Molecular and Cellular Biology of Plasminogen Activation

i010i
Activation of Latent PDGF-CC by Tissue Plasminogen Activator
Impairs Blood Brain Barrier Integrity during Ischemic Stroke
Su EJ 1 , Fredriksson L 2 , Geyer M 1 , Folestad E 2 , Cale J 1 , Mann K 1 , Gao Y 3 , Pietras K 2 , Andreé J 4 , Yepes M 5 ,
Strickland D 3 , Betsholtz C 4 , Eriksson U 2 , Lawrence DA* 1
1Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan
Medical School, Ann Arbor, Michigan, USA;
2 Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institutet, Stockholm, Sweden;
3Center for Vascular and Inflammatory Disease and Departments of Surgery and Physiology, School of
Medicine, University of Maryland, Baltimore, Maryland, USA;
4Laboratory of Vascular Biology, Division of Matrix Biology, Department of Medical Biochemistry and
Biophysics, Karolinska Institutet, Stockholm, Sweden;
5Department of Neurology and Center for Neurodegenerative Disease, Emory University School of
Medicine, Atlanta, Georgia, USA
Presenting author e-mail: dlawrenc@umich.edu
The current treatment for ischemic stroke, intravenous tPA, only benefits a limited number of
patients. This is due in part to the requirement that tPA be administered within 3 hours of the
onset of symptoms. The reasons for this time constraint are not known but may be due to the
unique activities that tPA has in the brain beyond its well established role as a fibrinolytic enzyme.
For example, tPA has been shown to play a role in regulating cerebrovascular permeability
after stroke; however, the specific substrate for tPA in brain is not known. The recent discovery
that tPA cleaves latent PDGF-CC lead us to hypothesize that tPA may mediate cerebrovascular
permeability via activation of latent PDGF-CC. To test this possibility, active PDGF-CC was
injected directly into the CSF in the absence of ischemia and the extravasation of Evans Blue
dye in the brain was examined. These studies showed a significant increase in Evans Blue
extravasation after active PDGF-CC injection. This effect was similar to that seen with tPA
injection, suggesting that tPA and PDGF-CC may be acting on the same pathway. To test this
neutralizing antibodies against PDGF-CC were co-injected with tPA and were found to block
the effect of tPA. To evaluate whether PDGF-CC plays a role in regulating cerebrovascular
permeability during stroke, the PDGF receptor inhibitor Gleevec was used in a photothrombotic
stroke model. Stroke is induced specifically in the middle cerebral artery by the local activation
of intravenous Rose Bengal with a cold laser. Mice treated with Gleevec showed significant
reductions in Evans Blue extravasation at 24-hours and stroke volumes at 72-hours, indicating a
strong effect of PDGF signaling on cerebrovascular integrity. Taken together, these data suggest
that PDGF-CC is a downstream substrate of tPA in the CNS. These studies may provide important
insights into new therapeutic strategies for treating stroke patients.
22 X I t h I n t e r n a t i o n a l W o r k s h o p o n