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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 57:B232-B238 (2002)
© 2002 The Gerontological Society of America

Effects of Aging on Human Skeletal Muscle Myosin Heavy-Chain mRNA Content and Protein Isoform Expression

James O. Marxa, William J. Kraemerb, Bradley C. Nindlc and Lars Larssona,d

a Noll Physiological Research Center, The Pennsylvania State University, University Park.
b The Human Performance Laboratory, Department of Kinesiology, The University of Connecticut, Storrs.
c Military Performance Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts.
d Department of Cellular and Molecular Physiology, Hershey Medical Center, The Pennsylvania State University, Hershey.

Lars Larsson, Noll Physiological Research Center, The Pennsylvania State University, 129 Noll Laboratory, University Park, PA 16802 E-mail: lgl5{at}psu.edu.

Decision Editor: John A. Faulkner, PhD


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
The purpose of this investigation was to determine the role played by pretranslational events in the decreased rate of myosin heavy-chain (MyHC) protein synthesis in old age. It was hypothesized that the decreased rate of MyHC protein synthesis reported in the elderly population is, at least in part, related to lower MyHC messenger RNA (mRNA) in old age. MyHC protein expression and mRNA levels for the three MyHC isoforms expressed in human muscle, that is, types I, IIa, and IIx/d, were measured in percutaneous vastus lateralis muscle biopsies from 16 young and 16 old healthy men. The MyHC isoform mRNA content was determined by quantitative, real-time reverse transcriptase polymerase chain reaction, and it was normalized to 18S ribosomal RNA; the relative MyHC protein isoform content was measured on silver-stained 7% sodium dodecyl sulfate–polyacrylamide gel electrophoresis gels. The old men demonstrated signs of sarcopenia, such as loss of muscle force, a trend toward a loss in lean body mass, and an increased percentage of body fat. Statistically significant correlations were observed between the isoform expression of different MyHCs at the protein and mRNA levels. However, the expression of the different MyHC isoforms at the mRNA and protein levels did not differ between the young and old men. Thus, the present results do not support the hypothesis that pretranslational events in MyHC protein synthesis are playing a significant role in the development of sarcopenia.

THE strong influence of the aging-related loss of muscle mass, strength, and quality, that is, sarcopenia, on impaired motor function in old age has received increasing scientific attention in recent years. This is, at least in part, triggered by the increased awareness of the negative impact of sarcopenia on the ability of the elderly population to recover from a threatening fall and the risk of fracture (1). Sarcopenia, therefore, has important socioeconomic consequences, because falls are a major source of morbidity and mortality in the increasing population of elderly citizens (2). The decreased muscle mass in old age is secondary to the loss of {alpha}-motoneurons and motor units, and an incomplete reinnervation of previously denervated muscle fibers (3). In addition to the aging-related neurogenic loss of muscle mass, a decrease in the rate of synthesis of mixed muscle, mitochondrial, and myofibrillar proteins, including the myosin heavy-chain (MyHC), has been reported in old age (4)(5)(6)(7)(8). The effects of aging on the synthesis of the molecular motor protein myosin are very important, because myosin is the molecular motor protein in skeletal muscle that converts chemical energy into mechanical work. Further, cellular and molecular physiological studies have demonstrated specific aging-related changes in myosin function (9)(10)(11)(12)(13).

Aging has been shown to adversely affect the rate of protein translation (14)(15). Recently, the role of pretranslational events in the rate of protein synthesis was studied in human skeletal muscle (16)(17)(18). A consistent finding in these studies was the similar ß–slow (type I) MyHC transcript levels in both young and old subjects. In the fast-twitch fiber type population, Welle and colleagues (17) reported no differences in either type IIa or type IIx messenger RNA (mRNA) levels between young and old men and women. In a follow-up study, however, a decrease in type IIa MyHC mRNA, but not in type IIx MyHC mRNA, was observed in old men (18). Recently, Balagopal and colleagues (16) reported significant decreases in both type IIa and type IIx MyHC mRNA with aging in men and women.

