Microvascular endothelial cells differ in basal and hypoxia-regulated expression of angiogenic factors and their receptors.

Phenotypically and functionally different types of microvascular endothelial cells (MVECs) derived from the developing corpus luteum were isolated and characterized by our group. We investigated whether these cytokeratin-positive (CK+) and cytokeratin-negative (CK-) MVECs differed in the expression of angiogenic factors and their regulation under hypoxia. Using quantitative RT-PCR, VEGF and its receptors, Flk-1 and Flt-1, were detected in CK- MVECs. The mRNA expression of Flk-1 mRNA was 100 times as high as that of Flt-1 mRNA. CK+ MVECs expressed VEGF and Flt-1 mRNA, but were devoid of Flk-1 transcripts. No Ang-1 mRNA was demonstrated in either cell type, and Ang-2 mRNA was found only in CK- MVECs. Tie-2 mRNA was detected in both MVEC types, but levels were 150 times as high in CK- MVECs as in CK+ MVECs. mRNA of hypoxia-inducible factors Hif-1alpha and Hif-1beta was expressed in both MVEC types. After hypoxia, neither VEGF, nor Flk-1, nor Tie-2 mRNA expression was altered in either MVEC type. Flt-1 expression and Ang-2 mRNA expression were significantly increased at about 2.5-fold (P < 0.05) in CK- MVECs, but not in CK+ MVECs. Our study demonstrates the varying expression and regulation of angiogenesis-related factors and receptors in phenotypically different MVEC types.