Abstract
BackgroundAlternative splicing of Vascular endothelial growth factor-A mRNA transcripts (commonly referred as VEGF) leads to the generation of functionally differing isoforms, the relative amounts of which have potentially significant physiological outcomes in conditions such as acute respiratory distress syndrome (ARDS). The effect of such isoforms on pulmonary vascular permeability is unknown. We hypothesised that VEGF165a and VEGF165b isoforms would have differing effects on pulmonary vascular permeability caused by differential activation of intercellular signal transduction pathways.MethodTo test this hypothesis we investigated the physiological effect of VEGF165a and VEGF165b on Human Pulmonary Microvascular Endothelial Cell (HPMEC) permeability using three different methods: trans-endothelial electrical resistance (TEER), Electric cell-substrate impedance sensing (ECIS) and FITC-BSA passage. In addition, potential downstream signalling pathways of the VEGF isoforms were investigated by Western blotting and the use of specific signalling inhibitors.ResultsVEGF165a increased HPMEC permeability using all three methods (paracellular and transcellular) and led to associated VE-cadherin and actin stress fibre changes. In contrast, VEGF165b decreased paracellular permeability and did not induce changes in VE-cadherin cell distribution. Furthermore, VEGF165a and VEGF165b had differing effects on both the phosphorylation of VEGF receptors and downstream signalling proteins pMEK, p42/44MAPK, p38 MAPK, pAKT and peNOS. Interestingly specific inhibition of the pMEK, p38 MAPK, PI3 kinase and eNOS pathways blocked the effects of both VEGF165a and VEGF165b on paracellular permeability and the effect of VEGF165a on proliferation/migration, suggesting that this difference in cellular response is mediated by an as yet unidentified signalling pathway(s).ConclusionThis study demonstrates that the novel isoform VEGF165a and VEGF165b induce differing effects on permeability in pulmonary microvascular endothelial cells.
Highlights
Alternative splicing of Vascular endothelial growth factor-A mRNA transcripts leads to the generation of functionally differing isoforms, the relative amounts of which have potentially significant physiological outcomes in conditions such as acute respiratory distress syndrome (ARDS)
Specific inhibition of the pMEK, p38 mitogen activated protein kinase (MAPK), PI3 kinase and endothelial nitric oxide synthase (eNOS) pathways blocked the effects of both VEGF165a and VEGF165b on paracellular permeability and the effect of VEGF165a on proliferation/migration, suggesting that this difference in cellular response is mediated by an as yet unidentified signalling pathway(s)
This study demonstrates that the novel isoform VEGF165a and VEGF165b induce differing effects on permeability in pulmonary microvascular endothelial cells
Summary
Alternative splicing of Vascular endothelial growth factor-A mRNA transcripts (commonly referred as VEGF) leads to the generation of functionally differing isoforms, the relative amounts of which have potentially significant physiological outcomes in conditions such as acute respiratory distress syndrome (ARDS). The effect of such isoforms on pulmonary vascular permeability is unknown. VEGF165a and VEGF165b isoforms were shown to have contrasting effects on the epithelial and endothelial sides of the alveolar-capillary membrane [12] These data suggest a pneumotropic effect which could be beneficial within the alveolar space following ARDS. The effect of these isoforms on vascular permeability another key element of ARDS is unknown
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