Genetic variation is a key determinant of chromatin accessibility and drives differences in the regulatory landscape of C57BL/6J and 129S1/SvImJ mice

Most common genetic variants associated with disease are located in non-coding regions of the genome. One mechanism by which they function is through altering transcription factor (TF) binding. In this study, we explore how genetic variation is connected to differences in the regulatory landscape of livers from C57BL/6J and 129S1/SvImJ mice fed either chow or a high-fat diet. To identify sites where regulatory variation affects TF binding and nearby gene expression, we employed an integrative analysis of H3K27ac ChIP-seq (active enhancers), ATAC-seq (chromatin accessibility) and RNA-seq (gene expression). We show that, across all these assays, the genetically driven (i.e. strain-specific) differences in the regulatory landscape are more pronounced than those modified by diet. Most notably, our analysis revealed that differentially accessible regions (DARs, N = 29635, FDR < 0.01 and fold change > 50%) are almost always strain-specific and enriched with genetic variation. Moreover, proximal DARs are highly correlated with differentially expressed genes. We also show that TF binding is affected by genetic variation, which we validate experimentally using ChIP-seq for TCF7L2 and CTCF. This study provides detailed insights into how non-coding genetic variation alters the gene regulatory landscape, and demonstrates how this can be used to study the regulatory variation influencing TF binding.

Metabolic effects of nuclear receptor activation in vivo after 28-day oral exposure to three endocrine-disrupting chemicals

Environmental exposure to endocrine-disrupting chemicals (EDCs) can lead to metabolic disruption, resulting in metabolic complications including adiposity, dyslipidemia, hepatic lipid accumulation, and glucose intolerance. Hepatic nuclear receptor activation is one of the mechanisms mediating metabolic effects of EDCs. Here, we investigated the potential to use a repeated dose 28-day oral toxicity test for identification of EDCs with metabolic endpoints. Bisphenol A (BPA), pregnenolone-16α-carbonitrile (PCN), and perfluorooctanoic acid (PFOA) were used as reference compounds. Male and female wild-type C57BL/6 mice were orally exposed to 5, 50, and 500 μg/kg of BPA, 1000, 10 000, and 100 000 µg/kg of PCN and 50 and 300 μg/kg of PFOA for 28 days next to normal chow diet. Primary endpoints were glucose tolerance, hepatic lipid accumulation, and plasma lipids. After 28-day exposure, no changes in body weight and glucose tolerance were observed in BPA-, PCN-, or PFOA-treated males or females. PCN and PFOA at the highest dose in both sexes and BPA at the middle and high dose in males increased relative liver weight. PFOA reduced plasma triglycerides in males and females, and increased hepatic triglyceride content in males. PCN and PFOA induced hepatic expression of typical pregnane X receptor (PXR) and peroxisome proliferator-activated receptor (PPAR)α target genes, respectively. Exposure to BPA resulted in limited gene expression changes. In conclusion, the observed changes on metabolic health parameters were modest, suggesting that a standard repeated dose 28-day oral toxicity test is not a sensitive method for the detection of the metabolic effect of EDCs.

Electrophilic metabolites targeting the KEAP1/NRF2 partnership

Numerous electrophilic metabolites are formed during cellular activity, particularly under conditions of oxidative, inflammatory and metabolic stress. Among them are lipid oxidation and nitration products, and compounds derived from amino acid and central carbon metabolism. Here we focus on one cellular target of electrophiles, the Kelch-like ECH associated protein 1 (KEAP1)/nuclear factor erythroid 2 p45-related factor 2 (NRF2) partnership. Many of these reactive compounds modify C151, C273 and/or C288 within KEAP1. Other types of modifications include S-lactoylation of C273, N-succinylation of K131, and formation of methylimidazole intermolecular crosslink between two KEAP1 monomers. Modified KEAP1 relays the initial signal to transcription factor NRF2 and its downstream targets, the ultimate effectors that provide means for detoxification, adaptation and survival. Thus, by non-enzymatically covalently modifying KEAP1, the electrophilic metabolites discussed here serve as chemical signals connecting metabolism with stress responses.

Oncogenic KEAP1 mutations activate TRAF2-NFκB signaling to prevent apoptosis in lung cancer cells

The Kelch-like ECH-associated protein 1 (KEAP1) - Nuclear factor erythroid 2 -related factor 2 (NRF2) pathway is the major transcriptional stress response system in cells against oxidative and electrophilic stress. NRF2 is frequently constitutively active in many cancers, rendering the cells resistant to chemo- and radiotherapy. Loss-of-function (LOF) mutations in the repressor protein KEAP1 are common in non-small cell lung cancer, particularly adenocarcinoma. While the mutations can occur throughout the gene, they are enriched in certain areas, indicating that these may have unique functional importance. In this study, we show that in the GSEA analysis of TCGA lung adenocarcinoma RNA-seq data, the KEAP1 mutations in R320 and R470 were associated with enhanced Tumor Necrosis Factor alpha (TNFα) - Nuclear Factor kappa subunit B (NFκB) signaling as well as MYC and MTORC1 pathways. To address the functional role of these hotspot mutations, affinity purification and mass spectrometry (AP-MS) analysis of wild type (wt) KEAP1 and its mutation forms, R320Q and R470C were employed to interrogate differences in the protein interactome. We identified TNF receptor associated factor 2 (TRAF2) as a putative protein interaction partner. Both mutant KEAP1 forms showed increased interaction with TRAF2 and other anti-apoptotic proteins, suggesting that apoptosis signalling could be affected by the protein interactions. A549 lung adenocarcinoma cells overexpressing mutant KEAP1 showed high TRAF2-mediated NFκB activity and increased protection against apoptosis, XIAP being one of the key proteins involved in anti-apoptotic signalling. To conclude, KEAP1 R320Q and R470C and its interaction with TRAF2 leads to activation of NFκB pathway, thereby protecting against apoptosis.

A pan-cancer analysis shows immunoevasive characteristics in NRF2 hyperactive squamous malignancies

The NRF2 pathway is frequently activated in various cancer types, yet a comprehensive analysis of its effects across different malignancies is currently lacking. We developed a NRF2 activity metric and utilized it to conduct a pan-cancer analysis of oncogenic NRF2 signaling. We identified an immunoevasive phenotype where high NRF2 activity is associated with low interferon-gamma (IFNγ), HLA-I expression and T cell and macrophage infiltration in squamous malignancies of the lung, head and neck area, cervix and esophagus. Squamous NRF2 overactive tumors comprise a molecular phenotype with SOX2/TP63 amplification, TP53 mutation and CDKN2A loss. These immune cold NRF2 hyperactive diseases are associated with upregulation of immunomodulatory NAMPT, WNT5A, SPP1, SLC7A11, SLC2A1 and PD-L1. Based on our functional genomics analyses, these genes represent candidate NRF2 targets, suggesting direct modulation of the tumor immune milieu. Single-cell mRNA data shows that cancer cells of this subtype exhibit decreased expression of IFNγ responsive ligands, and increased expression of immunosuppressive ligands NAMPT, SPP1 and WNT5A that mediate signaling in intercellular crosstalk. In addition, we discovered that the negative relationship of NRF2 and immune cells are explained by stromal populations of lung squamous cell carcinoma, and this effect spans multiple squamous malignancies based on our molecular subtyping and deconvolution data.

The KEAP1-NRF2 pathway: Targets for therapy and role in cancer

The KEAP1-NRF2 pathway is the key regulator of cellular defense against both extrinsic and intrinsic oxidative and electrophilic stimuli. Since its discovery in the 1990s, its seminal role in various disease pathologies has become well appreciated, motivating research to elucidate the intricacies of NRF2 signaling and its downstream effects to identify novel targets for therapy. In this graphical review, we present an updated overview of the KEAP1-NRF2 signaling, focusing on the progress made within the past ten years. Specifically, we highlight the advances made in understanding the mechanism of activation of NRF2, resulting in novel discoveries in its therapeutic targeting. Furthermore, we will summarize new findings in the rapidly expanding field of NRF2 in cancer, with important implications for its diagnostics and treatment.

