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J Appl Physiol 92: 2617-2624, 2002. First published February 22, 2002; doi:10.1152/japplphysiol.01102.2001
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Vol. 92, Issue 6, 2617-2624, June 2002

Mitochondrial abnormalities are more frequent in muscles undergoing sarcopenia

Entela A. Bua1, Susan H. McKiernan1, Jonathan Wanagat2, Debbie McKenzie1, and Judd M. Aiken1

1 Department of Animal Health and Biomedical Sciences and 2 Medical Scientist Training Program, University of Wisconsin, Madison, Wisconsin 53706


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

The hypothesis that the accumulation of electron transport system (ETS) abnormalities and sarcopenia are linked was investigated. Vastus lateralis, soleus, and adductor longus muscles were studied in 5-, 18-, and 36-mo-old male Fischer 344 × Brown Norway F1 hybrid rats. A significant decrease in soleus and vastus lateralis muscle mass was observed with age. Adductor longus was resistant to muscle mass loss. Multiple serial sections were analyzed for the activities of cytochrome-c oxidase (COX) and succinate dehydrogenase (SDH). The number of fibers exhibiting a COX-/SDH++ phenotype increased with age in both vastus lateralis and soleus muscles. No ETS-abnormal fibers were identified in adductor longus at any age. Cross-sectional area of ETS-abnormal fibers decreased in the abnormal region (region displaying COX-/SDH++ phenotype), whereas control fibers did not. The vastus lateralis muscle, which undergoes a high degree of sarcopenia, exhibited more ETS abnormalities and associated fiber loss than the soleus and adductor longus muscles, which are more resistant to sarcopenia, suggesting a direct association between ETS abnormalities and fiber loss.

aging; ragged red fiber; rat; muscle atrophy


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

SARCOPENIA IS DEFINED AS the loss of skeletal muscle mass with age. It is a major contributor to loss of strength (20, 50), decreased metabolic rate (24), gradual reduction of bone density (5, 56), decreased aerobic capacity (23) and, consequently, an increase in physical frailty and a decrease in functional performance in aged individuals (34). This muscle mass loss presents as a decrease in the muscle cross-sectional area (CSA) with age (38, 49, 51, 52, 65, 66) and has been attributed to a reduction in muscle fiber number (28, 33, 38) and fiber atrophy (12, 38, 54). Type II (fast-twitch, white) fibers are more susceptible than type I (slow-twitch, red) fibers to age-related fiber atrophy and fiber loss (2, 27, 32, 35, 37). The extent of sarcopenia is muscle specific, with some muscles exhibiting substantial declines in weight with age [e.g., vastus lateralis (38), rectus femoris (63), soleus (12, 11, 16, 41), plantaris (11), gastrocnemius (57), and extensor digitorum longus (12)]. Other muscles show no change in weight with age [e.g., adductor longus, epitrochlearis (27), and flexor digitorum longus (62)].

A number of mechanisms have been proposed as causing sarcopenia, including selective decline and changes in motor unit organization (25, 26, 31, 32), contraction-induced injuries (9, 21), deficient satellite cell recruitment (15), increase of free radicals and oxidative stress (63, 64), and age-related accumulation of mitochondrial abnormalities [e.g., mitochondrial DNA (mtDNA) deletion mutations and electron transport system (ETS) abnormalities (3, 36, 40, 63)].

ETS abnormalities occur in a high proportion of muscle fibers in myopathy patients, particularly in chronic progressive external ophthalmoplegia and its variant Kearns-Sayre syndrome (8, 29, 44, 45). The most frequently observed morphological change that results from impaired oxidative phosphorylation is the ragged red fiber (43, 53). The increase in succinate dehydrogenase (SDH) activity gives a "ragged red" phenotype to the fiber due to its staining pattern (purple or red) with modified Gomori trichrome (19). Electron microscopy studies demonstrate that the ragged red appearance results from an abnormal proliferation of mitochondria beneath the sarcolemma of skeletal muscle fibers (8, 45). The increased SDH activity in the ragged red fibers is often accompanied by deficiencies of cytochrome-c oxidase (COX) activity. ETS abnormalities accumulate with age in humans and animals without muscular disease (3, 30, 36, 40, 43, 46, 53, 63). These abnormalities are distributed in a mosaic and segmental pattern and have been observed primarily in postmitotic tissues with high oxygen consumption, such as skeletal muscle (1, 6, 60, 13, 43), heart (42, 58, 59), and brain (7).

