Anti-inflammatory effect of MUC1 during respiratory syncytial virus infection of lung epithelial cells in vitro

Mucin 1 downregulation associates with corticosteroid resistance in chronic rhinosinusitis with nasal polyps

BACKGROUND

A number of patients with chronic rhinosinusitis with nasal polyps (CRSwNP) are resistant to oral corticosteroids. Mucin 1 (MUC1) shows anti-inflammatory properties, and its cytoplasmic tail (CT) interacts with transcription factors, facilitating their nuclear translocation. Because glucocorticoid receptor (GR) nuclear translocation is key to the anti-inflammatory effect of corticosteroids, we hypothesized that MUC1 is involved in the effectiveness of corticosteroids.

OBJECTIVE

To analyze the role of MUC1 in corticosteroid effectiveness in different cohorts of patients with CRSwNP and elucidate the possible mechanisms involved.

METHODS

Seventy-three patients with CRSwNP took oral corticosteroids for 15 days. Corticosteroid resistance was evaluated by nasal endoscopy. The expression of MUC1 and MUC1 CT was evaluated by real-time PCR, Western blotting, and immunohistochemistry. Beas-2B knockdown with RNA interference for MUC1 (siRNA-MUC1) was used to analyze the role of MUC1 in the anti-inflammatory effects of dexamethasone.

RESULTS

Nineteen patients had nasal polyps that were resistant to oral corticosteroids (NP-CR). MUC1 expression was downregulated in these patients. Primary epithelial cells from patients with NP-CR were insensitive to the anti-inflammatory effects of dexamethasone. In siRNA-MUC1 Beas-2B, dexamethasone showed weaker anti-inflammatory effects, a reduced inhibition of phospho-extracellular-signal-regulated kinases 1/2, a less severe mitogen-activated protein kinase phosphatase 1 increase, and a reduced GR nuclear translocation. Immunoprecipitation experiments revealed that MUC1-CT and GRα form protein complexes and translocate to the nucleus in response to dexamethasone. MUC1-CT-GRα complex was downregulated in NP-CR tissue.

CONCLUSION

MUC1-CT participates in the corticosteroid response that mediates GRα nuclear translocation. The low expression of MUC1 in patients with CRSwNP may participate in corticosteroid resistance.

MUC1: a multifaceted oncoprotein with a key role in cancer progression

The transmembrane glycoprotein Mucin 1 (MUC1) is aberrantly glycosylated and overexpressed in a variety of epithelial cancers, and plays a crucial role in progression of the disease. Tumor-associated MUC1 differs from the MUC1 expressed in normal cells with regard to its biochemical features, cellular distribution, and function. In cancer cells, MUC1 participates in intracellular signal transduction pathways and regulates the expression of its target genes at both the transcriptional and post-transcriptional levels. This review highlights the structural and functional differences that exist between normal and tumor-associated MUC1. We also discuss the recent advances made in the use of MUC1 as a biomarker and therapeutic target for cancer.

Simvastatin attenuates the lipopolysaccharideinduced inflammatory response of rat pulmonary microvascular endothelial cells by downregulating toll-like receptor 4 expression

Objective

The therapeutic potential of simvastatin as an anti-inflammatory agent was explored by investigating its effect on the lipopolysaccharide (LPS)-induced inflammatory response in rat pulmonary microvascular endothelial cells (RPMVECs).

Methods

RPMVECs were isolated and the mRNA and protein levels of different toll-like receptors (TLR) were assessed by qRT-PCR and western blotting. The LPS-induced expressions of TLR4, TNF-α and iNOS were analyzed in RPMVECs treated with different concentrations of simvastatin for different times. NF-κB activation was examined by immuofluroscence, luciferase reporter assay and western blotting.

Results

TLR4 is abundantly expressed in RPMVECs, and its expression is induced by LPS stimulation. Simvastatin inhibited LPS-induced TLR4 expression at the mRNA and protein levels in a time-dependent manner (p<0.01), and alleviated inflammation in RPMVECs by inhibiting the release of inflammatory factors such as TNF-α and iNOS. Further study indicated that simvastatin significantly attenuated NF-κB activity by inhibiting the degradation of IκB-α. Pretreatment with pyrrolidine dithiocarbamate (PDTC) and knock-down of TLR4 expression by RNA interference down-regulated the LPS-induced inflammatory response in RPMVECs.

