Expression of c-Fos in subcutaneous adipose tissue of the fetal pig

Developmental Stage, Muscle and Genetic Type Modify Muscle Transcriptome in Pigs: Effects on Gene Expression and Regulatory Factors Involved in Growth and Metabolism

Iberian pig production includes purebred (IB) and Duroc-crossbred (IBxDU) pigs, which show important differences in growth, fattening and tissue composition. This experiment was conducted to investigate the effects of genetic type and muscle (Longissimus dorsi (LD) vs Biceps femoris (BF)) on gene expression and transcriptional regulation at two developmental stages. Nine IB and 10 IBxDU piglets were slaughtered at birth, and seven IB and 10 IBxDU at four months of age (growing period). Carcass traits and LD intramuscular fat (IMF) content were measured. Muscle transcriptome was analyzed on LD samples with RNA-Seq technology. Carcasses were smaller in IB than in IBxDU neonates (p < 0.001), while growing IB pigs showed greater IMF content (p < 0.05). Gene expression was affected (p < 0.01 and Fold change > 1.5) by the developmental stage (5,812 genes), muscle type (135 genes), and genetic type (261 genes at birth and 113 at growth). Newborns transcriptome reflected a highly proliferative developmental stage, while older pigs showed upregulation of catabolic and muscle functioning processes. Regarding the genetic type effect, IBxDU newborns showed enrichment of gene pathways involved in muscle growth, in agreement with the higher prenatal growth observed in these pigs. However, IB growing pigs showed enrichment of pathways involved in protein deposition and cellular growth, supporting the compensatory gain experienced by IB pigs during this period. Moreover, newborn and growing IB pigs showed more active glucose and lipid metabolism than IBxDU pigs. Moreover, LD muscle seems to have more active muscular and cell growth, while BF points towards lipid metabolism and fat deposition. Several regulators controlling transcriptome changes in both genotypes were identified across muscles and ages (SIM1, PVALB, MEFs, TCF7L2 or FOXO1), being strong candidate genes to drive expression and thus, phenotypic differences between IB and IBxDU pigs. Many of the identified regulators were known to be involved in muscle and adipose tissues development, but others not previously associated with pig muscle growth were also identified, as PVALB, KLF1 or IRF2. The present study discloses potential molecular mechanisms underlying phenotypic differences observed between IB and IBxDU pigs and highlights candidate genes implicated in these molecular mechanisms.

Esculetin induces apoptosis and inhibits adipogenesis in 3T3-L1 cells

OBJECTIVE

To determine the effects of esculetin, a plant phenolic compound with apoptotic activity in cancer cells, on 3T3-L1 adipocyte apoptosis and adipogenesis.

RESEARCH METHODS AND PROCEDURES

3T3-L1 pre-confluent preadipocytes and lipid-filled adipocytes were incubated with esculetin (0 to 800 microM) for up to 48 hours. Viability was determined using the Cell Titer 96 Aqueous One Solution cell proliferation assay; apoptosis was quantified by measurement of single-stranded DNA. Post-confluent preadipocytes were incubated with esculetin for up to 6 days during maturation. Adipogenesis was quantified by measuring lipid content using Nile Red dye; cells were also stained with Oil Red O for visual confirmation of effects on lipid accumulation.

RESULTS

In mature adipocytes, esculetin caused a time- and dose-related increase in adipocyte apoptosis and a decrease in viability. Apoptosis was increased after only 6 hours by 400 and 800 microM esculetin (p < 0.05), and after 48 hours, as little as 50 microM esculetin increased apoptosis (p < 0.05). In preadipocytes, apoptosis was detectable only after 48 hours (p < 0.05) with 200 microM esculetin and higher concentrations. However, results of the cell viability assay indicated a reduction in preadipocyte number in a time- and dose-related manner, beginning as early as 6 hours with 400 and 800 microM esculetin (p < 0.05). Esculetin also inhibited adipogenesis of 3T3-L1 preadipocytes. Esculetin-mediated inhibition of adipocyte differentiation occurred during the early, intermediate, and late stages of the differentiation process. In addition, esculetin induced apoptosis during the late stage of differentiation.

