Role of Connective Tissue Growth Factor In Endothelin-Mediated Endothelial Cell Activation

Abstract 2107

Endothelial cell activation and elevated levels of circulating Endothelin-1 (ET-1) have been reported in patients with atherosclerosis and sickle cell disease (SCD). ET-1 is a well-described vasoconstrictor, mitogen and regulator of endothelial cells migration that has been shown to promote structural changes in blood vessels. ET-1 is produced in response to increases in vasoactive hormones, growth factors, hypoxia, shear stress and free radicals, events that are commonly observed in patients with SCD. Endothelial cell activation is in part characterized by increases of cytokines such as monocyte chemotactic protein-1 (MCP-1) and growth factors that are important in vascular maintenance and fibrogenesis such as connective tissue growth factor (CTGF) and vascular endothelial growth factor (VEGF). CTGF and VEGF are important for blood vessel remodeling, fibrogenesis and angiogenesis. Indeed there is evidence that incubation of smooth muscle cells with ET-1 leads to increases in CTGF and VEGF levels. However, the relationship between ET-1 and CTGF in endothelial cell activation is unclear. We hypothesize that increasing ET-1 would stimulate CTGF production and endothelial cell activation. We studied the effects of ET-1 on the human endothelial cell line, EA.hy926 (EA), as well as in primary cultures of mouse aortic endothelial cells (MAEC). We performed gene expression time course experiments (0, 2, 4, 8, 16, 24 Hr) on EA cells following incubation with 100nM ET-1 using quantitative RT-PCR with Taqman chemistries and GAPDH and beta-actin as endogenous controls. We observed increases of CTGF and VEGF expression between 4 and 8 hr for CTGF (1.74 fold increase vs time 0, n=6, P<0.03) and 4 hr for VEGF (2.14 fold increase vs time 0, n=3, P<0.04). Additional experiments on EA cells showed that incubation with 100nM ET-1 for 4 hr in the presence of BQ123 and BQ788, two inhibitors of ET-1 type A and B receptors, respectively, blocked the ET-1 stimulated rises in CTGF and VEGF as well as MCP-1 expression. We then performed western blot analyses (Abcam-CTGF antibody ab6992; Abcam VEGF antibody ab1316) and showed increases in cell associated CTGF protein levels following incubation of EA cells with 100nM ET-1 for 24 hr. The ET-1 stimulated rise in CTGF levels were significantly blunted by pre-incubation of EA cells with both BQ788 and BQ123. To study whether the effects of ET-1 were unique to EA cells, we also analyzed the effects of ET-1 on early cultures of MAEC isolated from C57BLJ mice. Consistent with our observations in human endothelial cells, incubation of MAEC with 100nM ET-1 for 4 hr were associated with increases of CTGF and VEGF expression (1.86 fold vs vehicle, n=3, P<0.03; 1.73 fold vs vehicle, n=3 P<0.04 respectively). Furthermore, ET-1 stimulated rises in CTGF and VEGF expressions were likewise blocked by pre-incubation with BQ123 andBQ788. We conclude that addition of ET-1 leads to activation of endothelial cells and increases in CTGF and VEGF from human and mouse endothelial cells. Thus we suggest that therapies designed to block ET-1 receptors will reduce endothelial cell activation in part by reducing CTGF production leading to alterations in cellular and tissue architecture. This work was supported by NIH R01HL090632 to AR and R01HL096518 to JRR.