Cigarette smoke-induced cell cycle arrest in spermatocytes [GC-2spd(ts)] is mediated through crosstalk between Ahr-Nrf2 pathway and MAPK signaling

NRF2 and the Moirai: Life and Death Decisions on Cell Fates

Significance: The transcription factor NRF2 (NF-E2-related factor 2) plays an important role as a master regulator of the cellular defense system by activating transcriptional programs of NRF2 target genes encoding multiple enzymes related to cellular redox balance and xenobiotic detoxication. Comprehensive transcriptional analyses continue to reveal an ever-broadening range of NRF2 target genes, demonstrating the sophistication and diversification of NRF2 biological signatures beyond its canonical cytoprotective roles. Recent Advances: Accumulating evidence indicates that NRF2 has a strong association with the regulation of cell fates by influencing key processes of cellular transitions in the three major phases of the life cycle of the cell (i.e., cell birth, cell differentiation, and cell death). The molecular integration of NRF2 signaling into this regulatory program occurs through a wide range of NRF2 target genes encompassing canonical functions and those manipulating cell fate pathways. Critical Issues: A singular focus on NRF2 signaling for dissecting its actions limits in-depth understanding of its intersection with the molecular machinery of cell fate determinations. Compensatory responses of downstream pathways governed by NRF2 executed by a variety of transcription factors and multifactorial signaling crosstalk require further exploration. Future Directions: Further investigations using optimized in vivo models and active engagement of overarching approaches to probe the interplay of widespread pathways are needed to study the properties and capabilities of NRF2 signaling as a part of a large network within the cell fate regulatory domain. Antioxid. Redox Signal. 38, 684-708.

Polycyclic aromatic hydrocarbons in bone homeostasis

Prolonged exposure to polycyclic aromatic hydrocarbons (PAHs) may result in autoimmune diseases, such as rheumatoid arthritis (RA) and osteoporosis (OP), which are based on an imbalance in bone homeostasis. These diseases are characterized by bone erosion and even a disruption in homeostasis, including in osteoblasts and osteoclasts. Current evidence indicates that multiple factors affect the progression of bone homeostasis, such as genetic susceptibility and epigenetic modifications. However, environmental factors, especially PAHs from various sources, have been shown to play an increasingly prominent role in the progression of bone homeostasis. Hence, it is essential to investigate the effects and pathogenesis of PAHs in bone homeostasis. In this review, recent progress is summarized concerning the effects and mechanisms of PAHs and their ligands and receptors in bone homeostasis. Moreover, strategies based on the effects and mechanisms of PAHs in the regulation of the bone balance and alleviation of bone destruction are also reviewed. We further discuss the future challenges and perspectives regarding the roles of PAHs in autoimmune diseases based on bone homeostasis.

Lycopene prevents DEHP-induced hepatic oxidative stress damage by crosstalk between AHR-Nrf2 pathway

Di (2-ethylhexyl) phthalate (DEHP) is a widespread plasticizer that persists in the environment and can significantly contribute to serious health hazards of liver especially oxidative stress injury. Lycopene (LYC) as a carotenoid has recently gained widespread attention because of antioxidant activity. However, the potential mechanism of DEHP-induced hepatotoxicity and antagonism effect of LYC on it are still unclear. To explore the underlying mechanisms of this hypothesis, the mice were given by gavage with LYC (5 mg/kg) and DEHP (500 or 1000 mg/kg). The data suggested that DEHP caused liver enlargement, reduction of antioxidant activity markers, increase of oxidative stress indicators and disorder of cytochrome P450 enzymes system (CYP450s) homeostasis. DEHP-induced reactive oxygen species (ROS) activated the NF-E2-relatedfactor2 (Nrf2) and nuclear xenobiotic receptors (NXRs) system including Aryl hydrocarbon receptor (AHR), Pregnane X receptor (PXR) and Constitutive androstane receptor (CAR). Interestingly, these disorders and injuries were prevented after LYC treatment. Taken together, DEHP administration resulted in hepatotoxicity including oxidative stress injury and disordered CYP450 system, but these alterations might be ameliorated by LYC via crosstalk between AHR-Nrf2 pathway.

