 2 and the SOCS domains. Their mRNAs were constitutively expressed in various tissues but changed among the tissues. Their mRNA expression in response to dietary carbohydrate levels were explored in the liver, muscle, intestine, testis and ovary. Dietary carbohydrate addition showed significant effects on the mRNA levels of the nine SOCS members. Moreover, their mRNA expressions in response to dietary carbohydrate levels were also tissue-dependent. These indicated that SOCS members potentially mediated the utilization of dietary carbohydrate in yellow catfish.