Suppression of Rho-kinase 1 is responsible for insulin regulation of the AMPK/SREBP-1c pathway in skeletal muscle cells exposed to palmitate

• Published in: Acta diabetologica Vol. 54; no. 7; pp. 635 - 644
• Main Authors: Tang, Sunyinyan, Wu, Wenjun, Tang, Wenjuan, Ge, Zhijuan, Wang, Hongdong, Hong, Ting, Zhu, Dalong, Bi, Yan
• Format: Journal Article
• Language: English
• Published: Milan Springer Milan 01.07.2017; Springer Nature B.V
• Subjects: 1-Phosphatidylinositol 3-kinase; AKT protein; AMP; AMP-activated protein kinase; AMP-Activated Protein Kinases - metabolism; Animal models; Animals; Cells, Cultured; Chronic exposure; Diabetes; Diabetes mellitus; Diabetes Mellitus, Type 2 - metabolism; High fat diet; Insulin; Insulin - metabolism; Insulin - pharmacology; Internal Medicine; Kinases; Male; Medicine; Medicine & Public Health; Metabolic Diseases; Metformin; Metformin - pharmacology; Mice; Mice, Inbred C57BL; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - metabolism; Muscle, Skeletal - metabolism; Musculoskeletal system; Myotubes; Original Article; Palmitic acid; Palmitic Acid - pharmacology; Phosphorylation; Protein kinase; Protein-serine/threonine kinase; Proteins; Rho-associated kinase; rho-Associated Kinases - antagonists & inhibitors; rho-Associated Kinases - metabolism; RhoA protein; Signal transduction; Signal Transduction - drug effects; siRNA; Skeletal muscle; Skeleton; Sterol Regulatory Element Binding Protein 1 - metabolism; Sterol regulatory element-binding protein; Sterol regulatory element-binding protein 1c; AMPK; Rho-kinase 1; Insulin; SREBP-1c; Skeletal muscle
• ISSN: 0940-5429; 1432-5233
• DOI: 10.1007/s00592-017-0976-z

Aims Clinical and experimental data suggest that early insulin therapy could reduce lipotoxicity in subjects and animal models with type 2 diabetes mellitus. However, the underlying mechanisms need to be clarified. Sterol regulatory element-binding protein 1c (SREBP-1c), which is negatively regulated by AMP-activated protein kinase (AMPK), plays a critical role in lipotoxicity and insulin resistance in skeletal muscle cells. Here, we investigated the effect and molecular mechanism of insulin intervention on the AMPK/SREBP-1c pathway in skeletal muscle cells with chronic exposure to palmitic acid (PA). Methods Male C57BL/6 mice were fed with a high-fat diet for 12 weeks and were then treated with insulin, AMPK inhibitor, or metformin. L6 myotubes incubated with palmitic acid (PA) were treated with insulin or metformin. Dominant-negative AMPKα2 (DN-AMPKα2) lentivirus, AMPKα2 siRNA, or Rho-kinase 1 (ROCK1) siRNA were transfected into PA-treated L6 myotubes. Results We found that the ability of PA to stimulate SREBP-1c and inhibit AMPK was reversed by insulin in L6 cells. Moreover, DN-AMPKα2 lentivirus and AMPKα2 siRNA were transfected into PA-treated L6 myotubes, and the decrease in SREBP-1c expression caused by insulin was blocked by AMPK inhibition independent of the phosphatidylinositol-4,5-biphosphate-3-kinase (PI3K)/AKT pathway. The serine/threonine kinase Rho-kinase (ROCK) 1, a downstream effector of the small G protein RhoA, was activated by PA. Interestingly, knockdown of ROCK1 by siRNA blocked the downregulation of AMPK phosphorylation under PA-treated L6 myotubes, which indicated that ROCK1 mediated the effect of insulin action on AMPK. Conclusions Our study indicated that insulin reduced lipotoxicity via ROCK1 and then improved AMPK/SREBP-1c signaling in skeletal muscle under PA-induced insulin resistance.