Increased sensitivity of apolipoprotein E knockout mice to copper-induced oxidative injury to the liver

Copper exposure induces mitochondrial dysfunction and hepatotoxicity via the induction of oxidative stress and PERK/ATF4 -mediated endoplasmic reticulum stress

Copper is an essential trace element, and excessive exposure could result in hepatoxicity, however, the underlying molecular mechanisms remain incompletely understood. The present study is aimed to investigate the molecular mechanisms of copper sulfate (CuSO4) exposure-induced hepatoxicity both in vivo and in vitro. In vitro, HepG2 and L02 cells were exposed to various doses of CuSO4 for 24 h. Cell viability, ROS production, oxidative stress biomarkers, mitochondrial functions, ultrastructure, intracellular calcium (Ca2+) concentration, and the expression of proteins related to mitochondrial apoptosis and endoplasmic reticulum (ER) stress were assessed. In vivo, C57BL/6 mice were treated with CuSO4 at doses of 10 and 30 mg/kg BW/day and co-treated with 4-PBA at 100 mg/kg BW/day for 35 days. Subsequently, liver function, histopathological features, and protein expression were evaluated. Results found that exposure to CuSO4 at concentrations of 100-400 μM for 24 h significantly decreased the viabilities of HepG2 and L02 cells and it was in a dose-dependent manner. Additionally, CuSO4 exposure induced significant oxidative stress and mitochondrial dysfunction in HepG2 cells, which were partially ameliorated by the antioxidant N-acetylcysteine (NAC). Furthermore, CuSO4 exposure prominently triggered ER stress, as evidenced by the upregulation of GRP94, GRP78, phosphorylated forms of PERK and eIF2α, and CHOP proteins in livers of mice and HepG2 cells. NAC treatment significantly inhibited CuSO4 exposure -induced ER stress in HepG2 cells. Pharmacological inhibition of ER stress through co-treatment with 4-PBA and the PERK inhibitor GSK2606414, as well as genetic knockdown of ATF4, partially mitigated CuSO4-induced cytotoxicity in HepG2 cells by reducing mitochondrial dysfunction and inhibiting the mitochondrial apoptotic pathway. Moreover, 4-PBA treatment significantly attenuated CuSO4-induced caspase activation and hepatoxicity in mice. In conclusion, these results reveal that CuSO4-induced hepatotoxicity involves mitochondrial dysfunction and ER stress by activating oxidative stress induction and PERK/ATF4 pathway.

Dynamic co-expression modular network analysis in nonalcoholic fatty liver disease

Background

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease affecting people’s health worldwide. Exploring the potential biomarkers and dynamic networks during NAFLD progression is urgently important.

Material and methods

Differentially expressed genes (DEGs) in obesity, NAFL and NASH were screened from GSE126848 and GSE130970, respectively. Gene set enrichment analysis of DEGs was conducted to reveal the Gene Ontology (GO) biological process in each period. Dynamic molecular networks were constructed by DyNet to illustrate the common and distinct progression of health- or obesity-derived NAFLD. The dynamic co-expression modular analysis was carried out by CEMiTool to elucidate the key modulators, networks, and enriched pathways during NAFLD.

Results

A total of 453 DEGs were filtered from obesity, NAFL and NASH periods. Function annotation showed that health-NAFLD sequence was mainly associated with dysfunction of metabolic syndrome pathways, while obesity-NAFLD sequence exhibited dysregulation of Cell cycle and Cellular senescence pathways. Nine nodes including COL3A1, CXCL9, CYCS, CXCL10, THY1, COL1A2, SAA1, CDKN1A, and JUN in the dynamic networks were commonly identified in health- and obesity-derived NAFLD. Moreover, CYCS, whose role is unknown in NAFLD, possessed the highest correlation with NAFLD activity score, lobular inflammation grade, and the cytological ballooning grade. Dynamic co-expression modular analysis showed that module 4 was activated in NAFL and NASH, while module 3 was inhibited at NAFLD stages. Module 3 was negatively correlated with CXCL10, and module 4 was positively correlated with COL1A2 and THY1.

Conclusion

Dynamic network analysis and dynamic gene co-expression modular analysis identified a nine-gene signature as the potential key regulator in NAFLD progression, which provided comprehensive regulatory mechanisms underlying NAFLD progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-021-00196-8.

