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 5

Autophagy perturbation contributes to muscle alterations in DM1.

Options: View larger image (or click on image) Download as PowerPoint
Autophagy perturbation contributes to muscle alterations in DM1. (A) Pro...
(A) Protein lysates from muscle biopsies of control individuals (C1–5) and DM1 patients (P1–3) were analyzed for phospho- (P) and total proteins of the AMPK and PKB/Akt–mTORC1 pathways. (B) MyoD-transduced fibroblasts from controls (Ctrl) and DM1 patients were differentiated to myotubes and subjected to growth medium (GM) or deprived conditions (PBS) for 3 hours. Immunoblots for phospho- (P) and total proteins reveal increased phospho-S6 levels upon deprivation in the 3 cell lines of DM1 patients (DM-L1–3), compared with controls. Samples were run on the same gel but were noncontiguous. Quantification is given for deprived conditions; values are mean ± SEM of technical replicates. (C) Immunoblots for LC3 marker show defective accumulation of LC3II in DM1 myotubes upon energy and amino acid deprivation (PBS) as well as with deprived conditions and chloroquine treatment (Chloro), compared with control cells (Ctrl). Quantification of LC3II/LC3I ratio is shown for 2 DM1 cell lines (DM-L1/2) in enriched (GM) and deprived conditions; values are mean ± SEM of technical replicates. (D) H&E stain reveals the presence of vacuolated fibers (arrows) in muscle biopsy from 1 DM1 patient, together with lysosomal accumulation (arrowheads) observed by immunostaining in some affected muscle fibers (red, bottom panel). Scale bars: 50 μm. (E) Vacuoles (arrows) are observed in muscle from aging HSALR mice; the periphery of the vacuoles is strongly reactive with anti-LAMP1 antibodies (red, bottom panel), indicating accumulation of lysosomal structures in these regions. High density of lysosomes is also observed in nonvacuolated muscle fibers from 12-month-old (12M) mutant mice (arrowheads), compared with muscle from age-matched control mice (Ctrl). Scale bars: 50 μm.