Endometrial Responses to Blastocyst Signaling: Peptidases and Gap Junctions
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Overview
Most investigators assume that the preimplantation blastocyst must send out locally acting signals that contribute to the preparation of the uterus for implantation. However, only few hard facts have been reported to verify and document this. This general paucity of data is true for the nature of the postulated signals as well as for any physiological responses of the uterus. Various different classes of compounds have been considered as candidates for such signals (e.g. steroids in the pig and the peptide hormone, interferon-tau, in ruminants). However, in these species implantation starts very late (and remains superficial) so that they may be poor models for the human. In the human, hCG (human chorionic gonadotrophin) production and secretion by the trophoblast appears to begin already before implantation. The same holds true for non-human primates. Apart from its well-known systemic role, any local effects that this hormone or others may have in the uterus remain largely obscure, however.
Any signals emitted by the blastocyst necessarily first hit the immediately surrounding parts of the endometrium, i.e. those tissues which will shortly later form the implantation chamber. It appears thus possible that these signals may have a direct function in preparing this specific part of the endometrium for trophoblast attachment and invasion. Morphological, biochemical and cell biological data documenting unequivocally that and how the uterus responds locally, in the implantation chamber, to blastocyst signals are rare, however. Monitoring endometrial responses based on such criteria would be required, on the other hand, in any experimental investigation on the postulated interplay between the two partner tissues.
Thus it appeared of interest that in our studies clear evidence was found that late preimplantation blastocysts already modulate the activity of certain peptidases in the surrounding endometrium, in the rabbit model. Of particular interest in this context is an aminopeptidase (addressed as leucine aminopeptidase, amino acid arylamidase, arylamidase 1, alanyl aminopeptidase, or aminopeptidase M/N; the terminology changed over the years while we were studying this enzyme, reflecting the progress of biochemical identification of the members of this class of enzymes). The enzyme has on one hand been found to be a very useful and sensitive parameter for monitoring the action of systemic steroid hormones on the uterus, in particular the endometrium. On the other hand it was also found to be an early indicator of local signaling of the blastocyst to the surrounding endometrium, starting already shortly before the onset of implantation. The signals emitted by the blastocyst may complete endometrial receptivity (initiated by systemic hormonal stimulation) locally in the implantation chamber. This aminopeptidase thus seems to be a very useful parameter that allows monitoring the local interplay. It appears to indicate a locally restricted stimulation of uterine secretion (extrusion of apical cytoplasmic contents including portions of apical membrane, i.e. apical protrusions), a phenomenon that may be an element of a modulation of the cell biological state of the uterine epithelium during acquisition of receptivity: Indeed, shedding of apical characteristics by the uterine epithelium in preparation for trophoblast attachment may be part of the ways how Mother Nature deals with the cell biological paradox of trophoblast attachment to the (originally non-adhesive) apical cell pole of the uterine epithelium at implantation (see research topic “Embryo Implantation III: Endometrial Receptivity”). In the course of our investigations it was interesting to see also that the aminopeptidase activity disappears around copper IUDs, in the rabbit model.
Quite comparably to this aminopeptidase, the formation of gap junctions between endometrial cells proved later on to be similarly useful in monitoring systemic steroid hormone actions on the uterus. Gap junction formation (as well as, on the molecular level, expression of connexins, the proteins constituting gap junction channels) is also a suitable indicator of local signaling of the early blastocyst to the surrounding endometrium, again like the aminopeptidase. In the case of connexins/gap junctions it is, however, not down-regulation but up-regulation.
