N-acetylcysteine protects alveolar epithelial cells from hydrogen peroxide–induced apoptosis through scavenging reactive oxygen species and suppressing c-Jun N-terminalkinase

Reactive oxygen species-scavenging nanomaterials for the prevention and treatment of age-related diseases

With increasing proportion of the elderly in the population, age-related diseases (ARD) lead to a considerable healthcare burden to society. Prevention and treatment of ARD can decrease the negative impact of aging and the burden of disease. The aging rate is closely associated with the production of high levels of reactive oxygen species (ROS). ROS-mediated oxidative stress in aging triggers aging-related changes through lipid peroxidation, protein oxidation, and DNA oxidation. Antioxidants can control autoxidation by scavenging free radicals or inhibiting their formation, thereby reducing oxidative stress. Benefiting from significant advances in nanotechnology, a large number of nanomaterials with ROS-scavenging capabilities have been developed. ROS-scavenging nanomaterials can be divided into two categories: nanomaterials as carriers for delivering ROS-scavenging drugs, and nanomaterials themselves with ROS-scavenging activity. This study summarizes the current advances in ROS-scavenging nanomaterials for prevention and treatment of ARD, highlights the potential mechanisms of the nanomaterials used and discusses the challenges and prospects for their applications.

Effects of Radiation-Induced Skin Injury on Hyaluronan Degradation and Its Underlying Mechanisms

Radiation-induced skin injury (RISI) is a frequent and severe complication with a complex pathogenesis that often occurs during radiation therapy, nuclear incidents, and nuclear war, for which there is no effective treatment. Hyaluronan (HA) plays an overwhelming role in the skin, and it has been shown that UVB irradiation induces increased HA expression. Nevertheless, to the best of our knowledge, there has been no study regarding the biological correlation between RISI and HA degradation and its underlying mechanisms. Therefore, in our study, we investigated low-molecular-weight HA content using an enzyme-linked immunosorbent assay and changes in the expression of HA-related metabolic enzymes using real-time quantitative polymerase chain reaction and a Western blotting assay. The oxidative stress level of the RISI model was assessed using sodium dismutase, malondialdehyde, and reactive oxygen species assays. We demonstrated that low-molecular-weight HA content was significantly upregulated in skin tissues during the late phase of irradiation exposure in the RISI model and that HA-related metabolic enzymes, oxidative stress levels, the MEK5/ERK5 pathway, and inflammatory factors were consistent with changes in low-molecular-weight HA content. These findings prove that HA degradation is biologically relevant to RISI development and that the HA degradation mechanisms are related to HA-related metabolic enzymes, oxidative stress, and inflammatory factors. The MEK5/ERK5 pathway represents a potential mechanism of HA degradation. In conclusion, we aimed to investigate changes in HA content and preliminarily investigate the HA degradation mechanism in a RISI model under γ-ray irradiation, to consider HA as a new target for RISI and provide ideas for novel drug development.

Maternal hyperglycemia inhibits pulmonary vasculogenesis during mouse fetal lung development by promoting GβL Ubiquitination-dependent mammalian target of Rapamycin assembly

BACKGROUND

Gestational diabetes mellitus (GDM) is associated with retarded lung development and poor lung health in offspring. Mammalian target of rapamycin (mTOR) is a key regulator of vasculogenesis and angiogenesis. The aim of this study was to investigate the role mTOR plays in pulmonary vasculogenesis during fetal lung development under maternal hyperglycemia.

METHODS

First, GDM was induced via streptozotocin injection in pregnant C57BL/6 mice before the radial alveolar count (RAC) in the fetal lungs was assessed using hematoxylin and eosin staining. The angiogenic ability of the cultured primary mouse fetal lung endothelial cells (MFLECs) was then assessed using the tube formation assay technique, while western blot and real-time polymerase chain reaction were performed to determine the expression of mTOR, regulatory-associated protein of mTOR (Raptor), rapamycin-insensitive companion of mTOR (Rictor), stress-activated protein kinase interacting protein 1 (Sin1), G protein beta subunit-like protein (GβL), Akt, tumor necrosis receptor associated factor-2 (TRAF2), and OTU deubiquitinase 7B (OTUD7B) in both the fetal lung tissues and the cultured MFLECs. Immunoprecipitation assays were conducted to evaluate the status of GβL-ubiquitination and the association between GβL and mTOR, Raptor, Rictor, and Sin1 in the cultured MFLECs.

