Autophagy Inhibition Favors Survival of Rubrospinal Neurons After Spinal Cord Hemisection

Abstract

Spinal cord injuries (SCIs) are devastating conditions of the central nervous system (CNS) for which there are no restorative therapies. Neuronal death at the primary lesion site and in remote regions that are functionally connected to it is one of the major contributors to neurological deficits following SCI.

Disruption of autophagic flux induces neuronal death in many CNS injuries, but its mechanism and relationship with remote cell death after SCI are unknown. We examined the function and effects of the modulation of autophagy on the fate of axotomized rubrospinal neurons in a rat model of spinal cord dorsal hemisection (SCH) at the cervical level. Following SCH, we observed an accumulation of LC3-positive autophagosomes (APs) in the axotomized neurons 1 and 5 days after injury. Furthermore, this accumulation was not attributed to greater initiation of autophagy but was caused by a decrease in AP clearance, as demonstrated by the build-up of p62, a widely used marker of the induction of autophagy. In axotomized rubrospinal neurons, the disruption of autophagic flux correlated strongly with remote neuronal death and worse functional recovery. Inhibition of AP biogenesis by 3-methyladenine (3-MA) significantly attenuated remote degeneration and improved spontaneous functional recovery, consistent with the detrimental effects of autophagy in remote damage after SCH. Collectively, our results demonstrate that autophagic flux is blocked in axotomized neurons on SCI and that the inhibition of AP formation improves their survival. Thus, autophagy is a promising target for the development of therapeutic interventions in the treatment of SCIs.

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Abbreviations

CNS:

Central nervous system

SCI:

Spinal cord injury

SCH:

Spinal cord hemisection

3-MA:

3-Methyladenine;

Rapa:

Rapamycin

FB:

Fast-blue

RN:

Red nucleus

LC3:

Light chain 3

mTOR:

Mammalian target of rapamycin

APs:

Autophagosomes

AMPK:

Adenosine monophosphate-activated protein kinase

cyt-c:

Cytochrome-c

Comp C:

Compound C

i.c.v.:

Intracerebroventricularly

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Acknowledgments

This work was supported by the International Research for Paraplegia (P141 to M.T.V.) and by the Italian Ministry of Health (Ricerca Corrente; to M. M.) and partially by the program Young Researchers of Italian Ministry of Health (GR-2010.2310524 to M.T.V.; GR-2011-02351457 to M.D.). The professional editorial work of Blue Pencil Science is also acknowledged.

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Correspondence to Marcello D’Amelio or Maria Teresa Viscomi.

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Elisa Bisicchia and Laura Latini contributed equally to this work.

Marcello D’Amelio and Maria Teresa Viscomi are equal senior authors

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Bisicchia, E., Latini, L., Cavallucci, V. et al. Autophagy Inhibition Favors Survival of Rubrospinal Neurons After Spinal Cord Hemisection. Mol Neurobiol 54, 4896–4907 (2017). https://doi.org/10.1007/s12035-016-0031-z

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Keywords

  • Autophagy
  • Autophagy flux
  • Spinal cord injury
  • Neurodegeneration
  • Autophagosomes
  • Remote damage