Selenium Ameliorated Oxidized Fish Oil-Induced Lipotoxicity via the Inhibition of Mitochondrial Oxidative Stress, Remodeling of Usp4-Mediated Deubiquitination, and Stabilization of Pparα.

Aims: Studies demonstrated that oxidized fish oil (OFO) promoted oxidative stress and induced mitochondrial dysfunction and lipotoxicity, which attenuated beneficial effects of fish oil supplements in the treatment of nonalcoholic fatty liver disease (NAFLD). The current study was performed on yellow catfish, a good model to study NAFLD, and its hepatocytes to explore whether selenium (Se) could alleviate OFO-induced lipotoxicity via the inhibition of oxidative stress and determine its potential mechanism. Results: The analysis of triglycerides content, oxidative stress parameters, and histological and transmission electronic microscopy observation showed that high dietary Se supplementation alleviated OFO-induced lipotoxicity, oxidative stress, and mitochondrial injury and dysfunction. RNA-sequencing and immunoblotting analysis indicated that high dietary Se reduced OFO-induced decline of peroxisome-proliferator-activated receptor alpha (Pparα) and ubiquitin-specific protease 4 (Usp4) protein expression. High Se supplementation also alleviated OFO-induced reduction of thioredoxin reductase 2 (txnrd2) messenger RNA (mRNA) expression level and activity. The txnrd2 knockdown experiments revealed that txnrd2 mediated Se- and oxidized eicosapentaenoic acid (oxEPA)-induced changes of mitochondrial reactive oxygen species (mtROS) and further altered Usp4 mediated-deubiquitination and stabilization of Pparα, which, in turn, modulated mitochondrial fatty acid ß-oxidation and metabolism. Mechanistically, Usp4 deubiquitinated Pparα and ubiquitin-proteasome-mediated Pparα degradation contributed to oxidative stress-induced mitochondrial dysfunction. Innovation: These findings uncovered a previously unknown mechanism by which Se and OFO interacted to affect lipid metabolism via the Txnrd2-mtROS-Usp4-Pparα pathway, which provides the new target for NAFLD prevention and treatment. Conclusion: Se ameliorated OFO-induced lipotoxicity via the inhibition of mitochondrial oxidative stress, remodeling of Usp4-mediated deubiquitination, and stabilization of Pparα. Antioxid. Redox Signal. 40, 433-452.

Manganese-Induced Oxidative Stress Contributes to Intestinal Lipid Deposition via the Deacetylation of PPARγ at K339 by SIRT1.

Aims: Excessive manganese (Mn) exposure is toxic, and induces lipid deposition, but the underlying mechanisms remain elusive. Herein, we explored how dietary Mn supplementation affects lipid deposition and metabolism in the intestine of vertebrates using the yellow catfish Pelteobagrus fulvidraco as the model. Results: High-Mn (H-Mn) diet increased intestinal Mn content, promoted lipid accumulation and lipogenesis, and inhibited lipolysis. In addition, it induced oxidative stress, upregulated metal-response element-binding transcription factor-1 (MTF-1), and peroxisome proliferator-activated receptor gamma (PPARγ) protein expression in the nucleus, induced PPARγ acetylation, and the interaction between PPARγ and retinoid X receptor alpha (RXRα), while it downregulated sirtuin 1 (SIRT1) expression and activity. Mechanistically, Mn activated the MTF-1/divalent metal transporter 1 (DMT1) pathway, increased Mn accumulation in the mitochondria, and induced oxidative stress. This in turn promoted lipid deposition via deacetylation of PPARγ at K339 by SIRT1. Subsequently, PPARγ mediated Mn-induced lipid accumulation through transcriptionally activating fatty acid translocase, stearoyl-CoA desaturase 1, and perilipin 2 promoters. Innovation: These studies uncover a previously unknown mechanism by which Mn induces lipid deposition in the intestine via the oxidative stress-SIRT1-PPARγ pathway. Conclusion: High dietary Mn intake activates MTF-1/DMT1 and oxidative stress pathways. Oxidative stress-mediated PPARγ deacetylation at K339 site contributes to increased lipid accumulation. Our results provided a direct link between Mn and lipid metabolism via the oxidative stress-SIRT1-PPARγ axis. Antioxid. Redox Signal. 37, 417-436.

