Abstract
Dynamin-2 is a ubiquitously expressed GTP-ase that mediates membrane remodeling. Recent findings indicate that dynamin-2 also regulates actin dynamics. Mutations in dynamin-2 cause dominant centronuclear myopathy (CNM), a congenital myopathy characterized by progressive weakness and atrophy of skeletal muscles. However, the muscle-specific roles of dynamin-2 affected by these mutations remain elusive. Here we show that, in muscle cells, the GTP-ase activity of dynamin-2 is involved in de novo actin polymerization as well as in actin-mediated trafficking of the glucose transporter GLUT4. Expression of dynamin-2 constructs carrying CNM-linked mutations disrupted the formation of new actin filaments as well as the stimulus-induced translocation of GLUT4 to the plasma membrane. Similarly, mature muscle fibers isolated from heterozygous knock-in mice that harbor the dynamin-2 mutation p.R465W, an animal model of CNM, exhibited altered actin organization, reduced actin polymerization and impaired insulin-induced translocation of GLUT4 to the sarcolemma. Moreover, GLUT4 displayed aberrant perinuclear accumulation in biopsies from CNM patients carrying dynamin-2 mutations, further suggesting trafficking defects. These results suggest that dynamin-2 is a key regulator of actin dynamics and GLUT4 trafficking in muscle cells. Our findings also support a model in which impairment of actin-dependent trafficking contributes to the pathological mechanism in dynamin-2-associated CNM.
Highlights
Dynamins are mechano-chemical large GTP-ases, whose catalytic activity is required in several membrane-based processes including endocytosis, vesicle trafficking, and exocytosis[1,2,3,4]
We observed an abnormal perinuclear accumulation of GLUT4 in biopsies from centronuclear myopathy (CNM)-patients harboring dynamin-2 middle domain mutations suggestive of trafficking defects. These findings demonstrate the key role played by dynamin-2 in the regulation of the actin cytoskeleton in skeletal muscles and provide a better understanding of the pathomechanisms of dynamin-2-related CNM, through the negative impact of the CNM-associated dynamin-2 mutations on actin dynamics and actin-dependent trafficking in muscle cells
In order to evaluate the role of dynamin-2 in actin dynamics in muscle cells, we first assessed the in vitro formation of new actin in RCMH myoblasts, a cell line derived from a skeletal muscle biopsy of a healthy patient[27]
Summary
Dynamins are mechano-chemical large GTP-ases, whose catalytic activity is required in several membrane-based processes including endocytosis, vesicle trafficking, and exocytosis[1,2,3,4]. These proteins exhibit a critical role in actin cytoskeleton dynamics by promoting elongation[5], remodeling[6] and stabilizing actin filaments[7]. Formation and maintenance of such muscle structures requires abundant intracellular membrane trafficking[17] Impairment in these cellular processes could underlie the structural alterations observed in dynamin-2-associated CNM. The skeletal muscle-specific ablation of gamma-actin in mice progressively leads to a CNM-like disease[26], suggesting that defects in actin dynamics may associate with myopathic phenotypes
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