Essential role of NF-κB and AP-1 transcription factors in TNF-α-induced TSLP expression in human airway smooth muscle cells

Evidence for a functional thymic stromal lymphopoietin signaling axis in fibrotic lung disease

Thymic stromal lymphopoietin (TSLP) recently has emerged as a key cytokine in the development of type 2 immune responses. Although traditionally associated with allergic inflammation, type 2 responses are also recognized to contribute to the pathogenesis of tissue fibrosis. However, the role of TSLP in the development of non-allergen-driven diseases, characterized by profibrotic type 2 immune phenotypes and excessive fibroblast activation, remains underexplored. Fibroblasts represent the key effector cells responsible for extracellular matrix production but additionally play important immunoregulatory roles, including choreographing immune cell recruitment through chemokine regulation. The aim of this study was to examine whether TSLP may be involved in the pathogenesis of a proto-typical fibrotic disease, idiopathic pulmonary fibrosis (IPF). We combined the immunohistochemical analysis of human IPF biopsy material with signaling studies by using cultured primary human lung fibroblasts and report for the first time, to our knowledge, that TSLP and its receptor (TSLPR) are highly upregulated in IPF. We further show that lung fibroblasts represent both a novel cellular source and target of TSLP and that TSLP induces fibroblast CCL2 release (via STAT3) and subsequent monocyte chemotaxis. These studies extend our understanding of TSLP as a master regulator of type 2 immune responses beyond that of allergic inflammatory conditions and suggest a novel role for TSLP in the context of chronic fibrotic lung disease.

UVB induces HIF-1α-dependent TSLP expression via the JNK and ERK pathways

Thymic stromal lymphopoietin (TSLP) may have a key role in the initiation and maintenance of allergic inflammatory diseases, including atopic dermatitis. The present study revealed that UVB radiation exposure could induce TSLP expression in human keratinocytes and a human skin equivalent model. In addition, we investigated the regulatory mechanism of UVB-induced TSLP expression in keratinocytes. TSLP expression was upregulated by transfection with pcDNA3-hypoxia-inducible factor (HIF)-1α (P402A and P564A), which stably expresses HIF-1α protein. UVB-induced TSLP induction in keratinocytes was suppressed in the treatment of mitogen-activated protein kinase inhibitors or small interfering RNAs against HIF-1α. The results of chromatin immunoprecipitation assays indicate the direct involvement of HIF-1α in UVB-mediated TSLP induction. Taken together, these findings indicate that UVB exposure may increase TSLP expression through a HIF-1α-dependent mechanism via the c-JUN N-terminal kinase and extracellular signal-regulated kinase pathways in human keratinocytes. Our data showed that UVB-induced TSLP might increase secretion of the T-helper type 2-attracting chemokine (c-c motif) ligand 17 by human dendritic cells. The present study suggests an important role of HIF-1α in UVB-mediated immune response in keratinocytes.

Functions of thymic stromal lymphopoietin in immunity and disease

Thymic stromal lymphopoietin (TSLP) is an interleukin 7-like cytokine expressed mainly by epithelial cells. Current studies provide compelling evidence that TSLP is capable of activating dendritic cells to promote T helper (Th) 2 immune responses. TSLP has also been shown to directly promote Th2 differentiation of naïve CD4(+) T cell and activate natural killer T cells, basophils and other innate immune cells at the initial stage of inflammation. In addition, TSLP affects B cell maturation and activation and can also influence regulatory T (Treg) cell differentiation and development. TSLP-induced Th2 responses are associated with the pathogenesis of allergic inflammatory diseases, including atopic dermatitis, asthma, and rhinitis. Based on recent findings in humans and mouse models, TSLP might also be involved in the pathogenesis of inflammatory bowel disease and progression of cancer. In this review, we will summarize our current understanding of the biology of TSLP and highlight the important issues for future investigations.

The high affinity IgE receptor (FcεRI) expression and function in airway smooth muscle

The airway smooth muscle (ASM) is no longer considered as merely a contractile apparatus and passive recipient of growth factors, neurotransmitters and inflammatory mediators signal but a critical player in the perpetuation and modulation of airway inflammation and remodeling. In recent years, a molecular link between ASM and IgE has been established through Fc epsilon receptors (FcεRs) in modulating the phenotype and function of these cells. Particularly, the expression of high affinity IgE receptor (FcεRI) has been noted in primary human ASM cells in vitro and in vivo within bronchial biopsies of allergic asthmatic subjects. The activation of FcεRI on ASM cells suggests a critical yet almost completely ignored network which may modulate ASM cell function in allergic asthma. This review is intended to provide a historical perspective of IgE effects on ASM and highlights the recent updates in the expression and function of FcεRI, and to present future perspectives of activation of this pathway in ASM cells.

Pentraxin 3 (PTX3) expression in allergic asthmatic airways: role in airway smooth muscle migration and chemokine production

Background

Pentraxin 3 (PTX3) is a soluble pattern recognition receptor with non-redundant functions in inflammation and innate immunity. PTX3 is produced by immune and structural cells. However, very little is known about the expression of PTX3 and its role in allergic asthma.

Objectives and Methods

We sought to determine the PTX3 expression in asthmatic airways and its function in human airway smooth muscle cells (HASMC). In vivo PTX3 expression in bronchial biopsies of mild, moderate and severe asthmatics was analyzed by immunohistochemistry. PTX3 mRNA and protein were measured by real-time RT-PCR and ELISA, respectively. Proliferation and migration were examined using ³H-thymidine incorporation, cell count and Boyden chamber assays.

