Integrated expression analysis of muscle hypertrophy identifies Asb2 as a negative regulator of muscle mass
Jonathan R. Davey, Kevin I. Watt, Benjamin L. Parker, Rima Chaudhuri, James G. Ryall, Louise Cunningham, Hongwei Qian, Vittorio Sartorelli, Marco Sandri, Jeffrey Chamberlain, David E. James, Paul Gregorevic
Jonathan R. Davey, Kevin I. Watt, Benjamin L. Parker, Rima Chaudhuri, James G. Ryall, Louise Cunningham, Hongwei Qian, Vittorio Sartorelli, Marco Sandri, Jeffrey Chamberlain, David E. James, Paul Gregorevic
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Research Article Aging Muscle biology

Integrated expression analysis of muscle hypertrophy identifies Asb2 as a negative regulator of muscle mass

Abstract

The transforming growth factor-β (TGF-β) signaling network is a critical regulator of skeletal muscle mass and function and, thus, is an attractive therapeutic target for combating muscle disease, but the underlying mechanisms of action remain undetermined. We report that follistatin-based interventions (which modulate TGF-β network activity) can promote muscle hypertrophy that ameliorates aging-associated muscle wasting. However, the muscles of old sarcopenic mice demonstrate reduced response to follistatin compared with healthy young-adult musculature. Quantitative proteomic and transcriptomic analyses of young-adult muscles identified a transcription/translation signature elicited by follistatin exposure, which included repression of ankyrin repeat and SOCS box protein 2 (Asb2). Increasing expression of ASB2 reduced muscle mass, thereby demonstrating that Asb2 is a TGF-β network–responsive negative regulator of muscle mass. In contrast to young-adult muscles, sarcopenic muscles do not exhibit reduced ASB2 abundance with follistatin exposure. Moreover, preventing repression of ASB2 in young-adult muscles diminished follistatin-induced muscle hypertrophy. These findings provide insight into the program of transcription and translation events governing follistatin-mediated adaptation of skeletal muscle attributes and identify Asb2 as a regulator of muscle mass implicated in the potential mechanistic dysfunction between follistatin-mediated muscle growth in young and old muscles.

Authors

Jonathan R. Davey, Kevin I. Watt, Benjamin L. Parker, Rima Chaudhuri, James G. Ryall, Louise Cunningham, Hongwei Qian, Vittorio Sartorelli, Marco Sandri, Jeffrey Chamberlain, David E. James, Paul Gregorevic

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Figure 1

Follistatin gene delivery promotes muscle hypertrophy, which is diminished in old mice.

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Follistatin gene delivery promotes muscle hypertrophy, which is diminish...
C57Bl/6 mice of indicated age were injected with rAAV:MCS in the left TA and rAAV:FST in the right TA. (A) The mass of TA muscles from rAAV:FST-injected mice were compared with the contralateral rAAV:MCS control (ratio-paired t test, P < 0.05, n = 10, ± SEM). The change in muscle mass between control and follistatin treatment is presented as a percentage of maximal response in 6-month-old mice (unpaired t test, P < 0.05, n = 10, ± SEM) (B) The muscle weights and response to follistatin treatment as presented in A for 7- and 32-month-old mice (ratio-paired t test; P < 0.05; 7 month, n = 5; 32 month, n = 4; ± SEM). Maximal response is defined by the follistatin response in 7-month-old mice (unpaired t test; P < 0.05; 7 month, n = 5; 32 month, n = 4; ± SEM). (C) The diameter of TA muscle fibers from mice reported in B (Holm-Sidak multiple t test; P < 0.05; 7 month, n = 5; 32 month, n = 4; ± SEM). (D) Immunoblot analysis of mice from A for detection of follistatin expression and SMAD signaling. Quantification of immunoblot analysis from D for (E) follistatin expression (ratio-paired t test, P < 0.05, n = 6, ± SEM). (F) Ratio of phosphorylated to total SMAD3 (ratio-paired t test, P < 0.05, n = 6, ± SEM), and (G) ratio of phosphorylated to total SMAD1/5 (ratio-paired t test, P < 0.05, n = 6, ± SEM). (H) Time course analysis of follistatin expression in TA muscles injected with rAAV:indFST. DOX was administered in food ad libitum for the indicated number of days. n = 2. (I) The mass of TA muscles from rAAV:indFST-injected mice were compared with the contralateral rAAV:MCS control (ratio-paired t test; P < 0.05; no DOX, n = 9; 2 days DOX, n = 7; 28 days DOX, n = 12; ± SEM). Recombinant adeno-associated virus, rAAV; control construct, MCS; follistatin, FST; tibialis anterior muscle, TA; doxycycline, DOX; tetracycline responsive follistatin, indFST.