Abstract:

Objective To investigate effects of leptin on gene and protein expression and tyrosine phosphorylation of leptin receptor in rat hepatocytes.Methods hepatocytes were isolated from new-born Sprague-Dawley rats,after incubation with leptin(5 nmol/L) for 12,24 and 36 h,Western bolt was used to assess the protein level of leptin-receptor.The mRNA expression level of leptin-receptor was assayed by RT-PCR.The tyrosine phosphorylation of leptin-receptor weas assayed by immuno-precipitation.Results After incubation with leptin(5 nmol/L) for 12,24 and 48 h,there was no difference in the protein contents of leptin receptors between leptin(5 nmol/L) treated and control hepatocytes(P>0.05).The mRNA content of leptin receptor in rat hepatocytes was similar to that of the control after incubation with leptin(5 nmol/L) for 12 h(P>0.05),but significantly decreased after 24 or 36 h(24 h: leptin(5 nmol/L) 0.37±0.05 vs control 0.33±0.03,P<0.05;;36 h: leptin(5 nmol/L) 0.36±0.04 vs control 0.32±0.01,P<0.05).The tyrosine phosphorylation of leptin-receptor was remarkably reduced after incubation with leptin(5 nmol/L) for 24 or 36 h(24 h: leptin(5 nmol/L) 0.30±0.05 vs control 0.27±0.05,P<0.05;36 h: leptin(5 nmol/L) 0.32±0.05 vs control 0.26±0.07,P<0.05).Conclusion Leptin(5 nmol/L) may up-regulate leptin receptor gene expression and its tyrosine phosphorylation in rat hepatocytes and may contribute to promoting the signal transduction of leptin itself.

Key words: leptin, leptin receptor, signal transduction, tyrosine phosphorylation