Background: Magnesium influences hepatic lipid deposition in vertebrates, but the underlying mechanism is unknown.Objective: We used yellow catfish a

The present study was performed to determine the effect of Zn exposure influencing endoplasmic reticulum (ER) stress, explore the underlying molecular mechanism of Zn-induced hepatic lipolysis in a fish species of significance for aquaculture, yellow catfish Pelteobagrus fulvidraco. We found that waterborne Zn exposure evoked ER stress and unfolded protein response (UPR), and activated cAMP/PKA pathway, and up-regulated hepatic lipolysis. The increase in ER stress and lipolysis were associated with activation of cAMP/PKA signaling pathway. Zn also induced an increase in intracellular Ca2+ level, which could be partially prevented by dantrolene (RyR receptor inhibitor) and 2-APB (IP3 receptor inhibitor), demonstrating that the disturbed Ca2+ homeostasis in ER contributed to ER stress and dysregulation of lipolysis. Inhibition of ER stress by PBA attenuated UPR, inhibited the activation of cAMP/PKA pathway and resulted in down-regulation of lipolysis. Inhibition of protein kinase RNA-activated-like ER kinase (PERK) by GSK2656157 and inositol-requiring enzyme (IRE) by STF-083010 differentially influenced Zn-induced changes of lipid metabolism, indicating that PERK and IRE pathways played different regulatory roles in Zn-induced lipolysis. Inhibition of PKA by H89 blocked the Zn-induced activation of cAMP/PKA pathway with a concomitant inhibition of ER stress-mediated lipolysis. Taken together, our findings highlight the importance of the ER stress-cAMP/PKA axis in Zn-induced lipolysis, which provides new insights into Zn toxicology in fish and probably in other vertebrates.

An 8-week feeding trial was conducted to assess the effects on growth, antioxidant capacity, digestive enzyme activity, and gene expression related to muscle growth and protein synthesis of juvenile greasyback shrimp (Metapenaeus ensis) using five experimental diets containing 29.37%, 34.30%, 39.11%, 44.05%, and 49.32% of protein. The results demonstrated that juvenile greasyback shrimp consuming 39.11%, 44.05%, and 49.32% dietary protein had a significantly higher final body weight (FBW), weight gain (WG), feed conversion ratio (FCR), and specific growth rate (SGR) than other groups (p < 0.05). The protein efficiency ratio (PER) showed a significantly quadratic pattern with increasing dietary protein levels (p < 0.05). The highest trypsin and pepsin activities were observed in the group with a protein level of 44.05% (p < 0.05). Relatively higher superoxide dismutase (SOD) activity was found in groups with protein levels of 39.11% (p < 0.05). Alkaline phosphatase (AKP) and catalase (CAT) activity showed a significantly linear increasing pattern with increasing protein intake up to 44.05%, and then decreased gradually (p < 0.05). Compared to the dietary 29.37% protein level, the expression levels of myogenic regulatory factors (mef2α, mlc, and myf5) and mTOR pathway (mtor, s6k, akt, and pi3k)-related genes were significantly up-regulated in muscle with 39.11%, 44.05%, and 49.32% dietary protein levels (p < 0.05). The AAR pathway (gcn2, eif2α, and atf4)-related gene expression levels were significantly lower in muscles with 39.11%, 44.05%, and 49.32% protein levels than in other groups (p < 0.05). Based on the broken-line regression analysis of SGR, the estimated appropriate dietary protein requirement for juvenile greasyback shrimp is 38.59%.

