title: Transthyretin internalization by sensory neurons is megalin mediated and necessary for its neuritogenic activity.
abstract: Mutated transthyretin (TTR) causes familial amyloid polyneuropathy, a neurodegenerative disorder characterized by TTR deposition in the peripheral nervous system (PNS). The origin/reason for TTR deposition in the nerve is unknown. Here we demonstrate that both endogenous mouse TTR and TTR injected intravenously have access to the mouse sciatic nerve. We previously determined that in the absence of TTR, both neurite outgrowth in vitro and nerve regeneration in vivo were impaired. Reinforcing this finding, we now show that local TTR delivery to the crushed sciatic nerve rescues the regeneration phenotype of TTR knock-out (KO) mice. As the absence of TTR was unrelated to neuronal survival, we further evaluated the Schwann cell and inflammatory response to injury, as well as axonal retrograde transport, in the presence/absence of TTR. Only retrograde transport was impaired in TTR KO mice which, in addition to the neurite outgrowth impairment, might account for the decreased regeneration in this strain. Moreover, we show that in vitro, in dorsal root ganglia neurons, clathrin-dependent megalin-mediated TTR internalization is needed for TTR neuritogenic activity. Supporting this observation, we demonstrate that in vivo, decreased levels of megalin lead to decreased nerve regeneration and that megalin's action as a regeneration enhancer is dependent on TTR. In conclusion, our work unravels the mechanism of TTR action during nerve regeneration. Additionally, TTR presence in the nerve, as is here shown, may underlie its preferential deposition in the PNS of familial amyloid polyneuropathy patients.
authors.affiliation: Instituto de Biologia Molecular e Celular-IBMC, Nerve Regeneration Group and Molecular Neurobiology Group, 4150-180 Porto, Portugal.
authors.forename: Carolina E
authors.initials: CE
authors.lastname: Fleming
authors.forename: Fernando Milhazes
authors.initials: FM
authors.lastname: Mar
authors.forename: Filipa
authors.initials: F
authors.lastname: Franquinho
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Saraiva
authors.forename: Mónica M
authors.initials: MM
authors.lastname: Sousa
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004705:Endocytosis / Q000235:genetics / Q000502:physiology; D005727:Ganglia, Spinal / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D006801:Humans; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000096:biosynthesis / Q000172:deficiency / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009416:Nerve Regeneration / Q000235:genetics / Q000502:physiology; D016501:Neurites / Q000378:metabolism*; D055495:Neurogenesis / Q000235:genetics / Q000502:physiology*; D011228:Prealbumin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011984:Sensory Receptor Cells / Q000166:cytology / Q000378:metabolism*
chemical_list: D026561:Low Density Lipoprotein Receptor-Related Protein-2; D011228:Prealbumin