Conclusion

Simvastatin inhibits the LPS-induced inflammatory response in RPMVECs by down-regulating TLR4 expression, suggesting its role as a potential inhibitor of LPS-induced inflammation

Tanshinone IIA inhibits lipopolysaccharide-induced MUC1 overexpression in alveolar epithelial cells

The anti-inflammatory function of tanshinone IIA (TIIA), an active natural compound from Chinese herbal medicine Danshen, has been well recognized, and therefore TIIA has been widely used to treat various inflammatory conditions associated with cardiac and lung diseases. Mucin 1 (Muc1) plays important anti-inflammatory roles in resolution of acute lung inflammation. In this study, we investigated the effects of TIIA on LPS-induced acute lung inflammation, as well as its relationship to Muc1 expression in mouse lung and MUC1 in human alveolar epithelial cells. TIIA pretreatment significantly inhibited LPS-induced pulmonary inflammation in both Muc1 wild-type (Muc1(+/+)) and knockout (Muc1(-/-)) mice, as manifested by reduced neutrophil infiltration and reduced TNF-α and keratinocyte chemoattractant levels in bronchoalveolar lavage fluid. The inhibitory effects of TIIA on airway inflammation were associated with reduced expression of Muc1 in Muc1(+/+) mouse lung. Moreover, pretreatment with TIIA significantly inhibited LPS-induced MUC1 expression and TNF-α release in A549 alveolar epithelial cells. TNF-α upregulated MUC1 mRNA and protein expression in A549 cells, which was inhibited by pretreatment with TIIA. The LPS-induced MUC1 expression was blocked when A549 cells were transfected with siRNA targeting for TNF-α receptor 1. Furthermore, TIIA inhibited LPS-induced nuclear translocation of NF-κB and upregulation of Toll-like receptor 4 in A549 cells. Taken together, these results demonstrate that TIIA suppressed LPS-induced acute lung inflammation regardless of the presence of Muc1, and TIIA inhibited LPS- and TNF-α-induced MUC1/Muc1 expression in airway epithelial cells, suggesting that MUC1/Muc1 does not account for the mechanisms of the anti-inflammatory effects of TIIA in the airway.

Histones-mediated lymphocyte apoptosis during sepsis is dependent on p38 phosphorylation and mitochondrial permeability transition

Lymphocyte apoptosis is one reason for immunoparalysis seen in sepsis, although the triggers are unknown. We hypothesized that molecules in plasma, which are up-regulated during sepsis, may be responsible for this. In this study, peripheral lymphocyte apoptosis caused by extracellular histones was confirmed both in mouse and human primary lymphocytes, in which histones induced lymphocyte apoptosis dose-dependently and time-dependently. To identify which intracellular signal pathways were activated, phosphorylation of various mitogen-activated protein kinases (MAPKs) were evaluated during this process, and p38 inhibitor (SB203580) was used to confirm the role of p38 in lymphocyte apoptosis induced by histones. To investigate the mitochondrial injury during these processes, we analyzed Bcl2 degradation and Rhodamine 123 to assess mitochondrial-membrane stability, via cyclosporin A as an inhibitor for mitochondrial permeability transition (MPT). Then, caspase 3 activation was also checked by western-blotting. We found that p38 phosphorylation, mitochondrial injury and caspase 3 activation occurred dose-dependently in histones-mediated lymphocyte apoptosis. We also observed that p38 inhibitor SB203580 decreased lymphocyte apoptotic ratio by 49% (P<0.05), and inhibition of MPT protected lymphocytes from apoptosis. Furthermore, to investigate whether histones are responsible for lymphocyte apoptosis, various concentrations of histone H4 neutralization antibodies were co-cultured with human primary lymphocytes and plasma from cecal ligation and puncture (CLP) mice or sham mice. The results showed that H4 neutralization antibody dose-dependently blocked lymphocyte apoptosis caused by septic plasma in vitro. These data demonstrate for the first time that extracellular histones, especially H4, play a vital role in lymphocyte apoptosis during sepsis which is dependent on p38 phosphorylation and mitochondrial permeability transition. Neutralizing H4 can inhibit lymphocyte apoptosis, indicating that it could be a potential target in clinical interventions for sepsis associated immunoparalysis.

