The loss of skeletal muscle mass with aging has been attributed to a decline in muscle fiber number and muscle fiber size.
To define to what extent differences in leg muscle cross-sectional area ...(CSA) between young and elderly men are attributed to differences in muscle fiber size.
Quadriceps muscle CSA and type I and type II muscle fiber size were measured in healthy young (n=25; 23±1y) and older (n=26; 71±1y) men. Subsequently, the older subjects performed 6months of resistance type exercise training, after which measurements were repeated. Differences in quadriceps muscle CSA were compared with differences in type I and type II muscle fiber size.
Quadriceps CSA was substantially smaller in older versus young men (68±2 vs 80±2cm2, respectively; P<0.001). Type II muscle fiber size was substantially smaller in the elderly vs the young (29%; P<0.001), with a tendency of smaller type I muscle fibers (P=0.052). Differences in type II muscle fiber size fully explained differences in quadriceps CSA between groups. Prolonged resistance type exercise training in the elderly increased type II muscle fiber size by 24±8% (P<0.01), explaining 100±3% of the increase in quadriceps muscle CSA (from 68±2 to 74±2cm2).
Reduced muscle mass with aging is mainly attributed to smaller type II muscle fiber size and, as such, is unlikely accompanied by substantial muscle fiber loss. In line, the increase in muscle mass following prolonged resistance type exercise training can be attributed entirely to specific type II muscle fiber hypertrophy.
► Age-related differences in muscle size can be attributed to smaller muscle fibers. ► Training-induced increase in muscle size is attributed to muscle fiber hypertrophy. ► Large in muscle fiber numbers changes in aging or after training are unlikely. ► Interventions for sarcopenia should target type II muscle fiber hypertrophy.
Context:
The metabolic syndrome, characterized by central obesity with dyslipidemia, hypertension, and hyperglycemia, identifies people at high risk for type 2 diabetes.
Objective:
Our objective was ...to determine how the insulin resistance of the metabolic syndrome is related to muscle fiber composition.
Design:
Thirty-nine sedentary men and women (including 22 with the metabolic syndrome) had insulin responsiveness quantified using euglycemic clamps and underwent biopsies of the vastus lateralis muscle. Expression of insulin receptors, insulin receptor substrate-1, glucose transporter 4, and ATP synthase were quantified with immunoblots and immunohistochemistry.
Participants and Setting:
Participants were nondiabetic, metabolic syndrome volunteers and sedentary control subjects studied at an outpatient clinic.
Main Outcome Measures:
Insulin responsiveness during an insulin clamp and the fiber composition of a muscle biopsy specimen were evaluated.
Results:
There were fewer type I fibers and more mixed (type IIa) fibers in metabolic syndrome subjects. Insulin responsiveness and maximal oxygen uptake correlated with the proportion of type I fibers. Insulin receptor, insulin receptor substrate-1, and glucose transporter 4 expression were not different in whole muscle but all were significantly less in the type I fibers of metabolic syndrome subjects when adjusted for fiber proportion and fiber size. Fat oxidation and muscle mitochondrial expression were not different in the metabolic syndrome subjects.
Conclusion:
Lower proportion of type I fibers in metabolic syndrome muscle correlated with the severity of insulin resistance. Even though whole muscle content was normal, key elements of insulin action were consistently less in type I muscle fibers, suggesting their distribution was important in mediating insulin effects.
Thyroid hormones are important for homeostatic control of energy metabolism and body temperature. Although skeletal muscle is considered a key site for thyroid action, the contribution of thyroid ...hormone receptor signaling in muscle to whole‐body energy metabolism and body temperature has not been resolved. Here, we show that T3‐induced increase in energy expenditure requires thyroid hormone receptor alpha 1 (TRα1) in skeletal muscle, but that T3‐mediated elevation in body temperature is achieved in the absence of muscle‐TRα1. In slow‐twitch soleus muscle, loss‐of‐function of TRα1 (TRαHSACre) alters the fiber‐type composition toward a more oxidative phenotype. The change in fiber‐type composition, however, does not influence the running capacity or motivation to run. RNA‐sequencing of soleus muscle from WT mice and TRαHSACre mice revealed differentiated transcriptional regulation of genes associated with muscle thermogenesis, such as sarcolipin and UCP3, providing molecular clues pertaining to the mechanistic underpinnings of TRα1‐linked control of whole‐body metabolic rate. Together, this work establishes a fundamental role for skeletal muscle in T3‐stimulated increase in whole‐body energy expenditure.
