COORDINATED INDUCTION OF VEGF RECEPTORS IN MESENCHYMAL CELL-TYPES DURING RAT HEPATIC WOUND-HEALING

Homology PCR has been used to identify receptor tyrosine kinases (RTKs ) expressed during activation of rat hepatic stellate cells, the key f ibrogenic mesenchymal element in the liver. Partial cDNAs encoding sev eral RTKs were cloned from stellate cells activated in vivo, including those of Flt-1, Flk-1, c-met, PDGFR, and Tyro10/DDR2, RNAse protectio n from cells activated ill vivo demonstrated biphasic induction of flt -1 and flk-1 mRNAs, receptors for vascular endothelial growth factor ( VEGF), Culture-activation of stellate cells was associated with increa sed [I-125]VEGF binding and Flt-1 and Flk-1 receptor protein. Inductio n of VEGF binding sites correlated with an 2.5-fold increase in DNA sy nthesis in response to VEGF, but only if cells were activated by growt h on collagen I, whereas cells maintained in a quiescent state on a ba sement membrane-like substratum (EHS matrix) were nonproliferative, In both stellate and endothelial cells VEGF-induced mitogenesis was augm ented by co-incubation with basic fibroblast growth factor (bFGF), a c ytokine with known synergy with VEGF, These findings suggest that the cellular targets of VEGF in liver may not be confined to sinusoidal en dothelial cells, and that VEGF responses reflect combined effects on b oth hepatic stellate cells and sinusoidal endothelium.