Angiotensin II facilitates fibrogenic effect of TGF-β1 through enhancing the down-regulation of BAMBI caused by LPS: a new pro-fibrotic mechanism of angiotensin II

Angiotensin II has progressively been considered to play an important role in the development of liver fibrosis, although the mechanism isn't fully understood. The aim of this study was to investigate a possible pro-fibrotic mechanism, by which angiotensin II would enhance the pro-fibrotic effect of transforming growth factor beta 1 (TGF-β1) through up-regulation of toll-like receptor 4 (TLR4) and enhancing down-regulation of TGF-β1 inhibitory pseudo-receptor-BAMBI caused by LPS in hepatic stellate cells (HSCs). Firstly, the synergistic effects of angiotensin II, TGF-β1 and LPS on collagen 1α production were confirmed in vitro by ELISA, in which angiotensin II, LPS and TGF-β1 were treated sequentially, and in vivo by immunofluorescence, in the experiments single or multiple intra-peritoneally implanted osmotic mini-pumps administrating angiotensin II or LPS combined with intra-peritoneal injections of TGF-β1 were used. We also found that only LPS and TGF-β1 weren't enough to induce obvious fibrogenesis without angiotensin II. Secondly, to identify the reason of why angiotensin II is so important, the minute level of TLR4 in activated HSCs - T6 and primary quiescent HSCs of rat, up-regulation of TLR4 by angiotensin II and blockage by different angiotensin II receptor type 1 (AT1) blockers in HSCs were assayed by western blotting in vitro and immunofluorescence in vivo. Finally, BAMBI expression level, which is regulated by LPS-TLR4 pathway, was detected by qRT-PCR and results showed angiotensin II enhanced the down-regulation of BAMBI mRNA caused by LPS in vitro and in vivo, and TLR4 neutralization antibody blocked this interactive effect. These data demonstrated that angiotensin II enhances LPS-TLR4 pathway signaling and further down-regulates expression of BAMBI through up-regulation of TLR4, which results in facilitation of pro-fibrotic activity of TGF-β1. Angiotensin II, LPS and TGF-β1 act synergistically during hepatic fibrogenesis, showing crosstalks between angiotensin II-AT1, LPS-TLR4 and TGF-β1-BAMBI signal pathways in rat HSCs.

Higher susceptibility to experimental autoimmune encephalomyelitis in Muc1-deficient mice is associated with increased Th1/Th17 responses

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system in which dendritic cells (DC) play an important role in the development of inflammatory responses. Recently it has been shown that Muc1, a membrane tethered glycoprotein, has an ability to suppress inflammatory responses in cultured DC. The objective of this study was to investigate the possible involvement of Muc1 in the development of MS using experimental autoimmune encephalomyelitis (EAE) in mice, a widely used animal model of MS. Our results showed that: (1) Muc1(-/-) mice developed greater EAE severity compared with wild type (wt) mice, which correlated with increased numbers of Th1 and Th17 cells infiltrating into the CNS; (2) upon stimulation, splenic DC from Muc1(-/-) mice produced greater amounts of IL-1β, IL-6, and IL-12 but less amounts of IL-10 compared with those from wt mice; and (3) the ability of splenic DC to differentiate antigen-specific CD4+ T cells into Th1 and Th17 cells was greater in Muc1(-/-) mice compared with wt mice. We conclude that Muc1 plays an anti-inflammatory role in EAE. This is the first report demonstrating the possible involvement of Muc1 in the development of MS and might provide a potential target for immunotherapy.

Role of Epithelial Cells in Chronic Inflammatory Lung Disease

Airborne pathogens entering the lungs first encounter the mucus layer overlaying epithelial cells as a first line of host defense [1, 2]. In addition to serving as the physical barrier to these toxic agents, intact epithelia also are major sources of various macromolecules including antimicrobial agents, antioxidants and antiproteases [3, 4] as well as proinflammatory cytokines and chemokines that initiate and amplify host defensive responses to these toxic agents [5]. Airway epithelial cells can be categorized as either ciliated or secretory [6]. Secretory cells, such as goblet cells and Clara cells, are responsible for the production and secretion of mucus along the apical epithelial surface and, in conjunction with ciliated cells, for the regulation of airway surface liquid viscosity. In addition, submucosal mucus glands connect to the airway lumen through a ciliated duct that propels mucins outward. These glands are present in the larger airways between bands of smooth muscle and cartilage. See Fig. 1.

