Localization of leukaemia inhibitory factor to airway epithelium and its amplification of contractile responses to tachykinins

Leukemia inhibitory factor in the neuroimmune communication pathways in allergic asthma

In the pathogenesis of asthma, central sensitization is suggested to be an important neural mechanism, and neurotrophins and cytokines are likely to be the major mediators in the neuroimmune communication pathways of asthma. However, their impact on the central nervous system in allergic asthma remains unclear. We hypothesize that central neurogenic inflammation develops in the pathogenesis of allergic asthma, and nerve growth factor (NGF) and leukemia inhibitory factor (LIF) are important mediators in its development. An asthma model of rats was established by sensitization and challenged with ovalbumin (OVA). For further confirmation of the role of LIF in neurogenic inflammation, a subgroup was pretreated with intraperitoneally (i.p.) LIF antibody before OVA challenge. The levels of LIF and NGF were measured with reverse transcription and polymerase chain reaction (RT-PCR), in situ hybridization (ISH) and immunohistochemistry stain in lung tissue, airway-specific dorsal root ganglia (DRG, C7-T5) and brain stem of asthmatic rats, anti-LIF pretreated rats and controls. A significantly increased number of LIF- and NGF-immunoreactive cells were detected in lung tissue, DRG and the brain stem of asthmatic rats. In the asthma group a significantly increase level of mRNA encoding LIF and NGF in lung tissue was detected, but not in DRG and the brain stem. Pretreatment with LIF antibody decreased the level of LIF and NGF in all tissues. LIF is an important mediator in the crosstalk between nerve and immune systems. Our study demonstrate that the increased level of LIF and NGF in DRG and brain stem may be not based on result from de novo synthesis, but rather on result from retrograde nerve transport or passage across the blood-brain-barrier.

Leukemia inhibitory factor signaling is required for lung protection during pneumonia

Lung infections represent a tremendous disease burden and a leading cause of acute lung injury. STAT3 signaling is essential for controlling lung injury during pneumonia. We previously identified LIF as a prominent STAT3-activating cytokine expressed in the airspaces of pneumonic lungs, but its physiological significance in this setting has never been explored. To do so, Escherichia coli was intratracheally instilled into C57BL/6 mice in the presence of neutralizing anti-LIF IgG or control IgG. Anti-LIF completely eliminated lung LIF detection and markedly exacerbated lung injury compared with control mice as evidenced by airspace albumin content, lung liquid accumulation, and histological analysis. Although lung bacteriology was equivalent between groups, bacteremia was more prevalent with anti-LIF treatment, suggestive of compromised barrier function rather than impaired antibacterial defense as the cause of dissemination. Inflammatory cytokine expression was also exaggerated in anti-LIF-treated lungs, albeit after injury had ensued. Interestingly, alveolar neutrophil recruitment was modestly but significantly reduced compared with control mice despite elevated cytokine levels, indicating that inflammatory injury was not a consequence of excessive neutrophilic alveolitis. Lastly, the lung transcriptome was dramatically remodeled during pneumonia, but far more so following LIF neutralization, with gene changes implicating cell death and epithelial homeostasis among other processes relevant to tissue injury. From these findings, we conclude that endogenous LIF facilitates tissue protection during pneumonia. The LIF-STAT3 axis is identified in this study as a critical determinant of lung injury with clinical implications for pneumonia patients.

Leukemia inhibitory factor in rat fetal lung development: expression and functional studies

Background

Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) are members of the family of the glycoprotein 130 (gp130)-type cytokines. These cytokines share gp130 as a common signal transducer, which explains why they show some functional redundancy. Recently, it was demonstrated that IL-6 promotes fetal lung branching. Additionally, LIF has been implicated in developmental processes of some branching organs. Thus, in this study LIF expression pattern and its effects on fetal rat lung morphogenesis were assessed.

Methodology/Principal Findings

LIF and its subunit receptor LIFRα expression levels were evaluated by immunohistochemistry and western blot in fetal rat lungs of different gestational ages, ranging from 13.5 to 21.5 days post-conception. Throughout all gestational ages studied, LIF was constitutively expressed in pulmonary epithelium, whereas LIFRα was first mainly expressed in the mesenchyme, but after pseudoglandular stage it was also observed in epithelial cells. These results point to a LIF epithelium-mesenchyme cross-talk, which is known to be important for lung branching process. Regarding functional studies, fetal lung explants were cultured with increasing doses of LIF or LIF neutralizing antibodies during 4 days. MAPK, AKT, and STAT3 phosphorylation in the treated lung explants was analyzed. LIF supplementation significantly inhibited lung growth in spite of an increase in p44/42 phosphorylation. On the other hand, LIF inhibition significantly stimulated lung growth via p38 and Akt pathways.

