Background & Aims
Although the aetiology of chronic widespread pain in fibromyalgia is unknown, several recent studies point towards a peripheral aetiology. We have recently shown a key role for neutrophils – polymorphonuclear granulocytes that normally exist in circulation to function as primary mediators of rapid innate host defence – in mediating the spatiotemporal spread of hypersensitivity in a hyperalgesic priming model of chronic widespread pain [1]. Our data also shows a fundamental pro-nociceptive action of neutrophils derived from patients or mice with chronic widespread pain when administered to naïve recipient mice.
The mechanisms by which neutrophils can sensitise sensory neurons to cause pain signalling is still unclear, but is likely linked to a subpopulation of neutrophils. We aim to identify which neutrophil subpopulation is responsible for causing pain and to investigate a causal link between neutrophils and nociceptive activity underlying chronic widespread pain in fibromyalgia.
Methods
To identify the pro-nociceptive neutrophil population, we used neutrophils from fibromyalgia patients and pain free controls, characterising proteomic differences between the cohorts by FACS and Mass Spectrometry. Furthermore, we have employed functional assays of neutrophil reactivity, including quantification of reaction oxygen species (ROS) production and neutrophil NETosis to characterise specific functional differences which may responsible their pro-nociceptive capacity.
Finally, we measure nociceptor activation using calcium imaging of dorsal root ganglia neurons to assess the effect of neutrophils on neuronal excitability and to identify whether neutrophils can directly sensitise peripheral sensory neurons.
Results
Proteomic profiling of neutrophils derived from patients versus pain free controls revealed distinct populations of neutrophils with phenotypic changes of cell surface markers. This is also observed when comparing mass spectrometry data of patient neutrophils compared to neutrophils from pain free controls. Quantification of ROS generation also reveals changes in cells derived from patients, alongside increased NETosis generation which may reflect specific mechanisms employed by cells to sensitise peripheral neurons following trafficking to DRG. These data support the enhanced activation state of neutrophils in fibromyalgia. Finally, using calcium imaging we show increased neuronal responses following exposure to patient-derived neutrophils.
Conclusions
We show a surprising role of neutrophils, a short-lived immune cell, in the aetiology of pain in fibromyalgia syndrome. Our data demonstrates altered proteomic profiles and distinct phenotypic differences in circulating neutrophils from patients, likely reflecting a specific pro-nociceptive population of cells, providing a peripheral target for nociplastic changes observed in fibromyalgia syndrome.
References
[1]- Caxaria S, Bharde S, Fuller AM, Evans R, Thomas B, Celik P, Dell’Accio F, Yona S, Gilroy D, Voisin MB, Wood JN, Sikandar S. Neutrophils infiltrate sensory ganglia and mediate chronic widespread pain in fibromyalgia. Proc Natl Acad Sci U S A. 2023 Apr 25;120(17):e2211631120. doi: 10.1073/pnas.2211631120. Epub 2023 Apr 18. PMID: 37071676; PMCID: PMC10151464.
Presenting Author
Romy Evans
Poster Authors
Topics
- Specific Pain Conditions/Pain in Specific Populations: Fibromyalgia