| Epidemiological and animal studies have demonstrated the impact of maternal nutrition during gestation and/or lactation on metabolic homeostasis and disease susceptibility of the offspring in later life. As the largest protein reserve in the body, skeletal muscle is considered to be highly responsive to dietary protein intake. It was reported that the influence of maternal high-energy diets or extra food intake during gestation and/or lactation on skeletal muscle development and structure in pig offspring, whereas the impact of maternal dietary protein level on skeletal muscle properties has not been adequately addressed, and the related epigenetic mechanism is rarely discussed. The present study aimed at the determination of the effects of maternal dietary protein level during gestation and lactation on skeletal muscle properties of weaning and finishing pigs and the underlying epigenetic mechanism, employing Meishan pigs as model.1 Effects of maternal dietary protein level on skeletal muscle properties of weaning and finishing pigsMeishan sows were fed traditionally on low-protein diets, whereas the standard commercial diets contain at least 2 folds higher crude protein (CP). In this study,14 primiparous purebred Meishan sows were fed on either low-protein (LP,6% and 7% CP) or standard-protein (HP,12% and 14% CP) diets, during gestation and lactation, respectively. Newborn pigs were counted and individually weighed at parturition. Litter size was adjusted to 7 to 8 pigs per litter at 24 h post farrowing in the same group. Newborn piglets were allowed free access to their mothers and weaned at 35 days (d) of age. After weaning, piglets were raised following the standard feeding regimen with the starter, grower and finisher diets recommended for the breed. Male pigs were killed at weaning (35 days of age) and finishing (8 months of age) stages, and the myofiber characteristics were observed.The longissimus dorsi (LD) and psoas major (PM) muscle were taken for measuring the cross-sectional areas and densities of each type of myo fibers using HE staining, myosin ATPase staining and myofiber typing by relative quantification of mRNA expression for four different types of myosin heavy chain(MyHC) and MyHCⅡprotein expression by Western blotting. Intramuscular triglyceride (IMTG) and glycogen were measured in LD and PM muscles. The results showed that:Body weight, as well as LD and PM muscle weights were significantly higher (p<0.05) in HP piglets at weaning with increased cross-sectional area muscle fiber (CSA) (p<0.05) and higher expression of myosin heavy chain (MyHC)Ⅱb mRNA and MyHC II protein in LD andⅡx mRNA in PM (p<0.05). At finishing stage, however, a conversed transition towards higher proportion of type I fibers in LD, together with decreased MyHC II protein and MyHCⅡb mRNA in both LD and PM (p<0.05), were observed in HP group, yet with no consequences on body weight, muscle weights or meat quality traits. IMTG content in LD and PM muscles finsihing pigs was not affected by maternal high-protein diet. However, glycogen content in LD showed a tendency of decrease (p=0.057) in HP pigs. These results suggest that maternal dietary protein level elicits divergent changes in offspring myofiber type transition at weaning and finishing stages. Although the slaughter weight and meat quality were not affected, the fast-to-slow shift in myofiber types detected at slaughter may benefit later life with higher oxidative capacity and insulin sensitivity.2 Maternal dietary protein level affects offspring skeletal muscle characteristics through epigenetic regulation of gene expressionUp to now, little is known whether epigenetic mechanisms are involved in the effects of maternal nutrition on myofiber type. As mentioned above, maternal dietary protein level changed offspring myofiber type composition as well as MyHCs mRNA transcription, especially for MyHCⅡb. In this study, we focused on MyHCⅡb and investigated whether maternal dietary protein level might exert influence on MyHCⅡb transcription through epigenetic regulation. Using Chromatin Immunoprecipitation (ChIP) and Immunoprecipitation of Methylated DNA (MeDIP), we examined histone modifications and DNA methylation at the MyHCⅡb gene promoter region in LD and PM muscles of weaning and finishing pigs. The results showed that:1) In the LD muscle of weaning piglets, higher levels of H3ac, H3K4me3 and H3K9mel in MyHCⅡb gene promoter were found in HP group compared with LP group (p< 0.05), being consistent with high MyHCⅡb mRNA levels (p<0.05). No significant differences were observed for H3K27me3 and DNA methylation.2) Distinct pattern of epigenetic modifications was seen in the finishing pigs. Both in LD and PM, lower H3ac, H3K4me3 were found in HP group (p<0.05), being consistent with lower MyHCⅡb mRNA levels (p<0.05), while H3K9mel was consistently higher in MyHCⅡb gene. No significant differences were detected for H3K27me3 and DNA methylation.3) H3ac and H3K4me3 were higher in LD (p<0.05), which also possessed higher MyHCⅡb mRNA aboundance. In HP group, H3K9mel and H3K27me3 were lower in LD than PM (p< 0.05), and a similar tendency of H3K9mel was observed in LP group (p=0.066). No significant differences were determined for H3K27me3 and DNA methylation between LD and PM muscles.In summary, H3ac and H3K4me3 modification could activate MyHCⅡb transcription, yet H3K9mel showed a bidirectional role depending on age. The inhibitory effect of H3K27me3 was only shown between tissues in HP group. In the present study, we did not find any hints implicating the involvement of DNA methylation in the regulation of MyHCⅡb transcription. All these data indicate that maternal dietary protein level affects offspring skeletal muscle MyHCⅡb transcription through epigenetic mechanisms. |
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