Proteomic profiling of cellular steatosis with concomitant oxidative stress in vitro

Future Perspectives in Oxidative Stress in Trisomy 13 and 18 Evaluation

Autosomal aneuploidies are the most frequently occurring congenital abnormalities and are related to many metabolic disorders, hormonal dysfunctions, neurotransmitter abnormalities, and intellectual disabilities. Trisomies are generated by an error of chromosomal segregation during cell division. Accumulating evidence has shown that deregulated gene expression resulting from the triplication of chromosomes 13 and 18 is associated with many disturbed cellular processes. Moreover, a disturbed oxidative stress status may be implicated in the occurrence of fetal malformations. Therefore, a literature review was undertaken to provide novel insights into the evaluation of trisomy 13 (T13) and 18 (T18) pathogeneses, with a particular concern on the oxidative stress. Corresponding to the limited literature data focused on factors leading to T13 and T18 phenotype occurrence, the importance of oxidative stress evaluation in T13 and T18 could enable the determination of subsequent disturbed metabolic pathways, highlighting the related role of mitochondrial dysfunction or epigenetics. This review illustrates up-to-date T13 and T18 research and discusses the strengths, limitations, and possible directions for future studies. The progressive unification of trisomy-related research protocols might provide potential medical targets in the future along with the implementation of the foundation of modern prenatal medicine.

Cell Models and Omics Techniques for the Study of Nonalcoholic Fatty Liver Disease: Focusing on Stem Cell-Derived Cell Models

Nonalcoholic fatty liver disease (NAFLD) is now the leading cause of chronic liver disease in western countries. The molecular mechanisms leading to NAFLD are only partially understood, and effective therapeutic interventions are clearly needed. Therefore, preclinical research is required to improve knowledge about NAFLD physiopathology and to identify new therapeutic targets. Primary human hepatocytes, human hepatic cell lines, and human stem cell-derived hepatocyte-like cells exhibit different hepatic phenotypes and have been widely used for studying NAFLD pathogenesis. In this paper, apart from employing the different in vitro cell models for the in vitro assessment of NAFLD, we also reviewed other approaches (metabolomics, transcriptomics, and high-content screening). We aimed to summarize the characteristics of different cell types and methods and to discuss their major advantages and disadvantages for NAFLD modeling.

A human pluripotent stem cell model for the analysis of metabolic dysfunction in hepatic steatosis

Nonalcoholic fatty liver disease (NAFLD) is currently the most prevalent form of liver disease worldwide. This term encompasses a spectrum of pathologies, from benign hepatic steatosis to non-alcoholic steatohepatitis, which have, to date, been challenging to model in the laboratory setting. Here, we present a human pluripotent stem cell (hPSC)-derived model of hepatic steatosis, which overcomes inherent challenges of current models and provides insights into the metabolic rewiring associated with steatosis. Following induction of macrovesicular steatosis in hepatocyte-like cells using lactate, pyruvate, and octanoate (LPO), respirometry and transcriptomic analyses revealed compromised electron transport chain activity. 13C isotopic tracing studies revealed enhanced TCA cycle anaplerosis, with concomitant development of a compensatory purine nucleotide cycle shunt leading to excess generation of fumarate. This model of hepatic steatosis is reproducible, scalable, and overcomes the challenges of studying mitochondrial metabolism in currently available models.

Validation of Reference Genes for Gene Expression Studies by RT-qPCR in HepaRG Cells during Toxicity Testing and Disease Modelling

Gene expression analysis by quantitative real-time polymerase chain reaction (RT-qPCR) is routinely used in biomedical studies. The reproducibility and reliability of the data fundamentally depends on experimental design and data interpretation. Despite the wide application of this assay, there is significant variation in the validation process of gene expression data from research laboratories. Since the validity of results depends on appropriate normalisation, it is crucial to select appropriate reference gene(s), where transcription of the selected gene is unaffected by experimental setting. In this study we have applied geNorm technology to investigate the transcription of 12 ‘housekeeping’ genes for use in the normalisation of RT-qPCR data acquired using a widely accepted HepaRG hepatic cell line in studies examining models of pre-clinical drug testing. geNorm data identified a number of genes unaffected by specific drug treatments and showed that different genes remained invariant in response to different drug treatments, whereas the transcription of ‘classical’ reference genes such as GAPDH (glyceralde- hyde-3-phosphate dehydrogenase) was altered by drug treatment. Comparing data normalised using the reference genes identified by geNorm with normalisation using classical housekeeping genes demonstrated substantial differences in the final results. In light of cell therapy application, RT-qPCR analyses has to be carefully evaluated to accurately interpret data obtained from dynamic cellular models undergoing sequential stages of phenotypic change.

