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Insulin stimulates nitric oxide production in rat adipocytes
Catherine Ribière1, Anne-Marie Jaubert, Dominique Sabourault
1Laboratory of Biochemistry and Molecular Biology, Faculté de Médecine Paris-Ouest, UFR Biomédicale des Saints-Pères, Université Paris V, 45 rue des Saints-Pères, Paris, France. catherine.ribiere@paris-ouest.univ-paris5.fr
Abstract:
In adipocytes, insulin regulates the activity of different protein kinases (PI3K/Akt, MAPK, PKC) and protein phosphatases (PP-1, PP-2A). Since these enzymes are implicated in the regulation of NOS activity which is present in adipose tissue, we tested the effects of insulin on white adipocyte NOS activity. Exposure of adipocytes to insulin resulted simultaneously in NOS activity stimulation and Akt activation with maximal effect observed at 1 nM. Higher concentrations of insulin induced a progressive decline of NOS activity. In the presence of wortmannin, a PI3K inhibitor, 1 nM insulin failed to stimulate NOS activity. Insulin (1 nM)-stimulated NOS activity was also abolished by U0126, an inhibitor of p42/p44 MAPK activation, and by 1 microM okadaic acid (OA), which inhibits both PP-1 and PP-2A but not by 1 nM OA which inhibits only PP-2A. Moreover, inhibition of cPKC allowed a high (1 microM) insulin concentration to stimulate NOS activity. These results (i) demonstrate that insulin activates NO production in adipocytes through both PI3K/Akt and MAPK/PP-1 activation and (ii) suggest that PP-1 activation protects NOS against the inhibitory effect of cPKC activation.
Insights
Insulin stimulates nitric oxide synthase (NOS) activity in white adipocytes via PI3K/Akt and MAPK/PP-1 pathways. Protein phosphatase 1 (PP-1) activation protects NOS from protein kinase C inhibition.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Insulin modulates adipocyte signaling pathways, including protein kinases and phosphatases.
- These enzymes are known regulators of nitric oxide synthase (NOS) activity.
- Adipose tissue NOS activity regulation by insulin remains incompletely understood.
Purpose of the Study:
- To investigate the effects of insulin on white adipocyte nitric oxide synthase (NOS) activity.
- To elucidate the specific signaling pathways involved in insulin-mediated NOS regulation in adipocytes.
Main Methods:
- Adipocytes were exposed to varying insulin concentrations.
- Inhibitors of PI3K (wortmannin), MAPK (U0126), and protein phosphatases (okadaic acid) were used.
- Akt activation and NOS activity were measured.
Main Results:
- Insulin (1 nM) stimulated NOS activity and Akt activation in adipocytes.
- PI3K/Akt and MAPK pathways were essential for insulin-stimulated NOS activity.
- PP-1 activation, but not PP-2A, was involved in mediating insulin's effect.
- Inhibition of PKC allowed higher insulin concentrations to stimulate NOS.
Conclusions:
- Insulin activates NO production in adipocytes through coordinated PI3K/Akt and MAPK/PP-1 signaling.
- PP-1 activation plays a protective role, preventing NOS inhibition by PKC in adipocytes.