239. Hormonal control of vascular mural cell recruitment in the mouse endometrium

Abstract

The human endometrium undergoes regular periods of growth and regression, including concomitant changes in the vasculature, and is one of the few adult tissues where significant angiogenesis (new blood vessel formation) and arteriogenesis (recruitment of vascular smooth muscle cells (VSMC) and pericytes) occurs on a routine, physiological basis. In this study, mouse models were used to investigate the effects of oestrogen and progesterone on endometrial vascular mural cell recruitment. The aim was to quantify changes in the proportion of vessels covered by α-smooth muscle actin (α-SMA, a marker of VSMC and pericytes) in hormone-treated ovariectomised mice. We hypothesised that relative vessel α-SMA coverage would increase following progesterone treatment (in conjunction with endothelial cell (EC) proliferation), but not following oestrogen treatment (when EC proliferation also occurs). Ovariectomised mice were given a single oestradiol (100 ng) or vehicle injection, before dissection 24 h later, or three consecutive daily injections of progesterone (1 mg) or vehicle. The percentage of vessel profiles with no, minimal, extensive or complete α-SMA coverage were quantified after CD31/α-SMA double immunostaining. There was a significant decrease in the percentage of vessel profiles with no α-SMA coverage following progesterone treatment (20 ± 4.3 % [mean ± SE] v. 57 ± 4.6 %, t₍₇₎ = 12.5, P < 0.001), and a significant increase in the percentage of vessels with minimal or extensive α-SMA coverage (44 ± 3.4 % v. 27 ± 3.7%, t₍₇₎ = 4.7, P < 0.001 and 27 ± 4.3% v. 5 ± 0.5%, t₍₇₎ = 5.8, P < 0.001, respectively), in comparison to vehicle-treated mice. The percentage of vessels with complete α-SMA coverage, representing vessels with a coat of VSMC, did not change significantly in comparison to vehicle-treated mice (8 ± 2.3% v. 10 ± 1.2%, t₍₇₎ = 0.6, P = 0.55). There were no significant changes in the percentage of vessels with differing α-SMA coverage in oestrogen-treated mice. In continuing studies, we will quantify the proportion of proliferating α-SMA positive cells and examine mouse endometrial tissues using a pericyte-specific marker.