Exploring axonal transport and microtubule defects in transthyretin amyloid polyneuropathy (ATTR-PN)

• Autor(a) principal: Dias, Vítor Daniel Pacheco
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/40867
• topic: Transthyretin; Axonopathy; Transthyretin amyloid polyneuropathy; Cytoskeleton; Microtubule dynamics; Axonal transport; Peripheral nervous system

Transthyretin Amyloid Polyneuropathy (ATTR-PN) is a rare, fatal neurodegenerative disease characterized by the deposition of mutant transthyretin (TTR) aggregates in the peripheral nervous system (PNS), leading to sensory axonopathy. Existing therapies do not address the irreversible neurodegeneration characteristic of this disease, highlighting the need for further understanding of ATTR-PN pathogenesis. This study investigated how mutant TTR affects the axonal cytoskeleton, particularly microtubule dynamics and axonal transport, known early markers of peripheral neuropathies. Specifically, we performed confocal live imaging of the sural nerve axons from hTTRᴬ⁹⁷S mice, an ATTR-PN mouse model with sensory impairment, to measure microtubule dynamics, by crossing the model with transgenic mice expressing green fluorescent protein-tagged EB3 (Thy1:EB3-GFP), and mitochondrial transport, by crossing the model with transgenic mice expressing red-fluorescent mitochondria (Thy1-MitoRFP). Our data revealed an increase in EB3 comet density, indicating microtubule instability, and impaired axonal transport, as determined by a decrease in the percentage of motile mitochondria and respective velocity, in hTTRᴬ⁹⁷S axons. Notably, these defects were present at an age preceding axonal loss. Additionally, sural nerve proteomics revealed alterations in molecular pathways related to actin and synapse organization in hTTRᴬ⁹⁷S mice. Building upon these findings, and as actin dysfunction in ATTR-PN was previously addressed, we investigated the axonal transport of synaptophysin (SYP) and the levels and distribution of the presynaptic marker synaptotagmin-2 ( molecular markers of presynaptic vesicle membranes, in hTTRᴬ⁹⁷S dorsal root ganglion (DRG) sensory neurons. We observed a notable impairment in SYP vesicle transport and a significant reduction in SYT2 in mutant neurons. Overall, we demonstrate for the first time that sensory axons from an ATTR-PN mouse model present microtubule instability, impaired transport of mitochondria and of presynaptic structures preceding the onset of neurodegeneration, which might relate to the proteomic results revealing dysregulation in the actin cytoskeleton and synapse organization. Nonetheless, the exact molecular mechanisms underlying these alterations require further research. Our findings offer new insights into axonal degeneration in ATTR-PN, paving the way for potential therapeutic targets.