Adverse outcome pathway for pregnane X receptor-induced hypercholesterolemia

Activation of nuclear receptor pregnane-X-receptor protects against abdominal aortic aneurysm by inhibiting oxidative stress

Abdominal aortic aneurysm (AAA) is a life-threatening condition, but effective medications to prevent its progression and rupture are currently lacking. The nuclear receptor pregnane-X-receptor (PXR) plays a crucial role in vascular homeostasis. However, the role of PXR in AAA development remains unknown. We first detected the PXR expression in human and murine AAA tissues by RT-qPCR and Western blot. To investigate the potential role of PXR in the development of AAA, we used adeno-associated virus-mediated overexpression of PXR and pharmacological activation of PXR by ginkgolide A (GA) in mouse AAA models induced by both angiotensin II (AngII) and calcium phosphate [Ca3(PO4)2]. The underlying mechanism was further explored using RNA-sequencing and molecular biological analyses. We found a significant decrease in both mRNA and protein levels of PXR in both human and murine aortic smooth muscle cells from AAA tissues, accompanied with phenotypic switching of vascular smooth muscle cell and increased oxidative stress. PXR overexpression in abdominal aortas and GA treatment successfully suppressed AAA formation in both mouse AAA models. RNA-sequencing data revealed that PXR activation inhibited gamma-aminobutyric acid type A receptor subunit alpha3 (GABRA3) expression. Additional mechanistic studies identified that PXR suppressed AAA through mitigating GABRA3-induced reactive oxygen species (ROS) generation and subsequent phosphorylation of c-Jun N-terminal kinase (JNK). Interestingly, p-JNK was found to induce ubiquitin-proteasome degradation of PXR. In summary, our data unveiled, for the first time, the protective role of PXR against AAA pathogenesis by inhibiting oxidative stress. These findings suggested PXR as a promising therapeutic target for AAA.

Retinoid X receptor heterodimers in hepatic function: structural insights and therapeutic potential

Nuclear receptors (NRs) are key regulators of multiple physiological functions and pathological changes in the liver in response to a variety of extracellular signaling changes. Retinoid X receptor (RXR) is a special member of the NRs, which not only responds to cellular signaling independently, but also regulates multiple signaling pathways by forming heterodimers with various other NR. Therefore, RXR is widely involved in hepatic glucose metabolism, lipid metabolism, cholesterol metabolism and bile acid homeostasis as well as hepatic fibrosis. Specific activation of particular dimers regulating physiological and pathological processes may serve as important pharmacological targets. So here we describe the basic information and structural features of the RXR protein and its heterodimers, focusing on the role of RXR heterodimers in a number of physiological processes and pathological imbalances in the liver, to provide a theoretical basis for RXR as a promising drug target.

Multigenerational effects of disperse blue 79 at environmentally relevant concentrations on zebrafish (Danio rerio) fecundity: An integrated approach

The brominated azo dye (BAD) Disperse Blue (DB79) is a widespread environmental pollutant. The long-term toxicological effects of DB79 and the mechanisms thereof must be understood to allow assessment of the risks of DB79 pollution. A dual-omics approach employing in silico analysis, bioinformatics, and in vitro bioassays was used to investigate the transgenerational (F0-F2) toxicity of DB79 in zebrafish at environmentally relevant concentrations and identify molecular initiating events and key events associated with DB79-induced fertility disorders. Exposure to 500 µg/L DB79 decreased fecundity in the F0 and F1 generations by > 30 % and increased the condition factor of the F1 generation 1.24-fold. PPARα/RXR and PXR ligand binding activation were found to be critical molecular initiating events associated with the decrease in fecundity. Several key events (changes in fatty acid oxidation and uptake, lipoprotein metabolism, and xenobiotic metabolism and transport) involved in lipid dysregulation and xenobiotic disposition were found to be induced by DB79 through bioinformatic annotation using dual-omics data. The biomolecular underpinnings of decreased transgenerational fertility in zebrafish attributable to BAD exposure were elucidated and novel biomolecular targets in the adverse outcome pathway framework were identified. These results will inform future studies and facilitate the development of mitigation strategies.

