[Show abstract][Hide abstract] ABSTRACT: Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S-1-P) are both low molecular weight lysophospholipid (LPL) ligands that are recognized by the Edg family of G protein-coupled receptors. In endothelial cells, these two ligands activate Edg receptors, resulting in cell proliferation and cell migration. The intercellular adhesion molecule-1 (ICAM-1, CD54) is one of many cell adhesion molecules belonging to the immunoglobulin superfamily. This study showed that LPA and S-1-P enhance ICAM-1 expression at both the mRNA and protein levels in human umbilical cord vein endothelial cells (HUVECs). This enhanced ICAM-1 expression in HUVECs was first observed at 2 h postligand treatment. Maximal expression appeared at 8 h postligand treatment, as detected by flow cytometry and Western blotting. Furthermore, the effects of S-1-P on ICAM-1 expression were shown to be concentration dependent. Prior treatment of HUVECs with pertussis toxin, a specific inhibitor of G(i), ammonium pyrrolidinedithiocarbamate and BAY 11-7082, inhibitors of the nuclear factor (NF)-kappaB pathway, or Clostridium difficile toxin B, an inhibitor of Rac, prevented the enhanced effect of LPL-induced ICAM-1 expression. However, pretreatment of HUVECs with exoC3, an inhibitor of Rho, had no effect on S-1-P-enhanced ICAM-1 expression. In a static cell-cell adhesion assay system, pretreatment of LPL enhanced the adhesion between HUVECs and U-937 cells, a human mononucleated cell line. The enhanced adhesion effect could be prevented by preincubation with a functional blocking antibody against human ICAM-1. These results suggest that LPLs released by activated platelets might enhance interactions of leukocytes with the endothelium through a G(i)-, NF-kappaB-, and possibly Rac-dependent mechanism, thus facilitating wound healing and inflammation processes.
No preview · Article · Jan 2005 · AJP Cell Physiology
[Show abstract][Hide abstract] ABSTRACT: It is well known that traumatic injuries of the CNS induce a gliotic reaction, characterized by the presence of reactive astrocytes. Reactive astrocytes exhibit enhanced expression of the astrocyte-specific intermediate filament, glial fibrillary acidic protein (GFAP), hypertrophy, and thickened processes. Recently, we have demonstrated that injuries of the CNS induce a re-expression of an embryonic intermediate filament-associated protein, IFAP-70/280 kDa. Based on IFAP-70/280 kDa immunolabeling, we have shown that reactive astrocytes, activated by stab-wound injury, can be divided into two major groups: 1. persistent IFAP+/GFAP+ cells which are close to the wound in the area of glial scar, and 2. transient IFAP-/GFAP+ cells which are farther from the wound. In this study, we use BrdU incorporation to examine proliferation in these two groups of reactive astrocytes induced by stab injury of the rat cerebrum. Triple/double-label immunofluorescence microscopy was performed using antibodies to IFAP-70/280 kDa, GFAP, and BrdU. The results showed that BrdU+ reactive astrocytes (GFAP+) were always IFAB-70/280 kDa+ as well. However, not all IFAP+ reactive astrocytes are BrdU+. BrdU+ signal was not observed in any IFAP- reactive astrocytes. At five days post-lesion, IFAP+ reactive astrocytes were increasing in the area of the wound (0-50 micrograms from the wound edge), but had reached a peak in the proximal area (50-800 micrograms away from the wound edge). At eight days post-lesion, IFAP+ reactive astrocytes achieved the highest percentage in the wound area. At the same time, BrdU-containing reactive astrocytes occupied an area closer to the wound. By 20 days post-lesion, following the formation of the gliotic scar at the stab-wound, a few IFAP+/GFAP+ cells still persisted. BrdU-containing reactive astrocytes were only observed in the scar. These results indicate that many IFAP+ reactive astrocytes close to the wound, in contrast to the IFAP- ones farther from the wound, appear to regain their proliferative potential to increase in number and participate in the formation of the gliotic scar.
No preview · Article · Nov 2003 · Neurological Research