Cellular and molecular biology of airway mucins

Airway mucus constitutes a thin layer of airway surface liquid with component macromolecules that covers the luminal surface of the respiratory tract. The major function of mucus is to protect the lungs through mucociliary clearance of inhaled foreign particles and noxious chemicals. Mucus is comprised of water, ions, mucin glycoproteins, and a variety of other macromolecules, some of which possess anti-microbial, anti-protease, and anti-oxidant activities. Mucins comprise the major protein component of mucus and exist as secreted and cell-associated glycoproteins. Secreted, gel-forming mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for effective mucociliary clearance. Cell-associated mucins shield the epithelial surface from pathogens through their extracellular domains and regulate intracellular signaling through their cytoplasmic regions. However, neither the exact structures of mucin glycoproteins, nor the manner through which their expression is regulated, are completely understood. This chapter reviews what is currently known about the cellular and molecular properties of airway mucins.

Suppression of IL-8 production in gastric epithelial cells by MUC1 mucin and peroxisome proliferator-associated receptor-γ

MUC1 is a membrane-tethered mucin expressed on the apical surface of epithelial cells. Our previous report (Guang W, Ding H, Czinn SJ, Kim KC, Blanchard TG, Lillehoj EP. J Biol Chem 285: 20547-20557, 2010) demonstrated that expression of MUC1 in AGS gastric epithelial cells limits Helicobacter pylori infection and reduces bacterial-driven IL-8 production. In this study, we identified the peroxisome proliferator-associated receptor-γ (PPARγ) upstream of MUC1 in the anti-inflammatory pathway suppressing H. pylori- and phorbol 12-myristate 13-acetate (PMA)-stimulated IL-8 production. Treatment of AGS cells with H. pylori or PMA increased IL-8 levels in cell culture supernatants compared with cells treated with the respective vehicle controls. Prior small interfering (si)RNA-induced MUC1 silencing further increased H. pylori- and PMA-stimulated IL-8 levels compared with a negative control siRNA. MUC1-expressing AGS cells pretreated with the PPARγ agonist troglitazone (TGN) had reduced H. pylori- and PMA-stimulated IL-8 levels compared with cells treated with H. pylori or PMA alone. However, following MUC1 siRNA knockdown, no differences in IL-8 levels were seen between TGN/H. pylori and H. pylori-only cells or between TGN/PMA and PMA-only cells. Finally, TGN-treated AGS cells had increased Muc1 promoter activity, as measured using a Muc1-luciferase reporter gene, and greater MUC1 protein levels by Western blot analysis, compared with vehicle controls. These results support the hypothesis that PPARγ stimulates MUC1 expression by AGS cells, thereby attenuating H. pylori- and PMA-induced IL-8 production.

Prevention of lung injury by Muc1 mucin in a mouse model of repetitive Pseudomonas aeruginosa infection

OBJECTIVE AND DESIGN

To determine whether repetitive airway Pseudomonas aeruginosa (Pa) infection results in lung inflammation and injury and, if so, whether these responses are affected by Muc1 mucin. Muc1 wild type (WT) and knockout (KO) mice were compared for body weights, lung inflammatory responses, and airspace enlargement using a chronic lung infection model system.

MATERIALS

Mice were treated intranasally with Pa (10(7) CFU) on days 0, 4, 7 and 10. On day 14, body weights, inflammatory cell numbers in bronchoalveolar lavage fluid (BALF), and airspace enlargement were measured. Differences in inflammatory responses between groups were statistically analyzed by the Student's t test and ANOVA.

RESULTS

Muc1 WT mice exhibited mild degrees of both inflammation and airspace enlargement following repetitive airway Pa infection. However, Muc1 KO mice exhibited significantly decreased body weights, greater macrophage numbers in the BALF, and increased airspace enlargement compared with Muc1 WT mice.

