Regular articleDisrupted axon-glia interactions at the paranode in myelinated nerves cause axonal degeneration and neuronal cell death in the aged Caspr mutant mouse shambling
Introduction
In human neurodegenerative diseases, pathophysiological processes and disease mechanisms remain elusive and are often controversial, despite great efforts over the past a few decades (Garden and La Spada, 2012, Liu et al., 2011, Morfini et al., 2009, Yuan et al., 2012). Central efforts have been undertaken during the investigation of these diseases, focusing on studies of protein misfolding, mitochondrial dysfunction, and oxidative stress. Recent progress in neurobiology, however, suggests that axonal degeneration is caused by impaired axonal transport and is a disease substrate in various neurodegenerative diseases such as Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) (Lamberts et al., 2015, Millecamps and Julien, 2013, Morfini et al., 2009). Axonal transport is an essential function of the neuron to maintain neuronal integrity and survival of the cell and is achieved through the functions of cytoskeletal and motor proteins (Maday et al., 2014, Millecamps and Julien, 2013). Impaired axonal transport implicates an early manifestation and progression of pathologies in axonal degeneration of the adult-onset neurodegenerative disease (Dadon-Nachum et al., 2011).
Nodes of Ranvier, which are specialized axonal domains in myelinated nerves (Arancibia-Carcamo and Attwell, 2014, Buttermore et al., 2013, Eshed-Eisenbach and Peles, 2013), have been shown to be critical sites for the pathogenesis of various neurodegenerative diseases (Arancibia-Carcamo and Attwell, 2014, Buttermore et al., 2013). Dysfunction and/or disruption of the nodes of Ranvier (node/paranode/juxtaparanode) have been demonstrated extensively (Cifuentes-Diaz et al., 2011, Devaux and Scherer, 2005, Howell et al., 2006, Wolswijk and Balesar, 2003). The paranodes flank both sides of the node and form septate-like adhesive junctions (paranodal junctions) between myelin loops and the axonal membrane. The paranodal junction is composed of contactin and Caspr (contactin-associated protein) on the axonal membrane (axolemma) and the 155-kDa isoform of neurofascin (Nfasc 155) on the glial side.
Previously, we reported that a mutated gene in the neurological mouse mutant shambling (shm) encodes Caspr, a trans-membrane protein (Sun et al., 2009). We found that, in shm mice, paranodal junctions are completely or partially absent from peripheral nervous system (PNS) and central nervous system (CNS) myelinated nerves and that nerve impulse conduction is impaired in both the PNS and CNS (Sun et al., 2009). Other paranodal mutants that are deficient in paranodal and myelin molecules [Caspr KO (Bhat et al., 2001, Einheber et al., 2006, Pillai et al., 2007), contactin KO (Boyle et al., 2001, Davisson et al., 2011), Nfasc 155 KO (Sherman et al., 2005), ceramide galactosyl transferase (CGT) KO (Dupree et al., 1998, Garcia-Fresco et al., 2006), and cerebroside sulfotransferase (CST) KO (Ishibashi et al., 2015)] also lack a normal paranodal junction and display ataxia, motor deficits, and dramatically reduced nerve conduction velocities.
In the course of our last study, we noticed that shm mice exhibited intriguing neurological phenotypes, including symptomatic worsening as the mice age (Sun et al., 2009). Here, we focus on the progressive motor disabilities and the pathological processes involved during the aging of shm mice. Further, we address whether disrupted paranodal junctions cause alterations in axons and neurons themselves. For this purpose, we investigated the pathophysiology of the disease in myelinated nerves and neurons by following the ages of shm mice from infancy to advanced age. We found that disrupted paranodal junctions in shm mice caused cytoskeletal alterations in the axonal cytoplasm of myelinated nerves and led to a loss of neurons. By verifying this pathophysiological process, we propose a causal mechanism underlying neuronal death accompanied by progressive neurological defects in aging shm mice and, consequently, attempt to provide a novel prospective in the study of human neurodegenerative diseases.
Section snippets
Animals
Shambling mice (B6.Cg-shm/Oda; C57BL/6J background) were introduced from RIKEN BioResource Centre (Tsukuba, Japan), and heterozygous (shm/+) mutant mice were maintained at the Research Institute of Environmental Medicine in Nagoya University in accordance to the Guidelines for Animal Experimentation of the Japanese Association for Laboratory Animal Science. All experiments were approved in accordance with the guidelines of the Committee for Animal Experiments of the Nagoya University.
