Human endothelial cells produce orosomucoid, an important component of thecapillary barrier

The serum protein orosomucoid (al-acid glycoprotein) is needed to maintain the high capillary permselectivity required for normal homeostasis. It is n ot known how the protein executes its action, but it seems to contribute to the charge barrier. Moreover, recent studies suggest that the endothelial glycocalyx is essential for the charge barrier. The main site of orosomucoi d synthesis is the liver, but we wanted to explore the possibility that oro somucoid was synthesized in endothelial cells. Primary cultures of human mi crovascular endothelial cells (HMVEC) from dermal tissue were established. Human liver cells were used as positive controls, and total RNA was prepare d from both cell types. Reverse transcription-polymerase chain reaction (RT -PCR) was performed and demonstrated orosomucoid expression. After RT-PCR, the identities of the PCR products were confirmed by sequencing. RNase prot ection assay performed on total RNA from the HMVEC confirmed the results fr om the RT-PCR, i.e., orosomucoid mRNA is expressed by endothelial cells. Sy nthesis of orosomucoid in both liver and endothelial cells was demonstrated by immunoprecipitation. In conclusion, endothelial cells normally produce orosomucoid, which is essential for capillary charge selectivity. We sugges t that orosomucoid exerts its effect by interacting with other components o f the endothelial glycocalyx.