MAPK- and PKC/CREB-dependent induction of interleukin-11 by the environmental contaminant formaldehyde in human bronchial epithelial cells

The impact of formaldehyde exposure on lung inflammatory disorders: Insights into asthma, bronchitis, and pulmonary fibrosis

Lung inflammatory disorders are a major global health burden, impacting millions of people and raising rates of morbidity and death across many demographic groups. An industrial chemical and common environmental contaminant, formaldehyde (FA) presents serious health concerns to the respiratory system, including the onset and aggravation of lung inflammatory disorders. Epidemiological studies have shown significant associations between FA exposure levels and the incidence and severity of several respiratory diseases. FA causes inflammation in the respiratory tract via immunological activation, oxidative stress, and airway remodelling, aggravating pre-existing pulmonary inflammation and compromising lung function. Additionally, FA functions as a respiratory sensitizer, causing allergic responses and hypersensitivity pneumonitis in sensitive people. Understanding the complicated processes behind formaldehyde-induced lung inflammation is critical for directing targeted strategies aimed at minimizing environmental exposures and alleviating the burden of formaldehyde-related lung illnesses on global respiratory health. This abstract explores the intricate relationship between FA exposure and lung inflammatory diseases, including asthma, bronchitis, allergic inflammation, lung injury and pulmonary fibrosis.

Extracellular stimulation of lung fibroblasts with arachidonic acid increases interleukin 11 expression through p38 and ERK signaling

Interleukin-11 (IL-11) is a pleiotropic cytokine that regulates proliferation and motility of cancer cells. Fibroblasts reside in the cancer microenvironment and are the primary source of IL-11. Activated fibroblasts, including cancer-associated fibroblasts that produce IL-11, contribute to the development and progression of cancer, and induce fibrosis associated with cancer. Changes in fatty acid composition or its metabolites, and an increase in free fatty acids have been observed in cancer. The effect of deregulated fatty acids on the development and progression of cancer is not fully understood yet. In the present study, we investigated the effects of fatty acids on mRNA expression and secretion of IL-11 in lung fibroblasts. Among the eight fatty acids added exogenously, arachidonic acid (AA) increased mRNA expression and secretion of IL-11 in lung fibroblasts in a dose-dependent manner. AA-induced upregulation of IL-11 was dependent on the activation of the p38 or ERK MAPK signaling pathways. Furthermore, prostaglandin E2, associated with elevated cyclooxygenase-2 expression, participated in the upregulation of IL-11 via its specific receptor in an autocrine/paracrine manner. These results suggest that AA may mediate IL-11 upregulation in lung fibroblasts in the cancer microenvironment, accompanied by unbalanced fatty acid composition.

Overexpressed Hsp70 alleviated formaldehyde-induced apoptosis partly via PI3K/Akt signaling pathway in human bronchial epithelial cells

Formaldehyde (FA) is a ubiquitous environmental pollutant, which can induce apoptosis in lung cell and is related to the pathogenesis of asthma, pneumonia, and chronic obstructive pulmonary disease. Heat shock protein 70 (Hsp70) is an ATP-dependent molecular chaperone and exhibits an anti-apoptosis ability in a variety of cells. Previous studies reported that the expression of Hsp70 was induced when organisms were exposed to FA. Whether Hsp70 plays a role in the FA-induced apoptosis and the involved cell signaling pathway remain largely unknown. In this study, human bronchial epithelial cells with overexpressed Hsp70 and the control were exposed to different concentrations of FA (0, 40, 80, and 160 μmol/L) for 24 hours. Apoptosis and the expression levels of PI3K, Akt, p-Akt, MEK, p-MEK, and GLI2 were detected by Annexin-APC/7AAD double-labeled flow cytometry and western blot. The results showed that overexpression of Hsp70 decreased the apoptosis induced by FA and alleviated the decline of PI3k and p-Akt significantly. Inhibitor (LY 294002, a specific inhibitor of PI3K-Akt) test result indicated that PI3K-Akt signaling pathway was involved in the inhibition of FA-induced apoptosis by Hsp70 overexpression and also active in the maintenance of GLI2 level. However, it also suggested that other signaling pathways activated by overexpressed Hsp70 participated in this process, which was needed to be elucidated in further research.