PI3Kβ inhibition enhances ALK-inhibitor sensitivity in ALK-rearranged lung cancer

Treatment with anaplastic lymphoma kinase (ALK) inhibitors significantly improves outcome for non-small-cell lung cancer (NSCLC) patients with ALK-rearranged tumors. However, clinical resistance typically develops over time and, in the majority of cases, resistance mechanisms are ALK-independent. We generated tumor cell cultures from multiple regions of an ALK-rearranged clinical tumor specimen and deployed functional drug screens to identify modulators of ALK-inhibitor response. This identified a role for PI3Kβ and EGFR inhibition in sensitizing the response regulating resistance to ALK inhibition. Inhibition of ALK elicited activation of EGFR, and subsequent MAPK and PI3K-AKT pathway reactivation. Sensitivity to ALK targeting was enhanced by inhibition or knockdown of PI3Kβ. In ALK-rearranged primary cultures, the combined inhibition of ALK and PI3Kβ prevented the EGFR-mediated ALK-inhibitor resistance, and selectively targeted the cancer cells. The combinatorial effect was seen also in the background of TP53 mutations and in epithelial-to-mesenchymal transformed cells. In conclusion, combinatorial ALK- and PI3Kβ-inhibitor treatment carries promise as a treatment for ALK-rearranged NSCLC.

A novel uterine leiomyoma subtype exhibits NRF2 activation and mutations in genes associated with neddylation of the Cullin 3-RING E3 ligase

Uterine leiomyomas, or fibroids, are the most common tumors in women of reproductive age. Uterine leiomyomas can be classified into at least three main molecular subtypes according to mutations affecting MED12, HMGA2, or FH. FH-deficient leiomyomas are characterized by activation of the NRF2 pathway, including upregulation of the NRF2 target gene AKR1B10. Here, we have identified a novel leiomyoma subtype showing AKR1B10 expression but no alterations in FH or other known driver genes. Whole-exome and whole-genome sequencing revealed biallelic mutations in key genes involved in neddylation of the Cullin 3-RING E3 ligase, including UBE2M, NEDD8, CUL3, and NAE1. 3′RNA sequencing confirmed a distinct molecular subtype with activation of the NRF2 pathway. Most tumors displayed cellular histopathology, perivascular hypercellularity, and characteristics typically seen in FH-deficient leiomyomas. These results suggest a novel leiomyoma subtype that is characterized by distinct morphological features, genetic alterations disrupting neddylation of the Cullin 3-RING E3 ligase, and oncogenic NRF2 activation. They also present defective neddylation as a novel mechanism leading to aberrant NRF2 signaling. Molecular characterization of uterine leiomyomas provides novel opportunities for targeted treatment options.

Global MicroRNA Profiling of Vascular Endothelial Cells

MicroRNA sequencing (miRNA-seq) enables the detection and characterization of the cell miRNome, including miRNA isoforms (isomiRs) and novel miRNA species. In roughly half of the cases, the most abundant isomiR in the cells is not the reference miRNA given in miRBase, which highlights the importance of isomiR-specific analysis. Here, we describe a gel-free protocol for global miRNA profiling in vascular endothelial cells and the main steps of the subsequent data analysis with two alternative analysis methods. In addition to endothelial cells, the protocol is suitable for other cell and tissue types and has been successfully used to obtain miRNA-seq data from human cardiac tissue, plasma, pericardial fluid, and biofluid exosomes.

A toxicogenomic data space for system-level understanding and prediction of EDC-induced toxicity

Endocrine disrupting compounds (EDCs) are a persistent threat to humans and wildlife due to their ability to interfere with endocrine signaling pathways. Inspired by previous work to improve chemical hazard identification through the use of toxicogenomics data, we developed a genomic-oriented data space for profiling the molecular activity of EDCs in an in silico manner, and for creating predictive models that identify and prioritize EDCs. Predictive models of EDCs, derived from gene expression data from rats (in vivo and in vitro primary hepatocytes) and humans (in vitro primary hepatocytes and HepG2), achieve testing accuracy greater than 90%. Negative test sets indicate that known safer chemicals are not predicted as EDCs. The rat in vivo-based classifiers achieve accuracy greater than 75% when tested for invitro to in vivoextrapolation. This study reveals key metabolic pathways and genes affected by EDCs together with a set of predictive models that utilize these pathways to prioritize EDCs in dose/time dependent manner and to predict EDCevokedmetabolic diseases.

NRF2 is a key regulator of endothelial microRNA expression under proatherogenic stimuli

AIMS

Oxidized phospholipids and microRNAs (miRNAs) are increasingly recognized to play a role in endothelial dysfunction driving atherosclerosis. NRF2 transcription factor is one of the key mediators of the effects of oxidized phospholipids, but the gene regulatory mechanisms underlying the process remain obscure. Here, we investigated the genome-wide effects of oxidized phospholipids on transcriptional gene regulation in human umbilical vein endothelial cells and aortic endothelial cells with a special focus on miRNAs.

METHODS AND RESULTS

We integrated data from HiC, ChIP-seq, ATAC-seq, GRO-seq, miRNA-seq, and RNA-seq to provide deeper understanding of the transcriptional mechanisms driven by NRF2 in response to oxidized phospholipids. We demonstrate that presence of NRF2 motif and its binding is more prominent in the vicinity of up-regulated transcripts and transcriptional initiation represents the most likely mechanism of action. We further identified NRF2 as a novel regulator of over 100 endothelial pri-miRNAs. Among these, we characterize two hub miRNAs miR-21-5p and miR-100-5p and demonstrate their opposing roles on mTOR, VEGFA, HIF1A, and MYC expressions. Finally, we provide evidence that the levels of miR-21-5p and miR-100-5p in exosomes are increased upon senescence and exhibit a trend to correlate with the severity of coronary artery disease.

CONCLUSION

Altogether, our analysis provides an integrative view into the regulation of transcription and miRNA function that could mediate the proatherogenic effects of oxidized phospholipids in endothelial cells.

HAS3-induced extracellular vesicles from melanoma cells stimulate IHH mediated c-Myc upregulation via the hedgehog signaling pathway in target cells

Intercellular communication is fundamental to the survival and maintenance of all multicellular systems, whereas dysregulation of communication pathways can drive cancer progression. Extracellular vesicles (EVs) are mediators of cell-to-cell communication that regulate a variety of cellular processes involved in tumor progression. Overexpression of a specific plasma membrane enzyme, hyaluronan synthase 3 (HAS3), is one of the factors that can induce EV shedding. HAS3, and particularly its product hyaluronan (HA), are carried by EVs and are known to be associated with the tumorigenic properties of cancer cells. To elucidate the specific effects of cancerous, HAS3-induced EVs on target cells, normal human keratinocytes and melanoma cells were treated with EVs derived from GFP-HAS3 expressing metastatic melanoma cells. We found that the HA receptor CD44 participated in the regulation of EV binding to target cells. Furthermore, GFP-HAS3-positive EVs induced HA secretion, proliferation and invasion of target cells. Our results suggest that HAS3-EVs contains increased quantities of IHH, which activates the target cell hedgehog signaling cascade and leads to the activation of c-Myc and regulation of claspin expression. This signaling of IHH in HAS3-EVs resulted in increased cell proliferation. Claspin immunostaining correlated with HA content in human cutaneous melanocytic lesions, supporting our in vitro findings and suggesting a reciprocal regulation between claspin expression and HA synthesis. This study shows for the first time that EVs originating from HAS3 overexpressing cells carry mitogenic signals that induce proliferation and epithelial-to-mesenchymal transition in target cells. The study also identifies a novel feedback regulation between the hedgehog signaling pathway and HA metabolism in melanoma, mediated by EVs carrying HA and IHH.

LDL Receptor Regulates the Reverse Transport of Macrophage-Derived Unesterified Cholesterol via Concerted Action of the HDL-LDL Axis: Insight From Mouse Models

RATIONALE

The HDL (high-density lipoprotein)-mediated stimulation of cellular cholesterol efflux initiates macrophage-specific reverse cholesterol transport (m-RCT), which ends in the fecal excretion of macrophage-derived unesterified cholesterol (UC). Early studies established that LDL (low-density lipoprotein) particles could act as efficient intermediate acceptors of cellular-derived UC, thereby preventing the saturation of HDL particles and facilitating their cholesterol efflux capacity. However, the capacity of LDL to act as a plasma cholesterol reservoir and its potential impact in supporting the m-RCT pathway in vivo both remain unknown.

OBJECTIVE

We investigated LDL contributions to the m-RCT pathway in hypercholesterolemic mice.

