Decreased expression of the IGF-II gene during porcine adipose cell differentiation

Increased expressions of genes and proteins involved in mitochondrial oxidation and antioxidant pathway in adipose tissue of pigs selected for a low residual feed intake

Adipose tissue is a primary sensor for nutrient availability and regulates many functions including feed intake and energy homeostasis. This study was undertaken to determine the molecular responses of adipose tissue to differences in feed intake and feed efficiency. Subcutaneous adipose tissue was collected from two lines of pigs divergently selected for residual feed intake (RFI), a measure of feed efficiency defined as the difference between actual and expected feed intake, and from a subset of high-RFI pigs that were feed-restricted at the level of the voluntary feed intake of low-RFI pigs during the growing-finishing period. Transcriptomics analyses indicated that the number of genes that were differentially expressed ( < 0.01) between low- and high-RFI pigs ( = 8 per group at each stage) in adipose tissue was much lower when pigs were considered at 19 kg (postweaning) than at 115 kg BW (market weight). Extended investigations were performed at 115 kg BW to compare low-RFI ( = 8), high-RFI ( = 8), and feed-restricted high-RFI ( = 8) pigs. They included in silico pathway analyses of the differentially expressed (DE) genes ( < 0.01) and a complementary proteomic investigation to list adipose proteins with a differential abundance ( < 0.10). Only 23% of the DE genes were affected by both RFI and feed restriction. This indicates that the responses of adipose tissue to RFI difference shared only some common mechanisms with feed intake modulation, notably the regulation of cell cycle (including ) and transferase activity pathway. Two carboxylesterase genes (, ) involved in lipolysis, were among the most overexpressed genes in the low-RFI pigs; they were also affected by feed restriction within the high-RFI line. About 60% of the molecular changes between low- and high-RFI pigs were specific to genetic divergence in feed efficiency, independently of feed intake. Different genes and proteins known to be associated with mitochondrial oxidative metabolism were overexpressed in adipose tissue of low-RFI pigs compared with high-RFI pigs; other proteins participating in the generation of energy were also affected by feed restriction within the high-RFI line. Finally, mitochondrial antioxidant genes were upregulated in low-RFI pigs vs. high-RFI pigs. Altogether, increased oxidative and antioxidant processes in adipose tissue might be associated with improved feed efficiency.

Effects of nutritional manipulation on body composition in the developing marsupial, Macropus eugenii

When 60-day-old tammar wallaby pouch young (Macropus eugenii) are fostered to mothers at 120 days of lactation, their growth, developmental rate and maturation of their GH/IGF axes are markedly accelerated. To determine the effect of fostering on energy intake, body composition and fat accretion, we first measured total body fat and lean mass in these young. Next, we mimicked the triglyceride oleic and palmitic acid composition of 120-day milk by supplementing 60 day young with these fatty acids and comparing their growth with that of growth accelerated young. There was no difference in the weight or growth axis maturation of supplemented young but there was significantly more body fat in these and in the growth-accelerated fostered young than in controls. We conclude that the accelerated growth and GH/IGF axis maturation observed previously in fostered young is most likely due to increased milk consumption and earlier access to specific nutrients.

Spontaneous intra-uterine growth restriction modulates the endocrine status and the developmental expression of genes in porcine fetal and neonatal adipose tissue

