Hepatic leptin signaling in obesity

Area of Science:

• Metabolic disease research
• Hormonal signaling pathways
• Liver physiology

Background:

• Obesity is linked to leptin and insulin resistance.
• Diet-induced obesity (DIO) impairs hepatic insulin signaling.
• The interplay between leptin and insulin signaling in DIO is not fully understood.

Purpose of the Study:

• To investigate the impact of DIO on leptin and insulin cross-signaling in the liver.
• To assess leptin receptor expression and downstream signaling in lean and DIO rats.
• To elucidate the role of nutritional status and AMPK in regulating these pathways.

Main Methods:

• Diet-induced obesity model in rats.
• Measurement of leptin receptor expression (in situ hybridization, immunoblotting).
• In vivo assessment of intracellular signaling pathways (JAK-2, IRS, PKB, GSK-3beta, AMPK) after leptin stimulation.

Main Results:

• DIO rats exhibited down-regulated leptin receptors and impaired basal insulin signaling.
• Leptin failed to stimulate key signaling molecules (JAK-2pY) in DIO rats.
• Leptin-induced phosphorylation of PKB and GSK-3beta occurred only in lean rats.
• AMPK activity was comparable between lean and DIO rats, suggesting its role in sensing nutritional status.

Conclusions:

• DIO significantly impairs liver leptin and insulin signaling pathways.
• Down-regulation of leptin receptors and signaling contributes to insulin resistance in obesity.
• The liver plays a critical role in modulating leptin signals and insulin resistance, influenced by nutritional status sensed by AMPK.