Metabolic And Productive Defects Of Intrauterine Growth Retarded Piglets And The Nutritional Regulatory Effects

Intrauterine growth retardation (IUGR) is a condition that the fetus does not reach its growth potential during pregnancy, which means the growth and development of mammalian fetus and organs are impaired in utero. IUGR induces persistent influences on the growth performance and energy metabolism of the offspring by regulating genomic DNA methylation and mitochondrial function. In order to ascertain the metabolic and productive defects of IUGR pigs and the nutritional regulatory effects, a series of four experiments were conducted to investigate the regulatory effects of dietary folic acid (FA) and lipids content on DNA methylation of gene promoters, mitochondrial DNA (mtDNA) biogenesis and function, meat quality, and skeletal muscle proteome in normal birth weight (NBW) and IUGR pigs.Experiment1:The objective is to study the effects of FA supplementation after weaning on hepatic DNA methylation of gene promoters, mtDNA biogenesis, and mitochondrial function in piglets with different birth weight. Sixteen normal birth weight (NBW) and sixteen intrauterine growth retarded (IUGR) piglets at d21were allocated randomly to a control group (without FA supplementation) or a FA-supplemented group (5mg/kg FA) for21d according to a2×2experimental design, which gave8replicates per treatment with1piglet per replicate. The results indicated that FA supplementation prevented the negative effects of IUGR on hepatic Mn-SOD activity (P<0.01), mtDNA content (P<0.01), DNA methylation status of GR and PPARa and mRNA expressions of related genes (P<0.05). Furthermore, IUGR reduced mRNA expression abundance of PGC-la, NRF-1, TFAM, mt SSB, mt polr, CS, ATPS, CcOXI, and CcOX V (P<0.01). FA supplementation decreased plasma homocysteine concentration, enhanced hepatic activity of GPx (P<0.01), and ameliorated the detrimental influences of IUGR on PGC-1a, NRF-1, TFAM, mt SSB, and mt polr mRNA expression (P<0.05).Experiment2:To determine the effects of maternal FA intake on hepatic DNA methylation of gene promoters, mtDNA biogenesis, and mitochondrial function in piglets with different birth weight, thirty-two sows were randomly assigned to a control diet (1.3mg/kg FA) or a FA-supplemented diet (30mg/kg FA) during gestation period. Sixteen NBW and sixteen IUGR piglets were selected at weaning for the collection of liver. The results showed that hepatic DNA methylation of GR promoter was decreased by maternal FA supplementation (P<0.01) and DNA methylation of PPARa promoter in IUGR piglets from sows fed a control diet was lower than that of other groups (P<0.05). Moreover, reduced oxygen consumption in state3, mitochondrial respiratory control index, membrane potential and ATP concentration were observed in the liver of IUGR piglets (P<0.01). Feeding a FA-supplemented diet prevented the influences of IUGR on mtDNA content, and mRNA expression of PGC-1α, TFAM, UCP-3, and CcOX IV in the liver of piglets (P<0.05).Experiment3:This study was conducted to investigate the effects of maternal FA supplementation, birth weight, and high-fat diet on mtDNA biogenesis and mitochondrial function in skeletal muscle of pigs. Sixteen NBW and sixteen IUGR pigs at20weeks of age from sows fed a control diet or a FA-supplemented diet during gestation (twenty weeks old, from experiment2) were randomly assigned to a low-fat diet (without lard supplementation) or a high-fat diet (HF, supplemented with10%lard) for four weeks. There were four replicates per treatment with one pig each replicate. The results indicated that IUGR decreased ADFI, ADG, and concentrations of plasma insulin and leptin in pigs (P<0.05). The decreased concentrations of glycogen and ATP, and increased malondialdehyde (MDA) content were observed in skeletal muscle of IUGR pigs (P<0.01). Feeding a HF diet reduced glycogen concentration and enhanced MDA and triglyceride contents in skeletal muscle, respectively (P<0.01).The activities of LDH and G6PD in skeletal muscle of pigs were decreased by IUGR and HF diet (P<0.01). IUGR pigs had lower oxygen consumption in state3, mitochondrial respiratory control index, membrane potential, and mRNA expression of PGC-1α, TFAM, NRF-1, mt polr, CS, CcOX I, and CcOX V in skeletal muscle than that of NBW pigs (P<0.05). Membrane potential and mtDNA content were reduced in pigs fed a HF diet (P<0.01).Experiment4:To explore the effects of postnatal HF diet on growth performance, meat quality, and skeletal muscle proteome in pigs with different birth weight, twenty NBW and twenty IUGR male piglets were randomly allotted to feed a low-fat diet (without lard supplementation) or a HF diet (supplemented with10%lard) from weaning to slaughter at110kg according to a2×2experimental design. There were ten replicates per treatment with one pig each replicate. The results showed that IUGR decreased ADFI, ADG, dressing yield, pH45min, L*values and drip loss, and increased the ratio of feed-to-gain, loin muscle area, back fat thickness, intramuscular fat content, shear force, a*and b*values, respectively (P<0.01). Feeding a HF diet enhanced ADG, a*and b*values in the skeletal muscle, but reduced ADFI and the ratio of feed-to-gain (P<0.01). Proteomic analysis indicated that IUGR decreased the expression abundances of shear force-related myosin heavy chain and troponin T, and energy metabolism-related pyruvate kinase and phosphoglycerate mutase (P<0.05). Furthermore, IUGR increased expression levels of fatty acid binding protein and apolipoprotein involved in lipids metabolism, L-lactate dehydrogenase involved in pH changes post mortem, and calmodulin and calreticulin involved in muscle contraction (P<0.05). Consumption of a HF diet affected the expression abundances of myosin, myosin light chain, phosphoglucomutase, heat shock protein, and enolase (P<0.05).In conclusion, our data demonstrated that:(1) The postnatal growth performance of pigs was impaired by IUGR. Furthermore, IUGR produced significant effects on carcass composition, intramuscular lipid deposition, and glycolytic process in skeletal muscle of the offspring by changing DNA methylation patterns and mRNA expressions of genes related to lipid metabolism, mtDNA biogenesis, and mitochondrial function and subsequent energy metabolism.(2) Dietary FA supplementation after weaning or during pregnancy could prevent the harmful influences of IUGR on mtDNA biogenesis, DNA methylation status of gene promoters and mRNA expressions of related genes in the liver of piglets. However, the harmful influences of IUGR and HF diets-induced oxidative damage on mitochondrial function in the skeletal muscle of growing-finishing pigs were not ameliorated by maternal FA supplementation. The abnormal mitochondrial function affected subsequent energy metabolism, and then increased intramuscular and backfat lipid deposition.