Low birth weight is correlated with low adiposity at birth, a phenotype that influences neonatal survival and later adiposity. A better understanding of events affecting the fetal adipose tissue development and its functionality around birth is thus needed. This study was undertaken to examine the impact of spontaneous intra-uterine growth restriction (IUGR) on circulating concentrations of hormones and nutrients together with the developmental expression patterns of various genes in subcutaneous adipose tissue of pig fetus during the last third of pregnancy and just after birth. At 71 and 112 days post-conception and 2 days postnatal, pairs of same-sex piglets were chosen within litters to have either a medium (MBW) or a low (LBW) weight (n=6 pairs at each stage). The results indicate that IUGR counteracts the temporal fall of DLK1 gene expression in developing adipose tissue across gestation. It also attenuates the time-dependent increase in expression levels of many genes promoting adipocyte differentiation (PPARG, CEBPA) and lipogenesis (LPL, SREBF1, FASN, FABP4). Opposite responses to IUGR were observed for the IGF system, so that IGF1 mRNA levels were lower (P<0.001) but IGF2 mRNA levels were greater in adipose tissue of LBW piglets compared with MBW piglets. The plasma insulin concentration and the mRNA levels of insulin receptor (INSR) and insulin-responsive glucose transporter (GLUT4) in adipose tissue were also greater in LBW piglets at day 2 postnatal. The data indicate that IUGR delays the normal ontogeny of adipose tissue across gestation and affects the insulin and IGF axes around birth.

Knockdown of ZBED6 is not associated with changes in murine preadipocyte proliferation or differentiation

ZBED6 was identified as a transcription factor that affects muscle mass and fat deposition in pigs. Mechanisms mediating effects on fat mass are unclear. The objective was to determine the effect of ZBED6 mRNA knockdown on 3T3-L1 preadipocyte differentiation and gene expression. Differentiation was associated with increased mRNA abundance of CEBP/α (P < 0.05), CEBP/β (P < 0.05), CEBP/δ (P < 0.05), FASN (P < 0.05), PPARγ (P < 0.05), and SREBP-1 (P < 0.05), and decreased abundance of PREF-1 (P < 0.05). Knockdown of ZBED6 was not associated with changes in mRNA abundance of selected genes, lipid accumulation, lipid droplet size, or cell number. These results suggest that ZBED6 does not play a major role in preadipocyte differentiation.

The production and regulation of IGF and IGFBPs in human adipose tissue cultures

BACKGROUND

Adipocytes express and secrete IGFs and IGFBPs; proteins with important effects on adipocyte homeostasis. However, the factors that control adipocyte generation of IGFs and IGFBPs are not clarified.

AIM

To identify regulators of the synthesis of IGFs and IGFBs in adipose tissue.

METHODS

Subcutaneous adipose tissue fragments (500 mg) from 7 healthy lean women were incubated for 48 h following addition of GH (50 μg/l), dexamethasone (DXM, 20 nM), insulin (100 nM), interleukin (IL)-1β (50 ng/l), IL-6 (50 ng/l) and tumor-necrosis factor (TNF)-α (10 ng/l). Outcome parameters included tissue mRNA and culture media IGF and IGFBP levels.

RESULTS

Adipose tissue cultures secreted more IGF-II than IGF-I protein (1.14±0.41 vs. 0.26±0.09 μg/l [mean±SEM]; P<0.02). IGF-I mRNA and protein levels were stimulated by GH (to 340% [153; 477] (median [interquartiles]) and 270±26%, respectively; P<0.003), and inhibited by IL-1β (to 28% [21; 77] and 68±11%, respectively; P<0.003). TNF-α reduced IGF-I and IGF-II protein levels to 51±8% and 69±8%, respectively (P≤0.002), without affecting mRNA levels. IGF protein levels were unaffected by DXM, insulin and IL-6. All IGFBPs IGFBP-1 were expressed. IGFBP-4 was by far the most predominant IGFBP by immunoassay and WLB revealed two bands at 28 and 24 kDa, most likely representing glycosylated and non-glycosylated IGFBP-4.

CONCLUSION

Adipose tissue cultures secrete more IGF-II than IGF-I, and predominantly IGFBP-4. The secretion of IGF-I is affected by GH, IL-1β and TNF-α, whereas IGF-II is affected by TNF-α only. Hence, cytokines may control adipocyte homeostasis by affecting local IGF-generation.

