ABSTRACT
Physical exercise has been repeatedly associated with decreased nociceptive responses but the underlying mechanisms have still not been fully clarified. In this study, we investigated exercise-induced effects after a single bout of treadmill running on the mouse model of formalin-induced inflammatory nociception. As potential molecular mediators, we focused on endogenous endocannabinoids as well as AMP-activated protein kinase (AMPK). Our results showed that wild type mice display a reduced nociceptive response in the formalin test after treadmill running, while exercise had no effect on inflammatory nociception in AMPKα2 knockout mice. Levels of the endocannabinoid anandamide (AEA) were increased after physical activity in both wild type and AMPKα2 knockout mice, in association with decreased expression of the AEA-hydrolyzing enzyme FAAH and an increased level of the cannabinoid receptor 1 (CB1). Accordingly, treatment of wild type mice with the CB1 inverse agonist AM251 prior to the treadmill running reversed exercise-induced antinociception. However, if mice received AM251 in combination with the AMPK activator 5-amino-1-ß-d-ribofuranosyl-imidazole-4-carboxamide (AICAR), the positive effect of treadmill running on inflammatory nociception was restored, indicating that AMPK affects exercise-induced antinociception downstream of endocannabinoids. This assumption was further supported by cell culture experiments showing AMPK activation after stimulation of neuronal cells with AEA. In conclusion, our data suggest that AMPK is an intermediate effector in endocannabinoid-mediated exercise-induced antinociception. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".
Subject(s)
AMP-Activated Protein Kinases/physiology , Nociception/physiology , Physical Conditioning, Animal/physiology , AMP-Activated Protein Kinases/genetics , AMP-Activated Protein Kinases/metabolism , Amidohydrolases/metabolism , Aminoimidazole Carboxamide/analogs & derivatives , Aminoimidazole Carboxamide/pharmacology , Animals , Arachidonic Acids/metabolism , Cells, Cultured , Endocannabinoids/metabolism , Female , Male , Mice , Mice, Knockout , Neurons/metabolism , Nociception/drug effects , Pain Measurement , Piperidines/pharmacology , Polyunsaturated Alkamides/metabolism , Pyrazoles/pharmacology , Receptor, Cannabinoid, CB1/metabolism , Ribonucleotides/pharmacologyABSTRACT
BACKGROUND: TANK-binding kinase (TBK1) is a non-canonical IκB kinase (IKK) involved in the regulation of type I interferons and of NF-κB signal transduction. It is activated by viral infections and inflammatory mediators and has therefore been associated with viral diseases, obesity, and rheumatoid arthritis. Its role in pain has not been investigated so far. Due to the important roles of NF-κB, classical IκB Kinases and the IKK-related kinase, IKKε, in inflammatory nociception, we hypothesized that TBK1, which is suggested to form a complex with IKKε under certain conditions, might also alter the inflammatory nociceptive response. METHODS: We investigated TBK1 expression and regulation in "pain-relevant" tissues of C57BL/6 mice by immunofluorescence, quantitative PCR, and Western blot analysis. Furthermore, nociceptive responses and the underlying signal transduction pathways were assessed using TBK1(-/-) mice in two models of inflammatory nociception. RESULTS: Our data show that TBK1 is expressed and regulated in the spinal cord after peripheral nociceptive stimulation and that a deletion of TBK1 alleviated the inflammatory hyperalgesia in mice while motor function and acute nociception were not altered. TBK1-mediated effects are at least partially mediated by regulation of NF-κB dependent COX-2 induction but also by alteration of expression of c-fos via modulation of MAP kinases as shown in the spinal cord of mice and in cell culture experiments. CONCLUSION: We suggest that TBK1 exerts pronociceptive effects in inflammatory nociception which are due to both modulation of NF-κB dependent genes and regulation of MAPKs and c-fos. Inhibition of TBK1 might therefore constitute a novel effective tool for analgesic therapy.
Subject(s)
Hyperalgesia/etiology , Hyperalgesia/metabolism , Inflammation/complications , Mitogen-Activated Protein Kinase Kinases/genetics , NF-kappa B/genetics , Protein Serine-Threonine Kinases/metabolism , Animals , Cell Line, Transformed , Cyclooxygenase 2/genetics , Cyclooxygenase 2/metabolism , Ganglia, Spinal/metabolism , Ganglia, Spinal/pathology , Gene Expression Regulation/genetics , Inflammation/pathology , Matrix Metalloproteinase 9/genetics , Matrix Metalloproteinase 9/metabolism , Mice , Mice, Inbred C57BL , Mice, Transgenic , Microfilament Proteins/genetics , Microfilament Proteins/metabolism , Mitogen-Activated Protein Kinase Kinases/metabolism , Motor Activity/genetics , NF-kappa B/metabolism , Nitric Oxide Synthase Type II/genetics , Nitric Oxide Synthase Type II/metabolism , Pain Threshold/physiology , Protein Serine-Threonine Kinases/genetics , Proto-Oncogene Proteins c-fos/genetics , Proto-Oncogene Proteins c-fos/metabolism , Spinal Cord/metabolism , Spinal Cord/pathology , Time FactorsABSTRACT
miRNAs are small noncoding RNAs that are important players in development, as well as in a number of physiological and pathophysiological processes. Due to their regulatory role in protein expression, it has been assumed that they are associated with peripheral and central sensitization mechanisms in the nervous system after nociceptive insults. However, the study of miRNAs in pain has emerged only recently. First reports mostly focused on miRNA regulations in different pain states while studies examining the functional role of individual miRNAs are only now arising. In this review, the authors summarize the current knowledge and progress in miRNA research in pain and discuss their potential role as therapeutic antinociceptive targets.