Background.: Liver ischemia/reperfusion injury (I/RI) is characterized by inflammatory actions. Understanding the mechanistic insights underpinning inflammation is critical to developing treatment strategies. In this study, we illustrated the mechanistic insights of transcription factor Yin-Yang 1 (YY1)-mediated microRNA (miR)-181a-5p/estrogen receptor alpha (ESR1)/epidermal growth factor receptor 2 (ERBB2) axis in liver I/RI. Methods.: First, we established liver I/RI models in mice and hypoxia-reperfusion (H/R) cell models in mouse hepatocytes (AML12). Subsequently, the expression of YY1, miR-181a-5p, and ESR1 was determined in the 2 models. I/RI mouse models were further injected with lentivirus carrying oe-YY1‚ and H/R-exposed AML12 cells were subjected to a series of inhibitors, mimics, and shRNAs to validate the mechanisms of YY1 in controlling miR-181a-5p and ESR1 in liver I/RI. Results.: Upregulated expression of miR-181a-5p and downregulated expression of YY1 were identified in the liver tissues of liver I/RI mice and H/R-exposed hepatocytes. Moreover, overexpression of YY1 inhibited the miR-181a-5p expression and thus repressed the H/R-induced hepatocyte apoptosis and inflammation. ESR1 was further validated as a target gene of miR-181a-5p and could be negatively regulated by miR-181a-5p. miR-181a-5p inhibition elevated ESR1 expression, which consequently enhanced the ERBB2 expression and reduced H/R-induced hepatocyte apoptosis and inflammation. Conclusions.: Overall, these findings highlighted that YY1 repressed the miR-181a-5p expression and stimulated ESR1-mediated activation of ERBB2, thereby ameliorating liver I/RI. This study provides insight into the development of novel targets for liver I/RI.

The present study was conducted to investigate the effects and the related signaling pathways of insulin influencing lipid metabolism in yellow catfish Pelteobagrus fulvidraco. As a result, hepatic lipid and intracellular triglyceride (TG) content, the activities and expression levels of several enzymes (CPT I, 6PGD, G6PD, FAS, ME and ICDH) as well as the mRNA expression of transcription factors (PPARα and PPARγ) involved in lipid metabolism were determined. Troglitazone (specific PPARγ pathway activator), GW6471 and fenofibrate (specific PPARα pathway inhibitor and activator, respectively), and wortmannin (PI 3-kinase/Akt pathway blocker) were used to explore the signaling pathways of insulin influencing lipid metabolism. Insulin tended to increase hepatic lipid accumulation, activities of lipogenic enzymes (6PGD, G6PD, ME, ICDH and FAS) and mRNA levels of FAS, G6PD, 6PGD, CPT IA and PPARγ, but down-regulated PPARα mRNA level. Insulin-induced effect could be stimulated by specific PPARγ activator troglitazone or reversed by PI 3-kinase/Akt inhibitor wortmannin, demonstrating that signaling pathways of PPARγ and PI 3-kinase/Akt were involved in the insulin-induced alteration of lipid metabolism. Fenofibrate reduced insulin-induced TG accumulation, down-regulated the mRNA levels of FAS, G6PD and 6PGD, and up-regulated mRNA levels of CPT IA, PPARα and PPARγ. GW6471 reduced insulin-induced changes of all the tested genes' expression, indicating that PPARα mediated the insulin-induced changes of lipid metabolism. The present results contribute to gain new knowledge on the regulatory role of insulin in hepatic metabolism in fish.

Zinc alleviates hepatic lipid deposition, but the transcriptional regulatory mechanisms are still unclear. In this study, we characterized the promoter of an SHP (short heterodimer partner) in a teleost Pelteobagrus fulvidraco. The binding sites of an FXR (farnesoid X receptor) were predicted by the SHP promoter, indicating that the FXR mediated its transcriptional activity. The site mutagenesis and the EMSA (electrophoretic mobility shift assay) found that the −375/−384 bp FXR site on the SHP promoter was the functional binding locus responsible for the Zn-induced transcriptional activation. A further study of yellow catfish hepatocytes suggested that the activation of the FXR/SHP is responsible for the effect of Zn on the decreasing lipid content. Thus, this study provides direct evidence of the interaction between the FXR and SHP promoter in fish, and accordingly elucidates the potential transcriptional mechanism by which Zn reduces hepatic lipid accumulation.