Our investigations have been performed predominantly in the rabbit model, but some comparative studies have been done also in the guinea pig, hamster, rat and cat. Years after our reports, other authors have also shown local effects of blastocysts on the surrounding endometrium when studying other parameters, e.g. HB-EGF, in some species. The chemistry of the putative signaling factors (steroids, peptide hormones, growth factors/cytokines?), however, still remains unclear. We have e.g. proposed that peptides liberated from the disintegrating blastocyst coverings by limited proteolysis (due to the action of the various endopeptidases and exopeptidases we studied) might play a role here (see research topic “Early Embryonic Coats”). Unfortunately, we have not been able to continue this line of research for lack of time, manpower and financial support. However, I still think that it has the potential to provide valuable insights into questions about the type of signals that the blastocyst sends out, about their effects on the endometrium and about any role that these may have for embryo implantation.
List of Publications
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DENKER, H.-W.:
Structural dynamics and function of early embryonic coats.
Cells Tissues Organs 166: 180-207 (2000). PubMed pdf-download (1.60 MB)
MITCHELL, J.A. and DENKER, H.-W.:
Endometrial arylamidase activitiy in the guinea pig: changes during the ostrous cycle, decidualization and ovarian steroid hormone treatment.
Comp. Biochem. Physiol. 99B, 709-712 (1991). PubMed
CLASSEN-LINKE, I. and DENKER, H.-W.:
Preparation of rabbit uterine epithelium for trophoblast attachment: Histochemical changes in the apical and lateral membrane compartment.
In: Trophoblast Invasion and Endometrial Receptivity. Novel Aspects of the Cell Biology of Embryo Implantation. (H.-W. Denker and J.D. Aplin, eds.) (Trophoblast Research, Vol. 4). New York and London: Plenum Medical Book Comp., 1990, pp. 307-322. pdf-download (30.5 MB, with kind permission of Springer Science and Business Media)
MITCHELL, J.A. and DENKER, H.-W.:
Implantation-induced changes in uterine arylamidase localization in the rabbit, rat, hamster and guinea-pig.
J. Reprod. Fert. 83, 355-364 (1988).
PubMed
Reproduction pdf-download
WINTERHAGER, E., BRÜMMER, F., DERMIETZEL, R., HÜLSER, D.F. and DENKER, H.-W.:
Gap junction formation in rabbit uterine epithelium in response to embryo recognition.
Dev. Biol. 126, 203-211 (1988). PubMed PDF (German National Library)
CLASSEN-LINKE, I., DENKER, H.-W. and WINTERHAGER, E.:
Apical plasma membrane-bound enzymes of rabbit uterine epithelium: Pattern changes during the periimplantation phase.
Histochemistry 87, 517-529 (1987). PubMed pdf-download (5.97 MB, with kind permission of Springer, Heidelberg)
WINTERHAGER, E., DERMIETZEL, R., BRÜMMER, F. und DENKER, H.-W.:
Immunhistochemischer Nachweis des 26k-Proteins der gap junctions im Uterusepithel des Kaninchens in Abhängigkeit von der Reproduktionsphase.
Verh. Anat. Ges. 81 (Lübeck 1986), Anat. Anz. Suppl. 162, 503-504 (1987). pdf-download (881 KB)
WINTERHAGER, E., BRÜMMER, F., DERMIETZEL, R. and DENKER, H.-W.:
Induction of cell coupling via gap junctions in the uterine epithelium of the rabbit prior to trophoblast invasion.
(Abstr.) 24th Annual Meeting of the Cell, Tissue and Organ Culture Study Group (C.T.O.C.), Heidelberg 1986, p. 18
pdf-download (200 KB)
WINTERHAGER, E., BRÜMMER, F. und DENKER, H.-W.:
Induktion von gap junctions im Uterusepithel gravider Kaninchen.
(Abstr.) 5. Arbeitstagung d. Anat. Ges., Würzburg 1985. Anat. Anz. 161, 176-177 (1986)
pdf-download (269 KB)
WINTERHAGER, E., DERMIETZEL, R., BRÜMMER, F. and DENKER, H.-W.:
Gap junction formation in rabbit uterine epithelium during the periimplantation phase.
