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

Eucommia ulmoides flavonoids alleviate intestinal oxidative stress damage in weaned piglets by regulating the Nrf2/Keap1 signaling pathway

This study examined how Eucommia ulmoides flavonoids (EUF) protect against intestinal oxidative stress induced by deoxynivalenol (DON) in weaned piglets. Forty weaned piglets were randomly assigned to four dietary groups for a period of 14 days. The piglets were fed a control diet (Control) or the Control diet supplemented with 100 mg EUF/kg (EUF group), 4 mg DON/kg diet (DON group) or both (EUF+DON group) in a 2×2 factorial design. DON-challenged piglets on the EUF-supplemented diet showed significant improvements in growth performance. They also had notably lower serum levels of alkaline phosphatase (ALP), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) compared to those not receiving supplementation (P<0.05). In the EUF group, the relative weights of the liver, spleen, and kidneys were significantly lower than those in the control group (P<0.05). However, there were no significant differences in the relative heart weights among the four groups (P>0.05). Piglets challenged with DON and fed a diet supplemented with EUF showed significantly lower levels of interleukin-8 (IL-8) and interferon-γ (IFN-γ) mRNA and protein expression in serum and intestinal tissues compared to those in the DON group (P < 0.05). The EUF+DON group significantly increased the serum levels of glutathione peroxidase (GSH-Px), reactive oxygen species (ROS), and total antioxidative capability enzymes compared to the DON group (P<0.05). The EUF and DON group had significantly higher villus height, crypt depth, and villus height to crypt depth ratio in the small intestine compared to the supplemented DON-challenged piglets (P<0.05). Moreover, compared to the DON group, EUF can significantly enhance the expression of nuclear factor erythroid 2-related factor 2(Nfr2)/Kelch-like ECH-associating protein 1(Keap1) and antioxidant genes (i.e., HO-1, GCLC, GCLM), as well as their proteins in the DON-induced small intestines of piglets (P<0.05). In conclusion, EUF helps protect piglets from intestinal oxidative stress caused by DON by influencing the Nrf2/Keap1 signaling pathway, thereby supporting their intestinal health.

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 β-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.

Ferroptosis at the crossroads of manganese-induced neurotoxicity: A retrospective study

Manganese is an essential trace element, but overexposure can cause neurotoxicity and subsequent neurodegenerative diseases. Ferroptosis is a form of cell death characterized by lipid peroxidation and iron overload inside cells, which is closely related to manganese neurotoxicity. Manganese can induce ferroptosis through multiple pathways: causing oxidative stress and increased cellular reactive oxygen species (ROS), resulting in lipid peroxidation; depleting glutathione (GSH) and weakening the antioxidant capacity of cells; disrupting iron metabolism and increasing iron-dependent lipid peroxidation; damaging mitochondrial function and disrupting the electron transport chain, leading to increased ROS production. Oxidative stress, iron metabolism disorders, lipid peroxidation, GSH depletion, and mitochondrial dysfunction, typical features of ferroptosis, have been observed in animal and cell models after manganese exposure. In summary, manganese can participate in the pathogenesis of neurodegenerative diseases by inducing events related to ferroptosis. This provides new insights into studying the mechanism of manganese neurotoxicity and developing therapeutic drugs.

Association between plasma and dietary trace elements and obesity in a rural Chinese population

Trace elements may play an important role in obesity. This study aimed to assess the plasma and dietary intake levels of four trace elements, Mn, Cu, Zn and Se in a rural Chinese population, and analyse the relationship between trace elements and obesity. A cross-sectional study involving 2587 participants was conducted. Logistic regression models were used to analyse the association between trace elements and obesity; restricted cubic spline (RCS) models were used to assess the dose-response relationship between trace elements and obesity; the weighted quantile sum (WQS) model was used to examine the potential interaction of four plasma trace elements on obesity. Logistic regression analysis showed that plasma Se concentrations in the fourth quartile (Q4) exhibited a lower risk of developing obesity than the first quartile (Q1) (central obesity: OR = 0·634, P = 0·002; general obesity: OR = 0·525, P = 0·005). Plasma Zn concentration in the third quartile (Q3) showed a lower risk of developing obesity in general obesity compared with the first quartile (Q1) (OR = 0·625, P = 0·036). In general obesity, the risk of morbidity was 1·727 and 1·923 times higher for the second and third (Q2, Q3) quartiles of dietary Mn intake than for Q1, respectively. RCS indicated an inverse U-shaped correlation between plasma Se and obesity. WQS revealed the combined effects of four trace elements were negatively associated with central obesity. Plasma Zn and Se were negatively associated with obesity, and dietary Mn was positively associated with obesity. The combined action of the four plasma trace elements had a negative effect on obesity.

