title: IL-6 selectively stimulates fat metabolism in human skeletal muscle.
abstract: Interleukin (IL)-6 is chronically elevated in type 2 diabetes but also during exercise. However, the exact metabolic role, and hence the physiological significance, has not been elucidated. The objective of this study was to investigate the in vivo effect of recombinant human (rh) IL-6 on human fat and glucose metabolism and signaling of both adipose tissue and skeletal muscle. Eight healthy postabsorptive males were infused with either rhIL-6 or saline for 4 h, eliciting IL-6 levels of ∼40 and ∼1 pg/ml, respectively. Systemic, skeletal muscle, and adipose tissue fat and glucose metabolism was assessed before, during, and 2 h after cessation of the infusion. Glucose metabolism was unaffected by rhIL-6. In contrast, rhIL-6 increased systemic fatty acid oxidation approximately twofold after 60 min, and it remained elevated even 2 h after the infusion. The increase in oxidation was followed by an increase in systemic lipolysis. Adipose tissue lipolysis and fatty acid kinetics were unchanged with rhIL-6 compared with saline infusion. Conversely, rhIL-6 infusion caused an increase in skeletal muscle unidirectional fatty acid and glycerol release, indicative of an increase in lipolysis. The increased lipolysis in muscle could account for the systemic changes. Skeletal muscle signaling increased after 1 h of rhIL-6 infusion, indicated by a fourfold increase in the phosphorylated signal transducer and activator of transcription (STAT) 3-to-STAT3 ratio, whereas no changes in phosphorylated AMP-activated protein kinase or acetyl-CoA carboxylase levels could be observed. Our findings suggest that an acute increase in IL-6 at a normophysiological level selectively stimulates lipolysis in skeletal muscle, whereas adipose tissue is unaffected.
authors.affiliation: The Centre of Inflammation and Metabolism, Department of Infectious Diseases, University of Copenhagen, Denmark. emil.wolsk@rh.regionh.dk
authors.forename: Emil
authors.initials: E
authors.lastname: Wolsk
authors.forename: Helene
authors.initials: H
authors.lastname: Mygind
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Grøndahl
authors.forename: Bente K
authors.initials: BK
authors.lastname: Pedersen
authors.forename: Gerrit
authors.initials: G
authors.lastname: van Hall
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism; D000273:Adipose Tissue / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D000328:Adult; D044963:Biopsy, Fine-Needle; D001823:Body Composition / Q000502:physiology; D002153:Calorimetry, Indirect; D005227:Fatty Acids / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D015850:Interleukin-6 / Q000008:administration & dosage*; D008066:Lipolysis / Q000187:drug effects / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011994:Recombinant Proteins / Q000008:administration & dosage; D050796:STAT3 Transcription Factor / Q000378:metabolism; D055815:Young Adult
chemical_list: D005227:Fatty Acids; D015850:Interleukin-6; D011994:Recombinant Proteins; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D000263:Adenylate Kinase; D005947:Glucose