(Abstr.) Ann. Meet. Deutsche Ges. Zellbiologie, Tübingen 1986. Europ. J. Cell Biol. 39, Suppl. 12, 37 (1985)
pdf-download (294 KB)
WINTERHAGER, E., BRÜMMER, F. and DENKER, H.-W.:
Gap junction formation in the uterine epithelium in response to embryo recognition.
(Abstr.) Annual Meeting Belgian Soc. Cell Biol./ German Soc. Cell Biol., Bonn 1985. Europ. J. Cell Biol. 36, Suppl. 7, 74 (1985)
pdf-download (315 KB)
BRÜMMER, F., WINTERHAGER, E., DENKER, H.-W. and HÜLSER, D.F.:
Cell-cell communication via gap junctions in rabbit uterine epithelium related to implantation.
(Abstr.) Annual Meeting Belgian Soc. Cell Biol. /German Soc. Cell Biol., Bonn 1985. Europ. J. Cell Biol. 36, Suppl. 7, 11 (1985)
pdf-download (301 KB)
WINTERHAGER, E. und DENKER, H.-W.:
Unterschiedliche Membrandifferenzierung im Uterusepithel gravider und pseudogravider Kaninchen während der Periimplantationsphase.
In: Physiologie und Pathologie der Fortpflanzung. Verhandlungsbericht, IX. Veterinär-Humanmedizinische Gemeinschaftstagung, Deutsche Gesellschaft zum Studium der Fertilität und Sterilität, Hannover 1984 (K. Semm, J. Hahn, H. Merkt, E. Grunert, L. Mettler, eds.) pp. 136-139 (Abstr. in: Zuchthygenie 19, 117, 1984)
pdf-download (1.19 MB)
DENKER, H.-W.:
Proteases of the blastocyst and of the uterus.
In: Proteins and Steroids in Early Pregnancy (H.M. Beier and P. Karlson, eds.). Berlin: Springer-Verlag, 1982, pp. 183-208. DOI: 10.1007/978-3-642-67890-5_16
SpringerLink
pdf-download (10.1 MB)
MITCHELL, J.A. and DENKER, H.-W.:
Changes in endometrial arylamidase during implantation in the guinea pig.
Abstract No. 66, Annual Conference of the Society for the Study of Fertility, Sutton Bonington, 1982
pdf-download (246 KB)
DENKER, H.-W.:
Endometrial arylamidase secretion: a sensitive parameter of steroid hormone action and of embryo-maternal interrelationships in the rabbit.
In: Steroid Induced Uterine Proteins (M. Beato, ed.) Amsterdam/New York: Elsevier/North-Holland Biomedical Press, 1980, pp. 121-131. pdf-download (3.73 MB)
DENKER, H.-W. and FRITZ, H.:
Enzymic characterization of rabbit blastocyst proteinase with synthetic substrates of trypsin-like enzymes.
Hoppe-Seyler’s Z. Physiol. Chem. 360, 107-113 (1979). PubMed pdf-download (3.19 MB)
DENKER, H.-W., ENG, L.A. and HAMNER, C.E.:
Studies on the early development and implantation in the cat. II. Implantation: proteinases.
Anat. Embryol. 154, 39-54 (1978).
PubMed
SpringerLink
DENKER, H.-W.:
The role of trophoblast-dependent and of uterine proteases in initiation of implantation.
In: Human Fertilization. International Workshop Essen, July 1976 (H. Ludwig and P.F. Tauber, eds.). Stuttgart: Georg Thieme Publishers, 1978, pp. 204-214. pdf-download (24.0 MB)
DENKER, H.-W.:
The role of trophoblastic factors in implantation.
In: Novel Aspects of Reproductive Physiology. Seventh Brook Lodge Workshop on Problems of Reproductive Physiology, 1977 (C.H. Spilman and J.W. Wilks, eds.). New York/London: Spectrum Publications, Inc., 1978 (distributed by Halsted Press, a division of John Wiley & Sons, New York etc.), pp. 181-212. pdf-download (67.7 MB)
DENKER, H.-W.:
Implantation: The Role of Proteinases, and Blockage of Implantation by Proteinase Inhibitors.
