ABSTRACT
Mitochondrial fission and fusion are essential processes in the maintenance of the skeletal muscle function. The contribution of these processes to muscle development has not been properly investigated in vivo because of the early lethality of the models generated so far. To define the role of mitochondrial fission in muscle development and repair, we have generated a transgenic mouse line that overexpresses the fission-inducing protein Drp1 specifically in skeletal muscle. These mice displayed a drastic impairment in postnatal muscle growth, with reorganisation of the mitochondrial network and reduction of mtDNA quantity, without the deficiency of mitochondrial bioenergetics. Importantly we found that Drp1 overexpression activates the stress-induced PKR/eIF2α/Fgf21 pathway thus leading to an attenuated protein synthesis and downregulation of the growth hormone pathway. These results reveal for the first time how mitochondrial network dynamics influence muscle growth and shed light on aspects of muscle physiology relevant in human muscle pathologies.
Subject(s)
Dynamins/metabolism , Muscle, Skeletal/metabolism , Animals , Blotting, Western , DNA, Mitochondrial/metabolism , Dynamins/genetics , Immunoprecipitation , Membrane Potential, Mitochondrial/genetics , Membrane Potential, Mitochondrial/physiology , Mice , Mice, Transgenic , Oxygen Consumption/physiologyABSTRACT
Improving stem cell therapy is a major goal for the treatment of muscle diseases, where physiological muscle regeneration is progressively exhausted. Vessel-associated stem cells, such as mesoangioblasts (MABs), appear to be the most promising cell type for the cell therapy for muscular dystrophies and have been shown to significantly contribute to restoration of muscle structure and function in different muscular dystrophy models. Here, we report that melanoma antigen-encoding gene (MAGE) protein necdin enhances muscle differentiation and regeneration by MABs. When necdin is constitutively overexpressed, it accelerates their differentiation and fusion in vitro and it increases their efficacy in reconstituting regenerating myofibres in the α-sarcoglycan dystrophic mouse. Moreover, necdin enhances survival when MABs are exposed to cytotoxic stimuli that mimic the inflammatory dystrophic environment. Taken together, these data demonstrate that overexpression of necdin may be a crucial tool to boost therapeutic applications of MABs in dystrophic muscle.
Subject(s)
Cell Survival/physiology , Muscular Dystrophy, Animal/metabolism , Nerve Tissue Proteins/metabolism , Nuclear Proteins/metabolism , Stem Cells/cytology , Stem Cells/metabolism , Animals , Apoptosis/genetics , Apoptosis/physiology , Cell Differentiation , Cell Survival/genetics , Cells, Cultured , Chromatin Immunoprecipitation , Flow Cytometry , Fluorescent Antibody Technique , Immunoblotting , Mice , Mice, Knockout , Muscular Dystrophy, Animal/genetics , Nerve Tissue Proteins/genetics , Nuclear Proteins/genetics , Reverse Transcriptase Polymerase Chain Reaction , Sarcoglycans/genetics , Sarcoglycans/metabolismABSTRACT
Dysferlin deficiency leads to a peculiar form of muscular dystrophy due to a defect in sarcolemma repair and currently lacks a therapy. We developed a cell therapy protocol with wild-type adult murine mesoangioblasts. These cells differentiate with high efficiency into skeletal muscle in vitro but differ from satellite cells because they do not express Pax7. After intramuscular or intra-arterial administration to SCID/BlAJ mice, a novel model of dysferlinopathy, wild-type mesoangioblasts efficiently colonized dystrophic muscles and partially restored dysferlin expression. Nevertheless, functional assays performed on isolated single fibers from transplanted muscles showed a normal repairing ability of the membrane after laser-induced lesions; this result, which reflects gene correction of an enzymatic rather than a structural deficit, suggests that this myopathy may be easier to treat with cell or gene therapy than other forms of muscular dystrophies.