METHODS AND RESULTS

Macrophage cholesterol efflux induced in vitro by LDL added to the culture media either alone or together with HDL or ex vivo by plasma derived from subjects with familial hypercholesterolemia was assessed. In vivo, m-RCT was evaluated in mouse models of hypercholesterolemia that were naturally deficient in CETP (cholesteryl ester transfer protein) and fed a Western-type diet. LDL induced the efflux of radiolabeled UC from cultured macrophages, and, in the simultaneous presence of HDL, a rapid transfer of the radiolabeled UC from HDL to LDL occurred. However, LDL did not exert a synergistic effect on HDL cholesterol efflux capacity in the familial hypercholesterolemia plasma. The m-RCT rates of the LDLr (LDL receptor)-KO (knockout), LDLr-KO/APOB100, and PCSK9 (proprotein convertase subtilisin/kexin type 9)-overexpressing mice were all significantly reduced relative to the wild-type mice. In contrast, m-RCT remained unchanged in HAPOB100 Tg (human APOB100 transgenic) mice with fully functional LDLr, despite increased levels of plasma APO (apolipoprotein)-B-containing lipoproteins.

CONCLUSIONS

Hepatic LDLr plays a critical role in the flow of macrophage-derived UC to feces, while the plasma increase of APOB-containing lipoproteins is unable to stimulate m-RCT. The results indicate that, besides the major HDL-dependent m-RCT pathway via SR-BI (scavenger receptor class B type 1) to the liver, a CETP-independent m-RCT path exists, in which LDL mediates the transfer of cholesterol from macrophages to feces. Graphical Abstract: A graphical abstract is available for this article.

NF-E2-related factor 2 activation boosts antioxidant defenses and ameliorates inflammatory and amyloid properties in human Presenilin-1 mutated Alzheimer's disease astrocytes

Alzheimer's disease (AD) is a common dementia affecting a vast number of individuals and significantly impairing quality of life. Despite extensive research in animal models and numerous promising treatment trials, there is still no curative treatment for AD. Astrocytes, the most common cell type of the central nervous system, have been shown to play a role in the major AD pathologies, including accumulation of amyloid plaques, neuroinflammation, and oxidative stress. Here, we show that inflammatory stimulation leads to metabolic activation of human astrocytes and reduces amyloid secretion. On the other hand, the activation of oxidative metabolism leads to increased reactive oxygen species production especially in AD astrocytes. While healthy astrocytes increase glutathione (GSH) release to protect the cells, Presenilin‐1‐mutated AD patient astrocytes do not. Thus, chronic inflammation is likely to induce oxidative damage in AD astrocytes. Activation of NRF2, the major regulator of cellular antioxidant defenses, encoded by the NFE2L2 gene, poses several beneficial effects on AD astrocytes. We report here that the activation of NRF2 pathway reduces amyloid secretion, normalizes cytokine release, and increases GSH secretion in AD astrocytes. NRF2 induction also activates the metabolism of astrocytes and increases the utilization of glycolysis. Taken together, targeting NRF2 in astrocytes could be a potent therapeutic strategy in AD.

In Vitro and In Vivo Pipeline for Validation of Disease-Modifying Effects of Systems Biology-Derived Network Treatments for Traumatic Brain Injury-Lessons Learned

We developed a pipeline for the discovery of transcriptomics-derived disease-modifying therapies and used it to validate treatments in vitro and in vivo that could be repurposed for TBI treatment. Desmethylclomipramine, ionomycin, sirolimus and trimipramine, identified by in silico LINCS analysis as candidate treatments modulating the TBI-induced transcriptomics networks, were tested in neuron-BV2 microglial co-cultures, using tumour necrosis factor α as a monitoring biomarker for neuroinflammation, nitrite for nitric oxide-mediated neurotoxicity and microtubule associated protein 2-based immunostaining for neuronal survival. Based on (a) therapeutic time window in silico, (b) blood-brain barrier penetration and water solubility, (c) anti-inflammatory and neuroprotective effects in vitro (p < 0.05) and (d) target engagement of Nrf2 target genes (p < 0.05), desmethylclomipramine was validated in a lateral fluid-percussion model of TBI in rats. Despite the favourable in silico and in vitro outcomes, in vivo assessment of clomipramine, which metabolizes to desmethylclomipramine, failed to demonstrate favourable effects on motor and memory tests. In fact, clomipramine treatment worsened the composite neuroscore (p < 0.05). Weight loss (p < 0.05) and prolonged upregulation of plasma cytokines (p < 0.05) may have contributed to the worsened somatomotor outcome. Our pipeline provides a rational stepwise procedure for evaluating favourable and unfavourable effects of systems-biology discovered compounds that modulate post-TBI transcriptomics.

Nrf2 and SQSTM1/p62 jointly contribute to mesenchymal transition and invasion in glioblastoma

Accumulating evidence suggests that constitutively active Nrf2 has a pivotal role in cancer as it induces pro-survival genes that promote cancer cell proliferation and chemoresistance. The mechanisms of Nrf2 dysregulation and functions in cancer have not been fully characterized. Here, we jointly analyzed the Broad-Novartis Cancer Cell Line Encyclopedia (CCLE) and the Cancer Genome Atlas (TCGA) multi-omics data in order to identify cancer types where Nrf2 activation is present. We found that Nrf2 is hyperactivated in a subset of glioblastoma (GBM) patients, whose tumors display a mesenchymal subtype, and uncover several different mechanisms contributing to increased Nrf2 activity. Importantly, we identified a positive feedback loop between SQSTM1/p62 and Nrf2 as a mechanism for activation of the Nrf2 pathway. We also show that autophagy and serine/threonine signaling regulates p62 mediated Keap1 degradation. Our results in glioma cell lines indicate that both Nrf2 and p62 promote proliferation, invasion and mesenchymal transition. Finally, Nrf2 activity was associated with decreased progression free survival in TCGA GBM patient samples, suggesting that treatments have limited efficacy if this transcription factor is overactivated. Overall, our findings place Nrf2 and p62 as the key components of the mesenchymal subtype network, with implications to tumorigenesis and treatment resistance. Thus, Nrf2 activation could be used as a surrogate prognostic marker in mesenchymal subtype GBMs. Furthermore, strategies aiming at either inhibiting Nrf2 or exploiting Nrf2 hyperactivity for targeted gene therapy may provide novel treatment options for this subset of GBM.

Characterizing valve dynamics in mice by high-resolution cine-MRI

AIMS

In calcific aortic valve disease (CAVD), progressive valvular sclerosis and calcification cause narrowing of the orifice and an impairment of the valve's function. We applied high-resolution cine-MRI to perform quantitative analysis of the dynamics of the aortic valve in a mice model of CAVD.

METHODS AND RESULTS

LDLr^-/- ApoB^100/100 mice were fed a Western diet (WD) or a standard diet (control) for 22 weeks. The mice were imaged in a 7 T horizontal MRI scanner, and aortic valve dynamics was examined by imaging the cross-section of the aorta at valve level using cine sequences. From these images, the area of the aortic valve orifice was determined during the heart cycle. MRI results were compared with echocardiographic and histopathologic results. The data revealed evidence of clear aortic valve dysfunction in WD mice as compared with control mice (interaction P < 0.001). MRI showed narrowing (14%, P < 0.05) of the orifice area, and this was also seen in histology (34%, P < 0.05), indicating more severe aortic stenosis after WD than in controls. Additionally, MRI revealed a reduction in the ejection fraction (EF) (-11%, P < 0.01), a result confirmed with echocardiography (-27%, P < 0.001) in mice fed with WD. EF detected by MRI and echocardiography also correlated strongly with the degree of stenosis assessed by histology.

CONCLUSIONS

Cine-MRI can be used for quantitative analysis of the aortic valve orifice over the cardiac cycle in mice. MRI showed the cusps clearly, and we were able to detect aortic valve dysfunction over time through the cardiac cycle.

Therapeutic targeting of the NRF2 and KEAP1 partnership in chronic diseases

The transcription factor NF-E2 p45-related factor 2 (NRF2; encoded by NFE2L2) and its principal negative regulator, the E3 ligase adaptor Kelch-like ECH-associated protein 1 (KEAP1), are critical in the maintenance of redox, metabolic and protein homeostasis, as well as the regulation of inflammation. Thus, NRF2 activation provides cytoprotection against numerous pathologies including chronic diseases of the lung and liver; autoimmune, neurodegenerative and metabolic disorders; and cancer initiation. One NRF2 activator has received clinical approval and several electrophilic modifiers of the cysteine-based sensor KEAP1 and inhibitors of its interaction with NRF2 are now in clinical development. However, challenges regarding target specificity, pharmacodynamic properties, efficacy and safety remain.

