Tissue plasminogen activator promotes matrix metalloproteinase-9 upregulation after focal cerebral ischemia.
OBJECTIVE
Thrombolytic therapy with tissue plasminogen activator (tPA) in ischemic stroke is limited by increased risks of cerebral hemorrhage and brain injury. In part, these phenomena may be related to neurovascular proteolysis mediated by matrix metalloproteinases (MMPs). Here, we used a combination of pharmacological and genetic approaches to show that tPA promotes MMP-9 levels in stroke in vivo.


METHODS
In the first experiment, spontaneously hypertensive rats were subjected to 3 hours of transient focal cerebral ischemia. The effects of tPA (10 mg/kg IV) on ischemic brain MMP-9 levels were assessed by zymography. In the second experiment, wild-type (WT) and tPA knockout mice were subjected to 2 hours of transient focal cerebral ischemia, and MMP-9 levels and brain edema during reperfusion were assessed. Phenotype rescue was performed by administering tPA to the tPA knockout mice.


RESULTS
In the first experiment, exogenous tPA did not change infarct size but amplified MMP-9 levels in ischemic rat brain at 24 hours. Coinfusion of the plasmin inhibitor tranexamic acid (300 mg/kg) did not ameliorate this effect, suggesting that it was independent of plasmin. In the second experiment, ischemic MMP-9 levels, infarct size, and brain edema in tPA knockouts were significantly lower than WT mice. Administration of exogenous tPA (10 mg/kg IV) did not alter infarction but reinstated the ischemic MMP-9 response back up to WT levels and correspondingly worsened edema.


CONCLUSIONS
These data demonstrate that tPA upregulates brain MMP-9 levels in stroke in vivo, and suggest that combination therapies targeting MMPs may improve tPA therapy.
Tsuji
Kiyoshi
K
Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA.
Aoki
Toshiaki
T
Tejima
Emiri
E
Arai
Ken
K
Lee
Sun-Ryung
SR
Atochin
Dmitriy N
DN
Huang
Paul L
PL
Wang
Xiaoying
X
Montaner
Joan
J
Lo
Eng H
EH
D000818:Animals; D001812:Blood-Brain Barrier; D001921:Brain / Q000473:pathology; D020520:Brain Infarction / Q000473:pathology; D002545:Brain Ischemia / Q000378:metabolism* / Q000628:therapy*; D004195:Disease Models, Animal; D004487:Edema / Q000378:metabolism / Q000473:pathology; D004591:Electrophoresis, Polyacrylamide Gel; D005341:Fibrinolysin / Q000378:metabolism; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D007150:Immunohistochemistry; D007511:Ischemia / Q000473:pathology; D020778:Matrix Metalloproteinase 2 / Q000096:biosynthesis; D020780:Matrix Metalloproteinase 9 / Q000096:biosynthesis* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010477:Perfusion; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011918:Rats, Inbred SHR; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D015854:Up-Regulation
D012333:RNA, Messenger; D006859:Hydrogen; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9