Human muscle damage impairs insulin-signal transduction at the level of IRS-1, PI3-kinase and AKT-kinase: Potential role for TNF-alpha inhibition of insulin action in skeletal muscle

• Main Author: Del Aguila, Luis F
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1999
• Subjects: Immunology; Molecular biology; Pathology
• ISBN: 0599423765; 9780599423763

Physiological stress associated with muscle damage results in insulin resistance and an acute phase immune response, leading to mononuclear cell release of cytokines, including tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β. We determined whether impaired insulin-signal transduction and/or increased cytokine production play a role in muscle damage-induced insulin resistance. Muscle biopsies were obtained before (BASE) and at 1 h during a hyperinsulinemic-euglycemic clamp (INS) (40 mU·kg-1 ·min-1) in 8 young (age 24 ± 1 yr), healthy sedentary (VO2max = 49.7 ± 2.4 ml·kg-1·min -1) males before (CTRL) and 24 h after eccentric exercise-induced muscle damage (ECC). Venous blood samples were obtained before and 24 h after ECC to determine ex vivo endotoxin-induced mononuclear cell secretion of TNF-α, IL-6 and IL-1β. Glucose disposal was 19% lower after ECC (P < 0.05). Insulin-stimulated IRS-1 tyrosine phosphorylation was 45% lower after ECC (P < 0.05). Insulin-stimulated PI3-kinase, Akt serine phosphorylation and Akt-kinase activity were reduced 34, 65 and 20%, respectively after ECC (P < 0.05). TNF-α, but not IL-6 or IL-1β production, increased 2.4-fold 24 h after ECC (P < 0.05). TNF-α production was positively correlated with reduced insulin-action on PI3-kinase (r = 0.77, P = 0.04). To further determine the effects of TNF-α on insulin action in skeletal muscle, we measured IRS-1-associated PI3-kinase activity, the phosphorylation of two mitogen-activated protein kinases (MAPK, known as p42 MAPK and p44MAPK) and insulin stimulated 2-deoxyglucose (2DG) uptake in cultured C2C12 myotubes. We observed that TNF-α decreased insulin stimulation of IRS-1-associated PI3-kinase activity by 54% (P < 0.05), p42MAPK and p44 MAPK tyrosine phosphorylation by 81% (P < 0.01) and 2 DG uptake by 27% (P < 0.05). Okadaic acid, a phosphatase inhibitor, was used to determine the mechanisms by which TNF-α impairs insulin-signal transduction in C2C12 muscle cells. Okadaic acid blocked TNF-α repression of insulin-induced p42MAPK and p44MAPK tyrosine phosphorylation, suggesting a phosphatase-dependent mechanism in the inhibition of p42MAPK and p44MAPK by TNF-α. In contrast, TNF-α attenuation of IRS-1-associated PI3-kinase activity was not reversed by okadaic acid. In summary, the physiological stress associated with muscle damage impairs insulin-signal transduction and decreases insulin-mediated glucose uptake. Furthermore, elevated TNF-α production after muscle damage may impair insulin-signal transduction. The data from okadaic acid suggest that TNF-α impairs insulin stimulation of PI3-kinase activation and MAPK tyrosine phosphorylation through two different mechanisms.