Different results have accordingly been obtained with regard to the effects of aging on the fast (type II) MyHC mRNA levels. As discussed by Welle and coworkers (18), the absence of information on MyHC protein isoform expression is one limiting factor in these studies, because: (a) MyHC protein expression and mRNA levels are linked (19)(20)(21)(22)(23); (b) there are significant differences in skeletal muscle MyHC isoform expression between individuals as a result of both genetic and environmental factors (24); (c) aging-related changes in MyHC isoform expression have been reported in different human limb muscles and jaw-closing muscles (25)(26)(27)(28)(29); and (d) slow-twitch fibers have been shown to have a greater amount of total RNA content than fast-twitch muscle fibers (22)(30). Thus, parallel MyHC mRNA and protein analyses are essential when the effects of aging on pretranslational MyHC synthesis events are studied.

In an attempt to improve our understanding of the role played by pretranslational events in the rate of MyHC protein synthesis, we have measured the MyHC protein expression and mRNA levels of the three adult MyHC isoforms expressed in human muscle, that is, types I, IIa, and IIx/d. We hypothesized that the decreased rate of MyHC protein synthesis reported in the elderly population is, at least in part, related to pretranslational events and lower MyHC mRNA levels in old age. However, in spite of signs of sarcopenia in elderly subjects (loss of muscle force, increased body fat, and a trend toward a decrease in lean body mass), there were no differences in either MyHC mRNA levels or protein expression between young and old subjects. These results indicate that pretranslational events are not playing an important role in explaining the aging-related decrease in MyHC synthesis associated with sarcopenia. These results have been presented in short form elsewhere (31).


   Methods
Top
 Abstract
 Methods
Results
 Discussion
 References
 
Subjects
Sixteen young men (18–25 years old) and sixteen old men (65–80 years old) volunteered for this study. All of the men were determined to be healthy by physical exam, routine blood work, and electrocardiogram. Body composition for each subject was determined by skin fold measurements. The physical characteristics for the two groups are given in Table 1 . None of the subjects participated in regular exercise for at least 6 months prior to the study. The Pennsylvania State University Institutional Review Board approved the project, and all of the subjects signed an informed consent form before participating in any aspect of the investigation.


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  		Table 1. Physical Characteristics of Young and Old Subjects

 
Protocol
The subjects refrained from any strenuous activity for 3 days prior to muscle biopsy sampling. They also received a eucaloric diet, providing 1.25 g of protein per kilogram of body mass per day for 2 days prior to the muscle biopsy (32). A percutaneous biopsy was obtained by using the conchotome technique under local anesthesia from the left vastus lateralis muscle. The muscle samples were frozen in isopentane chilled with liquid nitrogen within 60 seconds of removal, and they were stored at -80°C until further analysis.

Strength Testing
Immediately following the muscle biopsy, maximum voluntary strength was measured in the knee-extensor muscles with an isokinetic dynamometer (KinCom II, Chattanooga Corporation, Chattanooga, TN). Each subject sat on the couch of the isokinetic dynamometer with the right thigh fixed with straps, the lower leg fixed to the dynamometer's lever arm, and the knee joint axis aligned with the rotational axis of the lever arm. Each subject was instructed to avoid rotation or movement in the upper body during the testing session. Gravitational correction to torque at 45° (0° = straight leg) was measured, and corrections applicable to the full movement range were calculated by computer software. Further, (a) a trigger torque of 50 N m had to be overcome by the subject before the rotational movement of the lever arm was initiated, (b) the initial acceleration rate was controlled prior to attaining the preset speed of movement, and (c) torque was only measured in the part of the torque recording where the preset speed was constant. Acceleration control of this type reduces the disturbing overshoot and the subsequent oscillations in the torque recording regularly seen after free acceleration to high target velocities (33)(34)(35). Measurements were performed through a range of movement from 90° to 0°. The average torque was calculated at constant speed between 75° and 25° of knee angle and was corrected for gravitation. Torque over the same knee angle range, that is, muscle length range, was compared at the different speeds of movement (30°/s and 180°/s). The subjects did not have any prior experience with the isokinetic dynamometer and were familiarized with testing procedures by performing three consecutive submaximal warm-up trials for each speed.

Torque at maximum voluntary effort does not vary appreciably between repeated isokinetic movements, because the torque is set by the upper limit of the voluntary strength (33). Therefore, the following procedure was used for each selected speed to ensure that torque recordings were accepted only when maximal voluntary effort seemed likely. At each preselected speed of movement, the torque-angle curve of a maximal voluntary contraction was superimposed on preceding records. When three records matched closely, they were accepted as maximum voluntary activations, and the average torque at each angular position was calculated. The isometric and isokinetic results are given in Table 1 .

