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Aging affects the transcriptional regulation of human skeletal muscle disuse atrophy.

Suetta C, Frandsen U, Jensen L, Jensen MM, Jespersen JG, Hvid LG, Bayer M, Petersson SJ, Schrøder HD, Andersen JL, Heinemeier KM, Aagaard P, Schjerling P, Kjaer M - PLoS ONE (2012)

Bottom Line: The results reveal that irrespectively of age, mRNA expression levels of MuRF-1 and Atrogin-1 increased in the very initial phase (2-4 days) of human disuse-muscle atrophy along with a marked reduction in PGC-1α and PGC-1β (1-4 days) and a ~10% decrease in myofiber size (4 days).Further, an age-specific down-regulation of MuRF-1 and Atrogin-1 expression levels was observed following 2 weeks of immobilization, along with a slowing atrophy response in aged skeletal muscle.Collectively, these findings indicate that the time-course and regulation of human skeletal muscle atrophy is age dependent, leading to an attenuated loss in aging skeletal muscle when exposed to longer periods of immobility-induced disuse.

View Article: PubMed Central - PubMed

Affiliation: Institute of Sports Medicine and Center for Healthy Aging, University of Copenhagen, Bispebjerg Hospital, Copenhagen, Denmark. csuetta@gmail.com

ABSTRACT
Important insights concerning the molecular basis of skeletal muscle disuse-atrophy and aging related muscle loss have been obtained in cell culture and animal models, but these regulatory signaling pathways have not previously been studied in aging human muscle. In the present study, muscle atrophy was induced by immobilization in healthy old and young individuals to study the time-course and transcriptional factors underlying human skeletal muscle atrophy. The results reveal that irrespectively of age, mRNA expression levels of MuRF-1 and Atrogin-1 increased in the very initial phase (2-4 days) of human disuse-muscle atrophy along with a marked reduction in PGC-1α and PGC-1β (1-4 days) and a ~10% decrease in myofiber size (4 days). Further, an age-specific decrease in Akt and S6 phosphorylation was observed in young muscle within the first days (1-4 days) of immobilization. In contrast, Akt phosphorylation was unchanged in old muscle after 2 days and increased after 4 days of immobilization. Further, an age-specific down-regulation of MuRF-1 and Atrogin-1 expression levels was observed following 2 weeks of immobilization, along with a slowing atrophy response in aged skeletal muscle. Neither the immediate loss of muscle mass, nor the subsequent age-differentiated signaling responses could be explained by changes in inflammatory mediators, apoptosis markers or autophagy indicators. Collectively, these findings indicate that the time-course and regulation of human skeletal muscle atrophy is age dependent, leading to an attenuated loss in aging skeletal muscle when exposed to longer periods of immobility-induced disuse.

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Immobility induced skeletal muscle atrophy results in an age-specific decrease in Akt and ribosomal protein S6 phosphorylation.A. Western blotting of whole muscle protein homogenates of phosphorylated Akt and total Akt. B. Immobility decreased levels of phosphorylated Akt/total Akt ratio (p-Akt/Akt) at the early (2–4 days) phase of immobility in young but not aged skeletal muscle. * Time effect, p<0.05, compared to pre. # Age effect, p<0.001 young compared to old within time point. Due to lack of muscle tissue n = 6 (3 young and 3 old) in these analyses. C. Western blotting of whole muscle protein homogenates of total and phosphorylated S6 ribosomal protein. D. The percentage of the total number of subjects at each time point where p-S6 could be detected. Chi-square: Young p<0.001, Old p = 0.44. In a high number of especially young subjects phosphorylated S6 ribosomal protein (but not total S6 ribosomal protein) became non detectable after immobilization which made an exact quantification impossible.
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pone-0051238-g004: Immobility induced skeletal muscle atrophy results in an age-specific decrease in Akt and ribosomal protein S6 phosphorylation.A. Western blotting of whole muscle protein homogenates of phosphorylated Akt and total Akt. B. Immobility decreased levels of phosphorylated Akt/total Akt ratio (p-Akt/Akt) at the early (2–4 days) phase of immobility in young but not aged skeletal muscle. * Time effect, p<0.05, compared to pre. # Age effect, p<0.001 young compared to old within time point. Due to lack of muscle tissue n = 6 (3 young and 3 old) in these analyses. C. Western blotting of whole muscle protein homogenates of total and phosphorylated S6 ribosomal protein. D. The percentage of the total number of subjects at each time point where p-S6 could be detected. Chi-square: Young p<0.001, Old p = 0.44. In a high number of especially young subjects phosphorylated S6 ribosomal protein (but not total S6 ribosomal protein) became non detectable after immobilization which made an exact quantification impossible.

