Hyaluronate and CD44 expression patterns in the human placenta throughout pregnancy

Hyaluronan (HA) and CD44 are involved in several processes such as cell mig ration and differentiation. In the present study, we examined the expressio n and distribution of both hyaluronan and its cell surface receptor (CD44) in the human placenta, which is a rapidly growing and differentiating organ that plays a fundamental role in fetal;life. Hyaluronan was detected by a specific biotinylated binding probe, termed b-PG. In the first half of gest ation, HA was strongly expressed in the stroma of the mesenchymal villi whi ch have been previously identified as responsible for the growth and differ entation of the villous trees. The other villous types showed an intense st aining only in the fetal vessel walls and in the connective tissue closely underlying the trophoblastic cover. In addition, hyaluronan positive staini ng was also apparent in a restricted rim of villous stroma directly apposed to extravillous cytotrophoblastic cell islands and eel columns. In full te rm placentas, all villi expressed HA in their stromal tissue with a more ho mogenous staining than in the first half of gestation. In contrast to hyalu ronan, in the first trimester CD44 was restricted to some of the Hofbauer c ells which may be able to internalize hyaluronan, thus playing a significan t role in its removal in early pregnancy. CD44 was primarily expressed star ting from the 16(th) week of gestation. At the end of pregnancy it was expr essed in the Various villous types, especially in stem villi. Moreover, the plasma membrane of some extravillous cytotrophoblastic cells in the basal plate and the large majority of the decidual cells showed a positive immuno staining for this receptor. Taken together, these data suggest that HA is s trongly involved in early villous morphogenesis, whereas CD44 seem to be pl ay an important role in tissue remodelling later in gestation.