αVß3 Integrin regulates astrocyte reactivity.

BACKGROUND: Neuroinflammation involves cytokine release, astrocyte reactivity and migration. Neuronal Thy-1 promotes DITNC1 astrocyte migration by engaging αVß3 Integrin and Syndecan-4. Primary astrocytes express low levels of these receptors and are unresponsive to Thy-1; thus, inflammation and astrocyte reactivity might be necessary for Thy-1-induced responses. METHODS: Wild-type rat astrocytes (TNF-activated) or from human SOD1G93A transgenic mice (a neurodegenerative disease model) were used to evaluate cell migration, Thy-1 receptor levels, signaling molecules, and reactivity markers. RESULTS: Thy-1 induced astrocyte migration only after TNF priming. Increased expression of αVß3 Integrin, Syndecan-4, P2X7R, Pannexin-1, Connexin-43, GFAP, and iNOS were observed in TNF-treated astrocytes. Silencing of ß3 Integrin prior to TNF treatment prevented Thy-1-induced migration, while ß3 Integrin over-expression was sufficient to induce astrocyte reactivity and allow Thy-1-induced migration. Finally, hSOD1G93A astrocytes behave as TNF-treated astrocytes since they were reactive and responsive to Thy-1. CONCLUSIONS: Therefore, inflammation induces expression of αVß3 Integrin and other proteins, astrocyte reactivity, and Thy-1 responsiveness. Importantly, ectopic control of ß3 Integrin levels modulates these responses regardless of inflammation.

Human Thy-1 induces secretion of matrix metalloproteinase-9 and CXCL8 from human neutrophils.

Neutrophils are the first cells arriving at sites of acute inflammation. On their way from blood to the site of inflammation, neutrophils have to adhere to endothelial cells (EC), to transverse the basement membrane and subsequently to travel through the interstitial matrix. Recently, we have shown that human Thy-1 is an alternate EC receptor for the leukocyte integrin Mac-1 that contributes to leukocyte recruitment to sites of inflammation, providing a new pathway for adhesion and transmigration of neutrophils. Here, we studied the effect of Thy-1-mediated adhesion on neutrophil functions. Binding of neutrophils to recombinant human Thy-1 stimulated the release of MMP-9 from neutrophils, resulting in their enhanced migration through collagen-IV and matrigel. Further, we showed that neutrophil interaction with Thy-1 stimulated secretion of CXCL8 and thus could support the attraction of additional neutrophils to inflammatory sites. Blocking experiments confirmed the pivotal roles of Thy-1 on activated dermal EC or fibroblasts and its counter receptor CD18 on neutrophils for the regulation of MMP-9 and CXCL8 release from neutrophils. Our results support the general concept that the function of 'adhesion molecules' in particular of human Thy-1, may not only be to provide mechanical support but also regulate neutrophil functions.

A ligand of human thy-1 is localized on polymorphonuclear leukocytes and monocytes and mediates the binding to activated thy-1-positive microvascular endothelial cells and fibroblasts.

Thy-1 is known to be expressed on fibroblasts, nerve cells, and blood stem cells. Previous studies have shown the induction of Thy-1 on phorbol ester stimulated human dermal microvascular endothelial cells in vitro. In situ Thy-1 expression was found on activated endothelium. In this study we were interested in the localization of a Thy-1 ligand and the characterization of the function of Thy-1 on human dermal microvascular endothelial cells and fibroblasts. Human Thy-1 purified from fibroblast extracts was labeled and used as a probe for the detection of a Thy-1 ligand. In cryostat sections of bullous pemphigoid skin a Thy-1 ligand was found on inflammatory cells, whereas the Thy-1 antigen was expressed on the endothelial cells and fibroblasts. By flow cytometry we could show the expression of a Thy-1 ligand on polymorphonuclear leukocytes and monocytes, whereas lymphocytes did not express this Thy-1 ligand. To study whether Thy-1 is involved in cell-cell adhesion we separated Thy-1-positive and Thy-1-negative cells by magnetic cell separation using the monoclonal antibody AS02. Cell adhesion assays and blocking experiments revealed a direct involvement of the Thy-1/Thy-1 ligand interaction in the binding of monocytes and polymorphonuclear leukocytes to Thy-1-positive activated endothelial cells and fibroblasts.

Expression and properties of an aerolysin--Clostridium septicum alpha toxin hybrid protein.

Aerolysin is a bilobal channel-forming toxin secreted by Aeromonas hydrophila. The alpha toxin produced by Clostridium septicum is homologous to the large lobe of aerolysin. However, it does not contain a region corresponding to the small lobe of the Aeromonas toxin, leading us to ask what the function of the small lobe is. We fused the small lobe of aerolysin to alpha toxin, producing a hybrid protein that should structurally resemble aerolysin. Unlike aerolysin, the hybrid was not secreted when expressed in Aeromonas salmonicida. The purified hybrid was activated by proteolytic processing in the same way as both parent proteins and, after activation, it formed oligomers that corresponded to the aerolysin heptamer. Like aerolysin, the hybrid was far more active than alpha toxin against human erythrocytes and mouse T lymphocytes. Both aerolysin and the hybrid bound to human glycophorin, and both were inhibited by preincubation with this erythrocyte glycoprotein, whereas alpha toxin was unaffected. We conclude that aerolysin contains two receptor binding sites, one for glycosyl-phosphatidylinositol-anchored proteins that is located in the large lobe and is also found in alpha toxin, and a second site, located in the small lobe, that binds a surface carbohydrate determinant.