RESULTS

The GDM fetal lungs exhibited a decreased RAC and reduced expression of von Willebrand factor, CD31, and microvessel density. The high glucose level reduced the tube formation ability in the MFLECs, with the mTOR, p-mTOR, p-Raptor, and TRAF2 expression upregulated and the p-Rictor, p-Sin1, p-Akt, and OTUD7B expression downregulated in both the GDM fetal lungs and the high-glucose-treated MFLECs. Meanwhile, GβL-ubiquitination was upregulated in the high-glucose-treated MFLECs along with an increased GβL/Raptor association and decreased GβL/Rictor and GβL/Sin1 association. Furthermore, TRAF2 knockdown inhibited the high-glucose-induced GβL-ubiquitination and GβL/Raptor association and restored the tube formation ability of the MFLECs.

CONCLUSION

Maternal hyperglycemia inhibits pulmonary vasculogenesis during fetal lung development by promoting GβL-ubiquitination-dependent mTORC1 assembly.

N-Acetylcysteine Administration Improves the Redox and Functional Gene Expression Levels in Spleen, Mesenteric Lymph Node and Gastrocnemius Muscle in Piglets Infected with Porcine Epidemic Diarrhea Virus

Our previous study reported that N-acetylcysteine (NAC) administration improved the function of intestinal absorption in piglets infected with porcine epidemic diarrhea virus (PEDV). However, the effects of NAC administration on the functions of other tissues and organs in PEDV-infected piglets have not been reported. In this study, the effects of NAC on the liver, spleen, lung, lymph node, and gastrocnemius muscle in PEDV-infected piglets were investigated. Thirty-two 7-day-old piglets with similar body weights were randomly divided into one of four groups: Control group, NAC group, PEDV group, and PEDV+NAC group (eight replicates per group and one pig per replicate). The trial had a 2 × 2 factorial design consisting of oral administration of 0 or 25 mg/kg body weight NAC and oral administration of 0 or 1.0 × 10^4.5 TCID₅₀ PEDV. The trial lasted 12 days. All piglets were fed a milk replacer. On days 5-9 of the trial, piglets in the NAC and PEDV + NAC groups were orally administered NAC once a day; piglets in the control and PEDV groups were orally administered the same volume of saline. On day 9 of trial, piglets in the PEDV and PEDV+NAC groups were orally administrated 1.0 × 10^4.5 TCID₅₀ PEDV, and the piglets in the control and NAC groups were orally administrated the same volume of saline. On day 12 of trial, samples, including of the liver, spleen, lung, lymph node, and gastrocnemius muscle, were collected. PEDV infection significantly increased catalase activity but significantly decreased the mRNA levels of Keap1, Nrf2, HMOX2, IFN-α, MX1, IL-10, TNF-α, S100A12, MMP3, MMP13, TGF-β, and GJA1 in the spleens of piglets. NAC administration ameliorated abnormal changes in measured variables in the spleens of PEDV-infected piglets. In addition, NAC administration also enhanced the antioxidant capacity of the mesenteric lymph nodes and gastrocnemius muscles in PEDV-infected piglets. Collectively, these novel results revealed that NAC administration improved the redox and functional gene expression levels in the spleen, mesenteric lymph nodes, and gastrocnemius muscle in PEDV-infected piglets.