The insulin-like growth factors in adipogenesis and obesity

Adipose tissue has been recognized as a major target of growth hormone (GH) action. GH was shown to inhibit adipocyte differentiation but stimulated preadipocyte proliferation in vitro. GH acts directly via its receptor or via upregulating insulin-like growth factor (IGF)-I, which is a critical mediator of preadipocyte proliferation, differentiation, and survival. Results from clinical studies on GH treatment in patients with GH deficiency or GH insensitivity syndrome can be used to dissect GH and IGF as well as IGF-binding protein (IGFBP) actions in vivo. In this article, changes of the GH/IGF system during adipocyte differentiation in vitro as well as related signaling pathways and their impact on adipose tissue growth and function are discussed. Clinical considerations include the effects of GH and IGF-I on adipose tissue during treatment of GH deficiency, differences in the IGF system between visceral and subcutaneous adipose tissue depots as well as the recently emerging role for adipose tissue in the regulation of glucose homeostasis.

The IGF/IGFBP system in rainbow trout (Oncorhynchus mykiss) adipose tissue: expression related to regional localization and cell type

While in mammals, the IGF/IGFBP system is known to be involved in adipose tissue growth, the presence of such a system in fish is as yet undetermined. The present work aimed at investigating the influence of regional localization of adipose tissues and cell types on the expression of this system. Using quantitative real-time PCR (qPCR), the presence of IGFs, IGFBPs, IGFBP-rPs, and IGFR I (insulin-like growth factors, IGF-binding proteins, IGFBP-related proteins, type I IGF receptor) was studied in crude subcutaneous and visceral fat depots as well as in isolated stromal vascular (SV) cells and mature adipocytes from the latter depot in the prepubescent female rainbow trout. In adipose tissues, no differences were observed in the transcript expressions of IGFs and IGFBPs (1-6) and rP1 relative to their regional localization. On the other hand, the two paralogues of IGFR I were more strongly expressed in visceral than in subcutaneous depots which could be related to a differential receptivity to IGF between fat depots. The amount of IGF-I and IGFR Ia transcripts is larger in mature adipocytes than in SV cells, while a similar level of expression was observed for IGF-II and IGFR Ib. IGFBP-1, -2a, -4, -5, -6, and -rP1 were more strongly expressed in the SV cells than in adipocytes, while IGFBP-2b displayed comparable expression. These results indicate that the IGF/IGFBP system is expressed in rainbow trout fat depots, whatever their regional origin, and that cell types, i.e., SV cells or mature adipocytes, influence its expression.

Effects of limited and excess protein intakes of pregnant gilts on carcass quality and cellular properties of skeletal muscle and subcutaneous adipose tissue in fattening pigs

The aim of this study was to investigate whether dietary protein intake of gilts during gestation below (50%) or above (250%) recommendations affects body composition, carcass and meat quality, and properties of skeletal muscle and subcutaneous adipose tissue (SCAT) in offspring at d 83 and 188 of age. German Landrace gilts were fed isoenergetic gestation diets (~13.7 MJ of ME/kg) containing a low (LP, 6.5%; n = 18), an adequate (AP, 12.1%; n = 20), or a high (HP, 30%; n = 16) protein content from mating until farrowing. Within 48 h of birth, offspring were cross-fostered to sows fed a standard diet. On d 83 of age, no effects of the LP diet on BW and body composition were detected, whereas HP pigs showed a slight growth delay (P = 0.06) associated with increased relative weights of small intestine (P < 0.01) and brain (P = 0.08), and reduced relative thymus weight (P < 0.01). On d 188 of age, BW was not different among the dietary groups. However, the carcass of LP pigs contained less (P = 0.01) lean and more (P = 0.07) fat compared with AP and HP pigs, which was only pronounced in pigs originating from large litters (P < 0.05). Like skeletal muscles (P = 0.06), the heart muscle weighed less (P = 0.02) in LP than AP pigs. Compared with AP pigs, LP pigs exhibited a fewer (P = 0.09) total number of myofibers in semitendinosus muscle plus LM both at d 83 and 188 of age, whereas total muscular DNA was less (P = 0.02) at d 188 only. The mRNA abundance of IGF2 measured on d 188 was reduced in SCAT (P = 0.03) and LM (P = 0.07) of LP compared with AP pigs. No changes in muscular fiber type frequency, capillary density, or creatine kinase activity, as well as SCAT adipocyte size and number, were observed at either stages of age. Meat quality characteristics remained unchanged at d 83, whereas Warner-Bratzler shear force value in LM was decreased (P = 0.03) in LP compared with AP pigs on d 188 of age. The results suggest that the maternal LP diet impairs prenatal myofiber formation, reduces the potential of postnatal lean growth related to reduced IGF2 mRNA expression and myonuclear accumulation, and consequently changes carcass quality toward reduced lean proportion and improved tenderness at market weight. In contrast, except for a slight transient growth delay, excess dietary protein during gestation seems to have little effect on the fetal programming of postnatal muscle and adipose tissue phenotype of the progeny.

