Long Noncoding RNA UCA1 Correlates With Electropathology in Patients With Atrial Fibrillation

BACKGROUND

Perpetuation of atrial fibrillation (AF) is rooted in derailment of molecular proteostasis pathways that cause electrical conduction disorders that drive AF. Emerging evidence indicates a role for long noncoding RNAs (lncRNAs) in the pathophysiology of cardiac diseases, including AF.

OBJECTIVES

In the present study, the authors explored the association between 3 cardiac lncRNAs and the degree of electropathology.

METHODS

Patients had paroxysmal AF (ParAF) (n = 59), persistent AF (PerAF) (n = 56), or normal sinus rhythm without a history of AF (SR) (n = 70). The relative expression levels of urothelial carcinoma-associated 1 (UCA1), OXCT1-AS1 (SARRAH), and the mitochondrial lncRNA uc022bqs.q (LIPCAR) were measured by means of quantitative reverse-transcription polymerase chain reaction in the right atrial appendage (RAA) or serum (or both). A selection of the patients was subjected to high-resolution epicardial mapping to evaluate electrophysiologic features during SR.

RESULTS

The expression levels of SARRAH and LIPCAR were decreased in RAAs of all AF patients compared with SR. Also, in RAAs, UCA1 levels significantly correlated with the percentage of conduction block and delay, and inversely with conduction velocity, indicating that UCA1 levels in RAA reflect the degree of electrophysiologic disorders. Moreover, in serum samples, SARRAH and UCA1 levels were increased in the total AF group and ParAF patients compared with SR.

CONCLUSIONS

LncRNAs SARRAH and LIPCAR are reduced in RAA of AF patients, and UCA1 levels correlate with electrophysiologic conduction abnormalities. Thus, RAA UCA1 levels may aid staging of electropathology severity and act as a patient-tailored bioelectrical fingerprint.

Disruption of Sarcoplasmic Reticulum-Mitochondrial Contacts Underlies Contractile Dysfunction in Experimental and Human Atrial Fibrillation: A Key Role of Mitofusin 2

Background Atrial fibrillation (AF) is the most common and progressive tachyarrhythmia. Diabetes is a common risk factor for AF. Recent research findings revealed that microtubule network disruption underlies AF. The microtubule network mediates the contact between sarcoplasmic reticulum and mitochondria, 2 essential organelles for normal cardiomyocyte function. Therefore, disruption of the microtubule network may impair sarcoplasmic reticulum and mitochondrial contacts (SRMCs) and subsequently cardiomyocyte function. The current study aims to determine whether microtubule-mediated SRMCs disruption underlies diabetes-associated AF. Methods and Results Tachypacing (mimicking AF) and high glucose (mimicking diabetes) significantly impaired contractile function in HL-1 cardiomyocytes (loss of calcium transient) and Drosophila (reduced heart rate and increased arrhythmia), both of which were prevented by microtubule stabilizers. Furthermore, both tachypacing and high glucose significantly reduced SRMCs and the key SRMC tether protein mitofusin 2 (MFN2) and resulted in consequent mitochondrial dysfunction, all of which were prevented by microtubule stabilizers. In line with pharmacological interventions with microtubule stabilizers, cardiac-specific knockdown of MFN2 induced arrhythmia in Drosophila and overexpression of MFN2 prevented tachypacing- and high glucose-induced contractile dysfunction in HL-1 cardiomyocytes and/or Drosophila. Consistently, SRMCs/MFN2 levels were significantly reduced in right atrial appendages of patients with persistent AF compared with control patients, which was aggravated in patients with diabetes. Conclusions SRMCs may play a critical role in clinical AF, especially diabetes-related AF. Furthermore, SRMCs can be regulated by microtubules and MFN2, which represent novel potential therapeutic targets for AF.

Degree of Fibrosis in Human Atrial Tissue Is Not the Hallmark Driving AF

Background: The current paradigm is that fibrosis promotes electrophysiological disorders and drives atrial fibrillation (AF). In this current study, we investigated the relation between the degree of fibrosis in human atrial tissue samples of controls and patients in various stages of AF and the degree of electrophysiological abnormalities. Methods: The degree of fibrosis was measured in the atrial tissue and serum of patients in various stages of AF and the controls. Hereto, picrosirius and H&E staining were performed to quantify degree of total, endo-perimysial fibrosis, and cardiomyocyte diameter. Western blot quantified fibrosis markers: neural cell adhesion molecule, tissue inhibitor of metalloproteinase, lysyl oxidase, and α-smooth muscle actin. In serum, the ratio carboxyl-terminal telopeptide of collagen/matrix-metalloproteinase1 was determined. High-resolution epicardial mapping evaluated low-voltage areas and conduction abnormalities. Results: No significant differences were observed in the degree of fibrosis between the groups. Finally, no significant correlation—absolute nor spatial—was observed between all electrophysiological parameters and histological fibrosis markers. Conclusions: No differences in the degree of fibrosis were observed in patients from various stages of AF compared to the controls. Moreover, electrophysiological abnormalities did not correlate with any of the fibrosis markers. The findings indicate that fibrosis is not the hallmark of structural remodeling in AF.

Atrial heat shock protein levels are associated with early postoperative and persistence of atrial fibrillation

BACKGROUND

Early detection and staging of atrial fibrillation (AF) is of importance for clinical management. Serum (bio)markers, such as heat shock proteins (HSP), may enable AF staging and identify patients at risk for AF recurrence and postoperative AF (PoAF).

OBJECTIVE

This study evaluates the relation between serum and atrial tissue HSP levels, stages of AF, AF recurrence after treatment, and PoAF from patients undergoing cardiothoracic surgery.

METHODS

Patients without (control) and with paroxysmal, persistent (PerAF), or longstanding persistent (LSPerAF) AF were included. HSPB1, HSPA1, HSPB7, and HSPD1 levels were measured in serum obtained prior to and post intervention. HSPB1, HSPA1, HSPA5, HSPD1, HSPB5, and pHSF1 levels were measured in left and/or right atrial appendages (respectively, LAA and RAA).

RESULTS

In RAA, HSPA5 levels were significantly lower in LSPerAF and HSPD1 levels significantly higher in PerAF patients compared to controls. In RAA of controls who developed PoAF, HSPA1 and HSPA5 levels were significantly higher compared to those without PoAF. Also, HSPB1 RAA levels were lower and HSPA5 LAA levels higher in patients undergoing arrhythmia surgery who developed AF recurrence within 1 week after surgery compared to patients who did not.

CONCLUSION

HSPA5 RAA and HSPD1 RAA and LAA levels are altered in persistent stages of AF. RAA HSPA1 and HSPA5 levels associate with development of PoAF. Additionally, HSPB1 RAA and HSPA5 LAA levels can predict AF recurrence in patients who underwent arrhythmia surgery. Nevertheless, HSP levels in serum cannot discriminate AF stages from controls, nor predict PoAF or AF recurrence after treatment.

Cardioprotective Role of Heat Shock Proteins in Atrial Fibrillation: From Mechanism of Action to Therapeutic and Diagnostic Target

Atrial fibrillation (AF) is the most common age-related cardiac arrhythmia worldwide and is associated with ischemic stroke, heart failure, and substantial morbidity and mortality. Unfortunately, current AF therapy is only moderately effective and does not prevent AF progression from recurrent intermittent episodes (paroxysmal) to persistent and finally permanent AF. It has been recognized that AF persistence is related to the presence of electropathology. Electropathology is defined as structural damage, including degradation of sarcomere structures, in the atrial tissue which, in turn, impairs electrical conduction and subsequently the contractile function of atrial cardiomyocytes. Recent research findings indicate that derailed proteostasis underlies structural damage and, consequently, electrical conduction impairment. A healthy proteostasis is of vital importance for proper function of cells, including cardiomyocytes. Cells respond to a loss of proteostatic control by inducing a heat shock response (HSR), which results in heat shock protein (HSP) expression. Emerging clinical evidence indicates that AF-induced proteostasis derailment is rooted in exhaustion of HSPs. Cardiomyocytes lose defense against structural damage-inducing pathways, which drives progression of AF and induction of HSP expression. In particular, small HSPB1 conserves sarcomere structures by preventing their degradation by proteases, and overexpression of HSPB1 accelerates recovery from structural damage in experimental AF model systems. In this review, we provide an overview of the mechanisms of action of HSPs in preventing AF and discuss the therapeutic potential of HSP-inducing compounds in clinical AF, as well as the potential of HSPs as biomarkers to discriminate between the various stages of AF and recurrence of AF after treatment.

Blood-based 8-hydroxy-2'-deoxyguanosine level: A potential diagnostic biomarker for atrial fibrillation

BACKGROUND

Recent research findings have revealed a key role of oxidative DNA damage in the pathogenesis of atrial fibrillation (AF). Therefore, the circulating oxidative DNA damage marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) may represent a biomarker for staging AF and identifying patients at risk for AF recurrence and postoperative atrial fibrillation (POAF) after treatment.

OBJECTIVE

The purpose of this study was to investigate whether serum levels of 8-OHdG correlate with the stage of AF, recurrence after AF treatment, and onset of POAF after cardiac surgery.

