Abstract
Background: Peripheral Nerve Injury (PNI) represents a major clinical and economic burden. Despite the ability of peripheral neurons to regenerate their axons after an injury, patients are often left with motor and/or sensory disability and may develop chronic pain. Successful regeneration and target organ reinnervation require comprehensive transcriptional changes in both injured neurons and support cells located at the site of injury. The expression of most of the genes required for axon growth and guidance and for synapsis formation is repressed by a single master transcriptional regulator, the Repressor Element 1 Silencing Transcription factor (REST). Sustained increase of REST levels after injury inhibits axon regeneration and leads to chronic pain. REST is stabilized by the Carboxy-terminal domain small phosphatase 1 (CTDSP1), which prevents REST targeting to the proteasome. Here, we explore whether knockdown of CTDSP1 promotes neurotrophic factor expression in mesenchymal progenitor cells (MPCs), a type of support cells that can be harvested from the site of injury during surgical debridement, and in dorsal root ganglion (DRG) neurons. In addition, we explore whether CTDSP1 knockdown supports DRG neurite regeneration. Methods: Cultured human MPCs or rat DRG neurons were transfected with REST or CTDSP1 specific siRNA. Neurotrophic factor expression was analyzed by RT-qPCR and Western Blot. Brain-derived Neurotrophic Factor (BDNF) in cell culture medium was quantified by ELISA. Axon regeneration was quantified measuring the length of the longest neurite of a neuron. Results: Knockdown of REST or CTDSP1 in MPCs results in increased expression of BDNF and nerve growth factor (NGF). In addition, knockdown of CTDSP1 leads to increased release of BDNF in cell culture medium from MPCs and to reduced levels of REST protein. Finally, knockdown of CTDSP1 in DRG neurons results in increased levels of BDNF and increased DRG neurite growth rate.Conclusions: CTDSP1 knockdown promotes neurotrophic factor expression in both DRG neurons and the support cells MPCs. In addition, it promotes DRG neuron regeneration. Therapeutics targeting CTDSP1 activity may represent a novel epigenetic strategy to promote peripheral nerve regeneration after PNI by promoting the regenerative program repressed by injury-induced increased levels of REST in both neurons and support cells.
C-terminal domain small phosphatase 1 (CTDSP1) regulates growth factor expression and axonal regeneration