Non-aggregating tau phosphorylation by cyclin-dependent kinase 5 contributes to motor neuron degeneration in spinal muscular atrophy.

Abstract

Mechanisms underlying motor neuron degeneration in spinal muscular atrophy (SMA), the leading inherited cause of infant mortality, remain largely unknown. Many studies have established the importance of hyperphosphorylation of the microtubule-associated protein tau in various neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. However, tau phosphorylation in SMA pathogenesis has yet to be investigated. Here we show that tau phosphorylation on serine 202 (S202) and threonine 205 (T205) is increased significantly in SMA motor neurons using two SMA mouse models and human SMA patient spinal cord samples. Interestingly, phosphorylated tau does not form aggregates in motor neurons or neuromuscular junctions (NMJs), even at late stages of SMA disease, distinguishing it from other tauopathies. Hyperphosphorylation of tau on S202 and T205 is mediated by cyclin-dependent kinase 5 (Cdk5) in SMA disease condition, because tau phosphorylation at these sites is significantly reduced in Cdk5 knock-out mice; genetic knock-out of Cdk5 activating subunit p35 in an SMA mouse model also leads to reduced tau phosphorylation on S202 and T205 in the SMA;p35(-/-) compound mutant mice. In addition, expression of the phosphorylation-deficient tauS202A,T205A mutant alleviates motor neuron defects in a zebrafish SMA model in vivo and mouse motor neuron degeneration in culture, whereas expression of phosphorylation-mimetic tauS202E,T205E promotes motor neuron defects. More importantly, genetic knock-out of tau in SMA mice rescues synapse stripping on motor neurons, NMJ denervation, and motor neuron degeneration in vivo. Altogether, our findings suggest a novel mechanism for SMA pathogenesis in which hyperphosphorylation of non-aggregating tau by Cdk5 contributes to motor neuron degeneration.

• Authors: Nimrod Miller, Zhihua Feng, Brittany M Edens, Ben Yang, Han Shi, Christie C Sze, Benjamin Taige Hong, Susan C Su, Jorge A Cantu, Jacek Topczewski, Thomas O Crawford, Chien-Ping Ko, Charlotte J Sumner, Long Ma, Yong-Chao Ma
• Journal: The Journal of neuroscience : the official journal of the Society for Neuroscience (J Neurosci) Vol. 35 Issue 15 Pg. 6038-50 (Apr 15 2015) ISSN: 1529-2401 [Electronic] United States
• PMID: 25878277 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 the authors 0270-6474/15/356038-13$15.00/0.

Chemical References

• Cux1 protein, mouse
• Homeodomain Proteins
• Nerve Tissue Proteins
• Nuclear Proteins
• Oligodeoxyribonucleotides, Antisense
• Repressor Proteins
• Survival of Motor Neuron 1 Protein
• enhanced green fluorescent protein
• tau Proteins
• Green Fluorescent Proteins
• Cyclin-Dependent Kinase 5

Topics

• Animals
• Cells, Cultured
• Cyclin-Dependent Kinase 5 (metabolism)
• Disease Models, Animal
• Female
• Gene Expression Regulation (genetics)
• Green Fluorescent Proteins (genetics, metabolism)
• Homeodomain Proteins (metabolism)
• Humans
• Immunoprecipitation
• Infant
• Infant, Newborn
• Male
• Mice
• Mice, Transgenic
• Motor Neurons (metabolism, pathology)
• Muscle, Skeletal (pathology)
• Muscular Atrophy, Spinal (complications, genetics, pathology)
• Nerve Degeneration (etiology)
• Nerve Tissue Proteins (metabolism)
• Neuromuscular Junction (metabolism, pathology)
• Nuclear Proteins (metabolism)
• Oligodeoxyribonucleotides, Antisense (pharmacology)
• Phosphorylation
• Repressor Proteins (metabolism)
• Spinal Cord (pathology)
• Survival of Motor Neuron 1 Protein (genetics, metabolism)
• Zebrafish
• tau Proteins (deficiency, genetics, metabolism)