Studies on effects of Lp(a) lipoprotein on gene expression in endothelial cells in vitro.

The reason(s) for the atherogenic properties of Lp(a) lipoprotein is still unclear, and several mechanisms have been studied. Alterations in gene expression in endothelial cells (ECs) could be important with respect to risk for coronary heart disease (CHD). We have tested the effects of Lp(a) lipoprotein or the apolipoprotein of Lp(a) lipoprotein (apo(a)) on cultured human umbilical vein endothelial cells (HUVECs) with respect to: (1) the level of endothelin-1 (ET-1) mRNA; (2) release of ET-1 into the culture medium; (3) plasminogen activator inhibitor-1 (PAI-1) secretion into the culture medium and; (4) total gene expression in HUVECs, examined by a polymerase chain reaction (PCR)-based technique, differential display-reverse transcription-PCR (DD-RT-PCR). Lp(a) lipoprotein reduced the level of ET-1 mRNA as well as the release of ET-1. The reduction of ET-1 in the medium was even more pronounced when HUVECs were incubated with apo(a), but we found no effect of apo(a) on ET-1 mRNA level. Neither Lp(a) lipoprotein nor apo(a) had a significant influence on PAI-1 secretion. DD-RT-PCR revealed 11 fragments that could represent differences between cells exposed or not exposed to Lp(a) lipoprotein. Following subcloning and sequencing, 18 sequences that differed between exposed and unexposed cultures were obtained. Four of the subcloned fragments have up to now been used as a probe for northern blot analyses, and one fragment was confirmed to be regulated by Lp(a) lipoprotein. In conclusion, Lp(a) lipoprotein is shown to control ET-1 mRNA levels and the function of at least one more gene, the nature of which is unknown.