Anti-high-mobility group box-1 (HMGB1) mediates the apoptosis of alveolar epithelial cells (AEC) by receptor of advanced glycation end-products (RAGE)/c-Jun N-terminal kinase (JNK) pathway in the rats of crush injuries

Objectives

The lung injury is often secondary to severe trauma. In the model of crush syndrome, there may be secondary lung injury. We hypothesize that high-mobility group box 1 (HMGB1), released from muscle tissue, mediates the apoptosis of alveolar epithelial cells (AEC) via HMGB1/Receptor of advanced glycation end-products (RAGE)/c-Jun N-terminal kinase (JNK) pathway. The study aimed to investigate how HMGB1 mediated the apoptosis of AEC in the rat model.

Methods

Seventy-five SD male rats were randomly divided into five groups: CS, CS + vehicle, CS + Ethyl pyruvate (EP), CS + FPS-ZM1 group, and CS + SP600125 groups. When the rats CS model were completed after 24 h, the rats were sacrificed. We collected the serum and the whole lung tissues. Inflammatory cytokines were measured in serum samples. Western blot and RT-qPCR were used to quantify the protein and mRNA. Lastly, apoptotic cells were detected by TUNEL. We used SPSS 25.0 for statistical analyses.

Results

Nine rats died during the experiments. Dead rats were excluded from further analysis. Compared to the CS group, levels of HMGB1 and inflammatory cytokines in serum were downregulated in CS + EP, CS + FPS-ZM1, and CS + SP600125 groups. Western blot and RT-qPCR analysis revealed a significant downregulation of HMGB1, RAGE, and phosphorylated-JNK in CS + EP, CS + FPS-ZM1, and CS + SP600125 groups, compared with the CS groups, excluding total-JNK mRNA. Apoptosis of AEC was used TUNEL to assess. We found the TUNEL-positive cells were downregulated in CS + EP, CS + FPS-ZM1, and CS + SP600125 groups.

Conclusion

The remote lung injury begins early after crush injuries. The HMGB1/RAGE/JNK signaling axis is an attractive target to abrogate the apoptosis of AEC after crush injuries.

Water-Soluble C60 Protects Against Bleomycin-Induced Pulmonary Fibrosis in Mice

Background

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrotic interstitial pneumonia. And, oxidation/antioxidant imbalance plays an important role in the progress of IPF. Fullerene is considered to be a novel “structural” antioxidant. This study aimed to explore if water-soluble C₆₀ (C₆₀(OH)₂₂) can exhibit antifibrotic activity in its antioxidant role.

Methods

Healthy C57BL/6J mice were randomly grouped and induced pulmonary fibrosis by intratracheal injection of bleomycin.

Results

The survival rate of mice was observed and found that 10mg/kg was the optimal dose of water-soluble C₆₀ for pulmonary fibrosis. We observed that water-soluble C₆₀ can alleviate the severity of pulmonary fibrosis by observing the chest computed tomography, pulmonary pathology, and content of collagen, alpha smooth muscle actin and fibronectin in lung. Compared with bleomycin group, ROS, the content of TNF-α in BALF, and the number of fibroblasts was significantly decreased and the number of type Ⅱ alveolar epithelial cells was increased after treatment with C60.

Conclusion

Therefore, thanks to its powerful antioxidant action, water-soluble C₆₀ can reduce the severity of pulmonary fibrosis induced by bleomycin in mice.

Short-Term versus Long-Term Culture of A549 Cells for Evaluating the Effects of Lipopolysaccharide on Oxidative Stress, Surfactant Proteins and Cathelicidin LL-37

Alveolar epithelial type II (ATII) cells and their proper function are essential for maintaining lung integrity and homeostasis. However, they can be damaged by lipopolysaccharide (LPS) during Gram-negative bacterial infection. Thus, this study evaluated and compared the effects of LPS on short and long-term cultures of A549 cells by determining the cell viability, levels of oxidative stress and antimicrobial peptide cathelicidin LL-37 and changes in the expression of surfactant proteins (SPs). Moreover, we compared A549 cell response to LPS in the presence of different serum concentrations. Additionally, the effect of N-acetylcysteine (NAC) on LPS-induced oxidative stress as a possible treatment was determined. Our results indicate that A549 cells are relatively resistant to LPS and able to maintain integrity even at high LPS concentrations. Their response to endotoxin is partially dependent on serum concentration. NAC failed to lower LPS-induced oxidative stress in A549 cells. Finally, LPS modulates SP gene expression in A549 cells in a time dependent manner and differences between short and long-term cultures were present. Our results support the idea that long-term cultivation of A549 cells could promote a more ATII-like phenotype and thus could be a more suitable model for ATII cells, especially for in vitro studies dealing with surfactant production.

