Bv. Zlokovic et al., EXPRESSION OF TISSUE-PLASMINOGEN ACTIVATOR IN CEREBRAL CAPILLARIES - POSSIBLE FIBRINOLYTIC FUNCTION OF THE BLOOD-BRAIN-BARRIER, Neurosurgery, 37(5), 1995, pp. 955-961
PREVIOUS WORK HAS shown that tissue plasminogen activator (tPA) is a k
ey enzyme in the control of fibrinolysis within the vascular system. T
he sources of brain tPA and the mechanisms by which tPA secretion and
production occur within cerebral microcirculation are not well establi
shed. In this study, expression of tPA was investigated in cerebral ca
pillaries and capillary-depleted brain isolated from cortices of 4- to
5-week-old rats and guinea pigs. In both species, a single tPA band o
f M(T) 67,000 was detected in cerebral capillaries by Western blot ana
lysis. The tPA signal was absent from capillary-depleted brain. These
results were corroborated at the messenger ribonucleic acid level. Rev
erse transcription-polymerase chain reaction analysis revealed the pre
sence of tPA complementary deoxyribonucleic acid in samples derived fr
om cerebral microvessels and demonstrated very low or undetectable tPA
expression in capillary-depleted brain. Immunohistochemical analysis
confirmed tPA localization in endothelial cells of brain capillaries.
We conclude that microvascular endothelium, i.e., the blood-brain barr
ier, may have a role in promoting plasmin-dependent fibrinolysis in br
ain microcirculation, Delineation of the molecular mechanisms of blood
-brain barrier-mediated fibrinolysis will likely contribute to future
stroke prevention efforts.