Retrograde nerve growth factor signaling modulates tooth mechanical hyperalgesia induced by orthodontic tooth movement via acid-sensing ion channel 3

Meiya Gao,Jing Zhou,Wenli Lai,Xiaoqi Zhang,Lu Liu,Yan Wang,Linghuan Ren,Qianyun Kuang,Yanzhu Lu,Xinyu Yan,Hu Long,Shizhen Zhang

doi:10.1038/s41368-021-00124-6

Abstract

Orthodontic tooth movement elicits alveolar bone remodeling and orofacial pain that is manifested by tooth mechanical hyperalgesia. Nerve growth factor (NGF) is upregulated in periodontium and may modulate tooth mechanical hyperalgesia. The objectives were to examine the role of NGF in tooth mechanical hyperalgesia and to elucidate the underlying mechanisms. Tooth mechanical hyperalgesia was induced by ligating closed coil springs between incisors and molars in Sprague–Dawley rats. Retrograde labeling was performed by periodontal administration of fluor-conjugated NGF and the detection of fluorescence in trigeminal ganglia (TG). Lentivirus vectors carrying NGF shRNA were employed to knockdown the expression of NGF in TG. The administration of agonists, antagonists, and virus vectors into TG and periodontium was conducted. Tooth mechanical hyperalgesia was examined through the threshold of biting withdrawal. Our results revealed that tooth movement elicited tooth mechanical hyperalgesia that could be alleviated by NGF neutralizing antibody and that NGF was upregulated in periodontium (mainly in periodontal fibroblasts) and TG. Retrograde labeling revealed that periodontal NGF was retrogradely transported to TG after day 1. Acid-sensing ion channel 3 (ASIC3) and NGF were co-expressed in trigeminal neurons and the percentage of co-expression was significantly higher following tooth movement. The administration of NGF and NGF neutralizing antibody into TG could upregulate and downregulate the expression of ASIC3 in TG, respectively. NGF aggravated tooth mechanical hyperalgesia that could be alleviated by ASIC3 antagonist (APETx2). Moreover, NGF neutralizing antibody mitigated tooth mechanical hyperalgesia that could be recapitulated by ASIC3 agonist (GMQ). NGF-based gene therapy abolished tooth mechanical hyperalgesia and downregulated ASIC3 expression. Taken together, in response to force stimuli, periodontal fibroblasts upregulated the expressions of NGF that was retrogradely transported to TG, where NGF elicited tooth mechanical hyperalgesia through upregulating ASIC3. NGF-based gene therapy is a viable method in alleviating tooth-movement-induced mechanical hyperalgesia.

Highlights

Orofacial pain, with a prevalence of 16% among general population,[1] is a constellation of painful conditions in the orofacial regions and comprises trigeminal neuralgia, headaches, temporomandibular joint disorders, and dental pain.[2,3] Of particular, orofacial pain induced by orthodontic tooth movement is manifested by mechanical hyperalgesia in affected teeth.[4,5] It has been well-documented that patients’ masticatory functions are negatively influenced by orofacial pain induced by tooth movement.[6]
Nerve growth factor (NGF)-positive neurons; arrowheads, NGF-negative neurons; *P < 0.05 we previously found that the knockdown of acidsensing ion channel 3 (ASIC3) in the trigeminal ganglia through RNA interference could downregulate the expression of CGRP.[13]
We found that ASIC3 participated in the modulation of tooth mechanical hyperalgesia induced by tooth movement and that ASIC3-based gene therapy knocking down the expression of ASIC3 in trigeminal ganglia (TG) was able to attenuate tooth mechanical hyperalgesia.[13]

Summary

INTRODUCTION

With a prevalence of 16% among general population,[1] is a constellation of painful conditions in the orofacial regions and comprises trigeminal neuralgia, headaches, temporomandibular joint disorders, and dental pain.[2,3] Of particular, orofacial pain induced by orthodontic tooth movement is manifested by mechanical hyperalgesia in affected teeth.[4,5] It has been well-documented that patients’ masticatory functions are negatively influenced by orofacial pain induced by tooth movement.[6]. Nerve growth factor (NGF), an important protein in the process of neurogenesis and neuron growth,[7] plays an important role in pain modulation.[8] It has been revealed that the expression of NGF in periodontal tissues was upregulated in response to tooth movement.[9] Our previous study revealed that periodontal administration of NGF could cause tooth mechanical hyperalgesia and that periodontal administration of NGF neutralizing antibody mitigated tooth mechanical hyperalgesia,[10] suggesting that NGF participates in the modulation of tooth mechanical hyperalgesia. It has been revealed that acidsensing ion channel 3 (ASIC3) is expressed in periodontal Ruffini body that is a mechanical sensory structure.[11] Our previous studies found that ASIC3 participates in the modulation of orofacial pain induced by tooth movement in both periodontal tissues and trigeminal ganglia.[12,13] the expressions of ASIC3 in sensory neurons could be regulated by NGF.[14] All these findings suggest that ASIC3 could be a downstream of NGF in modulating tooth mechanical hyperalgesia. In this study, we aimed to examine the mechanisms whereby NGF modulates tooth mechanical hyperalgesia

RESULTS

CONCLUSION

MATERIALS AND METHODS

Findings

NGF Periodontal fibroblasts