RNA Extraction
Total RNA was extracted from 15 to 20 mg of frozen muscle tissue by using Trizol Reagent (Life Technologies, Rockville, MD), which is a single-step phenol–guanidine isothiocyanate extraction method (36). The pelleted RNA was then dissolved in diethylpyrocarbonate-treated water and stored at -80°C until further analysis. For RNA breakdown to be prevented, all reactions were performed by using sterile, ribonuclease (RNase)-free glassware. mRNA yield and protein contamination were determined by spectrophotometry. Prominent 18S and 28S ribosomal RNA bands on agarose gel electrophoresis confirmed the presence of a high-quality RNA product (17)(30). DNA contamination was tested for by using no-amplification controls (NACs; see the paragraphs that follow). The yield of total RNA was consistent with previous reports in the literature (30).

Real-Time Reverse Transcription Polymerase Chain Reaction
The complementary DNA (cDNA) for the polymerase chain reaction (PCR) was produced by reverse transcription (RT) of the RNA by using murine leukemia virus reverse transcriptase (MuLVRT; Applied Biosystems, Foster City, CA). The reverse primer for each gene was used to produce specific cDNA in the RT reaction. The sequences of reverse primers used for the production of the cDNA for each gene are listed in Table 2 . The reaction mixture for the RT reaction consisted of 0.5 ml of RNase inhibitor (40 U/ml), 2.0 ml of 10x TaqMan Universal Master Mix Buffer (Applied Biosystems), 3.6 ml of MgCl (10mM), 1.0 ml of the reverse primer of the gene of interest (10mM), 1.0 ml of reverse primer for 18S ribosomal RNA (0.25mM), 1.0 ml of deoxynucleoside triphoshates (dNTPS), adenosine, guanidine, cytosine, and uridine (10mM), and 5.0 ml of deionized, diethyl pyrocarbonate-treated water. A small sample of the reaction mixture was removed for a NAC in order to detect DNA contamination of the original sample. MuLVRT (0.44 ml, 50 U/ml) was then added to the reaction mix.


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  		Table 2. Sequences of Primers and Probes for Each of the Analyzed Genes

 
An amount of 20 ng of RNA was denatured by heating at 65° for 5 minutes, cooled on ice, and added to the RT reaction mixture and NAC. The reactions were incubated at 42°C for 1 hour. The MuLVRT was then denatured by incubating at 72°C for 5 minutes. An aliquot of this cDNA was then added to the PCR reaction. The PCR mix consisted of 5.0 ml of 10x TaqMan Universal Master Mix Buffer, 10.0 ml of MgCl2 (25mM), 1.0 ml of forward primer and reverse primer for the gene of interest (10mM), 1.0 ml of forward and reverse primer for 18S ribosomal RNA (0.25mM), 5 ml of the fluorogenic probe specific for the gene of interest (1mM), 1.5 ml of the fluorogenic probe specific for the 18S ribosomal RNA, 1.0 ml each of dNTPS, adenosine, guanidine, cytosine, and uridine (10mM), 0.25 ml of TAQ Gold (Applied Biosystems; 5 U/ml), 15.75 ml of deionized water, and 8.0 ml of the RT reaction product (containing 25 ng of cDNA). The fluorescent label used on the MyHC genes was 6-carboxyfluorescein (FAM) and the label on the 18S ribosomal RNA was VIC (Applera, Foster City, CA). The quencher at the 3' end of the probes was 6-carboxy-N, N, N', N'-tetramethylrhodamine. The sequences of the primers and probes are listed in Table 2 . The PCR reaction was run on a sequence detector (Applied Biosystems) with the following protocol: incubation for 2 minutes at 50°C and for 10 minutes at 95°, followed by 40 cycles of 95°C for 15 seconds, 60°C for 1 minute, and 2 minutes at 25°C. During the cycling, fluorescent emissions were collected every 8 seconds. The emissions were composed of spectra for FAM and VIC already specified by calibration. The PE Biosystems ABI PRISM 7700 Sequence Detection System was used to measure the fluorescent emission, and PE Biosystems Sequence Detection Software Version 1.6.3 was used to analyze the raw data (Applied Biosystems, Foster City, CA). Reactions were quantified as the difference in cycles between the 18S ribosomal RNA and the gene of interest at the threshold level for each. All samples were run in duplicate and the results were averaged for analysis. The average value for the group of young subjects' mRNA was set at "one" for all of the genes analyzed. The old subjects' results were then expressed relative to this value. The variability between subjects around this value allowed for the calculation of standard errors in both groups.

