The expression of peroxisome proliferator-activated receptor γ in pig fetal tissue and primary stromal-vascular cultures

Abstract

Objective: This study was designed to determine when peroxisome proliferator-activated receptor γ (PPARγ) is expressed in developing fetal adipose tissue and stromal-vascular adipose precursor cells derived from adipose tissue. In addition we examined developing tissue for CCAAT/enhancer-binding protein β (C/EBPβ) expression to see if it was correlated with PPARγ expression. Pituitary function and hormones involved with differentiation (dexamethasone and retinoic acid) were also tested for their effects on PPARγ expression to determine if hormones known to affect differentiation also effect PPARγ expression in vivo and in cell culture. Research Methods and Procedures: Developing subcutaneous adipose tissues from the dorsal region of the fetal pig were collected at different gestation times and assayed using Western blot analysis to determine levels of PPARγ and C/EBPβ. Hypophysectomy was performed on 75-day pig fetuses and tissue samples were then taken at 105 days for Western blot analysis. Adipose tissue was also taken from postnatal pigs to isolate stromal-vascular (S-V) cells. These adipose precursor cells were grown in culture and samples were taken for Western blot analysis to determine expression levels of PPARγ. Results: Our results indicate that PPARγ is expressed as early as 50 days of fetal development in adipose tissue and continues through 105 days. Expression of PPARγ was found to be significantly enhanced in adipose tissue from hypophysectomized fetuses at 105 days of fetal development (p < 0.05). C/EBPβ was not found in 50-or 75-day fetal tissues and was found only at low levels in 105-day tissues. C/EBPβ was not found in hypophysectomized (hypoxed) 105-day tissue where PPARγ was elevated. S-V cells freshly isolated from adipose tissue of 5-to 7-day postnatal pigs showed the expression of PPARγ1. When S-V cells were cultured, both PPARγ1 and 2 were expressed after the first day and continued as cells differentiated. High concentrations of retinoic acid decreased PPARγ expression in early S-V cultures (p < 0.05). Discussion: Our data indicate that PPARγ is expressed in fetal adipose tissue very early before distinct fat cells are observed and can be expressed without the expression of C/EBPβ. The increase in PPARγ expression after hypophysectomy may explain the increase in fat cell size under these conditions. Adipose precursor cells (S-V cells) from 5-to 7-day postnatal pigs also express PPARγ in the tissue before being induced to differentiate in culture. Thus S-V cells from newborn pig adipose tissue are probably more advanced in development than the 3T3-L1 cell model. S-V cells may be in a state where PPARγ and C/EBPα are expressed but new signals or vascularization are needed before cells are fully committed and lipid filling begins.