The effects of hydrogen peroxide and lipopolysaccharide on rat alveolar L2 cells

PURPOSE

This study aimed to investigate differential cell responses of alveolar epithelial cells (AECs) after treatments with lipopolysaccharide (LPS) and hydrogen peroxide (H₂O₂) to mimic the exposure to inflammation and oxidative stress and the mechanisms of a double-hit model of apoptosis.

MATERIALS AND METHODS

AECs were cultured and treated with combinations of 1 μg/mL of LPS and 500 μM H₂O₂ as follows: LPS-only at 0 h, LPS at 0 h with H₂O₂ at 6 h (LPS + H₂O₂), H₂O₂-only at 0 h, H₂O₂ at 0 h with LPS at 6 h (H₂O₂ + LPS), and control. We investigated mRNA expression (TNF-α, Fas, Fas ligand, Bax, Bcl-2, Caspase-7), protein expression (Fas, Bax, Bcl-2, Caspase-7) and apoptosis (Caspase-3 activity, TUNEL assay) at 0, 3, 6, 9, 12, and 24 h.

RESULTS

In the H₂O₂ + LPS group, the Caspase-7, and Fas mRNA levels were significantly higher than the other groups at 9 h and 12 h, and Bax was higher at 12 h. The Bax/Bcl-2 protein expression ratio was significantly higher in the H₂O₂ + LPS group than that of the other groups at 12h and 24h. Apoptotic index was highest in the H₂O₂ + LPS group at 24 h.

CONCLUSIONS

The sequence of stimulation may modify the cell response in rat AECs. The results suggest that previous oxidative stress and subsequent LPS-induced inflammation primarily influence apoptosis of L2 cells by up-regulation of cell signaling.

Upregulation of nuclear factor-κB activity mediates CYP24 expression and reactive oxygen species production in indoxyl sulfate-induced chronic kidney disease

AIM

Chronic kidney disease (CKD) is associated with an inflammation-mediated process, and the vitamin D (3) catabolizing enzyme, CYP24, is frequently overexpressed in CKD, where it may play a crucial role in kidney disease.

METHODS

Herein, in this study, we investigated CYP24, reactive oxygen species (ROS), and inflammatory responses in an indoxyl sulfate (IS)-induced CKD model to elucidate the role of CYP24 in CKD.

RESULTS

Our results showed that IS upregulates proinflammatory cytokine, CYP24 and nuclear factor-κB (NF-κB) expression in human renal proximal tubule epithelial cells. In addition, IS treatment increased ROS production and simultaneously upregulated CYP24 expression and NF-κB translocation. Moreover, the IS-induced upregulation of CYP24 expression was alleviated by an inhibitor of NF-κB, as well as a siRNA specific to NF-κB p65. Furthermore, the renal cortex of DN (Dahl salt-resistant normotensive) + IS, DH (Dahl salt-sensitive hypertensive), and DH + IS rats showed increased expression of NF-κB p65, CYP24, 8-hydroxydeoxyguanosine (8-OHdG), a marker of ROS and macrophage infiltration compared with DN rats.

CONCLUSIONS

These results provide evidence that administration of IS in human renal tubular epithelial cells upregulates NF-κB, which leads to increase CYP24 expression and ROS production. They also suggest that suppressing NF-κB signalling is promising for the development into a strategy for CKD treatment.