Axon Guidance-Related Factor FLRT3 Regulates VEGF-Signaling and Endothelial Cell Function

Vascular endothelial growth factors (VEGFs) are key mediators of endothelial cell (EC) function in angiogenesis. Emerging knowledge also supports the involvement of axon guidance-related factors in the regulation of angiogenesis and vascular patterning. In the current study, we demonstrate that fibronectin and leucine-rich transmembrane protein-3 (FLRT3), an axon guidance-related factor connected to the regulation of neuronal cell outgrowth and morphogenesis but not to VEGF-signaling, was upregulated in ECs after VEGF binding to VEGFR2. We found that FLRT3 exhibited a transcriptionally paused phenotype in non-stimulated human umbilical vein ECs. After VEGF-stimulation its nascent RNA and mRNA-levels were rapidly upregulated suggesting that the regulation of FLRT3 expression is mainly occurring at the level of transcriptional elongation. Blockage of FLRT3 by siRNA decreased survival of ECs and their arrangement into capillary-like structures but enhanced cell migration and wound closure in wound healing assay. Bifunctional role of FLRT3 in repulsive vs. adhesive cell signaling has been already detected during embryogenesis and neuronal growth, and depends on its interactions either with UNC5B or another FLRT3 expressed by adjacent cells. In conclusion, our findings demonstrate that besides regulating neuronal cell outgrowth and morphogenesis, FLRT3 has a novel role in ECs via regulating VEGF-stimulated EC-survival, migration, and tube formation. Thus, FLRT3 becomes a new member of the axon guidance-related factors which participate in the VEGF-signaling and regulation of the EC functions.

Regulation of stress signaling pathways by protein lipoxidation

Enzymatic and non-enzymatic oxidation of unsaturated fatty acids gives rise to reactive species that covalently modify nucleophilic residues within redox sensitive protein sensors in a process called lipoxidation. This triggers adaptive signaling pathways that ultimately lead to increased resistance to stress. In this graphical review, we will provide an overview of pathways affected by protein lipoxidation and the key signaling proteins being altered, focusing on the KEAP1-NRF2 and heat shock response pathways. We review the mechanisms by which lipid peroxidation products can serve as second messengers and evoke cellular responses via covalent modification of key sensors of altered cellular environment, ultimately leading to adaptation to stress.

Loss of NRF-2 and PGC-1α genes leads to retinal pigment epithelium damage resembling dry age-related macular degeneration

Age-related macular degeneration (AMD) is a multi-factorial disease that is the leading cause of irreversible and severe vision loss in the developed countries. It has been suggested that the pathogenesis of dry AMD involves impaired protein degradation in retinal pigment epithelial cells (RPE). RPE cells are constantly exposed to oxidative stress that may lead to the accumulation of damaged cellular proteins, DNA and lipids and evoke tissue deterioration during the aging process. The ubiquitin-proteasome pathway and the lysosomal/autophagosomal pathway are the two major proteolytic systems in eukaryotic cells. NRF-2 (nuclear factor-erythroid 2-related factor-2) and PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1 alpha) are master transcription factors in the regulation of cellular detoxification. We investigated the role of NRF-2 and PGC-1α in the regulation of RPE cell structure and function by using global double knockout (dKO) mice. The NRF-2/PGC-1α dKO mice exhibited significant age-dependent RPE degeneration, accumulation of the oxidative stress marker, 4-HNE (4-hydroxynonenal), the endoplasmic reticulum stress markers GRP78 (glucose-regulated protein 78) and ATF4 (activating transcription factor 4), and damaged mitochondria. Moreover, levels of protein ubiquitination and autophagy markers p62/SQSTM1 (sequestosome 1), Beclin-1 and LC3B (microtubule associated protein 1 light chain 3 beta) were significantly increased together with the Iba-1 (ionized calcium binding adaptor molecule 1) mononuclear phagocyte marker and an enlargement of RPE size. These histopathological changes of RPE were accompanied by photoreceptor dysmorphology and vision loss as revealed by electroretinography. Consequently, these novel findings suggest that the NRF-2/PGC-1α dKO mouse is a valuable model for investigating the role of proteasomal and autophagy clearance in the RPE and in the development of dry AMD.

•

NRF-2/PGC-1α dKO mouse model shows a dry AMD-like phenotype.

•

Loss of NRF-2/PGC-1α genes increased oxidative and ER stress in RPE cells.

•

High oxidative stress was associated with impaired autophagy and proteasomal clearance.

•

The pathology becomes manifest as an age-related loss of photoreceptor function.

MicroRNAs mediate the senescence-associated decline of NRF2 in endothelial cells

Oxidative stress predisposes to several aging-associated diseases, such as cardiovascular diseases and cancer. In aging, increase in the production of reactive oxygen species is typically accompanied with a decline in adaptive stress responses to oxidative stress. The decline is primarily due to a decrease in antioxidant production. Nuclear factor E2-Related Factor 2 (NRF2) is a key transcription factor regulating oxidative and electrophilic stress responses, but it has also been shown to play a role in the regulation of cell metabolism. NRF2 expression declines in aging, but the mechanisms remain unclear. In this study, we show that microRNAs (miRNAs) that are abundant in old endothelial cells decrease NRF2 expression by direct targeting of NRF2 mRNA. The effect is reversed by miRNA inhibition. The senescence-associated downregulation of NRF2 decreases endothelial glycolytic activity and stress tolerance both of which are restored after reinstating NRF2. Manipulation of the senescence-associated miRNA levels affects the glycolytic activity and stress tolerance consistently with the NRF2 results. We conclude that senescence-associated miRNAs are involved in the decline of NRF2 expression, thus contributing to the repression of adaptive responses during cell senescence.

•

A post-transcriptional mechanism for NRF2 downregulation in aging is proposed.

•

The mechanism implicates senescence-associated miRNA alterations in NRF2 decline.

•

Inhibition of senescence-associated miRNA function increases NRF2 expression in old cells.

•

Upregulation of NRF2 increases cell viability.

Nuclear factor E2-related factor 2 deficiency impairs atherosclerotic lesion development but promotes features of plaque instability in hypercholesterolaemic mice

Aims

Oxidative stress and inflammation play an important role in the progression of atherosclerosis. Transcription factor NF-E2-related factor 2 (Nrf2) has antioxidant and anti-inflammatory effects in the vessel wall, but paradoxically, global loss of Nrf2 in apoE deficient mice alleviates atherosclerosis. In this study, we investigated the effect of global Nrf2 deficiency on early and advanced atherogenesis in alternative models of atherosclerosis, LDL receptor deficient mice (LDLR−/−), and LDLR−/− mice expressing apoB-100 only (LDLR−/− ApoB100/100) having a humanized lipoprotein profile.

Methods and results

LDLR−/− mice were fed a high-fat diet (HFD) for 6 or 12 weeks and LDLR−/−ApoB100/100 mice a regular chow diet for 6 or 12 months. Nrf2 deficiency significantly reduced early and more advanced atherosclerosis assessed by lesion size and coverage in the aorta in both models. Nrf2 deficiency in LDLR−/− mice reduced total plasma cholesterol after 6 weeks of HFD and triglycerides in LDLR−/−ApoB100/100 mice on a chow diet. Nrf2 deficiency aggravated aortic plaque maturation in aged LDLR−/−ApoB100/100 mice as it increased plaque calcification. Moreover, ∼36% of Nrf2−/−LDLR−/−ApoB100/100 females developed spontaneous myocardial infarction (MI) or sudden death at 5 to 12 months of age. Interestingly, Nrf2 deficiency increased plaque instability index, enhanced plaque inflammation and calcification, and reduced fibrous cap thickness in brachiocephalic arteries of LDLR−/−ApoB100/100 female mice at age of 12 months.

Conclusions

Absence of Nrf2 reduced atherosclerotic lesion size in both atherosclerosis models, likely via systemic effects on lipid metabolism. However, Nrf2 deficiency in aged LDLR−/−ApoB100/100 mice led to an enhanced atherosclerotic plaque instability likely via increased plaque inflammation and oxidative stress, which possibly predisposed to MI and sudden death.

Regulation of stress signaling pathways by nitro-fatty acids

Electrophilic nitrated-fatty acids (NO2-FA, nitroalkenes) are formed during reactions of NO-derived oxidized species (•NO, •NO2) with either free or esterified polyunsaturated fatty acids. Due to their electrophilic character, they react with nucleophiles such as cysteine thiols in signaling proteins, thereby triggering downstream signaling cascades. Herein, we review two stress-signaling pathways activated by nitroalkenes, the KEAP1-NRF2 signaling pathway and the heat shock response (HSR) pathway. In addition, their biological and pharmacological relevance are discussed. Given that perturbations in both proteostasis and redox balance are common in many disease processes, dual activation of both pathways by nitroalkenes is a promising pharmacological approach for their treatment.

