Endometrial apoptosis and neutrophil infiltration during menstruation exhibits spatial and temporal dynamics that are recapitulated in a mouse model

Abstract

Menstruation is characterised by synchronous shedding and restoration of tissue integrity. An in vivo model of menstruation is required to investigate mechanisms responsible for regulation of menstrual physiology and to investigate common pathologies such as heavy menstrual bleeding (HMB). We hypothesised that our mouse model of simulated menstruation would recapitulate the spatial and temporal changes in the inflammatory microenvironment of human menses. Three regulatory events were investigated: cell death (apoptosis), neutrophil influx and cytokine/chemokine expression. Well-characterised endometrial tissues from women were compared with uteri from a mouse model (tissue recovered 0, 4, 8, 24 and 48 h after removal of a progesterone-secreting pellet). Immunohistochemistry for cleaved caspase-3 (CC3) revealed significantly increased staining in human endometrium from late secretory and menstrual phases. In mice, CC3 was significantly increased at 8 and 24 h post-progesterone-withdrawal. Elastase+ human neutrophils were maximal during menstruation; Ly6G+ mouse neutrophils were maximal at 24 h. Human endometrial and mouse uterine cytokine/chemokine mRNA concentrations were significantly increased during menstrual phase and 24 h post-progesterone-withdrawal respectively. Data from dated human samples revealed time-dependent changes in endometrial apoptosis preceding neutrophil influx and cytokine/chemokine induction during active menstruation. These dynamic changes were recapitulated in the mouse model of menstruation, validating its use in menstrual research.

Menstruation: science and society

“…menstruation has been reported to recapitulate several of the local events that occur in the human endometrium at the time of menstruation, these being apoptosis preceding cytokine and chemokine expression and extensive neutrophil influx into the endometrium. 82 There is an interesting recent discovery of a previously unrecognized menstruating rodent, the spiny mouse, which may provide another tool in the study of menstruation. 41 The combination of observational data generated from well-categorized human endometrial tissue and mechanistic studies in validated animal models will facilitate definitive experiments to determine menstrual physiology and pathology.…”

“…There is an increase in endometrial blood vessel permeability and fragility, tissue breakdown, and an influx of innate immune cells into the endometrium, particularly neutrophils and macrophages. 82,84,85 V. Cessation of menstruation. The cessation of menstrual bleeding and endometrial repair require 3 closely related events: these being vasoconstriction of the highly specialized spiral arterioles, local endometrial hemostasis, and reepithelialization of the injured endometrial mucosa ( Figure 6).…”

Impaired inflammatory state of the endometrium: a multifaceted approach to endometrial inflammation. Current insights and future directions

“…Leukocytes are scattered in the stroma with aggregations around the glands [36] in a menstrual cycle-dependent fashion: their proportion among stromal cells ranges from 8% in proliferative endometrium to 32% in early pregnancy decidua [31]. Neutrophils are the prominent leukocytes during menstruation and start increasing after progesterone withdrawal in late secretory phase [37]. Macrophages, eosinophils and activated mast cells have a similar distribution, yet in smaller proportions [17,30,37].…”

WOMEN IN REPRODUCTIVE SCIENCE: My WOMBan’s life: understanding human endometrial function

“…Colin Finn (Finn & Pope 1984) first developed a mouse model for menstruation, providing proof that both progesterone withdrawal and artificial decidualization (which occurs only in response to an embryo in mice), were essential for menstrual breakdown. This was refined by us in the early 2000s (Brasted et al 2003) and has since been modified by others (Menning et al 2012, Xu et al 2013, Cousins et al 2014, Armstrong et al 2017) providing insights into molecular and cellular mechanisms of breakdown and repair detailed below.…”