Lipid metabolism and cellular features of skeletal muscle and subcutaneous adipose tissue in pigs differing in IGF-II genotype

doi:10.1016/j.domaniend.2006.10.001

Domestic Animal Endocrinology

Volume 34, Issue 1, January 2008, Pages 45-53

https://doi.org/10.1016/j.domaniend.2006.10.001 Get rights and content

Abstract

In pigs, a paternally (pat) imprinted mutation in the IGF-II gene is associated with increased muscle mass and decreased backfat thickness. The aim of this study was to determine whether this mutation influenced cellular, biochemical and metabolic features of skeletal muscle and adipose tissue. Muscle (trapezius) and subcutaneous adipose tissue (SCAT) were collected from pigs (106 kg) carrying (Qpat, n = 6) or not carrying (qpat, n = 7) the mutation. Adipocytes were isolated from those tissues by collagenase treatment. Lipid content and activity of lipogenic enzymes were determined using standard assays. Gene expression levels were determined by real-time PCR. Levels of IGF-II mRNA were higher (P < 0.01) in muscle of Qpat than in that of qpat pigs, but they did not differ significantly between the two groups in SCAT. Whereas levels of IGF-I mRNA in muscle were similar in both groups, they were higher (P < 0.05) in SCAT of Qpat pigs than in that of qpat pigs. Muscle lipid content and intramuscular adipocyte diameters were not influenced significantly by the IGF-II genotype. In SCAT, the reduction of backfat thickness in Qpat pigs compared with qpat pigs was associated with lower (P < 0.05) lipid content and smaller (P < 0.05) adipocytes, with no significant genotype-effects on expressions and/or activities of lipogenic enzymes. In summary, our results suggest that the IGF-II mutation altered body composition in pigs by favoring myofiber hypertrophy and repressing adipose cell development in SCAT.

Introduction

The identification of genes that control body mass and body composition is of great interest for both human physiopathology and livestock animal production. In adult human, polymorphism in the insulin-like growth factor-II (IGF-II) gene has been reported to influence body mass index [1], [2], [3] and predisposition to metabolic disorders [4], although some controversies still exist [5]. In various breeds of pigs, a paternally (pat) expressed quantitative trait locus (QTL) affecting muscle growth and fat deposition was also mapped to the IGF-II locus [6], [7]. This QTL is caused by a single transition from G to A in intron 3 of the IGF-II gene, resulting in a three-fold increase in IGF-II mRNA expression in postnatal skeletal muscle of pigs carrying the Apat allele (Qpat genotype) versus Gpat allele (qpat genotype) [8]. It has been shown to be associated with increased muscle mass and decreased backfat thickness in pigs at commercial slaughter weight [9], [10]. Selection programs based on production performances and/or lean meat deposition have resulted in the selection of this mutation that is now widely distributed (∼80%) in pig commercial populations [8], [11].

The IGF-II gene encodes a 67 amino acid-long single chain polypeptide belonging to the IGF system [12], [13]. The IGFs are structurally homologous with insulin and are known to exert biological effects in an endo-, para- and/or autocrine manner. IGF-II stimulates both proliferation and differentiation of muscle cells [14], [15], and is involved in myofiber hypertrophy [16], [17], [18] and regeneration after injury [19]. The effects of IGF-II in adipose tissue development and lipid metabolism are poorly documented [20], [21], even though adipocytes from subcutaneous (SC) and visceral adipose tissues (AT) express IGF-II and other IGF receptor mRNA [21], [22], [23], [24]. Recently, we have also shown a higher IGF-II mRNA level in isolated intramuscular (IM) adipocytes than in SC or perirenal adipocytes [25].

Altogether, the physiological mechanisms involved in the regulation of body composition and especially fat versus muscle mass, by the IGF-II polymorphism remain largely unknown. Therefore, the present study was undertaken to determine whether the IGF-II mutation involved changes in cellular characteristics and in lipid-associated parameters in skeletal muscle and SCAT of pigs. Expressions of IGFs and IGF receptors were also examined. A special focus was made on adipocytes isolated from muscle or SCAT.

