The impact of endurance exercise on global and AMPK gene-specific DNA methylation.

Alterations in gene expression as a consequence of physical exercise are frequently described. The mechanism of these regulations might depend on epigenetic changes in global or gene-specific DNA methylation levels. The AMP-activated protein kinase (AMPK) plays a key role in maintenance of energy homeostasis and is activated by increases in the AMP/ATP ratio as occurring in skeletal muscles after sporting activity. To analyze whether exercise has an impact on the methylation status of the AMPK promoter, we determined the AMPK methylation status in human blood samples from patients before and after sporting activity in the context of rehabilitation as well as in skeletal muscles of trained and untrained mice. Further, we examined long interspersed nuclear element 1 (LINE-1) as indicator of global DNA methylation changes. Our results revealed that light sporting activity in mice and humans does not alter global DNA methylation but has an effect on methylation of specific CpG sites in the AMPKα2 gene. These regulations were associated with a reduced AMPKα2 mRNA and protein expression in muscle tissue, pointing at a contribution of the methylation status to AMPK expression. Taken together, these results suggest that exercise influences AMPKα2 gene methylation in human blood and eminently in the skeletal muscle of mice and therefore might repress AMPKα2 gene expression.

Age-Dependent Changes in the Inflammatory Nociceptive Behavior of Mice.

The processing of pain undergoes several changes in aging that affect sensory nociceptive fibers and the endogenous neuronal inhibitory systems. So far, it is not completely clear whether age-induced modifications are associated with an increase or decrease in pain perception. In this study, we assessed the impact of age on inflammatory nociception in mice and the role of the hormonal inhibitory systems in this context. We investigated the nociceptive behavior of 12-month-old versus 6-8-week-old mice in two behavioral models of inflammatory nociception. Levels of TRP channels, and cortisol as well as cortisol targets, were measured by qPCR, ELISA, and Western blot in the differently aged mice. We observed an age-related reduction in nociceptive behavior during inflammation as well as a higher level of cortisol in the spinal cord of aged mice compared to young mice, while TRP channels were not reduced. Among potential cortisol targets, the NF-κB inhibitor protein alpha (IκBα) was increased, which might contribute to inhibition of NF-κB and a decreased expression and activity of the inducible nitric oxide synthase (iNOS). In conclusion, our results reveal a reduced nociceptive response in aged mice, which might be at least partially mediated by an augmented inflammation-induced increase in the hormonal inhibitory system involving cortisol.

AMPK contributes to aerobic exercise-induced antinociception downstream of endocannabinoids.

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".

The protein kinase IKKepsilon contributes to tumour growth and tumour pain in a melanoma model.

Inhibitor-kappaB kinase epsilon (IKKε) constitutes a non-canonical I-κB kinase, which amongst others modulates NF-κB activity. IKKε and NF-κB have both been described for their role in cell proliferation and their dysregulation has been associated with tumourigenesis and metastasis in multiple cancer types. Accordingly, overexpression and constitutive activation of NF-κB have also been shown in melanoma, however, the role of IKKε in this cancer type has not been investigated so far. Thus, we determined IKKε expression in malignant melanoma cells and we were able to show a significant overexpression of IKKε in tumour cells in comparison to melanocytes. Inhibition of IKKε either by shRNA or the pharmacological inhibitor amlexanox resulted in reduced cell proliferation associated with a cell cycle block in the G1-phase. Functional analysis indicated that NF-κB, Akt1 and MAPK pathways might be involved in the IKKε-mediated effects. In vivo, we applied a mouse melanoma skin cancer model to assess tumour growth and melanoma-associated pain in IKKε knockout mice as well as C57BL/6 mice after inoculation with IKKε-negative cells. In IKKε knockout mice, tumour growth was not altered as compared to IKKε wild type mice. However, melanoma associated pain was strongly suppressed accompanied by a reduced mRNA expression of a number of pain-relevant genes. In contrast, after inoculation of IKKε-depleted tumour cells, the development of melanoma was almost completely prevented. In conclusion, our data suggest that IKKε in the tumour plays an essential role in tumour initiation and progression while IKKε expression in tumour surrounding tissues contributes to melanoma-associated pain.