The Expression Pattern Of PRKAG3 Gene And Its Relationships With Meat Quality In Pigs

PRKAG3 gene, which encodes AMP-activated protein kinase (AMPK)73 subunit,was associated with glycogen metabolism and considered as a major gene of affectingmeat quality traits such as muscle pH, color and water-holding capacity. In order to studythe expression pattern of PRKAG3 gene and the relationships between PRKAG3 geneexpression and meat quality, four experiments were conducted as follow:Exp 1:PRKAG3 gene Expression Differences in Tissues and Organs of DifferentBreeds of PigsIn order to investigate PRKAG3 gene expression Differences in tissues and organsof different breeds of pigs, 5 Ya-Nan and 5 DLY pigs were slaughtered at 80kg.Semi-quantitative RT-PCR was applied to determine the PRKAG3 gene expressiondifferences in the heart, liver, kidney and skeletal muscle.β-actin gene was used as aninternal control.The results showed that PRKAG3 was mainly expressed in skeletal muscle and lessin heart, but not in liver and kidney. In skeletal muscle, PRKAG3 gene expression ofYa-Nan pigs was higher than that of DLY pigs.The pattern of that PRKAG3 was mainly expressed in skeletal muscle indicated ithad distinct physiological functions in skeletal muscle.Exp 2: The Expression Pattern of PRKAG3 Gene At Different Physiological Phasesfor Different Breeds of Pigs and the Relationships Between PRKAG3 GeneExpression and Meat Quality This study was designed to compare the expression differences of PRKAG3 gene atdifferent physiological phases for different breeds of pigs in skeletal muscle, and toinvestigate the relationships between PRKAG3 gene expression and meat quality fromtwo genotypes of pigs. Seventeen Hampshire-sired barrows (BW=19.48±1.136 kg) andsixteen Landrance-Saba barrows(LS pigs) (BW=20.5±1.500kg) were fed with the samediet in individual pens. 5 or 6 pigs of each breed of pig were slaughtered at 20kg, 50kgand 100kg of bodyweight respectively, and determined for pH, muscle glycogen content,serum glucose, carcass GP, LDH and PRKAG3 gene expression. The results showed that:1. LS pigs had greater backfat thickness(P＜0.01), lower eye lean area, lower leanpercentage (P＜0.01) than Hampshire pigs. In comparison with LS pigs, Hampshire-siredpigs had lower pH2 (P＜0.05), shear force(P＜0.05), b values(P＜0.01), and greater drip loss(P＜0.05).2.Correlation analyses indicated that muscle glycogen content was correlated withmeat quality. The positive correlation coefficients of muscle glycogen content with leanpercentage, eye lean area, purge loss, and L value were 0.250, 0.327, 0.609 and 0.226respectively for Hampshire pigs. Negative correlation exsited between muscle glycogencontent with b value, pH1 and pH2 with the coefficients being 0.356, 0.408 and 0.571respectively. For LS pigs, muscle glycogen content had positive correlation with leanpercentage, eye lean area(P＜0.01), purge loss(P＜0.01), b value (P＜0.01), droploss(P＞0.05), L value(P＞0.05) and a value(P＞0.05), and negative correlation withbackfat thickness(P＞0.05), pH1 (P＞0.05), and pH2(P＜0.05).3.Live-animal GP of Hampshire-sired pigs had significantly positive correlation withlean percentage and eye lean area with correlation coefficient being 0.791 and 0.819, buthad negative correlation with backfat thickness, purge loss, cooked meat percentage, pH1and pH2(r=0.223, 0.306, 0.466, 0.211and 0.423, respectively). For LS pigs, Live-animalGP was positively correlated with lean percentage and eye lean area(P＜0.05), and wasnegatively correlated with backfat thickness, cooked meat percentage (P＞0.05), pH1(P＜0.05) and pH2 (P＜0.05). Carcass GP was significantly correlated with meat quality, especially pH2.4.PGKAG3 gene expression was increased as bodyweight increased with significantlyhigher expression at 100kg than at 20kg and 50kg(P＜0.05). LS pigs had higher expressionthan Hampshire pigs.5. The relationship of PRGAKG3 gene expression with pork quality was differentbetween the two breeds of pigs. For Hampshire pigs, PRKAG3 gene expression hadpositive relationship with eye lean area, lean percentage, and drip loss (r=0.218, 