Abstract
The endocannabinoid system regulates food intake, energy, and glucose metabolism at both central and peripheral levels. We have investigated the mechanism by which it may control glucose uptake in skeletal muscle cells. Detectable levels of the cannabinoid receptor type 1 (CB1) were revealed in L6 cells. Exposure of differentiated L6 myotubes to the CB1 antagonist rimonabant (SR141716) selectively increased 2-deoxyglucose uptake (2-DG) in a time- and dose-dependent manner. A similar effect was induced by genetic silencing of CB1 by small interfering RNA. Protein expression profiling revealed that both the regulatory p85 and the catalytic p110 subunits of the phosphatidylinositol-3-kinase (PI3K) were increased by SR141716. No significant change in the cellular content of other known molecules regulating PI3K was observed. However, phosphoinositide-dependent kinase-1, Akt/protein kinase B, and protein kinase Cζ activities were rapidly induced after SR141716 treatment of L6 cells in a PI3K-dependent manner. The stimulatory effect of SR141716 on PI3K expression and activity was largely prevented by N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H-89), an inhibitor of the cAMP-dependent protein kinase. Moreover, SR141716-stimulated 2-DG uptake was blunted by the coincubation either with H-89 or with the PI3K inhibitor 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002), both in L6 cells and in mouse primary myocytes. Thus, modulation of CB1 regulates glucose uptake at the level of the PI3K signaling system in skeletal muscle cells. Interfering with CB1 signaling may therefore ameliorate glucoregulatory functions in peripheral tissues.
Footnotes
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This study was supported in part by the European Community's FP6 EUGENE2 (LSHM-CT-2004-512013) and FP7 PREPOBEDIA (number 201-681), grants from the Associazione Italiana per la Ricerca sul Cancro (to F.B. and P.F.), the Ministero dell'Università e della Ricerca Scientifica (to F.B. and P.F. and FIRB Idea Progettuale RBIP0689BS), the Ministero della Salute, the European Federation for the Study of Diabetes, and by the Associazione Educazione e Ricerca Medica Salernitana (ERMES). The financial support of Telethon-Italy is also gratefully acknowledged. I.E. was awarded a travel grant from the Università di Napoli “Federico II”-International Exchange Program.
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ABBREVIATIONS: T2D, type 2 diabetes; 2-DG, 2-deoxyglucose; PKB, protein kinase B; CB1, cannabinoid receptor type 1; CHX, cycloheximide; CREB, cAMP response element-binding protein; DMEM, Dulbecco's modified Eagle's medium; ECS, endocannabinoid system; GLUT, glucose transporter; IRS, insulin receptor substrate; IRTX, iodoresinatoxin; PeSt, penicillin-streptomycin; PKCζ, protein kinase Cζ; PDK-1, phosphoinositide-dependent kinase-1; PI3K, phosphatidylinositol-3-kinase; PKA, protein kinase A; PTEN, phosphatase and tensin homolog; siRNA, small interfering RNA; SR141716, rimonabant; H-89, N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline; LY294002, 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride; PCR, polymerase chain reaction; RT-PCR, reverse transcriptase-polymerase chain reaction; PAGE, polyacrylamide gel electrophoresis.
- Received May 26, 2008.
- Accepted September 18, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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