103. ROLE OF CANDIDATE STEM/PROGENITOR CELLS IN A MOUSE MODEL OF ENDOMETRIAL MENSTRUAL BREAKDOWN AND REPAIR

Abstract

Adult stem/progenitor cells (SPC) identified in human and mouse endometrium may be responsible for its remarkable regenerative capacity (1), however a functional role for SPC in menstruation is yet to be established. This study aimed to identify label retaining cells (LRC) as candidate epithelial SPC involved in the rapid re-epithelisation of the uterine surface in a mouse model; tissue SPCs are quiescent and will retain label (BrdU), while label is diluted out as transit amplifying cells proliferate. Mice were ovariectomised and endometrial breakdown and repair induced, mimicking menstruation in women (2). BrdU (50µg/g) was administered intraperitoneally 8.5 days before endometrial repair. Tissue was collected to assess initial labelling, and following four chase periods prior to and during endometrial repair (n=3-5 animals/group) and immunostained for BrdU. LRC were categorised as minimal (<50% nuclear label), partial (50-75%) and full (100%) and counted in the luminal (LE) and glandular (GE) epithelial compartments for each group. The majority of LE (91.4±1.9%; mean±SEM) and 35±3.8% of GE were initially labelled. During breakdown and repair the percentage of full LE LRC (38±13.1% vs 1.3±1.1%) and partial LE LRC (49.1±4.3% vs 1.8±0.7%) significantly decreased (p≤0.01) whilst minimal LRC significantly increased (12.9±3.5% vs 85.2±4.3%; p≤0.001) indicating dilution of BrdU label as cells proliferated. In contrast full, partial and minimal GE LRC did not significantly change throughout endometrial breakdown and repair. The rapid dilution of BrdU label in the LE suggests that the transit amplifying population are responsible for the rapid proliferation observed, whilst the lack of change of BrdU in the GE suggests that GE may be a source of SPC. Double immunofluorescence and confocal microscopy are currently underway to further characterise the LRC population in this model. This study provides some of the first insights into the contribution of candidate SPC to endometrial repair.