Zac1 regulates IL-11 expression in osteoarthritis

Interleukin (IL)-11, a member of the IL-6 family of cytokines, exerts pleiotropic effects under normal and various disease conditions. We assessed IL-11 expression regulation and the IL-11/IL-6 ratio in osteoarthritis (OA) to better guide clinical therapeutic decision-making. Our findings suggest that Zac1, a zinc finger protein that regulates apoptosis and cell cycle arrest, is a transcription factor regulating IL-11 expression. Zac1 overexpression or knockdown respectively induced or suppressed IL-11 expression in HeLa cells. Zac1 acted synergistically with AP-1, human papillomavirus E2, and hypoxia inducible factor 1 alpha (HIF1α). IL-11 expression under various conditions, including hypoxia or treatment with phorbol 12-myristate 13-acetate or copper sulfate. Recombinant IL-11-induced phosphorylation of signal transducer and activator of transcription 3 at tyrosine 705 was reduced in a dose-dependent manner in HeLa cells. Cross-talk between Zac1, IL-11, p53, and suppressor of cytokine signaling 3 was differentially affected by copper sulfate, digoxin, and caffeine. Finally, aggressive vs. conventional treatment of OA patients was primarily determined by IL-6 levels. However, we suggest that OA patients with higher IL-11 levels may respond well to conventional treatments, even in the presence of high IL-6.

DNA Methylome Analysis of Saturated Aliphatic Aldehydes in Pulmonary Toxicity

Recent studies have investigated the epigenetic effects of environmental exposure to chemicals on human health. The associations of DNA methylation, environmental exposure and human diseases have been widely demonstrated. However, the use of gene methylation patterns as a predictive biomarker for exposure to environmental toxicants is relatively poorly understood. Here, we focused on low-molecular-weight saturated aliphatic aldehydes (LSAAs), which are important environmental risk factors in humans as major indoor air pollutants. Based on DNA methylation profiling in gene promoter regions, we analysed DNA methylation profiles following exposure of A549 cells to seven LSAAs (propanal, butanal, pentanal, hexanal, heptanal, octanal, and nonanal) to identify LSAA-characterized methylated sites and target genes, as well as to investigate whether exposure to LSAAs contributes to inducing of pulmonary toxicity. Additionally, by integrating DNA methylation and mRNA expression profile analyses, we identified core anti-correlated target genes. Gene ontology analysis of these target genes revealed several key biological processes. These findings suggest that alterations in DNA methylation by exposure to LSAAs provide novel epigenetic biomarkers for risk assessments. This DNA methylation-mRNA approach also reveals potential new mechanistic insights into the epigenetic actions of pulmonary toxicity.

Induction of thymic stromal lymphopoietin by a steroid alkaloid derivative in mouse keratinocytes

Thymic stromal lymphopoietin (TSLP) plays critical roles in inducing and exacerbating allergic diseases. Chemical compounds that induce TSLP production can enhance sensitization to antigens and exacerbate allergic inflammation. Hence, identifying such chemicals will be important to prevent an increase in allergic diseases. In the present study, we found, for the first time, that a steroid alkaloid derivative, code no. 02F04, concentration and time dependently induced mRNA expression and production of TSLP in a mouse keratinocyte cell line, PAM212. In particular, the activity of 02F04 was selective to TSLP. As an analogue of the liver X receptor (LXR) endogenous ligand, 02F04 rapidly increased ATP-binding cassette transporter A1 (ABCA1) expression by regulating the nuclear receptor of LXR. However, instead of being inhibited by the LXR antagonist, 02F04-induced TSLP production was delayed and markedly suppressed by inhibitors of phospholipase C (PLC), pan-protein kinase C (PKC), PKCδ, Rho-associated protein kinase (ROCK), extracellular signal-regulated kinase (ERK) 1/2, and IκΒ kinase 2 (IKK2). Treatment with 02F04 caused the formation of F-actin filaments surrounding the nucleus of PAM212 cells, which then disappeared following addition of ROCK inhibitor. 02F04 also induced phosphorylation of ERK1/2 from 2h after treatment, with a maximum at 24h, and increased nuclear factor-κB (NF-κB) promoter activity by 1.3-fold. Taken together, these results indicate that 02F04-induced TSLP production is regulated via distinct signal transduction pathways, including PLC, PKC, ROCK, ERK1/2, and NF-κB but not nuclear receptors. 02F04, with a unique skeletal structure in inducing TSLP production, can represent a potential new tool for investigating the role of TSLP in allergic diseases.