Conclusions/Significance

The present study describes that LIF and its subunit receptor LIFRα are constitutively expressed during fetal lung development and that they have an inhibitory physiological role on fetal lung branching.

Polarized secretion of leukemia inhibitory factor

Background

The direction of cytokine secretion from polarized cells determines the cytokine's cellular targets. Leukemia inhibitory factor (LIF) belongs to the interleukin-6 (IL-6) family of cytokines and signals through LIFR/gp130. Three factors which may regulate the direction of LIF secretion were studied: the site of stimulation, signal peptides, and expression levels. Stimulation with IL-1β is known to promote IL-6 secretion from the stimulated membrane (apical or basolateral) in the human intestinal epithelial cell line Caco-2. Since LIF is related to IL-6, LIF secretion was also tested in Caco-2 following IL-1β stimulation. Signal peptides may influence the trafficking of LIF. Two isoforms of murine LIF, LIF-M and LIF-D, encode different signal peptides which have been associated with different locations of the mature protein in fibroblasts. To determine the effect of the signal peptides on LIF secretion, secretion levels were compared in Madin-Darby canine kidney (MDCK) clones which expressed murine LIF-M or LIF-D or human LIF under the control of an inducible promoter. Low and high levels of LIF expression were also compared since saturation of the apical or basolateral route would reveal specific transporters for LIF.

Results

When Caco-2 was grown on permeable supports, LIF was secreted constitutively with around 40% secreted into the apical chamber. Stimulation with IL-1β increased LIF production. After treating the apical surface with IL-1β, the percentage secreted apically remained similar to the untreated, whereas, when the cells were stimulated at the basolateral surface only 20% was secreted apically. In MDCK cells, an endogenous LIF-like protein was detected entirely in the apical compartment. The two mLIF isoforms showed no difference in their secretion patterns in MDCK. Interestingly, about 70% of murine and human LIF was secreted apically from MDCK over a 400-fold range of expression levels within clones and a 200,000-fold range across clones.

Conclusion

The site of stimulation affected the polarity of LIF secretion, while, signal peptides and expression levels did not. Exogenous LIF is transported in MDCK without readily saturated steps.

LIF upregulates expression of NK-1R in NHBE cells

Leukemia inhibitory factor (LIF), a cytokine at the interface between neurobiology and immunology, is mainly mediated through JAK/STAT pathway and MAPK/ERK pathway. Evidence suggested LIF is related to the higher expression of neurokinin-1 receptor (NK-1R) in asthma. In this study, the immunohistochemistry stain showed the expressions of NK-1R, LIF, p-STAT3, and p-ERK1/2 in the lung tissues of allergic rats were increased compared with the controls, and the main positive cell type was airway epithelial cell. Normal human bronchial epithelial cells were treated with LIF in the presence or absence of AG490 (JAK2 inhibitor), PD98059 (MEK inhibitor), and the siRNA against STAT3. Western blot and RT-PCR indicated that LIF induced the expression of NK-1R, which was inhibited by the inhibitors mentioned above. No significant interaction was found between JAK/STAT pathway and MAPK/ERK pathway. In summary, bronchial epithelial cell changes in asthma are induced by LIF which promotes the expression of NK-1R, and JAK/STAT pathway and MAPK/ERK pathway may participate in this process.

