Neuropeptide regulation of adaptive immunity in the tibia fracture model of complex regional pain syndrome

Wen-Wu Li,Wade S. Kingery,Frank Birklein,J. David Clark,Tanja Schlereth,Xiaoyou Shi,Tian-Zhi Guo

doi:10.1186/s12974-018-1145-1

Abstract

BackgroundBoth dysfunctional neuropeptide signaling and immune system activation are characteristic of complex regional pain syndrome (CRPS). Unknown is whether substance P (SP) or calcitonin gene-related peptide (CGRP) support autoantibody production and, consequently, nociceptive sensitization.MethodsThese experiments involved the use of a well-characterized tibia fracture model of CRPS. Mice deficient in SP expression (Tac1−/−) and CGRP signaling (RAMP1−/−) were used to probe the neuropeptide dependence of post-fracture sensitization and antibody production. The deposition of IgM in the spinal cord, sciatic nerves, and skin was followed using Western blotting, as was expression of the CRPS-related autoantigen cytokeratin 16 (Krt16). Passive serum transfer to B-cell-deficient muMT mice was used to assess the production of functional autoantibodies in CRPS model mice. The use of immunohistochemistry allowed us to assess neuropeptide-containing fiber distribution and Langerhans cell abundance in mouse and human CRPS patient skin, while Langerhans cell-deficient mice were used to assess the functional contributions of these cells.ResultsFunctional SP and CGRP signaling were required both for the full development of nociceptive sensitization after fracture and the deposition of IgM in skin and neural tissues. Furthermore, the passive transfer of serum from wildtype but not neuropeptide-deficient mice to fractured muMT mice caused enhanced allodynia and postural unweighting. Langerhans cells were increased in number in the skin of fracture mice and CRPS patients, and those increases in mice were reduced in neuropeptide signaling-deficient animals. Unexpectedly, Langerhans cell-deficient mice showed normal nociceptive sensitization after fracture. However, the increased expression of Krt16 after tibia fracture was not seen in neuropeptide-deficient mice.ConclusionsCollectively, these data support the hypothesis that neuropeptide signaling in the fracture limb of mice is required for autoantigenic IgM production and nociceptive sensitization. The mechanism may be related to neuropeptide-supported autoantigen expression.

Highlights

Both dysfunctional neuropeptide signaling and immune system activation are characteristic of complex regional pain syndrome (CRPS)
Compared to no fracture control mice, the 3-week postfracture WT mice exhibited two- to fourfold IgM increases in all tissues (Fig. 2a–f). We demonstrated that this increase in IgM antibody-antigen deposition in skin, nerve, and cord is restricted to the fracture limb and corresponding lumbar cord with peak deposition occurring between 12 and 18 weeks after fracture and resolving by 23 weeks after fracture, corresponding to the time course for the development and resolution of nociceptive sensitization after tibia fracture and casting in mice [24]
To explore the ways neuropeptides might be involved in fracture-induced IgM deposition, we treated mice with the tachykinin 1 receptor antagonist LY303870 for 7 days starting at 2 weeks post-fracture

Summary

Introduction

Both dysfunctional neuropeptide signaling and immune system activation are characteristic of complex regional pain syndrome (CRPS). Complex regional pain syndrome (CRPS) is a highly enigmatic condition typically affecting a single extremity after surgery or limb trauma. Two potential CRPS mechanisms being extensively investigated are dysfunction of neuropeptide signaling contributing to facilitated neurogenic inflammation, and activation of the innate and adaptive immune systems [4,5,6]. How these systems might communicate in CRPS, so-called neuroimmune interactions, is unclear at this point

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