Berlin-Heidelberg-New York: Springer-Verlag, 1977 (= Adv. Anat. Embryol. Cell Biol., Vol. 53, Fasc. 5). (English version of Habilitation Thesis). Print-ISBN: 978-3-540-08479-2. DOI: 10.1007/978-3-642-66781-7
PubMed
actual flyer
original flyer (21.1 MB)
German National Library
DENKER, H.-W. und KÜHNEL, W.:
Experimente zum Wirkungsmechanismus von Kupfer-IUDs beim Kaninchen: Lokale Beeinflussung der endometrialen Aminosäure-Arylamidase-Aktivität durch Kupfer-IUDs.
Verh. Anat. Ges. 71, Anat. Anz. Suppl. 142, 531-535 (1977). PubMed pdf-download (1.89 MB)
DENKER, H.-W.:
Mechanismen der Implantation des Säugetierembryos und ihre experimentelle Beeinflussung.
Habilitationsschrift, Medizinische Fakultät an der Rheinisch-Westfälischen Technischen Hochschule, Aachen 1976. German National Library
DENKER, H.-W.:
Copper IUD-induced loss of endometrial arylamidase activity in the rabbit.
Biol. Reprod. 15, 519-522 (1976). DOI: 10.1095/biolreprod15.4.519
PubMed
Biol.Reprod. Website (free)
DENKER, H.-W. und STANGL, R.:
Versuche zur Lokalisierung und Abgrenzung verschiedener Aminosäure-Arylamidasen in Uterus und Blastozyste des Kaninchens.
XVII. Symp. Ges. f. Histochemie, Bozen 1974. Acta Histochemica, Suppl. XVI, 249-257 (1976). PubMed pdf-download (3.46 MB)
DENKER, H.-W.:
Wechselbeziehungen zwischen Blastozyste und Endometrium bei der Implantation: Beeinflussung der endometrialen Aminosäure-Arylamidase-Aktivität durch die Blastozyste.
Verh. Anat. Ges. 70, Anat. Anz. Suppl. 140, 839-847 (1976). PubMed pdf-download (3.49 MB)
DENKER, H.-W.:
Effects of blastocysts and of copper IUDs on endometrial arylamidase in the rabbit.
(Abstr.) Anatomical Society of Great Britain and Ireland, Spring Meeting, Cambridge, 1976. J. Anat. (Lond.) 122, 720 (1976)
pdf-download (246 KB)
VAN HOORN, G. and DENKER, H.-W.:
Effect of the blastocyst on a uterine amino acid arylamidase in the rabbit.
J. Reprod. Fert. 45, 359-362 (1975).
PubMed
Reproduction pdf-download
DENKER, H.-W. and VAN HOORN, G.:
Peptidases related to implantation in the rabbit: local stimulation of endometrial arylamidase secretion by the blastocyst immediately preceding implantation.
(Abstr.) VIIth Ann. Meet. Soc. Study of Reproduction, Ottawa, Canada, 1974
pdf-download (341 KB)
DENKER, H.-W.:
Blastocyst enzymes and implantation in the rabbit.
(Abstr.) VIth Ann. Meet. Soc. Study of Reproduction, Athens, Georgia, 1973. Biology of Reproduction 9, 102-103 (1973)
pdf-download (327 KB)
DENKER, H.-W.:
Enzym-Topochemie von Frühentwicklung und Implantation des Kaninchens. III. Proteasen.
Histochemie 25, 344-360 (1971). PubMed pdf-download (2.72 MB, with kind permission of Springer, Heidelberg)
DENKER, H.-W.:
Zur Enzym-Topochemie von Frühentwicklung und Implantation des Kaninchens.
Dissertation, Medizinische Fakultät der Philipps-Universität, Marburg/Lahn 1970. German National Library