Opposing Roles of apolipoprotein E in aging and neurodegeneration

Apolipoprotein E (APOE) effects on brain function remain controversial. Removal of APOE not only impairs cognitive functions but also reduces neuritic amyloid plaques in mouse models of Alzheimer's disease (AD). Can APOE simultaneously protect and impair neural circuits? Here, we dissociated the role of APOE in AD versus aging to determine its effects on neuronal function and synaptic integrity. Using two-photon calcium imaging in awake mice to record visually evoked responses, we found that genetic removal of APOE improved neuronal responses in adult APP/PSEN1 mice (8-10 mo). These animals also exhibited fewer neuritic plaques with less surrounding synapse loss, fewer neuritic dystrophies, and reactive glia. Surprisingly, the lack of APOE in aged mice (18-20 mo), even in the absence of amyloid, disrupted visually evoked responses. These results suggest a dissociation in APOE's role in AD versus aging: APOE may be neurotoxic during early stages of amyloid deposition, although being neuroprotective in latter stages of aging.

Apolipoprotein E deletion has no effect on copper-induced oxidative stress in the mice brain

The current study was designed to investigate effect of copper administration on oxidative damage to the brain in ApoE^−/− mice and to explore the putative neuroprotective effects rendered by apolipoprotein E (ApoE). Male C57BL/6 ApoE^−/− and wild-type mice were randomly assigned into four groups, ApoE^−/− mice wild-type mice treated with either copper or saline. Copper sulphate pentahydrate or saline (200 µl) were administered intragastrically daily for 12 weeks. Expression of malondialdehyde, superoxide dismutase (SOD), hemeoxygenase 1 (HO-1), and NAD(P)H: quinone oxidoreductase 1 (NQO1) were determined by a combination of biochemical assays. The concentration of copper in the brain of C57BL/6 mice and ApoE^−/− mice treated by copper significantly increased compared with mice treated by saline (P=0.0099 and P=0.0443). Compared with the C57BL/6 mice treated by copper, the level of the ApoE⁻/⁻ mice treated by copper was higher (P=0.018). TBARS and SOD activities or the expressions of NQO1 and HO-1 in the brain were not significantly different amongst the four experimental groups of mice. The relative value of NQO1/β-actin expression in the brain of the ApoE^−/− mice was similar in both saline and copper administration experimental groups. However, Western blot analysis showed that NQO1 expression was significantly higher in the ApoE^−/− mice brain treated with saline compared with saline treated wild-type mice (P=0.0449). ApoE does not function in protecting the brain from oxidative damage resulting from copper build-up in Wilson’s disease, but may play a role in regulating copper accumulation in the brain.

Interaction of Copper Toxicity and Oxidative Stress in Campylobacter jejuni

Copper is both a required micronutrient and a source of toxicity in most organisms, including Campylobacter jejuni Two proteins expressed in C. jejuni (termed CopA and CueO) have been shown to be a copper transporter and multicopper oxidase, respectively. We have isolated strains with mutations in these genes, and here we report that they were more susceptible to both the addition of copper in the growth media and to induced oxidative stress. Both mutant strains were defective in colonization of an avian host, and copper in the feed exacerbated the colonization deficiency. Overexpression of a cytoplasmic peptide derived from the normally periplasmic copper-binding region of CueO also caused copper intolerance compared to nonexpressing strains or strains expressing the non-copper-binding versions of the peptide. Taken together, the results indicate that copper toxicity in C. jejuni is due to a failure to effectively sequester cytoplasmic copper, resulting in an increase in copper-mediated oxidative damage.IMPORTANCE Copper is a required micronutrient for most aerobic organisms, but it is universally toxic at elevated levels. These organisms use homeostatic mechanisms that allow for cells to acquire enough of the element to sustain metabolic requirements while ensuring that lethal levels cannot build up in the cell. Campylobacter jejuni is an important foodborne pathogen that typically makes its way into the food chain through contaminated poultry. C. jejuni has a metabolic requirement for copper and encodes a copper detoxification system. In the course of studying this system, we have learned that it is important for avian colonization. We have also gained insight into how copper exerts its toxic effects in C. jejuni by promoting oxidative stress.