Shambling mice manifest a progressive motor disability with aging
We observed the progressive symptoms of shm mice by video observation (Appendix A. Videos 1–4) and foot print analysis (Fig. 1A). Shm mice developed ataxic gait, and wobbly walking caused by hindlimb weakness from around 2 weeks of age (Video 1). When compared to the foot pattern of normal mice walking along a straight line with regular steps (Fig. 1Aa–c, normal), the shm mice displayed an abnormal gait pattern with an irregular distance of each step and an absence of fore (blue) -hind (brown)
Discussion
Dysfunction and/or disruption of the paranode have been reported in human demyelination diseases such as Charcot-Marie-Tooth disease (Devaux and Scherer, 2005) and multiple sclerosis (Howell et al., 2006, Wolswijk and Balesar, 2003). The pathobiology of the paranode is gaining recognition in the neurobiology of diseases, including the human neurodegenerative disease ALS (Arancibia-Carcamo and Attwell, 2014, Buttermore et al., 2013, Cifuentes-Diaz et al., 2011, Susuki, 2013). The paranode
Conclusion
In this study, we showed that disrupted axon-glia interactions at the paranode in nodes of Ranvier causes alteration of the axonal cytoskeleton leading to axonal degeneration and neuronal cell death. This is first demonstration of severe damage to axons and neurons and their resultant loss in various regions of the PNS and CNS in shm mice in paranodal mutants. During the disease process, alterations in NF expression and distribution were observed in the axonal cytoplasm of myelinated nerves in
Disclosure statement
The authors declare that they have no competing interests.
Acknowledgements
The authors thank to Hiroyuki Oohori, Ikuma Sasaki, and Yusuke Yanagi who participated in this study as training for medical research (one of the School of Medicine curriculum) in the undergraduate course at the Nagoya University School of Medicine. We also thank Kazuya Fukumoto for the statistical analysis of mouse-behavior tests. This work was supported by the Grant-in-Aid for Scientific Research 20500370 and 23591241 (Yoshiko Takagishi).
References (54)
- et al.
Axon-glia interactions and the domain organization of myelinated axons requires neurexin IV/Caspr/Paranodin
Neuron
(2001) - et al.
The versatile electron microscope: an ultrastructural overview of autophagy
Methods
(2015) - et al.
Contactin orchestrates assembly of the septate-like junctions at the paranode in myelinated peripheral nerve
Neuron
(2001) - et al.
The making of a node: a co-production of neurons and glia
Curr. Opin. Neurobiol.
(2013) - et al.
Mouse models in aging research
- et al.
Intercellular (mis)communication in neurodegenerative disease
Neuron
(2012) - et al.
Pattern of axonal injury in murine myelin oligodendrocyte glycoprotein induced experimental autoimmune encephalomyelitis: implications for multiple sclerosis
Neurobiol. Dis.
(2008) - et al.
Participation of autophagy in storage of lysosomes in neurons from mouse models of neuronal ceroid-lipofuscinoses (Batten disease)
Am. J. Pathol.
(2005) - et al.
Spreading of α-synuclein in the face of axonal transport deficits in Parkinson's disease: a speculative synthesis
Neurobiol. Dis.
(2015) - et al.
Neurofilament protein levels: quantitative analysis in essential tremor cerebellar cortex
Neurosci. Lett.
(2012)
Axonal transport: cargo-specific mechanisms of motility and regulation
Neuron
Electron tomographic analysis of cytoskeletal cross-bridges in the paranodal region of the node of Ranvier in peripheral nerves
J. Struct. Biol.
Neurofascins are required to establish axonal domains for saltatory conduction
Neuron
Morphological and biochemical signs of age-related neurodegenerative changes in klotho mutant mice
Neuroscience
Autophagy in axonal and dendritic degeneration
Trends Neurosci.
The node of Ranvier in CNS pathology
Acta Neuropathol.
Organization and maintenance of molecular domains in myelinated axons
J. Neurosci. Res.
Autophagy activation and enhanced mitophagy characterize the Purkinje cells of pcd mice prior to neuronal death
Mol. Brain
Nodes of ranvier and paranodes in chronic acquired neuropathies
PLoS One
The “dying-back” phenomenon of motor neurons in ALS
J. Mol. Neurosci.
Neurofilament phosphorylation during development and disease: which Came first, the phosphorylation or the accumulation?
J. Amino Acids
Autophagy in neuronal cells: general principles and physiological and pathological functions
Acta Neuropathol.
A spontaneous mutation in contactin 1 in the mouse
PLoS One
Altered ion channels in an animal model of Charcot-Marie-Tooth disease type IA
J. Neurosci.
Myelin galactolipids are essential for proper node of Ranvier formation in the CNS
J. Neurosci.
Purkinje cell death: differences between developmental cell death and neurodegenerative death in mutant mice
Cerebellum
Disrupted axo-glial junctions result in accumulation of abnormal mitochondria at nodes of ranvier
Neuron Glia Biol.
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Present address: College of Life and Health Sciences, Chubu University, 1200 Matsumoto-cho, Kasugai, Aichi 487-8501, Japan.