A-41 Free Communication/Poster - Skeletal Muscle: Aging and Sex Differences: JUNE 1, 2011 7:30 AM - 12:30 PM: ROOM: Hall B
Reduction of muscle quality (force production/unit muscle tissue) is frequently reported in aging. Several mechanisms have been put forth to explain this phenomenon, including: impaired neuromuscular activation, disruption of excitation-contraction (E-C) coupling and contractile protein modification. Another potential mechanism, which has received little attention, is age-related alteration of the cytoskeleton, which could affect transmission of contractile force. Data from transgenic animals has shown that reduced expression of the intermediate filament protein desmin is associated with a loss of muscle quality.
PURPOSE: The purpose of this study was to determine if desmin expression was reduced in aging rat muscles.
METHODS: We determined contractile force and muscle mass of the entire plantarflexor muscle group of aging (24 months) and adult (6-8 months) F344/BN rats (n = 6/group). Using semi-quantitative immunoblotting, we determined the expression of desmin and synemin (another intermediate filament protein) in each of the 4 plantarflexor muscles.
RESULTS: Contractile force was reduced in aging vs. adult muscle groups (17.2 ± 1.3 vs. 21.7 ± 1.0 N; P = 0.020), despite modest changes in overall muscle mass. Thus, there was a significant age-related decline in muscle quality (6.72 ± 0.51 vs. 8.49 ± 0.61 N/g wet weight; P = 0.050). There was an overall effect for age to increase desmin expression (P= 0.003), and univariate comparisons revealed significant changes in the medial (7.5 +/- 1.4 vs. 16.4 +/- 4.2 AU) and lateral (11.8 +/- 2.4 vs. 25.1 +/- 4.4 AU) gastrocnemius muscles (P = 0.048 and 0.018, respectively)
CONCLUSIONS: Because desmin was increased with increasing age, loss of desmin cannot account for age-related loss of muscle quality in these rats. The lack of age-related changes observed in synemin suggests that this change in desmin was not related to a general increase in intermediate filament proteins. We have previously observed disruption of sarcoplasmic reticulum function with aging in the two muscles (gastrocnemii) where increases in desmin were significant. It has been suggested that desmin is involved in optimal E-C coupling. Thus, it is possible that the increase in desmin represents an unsuccessful attempt to compensate for impaired excitation-contraction coupling with aging.