Expression of leptin mRNA and CCAAT-enhancer binding proteins in response to insulin deprivation during preadipocyte differentiation in primary cultures of porcine stromal-vascular cells

The aim of this study was to examine the correlation between CCAAT-enhancer binding proteins (C/EBPs) and leptin gene expression in response to insulin deprivation in preadipocytes and adipocytes. Adipose tissue from 7 d-old pigs was digested enzymatically and stromal-vascular (S-V) cells were seeded and plated for 3 d in fetal bovine serum (FBS) with dexamethasone (DEX) followed by 6 d (Days 3–9) in serum-free medium with insulin (850 nM or 10 nM), transferrin, and selenium. During FBS+DEX treatment (Days 0–3) a large number of preadipocytes develop with no lipid accretion. In contrast, preadipocyte number does not change with lipid accretion during insulin treatment (Days 3–9). Total RNA and cells were harvested from S-V cultures after periods with and without insulin after FBS+DEX. Northern-blotting and Western blot analysis were used to study leptin mRNA and C/EBP protein expression in cultures, respectively. Insulin deprivation from Days 3–4 reduced leptin mRNA and C/EBP- protein expression. Treatment with 850 nM or 10 nM insulin from Days 3–9 induced leptin mRNA and C/EBP- expression at a similar level. In cultures treated with 10 nM insulin from Days 3–7, leptin and C/EBP- expression were reduced markedly by insulin deprivation from Days 7–9, but were restored by insulin treatment for 6 hr before harvesting. The restoration of leptin expression by insulin was blocked by cycloheximide treatment. However, C/EBP-β protein levels did not change regardless of insulin deprivation. Insulin deprivation from Days 7–9 in cultures treated with 850 nM insulin from Days 3–7 did not influence C/EBP- or leptin mRNA expression, whereas C/EBP- and leptin expression were reduced after treating these cultures with 1.5 uM okadaic acid for 45 min before harvesting on Day 9. However, cycloheximide treatment for 6 hr before harvesting did not reduce leptin mRNA expression. These results suggest that 1) leptin expression is positively correlated with C/EBP- expression, and 2) the maintenance of leptin expression after insulin deprivation in 850 nM insulin-treated cultures on Day 9 may be associated with the presence of C/EBP- expression and/or activation.