Dietary manganese supplementation decreases hepatic lipid deposition by regulating gene expression and enzyme activity involved in lipid metabolism in the liver of broilers

This study aimed to characterize the effects of different dietary forms of supplemental manganese (Mn) on hepatic lipid deposition, gene expression, and enzyme activity in liver fat metabolism in 42-d-old broiler chickens. In total 420 one-day-old Arbor Acres (AA) broilers (rooster:hen = 1:1) were assigned randomly based on body weight and sex to 1 of 6 treatments (10 replicate cages per treatment and 7 broilers per replicate cage) in a completely randomized design using a 2 (sex) × 3 (diet) factorial arrangement. The 3 diets were basal control diets without Mn supplementation and basal diets supplemented with either Mn sulfate or Mn proteinate. No sex × diet interactions were observed in any of the measured indexes; thus, the effect of diet alone was presented in this study. Dietary Mn supplementation increased Mn content in the plasma and liver, adipose triglyceride lipase (ATGL) activity, and ATGL mRNA and its protein expression in the liver by 5.3% to 24.0% (P < 0.05), but reduced plasma triglyceride (TG), total cholesterol, and low-density lipoprotein (LDL-C) levels, liver TG content, fatty acid synthase (FAS) and malic enzyme (ME) activities, mRNA expression of sterol-regulatory element-binding protein 1 (SREBP1), FAS, stearoyl-coA desaturase (SCD), and ME, as well as the protein expression of SREBP1 and SCD in the liver by 5.5% to 22.8% (P < 0.05). No differences were observed between the 2 Mn sources in all of the determined parameters. Therefore, it was concluded that dietary Mn supplementation, regardless of Mn source, decreased hepatic lipid accumulation in broilers by inhibiting SREBP1 and SCD expression, FAS and ME activities, and enhancing ATGL expression and activity.

SIRT1-NRF2-TFEB axis-mediated hepatic lipophagy alleviates the lipid deposition induced by high glucose in yellow catfish Pelteobagrus fulvidraco

Metabolic stress induces lipophagy, a crucial process in lipid catabolism, which is under the regulation of autophagy involving transcription factor EB (TFEB). However, the precise mechanisms underlying TFEB's control remain enigmatic. In this study, we focused on yellow catfish (Pelteobagrus fulvidraco) as the model to investigate lipophagy activation under high glucose-induced lipid deposition. We hypothesized that lipophagy mediates high glucose-induced lipid deposition and proposed the involvement of the SIRT1-NRF2-TFEB pathway in the activation of lipophagy. We found that there was a functional antioxidative responsive element (ARE) on the tfeb gene promoter; high glucose (HG) increased the nuclear translocation of nuclear factor E2-related factor 2 (NRF2) recruitment to the tfeb promoter; TFEB, whose expression is regulated by NRF2, mediated the HG-induced activation of lipophagy and lipolysis. Moreover, we found that HG increased the silencing information regulator 2 related enzymes 1 (SIRT1) expression, and that the SIRT1 mediates NRF2 translocation to the nucleus, increased TFEB expression and activated autophagy. In the glucose tolerance test, blood glucose increased rapidly and plateaued at 4-h glucose after injection and then declined until 48-h post-injection. Generally speaking, the transcript level and protein expression of SIRT1, NRF2, TFEB, microtubule-associated proteins 1A/1B light chain 3B (LC3B), and autophagy-related 6 (Beclin1) showed similar trend after glucose injection, and trends to increase and plateau at 4-h injection, then decline until 16-h post-injection, and finally increased until 48-h post-injection. These results indicated that the SIRT1-NRF2-TFEB axis-mediated lipophagy may be an adaptive response to glucose injection. Collectively, for the first time, we found that NRF2 was associated directly with TFEB-mediated transcriptional control of hepatic lipophagy, and that lipophagy helps to alleviate the HG-induced lipid deposition via SIRT1-NRF2-TFEB activation in yellow catfish.

