Understanding the role of the IL-6 -174 G/C (rs1800795) promoter variant in regulation of IL-6 transcription

Abstract

Introduction: IL-6 is a pleiotropic cytokine that is produced and secreted by immune cells in response to infection and inflammation, and by skeletal muscle during exercise. As such, IL-6 plays an important role in orchestrating immune responses and mediating metabolic responses to exercise. The promoter region of IL-6 contains a common genetic variant (-174 G/C rs1800795) that may alter the transcriptional activity of IL-6. However, human studies have shown conflicting effects of rs1800795 on circulating IL-6 levels, and this appears to at least be partially dependent on the type of stimulus that promotes IL-6 transcription. TAp63 plays a role in transcriptional regulation of genes involved in lipid and glucose metabolism and has been proposed to function as a transcriptional regulator of IL-6, and its role in regulation of IL-6 transcription may be influenced by the IL-6 -174 G/C promoter variant. Aims: To examine the transcriptional response of the IL-6 -174 G/C promoter variant in response to both acute exercise and acute inflammatory stimuli, and to additionally examine the potential role of TAp63 as a novel transcriptional regulator of IL-6. Methods: Knock-in mice were generated with a GG or CC genotype for the IL-6 -174 promoter variant and transcription of IL-6 was induced in response to a high-intensity exercise protocol and an acute inflammatory stimulation. Wild-type and with a knockout of Trp63 C2C12 cells were generated and transfected with IL-6 -174 G/C promoter variant plasmid constructs. Transcriptional activity was measured at basal conditions and in response to stimulation in vitro using a luciferase reporter assay. Correlation analyses were performed to compare basal expression of TAp63 and IL-6 in human skeletal muscle. Results: The C allele was associated with a greater increase in skeletal muscle IL-6 mRNA and circulating IL-6 following exercise, but the IL-6 -174 G/C genotype did not affect basal (resting) or inflammation-induced circulating IL-6 and IL-6 mRNA expression in the spleen and skeletal muscle. The IL-6 -174 G/C genotype additionally did not alter basal or inflammation-induced transcriptional activity of the IL-6 promoter plasmids in vitro. Knockout of Trp63 did not result in altered transcriptional activity of IL-6 in C2C12 cells at basal or stimulated conditions, and no correlations were observed between basal TAp63 and IL-6 expression in human skeletal muscle. Conclusions: The IL-6 -174 G/C promoter variant results in altered IL-6 transcriptional activity in response to exercise-specific stimuli and does not result in altered basal transcriptional activity or phenotypic differences under normal chow-fed conditions in young mice. TAp63 does not transcriptionally activate IL-6 at basal conditions or in response to inflammatory stimuli.