Objective: To study the leptin receptor isoforms regulation by leptin and insulin.
Methods: Human hepatocellular carcinoma cells of the line HepG2 were cultured in DMEM containing 10% FBS in six-well plate and were incubated for 24 hours in serum-free medium containing 0, 10(-9), 10(-8), 10(-7), and 10(-6) mol/L of human leptin or insulin. Using the semi-quantitative RT-PCR technique, the mRNA expressions of long (OB-Rb) and short (OB-Ra: OB-R219.3) leptin receptor isoforms were measured.
Results: OB-Rb and OB-R219.3 mRNAs were expressed in this cell line. Leptin of the concentrations of 10(-7) approximately 10(-6) mol/L significantly inhibited the OB-Rb mRNA expression, with the maximum decrease (by 43%) at the concentration of 10(-6) mol/L. Similarly the mRNA expression of OB-R219.3 was also markedly reduced in cells treated with leptin of the concentrations of 10(-8) approximately 10(-6) (mol/L), with the maximum inhibition (by 49%) at the concentrations of 10(-6) mol/L. Insulin showed no effect on OB-Rb and OB-R219.3 mRNAs expression in HepG2 cell.
Conclusion: In HepG2 cells, leptin down-regulates the expressions of OB-Rb and OB-R219.3 mRNAs, and insulin has no effect on OB-Rb and OB-R219.3 mRNAs, which contributes at least partly to an understanding of the mechanism of leptin resistance in vivo and suggests that leptin-induced receptor down-regulation may be relevant to leptin resistance at sites of peripheral action.