Increased Expression of Axl Tyrosine Kinase After Vascular Injury and Regulation by G Protein–Coupled Receptor Agonists in Rats

Abstract

Axl is a receptor tyrosine kinase originally identified as a transforming gene product in human myeloid leukemia cells. Cultured rat vascular smooth muscle cells also express Axl, where it has been proposed that Axl may play a role in cell proliferation. In the current study, we tested the hypotheses that Axl expression would parallel neointima formation in balloon-injured rat carotid, and that Axl expression would be regulated by growth factors present at sites of vascular injury. Ribonuclease protection assay showed dynamic increases in Axl mRNA in vessels, with peak expression 7 and 14 days after injury. Immunohistochemical analysis confirmed these results and demonstrated that Axl protein expression was localized primarily to cells of the neointima after injury. Northern blot analysis indicated increased mRNA expression for the secreted Axl ligand, Gas6, in injured carotids, with a time course paralleling that of Axl upregulation. Axl and Gas6 expression were temporally correlated with neointima formation, suggesting a role for Axl signaling in this process. Other studies, performed in cultured rat vascular smooth muscle cells, revealed positive regulation of Axl mRNA expression by thrombin or angiotensin II but not by basic fibroblast growth factor, platelet-derived growth factor-BB, or transforming growth factor-ss1. Western blot analysis confirmed these results, showing that Axl protein expression was specifically increased by thrombin or angiotensin II. Our results implicate Axl as a potential mediator of vascular smooth muscle migration and proliferation caused by vascular injury and G protein-coupled receptor agonists.

Induction of Gas6 protein in CCl4-induced rat liver injury and anti-apoptotic effect on hepatic stellate cells

“…Gas6 involvement in tissue repair has been documented in injured rat carotid where Axl and Gas6 expression was related to neointima formation. 12 Another role for Gas6 could be its involvement in clearance of dying cells that is carried out by macrophages and HSC/MFB 42 and precedes regeneration. Recognition of dying cells involves surface receptors on phagocytes and extracellular ligands with binding sites on both damaged cells and phagocytes.…”

“…Gas6 supports haematopoietic stem cell growth 6 and promotes fibroblast and endothelial cell survival. [7][8][9] Gas6/Axl signaling induces accumulation of mesangial cells in kidney fibrosis, 10,11 vascular smooth muscle cells in response to intimal vascular injury, 12 and cardiac fibroblasts 9 during the wound healing process. Thus, this pathway has been increasingly implicated in growth and survival processes during development, regeneration, and tissue repair.…”

GIT1 Mediates Src-dependent Activation of Phospholipase Cγ by Angiotensin II and Epidermal Growth Factor

“…Cells and Transfection-VSMC were obtained from rat aorta as described (36). HEK293 cells and VSMC were cultured in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, penicillin, and streptomycin at 37°C in 5% CO 2 .…”

The vitamin K–dependent anticoagulant factor, protein S, inhibits multiple VEGF-A–induced angiogenesis events in a Mer- and SHP2-dependent manner

“…7,11 ProS/TAM interactions may play a role in vascular function, because ProS and TAM receptors are expressed by ECs, 14,18 pericytes, 19 and vascular smooth muscle cells. 20 Recently, using tissue-specific conditional PROS1 knockout mice, it was demonstrated that extrahepatic ProS represents ϳ 45% of normal circulating ProS and that much of this residual ProS is produced by ECs. 4 ECs play key roles in many processes, among which angiogenesis is a major one.…”