GPX2 Gene Affects Feed Efficiency of Pigs by Inhibiting Fat Deposition and Promoting Muscle Development

Abstract

GPX2 has been recognized as a potential candidate gene for feed efficiency in pigs. This article aimed to elucidate polymorphism of GPX2 associated with feed efficiency and its related molecular mechanism. In this study, seven single nucleotide polymorphisms (SNP) of GPX2 were found among 383 Duroc pigs. In addition, seven SNPs and ALGA0043483 (PorcineSNP60 BeadChip data in 600 Duroc pigs), which are near the GPX2 gene, were identified in one haplotypes block. Furthermore, associated studies showed that the genotype of GPX2 has significant association with weaning weight and 100 kg BF in Duroc pigs. In addition, the AG had no effect when the backfat became thinner, and the FCR and RFI traits had a tendency to decrease in the G3 + TT combination genotype, accompanied by an increase of GPX2 expression in backfat and muscle tissues. At the cellular level, the adipocyte proliferation and ability of adipogenic differentiation were reduced, and the lipid degradation increased in 3T3-L1 when there was overexpression of GPX2. In contrast, overexpression of the GPX2 gene can promote the muscle cell proliferation and myogenic differentiation in C2C12 cells. In other words, GPX2 has the effect of reducing fat deposition and promoting muscle development, and it is a candidate gene for backfat and feed efficiency.

Keywords: GPX2; SNP; adipocyte; backfat; development; feed efficiency; molecular mechanism; muscle cells.

Figure 1

Genetic information for the pig GPX2 gene.

Figure 1

Genetic information for the pig GPX2 gene.

Figure 2

Linkage disequilibrium and haplotype block analysis using the seven SNPs for GPX2 and ALGA0043483 in 377 Duroc pigs. Solid lines mark the block identified. Linkage disequilibrium between each SNP is shown by the diamonds.

Figure 3

mRNA expression of GPX2 in different tissues for combination genotype G1 and G3 in Duroc pigs. combination genotype G1: GG-TT-CC-TT-CC-GG-GG, combination genotype G3: AA-CC-TT-GG-TT-AA-CC. * indicates p < 0.05, ** indicates p < 0.01.

Figure 4

Overexpression of GPX2 inhibited the proliferation of 3T3-L1 cell. (A) 3T3-L1 infected with adenovirus carrying GPX2, and the mRNA and protein of GPX2 stable expressed in 3T3-L1 cell. (B) Representative immunostaining images comparing the cells in the proliferative phase from negative control and overexpression GPX2, the nuclei are stained with Hoechest 33342. Quantification graph showing the percentage of cells positive for the red cell (EdU). (C) mRNA expression of proliferation related gene between overexpression GPX2 and control group. (D) Protein levels and abundance analysis for GPX2 and CDK2 at 48 h after overexpression GPX2 in 3T3-L1 cell. * indicates p < 0.05, ** indicates p < 0.01, ns indicates not significant.

Figure 5

Overexpression of GPX2 inhibited adipogenic differentiation and promoted the lipid degradation of 3T3-L1. (A) Photograph and micrographs of 3T3-L1 stained with Oil red O, extraction and detection of lipid contents from negative control and overexpression of GPX2. (B) mRNA expression of adipogenic regulator and (C) lipid degradation in negative control and overexpression of GPX2 group of 3T3-L1 after 7 days’ differentiation. (D) Protein expressions and abundance analysis for adipogenic regulator and lipid degradation in 3T3-L1 after 7 days’ differentiation from negative control and overexpression of GPX2. * indicates p < 0.05, ** indicates p < 0.01, ns indicates not significant.

Figure 6

Overexpression of GPX2 inhibited the proliferation of C2C12 cell. (A) C2C12 infected with adenovirus carrying GPX2, and the mRNA and protein of GPX2 stable expressed in the C2C12 cell. (B) Representative immunostaining images comparing the cells in the proliferative phase from negative control and overexpression of GPX2, the nuclei are stained with Hoechest 33342. Quantification graph showing the percentage of cells positive for the red cell (EdU). (C) mRNA expression of proliferation related gene between overexpression of GPX2 and control group. (D) Protein levels for GPX2 and CDK2 at 48 h after overexpression of GPX2 in the C2C12 cell. In addition, abundance analysis was compared with the GAPDH protein. * indicates p < 0.05, ** indicates p < 0.01, ns indicates not significant.

Figure 7

Overexpression of GPX2 promoted the C2C12 myogenic differentiation. (A) Representative immunostaining images comparing the cells in the myogenic differentiation stage from negative control and overexpression of GPX2. Blue represents nuclear staining; Green represents green fluorescent protein. The differentiation index was calculated as the percentage of the number of nuclei in the myotube to the total nucleus. The fusion index was calculated as the percentage of the number of myotubes with more than two nuclei in the total nucleus. (B) The mRNA and protein expression. (C) level of GPX2 and myogenic marker protein were analyzed at 7-day differentiation after overexpression of GPX2 in the C2C12 cell. * indicates p < 0.05, ** indicates p < 0.01, ns indicates not significant.

Figure 8

Hypothesis schematic models illustrating the GPX2 affects the backfat thickness and feed utilization efficiency of pigs by regulating the development of adipocytes and muscle cells. The left dashed box shows the correlation between SNP of GPX2 and feed utilization efficiency of Duroc pigs (n = 376 or 600). The individual genotype G3(TT) of GPX2 has the thinner 100 kg backfat, lower residual feed intake, lower feed convers than G1(CC) individuals. The reason for this conclusion is that the GPX2 gene could inhibit the proliferation and differentiation of adipocytes, promote the degradation of fat (mechanism diagram on the right) and advance the proliferation and differentiation of muscle cells. After the high expression of GPX2, the nutrients in pigs were transferred to higher feed utilization efficiency. ↑ Indicates expression up-regulation, ↓ Indicates expression down-regulation.