METHODS

In this prospective observational study, 8-OHdG levels were detected by enzyme-linked immunosorbent assay in human serum samples. Blood samples were collected from control patients without AF history; patients with paroxysmal AF and persistent AF undergoing electrical cardioversion or pulmonary vein isolation (PVI); and patients with sinus rhythm (SR) undergoing cardiac surgery. AF recurrence was determined during 12-month follow-up. Univariate and multivariate analyses were used to identify changes in 8-OHdG levels between the groups.

RESULTS

Compared to the control group, 8-OHdG levels in the patient groups gradually and significantly increased during arrhythmia progression. 8-OHdG levels in AF patients showing AF recurrence after PVI treatment were significantly increased compared to patients without AF recurrence. Moreover, in SR patients undergoing cardiac surgery, 8-OHdG levels were significantly elevated in those showing POAF compared to patients without POAF.

CONCLUSION

8-OHdG level may represent a potential diagnostic biomarker for AF staging as well as for predicting AF recurrence and POAF after treatment.

Evaluating Serum Heat Shock Protein Levels as Novel Biomarkers for Atrial Fibrillation

Background: Staging of atrial fibrillation (AF) is essential to understanding disease progression and the accompanied increase in therapy failure. Blood-based heat shock protein (HSP) levels may enable staging of AF and the identification of patients with higher risk for AF recurrence after treatment. Objective: This study evaluates the relationship between serum HSP levels, presence of AF, AF stage and AF recurrence following electrocardioversion (ECV) or pulmonary vein isolation (PVI). Methods: To determine HSP27, HSP70, cardiovascular (cv)HSP and HSP60 levels, serum samples were collected from control patients without AF and patients with paroxysmal atrial fibrillation (PAF), persistent (PeAF) and longstanding persistent (LSPeAF) AF, presenting for ECV or PVI, prior to intervention and at 3-, 6- and 12-months post-PVI. Results: The study population (n = 297) consisted of 98 control and 199 AF patients admitted for ECV (n = 98) or PVI (n = 101). HSP27, HSP70, cvHSP and HSP60 serum levels did not differ between patients without or with PAF, PeAF or LSPeAF. Additionally, baseline HSP levels did not correlate with AF recurrence after ECV or PVI. However, in AF patients with AF recurrence, HSP27 levels were significantly elevated post-PVI relative to baseline, compared to patients without recurrence. Conclusions: No association was observed between baseline HSP levels and the presence of AF, AF stage or AF recurrence. However, HSP27 levels were increased in serum samples of patients with AF recurrence within one year after PVI, suggesting that HSP27 levels may predict recurrence of AF after ablative therapy.

DNA Damage, an Innocent Bystander in Atrial Fibrillation and Other Cardiovascular Diseases?

Atrial Fibrillation (AF) is the most common clinical tachyarrhythmia with a strong tendency to progress in time. AF is difficult to treat and therefore there is a great need to dissect root causes of AF with the ultimate goal to develop mechanism-based (drug) therapies. New findings related to mechanisms driving AF progression indicate a prime role for DNA damage-induced metabolic remodeling. A recent study uncovered that AF results in oxidative DNA damage and consequently excessive poly-ADP-ribose polymerase 1 (PARP1) activation and nicotinamide adenine dinucleotide (NAD+) depletion and finally atrial cardiomyocyte electrical and contractile dysfunction. This newly elucidated role of DNA damage in AF opens opportunities for novel therapeutic strategies. Recently developed PARP inhibitors, such as ABT-888 and olaparib, provide beneficial effects in limiting experimental AF, and are also found to limit atherosclerotic coronary artery disease and heart failure. Another therapeutic option to protect against AF is to replenish the NAD+ pool by supplementation with NAD+ or its precursors, such as nicotinamide and nicotinamide riboside. In this review, we describe the role of DNA damage-mediated metabolic remodeling in AF and other cardiovascular diseases, discuss novel druggable targets for AF and highlight future directions for clinical trials with drugs directed at PARP1-NAD+ pathway with the ultimate aim to preserve quality of life and to attenuate severe complications such as heart failure or stroke in patients with AF.

Atrial fibrillation fingerprinting; spotting bio-electrical markers to early recognize atrial fibrillation by the use of a bottom-up approach (AFFIP): Rationale and design

Background

The exact pathophysiology of atrial fibrillation (AF) remains incompletely understood and treatment of AF is associated with high recurrence rates. Persistence of AF is rooted in the presence of electropathology, defined as complex electrical conduction disorders caused by structural damage of atrial tissue. The atrial fibrillation fingerprinting (AFFIP) study aims to characterize electropathology, enabling development of a novel diagnostic instrument to predict AF onset and early progression.

Hypotheses

History of AF, development of post‐operative AF, age, gender, underlying heart disease, and other clinical characteristics impact the degree of electropathology.

Methods

This study is a prospective observational study with a planned duration of 48 months. Three study groups are defined: (1) patients with (longstanding) persistent AF, (2) patients with paroxysmal AF, and (3) patients without a history of AF, all undergoing open‐chest cardiac surgery. Intra‐operative high‐resolution epicardial mapping is performed to identify the patient‐specific electrical profile, whereas the patient‐specific biological profile is assessed by evaluating proteostasis markers in blood samples and atrial appendage tissue samples. Post‐operative continuous rhythm monitoring is performed for detection of early post‐operative AF. Late post‐operative AF (during 5‐year follow‐up) is documented by either electrocardiogram or 24‐hour Holter registration.

Results

The required sample size for this study is estimated at 447 patients. Up till now, 105 patients were included, of whom 36 have a history of AF.

Conclusion

The AFFIP study will elucidate whether electrophysiological and structural characteristics represent a novel diagnostic tool, the AF fingerprint, to predict onset and early progression of AF in cardiac surgery patients.

Lung genotoxicity of benzo(a)pyrene in vivo involves reactivation of LINE-1 retrotransposon and early reprogramming of oncogenic regulatory networks

Several lines of evidence have implicated long interspersed nuclear element-1 (LINE-1) retroelement in the onset and progression of lung cancer. Retrotransposition-dependent mechanisms leading to DNA mobilization give rise to insertion mutations and DNA deletions, whereas retrotransposition-independent mechanisms disrupt epithelial programming and differentiation. Previous work by our group established that tobacco carcinogens such as benzo(a)pyrene (BaP) reactivate LINE-1 in bronchial epithelial cells through displacement of nucleosome remodeling and deacetylase (NuRD) corepressor complexes and interference with retinoblastoma-regulated epigenetic signaling. Whether LINE-1 in coordination with other genes within its regulatory network contributes to the in vivo genotoxic response to BaP remains largely unknown. Evidence is presented here that intratracheal instillation of ORFeus^LSL mice with BaP alone or in combination with adenovirus (adeno)-CRE recombinase is genotoxic to the lung and associated with activation of the human LINE-1 transgene present in these mice. LINE-1 reactivation modulated the expression of genes involved in oncogenic signaling, and these responses were most pronounced in female mice compared with males and synergized by adeno-CRE recombinase. This is the first report linking LINE-1 and genes within its oncogenic regulatory network with early sexually dimorphic responses of the lung in vivo.

A computerized scoring system to improve assessment of heparin-induced thrombocytopenia risk

Essentials Current risk scores for heparin-induced thrombocytopenia (HIT) are not computer-friendly. We compared a new computerized risk score with the 4Ts score in a large healthcare system. The computerized risk score agrees with the 4Ts score 85% of the time. The new score could potentially improve HIT diagnosis via incorporation into decision support. SUMMARY: Background (HIT) is an immune-mediated adverse drug event associated with life-threatening thrombotic complications. The 4Ts score is widely used to estimate the risk for HIT and guide diagnostic testing, but it is not easily amenable to computerized clinical decision support (CDS) implementation. Objectives Our main objective was to develop an HIT computerized risk (HIT-CR) scoring system that provides platelet count surveillance for timing and degree of thrombocytopenia to identify those for whom diagnostic testing should be considered. Our secondary objective was to evaluate clinical management and subsequent outcomes in those identified as being at risk for HIT. Methods We retrospectively analyzed data from a stratified sample of 150 inpatients treated with heparin to compare the performance of the HIT-CR scoring system with that of a clinically calculated 4Ts score. We took a 4Ts score of ≥ 4 as the gold standard to determine whether HIT diagnostic testing should be performed. Results The best cutoff point of the HIT-CR score was a score of 3, which yielded 85% raw agreement with the 4Ts score and a kappa of 0.69 (95% confidence interval 0.57-0.81). Ninety per cent of patients with 4Ts score of ≥ 4 failed to undergo conventionally recommended diagnostic testing; 38% of these experienced persistent, unexplained thrombocytopenia, and 4% suffered life-threatening thrombotic complications suggestive of undiagnosed HIT. Conclusion The HIT-CR scoring system is practical for computerized CDS, agrees well with the 4Ts score, and should be prospectively evaluated for its ability to identify patients who should be tested for HIT.