Effects of Different Components of PM2.5 on the Expression Levels of NF-κB Family Gene mRNA and Inflammatory Molecules in Human Macrophage

Background: Studies have found that exposure to fine particulate matter with sizes below 2.5 µm (PM2.5) might cause inflammation response via the NF-κB pathway. To date, only a few studies have focused on the toxicity of different components of PM2.5. We aimed to explore the effects of PM2.5 with different components on the expression levels of NF-κB family gene mRNA and inflammatory molecules in human macrophages. Methods: Human monocytic cell line THP-1-derived macrophages were exposed to water-soluble (W-PM2.5), fat-soluble (F-PM2.5), and insoluble (I-PM2.5) PM2.5. The cell survival rate was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The levels of inflammatory molecules were determined by enzyme-linked immunosorbent assay (ELISA), and the relative mRNA levels of the NF-κB family gene were determined by real time PCR. Results: PM2.5 could decrease the cell viability. After exposure to W-PM2.5, the levels of interleukins (IL)-1β and IL-12 p70 significantly increased. After exposure to F-PM2.5, the levels of IL-12 p70 significantly increased. The levels of IL-12 p70 and TNF-α after exposure to I-PM2.5 were significantly higher than that in W- and F-PM2.5 treatment groups. The levels of IL-8, C reactive protein (CRP), and cyclooxygenase (COX)-2 increased only after exposure to I-PM2.5. F-PM2.5 increased the mRNA levels of NF-κB genes, especially NF-κB1 and RelA. Conclusions: PM2.5 can decrease the cell survival rate and up-regulate the expression of NF-κB family gene mRNA and inflammatory molecules. The main toxic components of PM2.5 related to inflammatory response in macrophages were the I-PM2.5.

Inflammatory marker and aryl hydrocarbon receptor-dependent responses in human macrophages exposed to emissions from biodiesel fuels

Biodiesel or renewable diesel fuels are alternative fuels produced from vegetable oil and animal tallow that are being considered to help reduce the use of petroleum-based fuels and emissions of air pollutants including greenhouse gases. Here, we analyzed the gene expression of inflammatory marker responses and the cytochrome P450 1A1 (CYP1A1) enzyme after exposure to diesel and biodiesel emission samples generated from an in-use heavy-duty diesel vehicle. Particulate emission samples from petroleum-based California Air Resource Board (CARB)-certified ultralow sulfur diesel (CARB ULSD), biodiesel, and renewable hydro-treated diesel all induced inflammatory markers such as cyclooxygenase-2 (COX)-2 and interleukin (IL)-8 in human U937-derived macrophages and the expression of the xenobiotic metabolizing enzyme CYP1A1. Furthermore, the results indicate that the particle emissions from CARB ULSD and the alternative diesel fuel blends activate the aryl hydrocarbon receptor (AhR) and induce CYP1A1 in a dose- and AhR-dependent manner which was supported by the AhR luciferase reporter assay and gel shift analysis. Based on a per mile emissions with the model year 2000 heavy duty vehicle tested, the effects of the alternative diesel fuel blends emissions on the expression on inflammatory markers like IL-8 and COX-2 tend to be lower than emission samples derived from CARB ULSD fuel. The results will help to assess the potential benefits and toxicity from biofuel use as alternative fuels in modern technology diesel engines.

The antioxidant transcription factor Nrf2 modulates the stress response and phenotype of malignant as well as premalignant pancreatic ductal epithelial cells by inducing expression of the ATF3 splicing variant ΔZip2