Increased secretion of leukemia inhibitory factor by immature airway smooth muscle cells enhances intracellular signaling and airway contractility

Airway smooth muscle cells (ASMC) play a major role in airway inflammation, hyperresponsiveness, and obstruction in asthma. However, very little is known regarding the relation between inflammatory mediators and cytokines and immature ASMC. The aim of this study was to evaluate 1) the secretion of leukemia inhibitory factor (LIF) (an IL-6 family neurotrophic cytokine) by ASMC; 2) intracellular calcium concentration ([Ca(2+)](i)) signaling; and 3) the effect of LIF on mast cell chemotaxis and rat airway contractility. Immature and adult human ASMC were cultured. ELISA and real-time PCR were performed to assess LIF protein secretion and mRNA production, [methyl-(3)H]thymidine incorporation to quantify ASMC DNA synthesis, a Boyden chamber to evaluate the effect of LIF on mast cell chemotaxis, microspectroflurimetry using indo-1 (at baseline and after stimulation bradykinin, U-46619, histamine, and acetylcholine, in the presence or absence of LIF or TNF-alpha) for [Ca(2+)](i) signaling, and isolated rat pup tracheae to determine the effect of LIF on airway contractility to ACh. TNF-alpha-stimulated immature ASMC produce more LIF mRNA and protein than adult ASMC, although this cytokine induces a moderate increase in DNA synthesis (+20%) in adult ASMC only. Human recombinant LIF exerts no chemotactic effect on human mast cells. In immature ASMC, ACh-induced [Ca(2+)](i) response was enhanced twofold after incubation with LIF, whereas TNF-alpha increased the [Ca(2+)](i) to U-46619 threefold. In TNF-alpha-exposed adult ASMC, [Ca(2+)](i) responses to ACh were of greater magnitude (sixfold increase) than in immature ASMC. Human recombinant LIF increased contractility to ACh by 50% in immature, isolated rat tracheae. Stimulated immature human ASMC greatly secrete LIF, thus potentially contributing to neuroimmune airway inflammation and subsequent remodeling. Increased LIF secretion enhances airway reactivity and [Ca(2+)](i) signaling.

Cardiotrophin-1 alters airway smooth muscle structure and mechanical properties in airway explants

Induction of hypertrophy and inhibition of apoptosis may be important mechanisms contributing to increased airway smooth muscle (ASM) mass in asthma. Data from our laboratory indicate that cardiotrophin-1 (CT-1) induces hypertrophy and inhibits apoptosis in isolated human ASM cells. To determine whether these novel effects of CT-1 also occur in the airway tissue milieu and to determine whether structural changes are accompanied by functional changes, matched pairs of guinea pig airway explants were treated with or without CT-1 for 7 days, and structural features as well as isometric and isotonic contractile and relaxant mechanical properties were measured. CT-1 (0.2-5 ng/ml) increased both myocyte mass and extracellular matrix in a concentration-dependent fashion. CT-1 (10 ng/ml)-treated tissues exhibited a significant increase in passive tension at all lengths on day 7; at optimal length, passive tension generated by CT-1-treated tissues was 1.72 +/- 0.12 vs. 1.0 +/- 0.1 g for control. Maximal isometric stress was decreased in the CT-1-treated group on day 7 (0.39 +/- 0.10 kg/cm(2)) vs. control (0.77 +/- 0.15 kg/cm(2), P < 0.05). Isoproterenol-induced relaxant potency was reduced in CT-1-treated tissues, log EC(50) being -7.28 +/- 0.34 vs. -8.12 +/- 0.25 M in control, P < 0.05. These data indicate that CT-1 alters ASM structural and mechanical properties in the tissue environment and suggest that structural changes found in the airway wall in asthma are not necessarily associated with increased responsiveness.

Expression and effects of cardiotrophin-1 (CT-1) in human airway smooth muscle cells

1. Cellular hypertrophy and/or a reduced rate of apoptosis could increase airway smooth muscle mass. As cardiotrophin-1 (CT-1) induces hypertrophy and inhibits apoptosis in cardiomyocytes, we tested for the expression and effects of CT-1 in human bronchial smooth muscle cells (HBSMC). 2. CT-1 was detected in abundance in normal adult human lung and was expressed in both fetal and adult HBSMC. 3. Following serum deprivation, CT-1 was released by reintroduction of serum and by TGF-beta 2/IL-4 in fetal but not adult cells. TGF-beta 2/IL-4 triggered the release of CT-1 in serum-fed adult cells. Hypoxia and strain had no effect on the release of CT-1. 4. CT-1 reduced the apoptosis induced both by serum deprivation and by Fas antibody/TNF-alpha treatment in adult cells, with greater efficacy than other members of the IL-6 superfamily. The MAPK/ERK kinase inhibitor PD98059 (1-10 microM) reduced the effect of CT-1. Fetal cells were more resistant to apoptosis. 5. CT-1 (10 ng ml-1) induced a significant increase in cell size as judged by protein/DNA ratios and flow cytometry. No effects on smooth muscle alpha-actin or vimentin proteins were noted, although CT-1 qualitatively alters the cytostructural distribution of SM22, an actin filament-associated protein, and increased SM22 protein abundance. No effect on proliferation or migration was evident. 6. These data suggest CT-1 expression primarily in fetal and synthetic HBSMC phenotypes. By reducing the rates of apoptosis and inducing hypertrophy, CT-1 may contribute to increased smooth muscle mass in airway disease.