GATA depletion impacts insulin-like growth factor 1 mRNA and protein levels in luteinizing porcine granulosa cells

GATA4 and GATA6 are zinc-finger transcription factors that regulate specific genes involved in steroidogenesis. Using RNA interference (RNAi)-mediated reduction of GATA4 and/or GATA6 with microarray analysis, we aimed to identify novel GATA target genes in luteinizing porcine granulosa cells under vehicle- and cAMP-treated conditions. Microarray analysis identified IGF1 mRNA to be cAMP- and GATA-responsive, and real-time PCR demonstrated that the cAMP-induced increase in IGF1 mRNA was reduced under conditions of GATA6 depletion and GATA4 plus GATA6 depletion, but not GATA4 depletion. Insulin-like growth factor 1 protein levels in media were also decreased by GATA6 or GATA4 plus GATA6 reduction. IGFBP2 and IGFBP4 mRNAs were increased and IGFBP5 mRNA decreased with vehicle and cAMP treatment under GATA4 plus GATA6 RNAi conditions. GATA6 reduction alone increased basal IGFBP4 and decreased IGFBP5 with both vehicle and cAMP, and GATA4 reduction alone lowered cAMP IGFBP5 levels with cAMP. No changes in IGFBP3 mRNA were observed with GATA reduction relative to the control RNAi condition. Levels of insulin-like growth factor binding proteins 2-5 in media as assessed by Western ligand blotting were not altered by GATA reduction. Electromobility gel shift assays with two GATA-containing oligonucleotides of the IGF1 5'-regulatory region showed GATA4 and GATA6 could bind the more proximal GATA-B site. These studies indicate that although GATA4 and GATA6 can bind the porcine IGF1 5'-region, GATA6 is functionally most important for cAMP-stimulated mRNA levels. Using microarray analysis, we identified other mRNAs that were altered by GATA-reduced conditions, including ALDH1, DIO2, and EDNRB. Our findings further support GATA as a coordinator of endocrine/paracrine/autocrine signals in the ovary.

Actions of IGF binding proteins and related proteins in adipose tissue

The insulin-like growth factors (IGFs), their binding proteins (IGFBPs) and structurally related proteins have been identified in adipose tissue but their roles in adipose tissue are poorly understood. IGF-I and IGFBP-3 expression increase during human preadipocyte differentiation. However, whereas IGF-I stimulates this process, IGFBP-3 is inhibitory both to preadipocyte differentiation and to differentiated adipocyte function. The direct interaction of IGFBP-3 with peroxisome proliferator-activated receptor-gamma is believed to contribute to its inhibitory effect on differentiation. Connective tissue growth factor (CTGF/CCN2) shares weak structural homology and functional similarities with IGFBP-3, including inhibition of preadipocyte differentiation. This review examines the current knowledge of IGFBP regulation and actions in adipocytes and proposes a common regulatory pathway involving IGFBP-3 and CTGF/CCN2.