P-361 Is HIF-2α involved in pre-menstrual conditioning of the endometrium to ensure optimal repair and prevent heavy menstrual bleeding?
Authors: Martínez Aguilar R , Rowley B , Walker K , Critchley H , Maybin J 
Published: June 2023

Abstract

Study question
Does HIF-2α play a key role in pre-menstrual conditioning of the non-pregnant endometrium to optimise menstrual breakdown/repair and prevent heavy menstrual bleeding (HMB)?

Summary answer
HIF-2 was higher in secretory endometrium of women with HMB versus controls, but manipulation of HIF-2α in the mouse model did not impact endometrial breakdown/repair.

What is known already
Hypoxia inducible factor (HIF) is the master regulator of the cellular response to hypoxia and has two common alpha isoforms (HIF-1α/HIF-2α) with overlapping but distinct target genes. We revealed that menstrual endometrial HIF-1α is necessary for normal menstrual endometrial repair. We detected HIF-2α in human endometrium exclusively during the secretory phase. The role of HIF-2α in the non-pregnant endometrium remains undetermined but was important for successful uterine implantation and lung vascular remodelling in mice. We hypothesised that endometrial HIF-2 is required for optimising the endometrial vasculature pre-menstrually to ensure appropriate vasoconstriction and endometrial repair during menstruation.

Study design, size, duration
HIF-2 was examined in human endometrial tissue and a mouse model of simulated menstruation. Hif2α +/- mice provided genetic reduction of HIF-2 during simulated menses versus wild-type littermates. HIF-2α was also pharmacologically inhibited during the secretory phase (PT2385 vs vehicle controls). To increase HIF-2, Hif1α +/- mice were treated with a HIF stabiliser (DMOG) during the secretory phase to increase HIF-2α followed by decreased HIF-1α at menses –mimicking human endometrial findings in women with HMB.

Participants/materials, setting, methods
Human secretory endometrium was collected (ethically approved and consented) from women with objectively measured HMB (n = 5) and controls (n = 4) and HIF-2 detected by Western blot. Mouse uterus was collected at the time of progesterone withdrawal (T0, decidualisation) and 8h (T8, endometrial breakdown) and 24h (T24, endometrial repair) after progesterone withdrawal. Histological endometrial repair and menstrual blood loss (MBL) were quantified. Decidualisation markers were examined by RT-qPCR. Endometrial vessel maturity and hypoxia were assessed using immunohistochemistry/immunofluorescence.

Main results and the role of chance
Human secretory endometrial HIF-2α protein levels were higher in those with HMB compared to controls (P &lt; 0.05). Genetic reduction of HIF-2α in our mouse model of menses (Hif2α +/-) revealed no significant differences in endometrial breakdown (T8) or repair grade (T24) and no difference in MBL at T8 versus controls. There were no significant differences in expression of decidualisation markers (Prlr/Prl3c1) and vessel maturity at T0 (CD31/α-SMA immunofluorescence staining), or the presence of hypoxia at T8 (pimonidazole immunohistochemistry staining). Pharmacological inhibition of HIF-2 at the time of decidualisation also showed no significant difference in endometrial repair at T24 versus controls. Increasing pre-menstrual HIF-2 via pharmacological stabilisation of HIF-2α in Hif1α+/- mice similarly did not significantly affect endometrial breakdown (T8) or repair (T24) or MBL at T8 versus vehicle treated controls, in contrast to our findings in women with HMB.

Limitations, reasons for caution
Histological scoring of endometrial breakdown/repair in the menstruation mouse model may not be sensitive enough to detect subtle endometrial changes with increased HIF-2α. As HIF-1α delays endometrial repair, an additional timepoint 36h after progesterone withdrawal may better capture any delay in endometrial repair as a result of increased secretory HIF-2.

Wider implications of the findings
HIF-2α may play a greater role in implantation than pre-menstrual conditioning of the endometrium to optimise menstrual breakdown/repair and limit menstrual blood loss. Although endometrial breakdown was not significantly affected by HIF-2, the impact on repair warrants further investigation to fully delineate the role of HIF-2 in the non-pregnant endometrium.

Trial registration number
Not applicable