| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
FJ
EXPRESS SUMMARY ARTICLE The Full-length version of this article is also available, published online January 20, 2004 as doi:10.1096/fj.03-0668fje. |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, Wisconsin, USA
2Correspondence: Department of Animal Health and Biomedical Sciences, University of Wisconsin, 1656 Linden Dr., Madison, WI 53706, USA. E-mail: aiken{at}svm.vetmed.wisc.edu
SPECIFIC AIMS
Normal aging is associated with a progressive decline in lean body mass and function, a phenomenon known as sarcopenia. This loss of muscle mass with age contributes to loss of strength, altered thermoregulation, obesity, decreased aerobic capacity, and consequently functional decline and disability. Sarcopenia is a result of the decline in both the number and the cross-sectional area of muscle fibers. The etiology of sarcopenia is clearly multifactorial; however, mitochondrial DNA (mtDNA) deletion mutations and associated electron transport system (ETS) enzymatic abnormalities have been implicated in the loss of skeletal muscle fibers with age. Calorie restriction (CR) is the only experimental intervention known to extend life span and retard aging in mammals and has profound beneficial effects on skeletal muscle. In this study, we addressed the question of the effect of calorie restriction on ETS abnormalities in aged rat skeletal muscle. We determined whether CR affected the abundance of muscle fibers exhibiting mitochondrial enzymatic abnormalities and analyzed the phenotype (length and severity of intrafiber atrophy) of the abnormal regions.
PRINCIPAL FINDINGS
1. ETS abnormalities accumulate with age in skeletal muscle: calorie restriction reduces the abundance of ETS abnormal fibers
The prevalence of ETS abnormal fibers was examined in two quadriceps muscles (vastus lateralis and rectus femoris) from ad libitum (5, 18, and 36 months) and calorie-restricted rats (36 months). Eighteen animals were used from ad libitum-fed group (six at each age) and seven from 36-month-old calorie restricted. These histologic studies involved analysis of 100–200 ten micron-thick cross sections of skeletal muscle. Starting at the midbelly of the muscle, individual muscle fibers were analyzed for cytochrome c oxidase (COX) and succinate dehydrogenase (SDH) activities along the length of 1000–2000 µ of tissue. Abnormal fibers (COX-/SDH++) were not present in rectus femoris and vastus lateralis muscles of 5-month-old ad libitum-fed animals. A single abnormal fiber was observed in vastus lateralis muscle from an 18-month-old rat whereas none were found in rectus femoris muscle of the same age. In the 36-month-old ad libitum-fed rats, an average of 14 ± 7 abnormal fibers were observed in rectus femoris muscle and 18 ± 9 in vastus lateralis muscle.
Calorie restriction (40% restriction without nutrition deficiencies) reduced the abundance of muscle fibers containing the COX-/SDH++ phenotype. An average of 3 ± 2 fibers exhibiting COX-/SDH++ phenotype were found in the 1000–2000 µ of tissue analyzed from the rectus femoris and an average of 2 ± 1 fibers in vastus lateralis muscles of the 36-month-old calorie-restricted rats.
2. ETS abnormalities extend along the length of muscle fibers: calorie restriction does not affect progression of these abnormalities
Longitudinal analysis (multiple serial sections) of individual fibers and the segmental nature of ETS abnormalities facilitated measurement of the length of the COX-/SDH++ regions. ETS abnormal region lengths in vastus lateralis muscle were similar to the ETS abnormal region lengths in rectus femoris muscles for each diet, so measurements from both muscles were grouped together. Only those fibers with abnormal regions that started and ended within the region of muscle sectioned were included: 128 COX-/SDH++ fibers in the ad libitum and 31 COX-/SDH++ fibers in calorie-restricted rats. Abnormal regions from both diet groups had similar minimum ETS abnormal lengths of 100 µm (ad libitum) and 60 µm (CR), respectively. Mean abnormality lengths were 442.5 ± 277 µm and 531.6 ± 212 µm for ad libitum and calorie-restricted groups, respectively. The t test did not show a significant difference between the mean length of abnormal regions in the two groups studied (P=0.07). The maximum length of COX-/SDH++ regions in ad libitum-fed animals was 1710 µm whereas the maximum abnormality observed in the CR animals was 1000 µm. Approximately 30% of fibers from both groups had abnormal regions with lengths >500 µm.