Examination of COX and SDH activities from skeletal muscle of rhesus monkeys (36, 40) and rats (3, 63) demonstrates that the number of fibers containing ETS abnormalities (COX- and/or SDH++) increases with age. Our laboratory recently identified an association of ETS abnormalities with a marker of cellular dysfunction, intrafiber atrophy, in rhesus monkey quadriceps (36, 40) and rat rectus femoris muscle (63).

The question arises whether different muscles accumulate different levels of ETS abnormalities during normal aging. The present study investigated the abundance of ETS-abnormal fibers (COX-/SDH++) in muscles that exhibit varying degrees of sarcopenia during normal aging. We hypothesized that muscles exhibiting higher levels of sarcopenia would have more ETS abnormalities compared with muscles with reduced muscle mass loss. To address this hypothesis, muscle mass, fiber number, muscle CSA at midbelly, and abundance of ETS-abnormal fibers (fibers displaying COX-/SDH++ phenotype) were characterized in muscles known to undergo considerable sarcopenia (vastus lateralis) or intermediate sarcopenia (soleus) and in a muscle resistant to sarcopenia (adductor longus).


    MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Animals and tissue preparation. Skeletal muscle was obtained from 5- (n = 7), 18- (n = 7), and 36-mo-old (n = 6) male Fischer 344 × Brown Norway F1 (F344×BNF1) hybrid rats that had been purchased from the National Institute on Aging colony maintained by Harlan Sprague Dawley (Indianapolis, IN). The F344×BNF1 rat was chosen because it is a long-lived strain (mean life span of the male F344×BNF1 rat is ~33 mo) and it is less susceptible to many age-related pathologies (e.g., nephropathy) that develop in other rat strains (39).

The rats were killed by exsanguination. The vastus lateralis, soleus, and adductor longus muscles were carefully dissected free from surrounding tissue, and the wet weights were measured. Whole muscle samples were then bisected at midbelly perpendicular to their longitudinal axis, placed in OCT mounting media (Miles, Elkhart, IN), frozen in liquid nitrogen, and stored at -80°C. The tissues were brought to the temperature of the cryostat (-20°C) before sectioning. One hundred serial, transverse frozen sections, 10 µm thick, were cut, starting from midbelly, and placed on Probe-On Plus slides (Fisher Scientific, Pittsburgh, PA).

Histochemistry. Enzymatic staining for COX (55) and SDH activity (17) was performed on serial sections to identify fibers containing ETS-abnormal regions. COX and SDH incubation media were prepared as described in Lee et al. (36). For the longitudinal study of individual fibers, the staining was performed as described in Van Zeeland et al. (61). Briefly, the first slide was stained with hematoxylin and eosin (H&E), the second slide for COX activity, and the third slide for SDH activity. The fourth, fifth, sixth, and seventh slides were stored at -80°C for future studies; the eighth, ninth, and tenth slides were stained again with H&E, for COX activity, and for SDH activity, respectively. This staining pattern was repeated throughout the 100 slides for each muscle. After staining, the slides were rinsed in distilled water and mounted with aqueous media (Aqua Poly/Mount, Polysciences, Warrington, PA).

Characterization of ETS-abnormal fibers and fiber atrophy. To characterize COX-negative (COX-) fibers, each COX-stained muscle section was screened on an Olympus BH2 microscope under bright-field illumination. When a COX- fiber was found, the fiber was identified in the adjacent section stained for SDH activity. The phenotype and CSA of each abnormal and normal fiber were recorded along the length of 1,000 µm at 70-µm intervals. Fibers that stained negative for COX activity and hyperreactive for SDH activity were scored as ETS-abnormal fibers (Fig. 1).


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  		Fig. 1.   Serial cross-section photomicrographs of 36-mo-old rat vastus lateralis muscle, stained for cytochrome-c oxidase (COX; A) and succinate dehydrogenase (SDH; B) activity. Arrows indicate muscle fibers deficient for COX activity (COX-) and hyperreactive for SDH activity (SDH++). Bar, 50 µm.

The muscle fiber CSA of individual ETS-normal (randomly selected) and ETS-abnormal fibers was measured along the length of the 1,000 µm by use of Image Pro-Plus software (Media Cybernetics, Atlanta, GA). The smallest (minimum CSA) value of the fiber CSA in the ETS-abnormal region was divided by the average value of the fiber CSA in the ETS-normal region within the same fiber. In the ETS-normal fibers, the ratio between minimum CSA and average CSA was determined. Kernel densities were used to determine the distribution of CSA ratios.

