Excessive ovarian stimulation up-regulates the Wnt-signaling molecule DKK1 in human endometrium and may affect implantation: an in vitro co-culture study.
BACKGROUND
High serum estradiol (E2) levels following ovarian stimulation lead to reduced implantation and pregnancy rates, yet the underlying mechanisms remain unknown. We investigated if aberrant expression of genes in the Wnt-signaling pathway may be involved.


METHODS
Microarray and real-time PCR analysis were performed to analyze gene expression profiles of endometrial samples taken at day hCG + 7 in stimulated cycles, and days LH + 7 and LH + 10 in natural cycles. Expression of several Wnt-signaling transcripts, including Dickkopf homolog 1 (DKK1), DKK2 and secreted frizzled-related protein 4 (sFRP4), was analyzed throughout the menstrual cycle. JAr spheroid/Ishikawa endometrial cell co-culture experiments were established to study effects of DKK1 on spheroid attachment in vitro.


RESULTS
We identified 351 differentially expressed genes. Endometrial samples taken at hCG + 7 had similar expression profiles to those at LH + 10. DKK1 transcripts were up-regulated and DKK2 and sFRP4 were down-regulated in the stimulated compared with LH + 7 group (all P < 0.05). DKK1 transcripts were low in proliferative phase (PS) and increased in late-secretory phase (LS, P < 0.05), although DKK2 peaked in mid-secretory phase (P < 0.05). sFRP4 transcripts were high in PS. Treatment of spheroid with recombinant human DKK-1 protein dose-dependently suppressed (P < 0.05 versus control) spheroids attachment onto endometrial cells (associated with decreased beta-catenin protein): this suppression was nullified by anti-DKK1 antibody.


CONCLUSIONS
Gene expression patterns in stimulated cycles resembled those of LS in natural cycles, when the implantation window is about to close, suggesting high serum E2 and/or progesterone concentrations may advance endometrial development, altering the implantation window and possibly decreasing pregnancy rate. Aberrant expression of DKK1 might impair embryo attachment and implantation in vivo.
Liu
Yunao
Y
Department of Obstetrics and Gynaecology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China.
Kodithuwakku
Suranga P
SP
Ng
Pak-Yiu
PY
Chai
Joyce
J
Ng
Ernest H Y
EH
Yeung
William S B
WS
Ho
Pak-Chung
PC
Lee
Kai-Fai
KF
D018920:Coculture Techniques; D015536:Down-Regulation; D010064:Embryo Implantation / Q000235:genetics*; D004717:Endometrium / Q000187:drug effects* / Q000378:metabolism*; D005260:Female; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis*; D010062:Ovulation Induction / Q000009:adverse effects*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D015854:Up-Regulation; D051153:Wnt Proteins / Q000502:physiology*; D000094742:Secreted Frizzled-Related Proteins
D036341:Intercellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D051153:Wnt Proteins; C501126:DKK1 protein, human; C498622:DKK2 protein, human; C118723:SFRP4 protein, human; D000094742:Secreted Frizzled-Related Proteins