Dilated Thin-Walled Blood and Lymphatic Vessels in Human Endometrium: A Potential Role for VEGF-D in Progestin-Induced Break-Through Bleeding

Abstract

Progestins provide safe, effective and cheap options for contraception as well as the treatment of a variety of gynaecological disorders. Episodes of irregular endometrial bleeding or breakthrough bleeding (BTB) are a major unwanted side effect of progestin treatment, such that BTB is the leading cause for discontinued use of an otherwise effective and popular medication. The cellular mechanisms leading to BTB are poorly understood. In this study, we make the novel finding that the large, dilated, thin walled vessels characteristic of human progestin-treated endometrium include both blood and lymphatic vessels. Increased blood and lymphatic vessel diameter are features of VEGF-D action in other tissues and we show by immunolocalisation and Western blotting that stromal cell decidualisation results in a significant increase in VEGF-D protein production, particularly of the proteolytically processed 21 kD form. Using a NOD/scid mouse model with xenografted human endometrium we were able to show that progestin treatment causes decidualisation, VEGF-D production and endometrial vessel dilation. Our results lead to a novel hypothesis to explain BTB, with stromal cell decidualisation rather than progestin treatment per se being the proposed causative event, and VEGF-D being the proposed effector agent.

Lymphatic Vessel Network Structure and Physiology

“…In women treated with progestin prior to hysterectomy for heavy menstrual bleeding, podoplanin-positive lymphatic vessels were enlarged in the endometrium compared to controls (Fig. 16) (277). …”

Cyclic Changes of Lymphatic and Venous Vessels in Human Endometrium

“…Arteries/arterioles drain into the corresponding venous system: the spiral artery/arterioles in the functionalis drain into capillary plexus which subsequently drain into venous lakes. Thus, all spinal arteries in the functionalis eventually drain into the draining venous vessels in the functionalis whereas straight arteries drain into the venous vessels in the basalis [29]- [31]. As mentioned above, all arterial, capillary plexus, venous and lymphatic vessels undergo menstrual cyclic changes and disintegrate for the menstrual bleeding.…”

“…In the late-secretory phase, when estradiol and progesterone levels decline, blood flow in the functionalis declines. Dilated lymphatic and venous vessels characteristically appear at the premenstrual phase, and this thin-walled lymphatic and venous vessels are also observed in progestin-induced break-through bleeding [26]- [29]. By functional study using mouse models, Rodgers et al reported that menstrual bleeding commences from the wall of an arterial or capillary vessels once previously constricted spiral arteries relax and blood flow recommences, which is responsible for 70% of blood loss [26].…”

“…The presence of dilated, disintegrating venous vessels in upper functionalis from the Day 25 -26 late-secretory phase also supports the venous bleeding for menstrual bleeding (Figure 3 and Figure 4). Endometrium exposed to progestin undergoes a well characterized series of morphological changes, including pseudo-decidualization of the stroma and appearance of abnormally dilated and thin-walled endometrial vessels [26]- [29]. This change represents dilated and disintegrating lymphatic and venous vessels observed in the premenstrual upper functionalis (Figure 4).…”

Pre-vascularization Enhances Therapeutic Effects of Human Mesenchymal Stem Cell Sheets in Full Thickness Skin Wound Repair

“…Measurements of epidermal thickness 34, collagen index 35, and microvessels, hair follicles and cell counting 36-38 in high-power field (HPF) were performed with ImageJ software. The vessel area, which is defined as the sum of all vessel segments/HPF, was quantified by ImageJ using the technique described previously 39. Five stained sections in each group for each time point were visualized using an Olympus IX71 microscopy, and three random views in each section were selected for quantitative assay.…”