Oxygen regulates molecular mechanisms of cancer progression and metastasis

Oxygen is the basic molecule which supports life and it truly is "god's gift to life." Despite its immense importance, research on "oxygen biology" has never received the light of the day and has been limited to physiological and biochemical studies. It seems that in modern day biology, oxygen research is summarized in one word "hypoxia." Scientists have focused on hypoxia-induced transcriptomics and molecular-cellular alterations exclusively in disease models. Interestingly, the potential of oxygen to control the basic principles of biology like homeostatic maintenance, transcription, replication, and protein folding among many others, at the molecular level, has been completely ignored. Here, we present a perspective on the crucial role played by oxygen in regulation of basic biological phenomena. Our conclusion highlights the importance of establishing novel research areas like oxygen biology, as there is great potential in this field for basic science discoveries and clinical benefits to the society.

Curcumin-induced heme oxygenase-1 expression prevents H2O2-induced cell death in wild type and heme oxygenase-2 knockout adipose-derived mesenchymal stem cells

Mesenchymal stem cell (MSC) administration is a promising adjuvant therapy to treat tissue injury. However, MSC survival after administration is often hampered by oxidative stress at the site of injury. Heme oxygenase (HO) generates the cytoprotective effector molecules biliverdin/bilirubin, carbon monoxide (CO) and iron/ferritin by breaking down heme. Since HO-activity mediates anti-apoptotic, anti-inflammatory, and anti-oxidative effects, we hypothesized that modulation of the HO-system affects MSC survival. Adipose-derived MSCs (ASCs) from wild type (WT) and HO-2 knockout (KO) mice were isolated and characterized with respect to ASC marker expression. In order to analyze potential modulatory effects of the HO-system on ASC survival, WT and HO-2 KO ASCs were pre-treated with HO-activity modulators, or downstream effector molecules biliverdin, bilirubin, and CO before co-exposure of ASCs to a toxic dose of H₂O₂. Surprisingly, sensitivity to H₂O₂-mediated cell death was similar in WT and HO-2 KO ASCs. However, pre-induction of HO-1 expression using curcumin increased ASC survival after H₂O₂ exposure in both WT and HO-2 KO ASCs. Simultaneous inhibition of HO-activity resulted in loss of curcumin-mediated protection. Co-treatment with glutathione precursor N-Acetylcysteine promoted ASC survival. However, co-incubation with HO-effector molecules bilirubin and biliverdin did not rescue from H₂O₂-mediated cell death, whereas co-exposure to CO-releasing molecules-2 (CORM-2) significantly increased cell survival, independently from HO-2 expression. Summarizing, our results show that curcumin protects via an HO-1 dependent mechanism against H₂O₂-mediated apoptosis, and likely through the generation of CO. HO-1 pre-induction or administration of CORMs may thus form an attractive strategy to improve MSC therapy.

Krüppel-like factor 5 mediates proinflammatory cytokine expression in lipopolysaccharide-induced acute lung injury through upregulation of nuclear factor-κB phosphorylation in vitro and in vivo

Acute lung injury (ALI) is associated with an inflammation-mediated process, and the transcription factor, Krüppel-like factor 5 (KLF5), might play a crucial role in inflammatory lung disease. In this study, we evaluated KLF5, reactive oxygen species (ROS), and inflammatory responses in a lipopolysaccharide- (LPS-) induced ALI model to elucidate the role of KLF5 in ALI. Our data indicated that LPS upregulates proinflammatory cytokine expression in human bronchial epithelial cells in a dose-dependent manner. We observed upregulated KLF5 protein expression in human bronchial epithelial cells exposed to LPS, with peak expression 1 h after LPS treatment, and subsequent upregulation of p65 protein expression and p65 phosphorylation at Ser276. These results indicate that KLF5 mediates proinflammatory cytokine expression by upregulating nuclear factor-kappaB (NF-κB) phosphorylation at p65 in response to LPS. LPS treatment also increased ROS production and simultaneously upregulated KLF5 expression and NF-κB translocation. N-acetylcysteine significantly reduced ROS levels and KLF5 and NF-κB translocation in nuclear extracts. Therefore, N-acetylcysteine pretreatment before LPS exposure reduces ROS, downregulates KLF5 expression, and subsequently reduces inflammatory responses by scavenging ROS. Overall, our study results indicate that KLF5 mediates proinflammatory cytokine expression through upregulation of NF-κB phosphorylation at p65 in LPS-induced ALI.

