Targeted myostatin loss-of-function mutation increases type Ⅱ muscle fibers in Meishan pigs

Myostatin(MSTN) is a negative regulator of skeletal muscle growth and development. The skeletal muscle in MSTN^(-/-)mice is significantly hypertrophied, with muscle fiber type II increasing significantly while muscle fiber type I decreasing.However, it is still not clear how the skeletal muscle types change in MSTN^(-/-)pigs, and how the mechanism for MSTN regulates fiber types, especially in large animals like pigs. This study conducted a comprehensive analysis of the composition of skeletal muscle fibers in MSTN^(-/-)pigs produced in our laboratory. It was observed that, compared with wild-type(WT) pigs, both the total mass of skeletal muscle and type IIb muscle fibers increased significantly(P<0.01),while the type I and type IIa muscle fibers decreased significantly(P<0.01), in MSTN^(-/-)Meishan pigs. In addition, to explore the influence of MSTN on muscle fiber type and its regulation mechanism in the embryonic stage, this study selected a few genes(Myf5, Mef2 d, MyoD and Six1) associated with muscle fiber type and validated their expression by quantitative RT-PCR. Herein, it was found that Myh7, Myh2, Myh4 and Myh1 can be detected in the skeletal muscle of pigs at 65 days of gestation(dg). Compared with WT pigs, in MSTN^(-/-)Meishan pigs, Myh7 decreased significantly(P<0.01), while Myh4(P<0.001) and Myh1(P<0.05) increased significantly. Meanwhile, the increased expression of Myf5(P<0.05), Mef2 d(P<0.01) and Six1(P<0.05) in MSTN^(-/-)Meishan pigs suggested that MSTN should regulate the directional development of muscle fiber types in the early stage of embryonic development. Thus, at the embryonic stage, the type II muscle fibers began to increase in MSTN^(-/-)pigs. These results can provide valuable information not only for pig meat quality improvement, but also for the study of human skeletal muscle development and disease treatment.

Vitamin A regulates mitochondrial biogenesis and function through p38 MAPK‑PGC‑1α signaling pathway and alters the muscle fiber composition of sheep

Background Vitamin A(VA)and its metabolite,retinoic acid(RA),are of great interest for their wide range of physiological functions.However,the regulatory contribution of VA to mitochondrial and muscle fiber composition in sheep has not been reported.Method Lambs were injected with 0(control)or 7,500 IU VA palmitate into the biceps femoris muscle on d 2 after birth.At the age of 3 and 32 weeks,longissimus dorsi(LD)muscle samples were obtained to explore the effect of VA on myofiber type composition.In vitro,we investigated the effects of RA on myofiber type composition and intrinsic mechanisms.Results The proportion of type I myofiber was greatly increased in VA-treated sheep in LD muscle at harvest.VA greatly promoted mitochondrial biogenesis and function in LD muscle of sheep.Further exploration revealed that VA elevated PGC-1αmRNA and protein contents,and enhanced the level of p38 MAPK phosphorylation in LD muscle of sheep.In addition,the number of type I myofibers with RA treatment was significantly increased,and type IIx myofibers was significantly decreased in primary myoblasts.Consistent with in vivo experiment,RA significantly improved mitochondrial biogenesis and function in primary myoblasts of sheep.We then used si-PGC-1αto inhibit PGC-1αexpression and found that si-PGC-1αsignificantly abrogated RA-induced the formation of type I myofibers,mitochondrial biogenesis,MitoTracker staining intensity,UQCRC1 and ATP5A1 expression,SDH activity,and enhanced the level of type IIx muscle fibers.These data suggested that RA improved mitochondrial biogenesis and function by promoting PGC-1αexpression,and increased type I myofibers.In order to prove that the effect of RA on the level of PGC-1αis caused by p38 MAPK signaling,we inhibited the p38 MAPK signaling using a p38 MAPK inhibitor,which significantly reduced RA-induced PGC-1αand MyHC I levels.Conclusion VA promoted PGC-1αexpression through the p38 MAPK signaling pathway,improved mitochondrial biogenesis,and altered the composition of muscle fiber type.

