Aflatoxin B1 exposure triggers hepatic lipotoxicity via p53 and perilipin 2 interaction-mediated mitochondria-lipid droplet contacts: An in vitro and in vivo assessment

Fluorescent Probe as Dual-Organelle Localizer Through Differential Proton Gradients Between Lipid Droplets and Mitochondria

Dual-organelle molecular localizers represent powerful new tools allowing the exploration of interorganelle physical contacts and subcellular chemical communication. Here, we describe new dynamic molecular probes to localize mitochondria and lipid droplets taking advantage of the differential proton gradients present in these organelles as well as the activity of mitochondrial esterase. We unveil their potential utility when organelle retention mechanisms and proton gradients are synchronized, an insight that has not been documented previously. Our discoveries indicate that dual-organelle probes serve as a valuable multiplexing assay during starvation-induced autophagy. The pioneering molecular mechanism they employ opens doors to avoid using labile esters such as acetoxymethyl derivatives which are not optimal in imaging microscopy assays.

Macrophage AHR-TLR4 cross-talk drives p-STAT3 (Ser727)-mediated mitochondrial oxidative stress and upregulates IDO/ICAM-1 in the steatohepatitis induced by aflatoxin B1

Aflatoxin B1 (AFB1) is a major mycotoxin contaminant showing in the environment and foods. In this study, the molecular initiating events (MIEs) of AFB1-induced steatohepatitis were explored in mice and human cell model. We observed dose-dependent steatohepatitis in the AFB1-treated mice, including triglyceride accumulation, fibrotic collagen secretion, enrichment of CD11b + and F4/80+ macrophages/Kupffer cells, cell death, lymphocytes clusters and remarkable atrophy areas. The gut barrier and gut-microbiota were also severely damaged after the AFB1 treatment and pre-conditioned colitis in the experimental mice aggravated the steatohepatitis phenotypes. We found that macrophages cells can be pro-inflammatorily activated to M1-like phenotype by AFB1 through an AHR/TLR4/p-STAT3 (Ser727)-mediated mitochondrial oxidative stress. The phenotypes can be rescued by AHR inhibitors in the mice model and human cell model. We further showed that this signaling axis is based on the cross-talk interaction between AHR and TLR4. Gene knock-up experiment found that the signaling is dependent on AFB1 ligand-binding with AHR, but not protein expressions of TLR4. The signaling elevated NLRP3 and two immune metabolic enzymes ICAM-1 and IDO that are associated with macrophage polarization. Results from intervention experiments with natural anti-oxidant and AHR inhibitor CH223191 suggest that the macrophage polarization may rely on AHR and ROS. Our study provides novel and critical references to the food safety and public health regulation of AFB1.

Downregulation of PLIN2 in human dermal fibroblasts impairs mitochondrial function in an age-dependent fashion and induces cell senescence via GDF15

Perilipin 2 (PLIN2) is a lipid droplet (LD)-coating protein playing important roles in lipid homeostasis and suppression of lipotoxicity in different tissues and cell types. Recently, a role for PLIN2 in supporting mitochondrial function has emerged. PLIN2 dysregulation is involved in many metabolic disorders and age-related diseases. However, the exact consequences of PLIN2 dysregulation are not yet completely understood. In this study, we knocked down (KD) PLIN2 in primary human dermal fibroblasts (hDFs) from young (mean age 29 years) and old (mean age 71 years) healthy donors. We have found that PLIN2 KD caused a decline of mitochondrial function only in hDFs from young donors, while mitochondria of hDFs from old donors (that are already partially impaired) did not significantly worsen upon PLIN2 KD. This mitochondrial impairment is associated with the increased expression of the stress-related mitokine growth differentiation factor 15 (GDF15) and the induction of cell senescence. Interestingly, the simultaneous KD of PLIN2 and GDF15 abrogated the induction of cell senescence, suggesting that the increase in GDF15 is the mediator of this phenomenon. Moreover, GDF15 KD caused a profound alteration of gene expression, as observed by RNA-Seq analysis. After a more stringent analysis, this alteration remained statistically significant only in hDFs from young subjects, further supporting the idea that cells from old and young donors react differently when undergoing manipulation of either PLIN2 or GDF15 genes, with the latter being likely a downstream mediator of the former.

