| Summary: | Vascular endothelial growth factor (VEGF) is a potent mitogenic, angiogenic and permeability factor that has been associated with the development of lung disease. The VEGF gene undergoes alternate splicing of exon 8 to produce two isoform families with differing functional effects. VEGF16sa is the most biologically active member of the VEGFxxxa family. One member of the VEGFxxxb family, VEGF16Sb, has "inhibitory" effects on VEGF16sa induced endothelial proliferation, migration and permeability. This study is based upon the hypothesis that these isoforms utilise differing signalling pathways, identification of which would enable manipulation of their functional effects. To investigate this hypothesis, mRNA and protein expression of VEGF receptors and coreceptors in human pulmonary microvascular endothelial cells (HPMEC) were compared to those of systemic human umbilical vein endothelial cells (HUVEC). Potential downstream signalling pathways and mechanisms underlying VEGF165a and VEGF165b induced changes in cell permeability were investigated using signalling inhibitors and cellular distribution of the cell-junctions proteins VE-cadherin and ZO-l. Finally, PCR array profiles were utilised to screen potential differences in gene expression downstream ofVEGF and nitric oxide. The work presented shows that HPMEC and HUVEC cells differ in basal expression ofVEGF receptors and co-receptors, and that they are modified in response to chronic stimulation with VEGF isoforms. Cell signalling pathways downstream of VEGF-R2 differ between VEGF16sa and 16Sb and between the cell types. Three different methods (Endohm, ECIS and FITC-BSA passage) showed that VEGF16sa induced an increase and VEGF16Sb a decrease, in permeability for both HPMEC and HUVEC. L-NAME, L-NIO and PI3K (AKT leNOS pathways) inhibitors, blocked both VEGF isoforms suggesting no differential signalling in this pathway. Observation of changes in VE-cadherin and ZO-l expression pattern at cell junctions after VEGF16sa stimulation but not after VEGF16Sb suggested that this was a possible mechanism involved in the regulation of HPMEC and HUVEC permeability. PCR profiling array suggested some potential differential gene expression following VEGF16sa and VEGF16Sb stimulation. Understanding the signalling pathways utilised by VEGF isoforms to regulate lung biology could enable us to preferentially induce specific beneficial effects in the lung such as epithelial mitosis, whilst inhibiting detrimental effects such as increased permeability.
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