Pulmonary expression of leukemia inhibitory factor induces B cell hyperplasia and confers protection in hyperoxia

Leukemia inhibitory factor (LIF) is produced by a large number of pulmonary cells in response to diverse stimuli. Exaggerated levels of LIF have also been detected in the adult respiratory distress syndrome and other disorders. The biologic effects of LIF in the lung, however, have not been elucidated. To define the respiratory effects of LIF, we generated transgenic mice in which human LIF was selectively targeted to the mature lung. In these mice, transgene activation caused an impressive increase in bronchoalveolar lavage (BAL) cellularity with a significant increase in BAL and tissue B lymphocytes. LIF also conferred protection in 100% O2 where it decreased alveolar-capillary protein leak and enhanced survival. This protective effect was associated with the induction of interleukin (IL)-6 mRNA and protein. LIF transgenic mice with a null mutation in IL-6 were more sensitive to the toxic effects of 100% O2 than LIF-transgenic animals with a wild-type IL-6 locus. These studies demonstrate that LIF induces B cell hyperplasia and confers protection in hyperoxic acute lung injury. They also demonstrate that LIF induces IL-6 and that the protective effects of LIF are mediated, in part, via this inductive event. LIF may be an important regulator of B cell-mediated responses and oxidant injury in the lung.

Effects of cytokines on contractile and dilator responses of airway smooth muscle

1. Increased bronchoconstrictor responses to contractile agonists and decreased dilator responses to beta-adrenoceptor agonists are characteristics of human asthma. One explanation for these features of asthma is that cytokines released in the asthmatic airway have direct effects on airway smooth muscle cells that alter their phenotype. 2. The present review summarizes data indicating that inflammatory cytokines, such as interleukin (IL)-1 beta and tumour necrosis factor-alpha, T helper (h) 1 cytokines, such as interferon-gamma, and Th2 cytokines, such as IL-13 and IL-5, have the capacity to enhance contractile responses and/or decrease relaxant responses of airway smooth muscle. These effects are observed in smooth muscle from human airways and airway smooth muscle of other species. 3. Understanding the mechanistic basis for the effects of these cytokines may prove to be an important step in improving the efficacy of beta-adrenoceptor agonists for the treatment of asthma.

Leukaemia inhibitory factor (LIF): a cytokine of emerging importance in chronic airway inflammation

Inflammation is a complex set of mechanisms by which tissues respond to an injury. These responses involve the coordinated interaction between the nervous and immune systems. An integral part of this interaction is the release of a variety of cytokines that regulate cellular and molecular responses. Leukaemia Inhibitory Factor (LIF), a member of the IL-6 family of cytokines, has been shown to be an integral component of the interface between nerves and the immune system. However, little is known about this cytokine in the context of normal lung function or indeed, inflammation. Evidence is emerging that this cytokine may play an important role in regulating the neural-immune system interaction during acute inflammatory insult and the subsequent healing and restitution process. However, LIF may act as either a pro- or antiinflammatory cytokine, depending on the cell type and a number of other variables. In this review, the role of LIF in airway inflammation and resolution of inflammation is discussed. In particular, recent work suggesting that LIF is a mediator of bi-directional cross-talk between neural tissue and the immune system is highlighted.