L1 retrotransposon and retinoblastoma: molecular linkages between epigenetics and cancer

Long interspersed nuclear elements (LINEs) are mobile sequences shown to play a fundamental role in eukaryotic genome evolution. Recently, increasing interest has been directed at unveiling molecular mechanisms by which LINE-1 (L1), a ubiquitous member of this family, regulates gene expression and mammalian cell development, differentiation, and cancer. This mini review summarizes recent studies conducted to examine stress-induced L1 reactivation, with special attention given to the role of E2F/Rb transcription factors in epigenetic silencing of L1 and its potential role as a global modifier of chromatin structure and function. The last section focuses on the impact of histone deacetylase inhibitors in the regulation of gene function, chromatin structure, and cancer treatment through alterations in epigenetic signaling.

Negative regulation of the tumor suppressor p53 gene by microRNAs

The tumor suppressor p53, encoded by the TP53 gene, is recognized as the guardian of the human genome because it regulates many downstream genes to exercise its function in cell cycle and cell death. Recent reports have revealed that several microRNAs (miRNAs) are important components of the p53 tumor suppressor network with miR-125b and miR-504 directly targeting TP53. In this report, we use a screening method to identify that two miRNAs (miR-25 and miR-30d) directly target the 3'UTR of TP53 to down-regulate p53 protein levels and reduce the expression of genes that are transcriptionally activated by p53. Correspondingly, both miR-25 and miR-30d adversely affect apoptotic cell death, cell cycle arrest, and cellular senescence. Inhibition of either miR-25 or miR-30d expression increases endogenous p53 expression and elevates cellular apoptosis in several cell lines, including one from multiple myeloma that has little TP53 mutations. Thus, beyond miR-125b and miR-504, the human TP53 gene is negatively regulated by two more miRNAs: miR-25 and miR-30d.

Toxicogenomic profile of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the murine fetal heart: modulation of cell cycle and extracellular matrix genes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and similar environmental contaminants have been demonstrated to be potent cardiovascular teratogens in developing piscine and avian species. In the present study, we investigated the effects of TCDD on gene expression during murine cardiovascular development. C57Bl6N pregnant mice were dosed with 1.5, 3.0, or 6.0 microg TCDD/kg on gestational day (GD) 14.5, and microarray analysis was used to characterize the global changes in fetal cardiac gene expression on GD 17.5. TCDD significantly altered expression of a number of genes involved in xenobiotic metabolism, cardiac homeostasis, extracellular matrix production/remodeling, and cell cycle regulation. Interestingly, while the AhR-responsive genes Cyp1A1, Cyp1B1, Ugt1a6, and Ahrr, were all induced by TCDD in the fetal murine heart, other AhR-responsive genes, Cyp1a2, Nqo1, and Gsta1, were not. Quantitative real-time polymerase chain reactions confirmed the changes in expression of several G1/S-type cyclins and extracellular matrix-related genes. These results demonstrate the global changes in cardiac gene expression that result from TCDD exposure of the fetal murine heart and implicate genes involved in cell cycle and extracellular matrix regulation in TCDD-induced cardiac teratogenicity and functional deficits.

Novel genomic targets in oxidant-induced vascular injury

To study the complex interaction between oxidative injury and the pathogenesis of vascular disease, vascular gene expression was examined in male Sprague-Dawley rats given 35 or 70 mg/kg allylamine, a synthetic amine converted to acrolein and hydrogen peroxide within the vascular wall. Vascular lesions and extensive vascular remodeling, coupled to increased production of 8-epi-PGF2alpha, nuclear localization of NFkappaB, and alterations in glutathione homeostasis, were observed in animals treated with allylamine for up to 20 days. Transcriptional profiling, immunohistochemistry, and in situ hybridization showed that genes involved in adhesion and extracellular matrix (ECM) (alpha(1) integrin, collagen), cytoskeletal rearrangements (alpha-smooth muscle actin, alpha-tropomyosin), and signal transduction (NFkappaB, osteopontin, and LINE) were altered by oxidant treatment. To evaluate mechanisms of gene dysregulation, cultured aortic smooth muscle cells were challenged with allylamine or its metabolites and processed for molecular analysis. These agents increased formation of reactive oxygen species and elicited changes in gene expression similar to those observed in vivo. Oxidative stress and changes in gene expression were inhibited by N-acetyl cysteine, a precursor of glutathione. These results indicate that genes along the ECM-integrin-cytoskeletal axis, in addition to LINE, are molecular targets in oxidant-induced vascular injury.

Inducible cytochrome P450 activities in renal glomerular mesangial cells: biochemical basis for antagonistic interactions among nephrocarcinogenic polycyclic aromatic hydrocarbons

Background

Benzo(a)pyrene (BaP), anthracene (ANTH) and chrysene (CHRY) are polynuclear aromatic hydrocarbons (PAHs) implicated in renal toxicity and carcinogenesis. These PAHs elicit cell type-specific effects that help predict toxicity outcomes in vitro and in vivo. While BaP and ANTH selectively injure glomerular mesangial cells, and CHRY targets cortico-tubular epithelial cells, binary or ternary mixtures of these hydrocarbons markedly reduce the overall cytotoxic potential of individual hydrocarbons.

Methods

To study the biochemical basis of these antagonistic interactions, renal glomerular mesangial cells were challenged with BaP alone (0.03 – 30 μM) or in the presence of ANTH (3 μM) or CHRY (3 μM) for 24 hr. Total RNA and protein will be harvested for Northern analysis and measurements of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin-O-deethylase (EROD) activity, respectively, to evaluate cytochrome P450 mRNA and protein inducibility. Cellular hydrocarbon uptake and metabolic profiles of PAHs were analyzed by high performance liquid chromatography (HPLC).

Results

Combined hydrocarbon treatments did not influence the cellular uptake of individual hydrocarbons. ANTH or CHRY strongly repressed BaP-inducible cytochrome P450 mRNA and protein expression, and markedly inhibited oxidative BaP metabolism.

Conclusion

These findings indicate that antagonistic interactions among nephrocarcinogenic PAHs involve altered expression of cytochrome P450s that modulate bioactivation profiles and nephrotoxic/ nephrocarcinogenic potential.

2,3,7,8-Tetrachlorodibenzo-p-dioxin elicits aryl hydrocarbon receptor-mediated apoptosis in the avian DT40 pre-B-cell line through activation of caspases 9 and 3

The halogenated aromatic hydrocarbon 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is known to induce immunotoxicity, but relatively little is known regarding its effects on B-lymphocytes, and on avian B-cells in particular. In this study, the avian bursal pre-B-cell line DT40 was exposed to TCDD ranging from 1 to 500 nM for 1 and 6 h. At 100 nM, TCDD caused a significant increase in the number of apoptotic cells, as assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling (TUNEL) assay, and induced the expression of the chicken cytochrome P450 1A4 (CYP1A4) mRNA, a hallmark of TCDD exposure. TCDD induced transient upregulation of aryl hydrocarbon receptor (AhR) mRNA. At 100 nM, both caspase 3 and caspase 9 were transiently upregulated after 1 h, but returned to normal levels after 6 h of exposure. Challenge with TCDD after AhR blockade with resveratrol, a competitive AhR antagonist, prevented changes in caspases 3 and 9 and in the AhR message itself, suggesting that the effects of TCDD were mediated via the AhR. TCDD did not cause significant changes in the relative gene expression of caspase 8, Bcl-2 and Bcl-xL. We conclude that avian DT40 pre-B-cells exposed to TCDD are susceptible to apoptosis, likely through activation of executioner caspase 3.

Genomic profiles and predictive biological networks in oxidant-induced atherogenesis

Atherogenic stimuli trigger complex responses in vascular smooth muscle cells (VSMCs) that culminate in activation/repression of overlapping signal transduction cascades involving oxidative stress. In the case of benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon present in tobacco smoke, the atherogenic response involves interference with redox homeostasis by oxidative intermediates of BaP metabolism. The present studies were conducted to define genomic profiles and predictive gene biological networks associated with the atherogenic response of murine (aortic) VSMCs to BaP. A combined oxidant-antioxidant treatment regimen was used to identify redox-sensitive targets during the early course of the atherogenic response. Gene expression profiles were defined using cDNA microarrays coupled to analysis of variance and several clustering methodologies. A predictor algorithm was then applied to gain insight into critical gene-gene interactions during atherogenesis. Supervised and nonsupervised analyses identified clones highly regulated by BaP, unaffected by antioxidant, and neutralized by combined chemical treatments. Lymphocyte antigen-6 complex, histocompatibility class I component factors, secreted phosphoprotein, and several interferon-inducible proteins were identified as novel redox-regulated targets of BaP. Predictor analysis confirmed these relationships and identified immune-related genes as critical molecular targets of BaP. Redox-dependent patterns of gene deregulation indicate that oxidative stress plays a prominent role during the early stages of BaP-induced atherogenesis.

