A peptide of the alpha3 chain of type IV collagen protects basement membrane against damage by PMN

The Effects of Tumstatin on Vascularity, Airway Inflammation and Lung Function in an Experimental Sheep Model of Chronic Asthma

Tumstatin, a protein fragment of the alpha-3 chain of Collagen IV, is known to be significantly reduced in the airways of asthmatics. Further, there is evidence that suggests a link between the relatively low level of tumstatin and the induction of angiogenesis and inflammation in allergic airway disease. Here, we show that the intra-segmental administration of tumstatin can impede the development of vascular remodelling and allergic inflammatory responses that are induced in a segmental challenge model of experimental asthma in sheep. In particular, the administration of tumstatin to lung segments chronically exposed to house dust mite (HDM) resulted in a significant reduction of airway small blood vessels in the diameter range 10⁺–20 μm compared to controls. In tumstatin treated lung segments after HDM challenge, the number of eosinophils was significantly reduced in parenchymal and airway wall tissues, as well as in the bronchoalveolar lavage fluid. The expression of VEGF in airway smooth muscle was also significantly reduced in tumstatin-treated segments compared to control saline-treated segments. Allergic lung function responses were not attenuated by tumstatin administration in this model. The data are consistent with the concept that tumstatin can act to suppress vascular remodelling and inflammation in allergic airway disease.

Regulation of endothelial cell functions by basement membrane- and arachidonic acid-derived products

Angiogenesis, the formation of new blood vessels from preexisting vasculature, is required for normal physiological as well as pathological events. The angiogenic process requires endothelial cells to proliferate, migrate, and undergo tubulogenesis. These multistep processes necessitate secretion of pro-angiogenic growth factors, activation of specific intracellular signaling, and interaction of endothelial cells with basement membrane (BM) extracellular matrix components. The generation and release of angiogenic molecules are highly regulated and are influenced by numerous factors, including BM-derived fragments, proteolytic enzymes, as well as metabolites of arachidonic acid (AA). The interactions between these key modulators of angiogenesis is extremely complex, as AA metabolites can regulate the synthesis of soluble angiogenic factors, BM components, as well as enzymes capable of cleaving BM components, which result in the generation of pro- and/or anti-angiogenic products. Furthermore, some BM-derived fragments can alter the expression of AA-converting enzymes and consequently the synthesis of angiogenic factors. In this review we describe the relationship between BM components and AA metabolites with respect to the regulation of endothelial cell functions in health and disease.

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 role of the extracellular matrix and specific growth factors in the regulation of inflammation and remodelling in asthma

Asthma is a disease characterised by persistent inflammation and structural changes in the airways, referred to as airway remodelling. The mechanisms underlying these processes may be interdependent or they may be separate processes that are driven by common factors. The levels of a variety of growth factors (including transforming growth factor beta, granulocyte macrophage colony stimulating factor, and vascular endothelial growth factor) are known to be changed in the asthmatic airway. These and other growth factors can contribute to the development and persistence of inflammation and remodelling. One of the prominent features of the structural changes of the airways is the increased deposition and alterations in the composition of the extracellular matrix proteins. These proteins include fibronectin, many different collagen types and hyaluronan. There is a dynamic relationship between the extracellular matrix proteins and the airway mesenchymal cells such that the changes in the extracellular matrix proteins can also contribute to the persistence of inflammation and the airway remodelling. This review aims to summarise the role growth factors and extracellular matrix proteins play in the regulation of inflammation and airway remodelling in the asthmatic airway.

Signal regulatory protein (SIRPalpha), a cellular ligand for CD47, regulates neutrophil transmigration

Recent studies have demonstrated that CD47 plays an important role in regulating human neutrophil (PMN) chemotaxis. Two ligands for CD47, thrombospondin and SIRPalpha, have been described. However, it is not known if SIRP-CD47 interactions play a role in regulating PMN migration. In this study, we show that SIRPalpha1 directly binds to the immunoglobulin variable domain loop of purified human CD47 and that such SIRP-CD47 interactions regulate PMN transmigration. Specifically, PMN migration across both human epithelial monolayers and collagen-coated filters was partially inhibited by anti-SIRP monoclonal antibodies. Similar kinetics of inhibition were observed for PMN transmigration in the presence of soluble, recombinant CD47 consisting of the SIRP-binding loop. In contrast, anti-CD47 monoclonal antibodies inhibited PMN transmigration by markedly different kinetics. Results of signal transduction experiments suggested differential regulation of PMN migration by SIRP versus CD47 by phosphatidylinositol 3-kinase and tyrosine kinases, respectively. Immunoprecipitation followed by Western blotting after SDS-PAGE under nonreducing conditions suggested that several SIRP protein species may be present in PMN. Stimulation of PMN with fMLP resulted in increased surface expression of these SIRP proteins, consistent with the existence of intracellular pools. Taken together, these results demonstrate that PMN migration is regulated by CD47 through SIRPalpha-dependent and SIRPalpha-independent mechanisms.