3. Intrafiber atrophy is concomitant with ETS abnormalities: calorie restriction does not prevent fiber atrophy in ETS abnormal regions
The cross-sectional area (CSA) ratio provides an estimate of the severity of intrafiber atrophy and was calculated by dividing the minimum CSA value in the COX-/SDH++ region by the average CSA value of normal region within the same fiber. Whereas the ETS normal fibers exhibited little evidence of fiber atrophy (minimum CSA of 0.7), considerable atrophy was evident in ETS abnormal fibers of aged ad libitum-fed rats. Calorie restriction did not prevent fiber atrophy in ETS abnormal fibers. In ad libitum and calorie-restricted rats, 
50% of the abnormal fibers had CSA ratios lower than the minimum ratio in normal control fibers (Fig. 1
).
|
4. ETS abnormal region length is associated with fiber atrophy and fiber breakage
Following fibers through 1000–2000 µ, we observed that fibers with longer ETS abnormal regions were more likely to have smaller CSA ratios (more atrophic in COX-/SDH++ region). Spearman Rank Order Correlation test showed a negative relationship between ETS abnormal region length and CSA ratio in both ad libitum (r=–577;P=0.017) and calorie-restricted (r=–426; P<0.001) group (Fig. 2
).
|
CONCLUSIONS AND SIGNIFICANCE
A progressive loss of muscle mass and function (sarcopenia) is characteristic of normal aging. Mitochondrial abnormalities have been implicated in the loss of skeletal muscle fibers with age. Skeletal muscle fibers containing mtDNA deletion mutations exhibit abnormal electron transport system phenotype (COX-/SDH++) as seen by histological analysis. The number of ETS abnormal fibers increases with age, with fiber atrophy and fiber breakage being concomitant with these abnormalities. The longer the ETS abnormal region, the more prone the fiber is to atrophy, break, and be lost. Animals maintained on a diet containing 40% fewer calories were found to exhibit significantly fewer COX-/SDH++ abnormal fibers. In a companion study, calorie restriction reduced the severity of sarcopenia by maintaining fiber number. In this study we have characterized a cellular process, accumulation of electron transport system enzymatic abnormalities, that provides a molecular and cellular basis for age-associated muscle fiber loss. Our data strongly suggest that CR results in the generation of fewer ETS abnormalities, thus affecting/inhibiting a process that ultimately results in fiber loss.
|
FOOTNOTES
1 To read the full text of this article, go to http://www.fasebj.org/cgi/doi/10.1096/fj.03-0668fje; 
This article has been cited by other articles:
|
|
 |
|
  R. J. Colman, T. M. Beasley, D. B. Allison, and R. Weindruch Attenuation of Sarcopenia by Dietary Restriction in Rhesus Monkeys J. Gerontol. A Biol. Sci. Med. Sci., June 1, 2008; 63(6): 556 - 559. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. A. Vernace, L. Arnaud, T. Schmidt-Glenewinkel, and M. E. Figueiredo-Pereira Aging perturbs 26S proteasome assembly in Drosophila melanogaster FASEB J, September 1, 2007; 21(11): 2672 - 2682. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Zangarelli, E. Chanseaume, B. Morio, C. Brugere, L. Mosoni, P. Rousset, C. Giraudet, V. Patrac, P. Gachon, Y. Boirie, et al. Synergistic effects of caloric restriction with maintained protein intake on skeletal muscle performance in 21-month-old rats: a mitochondria-mediated pathway FASEB J, December 1, 2006; 20(14): 2439 - 2450. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