Muscle mass, fiber number, and muscle CSA. To characterize sarcopenia, muscle mass, fiber number, and muscle CSA at midbelly were determined. Wet weights were obtained from each tissue sample immediately after dissection. After sectioning, an H&E-stained section at the midbelly of the muscle was used for fiber count. The section was photographed with a digital camera (Hitachi HV-C/C20M) at ×4 magnification. Digital images of the entire muscle cross section were reconstructed. Every fiber in the composite digital image was marked using Adobe Photoshop software, followed by counting using Image Pro-Plus software (Media Cybernetics, Atlanta, GA). The whole muscle section reconstruction was also used to measure the whole muscle CSA at the midbelly. Image Pro-Plus software (Media Cybernetics) was used for this purpose.

Fiber type. Immunohistochemistry, as described in Aspnes et al. (3), was used to determine fiber type composition. Briefly, sections were incubated with the monoclonal antiskeletal myosin clone, MY-32 (Sigma Chemical, St. Louis, MO), at a 1:400 dilution for 2 h, followed by a 1-h incubation with anti-mouse IgG alkaline phosphatase-conjugated antibody (1:200). MY-32 antibody reacts with type II fibers. Samples were mounted with aqueous Aqua Poly/Mount (Polysciences, Warrington, PA). Type I and type II fibers were identified, counted, and proportions were determined.

Statistical analysis. The statistical package SigmaStat 2.0 (SPSS) was utilized for all statistical analysis. Means and SE were calculated from individual values. One-way ANOVA was used to determine significance between the three age groups. The Tukey test was used for multiple comparisons. The distributions of fiber CSA were estimated by using Kernel densities. The strength of the association between ETS abnormality length and CSA ratio was determined using Spearman rank-order correlation. Differences were considered significant at P < 0.05.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Body weight, muscle mass, fiber number, and muscle CSA. Body weights of 5-mo (n = 7), 18-mo (n = 7), and 36-mo-old (n = 6) F344×BNF1 rats (Table 1) increased significantly (P < 0.001) between 5 and 18 mo and between 5 and 36 mo. No significant differences were found in the body weights between 18- and 36-mo-old rats.

                              
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  		Table 1.   Body weight and muscle cross-sectional area with age

Muscle mass and fiber number of vastus lateralis, soleus, and adductor longus muscles from 5-, 18-, and 36-mo-old animals were determined (Fig. 2). Both soleus and vastus lateralis muscles showed significant declines in muscle mass, with vastus lateralis exhibiting the greatest decrease. The vastus lateralis and soleus muscle mass significantly decreased in 36-mo-old rats compared with 5- and 18-mo-old rats (P < 0.05). Adductor longus muscles showed no decline in muscle mass with age.


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  		Fig. 2.   Muscle mass and fiber number with age for vastus lateralis (A), soleus (B), and adductor longus (C). Solid bars, muscle mass; open bars, fiber number determined at midbelly. Values are means ± SD. Numbers in parentheses represent number of animals. * Values are significantly different from 5 and 18 mo. ** Values are significantly different from 5 mo. Differences were considered significant at P < 0.05.

A significant decline in fiber number (fibers present in the midbelly of each muscle) was observed in vastus lateralis muscle from 5- to 36-mo-old (P = 0.015) and from 18- to 36-mo-old rats (P = 0.013). No significant changes in fiber number were found in soleus and adductor longus muscles at any age (Fig. 2).

CSA of 5- (n = 5), 18- (n = 5), and 36-mo-old (n = 5) vastus lateralis, soleus, and adductor longus muscles was measured at midbelly (Table 1). CSA of vastus lateralis muscle significantly increased from 5 to 18 mo and decreased at 36 mo compared with the muscles of the 5- and 18-mo-old animals. The soleus muscle displayed a significant decline in CSA at 36 mo compared with 5 mo. Unlike vastus lateralis and soleus, adductor longus muscle demonstrated a significant increase in CSA at 18 and 36 compared with 5 mo. An increase in the individual fiber CSA also was observed in 36-mo-old rat adductor longus muscle.

