Background Prolonged postoperative pain is a major concern and occurs more frequently in women, but mechanisms remain elusive. NR2B-containging N-methyl-d-aspartate (NMDA) receptor is a key component of nociception transduction. Divalent metal transporter 1 (DMT1)-mediated iron overload involves NMDA-induced neurotoxicity in males. Kalirin-7 is vital in synaptic plasticity underlying pathological pain in males. Herein, the requirement for kalirin-7 in NR2B phosphorylation-dependent iron accumulation and spine plasticity in postoperative pain after tibial fracture in female mice has been examined.
Methods Pain-related behavior, spinal NR2B phosphorylation at Tyr1472, kalirin-7 expression, DMT1 with/without iron-responsive element (IRE (+) DMT1 and IRE (−) DMT1) level, iron concentration and spine morphology were assessed in females. NR2B antagonist Ro25-6981, iron chelator deferoxamine and kalirin-7 knockdown by short hairpin RNA were employed to assess the potential cascade.
Results Tibial fracture initiates long-term allodynia lasting at least 21 days postoperatively, and upregulates spinal NR2B phosphorylation, kalirin-7 and IRE (−) DMT1 expression, iron overload and spine density. Ro25-6981 reduces postoperative mechanical and cold allodynia, spinal NR2B phosphorylation, kalirin-7 level and IRE (−) DMT1-mediated iron overload. Kalirin-7 knockdown impairs fracture-associated allodynia, IRE (−) DMT1-mediated iron overload and spine plasticity. Deferoxamine also attenuates behavioral allodynia and spine plasticity. Spinal NMDA application elicits NR2B-dependent mechanical allodynia and iron overload, which is reversed by kalirin-7 knockdown or coadministration of deferoxamine.
Conclusion Spinal NR2B phosphorylation at Tyr1472 upregulates kalirin-7 expression to facilitate IRE (−) DMT1-mediated iron accumulation and spine morphogenesis in the development of fracture-associated postoperative pain in female mice.
- pain management
- chronic pain
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LZ and ZW contributed equally.
Contributors WC and LZ conceived the experiment; ZW, CS, YL and HL collected the data; LZ, JL and YY analyzed the data; LZ, GW and WC wrote the paper.
Funding This work was supported by research grants from the National Natural Science Foundation of China (81801107, 81571077 and 81400908).
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval All experimental procedures were approved by the Institutional Animal Care and Use Ethics Committee of Tianjin Medical University (Tianjin, China) and were conducted in conformation to the National Institutes of Health Guide for Care and Use of Laboratory Animals.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request. No data are available. All data relevant to the study are included in the article or uploaded as online supplemental information. All data relevant to the study are included in the article for figures and tables. No data are publicly available. Data are available from the corresponding author on reasonable request.