Differential expression and responsiveness of chemokine receptors (CXCR1-3) by human microvascular endothelial cells and umbilical vein endothelial cells

The basis for the angiogenic effects of CXC chemokines such as interleukin 8 (IL-8) and for angiostatic chemokines such as interferon-inducible protei n 10 (IP-10) has been difficult to assess. We recently reported, based on a n RNase protection assay, that human umbilical vein endothelial cells (HUVE Cs) did not express detectable mRNA for the IL-8 receptors CXCR1 and CXCR2. This raised the possibility of heterogeneity of receptor expression by dif ferent endothelial cell (ECs) types. Since systemic angiogenesis induced by IL-8 would more likely involve microvessel ECs, we investigated CXC recept or expression on human microvascular dermal endothelial cells (HMECs). By c onfocal microscopy and immunofluorescence we observed that HMECs consistent ly expressed high levels of CXCR1 and CXCR4 (mean fluorescence intensity of 261+/-22.1 and 306.2+/-19, respectively) and intermediate levels of CXCR3 and CXCR2 (173.9+/-30.2 and 156+/-30.9, respectively). In contrast, only a small proportion of HUVEC preparations expressed low levels of CXCR1, -2; a nd -3 (66+/-19.9; 49+/-15, and 81.4+/-17.9, respectively). However, both HM ECs and HUVECs expressed equal levels of CXCR4. As expected, HMECs had more potent chemotactic responses to IL-8 than HUVECs, and this was correlated with the levels of IL-8 receptors on the ECs. Antibodies to CXCR1 and CXCR2 each had inhibitory effects on chemotaxis of HMECs to IL-8, indicating tha t both IL-8 receptors contributed to the migratory response of these cells toward IL-8. Assessment of the functional capacity of CXCR3 unexpectedly re vealed that HMECs migrated in response to relatively higher concentrations (100-500 ng/ml) of each of the 'angiostatic' chemokines IP-10, ITAC, and MI G. Despite this, the 'angiostatic' chemokines inhibited the chemotactic res ponse of HMECs to IL-8. IL-8 and SDF-1 alpha but not IP-10 induced calcium mobilization in adherent ECs, suggesting that signaling events associated w ith calcium mobilization are separable from those required for chemotaxis. Taken together, our data indicated that functional differences among EC typ es is dependent on the level of the expression of CXC chemokine receptors. Whether this heterogeneity in receptor expression by ECs reflects distinct differentiation pathways remains to be established.