Effects of Dietary Fish Meal Replaced by Fish Steak Meal on Growth Performance, Antioxidant Capacity, Intestinal Health and Microflora, Inflammatory Response, and Protein Metabolism of Large Yellow Croaker Larimichthys crocea

Although fish steak meal (FSM) is a potentially available protein source, its efficiency as a fish meal (FM) substitute remains unclear to date. To this end, this study was carried out to determine the effects of dietary FM replaced by FSM on growth performance, antioxidant capacity, intestinal health and microflora, inflammatory response, and protein metabolism of large yellow croaker. Five isolipidic and isonitrogenous diets were formulated by substituting FM with FSM at levels of 0% (FSM0, control diet), 25% (FSM25), 50% (FSM50), 75% (FSM75), and 100% (FSM100), and were fed to juvenile large yellow croaker for 8 weeks. Compared with the control diet, the replacement of 25% dietary FM with FSM did not markedly alter the weight gain (WG) and specific growth rate (SGR). When the FM substitution level was over 25%, WG and SGR markedly reduced. The intestinal structure observation found that the FSM75 and FSM100 diets markedly decreased villus height, villus width, and muscle thickness of the anterior intestine. The FSM75 and FSM100 diets significantly decreased enzyme activities of amylase (AMS), lipase (LPS), trypsin, catalase (CAT), and total superoxide dismutase (T-SOD) and the total antioxidant capacity (T-AOC), and increased the malondialdehyde (MDA) content in the liver of large yellow croaker. The mRNA expression levels of intestinal barrier and inflammatory response-related genes suggested that the FSM50, FSM75, and FSM100 diets significantly decreased the mRNA abundances of intestinal barrier-related genes and anti-inflammatory response-related genes, and increased the mRNA abundances of proinflammatory gene il-6 in the anterior intestine. The compositions of intestinal microflora displayed that the FSM50, FSM75, and FSM100 diets decreased relative abundances of Firmicutes phylum and increased relative abundances of Proteobacteria phylum. In addition, the results of protein expression levels showed that the phosphorylation level of mammalian target of rapamycin (mTOR) and 4E-binding protein 1 (4E-BP1) in FSM75 and FSM100 groups were markedly reduced. In conclusion, FSM can replace up to 25% dietary FM without compromising the growth performance, intestinal health, and protein metabolism of the large yellow croaker.

MnO2 nanoparticles and MnSO4 differentially affected hepatic lipid metabolism through miR-92a/acsl3-dependent de novo lipogenesis in yellow catfish Pelteobagrusfulvidraco

With the increasing production and use of MnO2 NPs and MnSO4 in various fields, their discharge into the aquatic environment is inevitable, which poses potential threats to aquatic organisms and humans. However, to date, few studies have been conducted to investigate the potential mechanism of the toxicity of MnO2 NPs, and a comprehensive understanding of the differences between this mechanism and the toxicity mechanism of inorganic Mn (MnSO4) is still lacking. Since lipid metabolism-relevant parameters have been widely recognized as novel biomarkers for risk assessment of environmental contaminants, the present study investigated the differential mechanisms of how MnO2 NPs and MnSO4 affect hepatic lipid metabolism in a freshwater fish yellow catfish. Compared to MnSO4, dietary MnO2 NPs caused liver injury, increased hepatic lipid accumulation and induced lipotoxicity, and up-regulated mRNA expression of de novo lipogenic genes. Moreover, MnO2 NPs downregulated the expression of miR-92a and miR-92b-3p, microRNAs involved in regulation of lipid metabolism, in the liver. Mechanistically, we found that acls3, an acetyl-coenzyme A synthetase, is target gene of miR-92a, and miR-92a-acsl3-dependent de novo lipogenesis contributes to lipid accumulation and lipotoxicity induced by MnO2 NPs. Collectively, these findings provided novel insights into mechanism whereby miRNAs mediate nanoparticles- and inorganic Mn-induced hepatic lipotoxicity and changes of lipid metabolism in vertebrates. Our findings also shed new perspective for ecotoxicity and ecological risk of MnO2 NPs and MnSO4 in aquatic environment.

