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.
BACKGROUND
Neovascularization is necessary for follicular growth. Vascularization is first observed in preantral follicles, and thereafter the vasculature markedly increases in follicles undergoing development. Neovascularization includes angiogenesis and vasculogenesis. Vasculogenesis is the formation of new blood vessels by bone marrow-derived endothelial progenitor cells. It is unclear whether vasculogenesis occurs during follicular growth. Blood vessels must be mature to be functional blood vessels. Mature blood vessels are characterized by the recruitment of pericytes. However, it is unclear where pericytes come from and whether they contribute to neovascularization in the follicle during follicular growth. In this study, we investigated whether bone marrow-derived progenitor cells that differentiate into vascular endothelial cells or pericytes contribute to neovascularization during follicular growth.


METHODS
A parabiosis model was used in this study. Six-week-old wild-type and transgenic female mice expressing green fluorescent protein (GFP) were conjoined between the lateral abdominal regions to create a shared circulatory system. After 6 weeks, the ovaries were obtained and immunostained for CD31/CD34 (a vascular endothelial cell marker), platelet-derived growth factor receptor-β (PDGFR-β) (a pericyte marker), and GFP (a bone marrow-derived cell marker).


RESULTS
Cells that were positive for CD34 and PDGFR-β were observed in the stroma adjacent to the primary or early preantral follicles and in the theca cell layer of the follicles from the late preantral stage to the preovulatory stage. CD31/CD34 and GFP double-positive cells were observed in the theca cell layer of the follicle from the antral stage to the preovulatory stage while the number of double-positive cells in the preovulatory follicles did not increase. PDGFR-β and GFP double-positive cells were observed in the theca cell layer of the preovulatory follicle but not in the smaller follicle.


CONCLUSIONS
Locally existing endothelial cells and pericytes in the stroma play a central role in the neovascularization during follicular growth, while bone marrow-derived endothelial cells and pericytes partially contribute to this process.
Fumie
F
Kizuka-Shibuya
Nobuko
N
Tokuda
Kiyoshi
K
Takagi
Yasuhiro
Y
Adachi
Lifa
L
Lee
Isao
I
Tamura
Ryo
R
Maekawa
Hiroshi
H
Tamura
Takashi
T
Suzuki
Yuji
Y
Owada
Department of Obstetrics and Gynecology, Yamaguchi University Graduate School of Medicine, Minamikogushi 1-1-1, Ube 755-8505, Japan. sugino@yamaguchi-u.ac.jp.
Norihiro
N
Sugino
D000818:Animals; D018952:Antigens, CD34 / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D002450:Cell Communication; D042783:Endothelial Cells / Q000378:metabolism / Q000502:physiology*; D066026:Endothelial Progenitor Cells / Q000378:metabolism / Q000502:physiology*; D005260:Female; D049452:Green Fluorescent Proteins / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D018919:Neovascularization, Physiologic; D006080:Ovarian Follicle / Q000098:blood supply*; D010227:Parabiosis; D020286:Pericytes / Q000378:metabolism / Q000502:physiology*; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction; D017154:Stromal Cells / Q000378:metabolism / Q000502:physiology*
D018952:Antigens, CD34; D015415:Biomarkers; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D049452:Green Fluorescent Proteins; D020797:Receptor, Platelet-Derived Growth Factor beta