To investigate the relationships between muscle fiber characteristics and meat quality traits of Korean native cattle, Hanwoo,
Longissimus dorsi (LD),
Psoas major (PM) and
Semimembranosus (SM) ...muscles obtained from 18 Hanwoo steers and the muscle fiber characteristics were measured by histochemical analysis. Fiber number, area percentages and density of type IIA and IIB were lower in SM muscle, but higher in PM muscle than other muscles. LD muscle had higher pH
24h,
L
⁎ value and fat content whereas SM muscle had lower
L
⁎ value and fat content. The lowest WBSF with longer sarcomere length was observed in PM muscle, while SM muscle showed the highest WBSF with shorter sarcomere length. Consequently, the percentage of type I and IIB were highly correlated with meat quality traits and inversely correlated with fat content,
L
⁎ value and WBSF. Fiber number and area percentage of type I had a positive correlation with fat content and
L
⁎ value and a negative correlation with WBSF. These results suggest that Hanwoo steers had high marbling, more lightness and tenderness when the percentage of type I was high and the percentage of type IIB was low in muscle.
Muscle wasting occurs in a variety of conditions, including both genetic diseases, such as muscular dystrophies, and acquired disorders, ranging from muscle disuse to cancer cachexia, from heart ...failure to aging sarcopenia. In most of these conditions, the loss of muscle tissue is not homogeneous, but involves specific muscle groups, for example Duchenne muscular dystrophy affects most body muscles but spares extraocular muscles, and other dystrophies affect selectively proximal or distal limb muscles. In addition, muscle atrophy can affect specific fiber types, involving predominantly slow type 1 or fast type 2 muscle fibers, and is frequently accompanied by a slow-to-fast or fast-to-slow fiber type shift. For example, muscle disuse, such as spinal cord injury, causes type 1 fiber atrophy with a slow-to-fast fiber type shift, whereas cancer cachexia leads to preferential atrophy of type 2 fibers with a fast-to-slow fiber type shift. The identification of the signaling pathways responsible for the differential response of muscles types and fiber types can lead to a better understanding of the pathogenesis of muscle wasting and to the design of therapeutic interventions appropriate for the specific disorders.
This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.
Fiber typing in aging muscle Purves-Smith, Fennigje M; Sgarioto, Nicolas; Hepple, Russell T
Exercise and sport sciences reviews,
04/2014, Letnik:
42, Številka:
2
Journal Article
Recenzirano
Odprti dostop
It is accepted widely that fast-twitch muscle fibers are preferentially impacted in aging muscle, yet we hypothesize that this is not valid when aging muscle atrophy becomes severe. In this review, ...we summarize the evidence of fiber type-specific effect in aging muscle and the potential confounding roles of fibers coexpressing multiple myosin heavy-chain isoforms and their histochemical identification.
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•Puerarin ameliorates muscle wasting in type 1 diabetic rats.•Puerarin improves skeletal muscle weight and strength in type 1 diabetic rats.•Puerarin promotes transformation of muscle ...fiber types from slow-twitch to fast-twitch in type 1 diabetic rats.•Puerarin activates Akt/mTOR while inhibites autophagy in skeletal muscle.
Puerarin is an isoflavonoid extracted from Pueraria lobate with extensive pharmacological effects in traditional Chinese medicine. The evidence implicates that puerarin mitigates hyperglycemia and various relevant complications. Here, the effect of puerarin on skeletal muscle wasting induced by type 1 diabetes (T1D) was explored. Streptozotocin (STZ)-induced T1D male Sprague Dawley (SD) rats were used in this study. Muscle strength, weight and size were measured. L6 rat skeletal muscle cells were applied for in vitro study. Our results showed that eight-week oral puerarin administration (100 mg/kg) increased muscle strengths and weights accompanied by enhanced skeletal muscle cross-sectional areas in diabetic rats. Simultaneously, puerarin also reduced expressions of several muscle wasting marker genes including F-box only protein 32 (Atrogin-1) and muscle-specific RING-finger 1 (Murf-1) in diabetic group both in vitro and in vivo. Transformation from type I fibers (slow muscle) to type II fibers (fast muscle) were also observed under puerarin administration in diabetic rats. Puerarin promoted Akt/mTOR while inhibited LC3/p62 signaling pathway in skeletal muscle cells. In conclusion, our study showed that puerarin mitigated skeletal muscle wasting in T1D rats and closely related with Akt/mTOR activation and autophagy inhibition. Whether this effect in murine applies to humans remains to be determined.