ETS-abnormal fibers. Tissue sections were stained for COX and SDH activity to define the ETS phenotype of individual fibers along the 1,000-µm length of muscle tissue. Fibers that stained negative for COX activity and hyperreactive for SDH activity (COX-/SDH++) were scored as ETS-abnormal fibers. The largest number of ETS-abnormal fibers was identified in vastus lateralis muscles (a total of 50) of 36-mo-old rats, whereas no COX-/SDH++ fibers were observed in the vastus lateralis of 5-mo-old rats within the 1,000 µm of tissue examined (Fig. 3). In contrast, a single ETS-abnormal fiber was identified in the vastus lateralis muscle of 18-mo-old rats per 1,000-µm. In the soleus muscle, a single COX-/SDH++ fiber per 1,000 µm was found in 36-mo-old rats, and no ETS-abnormal fibers were identified in 5- and 18-mo-old rats. COX-/SDH++ fibers were not identified in adductor longus muscle in any age group (Fig. 3).


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  		Fig. 3.   Number of electron transport system (ETS)-abnormal fibers displaying the COX-/SDH++ phenotype in the vastus lateralis, soleus, and adductor longus muscles. Values are number of abnormal fibers in 1,000 µm of muscle characterized at 5 mo (n = 3; gray bars), 18 mo (n = 3; open bars), and 36 mo old (n = 3; solid bars).

ETS abnormalities and intrafiber atrophy. Intrafiber atrophy is linked to ETS abnormalities in rat rectus femoris muscle and rhesus monkey vastus lateralis muscle. Because this atrophy can be quite severe, resulting in some fibers having a complete breakage, we measured the CSAs of 90 individual, randomly selected ETS-normal (control) and 55 individual ETS-abnormal fibers along a length of 1,000 µm. The ratio of minimum CSA, in the COX-/SDH++ region of the ETS-abnormal fibers, to the average of CSA in the normal region of the same fibers was determined (see MATERIALS AND METHODS). For ETS-normal fibers, the ratio of minimum CSA to the average CSA of the entire 1,000-µm length was calculated. Kernel density distribution of CSA ratio in ETS-abnormal fibers and ETS-normal fibers (Fig. 4) showed that none of the control fibers had a CSA ratio smaller than 0.7. One-half of the ETS-abnormal fibers, however, had a ratio below 0.7. Figure 5 is a computer reconstruction of CSAs along the length of two fibers containing COX-/SDH++ regions (Fig. 5, C and D) and one ETS-normal fiber (Fig. 5E). Figure 5, A and B, presents photomicrographs of cross sections (stained for COX and SDH activity, respectively) of the muscle fiber in Fig. 5C. The CSA in the normal region (normal for COX and SDH activity) of the ETS-abnormal fiber was not different from the CSA of the ETS-normal fibers. The CSA significantly decreased within the ETS-abnormal region, where it displayed both COX- and SDH++ phenotypes, and it eventually decreased to zero (Fig. 5C, tissue sections 3 and 4). Further along the fiber, where normal COX and SDH activities resumed, the CSA was similar to normal fibers.


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  		Fig. 4.   Histograms (bars) and Kernel density estimates (line) of ETS-normal (B) and ETS-abnormal (A) fiber cross-sectional area (CSA) ratio. CSA was measured for each ETS-abnormal and ETS-normal (control) fiber, and the ratio of minimum CSA in the ETS-abnormal region to the average of CSA in the ETS-normal region was calculated. The ratio of the minimum CSA to the average CSA in the normal fibers was also calculated.



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  		Fig. 5.   Representation of CSAs along the length of 2 fibers that contain COX-/SDH++ regions (C and D) and 1 ETS-normal fiber (E). A and B: photomicrographs of cross sections (stained for COX and SDH activity, respectively) of the muscle fiber in C. Individual fiber denoted by arrowheads in A and B displays COXnormal/SDHnormal phenotype in the first tissue sections analyzed. The fiber presents a COX-/SDH++ phenotype (tissue section 2); 170 µm from the initial sections, it breaks (tissue sections 3 and 4) and displays COX-/SDH++ phenotype in tissue section 5. Later (tissue section 6), the fiber returned to COXnormal/SDHnormal phenotype. This pattern is illustrated in the fiber reconstruction in C, where the solid bar represents the COX-/SDH++ region and the open bar the COXnormal/SDHnormal region.

