9 This family consists of four ligands, of which Ang-1 and Ang-2 are the best characterized factors: they have similar binding affinities to their specific tyrosine kinase receptor [tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (Tie-2)], to which they bind in a competitive manner. Ang-1 has an antiapoptotic effect on endothelial cells (ECs), stimulates BGJ398 EC sprouting, and increases vascular stability by inducing recruitment of pericytes and stimulation of
mesenchymal cells to differentiate into vascular smooth muscle cells (SMCs). As such, Ang-1 has a major role in maintaining vascular quiescence and integrity.9, 10 Ang-1 is predominantly expressed by nonendothelial cells, such as pericytes and myofibroblasts, and in the liver by hepatic stellate cells, cholangiocytes,
hepatoblasts, and hepatocytes.8, 11-13 Ang-2 Belnacasan mouse is predominantly produced by ECs and released during EC activation, and it promotes vessel destabilization and increases endothelial responsiveness to other growth factors such as vascular endothelial growth factor A (VEGF-A). The significant role of Ang-1 in hepatic vascular morphogenesis has been demonstrated in several experimental animal studies. Prolonged overexpression of Ang-1 in mouse hepatocytes resulted in abnormal vessel formation, including arterial sprouting, the formation of enlarged arteries, hepatic vein dilation, the loss of portal vein radicles, and arteriovenous shunting. More importantly, Ang-1 overexpression also generated nodular parenchymal changes resembling FNH.14 In a study of transgenic expression of Ang-1 in mouse livers, aberrant dilated vessels resembled the peliotic changes observed in HCA,15 and together, these results emphasize the importance of Ang-1 for hepatic vascular morphology. On the basis MCE公司 of these experimental results, the findings of Paradis et al.,6 and our own previous findings in HCC,8 we hypothesized that altered expression and a distorted
balance of angiogenic growth factors could be responsible for the aberrant vascular features in FNH and HCA. Therefore, in the present study, we investigated the expression profiles of the ligands and cognate receptors of the two currently most influential families of angiogenic growth factors, the angiopoietins and VEGF-A. Besides gene and protein expression levels, we established their location in the lesions and in adjacent tissues. Our main finding is that a significant increase in Ang-1 expression exists in FNH and, though less prominently, in HCA without a significant alteration of Ang-2 and VEGF-A expression. As overexpression of Ang-1 in FNH and HCA does not necessarily imply that a similar remodeling process is responsible for the vascular abnormalities in both lesions, we discuss this finding in light of the different etiologies of FNH and HCA.