Sarcopenia is a musculoskeletal disease that reduces muscle mass and strength in older individuals. The study investigates the effects of azilsartan (AZL) on skeletal muscle loss in natural ...sarcopenic rats. Male Sprague-Dawley rats aged 4-6 months and 18-21 months were selected as young-matched control and natural-aged (sarcopenic) rats, respectively. Rats were allocated into young and old control (YC and OC) and young and old AZL treatment (YT and OT) groups, which received vehicles and AZL (8 mg/kg, orally) for 6 weeks. Rats were then sacrificed after muscle function analysis. Serum and gastrocnemius (GN) muscles were isolated for further endpoints. AZL significantly improved muscle grip strength and antioxidant levels in sarcopenic rats. AZL also restored the levels of insulin, testosterone, and muscle biomarkers such as myostatin and creatinine kinase in sarcopenic rats. Furthermore, AZL treatment improved the cellular and ultrastructure of GN muscle and prevented the shift of type II (glycolytic) myofibers to type I (oxidative) myofibers. The results showed that AZL intervention restored protein synthesis in natural sarcopenic rats by increasing p-Akt-1 and decreasing muscle RING-finger protein-1 and tumor necrosis factor alpha immunoexpressions. In conclusion, the present findings showed that AZL could be an effective intervention in treating age-related muscle impairments.
Aim
To develop a method for direct measurement of the fluorescent d‐glucose analogue 2‐NBDG transport across the plasma membrane of single skeletal muscle fibres and derive the theoretical framework ...for determining the kinetic parameters for d‐glucose transport under basal conditions.
Methods
A novel method is described for measuring free 2‐NBDG transport across plasma membrane of single rat muscle fibres at rest. The 2‐NBDG uptake was >90% suppressed by 100 µM cytochalasin B in both fast‐twitch and slow‐twitch fibres, indicating that the 2‐NBDG transport is GLUT‐mediated. Fibres were identified as fast‐twitch or slow‐twitch based on the differential sensitivity of their contractile apparatus to Sr2+.
Results
The time course of 2‐NBDG uptake in the presence of 50 µM 2‐NBDG follows a one‐phase exponential plateau curve and is faster in fast‐twitch (rate constant 0.053 ± 0.0024 s‐1) than in slow‐twitch fibres (rate constant 0.031 ± 0.0021 s‐1). The rate constants were markedly reduced in the presence of 20 mM d‐glucose to 0.0082 ± 0.0004 s‐1 and 0.0056 ± 0.0002 s‐1 in fast‐twitch and slow‐twitch fibres respectively. 2‐NBDG transport was asymmetric, consistent with GLUT1 being the major functional GLUT isoform transporting 2‐NBDG in muscle fibres at rest. The parameters describing the transport kinetics for both 2‐NBDG and d‐glucose (dissociation constants, Michaelis–Menten constants, maximal rates of uptake and outflow) were calculated from the measurements made with 2‐NBDG.
Conclusion
Free 2‐NBDG and d‐glucose transport across the plasma membrane of single rat muscle fibres at rest is fast, conclusively showing that the rate‐limiting step in d‐glucose uptake in skeletal muscle is not necessarily the GLUT‐mediated transport of d‐glucose.
MicroRNAs (miRNAs) are a class of small non-coding RNAs that are widely involved in a variety of biological processes. Different skeletal muscle fiber type composition exhibits characteristic ...differences in functional properties and energy metabolism of skeletal muscle. However, the molecular mechanism by which miRNAs control the different type of muscle fiber formation is still not fully understood. In the present study, we characterized the role of microRNA-139-5p (miR-139-5p) in the regulation of myosin heavy chain (MyHC) isoform expression and its underlying mechanisms. Here we found that the expression of miR-139-5p was significantly higher in mouse slow-twitch muscle than in fast-twitch muscle. Overexpression of miR-139-5p downregulated the expression of MyHC I and MyHC IIa, whereas inhibition of miR-139-5p upregulated them. We also found that the levels of calcineurin (CaN), NFATc1, MEF2C and MCIP1.4, which are the components of CaN/NFAT signaling pathway that has shown to positively regulate slow fiber-selective gene expression, were notably inhibited by miR-139-5p overexpression. Furthermore, treatment of phenylephrine (PE), a α1-adrenoceptor agonist, abolished the inhibitory effect of miR-139-5p on MyHC I and MyHC IIa expression. Together, our findings indicated that the role of miR-139-5p in regulating the MyHC isoforms, especially MyHC I and MyHC IIa, may be achieved through inhibiting CaN/NFAT signaling pathway.
•MiR-139-5p was higher in mouse slow-twitch than in fast-twitch muscle.•MiR-139-5p overexpression downregulated the expression of MyHC I and MyHC IIa.•CaN/NFAT signaling was notably inhibited by miR-139-5p overexpression.•MiR-139-5p suppressed MyHC I and IIa expression via inhibiting CaN/NFAT signaling.
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