Dietary Marginal and Excess Selenium Increased Triglycerides Deposition, Induced Endoplasmic Reticulum Stress and Differentially Influenced Selenoproteins Expression in the Anterior and Middle Intestines of Yellow Catfish Pelteobagrus fulvidraco.

Selenium (Se) is an essential micro-mineral and plays important roles in antioxidant responses, and also influences lipid metabolism and selenoprotein expression in vertebrates, but the effects and mechanism remain unknown. The study was undertaken to decipher the insights into dietary Se influencing lipid metabolism and selenoprotein expression in the anterior and middle intestine (AI and MI) of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (weight: 8.27 ± 0.03 g) were fed a 0.03- (M-Se), 0.25- (A-Se), or 6.39- (E-Se) mg Se/kg diet for 12 wk. AI and MI were analyzed for triglycerides (TGs) and Se concentrations, histochemistry and immunofluorescence, enzyme activities, and gene and protein levelsassociated with antioxidant responses, lipid metabolism, endoplasmic reticulum (ER) stress, and selenoproteome. Compared to the A-Se group, M-Se and E-Se diets significantly decreased weight gain (WG) and increased TGs concentration in the AI and MI. In the AI, compared with A-Se group, M-Se and E-Se diets significantly increased activities of fatty acid synthase, expression of lipogenic genes, and suppressed lipolysis. In the MI, compared to the A-Se group, M-Se and E-Se diets significantly increased activities of lipogenesis and expression of lipogenic genes. Compared with A-Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the AI and MI, and M-Se diet did not significantly reduce GPX activities in the AI and MI. Compared with the A- Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the plasma and liver, and M-Se diet significantly reduced GPX activities in the plasma and liver. Compared with the A-Se group, M-Se and E-Se groups also increased glucose-regulated protein 78 (GRP78, ER stress marker) protein expression of the intestine. Dietary Se supplementation also differentially influenced the expression of the 28 selenoproteins in the AI and MI, many of which possessed antioxidant characteristics. Compared with the A-Se group, the M-Se group significantly decreased mRNA levels of txnrd2 and txnrd3, but made no difference on mRNA levels of these seven GPX proteins in the MI. Moreover, we characterized sterol regulatory element binding protein 1c (SREBP1c) binding sites of three ER-resident proteins (selenom, selenon, and selenos) promoters, and found that Se positively controlled selenom, selenon, and selenos expression via SREBP1c binding to the selenom, selenon, and selenos promoter. Thus, dietary marginal and excess Se increased TGs deposition of yellow catfish P. fulvidraco, which might be mediated by ER-resident selenoproteins expression and ER stress.

Isolation and Characterization of Three Sodium-Phosphate Cotransporter Genes and Their Transcriptional Regulation in the Grass Carp Ctenopharyngodon idella.

It is important to explore the regulatory mechanism of phosphorus homeostasis in fish, which help avoid the risk of P toxicity and prevent P pollution in aquatic environment. The present study obtained the full-length cDNA sequences and the promoters of three SLC20 members (slc20a1a, slc20a1b and slc20a2) from grass carp Ctenopharyngodon idella, and explored their responses to inorganic phosphorus (Pi). Grass carp SLC20s proteins possessed conservative domains and amino acid sites relevant with phosphorus transport. The mRNAs of three slc20s appeared in the nine tissues, but their expression levels were tissue-dependent. The binding sites of three transcription factors (SREBP1, NRF2 and VDR) were predicted on the slc20s promoters. The mutation and EMSA analysis indicated that: (1) SREBP1 binding site (-783/-771 bp) negatively but VDR (-260/-253 bp) binding site positively regulated the activities of slc20a1a promoter; (2) SREBP1 (-1187/-1178 bp), NRF2 (-572/-561 bp) and VDR(615/-609 bp) binding sites positively regulated the activities of slc20a1b promoter; (3) SREBP1 (-987/-977 bp), NRF2 (-1469/-1459 bp) and VDR (-1124/-1117 bp) binding sites positively regulated the activities of the slc20a2 promoter. Moreover, Pi incubation significantly reduced the activities of three slc20s promoters, and Pi-induced transcriptional inactivation of slc20s promoters abolished after the mutation of the VDR element but not SREBP1 and NRF2 elements. Pi incubation down-regulated the mRNA levels of three slc20s. For the first time, our study elucidated the transcriptional regulatory mechanisms of SLC20s and their responses to Pi, which offered new insights into the Pi homeostatic regulation and provided the basis for reducing phosphorus discharge into the waters.