Insulin inhibits leptin receptor signalling in HEK293 cells at the level of janus kinase-2: a potential mechanism for hyperinsulinaemia-associated leptin resistance

Aims/hypothesis. Leptin resistance in obese humans seems to be predominantl y caused by signalling abnormalities at the post receptor level. Leptin res istance in obese individuals is frequently associated with insulin resistan ce and pronounced hyperinsulinaemia indicating a negative crosstalk of the insulin and leptin signalling chain. Methods. This hypothesis was tested us ing a cell model of peripheral leptin signalling, i.e. insulin-secreting ce ll lines (RINr1046-38). Mechanisms for a crosstalk between the insulin and leptin signalling pathway were also studied in rat-1 and HEK293 cells overe xpressing elements of the insulin and leptin signalling chain. Results. The effects of leptin on insulin secretion are completely cancelled by a 4-h p reincubation with 1 nmol/l insulin, supporting the hypothesis of a negative crosstalk of insulin and leptin signalling. We investigated the potential molecular mechanisms in more detail in HEK293 cells and Rat-1 fibroblasts t hat overexpressed proteins of the insulin and leptin signalling chain. Lept in (60 ng/ml) stimulated autophosphorylation of JAK-2 in HEK 293 cells. Thi s leptin effect could be inhibited by simultaneous treatment of cells with insulin. Furthermore, overexpression of the insulin receptor in HEK 293 cel ls clearly reduced JAK-2 phosphorylation and led further downstream to a di minished phosphatidylinositol 3-kinase activity. The inhibitory effect of t he insulin signal could be partially prevented by transfection of the cells with an inactive mutant of the tyrosine phosphatase SHP-1. Conclusion/inte rpretation. In summary, our data suggest that the insulin receptor signalli ng pathway interferes with leptin signalling at the level of JAK-2. Inhibit ion of JAK-2 phosphorylation might occur through SHP-1-dependent pathways, indicating that hyperinsulinaemia contributes to the pathogenesis of leptin resistance.