NRF2 regulates endothelial glycolysis and proliferation with miR-93 and mediates the effects of oxidized phospholipids on endothelial activation

Phospholipids, such as 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC), are the major components of cell membranes. Their exposure to reactive oxygen species creates oxidized phospholipids, which predispose to the development of chronic inflammatory diseases and metabolic disorders through endothelial activation and dysfunction. Although the effects of oxidized PAPC (oxPAPC) on endothelial cells have been previously studied, the underlying molecular mechanisms evoking biological responses remain largely unknown. Here, we investigated the molecular mechanisms of oxPAPC function with a special emphasis on NRF2-regulated microRNAs (miRNAs) in human umbilical vein endothelial cells (HUVECs) utilizing miRNA profiling, global run-on sequencing (GRO-seq), genome-wide NRF2 binding model, and RNA sequencing (RNA-seq) with miRNA overexpression and silencing. We report that the central regulators of endothelial activity, KLF2 for quiescence, PFKFB3 for glycolysis, and VEGFA, FOXO1 and MYC for growth and proliferation, are regulated by transcription factor NRF2 and the NRF2-regulated miR-106b∼25 cluster member, miR-93, in HUVECs. Mechanistically, oxPAPC was found to induce glycolysis and proliferation NRF2-dependently, and oxPAPC-dependent induction of the miR-106b∼25 cluster was mediated by NRF2. Additionally, several regulatory loops were established between NRF2, miR-93 and the essential regulators of healthy endothelium, collectively implying that NRF2 controls the switch between the quiescent and the proliferative endothelial states together with miR-93.

Pro-nociceptive migraine mediator CGRP provides neuroprotection of sensory, cortical and cerebellar neurons via multi-kinase signaling

Background Blocking the pro-nociceptive action of CGRP is one of the most promising approaches for migraine prophylaxis. The aim of this study was to explore a role for CGRP as a neuroprotective agent for central and peripheral neurons. Methods The viability of isolated rat trigeminal, cortical and cerebellar neurons was tested by fluorescence vital assay. Engagement of Nrf2 target genes was analyzed by qPCR. The neuroprotective efficacy of CGRP in vivo was tested in mice using a permanent cerebral ischemia model. Results CGRP prevented apoptosis induced by the amino acid homocysteine in all three distinct neuronal populations. Using a set of specific kinase inhibitors, we show the role of multi-kinase signaling pathways involving PKA and CaMKII in neuronal survival. Forskolin triggered a very similar signaling cascade, suggesting that cAMP is the main upstream trigger for multi-kinase neuroprotection. The specific CGRP antagonist BIBN4096 reduced cellular viability, lending further support to the proposed neuroprotective function of CGRP. Importantly, CGRP was neuroprotective against permanent ischemia in mice. Conclusion Our data show an unexpected 'positive' role for the endogenous pro-nociceptive migraine mediator CGRP, suggesting more careful examination of migraine prophylaxis strategy based on CGRP antagonism although it should be noted that homocysteine induced apoptosis in primary neuronal cell culture might not necessarily reproduce all the features of cell loss in the living organism.

Hemin and Cobalt Protoporphyrin Inhibit NLRP3 Inflammasome Activation by Enhancing Autophagy: A Novel Mechanism of Inflammasome Regulation

Inflammasomes are intracellular protein platforms, which, upon activation, produce the highly proinflammatory cytokines interleukin (IL)-1β and IL-18. Heme, hemin and their degradation products possess significant immunomodulatory functions. Here, we studied whether hemin regulates inflammasome function in macrophages. Both hemin and its derivative, cobalt protoporphyrin (CoPP), significantly reduced IL-1β secretion by cultured human primary macrophages, the human monocytic leukemia cell line and also mouse bone marrow-derived and peritoneal macrophages. Intraperitoneal administration of CoPP to mice prior to urate crystal-induced peritonitis alleviated IL-1β secretion to the peritoneal cavity. In cultured macrophages, hemin and CoPP inhibited NLRP3 inflammasome assembly by reducing the amount of intracellular apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC). The reduction of ASC was associated with enhanced autophagosome formation and autophagic flux. Inhibition of autophagy prevented the CoPP-induced depletion of ASC, implying that the depletion was caused by increased autophagy. Our data indicate that hemin functions as an endogenous negative regulator of the NLRP3 inflammasome. The inhibition is mediated via enhanced autophagy that results in increased degradation of ASC. This regulatory mechanism may provide a novel approach for the treatment of inflammasome-related diseases.

Pyrrolidine dithiocarbamate activates the Nrf2 pathway in astrocytes

Background

Endogenous defense against oxidative stress is controlled by nuclear factor erythroid 2-related factor 2 (Nrf2). The normal compensatory mechanisms to combat oxidative stress appear to be insufficient to protect against the prolonged exposure to reactive oxygen species during disease. Counterbalancing the effects of oxidative stress by up-regulation of Nrf2 signaling has been shown to be effective in various disease models where oxidative stress is implicated, including Alzheimer’s disease. Stimulation of Nrf2 signaling by small-molecule activators is an appealing strategy to up-regulate the endogenous defense mechanisms of cells.

Methods

Here, we investigate Nrf2 induction by the metal chelator and known nuclear factor-κB inhibitor pyrrolidine dithiocarbamate (PDTC) in cultured astrocytes and neurons, and mouse brain. Nrf2 induction is further examined in cultures co-treated with PDTC and kinase inhibitors or amyloid-beta, and in Nrf2-deficient cultures.

Results

We show that PDTC is a potent inducer of Nrf2 signaling specifically in astrocytes and demonstrate the critical role of Nrf2 in PDTC-mediated protection against oxidative stress. This induction appears to be regulated by both Keap1 and glycogen synthase kinase 3β. Furthermore, the presence of amyloid-beta magnifies PDTC-mediated induction of endogenous protective mechanisms, therefore suggesting that PDTC may be an effective Nrf2 inducer in the context of Alzheimer’s disease. Finally, we show that PDTC increases brain copper content and glial expression of heme oxygenase-1, and decreases lipid peroxidation in vivo, promoting a more antioxidative environment.

Conclusions

PDTC activates Nrf2 and its antioxidative targets in astrocytes but not neurons. These effects may contribute to the neuroprotection observed for PDTC in models of Alzheimer’s disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0515-9) contains supplementary material, which is available to authorized users.

The Effects of Sequence Variation on Genome-wide NRF2 Binding--New Target Genes and Regulatory SNPs

Transcription factor binding specificity is crucial for proper target gene regulation. Motif discovery algorithms identify the main features of the binding patterns, but the accuracy on the lower affinity sites is often poor. Nuclear factor E2-related factor 2 (NRF2) is a ubiquitous redox-activated transcription factor having a key protective role against endogenous and exogenous oxidant and electrophile stress. Herein, we decipher the effects of sequence variation on the DNA binding sequence of NRF2, in order to identify both genome-wide binding sites for NRF2 and disease-associated regulatory SNPs (rSNPs) with drastic effects on NRF2 binding. Interactions between NRF2 and DNA were studied using molecular modelling, and NRF2 chromatin immunoprecipitation-sequence datasets together with protein binding microarray measurements were utilized to study binding sequence variation in detail. The binding model thus generated was used to identify genome-wide binding sites for NRF2, and genomic binding sites with rSNPs that have strong effects on NRF2 binding and reside on active regulatory elements in human cells. As a proof of concept, miR-126–3p and -5p were identified as NRF2 target microRNAs, and a rSNP (rs113067944) residing on NRF2 target gene (Ferritin, light polypeptide, FTL) promoter was experimentally verified to decrease NRF2 binding and result in decreased transcriptional activity.

Applications of the Keap1-Nrf2 system for gene and cell therapy

Oxidative stress has been implicated to play a role in a number of acute and chronic diseases including acute injuries of the central nervous system, neurodegenerative and cardiovascular diseases, and cancer. The redox-activated transcription factor Nrf2 has been shown to protect many different cell types and organs from a variety of toxic insults, whereas in many cancers, unchecked Nrf2 activity increases the expression of cytoprotective genes and, consequently, provides growth advantage to cancerous cells. Herein, we discuss current preclinical gene therapy approaches to either increase or decrease Nrf2 activity with a special reference to neurological diseases and cancer. In addition, we discuss the role of Nrf2 in stem cell therapy for neurological disorders.

