Targeting deregulated AMPK/mTORC1 pathways improves muscle function in myotonic dystrophy type I
Marielle Brockhoff, Nathalie Rion, Kathrin Chojnowska, Tatiana Wiktorowicz, Christopher Eickhorst, Beat Erne, Stephan Frank, Corrado Angelini, Denis Furling, Markus A. Rüegg, Michael Sinnreich, Perrine Castets
Marielle Brockhoff, Nathalie Rion, Kathrin Chojnowska, Tatiana Wiktorowicz, Christopher Eickhorst, Beat Erne, Stephan Frank, Corrado Angelini, Denis Furling, Markus A. Rüegg, Michael Sinnreich, Perrine Castets
View: Text | PDF
Research Article Muscle biology

Targeting deregulated AMPK/mTORC1 pathways improves muscle function in myotonic dystrophy type I

Abstract

Myotonic dystrophy type I (DM1) is a disabling multisystemic disease that predominantly affects skeletal muscle. It is caused by expanded CTG repeats in the 3′-UTR of the dystrophia myotonica protein kinase (DMPK) gene. RNA hairpins formed by elongated DMPK transcripts sequester RNA-binding proteins, leading to mis-splicing of numerous pre-mRNAs. Here, we have investigated whether DM1-associated muscle pathology is related to deregulation of central metabolic pathways, which may identify potential therapeutic targets for the disease. In a well-characterized mouse model for DM1 (HSALR mice), activation of AMPK signaling in muscle was impaired under starved conditions, while mTORC1 signaling remained active. In parallel, autophagic flux was perturbed in HSALR muscle and in cultured human DM1 myotubes. Pharmacological approaches targeting AMPK/mTORC1 signaling greatly ameliorated muscle function in HSALR mice. AICAR, an AMPK activator, led to a strong reduction of myotonia, which was accompanied by partial correction of misregulated alternative splicing. Rapamycin, an mTORC1 inhibitor, improved muscle relaxation and increased muscle force in HSALR mice without affecting splicing. These findings highlight the involvement of AMPK/mTORC1 deregulation in DM1 muscle pathophysiology and may open potential avenues for the treatment of this disease.

Authors

Marielle Brockhoff, Nathalie Rion, Kathrin Chojnowska, Tatiana Wiktorowicz, Christopher Eickhorst, Beat Erne, Stephan Frank, Corrado Angelini, Denis Furling, Markus A. Rüegg, Michael Sinnreich, Perrine Castets

×

Figure 6

AICAR markedly decreases myotonia in HSALR mice and reduces mis-splicing in mutant muscle.

Options: View larger image (or click on image) Download as PowerPoint
AICAR markedly decreases myotonia in HSALR mice and reduces mis-splicing...
(A) In vitro tetanic stimulation of EDL muscle reveals strongly increased relaxation time in HSALR muscle. (B) Metformin (MetF) treatment does not reduce muscle late relaxation time in 4-month-old (Ctrl, n = 5; HSALR, n = 6 Veh and 8 MetF) and 12-month-old (Ctrl, n = 3; HSALR, n = 7 Veh and 8 MetF) HSALR mice, as compared with vehicle-treated mutant mice. (C) Inclusion of exon 7a of the Clcn1 gene is not changed in muscle from metformin-treated (MetF) HSALR mice, compared with vehicle-treated mice (n = 3). (D) Immunoblots for phospho- and total S6 protein reveal efficient inhibition of indirect AMPK target in muscle from control (Ctrl) and mutant mice treated with AICAR. Samples were run on the same gel but were noncontiguous. (E) AICAR treatment normalizes the time to relax of HSALR muscle upon tetanic stimulation, compared with muscle from vehicle-treated (Veh) mutant mice. (F) Late relaxation time is significantly reduced in EDL muscle from 2-month-old (n = 3 Ctrl and 4 HSALR), 8-month-old (Ctrl, n = 3; HSALR, n = 6 Veh and 7 AICAR), and 12-month-old (n = 4 Veh and 5 AICAR) HSALR mice that were treated with AICAR, as compared with age-matched vehicle-treated (Veh) mutant mice. (G–K) End-point PCR (G) and quantitative PCR (H and I) reveal strong reduction in exon 7a inclusion of the Clcn1 gene in muscle from HSALR mice treated with AICAR, compared with vehicle-treated (Veh) mutant mice (Ctrl, n = 3; HSALR, n = 5 Veh and 4 AICAR [G], n = 5 [I]). Protein levels of CLC-1 are also increased in mutant muscle from AICAR-treated mice (J and K, n = 3 Ctrl and 4 HSALR). (L) Quantitative PCR shows similar transcript levels of Rbm3 in muscle from AICAR-treated and untreated mice (n = 3 Ctrl and 4 HSALR). Data represent mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, 2-way ANOVA with Tukey’s multiple comparisons test correction (except 12M AICAR, unpaired 2-tailed Student’s t test).