Influence of the pituitary on lipolysis and lipogenesis in fetal pig adipose tissue

Identification of Molecular Mechanisms Related to Pig Fatness at the Transcriptome and miRNAome Levels

Fat deposition and growth rate are closely related to pork quality and fattening efficiency. The next-generation sequencing (NGS) approach for transcriptome and miRNAome massive parallel sequencing of adipocyte tissue was applied to search for a molecular network related to fat deposition in pigs. Pigs were represented by three breeds (Large White, Pietrain, and Hampshire) that varied in fat content within each breed. The obtained results allowed for the detection of significant enrichment of Gene Ontology (GO) terms and pathways associated directly and indirectly with fat deposition via regulation of fatty acid metabolism, fat cell differentiation, inflammatory response, and extracellular matrix (ECM) organization and disassembly. Moreover, the results showed that adipocyte tissue content strongly affected the expression of leptin and other genes related to a response to excessive feed intake. The findings indicated that modification of genes and miRNAs involved in ECM rearrangements can be essential during fat tissue growth and development in pigs. The identified molecular network within genes and miRNAs that were deregulated depending on the subcutaneous fat level are proposed as candidate factors determining adipogenesis, fatness, and selected fattening characteristics in pigs.

Growth impairment in individuals with citrin deficiency

Citrin deficiency causes neonatal intrahepatic cholestasis (NICCD), failure to thrive and dyslipidemia (FTTDCD), and adult-onset type II citrullinemia (CTLN2). Owing to a defect in the NADH-shuttle, citrin deficiency impairs hepatic glycolysis and de novo lipogenesis leading to hepatic energy deficit. To investigate the physiological role of citrin, we studied the growth of 111 NICCD-affected subjects (51 males and 60 females) and 12 NICCD-unaffected subjects (five males and seven females), including the body weight, height, and genotype. We constructed growth charts using the lambda-mu-sigma (LMS) method. The NICCD-affected subjects showed statistically significant growth impairment, including low birth weight and length, low body weight until 6 to 9 months of age, low height until 11 to 13 years of age, and low body weight in 7 to 12-year-old males and 8-year-old females. NICCD-unaffected subjects showed similar growth impairment, including low birth weight and height, and growth impairment during adolescence. In the third trimester, de novo lipogenesis is required for deposition of body fat and myelination of the developing central nervous system, and its impairment likely causes low birth weight and length. The growth rate is the highest during the first 6 months of life and slows down after 6 months of age, which is probably associated with the onset and recovery of NICCD. Adolescence is the second catch-up growth period, and the proportion and distribution of body fat change depending on age and sex. Characteristic growth impairment in citrin deficiency suggests a significant role of citrin in the catch-up growth via lipogenesis.

Endocrine Regulation of Fetal Adipose Tissue Metabolism in the Pig: Role of Hydrocortisone

Glucocorticoids have been shown to be essential for the excessive fat deposition and development of obesity in several animal models. This study was performed to characterize the role of glucocorticoids in the developmental regulation of adipose tissue metabolism. On day 70 of gestation, pig fetuses were hypophysectomized by micro-cauterization. Hypophysectomized fetuses were implanted subcutaneously with hydrocortisone pellets or received no hormone replacement. Fetuses were removed by laparotomy on day 90 of gestation. Additional fetuses were hypophysectomized on day 70, implanted with hydrocortisone pellets on day 90 and removed on day 105 of gestation. Several intact fetuses were also implanted subcutaneously with hydrocortisone pellets during this later gestational period. Serum cortisol concentrations were reduced in hypophysectomized pigs at both fetal ages and were restored to intact levels by hydrocortisone treatment. Hydrocortisone supplementation enhanced lipolytic response to isoproterenol in intact fetuses but failed to restore lipolytic response to isoproterenol in hypophysectomized animals at either fetal age. Hydrocortisone induced a slight increase in lipogenesis in hypophysectomized fetuses when administered from 70 to 90 days of gestation and a more dramatic increase when administered from days 90 to 105 of gestation. However, hydrocortisone had no effect on basal or insulin stimulated lipogenesis in intact fetuses when administered from days 90 to 105 of gestation. These results indicate that hydrocortisone may have a primary influence on adipose tissue metabolism during late fetal development only in the absence of inhibition from counterregulatory hormones of pituitary origin.

Triglyceride metabolism in pregnancy

During pregnancy, complex changes occur in lipid profiles. From the 12th week of gestation, phospholipids, cholesterol (total, LDL, HDL), and triglycerides (TG) increase in response to estrogen stimulation and insulin resistance. Transition to a catabolic state favors maternal tissue lipid use as energy sources, thus sparing glucose and amino acids for the fetus. In addition, maternal lipids, that is, cholesterol, are available for fetal use in building cell membranes and as precursor of bile acids and steroid hormones. It is also required for cell proliferation and development of the growing body. Free-fatty acids (FFA), oxidized in the maternal liver as ketone-bodies, represent an alternative fuel for the fetus. Maternal hypertriglyceridemia (vs. other lipids) has many positive effects such as contributing to fetal growth and development and serving as an energy depot for maternal dietary fatty acids. However, increased TG during pregnancy appears to increase risk of preeclampsia and preterm birth. Some have suggested that maternal hypertriglyceridemia has a role in increasing cardiovascular risk later in life. This chapter reviews lipid metabolism during pregnancy to elucidate its effect on fetal growth and its potential role in pregnancy-associated complications and future cardiovascular risk.