Role of the Keap1-Nrf2 pathway in cancer

The Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor E2-related factor 2 (Nrf2) pathway is one of the major signaling cascades involved in cell defense and survival against endogenous and exogenous stress. While Nrf2 and its target genes provide protection against various age-related diseases including tumorigenesis, constitutively active Nrf2 in cancer cells increases the expression of cytoprotective genes and, consequently, enhances proliferation via metabolic reprogramming and inhibition of apoptosis. Herein, we review the current understanding of the regulation of Nrf2 in normal cells as well as its dual role in cancer. Furthermore, the mechanisms of Nrf2 dysregulation in cancer, consequences of unchecked Nrf2 activity, and therapies targeting the Keap1-Nrf2 system are discussed.

Nrf2 regulates neurogenesis and protects neural progenitor cells against Aβ toxicity

Neural stem/progenitor cells (NPCs) proliferate and produce new neurons in neurogenic areas throughout the lifetime. While these cells represent potential therapeutic treatment of neurodegenerative diseases, regulation of neurogenesis is not completely understood. We show that deficiency of nuclear factor erythroid 2-related factor (Nrf2), a transcription factor induced in response to oxidative stress, prevents the ischemia-induced increase in newborn neurons in the subgranular zone of the dentate gyrus. Consistent with this finding, the growth of NPC neurospheres was increased by lentivirus-mediated overexpression of Nrf2 gene or by treatment with pyrrolidine dithiocarbamate (PDTC), an Nrf2 activating compound. Also, neuronal differentiation of NPCs was increased by Nrf2 overexpression or PDTC treatment but reduced by Nrf2 deficiency. To investigate the impact of Nrf2 on NPCs in Alzheimer's disease (AD), we treated NPCs with amyloid beta (Aβ), a toxic peptide associated with neurodegeneration and cognitive abnormalities in AD. We found that Aβ1-42-induced toxicity and reduction in neurosphere proliferation were prevented by Nrf2 overexpression, while Nrf2 deficiency enhanced the Aβ1-42-induced reduction of neuronal differentiation. On the other hand, Aβ1-40 had no effect on neurosphere proliferation in wt NPCs but increased the proliferation of Nrf2 overexpressing neurospheres and reduced it in Nrf2-deficient neurospheres. These results suggest that Nrf2 is essential for neuronal differentiation of NPCs, regulates injury-induced neurogenesis and provides protection against Aβ-induced NPC toxicity.

Activation of stress signaling pathways by oxidized and nitrated lipids

Oxygen and nitric oxide-derived reactive species at high concentrations can mediate the oxidation of macromolecules such as lipids, thereby contributing to disease pathology. At lower rates of generation, the oxidation and nitration of free or phospholipid-esterified unsaturated fatty acids also mediate more subtle, specific and highly-evolved cell signaling reactions. Notably, electrophilic products of unsaturated fatty acid oxidation and nitration can elicit cytoprotective responses such as those regulated by the Keap1-Nrf2-ARE pathway. The molecular characteristics of lipid-derived signaling mediators that define their ability to trigger stress signaling responses is constrained by their protein targets within the signaling pathways. Recent findings on the Nrf2-activating properties of nitrated fatty acids will be presented, with special reference to interactions with the endothelin signaling system. The functionally significant interactions of Keap1-Nrf2-ARE-mediated signaling with other stress signaling pathways, interrogated utilizing novel genome-wide deep sequencing methods, is also discussed in the context of electrophilic fatty acid signaling. Interrogating the stress signaling pathways elicited by electrophilic lipid mediators will yield important insights into their signaling functions, which ultimately leads to better understanding of the pathogenesis of cardiovascular diseases and the potential for lipid-derived electrophiles as therapeutic agents.

Robust hydrolysis of prostaglandin glycerol esters by human monoacylglycerol lipase (MAGL)

The primary route of inactivation of the endocannabinoid 2-arachidonoylglycerol in the central nervous system is through enzymatic hydrolysis, mainly carried out by monoacylglycerol lipase (MAGL), along with a small contribution by the α/β-hydrolase domain (ABHD) proteins ABHD6 and ABHD12. Recent methodological progress allowing kinetic monitoring of glycerol liberation has facilitated substrate profiling of the human endocannabinoid hydrolases, and these studies have revealed that the three enzymes have distinct monoacylglycerol substrate and isomer preferences. Here, we have extended this substrate profiling to cover four prostaglandin glycerol esters, namely, 15-deoxy-Δ(12,14)-prostaglandin J2-2-glycerol (15d-PGJ2-G), PGD2-G, PGE2-G, and PGF2 α-G. We found that the three enzymes hydrolyzed the tested substrates, albeit with distinct rates and preferences. Although human ABHD12 (hABHD12) showed only marginal activity toward PGE2-G, hABHD6 preferentially hydrolyzed PGD2-G, and human MAGL (hMAGL) robustly hydrolyzed all four. This was particularly intriguing for MAGL activity toward 15d-PGJ2-G whose hydrolysis rate rivaled that of the best monoacylglycerol substrates. Molecular modeling studies combined with kinetic analysis supported favorable interaction with the hMAGL active site. Long and short MAGL isoforms shared a similar substrate profile, and hMAGL hydrolyzed 15d-PGJ2-G also in living cells. The ability of 15d-PGJ2-G to activate the canonical nuclear factor erythroid 2-related factor (Nrf2) signaling pathway used by 15d-PGJ2 was assessed, and these studies revealed for the first time that 15d-PGJ2 and 15d-PGJ2-G similarly activated Nrf2 signaling as well as transcription of target genes of this pathway. Our study challenges previous claims regarding the ability of MAGL to catalyze PG-G hydrolysis and extend the MAGL substrate profile beyond the classic monoacylglycerols.

Redox regulation of antioxidants, autophagy, and the response to stress: implications for electrophile therapeutics

Redox networks in the cell integrate signaling pathways that control metabolism, energetics, cell survival, and death. The physiological second messengers that modulate these pathways include nitric oxide, hydrogen peroxide, and electrophiles. Electrophiles are produced in the cell via both enzymatic and nonenzymatic lipid peroxidation and are also relatively abundant constituents of the diet. These compounds bind covalently to families of cysteine-containing, redox-sensing proteins that constitute the electrophile-responsive proteome, the subproteomes of which are found in localized intracellular domains. These include those proteins controlling responses to oxidative stress in the cytosol-notably the Keap1-Nrf2 pathway, the autophagy-lysosomal pathway, and proteins in other compartments including mitochondria and endoplasmic reticulum. The signaling pathways through which electrophiles function have unique characteristics that could be exploited for novel therapeutic interventions; however, development of such therapeutic strategies has been challenging due to a lack of basic understanding of the mechanisms controlling this form of redox signaling. In this review, we discuss current knowledge of the basic mechanisms of thiol-electrophile signaling and its potential impact on the translation of this important field of redox biology to the clinic. Emerging understanding of thiol-electrophile interactions and redox signaling suggests replacement of the oxidative stress hypothesis with a new redox biology paradigm, which provides an exciting and influential framework for guiding translational research.

Does Nrf2 gene transfer facilitate recovery after contusion spinal cord injury?

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) modulates gene expression in response to oxidative damage in neurodegenerative diseases, including spinal cord injury (SCI). We noticed that activation of Nrf2 pathway persists for an extended time after clinically relevant contusion model of SCI. Injured Nrf2(-/-) mice were impaired in hindlimb function, exhibited increased atrophy, demyelination, and astrogliosis of the SC concomitant with altered expression of genes controlling apoptosis, inflammation, and neurotrophic factors suggesting the importance of Nrf2 for recovery. We used lentiviral gene transfer to increase Nrf2 expression and improve functional recovery after SCI. Although the transferred Nrf2 was expressed in neurons and astrocytes, we noticed hindlimb function impairment and elevated expression of pro-inflammatory cytokines as an adverse effect. These toxic effects were not reduced by including Nrf2 in the lentiviral vector. Augmenting the amount of delivered Nrf2 gene diminished toxic effects of the lentivirus, yet was not sufficient to improve functional recovery. Results of this study lead to the hypothesis that Nrf2 plays a crucial and multifaceted role in recovery from SCI, but even high overexpression of Nrf2 in injured SC may not offer extra benefit, providing protection only against lentivirus-induced toxicity that is manifested in the SC.