Proteomic Analysis Reveals Novel Mechanisms by Which Polychlorinated Biphenyls Compromise the Liver Promoting Diet-Induced Steatohepatitis

Environmental pollution contributes to fatty liver disease pathogenesis. Polychlorinated biphenyl (PCB) exposures have been associated with liver enzyme elevation and suspected steatohepatitis in cohort studies. Male mice treated with the commercial PCB mixture, Aroclor 1260 (20 mg/kg), and fed high fat diet (HFD) for 12 weeks developed steatohepatitis. Receptor-based modes of action including inhibition of the epidermal growth factor (EGF) receptor were previously proposed, but other mechanisms likely exist. Objectives were to identify and validate the pathways, transcription factors, and mechanisms responsible for the steatohepatitis associated with PCB and HFD coexposures. Comparative proteomics analysis was performed in archived mouse liver samples from the aforementioned chronic exposure study. Pathway and transcription factor analysis (TFA) was performed, and selected results were validated. Liver proteomics detected 1103 unique proteins. Aroclor 1260 upregulated 154 and downregulated 93 of these. Aroclor 1260 + HFD coexposures affected 55 pathways including glutathione metabolism, intermediary metabolism, and cytoskeletal remodeling. TFA of Aroclor 1260 treatment demonstrated alterations in the function of 42 transcription factors including downregulation of NRF2 and key nuclear receptors previously demonstrated to protect against steatohepatitis (e.g., HNF4α, FXR, PPARα/δ/γ, etc.). Validation studies demonstrated that Aroclor 1260 significantly reduced HNF4α protein levels, while Aroclor 1260 + HFD reduced expression of the HNF4α target gene, albumin, in vivo. Aroclor 1260 attenuated EGF-dependent HNF4α phosphorylation and target gene activation in vitro. Aroclor 1260 reduced levels of NRF2, its target genes, and glutathione in vivo. Aroclor 1260 attenuated EGF-dependent NRF2 upregulation, in vitro. Aroclor 1260 indirectly activated hepatic stellate cells in vitro via induction of hepatocyte-derived TGFβ. PCB exposures adversely impacted transcription factors regulating liver protection, function, and fibrosis. PCBs, thus, compromised the liver by reducing its protective responses against nutritional stress to promote diet-induced steatohepatitis. The identified mechanisms by which environmental pollutants influence fatty liver disease pathogenesis require confirmation in humans.

Hepatic signalling disruption by pollutant Polychlorinated biphenyls in steatohepatitis

BACKGROUND

Polychlorinated biphenyl-mediated steatohepatitis has been shown to be due in part to inhibition of epidermal growth factor receptor (EGFR) signalling. EGFR signalling regulates many facets of hepatocyte function, but it is unclear which other kinases and pathways are involved in the development of toxicant-associated steatohepatitis (TASH).

METHODS

Comparative hepatic phosphoproteomic analysis was used to identify which kinases were affected by either PCB exposure (Aroclor 1260 mixture), high fat diet (HFD), or their interaction in a chronic exposure model of TASH. Cellular assays and western blot analysis were used to validate the phosphoproteomic findings.

RESULTS

1760 unique phosphorylated peptides were identified and of those 588 were significantly different. PCB exposure and dietary interaction promoted a near 25% reduction of hepatic phospho-peptides. Leptin and insulin signalling were pathways highly affected by PCB exposure and liver necrosis was a pathologic ontology over represented due to interaction between PCBs and a HFD. Casein kinase 2 (CK2), Extracellular regulated kinase (ERK), Protein kinase B (AKT), and Cyclin dependent kinase (CDK) activity were demonstrated to be downregulated after PCB exposure and this downregulation was exacerbated with a HFD. PCB exposure led to a loss of hepatic CK2 subunit expression limiting CK2 kinase activity and negatively regulating caspase-3 (CASP3). PCBs promoted secondary necrosis in vitro validating the latter observation. The loss of hepatic phosphoprotein signalling appeared to be due to decreased signal transduction rather than phosphatase upregulation.

CONCLUSIONS

PCBs are signal disrupting chemicals that promote secondary necrosis through affecting a myriad of liver processes including metabolism and cellular maintenance. PCB exposure, particularly with interaction with a HFD greatly down-regulates the hepatic kinome. More data are needed on signalling disruption and its impact on liver health.

Human-based systems: Mechanistic NASH modelling just around the corner?

Non-alcoholic steatohepatitis (NASH) is a chronic liver disease characterized by excessive triglyceride accumulation in the liver accompanied by inflammation, cell stress and apoptosis. It is the tipping point to the life-threatening stages of non-alcoholic fatty liver disease (NAFLD). Despite the high prevalence of NASH, up to five percent of the global population, there are currently no approved drugs to treat this disease. Animal models, mostly based on specific diets and genetic modifications, are often employed in anti-NASH drug development. However, due to interspecies differences and artificial pathogenic conditions, they do not represent the human situation accurately and are inadequate for testing the efficacy and safety of potential new drugs. Human-based in vitro models provide a more legitimate representation of the human NASH pathophysiology and can be used to investigate the dysregulation of cellular functions associated with the disease. Also in silico methodologies and pathway-based approaches using human datasets, may contribute to a more accurate representation of NASH, thereby facilitating the quest for new anti-NASH drugs. In this review, we describe the molecular components of NASH and how human-based tools can contribute to unraveling the pathogenesis of this disease and be used in anti-NASH drug development. We also propose a roadmap for the development and application of human-based approaches for future investigation of NASH.