Dual modal improved enzyme-linked immunosorbent assay for aflatoxin B1 detection inspired by the interaction of amines with Prussian blue nanoparticles

This work reports an improved enzyme-linked immunosorbent assay (ELISA) via the interaction between prussian blue nanoparticles (PBNPs) and amines for aflatoxin B1 (AFB1) detection. The effect of different amines on the structure and properties of PBNPs was systematically investigated. Amines with pKb < 7, like ethylenediamine (EDA), can decompose structure of PBNPs, leading to the reduction of extinction coefficient and photothermal effect. Whereas, amines with large pKb > 7, such as o-phenylenediamine (OPD), could undergo catalytic oxidation by PBNPs, resulting in the production of fluorescent and colored oxidation products. Accordingly, EDA and OPD were used to construct improved ELISA. Specifically, silica nanoparticles, on which AFB1 aptamer and amino binding agent (ethylenediaminetetraacetic acid disodium salt, EDTA•2Na) were previously assembled via carboxyl-amino linkage, are anchored to microplates by AFB1 and antibody. EDA concentration can be regulated by EDTA•2Na to affect extinction coefficient and photothermal effect of PBNPs, thereby achieving visual colorimetric and portable photothermal signal readout (Model 1). OPD concentration can also be controlled by EDTA•2Na, thus generating colorimetric and ultrasensitive fluorescent signals through PBNPs catalysis (Model 2). The proposed strategy not only opens new avenue for signal readout mode of biosensing, but also provides universal technique for hazards.

miR-20a-5p targeting mfn2-mediated mitochondria-lipid droplet contacts regulated differential changes in hepatic lipid metabolism induced by two Mn sources in yellow catfish

Understanding the hazards of different forms of metal elements provided innovative insights into their toxicity and environmental risk assessment. To date, few studies had been conducted to investigate the differential effects and mechanisms of MnO2 NPs and MnSO4, two widely distributed environmental pollutants, on hepatic toxicity and lipid metabolism since lipid metabolism-relevant parameters were broadly used as biomarkers for risk assessment of hazardous contaminants. Thus, using yellow catfish Pelteobagrus fulvidraco, an ecologically and economically important freshwater fish as the model, the present study investigated the differential effects and mechanisms of MnO2 NPs and MnSO4 influencing hepatic lipid metabolism. Compared to MnSO4, MnO2 NPs increased hepatic Mn content, induced lipotoxicity, up-regulated the mRNA expression of lipogenic genes, increased peridroplet mitochondrial (PDM) contents, intensified the contact between mitochondria and lipid droplets (LDs), and downregulated miR-20a-5p abundance. Importantly, miR-20a-5p targeted mfn2, which mediated the contact between mitochondria and LDs and influenced changes in lipid metabolism induced by MnO2 NPs. Mechanistically, the direct Mfn2-Plin2 binding and Mfn2 GTPase activity promoted the MnO2 NPs-induced interactions between mitochondria and LDs, which in turn influenced MnO2 NPs-induced changes in hepatic lipid metabolism. For the first time, our findings indicated the significant differences between the changes in body metabolism induced by nanoparticles and inorganic elements, which helped to illuminate different mechanisms governing the responses of aquatic vertebrates to hazardous metal pollutants (MnO2 NPs and MnSO4).

Cyclosporine-A induced cytotoxicity within HepG2 cells by inhibiting PXR mediated CYP3A4/CYP3A5/MRP2 pathway

Cyclosporine-A (CsA) is currently used to treat immune rejection after organ transplantation as a commonly used immunosuppressant. Liver injury is one of the most common adverse effects of CsA, whose precise mechanism has not been fully elucidated. Pregnane X receptor (PXR) plays a critical role in mediating drug-induced liver injury as a key regulator of drug and xenobiotic clearance. As a nuclear receptor, PXR transcriptionally upregulates the expression of drug-metabolizing enzymes and drug transporters, including cytochrome P4503A (CPY3A) and multidrug resistance-associated protein 2 (MRP2). Our study established CsA-induced cytotoxic hepatocytes in an in vitro model, demonstrating that CsA dose-dependently increased the aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) level secreted in the HepG2 cell supernatant, as well as viability and oxidative stress of HepG2 cells. CsA also dose-dependently decreased the PXR, CYP3A4, CPY3A5, and MRP2 levels of HepG2 cells. Mechanistically, altering the expression of PXR, CYP3A4, CYP3A5, and MRP2 affected the impact of CsA on AST and LDH levels. Moreover, altering the expression of PXR also changed the level of CYP3A4, CPY3A5, and MRP2 of HepG2 cells treated by CsA. Our presented findings provide experimental evidence that CsA-induced liver injury is PXR tightly related. We suggest that PXR represents an attractive target for therapy of liver injury due to its central role in the regulation of the metabolizing enzymes CYP3A and MRP2-mediated bile acid transport and detoxification.

