Although the importance of the intestinal microbiota in host growth and health is well known, the relationship between microbiota colonization and muscle development is unclear. In this study, the direct causal effects of the colonization of gut microorganisms on the muscle tissue of piglets were investigated. The body weight and lean mass of germ-free (GF) piglets were approximately 40% lower than those of normal piglets. The deletion of the intestinal microbiota led to weakened muscle function and a reduction in myogenic regulatory proteins, such as MyoG and MyoD, in GF piglets. In addition, the blinded IGF1/AKT/mTOR pathway in GF piglets caused muscle atrophy and autophagy, which were characterized by the high expression of Murf-1 and KLF15. Gut microbiota introduced to GF piglets via fecal microbiota transplantation not only colonized the gut but also partially restored muscle growth and development. Furthermore, the proportion of slow-twitch muscle fibers was lower in the muscle of GF piglets, which was caused by the reduced short-chain fatty acid content in the circulation and impaired mitochondrial function in muscle. Collectively, these findings suggest that the growth, development and function of skeletal muscle in animals are mediated by the intestinal microbiota.
The change characteristics of intestinal microbial succession and the correlation with the production of two important types of bacterial metabolites (short chain fatty acids and bioamine) in piglets during the early stage were fully explored in this study. Six piglets from different litters with the same birth time were selected, weighted and euthanized at 1, 7, 14, 21, 28, 35, and 42 days of age. During this stage, the piglets grew quickly with gradual increases in blood levels of growth hormone and insulin, and in the intestinal developmental index and immunity. 16s rRNA analysis indicated the alpha diversity of colonic microbiome community was higher than ileum. However, the composition change in the ileal microbiota was more dramatic over time. Lactobacillus genus was the dominant bacteria in piglets' ileum while Prevotella and Ruminococcaceae genera were the dominant bacteria in colon up to weaning. Gut bacterial community of the piglets showed obvious differences between the three different phases: newborn, before weaning, and post weaning. This was similar to the morphological change pattern of pigs' gut. Total SCFA content in the colon of pigs showed almost a 20-fold increase at day 42 compared to the value at day 1. The percentage of acetic acid among the total SCFAs dropped quickly from 74.5% at day 1 to 36.5% at day 42, while butyric acid and propionic acid showed significant increases at the stage. The histamine level increased and putrescine level decreased markedly in the colon with time while the amounts of total bioamines, tyramine and spermidine were devoid of changes. Dozens bacteria taxa showed highly correlations with SCFAs and bioamines. These findings provide an expanded view of the dynamic pig gut and gut microbiome at the important early growth stage.
In the present study we have examined whether p38 mitogen activated protein kinase (p38 MAPK) signal pathway interacts with calcium signal on lipid accumulation in primary preadipocytes of mice. The primary preadipocytes were treated with p38 MAPK inhibitor SB203580, blockers and excitomotors of calcium channel for 24 h, respectively. Intracellular triglyceride (TG) content was measured by triglyceride kit and lipid accumulation was determined by Oil Red O staining. Meanwhile, the mRNA expressions of peroxisome proliferators-activated receptor gamma (PPARγ) gene, fatty acid synthetase (FAS) gene, lipoprotein lipase (LPL) gene, vitamin D receptor (VDR) gene and extracellular Ca(2+)-sensing receptor (CaSR) gene were analyzed with real-time PCR. The protein content and phosphorylation of VDR and p38 were tested with Western Blotting. The data showed that intracellular TG content and the mRNA expression levels of PPARγ, FAS, LPL in N group and L group as well as FAS, LPL in C group were increased significantly (P < 0.01) compared to the control. On the contrary, intracellular TG content and the mRNA expression levels of PPARγ, FAS in B group as well as intracellular TG content and PPARγ, FAS, LPL in SB group and B+SB group were decreased significantly (P < 0.01). VDR mRNA expression and protein content were decreased in B, C, and SB added groups (P < 0.01). In addition, p38 phosphorylation levels increased in N and L groups (P < 0.01) and decreased in SB added groups (P < 0.01). These findings suggest that p38 MAPK pathway through regulating VDR mRNA expression participates in mediation of calcium signal and affects calcium signal regulating lipid accumulation in mice preadipocytes through changing PPARγ, FAS and LPL mRNA expression. In addition, calcium signal have a feedback effect in phosphorylation of p38.
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