Identification of albumin precursor protein, Phi AP3, and alpha-smooth muscle actin as novel components of redox sensing machinery in vascular smooth muscle cells

Aerobic organisms are continually subjected to environmental stressors that compromise redox homeostasis and induce cellular injury. In vascular smooth muscle cells (vSMCs), the activation/repression of redox-regulated genes after environmental stress often involves protein binding to cis-acting antioxidant response elements (AREs). The present study was conducted to identify proteins that participate in redox-regulated protein binding to human c-Ha-ras and mouse glutathione S-transferase A1 AREs in vSMCs after oxidant injury. Challenge of vSMCs with 0.3 or 3 microM hydrogen peroxide, 3-methylcholanthrene, benzo[a]pyrene-7,8-diol, 3-hydroxy benzo[a]pyrene, and benzo[a]pyrene-3,6-quinone induced concentration-related increases in ARE protein binding. The profiles of ARE complex assembly were comparable, but exhibited chemical specificity. Pretreatment with 0.5 mM N-acetylcysteine inhibited activation of ARE protein binding in hydrogen peroxide-treated cells. Preparative electrophoretic mobility shift assays coupled to Western analysis identified NF-E2-related proteins 1 and 2 and JunD in complexes assembled on AREs. Polyethylenimine affinity and sequence-specific serial immobilized DNA affinity chromatography followed by N-terminal sequencing identified albumin precursor protein, phi AP3, and alpha-smooth muscle actin as members of the ARE signaling pathway. Sequence analysis of albumin protein revealed homology to the redox-regulated transcription factors Bach1 and 2, as well as cytoskeletal and molecular motor proteins. These results implicate albumin precursor protein, phi AP3, and alpha-smooth muscle actin as participants in redox sensing in vSMCs, and suggest that protein complex assembly involves interactions between leucine zipper and zinc finger transcription factors with cytoskeletal proteins.

Differential expression of ribosomal L31, Zis, gas-5 and mitochondrial mRNAs following oxidant induction of proliferative vascular smooth muscle cell phenotypes

Treatment of cultured vascular smooth muscle cells (vSMCs) with benzo(a)pyrene (BaP), a prooxidant present in the particulate phase of tobacco smoke, induces highly proliferative (i.e. atherogenic) phenotypes. Critical early target genes in vSMCs have been identified, but patterns of gene expression following repeated cycles of carcinogen treatment in vivo have yet to be evaluated. In the present study, male Sprague-Dawley rats (175-200 g) were given weekly injections of BaP (10 mg/kg) for 8 weeks to induce atherogenic phenotypes. At the end of this atherogenic regimen, vSMCs were established in serial culture and monitored for patterns of proliferative activity and gene expression. vSMCs isolated from BaP-treated animals (hence forth referred to as BaP cells) exhibited constitutively increased growth rates, and marked enhancement of proliferation in response to serum mitogens. Differential display polymerase chain reaction (DD-PCR) and Northern blot analyses revealed that mRNAs for ribosomal protein L31 and Zis genes were suppressed, while gas-5 and mitochondrial mRNAs were overexpressed in BaP cells relative to control mRNA populations. In situ hybridization experiments in vascular tissue confirmed these alterations in vivo. This is the first report linking expression of these genes to proliferative dysregulation during the course of experimentally-induced atherogenesis.

Induction of 78 kD glucose-regulated protein (GRP78) expression and redox-regulated transcription factor activity by lead and mercury in C6 rat glioma cells

Lead (Pb) and mercury (Hg) are widespread environmental contaminants that induce prominent neural toxicity. Although the brain is not the major Pb and Hg depot in the body, these metals preferentially accumulate in astroglia to exert toxic effects. In this study, we examined the effects of Pb acetate and HgCl(2) on the expression of GRP78, a molecular chaperone in the endoplasmic reticulum (ER) that may provide cytoprotection in response to cellular stresses in the C6 rat glioma cell line. We also evaluated the DNA binding activities of several redox-regulated transcription factors in metal-treated cells. Our results showed that mRNA levels of GRP78 were up-regulated by Pb and Hg at 0.1 and 1 micro M, but down-regulated at higher concentrations (10 micro M). GRP78 protein levels increased in a concentration- and time-dependent manner in Pb and/or Hg-treated cells. Pb increased protein binding to the GST- Upsilon a antioxidant/electrophile response element (ARE/EpRE) and to the NF- kappaB consensus binding sequence of the cytomegalovirus 2 (CMB2) promoter, but decreased protein binding to the Ha-ras ARE/EpRE or to the c-fos 12-O-tetradecanoyl-phorbol-13-acetate (TPA) response element (TRE). In contrast, Hg activated DNA binding by all redox-regulated transcription factors. These studies shed some light on the molecular mechanisms of Pb and Hg toxicity in C6 rat glioma cells and suggest that GRP78 and oxidative stress may participate in the neurotoxic response to these metals.

Constitutive and inducible expression of Cyp1a1 and Cyp1b1 in vascular smooth muscle cells: role of the Ahr bHLH/PAS transcription factor

Ahr is a ligand-activated bHLH/PAS transcription factor involved in cytochrome P450 (CYP) gene regulation and murine susceptibility to atherogenic stimuli. The present studies were conducted to examine constitutive and inducible expression of Cyp1a1 and Cyp1b1 in vascular smooth muscle cells (VSMCs) from Ahr(+/+) and Ahr(-/-) mice. Cyp1a1 mRNA was not expressed constitutively in VSMCs irrespective of Ahr phenotype. Although Cyp1a1 was inducible in Ahr(+/+) by 3 micromol/L benzo(a)pyrene, a known hydrocarbon inducer, the protein was uninducible. In contrast, Cyp1b1 mRNA and protein were expressed under constitutive and inducible conditions irrespective of Ahr phenotype or growth status. CYP-encoded aryl hydrocarbon hydroxylase activity was higher in Ahr(-/-) VSMCs under constitutive conditions and induced by benzo(a)pyrene in Ahr(+/+) and Ahr(-/-) VSMCs. CYP expression was influenced by mitogenic status, because randomly cycling cells consistently exhibited higher levels than growth-arrested counterparts. Actinomycin D (2 microgram/mL) or cycloheximide (10 micromol/L) did not inhibit constitutive or hydrocarbon-inducible aryl hydrocarbon hydroxylase activity in VSMCs. These data indicate that in murine VSMCs, expression of Cyp1al and Cyp1b1 is differentially influenced by Ahr phenotype and mitogenic status, with patterns that may dictate inherent susceptibility to atherogenic stimuli.

Dietary gamma-linolenic acid suppresses aortic smooth muscle cell proliferation and modifies atherosclerotic lesions in apolipoprotein E knockout mice

The present study was conducted to evaluate the antiatherogenic effects of dietary gamma-linolenic acid (GLA) (primrose oil) in apolipoprotein E (apoE) genetic knockout mice. Five-wk-old male mice were fed cholesterol-free diets containing 10 g/100 g lipid as corn oil (CO) [control diet, 0 mol/100 mol GLA and (n-3) polyunsaturated fatty acids (PUFA)], primrose oil (PO, 10 mol/100 mol GLA), fish oil-CO mix [FC; 9:1 wt/wt, 0 mol/100 mol GLA and 17 mol/100 mol (n-3) PUFA] or fish oil-PO mix [FP, 1:3 wt/wt, 8 mol/100 mol GLA and 5 mol/100 mol (n-3) PUFA] for 15 wk. Subsequently, diets were supplemented with cholesterol (1.25 g/100 g) and sodium cholate (0.5 g/100 g) and fed for an additional 10 and 16 wk. Plasma cholesterol and triglyceride levels generally did not differ among groups at 20, 30 and 36 wk of age. Mice fed GLA-containing diets (PO and FP) had significantly (P < 0.05) higher liver phospholipid levels of dihomo-gamma-linolenic acid, the elongated product of GLA, relative to CO and FC groups. Consumption of GLA (PO and FP diets) significantly reduced (P < 0.05) aortic vessel wall medial layer thickness at 20 and 30 wk. A parallel GLA-dependent suppression in the number of proliferating (proliferating cell nuclear antigen positive) aortic smooth muscle cells was also observed. Diets containing either GLA or (n-3) PUFA reduced (P < 0.05) atherosclerotic lesion size in 30-wk-old mice. These results indicate that dietary GLA can suppress smooth muscle cell proliferation in vivo and retard the development of diet-induced atherosclerosis in apoE knockout mice.

