NMDA receptors in the BBB
Pr. Vivien’s team is a leading expert in the molecular mechanisms sustaining the functions of the serine protease tissue plasminogen activator (tPA). The team has previously demonstrated that vascular tPA can cross the blood bran barrier (BBB) through LRP-dependent transcytosis in normal conditions and through LRP-independent transcytosis in ischemic-like conditions. Accordingly, invading tPA may participate (with endogenous tPA) in deleterious cascades, including promotion of excitotoxic neuronal loss, BBB leakage and inflammatory processes. tPA exerts some of its functions via its ability to promote N-methyl-D-aspartate glutamatergic receptors NMDARs signalling. Although, increasing evidence suggests that NMDARS are expressed on brain endothelial cells, little is known about the actual function of endothelial NMDARs.
The ESR will develop in vitro models to investigate the pathophysiology of the BBB and the neurovascular unit, with a special focus on the relationship between tPA and NMDARs signalling during stroke and multiple sclerosis. In cooperation with partner 5, the influence of tPA will be determined including its ability to alter BBB integrity, to influence endothelial NMDAR-mediated signalling (calcium videomicroscopy, ERK signalling) and toxicity. If endothelial NMDARs are confirmed to exert an important effect in stroke and/or multiple sclerosis, a mouse strain will be established in cooperation with partner 1, by crossing Slco1c1-CreERT2 mice (expressing Cre recombinase under the control of the brain endothelial specific Slco1c1 locus) with LoxP-GluN1 mice (Collaboration: P. Gressens, INSERM U676). This breeding should produce a mouse strain with selective disrupted expression of the GluN1 subunit of NMDA receptors in brain endothelial cells. When established, the colony will be used for in vitro experiments as described above, and in vivo, by performing the model of thromboembolic stroke established by Pr. Vivien’s team as well as the EAE (Experimental Autoimmune Encephalopathy) model of multiple sclerosis.
- Correa F, Gauberti M, Parcq J, Macrez R, Hommet Y, Obiang P, Hernangómez M, Montagne A, Liot G, Guaza C, Maubert E, Ali C, Vivien D, Docagne F (2011) Tissue plasminogen activator prevents white matter damage following stroke. J Exp Med 208: 1229-42.
- Parcq J, Bertrand T, Montagne A, Baron AF, Macrez R, Billard JM, Briens A, Hommet Y, Wu J, Yepes M, Lijnen HR, Dutar P, Anglés-Cano E, Vivien D (2012) Unveiling an exceptional zymogen: the single-chain form of tPA is a selective activator of NMDA receptor-dependent signaling and neurotoxicity. Cell Death Differ. 19:1983-91.
Tasks and methodology
- Mouse model of stroke
- Calcium videomicroscopy
- In vitro model of the BBB
- Characterization of a conditional gene deletion
University of Bern, Establishment of in vitro model of the BBB, 8 month
Schematic views of the current knowledge of the effects of tPA in the brain parenchyma
Effect of exogenous and endogenous tPA at the blood–brain barrier (BBB)
(1) Tissue-type plasminogen activator (tPA)-mediated plasminogen activation promotes clot lysis and subsequent blood flow restoration. (2) tPA interacts with endothelial LRPs, leading to NFkB activation and MMPs overexpression. (3) tPA can shed the ectodomain of astrocytic LRP receptors, inducing detachment of astrocytic end-feet processes. (4) tPA bound to LRP can activate latent PDGF-CC. Active PDGF-CC binds PDGF-R? on perivascular cells leading to BBB opening. LRP, lipoprotein receptor-related protein; MMPs, metalloproteinases; PDGF-CC, platelet-derived growth factor-CC (from Vivien et al., 2011).
Tissue-type plasminogen activator (tPA) in the brain parenchyma
In the brain parenchyma, tPA, released by neurons, was reported to potentiate NMDA receptors signalling to display either neurotrophic or neurotoxic effects, to reduce apoptotic neuronal and oligodendroglial deaths, to activate microglia after binding to annexin II and LRP and to be cleared from the extracellular space by astrocytes through a LRP-dependent mechanism. LRP, lipoprotein receptor-related protein; NMDA, N-methyl-D-aspartate receptor; EGF, epidermal growth factor (from Vivien et al., 2011).