The COX-/SDH++ phenotype extended through only a portion of the affected muscle fibers (i.e., a segmental distribution). The length of these ETS-abnormal regions varied from 110 to 680 µm, a range that is an underestimate of the maximum values because many of the ETS-abnormal regions extended outside of the 1,000-µm length of muscle examined. Fibers with longer ETS-abnormal regions were more likely to have smaller CSA ratios (more atrophic in COX-/SDH++ region). The Spearman correlation test showed a negative correlation (P < 0.001; r = 0.352) between ETS-abnormal region length and CSA ratio.

Fiber type. The proportions of type I and type II fibers in the three muscles were determined immunohistochemically by using an antibody against skeletal myosin (specific for type II fibers). The vastus lateralis muscle is predominantly composed of type II fibers. The average proportions of type I and type II fibers in the vastus lateralis muscle did not significantly (P = 0.126) change with age (Table 2). The soleus and adductor longus muscles were predominantly composed of type I fibers with a small percentage of type II fibers. The soleus muscle showed a significant increase in type I muscle fibers (P < 0.05) and a significant decrease in type II muscle fibers (P < 0.05) from 18- to 36-mo-old rats. The adductor longus muscle showed a significant decline in type II fibers with age, 5-36 mo (P = 0.027). Most of the ETS-abnormal fibers (94%) were type II.

                              
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  		Table 2.   Muscle fiber-type changes with age


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

The purpose of this study was to characterize and provide a comprehensive overview of the abundance of ETS-abnormal fibers displaying COX-/SDH++ phenotype in muscles exhibiting different degrees of sarcopenia. We hypothesized that muscles that undergo age-associated fiber loss would contain significantly higher levels of mitochondrial abnormalities compared with muscles that have limited or no sarcopenic changes.

Fiber loss with age is an important component of sarcopenia in rat vastus lateralis muscle. The results confirm age-associated fiber loss data from vastus lateralis muscle of Lobund-Wistar rats (3) as well as another quadriceps muscle, rectus femoris (63), in very old F344×BNF1 rats. In soleus muscle, although a trend for decreasing fiber number with age was present, we did not observe a significant decline in fiber number. The trend of soleus muscle toward fiber loss with age is evident from other rodent studies, with some investigators reporting a decline in fiber number with age (25, 28, 33), whereas other investigators did not (10, 18).

The decline in muscle mass can result from both individual fiber loss and fiber atrophy. Group fiber atrophy (clusters of small fibers) was observed in vastus lateralis muscles from 36-mo-old rats, whereas a general atrophy of individual fibers was observed in the soleus muscle (E. A. Bua, unpublished observations). This overall decrease in the CSA of individual fibers in soleus muscle in 36-mo-old rats may account for the declines in muscle mass and whole muscle CSA with age while fiber number is maintained. The CSA of individual fibers in adductor longus muscle from 36-mo-old rats was larger than that from the 5- and 18-mo-old rats (E. A. Bua, unpublished observations). A significant decrease in the percentage of type II fibers and a concomitant increase in percent type I fibers was observed in both the soleus and adductor longus muscles. This fiber type switching may be due to a transformation of fibers from type II to type I or to a selective loss of type II fibers. A shift from type II fibers to type I fibers has been described previously (27).

Our laboratory previously demonstrated an age-related increase in ETS-abnormal fibers in rhesus monkey (36, 40) and rat (3, 63) quadriceps muscle. Characterizing three ETS-abnormal phenotypes (COX-/SDH++; COX-/SDHnormal; COX-/SDHlow), Wanagat et al. (63) and Lopez et al. (40) estimated that ~15% of the fibers contain ETS-abnormal regions in old rats and 60% in old rhesus monkeys. In the present study, we analyzed the abundance of COX-/SDH++ fibers in vastus lateralis, soleus, and adductor longus muscles. Longitudinal analyses were used to characterize individual ETS fibers containing COX-/SDH++ regions, because the abnormalities are segmental in nature (40, 63). The number of ETS-abnormal fibers per cubic millimeter of tissue (volume density) showed a significant (P < 0.001) increase from 18 mo (0.01 ± 0.00) to 36 mo (0.55 ± 0.19) in the vastus lateralis muscle. The number of ETS-abnormal fibers/muscle was estimated by using the volume of the entire muscle (number of COX-/SDH++ regions/mm3 × muscle volume). The total volume of the muscle was determined by dividing muscle mass by 1.06 g/ml, the mammalian muscle tissue specific gravity (volume = muscle mass/gravity) (4). Using the volume of the entire muscle, we estimated that ~5.25% (361 ± 127) of the muscle fibers in the vastus lateralis and 1% (0.19 ± 0.03) in the soleus contain COX-/SDH++ regions in 36-mo-old rats. Most of the abnormal regions (63%) started and ended within 1,000 µm of length, and a few fibers (10%) exhibited more than one abnormal region within the 1,000-µm length analyzed, illustrating the segmental nature of these abnormalities.

