Expression of endoglin mRNA and protein in human vascular smooth muscle cells

Endoglin, the gene linked to the autosomal dominant vascular disorder hereditary hemorrhagic telangiectasia type 1 (HHT1), encodes a 95-kDa membrane-bound proteoglycan which binds TGF beta 1 and regulates signaling via the type I and II TGF beta receptors on the surface of vascular endothelial cells. Using reverse-transcription polymerase chain reaction (RT-PCR) and Northern blot analysis we have shown that endoglin mRNA is expressed in both cultured human VSMCs and VSMCs freshly isolated from human aortas. Northern blot analysis was also used to demonstrate that endoglin expression decreased in serum-stimulated cultured human VSMCs but could be maintained by exogenous TGF beta 1. Endoglin protein expression in human VSMCs was shown by immunocytochemistry. These data, the first describing the existence of endoglin in VSMCs, suggest that through regulating TGF beta 1 signaling endoglin may mediate the effects of TGF beta 1 on VSMC behavior in vitro and in vivo.