Pathophysiology of tobacco smoke exposure: recent insights from comparative and redox proteomics

First-hand and second-hand tobacco smoke are causally linked to a huge number of deaths and are responsible for a broad spectrum of pathologies such as cancer, cardiovascular, respiratory, and eye diseases as well as adverse effects on female reproductive function. Cigarette smoke is a complex mixture of thousands of different chemical species, which exert their negative effects on macromolecules and biochemical pathways, both directly and indirectly. Many compounds can act as oxidants, pro-inflammatory agents, carcinogens, or a combination of these. The redox behavior of cigarette smoke has many implications for smoke related diseases. Reactive oxygen and nitrogen species (both radicals and non-radicals), reactive carbonyl compounds, and other species may induce oxidative damage in almost all the biological macromolecules, compromising their structure and/or function. Different quantitative and redox proteomic approaches have been applied in vitro and in vivo to evaluate, respectively, changes in protein expression and specific oxidative protein modifications induced by exposure to cigarette smoke and are overviewed in this review. Many gel-based and gel-free proteomic techniques have already been used successfully to obtain clues about smoke effects on different proteins in cell cultures, animal models, and humans. The further implementation with other sensitive screening techniques could be useful to integrate the comprehension of cigarette smoke effects on human health. In particular, the redox proteomic approach may also help identify biomarkers of exposure to tobacco smoke useful for preventing these effects or potentially predictive of the onset and/or progression of smoking-induced diseases as well as potential targets for therapeutic strategies.

N-Acetylcysteine counteracts oxidative stress and protects alveolar epithelial cells from lung contusion-induced apoptosis in rats with blunt chest trauma

The aim of this study was to investigate the protective effects of N-acetylcysteine (NAC) on peroxidative and apoptotic changes in the contused lungs of rats following blunt chest trauma. The rats were randomly divided into three groups: control, contusion, and contusion + NAC. All the rats, apart from those in the control group, performed moderate lung contusion. A daily intramuscular NAC injection (150 mg/kg) was given immediately following the blunt chest trauma and was continued for two additional days following cessation of the trauma. Samples of lung tissue were taken in order to evaluate the tissue malondialdehyde (MDA) level, histopathology, and epithelial cell apoptosis using terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay and active caspase-3 immunostaining. In addition, we immunohistochemically evaluated the expression of surfactant protein D (SP-D) in the lung tissue. The blunt chest trauma-induced lung contusion resulted in severe histopathological injury, as well as an increase in the MDA level and in the number of cells identified on TUNEL assay together with active caspase-3 positive epithelial cells, but a decrease in the number of SP-D positive alveolar type 2 (AT-2) cells. NAC treatment effectively attenuated histopathologic, peroxidative, and apoptotic changes, as well as reducing alterations in SP-D expression in the lung tissue. These findings indicate that the beneficial effects of NAC administrated following blunt chest trauma is related to the regulation of oxidative stress and apoptosis.

Regulation of NF-κB-induced inflammatory signaling by lipid peroxidation-derived aldehydes