The COX-/SDH++ phenotype in skeletal muscle is likely caused by mtDNA deletion mutations. ETS-abnormal segments of skeletal muscle fibers are associated with mtDNA deletion mutations (14, 30, 36, 47, 63). Histological analyses indicate that mtDNA deletions are distributed in a mosaic pattern and that mtDNA deletion mutations and ETS abnormalities are linked (36, 40, 47, 63). Through the use of in situ hybridization methods, mtDNA deletions were detected in ~90% of ETS-abnormal fibers in rhesus monkey vastus lateralis muscle (36). Using laser-capture microdissection and PCR analysis of ETS-abnormal fibers, Cao et al. (14) found that mtDNA deletions were present in all ETS-abnormal fibers displaying COX-/SDH++ phenotype (29 ETS-abnormal fibers examined) in hybrid rat skeletal muscle. These findings suggest the following mechanism for the role of mitochondrial abnormalities in muscle fiber loss with age. MtDNA deletion mutations are produced during normal aging and clonally accumulate within a small region of a muscle fiber. This accumulation results in the loss of COX activity (COX-) and the concomitant increase in the number of mitochondria, producing the SDH++ (ragged red) phenotype. The accumulation of abnormal mitochondria expanding along the length of the fiber producing an energy deficiency, impaired cellular activity, and compromised ability to adapt to various physiological stresses will give rise to intrafiber atrophy, fiber breakage, and inevitably fiber loss. Our estimation of ~5.25% of the fibers containing ETS-abnormal regions in vastus lateralis and 1% in the soleus muscle of 36-mo-old rats demonstrates the steady-state level of these abnormalities at this age. These are likely considerable underestimates of the total number of abnormalities that have occurred in a given muscle because ETS abnormalities that caused fiber loss previously would no be longer present and thus would not be included in the count.

The mechanism(s) responsible for the differences in the abundance of ETS-abnormal fibers displaying COX-/SDH++ phenotype in the three muscles analyzed is unknown. Differences in fiber-type proportions and in the morphological, structural, and physiological properties may play a role. Because type I fibers have more mitochondria than type IIb fibers (48), fewer mitochondria containing the deleted genomes in a type IIb fiber are needed to overcome the wild-type genome. Furthermore, the onset of the ETS abnormalities could be evident earlier in type IIb fibers than in type I fibers. In vastus lateralis muscle, composed predominantly of type II (IIa and IIb) fibers, COX-/SDH++ fibers were first detected at 18 mo of age, whereas, in soleus muscle, composed predominantly of type I fibers, COX-/SDH++ fibers were first detected at 36 mo of age.

In summary, ragged red fibers were associated with the muscle mass loss and fiber number decline. Vastus lateralis, which exhibited the greatest muscle mass loss with age, also exhibited the largest loss of fibers, the greatest number of ragged red fibers, and associated atrophy. In contrast, the adductor longus muscle, which exhibited no muscle mass loss and little change in fiber number with age, did not have detectable levels of ETS abnormalities. Soleus muscle, which exhibited intermediate levels of sarcopenia and fiber number decline, showed intermediate levels of ETS abnormalities. The present study suggests that different muscles accumulate different levels of ETS abnormalities during normal aging and supports the hypothesis that ETS abnormalities contribute to senescent muscle atrophy.


    ACKNOWLEDGEMENTS

This work was supported by National Institute on Aging Grants RO1 AG-11604, RO1 AG-17543, and PO1 AG-11915.


    FOOTNOTES

Address for reprint requests and other correspondence: J. M. Aiken, Dept. of Animal Health and Biomedical Sciences, Univ. of Wisconsin, 1656 Linden Drive, Madison, WI 53706 (E-mail: jma{at}ahabs.wisc.edu).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

First published February 22, 2002;10.1152/japplphysiol.01102.2001

Received 2 November 2001; accepted in final form 18 February 2002.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

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