| Skeletal muscle is a major peripheral tissue which can account for the 40%of whole body weight.Tenderness is one of key factors to determine the quality of meat,and it principally depends on the content and crosslinking manner of collagen.So,it is very important to figure out the mechanism of muscle development and collagen bio-synthesis to improve the meat quality.This present study aims at determining the effect of different dietary energy intake on the development and collagen deposit of skeletal muscle in lambs.Twelve Dorper × Small Thin-Tailed ram lambs(three months of age,20±0.5kg BW)were selected and divided into two groups in a completely randomized design.Animals were offered diets at 100%or 65%of control intake,which was referred to NRC.Lambs were slaughtered when BW in control reached 35kg.In order to study the development of skeletal muscle at different feeding levels,we used H&E staining to analyze the size distribution and cross-section area of muscle fibers.In addition,the collagen deposition of semitendinosus was analyzed by hydroxyproline and Masson Trichrome staining,to further verify the effect of collagen deposition on the tenderness of skeletal muscle,we examined the shear-force of skeletal muscle.Finally,Real-Time PCR and western blotting were used to detect the expression of related proteins and genes in skeletal muscle development and collagen deposition.which aimed at elucidating the mechanism of different feeding levels on skeletal muscle development and collagen deposition.The result showed that Final BW and skeletal muscle weight were decreased(P<0.01)by feed restriction.Both muscle fiber size distribution and myofibril cross-sectional area were altered by feed restriction.Insulin-like growth factor 1(IGF-1)messenger RNA(mRNA)content was decreased(P<0.05)when lambs were underfed,whereas no difference for IGF-2 mRNA expression was observed(P>0.05).Feed restriction also altered phosphor-Akt protein abundance(P<0.01).Moreover,the mammalian target of rapamycin(mTOR)pathway was inhibited by feed restriction,which was associated with decreased phosphor-mTOR,phosphorylated eukaryotic initiation factor 4E binding protein 1(phosphor-4EBP1),and phosphorylated ribosomal protein p70 S6 kinase(phosphor-p70).Both mRNA expression of myostatin and its protein content were elevated in feed-restricted lambs(P<0.05).In addition,mRNA expression of both muscle RING finger 1 and muscle atrophy F-hox was increased when lambs were underfed.Warner-Bratzler shear force(WBSF)was significantly increased when lambs were fed an energy-restricted diet(P<0.05).Masson trichrome stain and hydroxyproline assay demonstrated increased collagen content in ST muscle of feed restriction lambs.Both collagen I and fibronectin mRNA contents were significantly increased when lambs were fed an energy-restricted diet(P<0.05),whereas no difference for collagen III mRNA expression was observed(P>0.05).Expression of prolyl 4-hydroxy-lase a(P4HA)was greater in the feed restriction group(P<0.01),and no differences were observed for both lysyl oxidase(LO)and lysyl hydroxylase 2b(LH2b)mRNA contents(P>0.05).In addition,matrix metal-loproteinase 1,2,9,and 13(MMP1,MMP2,MMP9,and MMP13)did not change with the feed restriction,whereas both tissue inhibitor of matrix metallopro-teinase 1 and 2(TIMP1 and TIMP2)were increased(P<0.05).Feed restriction did not alter TGF-? and SMAD protein contents,but phosphor-p38 protein content was elevated(P<0.05).In conclusion,different diet level can affect the development and collagen accumulation of skeletal muscle by PI3K/Akt and p38 signaling pathway respectively. |
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