Glycophagy mediated glucose-induced changes of hepatic glycogen metabolism via OGT1-AKT1-FOXO1Ser238 pathway

Glycophagy is the autophagy degradation of glycogen. However, the regulatory mechanisms for glycophagy and glucose metabolism remain unexplored. Herein, we demonstrated that high-carbohydrate diet (HCD) and high glucose (HG) incubation induced glycogen accumulation, AKT1 expression and AKT1-dependent phosphorylation of forkhead transcription factor O1 (FOXO1) at Ser238 in the liver tissues and hepatocytes. The glucose-induced FOXO1 phosphorylation at Ser238 prevents FOXO1 entry into the nucleus and the recruitment to the gabarapl1 promoter, reduces the gabarapl1 promoter activity, and inhibits glycophagy and glucose production. The glucose-dependent O-GlcNAcylation of AKT1 by OGT1 enhances the stability of AKT1 protein and promotes its binding with FOXO1. Moreover, the glycosylation of AKT1 is crucial for promoting FOXO1 nuclear translocation and inhibiting glycophagy. Our studies elucidate a novel mechanism for glycophagy inhibition by high carbohydrate and glucose via OGT1-AKT1-FOXO1^Ser238 pathway in the liver tissues and hepatocytes, which provides critical insights into potential intervention strategies for glycogen storage disorders in vertebrates, as well as human beings.

Association between Blood Manganese Levels and Visceral Adipose Tissue in the United States: A Population-Based Study

Background: Manganese (Mn) is an essential trace element with a narrow toxic margin for human health. The association between Mn exposure and adverse visceral adipose tissue (VAT) accumulation is unclear. Objective: This study aimed to estimate the associations of blood Mn levels with VAT mass or visceral obesity in the general population in the United States. Method: This cross-sectional study included data of 7297 individuals released by National Health and Nutrition Examination Survey (NHANES). VAT was quantified with dual-energy X-ray absorptiometry, and blood Mn was measured using inductively coupled plasma mass spectrometry. The generalized linear model and generalized additive model (GAM) were applied to estimate the linear and non-linear associations between Mn levels and VAT mass, respectively. Logistic regression was used to estimate the associations between blood Mn levels and the risk of visceral obesity. Results: Fully adjusted generalized linear regression revealed that individuals in the higher quantile of Mn had increased VAT mass compared with those in the lower quantile (β per quantile change = 0.025; 95% CI of 0.017, 0.033; p < 0.001). Positive associations were also observed in males and females (males: β per quantile change = 0.012, 95% CI of 0.002, 0.022 (p = 0.020); female: β per quantile change = 0.036; 95% CI of 0.023, 0.048 (p < 0.001)). The GAM illustrated that the non-linear associations between blood Mn levels and VAT mass were in U-shape patterns (effective degree of freedom >1 in total participants, males, and females). A stratified analysis found significant interactions between Mn and the family income-to-poverty ratio (PIR) in males, with stronger associations in males with a PIR < 1.3 (β = 0.109; 95% CI of 0.048, 0.170). Additional analyses revealed that individuals in the highest quantile of Mn had a 39% higher risk of visceral obesity (OR = 1.39; 95% CI of 1.15−1.69; p < 0.001). Conclusions: Higher blood Mn levels were positively associated with increased VAT mass and visceral obesity risk. The adverse VAT phenotype associated with excessive blood Mn levels should be further investigated.

Sirt3-Sod2-mROS-Mediated Manganese Triggered Hepatic Mitochondrial Dysfunction and Lipotoxicity in a Freshwater Teleost

Exposure to excessive manganese (Mn) is toxic to humans and animals. However, the toxic effects and mechanisms of excessive Mn influencing the vertebrates have been highly overlooked. In the present study, dietary Mn overload significantly increased hepatic lipid and Mn contents, decreased superoxide dismutase 2 (Sod2) activity, increased the Sod2 acetylation level, and induced mitochondrial dysfunction; Mn induced mitochondrial dysfunction through Mtf1/sirtuin 3 (Sirt3)-mediated acetylation of Sod2 at the sites K55 and K70. Meanwhile, mitochondrial oxidative stress was involved in Mn-induced lipotoxicity. Mechanistically, Mn-induced lipotoxicity was via oxidative stress-induced Hsf1 nucleus translocation and its DNA binding capacity to the regions of a peroxisome proliferator-activated receptor g (pparg) promoter, which in turn induced the transcription of lipogenic-related target genes. For the first time, our study demonstrated that Mn-induced hepatic lipotoxicity via a mitochondrial oxidative stress-dependent Hsf1/Pparg pathway and Mtf1/sirt3-mediated Sod2 acetylation participated in mitochondrial dysfunction. Considering that lipid metabolism and lipotoxicity are widely used as the biomarkers for environmental assessments of pollutants, our study provided innovative and important insights into Mn toxicological and environmental evaluation in aquatic environments.