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Down-regulation of the potassium-chloride cotransporter KCC2 contributes to spasticity after spinal cord injury

Abstract

Hyperexcitability of spinal reflexes and reduced synaptic inhibition are commonly associated with spasticity after spinal cord injury (SCI). In adults, the activation of γ-aminobutyric acidA (GABAA) and glycine receptors inhibits neurons as a result of low intracellular chloride (Cl) concentration, which is maintained by the potassium-chloride cotransporter KCC2 (encoded by Slc12a5). We show that KCC2 is downregulated after SCI in rats, particularly in motoneuron membranes, thereby depolarizing the Cl equilibrium potential and reducing the strength of postsynaptic inhibition. Blocking KCC2 in intact rats reduces the rate-dependent depression (RDD) of the Hoffmann reflex, as is observed in spasticity. RDD is also decreased in KCC2-deficient mice and in intact rats after intrathecal brain-derived neurotrophic factor (BDNF) injection, which downregulates KCC2. The early decrease in KCC2 after SCI is prevented by sequestering BDNF at the time of SCI. Conversely, after SCI, BDNF upregulates KCC2 and restores RDD. Our results open new perspectives for the development of therapeutic strategies to alleviate spasticity.

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Figure 1: Altered KCC2 expression in lumbar motoneurons after thoracic SCI in adult rats.
Figure 2: Depolarizing shift of EIPSP after SCI and consequences on neuronal excitability.
Figure 3: Blockade of KCC2 with DIOA increases polysynaptic reflexes in the in vitro spinal cord preparation isolated from neonatal rats.
Figure 4: Decreased rate-dependent depression of the Hoffmann reflex after blocking or lowering the expression of KCC2.
Figure 5: Interaction between BDNF and KCC2 expression.

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Acknowledgements

This study was supported by grants from the Christopher and Dana Reeve Foundation (VB1-0502-2 and VB2-0801-2 to L.V.), the French Agence Nationale pour la Recherche (to L.V.), the French Institut pour la Recherche sur la Moelle épinière et l'Encéphale (to L.V.), the US National Institutes of Health (GM074771 to E.D. and NS051644 to M.M.) and the Slovak Research and Development Agency (APVV-0314-06 to M.M.). We thank the company Pharmaxon for their help and expertise concerning SCI in rats. We also thank all team members, particularly F. Brocard, P. Coulon, K. Sadlaoud and S. Tazerart, for their assistance throughout the experiments, and F. Clarac for his support.

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P.B. designed and performed all in vivo experiments and some in vitro experiments (polysynaptic reflex recordings). S.L. designed and performed the immunohistochemistry, western blot and genotyping experiments. R.B. performed some in vitro experiments (RDD of the monosynaptic reflex and effects of DIOA on motoneurons). H.B. was involved in the confocal analysis and quantification of cell surface expression of KCC2. C.J.-X. contributed to the in vitro studies (EIPSP measurements). C.B., A.S. and P.D. participated in immunohistochemistry, western blot and genotyping experiments and analysis. D.C. designed the cell model used for simulations and participated in the analysis. E.D. generated the mutant mouse and provided valuable advice and expertise for KCC2 regulation. M.M. provided valuable expertise for the in vivo experiments. P.B., S.L. and L.V. wrote the manuscript. L.V. designed and supervised the whole project and contributed to the in vitro experiments, confocal analysis and simulations.

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Correspondence to Laurent Vinay.

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Boulenguez, P., Liabeuf, S., Bos, R. et al. Down-regulation of the potassium-chloride cotransporter KCC2 contributes to spasticity after spinal cord injury. Nat Med 16, 302–307 (2010). https://doi.org/10.1038/nm.2107

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