Oxidative stress plays a critical role in the pathophysiology of a wide range of diseases including cancer. This view has broadened significantly with the recent discoveries that reactive oxygen species initiated lipid peroxidation leads to the formation of potentially toxic lipid aldehyde species such as 4-hydroxy-trans-2-nonenal (HNE), acrolein, and malondialdehyde which activate various signaling intermediates that regulate cellular activity and dysfunction via a process called redox signaling. The lipid aldehyde species formed during synchronized enzymatic pathways result in the posttranslational modification of proteins and DNA leading to cytotoxicity and genotoxicty. Among the lipid aldehyde species, HNE has been widely accepted as a most toxic and abundant lipid aldehyde generated during lipid peroxidation. HNE and its glutathione conjugates have been shown to regulate redox-sensitive transcription factors such as NF-κB and AP-1 via signaling through various protein kinase cascades. Activation of redox-sensitive transcription factors and their nuclear localization leads to transcriptional induction of several genes responsible for cell survival, differentiation, and death. In this review, we describe the mechanisms by which the lipid aldehydes transduce activation of NF-κB signaling pathways that may help to develop therapeutic strategies for the prevention of a number of inflammatory diseases.

Estradiol modulates tumor necrosis factor-induced endothelial inflammation: role of tumor necrosis factor receptor 2

The sex hormone estradiol (E(2)) appears to mediate both anti-atherogenic and pro-inflammatory effects in premenopausal women, suggesting a complex immunomodulatory role. Tumor necrosis factor (TNF) is a key pro-inflammatory cytokine involved in the pathogenesis of atherosclerosis and other inflammatory diseases. Alterations at the TNF receptors (TNFRs) and their downstream signaling/transcriptional pathways can affect inflammatory responses. Given this background, we hypothesized that chronic E(2) exposure would alter endothelial inflammatory response involving modulation at the levels of TNFRs and signaling pathways. HUVECs were used as the model system. Pre-treatment with E(2) did not significantly alter TNF-induced upregulation of pro-inflammatory molecules ICAM-1 (3-6 times) and VCAM-1 (5-7 times). However, pharmacological inhibition of transcriptional pathways suggested a partial shift from NF-ĸB (from 97 to 64%) towards the JNK/AP-1 pathway in ICAM-1 upregulation on E(2) treatment. In contrast, VCAM-1 expression remained NF-ĸB dependent in both control (∼96%) and E(2) treated (∼85%) cells. The pro-inflammatory TNF effects were mediated by TNFR1. Interestingly, E(2) pre-treatment increased TNFR2 levels in these cells. Concomitant TNFR2 activation (but not TNFR1 activation alone) led to the shift towards JNK/AP-1-mediated ICAM-1 upregulation in E(2)-treated cells, suggesting the effects of chronic E(2) to be dependent on TNFR2 signaling.

Role of JNK-1 regulation in the protection of contact-inhibited fibroblasts from oxidative stress

The molecular signaling events leading to protection from oxidative stress-induced apoptosis upon contact inhibition have not been fully investigated. Previous research has indicated a role for mitogen-activated protein kinases (MAPKs) in the regulation of contact inhibition, and these proteins have also been associated with cell cycle regulation and stress-induced apoptosis. The potential role of the MAPK JNK-1 in the stress-response of actively proliferating and contact-inhibited cells was investigated. Actively proliferating normal fibroblasts (BJ) and fibrosarcoma cells (HT-1080) were stressed with H2O2, and levels of activated JNK-1 and cleaved PARP were ascertained. Similarly, these results were compared with levels of activated JNK-1 and cleaved PARP detected in H2O2-stressed confluent fibrosarcoma or contact-inhibited fibroblast cells. Contact-inhibited fibroblasts were protected from apoptosis in comparison to subconfluent fibroblasts, concurrent with decreased JNK-1 activation. Increased culture density of fibrosarcoma cells was not protective against apoptosis, and these cells did not demonstrate density-dependent alterations in the JNK-1 stress response. This decreased activation of JNK-1 in stressed, contact-inhibited cells did not appear to be dependent upon increased expression of MKP-1; however, over-expression of MKP-1 was sufficient to result in a slight decrease in H2O2-stimulated PARP cleavage. Increasing the antioxidant capacity of fibroblasts through NAC-treatment not only lessened H2O2-stimulated JNK-1 activation, but also did not influence the expression of MKP-1. Taken together, these results suggest that regulation of negative regulation of JNK-1 upon contact inhibition is protective against apoptosis, and that this regulation is independent of MKP-1.