The Role of Human Chorionic
Gonadotropin in Successful Pregnancies
At least 30% of all human pregnancies spontaneously fail for
unknown causes. The research performed by Dr. Elliott Bedows’ laboratory is
dedicated to improving women’s health by clarifying the molecular basis by
which the hormone human chorionic gonadotropin (hCG) facilitates embryo
implantation. In doing so, he hopes to determine why this critical event in
early pregnancy is so sensitive to adverse outcome.
Trophoblasts (cells surrounding the embryo which attach to
the uterine wall and provide nutrition) undergo dramatic transformation during
the first several days of pregnancy and ultimately lead to the development of
the placenta. Dr. Bedows feels that "monitoring biochemical changes that
occur within the trophoblast cells during this period will allow him to
characterize events that will be predictive of pregnancy outcome." The
pregnancy-induced hormone hCG is secreted by the trophoblast. Human CG appears
to have two distinct roles in maintaining pregnancy. First, the earliest form of
hCG expressed by trophoblasts seems to facilitate embryo implantation. This form
of hCG, which is expressed 6-10 days following conception, does not efficiently
stimulate ovarian progesterone production. Over the course of the subsequent
week, hCG matures into a form that is capable of stimulating ovarian
progesterone secretion. The second role of hCG is to stimulate ovarian
progesterone secretion in quantities sufficient for the maintenance of
pregnancy. If hCG does not mature from its early form into a form capable of
stimulating progesterone secretion, early pregnancy loss occurs.
Dr. Bedows indicated, "It is the earliest detectable form of hCG that
interests us most because the genes that are regulated during embryo
implantation may be the key to determining a successful pregnancy. We are now
determining the identity of the genes being regulated following hCG exposure in
human endometrial tissues in an attempt to better understand the role of hCG in
normal pregnancy and why alterations in this process may lead to early pregnancy
loss." Dr. Bedows’ research is currently testing the hypothesis that the
early form of hCG modulates the expression of enzymes that promote tissue
remodeling (matrix metalloproteases) and proteins that stimulate new blood
vessel growth, both of which contribute to embryo implantation.
Contributed by John S. Davis, UNMC Olson Center for Women's Health