Antagonistic interactions among nephrotoxic polycyclic aromatic hydrocarbons

Although the liver and pulmonary toxicity of polycyclic aromatic hydrocarbons (PAHs) has been extensively characterized, limited data concerning the nephrotoxic potential of these chemicals are available. The present studies were conducted to define the kidney cell-specific toxic responses to anthracene (ANTH), benzo[a]pyrene (BaP), and chrysene (CHRY). Given that exposure to environmental chemicals from a specific source is rarely limited to a single compound, a second goal was to evaluate the nephrotoxic potential of binary and ternary mixtures of these chemicals. Cultured rat glomerular mesangial cells (rGMCs) and porcine cortico-tubular epithelial kidney cells (LLCPK-1) were challenged with hydrocarbon concentrations ranging from 0.03 to 30 microM for up to 24 h and were processed for measurements of mitochondrial membrane permeability, trypan blue dye exclusion, cytoplasmic enzyme leakage, and protein synthesis. BaP induced a threefold increase in mitochondrial fragility, a modest increase in cellular death, and 40% decrease in the rate of protein synthesis in rGMCs. Anthracene was also cytotoxic to rGMCs, inducing a twofold increase in mitochondrial fragility and a 40% decrease in the rate of protein synthesis, but no changes in cellular viability. Although CHRY was devoid of toxicity to rGMCs, a 40% decrease in the rate of protein synthesis was observed in LLCPK-1 cells treated with this hydrocarbon. BaP and ANTH were not overtly cytotoxic to LLCPK-1 cells at any of the concentrations tested. Binary and ternary mixtures of BaP with ANTH and CHRY in rGMCs, and mixtures of CHRY with ANTH and BaP in LLCPK-1 cells, yielded antagonistic interactions. Based on these data, it is concluded that PAHs exhibit chemical- and cell-specific nephrotoxicity, but that toxicological outcomes are influenced by the presence of multiple hydrocarbons in complex mixtures.

Environmental health training of promotoras in colonias along the Texas-Mexico border

Poverty, overpopulation, and a lack of environmental controls have combined with cultural and linguistic division to produce a looming public health threat in unincorporated communities on the US-Mexico border. These rapidly multiplying colonias, from a Spanish term for neighborhoods, are settlements of varying size located along the border. Along the American side of the Texas-Mexico border alone, there are approximately 1800 colonias--the largest number of any border state--most of which lack basic water and sewer systems, paved roads, and safe and sanitary housing. Promotoras, from a Spanish term for lay community educators, are community leaders who live in the colonias and build important bridges between residents and the federal and state bureaucracies. These women have been trained to introduce their neighbors to state "systems" of government, education, and medical and social services that otherwise may lie out of reach. Promotoras are able to "translate" this training into culturally meaningful instruction that empowers community self-development. When neighbors teach neighbors, the message is received with greater trust and readiness to act.

Impact of cellular metabolism on the biological effects of benzo[a]pyrene and related hydrocarbons

Polycyclic aromatic hydrocarbons are ubiquitous contaminants in the environment. Benzo[a]pyrene (BaP), a prototypical member of this class of chemicals, has been extensively studied for its toxic effects in laboratory animals and human populations. BaP toxicity is often mediated by oxidative metabolism to reactive intermediates that interact with macromolecules leading to alterations in target cell structure and function. More recent evidence suggests that disruption of cellular signaling pathways involved in the regulation of growth and differentiation contribute significantly to the toxicity of BaP and its metabolites. This review summarizes recent advances in our understanding of biological mechanisms of BaP toxicity at the molecular level, and the role of metabolic intermediates in carcinogenesis, atherogenesis, and teratogenesis.

Benzo(a)pyrene activates L1Md retrotransposon and inhibits DNA repair in vascular smooth muscle cells

Benzo(a)pyrene (BaP) modulates vascular smooth muscle cells (vSMCs) from a quiescent to proliferative phenotype, a shift associated with activation of L1Md retrotransposon [K.P. Lu, K.S. Ramos, Biochem. Biophys. Res. Commun. 253 (1998) 828-833]. The present studies were conducted to evaluate L1Md activation profiles in murine vSMCs treated with BaP or its oxidative metabolites, and to screen for possible insertional mutations into p53 and retinoblastoma (RB) genes. We also sought to examine the profile of DNA damage and repair in BaP-treated vSMCs. Northern analysis revealed that BaP (0. 03-3microM), and its major reactive 7,8-diol metabolite (0. 03-3microM), activate L1Md gene in a concentration-dependent manner. Two other metabolites, 3-OH BaP and 3,6-BaP quinone (0.03-3microM), as well as hydrogen peroxide (25-75microM) also activated L1Md. No insertional mutations into either p53 or RB genes were observed in vSMCs treated with BaP in vitro, although a slight elevation of p53 mRNA was observed as early as 4h after chemical challenge. Treatment of vSMCs with 3 or 30microM BaP for 4h increased unscheduled DNA synthesis (UDS) 1.4- and 2.5-fold, respectively. Challenge with 0. 3microM BaP for 24h inhibited DNA repair capacity in vSMCs for up to 48h. These results demonstrate that BaP and its oxidative metabolites activate L1Md retrotransposon in vSMCs, which coupled to DNA damage and inhibition of DNA repair are part of the atherogenic response elicited by BaP and related hydrocarbons.

Profiles of antioxidant/electrophile response element (ARE/EpRE) nuclear protein binding and c-Ha-ras transactivation in vascular smooth muscle cells treated with oxidative metabolites of benzo[a]pyrene

Activation of nuclear protein binding to the antioxidant/electrophile response element (ARE/EpRE) by benzo[a]pyrene (BaP) in vascular smooth muscle cells (vSMCs) is associated with transcriptional deregulation of c-Ha-ras. This response may be mediated by oxidative intermediates of BaP generated during the course of cellular metabolism. To test this hypothesis, the profile of ARE/EpRE protein binding and transactivation elicited by BaP was compared with that of 3-hydroxy BaP (3-OH BaP) (0.03 to 3.0 microM), BaP 7,8-dihydrodiol (BaP 7,8-diol) (0.03 to 3.0 microM), BaP 3,6-quinone (BaP 3,6-Q) (0.0003 to 3.0 microM), and H(2)O(2) (25 to 100 microM). Specific protein binding to the consensus c-Ha-ras ARE/EpRE was observed in vSMCs treated with all BaP metabolites at concentrations considerably lower than those required for the parent compound. H(2)O(2), a by-product of BaP 3,6-Q redox cycling, also increased binding to the ARE/EpRE. Treatment of vSMCs with oxidative BaP metabolites or H(2)O(2) transactivated the c-Ha-ras promoter in all instances, but the response was consistently half of the maximal induction elicited by BaP. Similar proteins cross-linked specifically to the consensus c-Ha-ras ARE/EpRE sequence in cells treated with BaP or its oxidative intermediates. The protein binding profile in the c-Ha-ras promoter was similar to that in the NADPH:quinone reductase gene (NQO(1)) and the glutathione S-transferase Ya gene (GSTYa) promoters, but the relative abundance of individual complexes was promoter-specific. We conclude that oxidative intermediates of BaP mediate activation of nuclear protein binding to ARE/EpRE and contribute to transcriptional de-regulation of c-Ha-ras in vSMCs.

A CCAAT/enhancer-binding protein site within antioxidant/electrophile response element along with CREB-binding protein participate in the negative regulation of rat GST-Ya gene in vascular smooth muscle cells

Studies were conducted to evaluate the negative regulatory function of rat (r)GST-Ya antioxidant/electrophile response element (ARE/EpRE) in vascular smooth muscle cells (vSMCs). We report that CCAAT/enhancer-binding protein (C/EBP)-beta interacts with ARE/EpRE in the rGST-Ya promoter and that aryl hydrocarbon receptor (AhR) is present within the protein complex binding to the C/EBP site. Overexpression of C/EBP-beta or C/EBP-alpha repressed, whereas AhR enhanced, 1.6CAT reporter activity in cells treated with benzo(a)pyrene (BaP). Overexpression of CREB-binding protein (CBP) nullified repression of rGST-Ya transcription. Human adenovirus E1A protein abrogated cotransactivation by CBP but an E1A mutant did not. Overexpression of C/EBPs abrogated stimulation of 1.6CAT by CBP or AhR alone, or in combination, regardless of BaP treatment. Similar profiles were observed using an AhRECAT construct. The C/EBP site within the ARE/EpRE inhibited chemical inducibility of the AhRE. The pattern of mouse GST-Ya regulation by BaP was similar to that of rGST-Ya. We conclude that multiple mechanisms mediate negative regulation of GST-Ya gene in vSMCs, most significant of which are that C/EBP-beta inhibits AhRE or ARE/EpRE inducibility of GST-Ya, limiting CBP levels compromise gene induction, functional interference exists between AhRE and ARE/EpRE, and AhR alone, or in combination with C/EBP-beta, functions as a repressor of the ARE/EpRE.

