Fibulin-1 is increased in asthma--a novel mediator of airway remodeling?

BACKGROUND: The extracellular matrix is a dynamic and complex network of macromolecules responsible for maintaining and influencing cellular functions of the airway. The role of fibronectin, an extracellular matrix protein, is well documented in asthma. However, the expression and function of fibulin-1, a secreted glycoprotein which interacts with fibronectin, has not been reported. Fibulin-1 is widely expressed in basement membranes in many organs including the lung. There are four isoforms in humans (A-D) of which fibulin-1C and 1D predominate. The objective of this study was to study the expression of fibulin-1 in volunteers with and without asthma, and to examine its function in vitro. METHODOLOGY/PRINCIPAL FINDINGS: We used immunohistochemistry and dot-blots to examine fibulin-1 levels in bronchial biopsies, bronchoalveolar lavage fluid and serum. Real-time PCR for fibulin-1C and 1D, and ELISA and western blotting for fibulin-1 were used to study the levels in airway smooth muscle cells. The function of fibulin-1C was determined by assessing its role, using an antisense oligonucleotide, in cell proliferation, migration and wound healing. A murine model of airway hyperresponsiveness (AHR) was used to explore the biological significance of fibulin-1. Levels of fibulin-1 were significantly increased in the serum and bronchoalveolar lavage fluid of 21 asthmatics compared with 11 healthy volunteers. In addition fibulin-1 was increased in asthma derived airway smooth muscle cells and fibulin-1C contributed to the enhanced proliferation and wound repair in these cells. These features were reversed when fibulin-1C was suppressed using an antisense oligomer. In a mouse model of AHR, treatment with an AO inhibited the development of AHR to methacholine. CONCLUSIONS: Our data collectively suggest fibulin-1C may be worthy of further investigation as a target for airway remodeling in asthma.

Differential expression of peroxisome proliferator activated receptor gamma and cyclin D1 does not affect proliferation of asthma- and non-asthma-derived airway smooth muscle cells.

UNLABELLED: PPARgamma levels in asthma- and non-asthma-derived airway smooth muscle cells and PPARgamma activation-induced cell proliferation were investigated. In the presence of FBS, PPARgamma levels were higher in subconfluent asthma-derived cells but lower in confluent cells compared with non-asthma-derived. However, PPARgamma activation did not alter cell proliferation. BACKGROUND AND OBJECTIVE: Airway remodelling involves thickening of the airway smooth muscle (ASM) bulk. Proliferation of asthma-derived ASM cells is increased in vitro, but underlying mechanisms remain unknown. Peroxisome proliferators activated receptor-gamma (PPARgamma) regulates the cell cycle. It is suggested that PPARgamma agonists have anti-inflammatory effects, which may be valuable in the treatment of asthma, but information regarding their antiproliferative properties in ASM is lacking. Although corticosteroids reduce airway inflammation, in vitro they inhibit proliferation in only non-asthma ASM cells by reducing cyclin D1. We therefore investigated the effects of mitogenic stimulation (foetal bovine serum (FBS)), and a PPARgamma ligand (ciglitazone), on PPARgamma and cyclin D1 expression and proliferation of ASM cells. In addition, we examined the effects of ciglitazone on ASM cell proliferation. METHODS: We assessed PPARgamma and cyclin D1 mRNA and protein levels using quantitative PCR and immunoblotting. Cell proliferation was assessed using bromodeoxyuridine uptake. RESULTS: In the presence of 5% FBS, PPARgamma and cyclin D1 expression decreased over time in non-asthmatic cells but increased in asthmatic cells (compared with sub-confluent cells). FBS-induced proliferation of asthmatic cells increased at all time points, but occurred only at day 7 with non-asthmatic cells (compared with unstimulated time-matched control). Ciglitazone increased PPARgamma expression in both groups, but did not alter cell proliferation, while fluticasone increased PPARgamma protein only in asthmatic cells. CONCLUSIONS: Although in the presence of a mitogenic stimulus, PPARgamma was differentially expressed in asthma- and non-asthma-derived ASM; its expression was not related to the increased proliferation observed in asthmatic ASM.

Reduction of tumstatin in asthmatic airways contributes to angiogenesis, inflammation, and hyperresponsiveness.

RATIONALE: Angiogenesis is a prominent feature of remodeling in asthma. Many proangiogenic factors are up-regulated in asthma, but little is known about levels of endogenous antiangiogenic agents. Collagen IV is decreased in the airway basement membrane in asthma. It has six alpha chains, of which the noncollagenous domain-1 domains have endogenous antiangiogenic properties. OBJECTIVES: To study the expression of the noncollagenous domain-1 of the alpha3 chain of collagen IV, tumstatin, in the airways of subjects with and without asthma and to examine the potential for tumstatin to regulate angiogenesis and inflammation. METHODS: We used immunohistochemistry and dot blots to examine the expression of tumstatin in bronchial biopsies, bronchoalveolar lavage fluid, and serum. We then used an in vitro angiogenesis assay and a murine model of allergic airways disease to explore tumstatin's biological function. MEASUREMENTS AND MAIN RESULTS: The level of tumstatin is decreased 18-fold in the airways of patients with asthma but not in subjects without asthma, including those with chronic obstructive pulmonary disease, cystic fibrosis, and bronchiectasis. In vitro, recombinant tumstatin inhibited primary pulmonary endothelial cell tube formation. In a mouse model of chronic allergic airways disease, tumstatin suppressed angiogenesis, airway hyperresponsiveness, inflammatory cell infiltration, and mucus secretion and decreased levels of vascular endothelial growth factor and IL-13. CONCLUSIONS: The observation that tumstatin is decreased in asthmatic airways and inhibits airway hyperresponsiveness and angiogenesis demonstrates the potential use of antiangiogenic agents such as tumstatin as a therapeutic intervention in diseases that are characterized by aberrant angiogenesis and tissue remodeling, such as asthma.

The effect of asthma therapeutics on signalling and transcriptional regulation of airway smooth muscle function.

SCOPE OF THE REVIEW: Our knowledge of the multifunctional nature of airway smooth muscle (ASM) has expanded rapidly in the last decade, but the underlying molecular mechanisms and how current therapies for obstructive airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD), affect these are still being elucidated. Our current knowledge has built on the pharmacology of human ASM contraction and relaxation established prior to that and which is reviewed in detail elsewhere in this issue. The advent of methods to isolate and culture ASM cells, especially human ASM cells, has made it possible to study how they may contribute to airway remodelling through their synthetic, proliferative, and migratory capacities. Now the underlying molecular mechanisms of ASM growth factor secretion, extracellular matrix (ECM) production, proliferation and migration, as well as contraction and relaxation, are being determined. A complex network of signalling pathways leading to gene transcription in ASM cells permits this functional plasticity in healthy and diseased airways. This review is an overview of the effects of current therapies, and some of those in development, on key signalling pathways and transcription factors involved in these ASM functions.