Differential effects of formaldehyde exposure on airway inflammation and bronchial hyperresponsiveness in BALB/c and C57BL/6 mice

Epidemiological evidence suggests that formaldehyde (FA) exposure may influence the prevalence and severity of allergic asthma. However, the role of genetic background in FA-induced asthma-like responses is poorly understood. In the present study, we investigated the nature and severity of asthma-like responses triggered by exposure to different doses of FA together with or without ovalbumin (OVA) in two genetically different mouse strains—BALB/c and C57BL/6. Both mouse strains were divided into two main groups: the non-sensitized group and the OVA-sensitized group. All the groups were exposed to 0, 0.5 or 3.0 mg/m³ FA for 6 h/day over 25 consecutive days. At 24 h after the final FA exposure, the pulmonary parameters were evaluated. We found that FA exposure induced Th2-type allergic responses in non-sensitized BALB/c and C57BL/6 mice. In addition, FA-induced allergic responses were significantly more prominent in BALB/c mice than in C57BL/6 mice. In sensitized BALB/c mice, however, FA exposure suppressed the development of OVA-induced allergic responses. Exposure to 3.0 mg/m³ FA in sensitized C57BL/6 mice also led to suppressed allergic responses, whereas exposure to 0.5 mg/m³ FA resulted in exacerbated allergic responses to OVA. Our findings suggest that FA exposure can induce differential airway inflammation and bronchial hyperresponsiveness in BALB/c and C57BL/6 mice.

From the Field to the Laboratory: Air Pollutant-Induced Genomic Effects in Lung Cells

Current in vitro studies do not typically assess cellular impacts in relation to real-world atmospheric mixtures of gases. In this study, we set out to examine the feasibility of measuring biological responses at the level of gene expression in human lung cells upon direct exposures to air in the field. This study describes the successful deployment of lung cells in the heavily industrialized Houston Ship Channel. By examining messenger RNA (mRNA) levels from exposed lung cells, we identified changes in genes that play a role as inflammatory responders in the cell. The results show anticipated responses from negative and positive controls, confirming the integrity of the experimental protocol and the successful deployment of the in vitro instrument. Furthermore, exposures to ambient conditions displayed robust changes in gene expression. These results demonstrate a methodology that can produce gas-phase toxicity data in the field.

Analysis of microRNA and mRNA expression profiles highlights alterations in modulation of the MAPK pathway under octanal exposure

Previous environmental microRNA (miRNA) studies have investigated a limited number of candidate miRNAs and have not evaluated functional effects on gene expression. In this study, we aimed to identify octanal (OC)-sensitive miRNAs and to characterize the relationships between miRNAs and expression of candidate genes involved in OC-induced toxicity. Microarray analysis identified 15 miRNAs that were differentially expressed in OC-exposed A549 human alveolar cells. Integrated analyses of miRNA and mRNA expression profiles identified significant miRNA-mRNA anti-correlations. GO analysis of 101 putative target genes showed that the biological category 'MAPK signaling pathway' was prominently annotated. Moreover, we detected increased phosphorylation of p38 MAPK in the OC-exposed group. By integrating the transcriptome and microRNAome, we provide evidence that OC can affect MAPK-induced toxicity signaling. Therefore, this study demonstrates the added value of an integrated miRNA-mRNA approach for identifying molecular events induced by environmental pollutants in an in vitro human model.

Dibenzofuran-induced mitochondrial dysfunction: Interaction with ANT carrier

Exposure to environmental pollutants such as dibenzofurans and furans is linked to the pathophysiology of several diseases. Dibenzofuran (DBF) is listed as a pollutant of concern due to its persistence in the environment, bioaccumulation and toxicity to humans, being associated with the development of lung diseases and cancers, due to its extremely toxic properties such as carcinogenic and teratogenic. Mitochondria play a key role in cellular homeostasis and keeping a proper energy supply for eukaryotic cells is essential in the fulfillment of the tissues energy-demand. Therefore, interference with mitochondrial function leads to cell death and organ failure. In this work, the effects of DBF on isolated rat liver mitochondria were analyzed. DBF exposure caused a markedly increase in the lag phase that follows depolarization induced by ADP, indicating an effect in the phosphorylative system. This was associated with a dose-dependent decrease in ATPase activity. Moreover, DBF also increased the threshold to the induction of the mitochondrial permeability transition (MPT) by calcium. Pretreatment of mitochondria with DBF also increased the concentration of carboxyatractyloside (CAT) necessary to abolish ADP phosphorylation and to induce the MPT, suggesting that DBF may interfere with mitochondria through an effect on the adenine nucleotide translocase (ANT). By co-immunoprecipitating ANT and Cyclophilin D (CypD) following MPT induction, we observed that in the presence of DBF, the ratio CypD/ANT was decreased. This demonstrates that DBF interferes with the ANT and so prevents CypD binding to the ANT, causing decreased phosphorylative capacity and inhibiting the MPT, which is also reflected by an increase in calcium retention capacity. Clarifying the role of pollutants in some mechanisms of toxicity, such as unbalance of bioenergetics status and mitochondrial function, may help to explain the progressive and chronic evolution of diseases derived from exposure to environmental pollutants.