DISCUSSION

These findings suggest that esculetin can alter fat cell number by direct effects on cell viability, adipogenesis, and apoptosis in 3T3-L1 cells.

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 proliferator-activated receptor gamma (PPARgamma) 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 beta (C/EBPbeta) expression to see if it was correlated with PPARgamma expression. Pituitary function and hormones involved with differentiation (dexamethasone and retinoic acid) were also tested for their effects on PPARgamma expression to determine if hormones known to affect differentiation also effect PPARgamma 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 PPARgamma and C/EBPbeta. 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 PPARgamma.

RESULTS

Our results indicate that PPARgamma is expressed as early as 50 days of fetal development in adipose tissue and continues through 105 days. Expression of PPARgamma was found to be significantly enhanced in adipose tissue from hypophysectomized fetuses at 105 days of fetal development (p<0.05). C/EBPbeta was not found in 50- or 75-day fetal tissues and was found only at low levels in 105-day tissues. C/EBPbeta was not found in hypophysectomized (hypoxed) 105-day tissue where PPARgamma was elevated. S-V cells freshly isolated from adipose tissue of 5- to 7-day postnatal pigs showed the expression of PPARgamma1. When S-V cells were cultured, both PPARgamma1 and 2 were expressed after the first day and continued as cells differentiated. High concentrations of retinoic acid decreased PPARgamma expression in early S-V cultures (p<0.05).

DISCUSSION

Our data indicate that PPARgamma is expressed in fetal adipose tissue very early before distinct fat cells are observed and can be expressed without the expression of C/EBPbeta. The increase in PPARgamma 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 PPARgamma 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 PPARgamma and C/EBPalpha are expressed but new signals or vascularization are needed before cells are fully committed and lipid filling begins.

Expression of CCAAT/enhancer binding protein C/EBPalpha, beta and delta in rat adipose stromal-vascular cells in vitro

Stromal-vascular (S-V) cells from rat inguinal fat depots were isolated and cultured in medium containing fetal bovine serum (FBS) and differentiated in defined medium until lipid accumulation was apparent. C/EBPalpha, beta and delta levels were evaluated for different growth conditions and at different times using Western blots. Immediately after isolation C/EBPalpha, beta and delta could not be detected in S-V cells. After seeding for 24 h in Dulbecco's modified Eagle's medium (DMEM) with FBS, C/EBPalpha, beta and delta could all be detected. Cells at day 1 of culture in insulin, transferrin, triiodothyronine and selenium (ITTS) had increased levels of C/EBPalpha and continued steady high levels to day 6 of culture. Cultures grown in DMEM alone, with no ITTS, showed C/EBPalpha levels similar to ITTS cultures at day 1 and day 3; however, levels diminished after day 3. DMEM cultures also showed lipid accumulation at day 6; however, the number of cells and the amount of lipid cell were reduced from levels observed in ITTS cultures. C/EBPbeta was expressed uniformly throughout the culture period in either DMEM or ITTS cultures while C/EBPdelta expression was higher with DMEM treatment than with ITTS. Treatment of 2 day DMEM cultures with FBS increased levels of C/EBPbeta and delta but significantly reduced levels of C/EBPalpha. Immunocytochemical analysis of S-V cells at day 1 of culture showed a similar percentage of cells stained in DMEM cultures and ITTS cultures. However, by day 6 of culture the percentage of cells staining positively for C/EBPalpha in DMEM had been reduced by one half while in ITTS the percent positive cells remained about the same. Our results indicate that ITTS is not necessary for the induction of C/EBPalpha and accumulation of lipid in S-V cells. However, ITTS is responsible for maintaining C/EBPalpha and enhanced lipid accumulation. Because C/EBPalpha, beta and delta expression occurs very early in cell culture and C/EBPalpha and delta expression continues to increase in DMEM without any apparent inducing agents, our results suggest that these factors may be expressed by the same cells in vivo before being placed in culture. Thus, a large fraction of S-V cells may be further along in the differentiation program than 3T3 cells are when they begin differentiation.