Biochemical properties of porcine white adipose tissue mitochondria and relevance to fatty acid oxidation

Molecular characterization and expression analysis of NDUFS4 gene in m. longissimus dorsi of Laiwu pig (Sus scrofa)

To study the molecular basis of intramuscular fat (IMF) deposition, suppression subtractive hybridization was used to investigate the differences in gene expression between m. longissimus dorsi (LD) of high IMF Laiwu pig group and low IMF Laiwu pig group. From two specific subtractive cDNA libraries, the expression-upregulated clone HL-27 was selected by reverse Northern high-density blot, and then identified to be pig mitochondrial NADH dehydrogenase (ubiquinone) Fe-S protein 4 (NDUFS4). Pig NDUFS4 full-length cDNA was cloned by RACE, and contains a 528 bp-open reading frame (ORF) encoding 175 amino acid residues. The derived amino acid sequence of NDUFS4 is well conserved compared with NDUFS4 of various species with higher degree of sequence similarity with other mammalian (86.3-92.6 %) than amphibian, aves, and fishes (70.2-81.1 %), and contains one N-linked glycosylation site, one O-linked glycosylation site, seven Ser phosphorylation sites and five Thr phosphorylation sites. A-G mutation was found at nt 122 site of ORF between Laiwu pig and Large White, which results in the K-R mutation at 41 site of protein sequence. Real-time PCR analysis indicated that the level of NDUFS4 mRNA expression was higher in high IMF Laiwu pig group than in low IMF Laiwu pig group, and in Laiwu pig than in Large White. The tissue expression of the pig NDUFS4 gene showed a tissue-specific pattern: highly expressed in LD muscle, spleen and kidney, but hardly expressed in lung, stomach and large intestine. The possible role of NDUFS4 and its relation to IMF deposition are discussed.

Identification of differentially expressed genes in a porcine in vivo model of adipogenesis using suppression subtractive hybridization

Although they provide valuable information, in vitro models of adipocyte development often require high doses of hormones and growth factors, which may influence gene expression and adipocyte differentiation patterns. To overcome these problems, a novel in vivo model of adipose tissue development was used to characterize genes involved in adipogenesis. The suppression subtractive hybridization technique was used to identify genes showing differential expression between the adipose tissue of a day 90 gestating sow, which is enriched in adipocytes, and day 90 fetal adipose tissue, which is enriched in preadipocytes. A total of 149 expressed sequence tags corresponding to identified genes and tentative consensus sequences emerged. Thirty-seven clones matched expressed sequence tags or genomic DNA sequences and six novel sequences were also identified. Adipogenesis-related genes were identified, many of which have never been reported to be expressed in mammalian adipose tissue, and may play a role in regulation of adipose tissue differentiation. Validation of differentially expressed genes was confirmed for perilipin, monocyte to macrophage differentiation-associated, myocilin, paraoxonase 3, stearoyl-CoA desaturase, angiotensinogen and adiponectin genes using real-time RT-PCR.

Adipocyte- and heart-type fatty acid binding proteins are both expressed in subcutaneous and intramuscular porcine ( Sus scrofa ) adipocytes

Adipocyte- (A) and heart- (H) type fatty acid binding proteins (FABP) contribute to efficient fat storage and utilization, respectively. To understand regional-differences in lipid metabolism between tissues, A- and H-FABP transcript and protein levels were studied in adipocytes isolated from subcutaneous adipose tissue or skeletal muscle in growing pigs (Sus scrofa). Interestingly, H-FABP was expressed in adipocytes isolated from both sites. We also showed that A-FABP and H-FABP were expressed at a lower level in intramuscular adipocytes than in subcutaneous adipocytes. A discrepancy was observed between age-related changes in A-FABP content in isolated adipocytes and cell diameter or lipid content variations in tissues during growth.

