Maturation of the fetal human choriocapillaris.
OBJECTIVE
The purpose of this study was to examine the structural and functional maturation of the choriocapillaris (CC) and to determine when fenestrations form, the capillaries are invested with pericytes, and the endothelial cells (ECs) became functional.


METHODS
Immunohistochemistry was performed on cryopreserved sections of embryonic/fetal human eyes from 7 to 22 weeks' gestation (WG), using antibodies against PAL-E, PV-1 (fenestrations), carbonic anhydrase IV (CA IV), eNOS, and alpha-smooth muscle actin (alphaSMA) and NG2 (two pericyte markers) and the EC marker (CD31). Alkaline phosphatase (APase) enzymatic activity was demonstrated by enzyme histochemistry. Transmission electron microscopy (TEM) was performed on eyes at 11, 14, 16, and 22 WG. Adult human eyes were used as the positive control.


RESULTS
All EC markers were present in the CC by 7 WG. PAL-E, CA IV, and eNOS immunoreactivities and APase activity were present in the CC by 7 to 9 WG. TEM analysis demonstrated how structurally immature this vasculature was, even at 11 WG: no basement membrane, absence of pericytes, and poorly formed lumens that were filled with filopodia. The few fenestrations that were observed were often present within the luminal space in the filopodia. Contiguous fenestrations and significant PV-1 were not observed until 21 to 22 WG. alphaSMA was prominent at 22 WG, and the maturation of pericytes was confirmed by TEM.


CONCLUSIONS
It appears that ECs and their precursors express enzymes present in adult CC well before they are structurally mature. Although ECs make tight junctions early in development, contiguous fenestrations and mature pericytes occur much later in development.
Baba
Takayuki
T
Wilmer Ophthalmological Institute, Johns Hopkins Hospital, Baltimore, Maryland 21287-9115, USA.
Grebe
Rhonda
R
Hasegawa
Takuya
T
Bhutto
Imran
I
Merges
Carol
C
McLeod
D Scott
DS
Lutty
Gerard A
GA
D000199:Actins / Q000378:metabolism; D000368:Aged; D000469:Alkaline Phosphatase / Q000378:metabolism; D000941:Antigens / Q000378:metabolism; D015415:Biomarkers; D002196:Capillaries / Q000196:embryology* / Q000378:metabolism / Q000648:ultrastructure; D030741:Carbonic Anhydrase IV / Q000378:metabolism; D002829:Choroid / Q000098:blood supply* / Q000196:embryology* / Q000378:metabolism; D004730:Endothelium, Vascular / Q000196:embryology / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D005865:Gestational Age; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000196:embryology / Q000378:metabolism / Q000648:ultrastructure; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D020286:Pericytes / Q000378:metabolism / Q000648:ultrastructure; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism; D000099216:Chondroitin Sulfate Proteoglycan 4
D000199:Actins; D000469:Alkaline Phosphatase; D000941:Antigens; D015415:Biomarkers; D030741:Carbonic Anhydrase IV; D052250:Nitric Oxide Synthase Type III; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D011509:Proteoglycans; D000099216:Chondroitin Sulfate Proteoglycan 4; C541116:ACTA2 protein, human