Dynamin-2 mutations associated with centronuclear myopathy are hypermorphic and lead to T-tubule fragmentation

Abstract

Skeletal muscle requires adequate membrane trafficking and remodeling to maintain its normal structure and functions. Consequently, many human myopathies are caused by mutations in membrane trafficking machinery. The large GTPase dynamin-2 (Dyn2) is best known for catalyzing membrane fission during clathrin-mediated endocytosis (CME), which is critical for cell signaling and survival. Despite its ubiquitous expression, mutations of Dyn2 are associated with two tissue-specific congenital disorders: centronuclear myopathy (CNM) and Charcot-Marie-Tooth (CMT) neuropathy. Several disease models for CNM-Dyn2 have been established to study its pathogenic mechanism; yet the cellular and biochemical effects of these mutations are still not fully understood. Here we comprehensively compared the biochemical activities of disease-associated Dyn2 mutations and found that CNM-Dyn2 mutants are hypermorphic with enhanced membrane fission activity, whereas CMT-Dyn2 is hypomorphic. More importantly, we found that the expression of CNM-Dyn2 mutants does not impair CME in myoblast, but leads to T-tubule fragmentation in both C2C12-derived myotubes and Drosophila body wall muscle. Our results demonstrate that CNM-Dyn2 mutants are gain-of-function mutations, and their primary effect in muscle is T-tubule disorganization, which explains the susceptibility of muscle to Dyn2 hyperactivity.

Amphiphysin (BIN1) negatively regulates dynamin 2 for normal muscle maturation

“…Biochemical studies indicated that several DNM2 mutations causing CNMs increase dynamin oligomer stability and GTPase activity (15)(16)(17). Moreover, overexpression of WT or a DNM2-CNM mutation leads to CNM-like features in mice and perturbation of muscle and T-tubules in Drosophila (17)(18)(19). We hypothesize that CNM mutations in BIN1 are loss-of-function while CNM mutations in DNM2 create a gain of function.…”

“…Recessive BIN1-CNM is due to BIN1 loss of function and dominant DNM2-CNM is probably due to DNM2 gain of function (5,7,(15)(16)(17). We hypothesize that these 2 proteins are working antagonistically in the same pathway for muscle maturation and that reducing DNM2 expression might rescue the neonatal lethality observed in …”

“…DNM2 is a large GTPase involved in membrane fission and endocytosis (13,14). Biochemical studies indicated that several DNM2 mutations causing CNMs increase dynamin oligomer stability and GTPase activity (15)(16)(17). Moreover, overexpression of WT or a DNM2-CNM mutation leads to CNM-like features in mice and perturbation of muscle and T-tubules in Drosophila (17)(18)(19).…”

Human phenotypes caused by PIEZO1 mutations; one gene, two overlapping phenotypes?

“…Chin and colleagues demonstrated that the mutations had different effects on protein function and that CMT was caused by loss‐of‐function mechanisms and CNM was caused by gain‐of‐function mechanisms (Chin et al . ).…”

Dynamin-2 mutations linked to Centronuclear Myopathy impair actin-dependent trafficking in muscle cells

“…Congruently, the specific ablation of dynamin-2 modifies the organization and size of myofibers in mice 13 and zebrafish 14 and dramatically decreases the muscle mass in mice 13 . Remarkably, CNM-associated dynamin-2 mutations have been shown to cause sarcomere and neuromuscular junction disorganization in mice 13 and zebrafish skeletal muscles 14, 15 , as well as T-tubule fragmentation in Drosophila melanogaster muscles 16 . Formation and maintenance of such muscle structures requires abundant intracellular membrane trafficking 17 .…”