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Skelet Muscle. 2017 Dec 14;7(1):27. doi: 10.1186/s13395-017-0146-6.

Impaired regeneration in calpain-3 null muscle is associated with perturbations in mTORC1 signaling and defective mitochondrial biogenesis.

Author information

1
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, USA.
2
Current Address: King Chulalongkorn Memorial Hospital and Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
3
Department of Pediatrics and Neurology, Nationwide Children's Hospital and The Ohio State University, Columbus, USA.
4
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, USA. zarife.sahenk@nationwidechildrens.org.
5
Department of Pediatrics and Neurology, Nationwide Children's Hospital and The Ohio State University, Columbus, USA. zarife.sahenk@nationwidechildrens.org.
6
Department of Pathology and Laboratory Medicine, Nationwide Children's Hospital, Columbus, OH, USA. zarife.sahenk@nationwidechildrens.org.
7
Neuromuscular Pathology, Nationwide Children's Hospital, 700 Children's Drive Rm WA 3024, Columbus, USA. zarife.sahenk@nationwidechildrens.org.

Abstract

BACKGROUND:

Previous studies in patients with limb-girdle muscular dystrophy type 2A (LGMD2A) have suggested that calpain-3 (CAPN3) mutations result in aberrant regeneration in muscle.

METHODS:

To gain insight into pathogenesis of aberrant muscle regeneration in LGMD2A, we used a paradigm of cardiotoxin (CTX)-induced cycles of muscle necrosis and regeneration in the CAPN3-KO mice to simulate the early features of the dystrophic process in LGMD2A. The temporal evolution of the regeneration process was followed by assessing the oxidative state, size, and the number of metabolic fiber types at 4 and 12 weeks after last CTX injection. Muscles isolated at these time points were further investigated for the key regulators of the pathways involved in various cellular processes such as protein synthesis, cellular energy status, metabolism, and cell stress to include Akt/mTORC1 signaling, mitochondrial biogenesis, and AMPK signaling. TGF-β and microRNA (miR-1, miR-206, miR-133a) regulation were also assessed. Additional studies included in vitro assays for quantifying fusion index of myoblasts from CAPN3-KO mice and development of an in vivo gene therapy paradigm for restoration of impaired regeneration using the adeno-associated virus vector carrying CAPN3 gene in the muscle.

RESULTS:

At 4 and 12 weeks after last CTX injection, we found impaired regeneration in CAPN3-KO muscle characterized by excessive numbers of small lobulated fibers belonging to oxidative metabolic type (slow twitch) and increased connective tissue. TGF-β transcription levels in the regenerating CAPN3-KO muscles were significantly increased along with microRNA dysregulation compared to wild type (WT), and the attenuated radial growth of muscle fibers was accompanied by perturbed Akt/mTORC1 signaling, uncoupled from protein synthesis, through activation of AMPK pathway, thought to be triggered by energy shortage in the CAPN3-KO muscle. This was associated with failure to increase mitochondria content, PGC-1α, and ATP5D transcripts in the regenerating CAPN3-KO muscles compared to WT. In vitro studies showed defective myotube fusion in CAPN3-KO myoblast cultures. Replacement of CAPN3 by gene therapy in vivo increased the fiber size and decreased the number of small oxidative fibers.

CONCLUSION:

Our findings provide insights into understanding of the impaired radial growth phase of regeneration in calpainopathy.

KEYWORDS:

Impaired radial growth; LGMD2A; Mitochondrial biogenesis; Skeletal muscle regeneration; mTORC1

PMID:
29241457
PMCID:
PMC5731057
DOI:
10.1186/s13395-017-0146-6
[Indexed for MEDLINE]
Free PMC Article

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