Cross-talk between the insulin and leptin signaling systems in rat hypothalamus.
OBJECTIVE
To investigate whether insulin and leptin share common intracellular signal transduction pathways and to determine whether these hormonal signaling systems modulate each other's action in rat hypothalamus.


METHODS
Male Wistar rats were studied after chronic implantation of an intracerebroventricular catheter into the third ventricle. Immunoprecipitation and immunoblotting were used to examine the activation of insulin and leptin signaling molecules in the rat hypothalamus.


RESULTS
Insulin alone is able to produce molecular activation of insulin receptor substrates (IRSs)/phosphatidylinositol 3-kinase (PI 3-kinase)/Akt and mitogen-activated protein (MAP) kinase signaling pathways in hypothalamus, whereas leptin alone activates MAP kinase and IRSs/PI 3-kinase signaling with no effect on Akt. Combined infusion of leptin and insulin provokes a dual action. There was no quantitative potentialization of any single hormone's action on the elements of the insulin signaling pathway, IRSs/PI 3-kinase/Akt, and MAP kinase. Conversely, leptin plus insulin leads to quantitative potentialization of molecular signaling through the Janus kinase/signal transducer and activator of transcription pathway.


CONCLUSIONS
We provide evidence for a convergence of leptin and insulin signaling at the level of IRSs-PI 3-kinase and a divergence at the level of Akt. Moreover, our results indicate a direct and positive cross-talk between insulin and leptin at the level of Janus kinase 2 and signal transducer and activator of transcription 3 tyrosine phosphorylation. This mechanism may serve to potentiate the activity of both insulin and leptin pathways and to increase stimulation in physiological processes such as the control of food intake and body weight, which are under the combined control of insulin and leptin.
Carvalheira
José B C
JB
Department of Internal Medicine, State University of Campinas (UNICAMP), Campinas SP, Brazil.
Torsoni
Márcio A
MA
Ueno
Mirian
M
Amaral
Maria E
ME
Araújo
Eliana P
EP
Velloso
Lício A
LA
Gontijo
José A R
JA
Saad
Mario J A
MJ
D000818:Animals; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000502:physiology; D004435:Eating / Q000502:physiology; D007031:Hypothalamus / Q000502:physiology*; D007276:Injections, Intraventricular; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin / Q000502:physiology*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010750:Phosphoproteins / Q000502:physiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology
D004268:DNA-Binding Proteins; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; C494088:Stat3 protein, rat; C494920:Akt1 protein, rat