title: Brain ischaemia induces shedding of a BDNF-scavenger ectodomain from TrkB receptors by excitotoxicity activation of metalloproteinases and γ-secretases.
abstract: Stroke remains a leading cause of death and disability in the world with limited therapies available to restrict brain damage or improve functional recovery after cerebral ischaemia. A promising strategy currently under investigation is the promotion of brain-derived neurotrophic factor (BDNF) signalling through tropomyosin-related kinase B (TrkB) receptors, a pathway essential for neuronal survival and function. However, TrkB and BDNF-signalling are impaired by excitotoxicity, a primary pathological process in stroke also associated with neurodegenerative diseases. Pathological imbalance of TrkB isoforms is critical in neurodegeneration and is caused by calpain processing of BDNF high affinity full-length receptor (TrkB-FL) and an inversion of the transcriptional pattern of the Ntrk2 gene, to favour expression of the truncated isoform TrkB-T1 over TrkB-FL. We report here that both TrkB-FL and neuronal TrkB-T1 also undergo ectodomain shedding by metalloproteinases activated after ischaemic injury or excitotoxic damage of cortical neurons. Subsequently, the remaining membrane-bound C-terminal fragments (CTFs) are cleaved by γ-secretases within the transmembrane region, releasing their intracellular domains (ICDs) into the cytosol. Therefore, we identify TrkB-FL and TrkB-T1 as new substrates of regulated intramembrane proteolysis (RIP), a mechanism that highly contributes to TrkB-T1 regulation in ischaemia but is minor for TrkB-FL which is mainly processed by calpain. However, since the secreted TrkB ectodomain acts as a BDNF scavenger and significantly alters BDNF/TrkB signalling, the mechanism of RIP could contribute to neuronal death in excitotoxicity. These results are highly relevant since they reveal new targets for the rational design of therapies to treat stroke and other pathologies with an excitotoxic component.
authors.affiliation: Instituto de Investigaciones Biomédicas 'Alberto Sols', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Gonzalo S
authors.initials: GS
authors.lastname: Tejeda
authors.affiliation: Instituto de Investigaciones Biomédicas 'Alberto Sols', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Sara
authors.initials: S
authors.lastname: Ayuso-Dolado
authors.affiliation: Instituto de Investigaciones Biomédicas 'Alberto Sols', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Arbeteta
authors.affiliation: Instituto de Investigaciones Biomédicas 'Alberto Sols', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Gema M
authors.initials: GM
authors.lastname: Esteban-Ortega
authors.affiliation: Instituto de Investigaciones Biomédicas 'Alberto Sols', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Oscar G
authors.initials: OG
authors.lastname: Vidaurre
authors.affiliation: Instituto de Investigaciones Biomédicas 'Alberto Sols', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Margarita
authors.initials: M
authors.lastname: Díaz-Guerra
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism*; D000818:Animals; D002545:Brain Ischemia / Q000201:enzymology* / Q000473:pathology; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000201:enzymology* / Q000473:pathology; D004195:Disease Models, Animal; D004789:Enzyme Activation; D018846:Excitatory Amino Acids / Q000378:metabolism*; D005865:Gestational Age; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D045726:Metalloproteases / Q000378:metabolism*; D008807:Mice, Inbred BALB C; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D017208:Rats, Wistar; D015398:Signal Transduction; D013997:Time Factors; D020813:Receptor, trkB
chemical_list: D053829:Amyloid Precursor Protein Secretases; D019208:Brain-Derived Neurotrophic Factor; D002154:Calpain; D018846:Excitatory Amino Acids; D008562:Membrane Glycoproteins; D045726:Metalloproteases; D011505:Protein-Tyrosine Kinases; C064371:Ntrk2 protein, mouse; D020813:Receptor, trkB
keywords: TrkB; excitotoxicity; ischaemia; metalloproteinases; stroke; γ-secretases