Mentions: A part from total and phosphorylated S6 ribosomal protein, all mRNA and Western blot data were log-transformed prior to statistical analyses and are presented as geometric means ± back-transformed SEM. To test for changes over time (mRNA, TUNEL, Immunohistochemistry and Western blot analyses) one-way Bonferroni corrected repeated-measures ANOVA was performed separately for young and old individuals, respectively, as well as for young and old combined (SPSS). Pair wise multitude comparison procedures were evaluated using Student-Newman-Keuls Method post-hoc testing. Independent-samples t-testing were used to test for differences between groups' with a subsequent Bonferroni correction. As phosphorylated S6 ribosomal protein (but not total S6 ribosomal protein) became non-detectable after immobilization in a high number of especially young subjects, quantification of phosphorylated S6 ribosomal protein/total S6 ribosomal protein was not possible and we therefore decided to perform a Chi-square test (young p<0.001, old p = 0.44). The percentage of the total number of subjects where p-S6 could be detected, at each time-point, are visualized in figure 4D. Non-parametric statistics were used to analyze changes in muscle fiber CSA, since not all of these data were normally distributed. To evaluate the effect of intervention over time a repeated-measures Friedman test was used with post-hoc Wilcoxon testing. Between-group differences were analyzed with Kruskall-Wallis tests and subsequent Mann-Whitney U testing. Data are presented as mean values ± SEM. A p-value of less than 0.05 was considered statistically significant.


Aging affects the transcriptional regulation of human skeletal muscle disuse atrophy.

Suetta C, Frandsen U, Jensen L, Jensen MM, Jespersen JG, Hvid LG, Bayer M, Petersson SJ, Schrøder HD, Andersen JL, Heinemeier KM, Aagaard P, Schjerling P, Kjaer M - PLoS ONE (2012)

Immobility induced skeletal muscle atrophy results in an age-specific decrease in Akt and ribosomal protein S6 phosphorylation.A. Western blotting of whole muscle protein homogenates of phosphorylated Akt and total Akt. B. Immobility decreased levels of phosphorylated Akt/total Akt ratio (p-Akt/Akt) at the early (2–4 days) phase of immobility in young but not aged skeletal muscle. * Time effect, p<0.05, compared to pre. # Age effect, p<0.001 young compared to old within time point. Due to lack of muscle tissue n = 6 (3 young and 3 old) in these analyses. C. Western blotting of whole muscle protein homogenates of total and phosphorylated S6 ribosomal protein. D. The percentage of the total number of subjects at each time point where p-S6 could be detected. Chi-square: Young p<0.001, Old p = 0.44. In a high number of especially young subjects phosphorylated S6 ribosomal protein (but not total S6 ribosomal protein) became non detectable after immobilization which made an exact quantification impossible.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3526599&req=5