0.362,and 0.486 respectively), but negative relationship with cooked meat percentage and pH2(P＜0.05). For LS pigs, PRAKAG3 gene expression had positive relationship with leanpercentage, eye lean area, drip loss and purge loss(r=0.300, 0.341, 0.596 and 0.311respectively), but negative relationship with pH2 (P＞0.05).These results suggested that PRKAG3 gene expression in skeletal muscle waschanged with different physiological phases and different breeds of pigs. PRKAG3 geneexpression was correlated with meat quality, especially with pH2.Exp 3: Effect of Activated PRKAG3 Gene Expression on Glyco-Metabolism inSkeletal Muscle for PigsAn experiment was conducted to investigate the effect of PRKAG3 gene expressionactivated with metformin on on glyco-metabolism in skeletal muscle and pork quality. 10DLY pigs (80kg) were randomly divided into control and experimental group fed dietsupplemented with metformin at dose of 400mg/kg body weight. When pigs reached 100kg of bodyweight, all pigs were slaughtered to determine growth performance, PRKAG3gene expression, mRNA abundance of glycogen synthase and glycogen phosphatase,protein expression of glucose transporter 4 in cellular membrane, and concentrations ofglycogen and lactic acid, lactate dehydrogenase. The results showed that:1.Compared with control group, experimental group had 13.92% higher AMPKactivity (p＜0.05), 4.39-fold PRKAG3 gene expression (p＜0.05).2. Experimental group had 13.80% lower feed intake (p＜0.05), 13.14% lower average daily gain and 6.67％higher feed conversion efficiency than the control.3. Compared with control group, experimental group had 5.05％lower blood glucoseconcentration, 11.39％higher lactic acid concentration in blood and 9.50％in muscle,18.37％higher glycogen concentration (p＜0.05) and 16.33％higher LDH activity(p=0.084).4. In comparison with control group, activation of PRKAG3 gene expressionincreased mRNA abundance of glycogen synthase gene by 10.00％and of LDH activityby 16.33％(p=0.084). There was no significance of gene expression of glycogenphosphatase (p＞0.05).5. Activated PRKAG3 gene expression increased protein expression of GLUT4 incellular membrane up to 29.45％(p＜0.05).These results suggested that supplementary 400mg/kg metformin in diet activatedAMPK and PRAKAG3 gene expression, leading to the increase of protein expression ofGLUT4 in cellular membrane and high glucose intake in muscle. The possiblemechanism of PRKAG3 gene expression on pork quality was due to its regulatory effecton glyco-metabolism in skeletal muscle.Exp 4: Effect of nutrition level on PRKAG3 gene expression and pork quality12 DLY pigs (70kg) were randomly divided into two groups fed with diet of high(DE13.81MJ/kg, CP 14％) or low (DE 12.55MJ/kg, CP 11％) nutritional level. All pigswere slaughtered at 100kg, and determined for PRKAG3 gene expression, carcasscharacteristics and meat quality traits.The results showed that lower nutritional level increased PRKAG3 gene expression,which was positive related to lean percentage, eye lean area, a values, b values and driploss, but was nonlinearly negatively related to pH2 (p＜0.05). Higher nutritional levelincreased dressing percentage, lean percentage, eye lean area, a values, b values and Lvalues, but drop loss was lower than low nutritional level.It is concluded that nutritional level had effects on PRKAG3 gene expression and meat quality.Through the above four experiments, we concluded that:PRKAG3 was mainly expressed in skeletal muscle, and changed with differentphysiological phases and different breeds in skeletal muscle of pigs. PRKAG3 geneexpression was related to meat quality, especially to pH2 at negative manner.Supplementation of 400mg/kg metformin in diet activated AMPK and PRAKAG3 geneexpression, increased protein expression of GLUT4 in cellular membrane and glucoseintake in muscle indicating the regulatory effects of PRKAG3 gene expression onglyco-metabolism in skeletal muscle. Nutritional level affected PRKAG3 geneexpression and meat quality. These results showed that PRKAG3 gene maybe one ofthe major genes of affecting meat quality traits.