MyHC Protein Analysis
Two 10-µm-thick sections were cut from the frozen muscle tissue and were added to sodium dodecyl sulfate (SDS) sample buffer. MyHC isoform composition was determined by 7% SDS polyacrylamide gel electrophoresis. The total acrylamide and Bis concentrations were 4% (wt/vol) in the stacking gel and 7% in the separating gel. The gel matrix included 30% glycerol. The ammonium persulfate concentrations were 0.04% and 0.03% in the stacking and separating gels, respectively. Polymerization was subsequently activated by adding N, N, N', N'-tetramethylethylenediamene to the stacking (0.1%) and separating (0.07%) gels. Electrophoresis was performed at 120 V for 22–24 hours with a tris(hydroxymethyl)aminomethane-glycine electrode buffer (pH 8.3) at 15°C (SE 600 vertical slab gel unit, Hoefer Scientific Instruments, San Francisco, CA). For the resolution of the MyHC bands to be improved, the sample quantity loaded in each lane was kept small (6 µl). The separating gels were then silver stained and scanned in a soft laser densitometer (Molecular Dynamics, Sunnyvale, CA). Identification of MyHC protein isoforms was based on electrophoretic mobility. A volume-integration program (ImageQuant Software Version 3.3, Molecular Dynamics) was used to quantify the relative amount of each MyHC isoform on the gel, using high spatial resolution (50-mm pixel spacing) and 4096 optical density levels (37)(38)(39).

Statistics
One-tailed Pearson product correlations between MyHC isoform content and transcript level were determined for each of the three MyHC isoforms, and a regression analysis was also performed to test for differences between young and old subjects. A Student's t test was performed on actin mRNA content between young and old subjects. Differences were considered significant at p < .05.


   Results
Top
 Abstract
 Methods
 Results
Discussion
 References
 
The old subjects in this investigation demonstrated several of the changes consistent with sarcopenia, such as a decrease in maximum voluntary force, an increase in percentage of body fat, and a trend toward a decrease in lean body mass (Table 1 ).

There was no difference in MyHC isoform expression between the young and old subjects, and a predominance of fast (types IIa and IIx) MyHC isoforms (~70%) was observed in both groups (Table 3 ). Consistent with previous reports in the literature, the total RNA extracted and the concentration of the housekeeper gene, 18S ribosomal RNA, were not affected by age (17)(40)(41). Further, the types I, IIa, and IIx MyHC mRNA levels did not differ between the young and old subjects (Table 4 ). An analysis of actin mRNA levels did not demonstrate any significant differences between young and old subjects (Table 4 ).


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  		Table 3. Results of MyHC Protein Composition for Young and Old Subjects

 

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  		Table 4. Results for the Total RNA Extracted From the Muscle Tissue and the PCR Threshold Reaction for Young and Old Subjects

 
The relationships between the MyHC protein and mRNA contents for each of the three MyHC isoforms analyzed are shown in Fig. 1. A positive correlation between the MyHC protein and mRNA content was observed for each of the three MyHC isoforms, achieving statistical significance for the type I and type IIx isoforms (Type I, r = .480, p < .05; Type IIx, r = .570, p < .01). Regression analyses of these relationships did not show any significant differences between young and old subjects. In addition, independent of age, a significant variability in MyHC mRNA concentrations was observed between subjects. This is consistent with previous observations on the variability in MyHC mRNA levels between human subjects (16)(17)(18).



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  		Figure 1. Relationships between myosin heavy chain (MyHC) isoform proportion and MyHC messenger RNA (mRNA) levels normalized to 18S ribosomal RNA for types I, IIa, and IIx isoforms in young (•) and old ({circ}) men. The regression lines for the young men (solid curve) and the old men (dashed curve) are shown.

