Acute P38-Mediated Enhancement of P2X3 Receptor Currents by TNF-α in Rat Dorsal Root Ganglion Neurons

Abstract

Purpose

Tumor necrosis factor-α (TNF-α) is a pro-inflammatory cytokine and involves in a variety of pain conditions. Some findings suggest that TNF-α may act directly on primary afferent neurons to induce acute pain hypersensitivity through non-transcriptional regulation. This study investigated whether TNF-α had an effect on functional activity of P2X3 receptors in primary sensory neurons. Herein, we report that a brief (5 min) application of TNF-α rapidly enhanced the electrophysiological activity of P2X3 receptors in rat dorsal root ganglia (DRG) neurons.

Methods

Electrophysiological recordings were carried out on rat DRG neurons, and nociceptive behavior was quantified in rats.

Results

A brief (5 min) exposure of TNF-α rapidly increased P2X3 receptor-mediated and α,β-methylene-ATP (α,β-meATP)-evoked inward currents in a dose-dependent manner. The potentiation of P2X3 receptor-mediated ATP currents by TNF-α was voltage-independent. TNF-α shifted the concentration–response curve for α,β-meATP upwards, with an increase of 31.57 ± 6.81% in the maximal current response to α,β-meATP. This acute potentiation of ATP currents by TNF-α was blocked by p38 mitogen-activated protein kinase (MAPK) inhibitor SB202190, but not by non-selective cyclooxygenase inhibitor indomethacin, suggesting involvement of p38 MAPK, but not cyclooxygenase. Moreover, intraplantar injection of TNF-α and α,β-meATP produced a synergistic effect on mechanical allodynia in rats. TNF-α-induced mechanical allodynia was also alleviated after local P2X3 receptors were blocked.

Conclusion

These results suggested that TNF-α rapidly sensitized P2X3 receptors in primary sensory neurons via a p38 MAPK dependent pathway, which revealed a novel peripheral mechanism underlying acute mechanical hypersensitivity by peripheral administration of TNF-α.

Keywords:

• electrophysiology
• dorsal root ganglion neuron
• nociceptive response
• P2X3 receptor
• tumor necrosis factor-α

Abbreviations

α,β-methylene-ATP, α,β-meATP; ANOVA, one-way analysis of variance; APs, action potentials; COX, cyclooxygenase; DMEM, Dulbecco’s modified Eagle’s medium; DRG, dorsal root ganglion; EC₅₀, half-maximal response; I_ATP, α,β-methylene-ATP activated current; I–V, current–voltage; MAPK, mitogen-activated protein kinase; PWTs, paw withdrawal thresholds; TNF-α, tumor necrosis factor-α; TNFR, tumor necrosis factor receptor; TRPV1, transient receptor potential vanilloid type 1; TTX-R, tetrodotoxin-resistant.

Ethics Approval and Consent to Participate

The experimental protocol was approved by the animal research ethics committee of Hubei University of Science and Technology (No. 2020-08) and complied with the National Institutes of Health Guide for the Care and Use of Laboratory Animals.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 81671101).

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising, or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors have no conflict of interest to declare.