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

Objective: This study was designed to determine when peroxisome proliferato r-activated receptor gamma (PPAR gamma) is expressed in developing fetal ad ipose tissue and stromal-vascular adipose precursor cells derived from adip ose tissue. In addition we examined developing tissue for CCAAT/enhancer-bi nding protein beta (C/EBP beta) expression to see if it was correlated with PPAR gamma expression. Pituitary function and hormones involved with diffe rentiation (dexamethasone and retinoic acid) were also tested for their eff ects on PPAR gamma expression to determine if hormones known to affect diff erentiation also effect PPAR gamma expression in vivo and in cell culture. Research Methods and Procedures: Developing subcutaneous adipose tissues fr om the dorsal region of the fetal pig were collected at different gestation times and assayed using Western blot analysis to determine levels of PPAR gamma and C/EBP beta. Hypophysectomy was performed on 75-day pig fetuses an d tissue samples were then taken at 105 days for Western blot analysis. Adi pose tissue was also taken from postnatal pigs to isolate stromal-vascular (S-V) cells. These adipose precursor cells were grown in culture and sample s were taken for Western blot analysis to determine expression levels of PP AR gamma. Results: Our results indicate that PPAR gamma is expressed as early as 50 d ays of fetal development in adipose tissue and continues through 105 days. Expression of PPAR gamma was found to be significantly enhanced in adipose tissue from hypophysectomized fetuses at 105 days of fetal development (p < 0.05). C/EBP beta was not found in 50- or 75-day fetal tissues and was fou nd only at low levels in 105-day tissues. C/EBP beta was not found in hypop hysectomized (hypoxed) 105-day tissue where PPAR gamma was elevated. S-V ce lls freshly isolated from adipose tissue of 5- to 7-day postnatal pigs show ed the expression of PPAR gamma 1. When S-V cells were cultured, both PPAR gamma 1 and 2 were expressed after the first day and continued as cells dif ferentiated. High concentrations of retinoic acid decreased PPAR gamma expr ession in early S-V cultures (p < 0.05). Discussion: Our data indicate that PPAR gamma is expressed in fetal adipose tissue very early before distinct fat cells are observed and can be expres sed without the expression of C/EBP beta. The increase in PPAR gamma expres sion after hypophysectomy may explain the increase in fat cell size under t hese conditions. Adipose precursor cells (S-V cells) from 5- to 7-day postn atal pigs also express PPAR gamma in the tissue before being induced to dif ferentiate in culture. Thus S-V cells from newborn pig adipose tissue are p robably more advanced in development than the 3T3-L1 cell model. S-V cells may be in a state where PPAR gamma and C/EBP alpha are expressed but new si gnals or vascularization are needed before cells are fully committed and li pid filling begins.