 

   Discussion
Top
 Abstract
 Methods
 Results
 Discussion
References
 
Recent reports in the literature have demonstrated significant aging-related decreases in the rate of MyHC synthesis (4)(5). In three recent studies, the influence of pretranslational events on the aging-related decrease in MyHC protein synthesis was investigated (16)(17)(18). Unfortunately, none of these investigations measured MyHC protein isoform composition in parallel with MyHC mRNA content, which is critical to MyHC mRNA analysis because of the close relationship between MyHC protein and mRNA content and the high variability between individuals in MyHC isoform composition. Therefore, the aim of the current investigation was to measure MyHC mRNA levels and express these levels relative to MyHC protein isoform expression. Comparing the relationship between MyHC protein and mRNA isoform expression and normalizing MyHC mRNA to MyHC isoform composition allows for meaningful comparisons of MyHC mRNA content between groups with different MyHC protein isoform proportions. Contrary to our hypothesis, the main finding of the current investigation is the absence of an aging-related change in the concentrations of skeletal muscle MyHC and actin mRNA levels, thus indicating that a decrease in MyHC mRNA is not responsible for the signs of sarcopenia observed in the old subjects in this study.

An important strength of the current investigation is the parallel analyses of both MyHC mRNA and protein expression. The need for measuring both MyHC protein isoform expression and mRNA levels was originally forwarded by Welle and coworkers (18), who found that MyHC protein expression and mRNA levels are related; this relationship is confirmed in both the young and the old men in this study (Fig. 1). The need for parallel measurements of both MyHC mRNA and protein isoform expressions is further supported by the significant individual differences in MyHC protein isoform expression, related to genetic and environmental factors (24), and the aging-related changes in myosin isoform expression (25)(26)(27)(28)(29). The decreased fast MyHC mRNA levels reported in the studies by Welle and associates (18) and by Balagopal and colleagues (16) offer an interesting and probable mechanism underlying the fast-to-slow MyHC isoform transition reported in human tibialis anterior, quadriceps, and biceps brachi muscles during aging (25)(26)(27)(28)(29).

In the present study, the relative proportions of types I, IIa, and IIx MyHC protein isoforms were almost identical in young and old subjects. Both groups expressed approximately 30% type I MyHC isoform, which is lower than that typically observed in both young and old sedentary men (29)(42). The mechanism underlying the low content of the slow myosin is not known. However, more importantly, the expression of types I, IIa, and IIx MyHC isoforms, both at the protein and mRNA levels, was not affected by aging in spite of signs of sarcopenia. Thus, altered MyHC mRNA expression reported in some studies (16)(18) in human skeletal muscle during aging may play an important role in aging-related MyHC isoform transitions, but it appears to be an unlikely mechanism underlying the aging-related loss of muscle force and mass.

The similar mRNA levels of actin and MyHC isoforms in young and old subjects observed in this study are in agreement with an earlier study by Welle and colleagues (17). They hypothesized that the aging-related decrease in MyHC synthesis was secondary to a slowing of the rate of MyHC mRNA translation at the ribosomal level. Alternatively, it cannot be ruled out that the decrease in protein synthesis is related to a lower translational efficiency of the mRNA in the older subjects. The latter alternative is supported by the lower amount of protein synthesized by mRNA from old rats compared with the mRNA from young rats in a cell-free system, reported by Horbach and associates (43).

Positive relationships between protein expression and mRNA levels were observed for the different MyHC isoforms. However, these relationships were not as strong as anticipated. It is unlikely that this weak relationship is secondary to methodological limitations, because very sensitive techniques were used to measure both protein and transcript levels. The silver-stained electrophoretic technique used in this study detects MyHC levels as low as 2–3% of the protein content from short single-muscle fiber segments (37)(39). Further, the real-time quantitative PCR method is the most sensitive technique available for quantitative mRNA analyses (44)(45). We therefore favor a biological mechanism underlying the weak correlation between MyHC protein expression and mRNA levels. This may be related to differences in mRNA stability or translational efficiency (46). In addition, it is well known that skeletal muscle MyHC has a long turnover rate, and its half-life has been reported to be as long as 30 days (47). MyHC mRNA, in contrast, has a half-life that is significantly shorter than the half-life of the MyHC protein (48)(49). Skeletal muscle responds rapidly to altered functional demands at the transcriptional level, whereas the protein response is significantly slower or absent (50)(51). This may in turn result in a mismatch between MyHC protein expression and mRNA levels (51)(52). In addition, transcription in muscle cells occurs in a stochastic or pulsatile fashion (53). Therefore, it is suggested that the lack of a strong correlation between MyHC protein expression and transcript levels is secondary to the combined effect of different turnover rates and the fact that MyHC transcription is not a continuous event.

