Up-Regulation of ProBDNF/p75^NTR Signaling in Spinal Cord Drives Inflammatory Pain in Male Rats

Abstract

Background

The spinal cord expresses brain-derived neurotrophic factor precursor (proBDNF) and its receptor pan neurotrophin receptor 75 (p75^NTR). However, the role of spinal proBDNF signaling in the pathogenesis of inflammatory pain remains unknown.

Methods

Rats were locally injected with complete Freund’s adjuvant (CFA) to induce inflammatory pain. The proBDNF signal expression was detected by double-labeled immunofluorescence. ProBDNF protein, p75^NTR extracellular domain (p75^NTR-ECD), or monoclonal anti-proBDNF (McAb-proB) were administrated by intrathecal injection to investigate their effects on pain behavior. Paw withdrawal thermal latency (PWL) and paw withdrawal mechanical threshold (PWT) were performed to evaluate pain behavior. Immunoblotting, immunohistochemistry, and immunofluorescence were used to assess inflammation-induced biochemical changes.

Results

CFA induced a rapid increase in proBDNF in the ipsilateral spinal cord, and immunofluorescence revealed that CFA-enhanced proBDNF was expressed in NeuN positive neurons and GFAP positive astrocytes. The administration of furin cleavage-resistant proBDNF via intrathecal injection (I.t.) significantly decreased the PWT and PWL, whereas McAb-proB by I.t. alleviated CFA-induced pain-like hypersensitivity in rats. Meanwhile, CFA administration triggered the activation of p75^NTR and its downstream signaling extracellular signal-regulated kinase 1/2 (ERK1/2) and nuclear factor (NF)-kappaB p65 in the spinal cord. I.t. administration of p75^NTR-ECD suppressed CFA-induced pain and neuroinflammation, including the expression of p-ERK1/2, p-p65, and the gene expression of tumor necrosis factor-α (TNF-α), and interleukin 6 (IL-6).

Conclusion

Our study reveals that the activated proBDNF/p75^NTRsignaling in the spinal cord contributes to the development of CFA-induced inflammatory pain. McAb-proB and p75^NTR-ECD appear to be promising therapeutic agents for inflammatory pain.

Keywords:

• brain-derived neurotrophic factor precursor
• inflammatory pain
• spinal cord
• neuron
• pan neurotrophin receptor 75

Abbreviations

proBDNF, brain-derived neurotrophic factor precursor; p75^NTR, pan neurotrophin receptor 75; p75^NTR-ECD, p75^NTR extracellular domain; McAb-proB, monoclonal anti-proBDNF; PWL, paw withdrawal thermal latency; PWT, paw withdrawal mechanical threshold; I.t., intrathecal injection; NS, normal saline; ERK1/2, extracellular signal-regulated kinase 1/2; NF-κB, nuclear factor kappa B; CFA, Complete Freund’s adjuvant; rip2, receptor-interacting protein 2; DRG, Dorsal root ganglia; IL-6, interleukin 6; TNF-α, tumor necrosis factor-α.

Acknowledgments

The authors would like to thank all of the co-investigators and colleagues who made this study possible.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This research was supported by the National Natural Science Foundation of China (NSFC 81873770 to HL).