Protein-interaction Patterns Differ Between Fibromyalgia Patients and Healthy Controls

Background & Aims

The past decades of research have revealed several physiological aberrations in fibromyalgia (FM) patients, compared to healthy controls (HC), regarding central, as well as peripheral and immune system related mechanisms. Yet, the pathophysiological cause of FM is still to be elucidated.
Studies on blood biomarkers in FM have showed aberrations in inflammatory proteins, but results have been inconsistent between studies, and a system biology oriented approach has been suggested (1). IgG antibodies from FM patients have been shown to bind dorsal root ganglia satellite glia cells (SGC), and induce FM characteristics in mice (2), and to be associated with FM symptom severity (3). The aim of this study is continued exploration of FM pathophysiology and relevant blood biomarkers by analyzing and further processing IgG- and protein panel-related results.

Methods

Proteins in serum were analyzed using Olink® Explore 384 Inflammation panel, a high-throughput protein biomarker platform using Proximity Extension Assay (PEA) technology. The proteins were analyzed regarding differences between FM (n=93) and HC (n=40) and, within the FM group, regarding differences between FM-subjects with high (?50%) and low (< 50%) anti-SGC IgG-binding. The levels of anti-SGC IgG were quantified using an immunofluorescence assay exhibiting percentage of murine SGC, in cell cultures, binding human IgG (3). Proteins found to differ between groups (VIP?1.3) were further analyzed regarding protein-interactions using the online software tool STRING (FM vs HC n = 56, high vs low anti-SGC IgG-binding n = 55).

Results

In FM, a cluster of immune system-related proteins was found among upregulated proteins, including CD40 and CD40LG, key modulators of B-cell activation and antibody production (4). CD40 levels were associated with more severe FM symptoms. In contrast, a cluster of tissue development/regeneration-related proteins was found among downregulated proteins. In FM patients with high anti-SGC IgG-binding, clusters dominated by immune system-related proteins were found both in upregulated and downregulated proteins. The cluster of up-regulated proteins included CD4, a protein of profound importance for T-helper cell activation. T-helper cells in turn activate various immune cells, including B-cells and macrophages (5). Positive correlations were seen between some of these proteins and pain, FM severity and pressure pain sensitivity. On the contrary, several of the downregulated proteins correlated negatively to pain intensity, suggesting an analgesic, possibly protective role.

Conclusions

These categorical differences in protein-interaction patterns indicate different pathophysiological background between sub-groups and might be more relevant as blood biomarkers than specific proteins. Overall, our data support the involvement of autoimmune mechanisms in FM. We found a very limited overlap between proteins differentiating between FM patients and HC and those related to the levels of anti-SGC IgG within the FM group, which is in accordance with the view of FM as a heterogenous condition regarding pathophysiological mechanisms.

References

1.Gerdle B, Ghafouri B. Proteomic studies of common chronic pain conditions – a systematic review and associated network analyses. Expert Rev Proteomics. 2020;17(6):483-505.
2.Goebel A, Krock E, Gentry C, Israel MR, Jurczak A, Urbina CM, et al. Passive transfer of fibromyalgia symptoms from patients to mice. J Clin Invest. 2021;131(13).
3.Krock E, Morado-Urbina CE, Menezes J, Hunt MA, Sandström A, Kadetoff D, et al. Fibromyalgia patients with elevated levels of anti-satellite glia cell immunoglobulin G antibodies present with more severe symptoms. Pain. 2023;164(8):1828-40.
4.Elgueta R, Benson MJ, de Vries VC, Wasiuk A, Guo Y, Noelle RJ. Molecular mechanism and function of CD40/CD40L engagement in the immune system. Immunol Rev. 2009;229(1):152-72.
5.Luckheeram RV, Zhou R, Verma AD, Xia B. CD4?T cells: differentiation and functions. Clin Dev Immunol. 2012;2012:925135.
6.Wolfe F, Smythe HA, Yunus MB, Bennett RM, Bombardier C, Goldenberg DL, et al. The American College of Rheumatology 1990 Criteria for the Classification of Fibromyalgia. Report of the Multicenter Criteria Committee. Arthritis Rheum. 1990;33(2):160-72.
7.Wolfe F, Clauw DJ, Fitzcharles MA, Goldenberg DL, Katz RS, Mease P, et al. The American College of Rheumatology preliminary diagnostic criteria for fibromyalgia and measurement of symptom severity. Arthritis Care Res (Hoboken). 2010;62(5):600-10.
8.Wolfe F, Clauw DJ, Fitzcharles MA, Goldenberg DL, Häuser W, Katz RL, et al. 2016 Revisions to the 2010/2011 fibromyalgia diagnostic criteria. Semin Arthritis Rheum. 2016;46(3):319-29.