In summary, MyHC mRNA levels in vastus lateralis muscles were not affected by aging in a population of 16 healthy young and 16 healthy old men who were showing signs of sarcopenia, such as loss of maximum force and a tendency toward loss of lean body mass. Altered MyHC transcript levels do not appear to be an important factor explaining sarcopenia. The present results support the hypothesis that the bioactivity of the mRNA or translational events are the dominating factors underlying the decreased MyHC synthesis reported in old age. Alternatively, the aging-related loss of muscle mass and force is primarily caused by other mechanisms, such as neurogenic mechanisms (3), whereas myosin synthesis rate is of minor importance.


   Acknowledgments
 
We thank Deborah Grove, PhD, for her invaluable help with the real-time quantitative RT-PCR, and Parinaz Pircher for the SDS–polyacrylamide gel electrophoresis analysis.

This study was supported by Grants AR 45627 and M01-RR10732-03 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases to L. Larsson, and National Research Service Award F32 AR08603-02 and grants from the Pennsylvania State University Gerontology Center to J. Marx.

Received November 13, 2001

Accepted March 12, 2002


   References
Top
 Abstract
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 Results
 Discussion
 References
 

  1. Schultz AB, Ashton-Miller JA, Alexander NB, 1997. What leads to age and gender differences in balance maintenance and recovery?. Muscle Nerve Suppl. 5:S60-S64. [Medline]
  2. Mahoney J, Sager M, Dunham NC, Johnson J, 1994. Risk of falls after hospital discharge. J Am Geriatr Soc. 42:269-274. [Medline]
  3. Larsson L, Ansved T, 1995. Effects of ageing on the motor unit. Prog Neurobiol. 45:397-458. [Medline]
  4. Balagopal P, Rooyackers OE, Adey DB, Ades PA, Nair KS, 1997. Effects of aging on in vivo synthesis of skeletal muscle myosin heavy-chain and sarcoplasmic protein in humans. Am J Physiol. 273: (4 Pt 1) E790-E800. [Abstract/Free Full Text]
  5. Hasten DL, Pak-Loduca J, Obert KA, Yarasheski KE, 2000. Resistance exercise acutely increases MHC and mixed muscle protein synthesis rates in 78–84 and 23–32 yr olds. Am J Physiol Endocrinol Metab. 278:E620-E626. [Abstract/Free Full Text]
  6. Rooyackers OE, Adey DB, Ades PA, Nair KS, 1996. Effect of age on in vivo rates of mitochondrial protein synthesis in human skeletal muscle. Proc Natl Acad Sci USA. 93:15,364-15,369. [Abstract/Free Full Text]
  7. Welle S, Thornton C, Jozefowicz R, Statt M, 1993. Myofibrillar protein synthesis in young and old men. Am J Physiol. 264: (5 Pt 1) E693-E698. [Abstract/Free Full Text]
  8. Yarasheski KE, Zachwieja JJ, Bier DM, 1993Erratum. Am J Physiol. 1993;265(4 Pt 1): following table of contents.. Acute effects of resistance exercise on muscle protein synthesis rate in young and elderly men and women. Am J Physiol. 265: (2 Pt 1) E210-E214. [Abstract/Free Full Text]
  9. Hook P, Li X, Sleep J, Hughes S, Larsson L, 1999. In vitro motility speed of slow myosin extracted from single soleus fibres from young and old rats. J Physiol (London). 520: (Pt 2) 463-471. [Abstract/Free Full Text]
  10. Larsson L, Li X, Yu F, Degens H, 1997. Age-related changes in contractile properties and expression of myosin isoforms in single skeletal muscle cells. Muscle Nerve Suppl. 5:S74-S78. [Medline]
  11. Li X, Larsson L, 1996. Maximum shortening velocity and myosin isoforms in single muscle fibers from young and old rats. Am J Physiol. 270: (1 Pt 1) C352-C360. [Abstract/Free Full Text]
  12. Lowe DA, Surek JT, Thomas DD, Thompson LV, 2001. Electron paramagnetic resonance reveals age-related myosin structural changes in rat skeletal muscle fibers. Am J Physiol Cell Physiol. 280: (3) C540-C547. [Abstract/Free Full Text]
