Homeobox genes are differentially expressed in macrovascular human umbilical vein endothelial cells and microvascular placental endothelial cells.

Angiogenesis is fundamental to normal placental development. Aberrant angiogenesis within the placental terminal villi is a characteristic of significant placental pathologies and includes structural and vascular abnormalities as well as altered endothelial cell function, which substantially impacts on maternal-fetal exchange. Homeobox gene transcription factors regulate vascular development in embryonic and adult tissues, but their role in the placental microvasculature is not well known. In this study, we isolated and enriched human placental microvascular endothelial cells (PLEC) by a perfusion-based method and compared homeobox gene expression between PLEC and macrovascular human umbilical vein endothelial cells (HUVEC). Reverse transcriptase PCR detected mRNA expression of homeobox genes DLX3, DLX4, MSX2, GAX and HLX1 in both PLEC and HUVEC. DLX4 and HLX1 have not been previously detected in PLEC and with the exception of GAX, none of these homeobox genes have been previously identified in HUVEC. There was lower expression of HLX1 mRNA in HUVEC compared with PLEC. Using real-time PCR analysis PLEC HLX1 mRNA expression relative to housekeeping gene GAPDH was 0.9+/-0.06 fold of the calibrator (n=6) versus 0.2+/-0.06 (n=6) for HUVEC, p<0.001. These data provided evidence of heterogeneity in homeobox gene expression between microvascular PLEC and macrovascular HUVEC that most likely reflects significant differences in endothelial cell function in the two different cellular environments.