Lipid accumulation, lipid oxidation, and low plasma levels of acquired antibodies against oxidized lipids associate with degeneration and rupture of the intracranial aneurysm wall

Background

Rupture of a saccular intracranial aneurysm (sIA) causes an often fatal subarachnoid hemorrhage (SAH). Why some sIAs rupture remains unknown. Since sIA walls bear some histological similarities with early atherosclerotic lesions, we hypothesized that accumulation and oxidation of lipids might occur in the sIA wall and might associate with sIA wall degeneration. Tissue samples from sIA fundi (n = 54) were studied with histochemistry and a panel of previously characterized antibodies for epitopes of oxidized LDL (OxLDL). Plasma samples from sIA carriers (n = 125) were studied with ELISA and EIA for IgG and IgM -antibodies against a panel of OxLDL epitopes.

Results

Lipid accumulation, foam cells, and oxidized lipids were found both in unruptured and ruptured sIA walls. Lipid accumulation associated with wall degeneration (P < 0.001), as did the expression of adipophilin, a marker of lipid ingestion by cells. Lipid accumulation associated also with loss of mural cells (P < 0.001), as did the accumulation of OxLDL (P < 0.001). Plasma IgG antibody titers against OxLDL or malondialdehyde modified LDL were higher in patients with unruptured sIAs than in patients with aneurysmal SAH (P ≤ 0.001). A trend but not statistically significant differences were found in plasma IgM antibodies against oxidized lipids.

Conclusions

Accumulation of lipids and their oxidation in the sIA wall associates with the degeneration of the sIA wall. Acquired immunity against oxidized lipid epitopes may be protective of lipid associated sIA wall degeneration, but warrants further studies.

Abstract 141: The Loss of Nrf2 Enhances Vascular Inflammation but Reduces Atherosclerosis via Effects on Plasma Lipids in LDL Receptor Deficient Mice Fed High Fat Diet

OBJECTIVE

Transcription factor NF-E2-related factor 2 (Nrf2) regulates antioxidant and detoxifying enzymes affording cytoprotection in the cardiovascular system. We have previously reported that Nrf2 deficiency specific to bone marrow derived cells aggravates atherosclerosis in LDL receptor deficient (LDLR-/-) mice. Furthermore, Nrf2 deficiency in macrophages enhances foam cell formation and promotes the proinflammatory phenotype. In contrast, the total loss of Nrf2 has been shown to protect against atherogenesis in apoE-deficient mice. The mechanism by which Nrf2 deficiency affords atheroprotection in apoE-model is currently unknown, but combined systemic and local vascular effects have been proposed. Given these contrasting results, we aimed at assessing the effect of total loss of Nrf2 on atherogenesis in hypercholesterolemic LDLR-/- mice.

METHODS AND RESULTS

Nrf2-/- mice were cross-bred to LDLR-/- mice and fed a high fat diet (HFD) for 6 or 12 weeks. The degree of atherosclerosis was assessed from the cross-sections of proximal aorta. Nrf2 deficiency decreased atherosclerosis in females from 17.2±8.7 % (mean ±SD, n=11-25) to 12.3±4.6 % (p=0.1) and in males from 11.2±3.9 % to 7.6±4.6 % (p=0.025) after 6 weeks on HFD. After 12 weeks on HFD the effects were more pronounced, as Nrf2 deficiency decreased atherosclerosis from 36.5±5.5 % to 30.3±3.5 % in females (p=0.001) and from 30.6±5.7 % to 21.3±6.9 % in males (p=0.005). Nrf2 deficiency also increased the macrophage content relative to lesion area. Supporting systemic effects, Nrf2 deficiency reduced plasma total cholesterol from 24.0±8.4 mmol/l to 10.6±6,7 mmol/l (p=0.006) and triglyceride levels from 3.6±1.4 mmol/l to 1.7±1.2 mmol/l (p=0.008) in males after 6 weeks on HFD.

CONCLUSIONS

In contrast to bone marrow specific Nrf2 deficiency, total loss of Nrf2 aggravates atherosclerosis in LDLR-/- mice likely via systemic effects on lipid metabolism.

The absence of macrophage Nrf2 promotes early atherogenesis

AIMS

The loss of nuclear factor E2-related factor 2 (Nrf2) has been shown to protect against atherogenesis in apoE-deficient mice. The mechanism by which Nrf2 deficiency affords atheroprotection in this model is currently unknown, but combined systemic and local vascular effects on lesion macrophages have been proposed. We investigated the effect of bone marrow-specific loss of Nrf2 on early atherogenesis in low-density lipoprotein (LDL) receptor-deficient (LDLR(-/-)) mice, and assessed the effect of Nrf2 on cellular accumulation of modified LDLs and the expression of inflammatory markers in macrophages.

METHODS AND RESULTS

The effect of bone marrow-specific loss of Nrf2 on atherogenesis was studied using bone marrow transplantation of wild-type (WT) or Nrf2(-/-) bone marrow to LDLR(-/-) mice. Mice transplanted with Nrf2(-/-) bone marrow and fed a high-fat diet for 6 weeks exhibited significantly larger atherosclerotic lesions than WT bone marrow transplanted mice. Moreover, in thioglycollate-elicited Nrf2(-/-) macrophages, the uptake of acetylated and malondialdehyde-modified LDLs was increased in comparison with WT controls, with the concomitant increase in the expression of scavenger receptor A and toll-like receptor 4. In addition, the expression of pro-inflammatory monocyte chemoattractant protein-1 and interleukin-6 were increased in Nrf2(-/-) vs. WT macrophages.

CONCLUSION

Nrf2 deficiency specific to bone marrow-derived cells aggravates atherosclerosis in LDLR(-/-) mice. Furthermore, the loss of Nrf2 in macrophages enhances foam cell formation and promotes the pro-inflammatory phenotype.

The Keap1-Nrf2 pathway: Mechanisms of activation and dysregulation in cancer

The Keap1-Nrf2 pathway is the major regulator of cytoprotective responses to oxidative and electrophilic stress. Although cell signaling pathways triggered by the transcription factor Nrf2 prevent cancer initiation and progression in normal and premalignant tissues, in fully malignant cells Nrf2 activity provides growth advantage by increasing cancer chemoresistance and enhancing tumor cell growth. In this graphical review, we provide an overview of the Keap1-Nrf2 pathway and its dysregulation in cancer cells. We also briefly summarize the consequences of constitutive Nrf2 activation in cancer cells and how this can be exploited in cancer gene therapy.

Prostaglandin 15d-PGJ(2) inhibits androgen receptor signaling in prostate cancer cells

Androgen signaling, in particular overexpression of the androgen receptor (AR), is critical for the growth and progression of prostate cancer. Because the AR is amenable to targeting by small-molecule inhibitors, it remains the major druggable target for the advanced disease. Inflammation has also been implicated in the cancerous growth in the prostate. Here we show that 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), an endogenously produced antiinflammatory prostaglandin, targets the AR and acts as a potent AR inhibitor, rapidly repressing AR target genes, such as FKBP51 and TMPRSS2 in prostate cancer cells. However, exposure of prostate cancer cells to 15d-PGJ(2) does not simply evoke a general inhibition of nuclear receptor activity or transcription because under the same conditions, peroxisome proliferator-activated receptor-γ is activated by 15d-PGJ(2). Moreover, 15d-PGJ(2) rapidly triggers modifications of AR by small ubiquitin-related modifier-2/3 (SUMO-2/3), which may modulate the repressing effect of 15d-PGJ(2) on AR-dependent transcription. Chromatin immunoprecipitation assays indicate that the inhibitory effect of 15d-PGJ(2) on FKBP51 and TMPRSS2 expression occurs in parallel with the inhibition of the AR binding to the regulatory regions of these genes. However, the DNA-binding activity is not the only AR function targeted by 15d-PGJ(2) because the prostaglandin also blunted the androgen-dependent interaction between the AR amino and carboxy termini. In conclusion, our results identify 15d-PGJ(2) as a potent and direct inhibitor of androgen signaling, suggesting novel possibilities in restricting the AR activity in prostate cancer cells.