Activation of c-Ha-ras by benzo(a)pyrene in vascular smooth muscle cells involves redox stress and aryl hydrocarbon receptor

Repeated cycles of vascular injury by benzo(a)pyrene (BaP) increase the onset and progression of atherosclerotic lesions in laboratory animals. This atherogenic response is partly mediated by activation of cis-acting antioxidant/electrophile response elements that enhance c-Ha-ras transcription in vascular smooth muscle cells (vSMCs). Activation of antioxidant/electrophile responsive cis-acting elements may depend on metabolism of BaP by cytochrome P450s to intermediates that induce oxidative stress and modulate gene expression. To test this hypothesis, we evaluated mitogen-activated c-Ha-ras expression in vSMCs treated with BaP or its metabolic intermediates alone, and in combination with agents that modulate cellular redox status. BaP (0.3 and 3 microM), BaP-3, 6-quinone (0.3 microM), or hydrogen peroxide (50 microM) enhanced serum-activated c-Ha-ras. Ellipticine (0.01 nM), a known inhibitor of cytochrome P450 metabolism and aryl hydrocarbon receptor (AhR) antagonist, inhibited c-Ha-ras induction by BaP (3 microM). Serum challenge of G(0) synchronized cultures of vSMCs with DL-buthionine-(S,R)-sulfoximine (0.1 mM), a depletor of cellular glutathione, increased c-Ha-ras mRNA levels during the early phase of the mitogenic response. Combined BaP/DL-buthionine-(S, R)-sulfoximine challenge was cytotoxic to the cells and inhibited c-Ha-ras expression, whereas up-regulation of antioxidant capacity by N-acetylcysteine (0.5 mM) precluded BaP-induced ras expression. BaP increased formation of reactive oxygen species and depleted cellular glutathione, but these changes did not correlate with the kinetics of c-Ha-ras induction. BaP did not enhance c-Ha-ras expression in vSMCs from AhR knockout mice, although aryl hydrocarbon hydroxylase activity was constitutively expressed in these cells. These results suggest that c-Ha-ras activation in vSMCs by BaP involves a redox-sensitive mechanism that is coupled to AhR receptor-dependent functions.

Phenotypic profiles of cultured glomerular cells following repeated cycles of hydrocarbon injury

BACKGROUND

The glomerulus has been implicated as a target of hydrocarbon injury in vitro and in vivo. In the present studies, the phenotypic profiles of cultured rat glomerular cells (GCs) following repeated cycles of hydrocarbon injury were evaluated. Cultured GCs were incubated for 24 hours with benzo[a]pyrene (BaP; 3 micromol/L), a prototypical polycyclic aromatic hydrocarbon, and were allowed to recover overnight before two additional cycles of chemical challenge during serial propagation in vitro. At the end of this regimen, control cultures were characterized by predominance of fusiform cells that grew in "hills and valleys," while GCs subjected to hydrocarbon injury displayed an epithelial morphology characterized by a rounded, polygonal shape clearly distinct from that normally exhibited by glomerular mesangial cells (GMCs) in culture.

METHODS

Indirect immunofluorescent detection of cell markers was conducted to identify cells of mesenchymal or epithelial origin. Measurements of DNA synthesis and cell number were performed to determine proliferative capacities of the different cell types in response to hydrocarbon challenge.

RESULTS

Immunofluorescence studies revealed that control GC cultures contained mostly alpha-smooth muscle (SM) actin-positive cells, with a few (5.1% +/- 2.6) E-cadherin-positive cells occasionally identified. In contrast, BaP-treated cultures exhibited a mixed cell population in which E-cadherin-positive cells were predominant (66.6% +/- 4.1). Single-cell cloning of naive cultures of GCs yielded four clones, three of which exhibited a fusiform morphology and were alpha-SM actin positive (SCC 1 through SCC 3) and one (SCC 4E) that exhibited epithelial characteristics similar to those found in hydrocarbon-treated cultures. Immunofluorescence studies showed that epithelial cells in hydrocarbon-treated cultures, as well as SCC 4E-derived clones, were vimentin positive and cytokeratin negative, characteristics similar to glomerular visceral epithelial cells (GVECs). DNA synthesis and cell proliferation in clone SCC 1 were decreased following acute BaP challenge, while growth rates in SCC 4E-derived clones were unaffected by hydrocarbon injury. Repeated cycles of hydrocarbon challenge in clonal populations yielded different profiles of DNA synthesis, with significant decreases in SCC 1 and no changes in SCC 4E.

CONCLUSIONS

These observations suggest that hydrocarbon injury induces differential responses in cells of the glomerulus, resulting in inhibition of GMCs and selective growth advantage of GVECs. These alterations are reminiscent of critical events described in the pathogenesis of focal segmental glomerulosclerosis and raise important questions about the pathogenesis of hydrocarbon-induced nephropathies.

Modulation of atherogenesis by dietary gamma-linolenic acid

Data from our in vitro studies indicate that macrophages isolated from mice fed GLA-enriched diets inhibit vascular SMC proliferation via a PGE1-cAMP dependent mechanism. Since SMC proliferation is one of the main events implicated in the pathogenesis of atherosclerosis (Ross, 1993), this anti-proliferative effect observed by dietary GLA is noteworthy. In vivo studies have established that dietary GLA is capable of retarding the atherosclerotic lesion formation in ApoE knock out mice, an animal model that develops atherosclerosis similar to humans (Reddick, 1994). We propose that dietary GLA has the potential to inhibit SMC proliferation leading to retardation of atherosclerotic lesion formation, and therefore favorable modulation of the atherogenic process.

Analysis of benzo[a]pyrene partitioning and cellular homeostasis in a rat liver cell line

The uptake and subcellular partitioning of benzo[a]pyrene (BaP) were examined in a rat-liver cell line (Clone 9) using confocal and multiphoton microscopy. Following a 16-h treatment, intracellular accumulation of BaP increased with increasing concentration, and cytoplasmic BaP fluorescence reached saturation at 10 microM. Analysis of the kinetics of BaP uptake at this concentration indicated that BaP is rapidly partitioned into all cytoplasmic membranes within several min, although saturation was not reached until 4 h. Based upon the rapid uptake of BaP into membranes, the chronology of changes in gap junction-mediated intercellular communication (GJIC), plasma membrane potential (PMP), and steady state levels of intracellular Ca2+ in relation to the time-course for induction of microsomal ethoxyresorufin-0-deethylase (EROD) activity were examined. EROD activity in Clone 9 cells treated for 16 h increased with increasing concentrations of BaP and reached the highest levels at 40 microM BaP. In addition, kinetic analysis of EROD activity in Clone 9 cells treated with 10 microM BaP indicated that significant induction of EROD activity was not detected before 3 h, and it reached maximal levels by 16 h of treatment at this concentration. Both GJIC and PMP were directly affected by the partitioning of BaP into cellular membranes. The most sensitive index of BaP-induced changes in membrane function was GJIC which revealed a 25% suppression in cells exposed to 0.4 microM BaP for 16 h. Kinetic analysis revealed that suppression of GJIC occurred within 15 min of exposure of cells to 10 microM BaP, whereas significant suppression of PMP was not detected prior to 30-min exposure at this concentration. Elevation of basal Ca2+ level was also detected simultaneously with PMP at this dose. These data suggest that early changes in cellular membrane functions occur prior to detectable induction of EROD activity, although basal metabolic activation of BaP may contribute to these changes.

Activation of nuclear protein binding to the antioxidant/electrophile response element in vascular smooth muscle cells by benzo(a)pyrene

This laboratory has previously shown that binding of nuclear proteins to the antioxidant/electrophile response element (ARE/EpRE) participates in deregulation of vascular gene expression by benzo(a)pyrene (BaP), a suspected atherogen. In the present study, oligonucleotides representing ARE/EpREs within the c-Ha-ras and glutathione-S-transferase (GST-Ya) promoters were employed to evaluate the role of flanking sequences in stabilizing protein:DNA interactions in BaP-treated vascular smooth muscle cells (vSMCs). We also wanted to define promoter-specific patterns of protein recognition to ARE/EpREs in this cell system. In electrophoretic mobility shift assays (EMSA), optimal protein binding to a human Ha-ras ARE/EpRE variant sequence fitted to match the extended mouse(m) GST-Ya ARE/EpRE core (5'-TMAnnRTGAYnnnGCR-3') was dependent on 5' nucleic acid sequence. Using immobilized DNA affinity chromatography (IDAC), we identified four nuclear proteins of M(r) 62, 60, 50, and 30 kDa that associated specifically with the mGSTYa ARE/EpRE. Photo crosslinking to a BrdU-substituted hHa-ras or mGST ARE/EpRE probe identified specific proteins of M(r) 80, 60, 55, 25, 23 kDa or 80, 60, 55, 27, 25, 23 kDa, respectively. Protein:DNA complexes detected using IDAC eluate overlapped with those observed in crude nuclear extracts. Chemical treatments known to modulate ARE/EpRE protein binding in vSMCs did not alter overall protein:DNA affinity and/or sequence recognition to either hHa-ras or mGST-Ya elements. We conclude that nucleotide sequences 5' to the core ARE/EpRE influence specific binding of nuclear proteins and that multiple proteins bind to ARE/EpREs in a promoter-specific manner in vSMCs.

Negative regulation of rat GST-Ya gene via Antioxidant/Electrophile response element is directed by a C/EBP-like site

The present studies were conducted to evaluate functional interactions between aryl hydrocarbon and antioxidant/electrophile response elements (AhRE and ARE/EpRE, respectively) in transcriptional regulation of the rat (r)GST-Ya gene. Transient transfection of an AhRECAT reporter construct into vascular smooth muscle cells (vSMCs) or HepG2 cells showed that benzo(a)pyrene (BaP) (0.3-30 microM) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0. 1-10 nM), but not hydrogen peroxide (H(2)O(2)) (100-400 microM), increased gene transcription. ARE/EpRE did not mediate gene inducibility by any of the chemicals in vSMCs but increased transcription in HepG2 cells treated with BaP or H(2)O(2), but not TCDD. Gene inducibility in response to all chemicals was repressed in both cell types transfected with a 1.6CAT full-length promoter construct containing the AhRE and ARE/EpRE in genomic context. Site-directed mutagenesis of 1.6CAT showed that a CCAAT/enhancer-binding protein (C/EBP)-like site within the ARE/EpRE directed negative regulation of the rGST-Ya gene in vSMCs and HepG2 cells. These results show that ARE/EpRE in rGST-Ya does not function as a positive cis-acting regulatory element in all cell types, and that in the context of the full-length rGST-Ya promoter a C/EBP-like site directs negative regulation of the gene by BaP and related chemicals.