  13. Thompson LV, 1999. Contractile properties and protein isoforms of single skeletal muscle fibers from 12- and 30-month-old Fischer 344 brown Norway F1 hybrid rats. Aging (Milano) 11:109-118. [Medline]
  14. Van Remmen H, Ward WF, Sabia RV, Richardson A, 1995. Gene expression and protein degradation. Masoro EJ, , ed.Handbook of Physiology—Aging 171-234. Oxford University Press, New York.
  15. Blazejowski CA, Webster GC, 1984. Effect of age on peptide chain initiation and elongation in preparations from brain, liver, kidney and skeletal muscle of the C57B1/6J mouse. Mech Ageing Dev. 25:323-333. [Medline]
  16. Balagopal P, Schimke JC, Ades P, Adey D, Nair S, 2001. Age effect on transcript levels and synthesis rate of muscle MHC and response to resistance exercise. Am J Physiol. 280:E203-E208.
  17. Welle S, Bhatt K, Thornton C, 1996. Polyadenylated RNA, actin mRNA, and myosin heavy chain mRNA in young and old human skeletal muscle. Am J Physiol. 270: (2 Pt 1) E224-E229. [Abstract/Free Full Text]
  18. Welle S, Bhatt K, Thornton CA, 2000. High-abundance mRNAs in human muscle: comparison between young and old. J Appl Physiol. 89:297-304. [Abstract/Free Full Text]
  19. Periasamy M, Gregory P, Martin BJ, Stirewalt WS, 1989. Regulation of myosin heavy-chain gene expression during skeletal-muscle hypertrophy. Biochem J. 257:691-698. [Medline]
  20. Hortobagyi T, Dempsey L, Fraser D, et al. 2000. Changes in muscle strength, muscle fibre size and myofibrillar gene expression after immobilization and retraining in humans. J Physiol. 524: (Pt 1) 293-304. [Abstract/Free Full Text]
  21. Haddad F, Qin AX, Zeng M, McCue SA, Baldwin KM, 1998. Effects of isometric training on skeletal myosin heavy chain expression. J Appl Physiol. 84:2036-2041. [Abstract/Free Full Text]
  22. Habets PE, Franco D, Ruijter JM, Sargeant AJ, Pereira JA, Moorman AF, 1999. RNA content differs in slow and fast muscle fibers: implications for interpretation of changes in muscle gene expression. J Histochem Cytochem. 47:995-1004. [Abstract/Free Full Text]
  23. Caiozzo VJ, Haddad F, Baker MJ, Baldwin KM, 1996. Influence of mechanical loading on myosin heavy-chain protein and mRNA isoform expression. J Appl Physiol. 80:1503-1512. [Abstract/Free Full Text]
  24. Simoneau JA, Bouchard C, 1995. Genetic determinism of fiber type proportion in human skeletal muscle. FASEB J. 9:1091-1095. [Abstract]
  25. Jakobsson F, Borg K, Edstrom L, Grimby L, 1988. Use of motor units in relation to muscle fiber type and size in man. Muscle Nerve. 11:1211-1218. [Medline]
  26. Larsson L, Sjodin B, Karlsson J, 1978. Histochemical and biochemical changes in human skeletal muscle with age in sedentary males, age 22–65 years. Acta Physiol Scand. 103:31-39. [Medline]
  27. Monemi M, Eriksson PO, Eriksson A, Thornell LE, 1998. Adverse changes in fibre type composition of the human masseter versus biceps brachii muscle during aging. J Neurol Sci. 154:35-48. [Medline]
  28. Tomonaga M, 1977. Histochemical and ultrastructural changes in senile human skeletal muscle. J Am Geriatr Soc. 25:125-131. [Medline]
  29. Klitgaard H, Mantoni M, Schiaffino S, et al. 1990. Function, morphology and protein expression of ageing skeletal muscle: a cross-sectional study of elderly men with different training backgrounds. Acta Physiol Scand. 140:41-54. [Medline]
  30. Hood DA, Simoneau JA, 1989. Rapid isolation of total RNA from small mammal and human skeletal muscle. Am J Physiol. 256: (5 Pt 1) C1092-C1096. [Abstract/Free Full Text]
  31. Marx JO, Nindl BC, Larsson L, Pircher P, Kraemer WJ. The Effect of Aging on Skeletal Muscle Myosin Heavy Chain mRNA. Indianapolis, IN: American College of Sports Medicine; 2000.
  32. Campbell WW, Crim MC, Dallal GE, Young VR, Evans WJ, 1994. Increased protein requirements in elderly people: new data and retrospective reassessments. Am J Clin Nutr. 60:501-509. [Abstract/Free Full Text]
