Gene-to-gene interactions regulate endogenous pain modulation in fibromyalgia patients and healthy controls-antagonistic effects between opioid and serotonin-related genes

• Published in: Pain (Amsterdam) Vol. 158; no. 7; pp. 1194 - 1203
• Main Authors: Tour, Jeanette, Löfgren, Monika, Mannerkorpi, Kaisa, Gerdle, Björn, Larsson, Anette, Palstam, Annie, Bileviciute-Ljungar, Indre, Bjersing, Jan, Martin, Ingvar, Ernberg, Malin, Schalling, Martin, Kosek, Eva
• Format: Journal Article
• Language: English
• Published: United States Wolters Kluwer 2017
• Subjects: 5-HT1a; 5-HT1a receptor; 5-HTT; Adult; Alleles; Autoimmunitet och inflammation; Chronic pain; Epistasis, Genetic; Exercise; Exercise Therapy; Exercise-induced hypoalgesia; Female; Fibromyalgia; Fibromyalgia - genetics; Fibromyalgia - therapy; Functional genetic polymorphisms; Genotype; Humans; Klinisk medicin; Medicin och hälsovetenskap; Medicinsk genetik; Medicinska och farmaceutiska grundvetenskaper; Middle Aged; Opioid receptor; OPRM1; Pain - genetics; Pain inhibition; Pain Management; Pain Measurement; Pain Threshold - physiology; Polymorphism, Single Nucleotide; Pressure; Promoter Regions, Genetic; Receptor, Serotonin, 5-HT1A - genetics; Receptors, Opioid, mu - genetics; Research Paper; Reumatologi och inflammation; Rheumatology and Autoimmunity; Serotonin Plasma Membrane Transport Proteins - genetics; Serotonin transporter; Treatment Outcome; Young Adult; 5-HTT; Exercise; Serotonin transporter; Opioid receptor; Pain inhibition; Fibromyalgia; 5-HT1a; Exercise-induced hypoalgesia; OPRM1; Functional genetic polymorphisms; 5-HT1a receptor; Chronic pain
• ISSN: 0304-3959; 1872-6623; 1872-6623
• DOI: 10.1097/j.pain.0000000000000896

Chronic pain is associated with dysfunctional endogenous pain modulation, involving both central opioid and serotonergic (5-HT) signaling. Fibromyalgia (FM) is a chronic pain syndrome, characterized by widespread musculoskeletal pain and reduced exercise-induced hypoalgesia (EIH). In this study, we assessed the effects of 3 functional genetic polymorphisms on EIH in 130 patients with FM and 132 healthy controls. Subjects were genotyped regarding the mu-opioid receptor (OPRM1) gene (rs1799971), the serotonin transporter (5-HTT) gene (5-HTTLPR/rs25531), and the serotonin-1a receptor (5-HT1a) gene (rs6296). The patients with FM had increased pain sensitivity and reduced EIH compared with healthy controls. None of the polymorphisms had an effect on EIH on their own. We found significant gene-to-gene interactions between OPRM1 x 5-HTT and OPRM1 x 5-HT1a regarding activation of EIH, with no statistically significant difference between groups. Better EIH was found in individuals with genetically inferred strong endogenous opioid signaling (OPRM1 G) in combination with weak 5-HT tone (5-HTT low/5-HT1a G), compared with strong 5-HT tone (5-HTT high/5-HT1a CC). Based on the proposed mechanisms of these genetic variants, the findings indicate antagonistic interactions between opioid and serotonergic mechanisms during EIH. Moreover, despite different baseline pain level, similar results were detected in FM and controls, not supporting an altered interaction between opioid and 5-HT mechanisms as the basis for dysfunction of EIH in patients with FM. In summary, our results suggest that, by genetic association, the mu-opioid receptor interacts with 2 major serotonergic structures involved in 5-HT reuptake and release, to modulate EIH.