AFB1 Triggers Lipid Metabolism Disorders through the PI3K/Akt Pathway and Mediates Apoptosis Leading to Hepatotoxicity

As the most prevalent mycotoxin in agricultural products, aflatoxin B1 not only causes significant economic losses but also poses a substantial threat to human and animal health. AFB1 has been shown to increase the risk of hepatocellular carcinoma (HCC) but the underlying mechanism is not thoroughly researched. Here, we explored the toxicity mechanism of AFB1 on human hepatocytes following low-dose exposure based on transcriptomics and lipidomics. Apoptosis-related pathways were significantly upregulated after AFB1 exposure in all three hES-Hep, HepaRG, and HepG2 hepatogenic cell lines. By conducting a comparative analysis with the TCGA-LIHC database, four biomarkers (MTCH1, PPM1D, TP53I3, and UBC) shared by AFB1 and HCC were identified (hazard ratio > 1), which can be used to monitor the degree of AFB1-induced hepatotoxicity. Simultaneously, AFB1 induced abnormal metabolism of glycerolipids, sphingolipids, and glycerophospholipids in HepG2 cells (FDR < 0.05, impact > 0.1). Furthermore, combined analysis revealed strong regulatory effects between PIK3R1 and sphingolipids (correlation coefficient > 0.9), suggesting potential mediation by the phosphatidylinositol 3 kinase (PI3K) /protein kinase B (AKT) signaling pathway within mitochondria. This study revealed the dysregulation of lipid metabolism induced by AFB1 and found novel target genes associated with AFB-induced HCC development, providing reliable evidence for elucidating the hepatotoxicity of AFB as well as assessing food safety risks.

Immunotoxicity and the mechanisms of aflatoxin B1-induced growth retardation in shrimp and alleviating effects of bile acids

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins prevalent in the environment and food chain, posing severe health risks to humans and animals. Bile acids are natural detergents synthesized from cholesterol and play a key role in the excretion of toxins in vertebrates. Here, pacific white shrimp (Litopenaeus vannamei) served as an animal model to examine the toxicity mechanisms of AFB1 and assess the potential alleviating effects of bile acids against AFB1. Our results revealed that AFB1 exposure significantly inhibited the growth performance and immune response of shrimp, accompanied by AFB1 accumulation and histological damage. Mechanistically, AFB1-induced DNA damage activated DNA repair mechanisms and induced the arrest of cell cycle via the ATR-cyclin B/cdc2 pathway. Additionally, AFB1 directly suppressed the immune response and growth performance of shrimp by inhibiting Toll and IMD pathways and the secretion of digestive enzymes. Notably, dietary bile acids significantly reduced AFB1 accumulation and alleviated AFB1-induced growth retardation and immunotoxicity in shrimp, and CCKAR, ATR, and Relish may be key mediators of the alleviating effects of bile acids. Our study provided new insights into the toxicity mechanisms of AFB1 in invertebrates and highlighted the potential of bile acids to alleviate AFB1 toxicity.

Rab7a-mTORC1 signaling-mediated cholesterol trafficking from the lysosome to mitochondria ameliorates hepatic lipotoxicity induced by aflatoxin B1 exposure

Aflatoxin B1 (AFB1) is a common contaminant in many foodstuffs and is considered a public health concern worldwide due to its hepatotoxicity caused by lipid metabolism disorders. However, the molecular mechanism underlying AFB1-induced lipotoxicity-dependent liver injury via regulating cholesterol metabolism remains unclear. We established a cholesterol trafficking disorder-mediated hepatic lipotoxicity model with AFB1 mixture exposure in vitro (HepaRG and HepG2 cells, 1.6 μM for 36 h) and in vivo (C57BL/6 mice, 3 mg kg^-1, i.g., every other day for 6 weeks). In vitro, the interaction between lysosomal Niemann-Pick type C1 (NPC1) protein and mitochondrial translocator protein (TSPO) regulated lipotoxicity induced by AFB1 mixture exposure, including lysosomal membrane permeabilization and mitochondria-dependent necroptosis. Moreover, the downregulation of lysosomal Ras-associated protein 7a (Rab7a) enhanced the mammalian target of rapamycin complex 1 (mTORC1)-mediated disorders of cholesterol trafficking from the lysosome to mitochondria. Furthermore, cholesterol trafficking disorder-mediated hepatic lipotoxicity induced by the low-dose level of AFB1 exposure was relieved by genetic or pharmaceutic activation of Rab7a to inhibit mTORC1 in vitro and ex vivo. In vivo, mTORC1 inhibitor (Torin1, 4 mg kg^-1, i.p., every other day for 3 weeks) alleviated the cholesterol trafficking disorder-mediated hepatic lipotoxicity via upregulating the molecular machinery of lysosomes and mitochondria contact mediated by NPC1 and TSPO interaction in the low dose of AFB1 exposure. Altogether, our data suggested a novel mechanism that lysosomal Rab7a-mTORC1 signaling determined the cholesterol trafficking regulated by NPC1-TSPO from the lysosome to mitochondria, which promoted hepatic lipotoxicity via lysosomal quality control and mitochondria-dependent necroptosis signaling pathways in chemical mixture exposure.