HORMONAL-REGULATION OF LEPTIN MESSENGER-RNA EXPRESSION AND PREADIPOCYTE RECRUITMENT AND DIFFERENTIATION IN PORCINE PRIMARY CULTURES OF S-V CELLS

The hormonal regulation of leptin mRNA expression and the association between leptin expression and adipocyte differentiation were examined in primary cultures of porcine S-V cells with Northern blot and immuno cytochemical analysis, Seeding for 3 days,vith fetal bovine serum (FBS ) with varying levels of dexamethasone (Dex) increased levels of lepti n mRNA in a dose-dependent manner in parallel with increases in the pr oportion of preadipocytes (AD-3 positive cells; AD-3, a preadipocyte m arker). Six-day treatment with 10 or 850 nM insulin after FBS+Dex trea tment resulted in a similar increase in leptin mRNA expression and mor phological differentiation. However, significantly lower levels of lep tin mRNA and smaller fat cells were observed in cultures treated with 1 nM insulin or 10 nM insulin-like growth factor-I (IGF-I), Dex-induce d increases in leptin mRNA levels and AD-3 cell numbers were blocked c ompletely by the addition of transforming growth factor-beta (TGF-beta ) to FBS+Dex-treated cultures. However TGF-beta significantly increase d fat cell size and leptin mRNA expression when added to ITS (insulin, 850 nM; transferrin, 5 mu g/ml; and selenium, 5 mu g/mL) treated cult ures during the lipid-filling stage. When added with FBS+DEX for the f irst 3 days, growth hormone (GH) did not influence the Dex-induced inc rease in AD-3 cells and leptin mRNA expression, but GH reduced leptin mRNA levels when added with insulin for 6 days after FBS+Dex, These re sults demonstrated that regulation of leptin mRNA expression by Dex, i nsulin, IGF-I, TGF-beta, and GH may be associated with changes in prea dipocyte number and fat cell size.