Role of Corticosterone in Lipid Metabolism in Broiler Chick White Adipose Tissue

Excessive accumulation of body fat in broiler chickens has become a serious problem in the poultry industry. However, the molecular mechanism of triglyceride accumulation in chicken white adipose tissue (WAT) has not been elucidated. In the present study, we investigated the physiological importance of the catabolic hormone corticosterone, the major glucocorticoid in chickens, in the regulation of chicken WAT lipid metabolism. We first examined the effects of fasting on the mRNA levels of lipid metabolism-related genes associated with WAT, plasma corticosterone, and non-esterified fatty acid (NEFA). We then examined the effects of corticosterone on the expression of these genes in vivo and in vitro. In 10-day-old chicks, 3 h of fasting significantly decreased mRNA levels of lipoprotein lipase (LPL) in WAT and significantly elevated plasma concentrations of NEFA. Six hours of fasting significantly increased mRNA levels of adipose triglyceride lipase (ATGL) in WAT and significantly elevated plasma concentrations of corticosterone. On the other hand, fasting significantly reduced mRNA levels of LPL in WAT and elevated plasma concentrations of NEFA in 29-day-old chicks without affecting mRNA levels of ATGL in WAT or plasma corticosterone concentrations. Oral administration of corticosterone significantly reduced mRNA levels of LPL and significantly increased the mRNA levels of ATGL in WAT in 29-day-old chicks without affecting plasma NEFA concentrations. The addition of corticosterone to primary chicken adipocytes significantly increased mRNA levels of ATGL, whereas mRNA levels of LPL tended to decrease. NEFA concentrations in the culture medium were not influenced by corticosterone levels. These results suggest that plasma corticosterone partly regulates the gene expression of lipid metabolism-related genes in chicken WAT and this regulation is different from the acute elevation of plasma NEFA due to short-term fasting.

Characterization and functional analysis of porcine estrogen-related receptors and their alternative splicing variants

Estrogen-related receptors (ESRR) are orphan nuclear hormone receptors with unidentified ligands; they play important roles in tissue regulation and development and maintenance of pluripotent cell identity. The splicer variant, genomic organization, and physiological roles of ESRR have been elucidated in the human and the mouse. However, in livestock, they remain elusive. In this study, we cloned porcine ESRR family members , , and . Two alternative splicing variants, and , and a novel were identified. To determine the domain function, we constructed vectors with sequential deletions of the ESRRB coding sequence. The functional analysis showed that the C domain of ESRR plays a core role in promoting the activation of estrogen response elements that are found in all kinds of ESRR-targeting genes, whereas the E domain is not essential for transcription regulation of ESRR unless a specific and identified ligand is applied.

Influence of hatch time and access to feed on intramuscular adipose tissue deposition in broilers

The effect of hatch time and subsequent access to feed on intramuscular adipose tissue deposition was studied in the pectoralis major muscle of male Ross 308 broiler chickens. Based on their hatch time chicks were classified as early (EH), midterm (MH), or late (LH) hatchers, with an average incubation duration of 497.7 h for EH, 508.8 h for MH, and 514.5 h for LH birds. Chicks were provided access to feed either immediately at hatch, or 24 h after the conclusion of the hatch window. Expression of the adipogenic regulatory genes peroxisome proliferator-activated receptor gamma (PPARγ), and stearoyl-CoA desaturase (SCD), were measured at the time of hatch, and zero, one, 4, 7, 28, and 40 d. Intramuscular adipocyte cell width and visualization of adipose tissue deposition was observed at 28 and 40 d. Expression of PPARγ was increased in the pectoralis major of LH birds at the time of hatch, zero, and one d. The expression of PPARγ at one and 7 d, and SCD at 7 d were increased in all birds that received delayed access to feed. At 28 d, adipocyte cell width was increased in LH birds with delayed access to feed, compared to EH and MH birds with delayed access to feed and LH birds with immediate access to feed. At 40 d, adipocyte cell width was increased in all birds that received delayed access to feed. Also at 40 d, there was a trend (P = 0.078) for more extensive intramuscular adipose tissue deposition in LH than EH birds, and in birds with delayed access to feed (P = 0.075). These data indicate delayed access to feed increases intramuscular adipose tissue deposition in the pectoralis major muscle, and suggest that hatch time influences this regulation.

