Increased expression of VE-cadherin correlates temporally with differentiation of a restrictive endothelial barrier during normal angiogenesis in vivo

Differential phosphodiesterase activity contributes to restrictive endothelial barrier function during angiogenesis

Angiogenic endothelial hyperpermeability is abruptly diminished between days 4.5 and 5.0 of the 18-day lifespan of the chick chorioallantoic membrane. Here, we evaluated phosphodiesterase (PDE) activity during the differentiation of barrier function. At day 4.5, rolipram-mediated inhibition of cAMP-specific PDE IV reduced FITC-dextran extravasation. Moreover, inhibition of PDE III by HL 725, but not PDE I by 8-IBMX, decreased the temporal angiogenic endothelial hyperpermeability. Reduced FITC-dextran was also observed at day 4.5 after application of KT 5823, a selective inhibitor of cGMP-specific protein kinase G (PKG), LY 83583, an inhibitor of soluble guanylate cyclase, or LNMMA, an inhibitor of nitric oxide synthase. At day 5.0, Rp-cAMPS-mediated inhibition of cAMP-specific protein kinase A (PKA) diminished barrier function and interstitial accumulation of FITC-dextran was increased. In all cases, the mean widths of interendothelial separation remained uniform. Together, the results support the concept that differentiation of restrictive angiogenic endothelial barrier function in vivo includes inactivation of PDE III and PDE IV with consequent up-regulation of cAMP/PKA signaling and down-regulation of the cGMP/PKG pathway.

Differentiation of endothelial barrier function during normal angiogenesis requires homotypic VE-cadherin adhesion

Endothelial cells express two principal cadherins: VE-cadherin and N-cadherin. We established previously that only VE-cadherin expression was increased during differentiation of barrier function by angiogenic endothelium of the chick chorioallantoic membrane (CAM). Presently anti-VE-cadherin mAb, applied to the CAM at day 4.5 of gestation, served to inhibit the abrupt reduction of macromolecular extravasation that occurs normally at day 5.0. Neither anti-N-cadherin nor nonimmune IgG, on the other hand, prevented this temporal decrease of endothelial permeability. Despite the differential permeability responses, morphometric evaluations defined a reduction of mean paracellular cleft width after the application of either anti-VE-cadherin or anti-N-cadherin. Hence, alteration of molecular sieving characteristics within the junctional clefts, rather than modification of cleft dimensions; likely served as the principal modulator of macromolecular extravasation after inhibition of homotypic VE-cadherin adhesion. These results provide support to the concept that VE-cadherin contributes to the normal differentiation of endothelial barrier function during CAM angiogenesis in vivo.

Restrictive endothelial barrier function during normal angiogenesis in vivo: partial dependence on tyrosine dephosphorylation of beta-catenin

Differentiation of a restrictive endothelial barrier in the chick chorioallantoic membrane (CAM) occurs between Day 4.5 and Day 5.0 of the normal 21-day gestation. Whether molecular changes in the endothelial cell-cell junctional protein complex contribute to the ontogeny of barrier function represents the principal focus of this study. VE-cadherin has been shown to contribute to the regulation of endothelial cell monolayer permeability in vitro. Accordingly, VE-cadherin is complexed to the cytosolic catenins, and changes in monolayer permeability have been linked to alterations of the cadherin/catenin complex. Currently, a CAM endothelial VE-cadherin/beta-catenin complex was identified, and phosphotyrosine labeling of beta-catenin was decreased concurrently with the abrupt increase in CAM endothelial selectivity between Day 4.5 and Day 5.0. Further, inhibition of protein tyrosine phosphatases impeded regular tyrosine dephosphorylation of beta-catenin at Day 5.0 and this served to partially restore macromolecular extravasation to elevated levels normally present at Day 4.5. Thus, differentiation of selective barrier function in the angiogenic CAM endothelium in vivo is dependent, in part, on tyrosine dephosphorylation of beta-catenin.