Tissue-type plasminogen activator is a neuroprotectant in the mouse hippocampus
Ramiro Echeverry, … , Johanna Guzman, Manuel Yepes
Ramiro Echeverry, … , Johanna Guzman, Manuel Yepes
Published May 3, 2010
Citation Information: J Clin Invest. 2010;120(6):2194-2205. https://doi.org/10.1172/JCI41722.
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Research Article Neuroscience

Tissue-type plasminogen activator is a neuroprotectant in the mouse hippocampus

Abstract

The best-known function of the serine protease tissue-type plasminogen activator (tPA) is as a thrombolytic enzyme. However, it is also found in structures of the brain that are highly vulnerable to hypoxia-induced cell death, where its association with neuronal survival is poorly understood. Here, we have demonstrated that hippocampal areas of the mouse brain lacking tPA activity are more vulnerable to neuronal death following an ischemic insult. We found that sublethal hypoxia, which elicits tolerance to subsequent lethal hypoxic/ischemic injury in a natural process known as ischemic preconditioning (IPC), induced a rapid release of neuronal tPA. Treatment of hippocampal neurons with tPA induced tolerance against a lethal hypoxic insult applied either immediately following insult (early IPC) or 24 hours later (delayed IPC). tPA-induced early IPC was independent of the proteolytic activity of tPA and required the engagement of a member of the LDL receptor family. In contrast, tPA-induced delayed IPC required the proteolytic activity of tPA and was mediated by plasmin, the NMDA receptor, and PKB phosphorylation. We also found that IPC in vivo increased tPA activity in the cornu ammonis area 1 (CA1) layer and Akt phosphorylation in the hippocampus, as well as ischemic tolerance in wild-type but not tPA- or plasminogen-deficient mice. These data show that tPA can act as an endogenous neuroprotectant in the murine hippocampus.

Authors

Ramiro Echeverry, Jialing Wu, Woldeab B. Haile, Johanna Guzman, Manuel Yepes

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Figure 5

tPA-induced delayed preconditioning.

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tPA-induced delayed preconditioning. (A–C) Mean survival in hippocampal ...
(A–C) Mean survival in hippocampal neurons exposed to OGD conditions (55 minutes) 24 hours after treatment with 60 nM tPA or 1 μM itPA (A); or with a combination of 60 nM tPA and 140 nM α2-antiplasmin, 1.4 μM aprotinin (Apro), 20 mM EACA, 100 nM RAP, 10 μM MK-801, or 50 μM DL-AP5; or with 200 nM plasminogen (Plg) alone or 100 nM plasmin alone or RAP alone (B and C). In A: *P < 0.05 compared with cells under normoxic conditions; **P < 0.05 compared with untreated neurons under OGD conditions and with cells treated with itPA. In B and C: *P < 0.05 compared with untreated cells under OGD conditions; **P < 0.05 compared with untreated cells; ***P < 0.05 compared with cells treated with tPA or plasmin alone. n = 20 for each observation in A and B and n = 15 in C. Error bars denote SD. (D) Western blot analysis detecting the expression of the NR2A subunit of the NMDAR in hippocampal neurons incubated with 60 nM tPA or 100 nM plasmin. (E) Mean neuronal survival following incubation with 250 μM KA alone or 24 hours after treatment with 60 nM tPA. *P < 0.05 compared with untreated cells; **P < 0.05 compared with KA-treated cells. n = 10. Error bars denote SD in all panels.