Lipid metabolism in the fetus and the newborn

During late gestation, although maternal adipose tissue lipolytic activity becomes enhanced, lipolytic products cross the placenta with difficulty. Under fasting conditions, free fatty acids (FFA) are used for ketogenesis by the mother, and ketone bodies are used as fuels and lipogenic substrates by the fetus. Maternal glycerol is preferentially used for glucose synthesis, saving other gluconeogenic substrates, like amino acids, for fetal growth. Placental transfer of triglycerides is null, but essential fatty acids derived from maternal diet, which are transported as triglycerides in lipoproteins, become available to the fetus owing to the presence of both lipoprotein receptors and lipase activities in the placenta. Diabetes in pregnancy promotes lipid transfer to the fetus by increasing the maternal-fetal gradient, which may contribute to an increase in body fat mass in newborns of diabetic women. Deposition of fat stores in the fetus is very low in the rat but high in humans, where body fat accretion occurs essentially during the last trimester of intra-uterine life. This is sustained by the intense placental transfer of glucose and by its use as a lipogenic substrate, as well as by the placental transfer of fatty acids and to their low oxidation activity. During the perinatal period an active ketonemia develops, which is maintained in the suckling newborn by several factors: (i) the high-fat and low-carbohydrate content in milk, (ii) the enhanced lipolytic activity occurring during the first few hours of life, and (iii) both the uptake of circulating triglycerides by the liver due to the induction of lipoprotein lipase (LPL) activity in this organ, and the presence of ketogenic activity in the intestinal mucose. Changes in LPL activity, lipogenesis and lipolysis contribute to the sequential steps of adipocyte hyperplasia and hypertrophia occurring during the extra-uterine white adipose tissue development in rat, and this may be used as a model to extrapolate the intra-uterine adipose tissue development in other species, including humans.

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.

Endocrine regulation of fetal adipose tissue metabolism in the pig: interaction of porcine growth hormone and thyroxine

OBJECTIVE

This study tested the hypothesis that combined treatment of thyroxine (T4) and growth hormone (GH) could normalize cellular and metabolic aspects of adipose tissue development of hypophysectomized fetal pigs.

RESEARCH METHODS AND PROCEDURES

On day 70 of gestation, pig fetuses were hypophysectomized by microcauterization or remained intact. Hypophysectomized fetuses remained untreated or were treated from day 90 to day 105 of gestation with T4, GH, or a combination of both hormones.

RESULTS

Body weights were unaffected by hypophysectomy or hormone treatment. De novo lipogenesis in subcutaneous adipose tissue was increased 10-fold by hypophysectomy, consistent with our previous results. This increase was abolished by GH treatment in the hypophysectomized fetuses. In contrast, T4 treatment of the hypophysectomized fetuses resulted in a 12-fold further increase in adipose tissue lipogenesis, an effect that was negated by concomitant administration of GH. Lipolytic response to isoproterenol was decreased by hypophysectomy, unaffected by GH treatment, and restored to intact values by T4 or by T4+GH treatment in the hypophysectomized fetuses.

DISCUSSION

In contrast to T4, GH does not influence serum insulin-like growth factor-I or adipose tissue lipolysis, but decreases lipogenesis in the fetal pig. However, replacing both T4 and GH normalized hypophysectomized fetuses to a greater extent than either GH or T4 alone. Thus, any influence of thyroid hormones on stimulating adipose tissue lipogenesis in the developing fetal pig may be normally counterregulated by pituitary-derived growth hormone.

Influence of adenosine or adrenergic agonists on growth hormone stimulated lipolysis by chicken adipose tissue in vitro

In vitro lipolysis by chicken adipose explants was stimulated by growth hormone (GH) or glucagon. Adenosine or the adenosine agonist, N6-phenylisopropyladenosine (PIA), inhibited GH stimulated lipolysis, the effect of adenosine not being observed in the presence or adenosine deaminase. Glucagon induced lipolysis was also reduced by PIA. It is suggested that adenosine may act by Gi linked to either adenylate cyclase (for glucagon) or the signal transduction mechanism for GH. Lipolysis was not stimulated by GH in the presence of phenylephrine (alpha 1 adrenergic agonist), isoproterenol (beta adrenergic agonist), adrenaline or glucagon. Although the presence of p-amino clonidine (alpha 2 adrenergic agonist) depressed basal lipolysis, a response to GH was still present. Either glucagon or beta-adrenergic agonists (isoproterenol, adrenaline) stimulated lipolysis. In both cases, GH attenuated the lipolytic response to these hormones, which act via a cyclic adenosine monophosphate signal transduction mechanism.