G protein-coupled Receptor Kinase 2 (GRK2) and Toll-like Receptors as Regulators of Central Sensitization in Fibromyalgia and Chronic Temporomandibular Disorders

Thesis (Master's)--University of Washington, 2018Background. Fibromyalgia (FM) and chronic temporomandibular disorders (TMD) are highly debilitating disorders characterized by pain that is not explained by tissue lesions. Central sensitization (CS) is proposed to be a common etiology of both syndromes. However, the mechanism underlying CS is unclear. Glial cell activation via toll-like receptor (TLR) signaling has been consistently demonstrated in animal models to play an essential role in the initiation and persistence of chronic pain. TLR activation also suppresses GRK2 expression, partly via the release of IL-1β. GRK2 expression and TLR activation are not measurable in human glial cells but can be assessed in peripheral blood mononuclear cells (PBMCs). Preliminary studies have shown that that GRK2 expression and TLR activity are altered in PBMCs of chronic pain patients, potentially providing a clinically accessible marker of a pathway involved in the pathophysiology of central sensitization. Hypotheses. 1) In comparison to normal controls, patients with FM and chronic TMD display lower basal GRK2 levels in PMBCs. 2) Basal GRK2 levels are correlated negatively with indices of central sensitization.3) In comparison to normal pain-free controls, patients with FM and TMD display higher IL-1β production after TLRs stimulation. 4) IL1β levels are correlated negatively with all indices of CS. Methods. We assessed IL1β and GRK2 level, as well as CS in 18 women with fibromyalgia, 18 with chronic TMD, and 18 pain-free female controls. Whole blood was stimulated in vitro by TLR 2, 4, 7 agonists at various concentrations. IL1β levels following stimulation were measured using ELISA. GRK 2 levels on PBMCs were visualized with fluorescent secondary antibodies and quantified using Western blot technique. CS was quantified by pain reports in response to pressure, electrical and repeated mechanical stimulation, areas of pain, and withdrawal reflex of the leg. Results. Basal GRK 2 levels are pending to be analyzed by Western blot. The study, therefore, focused mainly on TLR 2 responsiveness as the preliminary data, No statistically significant difference was identified between the IL1β expression following TLR 2 stimulation among pain-free controls, TMD and FM subjects. Nociceptive reflex threshold was negatively correlated with IL1β level following TLR 2 (1000ng/ml) stimulation. Conclusion. IL1β expression after TLR 2 stimulation in peripheral blood cells did not differ in FM participants and chronic TMD participants when compared to controls. The negative correlation between IL1β expression and spinal nociceptive reflex suggested that TLR