CONCLUSIONS

This is the first report demonstrating that Muc1 deficiency can lead to lung injury during chronic Pa infection in mice. These results suggest that MUC1 may play a crucial role in the resolution of inflammation during chronic respiratory infections and that MUC1 dysfunction likely contributes to the pathogenesis of chronic inflammatory respiratory disease.

Antiinflammatory role of MUC1 mucin during infection with nontypeable Haemophilus influenzae

MUC1 (or Muc1 in nonhuman species) is a membrane-tethered mucin expressed on the apical surface of mucosal epithelia (including those of the airways) that suppresses Toll-like receptor (TLR) signaling. We sought to determine whether the anti-inflammatory effect of MUC1 is operative during infection with nontypeable Haemophilus influenzae (NTHi), and if so, which TLR pathway was affected. Our results showed that: (1) a lysate of NTHi increased the early release of IL-8 and later production of MUC1 protein by A549 cells in dose-dependent and time-dependent manners, compared with vehicle control; (2) both effects were attenuated after transfection of the cells with a TLR2-targeting small interfering (si) RNA, compared with a control siRNA; (3) the NTHi-induced release of IL-8 was suppressed by an overexpression of MUC1, and was enhanced by the knockdown of MUC1; (4) the TNF-α released after treatment with NTHi was sufficient to up-regulate MUC1, which was completely inhibited by pretreatment with a soluble TNF-α receptor; and (5) primary murine tracheal surface epithelial (MTSE) cells from Muc1 knockout mice exhibited an increased in vitro production of NTHi-stimulated keratinocyte chemoattractant compared with MTSE cells from Muc1-expressing animals. These results suggest a hypothetical feedback loop model whereby NTHi activates TLRs (mainly TLR2) in airway epithelial cells, leading to the increased production of TNF-α and IL-8, which subsequently up-regulate the expression of MUC1, resulting in suppressed TLR signaling and decreased production of IL-8. This report is the first, to the best of our knowledge, demonstrating that the inflammatory response in airway epithelial cells during infection with NTHi is controlled by MUC1 mucin, mainly through the suppression of TLR2 signaling.

PPARγ inhibits airway epithelial cell inflammatory response through a MUC1-dependent mechanism

This study was conducted to examine the relationship between the peroxisome proliferator-associated receptor-γ (PPARγ) and MUC1 mucin, two anti-inflammatory molecules expressed in the airways. Treatment of A549 lung epithelial cells or primary mouse tracheal surface epithelial (MTSE) cells with phorbol 12-myristate 13-acetate (PMA) increased the levels of tumor necrosis factor (TNF)-α in cell culture media compared with cells treated with vehicle alone. Overexpression of MUC1 in A549 cells decreased PMA-stimulated TNF-α levels, whereas deficiency of Muc1 expression in MTSE cells from Muc1 null mice increased PMA-induced TNF-α levels. Treatment of A549 or MTSE cells with the PPARγ agonist troglitazone (TGN) blocked the ability of PMA to stimulate TNF-α levels. However, the effect of TGN required the presence of MUC1/Muc1, since no differences in TNF-α levels were seen between PMA and PMA plus TGN in MUC1/Muc1-deficient cells. Similarly, whereas TGN decreased interleukin-8 (IL-8) levels in culture media of MUC1-expressing A549 cells treated with Pseudomonas aeruginosa strain K (PAK), no differences in IL-8 levels were seen between PAK and PAK plus TGN in MUC1-nonexpressing cells. EMSA confirmed the presence of a PPARγ-binding element in the MUC1 gene promoter. Finally, TGN treatment of A549 cells increased MUC1 promoter activity measured using a MUC1-luciferase reporter gene, augmented MUC1 mRNA levels by quantitative RT-PCR, and enhanced MUC1 protein expression by Western blot analysis. These combined data are consistent with the hypothesis that PPARγ stimulates MUC1/Muc1 expression, thereby blocking PMA/PAK-induced TNF-α/IL-8 production by airway epithelial cells.

