Growth factor- and heparin-dependent regulation of constitutive and agonist-mediated human endothelial barrier function

The 'sweet' and 'bitter' involvement of glycosaminoglycans in lung diseases: pharmacotherapeutic relevance

The extracellular matrix (ECM) plays a significant role in the structure and function of the lung. The ECM is a three-dimensional fibre mesh, comprised of various interconnected and intercalated macromolecules, among which are the glycosaminoglycans (GAG). GAG are long, linear and highly charged, heterogeneous polysaccharides that are composed of a variable number of repeating disaccharide units (macromolecular sugars) and most of them, as their name implies, have a sweet taste. In the lung, GAG support the structure of the interstitium, the subepithelial tissue and the bronchial walls, and are secreted in the airway secretions. Besides maintaining lung tissue structure, GAG also play an important role in lung function as they regulate hydration and water homeostasis, modulate the inflammatory response and influence lung tissue repair and remodelling. However, depending on their size and/or degree of sulphation, and their immobilization or solubilization in the ECM, specific GAG in the lung either live up to their sweet taste/name, supporting normal lung physiology, or they are associated to 'bitter' effects, related to lung pathology. The present review discusses the biological role of GAG in the lung as well as the involvement of these molecules in various respiratory diseases. Given the great structural diversity of GAG, understanding the changes in GAG expression that occur in lung diseases may lead to novel targets for pharmacological intervention in order to prevent and/or to treat a range of lung diseases.

VEGF-C alters barrier function of cultured lymphatic endothelial cells through a VEGFR-3-dependent mechanism

BACKGROUND

The lymphatic endothelium is an important semi-permeable barrier separating lymph from the interstitial space. However, there is currently a limited understanding of the lymphatic endothelial barrier and the mechanisms of lymph formation. The objectives of this study were to investigate the potential active role of lymphatic endothelial cells in barrier regulation, and to test whether the endothelial cell agonists VEGF-A and VEGF-C can alter lymphatic endothelial barrier function.

METHODS AND RESULTS

Cultured adult human dermal microlymphatic endothelial cells (HMLEC-d) and human umbilical vein endothelial cells (HUVEC) were respectively used as models of lymphatic and vascular endothelium. Transendothelial electrical resistance (TER) of endothelial monolayers served as an index of barrier function. Cells were treated with VEGF-A, VEGF-C, or the VEGFR-3 selective mutant VEGF-C156S. MAZ51 was used to inhibit VEGFR-3 signaling. The results show that while VEGF-A causes a time-dependent decrease in TER in HUVEC, there is no response in HMLEC-d. In contrast, VEGF-C and VEGF-C156S cause a similar decrease in TER in HMLEC-d that is not observed in HUVEC. These results corresponded to the protein expression of VEGFR-2 and VEGFR-3 in these cell types, determined by Western blotting. In addition, the VEGF-C- and VEGF-C156S-induced TER changes were inhibited by MAZ51.

CONCLUSIONS

The results indicate differential responses of the lymphatic and vascular endothelial barriers to VEGF-A and VEGF-C. Furthermore, our data suggest that VEGF-C alters lymphatic endothelial function through a mechanism involving VEGFR-3.