Leukemia inhibitory factor, interleukin-6, and their receptors are expressed transiently in the olfactory mucosa after target ablation

Removal of the synaptic targets of olfactory receptor neurons by olfactory bulb ablation results in apoptosis of olfactory receptor neurons and up-regulation of proliferation of their progenitors. This study focuses on the expression of the neuropoietic cytokines leukemia inhibitory factor (LIF) and its receptor (LIFR) and interleukin 6 (IL-6) and its receptor (IL-6R) in intercellular signaling pathways in the olfactory mucosa after target ablation. Olfactory bulbectomy (OBX) resulted in several transient, early-onset, temporally integrated events that were detected immunohistochemically. Macrophages infiltrated the olfactory epithelium (OE) by 16 hours post-OBX. LIF expression was up-regulated transiently at 2 days post-OBX, when up-regulated expression of LIFR also was detected on globose basal cells (GBCs), a subpopulation of which are immediate progenitors of olfactory receptor neurons. GBC proliferation peaked at 3--4 days post-OBX. In the olfactory nerve (ON), LIF-positive and IL-6-positive macrophage infiltration was followed by the transient up-regulation of expression of LIFR, IL-6, and IL-6R in ensheathing cells by 3 days post-OBX. The mRNAs for LIF/LIFR, IL-6/IL-6R, and their common signal-transduction molecule, gp130, in olfactory-nasal mucosa from control mice and from 3-day post-OBX mice were detected with reverse transcriptase-polymerase chain reaction (RT-PCR). Analysis of Northern blot and relative quantitative RT-PCR demonstrated similar temporal patterns of changes in relative mRNA levels for both LIF and IL-6, which were up-regulated by 16 hours post-OBX and peaked at 2--3 days post-OBX. These data indicate that LIF from infiltrating macrophages acts as a mitogen for GBCs and that LIF from infiltrating macrophages and IL-6 from infiltrating macrophages and ensheathing cells act as repair factors in the ON.

Leukaemia inhibitory factor (LIF) upregulates excitatory non-adrenergic non-cholinergic and maintains cholinergic neural function in tracheal explants

The effect of leukaemia inhibitory factor (LIF) in modulating cholinergic and sensory nerve function was examined using guinea-pig tracheal explants. Specific LIF receptors (LIFR) were immunolocalized to both cholinergic and sensory nerves. Release of SP in culture was not influenced by LIF. Similarly, maximum contraction to carbachol (C(max)) was not influenced by LIF. After 3 h, maximum (E(max)) eNANC-induced contraction in controls was 32+/-2. 5% of C(max). In LIF-treated preparations, E(max) was enhanced to 50+/-4.5% C(max) (P<0.05). Cholinergic nerve-induced contractions after 3 h incubation with LIF were similar to control. After 24 h, control E(max) was 25+/-4.5% C(max) (58% smaller than E(max) at 3 h). In contrast, in LIF-treated preparations, E(max) was 37+/-2.5% C(max), (24% smaller than at 3 h, P<0.05). This did not appear to be due to the effect of LIF on muscarinic M(2) receptor expression or function. Thus LIF appears to differentially influence the function of airway nerves and thus may provide an important link between the immune and neural systems.

Leukemia inhibitory factor (LIF) and LIF receptor in human lung. Distribution and regulation of LIF release

The distribution and regulation of leukemia inhibitory factor (LIF) and its receptor (LIFR) in human lung tissue is unknown. We recently found that LIF was immunolocalized to several cell types in human airways, and that exogenous LIF modulated neural and contractile responses of explanted airways. The present study aimed to determine the cellular distribution and regulation of gene transcripts for LIF and LIFR in human lung, and measured the release of LIF in response to anti-immunoglobulin (Ig)E, interleukin (IL)-1beta, and IL-6. Exposure of human lung to IL-1beta (100 pg/ml) resulted in the rapid induction of LIF messenger RNA (mRNA) (1 h) and subsequent protein release (6 h). Similar results were observed when lung tissue was exposed to anti-IgE (6 U/ml). Gene transcripts for LIF were observed in nine pulmonary cell types, with the greatest expression occurring in fibroblasts. LIFR transcripts were also widely expressed in these cell types. In cultures of nontransformed epithelial cells, lung fibroblasts, and airway smooth-muscle cells, IL-1beta (100 pg/ml) induced the rapid accumulation of LIF mRNA and protein release, with fibroblasts liberating the greatest amount. IL-6 also induced the expression of LIF mRNA and release of LIF in airway smooth-muscle cells, whereas exogenous LIF itself had no effect. Expression of LIFR mRNA was not influenced by exposure to IL-1beta or LIF in any of the cell lines used. These results highlight the widespread distribution and rapid release of LIF in human lung tissue and, in conjunction with our previous report, suggest that this cytokine may play an important role in lung inflammatory processes and neuroimmune interactions.