Proangiogenic Role of Tumor–Activated Hepatic Stellate Cells in Experimental Melanoma Metastasis

Abstract

Myofibroblasts infiltrate malignant liver tumors, although their pathogenic implications are unclear. Immunohistochemical detection of ␣-smooth muscle actin, glial fibrillary acidic protein (GFAP), and CD31 and CD34 expression was used to analyze the contribution of myofibroblasts to angiogenesis in hepatic metastasis produced by intrasplenically-injected B16 melanoma (B16M). Because activated hepatic stellate cells (HSCs) are oxygen-sensing myofibroblasts producing vascular endothelial growth factor (VEGF), the effect of B16M and human A375 melanoma supernatants on VEGF production by immortalized rat HSC line T6 and primary cultured human HSCs also was studied under an hypoxic atmosphere mimicking a tumor microenvironment. Myofibroblast infiltration preceded endothelium recruitment in avascular micrometastasis and generated specific stroma for sinusoidal-type and portal-type angiogeneses. Thereafter, myofibroblasts and endothelial cells colocalized within both angiogenic patterns and their numerical densities correlated with metastasis development. Myofibroblasts often were GFAPpositive, suggesting an HSC origin. Melanoma supernatants stimulated VEGF messenger RNA and protein synthesis by HSCs. These effects were potentiated by hypoxia. VEGF up-regulation was accompanied by increased expression of cyclooxygenase type 2 (COX-2) and PGE2 synthesis. HSC production of VEGF decreased under COX-2 inhibition, whereas it was increased by exogenous PGE2. The high VEGF expression in HSCs induced by melanoma factors and hypoxia resulted in mitogenic, antiapoptotic, and motogenic stimulation of both murine hepatic sinusoidal endothelium and human umbilical vein endothelium. In conclusion, temporal and positional relationships evolve between myofibroblast and endothelium recruitment during metastasis development. Mechanistically, hypoxic induction of VEGF in tumor-activated HSCs may create a proangiogenic microenvironment, facilitating endothelial cell recruitment and survival during hepatic metastasis transition from an avascular to a vascular stage. (HEPATOLOGY 2003;37:674-685.)

Development of the vasculature in “pushing‐type” liver metastases of an experimental colorectal cancer

“…for the capsule formation, such as transforming growth factor-b, hypoxia and simple mechanical pressure. 19,20 There is evidence that the main cellular components of these capsules are activated SMA-expressing hepatic stellate cells. 19 The mechanical pressure exerted by differentiated carcinomas (pushing growth pattern) can be a major factor for the activation and accumulation of hepatic stellate cells around metastases.…”

“…19,20 There is evidence that the main cellular components of these capsules are activated SMA-expressing hepatic stellate cells. 19 The mechanical pressure exerted by differentiated carcinomas (pushing growth pattern) can be a major factor for the activation and accumulation of hepatic stellate cells around metastases. 20 An important role of these contractile cells can be to decrease the size of the ''wound'' in the liver caused by the growing tumor.…”

Mechanisms of Hepatic Fibrogenesis

“…Moreover, progressive fibrosis with angiogenesis also contributes to tumor vascularization in which activated stellate cells play a vital role. 10,154 As fibrosis advances, the collagenous bands typical of end-stage cirrhosis contain large numbers of activated stellate cells. 155 These cells progressively impede portal blood flow by both constricting individual sinusoids and by contracting the cirrhotic liver, mediated by pathways that allow interaction with the ECM.…”

Downregulation of discoidin domain receptor 2 in A375 human melanoma cells reduces its experimental liver metastasis ability

“…In this study, we utilized the siRNA technique to correlate DDR2 expression in A375 melanoma cell clones with their hepatic metastatic potential in vivo. To study DDR2 contribution to tumor cell colonization and growth we utilized our experimental model of intrasplenically inoculated cancer cells (18,19). We also used a melanoma cell line to test DDR2 implication in metastatic development because melanoma is one of the most frequent primary tumors that metastasize to the liver.…”