Oxygen glucose deprivation switches the transport of tPA across the blood-brain barrier from an LRP-dependent to an increased LRP-independent process.
OBJECTIVE
Despite uncontroversial benefit from its thrombolytic activity, the documented neurotoxic effect of tissue plasminogen activator (tPA) raises an important issue: the current emergency stroke treatment might not be optimum if exogenous tPA can enter the brain and thus add to the deleterious effects of endogenous tPA within the cerebral parenchyma. Here, we aimed at determining whether vascular tPA crosses the blood-brain barrier (BBB) during cerebral ischemia, and if so, by which mechanism.


METHODS
First, BBB permeability was assessed in vivo by measuring Evans Blue extravasation following intravenous injection at 0 or 3 hours after middle cerebral artery electrocoagulation in mice. Second, the passage of vascular tPA was investigated in an in vitro model of BBB, subjected or not to oxygen and glucose deprivation (OGD).


RESULTS
We first demonstrated that after focal permanent ischemia in mice, the BBB remains impermeable to Evans Blue in the early phase (relative to the therapeutic window of tPA), whereas at later time points massive Evans Blue extravasation occurs. Then, the passage of tPA during these 2 phases, was investigated in vitro and we show that in control conditions, tPA crosses the intact BBB by a low-density lipoprotein (LDL) receptor-related protein (LRP)-dependent transcytosis, whereas OGD leads to an exacerbation of tPA passage, which switches to a LRP-independent process.


CONCLUSIONS
We evidence 2 different mechanisms through which vascular tPA can reach the brain parenchyma, depending on the state of the BBB. As discussed, these data show the importance of taking the side effects of blood-derived tPA into account and offer a basis to improve the current thrombolytic strategy.
Benchenane
Karim
K
INSERM-Avenir, Centre Cyceron, Université de Caen, France.
Berezowski
Vincent
V
Fernández-Monreal
Mónica
M
Brillault
Julien
J
Valable
Samuel
S
Dehouck
Marie-Pierre
MP
Cecchelli
Roméo
R
Vivien
Denis
D
Touzani
Omar
O
Ali
Carine
C
D000818:Animals; D001812:Blood-Brain Barrier / Q000378:metabolism*; D002545:Brain Ischemia / Q000209:etiology / Q000378:metabolism*; D015687:Cell Hypoxia; D022162:Cytoplasmic Vesicles / Q000737:chemistry; D004730:Endothelium, Vascular / Q000166:cytology / Q000648:ultrastructure; D005947:Glucose / Q000502:physiology; D020244:Infarction, Middle Cerebral Artery / Q000150:complications; D026502:LDL-Receptor Related Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D008297:Male; D051379:Mice; D021381:Protein Transport; D010959:Tissue Plasminogen Activator / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology
D026502:LDL-Receptor Related Proteins; D010959:Tissue Plasminogen Activator; D005947:Glucose