Comparison of Soleus Muscle Fibers in Rats and Rabbits at Different Stages of Postnatal Development

In the present study,the effects of postnatal development on the number and distribution of skeletal muscle fibers of different types in hind leg of rat and rabbit were studied.The soleus muscles of rats aged 2 days,2,4,6,8,and 10 weeks (body weight 10,32,95,190,280,and 320 g),and rabbits aged 2 days,2,4,8,12,16,20,and 24 weeks (body weight 100,220,400,750,1 200,1 600,2 100,and 2 500 g) were stained with succinic dehydrogenase.With an image analysis system,the X-Y coordinates of fibers were used to analyze the growth-related changes.The results of present study showed that three types of fibers were found in the soleus muscles of rat and rabbit,i.e.,type Ⅰ (slow oxidative),ⅡX (fast oxidative),and ⅡA (fast oxidative glycolytic).The type Ⅰ fibers were present throughout the muscle that had a uniform distribution and tended to increase in number with aging.Type ⅡX fibers were scattered throughout the muscle and decreased markedly in number with aging.Type ⅡA fibers were located at the central and deep regions,and showed a little or no change in number and distribution with aging.While be of age,type ⅡA and ⅡX fibers became restricted to the superficial region.No type ⅡB fibers were detected.Type ⅡA fibers had the largest diameter,type Ⅰ intermediate and type ⅡX the smallest.Mean cross-sectional area of each type fibers of rabbits was larger than that of rats.The present results indicate that the number and distribution of muscle fibers of different types in hind limb of rat and rabbit change with the process of postnatal growth.

Effects of dietary protein restriction on muscle fiber characteristics and m TORC1 pathway in the skeletal muscle of growing-finishing pigs

Background： To investigate the effects of dietary crude protein（CP） restriction on muscle fiber characteristics and key regulators related to protein deposition in skeletal muscle, a total of 18 growing-finishing pigs（62.30 ± 0.88 kg）were allotted to 3 groups and fed with the recommended adequate protein（AP, 16 % CP） diet, moderately restricted protein（MP, 13 % CP） diet and low protein（LP, 10 % CP） diet, respectively. The skeletal muscle of different locations in pigs, including longissimus dorsi muscle（LDM）, psoas major muscle（PMM） and biceps femoris muscle（BFM） were collected and analyzed.Results： Results showed that growing-finishing pigs fed the MP or AP diet improved（P 〈 0.01） the average daily gain and feed： gain ratio compared with those fed the LP diet, and the MP diet tended to increase（P = 0.09） the weight of LDM. Moreover, the ATP content and energy charge value were varied among muscle samples from different locations of pigs fed the reduced protein diets. We also observed that pigs fed the MP diet up-regulated（P 〈 0.05） muscular m RNA expression of all the selected key genes, except that myosin heavy chain（My HC） IIb,My HC IIx, while m RNA expression of ubiquitin ligases genes was not affected by dietary CP level. Additionally, the activation of mammalian target of rapamycin complex 1（m TORC1） pathway was stimulated（P 〈 0.05） in skeletal muscle of the pigs fed the MP or AP diet compared with those fed the LP diet.Conclusion： The results suggest that the pigs fed the MP diet could catch up to the growth performance and the LDM weight of the pigs fed the AP diet, and the underlying mechanism may be partly due to the alteration in energy status, modulation of muscle fiber characteristics and m TORC1 activation as well as its downstream effectors in skeletal muscle of different locations in growing-finishing pigs.

Skeletal Muscle Adaptation to Endurance and Resistance Training

Endurance training in the aerobic zone of metabolism promotes a transition from type II to type I muscle fibers, influences the enzyme system of the Krebs cycle, electron transport chain, capillary supply, changes in key metabolic enzymes involved in fatty acid activation, and increased oxygen uptake in skeletal muscle. First of all, the transition process is related to the contractile apparatus. 5＇adenosine monophosphate-activated protein kinase is activated in response to endurance training and related to the metabolic adaptation of skeletal muscle. The peroxisome proliferator-activated receptor isoform δ is an important regulator of skeletal muscle endurance capacity. Resistance training improves muscle contractile function and increases muscle mass as a result of an anabolic and anti catabolic effect in fast-twitch fibers. Resistance training expands the amount of the contractile apparatus in order to enlarge fiber cross-sectional area. A concomitant alteration in proteins phenotype of contractile apparatus and metabolic enzyme levels occurs in accordance with activity-induced changes in the muscle＇s fiber-type profile. Recovery of skeletal muscle mechanical properties depends on the structural and metabolic peculiarities of muscle and the character of training.