Pancreatic ductal adenocarcinoma (PDAC) exhibits one of the worst survival rates of all cancers. While death rates show declining trends in the majority of cancers, PDAC registers rising rates. Based on the recently described crosstalk between TGF-β1 and Nrf2 in the PDAC development, the involvement of ATF3 and its splice variant ΔZip2 in TGF-β1- and Nrf2-driven pancreatic tumorigenesis was investigated. As demonstrated here, PDAC (Panc1, T3M4) cells or premalignant H6c7 pancreatic ductal epithelial cells differentially express ΔZip2- and ATF3, relating to stronger Nrf2 activity seen in Panc1 cells and TGF-ß1 activity in T3M4 or H6c7 cells, respectively. Treatment with the electrophile/oxidative stress inducer tBHQ or the cytostatic drug gemcitabine strongly elevated ΔZip2 expression in a Nrf2-dependent fashion. The differential expression of ATF3 and ΔZip2 in response to Nrf2 and TGF-ß1 relates to differential ATF3-gene promoter usage, giving rise of distinct splice variants. Nrf2-dependent ΔZip2 expression confers resistance against gemcitabine-induced apoptosis, only partially relating to interference with ATF3 and its proapoptotic activity, e.g., through CHOP-expression. In fact, ΔZip2 autonomously activates expression of cIAP anti-apoptotic proteins. Moreover, ΔZip2 favors and ATF3 suppresses growth and clonal expansion of PDAC cells, again partially independent of each other. Using a Panc1 tumor xenograft model in SCID-beige mice, the opposite activities of ATF3 and ΔZip2 on tumor-growth and chemoresistance were verified in vivo. Immunohistochemical analyses confirmed ΔZip2 and Nrf2 coexpression in cancerous and PanIN structures of human PDAC and chronic pancreatitis tissues, respectively, which to some extent was reciprocal to ATF3 expression. It is concluded that depending on selective ATF3-gene promoter usage by Nrf2, the ΔZip2 expression is induced in response to electrophile/oxidative (here through tBHQ) and xenobiotic (here through gemcitabine) stress, providing apoptosis protection and growth advantages to pancreatic ductal epithelial cells. This condition may substantially add to pancreatic carcinogenesis driven by chronic inflammation.

Norisoboldine, a natural aryl hydrocarbon receptor agonist, alleviates TNBS-induced colitis in mice, by inhibiting the activation of NLRP3 inflammasome

Although the etiology of inflammatory bowel disease is still uncertain, increasing evidence indicates that the excessive activation of NLRP3 inflammasome plays a major role. Norisoboldine (NOR), an alkaloid isolated from Radix Linderae, has previously been demonstrated to inhibit inflammation and IL-1β production. The present study was to examine the effect of NOR on colitis and the underlying mechanism related to NLRP3 inflammasome activation. Our results showed that NOR alleviated colitis symptom in mice induced by 2, 4, 6-trinitrobenzene sulfonic acid (TNBS). Moreover, it significantly reduced expressions of cleaved IL-1β, NLRP3 and cleaved Caspase-1 but not ASC in colons of mice. In THP-1 cells, NOR suppressed the expressions of NLRP3, cleaved Caspase-1 and cleaved IL-1β but not ASC induced by lipopolysaccharide (LPS) and adenosine triphosphate (ATP). Furthermore, NOR could activate aryl hydrocarbon receptor (AhR) in THP-1 cells, inducing CYP1A1 mRNA expression, and promoting dissociation of AhR/HSP90 complexes, association of AhR and ARNT, AhR nuclear translocation, XRE reporter activity and binding activity of AhR/ARNT/XRE. Both siAhR and α-naphthoflavone (α-NF) markedly diminished the inhibition of NOR on NLRP3 inflammasome activation. In addition, NOR elevated Nrf2 level and reduced ROS level in LPS- and ATP-stimulated THP-1 cells, which was reversed by either siAhR or α-NF treatment. Finally, correlations between activation of AhR and attenuation of colitis, inhibition of NLRP3 inflammasome activation and up-regulation of Nrf2 level in colons were validated in mice with TNBS-induced colitis. Taken together, NOR ameliorated TNBS-induced colitis in mice through inhibiting NLRP3 inflammasome activation via regulating AhR/Nrf2/ROS signaling pathway.

Xenobiotic pregnane X receptor promotes neointimal formation in balloon-injured rat carotid arteries

Pregnane X receptor (PXR) is a member of nuclear receptor superfamily and responsible for the detoxification of xenobiotics. Recent studies demonstrated that PXR was also expressed in the vasculature and protected the vessels from endogenous and exogenous insults, thus representing a novel gatekeeper in vascular defense. In this study, we examined the potential function of PXR in the neointimal formation following vascular injury. In the rat carotid artery after balloon injury, overexpression of a constitutively active PXR increased the intima-to-media ratio in the injured region. PXR increased cell proliferation and migration in cultured rat aortic smooth muscle cells (SMCs) by inducing the expressions of cyclins (cyclin A, D1, and E) and cyclin-dependent kinase 2. In addition, PXR increased the phosphorylation and activation of extracellular-signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). Inactivation of ERK1/2 and p38 MAPK pathways using selective inhibitors (U0126 and SB203580) abrogated PXR-induced SMC proliferation and migration. Furthermore, cigarette smoke particles (CSP) activated PXR in SMCs. Knockdown of PXR by small interfering RNA suppressed the cell proliferation, migration, and activation of the MAPK pathways by CSP. These findings suggested a novel role for PXR in promoting SMC proliferation and migration, and neointimal hyperplasia. Therefore, PXR may be a potential therapeutic target for vascular disease related to xenobiotics such as cigarette smoking and other environmental pollutants.

