Aberrant angiopoietins 1 to 2 and angiopoietin 2 to VEGF ratio in endometrium of excessive ovarian responders during in-vitro fertilization treatment

Abstract

Objectives: Angiogenesis is a process regulated by various angiogenic and anti-angioenic factors. To study the regulation of angiogenesis in human endometrium during the implantation window, we compared the expression of Angiopoietin 1 (Ang-1), Angiopoietin 2 (Ang-2) and VEGF mRNA and protein expression in the peri-implantation endometrium of patients between natural and stimulated cycles in assisted reproduction cycles. Methods: Human endometrial biopsies were collected 7 days after human chorionic gonadotrophins injection in stimulated cycles or after leutinizing hormone surge in natural cycles. Ang-1, Ang-2 and VEGF mRNA and protein expression were compared in natural cycles (N), stimulated cycles with peak serum E2 <20,000 pmol/L (moderate responders, M) and ≥20 000 pmol/ L (excessive responders, H) using real time PCR and Western blot analysis. Results: The expression of Ang-1 mRNA in endometrial tissue from Groups M and H was significantly lower (P<0.001) than that of Group N. However, Group H had significantly higher Ang-2 (P=0.002) and VEGF (P<0.05) mRNA expressions than that in Group M and N. Ang-1 to Ang-2 ratio was significantly lower in Groups M and H when compared to Group N, while Ang-2 to VEGF ratio was significantly higher in Group H than in Groups M and N (P=0.006). Negative correlation was found between Ang-1 to Ang-2 mRNA ratio and serum estrogen level (P=0.001). Using Western blot analysis, Ang-1 was down-regulated while Ang-2 was up-regulated in Group H. No significant difference was found in VEGF protein expression among the three groups. Conclusion: The decreased Ang-1 to Ang-2 ratio and increased Ang-2 to VEGF ratio in excessive responder suggested dys-regulation of angiogenesis during perimplantation period may affect normal endometrial development leading to lower implantation and pregnancy rate in these patients.