Vascular endothelial growth factor (VEGF) regulation by hypoxia inducible factor-1 alpha (HIF1A) starts and peaks during endometrial breakdown, not repair, in a mouse menstrual-like model

STUDY QUESTION: How is vascular endothelial growth factor (VEGF) expression regulated by hypoxia inducible factor 1 alpha (HIF1A) during menstruation? SUMMARY ANSWER: After progesterone (P4) withdrawal, HIF1A was activated and it directly up-regulated VEGF mRNA expression and this regulation was the highest during endometrium breakdown in the mouse menstrual-like model. WHAT IS KNOWN ALREADY: VEGF, an important angiogenic factor, is known to be essential for endometrial repair, particularly in angiogenesis and re-epithelialization. However, its upstream regulation has not been fully clarified. HIF1 is the first transcription factor response to hypoxia and is closely associated with angiogenesis; it is also an upstream regulator of VEGF mRNA. STUDY DESIGN, SIZE, DURATION: We investigated the changes in the expression of HIF1A and VEGF after P4 withdrawal and after HIF1A inhibition. The total number of mice used was 62. The treatment duration in the mouse menstrual-like model was 8 days. PARTICIPANTS/MATERIALS, SETTING, METHODS: The mouse menstrual-like model and mouse and human decidual endometrial stromal cells were established to mimic menstruation. Protein and mRNA expressions of HIF1A and VEGF were investigated by immunohistochemistry, Western blot and quantitative PCR. The direct interaction between HIF1A and the Vegf promoter was also investigated by chromatin immunoprecipitation. HIF1A inhibition in vivo and in vitro was achieved by administration of an HIF1A inhibitor and by siRNA knockdown, respectively. MAIN RESULTS AND THE ROLE OF CHANCE: HIF1A was translocated to the nucleus from 8 to 16 h after P4 withdrawal, while VEGF mRNA expression was the highest at 12 h. HIF1A directly bound to Vegf promoter during endometrial breakdown, which peaked at 12 h. HIF1A inhibition suppressed VEGF mRNA and protein expression in the mouse menstrual-like model and decidualized stromal cells. Inhibition of HIF1A also suppressed endometrial breakdown. LIMITATIONS, REASONS FOR CAUTION: Although HIF1A regulation of VEGF mRNA was confirmed in the mouse menstrual-like model and decidual endometrium stromal cells, the functional regulation of VEGF protein was not further determined. WIDER IMPLICATIONS OF THE FINDINGS: Here, we report that the functional regulation of VEGF was complicate in menstruation. We also report that HIF1A plays a key role in endometrial breakdown. STUDY FUNDING/COMPETING INTERESTS: The National Nature Science Foundation of China (No. 30901608), the National Basic Research Program of China (2010CB530403) and the National Science and Technology Support Program (No. 2012BAI32B05). The authors have no conflicts of interest to disclose. TRIAL REGISTRATION NUMBER: This study is not a clinical trial.