Reassessing the Potential Activities of Plant CGI-58 Protein

Comparative Gene Identification-58 (CGI-58) is a widespread protein found in animals and plants. This protein has been shown to participate in lipolysis in mice and humans by activating Adipose triglyceride lipase (ATGL), the initial enzyme responsible for the triacylglycerol (TAG) catabolism cascade. Human mutation of CGI-58 is the cause of Chanarin-Dorfman syndrome, an orphan disease characterized by a systemic accumulation of TAG which engenders tissue disorders. The CGI-58 protein has also been shown to participate in neutral lipid metabolism in plants and, in this case, a mutation again provokes TAG accumulation. Although its roles as an ATGL coactivator and in lipid metabolism are quite clear, the catalytic activity of CGI-58 is still in question. The acyltransferase activities of CGI-58 have been speculated about, reported or even dismissed and experimental evidence that CGI-58 expressed in E. coli possesses an unambiguous catalytic activity is still lacking. To address this problem, we developed a new set of plasmids and site-directed mutants to elucidate the in vivo effects of CGI-58 expression on lipid metabolism in E. coli. By analyzing the lipid composition in selected E. coli strains expressing CGI-58 proteins, and by reinvestigating enzymatic tests with adequate controls, we show here that recombinant plant CGI-58 has none of the proposed activities previously described. Recombinant plant and mouse CGI-58 both lack acyltransferase activity towards either lysophosphatidylglycerol or lysophosphatidic acid to form phosphatidylglycerol or phosphatidic acid and recombinant plant CGI-58 does not catalyze TAG or phospholipid hydrolysis. However, expression of recombinant plant CGI-58, but not mouse CGI-58, led to a decrease in phosphatidylglycerol in all strains of E. coli tested, and a mutation of the putative catalytic residues restored a wild-type phenotype. The potential activities of plant CGI-58 are subsequently discussed.

Identification of the avian RBP7 gene as a new adipose-specific gene and RBP7 promoter-driven GFP expression in adipose tissue of transgenic quail

The discovery of an increasing number of new adipose-specific genes has significantly contributed to our understanding of adipose tissue biology and the etiology of obesity and its related diseases. In the present study, comparison of gene expression profiles among various tissues was performed by analysis of chicken microarray data, leading to identification of RBP7 as a novel adipose-specific gene in chicken. Adipose-specific expression of RBP7 in the avian species was further confirmed at the protein and mRNA levels. Examination of the transcription factor binding sites within the chicken RBP7 promoter by Matinspector software revealed potential binding sites for adipogenic transcription factors. This led to the hypothesis that the RBP7 promoter can be utilized to overexpress a transgene in adipose tissue in order to further investigate the function of a transgene in adipose tissue. Several lines of transgenic quail containing a green fluorescent protein (GFP) gene under the control of the RBP7 promoter were generated using lentivirus-mediated gene transfer. The GFP expression in transgenic quail was specific to adipose tissue and increased after adipocyte differentiation. This expression pattern was consistent with endogenous RBP7 expression, suggesting the RBP7 promoter is sufficient to overexpress a gene of interest in adipose tissue at later developmental stages. These findings will lead to the establishment of a novel RBP7 promoter cassette which can be utilized for overexpressing genes of interest in adipose tissue in vivo to study the function of genes in adipose tissue development and lipid metabolism.

Inhibition of lipolysis in the novel transgenic quail model overexpressing G0/G1 switch gene 2 in the adipose tissue during feed restriction

In addition to the issue of obesity in humans, the production of low-fat meat from domestic animals is important in the agricultural industry to satisfy consumer demand. Understanding the regulation of lipolysis in adipose tissue could advance our knowledge to potentially solve both issues. Although the G₀/G₁ switch gene 2 (G0S2) was recently identified as an inhibitor of adipose triglyceride lipase (ATGL) in vitro, its role in vivo has not been fully clarified. This study was conducted to investigate the role of G0S2 gene in vivo by using two independent transgenic quail lines during different energy conditions. Unexpectedly, G0S2 overexpression had a negligible effect on plasma NEFA concentration, fat cell size and fat pad weight under ad libitum feeding condition when adipose lipolytic activity is minimal. A two-week feed restriction in non-transgenic quail expectedly caused increased plasma NEFA concentration and dramatically reduced fat cell size and fat pad weight. Contrary, G0S2 overexpression under a feed restriction resulted in a significantly less elevation of plasma NEFA concentration and smaller reductions in fat pad weights and fat cell size compared to non-transgenic quail, demonstrating inhibition of lipolysis and resistance to loss of fat by G0S2. Excessive G0S2 inhibits lipolysis in vivo during active lipolytic conditions, such as food restriction and fasting, suggesting G0S2 as a potential target for treatment of obesity. In addition, transgenic quail are novel models for studying lipid metabolism and mechanisms of obesity.

