Hexosamines and nutrient excess induce leptin production and leptin receptor activation in pancreatic islets and clonal beta-cells.
Activation of the hexosamine biosynthesis pathway leads to insulin resistance in muscle and adipose tissue. In these tissues leptin gene expression is increased by glucosamine. In the present study we found that glucosamine rapidly activates the production of leptin and OB-Rb, which encodes the functional leptin receptor, in both primary pancreatic islets and clonal beta-cells. Secretion of leptin from clonal beta-cells into the medium was detected readily. In addition, the level of the transcripts encoding signal transducer and activator of transcription-3 and -5, both implicated in leptin signal transduction in islet beta-cells, was increased by glucosamine, although to a lesser degree than mRNA levels of leptin and OB-Rb. High glucose (16.7 mM) induced leptin biosynthesis in primary pancreatic islet cells, and the addition of 1 mM palmitate caused an additional incremental effect. The hexosamine-mediated induction of the leptin system in clonal beta-cells was associated with increased responsiveness to leptin, as demonstrated by a 2.6 +/- 0.3-fold (P < 0.01) increase in tyrosine phosphorylation of signal transducer and activator of transcription-3. These findings are the first evidence of inducible leptin production in pancreatic islets and suggest that islet cells, like skeletal muscle, demonstrate a linkage between increased nutrient availability and both leptin expression and leptin responsiveness.