Lipid metabolism related gene-expression profiling in liver, skeletal muscle and adipose tissue in crossbred Duroc and Pietrain Pigs

Body-weight differences in animals may be ascribed to genetic and environmental factors. Here we utilized two divergent porcine genotypes, the highly muscled, leaner PietrianxYorkshire pigs and less muscled, fatter DurocxYorkshire growing pigs (75-110 kg), to examine the role of genetic background on expression of genes associated with anabolic (Fatty acid synthase, FAS; glucose transporter 4, GLUT-4; stearoyl CoA desaturase, SCD; Sterol regulatory binding protein-1, SREBP-1; leptin) and catabolic lipid metabolism (Carnitine palmitoyltransferase-1B, CPT-1B; acyl-CoA dehydrogenase, ACDH) in adipose tissue (AT), liver (L) and skeletal muscle (SKM). Pietrain pigs had lower mRNA abundance for FAS, SREBP-1, SCD and leptin in AT and L, but higher mRNA abundance for L ACDH and SKM ACDH and CPT-1B than Durocs. Duroc pigs exhibited higher expression of FAS, SREBP-1, SCD, leptin in AT and FAS in L and lower expression of ACDH and CPT-1B in L SKM. GLUT-4 expression did not differ in SKM between the two genotypes. Feeding of a beta adrenergic agonist (Paylean) for 52 days lowered expression of lipid anabolic and enhanced lipid catabolic genes expressions similarly in both genotypes. Overall, the lipid metabolism genes differential expression patterns documented here showed that in Pietrain pigs mRNA abundances of synthesis genes were lower and of catabolic genes were higher than in Duroc pigs.

Regulation of global gene expression by ovariectomy and estrogen in female adipose tissue

OBJECTIVE

To study the effects of ovariectomy (OVX) and estrogen replacement on global gene expression in white adipose tissue.

RESEARCH METHODS AND PROCEDURES

Female mice were randomly divided into four groups: 1) intact, 2) OVX, 3) OVX plus estradiol (E2) injection 3 hours before death (E(2)-3 hours), and 4) E(2)-24 hours. The serial analysis of gene expression was performed to detect the transcriptomic changes.

RESULTS

A total of 15 transcripts, including several novel transcripts, were found to be modulated by OVX or E2 (p<0.05). Secreted acidic cysteine-rich glycoprotein, which regulates the extracellular matrix (ECM) components, was increased after OVX. Moreover, OVX up-regulated several transcripts involved in ECM, such as procollagen types Ialpha1 and 2. In cell defense, glutathione peroxidase 3 was lower in OVX than in intact mice. Cytochrome c oxidase I and three novel transcripts were up-regulated by estrogen treatment.

DISCUSSION

This study underlines the importance of cell shape and ECM regulation by OVX on adiposity. Moreover, some novel transcripts may also play a relevant role in OVX-induced obesity and estrogen therapy.

Metabolic partitioning of endogenous fatty acid in adipocytes

OBJECTIVE

To develop an accurate new method to measure the partitioning of adipocyte endogenous fatty acids among different metabolic pathways, a critical step toward understanding the regulatory mechanism by which fat disposition is modulated.

RESEARCH METHODS AND PROCEDURES

Isolated primary rat adipocytes were pre-incubated with isotope-labeled fatty acids. This allows determination of the specific activity of labeled fatty acids in the endogenous lipid pool. After the removal of exogenous fatty acids, the disposition of endogenous fatty acids into the three major metabolic pathways, namely, oxidation, re-esterification, and release into the medium, was measured independently. This was compared with the total lipolytic release of endogenous fatty acids, as measured by glycerol release. Adipocytes from normal fed and fasted animals were used to determine the effects of physiological variations on the metabolic fate of endogenous fatty acids.

RESULTS

In normal fed animals, 0.2% of endogenous fatty acids were oxidized, 50.1% were released, and 49.7% were re-esterified. Fasting doubled the partitioning of fatty acids toward oxidation (p < 0.05) in association with increased lipolysis (1.4-fold increase) (p < 0.05). This effect was completely abolished by the addition of insulin to the cells (61% reduction) (p < 0.05).

DISCUSSION

The endogenous fatty acids in adipocytes are actively oxidized. This process can be regulated by altered physiological conditions or by insulin. Over time, it is possible that a small shift of fatty acids toward oxidation could have a significant impact on body fuel economy. This hypothesis needs to be tested.