Novel keto-phospholipids are generated by monocytes and macrophages, detected in cystic fibrosis, and activate peroxisome proliferator-activated receptor-γ

12/15-Lipoxygenases (LOXs) in monocytes and macrophages generate novel phospholipid-esterified eicosanoids. Here, we report the generation of two additional families of related lipids comprising 15-ketoeicosatetraenoic acid (KETE) attached to four phosphatidylethanolamines (PEs). The lipids are generated basally by 15-LOX in IL-4-stimulated monocytes, are elevated on calcium mobilization, and are detected at increased levels in bronchoalveolar lavage fluid from cystic fibrosis patients (3.6 ng/ml of lavage). Murine peritoneal macrophages generate 12-KETE-PEs, which are absent in 12/15-LOX-deficient mice. Inhibition of 15-prostaglandin dehydrogenase prevents their formation from exogenous 15-hydroxyeicosatetraenoic acid-PE in human monocytes. Both human and murine cells also generated analogous hydroperoxyeicosatetraenoic acid-PEs. The electrophilic reactivity of KETE-PEs is shown by their Michael addition to glutathione and cysteine. Lastly, both 15-hydroxyeicosatetraenoic acid-PE and 15-KETE-PE activated peroxisome proliferator-activated receptor-γ reporter activity in macrophages in a dose-dependent manner. In summary, we demonstrate novel peroxisome proliferator-activated receptor-γ-activating oxidized phospholipids generated enzymatically by LOX and 15-prostaglandin dehydrogenase in primary monocytic cells and in a human Th2-related lung disease. The lipids are a new family of bioactive mediators from the 12/15-LOX pathway that may contribute to its known anti-inflammatory actions in vivo.

Oxidative stress-regulated lentiviral TK/GCV gene therapy for lung cancer treatment

Nuclear factor erythroid-2 related factor 2 (Nrf2) is a transcription factor that regulates protection against a wide variety of toxic insults to cells, including cytotoxic cancer chemotherapeutic drugs. Many lung cancer cells harbor a mutation in either Nrf2 or its inhibitor Keap1 resulting in permanent activation of Nrf2 and chemoresistance. In this study, we sought to examine whether this attribute could be exploited in cancer suicide gene therapy by using a lentiviral (LV) vector expressing herpes simplex virus thymidine kinase (HSV-TK/GCV) under the regulation of antioxidant response element (ARE), a cis-acting enhancer sequence that binds Nrf2. In human lung adenocarcinoma cells in which Nrf2 is constitutively overexpressed, ARE activity was found to be high under basal conditions. In this setting, ARE-HSV-TK was more effective than a vector in which HSV-TK expression was driven by a constitutively active promoter. In a mouse xenograft model of lung cancer, suicide gene therapy with LV-ARE-TK/GCV was effective compared with LV-PGK-TK/GCV in reducing tumor size. We conclude that ARE-regulated HSV-TK/GCV therapy offers a promising approach for suicide cancer gene therapy in cells with high constitutive ARE activity, permitting a greater degree of therapeutic targeting to those cells.

Heme and heme biosynthesis intermediates induce heme oxygenase-1 and cytochrome P450 2A5, enzymes with putative sequential roles in heme and bilirubin metabolism: different requirement for transcription factor nuclear factor erythroid- derived 2-like 2

Cytochrome P450 2A5 (CYP2A5) oxidizes bilirubin to biliverdin and represents a putative candidate for maintaining bilirubin at safe but adequate antioxidant levels. Curiously, CYP2A5 is induced by both excessive heme and chemicals that inhibit heme synthesis. We hypothesized that heme homeostasis is a key modifier of Cyp2a5 expression via transcription factor nuclear factor erythroid-derived 2-like 2 (Nrf2) and characterized the coordination of CYP2A5 and heme oxygenase-1 (HMOX1) responses using wild-type and Nrf2(-/-) primary mouse hepatocytes. HMOX1 was rapidly elevated by exogenous hemin, thereby limiting the transactivation of Cyp2a5 until high heme (> 5µM) exposure. Nrf2 was mandatory for CYP2A5 but not for HMOX1 induction by heme. CYP2A5 was intensively and HMOX1 moderately elevated in heme synthesis blockades by succinylacetone and N-methyl protoporphyrin IX, and Nrf2 partially mediated the induction of CYP2A5. Immunoelectron microscopy revealed that CYP2A5 is targeted Nrf2 dependently both to the endoplasmic reticulum (ER) and mitochondria. However, excessive heme increased CYP2A5 predominantly in the ER. Phenobarbital, dibutyryl-cAMP, and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) overexpression stimulate heme biosynthesis and induce CYP2A5. Acute but not chronic CYP2A5 induction by phenobarbital required Nrf2, whereas CYP2A5 induction by dibutyryl-cAMP and PGC-1α was potentiated by Nrf2 knockout. Collectively, heme homeostasis is established as a crucial regulator of hepatic Cyp2a5 expression mediated via Nrf2 activation, whereas Nrf2 is redundant for Hmox1 induction by heme. Similar subcellular targeting and coordination of CYP2A5 and HMOX1 responses suggest favorable conditions for enhanced CYP2A5-mediated bilirubin maintenance in altered heme homeostasis that predisposes to oxidative stress.

Abstract 203: Silencing of Macrophage Scavenger Receptor SR-A or CD36 Modulates Transcription Factor NF-κB Activity by Distinct Mechanisms

Background: Macrophage scavenger receptors SR-A and CD36 play a key role in the pathogenesis of atherosclerosis by participating in the uptake of modified lipoproteins, further leading to formation of foam cells. We have recently shown that RNAi-mediated silencing of these receptors decreases atherogenesis in hyperlipidemic LDLR -/- /ApoB 100/100 mice. Additionally, we discovered that there is a reciprocal regulation mechanism between these two receptors in mouse macrophages. Because there is limited information on the involvement of transcription factor NF-κB to SR-A and CD36 expression, the aim of this study was to investigate the role of NF-κB in the regulation of these receptors in detail.

Methods and Results: Lentiviral vector mediated silencing of SR-A and CD36 alters the behavior of transcription factor NF-κB in mouse macrophages. After LPS exposure, SR-A silencing enhanced the classical NF-κB activation measured by activation of NF-κB responsive genes such as M-CSF, MCP-1 and ICAM-1. Moreover, CD36 silencing increased the expression of NF-κB subunit p50 with and without LPS stimulation by 2.7-fold (p<0.001) and 1.4-fold (p<0.01), respectively. Consequently, expressions of several p50 homodimer target genes, such as IL-6 and IL-10, were increased when CD36 was silenced. Finally, two putative NF-κB binding sites and increased p50 binding to SR-A promoter were found by EMSA, suggesting that SR-A is a p50 responsive gene, and that p50 is responsible for the reciprocal upregulation of SR-A when CD36 is silenced.

Conclusion: These results suggest that SR-A and CD36 modulate macrophage functions under inflammatory conditions, and imply that SR-A and CD36 are important signal transducers in inflammatory events involving NF-κB.

Activation of stress signaling pathways by electrophilic oxidized and nitrated lipids

Unsaturated fatty acids are prone to radical reactions that occur in biological situations where extensive formation of reactive oxygen and nitrogen species (ROS and RNS) takes place. These reactions are frequent in inflammatory conditions such as atherosclerosis, and yield a variety of biologically active species, many of which are electrophilic in nature. Electrophilic lipid oxidation and nitration products can influence redox cell signaling via S-alkylation of protein thiols, and moderate exposure to these species evokes protective cell signaling responses through this mechanism. Herein, we review the stress signaling pathways elicited by electrophiles derived from unsaturated fatty acids, focusing on the Keap1-Nrf2 pathway, the heat shock response pathway (HSR), and the unfolded protein response pathway (UPR).

Heme oxygenase 1 is induced by miR-155 via reduced BACH1 translation in endothelial cells

Heme oxygenase 1 (HO-1) is a stress-inducible enzyme that degrades redox-active heme-producing biliverdin, carbon monoxide, and Fe(2+). It protects cells under various stress conditions and mediates anti-inflammatory and vasodilatory effects in the endothelium. The expression of HMOX1, the HO-1 gene, is highly inducible and its transcriptional regulation is complex. HMOX1 is induced by various proinflammatory stimuli via NF-κB in human endothelial cells, but functional NF-κB-binding elements have not been identified from the human gene. However, the regulation of HMOX1 by the antioxidant-response element is firmly established, with the transcription factor BACH1 serving as a repressor and Nrf2 as an enhancer. miR-155 is one of the TNFα-inducible endothelial microRNAs predicted to bind to the BACH1 mRNA. Oligonucleotides mimicking miR-155 efficiently inhibited BACH1 protein translation, resulting in a concentration-dependent increase in HMOX1 mRNA and protein expression in human umbilical vein endothelial cells. Moreover, endogenous miR-155 was upregulated by TNFα via an NF-κB-dependent mechanism with a subsequent increase in HMOX1 expression. We propose that increased HMOX1 expression in endothelial cells by TNFα results from miR-155-induced repression of BACH1 rather than direct induction of HMOX1 via NF-κB, and that miR-155 is cytoprotective during inflammation by elevating HO-1 expression in endothelial cells.