Lack of GDAP1 induces neuronal calcium and mitochondrial defects in a knockout mouse model of charcot-marie-tooth neuropathy.

Manuela Barneo-Muñoz,María Sánchez-Aragó,Roman Chrast,David Pla-Martin,Carmen Cuevas-Martín,Paula Juárez,Jennifer Zenker,Anna Estela,Laura Yndriago,Jerónimo Forteza-Vila,Azahara Civera-Tregón,Francesc Palau,José M Cuezva,Gregory A Cox

doi:10.1371/journal.pgen.1005115

Abstract

Mutations in GDAP1, which encodes protein located in the mitochondrial outer membrane, cause axonal recessive (AR-CMT2), axonal dominant (CMT2K) and demyelinating recessive (CMT4A) forms of Charcot-Marie-Tooth (CMT) neuropathy. Loss of function recessive mutations in GDAP1 are associated with decreased mitochondrial fission activity, while dominant mutations result in impairment of mitochondrial fusion with increased production of reactive oxygen species and susceptibility to apoptotic stimuli. GDAP1 silencing in vitro reduces Ca2+ inflow through store-operated Ca2+ entry (SOCE) upon mobilization of endoplasmic reticulum (ER) Ca2+, likely in association with an abnormal distribution of the mitochondrial network. To investigate the functional consequences of lack of GDAP1 in vivo, we generated a Gdap1 knockout mouse. The affected animals presented abnormal motor behavior starting at the age of 3 months. Electrophysiological and biochemical studies confirmed the axonal nature of the neuropathy whereas histopathological studies over time showed progressive loss of motor neurons (MNs) in the anterior horn of the spinal cord and defects in neuromuscular junctions. Analyses of cultured embryonic MNs and adult dorsal root ganglia neurons from affected animals demonstrated large and defective mitochondria, changes in the ER cisternae, reduced acetylation of cytoskeletal α-tubulin and increased autophagy vesicles. Importantly, MNs showed reduced cytosolic calcium and SOCE response. The development and characterization of the GDAP1 neuropathy mice model thus revealed that some of the pathophysiological changes present in axonal recessive form of the GDAP1-related CMT might be the consequence of changes in the mitochondrial network biology and mitochondria–endoplasmic reticulum interaction leading to abnormalities in calcium homeostasis.

Highlights

Charcot-Marie-Tooth (CMT) disease is one of the most frequent inherited neurological disorders and is characterized by either demyelinating or axonal neuropathy of motor and sensory peripheral nerves [1,2,3]
GDAP1 is located in the mitochondrial outer membrane and seems to participate in the mitochondrial network dynamics
To investigate the biological and functional consequences of lack of GDAP1 and to gain insight into the pathophysiology of the GDAP1-related neuropathies we have generated a GDAP1 ortholog (Gdap1) knockout mouse. Characterization of this model revealed that the absence of GDAP1 induces a peripheral neuropathy with loss of motor neurons and abnormal neuromuscular junctions

Summary

Introduction

Charcot-Marie-Tooth (CMT) disease is one of the most frequent inherited neurological disorders and is characterized by either demyelinating or axonal neuropathy of motor and sensory peripheral nerves [1,2,3]. Mutations in GDAP1, which maps at human chromosome 8q21.1, are causative for several types of neuropathy and are transmitted through various modes of inheritance including autosomal recessive demyelinating CMT4A with reduced nerve condition velocities (NCVs) [6], autosomal recessive axonal AR-CMT2K with preserved NCVs and abnormal compound motor action potentials (CMAPs) [7], and the less frequent autosomal dominant CMT2K [8,9] and recessive intermediate RI-CMT [10]. Through characterization of fibroblasts derived from CMT4A patients, Noack and colleagues [16]

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Discussion

Conclusion