Menstruation is triggered by a fall in circulating progesterone (P4), and to a lesser
extent, oestradiol (E2) concentrations, and characterised by classical inflammatory
features in the endometrium: breakdown of the basal lamina, tissue oedema and an
influx of migratory leucocytes. During and following menstruation, endometrial
inflammation is resolved and the endometrium is repaired. The successful resolution
of acute inflammation in other tissues involves apoptosis and the phagocytic clearance
of apoptotic cells.
Human endometrial tissues were collected with informed patient consent and local
research ethics committee approval. C57Bl/6 mice underwent an induced
menstruation protocol (via sequential E2 and P4 exposure followed by P4 withdrawal),
both with and without experimental inhibition of apoptosis (using the pan-caspase
inhibitor, Q-VD-OPh).
Coordinated apoptosis and neutrophil recruitment were hypothesised to be
components of the menstrual event and to precede menstrual shedding in the human
endometrium. Immunoreactivity histoscoring for cleaved caspase-3 (CC3) revealed
extensive apoptosis in the normal human endometrium early in the ‘perimenstrual’
period, and careful stereological delineation of neutrophil (elastase+) recruitment
showed a significant influx coincident with menstrual tissue breakdown.
Apoptosis and neutrophil recruitment were hypothesised to follow similar courses in
the endometria of mice undergoing an induced menstruation protocol, recapitulating
human menstrual events. Immunoreactivity histoscoring for CC3 and stereological
investigation into neutrophil (Ly6G+) recruitment in mouse endometrial tissues
revealed almost identical extents and timings of apoptosis and neutrophil recruitment
in women. Whole genome array evidence of differential apoptosis-related gene transcription in
the endometria of women with heavy menstrual bleeding (HMB) compared to those of
women with normal menstrual bleeding (NMB) led to the hypothesis that apoptosis
may be dysregulated in women with HMB and that perhaps this may delay timely
repair of the endometrium and lead to prolonged bleeding in consequence. Candidate
differentially-regulated gene transcripts identified by the whole genome array were
validated by means of RT-qPCR, although immunoreactivity histoscoring for CC3 did
not reveal any differences in apoptosis or its localisation between women with NMB
and HMB at the menstrual cycle time-points examined.
Building on evidence of apoptotic transcriptional dysregulation in the endometria of
women with HMB, it was hypothesised that experimental inhibition of apoptosis (via
Q-VD-OPh) in a mouse model of induced menstruation could delay endometrial repair
and delay resolution of endometrial inflammation. Some evidence of delayed early
repair was obtained, alongside the discoveries of delayed inflammatory gene
transcription and increased decidual proliferation (BrdU+) in apoptosis-inhibited mice.
Apoptosis precedes the classical inflammatory features of menstruation in the human
and mouse endometrium, with inhibition of apoptosis in the latter altering repair and
the inflammatory micro-environment. An apoptosis-inhibited mouse model of
menstruation may therefore represent a viable model for the further study of heavy
menstrual bleeding
