VEGF-A induced hyperpermeability of blood-retinal barrier endothelium in vivo is predominantly associated with pinocytotic vesicular transport and not with formation of fenestrations. Vascular endothelial growth factor-A.
OBJECTIVE
In tissues outside the brain, vascular endothelial growth factor-A (VEGF) causes vascular hyper-permeability by opening of inter-endothelial junctions and induction of fenestrations and vesiculo-vacuolar organelles (VVOs). In preliminary studies, we observed that in blood-retinal barrier endothelium, other cellular mechanisms may underlie increased permeability caused by VEGF. This was further investigated in material of an in vivo experimental model of VEGF-induced retinopathy.


METHODS
Two monkeys received 4 intravitreal injections of 0.5 microg VEGF in one eye and PBS in the other eye prior to sacrifice at day 9. One monkey received 12 injections of 1.25 microg VEGF in one eye and PBS in the other eye prior to sacrifice at day 24. As a control, an untreated eye of a fourth monkey was studied.


RESULTS
In the high-dose VEGF-injected eye, fluorescein angiography showed intense retinal micro-vascular leakage. This leakage was also demonstrated by immunohistochemistry demonstrating extravasation of endogenous fibrinogen and IgG. However, in these leaky blood vessels the number of pinocytotic vesicles (caveolae) at the endothelial luminal membrane were significantly higher and, only in the VEGF-injected eyes, these pinocytotic vesicles transported plasma IgG. By electron microscopy, no fenestrations or VVOs were found in the endothelial cells of the VEGF-injected eyes.


CONCLUSIONS
We conclude that increased vascular permeability for plasma proteins induced by VEGF in blood-retinal barrier endothelium is predominantly caused by a mechanism involving active trans-endothelial transport via pinocytotic vesicles and not by formation of endothelial fenestrations or VVOs.
Hofman
P
P
Department of Ophthalmology, Academic Medical Center, Amsterdam, The Netherlands. p.hofman@ioi.knaw.nl
Blaauwgeers
H G
HG
Tolentino
M J
MJ
Adamis
A P
AP
Nunes Cardozo
B J
BJ
Vrensen
G F
GF
Schlingemann
R O
RO
D000818:Animals; D001813:Blood-Retinal Barrier / Q000187:drug effects* / Q000502:physiology*; D002199:Capillary Permeability / Q000187:drug effects*; D016228:Endothelial Growth Factors / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005451:Fluorescein Angiography; D007150:Immunohistochemistry; D008252:Macaca fascicularis; D008854:Microscopy, Electron; D016253:Microscopy, Immunoelectron; D010873:Pinocytosis / Q000502:physiology*; D012171:Retinal Vessels / Q000378:metabolism / Q000648:ultrastructure; D022161:Transport Vesicles / Q000502:physiology*; D042461:Vascular Endothelial Growth Factor A
D016228:Endothelial Growth Factors; D042461:Vascular Endothelial Growth Factor A