Effect Of Saturated And Unsaturated Fatty Acids On Porcine Muscle Fiber Composition And AMPK Expression

Muscle fiber composition which determines the growth and energy metabolism of porcine skeletal muscle is one of the key factors affecting pork quality. AMPK (adenosine monophosphate activated protein kinase) is closely related to energy metabolism. It has been reported that AMPK could regulate glucose and lipid metabolism in muscle and then affect muscle fiber transformation in mice. As an energy substance, fatty acids can also regulate the expression of AMPK in mice. But the relationship between AMPK and porcine muscle fiber composition and whether fatty acids can affect muscle fiber composition through AMPK is still not well understood. Therefore, this study was conducted as the following three experiments: Firstly, Jinhua and Landrace pigs were used as animal models to investigate the breed difference of muscle fiber composition as well as AMPK expression in order to explore the relationship between AMPK and porcine muscle fiber composition. Then effects of dietary saturated and unsaturated fatty acids on AMPK gene expression and muscle fiber composition in mice were detected in vivo and in vitro. The effects of maternal dietary fatty acids on AMPK expression and muscle fiber composition in suckling piglets were also studied. The major results are showed as following:1. Breed difference of AMPK expression and muscle fiber composition between Jinhua and Landrace pigsBreed difference of AMPK expression and muscle fiber composition in soleus muscle were investigated between Jinhua and Landrace pigs at30,90and150d. The results showed that Jinhua pigs had a lower mRNA expression of MyHC I (myosin heavy chain gene I, p<0.05) in soleus muscle compared with Landrace pigs at30d. While at90d and150d, Jinhua pigs possessed greater mRNA expression of MyHC I and MyHC II a than Landrace pigs (p<0.01). The mRNA level of MyHC Ⅱb was lower in Jinhua pigs at90d and150d comparatively. Results of metabolic enzymes activity showed that the activity of SDH was lower in Jinhua pigs at30d but significantly higher at90d and150d than Landrace pigs. The activity of MDH was lower in the soleus muscle of Jinhua pigs at30d and90d but higher at150d compared with Landrace pigs. This indicated that the expression pattern of SDH and MDH is dissimilar. The expression of AMPK was always examined. The mRNA level of AMPK in soleus muscle of Jinhua pigs was lower than Landrace pigs (p<0.01). But Jinhua pigs have greater mRNA level and phosphorylated protein abundance of AMPK at90d and150d compared with Landrace pigs. The breed differences of genes related to muscle fiber transformation such as PGC-1α, MEF2c and NFAT were similar to AMPK gene. All the results implied that AMPK might be affect porcine muscle fiber composition by regulating the expression of genes related to muscle fiber transformation.2. Effects of dietary saturated or unsaturated fatty acids on gene expression of AMPK and muscle fiber composition in miceBased on previous studies, effects of dietary saturated and unsaturated fatty acids on gene expression of AMPK and muscle fiber composition in mice were investigated. Dietary saturated fatty acid (the main component was palmitic acid) and unsaturated fatty acid (the main component was linoleic acid) had no effect on mice growth performance. But unsaturated fatty acid significantly reduced the average daily intake. The level of serum adiponectin was increased in mice fed with unsaturated fatty acid. In addition, the level of serum leptin had no difference between the two treatment groups. Additionally, mice fed with unsaturated fatty acid had greater mRNA expression of MyHC I (p<0.01) but lower mRNA level of MyHC II b (p<0.01) comparatively. Furthermore, the gene expression of AMPK as well as PGC-1α. was significantly greater in unsaturated fatty acid treatment group. The expression of genes related to lipolysis was also studied. Results showed that diet supplemented with unsaturated fatty acid elevated the mRNA expression of Sirtl and CPT1in muscle compared with saturated fatty acid. Then a comparative study of the effects of different fatty acids on gene expression of AMPK and MyHC was conducted in vitro. The time-dependent effects of different fatty acids on AMPK gene expression were similar. Saturated fatty acids significantly inhibited the gene expression of AMPK in C2C12myocytes and the mRNA level of muscle fiber type transformation-related genes PGC-1α was also reduced. However, gene expression of AMPK as well as MyHC I was significantly greater in unsaturated fatty acids especially polyunsaturated fatty acids treatment group than saturated fatty acids treatment group. These results were consistent with that in vivo. The results above indicated that compared with saturated fatty acids, diet supplemented with5%unsaturated fatty acids could elevate the proportion of type I (oxidative) fibers in mouse muscle which might be correlated to AMPK energy metabolism pathway. 3. Effects of maternal dietary fatty acids (saturated or unsaturated fatty acids) on AMPK expression and muscle fiber composition in suckling pigletsBased on the comparative study of saturated and unsaturated fatty acids on muscle fiber composition and AMPK gene expression, the current study was conducted to investigate the effects of maternal dietary fatty acids on AMPK expression and muscle fiber composition in suckling piglets. Sows in late pregnancy (gestation80d) were fed diet supplemented with either saturated fatty acids (the main component was palmitic acid) or unsaturated fatty acids (the main component was linoleic acid) until the end of lactation. Results showed that diet supplemented with3%unsaturated fatty acids significantly increased the proportion of total unsaturated fatty acids in colostrum and mature milk and significantly reduced the proportion of total saturated fatty acids compared with saturated fatty acids treatment. Furthermore, the muscle fiber composition was examined. Maternal diet supplemented with unsaturated fatty acids significantly promoted gene expression of MyHC I, MyHC Ⅱ a and MyHC II x and reduced the expression of MyHC Ⅱb (p<0.05) in muscle of suckling piglets than that in diet supplemented with saturated fatty acids group. Troponin I SS which was a mark protein in slow and oxidative muscle was also detected by immunofluorescence. Consistent with MyHC gene expression, suckling piglets in unsaturated fatty acids treatment group had more protein abundance of Troponin I SS comparatively. The gene expression of AMPK was in accordance with muscle fiber composition between the two groups. Maternal diet supplemented with unsaturated fatty acids significantly elevated mRNA expression and phosphorylated protein abundance of AMPK (p<0.05) as well as PGC-lα gene expressionin muscle of suckling piglets than saturated fatty acids diet.The above findings revealed that breeds possessing more oxidative muscle fibers (I type and II a type) had a significantly greater expression of AMPK comparatively. Compared with saturated fatty acids, unsaturated fatty acids could increase the ratio of oxidative muscle fibers (I type and Ⅱ a type) and this effect was closely related to the AMPK energy metabolism pathway.