Construction of an adverse outcome pathway framework for arsenic-induced lung cancer using a network-based approach

Environmental pollutants are considered as a cause of tumorigenesis, but approaches to assess their risk of causing tumors remain insufficient. As an alternative approach, the adverse outcome pathway (AOP) framework is used to assess the risk of tumors caused by environmental pollutants. Arsenic is a pollutant associated with lung cancer, but early assessment of lung cancer risk is lacking. Therefore, we applied the AOP framework to arsenic-induced lung cancer. A systematic review revealed increased risks of lung cancer following exposure to a range of arsenic concentrations in drinking water (OR = 1.83, 95 % CI = 1.46-2.30). We obtained, from public databases, genes related to risk of arsenic-induced lung cancer. Then, Cox and LASSO regressions were used to screen target genes from the risk genes. Subsequently, target genes, phenotypes, and pathways were used to construct the computational AOP network, which was determined by Cytoscape to have 156 edges and 45 nodes. Further, target genes, phenotypes, and pathways were used as molecular initiating events and key events to construct the AOP framework depending on upstream and downstream relationships. In the AOP framework, by Weight of Evidence, arsenic exposure increased levels of EGFR, activated the PI3K/AKT pathway, regulated cell proliferation by promoting the G1/S phase transition, and caused generation of lung cancers. External validation was achieved through arsenite-induced, malignant transformed human bronchial epithelial (HBE) cells. Overall, these results, by integration into existing data to construct an AOP framework, provide insights into the assessment of lung cancer risk for arsenic exposure. Special attention needs to be focused on populations with low-dose arsenic exposure.

Moldable Plastics (Polycaprolactone) can be Acutely Toxic to Developing Zebrafish and Activate Nuclear Receptors in Mammalian Cells

Popularized on social media, hand-moldable plastics are formed by consumers into tools, trinkets, and dental prosthetics. Despite the anticipated dermal and oral contact, manufacturers share little information with consumers about these materials, which are typically sold as microplastic-sized resin pellets. Inherent to their function, moldable plastics pose a risk of dermal and oral exposure to unknown leachable substances. We analyzed 12 moldable plastics advertised for modeling and dental applications and determined them to be polycaprolactone (PCL) or thermoplastic polyurethane (TPU). The bioactivities of the most popular brands advertised for modeling applications of each type of polymer were evaluated using a zebrafish embryo bioassay. While water-borne exposure to the TPU pellets did not affect the targeted developmental end points at any concentration tested, the PCL pellets were acutely toxic above 1 pellet/mL. The aqueous leachates of the PCL pellets demonstrated similar toxicity. Methanolic extracts from the PCL pellets were assayed for their bioactivity using the Attagene FACTORIAL platform. Of the 69 measured end points, the extracts activated nuclear receptors and transcription factors for xenobiotic metabolism (pregnane X receptor, PXR), lipid metabolism (peroxisome proliferator-activated receptor γ, PPARγ), and oxidative stress (nuclear factor erythroid 2-related factor 2, NRF2). By nontargeted high-resolution comprehensive two-dimensional gas chromatography (GC × GC-HRT), we tentatively identified several compounds in the methanolic extracts, including PCL oligomers, a phenolic antioxidant, and residues of suspected antihydrolysis and cross-linking additives. In a follow-up zebrafish embryo bioassay, because of its stated high purity, biomedical grade PCL was tested to mitigate any confounding effects due to chemical additives in the PCL pellets; it elicited comparable acute toxicity. From these orthogonal and complementary experiments, we suggest that the toxicity was due to oligomers and nanoplastics released from the PCL rather than chemical additives. These results challenge the perceived and assumed inertness of plastics and highlight their multiple sources of toxicity.

AhR, PXR and CAR: From Xenobiotic Receptors to Metabolic Sensors

Traditionally, xenobiotic receptors are known for their role in chemical sensing and detoxification, as receptor activation regulates the expression of various key enzymes and receptors. However, recent studies have highlighted that xenobiotic receptors also play a key role in the regulation of lipid metabolism and therefore function also as metabolic sensors. Since dyslipidemia is a major risk factor for various cardiometabolic diseases, like atherosclerosis and non-alcoholic fatty liver disease, it is of major importance to understand the molecular mechanisms that are regulated by xenobiotic receptors. In this review, three major xenobiotic receptors will be discussed, being the aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR) and the constitutive androstane receptor (CAR). Specifically, this review will focus on recent insights into the metabolic functions of these receptors, especially in the field of lipid metabolism and the associated dyslipidemia.