Salidroside protects against foam cell formation and apoptosis, possibly via the MAPK and AKT signaling pathways

Background

Foam cell formation and apoptosis are closely associated with atherosclerosis pathogenesis. We determined the effect of salidroside on oxidized low-density lipoprotein (ox-LDL)-induced foam cell formation and apoptosis in THP1 human acute monocytic leukemia cells and investigated the associated molecular mechanisms.

Methods

THP1-derived macrophages were incubated with salidroside for 5 h and then exposed to ox-LDL for 24 h to induce foam cell formation. Cytotoxicity, lipid deposition, apoptosis, and the expression of various proteins were tested using the CCK8 kit, Oil Red O staining, flow cytometry, and western blotting, respectively.

Results

Ox-LDL treatment alone promoted macrophage-derived foam cell formation, while salidroside treatment alone inhibited it (p < 0.05). The number of early/late apoptotic cells decreased with salidroside treatment in a dose-dependent manner (p < 0.05). Salidroside dramatically upregulated nuclear factor erythroid 2-related factor 2, but had no effect on heme oxygenase-1 expression; moreover, it markedly downregulated ox-LDL receptor 1 and upregulated ATP-binding cassette transporter A1. Salidroside also obviously decreased the phosphorylation of JNK, ERK, p38 MAPK, and increased that of Akt. However, the total expression of these proteins was not affected.

Conclusion

Based on our findings, we speculate that salidroside can suppress ox-LDL-induced THP1-derived foam cell formation and apoptosis, partly by regulating the MAPK and Akt signaling pathways.

Paternal smoking and germ cell death: A mechanistic link to the effects of cigarette smoke on spermatogenesis and possible long-term sequelae in offspring

Paternal exposure to constituents of cigarette smoke (CS) is reportedly associated with infertility, birth defects and childhood cancers even though the mechanism behind this relationship is still unclear. Chronic cigarette smoking by men leads to poor sperm quality and quantity mainly through oxidative stress and also direct assault by CS metabolites. Among several carcinogenic and teratogenic components of cigarette smoke condensate (CSC), polycyclic aromatic hydrocarbons (PAHs) display a preeminent role in accelerating germ cell death via the cytoplasmic transcription factor, aryl hydrocarbon receptor (AHR) that is present across all stages of spermatogenesis. Activation of AHR by growth factors though benefits normal cellular functions, its mediation by CSC in a spermatocyte cell line [Gc2(spd)ts] adversely affects the expression of a battery of genes associated with antioxidant mechanisms, cell proliferation and apoptosis, and cell cycle progress. Besides, the CSC-mediated cross talk either between AHR and NRF2 or AHR-NRF2 and MAPKs pathways inhibits normal proliferation of the spermatogenic GC-2spd(ts) cells in vitro and cell death of spermatocytes in vivo. Pharmacological inactivation of CSC-induced AHR but not its genetic manipulation seems preventing DNA and cell membrane damage in Gc2(spd)ts. Data from recent reports suggest that the cigarette smoke affects both the genomic and epigenomic components of the sperm and attributes any associated changes to developmental defects in the offspring. Thus, the studies discussed here in this review shed light on possible mechanistic factors that could probably be responsible for the paternally mediated birth defects in the offspring following exposure to the toxic constituents of cigarette smoke.

Paternal exposure to cigarette smoke condensate leads to reproductive sequelae and developmental abnormalities in the offspring of mice

Paternal smoking is associated with infertility, birth defects and childhood cancers. Our earlier studies using cigarette smoke condensate (CSC) demonstrated several deleterious changes in male germ cells. Here, we hypothesize that chronic paternal exposure to CSC causes molecular and phenotypic changes in the sire and the offspring, respectively. In this mouse study, CSC caused DNA damage and cytotoxicity in testes via accumulation of benzo(a)pyrene (B[a]P) and cotinine. Decreased expression of growth arrest and DNA damage inducible alpha (Gadd45a), aryl hydrocarbon receptor (Ahr), and cyclin-dependent kinase inhibitor 1A (P21) was seen in CSC exposed testes. Apoptotic germ cell death was detected by induction of Fas, FasL, and activated caspase-3. The CSC-exposed males displayed reduction in sperm motility and fertilizing ability and sired pups with reduced body weight and crown-rump length, and smaller litter size with higher numbers of resorption. This model of CSC exposure demonstrates testicular toxicity and developmental defects in the offspring.

