title: Granule-derived granzyme B mediates the vulnerability of human neurons to T cell-induced neurotoxicity.
abstract: Multiple sclerosis (MS) is considered an autoimmune disease of the CNS and is characterized by inflammatory cells infiltrating the CNS and inducing demyelination, axonal loss, and neuronal death. Recent evidence strongly suggests that axonal and neuronal degeneration underlie the progression of permanent disability in MS. In this study, we report that human neurons are selectively susceptible to the serine-protease granzyme B (GrB) isolated from cytotoxic T cell granules. In vitro, purified human GrB induced neuronal death to the same extent as the whole activated T cell population. On the contrary, activated T cells isolated from GrB knockout mice failed to induce neuronal injury. We found that following internalization through various parts of neurons, GrB accumulated in the neuronal soma. Within the cell body, GrB diffused out of endosomes possibly through a perforin-independent mechanism and induced subsequent activation of caspases and cleavage of α-tubulin. Inhibition of caspase-3, a well-known substrate for GrB, significantly reduced GrB-mediated neurotoxicity. We demonstrated that treatment of neurons with mannose-6-phosphate prevented GrB entry and inhibited GrB-mediated neuronal death, suggesting mannose-6-phosphate receptor-dependent endocytosis. Together, our data unveil a novel mechanism by which GrB induces selective neuronal injury and suggest potential new targets for the treatment of inflammatory-mediated neurodegeneration in diseases such as MS.
authors.affiliation: Department of Medicine, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Yohannes
authors.initials: Y
authors.lastname: Haile
authors.forename: Katia Carmine
authors.initials: KC
authors.lastname: Simmen
authors.forename: Dion
authors.initials: D
authors.lastname: Pasichnyk
authors.forename: Nicolas
authors.initials: N
authors.lastname: Touret
authors.forename: Thomas
authors.initials: T
authors.lastname: Simmen
authors.forename: Jian-Qiang
authors.initials: JQ
authors.lastname: Lu
authors.forename: R Chris
authors.initials: RC
authors.lastname: Bleackley
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Giuliani
mesh_terms: D000328:Adult; D000818:Animals; D001921:Brain / Q000196:embryology / Q000201:enzymology / Q000276:immunology; D016923:Cell Death / Q000276:immunology; D002478:Cells, Cultured; D018920:Coculture Techniques; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D003601:Cytotoxicity Tests, Immunologic / Q000379:methods; D053804:Granzymes / Q000378:metabolism / Q000502:physiology* / Q000633:toxicity; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000166:cytology / Q000201:enzymology* / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism
chemical_list: C509213:GZMB protein, human; D053804:Granzymes