Progressive Motor Deficit is Mediated by the Denervation of Neuromuscular Junctions and Axonal Degeneration in Transgenic Mice Expressing Mutant (P301S) Tau Protein

Article type: Research Article

Authors: Yin, Zhuoran^{a; b; 1} | Valkenburg, Femke^{c; 1} | Hornix, Betty E.^d | Mantingh-Otter, Ietje^a | Zhou, Xingdong^{e; f} | Mari, Muriel^e | Reggiori, Fulvio^e | Van Dam, Debby^{c; g} | Eggen, Bart J.L.^a | De Deyn, Peter P.^{c; g; h} | Boddeke, Erik^{a; *}

Affiliations: [a] Department of Neuroscience, Section Medical Physiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands | [b] Department of Medical Ultrasound, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China | [c] Laboratory of Neurochemistry and Behavior, Institute Born-Bunge, University of Antwerp, Antwerp, Belgium | [d] Department of Neurobiology, Groningen Institute for Evolutionary Life Science, University of Groningen, Groningen, The Netherlands | [e] Department of Cell Biology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands | [f] Department of Preventive Veterinary Medicine, College of Veterinary Medicine, Northeast Agricultural University, Harbin, China | [g] Department of Neurology and Alzheimer Research Center, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands | [h] Biobank, Institute Born-Bunge, Antwerp, Belgium

Correspondence: [*] Correspondence to: Erik Boddeke, Department of Neuroscience, Section Medical Physiology, University Medical Center Groningen, Antonius Deusinglaan 1, Groningen, 9713 AV,The Netherlands. Tel.: +31 503616443; Fax: +31 503632751; E-mail: h.w.g.m.boddeke@umcg.nl.

Note: [1] These authors contributed equally to this work.

Abstract: Tauopathies include a variety of neurodegenerative diseases associated with the pathological aggregation of hyperphosphorylated tau, resulting in progressive cognitive decline and motor impairment. The underlying mechanism for motor deficits related to tauopathy is not yet fully understood. Here, we use a novel transgenic tau mouse line, Tau 58/4, with enhanced neuron-specific expression of P301S mutant tau to investigate the motor abnormalities in association with the peripheral nervous system. Using stationary beam, gait, and rotarod tests, motor deficits were found in Tau 58/4 mice already 3 months after birth, which deteriorated during aging. Hyperphosphorylated tau was detected in the cell bodies and axons of motor neurons. At the age of 9 and 12 months, significant denervation of the neuromuscular junction in the extensor digitorum longus muscle was observed in Tau 58/4 mice, compared to wild-type mice. Muscle hypotrophy was observed in Tau 58/4 mice at 9 and 12 months. Using electron microscopy, we observed ultrastructural changes in the sciatic nerve of 12-month-old Tau 58/4 mice indicative of the loss of large axonal fibers and hypomyelination (assessed by g-ratio). We conclude that the accumulated hyperphosphorylated tau in the axon terminals may induce dying-back axonal degeneration, myelin abnormalities, neuromuscular junction denervation, and muscular atrophy, which may be the mechanisms responsible for the deterioration of the motor function in Tau 58/4 mice. Tau 58/4 mice represent an interesting neuromuscular degeneration model, and the pathological mechanisms might be responsible for motor signs observed in some human tauopathies.

Keywords: Alzheimer’s disease, axonal degeneration, motor dysfunction, neuromuscular junction denervation, tauopathy

DOI: 10.3233/JAD-161206

Journal: Journal of Alzheimer's Disease, vol. 60, no. s1, pp. S41-S57, 2017