pone-0051238-g004: Immobility induced skeletal muscle atrophy results in an age-specific decrease in Akt and ribosomal protein S6 phosphorylation.A. Western blotting of whole muscle protein homogenates of phosphorylated Akt and total Akt. B. Immobility decreased levels of phosphorylated Akt/total Akt ratio (p-Akt/Akt) at the early (2–4 days) phase of immobility in young but not aged skeletal muscle. * Time effect, p<0.05, compared to pre. # Age effect, p<0.001 young compared to old within time point. Due to lack of muscle tissue n = 6 (3 young and 3 old) in these analyses. C. Western blotting of whole muscle protein homogenates of total and phosphorylated S6 ribosomal protein. D. The percentage of the total number of subjects at each time point where p-S6 could be detected. Chi-square: Young p<0.001, Old p = 0.44. In a high number of especially young subjects phosphorylated S6 ribosomal protein (but not total S6 ribosomal protein) became non detectable after immobilization which made an exact quantification impossible.
Mentions: A part from total and phosphorylated S6 ribosomal protein, all mRNA and Western blot data were log-transformed prior to statistical analyses and are presented as geometric means ± back-transformed SEM. To test for changes over time (mRNA, TUNEL, Immunohistochemistry and Western blot analyses) one-way Bonferroni corrected repeated-measures ANOVA was performed separately for young and old individuals, respectively, as well as for young and old combined (SPSS). Pair wise multitude comparison procedures were evaluated using Student-Newman-Keuls Method post-hoc testing. Independent-samples t-testing were used to test for differences between groups' with a subsequent Bonferroni correction. As phosphorylated S6 ribosomal protein (but not total S6 ribosomal protein) became non-detectable after immobilization in a high number of especially young subjects, quantification of phosphorylated S6 ribosomal protein/total S6 ribosomal protein was not possible and we therefore decided to perform a Chi-square test (young p<0.001, old p = 0.44). The percentage of the total number of subjects where p-S6 could be detected, at each time-point, are visualized in figure 4D. Non-parametric statistics were used to analyze changes in muscle fiber CSA, since not all of these data were normally distributed. To evaluate the effect of intervention over time a repeated-measures Friedman test was used with post-hoc Wilcoxon testing. Between-group differences were analyzed with Kruskall-Wallis tests and subsequent Mann-Whitney U testing. Data are presented as mean values ± SEM. A p-value of less than 0.05 was considered statistically significant.

Bottom Line: The results reveal that irrespectively of age, mRNA expression levels of MuRF-1 and Atrogin-1 increased in the very initial phase (2-4 days) of human disuse-muscle atrophy along with a marked reduction in PGC-1α and PGC-1β (1-4 days) and a ~10% decrease in myofiber size (4 days).Further, an age-specific down-regulation of MuRF-1 and Atrogin-1 expression levels was observed following 2 weeks of immobilization, along with a slowing atrophy response in aged skeletal muscle.Collectively, these findings indicate that the time-course and regulation of human skeletal muscle atrophy is age dependent, leading to an attenuated loss in aging skeletal muscle when exposed to longer periods of immobility-induced disuse.

View Article: PubMed Central - PubMed

Affiliation: Institute of Sports Medicine and Center for Healthy Aging, University of Copenhagen, Bispebjerg Hospital, Copenhagen, Denmark. csuetta@gmail.com

ABSTRACT
Important insights concerning the molecular basis of skeletal muscle disuse-atrophy and aging related muscle loss have been obtained in cell culture and animal models, but these regulatory signaling pathways have not previously been studied in aging human muscle. In the present study, muscle atrophy was induced by immobilization in healthy old and young individuals to study the time-course and transcriptional factors underlying human skeletal muscle atrophy. The results reveal that irrespectively of age, mRNA expression levels of MuRF-1 and Atrogin-1 increased in the very initial phase (2-4 days) of human disuse-muscle atrophy along with a marked reduction in PGC-1α and PGC-1β (1-4 days) and a ~10% decrease in myofiber size (4 days). Further, an age-specific decrease in Akt and S6 phosphorylation was observed in young muscle within the first days (1-4 days) of immobilization. In contrast, Akt phosphorylation was unchanged in old muscle after 2 days and increased after 4 days of immobilization. Further, an age-specific down-regulation of MuRF-1 and Atrogin-1 expression levels was observed following 2 weeks of immobilization, along with a slowing atrophy response in aged skeletal muscle. Neither the immediate loss of muscle mass, nor the subsequent age-differentiated signaling responses could be explained by changes in inflammatory mediators, apoptosis markers or autophagy indicators. Collectively, these findings indicate that the time-course and regulation of human skeletal muscle atrophy is age dependent, leading to an attenuated loss in aging skeletal muscle when exposed to longer periods of immobility-induced disuse.

Show MeSH
Related in: MedlinePlus