Dynamin-2 is a ubiquitously expressed mechano-GTPase involved in different stages of the secretory pathway. Its most well-known function relates to the scission of nascent vesicles from the plasma membrane during endocytosis; however, it also participates in the formation of new vesicles from the Golgi network, vesicle trafficking, fusion processes and in the regulation of microtubule and actin cytoskeleton dynamics. Over the last eight years, more than twenty mutations in the dynamin-2 gene have been associated to two hereditary neuromuscular disorders: Charcot-Marie-Tooth neuropathy and Centronuclear myopathy. Most of these mutations are grouped in the pleckstrin homology domain; however, there are no common mutations associated with both disorders, suggesting that they differently impact on dynamin-2 function in diverse tissues. In this review, we discuss the impact of these disease-related mutations on dynamin-2 function during vesicle trafficking and endocytotic processes.

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.

The role of dopamine in iron uptake into catecholaminergic neurons, and dopamine oxidation to aminochrome and its one‐electron reduction in iron‐mediated neurotoxicity, was studied in RCSN‐3 cells, which express both tyrosine hydroxylase and monoamine transporters. The mean ± SD uptake of 100 µm⁵⁹FeCl₃ in RCSN‐3 cells was 25 ± 4 pmol per min per mg, which increased to 28 ± 8 pmol per min per mg when complexed with dopamine (Fe(III)–dopamine). This uptake was inhibited by 2 µm nomifensine (43%p < 0.05), 100 µm imipramine (62%p < 0.01), 30 µm reboxetine (71%p < 0.01) and 2 mm dopamine (84%p < 0.01). The uptake of ⁵⁹Fe–dopamine complex was Na⁺, Cl^– and temperature dependent. No toxic effects in RCSN‐3 cells were observed when the cells were incubated with 100 µm FeCl₃ alone or complexed with dopamine. However, 100 µm Fe(III)–dopamine in the presence of 100 µm dicoumarol, an inhibitor of DT‐diaphorase, induced toxicity (44% cell death; p < 0.001), which was inhibited by 2 µm nomifensine, 30 µm reboxetine and 2 mm norepinephrine. The neuroprotective action of norepinephrine can be explained by (1) its ability to form complexes with Fe³⁺, (2) the uptake of Fe–norepinephrine complex via the norepinephrine transporter and (3) lack of toxicity of the Fe–norepinephrine complex even when DT‐diaphorase is inhibited. These results support the proposed neuroprotective role of DT‐diaphorase and norepinephrine.

Dysferlinopathy is an autosomal recessive muscular dystrophy resulting from mutations in the dysferlin gene. Absence of dysferlin in the sarcolemma and progressive muscle wasting are hallmarks of this disease. Signs of oxidative stress have been observed in skeletal muscles of dysferlinopathy patients, as well as in dysferlin-deficient mice. However, the contribution of the redox imbalance to this pathology and the efficacy of antioxidant therapy remain unclear. Here, we evaluated the effect of 10 weeks diet supplementation with the antioxidant agent N-acetylcysteine (NAC, 1%) on measurements of oxidative damage, antioxidant enzymes, grip strength and body mass in 6 months-old dysferlin-deficient Bla/J mice and wild-type (WT) C57 BL/6 mice. We found that quadriceps and gastrocnemius muscles of Bla/J mice exhibit high levels of lipid peroxidation, protein carbonyls and superoxide dismutase and catalase activities, which were significantly reduced by NAC supplementation. By using the Kondziela’s inverted screen test, we further demonstrated that NAC improved grip strength in dysferlin deficient animals, as compared with non-treated Bla/J mice, without affecting body mass. Together, these results indicate that this antioxidant agent improves skeletal muscle oxidative balance, as well as muscle strength and/or resistance to fatigue in dysferlin-deficient animals.