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  • Title: IGF-I transcript levels in whole-liver tissue, in freshly isolated hepatocytes, and in cultured hepatocytes from lean and obese Zucker rats.
    Author: Tenoutasse S, Van Vliet G, Ledru E, Deal C.
    Journal: Horm Res; 2003; 59(3):135-41. PubMed ID: 12637793.
    Abstract:
    BACKGROUND: The mechanisms underlying the maintenance of normal to high rates of linear growth and plasma insulin-like growth factor I (IGF-I) levels in spite of a low growth hormone secretion in obese children remain unknown. Among the animal models of early-onset obesity, obese Zucker (FA/FA) rats (which are homozygous for an inactivating missense mutation in the leptin receptor) are particularly appropriate, because their linear growth shows this growth hormone independence. METHODS: To study the regulation of IGF-I synthesis in this model, we have established primary cultures of hepatocytes derived from 12-week-old Zucker male obese and lean rats. The rat IGF-I gene contains six exons, and alternative splicing generates different mRNAs, one of which (called IGF-1B) has been shown to be decreased by fasting. We report steady state mRNA levels for IGF-I (all transcripts) and for IGF-IB in hepatocytes after 3 days in culture, in freshly isolated hepatocytes, and in whole-liver tissue. RT-PCRs using primers specific for IGF-I or IGF-IB were performed with two different internal competitors for quantification. RESULTS: In primary cultures of hepatocytes, the IGF-IB mRNA was increased by >50-fold (p = 0.01) in cells derived from obese animals as compared with cells from lean animals. However, these transcript levels were not significantly different when measured in freshly isolated hepatocytes or in whole-liver tissue. CONCLUSIONS: Increased IGF-IB transcription could be an intrinsic characteristic of cultured hepatocytes harbouring leptin receptors that bear the FA mutation. However, the modulation of this characteristic by cell-cell interactions and by in vivo hormone and metabolic status remains to be studied.
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