Abstract
There are two independent variants of human chorionic gonadotropin (hCG) with totally independent functions. Both forms share the 92 amino acid α-subunit and the 145 amino acid β-subunit. Regular hCG is a hormone with eight sugar side chains, four biantennary N-linked sugar structures and four trisaccharide O-linked sugar structures (molecular weight: 36,700). Hyperglycosylated hCG is an autocrine with eight sugar side chains, four triantennary N-linked oligosaccharides and four hexasaccharide O-linked oligosaccharides (molecular weight: 40,500). Hyperglycosylated hCG is produced by cytotrophoblast cells and regular hCG is formed by fused differentiated syncytiotrophoblast cells. These two molecules together coordinate most aspects of pregnancy. Research over the past 40 years has demonstrated that regular hCG promotes progesterone production by the corpus luteum, promotes angiogenesis of uterine spiral arteries, inhibits macrophage rejection of the implanting placenta, promotes growth of the umbilical cord, suppresses contractions in the myometrium during pregnancy, promotes the growth of the uterus in line with the growth of the fetus, promotes differentiation of cytotrophoblast cells to syncytiotrophoblast cells, communicates between blastocyst and the uterus prior to implantation, and promotes growth of fetal organs during pregnancy. Hyperglycosylated hCG is responsible for implantation of the blastocyst or implantation of pregnancy, promotes continued invasion following implantation, and also promotes growth of cytotrophoblast cells. Regular hCG and hyperglycosylated hCG together promote growth and differentiation of the placenta during pregnancy or villous structure formation, leading to hemochorial placentation.
Financial & competing interests disclosure
The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
Notes
hCG: Human chorionic gonadotropin.