Results

PTX3 immunoreactivity was increased in bronchial tissues of allergic asthmatics compared to healthy controls, and mainly localized in the smooth muscle bundle. PTX3 protein was expressed constitutively by HASMC and was significantly up-regulated by TNF, and IL-1β but not by Th2 (IL-4, IL-9, IL-13), Th1 (IFN-γ), or Th-17 (IL-17) cytokines. In vitro, HASMC released significantly higher levels of PTX3 at the baseline and upon TNF stimulation compared to airway epithelial cells (EC). Moreover, PTX3 induced CCL11/eotaxin-1 release whilst inhibited the fibroblast growth factor-2 (FGF-2)-driven HASMC chemotactic activity.

Conclusions

Our data provide the first evidence that PTX3 expression is increased in asthmatic airways. HASMC can both produce and respond to PTX3. PTX3 is a potent inhibitor of HASMC migration induced by FGF-2 and can upregulate CCL11/eotaxin-1 release. These results raise the possibility that PTX3 may play a dual role in allergic asthma.

TSLP expression: cellular sources, triggers, and regulatory mechanisms

Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine initially identified in the culture supernatant of a thymic stromal cell line. Highly expressed in the epidermis in skin lesions of atopic dermatitis patients, TSLP was subsequently found to be a critical factor linking responses at interfaces between the body and environment (skin, airway, gut, ocular tissues, and so on) to Th2 responses. Recent studies have revealed that various cell types other than epithelial cells and epidermal keratinocytes (such as mast cells, airway smooth muscle cells, fibroblasts, dendritic cells, trophoblasts, and cancer or cancer-associated cells) also express TSLP. Environmental factors such as Toll-like receptor ligands, a Nod2 ligand, viruses, microbes, allergen sources, helminths, diesel exhaust, cigarette smoke, and chemicals trigger TSLP production. Proinflammatory cytokines, Th2-related cytokines, and IgE also induce or enhance TSLP production, indicating cycles of amplification. Skin barrier injury, increased epidermal endogenous protease activity, and less epidermal Notch signaling, all of which have been reported in atopic dermatitis, and keratinocyte-specific loss of retinoid X receptors and treatment of skin with agonists for vitamin D receptor in mice induce TSLP production, Th2 response, or atopic dermatitis-like inflammation. The transcription factors NF-κB and AP-1, nuclear receptors, single nucleotide polymorphisms, microRNAs, and the peptidyl-proryl isomerase Pin1 regulate TSLP mRNA expression transcriptionally or posttranscriptionally. This review focuses on events upstream of TSLP production, which is critical in allergic diseases and important in other TSLP-related disorders i.e. production sites, cellular sources, environmental and endogenous triggers and regulatory factors, and regulatory mechanisms of gene expression.

Mechanisms of the inhibition of nuclear factor-κB by morphine in neuronal cells

Opioids potently modulate neuronal functions, for example, by regulating the activity of transcription factors. Here, we investigated the effect of morphine on the activity of the transcription factor nuclear factor κB (NF-κB). Establishing cellular models for our investigations, we demonstrated that NF-κB mediated the tumor necrosis factor (TNF)-induced transcription of the cannabinoid receptor type 1 gene in primary fetal striatal neurons from rats and the human neuroblastoma cell line SH SY5Y. The activity of NF-κB in these models was strongly inhibited by morphine, which was achieved by a marked up-regulation of the inhibitor of nuclear factor-κB (IκB). The opioid-induced up-regulation of IκB was dependent on the transcription factors NF-κB itself and activator protein-1 (AP-1). In fact, stimulation of the cells with morphine resulted in a transient activation of NF-κB and a strong induction of c-Fos, one of the constituents of AP-1. This resulted in IκB levels significantly exceeding the basal, constitutive levels of IκB. These data, together with experiments in which AP-1 and IκB were down-regulated by decoy oligonucleotides and siRNA, suggest that the morphine-induced activation of AP-1 and the subsequent overexpression of IκB are key factors in the inhibition of NF-κB by the drug. In contrast, stimulation of primary neurons from rats and SH SY5Y cells with TNF, which is a classic activator of NF-κB, resulted in a resynthesis of IκB, in which the basal levels of IκB were restored only but did not result in an activation of AP-1 and overexpression of IκB.

Function and mechanisms of TSLP/TSLPR complex in asthma and COPD

Thymic stromal lymphopoietin (TSLP) is a key pro-allergic cytokine that has recently been linked to chronic airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD). High levels of TSLP were detected in bronchial mucosa of asthma and COPD patients suggesting TSLP's biological role beyond a signature 'Th2-favoring' or 'pro-allergic cytokine'. Besides inflammatory cells, airway structural cells produce and are targets of TSLP suggesting a potential autocrine loop that may have a profound effect on local inflammatory response and airway remodelling. This review sums up diverse mechanisms that mediate TSLP/TSLP receptor-signalling network in chronic airway diseases.

Targeting airway smooth muscle in airways diseases: an old concept with new twists

Airway smooth muscle (ASM) manifests a hyper-responsive phenotype in airway disorders such as asthma. ASM also modulates immune responses by secreting mediators and expressing cell-surface molecules that promote recruitment of inflammatory cells to the lungs. The aim of the current article is to highlight therapeutics that may modulate ASM responses in airway disorders and exacerbations.

Airway smooth muscle and immunomodulation in acute exacerbations of airway disease

Airway smooth muscle (ASM) manifests a hyperresponsive phenotype in airway disorders such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. Current evidence also suggests that ASM modulates immune responses by secreting mediators and expressing cell surface molecules. Such processes amplify or dampen inflammation by inflammatory cells in the airways or by altering cellular responses to viruses, bacteria, or pathogens known to exacerbate airways diseases.