Skeletal muscle characterization of Japanese quail line selectively bred for lower body weight as an avian model of delayed muscle growth with hypoplasia

This study was designed to extensively characterize the skeletal muscle development in the low weight (LW) quail selected from random bred control (RBC) Japanese quail in order to provide a new avian model of impaired and delayed growth in physically normal animals. The LW line had smaller embryo and body weights than the RBC line in all age groups (P<0.05). During 3 to 42 d post-hatch, the LW line exhibited approximately 60% smaller weight of pectoralis major muscle (PM), mainly resulting from lower fiber numbers compared to the RBC line (P<0.05). During early post-hatch period when myotubes are still actively forming, the LW line showed impaired PM growth with prolonged expression of Pax7 and lower expression levels of MyoD, Myf-5, and myogenin (P<0.05), likely leading to impairment of myogenic differentiation and consequently, reduced muscle fiber formation. Additionally, the LW line had delayed transition of neonatal to adult myosin heavy chain isoform, suggesting delayed muscle maturation. This is further supported by the finding that the LW line continued to grow unlike the RBC line; difference in the percentages of PMW to body weights between both quail lines diminished with increasing age from 42 to 75 d post-hatch. This delayed muscle growth in the LW line is accompanied by higher levels of myogenin expression at 42 d (P<0.05), higher percentage of centered nuclei at 42 d (P<0.01), and greater rate of increase in fiber size between 42 and 75 d post-hatch (P<0.001) compared to the RBC line. Analysis of physiological, morphological, and developmental parameters during muscle development of the LW quail line provided a well-characterized avian model for future identification of the responsible genes and for studying mechanisms of hypoplasia and delayed muscle growth.

Selenium promotes adipogenic determination and differentiation of chicken embryonic fibroblasts with regulation of genes involved in fatty acid uptake, triacylglycerol synthesis and lipolysis

Selenium (Se) has been utilized in the differentiation of primary pig and rat preadipocytes, indicating that it may have proadipogenic potential; however, some studies have also demonstrated that Se has antiadipogenic activity. In this study, chicken embryonic fibroblasts (CEFs) were used to investigate the role of Se in adipogenesis in vitro and in ovo. Se supplementation increased lipid droplet accumulation and inhibited proliferation of cultured CEFs isolated from 6-day-old embryos dose-dependently. This suggests that Se may play a role in cell cycle inhibition, thereby promoting the differentiation of fibroblasts to adipocytes. Se did not stimulate adipogenic differentiation of CEFs isolated from 9- to 12-day-old embryos, implying a permissive stage of adipogenic determination by Se at earlier embryonic ages. Microarray analysis comparing control and Se treatments on CEFs from 6-day-old embryos and confirmatory analysis by quantitative real-time polymerase chain reaction revealed that genes involved in adipocyte determination and differentiation, fatty acid uptake and triacylglycerol synthesis were up-regulated. In addition, up-regulation of an anti-lipolytic G0/G1 switch gene 2 and down-regulation of a prolipolytic monoglyceride lipase may lead to inhibition of lipolysis by Se. Both osteogenic and myogenic genes were down-regulated, and several genes related to oxidative stress response during adipogenesis were up-regulated. In ovo injection of Se at embryonic day 8 increased adipose tissue mass by 30% and caused adipocyte hypertrophy in 17-day-old chicken embryos, further supporting the proadipogenic role of Se during the embryonic development of chickens. These results suggest that Se plays a significant role in several mechanisms related to adipogenesis.

Loss of fat with increased adipose triglyceride lipase-mediated lipolysis in adipose tissue during laying stages in quail

The goal of the current study was to investigate regulation of key genes involved in lipid metabolism in adipose and liver to relate lipolytic and lipogenic capacities with physiological changes at the pre-laying, onset of laying, and actively laying stages of quail. Followed by a 50 % increase from pre-laying to onset of laying, adipose to body weight ratio was significantly reduced by 60 % from the onset of laying to the actively laying stage (P < 0.05), mainly resulting from the significantly increased adipocyte size from the pre-laying stage to the onset of laying and reduction of adipocyte size from the onset of laying to the actively laying stage (P < 0.05). In the adipose tissue of actively laying quail, increased protein expression and phosphorylation of adipose triglyceride lipase (ATGL) together with an elevated mRNA expression of comparative gene identification-58, an activator of ATGL, contributes to increased lipolytic activity, as proved by increased amounts of plasma non-esterified fatty acid (P < 0.05). In addition, decreased mRNA expression of fatty acid transport protein in the actively laying quail could contribute to the adipocyte hypotrophy (P < 0.05). In the liver, relative mRNA expression of apo-very low density lipoprotein (VLDL)-II increased significantly from the pre-laying to actively laying stages (P < 0.05), indicating increased apoVLDL-II actively facilitated VLDL secretion in the actively laying quail. These results suggest that the laying birds undergo active lipolysis in the adipocyte, and increase VLDL secretion from the liver in order to secure a lipid supply for yolk maturation.