Landomycin A inhibits DNA synthesis and G1/S cell cycle progression

Landomycin A was found to inhibit the uptake of [3H]thymidine into DNA in murine smooth muscle cells indicating decreased DNA synthesis. Subsequent studies showed that landomycin A inhibits cell cycle progression.

Redox regulation of c-Ha-ras and osteopontin signaling in vascular smooth muscle cells: implications in chemical atherogenesis

Reduction/oxidation (redox) reactions play a central role in the regulation of vascular cell functions. Recent studies in this laboratory have identified c-Ha-ras and osteopontin genes as critical molecular targets during oxidant-induced atherogenesis. This review focuses on the deregulation of gene transcription by redox-activated trans-acting factors after benzo(a)pyrene challenge and the modulation of extracellular matrix signaling in vascular smooth muscle cells by allylamine-induced oxidative injury. The induction of atherogenic vascular smooth muscle cell phenotypes by chemical injury exhibits remarkable parallels with those seen in other forms of atherogenesis.

Identification of genes differentially expressed in vascular smooth muscle cells following benzo[a]pyrene challenge: implications for chemical atherogenesis

We have previously shown that serial passage of vascular smooth muscle cells (vSMCs) treated with a single low dose of benzo[a]pyrene (BaP) induces acquisition of highly proliferative (i.e. atherogenic) phenotypes. To define the molecular basis of this response, differential display polymerase chain reaction was used to identify early target genes in murine vSMCs challenged with 3 microM BaP for 8 hr. Of 170 differentially expressed cDNAs, 111 were re-amplified, and 64 examined for homology to known genes. Aac11 apoptosis inhibitor, aldose reductase, GalNAc transferase, TCP-1 chaperonin gene, and mouse mitochondrial gene, were downregulated in vSMCs treated with BaP. In contrast, enhanced expression of unique retrotransposon cDNAs were found in BaP-treated cells. This is the first report showing that BaP modulates the expression of these genes in mammalian cells. Of particular interest is the modulation of retrotransposon mRNAs which coupled to other genetic events, may play a significant role in the atherogenic response to this carcinogen.

Benzo(a)pyrene-induced alterations in growth-related gene expression and signaling in precision-cut adult rat liver and kidney slices

Benzo(a)pyrene (BaP) and related aromatic hydrocarbons are suspected carcinogens; however, the molecular basis underlying tumorigenesis remains unclear. To identify acute molecular targets of BaP within the liver and kidney, precision-cut slices harvested from naive, adult female Sprague-Dawley rats were challenged with BaP (0.3-30 microM) for 0.5 to 24 h. BaP did not elicit cytotoxicity, as assessed by intracellular K+ and ATP content and histological evaluation over the 24-h period. To determine if molecular signaling pathways were maintained in precision-cut slices, induction of the aryl hydrocarbon receptor (AhR) pathway was assessed following BaP challenge. Induction of cytochrome P450IA1 (P450IA1) mRNA and protein expression was observed in both liver and kidney slices. c-fos and c-Ha-ras gene expression was enhanced in liver, but not kidney, slices by BaP. c-jun mRNA levels were decreased in liver and kidney slices, although the effect was earlier (0.5 h) in liver slices compared to kidney slices. BaP increased the DNA binding of nuclear proteins to the AP-1 consensus recognition element in liver, but decreased DNA binding in kidney slices. In contrast, DNA binding of NF-kappa B was not affected by BaP in either liver or kidney slices. These results suggest that acute BaP challenge is associated with altered expression of several growth-related genes and AP-1 signaling and establish precision-cut slices as a useful in vitro system to investigate the molecular basis of BaP-induced tumorigenesis, including organ-specific differences.

Ah receptor-independent induction of CYP1A2 gene expression in genetically inbred mice

Acenaphthylene is a tricyclic aromatic hydrocarbon which induces hepatic methoxyresorufin O-demethylase (MROD) activity and CYP1A2 mRNA levels in 2 week-old male B6C3F1 mice. In the present study, this induction response was further investigated in genetically-inbred mice which differ in their aryl-hydrocarbon (Ah)-responsiveness. Acenapthylene (300 mg/kg) induced a 5- to 23-fold induction of MROD activity in Ah-nonresponsive (DBA and SJL) and responsive (C3H, C57/BL6, A/J, CBA and B6C3F1) mice. The highest induction response was observed in the DBA strain in which there was a 23- and 15-fold increase in activity in males and females, respectively. Acenaphthylene also caused a 2-fold increase in CYP1A2 mRNA and immunoreactive protein levels in 2 week-old DBA mice; however, this induction response was not observed in 6 week-old animals. For example, MROD activity in 6 week-old DBA mice was induced <2-fold by acenaphthylene, mainly as a consequence of increased basal CYP1A2 expression and MROD activity which, at the age of 6 weeks, approached levels induced by acenaphthylene in the 2 week-old mice. This was also observed by immunohistochemical staining with CYP1A2 antibodies of 2 and 6 week-old hepatic tissue from treated and control mice which also showed that CYP1A2 induction was dependent on the age of the animals.

Identification of benzo[a]pyrene-inducible cis-acting elements within c-Ha-ras transcriptional regulatory sequences

Previous studies in this laboratory have demonstrated that transcriptional deregulation of c-Ha-ras expression is associated with the induction and maintenance of proliferative vascular smooth muscle cell (SMC) phenotypes by benzo[a]pyrene (BaP). We examined previously undescribed cis-acting elements within the proximal 5' regulatory region of c-Ha-ras (-550 to +220) for their ability to influence BaP-induced transcription in murine SMCs. BaP-inducible DNA binding activity was demonstrated at a site located -30 relative to the major start site cluster at +1 that exhibits extensive homology to a consensus aryl hydrocarbon response element (AHRE), as well as a site located at -543 that contains a consensus electrophile response element (EpRE). In vitro cross-linking studies revealed the specific interaction of 104- and 96-kDa proteins with the putative AHRE and of an 80-kDa protein with the EpRE. The use of monoclonal antibodies to the aryl hydrocarbon receptor transcription factor in competition electrophoretic mobility shift assays indicated this protein is specifically induced by BaP to interact at the AHRE within the c-Ha-ras 5' regulatory region. Transient transfection with an Ha-ras promoter construct containing the putative AHRE but lacking the EpRE linked to the chloramphenicol acetyl transferase reporter gene, followed by challenge with BaP (0.3, 3.0, and 30 microM), revealed transcriptional activation that was not statistically significant. However, insertion of an oligonucleotide composed of the EpRE immediately upstream of basal sequences at -330 was associated with strong activation of transcription by BaP. These data indicate that c-Ha-ras gene expression is modulated by BaP via a complex mechanism that likely involves interactions among multiple regulatory elements. We conclude that c-Ha-ras expression is regulated by BaP at the transcriptional level, a response that may constitute an epigenetic basis of atherogenesis.

c-Ha-rasEJ transfection in vascular smooth muscle cells circumvents PKC requirement during mitogenic signaling

In view of the prominent role of protein kinase C (PKC) in the regulation of vascular smooth muscle cell (VSMC) growth and differentiation, the present studies were conducted to assess the impact of c-Ha-rasEJ transfection on PKC-dependent growth programming. PKC activity was elevated in the cytosolic and particulate compartments of c-Ha-rasEJ VSMC, relative to naive or pSV2neo vector controls. Constitutive and 12-O-tetradecanoyl phorbol 13-acetate (TPA)-inducible binding to a TPA-responsive element (TRE) was also enhanced in c-Ha-rasEJ VSMC. Fetal bovine serum (FBS) did not increase TRE-binding activity in serum-starved c-Ha-rasEJ VSMC but increased TRE-binding activity in pSV2neo VSMC. FBS-mediated TRE-binding activity was dramatically decreased in serum-starved pSV2neo VSMC pretreated with 100 ng/ml TPA for 24 h to downregulate PKC activity. c-Ha-rasEJ VSMC exhibited a marked proliferative advantage over controls under both restrictive and growth-permissive serum conditions. PKC downregulation did not influence the mitogenic response to serum in c-Ha-rasEJ VSMC but ablated [3H]thymidine incorporation into DNA in naive or pSV2neo vector counterparts. Western blot analysis demonstrated increased expression of extracellular signal-regulated kinase 2 (ERK2), but not ERK1, in c-Ha-rasEJ VSMC, relative to pSV2neo control. Immunoblots of serum-starved and PKC-depleted c-Ha-rasEJ VSMC demonstrated a dramatic increase in the phosphorylated form of ERK2, relative to pSV2neo controls. These data suggest that oncogenic c-Ha-rasEJ circumvents a requirement for a TPA-responsive PKC isoform(s) during mitogenic stimulation of VSMC.