Section snippets

Materials

Collagenase A (0.22 U/mg) was purchased from Roche Applied Science (Meylan, France). Dulbecco's modified Eagle's medium (DMEM), HEPES, and antibiotics were obtained from Invitrogen (Cergy-Pontoise, France). The bicinchoninic acid protein assay kit was purchased from Pierce (Rockford, IL, USA). DNA-free™ kit was obtained from Ambion (Austin, TX, USA). Random hexamer primers and murine Moloney leukemia virus reverse transcriptase were from Amersham Biosciences (Orsay, France). Highly purified

Body composition, tissue lipid content, and cell size in skeletal muscle and SCAT

Average daily gain from birth to slaughter was similar (P = 0.24) in the two groups of pigs. At a similar live weight and age at slaughter, Qpat pigs displayed a higher lean meat content (P < 0.01), and tended to have a lower backfat thickness (P = 0.08) than qpat pigs (Table 2). Lipid content in muscle was not influenced by IGF-II genotype (P = 0.86), while it was lower (−6.5%, P = 0.02) in SCAT from Qpat pigs than qpat animals (Table 2). Mean cross-sectional area of myofibers tended to be higher (P =

Discussion

In the current study, an increase in IGF-II gene expression was clearly observed in trapezius skeletal muscle of Qpat versus qpat pigs, as previously reported in gluteus skeletal muscle and heart of boars typed for the same mutation in the intron 3 of IGF-II gene [8]. Skeletal muscle is a heterogeneous tissue essentially composed of muscle fibers embedded into connective tissue, with some adipocytes clustered along the myofiber fasciculi. We suggest that the increase in IGF-II mRNA levels

Acknowledgments

We thank Carole Roué, Daisy Baeyens, Sabine Coolsaet, Erik Claeys, Stefaan Lescouhier for their expert technical assistance. Delphine Gardan was supported by a grant from the French Ministry of Education and Research.

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Lipid metabolism and cellular features of skeletal muscle and subcutaneous adipose tissue in pigs differing in IGF-II genotype

Abstract

Introduction

Section snippets

Materials

Body composition, tissue lipid content, and cell size in skeletal muscle and SCAT

Discussion

Acknowledgments

Meat Sci

Int J Biochem Cell Biol

Domest Anim Endocrinol

Domest Anim Endocrinol

Exp Cell Res

Cell Biol Int

J Lipid Res

J Biol Chem

Anal Biochem

Anal Biochem

Vet J

J Biol Chem

Int J Biochem Cell Biol

Apal polymorphism in insulin-like growth factor II (IGF2) gene and weight in middle-aged males

Int J Obes Relat Metab Disord

Positive associations between single nucleotide polymorphisms in the IGF2 gene region and body mass index in adult males

Hum Mol Genet

Evidence of multiple causal sites affecting weight in the IGF2-INS-TH region of human chromosome 11

Hum Genet

Insulin-like growth factor 2 (IGF2) and IGF-binding protein 1 (IGFBP1) gene variants are associated with overfeeding-induced metabolic changes

Diabetologia

IGF2 genotype and obesity in men and women across the adult age span

Int J Obes Relat Metab Disord

A paternally expressed QTL affecting skeletal and cardiac muscle mass in pigs maps to the IGF2 locus

Nat Genet

An imprinted QTL with major effect on muscle mass and fat deposition maps to the IGF2 locus in pigs

Nat Genet

A regulatory mutation in IGF2 causes a major QTL effect on muscle growth in the pig

Nature

Effect of the porcine IGF2-intron3-G3072A substitution in an outbred Large White population and in an Iberian × Landrace cross

J Anim Sci

The IGF2-intron3-G3072A substitution explains a major imprinted QTL effect on backfat thickness in a Meishan × European white pig intercross

Genet Res

Insulin-like growth factors and their binding proteins: biological actions

Endocr Rev

Hypertrophy of cultured adult rat ventricular cardiomyocytes induced by antibodies against the insulin-like growth factor (IGF)-I or the IGF-I receptor is IGF-II-dependent

Mol Cell Biochem