Octanal-induced inflammatory responses in cells relevant for lung toxicity

Inhalation is an important route of aldehyde exposure, and lung is one of the main targets of aldehyde toxicity. Octanal is distributed ubiquitously in the environment and is a component of indoor air pollutants. We investigated whether octanal exposure enhances the inflammatory response in the human respiratory system by increasing the expression and release of cytokines and chemokines. The effect of octanal in transcriptomic modulation was assessed in the human alveolar epithelial cell line A549 using oligonucleotide arrays. We identified a set of genes differentially expressed upon octanal exposure that may be useful for monitoring octanal pulmonary toxicity. These genes were classified according to the Gene Ontology functional category and Kyoto Encyclopedia of Genes and Genomes analysis to explore the biological processes related to octanal-induced pulmonary toxicity. The results show that octanal affects the expression of several chemokines and inflammatory cytokines and increases the levels of interleukin 6 (IL-6) and IL-8 released. In conclusion, octanal exposure modulates the expression of cytokines and chemokines important in the development of lung injury and disease. This suggests that inflammation contributes to octanal-induced lung damage and that the inflammatory genes expressed should be studied in detail, thereby laying the groundwork for future biomonitoring studies.

IL-11 is required for A1 adenosine receptor-mediated protection against ischemic AKI

A1 adenosine receptor activation ameliorates ischemic AKI through the induction of renal proximal tubular sphingosine kinase-1. However, systemic adverse effects may limit A1 adenosine receptor-based therapy for ischemic AKI, indicating a need to identify alternative therapeutic targets within this pathway. Here, we evaluated the function of renal proximal tubular IL-11, a clinically approved hematopoietic cytokine, in A1 adenosine receptor-mediated induction of sphingosine kinase-1 and renal protection. Treatment of human proximal tubule epithelial (HK-2) cells with a selective A1 adenosine receptor agonist, chloro-N(6)-cyclopentyladenosine (CCPA), induced the expression of IL-11 mRNA and protein in an extracellular signal-regulated kinase-dependent manner, and administration of CCPA in mice induced renal synthesis of IL-11. Pretreatment with CCPA protected against renal ischemia-reperfusion injury in wild-type mice, but not in IL-11 receptor-deficient mice. Administration of an IL-11-neutralizing antibody abolished the renal protection provided by CCPA. Similarly, CCPA did not induce renal IL-11 expression or protect against renal ischemia-reperfusion injury in mice lacking the renal proximal tubular A1 adenosine receptor. Finally, treatment with CCPA induced sphingosine kinase-1 in HK-2 cells and wild-type mice, but not in IL-11 receptor-deficient or renal proximal tubule A1 adenosine receptor-deficient mice. Taken together, these results suggest that induction of renal proximal tubule IL-11 is a critical intermediary in A1 adenosine receptor-mediated renal protection that warrants investigation as a novel therapeutic target for the treatment of ischemic AKI.

In vitro effects of aldehydes present in tobacco smoke on gene expression in human lung alveolar epithelial cells

Tobacco smoke consists of thousands of harmful components. A major class of chemicals found in tobacco smoke is formed by aldehydes, in particular formaldehyde, acetaldehyde and acrolein. The present study investigates the gene expression changes in human lung alveolar epithelial cells upon exposure to formaldehyde, acrolein and acetaldehyde at sub-cytotoxic levels. We exposed A549 cells in vitro to aldehydes and non-aldehyde chemicals (nicotine, hydroquinone and 2,5-dimethylfuran) present in tobacco smoke and used microarrays to obtain a global view of the transcriptomic responses. We compared responses of the individual aldehydes with that of the non-aldehydes. We also studied the response of the aldehydes when present in a mixture at relative concentrations as present in cigarette smoke. Formaldehyde gave the strongest response; a total of 66 genes were more than 1.5-fold differentially expressed mostly involved in apoptosis and DNA damage related processes, followed by acetaldehyde (57 genes), hydroquinone (55 genes) and nicotine (8 genes). For acrolein and the mixture only one gene was upregulated involved in oxidative stress. No gene expression effect was found for exposure to 2,5-dimethylfuran. Overall, aldehyde responses are primarily indicative for genotoxicity and oxidative stress. These two toxicity mechanisms are linked to respiratory diseases such as cancer and COPD, respectively. The present findings could be important in providing further understanding of the role of aldehydes emitted from cigarette smoke in the onset of pulmonary diseases.