UNEXPECTED EXPRESSION OF GLUCOSE-TRANSPORTER-4 IN VILLOUS STROMAL CELLS OF HUMAN PLACENTA

Glucose transporter 4 (GLUT4) protein expression was characterized in human and rodent term placentas. A 50-kDa protein was detected, by imm unoblotting, in term human placenta at levels averaging 25% of those f ound in white adipose tissue. It was also present, albeit at lower lev els, in mouse and rat placentas. The specificity of the 50-kDa signal was established by using skeletal muscle and placental tissues obtaine d from GLUT4-null mice as controls. Indirect immunohistochemistry, per formed in human placentas, showed that intravillous stromal cells were conspicuously labeled by GLUT4 and revealed colocalization of GLUT4 t ransporters with insulin receptors. This study provides the first evid ence that the insulin-responsive GLUT4 glucose transporter is present in human and rodent hemochorial placentas. Placental GLUT4 gene and pr otein levels were not modified in human pregnancy complicated by insul in-dependent diabetes mellitus. The significance of the high level of GLUT4 protein in human placenta remains to be elucidated, because, so far, this organ was not considered to be insulin-sensitive, with regar d to glucose transport.