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Interleukin-6 Regulation of AMP-Activated Protein Kinase

Potential Role in the Systemic Response to Exercise and Prevention of the Metabolic Syndrome

¹ Diabetes Unit, Section of Endocrinology, Boston Medical Center, and Departments of Medicine and Physiology, Boston University School of Medicine, Boston, Massachusetts
² Copenhagen Muscle Research Centre, Centre of Inflammation and Metabolism Rigshospitalet, Copenhagen, Denmark
³ Obesity Research Unit, Boston University School of Medicine, Boston, Massachusetts
⁴ Institute of Neurosciences and Department of Cellular Biology, Physiology, and Immunology, Animal Physiology Unit, Faculty of Sciences Universidad Autónoma de Barcelona, Barcelona, Spain
⁵ Division of Endocrinology and Metabolism, University of Pittsburgh, Pittsburgh, Pennsylvania

Address correspondence and reprint requests to Meghan Kelly, Section of Endocrinology, Diabetes Unit, Boston Medical Center, 650 Albany St., X-820, Boston, MA 02118. E-mail: meghankelly79{at}gmail.com

Abbreviations: ACC, acetyl-CoA carboxylase; AMPK, AMP-activated protein kinase; CPT-1, carnitine palmitoyltransferase 1; FA-CoA, fatty acyl-CoA; IL, interleukin; MCD, malonyl-CoA decarboxylase

Interleukin (IL)-6 is a pleiotropic hormone that has both proinflammatory and anti-inflammatory actions. AMP-activated protein kinase (AMPK) is a fuel-sensing enzyme that among its other actions responds to decreases in cellular energy state by enhancing processes that generate ATP and inhibiting others that consume ATP but are not acutely necessary for survival. IL-6 is synthesized and released from skeletal muscle in large amounts during exercise, and in rodents, the resultant increase in its concentration correlates temporally with increases in AMPK activity in multiple tissues. That IL-6 may be responsible in great measure for these increases in AMPK is suggested by the fact it increases AMPK activity both in muscle and adipose tissue in vivo and in incubated muscles and cultured adipocytes. In addition, we have found that AMPK activity is diminished in muscle and adipose tissue of 3-month-old IL-6 knockout (KO) mice at rest and that the absolute increases in AMPK activity in these tissues caused by exercise is diminished compared with control mice. Except for an impaired ability to exercise and to oxidize fatty acids, the IL-6 KO mouse appears normal at 3 months of age. On the other hand, by age 9 months, it manifests many of the abnormalities of the metabolic syndrome including obesity, dyslipidemia, and impaired glucose tolerance. This, plus the association of decreased AMPK activity with similar abnormalities in a number of other rodents, suggests that a decrease in AMPK activity may be a causal factor. Whether increases in IL-6, by virtue of their effects on AMPK, contribute to the reported ability of exercise to diminish the prevalence of type 2 diabetes, coronary heart disease, and other disorders associated with the metabolic syndrome remains to be determined.

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