Involvement of Bone Marrow-Derived Vascular Progenitor Cells in Neovascularization During Formation of the Corpus Luteum in Mice1

Abstract

Neovascularization is necessary for formation of the corpus luteum (CL) and includes angiogenesis and vasculogenesis. Vasculogenesis is the formation of new blood vessels by bone marrow-derived endothelial progenitor cells. Here we investigated whether vasculogenesis occurs in neovascularization during CL formation. Mice transplanted with bone marrow from transgenic mice expressing green fluorescent protein (GFP) were injected with equine chorionic gonadotropin and human chorionic gonadotropin (hCG) to induce ovulation and subsequent CL formation. Immunohistochemistry was performed on the ovaries obtained before hCG injection and at 6, 12, and 24 h after hCG injection using antibodies for CD34 or CD31 (an endothelial cell marker), platelet-derived growth factor receptor beta (PDGFR-beta, a pericyte marker), F4/80 (a macrophage marker), and GFP (a bone marrow-derived cell marker). Cells immunostained for CD34, PDGFR-beta, F4/80, and GFP were present in the theca cell layer of the preovulatory follicle before hCG injection. Each of these cell types invaded the granulosa cell layer after hCG injection, and a number of them were observed in the CL 24 h after hCG injection. Fluorescence-based immunohistochemistry or double immunohistochemical staining revealed that a few CD34/CD31-positive cells and PDGFR-beta-positive cells were also positive for GFP in the preovulatory follicle and CL, and that many of the GFP-positive cells recruited to the CL during CL formation were F4/80-positive macrophages. In conclusion, bone marrow-derived vascular progenitor cells and macrophages contribute to neovascularization during CL formation.

Locally existing endothelial cells and pericytes in ovarian stroma, but not bone marrow-derived vascular progenitor cells, play a central role in neovascularization during follicular development in mice

“…In this model, bone marrow-derived vascular progenitor cells are tracked by transplanting bone marrow cells from GFP-transgenic mice into the recipient mice whose immune systems were compromised by irradiation. The irradiation damages the ovaries [10], which makes it difficult to examine physiological development of follicles in the BMT model. In addition, when the mice are treated with gonadotropins, the damaged basement membrane of the preovulatory follicle allows vascular endothelial cells to enter the granulosa cell layer before ovulatory LH surge [10].…”

“…The irradiation damages the ovaries [10], which makes it difficult to examine physiological development of follicles in the BMT model. In addition, when the mice are treated with gonadotropins, the damaged basement membrane of the preovulatory follicle allows vascular endothelial cells to enter the granulosa cell layer before ovulatory LH surge [10]. Furthermore, low dose irradiation is reported to stimulate vasculogenesis in various organs [16,17].…”

“…Regarding the onset of vascularization of the theca cell layer, it has been thought that endothelial cells are recruited to the thecal layer from the blood vessels in the adjacent stroma. Interestingly, we recently found that bone marrow-derived vascular progenitor cells contribute to neovascularization during corpus luteum formation, suggesting the involvement of vasculogenesis in corpus luteum formation [10]. Neovascularization includes angiogenesis and vasculogenesis.…”

“…Pericytes serve as structural components of blood vessels that maintain vascular integrity [13,14]. Recently, we reported that pericytes are present in the ovary and contribute to neovascularization during the corpus luteum formation in mice [10] although the presence of pericytes in the rodent ovary has been controversial [15]. However, it is unclear how the pericyte distribution changes during follicular growth, where pericytes come from, and whether pericytes contribute to neovascularization in the follicle during follicular growth.…”

The critical importance of ovarian angiogenesis

“…Whilst, Turner et al (2011) recently demonstrated that macrophages play a crucial role in maintaining vascular integrity in mice. This concept is further supported by the observations that bone marrow-derived vascular progenitor cells and macrophages contribute to neovascularisation during CL formation (Kizuka et al 2012). The role of macrophages is potentially the most important since these cell can be differentiated into the 'tissue remodelling' M2 phenotype by the luteal microenvironment.…”