Type ⅡB human skeletal muscle fibers positively correlate with bone mineral density irrespective to age

Background Age-associated decrease in type ⅡA/B human skeletal muscle fibers was detected in human biopsies in our previous study. The relationship between change in muscle fiber typing and bone mineral density （BMD） is, however,unknown either cross-sectionally or longitudinally. We therefore conducted a cross-sectional study to investigate their correlation using human muscle biopsies.Methods Forty human subjects aged （53.4±20.2） years were recruited. Histomorphometric parameters of their muscle biopsies were measured by ATPase staining and image analysis, including average area percentage, fiber number percentage, mean fiber area, and area percentage of connective tissues. Hip and spine BMD was measured by dual-energy X-ray absorptiometry. Partial correlation with adjusting age was performed.Results Type ⅡB muscle fiber was found positively correlated with hip BMD irrespective to age and demonstrated significantly stronger relationship with BMD among all fiber types, in terms of its cross-sectional area （r=0.380, P=0.029）and size （r=0.389, P=0.025）. Type ⅡA muscle fibers associated with hip BMD in mean fiber area only （r=0.420, P=0.015）.Conclusions Type ⅡB muscle fiber may play an important role in maintaining bone quality. This may also be a relatively more sensitive fiber type of sarcopenia and osteoporosis. These findings further consolidate the muscle-bone relationship.

Dietary lycopene supplementation improves meat quality,antioxidant capacity and skeletal muscle fiber type transformation in finishing pigs

This study aimed to investigate effects of dietary lycopene supplementation on meat quality,antioxidant ability and muscle fiber type transformation in finishing pigs.In a 70-day experiment,18 DurocLandraceYorkshire barrows were randomly allocated to 3 dietary treatments including a basal diet supplemented with 0,100 and 200 mg/kg lycopene,respectively.Each dietary treatment had 6 replicates with one pig each.Results showed that dietary 200 mg/kg lycopene supplementation increased muscle redness a^(*)value,intramuscular fat and crude protein contents,and decreased muscle lightness L^(*)and yellowness b^(*)values(P<0.05),suggesting that addition of 200 mg/kg lycopene to the diet of finishing pigs improved color,nutritional value and juiciness of pork after slaughter.Results also showed that dietary lycopene supplementation enhanced antioxidant capacity of finishing pigs(P<0.05).Moreover,dietary supplementation of 200 mg/kg lycopene significantly increased slow myosin heavy chain(MyHC)protein level and slow-twitch fiber percentage,and decreased fast MyHC protein level and fast-twitch fiber percentage(P<0.05),suggesting that the addition of 200 mg/kg lycopene to the diet of finishing pigs promoted muscle fiber type conversion from fast-twitch to slow-twitch.Together,we provide the first evidence that dietary 200 mg/kg lycopene supplementation improves meat quality,enhances antioxidant capacity and promotes muscle fiber type transformation from fast-twitch to slow-twitch in finishing pigs.

Nerve Growth Factor Promotes Angiogenesis and Skeletal Muscle Fiber Remodeling in a Murine Model of Hindlimb Ischemia

Background： Therapeutic angiogenesis has been shown to promote blood vessel growth and improve tissue perfusion.Nerve growth factor （NGF） has been reported to play an important role in both physiological and pathological angiogenesis.This study aimed to investigate the effects of NGF on angiogenesis and skeletal muscle fiber remodeling in a murine model of hindlimb ischemia and study the relationship between NGF and vascular endothelial growth factor （VEGF） in angiogenesis.Methods： Twenty-four mice were randomly allocated to normal control group （n =6）, blank control group （n =6）, VEGF gene transfection group （n =6）, and NGF gene transfection group （n =6）.The model of left hindlimb ischemia model was established by ligating the femoral artery.VEGF165 plasmid （125 μg） and NGF plasmid （125 μg） was injected into the ischemic gastrocnemius of mice from VEGF group and NGF group, respectively.Left hindlimb function and ischemic damage were assessed with terminal points at 21th day postischemia induction.The gastrocnemius of four groups was tested by hematoxylin-eosin staining, proliferating cell nuclear antigen and CD34 immunohistochemistry staining, and myosin ATPase staining.NGF and VEGF protein expression was detected by enzyme-linked immunosorbent assay.Results： On the 21th day after surgery, the functional assessment score and skeletal muscle atrophy degree of VEGF group and NGF group were significantly lower than those of normal control group and blank control group.The endothelial cell proliferation index and the capillary density of VEGF group and NGF group were significantly increased compared with normal control group and blank control group （P 〈 0.05）.The NGF and VEGF protein expression of NGF group showed a significant rise when compared with blank control group （P 〈 0.05）.Similarly, the VEGF protein expression of VEGF group was significantly higher than that of blank control group （P 〈 0.05）, but there was no significant difference of the NGF protein expression between VEGF group and blank control group （P 〉 0.05）.The type Ⅰ skeletal muscle fiber proportion in gastrocnemius of NGF group and VEGF group was significantly higher than that of blank control group （P 〈 0.05）.Conclusions： NGF transfection can promote NGF and VEGF protein expression which not only can induce angiogenesis but also induce type Ⅰ muscle fiber expression in ischemic limbs.