The molecular basis of embryo implantation in humans

Summary

The implantation of the human embryo is a double paradox, immunological and biological. The immunological paradox is that it consists of a heterologous graft in which the uterine immune system (via the cytokines) and the embryo's antigenicity (HLAG) collaborate to make possible both implantation and the maintenance of the pregnancy. The biological paradox arises because several different mechanisms must be successively implemented for these two epithelia to fuse and then for one to allow invasion by the other (that is, the for the endometrium to be decidualized by the trophoblast): preparation of the endometrium throughout the menstrual cycle under the influence of estrogens and then progesterone, with the involvement of growth factors (EGF, TGF and IGF), neoangiogenesis (estradiol, FGF and VEGF), recognition by the trophoblastic cells of the various components of the decidua and of the extracellular matrix (integrins and cadherin) and the progressive invasion of the decidua, to the depth of the spiral arteries (by the trophoblastic secretion of metalloproteases). A defective or excessive trophoblastic invasion can result in complications of pregnancy : early spontaneous miscarriage, preeclampsia and growth retardation of vascular origin in the case of defects, placenta accreta or percreta in the case of excess.

Molekularbiologische Grundlagen der Implantation beim Menschen

Zusammenfassung

Die Implantierung menschlicher Embryonen stellt ein zweifaches Paradox dar. Aus immunologischer Sicht wird eine heterologe Einpflanzung vorgenommen, bei der das uterine Immunsystem (über die Zytokine) und die embryonale Antigenizität (HLAG) zusammenwirken, so dass sowohl die Implantierung als auch der Schwangerschaftserhalt möglich sind. Das biologische Paradox entsteht, weil viele verschiedene Mechanismen nacheinander implementiert werden müssen, um die Fusion dieser beiden Epithelien und die darauffolgende Invasion des einen durch das andere zu ermöglichen (d. h. damit das Endometrium durch den Trophoblast deziduialisiert wird). Das Endometrium wird während des Monatszyklus unter dem Einfluss von Östrogene, dann von Progesterone vorbereitet, unter der Teilnahme von Wachstumsfaktoren (EGF, TGF und IGF); die Neoangiogenese (Östradiol, FGF und VEGF); die Erkennung durch die Trophoblastzellen der verschiedenen Bestandteile der Dezidua und des extrazellulären Matrix (Integrine und Kadherin) und die progressive Eindringung der Dezidua bis zur Tiefe der Spiralarterien (durch das trophoblastische Ausscheiden von Metalloproteasen). Eine unzulängliche oder exzessive Trophoblastinvasion kann zu Komplikationen in der Schwangerschaft führen: einem verfrühten, spontanen Abort, einer Präeklampsie und vaskulär bedingter Wachstumsretardierung im Falle der Unzulänglichkeit der Invasion; Plazentaakkreta oder -perkreta bei exzessiver Invasion.

Key words

Implantation - growth factors - integrins - endometrium - angiogenesis

Schlüsselwörter

Implantierung - Wachstumsfaktoren - Integrine - Endometrium - Angiogenese

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