Role of AhR in positive regulation of cell proliferation and survival

The aryl hydrocarbon receptor (AhR) is an important nuclear transcription factor that is best known for mediating toxic responses by adjusting numbers of metabolism-related enzymes, including CYP1A1 and CYP1B1. Previous findings have revealed that, in addition to negatively regulating cell proliferation and survival, AhR may also positively regulate these pathways. Here, we review these findings and summarize distinct mechanisms by which AhR promotes cell proliferation and survival, including modulation of receptor expression, growth factor signalling and apoptosis, regulating the cell cycle and promoting cytokine expression. This review will aid better understanding the role of AhR in positive regulation of cell proliferation and survival.

Cigarette smoke-induced cell death of a spermatocyte cell line can be prevented by inactivating the Aryl hydrocarbon receptor

Cigarette smoke exposure causes germ cell death during spermatogenesis. Our earlier studies demonstrated that cigarette smoke condensate (CSC) causes spermatocyte cell death in vivo and growth arrest of the mouse spermatocyte cell line (GC-2spd(ts)) in vitro via the aryl hydrocarbon receptor (AHR). We hypothesize here that inactivation of AHR could prevent the CSC-induced cell death in spermatocytes. We demonstrate that CSC exposure generates oxidative stress, which differentially regulates mitochondrial apoptosis in GC-2spd(ts) and wild type (WT) and AHR knockout (AHR-KO) mouse embryonic fibroblasts (MEFs). SiRNA-mediated silencing of Ahr augments the extent of CSC-mediated cellular damage while complementing the AHR-knockout condition. Pharmacological inhibition using the AHR-antagonist (CH223191) modulates the CSC-altered expression of apoptotic proteins and significantly abrogates DNA fragmentation though the cleavage of PARP appears AHR independent. Pretreatment with CH223191 at concentrations above 50 μM significantly prevents the CSC-induced activation of caspase-3/7 and externalization of phosphatidylserine in the plasma membrane. However, MAPK inhibitors alone or together with CH223191 could not prevent the membrane damage upon CSC addition and the caspase-3/7 activation and membrane damage in AHR-deficient MEF indicates the interplay of multiple cell signaling and cytoprotective ability of AHR. Thus the data obtained on one hand signifies the protective role of AHR in maintaining normal cellular homeostasis and the other, could be a potential prophylactic therapeutic target to promote cell survival and growth under cigarette smoke exposed environment by receptor antagonism via CH223191-like mechanism. Antagonist-mediated inactivation of the aryl hydrocarbon receptor blocks downstream events leading to cigarette smoke-induced cell death of a spermatocyte cell line.

Novel therapy for locally advanced triple-negative breast cancer

To evaluate a novel therapy for triple-negative breast cancer (TNBC), the biological responses to vitamin K3 (VK3) should be considered with the understanding of the features of breast cancer. In human breast cancer cell lines, the effects of VK3 on cell growth inhibition and the cellular signaling pathway were determined by MTT assay and western blotting. In the in vivo study, a subcutaneous tumor model of breast cancer was created, VK3 was injected into the subcutaneous tumors, and tumor size was measured. The IC₅₀ of VK3 for breast cancer cells was calculated to be 11.3–25.1 μM. VK3 induced phosphorylation of whole tyrosine and epidermal growth factor receptor. VK3 mediated phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) for 30 min. ERK but not JNK phosphorylation was maintained for at least 6 h. In contrast, another antioxidant agent, catalase, showed no effect on either ERK phosphorylation or growth inhibition. On built-up tumors under the skin of mice, local treatment with VK3 was effective in a time- and dose-dependent manner, and the experiments for total tumor volume also showed a dose-dependent effect of VK3. The expression of phosphorylated ERK was clearly detected at 10.9 times the control in tumor tissue, whereas ethanol itself showed no effect. In conclusion, ERK plays a critical role in VK3-induced growth inhibition, and it will be the focus of next steps in the development of molecular therapy for TNBC.