  33. Gransberg L, Knutsson E, 1983. Determination of dynamic muscle strength in man with acceleration controlled isokinetic movements. Acta Physiol Scand. 119:317-320. [Medline]
  34. Gransberg L, Knutsson E, Litton JE, 1980. A computer programmed system for the analysis of active and passive isokinetic movements. IEEE 1980 Frontiers of Engineering in Health Care, Washington 292-295. Institute of Electrical and Electronics Engineers, New York.
  35. Winter DA, Wells RP, Orr GW, 1981. Errors in the use of isokinetic dynamometers. Eur J Appl Physiol. 46:397-408.
  36. Chomczynski P, Sacchi N, 1987. Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal Biochem. 162:156-159. [Medline]
  37. Giulian GG, Moss RL, Greaser M, 1983. Improved methodology for analysis and quantitation of proteins on one-dimensional silver-stained slab gels. Anal Biochem. 129:277-287. [Medline]
  38. Larsson L, Moss RL, 1993. Maximum velocity of shortening in relation to myosin isoform composition in single fibres from human skeletal muscles. J Physiol (London). 472:595-614. [Abstract/Free Full Text]
  39. Larsson L, Muller U, Li X, Schiaffino S, 1995. Thyroid hormone regulation of myosin heavy chain isoform composition in young and old rats, with special reference to IIX myosin. Acta Physiol Scand. 153:109-116. [Medline]
  40. Forsberg AM, Nilsson E, Werneman J, Bergstrom J, Hultman E, 1991. Muscle composition in relation to age and sex. Clin Sci (Colch). 81:249-256.
  41. Thellin O, Zorzi W, Lakaye B, et al. 1999. Housekeeping genes as internal standards: use and limits. J Biotechnol. 75:291-295. [Medline]
  42. Staron RS, Hagerman FC, Hikida RS, et al. 2000. Fiber type composition of the vastus lateralis muscle of young men and women. J Histochem Cytochem. 48:623-629. [Abstract/Free Full Text]
  43. Horbach GJ, Princen HM, Van der Kroef M, Van Bezooijen CF, Yap SH, 1984. Changes in the sequence content of albumin mRNA and in its translational activity in the rat liver with age. Biochim Biophys Acta. 783:60-66. [Medline]
  44. Bustin SA, 2000. Absolute quantification of mRNA using real-time reverse transcription polymerase chain reaction assays. J Mol Endocrinol. 25:169-193. [Abstract]
  45. Heid CA, Stevens J, Livak KJ, Williams PM, 1996. Real time quantitative PCR. Genome Res. 6:986-994. [Abstract/Free Full Text]
  46. Pieples K, Wieczorek DF, 2000. Tropomyosin 3 increases striated muscle isoform diversity. Biochemistry. 39:8291-8297. [Medline]
  47. Kay J, 1978. Intracellular protein degradation. Biochem Soc Trans. 6:789-797. [Medline]
  48. Qi M, Puglisi JL, Byron KL, et al. 1997. Myosin heavy chain gene expression in neonatal rat heart cells: effects of [Ca2+]i and contractile activity. Am J Physiol. 273: (2 Pt 1) C394-C403. [Abstract/Free Full Text]
  49. Nadal-Ginard B, 1998. Structure and regulation of a mammalian sarcomeric myosin heavy chain gene. Pearson ML, Epstein HF, , ed.Muscle Development: Molecular and Cellular Control 143-168. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY.
  50. Andersen JL, Schiaffino S, 1997. Mismatch between myosin heavy chain mRNA and protein distribution in human skeletal muscle fibers. Am J Physiol. 272: (6 Pt 1) C1881-C1889. [Abstract/Free Full Text]
  51. Andersen JL, Gruschy-Knudsen T, Sandri C, Larsson L, Schiaffino S, 1999. Bed rest increases the amount of mismatched fibers in human skeletal muscle. J Appl Physiol. 86:455-460. [Abstract/Free Full Text]
  52. Izumo S, Nadal-Ginard B, Mahdavi V, 1986. All members of the MHC multigene family respond to thyroid hormone in a highly tissue-specific manner. Science. 231:597-600. [Abstract/Free Full Text]
  53. Newlands S, Levitt LK, Robinson CS, et al. 1998. Transcription occurs in pulses in muscle fibers. Genes Dev. 12:2748-2758. [Abstract/Free Full Text]



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