Role of epithelial mucins during airway infection

Airway surface fluid contains two layers of mucins consisting mainly of 5 different mucin gene products. While the outer layer contains two gel-forming mucins (MUC5AC and MUC5B) that are tightly associated with various biologically active, defensive molecules, the inner layer contains three membrane-tethered mucins (MUC1, MUC4 and MUC16) shed from the apical cell surface. During airway infection, all of these mucins serve as a major protective barrier against pathogens. MUC1 mucin produced by virtually all the surface columnar epithelial cells in the respiratory tract as well as Type II pneumocytes in the alveoli plays an additional, perhaps more critical role during respiratory infection by controlling the resolution of inflammation that is essential to prevent the development of inflammatory lung disease.

Genome-wide detection of natural selection in African Americans pre- and post-admixture

It is particularly meaningful to investigate natural selection in African Americans (AfA) due to the high mortality their African ancestry has experienced in history. In this study, we examined 491,526 autosomal single nucleotide polymorphisms (SNPs) genotyped in 5210 individuals and conducted a genome-wide search for selection signals in 1890 AfA. Several genomic regions showing an excess of African or European ancestry, which were considered the footprints of selection since population admixture, were detected based on a commonly used approach. However, we also developed a new strategy to detect natural selection both pre- and post-admixture by reconstructing an ancestral African population (AAF) from inferred African components of ancestry in AfA and comparing it with indigenous African populations (IAF). Interestingly, many selection-candidate genes identified by the new approach were associated with AfA-specific high-risk diseases such as prostate cancer and hypertension, suggesting an important role these disease-related genes might have played in adapting to a new environment. CD36 and HBB, whose mutations confer a degree of protection against malaria, were also located in the highly differentiated regions between AAF and IAF. Further analysis showed that the frequencies of alleles protecting against malaria in AAF were lower than those in IAF, which is consistent with the relaxed selection pressure of malaria in the New World. There is no overlap between the top candidate genes detected by the two approaches, indicating the different environmental pressures AfA experienced pre- and post-population admixture. We suggest that the new approach is reasonably powerful and can also be applied to other admixed populations such as Latinos and Uyghurs.

Limited effects of Muc1 deficiency on mouse adenovirus type 1 respiratory infection

Muc1 (MUC1 in humans) is a membrane-tethered mucin that exerts anti-inflammatory effects in the lung during bacterial infection. Muc1 and other mucins are also likely to form a protective barrier in the lung. We used mouse adenovirus type 1 (MAV-1, also known as MAdV-1) to determine the role of Muc1 in the pathogenesis of an adenovirus in its natural host. Following intranasal inoculation of wild type mice, we detected increased TNF-α, a cytokine linked to Muc1 production, but no consistent changes in the production of lung Muc1, Muc5ac or overall lung mucus production. Viral loads were modestly higher in the lungs of Muc1(-/-) mice compared to Muc1(+/+) mice at several early time points but decreased to similar levels by 14 days post infection in both groups. However, cellular inflammation and the expression of CXCL1, CCL5, and CCL2 did not significantly differ between Muc1(-/-) and Muc1(+/+) mice. Our data therefore suggest that Muc1 may contribute to a physical barrier that protects against MAV-1 respiratory infection. However, our data do not reveal an anti-inflammatory effect of Muc1 that contributes to MAV-1 pathogenesis.

Evaluation of the Calu-3 cell line as a model of in vitro respiratory syncytial virus infection

Respiratory syncytial virus (RSV) replication is primarily limited to the upper respiratory tract epithelium and primary, differentiated normal human bronchial epithelial cells (NHBE) have, therefore, been considered a good system for in vitro analysis of lung tissue response to respiratory virus infection and virus–host interactions. However, NHBE cells are expensive, difficult to culture, and vary with the source patient. An alternate approach is to use a continuous cell line that has features of bronchial epithelial cells such as Calu-3, an epithelial cell line derived from human lung adenocarcinoma, as an in vitro model of respiratory virus infection. The results show that Calu-3 fully polarize when grown on permeable supports as liquid-covered cultures. Polarized Calu-3 are susceptible to RSV infection and release infectious virus primarily from the apical surface, consistent with studies in NHBE cells. The data demonstrate that polarized Calu-3 may serve as a useful in vitro model to study host responses to RSV infection.