Dietary gamma-linolenic acid enhances mouse macrophage-derived prostaglandin E1 which inhibits vascular smooth muscle cell proliferation

We previously demonstrated that macrophages isolated from mice fed gamma-linolenic acid (GLA)-enriched diets reduce vascular smooth muscle cell (SMC) proliferation in a cyclooxygenase-dependent fashion and may therefore favorably modulate the atherogenic process. The present study was conducted to elucidate the mechanism(s) by which dietary GLA influences the ability of macrophages to modulate SMC growth programs. Resident peritoneal macrophages were isolated from C57BL/6 female mice fed diets containing variable GLA compositions at 10% (wt/wt), treated with various antibodies and co-cultured with cycling naive vascular SMC isolated from nonpurified diet-fed mice. Smooth muscle cell proliferation and intracellular cAMP levels were measured after co-culture. In parallel experiments, cycling naive vascular SMC isolated from nonpurified diet-fed mice were dosed with exogenous prostaglandin E1 (PGE1 ) for various periods and challenged with cycloheximide for 4 h (8-12 h after PGE1 addition), and intracellular cAMP levels were measured at various time points. Macrophages isolated from mice fed GLA-enriched dietary oils significantly reduced SMC proliferation in co-culture compared with controls (macrophages from mice fed a corn oil diet containing no GLA). Anti-PGE1 antiserum treatment (1:50 or 1:100) blocked the ability of GLA-enriched macrophages to down-regulate SMC proliferation, a response reversed by exogenous PGE1 treatment. Macrophages isolated from mice fed GLA-enriched dietary oils elevated SMC intracellular cAMP levels in a biphasic fashion. In addition, exogenous PGE1 (1 nmol/L to 10 micromol/L) exerted a similar biphasic cAMP response in SMC, and the second phase of cAMP elevation was antagonized by cycloheximide. In conclusion, dietary GLA enhances mouse macrophage-derived prostaglandin E1, which inhibits vascular SMC proliferation.

Growth-related signaling in vascular smooth muscle cells is deregulated by TCDD during the G0/G1 transition

Experiments have been conducted to examine the impact of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on growth-related signaling in vascular smooth muscle cells (SMCs). A 40% reduction of peak DNA synthesis was observed in SMCs only when TCDD was added during the G0/G1 transition of the cell cycle. Enhanced phosphorylation of several endogenous proteins during this period was coincident with increased tyrosine kinase activity as early as 15 min following TCDD challenge. No changes in protein phosphorylation status occurred in cells treated with TCDD during the G1/S transition or during S phase. Cotreatment of quiescent SMCs with 10 nM TCDD and serum for 3 h reduced serum-inducible binding activity to a 12-O-tetradecanoyl phorbol 13-acetate responsive element (TRE) by approximately 40%. No alterations of constitutive TRE binding were observed in quiescent SMCs treated with TCDD for up to 5 h. These data show that mitogen-related signaling in vascular SMCs is modulated by TCDD selectively during the G0/G1 transition, and these effects influence the growth behavior of these cells.

Transfection with c-Ha rasEJ modulates alpha-actin and alpha 1B-adrenoceptor gene expression in vascular smooth muscle cells

Co-ordinate down-regulation of smooth muscle-specific genes and acquisition of unregulated proliferative characteristics have been proposed as hallmarks of the atherosclerotic process. In the present study, we have evaluated this reciprocal relationship by examining the impact of c-Ha-rasEJ oncogene transfection on alpha-smooth muscle (SM) actin and alpha 1B-adrenoceptor (ADR) gene expression in vascular (aortic) smooth muscle cells (SMCs), c-Ha-rasEJ transfection of SMCs by lipofection (LF-1) was associated with enhanced DNA synthetic rates relative to vector controls and a significant reduction in alpha-SM actin and beta/gamma-actin mRNAs. Incubation of ras- and neo-LF-1 SMCs in a restrictive serum concentration (0.1%) for 72 h inhibited DNA synthesis in both cell types, but differentially influenced the pattern of alpha-actin gene expression. While neo-LF-1 cells incubated in 0.1% exhibited increased alpha-SM actin mRNA levels relative to 10% serum, slight decreases in alpha-SM actin were observed in ras-LF-1 cells under the same conditions. Cyclical stretch of randomly cycling cells, seeded on a flexible elastin substrate at a rate of 100 cycles/min for 72 h, did not significantly influence the pattern of alpha-SM or beta/gamma-actin mRNA expression in neo-LF-1 or ras-LF-1 cells. Steady-state mRNA levels of alpha 1B-ADR were higher in ras-LF-1 SMCs relative to neo-LF-1 cells, and stretch increased alpha 1B-ADR mRNA levels in neo-LF-1, but not ras-LF-1 cells. Stretch inhibited [1H]thymidine incorporation into DNA in both neo- and ras-LF-1 cells relative to unstretched counterparts. These results demonstrate that c-Ha-rasEJ transfection is associated with alterations in the expression of genes associated with muscle-specific functions in vascular SMCs and implicate c-Ha-ras in the regulation of phenotypic expression in SMCs.

Differential processing of osteopontin characterizes the proliferative vascular smooth muscle cell phenotype induced by allylamine

Repeated cycles of vascular injury by allylamine induce vascular lesions similar to those seen in atherosclerotic vessels, or following balloon catheterization. Vascular (aortic) smooth muscle cells harvested from allylamine-treated animals (i.e., allylamine cells) acquire a proliferative advantage relative to control counterparts that is associated with differential secretion and extracellular matrix sequestration of several proteins. In the present study, we have characterized two of these proteins (M(r) 52 and 36 kDa; pl 5.6 and 5.2, respectively) and their putative role in the expression of a proliferative phenotype. Because the physical properties of these proteins were comparable to those of osteopontin (OPN) and its thrombin-generated fragment(s), initial experiments were conducted to examine the expression and processing of OPN in this cell system. OPN mRNA expression was enhanced during early G1 cell cycle progression in allylamine cells relative to control counterparts. However, comparable amounts of OPN (M(r) 56, 52, and 50 kDa) were detected by Western analysis in media conditioned by both cell types using the OP-199 or B77-Rat1 antibodies to OPN. Allylamine cells, however, produced increased amounts of a 36 kDa protein recognized by the OP-199 antibody. Incubation of conditioned media from [35S]methionine-labeled allylamine cells with thrombin decreased the intensity of the 52 kDa protein, while increasing the intensity of a 36 kDa protein. RT-PCR analysis demonstrated expression of a 1.2 kb OPN band in both cell types consistent with the predicted size of OPN mRNA, suggesting that the 36 kDa fragment recognized by OP-199 in allylamine cells was likely not due to altered splicing of the OPN transcript. To determine if OPN and/or the 36 kDa fragment played a central role in the proliferative capacity of allylamine cells, the effect of an antibody to an alpha v integin subunit was examined. An antibody to the alpha v subunit, but not alpha 4, nullified the proliferative advantage of allylamine cells relative to control counterparts, suggesting that integrin-mediated signaling is a key feature of the proliferative phenotype of allylamine cells. We conclude that enhanced proteolytic cleavage of OPN may characterize the modulation of vascular SMCs to a more proliferative phenotype following chemical injury by allylamine.

The induction of proliferative vascular smooth muscle cell phenotypes by benzo[a]pyrene does not involve mutational activation of ras genes

Previous studies in this laboratory have suggested that benzo[a]pyrene (BaP) challenge in vivo and in vitro induces genomic changes that result in the acquisition of proliferative vascular smooth muscle cell (SMC) phenotypes. Because this phenotypic change correlates with alterations in ras gene expression, and ras genes are known mutational targets of BaP, the present studies were conducted to determine if BaP induces activating mutation(s) or ras genes in SMCs. For in vivo studies, male Sprague-Dawley rats were given weekly injections of an atherogenic dose of BaP (10 mg/kg) or vehicle for 8 weeks and SMCs were isolated from the thoracic aorta and established in culture. For in vitro studies, naive rat aortic SMCs were challenged with 3 micro M BaP for 24 h and then subjected to nine serial passages for the induction of proliferative phenotypes. Measurements of DNA synthesis and cell numbers were conducted to define patterns of proliferative behavior in BaP and control cells. In parallel studies, exons 1 and 2 of ras genes were amplified by reverse-transcription polymerase chain reaction and sequenced to screen for activating ras mutations. BaP treatment in vivo was associated with the development of aortic wall lesions characterized by loss of endothelial integrity, fragmentation of the elastic laminae, expansion of the smooth muscle cell mass, and change in the orientation of medial SMCs. Although BaP enhanced the growth rate of vascular SMCs relative to controls, no mutations were detected in the activating regions (codons 12, 13, 60, or 61) of c-Ha-, c-Ki-, or N-ras genes. These data demonstrate that BaP-induced alterations in the proliferative potential of SMCs do not involve activating mutations in the frequently mutated regions of ras genes.